JPH08306364A - Nonaqueous electrolytic solution and nonaqueous electrolyte battery - Google Patents

Abstract

PURPOSE: To prevent the precipitation of metals in dendrite state inn an anode by using a nonaqueous electrolytic solution containing a light metal salt as an electrolytic substance and a specified cyclic carbonate as a nonaqueous solvent. CONSTITUTION: A solution containing a light metal salt as an electrolytic substance and a cyclic carbonate having the shown formula as a nonaqueous solvent is used as a non-aqueous electrolytic solution. In the formula, R<1> R<2> , R<3> , and R<4> independently stand for hydrogen, lower alkyl, halogens, lower alkyl substituted with halogens and at least one of R<1> , R<2> , R<3> , and R<4> is a halogen and at least one of the rest is lower alkyl or lower alkyl substituted with halogens. Moreover, lithium or a lithium compound is preferably used as the anode active material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte solution for a non-aqueous electrolyte battery using a light metal such as lithium or its compound as a negative electrode active material and a non-aqueous electrolyte solution using the non-aqueous electrolyte solution. Regarding batteries.

[0002]

2. Description of the Related Art Conventionally, a non-aqueous electrolyte battery using a light metal such as lithium, sodium or aluminum as a negative electrode active material can theoretically generate a high voltage and has a high energy density. Is expected as a power source for In recent years, research and development for converting such a non-aqueous electrolyte battery into a secondary battery have been carried out. Above all, a lithium secondary battery can achieve high output and high energy density, and therefore, research and development is actively conducted. It is being appreciated.

Incidentally, in the case of a secondary battery in which these light metals are simply used as they are for the negative electrode, there is a problem that the metal is deposited in the form of dendrite on the negative electrode during the charging process, resulting in an internal short circuit of the battery. Therefore, in order to prevent the deposition of such dendrite-like metals, it has been proposed to use these light metals in the negative electrode not by using them as they are but by doping or alloying with a carbonaceous material or compound. . Such a negative electrode can enhance the safety and reliability of the battery to some extent.

[0004]

However, in recent years,
The demand for battery safety is increasing, and higher reliability than ever has been demanded. For example, even if a high voltage exceeding the battery voltage is applied to the battery due to a failure of the power supply circuit or the charger or the user's usage error, or if a high current exceeding the normal charging condition is applied to the battery, It is required that the battery is not damaged and safety is ensured.

The present invention is intended to solve such a problem of the prior art, and in a non-aqueous electrolyte battery using a light metal or a light metal compound as a negative electrode active material, light metal is deposited in a dendrite shape on the negative electrode. To prevent
The purpose is to improve the safety and reliability of the battery.

[0006]

Means for Solving the Problems As a result of intensive studies for achieving the above-mentioned object, the present inventor has stabilized a light metal ion used as a negative electrode active material as a solvent constituting a non-aqueous electrolyte. It was found that the above object can be achieved by using a specific solvent capable of achieving the above, and has completed the present invention.

That is, the present invention contains a light metal salt as an electrolyte and a cyclic carbonate of the following formula (1) as a non-aqueous solvent.

[0008]

[Chemical 6] (Wherein R ¹ , R ² , R ³ and R ⁴ are independently hydrogen, lower alkyl, halogen or halogenated lower alkyl, and at least one of R ¹ , R ² , R ³ and R ⁴ is Halogenated lower alkyl, or R ¹ , R
^At least one of ² , R ³ and R ⁴ is halogen,
And at least one of the other is lower alkyl or halogenated lower alkyl. The non-aqueous electrolyte solution is provided.

Further, the present invention provides a non-aqueous electrolyte battery using a light metal or a light metal compound as a negative electrode active material,
Provided is a non-aqueous electrolyte battery using the above non-aqueous electrolyte as a non-aqueous electrolyte.

Hereinafter, the present invention will be described in detail.

The non-aqueous electrolyte of the present invention is characterized by containing the cyclic carbonate represented by the above formula (1) as a non-aqueous solvent. Positions 4 and 5 of this cyclic carbonate
Positions R ¹ , R ² , R ³ and R ⁴ can each independently be hydrogen, lower alkyl, halogen or halogenated lower alkyl, in which case at least one is halogenated lower alkyl. Alternatively, at least one is halogen and the other at least one is lower alkyl or halogenated lower alkyl.
Here, examples of the halogen include fluorine, chlorine, bromine, and iodine. Further, examples of the lower alkyl include methyl, ethyl, propyl and the like,
The halogenated lower alkyl may be a lower alkyl dihalide, trihalide or the like.

