JP3222644B2 - Battery electrolyte and lithium battery using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a battery electrolyte.
In particular, the present invention relates to an electrolyte used for a non-aqueous electrolyte battery such as a lithium battery and a lithium battery using the electrolyte.

[0002]

2. Description of the Related Art Various types of nonaqueous solvents for battery electrolytes have been studied. Useful solvents include γ
-Butyrolactone (abbreviation: γ-BL, the same applies hereinafter), ethylene carbonate (EC), propylene carbonate (PC), sulfolane (SL), 1,3-dioxolan (DO), 1,2-dimethoxyethane (DME), 2 −
Methyltetrahydrofuran (2-MeTHF), diethyl carbonate (DEC) and the like have been used alone or as a mixture thereof.

[0003] In particular, PC is most often used as a non-aqueous solvent for a battery electrolyte, either as a single solvent or as a mixed solvent. However, by repeating charge and discharge, PC reacts with lithium of the negative electrode to produce a reduction product. However, there remains a problem that this accumulates on the surface of the negative electrode and causes a reduction in charge / discharge efficiency.

The above-mentioned various solvents, particularly PC, are also used in lithium primary batteries. Although it is not necessary to consider the problem of charging in the primary battery, there is a problem that the solvent is reduced by active lithium present at the time of discharging, which leads to deterioration of battery performance. In particular, when the weak discharge is performed for a long period of time under high temperature conditions, the reaction between the active lithium and the solvent is performed for a long period of time, which may cause a significant deterioration in battery performance.

We have the following structural formula:

Embedded image In the above, 1,3-dioxan-2-one having a structure in which all of R _{1 to} R ₆ are occupied by hydrogen has a high relative dielectric constant, and is a non-aqueous solvent constituting a battery electrolyte such as the PC. Based on the finding that the 1,3-dioxan-2-one was suitable as a substitute, the reduction resistance of 1,3-dioxan-2-one was examined.
As a result, it was found that the bond between oxygen and carbon in O ¹ -C ⁶ and O ³ -C ⁴ was easily cleaved. However, hydrogen bonded to both C ⁴ and C ⁶ carbons in the basic structure was found. Is substituted by an alkyl group or an alkoxyl group, and O ¹
It has been confirmed that the bond between oxygen and carbon of —C ⁶ , O ³ —C ⁴ is hardly cleaved, and that a sufficient level of reduction resistance that can be practically used as a nonaqueous solvent for a battery electrolyte is obtained.

The present inventors have previously applied for a patent application No. 137193 in 1992 based on such knowledge.

[0007]

SUMMARY OF THE INVENTION A 1,3-alkyl group obtained by replacing at least one of the hydrogen atoms bonded to both carbon atoms of C ⁴ and C ⁶ with an alkyl group or an alkoxyl group.
The dioxan-2-one derivative has excellent characteristics as a non-aqueous solvent used in an electrolyte solution for a battery, but it has been clarified that the combined electrolytes give rise to inferiority in battery performance.

[0008] The present invention has been made based on the above points, and it is an object of the present invention to have sufficient reduction resistance and completely satisfy other physicochemical properties required as an electrolyte for a battery. An object of the present invention is to provide an electrolyte solution for a battery including an electrolyte which contains a non-aqueous solvent as described above and which can sufficiently bring out the performance of the non-aqueous solvent, and a lithium battery using the electrolyte solution.

[0009]

In order to achieve the above object, an electrolyte for a battery according to the present invention comprises four kinds of lithium salts L
iClO ₄ , Li (CF ₃ SO ₂ ) ₂ N, LiPF ₆ ,
One type is selected from LiCF ₃ SO ₃ and used as an electrolyte.

Embedded image (However, R ₁ and R ₆ in the formula are represented by the general formula C _n H _{2n + 1} (n =
Alkyl group represented by 1-4), or the general formula OC _n H
An alkoxyl group represented by _{2n + 1} (n = 1 to 4),
_{2 to} R ₅ are hydrogen or a general formula C _n H _{2n + 1} (n = 1 to 4
Alkyl group represented by) or the general formula OC _n H _{2n + 1,}
(N = 1 to 4) is a non-aqueous solvent containing a 1,3-dioxan-2-one derivative represented by the following formula:

Here, the alkyl group is CH ₃ , C _{2
H 5, C 3 H 7,} CH (CH 3) 2, C (CH 3) is preferably selected from among _3.

