JP2003132949A - Non-aqueous secondary battery and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To provide a non-aqueous secondary battery excellent in overcharge safety, reduced in self-discharge during high-temperature storage, and capable of securing reliability after high-temperature storage. SOLUTION: In a method for manufacturing a non-aqueous secondary battery using a metal oxide or a metal sulfide as a positive electrode active material and using a carbon material or a Li-insertable material for a negative electrode, an organic electrolyte injected into a battery case. A) a compound in which an alkyl group and / or a halogen atom is bonded to a benzene ring is contained therein; A method for manufacturing a non-aqueous secondary battery, characterized by including a monomer material forming a polymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous secondary battery having excellent overcharge safety and ensuring reliability after high temperature storage.

[0002]

2. Description of the Related Art A non-aqueous secondary battery represented by a lithium ion battery using a metal oxide or a metal sulfide as a positive electrode active material and a carbon material or a material capable of inserting Li into a negative electrode has a high voltage and a high voltage. Due to its energy density, its demand is increasing. However, as the energy density increases, the safety decreases, so improving safety is also important. Since the energy density tends to decrease in the usual safety measures, it is desirable to improve the safety while maintaining the energy density.

Hitherto, it has been proposed to add biphenyl (Japanese Unexamined Patent Publication No. 9-171840) or cyclohexylbenzene (Japanese Unexamined Patent Publication No. 2001-015155) into a battery to improve safety during overcharge. ing. According to these additives, gas is generated during overcharging and the current cutoff valve is likely to operate, and in combination with this current cutoff valve, safety is ensured.

[0004]

However, as a result of investigations by the present inventors, in the non-aqueous secondary batteries containing the above-mentioned additives, particularly the batteries of the prismatic type or the laminate type,
It has been found that when this is stored for a long time in a charged state, particularly when it is stored at a high temperature for a long time, self-discharge becomes large and the reliability of the battery cannot be ensured.

In view of such circumstances, the present invention is a non-aqueous secondary battery which is excellent in overcharge safety and has reduced self-discharge during high temperature storage and can sufficiently secure reliability after high temperature storage. Is intended to provide.

[0006]

Means for Solving the Problems The inventors of the present invention have made earnest studies on the above-mentioned object, and as a result, added an additive such as cyclohexylbenzene to an organic electrolytic solution, and added it to the electrolytic solution or the positive electrode. By adding a monomer substance that is polymerized by precharging after battery assembly and forming a conductive polymer film on the positive electrode surface, it is excellent in overcharge safety,
Further, they have found that a non-aqueous secondary battery in which self-discharge during high temperature storage is reduced and which can sufficiently secure reliability after high temperature storage can be obtained, and thus the present invention has been completed.

That is, the present invention provides a non-aqueous secondary battery in which a metal oxide or a metal sulfide is used as a positive electrode active material and a carbon material or a Li-intercalable material is used in a negative electrode.
A) benzene ring has an alkyl group and /
Alternatively, the present invention relates to a non-aqueous secondary battery including a compound to which a halogen atom is bound and having a conductive polymer formed on the surface of the positive electrode. Particularly, in the present invention,
The component A is a compound in which an alkyl group is bonded to a benzene ring, and is 3 to 7% by weight in an organic electrolytic solution. The non-aqueous secondary battery having the above structure, and the conductive polymer being polypyrrole, polyaniline, or these It is possible to provide the non-aqueous secondary battery having the above-mentioned structure, which is a derivative of, and the non-aqueous secondary battery having the above-mentioned structure, which has a prismatic or laminated battery shape.

Further, the present invention provides a method for producing a non-aqueous secondary battery having the above-mentioned constitution, in which A) an alkyl group and / or a halogen atom is bonded to a benzene ring in an organic electrolyte injected into a battery case. Including the compound,
A method for producing a non-aqueous secondary battery, characterized in that B) a monomer substance that forms a conductive polymer on the surface of the positive electrode by precharging after battery assembly is included in the organic electrolyte or the positive electrode. It is related. In particular, the present invention relates to a method for producing a non-aqueous secondary battery having the above-mentioned constitution in which the monomer component of the B component is pyrrole, aniline or a derivative thereof, and the monomer substance of the B component is an alkyl group on the benzene ring of the A component. And / or a method for producing a non-aqueous secondary battery having the above structure, which is 30% by weight or less with respect to a compound to which a halogen atom is bound.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the component A of the present invention, a compound in which an alkyl group is bonded to a benzene ring is a compound in which hydrogen is bonded to a carbon directly bonded to the benzene ring among the carbons constituting the alkyl group. However, it is particularly desirable because it improves the safety of overcharge. Specifically, cyclohexylbenzene, isopropylbenzene, n-butylbenzene,
Examples include octylbenzene, toluene, xylene and the like. Among these, it is particularly desirable that the alkyl group bonded to the benzene ring has a long carbon number of 4 or more.
The alkyl group having a branched structure or the like and having a sterically bulky structure is preferable, and cyclohexylbenzene is particularly preferable. Further, the compound having a halogen atom bonded to the benzene ring may be fluorobenzene, difluorobenzene, or the like, or the compound having a halogen atom such as a fluorine atom or a chlorine atom further bonded to the compound having an alkyl group bonded to the benzene ring. In particular, a compound having a fluorine atom bonded is desirable.

