JPH0837024A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

PURPOSE:To provide a nonaqueous electrolytic secondary battery having a high capacity and excellent in the cyclic characteristics by allowing the electrolytic solution to contain a fluorine-containing ether. CONSTITUTION:A separator 5 consisting of a fine porous film is interposed between a positive electrode 1 and negative electrode 2, and these are laminated to form a spiral electrode. which is accommodated in a SUS battery vessel 6. In the vessel 6, propylene carbonate, ethylene carbonate, and gamma-butyrolactone are mixed together in a proportion by volume as 1:1:2 to provide a mixture solvent, to which a fluorine-containing ether is included. An electrolyte in which lithium tetrafluoro-borate is dissolved, is poured in, and the vessel 6 and a battery seal plate 7 are sealed through a packing 8, and thus a circular nonaqueous electrolyte battery is accomplished. The ratio of the number of fluorine atoms to the total number of fluorine atoms and hydrogen atoms in one molecule should preferably be 0.2-0.8-exceeding 0.9 lowers the solubility while a ratio below 0.2 does not ensure enhancement of the cyclic characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel secondary battery having high capacity and excellent cycleability, and more particularly to improvement of an electrolytic solution.

[0002]

2. Description of the Related Art In recent years, a secondary battery using an organic electrolytic solution, particularly a secondary battery using lithium has attracted attention because it has a high energy density. An important characteristic of a secondary battery is that it is required to have a small capacity change (cycle stability) when it is repeatedly charged and discharged, but it is not sufficient at present. The cause of this is that lithium grows in a dendritic manner on the surface of the negative electrode to cause an internal short circuit, and the positive electrode material gradually decomposes and deteriorates due to repeated charging and discharging,
It has been pointed out that the solvent and the electrolyte of the organic electrolytic solution are decomposed or deteriorated and the initial characteristics cannot be maintained. Regarding the solvent of the organic electrolytic solution, a mixed solvent of cyclic carbonic acid ester and cyclic ester is used as a solvent having higher stability (JP-A-2-215059), or a mixed solvent of carbonic acid ester and ether is used (USP527202).
2) It has been proposed to use an organic solvent containing at least one kind of halogen element such as tetrahydrofurfuryl chloride in order to enhance the stability of the solvent (Japanese Patent Laid-Open No. 5-198316). Furthermore, in order to prevent the deposition of dendritic lithium, it has been proposed to add, for example, a cyclic ether (JP-A-57-152684). However, even if these methods are used, there is a problem that the stability of the solvent used is not sufficient and therefore the cycle stability is not sufficient.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves these problems and provides a novel secondary battery having excellent cycle stability.

[0004]

Means for Solving the Problems As a result of intensive studies for improving the cycleability of an organic electrolyte secondary battery, the present inventors have found that the addition of a fluorine-containing ether to an organic electrolyte results in a marked cycle. The inventors have found that the stability is improved and have completed the present invention. That is, the present invention provides a secondary battery having a positive electrode, a negative electrode and an organic electrolytic solution as a basic configuration, wherein the organic electrolytic solution contains a fluorinated ether secondary battery. To do.

The present invention will be described in detail below. The present invention is characterized by containing a fluorine-containing ether as an organic electrolytic solution. As the fluorinated ether used in the present invention, a wide variety of fluorinated ethers are used, but normally it is desirable to use a fluorinated ether having a structure satisfying the following requirements.

<1> An ether compound containing at least one fluorine atom in the molecule, and the ratio of (number of fluorine atoms) / (number of fluorine atoms + number of hydrogen atoms) in the molecule is usually The range is 0.01 to 0.95, preferably 0.
The range is 1 to 0.9, and particularly preferably the range is 0.2 to 0.8. If the above ratio exceeds 0.95, the solubility in the electrolytic solution becomes low, which is not preferable. If it is less than 0.01, it becomes difficult to improve the cycle performance.

<2> The total number of carbon atoms and oxygen atoms in the molecule is usually in the range of 3 to 40, preferably 4 to 30. The number of oxygen atoms in the molecule is usually in the range of 1 to 8, preferably 1 to 4. Regarding <2> and <3>, if the respective ranges are exceeded, the viscosity of the electrolytic solution becomes too high, and if it is lower than this range, the cycle performance cannot be improved, which is not preferable.

