JPH09147910A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high capacity lithium secondary battery in which an electrolyte is provided with high ion conductivity by blending the nonaqueous electrolyte with the predetermined quantity of specific aliphatic carboxylate and/or specific chain ether. SOLUTION: In a secondary battery provided with a positive electrode, a negative electrode, and a nonaqueous electrolyte, one or more kind of aliphatic carboxylate A represented by a general formula R<1> -COO-R<2> (R<1> represents hydrogen or an alkyl group of C1-4 ; R<2> represents an alkyl group of C1-4 other than the R<1> ) and/or one or more kind of chain ether B represented by a general formula R<3> -O-CH2 CH2 -O-R<4> (R<3> and R<4> individually represent alkyl groups of C1-4 ) are contained at a ratio of 1-8% by volume in total A+B. For a solvent of the nonaqueous electrolyte, a mixture solvent of cyclic carbonate and non- cyclic carbonate is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly, to improvement of a non-aqueous electrolyte solution for the purpose of providing a high capacity lithium secondary battery.

[0002]

2. Description of the Related Art In recent years,
Lithium secondary batteries are attracting attention because they have advantages such as high energy density and high voltage because it is not necessary to consider the decomposition voltage of water.

However, since the electrolytic solution of the lithium secondary battery uses an organic solvent as a solvent, the ionic conductivity of the electrolytic solution is lower than that of the electrolytic solution using an aqueous solvent.
A high capacity battery has not been obtained.

The present invention has been made to solve this problem, and an object thereof is to provide a high-capacity lithium secondary battery in which the electrolytic solution has a high ionic conductivity.

[0005]

In a lithium secondary battery according to the present invention (hereinafter, referred to as "the present battery") for achieving the above object, a non-aqueous electrolyte is represented by the general formula R ¹ -CO.
OR ² (R ¹ is hydrogen or an alkyl group having 1 to 4 carbon atoms;
R ² is, independently of R ¹ , one or more aliphatic carboxylic acid ester (A) represented by an alkyl group having 1 to 4 carbon atoms), and / or the general formula R ³ —O—CH. ₂ CH ₂ −
1 to 8% by volume in total of one or more chain ethers (B) represented by OR ⁴ (R ³ and R ⁴ are each independently an alkyl group having 1 to 4 carbon atoms) It is contained.

A specific example of the battery of the present invention is a lithium secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolytic solution, wherein the non-aqueous electrolytic solution is methyl formate, ethyl formate, propyl formate, butyl formate. , Isobutyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate,
Methyl propionate, ethyl propionate, propyl propionate, butyl propionate, isobutyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, isobutyl butyrate, methyl isobutyrate, ethyl isobutyrate, propyl isobutyrate, butyl isobutyrate From isobutyl isobutyrate, methyl valerate, ethyl valerate, propyl valerate, butyl valerate, isobutyl valerate, methyl isovalerate, ethyl isovalerate, propyl isovalerate, butyl isovalerate and isobutyl isovalerate At least one aliphatic carboxylic acid ester (A) selected from the group consisting of, and / or 1,2-dimethoxyethane, 1,
2-diethoxyethane, 1,2-dipropoxyethane,
1,2-dibutoxyethane, 1,2-ethoxymethoxyethane, 1,2-propoxymethoxyethane, 1,2-
Butoxymethoxyethane, 1,2-propoxyethoxyethane, 1,2-butoxyethoxyethane and 1,2-
Examples thereof include those containing at least one chain ether (B) selected from the group consisting of butoxypropoxyethane in a total amount of 1 to 8% by volume.

The content of the aliphatic carboxylic acid ester (A) and / or the chain ether (B) in the non-aqueous electrolyte is
The total amount is regulated to 1 to 8% by volume because if the amount is out of this range, the solvent in the non-aqueous electrolytic solution is easily decomposed and it becomes difficult to obtain a high-capacity lithium secondary battery. .