The amount of the compound of the component A to be added in the organic electrolyte is
The amount is 1% by weight or more, preferably 2.5% by weight or more, more preferably 3% by weight or more, and further preferably 4% by weight or more. Further, in order to reduce self-discharge during high temperature storage, it is preferably 10% by weight or less, preferably 7% by weight or less, more preferably 6% by weight or less in the organic electrolyte.

According to the studies by the present inventors, in the battery constitution of the present invention, the compound of the above-mentioned component A, in particular, the compound in which an alkyl group is bonded to the benzene ring is added in an organic electrolytic solution to
Addition in the range of ~ 7 wt%, especially in the range of 4-6 wt%, it is possible to highly satisfy both overcharge safety and low self-discharge property during high temperature storage. In particular, regarding overcharge safety, It was found that even non-aqueous secondary batteries in the shape of prismatic or laminated batteries, which normally do not have a current cutoff valve, can provide sufficient overcharge safety. It was

In the present invention, the above-mentioned A is added to the organic electrolytic solution.
While containing the compound of the component in the above proportion, it is characterized by forming a conductive polymer on the surface of the positive electrode, by this conductive polymer, self-discharge during high temperature storage was reduced,
It is possible to obtain a non-aqueous secondary battery that can sufficiently secure reliability after high temperature storage. Examples of the conductive polymer include polypyrrole, polyaniline, and derivatives thereof. Although the reason why the above effect is achieved by the formation of such a conductive polymer is not clear, the active site on the positive electrode surface is covered with the conductive polymer, and the compound of the component A reacts on the positive electrode surface. It seems that this is to suppress the phenomenon of self-discharge.

In the present invention, the method for forming the conductive polymer on the surface of the positive electrode is not particularly limited, and any method can be adopted, but it is preferable to use a high conductive material as the B component in the organic electrolyte or the positive electrode. It is advisable to employ a method in which a monomer substance for forming a molecule is included, and this is polymerized by preliminary charging after battery assembly. If the conductive polymer is polypyrrole, polyaniline or a derivative thereof, pyrrole, aniline or a derivative thereof is used as the monomer substance. The above derivatives include methylpyrrole, phenylpyrrole, dimethylaniline,
Examples include phenylaniline and diphenylaniline. Among these, those that generate little gas during polymerization are preferable, and those in which the nitrogen atom is replaced by an atom or group other than hydrogen atom that does not generate gas, and particularly aromatic substitution products are preferable.

Such a monomer component of the B component causes swelling of the battery and an increase in impedance if too much thereof is contained, so that it is preferably 30% by weight or less, more preferably 10% by weight, based on the compound of the A component. The following is most preferable and it is 2.5% by weight or less. If the amount is too small, the above effect cannot be obtained. Therefore, the amount is preferably 0.1% by weight or more, more preferably 1% by weight or more, and most preferably 2% by weight or more based on the compound of the component A. . After the polymerization of such a monomer substance, the battery is disassembled and the surface of the positive electrode is observed and analyzed, whereby it can be confirmed that a film of a conductive polymer is formed on the surface of the positive electrode.

In the present invention, as the organic electrolytic solution containing the compound of the component A or the monomer substance of the component B, a solution prepared by dissolving a lithium salt as an electrolyte in an organic solvent is used. As the electrolyte, a polymer or solid may be used depending on the case. The organic solvent, ethylene carbonate, pyropyrene carbonate, butylene carbonate, dimethyl carbonate,
Carbonic acid esters such as methyl ethyl carbonate and diethyl carbonate, and esters such as methyl γ-butyrolactone acetate are used as the main solvent.

