KR20020027939A - Lithium secondary battery - Google Patents

Abstract

PURPOSE: Provided is a lithium secondary battery having improved safety and reliability, in which blowout and blast due to thermal runaway are prevented. CONSTITUTION: The lithium secondary battery comprises a winding electrode assembly(24) comprising a cathode(21), an anode(22) and a separator(23) positioned between the cathode and the anode; and a case which the electrode assembly is built in. A cavity in the winding electrode assembly, inner space of case, and at least one of the cathode, anode and separator comprise polyhydric alcohol which absorbs heat occurring from the electrode assembly and accomplishes a solid-solid phase transition at isothermal level.

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 preventing rupture and explosion due to thermal runaway.

Due to the development of advanced technology, portable electronic devices are gradually miniaturized and light weight, and thus, high performance is also required for secondary batteries that supply them. Accordingly, in response to these demands, development of lithium secondary batteries as a high energy density battery to replace lead batteries or nickel-cadmium batteries is rapidly progressing.

Lithium secondary batteries are in the limelight as future batteries due to their advantages such as higher energy density, easier processing, and easier battery manufacturing than other batteries. In lithium secondary batteries, lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, and the like are used as the cathode active material, and carbon, lithium metal, and alloys thereof are generally used as the anode active material. As the electrolyte, a polymer solid electrolyte based on a polymer matrix such as liquid organic electrolyte, poly (ethylene oxide), polyacrylonitrile, poly (vinylidene fluoride), or the like is used.

Meanwhile, lithium secondary batteries may be classified into lithium ion batteries and lithium ion polymer batteries according to the type of electrolyte. Among them, a lithium ion battery uses a liquid electrolyte as an electrolyte, and a lithium ion polymer battery uses a solid electrolyte as an electrolyte.

1 is a diagram schematically showing the structure of a conventional cylindrical lithium ion battery.

Referring to FIG. 1, the cylindrical lithium secondary battery 10 includes a cylindrical case 15 and an electrode assembly 14 installed inside the case 15. In this case, the electrode assembly 14 has a separator 13 interposed between the cathode 11 and the anode 12, and a cap assembly 16 is coupled to the upper portion of the electrode assembly 14.

The process of manufacturing the cylindrical lithium ion battery having the structure as described above will be described.

First, in the state where the separator is interposed between the cathode plate and the anode plate, the winding of the separator is attempted around the mandrel and the electrode roll is wound in a jellyroll manner. After removing the mandrel, the electrode assembly is inserted into the space of the can, and then the electrolyte is injected. When electrolyte injection is complete, the cap assembly is coupled to the top of the can to complete the lithium ion battery of FIG. 1. As discussed in the manufacturing process, an empty space remains after the mandrel is removed inside the electrode assembly.

On the other hand, lithium secondary batteries have better life and energy density characteristics than other types of batteries, whereas local internal short-circuits may occur due to mechanical shocks applied to the battery from outside or through the battery through nails, or thermal shock and overcharging. The temperature rises intensively in the area where the internal short circuit occurs. In particular, when an internal short circuit occurs in the active material layer regions formed on both surfaces of the electrode current collector, the internal temperature of the battery is further increased. However, when a local short circuit occurs, the separator does not properly perform a shutdown function (a function of suppressing current flow by suppressing ion movement when the temperature increases). Therefore, the temperature rise due to local short-circuit causes the separator and the anode to thermally decompose, which causes the heat generation to gradually increase, leading to thermal runaway, which eventually causes the battery to ignite and burst.

The technical problem to be achieved by the present invention is to provide a lithium secondary battery with improved safety and reliability by changing the heat release mechanism of the battery to prevent the burst and explosion due to heat generated inside the battery to solve the above problems.

1 is an exploded perspective view showing a part of a typical cylindrical lithium ion battery,

Figure 2 is an exploded perspective view showing a portion of the cylindrical lithium ion battery cut according to an embodiment of the present invention,

Figure 3 is an exploded perspective view showing a cut part of the cylindrical lithium ion battery according to another embodiment of the present invention.

