JP4035854B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

【００２９】
【発明の効果】
以上のように、少なくとも正極活物質、負極活物質、セパレータ、非水電解液からなる二次電池であって、これらを収納する電池容器内に沸点が２５℃以下の含フッ素有機化合物を存在させることにより、非水電解液二次電池の電池特性を損なうことなくその安全性を著しく向上でき、工業的意義は大きい。
【図面の簡単な説明】
【図１】図１は本願発明の非水電解液二次電池の一例を側面視した概念図である。
【図２】図２は本願発明の非水電解液二次電池の一例を側面視した概念図である。
【図３】図３は本願発明の非水電解液二次電池の一例を側面視した概念図である。
【図４】図４は本願発明の非水電解液二次電池の一例を側面視した概念図である。
【符号の説明】
１ 非水電解液
２ 含フッ素有機化合物[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery. In particular, the present invention relates to a non-aqueous electrolyte secondary battery used in a field having a large capacity, a high energy density, and a high demand for maintenance-free, such as for electric vehicles and power load leveling.
[0002]
[Prior art]
In recent years, in response to the reduction in size and weight of electronic devices, lithium-ion secondary batteries for electronics have been put into practical use as power sources and are used in handy video cameras, portable personal computers, and the like. Furthermore, electric vehicles are attracting attention due to environmental problems and the like, and attention is being focused on sealed, maintenance-free lithium-ion secondary batteries with high energy density.
[0003]
[Problems to be solved by the invention]
It is known that non-aqueous electrolyte secondary batteries generally use a flammable non-aqueous organic compound in the electrolyte and may cause ignition problems.
When lithium or a lithium alloy is used as the negative electrode active material, these serve as an ignition source and cause ignition.
[0004]
Even a lithium ion secondary battery using a compound capable of occluding and releasing lithium as the negative electrode active material causes problems if not used correctly. In particular, lithium ion secondary batteries can cause ignition problems when overcharged to a level far exceeding the recommended charging voltage.
Various lithium ion secondary batteries using solid electrolytes have been proposed from the viewpoint of the above-described battery safety, but sufficient performance has not been obtained yet.
[0005]
[Means for Solving the Problems]
As a result of intensive investigations in view of the above problems, it is possible to improve the safety of the battery without deteriorating the performance of the conventional non-aqueous electrolyte secondary battery by making the non-combustible gas exist in the battery container. It was found that it was possible to arrive at the present invention.
That is, the gist of the present invention is a secondary battery comprising at least a positive electrode active material, a negative electrode active material, a separator, and a non-aqueous electrolyte solution, and a self-incombustibility having a boiling point of 25 ° C. or less in a battery container housing these . Or it exists in the nonaqueous electrolyte secondary battery characterized by making a fire extinguishing fluorine-containing organic compound (however, excluding dibromodifluoromethane) exist.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The non-aqueous electrolyte secondary battery of the present invention comprises at least a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte.
The negative electrode active material may be lithium or a lithium alloy, but a carbon material that can occlude and release lithium with higher safety is preferable. The carbon material is not particularly limited, but graphite, coal-based coke, petroleum-based coke, coal-based pitch carbide, petroleum-based pitch carbide, needle coke, pitch coke, carbide such as phenol resin / crystalline cellulose, etc. Examples thereof include partially graphitized carbon materials, furnace black, acetylene black, and pitch-based carbon fibers.
[0007]
The positive electrode active material is preferably a metal oxide compound or a chalcogenite compound that can occlude or intercalate lithium, and examples thereof include LixCoO ₂ , LixMnO ₂ , LixMn ₂ O ₄ , LixV ₂ O ₅ , and LixTiS ₂ .
As the negative electrode, a material obtained by applying a slurry of a negative electrode active material and a binder (binder) with a solvent and drying it can be used.
[0008]
As the positive electrode, a product obtained by applying a slurry of a positive electrode active material, a binder (binder), and a conductive agent with a solvent and drying it can be used.
Examples of the binder (binder) for the negative electrode / positive electrode active material include polyvinylidene fluoride, polytetrafluoroethylene, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR ( (Acrylonitrile-butadiene rubber), fluororubber and the like, but are not limited thereto.
[0009]
As the conductive agent for the positive electrode, fine particles of graphite, carbon black such as acetylene black, and amorphous carbon fine particles such as needle coke are used, but are not limited thereto.
As the solvent for forming a slurry, an organic solvent that dissolves the binder is usually used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N 2 , N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like can be mentioned, but not limited thereto. . Moreover, a dispersing agent, a thickener, etc. are added to water, and an active material may be slurried with latex, such as SBR.
