KR100354259B1 - Lithium secondary battery - Google Patents

Abstract

The present invention relates to an electrode assembly comprising a cathode and an anode, a separator interposed between the cathode and the anode, an electrode assembly comprising a cathode and an anode, a separator interposed between the cathode and the anode, and a polysiloxane-poly A gel electrolyte prepared by curing a composition comprising an oxyalkylene compound, polyethylene glycol dimethacrylate, polyethylene glycol monomethyl acrylate, ethoxylated trimethylolpropane triacrylate, and an organic solvent containing a lithium salt, Provided is a lithium secondary battery having a case in which the electrode assembly and the electrolyte are incorporated. This lithium secondary battery effectively suppresses the swelling phenomenon caused by the electrolyte and there is no fear of leakage of the electrolyte to the outside, thereby preventing the reliability and safety degradation of the battery.

Description

Lithium secondary battery

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery having improved safety and reliability by using a gel electrolyte.

Lithium secondary batteries generate electricity by lithium reciprocating between the cathode and the anode. Compared to nickel cadmium and nickel hydride batteries, such lithium secondary batteries have a higher energy density and higher voltage / volume than the nickel cadmium and nickel hydride batteries. Suitable for small size, light weight and long time use.

As described above, lithium secondary batteries have received much attention as next generation high performance batteries because they have higher voltage, much more charge / discharge cycles, and do not cause environmental problems than conventional nickel cadmium batteries and nickel hydrogen batteries. However, the lithium secondary battery has a risk of explosion, etc., and ensuring safety is a key issue.

Meanwhile, lithium secondary batteries may be classified into lithium ion batteries using liquid electrolytes and lithium ion polymer batteries using solid electrolytes, depending on the type of electrolyte.

The lithium ion battery generally uses a cylindrical case or a rectangular case as a case for sealing the electrode assembly. Recently, however, the use of the pouch instead of the case has been in the spotlight. The reason is that the use of the pouch as a case not only increases the energy density per unit weight and volume, makes the battery thinner and lighter, but also lowers the case material cost.

1 is an exploded perspective view schematically showing an example of a lithium ion battery using a pouch as a case.

Referring to FIG. 1, a lithium ion battery includes an electrode assembly 10 including a cathode 11, an anode 12, and a separator 13, and a case 11 surrounding and sealing the electrode assembly 10. It is done by At this time, the electrode assembly is formed by inserting a separator between the cathode and the anode and winding it. The cathode tab 12 and the anode tab 12 ′, which serve as an external electrical passage with the electrode assembly 10, are drawn out from the cathode and the anode to form electrode terminals 13 and 13 ′.

2 is an exploded perspective view schematically showing an example of a conventional lithium ion polymer battery.

Referring to this, the lithium ion polymer battery includes an electrode assembly 21 having a cathode, an anode, and a separator, and a case 12 enclosing and sealing the electrode assembly 21. In addition, the electrode terminals (or lead wires) 24 and 24 ′ serving as electrical paths for guiding the current formed in the electrode assembly 21 to the outside are provided at the cathode tabs and the anode tabs 23 and 23 ′. It is connected to and installed to expose a predetermined length out of the case (22).

In the lithium ion battery of FIG. 1 and the lithium ion polymer battery of FIG. 2 as described above, the electrode assemblies in the cases 11 and 22 are exposed while only a portion of the electrode terminals 13 and 13 'and 24 and 24' are exposed. (10, 21) was added thereto, an electrolyte solution was injected therein, and heat and pressure were applied to bond the heat-adhesive material between the edge of the upper case and the edge of the lower case to seal the battery.

As described above, when using an organic solvent having a low boiling point by injecting the electrolyte into the post-process, the phenomenon of the electrode assembly or pouch is swollen. In addition, this lowers the reliability and safety of the battery.

In order to solve this problem, a method of hardening a planar battery by ultraviolet rays or an electron beam, or coating a gel on an electrode plate and separately injecting an electrolyte solution has been proposed (US Pat. No. 5,972,539, US Pat. No. 5,279,910, US Pat. 5,972,539, U.S. Patent 5,437,942 and U.S. Patent 5,340,368. However, when the above methods are practically applied, the swelling phenomenon of the electrode assembly or pouch can be alleviated somewhat, but still not satisfactory.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a lithium secondary battery that can solve the above problems and effectively suppress swelling caused by an electrolyte solution, thereby preventing a decrease in reliability and safety of the battery.

1 is an exploded perspective view schematically showing an example of a lithium ion battery according to the prior art,

2 is an exploded perspective view schematically showing another example of a lithium ion polymer battery according to the prior art.