The fluorine-containing ether used in the present invention includes chain ether and cyclic ether. Examples of the fluorine-containing chain ether used in the present invention include compounds represented by the general formula (1).

[0009]

Embedded image

(In the formula, n represents an integer of 0-8.
R ₁ , R ₂ and R ₃ are each a C _{1 to} C ₆ linear or branched monovalent or divalent hydrocarbon group, or a linear or branched monovalent or divalent hydrocarbon group containing at least one fluorine atom. Represents a fluorine-substituted hydrocarbon group of, but each may be the same or different. At least one of R ₁ , R ₂ and R ₃ contains at least one fluorine atom. ) Specific examples of the fluorine-containing chain ether include CF ₃ CF ₂ CH ₂ OCH ₃ , (L1) (CF ₃ ) ₂ CHCF ₂ OCH ₃ , (L2) CF ₃ CFHCF ₂ OCH ₃ , and (L3) CF ₃ CF ₂ CH ₂ OCF ₂ CF ₂ H, (L4) HCF ₂ CF ₂ OCH ₃ , (L 5) HCF ₂ CF ₂ OC ₂ H ₅ , (L 6) CF ₃ CH ₂ OCH ₂ CF ₃ , (L 7) C ₂ H ₅ OCF ₂ CHBrF, (L8) C ₄ H ₉ OCF ₂ CF ₂ H, (L 9) CF ₃ CHClOCHF ₂ , (L 10) CHClFCF ₂ OCHF ₂ , (L 11) CHClFCF ₂ OCH ₂ CH ₃ , (L 12) CHClFCF ₂ OCH ₃ , ( L13) CHCl ₂ CF ₂ OCH ₃ , (L 14) CF ₃ CH ₂ OCHF ₂ , (L 15) C ₃ F ₇ OCHFCF ₃ , (L 16) (CF ₃ ) ₂ CHOCH ₂ F, (L17) CF ₃ CFIOCF ₃ , (L18) (CF ₃ ) ₂ CFOCH ₂ CH ₂ CF ₂ CF ₂ I, (L19) F [CF (CF ₃ ) CF ₂ O] ₂ CHFCF ₃ , (L20) ( _{CF 3) 2 CFOCH 2 CH =} CH 2, (L21) CF 3 (CF 2) 2 CH 2 OCH 2 CH = CH 2, (L22) CF 3 (CF 2) 6 CH 2 OCH 2 CH = CH 2, ( _{L23) CF 3 CHFCF 2 OCH 2} CH = CH 2, (L24) CHF 2 CF 2 OCH 2 CH = CH 2, (L25) CF 3 CH 2 OCF = CF 2, (L26) CF 3 CH 2 OCH = CH 2 _{, (L27) CF 3 OCF =} CF 2, include _{(L28) CH 3 O- [CH} (CF 3) CH 2 O] n -CH 3 (n = 1~7) (L29).

Examples of the fluorine-containing cyclic ether used in the present invention include, for example, general formulas (2), (3), (4),
Examples thereof include the compounds represented by (5) and (6).

[0012]

Embedded image

(Wherein R _{1 to} R ₈ are hydrogen, fluorine, C ₁
To C ₆ linear or branched monovalent or divalent hydrocarbon group,
Alternatively, it is either a C _{1 to} C ₆ linear or branched monovalent or divalent fluorine-substituted hydrocarbon group, and the hydrocarbon group and the fluorine-substituted hydrocarbon group may contain an ether group. R _{1 to} R ₈ may be the same or different. However, at least one of R _{1 to} R ₈ contains a fluorine atom. )

[0014]

Embedded image

(In the formula, R _{1 to} R ₆ are hydrogen, fluorine, C ₁
To C ₆ linear or branched monovalent or divalent hydrocarbon group,
Alternatively, it is either a C _{1 to} C ₆ linear or branched monovalent or divalent fluorine-substituted hydrocarbon group, and the hydrocarbon group and the fluorine-substituted hydrocarbon group may contain an ether group. In addition, R _{1 to} R ₆ may be the same or different. However, at least one of R _{1 to} R ₆ contains a fluorine atom. )

[0016]

[Chemical 4]

