JPH07169505A - Lithium secondary battery - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a long-life and safe lithium secondary battery by sufficiently suppressing the generation of dendrites. [Structure] Formula [Chemical Formula 1] [M is a number from 1 to 4 substituents, R1 is hydrogen or an alkyl group having 1 to 4 carbon _{atoms, -C 6 H 5, -F,} -Cl,
_{-Br, -I, -OH, -OCH 3} , -OC 2 H 5, -
_{CN, -NH 2, -N (CH} 3) 2, -SO 3 H, -C
A quinone represented by OOR (R represents at least one substituent of the group consisting of hydrogen or an alkyl group having 1 to 4 carbon atoms) in an amount of 0.005 to 1.0 mol / mol of the electrolyte.
kg is included.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, batteries have become smaller, lighter and thinner.
Higher performance has been desired, and lithium is used as a negative electrode active material for high energy batteries that meet these requirements, and a nonaqueous electrolytic solution as a electrolyte, a solid electrolyte or a polymer matrix containing a nonaqueous electrolytic solution is used. A lithium secondary battery using is proposed. However, in a lithium secondary battery, since lithium, which is a negative electrode active material, does not deposit uniformly on the surface of the negative electrode active material during charging of the battery, dendritic dendrites form from the surface of the negative electrode active material when the battery is repeatedly charged and discharged. grow up. Therefore, there is a problem in that the grown dendrites fall off and the negative electrode active material cannot be fully utilized for charge / discharge, or the dendrites grow to the positive electrode active material to cause a short circuit between the electrode plates to lose the battery function. Further, when such a short circuit between the electrode plates occurs, an excessive current flows into the battery, the battery temperature rises abnormally, and the organic electrolyte solution volatilizes. Therefore, the internal pressure of the battery rises, and in the worst case, the battery bursts or explodes. In particular, when the battery explodes, chemically active lithium reacts with moisture in the air to generate hydrogen gas according to the reaction formula of Li + H ₂ O → LiOH + 1 / 2H ₂ , resulting in a serious safety problem.

Therefore, it has been proposed to use a lithium alloy such as Li-Al as the negative electrode active material. When a Li alloy is used as the negative electrode active material, an Li alloying reaction occurs at the time of charging the battery, and dendrite growth is suppressed. However, in this type of battery, the potential of the negative electrode shifts to the positive electrode side due to the alloying of the negative electrode active material, the electromotive force of the battery decreases, and the lithium alloy powders as the charging and discharging of the battery progress, There is a problem that the negative electrode active material is not used for charging and discharging.

A battery has also been proposed in which a negative electrode active material holder made of a carbonaceous material capable of electrochemically absorbing and desorbing lithium ions is arranged on the negative electrode side to prevent the generation of dendrites. However, this type of battery has a problem that the energy density is low and dendrite formation cannot be sufficiently suppressed during rapid charging.

Therefore, the addition of various additives to the electrolyte to improve the charge / discharge characteristics has been studied. For example, pyridine (JP-A-49-108525), crown compound (JP-A-57-141878), ethylenediamine (JP-A-58-87777), as an additive to be added to an electrolyte composed of a non-aqueous electrolyte solution, Nitrobenzene derivative (JP-A-58-214281), quaternary ammonium salt (JP-A-60-30065), polyethylene glycol (JP-A-60-41773), 4-alkylmorpholine (JP-A-62-80977). No.), a quaternary phosphonium salt (JP-A-63-112268), alkylbenzenes (JP-A-5-36439) and the like. These additives form a film on the surface of the negative electrode active material composed of lithium or a lithium alloy to make it difficult for the non-aqueous electrolyte and active lithium to come into contact with each other, or suppress the growth of dendrites to improve the charge / discharge cycle. It is intended to improve the characteristics.

[0006]

However, even if these additives were added to the electrolyte, the growth of dendrites could not be sufficiently suppressed.

An object of the present invention is to provide a lithium secondary battery which has a long life and is safe by sufficiently suppressing the generation of dendrites.

[0008]

SUMMARY OF THE INVENTION The present invention aims to improve a lithium secondary battery, and

[Chemical 7] formula

[Chemical 8] formula

[Chemical 9] formula

[Chemical 10] formula

[Chemical 11] And expression

[Chemical 12] [In the above formulas, m and n are the number of substituents of 1 to 4, p,
q, s is the number of the substituents of 1 to 6, r represents the number of substituents 1 to 8, R1-R6 is hydrogen or an alkyl group having 1 to 4 carbon _{atoms, -C 6 H 5, -F,} -Cl, - Br, -I, -O
_{H, -OCH 3, -OC 2 H} 5, -CN, -NH 2, -
It is at least one substituent of the group consisting of N (CH ₃ ) ₂ , —SO ₃ H, and —COOR (R is hydrogen or an alkyl group having 1 to 4 carbon atoms). ] And at least one of the reductants corresponding to the quinones of formulas 1 to 6 in an amount of 0.005 to 1.0 mol / kg with respect to the electrolyte.

