JPH06176793A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To provide a 4V-class nonaqueous electrolyte secondary battery excellent in high temperature reservation. CONSTITUTION:A positive electrode 1 uses at least one composite oxide selected of LiMn2O4, LiC0O2, LiNiO2 and LiFeO2 groups as positive electrode active material and a negative electrode 4 uses metal lithium or reversibly occluded and discharged lithium. Nonaqueous electrolyte is such that lithium fluoride or phosphatic lithium hexafluoride as solute is solved in mixed solvent of ethylene carbonate, 1, 2-dimethoxyethane and propylene carbonate. In this way, combined nonaqueous electrolyte as above-mentioned has almost no capacity decrease in reservation at a high temperature of 60 deg.C, compared with others, and is free from freeze at -20 deg.C, thus to provide a nonaqueous electrolyte secondary battery excellent in high temperature reservation property and low temperature property.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery using a non-aqueous electrolyte.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries using lithium or a lithium compound as a negative electrode are expected to have a high voltage and a high energy density, and have been actively studied.

Until now, the positive electrode activity of non-aqueous electrolyte secondary batteries has been improved.
V as a substance₂O_Five, Cr₂O_Five, MnO₂, TiS₂
Are known. In recent years, having higher energy density
As a positive electrode active material for a 4-volt class non-aqueous electrolyte secondary battery
LiMn₂O_Four, LiC₀O₂, LiNiO₂, Li
FeO₂Has been attracting attention. In particular, LiMn
₂O _Four, LiNiO₂And LiFeO₂Is low cost
In addition, the raw material supply is stable, and a large capacity of non-aqueous electrolyte
Active research is being conducted as an active material for secondary batteries.

[0004]

The use of _{LiMn 2 O 4, LiC 0 O} 2, LiNiO 2 or LiFeO ₂ as a way positive electrode active material [0008], can be realized a non-aqueous electrolyte secondary battery of high energy density, Charge voltage is 4
Since the voltage exceeds the voltage, there is a problem that the high temperature storage characteristics in a charged state are insufficient. High temperature storage of a non-aqueous electrolyte secondary battery is caused by decomposition of a trace amount of water and an electrolyte solvent in the battery, which causes problems such as an increase in internal resistance of the battery and a decrease in charge / discharge capacity. These phenomena become more remarkable as the battery voltage becomes higher.

As a means for solving the above problems, the applicant has proposed to use, as an electrolytic solution, a solution obtained by dissolving lithium borofluoride or lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and 1.2-dimethoxyethane. . However, this electrolyte has a problem that it freezes at -20 ° C.

It is an object of the present invention to provide a non-aqueous electrolytic secondary battery which is excellent in high temperature storage characteristics and low temperature storage characteristics in view of the above conventional problems.

[0007]

In order to achieve the above object, the present invention provides a negative electrode that reversibly absorbs and releases lithium metal or lithium, LiMn ₂ O ₄ , and LiC.
_In a non-aqueous electrolyte secondary battery having a positive electrode and a non-aqueous electrolyte, the positive electrode having at least one composite oxide selected from the group of O ₂ , LiNiO ₂ and LiFeO ₂ as an active material,
As the non-aqueous electrolyte, ethylene carbonate and 1,2
-A configuration in which lithium borofluoride or lithium hexafluorophosphate is dissolved in a mixed liquid of dimethoxyethane and propylene carbonate is used. The amount of propylene carbonate added is preferably 5 to 20% by volume with respect to ethylene carbonate.

[0008]

As described above, lithium borofluoride or lithium hexafluorophosphate is dissolved in the mixed solution of ethylene carbonate, 1,2-dimethoxyethane and propylene carbonate in the electrolyte of the 4V class non-aqueous electrolyte secondary battery. If the above-mentioned one is used, even if the battery is stored in a charged state at a high temperature for a long period of time, the decomposition of the electrolytic solution solvent can be suppressed, and the high temperature storage characteristics can be improved. Further, it does not freeze even at -20 ° C, and the low temperature characteristics can be improved.