The non-aqueous electrolytic solution containing the aliphatic carboxylic acid ester (A) and / or the chain ether (B) may be, for example, a cyclic carbonic acid ester such as ethylene carbonate, vinylene carbonate, propylene carbonate or butylene carbonate. (Dielectric constant solvent) or a mixed solvent of these and an acyclic carbonic acid ester such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, LiPF ₆ , LiClO ₄ , LiBF ₄ , Li
A solution in which a solute such as CF ₃ SO ₃ is dissolved at a ratio of 0.7 to 1.5 M (mol / liter) can be used. By using a mixed solvent of cyclic carbonic acid ester and non-cyclic carbonic acid ester in a predetermined ratio, it is possible to obtain a lithium secondary battery excellent in high-rate discharge characteristics and cycle characteristics (Japanese Patent Laid-Open No. Hei 5 (1993) -58). 13088).

The present invention solves the problem of low ionic conductivity of a non-aqueous electrolyte by adding a specific amount of a specific aliphatic carboxylic acid ester (A) and / or a specific chain ether (B) to the non-aqueous electrolyte. It was solved by including it.
Therefore, for the battery constituent members such as the positive electrode material and the negative electrode material, it is possible to use various materials that have been conventionally used or proposed for lithium secondary batteries.

Examples of the positive electrode material include LiCo
O ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ ,
Examples thereof include lithium-containing metal oxides such as LiFeO ₂ and LiCo _0.5 Ni _0.5 O ₂ .

Examples of the negative electrode material include substances capable of inserting and extracting lithium ions and metallic lithium. Examples of the substance capable of inserting and extracting lithium ions include coke, graphite, a carbon material such as an organic fired body, and a lithium-aluminum alloy,
Examples thereof include lithium alloys such as lithium-lead alloys and lithium-tin alloys. In particular, when a carbon material capable of inserting and extracting lithium ions is used as the negative electrode material, a lithium secondary battery having excellent discharge characteristics and a high capacity can be obtained.

Since the non-aqueous electrolyte contains a predetermined amount of the specific aliphatic carboxylic acid ester (A) and / or the specific chain ether (B), the reason is not clear, but the ionic conductivity of the electrolytic solution is not clear. Will increase. As a result, the charge / discharge capacity increases.

[0013]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention may be practiced by appropriately changing the gist of the invention. Is possible.

(Example 1) [Preparation of positive electrode] LiCoO ₂ powder 9 as a positive electrode active material
0 parts by weight and 5 parts by weight of artificial graphite powder as a conductive agent,
A slurry was prepared by kneading 5 parts by weight of polyvinylidene fluoride as a binder and a 5 wt% N-methylpyrrolidone solution. This slurry was applied to both sides of an aluminum foil as a positive electrode current collector by the doctor blade method,
Vacuum drying was performed at ° C for 2 hours to prepare a positive electrode.

[Preparation of Negative Electrode] Natural graphite powder (d ₀₀₂ =
3.35Å, L _c > 1000Å) 95 parts by weight and 5% by weight of N-containing 5 parts by weight of polyvinylidene fluoride as a binder
A slurry was prepared by kneading with a methylpyrrolidone solution. This slurry was applied on both surfaces of a copper foil as a negative electrode current collector by the doctor blade method and vacuum dried at 150 ° C. for 2 hours to prepare a negative electrode.

[Preparation of Non-Aqueous Electrolyte] A mixture of 95 parts by volume of a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1: 1 to 5 parts by volume of ethyl acetate was added as a solute. LiPF ₆ (lithium hexafluorophosphate) was dissolved at 1 mol / liter to prepare a non-aqueous electrolytic solution. Here, ethylene carbonate (E
Volume ratio of C) to diethyl carbonate (DEC) 1:
The mixed solvent of No. 1 was used because good battery characteristics can be obtained when the volume ratio of the cyclic ester carbonate to the acyclic ester carbonate is about 1: 1.

[Assembly of Battery] Using the above-mentioned positive and negative electrodes and the non-aqueous electrolyte, an AA size cylindrical lithium secondary battery (invention battery) A1 was assembled. As the separator, a lithium ion-permeable polypropylene microporous film was used, and the above nonaqueous electrolytic solution was impregnated into the microporous film.

