JP2001006735A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery having excellent heavy load characteristics at a high voltage and capable of suppressing production of a defective appearance by adding PC to an electrolyte containing EC, chain carbonic ester, and/or chain carbonic acid ester as main ingredients. SOLUTION: This nonaqueous electrolyte secondary battery has a structure in which a positive electrode case used also for a positive electrode terminal is sealed to a negative electrode case through a sealing material and at least a positive electrode, a negative electrode, a separator and a nonaqueous electrolyte are included, and a carbon material having a d002 spacing of not more than 0.338 nm is used for the negative electrode in it. The amount of PC added is preferably not less than 25% of an EC content in this electrolyte, and concentration of the PC to the entire electrolyte solvent is preferably not more than 17%. A positive electrode collector 2 is brought into internal contact with the inner surface of a positive electrode container 1 of stainless steel, the separator 4 is installed on the positive electrode 3 and a negative electrode carrying body 6 is provided on top of it. A negative electrode collector 7 is brought into internal contact with a negative electrode container 8, a gasket 5 is interposed in the opening part of the positive electrode container 5, the positive electrode collector 2 is sealed in the negative electrode container 8 and the electrolyte is filled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery having excellent heavy load characteristics.

[0002]

2. Description of the Related Art In recent years, as a power source for portable equipment, high voltage and high energy density are expected to be high. As a battery system having a high energy density, excellent heavy load characteristics and charge / discharge cycle characteristics. , A negative electrode having a carbon material capable of inserting and extracting lithium, and a positive electrode having LiCoO ₂ , LiN
Electrolysis using lithium-containing oxides such as iO ₂ , LiMn ₂ O ₄ , and LiCr ₂ O _4, or replacing the transition metal elements of these substances with other metal elements, or using lithium-containing oxides having different oxygen deficiencies. A non-aqueous electrolyte secondary battery using a non-aqueous electrolyte as a liquid has been studied. Some of them have already been put into practical use as cylindrical or square secondary batteries. Of these, those spacing of d ₀₀₂ was used carbon material is less than 0.338nm the negative electrode material has a high voltage at the end of charging, and a high energy density.

[0003] The electrolyte of these batteries is usually EC
(DCE) having a low viscosity to cyclic carbonates having a high dielectric constant such as (ethylene carbonate), PC (propylene carbonate), and BC (butylene carbonate).
Chain carbonates such as (dimethyl carbonate: dimethyl carbonate), DEC (diethyl carbonate: diethyl carbonate), MEC (methyl ethyl carbonate), and / or
Alternatively, a low-boiling solvent such as a chain carboxylic acid ester such as methyl acetate, ethyl acetate or ethyl propionate is mixed and used. Furthermore, spacing of d ₀₀₂ in the negative electrode 0.338n
In a battery using a carbonaceous material of m or less, decomposition of the electrolytic solution occurs when PC or BC is used alone as the cyclic carbonate. Therefore, in this battery only, a mixture of EC and the above-mentioned chain carbonate or chain carboxylate is used as a solvent.

[0004]

However, with the further miniaturization of the equipment used in recent years, the nonaqueous electrolyte secondary battery has also been required to be smaller and thinner.
The development of a flat non-aqueous electrolyte secondary battery such as a coin type or a card type was required.

In the case of the above-mentioned flat non-aqueous electrolyte secondary battery,
Compared with a normal cylindrical or prismatic battery, the electrolyte is easily volatilized because the cell structure is flat and the opening diameter is large. Also, in the production process, due to the characteristics of the shape of the flat battery, after excessively injecting the electrolyte into the battery, the battery case is fitted, and then the battery case is sealed while overflowing the electrolyte by swaging, and the battery is closed. Is being assembled. Further, usually, in order to absorb the electrolyte solution into the mixture, the electrolyte solution is left standing for about 5 minutes until the caulking process is performed after the electrolyte solution is injected. However, when an electrolyte consisting of a mixed solvent of EC and a low-boiling solvent is used, the low-boiling components in the overflowing electrolyte are volatilized before the caulking process is performed, and the electrolyte is solidified, and the electrolyte is solidified in the positive electrode case. The problem of sticking occurred. As a result, when sealing the battery by swaging, the positive electrode case is scratched,
The problem that appearance failure occurs frequently occurred.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and its object is to examine the components of an electrolytic solution,
An object of the present invention is to provide a non-aqueous electrolyte secondary battery that suppresses appearance defects and has excellent high-load characteristics at high voltage.