[0009]

Embodiments A non-aqueous electrolyte secondary battery and a method of manufacturing the same according to embodiments of the present invention will be described below with reference to the drawings. (Example 1) LiMn ₂ O ₄ is Li ₂ CO ₃ and Mn ₃ O.
₄ was mixed well at a molar ratio of 3: 4, and then this mixture was heated in the atmosphere at 900 ° C. for 10 hours to synthesize. LiC ₀ O ₂ is a mixture of Li ₂ CO ₃ and C ₀ CO ₃ 1: 2.
Was mixed at a molar ratio of and the mixture was heated at 900 ° C. in the atmosphere to synthesize. LiNiO ₂ is LiOH and Ni.
(NO ₃ ) ₂ was mixed at a molar ratio of 1: 1 and the mixture was mixed with 80
Obtained by heating at 0 ° C. LiFeO ₂ is Li
₂ CO ₃ and Fe (OH) ₃ were mixed in a molar ratio of 1: 2,
Obtained by heating at 650 ° C.

Next, the LiMn obtained as described above
₂O_Four, LiC₀O₂, LiNiO ₂And LiFeO
₂A positive electrode was prepared by using it as an active material. Preparation of positive electrode
First, these active materials and acetylene black which is a conductive agent
And polyfluorinated ethylene resin as a binder in weight ratio
Mix to a ratio of 7: 2: 1 and dry thoroughly.
It was used as a positive electrode mixture. 0.1 gram of this positive electrode mixture
1 ton / cm per 7.5 mm ²Pressed into pellets with
To form a positive electrode.

The negative electrode is manufactured by using a carbon material as a negative electrode active material and a polyfluorinated ethylene resin as a binder in a weight ratio of 10:
The mixture was mixed so as to be 1 and sufficiently dried to obtain a negative electrode mixture. 0.1 g of this negative electrode mixture was added to 17.5 mm in diameter.
A negative electrode was formed by pressure-molding into a pellet shape at ton / cm ² .

Volume ratio of EC, DME and PC is 50: 5.
Electrolyte solution A was prepared by dissolving 1 mol / 1 of lithium borofluoride in a solvent mixed at a ratio of 0:20, and electrolyte solution B was prepared by dissolving 1 mol / 1 of lithium hexafluorophosphate in the above solvent. Electrolyte solutions C and D are prepared by dissolving 1 mol / 1 of lithium borofluoride or lithium hexafluorophosphate in a solvent mixture of EC and DME having an equal volume.

Using the positive electrode and the negative electrode prepared as described above
A cross-sectional view of the manufactured non-aqueous electrolyte secondary battery is shown in (Fig. 1).
You The positive electrode 1 is placed in the case 2, and the separator 3 is placed on the positive electrode 1.
As a porous polypropylene film. Negative electrode
4 to the sealing plate 6 with the polypropylene gasket 5
Crimped. Next, the electrolytic solution is placed on the separator 3 and the positive electrode 1
And the negative electrode 4, the battery was sealed with a sealing plate 6.
LiMn was used as the positive electrode active material using the electrolytic solution A. ₂O_FourFor
The non-aqueous electrolyte secondary battery prepared by the above method.
Each (A₁), (A₂), (A₃), (A_Four).

LiM was used as the positive electrode active material using the electrolytic solution B.
n ₂ O ₄ , LiC ₀ O ₂ , LiNiO ₂ , LiFeO ₂
Non-aqueous electrolyte secondary batteries produced by the same method as above using (B ₁ ), (B ₂ ), (B ₃ ),
(B ₄ ).

As a comparative example, using electrolytes C and D,
LiMn as active material₂O_Four, LiC₀O₂, LiNi
O₂Non-aqueous electrolyte solution prepared in the same manner as above using
Each secondary battery (C₁), (C₂), (C₃),
(C_Four) And (D₁), (D ₂), (D₃),
(D_Four).

Table 1 shows EC-DME mixed solvent and EC.
-The result of having confirmed whether it freezes at -20 degreeC of a DME-PC mixed solvent is shown. Furthermore (Table 2) shows EC-DME
-The result of having confirmed whether it freezes at -20 degreeC of PC mixed solvent is shown. In this way, the electrolyte system containing PC is-
It does not freeze even at 20 ° C.