[0010]
When a current collector is used for the negative electrode, copper, nickel, stainless steel, nickel-plated steel or the like is used, and when a positive electrode current collector is used, aluminum, stainless steel, nickel-plated steel or the like is used.
As the separator, a microporous polymer film is used, and a material made of a polyolefin polymer such as nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, polybutene, or the like is used. . The chemical and electrochemical stability of the separator is an important factor. In this respect, a polyolefin-based polymer is preferable, and polyethylene is preferable from the viewpoint of the self-occluding temperature, which is one of the purposes of the battery separator.
[0011]
In the case of a polyethylene separator, ultrahigh molecular weight polyethylene is preferable from the viewpoint of maintaining high-temperature shape, and the lower limit of the molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1.5 million. On the other hand, the upper limit of the molecular weight is preferably 5 million, more preferably 4 million, and most preferably 3 million. This is because if the molecular weight is too large, the pores of the separator may not close when heated because the fluidity is too low.
[0012]
As the electrolytic solution, for example, an electrolytic solution in which a lithium salt is used as an electrolyte and dissolved in an organic solvent is used. Here, the organic solvent is not particularly limited, but for example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, amines, esters, amides. Further, phosphoric acid ester compounds can be used. Typical examples of these are listed: propylene carbonate, ethylene carbonate, vinylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 4-methyl-2-pentanone, 1,2-dimethoxyethane, 1,2 -Diethoxyethane, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, benzonitrile, butyronitrile, valeronitrile, 1,2 -A single or two or more kinds of mixed solvents such as dichloroethane, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, and triethyl phosphate can be used. Any conventionally known electrolyte can be used, and LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, etc. are used. It is done.
[0013]
The nonaqueous electrolyte secondary battery of the present invention is characterized in that a fluorine-containing organic compound (except for dibromodifluoromethane) having a boiling point of 25 ° C. or less is present in the battery container.
Examples of the fluorine-containing organic compound having a boiling point of 25 ° C. or less include compounds in which a hydrogen atom of an alkane having 4 or less carbon atoms is substituted with a halogen (at least one hydrogen atom needs to be substituted with a fluorine atom). However, this is not a limitation. The fluorine-containing organic compound of the present invention is preferably a self-incombustible fluorine-containing organic compound, and more preferably a fire-extinguishing fluorine-containing organic compound. Examples of the fire extinguishing fluorine-containing organic compound include CF ₃ CHFCF ₃ , CF ₃ Br , CF ₂ ClBr, CHF ₃ , and C ₄ F ₁₀ . On the other hand, a compound containing a fluorine atom and a halogen atom other than fluorine in one molecule has a high possibility of destruction of the ozone layer, and is not preferable from the viewpoint of influence on the environment. Therefore, a fluorine-containing organic compound having a fire extinguishing property that does not contain a halogen atom other than fluorine is most preferable, and CF ₃ CHFCF ₃ is the most preferable compound.
[0014]
The ignition of the battery is caused by the ignition of the combustible gas ejected from the battery container for some reason. The vapor of the organic electrolyte is a source of combustible gas. By diluting the jetted steam with the fluorine-containing organic compound gas of the present invention, it is substantially impossible to ignite, and the safety of the battery can be ensured. In the case of using a fire extinguishing fluorine-containing organic compound, in addition to the dilution effect described above, it has the effect of stopping the reaction by capturing the active radicals generated by the flammable gas igniting momentarily. It is more preferable in terms of ensuring the safety of the battery.
[0015]
Therefore, the boiling point of the fluorine-containing organic compound of the present invention needs to be 25 ° C. or less. This is because the possibility that the battery has a problem needs to be considered from around room temperature, and the vapor pressure of the fluorine-containing organic compound needs to be sufficiently high around room temperature.
The proportion of the fluorine-containing organic compound of the present invention in the gap of the battery container in a 25 ° C. atmosphere is preferably 10% by volume or more, more preferably 20% by volume or more, and most preferably 30% by volume or more. The higher the proportion of the fluorine-containing organic compound, the more nonflammability can be ensured.
[0016]
The specific gravity of the fluorine-containing organic compound of the present invention is preferably 2 × 10 ⁻³ g / cm ³ or more, more preferably 3 × 10 ⁻³ g / cm ³ or more, and most preferably 3 × 10 ⁻³ g / cm ^3. That's it. It is preferable that the specific gravity of the fluorine-containing organic compound is large because it is difficult to dissipate and effectively acts on nonflammability.
The non-aqueous electrolyte secondary battery of the present invention is effective when applied to a large battery having a large amount of organic electrolyte. It is particularly preferable to use it for a large battery represented by an automobile. In addition, compared with a small battery, a large battery can easily secure a void capable of holding a fluorine-containing organic compound, and can easily exert an effect.