Other solvents include 1,3-dioxolane,
Organic solvents such as ethers such as 1,2-dimethoxyethane, sulfur compounds such as sulfolane, nitrogen-containing compounds, silicon-containing compounds, fluorine-containing compounds and phosphorus-containing compounds can also be used. Further, it is desirable to dissolve a compound having a —SO ₂ bond, particularly a compound having a —O—SO ₂ bond, in these organic solvents. Specifically, 1,3
-Propane sultone, methyl ethyl sulphonate, diethyl sulphate etc. These compounds are preferably used in an organic solvent in an amount of 0.5 to 10% by weight, particularly preferably 1 to 5% by weight.

The lithium salt which is the electrolyte contains LiP
F ₆ , LiC _n F _{2n + 1} SO ₃ (n> 1), LiCl
O ₄ , LiBF ₄ , LiAsF ₆ , (C _n F _{2n + 1} S
O ₂ ) (C _m F _{2m +1} SO ₂ ) NLi (m, n ≧ 1). In addition, (RfOSO ₂ ) ₂ NLi [Rf is an alkyl group containing a halogen having 2 or more carbon atoms, two Rf's may be the same or different, and Rf's are bonded to each other, for example, in a polymer form. May be bound to
Can also be used, for example {CH ₂ (CF ₂ ) ₄ CH ₂ OS
_{O 2 N (Li) SO 2} O} n (n: integer) and the like. Of these, LiPF ₆ and fluorine-containing organic lithium salts having 2 or more carbon atoms are particularly preferable. Lithium salt
It is usually used at a rate of 0.1 to 2 mol / liter in an organic solvent.

In the present invention, the positive electrode active material is LiC.
lithium cobalt oxide such as oO ₂ , LiMn ₂ O ₄
Lithium manganese oxides such as, lithium nickel oxides such as LiNiO ₂ , metal oxides such as manganese dioxide, vanadium pentoxide, and chromium oxide, and metal sulfides such as titanium disulfide and molybdenum disulfide are used.
The positive electrode is a positive electrode mixture prepared by appropriately adding a conductive auxiliary agent or a binder such as polyvinylidene fluoride to these positive electrode active materials,
A molded product is used as a core material of a current collector such as aluminum foil. Especially LiNiO ₂ and LiCo
Like O ₂ and LiMn ₂ O ₄ , L when charged
It is desirable to use a positive electrode active material having a voltage of 4.2 V or higher on the basis of i. Further, it is desirable that the positive electrode active material be a lithium composite oxide showing an open circuit voltage after charging of 4.3 V or more on the Li basis.

KS6 having high crystallinity is used as the conductive additive for the positive electrode.
And graphite such as carbon black having low crystallinity are used. If the amount of the conductive additive is small, the reactivity with the organic electrolyte in the charged state can be reduced, but if it is too small, the battery characteristics deteriorate, and if it is too large, it causes gas generation. , 1 to 5% by weight, preferably 1.5 to
It is good to be 3% by weight, more preferably 2 to 2.5% by weight. The ratio of carbon with low crystallinity is 5 in the entire conductive additive.
It should be 0 to 90% by weight, preferably 70 to 80% by weight. When the amount of the conductive additive is small and the ratio of graphite having high crystallinity is high, the electrical characteristics tend to be deteriorated.

In the present invention, the negative electrode is made of a carbon material or a material into which Li can be inserted.
A material obtained by dispersing a binder, optionally a conductive auxiliary agent, in the above-mentioned material in a solvent, applying this to a current collecting material such as a copper foil, drying, and finishing into a molded body is used. In the above Li insertable material, a metal compound containing tin or silicon (for example, SnO _x , SiO _x, etc.) is used as a metal oxide, and Li _2.6 C is used as a metal nitride.
o _0.4 N or the like is used.

In the present invention, the positive electrode and the negative electrode described above are loaded into a battery case with various known separators interposed between both electrodes, and the organic electrolyte injected into the battery case contains the compound of the component A. Further, after assembling the battery by including the monomer substance of the component B in the organic electrolyte or in the positive electrode, the battery is preliminarily charged to polymerize the monomer substance to form a non-conductive polymer on the surface of the positive electrode. Use a water secondary battery.

The non-aqueous secondary battery of the present invention is particularly effective when it is formed into a prismatic type or a laminated type. However, various other forms such as a cylinder type, a button type, and a coin type may be used, and the battery form is not particularly limited.

[0023]

EXAMPLES The present invention will be described in more detail below by way of its examples. However, the present invention is not limited to the following examples.