[0017]

[Table 1]

[0018]

[Table 2]

A low temperature test of the non-aqueous electrolyte secondary battery is performed by the following method. The capacity of the non-aqueous electrolyte secondary battery is confirmed by charging / discharging the non-aqueous electrolyte secondary battery under the conditions of a charge / discharge current of 0.5 mA at 20 ° C. and a voltage range of 3.0 V to 4.5 V. The non-aqueous electrolyte secondary battery is charged at 20 ° C., transferred to an atmosphere of −20 ° C., and left for 10 hours. Then, the non-aqueous electrolyte secondary battery is discharged to 3 V with a current of 0.5 mA. The evaluation is performed by comparing the capacity ratio of −20 ° C. to the capacity of 20 ° C.

Low temperature capacity retention rate (%) = − 20 ° C. discharge capacity / 20 ° C. discharge capacity × 100 The results of the low temperature test are shown in Table 3.

[0021]

[Table 3]

A non-aqueous electrolyte secondary battery C1 which is a comparative example is
The capacity at −20 ° C. is 1% of 20 ° C., and almost no discharge is possible. Similarly, the nonaqueous electrolyte secondary batteries of Comparative Examples all had a capacity retention rate of 1% or less. On the other hand, the non-aqueous electrolyte secondary battery A1 of this example can be discharged even at −20 ° C., and its discharge capacity is 83% of 20 ° C. Similarly, the non-aqueous electrolyte secondary batteries A2, B1, and
Similarly, it was found that B2, C1, C2, D1 and D2 have a discharge capacity of -20 ° C which is more than 80% of that in the case of a temperature atmosphere of 20 ° C.

Next, a high temperature storage test of the non-aqueous electrolyte secondary battery was conducted by the following method. First, regarding the non-aqueous electrolyte secondary battery manufactured by the above method, charging at 20 ° C. with a constant current of 0.5 mA to 4.3 V and discharging to 3 V
The discharge was performed for 5 cycles. Then, when the charge of the 6th cycle was completed, the non-aqueous electrolyte secondary battery was stored in a constant temperature bath at 60 ° C. for 4 weeks. After storage, the non-aqueous electrolyte secondary battery was returned to 20 ° C. again and discharged under the same conditions. The evaluation of the non-aqueous electrolyte secondary battery was performed using the following values of the capacity retention rate and the capacity recovery rate.

Capacity maintenance rate (%) = (6th cycle discharge capacity / 5th cycle discharge capacity) × 100 Capacity recovery rate (%) = (7th cycle discharge capacity / 5th cycle discharge capacity) × 100 Table 4 also shows the capacity retention rate and capacity recovery rate of each non-aqueous electrolyte secondary battery after 4 weeks.

[0025]

[Table 4]

The non-aqueous electrolyte secondary batteries (C ₁ ) and (D ₁ ) which are comparative examples each have a capacity retention rate of 8 after storage.
They are 5% and 82%, respectively, and only have a capacity less than half of the discharge capacity before storage. Furthermore, the capacity recovery rate of these non-aqueous electrolyte secondary batteries (the value obtained by dividing the discharge capacity obtained when the non-aqueous electrolyte secondary battery was charged after storage and discharged again by the discharge capacity before storage) was They are 99% and 99%, respectively, and the capacity of the non-aqueous electrolyte secondary battery after storage at 60 ° C. for 4 weeks is about 20% by self-discharge, and the capacity becomes the same as that before storage.

On the other hand, in the non-aqueous electrolyte secondary battery (A ₁ ) of this example, the capacity retention rate after storage was 83%, which was about 17% lower than the discharge capacity before storage, but the capacity was The recovery rate is 98%, which is almost the capacity before storage. The capacity retention rate of the non-aqueous electrolyte secondary battery (B ₁ ) is also 8
Although it was 4%, the capacity recovery rate was 100%, and the discharge capacity before storage was recovered. Similarly, as the positive electrode active material, L
Non-aqueous electrolyte secondary batteries (A ₂ ), (B ₂ ), (A ₃ ), which use iC ₀ O ₂ , LiNiO ₂ or LiFeO ₂ .
The capacity recovery rate of (B ₃ ), (A ₄ ), and (B ₄ ) after storage is 97 to 100%, and the capacity is almost completely recovered by charging even after storage at 60 ° C. for 4 weeks. .