As described above, the cyclic carbonate into which at least one halogenated alkyl group is introduced or in which halogen and an alkyl group or a halogenated alkyl group are introduced is appropriately solvated with a light metal ion to be stabilized. Therefore, in a non-aqueous electrolyte battery using a light metal or a light metal compound as a negative electrode active material, when this cyclic carbonate is used as a non-aqueous solvent that constitutes the non-aqueous electrolyte, light metal is deposited in a dendrite state on the negative electrode. Therefore, it is possible to prevent an internal short circuit caused by the dendrite-like metal.

The stabilizing effect of the above cyclic carbonate is considered to be obtained as follows. That is, the radical anion of the solvent molecule generated by reduction at the negative electrode in the non-aqueous electrolyte battery and the neutral solvent molecule surround the light metal, and an unpaired spin chemical exchange reaction occurs between them. In this state, the decomposition of solvent molecules depends on the chemical exchange reaction rate of unpaired spins. This can be clarified by the electron spin resonance method. Then, by introducing a halogen, an alkyl or an alkyl halide as described above into the solvent molecule, it is possible to effectively suppress the chemical exchange reaction rate of the unpaired spin,
Therefore, the solvent molecules can be appropriately solvated with the metal ions.

Among the cyclic carbonates of the formula (1) having such an effect, for example, a specific example of the cyclic carbonate having fluorine introduced as halogen is most preferable from the viewpoint of stability as a solvent of the electrolyte. The following cyclic carbonates belonging to the first rank can be mentioned, and among them, compounds of 1) to 3) can be mentioned in order of preference. Hereinafter, similarly preferred cyclic carbonates include cyclic carbonates of the second to fourth ranks.

First rank: 1)

[Chemical 7] 2)

Embedded image 3)

[Chemical 9]

Second rank: 1)

[Chemical 10] 2)

[Chemical 11]

Third rank: 1)

[Chemical 12] 2)

[Chemical 13] 3)

Embedded image

Fourth rank: 1)

[Chemical 15] 2)

Embedded image The preferred specific examples of the cyclic carbonate in which fluorine is introduced as the halogen have been described above. As a preferred specific example of the cyclic carbonate in which chlorine is introduced, for example, the following formula (3)

[0019]

[Chemical 17] Etc. can be given.

In the non-aqueous electrolytic solution of the present invention, as the non-aqueous solvent, a single type of cyclic carbonate belonging to the above formula (1) may be used alone, or a plurality of types may be used in combination. Further, the cyclic carbonate belonging to the formula (1) may be used in combination with other various non-aqueous solvents. Examples of such a non-aqueous solvent include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 2-methyltetrahydrofuran, and 3-methyltetrahydrofuran. -Methyl-
1,3-dioxolane, methyl propionate, methyl butyrate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate and the like can be used. In particular, it is preferable to use cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate and vinylene carbonate, or chain carbonates such as dimethyl carbonate, diethyl carbonate and dipropyl carbonate, from the viewpoint of stable voltage. Further, such non-aqueous solvent may be used alone or in combination of two or more kinds.

When the non-aqueous solvent of the non-aqueous electrolytic solution of the present invention is a mixed solvent of the cyclic carbonate of the formula (1) and another non-aqueous solvent, the ratio of the cyclic carbonate of the formula (1) is the electrolyte. Although it depends on the type and the like, it is usually preferably 10% by volume or more, and more preferably 30% by volume or more of the whole non-aqueous solvent. Thereby, the compounding effect of the cyclic carbonate of the formula (1) can be obtained.

On the other hand, a salt of a light metal such as lithium, sodium, potassium, cesium or aluminum can be used as an electrolyte constituting the non-aqueous electrolyte of the present invention. It can be appropriately determined according to the type. For example, when a non-aqueous electrolyte is used in a lithium secondary battery, the electrolyte is LiClO 2.
₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ S
Lithium salts such as O ₃ and LiN (CF ₃ SO ₂ ) ₂ can be used. Of these, it is particularly preferable to use LiPF ₆ or LiBF ₄ .

The proportion of the electrolyte in the non-aqueous electrolytic solution can be appropriately selected depending on the application of the battery using the non-aqueous electrolytic solution and the combination of the electrolyte and the non-aqueous solvent constituting the non-aqueous electrolytic solution. , For example, when a non-aqueous electrolyte is used in a lithium secondary battery, the electrolyte concentration is 0.4 to 2.4 mol /
It is preferable that it is 1.

The non-aqueous electrolyte battery of the present invention is characterized by using a light metal or a light metal compound as the negative electrode active material and using the above non-aqueous electrolyte as the non-aqueous electrolyte.
Other configurations can be the same as those of various conventional non-aqueous electrolyte secondary batteries or primary batteries.