<Explanation of symbols for main parts of the drawings>

11, 21, 31 ... cathode 12, 22, 32 ... anode

13, 23, 33 ... Separators 14, 24, 34 ... Electrode Assembly

16, 26, 36 ... Cap assembly 27 ... Thermally conductive metal bag

37 ... heat absorbing film

In order to achieve the above technical problem, in the present invention, in the lithium secondary battery having a wound electrode assembly including a cathode and an anode and a separator interposed therebetween, and a case in which the electrode assembly is embedded,

At least one of a hollow portion in the wound electrode assembly, a space inside the case, and at least one of the cathode, the anode, and the separator;

It provides a lithium secondary battery comprising a polyhydric alcohol (polyhydric alcohol) that absorbs the heat generated from the electrode assembly to a solid-solid phase transition at isothermal.

The polyhydric alcohol is at least one selected from the group consisting of neopentyl glycol, trimethylol ethane and ?? pentaerythritol, and when the polyhydric alcohol is included in the hollow portion of the wound electrode assembly, a thermally conductive metal located in the hollow portion It is preferable to make it contain in a bag.

And when the polyhydric alcohol is included in the cathode, anode and / or separator, the content of the polyhydric alcohol in the cathode and anode is 2 to 10 parts by weight based on 100 parts by weight of the electrode active material, the polyvalent in the separator The content of alcohol is 1 to 5 parts by weight based on 100 parts by weight of the polymer resin.

In addition, a technical problem of the present invention is a lithium secondary battery having a wound electrode assembly including a cathode, an anode, and a separator interposed therebetween, and a case in which the electrode assembly is embedded.

Between the cathode and the separator and / or between the anode and the separator,

The lithium secondary battery is characterized in that the heat absorption film containing a polyhydric alcohol (polyhydric alcohol) to absorb the heat generated from the electrode assembly is a solid-solid phase transition at isothermal.

The present invention is characterized by adding a polyhydric alcohol having a solid-solid phase transition at an isothermal temperature to at least one selected from a hollow portion, a case empty space, a cathode, an anode, and a separator of the wound electrode assembly. In addition, the present invention is characterized in that a heat absorption film including a polyhydric alcohol is interposed between the cathode and the separator and / or between the anode and the separator.

The polyhydric alcohol is particularly preferably neopentyl glycol, trimethylol ethane and pentaerythritol, most preferably pentaerythritol. Pentaerythritol is a solid-solid phase transition material that absorbs 300J / g of heat at about 189 ° C. It has a melting point of 269 ° C and absorbs heat of about 35J / g. This is because heat can be absorbed effectively.

The separator of the present invention is not particularly limited, but when the electrode assembly is to be wound, a single layer structure made of a material selected from polyethylene (PE) and polypropylene (PP) or polypropylene is laminated on both sides of the polyethylene. Preference is given to using a layer structure. This is because such a separator is easy to wind up.

Hereinafter, an example of a lithium secondary battery according to the present invention will be described with reference to the accompanying drawings.

2 is an exploded perspective view showing a part of a lithium ion battery according to an exemplary embodiment of the present invention.

Referring to FIG. 2, the lithium ion battery 20 includes a cathode 21, an anode 22, and the cathode having a predetermined width and length wound around a mandrel in a jellyroll manner. An electrode assembly 24 comprising a separator 23 for insulating the 21 and the anode 22. In addition, a cylindrical can 25 having a space portion for accommodating the electrode assembly 24 is provided, and a cap assembly 26 is coupled to the can 25 to seal the inside to prevent the electrolyte solution. Combined. In this case, the cap assembly 26 includes a cap 26b having a rubber vent 26a therein, a cap cover 26c coupled to the cap 26b, a cap 26b and a cap cover 26c. ) And a gasket 26d interposed therebetween.

In the hollow portion from which the mandrel is removed from the electrode assembly 26, a rod-shaped thermally conductive metal bag 27 is positioned. At this time, although not shown in the metal bag 27, pentaerythritol powder or this pentaerythritol containing film is contained in various forms. Here, although the manufacturing method is not specifically limited, the pentaerythritol containing film is manufactured by the following method.

That is, a composition is prepared by mixing an ion conductive polymer, a polyhydric alcohol such as pentaerythritol, and a solvent for dissolving these components. The composition is cast on a separate support, dried to form a film, and then peeled from the support to obtain a pentaerythritol-containing film. Vinyl chloride here. One selected from homopolymers, copolymers and terpolymers comprising one or more repeating units selected from the group consisting of hexafluoropropylene, hexafluoroisobutene and acrylonitrile. N-methylpyrrolidone, acetone, a mixture thereof, and the like are used as the solvent.