The term "electrolyte" used herein does not mean only the electrolyte in the electrolyte layer laminated between the positive electrode active material layer and the negative electrode active material layer, but is contained in the positive electrode active material layer, for example. The electrolyte (ion conductor) and the like are included.

Examples of the quinones represented by the above formula (1) include p-benzoquinone, 2,6-di (tert-butyl) -1,4-benzoquinone, methyl-p-benzoquinone and phenyl-p-benzoquinone. , Chloro-p-benzoquinone, iodo-p-benzoquinone, 2,6-dichloro-p-benzoquinone, 2,6-dibromo-p-benzoquinone, p-chloranil, 2,3-dichloro-5,6-dicyano-p. -Benzoquinone, tetrafluoro-p-benzoquinone, tetramethyl-p-benzoquinone, 2,5-
Examples include dihydroxy-p-benzoquinone and 2,5-dimethoxy-p-benzoquinone. The reductants corresponding to the quinones represented by the above formula (1) include hydroquinones and quinhydrones corresponding to these quinones.

Examples of the quinones represented by the above formula (2) include o-benzoquinone, 4-methyl-o-benzoquinone, 3,5-di (tert-butyl) -o-benzoquinone, o-chloranil and the like. There is. The reductants corresponding to the quinones represented by the above formula (2) include hydroquinones and quinhydrones corresponding to these quinones. For example, as hydroquinones,
Examples include oxyhydroquinone, pyrogallol, gallic acid and protocatechuic acid.

Further, examples of the quinones represented by the above formula (3) include 1,4-naphthoquinone and 2-methyl-1,4.
-Naphthoquinone, 2-chloro-1,4-naphthoquinone,
There are 5,8-dioxy-1,4-naphthoquinone, 6-promo-1,4-naphthoquinone, 2-methoxy-1,4-naphthoquinone, 1,4-naphthoquinone-2-carboxylic acid methyl ester and the like. Further, examples of the reductant corresponding to the quinones represented by the above formula (3) include 1,4-dioxynaphthalene corresponding to each of these quinones.

Examples of the quinones represented by the above formula (4) include 1,2-naphthoquinone and 4-methyl-1,2.
-Naphthoquinone, 4-methoxy-1,2-naphthoquinone, 4-amino-1,2-naphthoquinone, 4-dimethylamino-1,2-naphthoquinone and the like. Further, examples of the reductant corresponding to the quinones represented by the above formula (4) include 1,4-dioxynaphthalene corresponding to each of these quinones. Examples of the quinones represented by the above formula (5) include anthraquinone, 2-aminoanthraquinone, anthraquinone-2-sulfonic acid, alizarin, 2,6-diaminoanthraquinone, 1,4-
Dimethoxyanthraquinone, 1,4,5,8-tetraoxyanthraquinone, 2-chloroanthraquinone, 2-
Examples include methyl anthraquinone. Further, examples of the reductant corresponding to the quinones represented by the formula (5) include anthraquinols corresponding to these quinones. Examples of quinones represented by the above formula (6) include 2,6-naphthoquinone. Also, the above formula (6)
Examples of the reduced form of the quinones shown in (2) include 2,6-dioxynaphthalene.

In the invention of claim 2, at least one of the quinones represented by the formulas 1 to 6 and the reductant corresponding to the quinones represented by the formulas 1 to 6 is added to the electrolyte in an amount of 0.05.
˜0.5 mol / kg.

[0015]

The compound (hereinafter simply referred to as an additive) selected from the quinones to be contained in the electrolyte or the reductant corresponding to the compound of these quinones in the present invention is a compound of lithium that is deposited during charging of the lithium secondary battery. It is adsorbed on the surface to suppress local deposition of lithium and deposit lithium substantially uniformly on the negative electrode active material surface. Therefore, according to the invention of claim 1, it is possible to suppress the generation of dendrites and prevent a short circuit between the electrode plates. The amount of the additive added is preferably in the range of 0.005 to 1 mol per 1 kg of the above electrolyte. If the amount added is less than 0.005 mol, the generation of dendrites cannot be suppressed sufficiently. On the other hand, when the amount added exceeds 1 mol, the additive hinders charge and discharge of the battery, the internal resistance of the battery increases, and dendrites are easily generated. The addition amount is 0.05 to 0.5 as in the invention of claim 2.
When it is in a molar amount, generation of dendrite can be further suppressed.