Therefore, the positive electrode can be constructed by using a metal oxide, a metal sulfide or a specific polymer as an active material depending on the kind of the intended battery. For example, when forming a lithium secondary battery, the positive electrode active material may be a metal sulfide or oxide containing no lithium such as TiS ₂ , MoS ₂ , NbSe ₂ , V ₂ O ₅ or Li _x.
A lithium composite oxide mainly composed of MO ₂ (wherein M represents one or more kinds of transition metals and usually 0.05 ≦ x ≦ 1.10) can be used. The transition metal M constituting this lithium composite oxide includes Co, Ni,
Mn and the like are preferable. Specific examples of such a lithium composite oxide include LiCoO ₂ , LiNiO ₂ , and Li _x Ni _y.
Co _1-y O ₂ (in the formula, x and y are different depending on the charging / discharging state of the battery, and are generally 0 <x <1, 0.7 <y <1.02), LiMn ₂ O _4, etc. You can These lithium composite oxides can generate a high voltage and become a positive electrode active material excellent in energy density.

For the positive electrode, plural kinds of these positive electrode active materials may be mixed and used. Further, when forming a positive electrode using the positive electrode active material as described above, a known conductive agent, binder or the like can be added.

The negative electrode uses a light metal or a light metal compound as its active material. Examples of such a light metal include lithium, sodium, potassium, cesium, aluminum and the like, and lithium is particularly preferable from the viewpoint of battery output and energy density. Therefore, as the constituent material of the negative electrode, such a light metal or a material capable of doping or dedoping its ion, a light metal, a light metal compound,
Light metal alloys can be used. Examples of materials that can be doped with or undoped from light metals such as lithium among the constituent materials of the negative electrode include, for example, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, glassy carbon. Use of carbonaceous materials, fired products of organic polymer compounds (carbonized by firing phenol resin, furan resin, etc. at an appropriate temperature), carbonaceous materials such as carbon fiber, activated carbon, or polymers such as polyacetylene, polypyrrole, etc. You can As the lithium alloy, lithium-aluminum alloy or the like can be used.

When forming the negative electrode from such a material, a known binder or the like can be added.

The shape of the battery of the present invention is not particularly limited. Various shapes such as a cylindrical shape, a square shape, a coin shape, and a button shape can be used. Further, it can be configured as either a primary battery or a secondary battery.

[0030]

In the non-aqueous electrolyte battery of the present invention using the non-aqueous electrolyte of the present invention, the cyclic carbonate of the formula (1) in the non-aqueous electrolyte becomes a radical anion. It is considered to be more stable than neutral molecules. Then, the radical anions form an ion pair with ions of a light metal such as lithium, which is the negative electrode active material, and stabilize the light metal ions to an appropriate degree. Therefore, in the battery of the present invention, deposition of dendrites on the negative electrode is prevented even under overcharge conditions in which high voltage or high current is applied. Therefore, the battery of the present invention has improved safety and reliability.

[0031]

EXAMPLES Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples with reference to FIG. Here, FIG.
[Fig. 4] is a vertical half cross-sectional view of the cylindrical non-aqueous electrolyte batteries prepared in Examples and Comparative Examples.

Example 1 (Production of Cylindrical Non-Aqueous Electrolyte Battery) In producing the positive electrode 1, first, commercially available lithium carbonate and cobalt carbonate were mixed so that the composition ratio Li / Co = 1: 1. , In the air 9
Lithium-cobalt oxide Li was fired at 00 ° C for 5 hours.
CoO ₂ was obtained. Next, 91 parts by weight of the obtained lithium-cobalt oxide was mixed as an active material, 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder, and further mixed with N-methyl-2-pyrrolidone. The mixture was kneaded to obtain a paste-like positive electrode mixture. This was applied on both sides of a strip-shaped aluminum foil to obtain a strip-shaped positive electrode.

On the other hand, in order to prepare the negative electrode 2, first, 90 parts by weight of crushed pitch coke is mixed with 10 parts by weight of polyvinylidene fluoride as a binder, and further kneaded with N-methyl-2-pyrrolidone to form a paste. A negative electrode mixture was obtained. This was applied on both sides of a strip-shaped copper foil to obtain a strip-shaped negative electrode.

Since the positive electrode 1 and the negative electrode 2 collect current,
The positive electrode lead terminal 3 made of aluminum and the negative electrode lead terminal 4 made of nickel were welded to each other.

A separator 5 made of a polypropylene microporous film was laminated between the positive electrode 1 and the negative electrode 2 and was wound many times to produce a spirally wound electrode body.