[0007]

Means for Solving the Problems As a result of intensive studies on the composition of the electrolytic solution, the present inventors have solved these problems by adding PC as a solvent other than EC and a low boiling point solvent to the electrolytic solution. Found to be solved. Furthermore, even after high-temperature storage, it succeeded in maintaining excellent heavy load characteristics. That is, according to the present invention, by adding PC, which is a high-boiling solvent, to the electrolytic solution, even when the low-boiling solvent evaporates, it is possible to suppress the deposition of EC and without causing poor appearance. , And a battery can be manufactured.
Further, by regulating the amount of PC added, it is possible to provide a battery with little deterioration in discharge characteristics and excellent in heavy load characteristics.

[0008] In addition, to suppress appearance defects that occur during battery manufacturing, a metal positive electrode case also serving as a positive electrode terminal is sealed with a negative electrode case via a sealing material, and at least the positive electrode, the negative electrode, the separator, and the non-aqueous solution. In a battery having a structure including an electrolytic solution, the non-aqueous electrolytic solution may be “soluble in EC”, “liquid at room temperature and hardly volatilizes (has a high boiling point)” “does not affect battery characteristics” This is realized by adding a new non-aqueous solvent satisfying the above conditions.

As a result of intensive studies on the additive solvent, the present inventors have found that PC is particularly preferable as the above-mentioned additive component in that it has little effect on battery characteristics. Although it was thought that γ-BL also satisfied the above three conditions, as a result of various studies, there was a problem that γ-BL had a reduced heavy load characteristic after storage at a high temperature or after long-term continuous charging.

The amount of PC added to the electrolytic solution is as follows:
It is preferable that the content of EC is 25% or more of the EC content, and the concentration of PC with respect to the whole electrolytic solution is 17% or less. This is because if it is not more than 25% of the EC, the EC cannot be completely dissolved, and the expected effect of preventing poor appearance cannot be obtained. On the other hand, if the content exceeds 17% of the total solvent of the electrolytic solution, the decomposition of PC proceeds, and gas is generated, resulting in a decrease in heavy load characteristics after high-temperature storage or after long-term continuous charging.

According to the present invention, in a non-aqueous electrolyte secondary battery, by adding a non-aqueous solvent that satisfies the above-mentioned conditions, even after the low-boiling-point components volatilize during the manufacturing process, EC added to the added new solvent. Can be dissolved beforehand. Therefore, it is possible to prevent the appearance defect from occurring without the EC being precipitated and solidified.

[0012]

(Embodiment 1-1) FIG. 1 is a sectional view of a battery according to this embodiment. In the figure, reference numeral 1 denotes a positive electrode container made of stainless steel, and a positive electrode current collector 2 made of stainless steel is inscribed on the inner surface of the positive electrode container 1. The positive electrode 3 is accommodated in the positive electrode container 1 including the current collector 2. This positive electrode 3 is composed of 90 parts by weight of LiCoO ₂ and artificial graphite 1
After mixing 0 parts by weight, 3 parts by weight of powdery polytetrafluoroethylene is added, kneaded, weighed in a predetermined amount, and pressed into a 0.8 mm thick pellet.

A separator 4 made of a polypropylene nonwoven fabric is provided on the positive electrode 3, and a negative electrode carrier 6 is provided on the upper surface of the separator 4. The negative electrode carrier 6 is obtained by graphitizing (d ₀₀₂ = 3.38 or less) mesophase pitch-based carbon fiber as a carbonaceous material, and then pulverizing 95 parts by weight of a styrene-butadiene copolymer as a binder. After mixing 5 parts by weight, weigh and mix
It was pressed into a pellet of mm.