[0016]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Example 1 FIG. 1 is a schematic sectional view of a battery of this example applied to a coin type lithium secondary battery using a non-aqueous electrolyte as an electrolyte. In this figure, 1 is a positive electrode current collector, 2 is a positive electrode active material layer, 3 is a negative electrode current collector, 4 is a negative electrode active material layer, 5 is an electrolyte layer, and 6 is a positive electrode. Reference numeral 7 denotes a can, 7 denotes a negative electrode can, and 8 denotes an annular gasket. This coin type lithium secondary battery was manufactured as follows. First, 70 parts by weight of amorphous vanadium pentoxide (a-V ₂ O ₅ ), 25 parts by weight of a conductive additive made of acetylene black, and 5 parts by weight of polytetrafluoroethylene (PTFE) were kneaded to prepare a kneaded product. Next, this kneaded product was rolled into a sheet and then cut into a disk to form pellets. Next, this pellet is used for the positive electrode can 6
The positive electrode active material layer 2 having a capacity of about 25 mAh was formed by placing it on the positive electrode current collector 1 made of stainless steel and spot-welded therein. Note a-V ₂ O ₅ amount of the positive electrode active material layer 2 was set to 100 mg. Then, the polypropylene-made annular gasket 8 was placed on the outer peripheral end portion 6b of the positive electrode can 6.

Next, a 0.1 mm-thick lithium foil is cut into a disk shape having the same diameter as the positive electrode active material layer 2 and spot-welded in the negative electrode can 7 to form a negative electrode current collector 3 made of a stainless steel net.
Then, the negative electrode active material layer 4 was formed by pressing.

Next, an additive described below was added to a mixed solution of propylene carbonate in which 1 mol / Kg of LiClO ₄ was dissolved and 1,2-dimethoxyethane at a volume ratio of 1: 1 to prepare an electrolytic solution. Next, this electrolytic solution is applied to the positive electrode active material layer 2
After 0.1 ml was dropped on the top, a separator made of polypropylene non-woven fabric was placed thereon, and 0.1 ml of the electrolytic solution was further dropped on the separator to form the electrolyte layer 5.

Next, the above-mentioned negative electrode can 7 having the negative electrode active material layer 4 formed thereon so that the negative electrode active material layer 4 and the electrolyte layer 5 were joined was placed on the electrolyte layer 5. Then, the positive electrode can 6 and the negative electrode can 7 were caulked via the annular gasket 8 to complete a coin-type lithium secondary battery.

The batteries of Examples 1-1 to 1-20 in which the additives added to the electrolytic solution were variously changed as shown in Table 1 below,
A charge / discharge test was conducted using the battery 1 of the comparative example prepared by the same method as the battery of the example except that the additive was not added to the electrolytic solution. In the charge / discharge test, the number of cycles until a short circuit occurs in each battery by repeating charging / discharging in which a constant current of 0.5 mA / cm ² is discharged at a final voltage of 2 V and then a final voltage of 3.6 V is charged. I asked. In this test, a polypropylene film which is not normally used is not used as a separator but a polypropylene non-woven fabric is used as a separator. This is because the generation of dendrites is promoted and the test is performed quickly. In addition, the determination of the occurrence of a short circuit is because the voltage during charging shows unstable behavior and the battery does not reach the charge end voltage (3.6 V), or the internal resistance of the battery becomes approximately 0.0Ω. went.

Table 1 shows the measurement results.

[0023]

[Table 1] From this table, it can be seen that the batteries of Examples 1-1 to 1-20 suppress dendrite generation and are less likely to cause a short circuit due to charge / discharge, as compared with the battery 1 of the comparative example.