[0024] Example 1 First, after obtained by dissolving LiPF ₆ in ethylene carbonate, added and mixed methyl ethyl carbonate, a LiPF ₆ in a mixed solvent of a volume ratio of 1/2 of ethylene carbonate and methyl ethyl carbonate 1. 2 mol / l was dissolved. 4% by weight of cyclohexylbenzene (compound of component A), 0.2% by weight of phenylpyrrole (monomer substance of component B), and 2% by weight of 1,3-propane sultone as additives were added to the mixture to prepare an organic compound. An electrolytic solution was prepared.

Next, 0.5% by weight of graphite and 2% by weight of carbon black were added to 93.5% by weight of LiCoO ₂ and mixed, and 4% by weight of polyvinylidene fluoride was dissolved in N-methylpyrrolidone in advance. It was dispersed in the above solution to obtain a positive electrode mixture slurry. This positive electrode mixture slurry,
It was evenly applied to both sides of an aluminum foil having a thickness of 15 μm as a positive electrode current collector (however, it was not applied to the innermost peripheral inner surface side not facing the negative electrode), dried, and then compressed by a roller press machine. After molding and cutting into a predetermined size, the lead body was welded to produce a strip-shaped positive electrode.

Separately from this, 95% by weight of the mesocarbon microbead fired body was dispersed in a solution in which 5% by weight of polyvinylidene fluoride was dissolved in N-methylpyrrolidone in advance to prepare a negative electrode mixture slurry. this,
After applying it to both sides of a strip-shaped copper foil having a thickness of 10 μm as a negative electrode current collector (however, it was not applied to the outermost peripheral outer surface side not facing the positive electrode), then drying, and then compression molding with a roller press machine. Then, after cutting into a predetermined size, the lead body was welded to produce a strip-shaped negative electrode.

Next, a current collecting tab is attached to each of the positive electrode and the negative electrode, and the positive electrode and the negative electrode have a thickness of 20.
An electrode body was obtained by stacking and winding via a separator made of a microporous polyethylene film of μm. An insulating tape was attached to this, and it was inserted into a battery case having a size of 5 mm × 30 mm × 48 mm, and the lead body was welded and the battery lid was laser-welded to the open end of the battery case. Then, the organic electrolyte solution was injected into the battery case from the electrolyte solution inlet provided in the battery lid, and after this injection, the electrolyte solution inlet was sealed to make the inside of the battery hermetically sealed. After that, preliminary charging was performed to manufacture a rectangular non-aqueous secondary battery.

FIG. 1 is a schematic view of the prismatic non-aqueous secondary battery thus manufactured. In the figure, 1 is a positive electrode, 2 is a negative electrode, and 3
Is a separator. In order to avoid complexity, the current collectors used in the production of the positive electrode 1 and the negative electrode 2 are not shown. Reference numeral 4 is a battery case made of aluminum, which also serves as a negative electrode terminal. An electrode body having a flat spiral structure composed of a positive electrode 1, a negative electrode 2 and a separator 3 and an organic electrolytic solution are housed in the battery case 4. An insulator 5 made of a polytetrafluoroethylene sheet is arranged at the bottom of the battery case 4, and the positive electrode 1 and the negative electrode 2 are made from the flat spiral structure electrode body 6 made of the positive electrode 1, the negative electrode 2 and the separator 3. Positive electrode lead body 7 connected to one end of each
And the negative electrode lead body 8 are pulled out. A terminal plate 11 made of stainless steel is attached to a cover plate 9 made of an aluminum alloy that seals the opening of the battery case 4 via an insulating packing 10 made of polypropylene, and a stainless steel terminal 11 is attached to the terminal 11 via an insulator 12. A steel lead plate 13 is attached. The lid plate 9 is inserted into the opening of the battery case 4, and the joint between the two is welded to seal the opening of the battery case 4 and seal the inside of the battery. It was confirmed from the result of disassembling this non-aqueous secondary battery and analyzing a part of the film of the above electrode that a conductive polymer was formed.

Comparative Example 1 A prismatic non-aqueous secondary battery was produced in the same manner as in Example 1 except that phenylpyrrole was not added to the organic electrolytic solution.

Comparative Example 2 A prismatic non-aqueous secondary battery was produced in the same manner as in Example 1 except that cyclohexylbenzene was not added to the organic electrolytic solution.

With respect to each of the non-aqueous secondary batteries of Example 1 and Comparative Examples 1 and 2 above, an overcharge safety test and a storage test were conducted by the following methods to evaluate the battery performance. The results are shown in Table 1.