<Explanation of symbols for the main parts of the drawings>

10, 21 ... electrode assembly 11, 22 ... case

13, 13 ', 24, 24' ... electrode terminals

The present invention to achieve the above technical problem,

An electrode assembly comprising a cathode and an anode, and a separator interposed between the cathode and the anode;

0.1 to 10% by weight of polysiloxane-polyoxyalkylene compound represented by Formula 1, 0.5 to 50% by weight of polyethylene glycol dimethacrylate, 0.4 to 50% by weight of polyethylene glycol monomethyl acrylate, ethoxylate trimethylolpropane A gel electrolyte prepared by curing a composition consisting of 50% to 95% by weight of an organic solvent containing 4% to 15% by weight of triacrylate and not more than 5 and lithium salt,

Provided is a lithium secondary battery having a case in which the electrode assembly and the electrolyte are incorporated.

R ₁ -O-{(CH ₂ ) _m- [Si (R ₂ R ₃ ) -O] _n -Si (R ₂ R ₃ )-(CH ₂ ) _n -O} _x- (CH ₂ -CHR _4- O-) _y -R ₅

[Wherein, R ₁ and R ₅ are each independently —C (O) CR ₆ ═C (R ₇ R ₈ ) or —CR ₉ (R ₁₀ R ₁₁ ), and R ₂ and R ₃ are each independently — CaH (2a + 1), where a is 1 to 5, phenyl, benzyl, allyl, R ₄ is hydrogen or -CaH (2a + 1), where a is 1 to 5, m Is 1 to 5, n is 1 to 100, x is 1 to 10, y is 1 to 50, and R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ , R ₁₁ are each independently hydrogen or -CbH (2b + 1), where b is 1 to 5

In the lithium secondary battery according to the present invention, the composition is 0.1 to 2 weight of any one or more polymerization initiators selected from the group consisting of benzophenone, benzoyl peroxide, acetyl peroxide, lauroyl peroxide, azobisisobutyronitrile It is preferable to further contain%.

In the lithium secondary battery according to the present invention, the curing is preferably performed by any one selected from the group consisting of thermal polymerization, polymerization by electron beam, and polymerization by UV, and polymerization by thermal polymerization. It is preferable that temperature is 60-100 degreeC.

In the lithium secondary battery according to the present invention, the lithium salt is lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), LiAsF ₆ , lithium trifluoride methane sulfonate (LiCF Preferably at least one selected from the group consisting of ₃ SO ₃ ) and lithium bistrifluoromethanesulfonylamide (LiN (CF ₃ SO ₂ ) ₂ ).

In the lithium secondary battery according to the present invention, the organic solvent is propylene carbonate, ethylene carbonate, dimethyl carbonate, methylethyl carbonate, diethyl carbonate, vinylene carbonate, triglyme, tetraglyme, γ-butyrolactone It is preferably at least one selected from the group consisting of.

In the lithium secondary battery according to the present invention, it is preferable that the electrode assembly is a wound type and the case is a pouch type.

In the case of the conventional gel polymer electrolyte, the polymer main chain is mainly used as a material having functional groups such as acrylic, vinyl, and epoxy on polyalkylene oxide-based materials such as polyethylene oxide and polypropylene oxide. Polysiloxane-polyoxyalkylene containing siloxane units and oxyalkylene units in addition to the ethylene oxide series is used to improve the physical and electrochemical properties of the electrolyte.

The gel electrolyte according to the present invention as described above is 0.1 to 10% by weight of a polysiloxane-polyoxyalkylene compound represented by the following formula (1), 0.5 to 50% by weight polyethylene glycol dimethacrylate, 0.4 to 50 polyethylene glycol monomethyl acrylate It is prepared by curing a composition consisting of weight percent, ethoxylated trimethylolpropane triacrylate greater than 0 and 5 weight percent, and 50 to 95 weight percent of an organic solvent containing 4 to 15 moles of lithium salt, the composition comprising It may further comprise 0.1 to 2% by weight of any one or more polymerization initiators selected from the group consisting of benzophenone, benzoyl peroxide, acetyl peroxide, lauroyl peroxide, azobisisobutyronitrile.

