JP3080609B2 - Electrolyte for non-aqueous battery and secondary battery using this electrolyte - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte for a non-aqueous battery in which a lithium salt is dissolved as a solute in an organic solvent and a non-aqueous secondary battery using the electrolyte. And a non-aqueous secondary battery using the electrolyte.

[0002]

2. Description of the Related Art In recent years, there has been a remarkable reduction in the size and weight of electronic devices, and accordingly, there has been a great demand for smaller and lighter batteries that serve as power supplies. In the field of primary batteries, small and lightweight batteries such as lithium batteries have already been put to practical use, but since these are primary batteries, they cannot be used repeatedly, and their uses have been limited. On the other hand, in the field of secondary batteries, lead storage batteries, nickel-cadmium storage batteries, nickel-hydrogen storage batteries, and the like have been conventionally used, but these have major problems in terms of size and weight reduction.

Therefore, lithium-ion batteries have come into practical use as small, lightweight, high-capacity, chargeable / dischargeable batteries, and are used in portable electronic and communication devices such as small video cameras, mobile phones, and notebook personal computers. Is now available. This type of lithium ion battery uses a carbon-based material capable of inserting and extracting lithium ions as a negative electrode active material, and uses LiCoO ₂ , LiNiO ₂ , L as a positive electrode active material.
using IMN ₂ O _4, LiFeO lithium-containing transition metal oxides such as _2, lithium using an electrolyte prepared by dissolving lithium salt as a solute in an organic solvent, after assembling a battery, exiting from the positive electrode active material by the first charging This is a battery in which ions can be charged and discharged by entering carbon particles.

[0004] In such a lithium ion battery, when overcharging is performed, excess lithium is extracted from the positive electrode as the overcharged state occurs, and excessive insertion of lithium occurs in the negative electrode, resulting in a positive charge. -Both electrodes of the negative electrode become thermally unstable. If both the positive and negative electrodes become thermally unstable, they will eventually act to decompose the organic solvent in the electrolytic solution, causing a rapid exothermic reaction and causing the battery to generate abnormal heat. There was a problem that safety was impaired. Such a situation becomes more important as the energy density of the lithium ion battery increases.

In order to solve such a problem, a technique has been proposed in which a small amount of an aromatic compound is added as an additive to an electrolytic solution to ensure safety against overcharging. It has been proposed in JP-A-7-302614 and JP-A-9-50822. In those proposed in JP-A-7-302614 and JP-A-9-50822, a carbon material is used for a negative electrode, and as an additive of an electrolytic solution, a positive electrode potential at full charge with a molecular weight of 500 or less is used. An aromatic compound such as an anisole derivative having a π-electron orbit that has a reversible oxidation-reduction potential at a more noble potential is used. Such an aromatic compound protects the battery by consuming the overcharge at the time of overcharge.

[0006] In addition, Japanese Patent Application Laid-Open No. 9-106835 has proposed a device capable of ensuring safety against overcharging by adding an additive to an electrolytic solution. In the method proposed in Japanese Patent Application Laid-Open No. 9-106835, a carbon material is used for a negative electrode, and as an additive for an electrolytic solution, polymerization is performed at a battery voltage equal to or higher than the maximum operating voltage of the battery. The voltage is increased so that the battery can be protected during overcharge.

[0007]

However, in those proposed in Japanese Patent Application Laid-Open Nos. 7-302614 and 9-50822, the anisole derivative effectively acts on overcharging. However, there is a problem that the battery characteristics such as cycle characteristics and storage characteristics are adversely affected. Further, the aromatic compound is oxidatively decomposed at a potential of about 4.5 V to generate gas and form a polymer, thereby consuming the overcharge and protecting the battery, but depending on the electrolyte composition, In some cases, the polymer dissolves and the overcharge cannot be consumed. As a result, aromatic compounds such as anisole derivatives having a π-electron orbit cannot always be said to suppress overcharge.

On the other hand, in the method proposed in Japanese Patent Application Laid-Open No. 9-106835, biphenyl used as an additive for the electrolyte has low polarity and low solubility in the electrolyte. There has been a problem that the additives are partially deposited to cause deterioration of battery characteristics. In addition, 3-chloro-thiophene is irritating, has a strong odor, is difficult to handle, and has a problem that it is easily decomposed by oxidation. Furan is also easily decomposed by oxidation,
All of these compounds have a problem that they adversely affect battery characteristics.

Accordingly, the present invention has been made in view of the above problems, and does not adversely affect battery characteristics such as low-temperature characteristics and storage characteristics even when added to an electrolytic solution, and is effective against overcharging. It is an object of the present invention to ensure the safety of a battery by using an additive that acts on the battery.