<Overcharge Safety Test> First, each battery was discharged at room temperature at 1 CmA to 3.0 V, and at 1 C, 4.2 V, C
After charging with CCV for 2.5 hours, the battery was discharged with 0.2 CmA to 3.0. The positive electrode potential when charged to 4.2V is
It was 4.3 V based on Li. As an overcharge safety test,
After charging the battery at 1 CmA to 4.2V and CCCV for 2.5 hours, 0.5V, 1A, 2A, 5A with 6V as the upper limit voltage.
Overcharged with A. The maximum current at which the surface temperature of the battery was 135 ° C. or lower was defined as the overcharge safe current value.

<Storage Test> The battery was 4.2 V at 1 CmA,
After charging at CCCV for 2.5 hours, the battery was discharged at 1 CmA to 3.0V (the capacity at this time is X). Then 1
Charging was performed at 4.2 V with CmA and 2.5 hours with CCCV. After that, after storing for 20 days in a constant temperature bath at 60 ° C,
It was discharged to 3.0 V at 1 CmA (the capacity at this time is Y). From these capacities X and Y, the self-discharge rate (%) = [(X−Y) / X] × 100 was calculated.

[0034]

From the results of Table 1 above, the battery of Example 1 has a higher overcharge safety than the battery of Comparative Example 2 in which only the monomer substance of component B was included and the compound of component A was not included. It can be seen that the self-discharge during high temperature storage can be suppressed and the reliability after high temperature storage can be ensured while increasing the value 10 times or more. On the other hand, the battery of Comparative Example 1 containing only the compound of the component A and not containing the monomer substance of the component B had an increased self-discharge during high temperature storage even though the overcharge safety was satisfied. , Reliability after high temperature storage could not be secured.

[0036]

As described above, according to the present invention, a metal oxide or a metal sulfide is used as a positive electrode active material, a carbon material or a Li insertable material is used for a negative electrode, and
By including a compound in which an alkyl group and / or a halogen atom is bonded to the benzene ring as a component and forming a conductive polymer on the surface of the positive electrode, it is excellent in overcharge safety, and moreover, after being stored at high temperature. A non-aqueous secondary battery with excellent reliability can be provided.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a configuration example of a non-aqueous secondary battery of the present invention.

[Explanation of symbols]

1 positive electrode 2 Negative electrode 3 separator 4 battery case

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Haruki Kamizure             Hitachima, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. F term (reference) 5H029 AJ12 AK02 AK03 AK05 AL01                       AL02 AL06 AL07 AL08 AM03                       AM04 AM05 AM07 BJ02 BJ04                       BJ14 DJ09 EJ13 HJ01                 5H050 AA10 AA15 BA17 CA02 CA07                       CA08 CA09 CA11 CB01 CB02                       CB07 CB08 CB09 DA09 DA13                       EA26 FA05 GA13 GA18 HA01

Claims (7)

[Claims] 1. A non-aqueous secondary battery using a metal oxide or a metal sulfide as a positive electrode active material and using a carbon material or a Li-intercalable material for a negative electrode in an organic electrolyte solution.
A) A non-aqueous secondary battery comprising a compound in which an alkyl group and / or a halogen atom is bonded to a benzene ring and having a conductive polymer formed on the surface of the positive electrode. 2. The non-aqueous secondary battery according to claim 1, wherein the component A is a compound in which an alkyl group is bonded to a benzene ring, and is 3 to 7% by weight in the organic electrolytic solution. 3. The non-aqueous secondary battery according to claim 1, wherein the conductive polymer is polypyrrole, polyaniline or a derivative thereof. 4. The non-aqueous secondary battery according to claim 1, wherein the battery has a rectangular shape or a laminated shape. 5. The method for producing a non-aqueous secondary battery according to claim 1, wherein A) a benzene ring has an alkyl group and / or an organic group in the organic electrolyte injected into the battery case. In addition to containing a compound to which a halogen atom is bound, B) a monomer substance that forms a conductive polymer on the surface of the positive electrode by precharging after battery assembly is included in the organic electrolyte or the positive electrode. A method for manufacturing a non-aqueous secondary battery, comprising: 6. The method for producing a non-aqueous secondary battery according to claim 5, wherein the monomer substance of the component B is pyrrole, aniline or a derivative thereof. 7. The non-aqueous diamine according to claim 5, wherein the content of the monomer component of the component B is 30% by weight or less based on the compound in which the benzene ring of the component A is bonded with an alkyl group and / or a halogen atom. Next battery manufacturing method.