<Formula 1>

R ₁ -O-{(CH ₂ ) _m- [Si (R ₂ R ₃ ) -O] _n -Si (R ₂ R ₃ )-(CH ₂ ) _n -O} _x- (CH ₂ -CHR _4- O-) _y -R ₅

[Wherein, R ₁ and R ₅ are each independently —C (O) CR ₆ ═C (R ₇ R ₈ ) or —CR ₉ (R ₁₀ R ₁₁ ), and R ₂ and R ₃ are each independently — CaH (2a + 1), where a is 1 to 5, phenyl, benzyl, allyl, R ₄ is hydrogen or -CaH (2a + 1), where a is 1 to 5, m Is 1 to 5, n is 1 to 100, x is 1 to 10, y is 1 to 50, and R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ , R ₁₁ are each independently hydrogen or -CbH (2b + 1), where b is 1 to 5

Looking at the process of producing a gel electrolyte using the composition as described above are as follows.

The polysiloxane-polyoxyacylene represented by Chemical Formula 1 may be prepared by various methods. For example, acrylic chloride is added to polysiloxane-polyoxyalkylene prepared by reacting dihydroxy terminated polysiloxane with ethylene oxide. Can be prepared by reaction.

The polysiloxane-polyoxyalkylene represented by the formula (1) prepared as described above, polyethylene glycol dimethacrylate, polyethylene glycol monomethyl acrylate, ethoxylated trimethylolpropane triacrylate are mixed in the ratio as described above. do. The ratio as described above is optimally selected in consideration of the electrochemical stability of the lithium secondary battery manufactured, the performance of the charging.

One or more polymerization initiators selected from the group consisting of benzophenone, benzoyl peroxide, acetyl peroxide, lauroyl peroxide and azobisisobutyronitrile may be further added to the composition.

Subsequently, an organic solvent containing 4 to 15 mol of lithium salt is further added to the composition as described above, stirred and mixed uniformly.

Next, a gel electrolyte can be obtained by polymerizing this mixture by thermal polymerization, electron beam polymerization or UV polymerization. In the case of thermal polymerization, the polymerization temperature is preferably 60 to 100 ° C.

Lithium salt and organic solvent constituting the electrolyte in the present invention can be used without particular limitation as long as it is widely known in the art to which the present invention belongs, lithium salt perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), At least one selected from the group consisting of lithium hexafluorophosphate (LiPF ₆ ), LiAsF ₆ , lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethanesulfonylamide (LiN (CF ₃ SO ₂ ) ₂ ) Preferably, the organic solvent is at least one selected from the group consisting of propylene carbonate, ethylene carbonate, dimethyl carbonate, methylethyl carbonate, diethyl carbonate, vinylene carbonate, triglyme, tetraglyme, and γ-butyrolactone. desirable.

Hereinafter, a method of manufacturing the lithium secondary battery of the present invention including the above-described electrolyte will be described.

First, an electrode active material layer is formed on a current collector using an electrode active material composition containing an electrode active material, a binder, a conductive agent, and a solvent. At this time, the method of forming the electrode active material layer is a method of directly coating the electrode active material composition on the current collector, or by coating and drying the electrode active material composition on a separate support, and peeling from the support, the film obtained on the current collector There is a method of lamination. Herein, the support may be used as long as it can support the active material layer, and specific examples thereof include a mylar film and a polyethylene terephthalate (PET) film.

In the electrode active material of the present invention, a lithium composite oxide such as LiCoO ₂ is used for the cathode, and carbon, graphite, etc. are used for the anode, and carbon black is used as the conductive agent. Herein, the content of the conductive agent is preferably 1 to 20 parts by weight based on 100 parts by weight of the electrode active material (eg, LiCoO ₂ ).

As the binder, vinylidene fluoride-hexafluoropropylene copolymer (VdF / HFP copolymer), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate and mixtures thereof are used, and the content thereof is an electrode. It is preferably 5 to 30 parts by weight based on 100 parts by weight of the active material.

The solvent may be used as long as it is used in a conventional lithium secondary battery, and specific examples thereof include acetone and N-methylpyrrolidone.

On the other hand, the separator of the present invention is not particularly limited, but in the present invention, a polyethylene separator and a polypropylene / polyethylene / polypropylene three-layer separator that are easy to wind up are used.

A separator is inserted between the cathode electrode plate and the anode electrode plate manufactured according to the above-described method, and the electrode assembly (FIG. 1) is wound up by winding it in a jellyroll manner, or the electrode assembly of the bi-cell structure (FIG. 2). ) This electrode assembly is then placed in a case.

