JPH07240232A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To improve cycle characteristics of a nonaqueous electrolyte secondary battery using lithium at any temperature including low temperature by containing specified annular carbonate in a nonaqueous solvent which composes the nonaqueous electrolyte. CONSTITUTION:A nonaqueous electrolyte secondary battery is composed of a negative electrode, a positive electrode, and a nonaqueous electrolyte dissolved in a nonaqueous solvent wherein the negative electrode consists of a material which can be doped with the desorb lithium together with metal lithium or a lithium alloy. The nonaqueous solvent contains a cyclic carbonate having the formula shown wherein at least one of X<1>, X<2>, X<3> stands for F, C, or Br. Moreover, in the point of improving the capacity of the battery and heightening energy density, it is preferable to use lithium and at least one kind of transition metal compounded compounded as positive electrode active materials for the positive electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery using lithium. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery having improved cycle characteristics by using a specific non-aqueous solvent.

[0002]

2. Description of the Related Art With the recent trend toward smaller and lighter electronic devices such as camera-integrated VTRs, telephones, laptop computers, etc., and portable devices, lightweight and high-capacity secondary batteries have been demanded and developed. Is being promoted. Among them, lithium secondary batteries are thinner, lighter in weight, have higher energy density, can generate high voltage, and are safer than nickel-cadmium secondary batteries and lead secondary batteries that have been conventionally used. Highly efficient and non-polluting batteries can be realized, so research is actively underway. Therefore, various proposals have been made.

For example, as the non-aqueous solvent constituting the non-aqueous electrolytic solution, propylene carbonate (PC) which is a high dielectric constant solvent, 1,2-dimethoxyethane (DME) and 2-methyltetrahydrofuran which are low viscosity solvents. (2-M
A mixed solvent with eTHF), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), etc. has been proposed as a solvent having high conductivity and capable of improving cycle characteristics.

[0004]

However, even if the above-mentioned propylene carbonate-based solvent is used,
The cycle characteristics of the lithium secondary battery cannot be sufficiently improved, and it has been desired to further improve the cycle characteristics.

In order to improve the cycle characteristics, it has been proposed to use a carbon material capable of doping and dedoping lithium in the negative electrode (Japanese Patent Laid-Open No. 62-90863).
When a propylene carbonate-based solvent such as that described above is used and graphite, which can be expected to achieve high energy density, is used as the carbon material for the negative electrode,
There is a problem that charging cannot be performed because propylene carbonate decomposes. For such problems,
It has been proposed to use ethylene carbonate instead of propylene carbonate, but when ethylene carbonate is used, there is a problem that the low-temperature characteristics are poor because the freezing point of ethylene carbonate itself is high.

The present invention is intended to solve the problems of the prior arts described above, and to improve the cycle characteristics of a non-aqueous electrolyte secondary battery using lithium, in particular, a cycle that does not solidify even at a low temperature. By using a non-aqueous solvent having excellent characteristics, it is intended to improve cycle characteristics even at low temperatures.

[0007]

Means for Solving the Problems As a result of various studies to achieve the above object, the present inventors have found that a specific cyclic carbonate is effective as a non-aqueous solvent used in a non-aqueous electrolytic solution. It was discovered that there is something, and the present invention was completed.

That is, the present invention provides a non-aqueous electrolyte comprising a negative electrode composed of a material capable of doping and de-doping lithium, metallic lithium or a lithium alloy, a positive electrode, and a non-aqueous electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent. In the electrolyte secondary battery,
The non-aqueous solvent is represented by the following formula (1)

[0009]

[Chemical 2] (Wherein at least one of X ¹ , X ² , X ³ and X ⁴ represents F, Cl or Br). A non-aqueous electrolyte secondary battery comprising a cyclic carbonate represented by the formula: I will provide a.

The present invention will be described in detail below.