(Wherein R _{1 to} R ₈ are hydrogen, fluorine, C ₁
To C ₆ linear or branched monovalent or divalent hydrocarbon group,
Alternatively, it is either a C _{1 to} C ₆ linear or branched monovalent or divalent fluorine-substituted hydrocarbon group, and the hydrocarbon group and the fluorine-substituted hydrocarbon group may contain an ether group. R _{1 to} R ₈ may be the same or different. However, at least one of R _{1 to} R ₈ contains a fluorine atom. )

[0018]

Embedded image

(In the formula, R _{1 to} R ₆ are hydrogen, fluorine, C ₁
To C ₆ linear or branched monovalent or divalent hydrocarbon group,
Alternatively, it is either a C _{1 to} C ₆ linear or branched monovalent or divalent fluorine-substituted hydrocarbon group, and the hydrocarbon group and the fluorine-substituted hydrocarbon group may contain an ether group. R _{1 to} R ₈ may be the same or different. However, at least one of R _{1 to} R ₆ contains a fluorine atom. )

[0020]

[Chemical 6]

(Wherein R _{1 to} R ₁₆ are hydrogen, fluorine, C ₁
To C ₆ linear or branched monovalent or divalent hydrocarbon group,
Or, it is either a C _{1 to} C ₁₆ linear or branched monovalent or divalent fluorine-substituted hydrocarbon group, and the hydrocarbon group and the fluorine-substituted hydrocarbon group may contain an ether group. R _{1 to} R ₈ may be the same or different. However, at least one of R _{1 to} R ₁₆ contains a fluorine atom. ) Specific examples of the fluorine-containing cyclic ether

[0022]

[Chemical 7]

[0023]

Embedded image

[0024]

[Chemical 9]

[0025]

[Chemical 10]

And the like. The reason why the cycle stability is improved by adding the fluorinated ether of the present invention is not clear, but the fluorinated ether added by charge / discharge reacts or decomposes and is deposited on the negative electrode to modify the negative electrode surface, It is presumed that this is to suppress the reaction between the electrolyte solution and the electrolyte. At this time, it is presumed that the ether compound containing a fluorine atom more effectively suppresses the reaction with the negative electrode.

The effect of adding the fluorine-containing ether of the present invention can be applied to a wide variety of electrolytic solutions, and in particular, cyclic carbonic acid ester, acyclic carbonic acid ester, cyclic ester, chain ester, cyclic ether, When chain ether is used as the electrolytic solution, good results are obtained with respect to the effects described below, and particularly when a plurality of mixed solvents selected from these are used as the solvent, particularly good results are obtained.

Specific examples of the cyclic carbonic acid ester mentioned here include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentene carbonate and 2,3.
-Pentene carbonate, 1,3-dioxa-2-cyclohexanone, 4-methyl-1,3-dioxa-2-cyclohexanone, 4-isopropyl-5,5-dimethyl-1,3-dioxa-2-cyclohexanone, cyclohexyl carbonate (Chemical formula 11)

[0029]

[Chemical 11]

And the like. Specific examples of the acyclic carbonic acid ester include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and butyl methyl carbonate. Specific examples of the cyclic ester include β-butyrolactone, γ-butyrolactone, γ-valerolactone, and δ-valerolactone.

Specific examples of the chain ester include methyl formate, ethyl formate, propyl formate, methyl acetate,
Ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, butyl propionate,
Examples include methyl butyrate and ethyl butyrate. Examples of cyclic ethers include cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, cyclic diethers such as 1,3-dioxolane and 1,4-dioxane,
Crown ethers such as 12-crown-4, 15-crown-5, 18-crown-6 and the like can be mentioned.

Examples of the chain ether include ethers such as ethyl ether, propyl ether, butyl ether, pentyl ether, hexyl ether and phenyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dimethoxy. Diethers such as propane, 1,2-diethoxypropane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and diethylene glycol dibutyl ether may be mentioned.

As the electrolyte, LiClO_Four, LiAs
F₆, LiCF₃SO₃, LiCF ₃CHFCF₂SO
₃, LiCF₂HCF₂SO₃, LiCF₂HSO₃,
LiBF_Four, LiPF₆, Li (CF₃S0₂)₂N
Dissolve in the above solvent either alone or as a mixture of multiple
Can be used. The fluorine-containing ether of the present invention is
0.1% to 30% by volume of the above electrolyte
When added in the range, the effect is large, 0.5 volume% or more 2
Addition in the range of 0% by volume is more preferable, and 0.5% by volume is preferable.
Addition in the range of 15% by volume is particularly preferable. 0.1 body
If it is less than product%, the effect of improving cycle stability is small,
Cycle stability improves at volume% or more, but capacity
Becomes smaller. Also, one type of fluorine-containing ether is used
However, a plurality of them may be mixed and used.