FIG. 1 is a sectional view of the assembled battery A1 of the present invention. The illustrated battery A1 of the present invention includes a positive electrode 1, a negative electrode 2,
A separator 3, a positive electrode lead 4, a negative electrode lead 5, a positive electrode external terminal 6, and a negative electrode can 7 that separate the two electrodes 1 and 2 from each other.
Etc.

The positive electrode 1 and the negative electrode 2 are housed in the negative electrode can 7 in a state of being spirally wound via the separator 3 impregnated with the non-aqueous electrolyte, and the positive electrode 1 is connected via the positive electrode lead 4. The positive electrode external terminal 6 and the negative electrode 2 are connected to the negative electrode can 7 via the negative electrode lead 5, respectively, so that the chemical energy generated in the battery can be extracted to the outside from the positive electrode external terminal 6 and the negative electrode can 7 as electric energy. It has become.

Example 2 A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 5 parts by volume of methyl propionate was used instead of 5 parts by volume of ethyl acetate. A battery A2 of the invention was assembled in the same manner as in Example 1 except that this nonaqueous electrolytic solution was used as the nonaqueous electrolytic solution.

Example 3 A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that 5 parts by volume of methyl formate was used instead of 5 parts by volume of ethyl acetate. A battery A3 of the invention was assembled in the same manner as in Example 1 except that this nonaqueous electrolytic solution was used as the nonaqueous electrolytic solution.

Example 4 A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 5 parts by volume of ethyl formate was used instead of 5 parts by volume of ethyl acetate. A battery A4 of the invention was assembled in the same manner as in Example 1 except that this nonaqueous electrolytic solution was used as the nonaqueous electrolytic solution.

Example 5 A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 5 parts by volume of propyl formate was used instead of 5 parts by volume of ethyl acetate. A battery A5 of the invention was assembled in the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

Example 6 A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 5 parts by volume of methyl acetate was used instead of 5 parts by volume of ethyl acetate. Battery A6 of the present invention was assembled in the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

Example 7 A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that 5 parts by volume of propyl acetate was used instead of 5 parts by volume of ethyl acetate. Battery A7 of the present invention was assembled in the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

Example 8 A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that 5 parts by volume of ethyl propionate was used instead of 5 parts by volume of ethyl acetate. A battery A8 of the invention was assembled in the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

Example 9 A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that 5 parts by volume of methyl butyrate was used instead of 5 parts by volume of ethyl acetate. Battery A9 of the present invention was assembled in the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

Example 10 A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that 5 parts by volume of ethyl butyrate was used instead of 5 parts by volume of ethyl acetate. Battery A10 of the present invention was assembled in the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

Example 11 The same as Example 1 except that 2.5 parts by volume of ethyl acetate and 2.5 parts by volume of 1,2-dimethoxyethane (DME) were used instead of 5 parts by volume of ethyl acetate. To prepare a non-aqueous electrolyte. A battery A11 of the invention was assembled in the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

Example 12 A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that 5 parts by volume of 1,2-dimethoxyethane (DME) was used instead of 5 parts by volume of ethyl acetate. Battery A12 of the present invention was assembled in the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

Example 13 A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that 5 parts by volume of 1,2-ethoxymethoxyethane (EME) was used instead of 5 parts by volume of ethyl acetate. . Battery A1 of the present invention was prepared in the same manner as in Example 1 except that this non-aqueous electrolyte was used as the non-aqueous electrolyte.
Assembled 3.

Example 14 A battery A14 of the present invention was assembled in the same manner as in Example 1 except that a metallic lithium foil was used for the negative electrode instead of natural graphite.

Example 15 A mixture of 95 parts by volume of a mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC) in a volume ratio of 1: 1 and 5 parts by volume of ethyl acetate was added to LiPF ₆ (solute). Lithium hexafluorophosphate) was dissolved at 1 mol / liter to prepare a non-aqueous electrolytic solution. Battery A1 of the present invention was prepared in the same manner as in Example 1 except that this non-aqueous electrolyte was used as the non-aqueous electrolyte.
Assembled 5.

