JP3463407B2 - Electrolyte for lithium ion batteries - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrolytic solution for a lithium ion battery.

[0002]

2. Description of the Related Art An electrochemical device is composed of a positive electrode, a negative electrode, an electrolytic solution, a separator and the like. Among them, the electrolytic solution has a purpose of promptly promoting an electrochemical reaction on the electrode surface, and therefore is required to have a property of smoothly moving ions. For the selection of the electrolytic solution, the reactivity with the electrode to be used, the working potential range, and the working temperature range are important requirements.For example, a non-aqueous electrolyte solution is used for a lithium primary battery, a lithium ion battery, an aluminum electrolytic capacitor, etc. It is commonly used.

For example, since a lithium-ion battery has a working potential range of 3 V or more and uses highly active lithium, battery performance is improved by using a highly stable organic solvent such as ethylene carbonate or propylene carbonate. It has been reported (“Functional Material” vol. 15, April issue, p. 48 (published in 1995)). In addition, as the organic solvent for the aluminum electrolytic capacitor, γ-butyrolactone, ethylene glycol, tetrahydrofuran, N, N-dimethylformamide, etc. (Japanese Patent Laid-Open No. Sho 5)
7-76826, 62-145715, 63-
226812, 63-261825, and WO 87.
/ 5149, JP-A-1-140030).

Conventionally used organic solvents for non-aqueous electrolytes are aliphatic esters, aliphatic carbonates and the like. Since these aliphatic organic solvents have low affinity with graphite-based carbon electrodes used in, for example, lithium-ion batteries, it can be said that the surface area of the electrodes is effectively used. It's hard. In order to solve this problem, it has been proposed to add toluene, benzene or the like to the electrolytic solution (JP-A-6-150970). These aromatic hydrocarbon solvents, γ-butyrolactone described above, aliphatic esters such as propylene carbonate, when added to the electrolyte because of its low affinity for aliphatic carbonates,
If left unattended, it may separate into two phases, which is contrary to the purpose of improving the affinity between the electrode and the electrolytic solution, but rather reduces the dedoping capacity of the electrode. Further, these aromatic hydrocarbon solvents have problems in terms of toxicity and safety.

[0005]

The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrolytic solution for a lithium ion battery having an improved affinity for a carbon electrode.

[0006]

The present invention provides an electrolytic solution for a battery, which basically comprises a positive electrode, a negative electrode made of a carbonaceous material, and an electrolytic solution, the electrolytic solution having a molecular weight (a) of 108.
To 220, a liquid organic solvent selected from the group consisting of esters, ethers and carbonates having a phenyl group represented by the following formula group: 1 to 50 mol%

[0007]

[Chemical 3]

(In the formula, R is an alkyl group having 1 to 4 carbon atoms or a phenyl group.)

[0009]

[Chemical 4]

(In the formula, R'is an alkyl group having 1 to 4 carbon atoms), and an organic solvent (b) 99 other than the above (a).
An electrolytic solution for a lithium ion battery, which is obtained by dissolving a lithium salt (c) as a solute in an organic solvent composed of ˜50% by volume.

(Summary of the Invention) Lithium Ion Battery A lithium ion battery basically comprises a positive electrode, a negative electrode made of a carbonaceous material, and an electrolytic solution. FIG. 1 shows an example of the structure. In FIG. 1, 1 is a positive electrode, 2 is a negative electrode of carbonaceous material, 3 is a separator, 4 is a battery can, 5 is a sealing lid, 6 is a positive electrode terminal, and 7 is an insulator.

Positive electrode The positive electrode is not particularly limited, but for example,
Metal sulfides such as TiS ₂ , TiS ₃ , MoS ₂ and FeS ₂ , metal oxides such as V ₂ O ₅ , V ₆ O ₁₃ and MoO ₃ , L
i _(1-x) MnO ₂ , Li _(1-x) CoO ₂ , Li _(1-x) N
Examples thereof include alkali metals such as iO ₂ , Li _{(1- x)} Co _y Sn ₂ O _{2 and the} like, and particularly lithium-containing composite metal oxides.