Next, 01 to 10% by weight of the polysiloxane-polyoxyalkylene compound represented by the following formula (1), 0.5 to 50% by weight of polyethylene glycol dimethacrylate, 0.4 to 50% by weight of polyethylene glycol monomethyl acrylate, ethoxylate Detrimethylolpropane triacrylate composition consisting of more than 0% by weight of 5 or less, and 50-97% by weight of organic solvent containing 4-15 mol of lithium salt or benzophenone, benzoyl peroxide, acetyl peroxide, lauroyl peroxide A composition comprising 0.1 to 2% by weight of any one or more polymerization initiators selected from the group consisting of azobisisobutyronitrile is injected into the case.

After that, the case is sealed, and the resultant product is left for a predetermined time in an oven adjusted to a predetermined temperature. At this time, the temperature of the oven is preferably adjusted to maintain the range of 60 to 100 ℃.

As a result of the reaction, a gel electrolyte can be obtained. As such, when the electrolyte is present in a gel state, it is less likely to leak to the outside, thereby preventing a decrease in safety and reliability of the battery due to leakage of the electrolyte.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited only to the following examples.

Example 1

15 g of polyvinylidene fluoride was added to 600 ml of acetone, and the mixture was dissolved in a ball mill for 2 hours. 470 g of LiCoO ₂ and 15 g of SuperP were added to the mixture, which was then mixed for 5 hours to form a cathode active material composition.

The cathode active material composition was coated and dried on an aluminum thin film having a thickness of 147 μm and a width of 4.9 cm using a doctor blade having a 320 μm gap to form a unit cathode electrode plate.

Meanwhile, the anode electrode plate was manufactured according to the following procedure.

50 g of polyvinylidene fluoride was added to 600 ml of acetone, and the mixture was dissolved in a ball mill for 2 hours. 449 g of mesocarbon fiber (MCF) and 1 g of oxalic acid were added to the mixture, which was then mixed for 5 hours to form an anode active material composition.

The anode active material composition was coated and dried on a copper thin film having a thickness of 178 µm and a width of 5.1 cm using a doctor blade having a gap of 420 µm to form a unit anode electrode plate.

Separately, a polyethylene separator (Asahi) was used as the separator, and the separator had a width of 5.25 cm and a thickness of 18 μm.

The polyethylene separator was interposed between the cathode electrode plate and the anode electrode plate, and then wound in a jellyroll manner to form an electrode assembly. This electrode assembly was placed in a pouch.

Meanwhile, 0.2 g of the polysiloxane-polyoxyalkylene compound represented by the formula (1), 1.8 g of polyethylene glycol dimethacrylate, 1 g of polyethylene glycol monomethyl acrylate, 0.05 g of ethoxylated trimethylolpropane triacrylate, and azobisiso 0.01 g of butyronitrile and 1 M of LiPF ₆ were mixed, and EC / DMC / DEC was mixed with 30 g of a solution mixed at a volume ratio of 3: 3: 1 to prepare a gel electrolyte composition. 3 g of this composition was injected into the pouch cell obtained according to the above procedure, and then sealed. Subsequently, the resultant was allowed to stand for 4 hours in an oven controlled at 80 ° C. to complete a lithium secondary battery.

Example 2

15 g of polyvinylidene fluoride was added to 600 ml of acetone, and the mixture was dissolved in a ball mill for 2 hours. 470 g of LiCoO ₂ and 15 g of SuperP were added to the mixture, which was then mixed for 5 hours to form a cathode active material composition.

The cathode active material composition was coated and dried on an aluminum thin film having a thickness of 147 μm and a width of 4.9 cm using a doctor blade having a 320 μm gap to form a unit cathode electrode plate.

Next, 0.2 g of the polysiloxane-polyoxyalkylene compound represented by the formula (1), 1.8 g of polyethylene glycol dimethacrylate, 1 g of polyethylene glycol monomethyl acrylate, 0.05 g of ethoxylated trimethylolpropane triacrylate, and benzophenone 0.01 g and 1 M of LiPF ₆ were mixed and EC / DMC / DEC was mixed with 30 g of a solution mixed at a volume ratio of 3: 3: 1 to prepare a gel electrolyte composition. The composition was cast on the cathode electrode plate prepared above using a doctor blade and then cured by UV irradiation.

Meanwhile, the anode electrode plate was manufactured according to the following procedure.

50 g of polyvinylidene fluoride was added to 600 ml of acetone, and the mixture was dissolved in a ball mill for 2 hours. 449 g of mesocarbon fiber (MCF) and 1 g of oxalic acid were added to the mixture, which was then mixed for 5 hours to form an anode active material composition.

The anode active material composition was coated and dried on a copper thin film having a thickness of 178 µm and a width of 5.1 cm using a doctor blade having a gap of 420 µm to form a unit anode electrode plate.