[0017]
In addition, although the concept of the structure of the storage container of the battery of this invention is illustrated with a figure, this invention is not limited to these, unless the summary is exceeded. FIG. 1 is an example of a conceptual diagram when the fluorine-containing organic compound 2 of the present invention is present on a non-aqueous electrolyte 1 as seen from the side. For example, when the pressure inside the secondary battery rises due to a temperature rise or the like, and the safety valve etc. is opened and ejected, the vaporized non-aqueous electrolyte should be ejected after being easily mixed with the fluorine-containing organic compound of the present invention. And nonflammability can be secured. Further, as shown in FIG. 2, if the side surface is filled, a larger amount of the fluorine-containing organic compound of the present invention can be filled. Further, as shown in FIG. 3, if the whole is encased in the fluorine-containing organic compound of the present invention, it is easy to ensure nonflammability even when a hole is opened in the battery due to some accident. As shown in FIG. 4, it is also effective to put several secondary batteries in one container and fill the periphery with the fluorine-containing organic compound of the present invention.
[0018]
In a large battery which is a preferred application of the battery of the present invention, a plurality of batteries are often used in combination, and the fluorine-containing organic compound of the present invention is present in a large container containing a plurality of batteries. May be.
[0019]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited by a following example, unless the summary is exceeded. In addition, the evaluation method in an Example is as follows. In the examples and comparative examples, “parts” means “parts by weight”.
[0020]
(Comparative Example 1)
(Negative electrode)
90 parts of coal-based needle coke having an average particle diameter of 10 μm (weight ratio; unless otherwise specified) is mixed with an N-methylpyrrolidone solution (2% by weight) of 10 parts of polyvinylidene fluoride to prepare a negative electrode mixture slurry. It was. It is applied to both sides of a 20 μm-thick copper foil, dried to evaporate the solvent, and roll-processed to make a negative electrode. The size of the application part of the negative electrode mixture was 12 cm × 15 cm, and the thickness was 250 μm on one side. On the left and right sides of the copper foil, the negative electrode mixture is designed so as to leave an ear of 25 mm on the left and 15 mm on the right.
In addition, the electrode which comprises the edge of a single cell applies a negative mix to only one side.
[0021]
(Positive electrode)
1 mol of lithium carbonate and 2 mol of cobalt carbonate were mixed and ground in a ball mill, heat-treated in air at 850 ° C. for 5 hours, then mixed and ground in a ball mill again, and further heat-treated in air at 850 ° C. for 5 hours. A mixture obtained by adding 5 parts of acetylene black as a conductive agent to 90 parts was mixed with an N-methylpyrrolidone solution (2 wt%) of 5 parts of polyvinylidene fluoride to obtain a positive electrode mixture slurry. It is applied to both sides of a 25 μm thick aluminum foil, dried to evaporate the solvent, and roll-processed to produce a positive electrode. The size of the application part of the positive electrode mixture was 12 cm × 15 cm, and the thickness was 250 μm on one side. On the left and right sides of the aluminum foil, the positive electrode material mixture is designed so as to leave 25 mm on the right and 15 mm on the left.
In addition, the electrode which comprises the edge of a cell is what apply | coated the positive mix to only one side.
[0022]
(Separator)
After feeding 20 parts of ultrahigh molecular weight polyethylene powder having a melting point of 135 ° C. and a molecular weight (average viscosity) of 2 × 10 ⁶ and 80 parts of ceryl alcohol to the extruder and continuously extruding from a T-die while kneading at 230 ° C. Then, melt deformation was applied in the MD direction to obtain a film having a thickness of 50 μm. The obtained film is immersed in isopropyl alcohol at 80 ° C., ceryl alcohol is extracted and removed from the film, and then heat-treated with a heated pinch roll having a surface temperature of 125 ° C. for 30 seconds to form a porous film having a thickness of 25 μm. Got.
[0023]
(Assembly of single cells)
The negative electrode and the positive electrode are alternately stacked via separators to assemble a unit cell. In that case, the electrode of both ends uses what applied the electrode mixture only to one side. The negative electrode and the positive electrode are separately welded with metal rods, and a current collector is formed in which the negative electrode and the positive electrode are separately electrically connected.
The unit cells are fastened with a non-conductive frame in the stacking direction. By stacking 26 sets of electrodes of the above size and half (the electrodes at both ends are half because the electrode mixture is applied only on one side), a unit cell having a charge / discharge capacity of about 350 Wh was produced.
[0024]
(Assembly of assembled battery)
The unit cell is vacuum degassed at 1 × 10 ⁻² Torr or less and then put into a dry box that has been replaced with Ar gas.