Negative Electrode The carbonaceous material used as the negative electrode in the present invention is not particularly limited, but it is obtained by calcining and carbonizing an organic polymer compound, pitch, coal, wood, or gas phase carbonization of an organic substance. Examples thereof include those obtained by the growth reaction and naturally occurring carbonaceous materials such as natural graphite.

Electrolyte Solution The electrolyte solution comprises (a) 1 to 50% by volume of an organic solvent selected from one or more of the above-mentioned esters, ethers and carbonates having a phenyl group having a molecular weight of 108 to 220, (B) The lithium salt of the electrolyte (c) is dissolved in a mixed solvent of 99 to 50% by volume of an organic solvent other than (a).

(A) Organic solvent: Examples of the organic compound (a) having a phenyl group and a molecular weight of 108 to 220 include (a ₁ ) methylphenyl carbonate, ethylphenyl carbonate, propylphenyl carbonate, butylphenyl carbonate, diphenyl carbonate. And the like; ethers such as (a ₂ ) anisole and phenetole; and (a ₃ ) phenyl acetate, phenyl propionate, phenyl butyrate, methyl benzoate, esters such as benzoate, and the like. These organic solvents having a phenyl group may be used alone or in combination of two or more. The liquid organic solvent (a) having the phenyl group is used in a proportion of 1 to 50% by volume, preferably 4.5 to 20% by volume of the total volume of the solvent with the other organic solvent (b) described later. 1% by volume in the solvent
If it is less than this, improvement in affinity with the electrode cannot be expected. If it is used in excess of 50% by volume, the electric conductivity will decrease.

(B) Other solvent : As the organic solvent (b) other than the component (a), conventionally used cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate; dimethyl carbonate, diethyl carbonate, Chain carbonates such as ethylmethyl carbonate; chain ethers such as dimethoxyethane and diethoxyethane; cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran and dioxane; glymes such as methyl diglyme and ethyl diglyme; acetic acid Ethyl, methyl propionate,
Esters such as ethyl propionate; Lactones such as γ-butyrolactone, γ-valerolactone and δ-valerolactone; Alcohols such as ethylene glycol, glycerin and methylcellosolve; Acetonitrile, propionitrile, methoxyacetonitrile, 3- Nitriles such as methoxypropionitrile; N-methylformamide, N-ethylformamide, N, N-dimethylformamide, N, N-diethylformamide, N-methylacetamide, N-ethylacetamide, N, N-dimethylacetamide, Examples thereof include amides such as N-methylpyrrolidone; sulfolanes such as sulfolane and 3-methylsulfolane; and phosphoric acid esters such as trimethyl phosphate and triethyl phosphate. These solvents are used alone or as a mixture.

In particular, 10 to 80% by volume of ethylene carbonate in an organic solvent, other propylene carbonate,
1 of diethyl carbonate, γ-butyrolactone, tetrahydrofuran, N-methylpyrrolidone, dioxane, etc.
The combined use of 0 to 89% by volume (based on the sum of the solvents (a) and (b)) gives an electrolytic solution having high electric conductivity.

(C) As the lithium salt of the electrolyte dissolved in the organic solvent of the electrolyte component (a) and the component (b), lithium perchlorate, lithium hexafluorophosphate, lithium borofluoride, lithium triflate, Lithium bis (trifluoromethanesulfonyl)
Examples thereof include imides and lithium salts such as lithium tetraphenylborate. Among these, inorganic lithium salts are particularly preferable, and lithium perchlorate, lithium hexafluorophosphate and lithium borofluoride are particularly preferable. The molar concentration of the electrolyte (c) in the electrolytic solution is 0.5 to 2.0 mol /
Liters are common.

Other materials: In the case of assembling a lithium ion battery, a separator may be mentioned. Examples of the separator include woven cloth, non-woven cloth, glass woven cloth, and synthetic resin microporous film. Furthermore, if necessary, a battery is constructed using components such as a current collector, terminals, and an insulating plate. As the structure of the battery, a positive electrode, a negative electrode, if necessary, a paper-type battery in which a separator is a single layer or multiple layers, a laminated battery, or a positive electrode, a negative electrode, and if necessary, a cylindrical battery in which a separator is wound in a roll shape. And the like.