As described above, the present invention provides a non-aqueous electrolyte secondary battery using lithium as a non-aqueous solvent.
A specific cyclic carbonate represented by the formula (1), that is, 1,3-dioxolan-2-ones whose 4-position or 5-position is substituted with at least one halogen atom is used. There is.

Here, as the non-aqueous solvent, one kind of the cyclic carbonate represented by the formula (1) may be used, or a plurality of kinds thereof may be mixed and used. In addition to the cyclic carbonate represented by the formula (1), propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone, etc., and 1,2-dimethoxyethane (DME), which is a low-viscosity solvent, 2 -Methyltetrahydrofuran (2-
MeTHF), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC) and the like may be mixed and used.

In preparing the non-aqueous electrolytic solution, the electrolyte to be dissolved in the non-aqueous solvent as described above is not particularly limited and may be the same as the conventional lithium secondary battery. For example, LiClO ₄ , LiAsF ₆ , LiP
F ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃
SO ₂ ) ₂ or the like can be used, among which LiPF ₆ or L
It is preferred to use iBF ₄ .

In the present invention, it is preferable to use a composite oxide of lithium and one or more kinds of transition metals as the positive electrode active material for the positive electrode from the viewpoint of improving battery capacity and energy density. For example, an active material mainly composed of Li _x MO ₂ (wherein M represents one or more kinds of transition metals, x varies depending on the charge / discharge state of the battery, and usually 0.05 ≦ x ≦ 1.10). Those consisting of can be preferably used. In this case, especially as the transition metal M, C
It is preferable to use at least one of o, Ni, and Mn. Here, when the transition metal M is Mn, Li _x M
Both n ₂ O ₄ and Li _x MnO ₂ can be used. When forming a positive electrode from such a composite oxide, a known conductive agent, a binder or the like can be added.

On the other hand, the negative electrode is made of a material capable of being doped or dedoped with lithium, metallic lithium or a lithium alloy. Examples of the material forming the negative electrode or the negative electrode active material capable of being doped and dedoped with lithium include, for example, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, and glass. Carbon, organic polymer compound fired product (phenolic resin, furan resin, etc. fired at a suitable temperature to carbonize), carbon fiber, carbon material such as activated carbon, or polymer such as polyacetylene or polypyrrole be able to. Also, as a lithium alloy,
A lithium-aluminum alloy or the like can be used.

Among these, it is preferable to use a carbon material from the viewpoint of improving cycle characteristics. Among the carbon materials, it is preferable to use graphites having a (002) plane spacing of 0.340 nm or less. Can be improved, which is preferable. In particular, (002)
Those having a crystal structure in which the interplanar spacing is 0.340 nm or less, the crystallite thickness in the C-axis direction is 16.0 nm or more, the G value in the Raman spectrum is 2.5 or more, and the true density is 2.1 g / cm ³ or more. Is preferred. Here, the G value represents the ratio of the signal intensity derived from the graphite structure of the carbon material to the signal intensity derived from the amorphous structure in the Raman spectrum, and is an index of microscopic crystal structure defects. It is a thing.

In forming the negative electrode from such a carbon material, a known binder or the like can be added.

The shape of the battery of the present invention is not particularly limited. Various shapes such as a cylindrical shape, a square shape, a coin shape, and a button shape can be used.

[0019]

According to the non-aqueous electrolyte secondary battery of the present invention, since the non-aqueous solvent constituting the non-aqueous electrolyte contains the specific cyclic carbonate represented by the formula (1), the lithium secondary battery The cycle characteristics of are improved. In particular, the specific cyclic carbonate represented by the formula (1) does not solidify even at a low temperature of about 0 ° C., so that the cycle characteristics at a low temperature of the battery are improved.

Further, the non-aqueous electrolyte used in the present invention is
Even if a lithium secondary battery is constructed using graphite for the negative electrode, it will not decompose. Therefore, according to the non-aqueous electrolyte secondary battery of the present invention, graphite can be used for the negative electrode in order to improve the energy density of the battery.