The alkoxyl group may be OCH ₃ ,
OC ₂ H ₅ , OC ₃ H ₇ , OCH (CH ₃ ) ₂ , OC
It is preferable to be selected from (CH ₃ ) ₃ .

A lithium battery according to the present invention comprises a negative electrode made of a carbonaceous material capable of occluding and releasing lithium metal, a lithium alloy, and lithium ions;
And the electrolytic solution for a battery according to the present invention. That is, the battery electrolyte according to the present invention uses a metal oxide or a sulfide as a positive electrode active material, and uses a carbonaceous material capable of occluding and releasing metal lithium, a lithium alloy, or lithium ions for a negative electrode. In addition to being used as a non-aqueous electrolyte for a rechargeable lithium secondary battery, it can be used as a non-aqueous electrolyte for a lithium primary battery.

[0013]

[Function] LiClO ₄ , Li (CF ₃ SO ₂ ) ₂ N, L
A kind of lithium salt selected from iPF ₆ and LiCF ₃ SO ₃ is provided as an electrolyte, and in the above structural formula, at least R ₁ and R ₆ have an alkyl group or an alkoxyl group in 1,3-dioxane-2- The charge / discharge cycle characteristics of a lithium secondary battery using a battery electrolyte containing a non-aqueous solvent composed of an ON derivative are remarkably improved as compared with battery electrolytes using PC and BC as a non-aqueous solvent under the same conditions. I do. In addition, when the battery electrolyte containing the non-aqueous solvent according to the present invention is used for the lithium primary battery, it is possible to prevent a decrease in battery characteristics particularly at the time of long-term discharge under a low load, and increase the discharge capacity.

[0014]

Next, an embodiment of the present invention will be described. However, the present invention is not limited only to the embodiments described below.

Conventionally, electrolytes for battery electrolytes include LiClO ₄ , LiPF ₆ , LiBF ₄ , and LiAs.
F ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, and the like have been frequently used. The present inventors prepared nine types of non-aqueous solvents shown in Table 1 below.

[0016]

[Table 1] In this embodiment, as the non-aqueous solvent of the battery electrolyte,
4,4,6-Trimethyl-1,3-dioxan-2-one + DMC = 1: 2, which is the blending No. 2 in Table 1 above, was selected and first obtained by combining with each of the lithium salts as an electrolyte. The conductivity of the resulting electrolyte was compared. In Table 1,,,, and are the following substances, respectively, which are constituent elements of the present invention.

[0017]

[Table 2] FIG. 1 shows the comparison result. In addition, LiAsF ₆ is A
Since it contains s, there is a problem in adopting it for safety reasons, so it was excluded from comparison. From the results in FIG.
As the electrolyte, in particular, Li (CF ₃ SO ₂ ) ₂ N, Li
It has been found that three kinds of lithium salts of CF ₃ SO ₃ and LiPF ₆ are excellent.

Next, in order to examine actual battery performance, a test cell shown in FIG. 2 was assembled using these three types of electrolytes.

First, a positive electrode mixture formed by mixing LiCoO ₂ , carbon powder as a conductive material, and Teflon powder as a binder at a weight ratio of 100: 10: 6 and rolling the mixture to form a sheet. 1 was pressed against a titanium net as a current collector 2 to obtain a positive electrode. Further, a carbonaceous powder obtained by firing pitch-based carbon fiber and EPDM (ethylene propylene diene monomer) as a binder are mixed at a ratio of 100: 7, rolled, and formed into a sheet shape. The negative electrode mixture 3 was pressed against a Ni net as a current collector 4 to form a negative electrode. Both the positive electrode mixture 1 and the negative electrode mixture 3 have a plane shape of 10 × 10 mm square,
The thickness of the positive electrode mixture 1 is 0.25 mm, and the thickness of the negative electrode mixture 3 is 0.40 mm. In addition, the distance between both mixture 1 and 3 is 2mm
And placed in the beaker 5 as shown. As the solvent, 4,4,6-trimethyl-1,3-dioxan-2-one + DMC = 1: 2 was used, and the concentration of the electrolyte was:
All were 1 mol / l.

The theoretical charging capacity of the positive electrode is 8.2 mAh,
The theoretical charge capacity of the negative electrode is 7 mAh. The reason why the theoretical charging capacity of the positive electrode is made larger than that of the negative electrode is that, after the first charging, the amount of lithium that can participate in the next discharging decreases below the charging capacity. This is because, only in the first charge / discharge cycle, a fixed amount of charged lithium is taken into the carbonaceous negative electrode, and discharge cannot be performed from the next time.