[0020]

EXAMPLES The present invention will be described more specifically below with reference to examples. Example 1 As a negative electrode, a sheet-shaped negative electrode molded from the following three kinds of carbonaceous materials was used. (1) Natural graphite powder (NG-7 manufactured by Kansai Thermo Chemical Co .; trade name) (2) Artificial graphite powder (KS-10 manufactured by LONZA; trade name) (3) Artificial graphite powder (KS-44 manufactured by LONZA) Trade name) As the organic solvent (b), 100 cc of propylene carbonate (PC) having a purity of 99.9% or more is used as the organic solvent (a).
Methyl phenyl carbonate (MPhC) as 0 cc (0% by volume), 5 cc (about 4.8% by volume),
A mixture of 11 cc (about 10% by volume) and 25 cc (20% by volume) was used.

Measurement of contact angle: The above-mentioned PC liquid or PC and M on each 5 points (width 5 mm, length 15 mm, thickness 2 mm) of the above-mentioned negative electrode sheet in a room at 23 ° C. and 50 ± 5% relative humidity.
The PhC mixed solution was dropped using a syringe, and the contact angle was measured using a goniometer-type contact angle measuring instrument G-1 type manufactured by Elma Optical Co., Ltd., and the average value of 5 points is shown in Table 1. Similarly, the contact angle on highly oriented pyrolytic graphite (HOPG) was also measured. The contact angle becomes smaller as the content of methylphenyl carbonate increases.

[0022]

[Table 1]

Example 2 Mixed solvent prepared by mixing 100 cc of propylene carbonate (PC) and 5 cc (about 4.8 vol%) and 11 cc (10 vol%) of methylphenyl carbonate (MPhC), respectively, on a KS-44 sheet electrode. The contact angle was measured. The results are shown in Table 2.

Example 3 The same measurement as in Example 2 was carried out except that MPhC was changed to anisole (MOB). The results are shown in Table 2. The mixing of anisole reduces the contact angle overall. Example 4 In Example 2, MPhC was replaced with methyl benzoate (MB
The same measurement was performed except that it changed to z). The results are shown in Table 2.
Shown in.

Example 5 In Example 2, MPhC was replaced with phenyl acetate (PhA).
The same measurement was performed except that it was changed to. The results are shown in Table 2. Example 6 The same measurement as in Example 2 was performed except that MPhC was changed to phenyl propionate (PhP). The results are shown in Table 2.

[0026]

[Table 2]

Comparative Example 1 A mixture of 106 g (1 mol) of lithium perchlorate which had been sufficiently dried in a dry argon atmosphere, 661 g (500 cc) of ethylene carbonate (EC) and 488 g (500 cc) of diethyl carbonate (DEC). An electrolytic solution was prepared by dissolving it in a solvent so that the total amount was 1000 cc. Sheet-shaped electrode coated with NG-7, metallic lithium,
The charge / discharge capacity was measured by using a half cell composed of a polypropylene separator. At this time, as a condition for impregnating the sheet electrode with the electrolytic solution, 35 kP
The vacuum impregnation with a was carried out for 1 minute or the impregnation at normal pressure for 1 minute. A charge / discharge test was performed using this coin-type cell to determine the dedoping capacity of the battery. The results are shown in Table 3.

Example 7 In Comparative Example 1, the electrolytic solution was 106 g of lithium perchlorate.
(1 mol) to EC661g (500 cc), DEC48
It was dissolved in a mixed solvent consisting of 8 g (500 cc) and the total amount was adjusted to 1000 cc.
g (1 mol), EC594g (500 cc), DEC
439 g (500 cc) and MPhC 114 g (10
Dissolved in a mixed solvent consisting of 0 cc) and the total amount is 1000 c
The same operation was carried out except that it was changed to c. The results are shown in Table 3.