As described above, since the pentatritol powder or pentaerythritol-containing film is accommodated in the conductive metal bag 27, there is no fear that the pentaerytol will escape from the hollow portion of the electrode assembly even if the electrolyte is injected in a subsequent step. Therefore, the effects according to the addition can be sufficiently obtained. The metal bag 27 is preferably made of aluminum, copper, or the like as a thermal conductor.

3 is an exploded perspective view showing a part of a lithium ion battery according to another embodiment of the present invention.

Referring to FIG. 3, the lithium ion battery 30 includes an electrode assembly 34 including a cathode 31 and an anode 32, and a separator 33 for insulating the cathode 31 and the anode 32. ). At this time, a heat absorption film 37 containing pentaerythritol is interposed between the cathode 31 and the separator 33. In addition, a cylindrical can 35 having a space for accommodating the electrode assembly 34 is provided, and a cap assembly 36 is formed on the upper portion of the can 35 to seal the inside to prevent electrolyte from being combined with the can. Combined. In this case, the cap assembly 36 includes a cap 36b having a rubber vent 36a therein, a cap cover 36c coupled to the cap 36b, a cap 36b, and a cap cover 36c. And a gasket 36d interposed therebetween.

The heat absorbing film 37 has almost the same composition and manufacturing method as the pentaerythritol containing film contained in the conductive metal bag 27 of FIG.

Looking at the manufacturing process of the lithium secondary battery according to the present invention including the battery of Figures 1 and 2 as follows.

First, prepare a cathode and an anode, respectively.

The cathode is a cathode active material, such as LiNiO ₂ , conductive agent. After the binder and the solvent are mixed to prepare a composition for forming a cathode, it is prepared by coating and drying on an aluminum current collector. And the anode is an anode active material such as graphite or the like. The binder and the solvent were mixed to prepare an anode forming composition. The composition is prepared by coating and drying on a copper current collector.

In the present invention, a polyhydric alcohol may be added to the composition for forming a cathode and / or the composition for forming an anode. At this time, the content of the polyhydric alcohol is preferably 2 to 10 parts by weight based on 100 parts by weight of the electrode active material. If the content of the polyhydric alcohol is more than 10 parts by weight, it is difficult to form the electrode plate, and if the content of the polyhydric alcohol is less than 2 parts by weight, the polyhydric alcohol addition effect is negligible, which is not preferable.

Polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, and the like are used as binders for the production of the cathode and the anode, and carbon black, ketjen black, acetylene black, and the like are used as the conductive agent. As the solvent, N-methylpyrrolidone (NMP), acetone, a mixture thereof, and the like are used. The content of these components is a level commonly used in lithium secondary batteries. The binder is used in an amount of 2 to 10 parts by weight based on 100 parts by weight of an electrode active material (eg, lithium composite oxide, graphite), and the conductive agent is an electrode. 1 to 5 parts by weight based on 100 parts by weight of the active material is used.

As the separator, a single layer structure made of polyethylene (PE) or polypropylene (PP) or a three layer separator in which polypropylene is laminated on both sides of polyethylene is used. Alternatively, it is also possible to use a separator obtained by mixing a matrix resin to form a composition for forming a separator by mixing a polymer resin, a solvent, and an inorganic filler, casting and drying the same on a separate support, and peeling from the support. Do. It is also possible to add a polyhydric alcohol at the time of manufacturing the separator as in the case of the cathode and anode production. The content of the polyhydric alcohol is 1 to 5 parts by weight based on 100 parts by weight of the polymer resin. In the case where the content of the polyhydric alcohol is more than 5 parts by weight, the conductivity is lowered. If the content of the polyhydric alcohol is less than 1 part by weight, the polyhydric alcohol addition effect is insignificant, which is not preferable.

The polymer resin is polyvinylidene fluoride, polyvinylidene-hexapropylene copolymer, polyvinyl chloride, polymethyl methacrylate, etc., the filler is used to improve the mechanical strength and ion conductivity of the separator As an addition, silica, kaolin, zeolite, etc. are used.