[0010]

Means for Solving the Problems and Actions and Effects Therefor, in the electrolyte for a non-aqueous battery of the present invention, the organic solvent contains a carbonate derivative represented by the following general formula (3). It is characterized by the following. However, R ¹ shown in Chemical formula 3 represents a phenyl group, a biphenylyl group or an alkylphenyl group, and R ² represents an alkyl group having 1 to 6 carbon atoms or a phenyl group.

[0011]

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The carbonate derivative represented by the general formula (3) has a good affinity for an organic solvent in an electrolytic solution.
It does not adversely affect battery characteristics such as low-temperature characteristics and storage characteristics. Therefore, the electrolytic solution containing the carbonate derivative represented by the general formula (3) does not deteriorate the battery performance. Further, the polymer produced by the polymerization reaction of the carbonate derivative is a substance that is unlikely to be redissolved in the electrolytic solution, and thus effectively acts on overcharging. Therefore, by using the electrolyte containing the carbonate derivative represented by the general formula (3), the safety of the battery can be ensured.

The above carbonate derivative is 2-
Biphenylylmethyl carbonate, 4-biphenylyl methyl carbonate, 4-biphenylyl-butyl carbonate, 3 - biphenylylmethyl carbonate, 4-biphenylyl phenyl carbonate Natick DOO or selected at least 1
It is preferred to have seeds.

Further, according to the present invention, a battery container is provided with an electrode body formed by laminating a positive electrode using a lithium-containing metal oxide as a positive electrode active material and a negative electrode using carbon as a negative electrode active material via a separator. A non-aqueous secondary battery provided with an electrolyte in which a lithium salt is dissolved as a solute in an organic solvent, wherein the electrolyte contains a carbonate derivative represented by the following general formula (4). I do. However,
R ¹ shown in Chemical Formula 4 represents a biphenylyl group , and R ² represents an alkyl group having 1 to 6 carbon atoms or a phenyl group.

[0015]

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Since the carbonate derivative represented by the general formula (4) has a good affinity for the organic solvent in the electrolytic solution, an electrolytic solution in which such a carbonate derivative is added to the organic solvent together with the lithium salt is used. It does not adversely affect battery characteristics such as low-temperature characteristics and storage characteristics.

When the battery voltage reaches an overcharged voltage, these additives start a decomposition reaction to generate gas and start a polymerization reaction to produce a polymer. This polymer acts as a resistor, and since this polymer is a substance that is unlikely to be redissolved in the electrolytic solution, it effectively acts on overcharging. After all,
The use of an electrolytic solution in which such a carbonate derivative is added to an organic solvent together with a lithium salt does not adversely affect battery characteristics such as low-temperature characteristics and storage characteristics, that is, does not degrade battery performance, and thus does not affect battery safety. Nature can be secured.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the lithium ion battery of the present invention will be described below with reference to FIGS. FIG. 1 is a cross-sectional view showing a state in which positive and negative electrodes stacked on each other via a separator of the lithium ion battery of one embodiment including the electrolytic solution of the present invention are wound and housed in an outer can. FIG. 2 is a partially cutaway view showing the current blocking sealing body attached to the opening of the outer can.

1. Preparation of Negative Electrode Plate A negative active material made of natural graphite (d = 3.36) and a binder made of polyvinylidene fluoride (PVDF) dissolved in an organic solvent made of N-methylpyrrolidone are mixed. Then, a slurry or a paste is obtained. These slurries or pastes are uniformly spread over both surfaces of a metal core (for example, a copper foil having a thickness of 20 μm) by a die coater, a doctor blade or the like in the case of a slurry, or by a roller coating method in the case of a paste. By coating, a negative electrode plate coated with the active material layer is formed.

Thereafter, the negative electrode plate coated with the active material layer is passed through a drier to remove an organic solvent necessary for preparing a slurry or a paste, followed by drying. Thereafter, the dried negative electrode plate is rolled by a roll press to obtain a negative electrode plate 10 having a thickness of 0.14 mm.

2. Preparation of Positive Electrode On the other hand, a positive electrode active material made of LiCoO ₂ , a carbon-based conductive agent such as acetylene black and graphite, a binder made of polyvinylidene fluoride (PVDF), and the like are combined with an organic material made of N-methylpyrrolidone. A solution dissolved in a solvent or the like is mixed to form a slurry or paste.

A metal core (for example, an aluminum foil having a thickness of 20 μm) is prepared by using a slurry such as a die coater or a doctor blade in the case of a slurry, or a roller coating method in the case of a paste.
To form a positive electrode plate coated with an active material layer. Thereafter, the positive electrode plate coated with the active material layer is passed through a drier to remove an organic solvent necessary for preparing a slurry or a paste, followed by drying. After drying, the dried positive electrode plate is rolled by a roll press to form a positive electrode plate 20 having a thickness of 0.17 mm.