This electrode body was housed in an iron battery container 6.
Then, the negative electrode lead 4 was connected to the inner bottom portion of the battery container 6 by spot welding, and the positive electrode lead terminal 3 was similarly connected to the battery sealing plate 7.

On the other hand, propylene carbonate (PC) and a cyclic carbonate of the following formula

[0038]

Embedded image A non-aqueous electrolytic solution was prepared by dissolving 1 mol / l of lithium hexafluorophosphate in a mixed solvent having a volume ratio of 1: 1. Then, this electrolytic solution was poured into the battery container 6, and the battery container 6 and the battery sealing plate 7 were fitted and crimped with the polypropylene packing 8 interposed therebetween, and sealed to manufacture a battery.

The size of the battery thus obtained has an outer diameter of 20.
mm, the height was 50 mm, and the capacity was 1000 mAhr.

Comparative Example 1 A non-aqueous electrolyte prepared by dissolving 1 mol / l of lithium hexafluorophosphate in a mixed solvent of propylene carbonate (PC) and diethyl carbonate at a volume ratio of 1: 1 was used. A battery was produced in the same manner as in Example 1 except that the above was performed.

Comparative Example 2 As a non-aqueous electrolyte, propylene carbonate (PC) and 1,2-dimethoxyethane in a volume ratio of 1:
A battery was produced in the same manner as in Example 1 except that 1 mol / l of lithium hexafluorophosphate was dissolved in the mixed solvent of 1 and used.

Evaluation (1) Constant Current Overcharge Test For each of the 20 batteries of Examples and Comparative Examples, 3 m
A constant current overcharge test of A / cm ² was performed. In this case, since each battery was manufactured in a discharged state, it was previously charged to 4.1 V by constant voltage charging, and then subjected to a constant current overcharge test.

This constant current overcharge test is carried out on the assumption that, for example, the control circuit of the charger has failed and the battery has advanced to the overcharge state under the rapid charging condition. The current value in 1 corresponds to about 1.5 C charging (current value for charging the standard capacity C for charging in 2/3 hours).

Table 1 shows the results of the accident rate and the ultimate voltage at which the battery became unusable by the constant current overcharge test.

[0045]

[Table 1] When the battery after the test was disassembled and observed, it was confirmed that a large amount of lithium was deposited in the form of dendrite on the surface of the negative electrode in the battery of Comparative Example 1. On the other hand, no lithium deposition was found on the negative electrodes of the batteries of Example 1 and Comparative Example 2.

As a result, the accident rate of the battery of Comparative Example 1 is extremely high because lithium is dendrite-like deposited on the surface of the negative electrode due to overcharging and penetrates the separator to reach the positive electrode, causing an internal short circuit. It is estimated to be.

According to another experiment, the non-aqueous electrolyte electrolyzes the deposited lithium on the negative electrode of the battery of Comparative Example 1,
It was found that lithium of the electrolyte, lithium hexafluorophosphate, was electrodeposited. Further, it was also found that the decomposition potential of lithium hexafluorophosphate was around 6.5V.

Therefore, since the voltage reached in the battery of Comparative Example 1 exceeds 6.5 V, it can be seen that the decomposition of lithium hexafluorophosphate has occurred. On the other hand, in the batteries of Example 1 and Comparative Example 2, the ultimate voltage did not reach 6.5 V, so it can be seen that the decomposition of lithium hexafluorophosphate did not occur.

The high accident rate in the battery of Comparative Example 2 is that the decomposition voltage of 1,2-dimethoxyethane used as the non-aqueous solvent is as low as 4.6 V, so that the solvent is rapidly decomposed by overcharging. Probably because a large amount of gas was generated and the battery was damaged.

As described above, since lithium was not deposited in the form of dendrite on the negative electrode of the battery of Example 1 and the accident rate was 0, the cyclic carbonate used in Example 1 contained lithium as a dendrite. It can be seen that it has an effect of suppressing the precipitation in the form of a particle and has a sufficiently high decomposition voltage as a non-aqueous solvent used in a lithium secondary battery.

(2) High-voltage application test In order to evaluate the high-voltage reliability, a voltage of 7 V was applied in the charging direction to each of the 20 batteries of the example and the comparative example, and the failure rate and the flow when applying the voltage The current value was checked. The high voltage application test is performed on the assumption that the voltage control of the battery becomes impossible due to the breakdown of the charging circuit and the high voltage is directly applied to the battery. The results are shown in Table 2.