As described above, EC and DM are used as the solvent of the electrolytic solution.
It can be seen that the non-aqueous electrolyte secondary battery using the mixed solution of E and PC and using lithium borofluoride or lithium hexafluorophosphate as the solute has excellent low temperature characteristics and high temperature storage characteristics. (Example 2) Next, PC was added to the EC-DME mixed solvent.
The amount added was investigated. LiM as the positive electrode active material
n ₂ O ₄ was used, and a carbon material was used as the negative electrode active material.
The positive electrode and the negative electrode were manufactured in the same manner as in Example 1. The non-aqueous electrolyte secondary battery used in the test was also manufactured by the same method as in Example 1. The mixing ratio of EC and DME is 1 by volume, and the addition amount of PC is 0, 3 by volume with respect to EC.
The cases of 0, 35, 40, 60, 65, 80, and 100% were examined. Non-aqueous electrolyte secondary batteries produced using these electrolytes are (a1), (a2), (a3), (a
4), (a5), (a6), (a7), and (a8).

The low temperature test and the high temperature storage test of the non-aqueous electrolyte secondary battery were carried out in the same manner as in Example 1. The results of the low temperature test are shown in (Fig. 2). Volume ratio of PC to EC is 3
The discharge capacity at −20 ° C. was almost 0 mAh up to 0%, but the capacity retention rate became about 70% at more than 35%, and it was slightly less than 85% in the region beyond that. The results of the high temperature storage test are shown in (Fig. 3). After a storage test at 60 ° C. for 4 weeks, the capacity recovery rate showed a value exceeding 95% up to a volume ratio of PC to EC of about 65%, but tends to decrease in a region exceeding this. From these, it can be said that the amount of PC added to EC is preferably in the range of 35% to 65% by volume.

In this example, LiMn ₂ was used as the positive electrode active material.
O ₄ The it has been described using, similarly DME concentration for the positive electrode active material _{LiC 0 O 2, LiNiO 2,} LiFeO 2 shown in Example 1 showed good high temperature storage characteristics in the range of 70% to 20% It was Also, only lithium borofluoride was described as the solute of the electrolytic solution, but the same result was obtained with lithium hexafluorophosphate.

In Examples 1 and 2, the carbon material was taken up as the negative electrode active material for explanation, but the result of the examination when lithium metal, aluminum alloy, aluminum or the like was used as the negative electrode active material was found to be the same. Got the result.

[0032]

As is apparent from the above description of the embodiments, lithium borofluoride or hexafluorophosphoric acid is used as a mixed solvent of EC, DME and PC in a non-aqueous electrolyte secondary battery of 4V class as a non-aqueous electrolyte. By using the one in which lithium is dissolved, a non-aqueous electrolyte secondary battery having excellent high temperature storage characteristics and low temperature characteristics can be obtained, which has great industrial significance.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the concentration of propylene carbonate with respect to ethylene carbonate and the low temperature capacity retention rate.

FIG. 3 is a diagram showing the relationship between the concentration of propylene carbonate relative to ethylene carbonate and the capacity recovery rate after storage at 60 ° C.

[Explanation of symbols]

 1 Positive electrode 2 Case 3 Separator 4 Negative electrode 5 Gasket 6 Sealing plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiko Mito 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Yoshinori Toyokuchi 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co.

Claims (2)

[Claims] 1. Lithium or a negative electrode that reversibly absorbs and releases lithium, and LiMn ₂ O ₄ , LiC ₀ O ₂ , and Li.
At least 1 selected from the group consisting of NiO ₂ and LiFeO _2.
A positive electrode using two composite oxides as an active material and a non-aqueous electrolytic solution are used. As the non-aqueous electrolytic solution, a mixed solution of ethylene carbonate, 1,2-dimethoxyethane and propylene carbonate is added to lithium borofluoride or phosphorus hexafluoride. A non-aqueous electrolyte secondary battery using a solution of lithium oxide. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the addition amount of propylene carbonate is 5 to 20% by volume with respect to ethylene carbonate.