3. Production of Electrode Body The negative electrode plate 10 and the positive electrode plate 20 produced as described above were prepared by forming a microporous film made of an inexpensive polyolefin resin having low reactivity with an organic solvent, preferably a polyethylene microporous film. (For example, the thickness is 0.025 mm), and the electrode plates 10 and 20 are overlapped with their center lines in the width direction coincided with each other. Thereafter, it is wound by a winder (not shown). Thereafter, the outermost periphery is taped to form a spiral electrode body. In the case of a prismatic battery, it is formed into a shape that can be inserted into a prismatic outer can with a press machine to form an electrode body.

4. Preparation of Electrolyte Example 1 A mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC)
An electrolyte a prepared by adding and mixing 1 M LiPF ₆ as an electrolyte salt and further adding and mixing 2% by weight of diphenyl carbonate represented by the following structural formula is used as an electrolyte of Example 1.

[0025]

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Example 2 In a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC),
An electrolyte b prepared by adding and mixing 1M LiPF ₆ as an electrolyte salt and further adding and mixing 2% by weight of 2-biphenylylmethyl carbonate represented by the following structural formula is used as an electrolyte of Example 2. .

[0027]

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Example 3 In a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC),
An electrolyte solution c prepared by adding and mixing 1 M LiPF ₆ as an electrolyte salt and further adding and mixing 2 wt% of 4-biphenylylmethyl carbonate represented by the following structural formula is used as an electrolyte solution of Example 3. .

[0029]

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Example 4 In a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC),
An electrolyte solution d prepared by adding and mixing 1 M LiPF ₆ as an electrolyte salt and further adding and mixing 2 wt% of 4-biphenylylbutyl carbonate represented by the following structural formula is used as an electrolyte solution of Example 4. .

[0031]

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Example 5 In a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC),
An electrolyte solution e prepared in Example 5 was prepared by adding and mixing 1 M LiPF ₆ as an electrolyte salt, and further adding and mixing 2% by weight of methyl 2,4,6-trimethylphenyl carbonate represented by the following structural formula. Electrolyte.

[0033]

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Example 6 In a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC),
An electrolyte f prepared by adding and mixing 1 M LiPF ₆ as an electrolyte salt, and further adding and mixing 2 wt% of 3-biphenylylmethyl carbonate represented by the following structural formula.
Is used as the electrolyte of Example 6.

[0035]

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Example 7 In a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC),
An electrolyte g prepared by adding and mixing 1 M LiPF ₆ as an electrolyte salt and further adding and mixing 2 wt% of 4-biphenylylphenyl carbonate represented by the following structural formula 11 is used as an electrolyte of Example 7. .

[0037]

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Example 8 A mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC) was
An electrolyte h prepared by adding and mixing 1 M LiPF ₆ as an electrolyte salt and further adding and mixing 2% by weight of benzyl 4-biphenylyl carbonate represented by the following structural formula is used as an electrolyte of Example 8. .

[0039]

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Example 9 In a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of dimethyl carbonate (DMC),
1M LiPF ₆ was added and mixed as an electrolyte salt, and diphenyl carbonate represented by the structural formula (5) was added to 2
The electrolytic solution i prepared by adding and mixing the weight% is used as the electrolytic solution of Example 9.

Example 10 1M LiPF ₆ as an electrolyte salt was added to and mixed with a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of methyl ethyl carbonate (MEC). An electrolyte j prepared by adding and mixing 2% by weight of diphenyl carbonate was used in Example 10.
Electrolyte solution.

Example 11 1 M LiPF ₆ as an electrolyte salt was added to a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC), 30 parts by weight of diethyl carbonate (DEC) and 30 parts by weight of dimethyl carbonate (DMC), and mixed. An electrolytic solution k prepared by adding and mixing 2% by weight of diphenyl carbonate represented by the structural formula of Chemical Formula 5 is used as an electrolytic solution of Example 11.

Example 12 A mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC) was
0.5 M LiPF ₆ and 0.5 M LiBF ₄ as electrolyte salts
Is added and mixed, and 2% by weight of diphenyl carbonate represented by the structural formula (1) is added and mixed.

Comparative Example 1 A mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC) was
An electrolyte m prepared by adding and mixing 1 M LiPF ₆ as an electrolyte salt is used as an electrolyte of Comparative Example 1.

Comparative Example 2 A mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC)
An electrolyte n prepared by adding and mixing 1 M LiPF ₆ as an electrolyte salt and further adding and mixing 2% by weight of biphenyl is used as an electrolyte of Comparative Example 2.

Comparative Example 3 A mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC) was
1M LiPF ₆ was added and mixed as an electrolyte salt.
-An electrolyte solution o prepared by adding and mixing 2% by weight of chloroanisole is used as an electrolyte solution of Comparative Example 3.