[0052]

[Table 2] When the battery after the test was disassembled and observed, it was confirmed that in the battery of Comparative Example 1, a large amount of lithium was dendrite-like deposited on the surface of the negative electrode as in the constant current overcharge test. On the other hand, although a small amount of lithium was deposited on the negative electrodes of the batteries of Example 1 and Comparative Example 2, the deposited form was fine powder, not dendrite.

From this, it is considered that the extremely high accident rate in the battery of Comparative Example 1 is due to the internal short circuit due to the dendrite-like deposition of lithium due to overcharge, as in the constant current overcharge test.

The high accident rate in the battery of Comparative Example 2 is that the decomposition voltage of 1,2-dimethoxyethane used as the non-aqueous solvent is as low as 4.6 V, so that the solvent is decomposed by applying a high voltage. It is considered that the battery proceeded rapidly and a large amount of gas was generated, damaging the battery.

On the other hand, since lithium was not deposited in dendrite form on the negative electrode of the battery of Example 1 and the accident rate was low, the cyclic carbonate used as the non-aqueous solvent in Example 1 was lithium. It can be seen that the compound has an effect of suppressing the precipitation as a dendrite and has a sufficiently high decomposition voltage as a non-aqueous solvent used in a lithium secondary battery.

Examples 2 to 7 Batteries were prepared in the same manner as in Example 1 except that the volume ratio of propylene carbonate (PC) to cyclic carbonate in the non-aqueous electrolyte was changed as shown in Table 3, and the same as above. It was subjected to a 7V high voltage application test. The results are shown in Table 3. For reference, the results of Example 1 are also shown in Table 3.

[0057]

[Table 3] PC: Cyclic Carbonate Lithium Precipitated Example 2 95: 5 dendrite Example 3 90:10 dendrite + fine powder Example 4 80: 20 fine powder + dendrite Example 5 70:30 fine powder Example 1 50: 50 Fine powder Example 6 30:70 Fine powder Example 7 10:90 Fine powder It can be seen from Table 3 that in this battery system, the dendrite suppressing effect is exhibited by mixing 10% or more of the cyclic carbonate in the non-aqueous solvent, and the content of 30% or more can satisfactorily prevent dendrite formation.

When a solvent such as ethylene carbonate or a carbonate such as diethyl carbonate and a solvent such as sulfolane is used instead of propylene carbonate (PC) as the non-aqueous solvent mixed with the cyclic carbonate, the cyclic carbonate is blended in the same manner. When the ratio was 10% or more, the dendrite suppressing effect appeared.

[0059]

INDUSTRIAL APPLICABILITY In the non-aqueous electrolyte battery, the use of the non-aqueous electrolyte solution of the present invention prevents metal from depositing on the negative electrode in the form of dendrite. Therefore, the safety of the battery,
The reliability is greatly improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of batteries of Examples and Comparative Examples.

[Explanation of symbols]

 1 Positive Electrode 2 Negative Electrode 3 Positive Electrode Lead Terminal 4 Negative Electrode Lead Terminal 5 Separator 6 Battery Container 7 Battery Sealing Plate 8 Packing

[Procedure amendment]

[Submission date] August 25, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Title: Non-aqueous electrolyte and non-aqueous electrolyte battery

Claims (7)

[Claims] 1. A cyclic carbonate of the following formula (1) containing a light metal salt as an electrolyte and a non-aqueous solvent: (Wherein R ¹ , R ² , R ³ and R ⁴ are independently hydrogen, lower alkyl, halogen or halogenated lower alkyl, and at least one of R ¹ , R ² , R ³ and R ⁴ is Halogenated lower alkyl, or R ¹ , R
^At least one of ² , R ³ and R ⁴ is halogen,
And at least one of the other is lower alkyl or halogenated lower alkyl. ) Is contained, The non-aqueous electrolyte solution characterized by the above-mentioned. 2. A non-aqueous solvent represented by the following formula (2): The non-aqueous electrolytic solution according to claim 1, which contains the cyclic carbonate of. 3. A non-aqueous solvent represented by the following formula (3): The non-aqueous electrolytic solution according to claim 1, which contains the cyclic carbonate of. 4. A non-aqueous solvent represented by the following formula (4): The non-aqueous electrolytic solution according to claim 1, which contains the cyclic carbonate of. 5. A non-aqueous solvent represented by the following formula (5): The non-aqueous electrolytic solution according to claim 1, which contains the cyclic carbonate of. 6. A non-aqueous electrolyte battery that uses a light metal or a light metal compound as a negative electrode active material, and a non-aqueous electrolyte solution that uses the non-aqueous electrolyte solution according to claim 1 as a non-aqueous electrolyte solution. battery. 7. The non-aqueous electrolyte battery according to claim 6, wherein lithium or a lithium compound is used as the negative electrode active material.