Separately, a polyethylene separator (Asahi) was used as the separator, and the separator had a width of 5.25 cm and a thickness of 18 μm.

The polyethylene separator was interposed between the cathode electrode plate and the anode electrode plate on which the gel electrolyte was formed, and then wound in a jelly roll manner to form an electrode assembly. This electrode assembly was placed in a pouch to complete a lithium secondary battery.

Example 3

A lithium secondary battery was completed in the same manner as in Example 4 except that the composition for preparing the gel electrolyte was cast on the anode electrode plate instead of the cathode electrode plate.

Example 4

A lithium secondary battery was completed in the same manner as in Example 4 except that the composition for preparing the gel electrolyte was cast on both the cathode electrode plate and the anode electrode plate.

Comparative example

A lithium secondary battery was completed in the same manner as in Example 1 except that a 1.15 M 1 M LiPF ₆ EC: DMC: DEC (3: 3: 4) solution (UBE) was used as the electrolyte.

In the lithium secondary battery manufactured according to Examples 1-4 and Comparative Examples, the reliability and safety of the battery were evaluated. Here, the battery reliability evaluation method was followed by battery life, and the safety evaluation method was implemented by penetration.

As a result of the evaluation, it was found that the lithium secondary battery of Example 1-4 was superior in reliability and safety as compared with the case of the comparative example. This is because the lithium secondary battery of Example 1-4 has no phenomenon that the electrolyte leaks to the outside or the electrode assembly or the pouch is not swollen by the electrolyte compared to the case of the comparative example using the liquid electrolyte. This is because there is no possibility of lowering reliability and safety.

According to the present invention, it is possible to obtain a lithium secondary battery that can effectively suppress the swelling phenomenon by the electrolyte and prevent the electrolyte from leaking to the outside, thereby preventing the reliability and safety of the battery from being lowered.

Although the present invention has been described with reference to the above embodiments, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (7)

An electrode assembly comprising a cathode and an anode, and a separator interposed between the cathode and the anode; 0.1 to 10% by weight of polysiloxane-polyoxyalkylene compound represented by Formula 1, 0.5 to 50% by weight of polyethylene glycol dimethacrylate, 0.4 to 50% by weight of polyethylene glycol monomethyl acrylate, ethoxylate trimethylolpropane A gel electrolyte prepared by curing a composition consisting of 50% to 97% by weight of an organic solvent containing 4% to 15% by weight of triacrylate and not more than 5 and lithium salt, A lithium secondary battery having a case in which the electrode assembly and the electrolyte are incorporated. <Formula 1> R ₁ -O-{(CH ₂ ) _m- [Si (R ₂ R ₃ ) -O] _n -Si (R ₂ R ₃ )-(CH ₂ ) _n -O} _x- (CH ₂ -CHR _4- O-) _y -R ₅ [Wherein, R ₁ and R ₅ are each independently —C (O) CR ₆ ═C (R ₇ R ₈ ) or —CR ₉ (R ₁₀ R ₁₁ ), and R ₂ and R ₃ are each independently — CaH (2a + 1), where a is 1 to 5, phenyl, benzyl, allyl, R ₄ is hydrogen or -CaH (2a + 1), where a is 1 to 5, m Is 1 to 5, n is 1 to 100, x is 1 to 10, y is 1 to 50, and R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ , R ₁₁ are each independently hydrogen or -CbH (2b + 1), where b is 1 to 5 The method of claim 1, wherein the composition further comprises 0.1 to 2% by weight of any one or more polymerization initiators selected from the group consisting of benzophenone, benzoyl peroxide, acetyl peroxide, lauroyl peroxide, azobisisobutyronitrile. A lithium secondary battery characterized by the above. The lithium secondary battery according to claim 1, wherein the curing is performed by any one selected from the group consisting of thermal polymerization, polymerization by electron beam, and polymerization by UV. The lithium secondary battery according to claim 3, wherein the polymerization temperature is 60 to 100 ° C. in the case of the thermal polymerization. The lithium secondary battery according to claim 1, wherein the lithium salt is at least one selected from the group consisting of LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ and LiN (CF ₃ SO ₂ ) ₂ . . The method of claim 1, wherein the organic solvent is one selected from the group consisting of propylene carbonate, ethylene carbonate, dimethyl carbonate, methylethyl carbonate, diethyl carbonate, vinylene carbonate, triglyme, tetraglyme, γ-butyrolactone Lithium secondary battery characterized by the above. The lithium secondary battery of claim 1, wherein the electrode assembly is wound and the case is in the form of a pouch.