5. Production of Lithium Ion Battery Next, as shown in FIG. 1, insulating plates 41 were arranged above and below the electrode body produced as described above, and then a negative electrode terminal formed into a cylindrical shape by pressing from one sheet was formed. This electrode body is inserted through the opening of the steel outer can 40 also serving as the outer case. Next, the negative electrode current collecting tab 10a extending from the negative electrode plate 10 of the electrode body is welded to the inner bottom portion of the outer can 40, and the positive current collecting tab 20a extending from the positive electrode plate 20 of the electrode body is connected to the current blocking sealing body 50. Is welded to the bottom of the bottom plate 54.

As shown in FIG. 2, the current blocking sealing body 50 includes a stainless steel positive electrode cap 51 formed in an inverted dish shape (cap shape) and a stainless steel bottom plate 54 formed in a dish shape. Consists of The positive electrode cap 51
A convex portion 52 swelling toward the outside of the battery, and a flat flange portion 53 forming a bottom portion of the convex portion 52;
A plurality of gas vent holes 52a are provided at the corners of the convex portion 52. On the other hand, the bottom plate 54 includes a concave portion 55 that swells toward the inside of the battery, and a flat flange portion 56 that forms the bottom of the concave portion 55. A gas vent hole 55a is provided at a corner of the concave portion 55.

Inside the positive electrode cap 51 and the bottom plate 54, a power lead-out plate 57 which is deformed when the gas pressure inside the battery rises to a predetermined pressure or more is accommodated. The power lead-out plate 57 is composed of a concave portion 57a and a flange portion 57b.
It is composed of 005 mm aluminum foil. Recess 57
The lowest portion of a is disposed in contact with the upper surface of the concave portion 55 of the bottom plate 54, and the flange portion 57b is sandwiched between the flange portion 53 of the positive electrode cap 51 and the flange portion 56 of the bottom plate 54. In addition, the positive electrode cap 51 and the bottom plate 54 are liquid-tightly sealed by a sealing body insulating gasket 59 made of polypropylene (PP).

The upper part of the flange portion 57b has a PT
A C (Positive Temperature Coefficient) thermistor element 58 is provided, and when an overcurrent flows in the battery and an abnormal heat generation phenomenon occurs, the resistance value of the PTC thermistor element 58 increases to reduce the overcurrent. When the gas pressure inside the battery rises to a predetermined pressure or more, the power outlet plate 5
Since the concave portion 57a of the base 7 is deformed, the contact between the power lead-out plate 57 and the concave portion 55 of the bottom plate 54 is cut off, so that overcurrent or short-circuit current is cut off.

Then, after the above-mentioned electrolytes a to o were respectively injected into the opening of the outer can 40, the current interruption sealing was carried out through the outer can insulating gasket 42 made of polypropylene (PP) into the opening of the outer can 40. The body 50 is placed and the outer can 40
The upper end of the opening is crimped to the current blocking sealing body 50 side and sealed in a liquid-tight manner, thereby producing 15 types of cylindrical lithium ion batteries. The nominal capacity of each of the lithium ion batteries A to O thus produced is 1350 mAh.

The battery A was prepared by injecting the electrolytic solution a of Example 1, the battery B was obtained by injecting the electrolytic solution b of Example 2, and the battery C was prepared by injecting the electrolytic solution c of Example 3. The battery D was the one injected with the electrolyte d of the fourth embodiment, the battery E was the one injected with the electrolyte e of the fifth embodiment, and the battery F was the electrolyte f of the sixth embodiment. , The battery G was injected with the electrolyte g of Example 7, the battery H was injected with the electrolyte h of Example 8, and the battery I was injected with the electrolyte h of Example 9. i was injected, the battery J was injected with the electrolyte j of Example 10, the battery K was injected with the electrolyte k of Example 11, and the battery L was injected with the electrolyte of Example 12. The liquid M was injected, the battery M was injected with the electrolyte m of Comparative Example 1, and the battery N was injected with the battery of Comparative Example 2. Is obtained by injecting the solution was n, the battery O is obtained by injecting an electrolyte solution o of Comparative Example 3.

6. Test a. Overcharge test Each of the 15 types of lithium ion batteries A to O produced as described above was charged at a charge current of 1350 mA (1 C) until the battery voltage reached 4.1 V, and then at a constant voltage of 4.1 V. The battery is charged for 3 hours to be fully charged. The positive and negative of each of the fifteen fully charged lithium ion batteries A to O in this manner.
Overcharging is performed by flowing a charging current of 2700 mA (2C) between the negative electrode terminals, and the time from the start of overcharging to the activation of the current cutoff sealing body 50 and the maximum temperature of each of the batteries A to O at that time are measured. The results were as shown in Table 1 below.

B. Low-temperature characteristics Each of the 15 types of lithium ion batteries A to O produced as described above was charged at room temperature (25 ° C.) with a charge current of 1350 mA (1 C) until the battery voltage reached 4.1 V. The battery is charged at a constant voltage of 0.1 V for 3 hours to reach a fully charged state. Then, after suspending for 3 hours at room temperature, 135 hours at room temperature.
Discharge was performed at a discharge current of 0 mA (1 C) until the final voltage reached 2.75 V, and the discharge capacity at room temperature (mA
h) was determined.