Although the positive electrode and the negative electrode in the present invention are not particularly limited, examples of the positive electrode include TiS ₂ and Ti.
Metal sulfides such as S ₃ , MoS ₃ and FeS ₂ , Li
_(1-x) CoO ₂ , Li _(1-x) NiO ₂ , Li _(1-x) Mn
O ₂ , Li _(1-x) Co _y Sn _z O ₂ , Li _(1-x) Co _y
Ni _z O ₂ , Li _(1-x) Co _y Fe _z O _2, and other alkali metal-containing composite oxides, V ₂ O ₅ , V ₆ O ₁₃ , MoO ₃
Metal oxides such as Further, examples of the negative electrode include lithium metal, lithium alloy, carbonaceous material, and conductive polymer. A particularly remarkable effect is found when a carbonaceous material is used as the negative electrode.

[0035]

The present invention will be described in more detail with reference to the following examples.

[0036]

Examples 1 to 7 and Comparative Example 1 The cylindrical non-aqueous electrolyte battery shown in FIG. 1 was produced as follows. First, LiCo
O ₂ was crushed with a ball mill to an average particle size of 3 μm, and then 0.025 part by weight of graphite, 0.025 part by weight of acetylene black, and 0.02 part by weight of polyvinylidene fluoride as a binder were added to 1 part by weight of this powder. The paste made with dimethylformamide has a thickness of 15μ
A positive electrode 1 was produced by applying a dry film thickness of 100 μm on one surface of an aluminum foil of m.

On the other hand, a commercially available petroleum needle coke (KOA-SJ Coke, manufactured by Koa Oil Co., Ltd.) was pulverized with a ball mill to an average particle size of 10 μm. BET surface area of this needle coke, true density, surface spacing d obtained from X-ray diffraction
₀₀₂ and Lc ₍₀₀₂₎ are 11 m ^{2 /} g and 2.13, respectively.
It was g / cm ³ , 3.44Å, 52Å. This powder 1
Polyvinylidene fluoride as a binder for 0.1 part by weight.
Add 05 parts by weight, and use dimethylformamide to make a paste, and a dry film thickness of 1 μm on one side of a copper foil with a thickness of 10 μm.
The negative electrode 2 was manufactured by applying the coating solution so as to have a thickness of 30 μm. A positive electrode lead terminal 3 made of aluminum and a negative electrode lead terminal 4 made of copper for collecting current were welded to the positive electrode 1 and the negative electrode 2, respectively.

Then, a separator 5 made of a polyethylene microporous film was interposed between the positive electrode 1 and the negative electrode 2, and the layers were laminated and wound many times to prepare a spirally wound electrode body. Then, this spiral-shaped electrode body is used for the SUS battery container 6
Stored inside. The negative electrode lead terminal 4 was connected to the inner bottom portion of the battery container 6 by spot welding, and the positive electrode lead terminal 3 was similarly connected to the battery sealing plate 7.

Next, in a battery can container 6 accommodating this electrode assembly, a mixed solvent of propylene carbonate, ethylene carbonate and γ-butyrolactone was mixed at a volume ratio of 1: 1, 2: CF ₃ ) ₂ C
HCF ₂ OCH ₃ (L2) (Daikin Chemical Products Sales Co., Ltd.)
T7311) produced in Table 1 was mixed, and an electrolyte prepared by dissolving lithium tetrafluoroborate (LiBF ₄ ) as an electrolyte in an amount of 1.0 mol / liter was poured into the battery. The container 6 and the battery sealing plate 7 were sealed by fitting and caulking via a polypropylene packing 8 to prepare a cylindrical non-aqueous electrolyte battery having an outer diameter of 20 mm and 50 mm.