(Example 16) Butylene carbonate (B
Volume ratio of C) to dimethyl carbonate (DMC) 1:
A nonaqueous electrolytic solution was prepared by dissolving LiPF ₆ as a solute at 1 mol / liter in a mixture of 95 parts by volume of the mixed solvent of 1 and 5 parts by volume of ethyl acetate. In the same manner as in Example 1 except that this non-aqueous electrolyte was used as the non-aqueous electrolyte,
The present invention battery A16 was assembled.

Example 17 Vinylene carbonate (V
C) and methyl ethyl carbonate (MEC) in a volume ratio of 1: 1 mixed with 95 parts by volume of ethyl acetate and 5 parts by volume of ethyl acetate, and 1 mol / liter of LiPF ₆ as a solute is dissolved in the non-aqueous electrolyte solution. Was prepared. Battery A17 of the present invention was assembled in the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

(Examples 18 to 30) 95 parts by volume of a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1: 1 was added to butyl acetate, isobutyl propionate, methyl isobutyrate, butyl isobutyrate. ,
Methyl valerate, butyl valerate, methyl isovalerate, butyl isovalerate, 1,2-diethoxyethane, 1,2-dipropoxyethane, 1,2-dibutoxyethane, 1,2
-Propoxymethoxyethane or 1,2-butoxymethoxyethane added to 5 parts by volume, L as a solute
A non-aqueous electrolyte was prepared by dissolving iPF ₆ at 1 mol / liter. In the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution, the present invention batteries A18 to
The A30 was assembled.

Comparative Example 1 A non-aqueous electrolytic solution was prepared in the same manner as in Example 1 except that ethyl acetate was not added.
Comparative battery B1 was assembled in the same manner as in Example 1 (using graphite for the negative electrode) except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

Comparative Example 2 A non-aqueous electrolytic solution was prepared in the same manner as in Example 1 except that ethyl acetate was not added.
Comparative battery B2 was assembled in the same manner as in Example 14 (using a lithium metal foil for the negative electrode) except that this non-aqueous electrolyte was used as the non-aqueous electrolyte.

(Comparative Example 3) A non-aqueous electrolytic solution was prepared in the same manner as in Example 15 except that ethyl acetate was not added. Comparative battery B3 was assembled in the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

Comparative Example 4 A nonaqueous electrolytic solution was prepared in the same manner as in Example 16 except that ethyl acetate was not added. Comparative battery B4 was assembled in the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

Comparative Example 5 A non-aqueous electrolyte was prepared in the same manner as in Example 17, except that ethyl acetate was not added. Comparative battery B5 was assembled in the same manner as in Example 1 except that this non-aqueous electrolytic solution was used as the non-aqueous electrolytic solution.

Inventive batteries A1 to A30 and comparative battery B1
Solvents for the positive electrode material, the negative electrode material and the non-aqueous electrolyte used for B5 to B5 are summarized in Tables 1 to 3 below.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

[Charge / Discharge Test] The batteries A1 to A30 of the present invention and the comparative batteries B1 to B5 were charged to 200 V to 4.2 V, and then discharged to 200 V to 2.75 V to determine the battery capacity of each battery. . The results are shown in Tables 1 to 3 above.

As shown in Tables 1 and 2, the battery A of the present invention was used.
1 to A30 have large discharge capacities of 595 to 615 mAh, as shown in Table 3, comparative batteries B1 to B5
Has a small discharge capacity of 535 to 570 mAh. From this fact, it can be seen that a high-capacity lithium secondary battery can be obtained by incorporating a specific aliphatic carboxylic acid ester (A) and / or chain ether (B) in the non-aqueous electrolyte.

[Relationship between Discharge Capacity and Content of Aliphatic Carboxylic Acid Ester (A) and / or Chain Ether (B) in Non-Aqueous Electrolyte] Volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) The ratio (volume ratio) of ethyl acetate added to the 1: 1 mixed solvent was 99: 1, 97:
3, 94: 6, 93: 7, 92: 8, 91: 9, 90:
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the ratio was 10 or 50:50. Eight types of lithium secondary batteries were assembled in the same manner as in Example 1 except that each of these nonaqueous electrolytic solutions was used as the nonaqueous electrolytic solution.