On the other hand, each of the fifteen kinds of lithium ion batteries A to O produced as described above was used at room temperature (25 ° C.) for 135
The battery is charged at a charge current of 0 mA (1 C) until the battery voltage reaches 4.1 V, and then charged at a constant voltage of 4.1 V for 3 hours to be fully charged. Thereafter, the battery was suspended at a temperature of 0 ° C. for 3 hours, and then discharged at a temperature of 0 ° C. with a discharge current of 1350 mA (1 C) until the final voltage reached 2.75 V. From the discharge time, the discharge capacity at a low temperature (mAh) ).

Next, based on the respective capacities obtained as described above, the ratio of the discharge capacity at low temperature (mAh) to the discharge capacity at room temperature (mAh) is calculated as a low-temperature characteristic by the following equation (1). The results were as shown in Table 1 below.

[0057]

(1) Low temperature characteristics = (discharge capacity at low temperature / discharge capacity at room temperature) × 100% (1) c. Storage Characteristics Each of the 15 types of lithium ion batteries A to O prepared as described above is charged at room temperature (25 ° C.) at a charge current of 1350 mA (1 C) until the battery voltage reaches 4.1 V, and thereafter,
The battery is charged at a constant voltage of 4.1 V for 3 hours to be fully charged.
Then, after storing in an atmosphere of 60 ° C. for 20 days, 13
The battery was discharged at a discharge current of 50 mA (1 C) until the battery voltage reached 2.75 V, and the discharge capacity after high-temperature storage was determined from the discharge time. Then, when the ratio of the discharge capacity after high-temperature storage to the discharge capacity at room temperature determined above was calculated as a storage characteristic by the following mathematical formula 2, the results shown in Table 1 below were obtained.

[0058]

## EQU2 ## Storage characteristics = (discharge capacity after high-temperature storage / discharge capacity at room temperature) × 100% (2)

[0059]

[Table 1]

As is clear from Table 1, the battery M using the electrolyte solution m of Comparative Example 1 in which no additive was added bursted 32 minutes after the start of overcharge, but the low-temperature characteristics And the storage characteristics were both good. In addition, in the battery N using the electrolyte n of Comparative Example 2 to which biphenyl as the conventional additive was added, the charging current was interrupted 20 minutes after the start of overcharge, and the maximum temperature at that time was 88. ° C.
Then, both the low temperature characteristics and the storage characteristics were low values. Further, in the battery O using the electrolyte solution o of Comparative Example 3 to which 4-chloroanisole as a conventional additive was added, the charging current was cut off 21 minutes after the start of overcharge, and the highest current at that time was observed. The temperature was 90C. Then, both the low temperature characteristics and the storage characteristics were low values.

On the other hand, diphenyl carbonate represented by the above formula (5), 2-biphenylylmethyl carbonate represented by the above formula (6), which is an additive of the present invention,
4-biphenylylmethyl carbonate represented by the structural formula of formula 7, 4-biphenylylbutyl carbonate represented by the structural formula of formula 8, and methyl 2,4,6 represented by the structural formula of formula 9 -Trimethylphenyl carbonate,
3-biphenylylmethyl carbonate represented by the structural formula of the above formula 10, 4-biphenylylphenyl carbonate represented by the structural formula of the above formula 11, benzyl 4-biphenylyl carbonate represented by the structural formula of the above formula 12 In the batteries A to L using the electrolytes a to l of Examples 1 to 12 to which the electrolyte was added, the charging current was interrupted 15 to 20 minutes after the start of overcharging, and the maximum temperature at that time was 75 ８４84 ° C., and both low-temperature characteristics and storage characteristics were good.

This is because, when the battery is overcharged after the battery voltage reaches 4.1 V and becomes overcharged, diphenyl carbonate, 2-biphenylylmethyl carbonate, 4-biphenylylmethyl carbonate, 4-biphenylylbutyl carbonate , Methyl 2,4,6-trimethyl phenyl carbonate, 3-biphenylylmethyl carbonate, 4-biphenylyl phenyl carbonate, benzyl 4-biphenylyl carbonate, etc., start a decomposition reaction to generate gas. . At the same time, the polymerization reaction is started to generate polymerization heat. If overcharging is further continued in this state, the amount of generated gas increases, and the current cutoff sealing body 50 operates 15 to 20 minutes after the start of overcharging to cut off the overcharge current. As a result, the battery temperature also gradually decreases.