[0021]

EXAMPLES The present invention will be specifically described below with reference to examples.

Example 1 FIG. 1 is a sectional view of a coin type non-aqueous electrolyte secondary battery (outer diameter 20 mm, height 2.5 mm) produced in this example and other examples and comparative examples described later. Is. In the battery shown in the figure, a negative electrode (negative electrode active material) 1 and a positive electrode (positive electrode active material) 2 are respectively housed in a negative electrode can 4 and a positive electrode can 5 via a porous separator 3 made of polypropylene, and a sealing gasket 6 is provided. It was produced by caulking through.

In Example 1, metallic lithium was used as the negative electrode active material 1 in manufacturing such a coin-type battery. On the other hand, when forming the positive electrode active material 2, first, 0.5% of lithium carbonate and cobalt carbonate was used.
LiCoO ₂ was obtained by mixing in a molar ratio of 1.0 and firing in air at 900 ° C. for 5 hours. And this LiCoO
90 parts by weight of ₂ , ₂ parts by weight of graphite as a conductive agent, and 3 parts by weight of fluororesin as a binder were mixed and pressure-molded to obtain a positive electrode active material 2. Further, as the electrolytic solution, LiPF ₆ was added to a non-aqueous solvent prepared by mixing 4,5-dichloro-1,3-dioxolan-2-one and dimethyl carbonate (DMC) at a volume ratio of 1: 1.
Was used at a ratio of 1.0 mol / l.

Examples 2 to 4 With respect to the non-aqueous solvent, 4,5-difluoro-1,3 was used in place of 4,5-dichloro-1,3-dioxolan-2-one.
-Dioxolan-2-one (Example 2), 4,4-dichloro-1,3-dioxolan-2-one (Example 3),
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that 4-chloro-1,3-dioxolan-2-one (Example 4) was used.

COMPARATIVE EXAMPLE 1 Regarding the non-aqueous solvent, propylene carbonate (P was used instead of 4,5-dichloro-1,3-dioxolan-2-one).
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that C) was used.

(Evaluation 1) The cycle characteristics of the non-aqueous electrolyte secondary batteries of Examples 1 to 4 and Comparative Example 1 were evaluated as follows.

First, the upper limit voltage was set to 4.2 V at 23 ° C., constant current and constant voltage charging was performed at 1 mA for 10 hours, and then 1
The battery was discharged to a final voltage of 3.0 V with a constant current of mA, and this charging / discharging was repeated as a predetermined number of cycles, and the charging / discharging efficiency at that time was plotted against the number of cycles. The result is shown in FIG.

It can be seen from FIG. 2 that the non-aqueous electrolyte secondary batteries of Examples 1 to 4 have excellent cycle characteristics as compared with the non-aqueous electrolyte secondary battery of Comparative Example 1.

Example 5 A test cell for negative electrode evaluation was prepared in the same manner as in Example 1 except that the following carbon material was used as the negative electrode at the position of the positive electrode active substance 2.

That is, by using petroleum pitch as a starting material, introducing 10 to 20% of a functional group containing oxygen into this (so-called oxygen crosslinking), and then calcining at 1000 ° C. in an inert gas stream, glass A non-graphitizable carbon material having properties close to those of linear carbon was obtained. When this non-graphitizable carbon material was subjected to X-ray diffraction, the (002) plane spacing was 0.376.
was nm. The true density was 1.58 g / cm ³ . This non-graphitizable carbon material is crushed to obtain an average particle size of 10
A powder having a diameter of μm was mixed, and 90 parts by weight of this powder and 10 parts by weight of a fluororesin as a binder were mixed, and this was pressure-molded to obtain a negative electrode.