Reference numeral 8 denotes a negative electrode container made of stainless steel, and a negative electrode current collector 7 made of Cu is inscribed on the inner surface of the negative electrode container 8. The positive electrode current collector 2, the separator 4, the negative electrode carrier 6, and the negative electrode current collector 7 are hermetically sealed in the negative electrode container 8 via the insulating gasket 5 at the opening of the positive electrode container 1.

After the positive electrode 3 is housed in the positive electrode container 1 in which the positive electrode current collector 2 is inscribed, a separator 4 is placed on the positive electrode 3.
And EC: MEC: PC = 28: 65: 7
An electrolytic solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / l in the mixed solvent was injected. Next, the negative electrode carrier 6 was installed, and the negative electrode container 8 was joined via the gasket 5. At this time, the electrolyte overflowing from the inside of the battery adhered to the positive electrode case.
Then, after leaving for 5 minutes for the purpose of permeating the electrolytic solution into the positive electrode 3, the separator 4, and the negative electrode 6, the positive electrode container 1 was sealed by caulking to produce a battery. The battery manufactured in this way has a diameter of 20 mm and a thickness of 2.5 mm.
The battery voltage was 4.2 V at a constant current of 0.5 mA.
To give a battery of Example 1-1.

Example 1-2 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 28: 60: 12.

Example 1-3 A battery was produced in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 28: 55: 17.

Example 1-4 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 21: 72: 7.

Example 1-5 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 21: 65: 14.

Example 1-6 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 35: 55: 10.

Example 1-7 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 35: 50: 15.

Comparative Example 1-1 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 28: 72: 0.

Comparative Example 1-2 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 28: 68: 4.

Comparative Example 1-3 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 28: 47: 25.

Comparative Example 1-4 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 21: 79: 0.

(Comparative Example 1-5) A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 21: 58: 21.

Comparative Example 1-6 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 35: 65: 0.

Comparative Example 1-7 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 35: 60: 5.

Comparative Example 1-8 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: MEC: PC = 35: 40: 25. Table 1 shows the appearance defect occurrence rate at the time of battery production for the batteries of this example and the comparative example produced as described above.

[0030]

[Table 1]

As is clear from Table 1, Example 1 in which PC was added at 25% or more to EC irrespective of the EC concentration.
-1 to the batteries of Example 1-7 and Comparative Examples 1-3, 1-5, and 1
It can be seen that in the battery of -8, the occurrence of poor appearance is suppressed in the battery of this example. Next, the total height increase of the battery 24 hours after the completion of the first charging was measured. In addition, a constant current of 7.5 mA was used for each battery.
Heavy load discharge was performed to 0V. Table 1 also shows the results. As is clear from Table 1, regardless of the EC concentration,
Comparative Examples 1-3 and 1- in which the amount of PC added was 21% or more.
The batteries 5 and 1-8 have a large increase in the total battery height. Also, the discharge capacity is small. Next, Table 1 shows the discharge results after storage at 60 ° C. for 20 days and the discharge results after continuous charging at 4.2 ° C. for 20 days at 60 ° C. In Table 1, those of Comparative Examples 1-3, 1-5, and 1-8 in which PC was added in an amount of 21% or more based on the entire electrolyte solvent were the same as those in Example 1
1 to Example 1-7 and Comparative Examples 1-1, 1-2, 1-
The discharge capacity after the test is significantly lower than those of the batteries 4, 1-6, and 1-7.

From these examination results, the amount of PC added was E
25% or more with respect to C, and 1% with respect to the entire electrolyte solvent.
Clearly, it is preferably at most 7%. Further, the MEC in the electrolyte was changed to DEC, and the following battery was produced.

Example 2-1 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: DEC: PC = 28: 60: 12.

Comparative Example 2-1 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: DEC: PC = 28: 72: 0.

Comparative Example 2-2 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: DEC: PC = 28: 68: 4.

Comparative Example 2-3 A battery was fabricated in the same manner as in Example 1-1, except that the composition of the electrolytic solution was EC: DEC: PC = 28: 47: 25.

The battery fabricated as described above was evaluated in the same manner as in Example 1. Table 2 shows the results. Even when the MEC in the electrolytic solution is changed to DEC, the same effect as in the case of Example 1 shown in Table 1 is obtained.