Ten unit cells are accommodated in a polypropylene container having a partition wall, an electrolyte is injected, and the upper lid is closed. At this time, the negative electrode terminal and the positive electrode terminal of each unit cell protrude through the upper part of the container through the upper lid. This terminal is sealed with an appropriate sealant at the penetrating portion of the upper lid. At this time, a hole having a diameter of 10 mm is made in the upper part of the polypropylene container. As the electrolytic solution, 1 mol / l of hexafluorophosphoric acid lithium salt (LiPF ₆ ) was dissolved in a mixed solvent having a ratio of ethylene carbonate and 1,2-dimethoxyethane of 1: 1.
After charging at a constant current density of 1 mA / cm ^{2 at} a constant current density of 25 ° C. until the battery voltage reaches 4.0 V, the hole at the top of the container is covered with a rubber stopper coated with an adhesive.
The volume of Ar gas at 25 ° C. is 92% by volume.
[0025]
(Battery evaluation)
After charging the above assembled battery in a 25 ° C. atmosphere at a constant current density of 1 mA / cm ² until the battery voltage reaches 4.3 V, remove the rubber stopper at the top of the container and remove the test flame in accordance with JIS K2810. When approached, it ignited. Table 1 shows the results of evaluation in the same manner by changing the temperature at which the assembled battery is placed.
[0026]
Example 1
In Comparative Example 1, an assembled battery was assembled in the same manner as in Comparative Example 1 except that CF ₃ CHFCF ₃ gas was used instead of Ar gas, and initial charging was performed.
The volume of CF ₃ CHFCF ₃ gas at 25 ° C. in the obtained battery is 92% by volume.
[0027]
The obtained battery was charged in a 25 ° C. atmosphere at a constant current density of 1 mA / cm ² until the battery voltage reached 4.3 V, and then the rubber stopper on the top of the container was removed, and the test was conducted for 1 second in accordance with JIS K2810. Even if the flame approached, it did not ignite. Thereafter, the temperature was changed in the same manner as described above, but none of them ignited.
The battery characteristics of Example 1 were equivalent to those of Comparative Example 1.
[0028]
[Table 1]

[0029]
【The invention's effect】
As described above, a secondary battery comprising at least a positive electrode active material, a negative electrode active material, a separator, and a non-aqueous electrolyte solution, and a fluorine-containing organic compound having a boiling point of 25 ° C. or less is present in a battery container that accommodates the secondary battery. Thus, the safety of the non-aqueous electrolyte secondary battery can be remarkably improved without impairing the battery characteristics, and the industrial significance is great.
[Brief description of the drawings]
FIG. 1 is a conceptual view of an example of a nonaqueous electrolyte secondary battery according to the present invention as viewed from the side.
FIG. 2 is a conceptual diagram showing a side view of an example of a nonaqueous electrolyte secondary battery of the present invention.
FIG. 3 is a conceptual diagram showing a side view of an example of a nonaqueous electrolyte secondary battery of the present invention.
FIG. 4 is a conceptual diagram showing a side view of an example of the nonaqueous electrolyte secondary battery of the present invention.
[Explanation of symbols]
1 Non-aqueous electrolyte 2 Fluorinated organic compound

Claims (6)

A secondary battery comprising at least a positive electrode active material, a negative electrode active material, a separator, and a non-aqueous electrolyte, and a self-incombustible or fire-extinguishing fluorine-containing organic compound having a boiling point of 25 ° C. or less in a battery container housing these (However, excluding dibromodifluoromethane) is present in the non-aqueous electrolyte secondary battery.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the fluorine-containing organic compound is a compound in which a hydrogen atom of an alkane having 4 or less carbon atoms is substituted with a halogen. The non-aqueous electrolysis according to claim 1 or 2 , wherein the fluorinated organic compound is a fluorinated organic compound selected from the group consisting of CF ₃ CHFCF ₃ , CF ₃ Br, CF ₂ ClBr, CHF ₃ , and C ₄ F _10. Liquid secondary battery. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3 , wherein a proportion of the fluorine-containing organic compound in a void portion of the battery container is 10% by volume or more in a 25 ° C atmosphere. Fluorine-containing organic _compound, a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4 is CF 3 CHFCF _3. A secondary battery comprising at least a positive electrode active material, a negative electrode active material, a separator, and a non-aqueous electrolyte, and a CF ₃ CHFCF ₃ , CF ₃ Br, CF ₂ ClBr, CHF ₃ , C ₄ F ₁₀ A non-aqueous electrolyte secondary battery comprising a fluorine-containing organic compound selected from the group consisting of:

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