Next, these lithium secondary batteries were subjected to a charge / discharge test under the same conditions as above to determine the discharge capacity of each battery. The results are shown in Table 4, Table 5 and Table 6. In addition,
Table 4 also shows the results for the present invention battery A1 and comparative battery B1, and Table 5 shows the present invention battery A12 and comparative battery B1.
Table 6 also shows the results for the present invention battery A11 and the comparative battery B1 which are transcribed from Tables 1 to 3.

[0050]

[Table 4]

[0051]

[Table 5]

[0052]

[Table 6]

As shown in Tables 4 to 6, a high capacity is obtained when the total amount of ethyl acetate and / or 1,2-dimethoxyethane in the non-aqueous electrolyte is 1 to 8% by volume. .
From this, in order to obtain a high-capacity lithium secondary battery, the total amount of the aliphatic carboxylic acid ester (A) and / or the chain ether (B) in the non-aqueous electrolyte is 1 to 8 volumes. It turns out that it needs to be set to%.

In the above embodiments, a specific example in which the present invention is applied to a cylindrical battery has been described. However, the shape of the battery is not particularly limited, and the present invention includes flat type, square type, film type, etc. It can be widely applied to lithium secondary batteries of various shapes.

[0055]

The ionic conductivity of the non-aqueous electrolyte is high,
The battery of the present invention has a high capacity.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cylindrical lithium secondary battery (the battery of the present invention) assembled in an example.

Front page continuation (72) Inventor Koji Nishio 2-5-5 Keihan Hon-dori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Toshihiko Saito 2-5-5 Keihan-hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. A lithium secondary battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolytic solution, wherein the nonaqueous electrolytic solution has the general formula R
^1- COO-R ² (R ¹ is hydrogen or an alkyl group having 1 to 4 carbon atoms; R ² independently of R ¹ is an alkyl group having 1 to 4 carbon atoms); Aliphatic carboxylic acid ester (A) and / or general formula R ³ —O—CH ₂ C
H ₂ —O—R ⁴ (R ³ and R ⁴ are each independently a carbon number of 1 to
1 or 2 or more types of chain ethers (B) represented by 4 alkyl groups) in a total amount of 1 to 8% by volume. 2. The non-aqueous electrolyte is methyl formate, ethyl formate, propyl formate, butyl formate, isobutyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, methyl propionate, ethyl propionate, Propyl propionate, butyl propionate, isobutyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, isobutyl butyrate, methyl isobutyrate, ethyl isobutyrate, propyl isobutyrate, butyl isobutyrate, isobutyl isobutylate, methyl valerate , Ethyl valerate, propyl valerate, butyl valerate, isobutyl valerate, methyl isovalerate, ethyl isovalerate, propyl isovalerate, butyl isovalerate and at least one selected from the group consisting of isobutyl isovalerate. Aliphatic carboxylic acid ester (A) of Alternatively, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dipropoxyethane, 1,2-dibutoxyethane, 1,2-ethoxymethoxyethane, 1,2-propoxymethoxyethane, 1 , 2-butoxymethoxyethane, 1,2-propoxyethoxyethane, 1,2-butoxyethoxyethane and 1,2-butoxypropoxyethane in a total amount of at least one chain ether (B) selected from the group consisting of The lithium secondary battery according to claim 1, containing 1 to 8% by volume. 3. The solvent of the non-aqueous electrolyte is at least one cyclic carbonate selected from the group consisting of propylene carbonate, ethylene carbonate, butylene carbonate and vinylene carbonate, and dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate. The lithium secondary battery according to claim 1, which is a mixed solvent with at least one acyclic carbonate selected from the group consisting of: 4. The lithium secondary battery according to claim 1, wherein the negative electrode uses a carbon material capable of inserting and extracting lithium ions as an electrode material.