The electrode assembly is manufactured by winding a separator between a cathode and an anode prepared according to the above process in a jellyroll manner with the mandrel inserted between the cathode and the anode.

The electrode assembly is then inserted into the space of the can and then the mandrel is removed from the electrode assembly. Thereafter, a conductive metal bag containing polyhydric alcohol is inserted into the hollow portion from which the mandrel is removed from the electrode assembly.

Thereafter, the electrolyte is injected into the space of the can containing the electrode assembly, including the hollow portion of the electrode assembly. In the electrolyte injection process, the inside of the battery can is vacuumed using the electrolyte injection device, and then the electrolyte is injected into the can while maintaining a predetermined injection pressure.

When the injection of the electrolyte is completed as described above, the cap assembly 26 is coupled to the upper portion of the can 25 to complete the lithium secondary battery of FIG. 2.

Subsequently, in order to provide good charge and discharge characteristics to the assembled battery as described above, a chemical conversion process is performed in which charge and discharge processes are performed a plurality of times.

As shown in FIG. 2, when the gel ion-conducting polymer is present in the hollow portion of the electrode assembly or in the inner space of the case, the reliability and safety of the battery are improved by the following working principle.

That is, when the polyhydric alcohol is added to the empty space in the electrode assembly and the case, the polyhydric alcohol absorbs heat generated due to a short circuit inside the battery, causing a solid-solid phase transition. In this way, even if the polyhydric alcohol has a phase change, the battery does not have any negative effect on the battery and prevents overheating and thermal runaway.

In addition, the lithium secondary battery of the present invention may be manufactured by forming an electrode assembly with a heat absorbing film interposed between the cathode and the separator or between the anode and the separator, as shown in FIG. 3, and winding the same. .

As the electrolyte solution used in the present invention, an electrolyte solution commonly used in a lithium secondary battery is used. The electrolyte is composed of a lithium salt and an organic solvent, the organic solvent is propylene carbonate, ethylene carbonate, γ-butyrolactone, 1,3-dioxolane, dimethoxyethane, dimethyl carbonate, methylethyl carbonate and diethyl At least one solvent selected from carbonate, tetrahydrofuran, dimethyl sulfoxide and polyethylene glycol dimethyl ether is used. And the content of the solvent is the usual level used in the lithium secondary battery. Lithium salts include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethanesulfonyl At least one ionic lithium salt selected from the group consisting of amides (LiN (CF ₃ SO ₂ ) ₂ ) is used and its content is at the usual level used in lithium secondary batteries.

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

94 parts by weight of LiNiO ₂ , 3 parts by weight of superpies, 3 parts by weight of PVDF, and an appropriate amount of NMP were mixed to prepare a composition for forming a cathode. The composition was coated and dried on an aluminum current collector to prepare a cathode.

Separately, 92 parts by weight of graphite, 8 parts by weight of PVDF and an appropriate amount of NMP were mixed to prepare an anode forming composition. The composition was coated and dried on a copper current collector to make an anode.

On the other hand, the polypropylene layer was laminated on both sides of the polyethylene layer, and then bonded to prepare a separator.

An electrode assembly was prepared by inserting a separator between the cathode and the anode. The electrode assembly was then wound around a mandrel and then placed in a cylindrical case. After removing the mandrel from inside the electrode assembly, an aluminum metal bag containing 1.5 parts by weight of pentaerythritol was inserted in the hollow thereof.

Then, the electrolyte solution was inject | poured into the resultant, and it sealed and completed the cylindrical lithium ion battery.

Example 2

91 parts by weight of LiNiO ₂ , 3 parts by weight of super blood. 3 parts by weight of PVDF and an appropriate amount of NMP were mixed, and then 3 parts by weight of pentaerythritol was added thereto to prepare a composition for forming a cathode. The composition was coated and dried on an aluminum current collector to prepare a cathode.

Separately, 92 parts by weight of graphite, 8 parts by weight of PVDF and an appropriate amount of NMP were mixed to prepare an anode forming composition. The composition was coated and dried on a copper current collector to make an anode.

On the other hand, the polypropylene layer was laminated on both sides of the polyethylene layer, and then bonded to prepare a separator.

An electrode assembly was prepared by inserting a separator between the cathode and the anode. The electrode assembly was then wound around a mandrel and then placed in a cylindrical case. Then, an electrolyte solution was injected into the resultant and then sealed to complete a cylindrical lithium ion battery.