The cycle performance characteristics of each battery thus manufactured were evaluated. Test condition is charge / discharge current 1
A, charge start-and-stop voltage 4.2V, discharge start-and-stop voltage 2.7V, charge and discharge is repeated 100 cycles at 20 ℃, 100
The ratio of the discharge capacity at the first cycle to the discharge capacity at the first cycle was calculated as the discharge capacity retention rate. Battery A-H 1
Table 1 shows the discharge capacity at the cycle and the discharge capacity retention rate at the 100th cycle. From Table 1, it is clear that the discharge capacity in the first cycle decreases with the addition of 20% or more, but the capacity retention rate improves as the addition amount increases.

[0041]

[Table 1]

[0042]

[Examples 8 to 14] Ethylene carbonate and γ were added to the electrolytic solution.
1 volume% of various fluorine-containing ethers shown in Table 2 was added to a solvent in which butyrolactone was mixed at a volume ratio of 1: 3 to prepare a solvent, and lithium tetrafluoroborate (L
A battery was produced in the same manner as in Example 1 except that the electrolyte solution prepared by dissolving iBF ₄ ) at a concentration of 1.5 mol / liter was injected. For each battery produced in this way,
Under the same conditions as in Example 1, the discharge capacity at the first cycle was 10
Table 2 shows the results of examining the capacity retention ratio at the 0th cycle.
Addition of any fluorine-containing ether improves cycle performance.

[0043]

[Table 2]

[0044]

Examples 15 to 21 To a solvent prepared by mixing propylene carbonate and diethyl carbonate at a volume ratio of 1: 1 to an electrolytic solution, 1% by volume of various fluorinated ethers shown in Table 3 was added as a solvent, and hexafluorophosphoric acid was used as an electrolyte. A battery was produced in the same manner as in Example 1 except that lithium (LiPF ₆ ) was dissolved at a concentration of 1.0 mol / liter and an adjusted electrolytic solution was injected. For each of the batteries thus manufactured, the discharge capacity at the first cycle under the same conditions as in Example 1,
Table 3 shows the results of examining the capacity retention rate at the 100th cycle. Addition of any fluorine-containing ether improves cycle performance.

[0045]

[Table 3]

[0046]

Comparative Example 2 A battery was prepared and evaluated in the same manner as in Example 15, except that 1% by volume of tetrahydrofurfuryl chloride, which is a chlorine-containing ether, was added in place of L2 as the ether. As a result, the discharge capacity in the first cycle is 10
Although it was as good as 60 mAh, the capacity retention ratio at the 100th cycle was 62.0%, which was worse than that without addition.

[0047]

Comparative Example 3 A battery was prepared and evaluated in the same manner as in Example 14 except that 12-crown-4 containing no fluorine was used as the ether instead of C2. As a result, the discharge capacity at the first cycle was as good as 1061 mAh,
The capacity retention rate at the 100th cycle was 58.3%, which was worse than that without addition.

[0048]

[Embodiments 22 and 23] In the electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (D
EC) and methyl propionate (MP) were mixed at a volume ratio of 2 to 3 to 1, and propylene carbonate (PC) and 1,2-dimethoxyethane (DME) were mixed at a volume ratio of 1 to 1. For each mixed solvent of composition,
1,2,2-tetrafluoroethyl ethyl ether (L
6) 1% by volume was added as a solvent, and lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte was dissolved at a concentration of 1.0 mol / liter to prepare an electrolytic solution, which was prepared in the same manner as in Example 1. A battery was made. Table 5 shows the results of examining the discharge capacity at the first cycle and the capacity retention rate at the 100th cycle for each of the batteries thus manufactured under the same conditions as in Example 1. Addition of any fluorine-containing ether improves cycle performance.

[0049]

[Table 4]

[0050]

[Table 5]

[0051]

As is apparent from the above description, by incorporating a fluorine-containing ether in the electrolytic solution of a non-aqueous electrolyte secondary battery, it is possible to obtain a new secondary battery with high capacity and excellent cycleability. You can

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of non-aqueous electrolyte batteries used in Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 1 band-shaped positive electrode 2 band-shaped negative electrode 3 positive electrode lead terminal 4 negative electrode lead terminal 5 separator 6 battery container 7 battery sealing plate 8 packing 9 insulating plate 10 insulating plate

Claims (1)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an organic electrolytic solution as a basic component, wherein the organic electrolytic solution contains a fluorine-containing ether.