Examples 6 to 8 Regarding the non-aqueous solvent, 4,5-difluoro-1,3 was used in place of 4,5-dichloro-1,3-dioxolan-2-one.
-Dioxolan-2-one (Example 6), 4,4-dichloro-1,3-dioxolan-2-one (Example 7),
A test cell for negative electrode evaluation was prepared in the same manner as in Example 5 except that 4-chloro-1,3-dioxolan-2-one (Example 8) was used.

COMPARATIVE EXAMPLE 2 Regarding the non-aqueous solvent, propylene carbonate (P was used instead of 4,5-dichloro-1,3-dioxolan-2-one).
A test cell for negative electrode evaluation was prepared in the same manner as in Example 5 except that C) was used.

(Evaluation 2) With respect to the negative electrode evaluation test cells of Examples 5 to 8 and Comparative Example 2, the cycle characteristics were evaluated as follows.

First, constant current charging was performed at 23 ° C. and 1 mA for 10 hours, and then discharging was performed at a constant current of 1 mA to a final voltage of 1.5 V. This charging / discharging was regarded as one cycle, and such charging / discharging was performed for a predetermined number of cycles. Repeatedly, the charging / discharging efficiency at that time was plotted against the number of cycles. The result is shown in FIG.

From FIG. 3, it can be seen that the negative electrode evaluation test cells of Examples 5 to 8 exhibit excellent cycle characteristics as compared with the negative electrode evaluation test cell of Comparative Example 2.

Example 9 A test cell for negative electrode evaluation was prepared in the same manner as in Example 1 except that the following carbon material was used as the negative electrode at the position of the positive electrode active substance 2.

That is, graphite ((002) plane spacing = 0.3358 nm, C-axis crystallite thickness = 25.4 n)
m, Raman spectrum G value = 8.82, true density = 2.2
90 parts by weight of ³ g / cm ³ and average particle size = 28.4 μm (KS-75 manufactured by Lonza Co., Ltd.) and 10 parts by weight of a fluororesin as a binder were mixed, and this was pressure-molded to obtain a negative electrode. . Examples 10-12 Regarding non-aqueous solvents, 4,5-difluoro-1,3 is used instead of 4,5-dichloro-1,3-dioxolan-2-one.
-Dioxolan-2-one (Example 10), 4,4-dichloro-1,3-dioxolan-2-one (Example 1)
A test cell for negative electrode evaluation was prepared in the same manner as in Example 9 except that 1) and 4-chloro-1,3-dioxolan-2-one (Example 12) were used.

Comparative Example 3 Regarding the non-aqueous solvent, propylene carbonate (P was used instead of 4,5-dichloro-1,3-dioxolan-2-one).
A test cell for negative electrode evaluation was prepared in the same manner as in Example 9 except that C) was used.

(Evaluation 3) With respect to the negative electrode evaluation test cells of Examples 9 to 12 and Comparative Example 3, the cycle characteristics were evaluated as follows.

First, the lower limit voltage was set to 0 V at 23 ° C., constant current and constant voltage charging were performed at 1 mA for 10 hours, and then 1 mA.
Was discharged to a final voltage of 1.0 V with a constant current of, and the potential change at this time was plotted against time. The result is shown in FIG.

It can be seen from FIG. 4 that the negative electrode evaluation test cells of Comparative Example 3 did not discharge, whereas the negative electrode evaluation test cells of Examples 9 to 12 showed excellent discharge characteristics. Therefore, it can be seen that the non-aqueous electrolytic solution used in this example can be favorably used even when graphite is used for the negative electrode of the lithium secondary battery.

(Evaluation 4) In order to investigate the relationship between the low temperature characteristics of the non-aqueous electrolyte solution and the non-aqueous solvent which constitutes the non-aqueous electrolyte solution, as shown in Table 1, the non-aqueous electrolyte solutions were tested in Examples 1 to 12 above. 1.0 mol of LiPF ₆ was added to the cyclic carbonate used as the water solvent.
What was melt | dissolved in the ratio of / l was prepared (solution ad).
Also, LiPF ₆ was added to ethylene carbonate at 1.0mo
What was melt | dissolved in the ratio of 1 / l was prepared (solution e). The solution e using this ethylene carbonate as a solvent is
At room temperature, it can be used as a non-aqueous electrolyte of a lithium battery using graphite for the negative electrode.