(Example 2) FIG. 2 is a schematic cross-sectional view of a battery of this example applied to a thin lithium secondary battery using a polymer solid electrolyte as an electrolyte. The battery of this example has a positive electrode active material layer 12 formed on one surface of a positive electrode current collector 11.
And a negative electrode active material layer 14 formed on one surface of the negative electrode current collector 13 with a solid polymer electrolyte layer 15 in between. This polymer solid electrolyte lithium secondary battery was manufactured as follows. First, methoxyoligoethyleneoxypolyphosphazene having an average molecular weight of 1.5 million (hereinafter referred to as MEP) and 0.5 mol / kg of the MEP.
LiBF ₄ and 1,2-dimethoxyethane (hereinafter D
An additive-containing MEP / DME solution was prepared by adding the additives described below to a mixed solution of 20% by weight dissolved in a solution (referred to as ME). Then, this additive-containing MEP / DME solution was mixed with a kneaded product of LiMn ₂ O ₄ and acetylene black (AB) with a weight ratio of 60:15, and this was stirred to form a mixture. The ratio of the kneaded product of LiMn ₂ O ₄ and AB and the additive-containing MEP / DME solution was set to a ratio in which the weight ratio of the kneaded product and MEP was 75:25. Then, DME was volatilized and removed from this mixture, and this was formed into a sheet by a roll press and cut into a suitable size to form a positive electrode active material layer 12 having a capacity of about 25 mAh and a thickness of 180 μm. Next, the positive electrode active material layer 12 is formed to a thickness of 20 μm.
The positive electrode current collector 11 made of stainless steel foil of m 2 was attached to the central portion 11a on one surface. Since the positive electrode active material layer 12 thus produced has adhesiveness, it can be attached to the positive electrode current collector 11 without using a binder or the like. Next, the same additive-containing MEP / DME as described above
The solution was applied on the positive electrode active material layer 12, and then DME was removed by volatilization to form a half portion of the solid polymer electrolyte layer 15 having a thickness of 50 μm.

Next, a negative electrode active material layer 14 was formed by placing a 40 μm thick lithium foil on one surface of the negative electrode current collector 13 made of a 20 μm thick stainless steel foil. Then, the same additive-containing MEP / DME solution as described above was applied on the negative electrode active material layer 14, and then DME was removed by volatilization to form a half portion of the solid polymer electrolyte layer 15 having a thickness of 50 μm. Next, the thermocompression-bonding type hot melt 16 is placed on the outer peripheral end 11b of the positive electrode current collector 11, and then the positive electrode current collector 11 is joined so that the half parts of the solid polymer electrolyte layer 15 are joined together.
The negative electrode current collector 13 having the negative electrode active material layer 14 formed thereon was placed on the half of the solid polymer electrolyte layer 15 formed in 1. Then, the hot melt 16 is heated to collect the current collectors 11 and 1.
3 was completely connected to the outer peripheral end portions 11b and 13b to complete a polymer solid electrolyte lithium secondary battery.

The batteries of Examples 2-1 to 2-18 in which the additives added to the electrolytic solution were variously changed as shown in Table 2 below,
A charge / discharge test was conducted using the battery 1 of the comparative example prepared by the same method as the battery of the example except that the additive was not added to the electrolytic solution. In the charge / discharge test, a constant current of 50 μA / cm ² was used to repeat charging / discharging in which each battery was discharged at a final voltage of 2 V and then charged at a final voltage of 4.2 V, and the number of cycles until a short circuit occurred in each battery was obtained. It was

Table 2 shows the measurement results.

[0028]

[Table 2] From this table, it can be seen that the batteries of Examples 2-1 to 2-18 are less susceptible to dendrite generation and less likely to cause short circuit due to charge / discharge, as compared with Battery 2 of Comparative Example.

In Example 1, the positive electrode active material was a
-V ₂ O ₅ was used, and in Example 2, Li was used as the positive electrode active material.
Although Mn ₂ O ₄ is used, the present invention is not limited to this, and other materials such as inorganic compounds and organic compounds may be used as the positive electrode active material. The inorganic compounds include MnO ₂ , LiV ₃ O ₈ , V ₆ O ₁₃ , and LiCo.
O ₂ , LiNiO ₂ , MoS ₂ , TiS ₂ or the like can be used as the positive electrode active material. As the organic compound, a polyaniline derivative, a polypyrrole derivative, a polythiophene derivative, or the like can be used as the positive electrode active material.