Next, a charge / discharge cycle characteristic test for performing a constant current charge / discharge at a charge current of 1 mA and a discharge current of 2 mA was performed on each test cell having the above specifications using the above-mentioned electrolytic solution. The result was obtained. The upper limit of the discharge end voltage was 2.8V and the upper limit of the charge voltage was 4.15V. Also,
A test cell similar to the above was assembled, and a similar charge / discharge cycle characteristic test was performed. In this case, as the solvent, the blending Nos. 1 to 9 shown in Table 1 were used, and the electrolyte was Li (CF ₃ SO ₂ ).
The ₂ N was dissolved in 1 mol / l solvent.

As is clear from FIG. 3 showing the results of the characteristic test, it has been found that particularly excellent characteristics can be obtained when Li (CF ₃ SO ₂ ) ₂ N is used as the electrolyte. As is clear from FIG. 4, this is the same for other solvents which are components of the present invention, and it can be seen that they are superior to the comparative examples. As described above, according to the present example, the non-aqueous solvent containing the 1,3-dioxan-2-one derivative according to the present invention and Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ , L
It was confirmed that the use of a non-aqueous electrolyte having an electrolyte composed of one selected from iPF ₆ can greatly improve the characteristics of the battery. Further, when Li (CF ₃ SO ₂ ) ₂ N is used as the electrolyte, the effect of improving the battery characteristics is more remarkable.

[0023]

As described in detail in each of the embodiments, the 1,3-dioxan-2-one derivative according to the present invention is used as a solvent constituent material, and LiC is used as an electrolyte.
10 ₄ , Li (CF ₃ SO ₂ ) ₂ N, LiPF ₆ , Li
By employing an electrolytic solution using a kind of lithium salt selected from CF ₃ SO ₃ , the performance of the battery can be greatly improved. That is, in the lithium secondary battery using the electrolytic solution according to the present invention, the charge and discharge cycle characteristics can be significantly improved, and when the electrolytic solution according to the present invention is applied to a lithium primary battery, In particular, it is possible to prevent deterioration of characteristics during long-term discharge at a low load.

[Brief description of the drawings]

FIG. 1 is a graph comparing the electric conductivity of an electrolytic solution according to the present invention.

FIG. 2 is a schematic diagram of a test cell in an example.

FIG. 3 is a graph comparing charge / discharge cycle characteristics of test cells.

FIG. 4 is a graph comparing charge / discharge cycle characteristics of test cells using other solvents.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-295178 (JP, A) JP-A-63-152886 (JP, A) JP-A-5-335033 (JP, A) JP-A-5-35033 290882 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 6/16

Claims (4)

(57) [Claims] 1. Four kinds of lithium salts LiClO ₄ , Li
(CF ₃ SO ₂ ) ₂ N, LiPF ₆ , LiCF ₃ SO ₃
While selecting one from among them and using it as the electrolyte,
The following structural formula: (However, R ₁ and R ₆ in the formula are represented by the general formula C _n H _{2n + 1} (n =
Alkyl group represented by 1-4), or the general formula OC _n H
An alkoxyl group represented by _{2n + 1} (n = 1 to 4),
_{2 to} R ₅ are hydrogen or a general formula C _n H _{2n + 1} (n = 1 to 4
Alkyl group represented by) or the general formula OC _n H _{2n + 1,}
(N = 1 to 4) is a non-aqueous solvent containing a 1,3-dioxan-2-one derivative represented by the formula (1): 2. The method according to claim 1, wherein said alkyl group is CH ₃ , C ₂ H ₅ , C
_{3 H 7, CH (CH 3} ) 2, C (CH 3) The electrolyte solution according to claim 1, characterized in that it is selected from among _3. 3. The method according to claim 1, wherein said alkoxyl group is OCH ₃ , OC ₂
H ₅ , OC ₃ H ₇ , OCH (CH ₃ ) ₂ , OC (C
Claim characterized in that it is selected from among H _{3) 3} 1
The battery electrolyte according to any one of the preceding claims. 4. A negative electrode made of a carbonaceous material capable of occluding and releasing lithium metal, a lithium alloy, or lithium ions, and the battery according to any one of claims 1 to 3. A lithium battery comprising: an electrolyte for use in a lithium battery.