Example 3

94 parts by weight of LiNiO ₂ , 3 parts by weight of superpies, 3 parts by weight of PVDF, and an appropriate amount of NMP were mixed to prepare a composition for forming a cathode. The composition was coated and dried on an aluminum current collector to prepare a cathode.

Separately, pentaerythritol, vinylidene fluoride-hexafluoropropylene copolymer, and NMP were mixed to prepare a composition for forming a heat absorbing film. The composition was cast on a polyethylene terephthalate (PET) substrate and hot-air dried to form a film, and then the film was peeled off with the PET substrate to obtain a heat absorbing film. The obtained heat absorption film was laminated on the cathode, and then bonded by heating and pressing it.

92 parts by weight of graphite, 8 parts by weight of PVDF and an appropriate amount of NMP were mixed to prepare an anode forming composition. The composition was coated and dried on a copper current collector to make an anode.

On the other hand, the polypropylene layer was laminated on both sides of the polyethylene layer, and then bonded to prepare a separator.

A separator was laminated on the cathode on which the heat absorbing film was stacked, and then an anode on which the heat absorbing film was stacked was stacked on the separator to prepare an electrode assembly. At this time, the separator and the anode were bonded to each other in the form of a heat absorbing film. The electrode assembly was then wound around a mandrel and then placed in a cylindrical case. The mandrel was removed inside the electrode assembly.

Then, the electrolyte solution was inject | poured into the resultant, and it sealed and completed the cylindrical lithium ion battery.

Comparative example

A cylindrical lithium ion battery was completed in the same manner as in Example 1, except that the space in which the mandrel was removed from the electrode assembly was left intact.

According to Examples 1-3 and Comparative Examples, each of five lithium ion batteries were manufactured, and then a penetration test was conducted to evaluate safety. Here, the penetration test is a test method that artificially causes an internal short by penetrating a cylindrical battery with a nail of 5 mm. At this time, the open circuit voltage of the lithium ion battery according to Example 1-3 was 4.170V.

As a result of the penetration test, in the lithium ion battery of the comparative example, leakage, sparks, fire, and explosion were observed in all five batteries, whereas in the lithium ion battery according to Examples 1-3, all five batteries were leaked, No sparks, fires or explosions were observed.

According to the present invention, it is possible to consume the heat generated in the battery, thereby suppressing the rupture and explosion of the battery it can be produced a lithium secondary battery with improved reliability and safety of the battery.

Claims (6)

A lithium secondary battery comprising a wound electrode assembly including a cathode and an anode, and a separator interposed therebetween, and a case in which the electrode assembly is embedded. At least one of a hollow portion in the wound electrode assembly, a space inside the case, and at least one of the cathode, the anode, and the separator; Lithium secondary battery characterized in that it comprises a polyhydric alcohol (polyhydric alcohol) that absorbs the heat generated from the electrode assembly to a solid-solid phase transition at isothermal. The lithium secondary battery according to claim 1, wherein the polyhydric alcohol is contained in a thermally conductive metal bag located in the hollow portion of the wound electrode assembly. The method of claim 1, wherein when the cathode, anode and / or separator comprises a polyhydric alcohol, The content of the polyhydric alcohol at the cathode and the anode is 2 to 10 parts by weight based on 100 parts by weight of the electrode active material, A lithium secondary battery, characterized in that the content of the polyhydric alcohol in the separator is 1 to 5 parts by weight based on 100 parts by weight of the polymer resin. The lithium secondary battery according to claim 1, wherein the polyhydric alcohol is selected from the group consisting of neopentyl glycol, trimethylol ethane and pentaerythritol. A lithium secondary battery comprising a wound electrode assembly including a cathode and an anode, and a separator interposed therebetween, and a case in which the electrode assembly is embedded. Between the cathode and the separator and / or between the anode and the separator, Lithium secondary battery, characterized in that the heat absorption film containing a polyhydric alcohol (polyhydric alcohol) that absorbs the heat generated from the electrode assembly to the solid-solid phase transition at isothermal. The lithium secondary battery according to claim 5, wherein the polyhydric alcohol is selected from the group consisting of neopentyl glycol, trimethylol ethane and pentaerythritol.