[0038]

[Table 2]

(Example 3-1) The composition of the electrolytic solution was EC: MEC: EPR: PC = 28: 4.
A battery was prepared in the same manner as in Example 1-1, except that the ratio was 0:20:12. EPR is ethyl propionate.

(Comparative Example 3-1) The composition of the electrolytic solution was EC: MEC: EPR: PC = 28: 4.
A battery was fabricated in the same manner as in Example 1-1, except that the ratio was 8: 24: 0.

(Comparative Example 3-2) The composition of the electrolytic solution was EC: MEC: EPR: PC = 28: 4.
A battery was prepared in the same manner as in Example 1-1, except that the ratio was 6: 23: 3.

(Comparative Example 3-3) The composition of the electrolytic solution was EC: MEC: EPR: PC = 28: 3.
A battery was fabricated in the same manner as in Example 1-1, except that the ratio was 2:16:24.

The battery fabricated as described above was evaluated in the same manner as in Example 1. Table 3 shows the results. Even when the MEC in the electrolytic solution is changed to MEC and EPR, the same effect as in Example 1 shown in Table 1 is obtained.

[0044]

[Table 3]

When the electrolyte composition was changed to PC, γ-BL
Was prepared as follows in which Comparative Example 4 was added. (Comparative Example 4-1) The electrolyte composition was EC: MEC: γ-BL = 28: 68: 4.
A battery was fabricated in the same manner as in Example 1-1, except that

(Comparative Example 4-2) The composition of the electrolytic solution was EC: MEC: γ-BL = 28: 60: 1.
A battery was fabricated in the same manner as in Example 1-1, except that the battery was No. 2.

(Comparative Example 4-3) The composition of the electrolytic solution was EC: MEC: γ-BL = 28: 47: 2.
A battery was fabricated in the same manner as in Example 1-1, except that the battery number was 5.

The battery fabricated as described above was evaluated in the same manner as in Example 1. Table 4 shows the results. From this, γ-BL is reduced by 12%.
Although the batteries of Comparative Examples 4-2 and 4-3 added as described above exhibited the effect of preventing appearance defects, the discharge capacity at the time of heavy load discharge was reduced, and particularly after storage at high temperatures and after continuous charge. Inferior results.

[0049]

[Table 4]

Further, the embodiments of the present invention have been described with reference to a coin-shaped non-aqueous solvent secondary battery using a non-aqueous solvent for the non-aqueous electrolyte. Naturally, the present invention can be applied to a polymer secondary battery or a solid electrolyte secondary battery using a solid electrolyte.
The shape of the battery is not limited to this, and the present invention is naturally applicable to other nonaqueous electrolyte secondary batteries such as a card type and a sheet type.

[0051]

As described above, according to the present invention, the occurrence of poor appearance can be remarkably reduced, and even if the battery is stored for a long time in a charged state after production, the capacity is small and the battery has excellent heavy load characteristics. Can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a battery of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode container, 2 ... Positive electrode collector, 3 ... Positive electrode, 4 ... Separator, 5 ... Gasket, 6 ... Negative electrode support, 7 ... Negative electrode current collector, 8 ... Negative electrode container.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaki Shikoda 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation F-term (reference) 5H003 AA01 AA08 BB01 BB12 BC06 BD02 BD06 5H029 AJ02 AJ14 AK03 AL06 AM03 AM05 BJ03 CJ05 DJ02 DJ03 DJ04 DJ05 HJ10 HJ13

Claims (2)

[Claims] A positive electrode case also serving as a positive electrode terminal is sealed with a negative electrode case via a sealing material, and at least a positive electrode, a negative electrode,
Having a structure that includes a separator, and a non-aqueous electrolyte,
In the nonaqueous electrolyte secondary battery using a carbon material spacing of d ₀₀₂ is less than 0.338nm the negative electrode, the electrolyte solution EC and chain carbonic ester, and / or a chain carboxylate as a main component, Non-aqueous electrolyte secondary battery characterized by adding PC. 2. The amount of PC added is 25 to the EC content.
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the concentration of the electrolyte is not less than 17% and the concentration of PC with respect to the entire electrolyte solution solvent is not more than 17%.