Then, each of them was put in a sample bottle and left for 2 hours in a constant temperature bath kept at a temperature of 0 ° C., and the state after that was observed. The results are shown in Table 1.

As shown in Table 1, the solutions ad did not coagulate, but the solution e coagulated. Therefore, it can be seen that when the solution e is a non-aqueous electrolyte, the low temperature characteristics of the battery are impaired, but when the solutions a to d are non-aqueous electrolytes, the low temperature characteristics of the battery are not impaired.

[0045]

[Table 1] Solution Non-aqueous solvent State at 0 ° C. a 4,5-Dichloro-1,3-dioxolan-2-one liquid b 4,5-Difluoro-1,3-dioxolan-2-one liquid c 4,4-dichloro- 1,3-dioxolan-2-one liquid d 4-chloro-1,3-dioxolan-2-one liquid …………………………………………………………………… ……………………………… e Ethylene carbonate solid Further, when the coagulation temperature of the mixed solvent of the cyclic carbonate and the low viscosity solvent used as the non-aqueous solvent in Examples 1 to 12 and the mixed solvent of the ethylene carbonate and the low viscosity solvent were compared, it was found that The mixed solvent of the cyclic carbonate and the low viscosity solvent did not solidify at the temperature at which the mixed solvent of the low viscosity solvent solidified. Therefore, it is understood that the use of the mixed solvent of the cyclic carbonate and the low-viscosity solvent as the non-aqueous solvent of the battery provides better low-temperature characteristics than the use of the mixed solvent of the ethylene carbonate and the low-viscosity solvent.

[0046]

According to the present invention, it becomes possible to improve the cycle characteristics of a non-aqueous electrolyte secondary battery using lithium, including at low temperatures.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a battery and a test cell for negative electrode evaluation manufactured in Examples and Comparative Examples.

FIG. 2 is a relationship diagram between the number of cycles and charge / discharge efficiency of the batteries manufactured in Examples and Comparative Examples.

FIG. 3 is a relationship diagram between the number of cycles and charge / discharge efficiency of the test cell for negative electrode evaluation manufactured in Examples and Comparative Examples.

FIG. 4 is a diagram showing the relationship between charge or discharge time and voltage of the negative-electrode evaluation test cells manufactured in Examples and Comparative Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Negative electrode (negative electrode active material) 2 Positive electrode (positive electrode active material) 3 Porous separator 4 Negative electrode can 5 Positive electrode can 6 Sealing gasket

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[Procedure amendment]

[Submission date] October 12, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

[0029] was prepared in Example 5 positive Katsubutsu quality 2 Similarly negative evaluation test cell as in Example 1 but using the following carbon material as a negative electrode in position.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction content]

[0036] was prepared in Example 9 positive Katsubutsu quality 2 Similarly negative evaluation test cell as in Example 1 but using the following carbon material as a negative electrode in position.

Claims (4)

[Claims] 1. A non-aqueous electrolytic solution secondary comprising a negative electrode made of a material capable of doping and de-doping lithium, metallic lithium or a lithium alloy, a positive electrode, and a non-aqueous electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent. In the battery, the non-aqueous solvent is represented by the following formula (1): (Wherein at least one of X ¹ , X ² , X ³ and X ⁴ represents F, Cl or Br). A non-aqueous electrolyte secondary battery comprising a cyclic carbonate represented by the formula: . 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode comprises a composite oxide of Li and one or more transition metals. 3. The negative electrode is made of a carbon material.
The non-aqueous electrolyte secondary battery described. 4. A carbon material having a (002) plane spacing of 0.
The non-aqueous electrolyte secondary battery according to claim 3, which has a thickness of 340 nm or less.