As apparent from comparison between the batteries A to H and the batteries I to L, no particular difference was observed even when the type of the organic solvent or the type of the solute in the electrolytic solution was changed. It can be said that the agent exerts the same effect regardless of the type of the electrolytic solution. Further, as is clear from the comparison of the batteries A to H, no particular difference was observed even when the additives were changed, so that the additive of the present invention was obtained from the diphenyl carbonate represented by the structural formula (5), 2-biphenylylmethyl carbonate represented by the chemical formula of Chemical Formula 6, 4-biphenylylmethyl carbonate represented by the chemical formula of Chemical Formula 7, 4-biphenylylbutyl carbonate represented by the chemical formula of Chemical Formula 8, Methyl 2,4,6-trimethylphenyl carbonate represented by the chemical formula of the above chemical formula 9, 3-biphenylylmethyl carbonate represented by the chemical formula of the above chemical formula 10, and 4- represented by the chemical formula of the above chemical formula 11 It is preferable to use at least one selected from biphenylylphenyl carbonate and benzyl 4-biphenylyl carbonate represented by the above structural formula.

7. Examination of the amount of additive to be added Next, the amount of additive to be added is examined. Example 13 In a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC),
1M LiPF ₆ was added and mixed as an electrolyte salt, and diphenyl carbonate represented by the above-mentioned formula (5) was added to the mixture.
The electrolytic solution p prepared by adding and mixing by weight% is used as the electrolytic solution of Example 13.

Example 14 A mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC) was
1M LiPF ₆ was added and mixed as an electrolyte salt, and diphenyl carbonate represented by the structural formula (5) was added to 3
The electrolyte q prepared by adding and mixing the components by weight was used as the electrolyte of Example 14.

Example 15 A mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC) was
1M LiPF ₆ was added and mixed as an electrolyte salt, and diphenyl carbonate represented by the above formula (5) was added to the mixture.
The electrolytic solution r prepared by adding and mixing by weight% is used as the electrolytic solution of Example 15.

Example 16 In a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of diethyl carbonate (DEC),
1M LiPF ₆ was added and mixed as an electrolyte salt, and diphenyl carbonate represented by the above-mentioned formula (5) was added to the mixture.
The electrolytic solution s produced by adding and mixing 0% by weight is used as the electrolytic solution of Example 16.

Thereafter, in the same manner as described above, the above-mentioned electrolytes p to s are respectively injected into the openings of the outer can 40, and then,
A current blocking sealing body 50 is placed in the opening of the outer can 40 via an insulating can insulating gasket 42 made of polypropylene (PP), and the upper end of the opening of the outer can 40 is swaged toward the current blocking sealing body 50. Lithium-ion battery P (injected electrolyte p), lithium-ion battery Q
(Injected electrolyte q), lithium ion battery R
(Injected electrolyte r), lithium ion battery S
(The one into which the electrolytic solution s is injected) is prepared.

Next, in the same manner as described above, these batteries P to S are overcharged, the time from the start of overcharging to the activation of the current cutoff sealing member 50, and the respective batteries at that time. When the maximum temperatures of PS were measured, the results shown in Table 2 below were obtained. When the low-temperature characteristics and the storage characteristics were measured in the same manner as described above, the results shown in Table 2 below were obtained.

[0070]

[Table 2]

As is clear from Table 2, when the amount of the additive is in the range of 1 to 10% by weight, the current interruption time,
No particular differences were observed in the maximum temperature, low temperature characteristics and storage characteristics. For this reason, the amount of the additive is desirably in the range of 1 to 10% by weight, and preferably 1 to 5% by weight. Although not shown in Table 2, an additive other than diphenyl carbonate represented by the structural formula of the above formula 5, namely 2-biphenylylmethyl carbonate represented by the structural formula of the above formula 6,
4-biphenylylmethyl carbonate represented by the following structural formula: 4-biphenylyl butyl carbonate represented by the above-mentioned chemical formula, and methyl 2,4,6-trimethylphenyl represented by the above-mentioned structural formula: Carbonate, 3-biphenylylmethyl carbonate represented by the above formula, 4-biphenylylphenyl carbonate represented by the above formula, benzyl 4-biphenyl represented by the above formula Approximately similar results were obtained with other additives such as rilcarbonate.

8. In the case where the current-blocking sealing body was not used In the above-described embodiment, an example was described in which the electrolyte solution to which the additive of the present invention was added was injected into the lithium ion battery including the current-blocking sealing body 50. Investigation was also made on a case where an electrolyte solution containing the additive of the present invention was injected into a prismatic lithium ion battery having no body.

Example 17 1M LiPF ₆ as an electrolyte salt was added to and mixed with a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of methyl ethyl carbonate (MEC). Example 17 was prepared using an electrolyte t prepared by adding and mixing 2% by weight of diphenyl carbonate.
Electrolyte solution.

Example 18 1M LiPF ₆ as an electrolyte salt was added to a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of methyl ethyl carbonate (MEC), and further mixed. Electrolytic solution u prepared by adding and mixing 2% by weight of 2-biphenylylmethyl carbonate
Is the electrolyte solution of Example 18.