Example 8 In Comparative Example 1, the electrolytic solution was 106 g of lithium perchlorate.
(1 mol) to EC661g (500 cc), DEC48
It was dissolved in a mixed solvent consisting of 8 g (500 cc) and the total amount was adjusted to 1000 cc.
g (1 mol), EC627g (500 cc), DEC
463 g (500 cc) and MOB 50 g (50 c
The same operation was performed except that the solvent was dissolved in the mixed solvent consisting of c) and the total amount was changed to 1000 cc. The results are shown in Table 3.

[0030]

[Table 3]

Comparative Example 2 The same operation as in Comparative Example 1 was performed except that the electrode NG-7 was changed to the electrode KS-44. The results are shown in Table 4. Example 9 The same operation as in Comparative Example 2 was performed except that the electrolytic solution used in Example 7 was changed. The results are shown in Table 4.
The capacity is increased by adding MPhC. Example 10 The same operation as in Comparative Example 2 was performed except that the electrolytic solution used in Example 8 was changed. The results are shown in Table 4.
The capacity is increased by adding MOB.

[0032]

[Table 4]

[0033]

EFFECTS OF THE INVENTION A non-aqueous electrolyte for a lithium ion battery having an improved affinity for a carbon electrode, which can effectively utilize the surface area of the carbon electrode, which makes the lithium ion battery smaller, more efficient, and more productive. Can contribute to the improvement of

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a lithium ion battery.

[Explanation of symbols] 1 Positive electrode 2 Negative electrode 3 separator 4 battery cans 5 Sealing lid 6 Positive terminal 7 insulator

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Yoshida 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Kagaku Co., Ltd. Yokkaichi Plant (56) Reference JP-A-8-273700 (JP, A) JP-A-8- 106909 (JP, A) JP-A-6-267589 (JP, A) JP-A-62-86673 (JP, A) JP-A-2-207465 (JP, A) JP-A-6-13107 (JP, A) JP-A-6-20721 (JP, A) JP-A-6-150970 (JP, A) JP-A-7-22069 (JP, A) JP-A-6-84525 (JP, A) JP-A 64-30178 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 10/40

Claims (4)

(57) [Claims] 1. An electrolytic solution for a battery comprising a positive electrode, a negative electrode made of a carbonaceous material, and an electrolytic solution as a basic component, wherein the electrolytic solution comprises (a) a molecular weight of 108 to 220 and a benzene ring. liquid organic solvents 1-1 with selected substituents from the following group in
0 % by volume, —O—R ′, —CO—O—R ′, —O—C
OR (in the formula, R'represents an alkyl group having 1 to 4 carbon atoms) (b) Organic solvent other than the above: (c) Lithium salt is dissolved as a solute in an organic solvent composed of 99 to 90 % by volume. An electrolyte solution for a lithium-ion battery, which is formed by: 2. The liquid organic solvent (a) is selected from the group consisting of anisole, phenetole, phenyl acetate, phenyl propionate, phenyl butyrate, methyl benzoate and ethyl benzoate, and the organic solvent (b). The electrolytic solution for a lithium ion battery according to claim 1, wherein is selected from the group consisting of ethylene carbonate, diethyl carbonate, and propylene carbonate. 3. The organic solvent (b) is a combination of ethylene carbonate and a solvent selected from the group consisting of propylene carbonate, diethyl carbonate, γ-butyrolactone, tetrahydrofuran, N-methylpyrrolidone and dioxane, and is in a liquid state. Ethylene carbonate is selected from the group consisting of 10 to 80% by volume of the total amount of the organic solvent (a) and the organic solvent (b), propylene carbonate, diethyl carbonate, γ-butyrolactone, tetrahydrofuran, N-methylpyrrolidone and dioxane. The electrolyte for lithium-ion batteries according to claim 1, wherein the electrolyte occupies 10 to 89% by volume. 4. The liquid organic solvent (a) accounts for 4.5 to 10 % by volume with respect to the total of the liquid organic solvent (a) and the organic solvent (b). Electrolyte for lithium-ion batteries.