In Example 1 above, LiC was used as the electrolyte.
A non-aqueous electrolyte prepared by dissolving a lithium salt composed of 10 _{4 in} an organic solvent composed of propylene carbonate was used, but the present invention is not limited to this, and LiBF ₄ , Li
AsF ₆ , LiPF ₆ , CF ₃ SO ₃ Li and the like can be used as the lithium salt. Further, ethylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane,
One or more selected from sulfolane and the like can be used as the organic solvent. In addition, the second embodiment
In the above, a polymer compound containing MEP containing a lithium salt was used, but the present invention is not limited to this, and polyethylene oxide, polymethacrylic acid oligoalkylene oxide, poly (vinyl butyrolactone) are used.
A polymer compound containing a lithium salt may be used as the polymer solid electrolyte. In addition to the non-aqueous electrolyte solution and the solid polymer electrolyte, a gel-like material or a viscous material containing a non-aqueous electrolyte solution in a polymer matrix can be used as the electrolyte. Something like this:
A viscous substance obtained by dissolving the above-mentioned organic solvent in the above-mentioned polymer solid electrolyte, a viscous substance obtained by adding an organic solvent dissolving both of them into a copolymer of an alkyl methacrylate and acrylonitrile and a lithium salt, methoxypoly (ethylene glycol) methacrylate. A gel-like cross-linked product containing an organic solvent by irradiating a solution comprising a polymer having a photosensitive group such as poly (ethylene glycol) dimethacrylate and cinnamoylated polyethylene oxide, an organic solvent and a lithium salt with ultraviolet light or the like. There are things that have been done.

Further, although Li foil is used as the negative electrode active material in the above-mentioned Examples 1 and 2, the present invention is not limited to this, and lithium-aluminum alloy, lithium-indium alloy, lithium-lead alloy is used. , Lithium-gallium alloy, lithium-magnesium alloy, lithium
Aluminum-tin alloy or the like can be used as the negative electrode active material.

Needless to say, a conductive auxiliary agent, a binder such as fluorine dispersion, a separator or the like for preventing mechanical short circuit may be used in the battery of the present invention, if necessary.

[0033]

According to the invention of claim 1, generation of dendrites can be suppressed to prevent a short circuit between electrode plates.
Therefore, a safer lithium secondary battery having a long life can be obtained. The additive amount is 1 kg of the above electrolyte
However, the range of 0.005 to 1 mol is preferable. If the amount added is less than 0.005 mol, the generation of dendrites cannot be suppressed sufficiently. If the addition amount exceeds 1 mol,
Dendrite is likely to occur.

According to the second aspect of the present invention, the amount of the additive added is 0.05 to 0.5 mol with respect to 1 kg of the electrolyte, so that the generation of dendrites can be further suppressed.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a lithium secondary battery of an embodiment of the present invention applied to a coin type lithium secondary battery.

FIG. 2 is a schematic cross-sectional view of a lithium secondary battery of an example of the present invention applied to a thin lithium secondary battery.

[Explanation of symbols]

 1, 11 Positive Electrode Current Collector 2, 12 Positive Electrode Active Material Layer 3, 13 Negative Current Collector 4, 14 Negative Electrode Active Material Layer 5, 15 Electrolyte Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hayakawa et al. ▲ Ku ▼ Beauty 2-1, 1-1 Nishinishinjuku, Shinjuku-ku, Tokyo Shin-Kindo Electric Co., Ltd. (72) Inventor Akio Komaki Nishishinjuku, Shinjuku-ku, Tokyo 2-1-1 No. 1 Shinshin Todo Electric Co., Ltd. (72) Inventor Akika Inubushi 463, Kagasuno, Kawauchi-cho, Tokushima City, Tokushima Prefecture Otsuka Chemical Co., Ltd., Tokushima Research Institute (72) Inventor Nakafumi, Weibun Tokushima, Tokushima Prefecture 463 Kagasuno, Ichikawauchi-machi, Tokushima Research Institute, Otsuka Chemical Co., Ltd. (72) Inventor, Michio Sasaoka, 463, Kagasuno, Kawauchi-machi, Tokushima, Tokushima Prefecture, Tokushima Research Institute, Otsuka Chemical Co., Ltd.

Claims (2)

[Claims] 1. The formula: Formula [2] Formula [3] Formula Formula And the formula: [In the above formulas, m and n are the number of substituents of 1 to 4, p,
q, s is the number of the substituents of 1 to 6, r represents the number of substituents 1 to 8, R1-R6 is hydrogen or an alkyl group having 1 to 4 carbon _{atoms, -C 6 H 5, -F,} -Cl, - Br, -I, -O
_{H, -OCH 3, -OC 2 H} 5, -CN, -NH 2, -
N (CH _{3) 2,} represent at least one substituent of -SO ₃ H, the group consisting of -COOR (R is hydrogen or an alkyl group having 1 to 4 carbon atoms). ] And at least one of the reductants corresponding to the quinones represented by the above formulas 1 to 6 is 0.005 to 1.0 with respect to the electrolyte.
A lithium secondary battery characterized by containing mol / kg. 2. At least one of the quinones represented by the formulas 1 to 6 and the reductant corresponding to the quinones represented by the formulas 1 to 6 is 0.05 to 0.5 mol with respect to the electrolyte. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is contained in an amount of 1 / kg.