Comparative Example 4 An electrolytic solution v prepared by adding and mixing 1 M LiPF ₆ as an electrolyte salt to a mixed solvent consisting of 40 parts by weight of ethylene carbonate (EC) and 60 parts by weight of methyl ethyl carbonate (MEC) was used. Electrolyte.

Thereafter, in the same manner as described above, the above-mentioned electrolytes t to v are respectively injected into the openings of the rectangular outer can (not shown), and the lithium ion battery T (injection of the electrolyte t) and the lithium ion battery U (the one into which the electrolyte u was injected) and the lithium ion battery V (the one into which the electrolyte v was injected) are prepared. The nominal capacity of each of the rectangular lithium ion batteries T to V thus manufactured is 600 mA.
h.

The three types of lithium-ion batteries T to V produced as described above are charged at a charging current of 600 mA (1 C) until the battery voltage reaches 4.1 V, and then charged at a constant voltage of 4.1 V. The battery is charged for a time to reach a fully charged state. Overcharging is performed by passing a charging current of 1200 mA (2C) between the positive and negative terminals of each of the three types of lithium-ion batteries T to V that are fully charged as described above, and the maximum temperature of each of the batteries T to V is measured. Overcharge test was performed. The result was as shown in Table 3 below.

Next, the three types of lithium ion batteries TV prepared as described above were placed at room temperature (25 ° C.) at 600 ° C.
The battery is charged at a charge current of mA (1C) until the battery voltage reaches 4.1 V, and then charged at a constant voltage of 4.1 V for 3 hours to obtain a fully charged state. Then, after resting at room temperature for 3 hours,
The cut-off voltage is 2. at a discharge current of 600 mA (1 C) at room temperature.
The battery was discharged until the voltage reached 75 V, and the discharge capacity (mAh) at room temperature was determined from the discharge time.

On the other hand, each of the three types of lithium-ion batteries TV prepared as described above was placed at room temperature (25 ° C.) for 600 m.
The battery is charged by the charging current of A (1C) until the battery voltage reaches 4.1 V, and then charged at a constant voltage of 4.1 V for 3 hours to be fully charged. Thereafter, the battery was suspended at a temperature of 0 ° C. for 3 hours, and then discharged at a temperature of 0 ° C. with a discharge current of 600 mA (1 C) until the final voltage reached 2.75 V. From the discharge time, the discharge capacity at a low temperature (mAh) ).

Next, based on each of the capacities measured as described above, the ratio of the discharge capacity at low temperature (mAh) to the discharge capacity at room temperature (mAh) is calculated as a low-temperature characteristic by the above-described equation (1). The results are as shown in Table 3 below.

Each of the three types of lithium ion batteries TV prepared as described above was placed at room temperature (25 ° C.) for 600 m.
The battery is charged by the charging current of A (1C) until the battery voltage reaches 4.1 V, and then charged at a constant voltage of 4.1 V for 3 hours to be fully charged. Thereafter, the battery was stored in an atmosphere of 60 ° C. for 20 days, and then discharged at a discharge current of 600 mA (1 C) until the battery voltage reached 2.75 V, and the discharge capacity after high-temperature storage was determined from the discharge time. Then, when the ratio of the discharge capacity after high-temperature storage to the discharge capacity at room temperature determined above was calculated as the storage characteristic using the above-described formula 2, the results shown in Table 3 below were obtained.

[0082]

[Table 3]

As is clear from Table 3, the battery V using the electrolyte solution v of Comparative Example 4 to which no additive was added was ruptured due to overcharging, but both low-temperature characteristics and storage characteristics were good. there were. On the other hand, a battery T using the electrolytic solution t of Example 17 to which diphenyl carbonate represented by the above formula (5) as an additive of the present invention was added, and 2-biphenyl represented by the above formula (6) In the battery U using the electrolyte solution u of Example 18 to which rilmethyl carbonate was added, the temperature rise was high but the battery did not burst when overcharged. In addition, the low-temperature characteristics and the storage characteristics were almost the same as those in the case where no additive was added, and both were good.

As described above, diphenyl carbonate of the present invention represented by the structural formula of the above formula (5), 2-biphenylylmethyl carbonate represented by the structural formula of the above formula (6), and the structural formula of the above formula (7) 4-biphenylylmethyl carbonate, 4-biphenylyl butyl carbonate represented by the structural formula of the above formula 8, methyl 2,4,6-trimethylphenyl carbonate represented by the structural formula of the above formula 9, Carbonate derivatives such as 3-biphenylylmethyl carbonate represented by the structural formula, 4-biphenylylphenyl carbonate represented by the structural formula 11 and benzyl 4-biphenylyl carbonate represented by the structural formula 12 When an additive consisting of is added to the electrolyte solution, it can be used without adversely affecting battery characteristics such as low-temperature characteristics and storage characteristics. Act effectively against electrostatic, it becomes possible to ensure the safety of the battery without deteriorating the battery performance.

In the above embodiment, an example in which natural graphite (d = 3.36) is used as the negative electrode active material has been described. In addition to natural graphite, carbon-based materials capable of inserting and extracting lithium ions, For example, graphite,
Carbon black, coke, vitreous carbon, carbon fiber, or a fired body thereof are suitable.

In the above-described embodiment, an example in which LiCoO ₂ is used as the positive electrode active material has been described. In addition to LiCoO ₂ , a lithium-containing transition metal compound that can accept lithium ions as a guest, for example,
LiNiO ₂ , LiCo _X Ni _(1-X) O ₂ , LiCrO ₂ ,
LiVO ₂ , LiMnO ₂ , αLiFeO ₂ , LiTi
O ₂ , LiScO ₂ , LiYO ₂ , LiMn ₂ O _{4 and the} like are preferable, and in particular, LiNiO ₂ , LiCo _X Ni _(1-X) O ₂ is used alone or a mixture of two or more thereof is used. Is preferred.

Further, the electrolyte is an ionic conductor in which a lithium salt is dissolved as a solute in an organic solvent and has a high ionic conductivity and is chemically and electrochemically stable with respect to each of the positive and negative electrodes. In this case, any one that has a wide usable temperature range, high safety, and inexpensive can be used. For example, in addition to the above organic solvents, propylene carbonate (PC), sulfolane (SL), tetrahydrofuran (THF), γ-butyrolactone (GBL), and the like, or a mixed solvent thereof are suitable. As the solute, a lithium salt having a strong electron-withdrawing property is used, and the above-described Li is used.
Other than PF ₆ or LiBF ₄ , for example, LiCl
O ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ S
O ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃
Etc. are preferred.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state in which positive and negative electrode plates superimposed via a separator of a battery provided with an electrolytic solution of the present invention are wound and housed in an outer can.

FIG. 2 is a partially cutaway view showing a current blocking sealing body attached to an opening of the outer can of FIG. 1;

[Explanation of symbols]

10: negative electrode plate, 10a: negative electrode current collecting tab, 20: positive electrode plate,
20a: positive electrode current collecting tab, 30: separator, 40: outer can, 41: spacer, 42: insulating gasket for outer can,
50 ... current interrupting sealing body

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koji Abe 5-1978 Kogushi, Oji, Ube City, Yamaguchi Prefecture Inside Ube Research Institute, Ltd. (72) Inventor: Tsutomu Takai, Inventor: Tsutomu Takai 1978 Kogushi, Ogushi, Ube City, Yamaguchi Prefecture Ube Industries, Ltd .: Ube Research Laboratory (56) References JP 9-22722 (JP, A) JP JP-A-8-298137 (JP, A) JP-A-8-293323 (JP, A) JP-A-8-306387 (JP, A) JP-A-8-106909 (JP, A) JP-A-11-329497 (JP) , A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 10/40

Claims (4)

(57) [Claims] An electrolyte for a non-aqueous battery in which a lithium salt is dissolved as a solute in an organic solvent, wherein the organic solvent contains a carbonate derivative represented by the following general formula (1). Electrolyte for non-aqueous batteries. Embedded image However, R ¹ shown in the chemical formula 1 is a biphenylyl group shows <br/>, R ² represents an alkyl group, a phenyl group having 1 to 6 carbon atoms. 2. The carbonate derivative may be 2 -biphenylylmethyl carbonate, 4-biphenylylmethyl carbonate, 4-biphenylylbutyl carbonate , or 3 -biphenylylmethyl carbonate .
- biphenylylmethyl carbonate, a non-aqueous battery electrolyte according to claim 1, characterized in that it comprises at least one selected et al or 4-biphenylyl phenyl carbonate Natick bets. 3. A battery container comprising an electrode body formed by laminating a positive electrode using a lithium-containing metal oxide as a positive electrode active material and a negative electrode using carbon as a negative electrode active material in a battery container, and further comprising an organic solvent. A non-aqueous secondary battery comprising an electrolyte solution in which a lithium salt is dissolved as a solute, wherein the electrolyte solution contains a carbonate derivative represented by the following general formula (2). Water-based secondary battery. Embedded image Here, R ¹ shown in Chemical Formula 2 represents a biphenylyl group , and R ² represents an alkyl group having 1 to 6 carbon atoms or a phenyl group. 4. The carbonate derivative may be 2 -biphenylyl methyl carbonate, 4-biphenylyl methyl carbonate, 4-biphenylyl butyl carbonate ,
- biphenylylmethyl carbonate, a non-aqueous secondary battery according to claim 3, characterized in that it comprises at least one selected et 4- biphenylene or alkylphenyl carbonate Natick bets.