JP3316221B2 - Non-aqueous electrolyte battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel solute used for a battery containing lithium as an active material and a non-aqueous electrolyte.

[0002]

2. Description of the Related Art In recent years, a battery using lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) instead of lithium perchlorate (LiClO ₄ ) as a solute of a battery using lithium as an active material has been put to practical use. ing. A battery using this kind of lithium trifluoromethanesulfonate has better discharge characteristics after storage at a low temperature than a battery using lithium perchlorate. The reason for this is that lithium trifluoromethanesulfonate has high solubility and hardly precipitates during storage at low temperatures.

Incidentally, it has been observed that this solute has an alkyl group containing fluorine, and that this fluorine atom preferentially adsorbs to lithium to form a film on the negative electrode. In addition, such a tendency is considered that lithium tris (triff
Fluorosulfone) methide [composition formula: LiC (CF ₃ SO ₂ ) ₃ ]
It is also observed when this type of battery is used as a solute constituting a non-aqueous electrolyte.

The present inventor has made various studies and found that
As a solute of the electrolytic solution, an alkyl group having an alkyl group
In the case of a compound in which all the hydrogen atoms such as F ₃ and C ₂ F ₅ are substituted by F (fluorine), the fluorine atoms are preferentially adsorbed on the surface of the negative electrode using lithium as an active material, and the fluorine atoms are not adsorbed on the negative electrode. An active film tends to be easily formed. As a result, they have found a problem that causes an increase in the internal impedance of the battery.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and the problems observed when a compound having an alkyl group containing fluorine is used as a solute of an electrolytic solution. To suppress the inactivation of the negative electrode. In addition, even when used under high voltage, the decomposition of the electrolyte is suppressed, the cycle characteristics of the secondary battery are improved, and the increase in the internal impedance of the battery due to storage is suppressed, and the cycle characteristics and storage characteristics of the battery are improved. The present invention proposes a solute suitable for such a battery.

[0006]

The present invention relates to a non-aqueous electrolyte battery comprising a positive electrode, a negative electrode using lithium as an active material, and a non-aqueous electrolyte, wherein the solute of the non-aqueous electrolyte is represented by the following formula: in LiC (RSO _{n) m,} R is an alkyl group, Ali
Lumpur groups or their substituents (provided that the hydrogen atoms replaced, all except those fluorine atoms) and, n, m
Is at least one compound represented by an integer of 2 or more.

Here, in the above formula, R is C
It is preferably at least one selected from the group consisting of H ₃ , C ₂ H ₅ , phenyl and tolyl .

[0008] and, as the compound. Among them, Li
Titanium tris (benzenesulfone) methide or lithium
It is particularly preferred to use umtris (toluenesulfone) methide .

The positive electrode may be an oxide of at least one metal selected from the group consisting of manganese, nickel, cobalt, chromium, and vanadium, and the negative electrode may be lithium metal or lithium occlusion / release. Possible alloys, oxides, carbon materials can be used.

[0010]

[Action] In the nonaqueous electrolyte battery, as the solute of the electrolyte, wherein: the LiC (RSO _{n) m,} R is an alkyl
Group, an aryl group or a substituted product thereof (except that all hydrogen atoms to be substituted are fluorine atoms), and a compound in which n and m are each represented by an integer of 2 or more. By using the type, the cycle characteristics of the secondary battery are improved, and an increase in the internal impedance of the battery due to storage is suppressed.

In general, the decomposition reaction of an electrolytic solution is accelerated by products such as radicals generated by decomposition of a solute. Therefore, in order to increase the stability of the electrolytic solution, the stability of the solute is improved together with the stability of the solvent molecules themselves. It is necessary to let At that point, the anion of the compound represented by the formula (1) is excellent in stability as an ion, so that it is difficult to generate highly reactive radicals and the like even under a high voltage, and is effective in suppressing the decomposition reaction of the electrolytic solution. It is thought that there is. The reason for this is presumed to be that the anion has symmetry about X and the electron distribution in the molecule is uniform.

In the case of a compound in which all hydrogen atoms such as CF ₃ and C ₂ F ₅ are substituted with F (fluorine),
Fluorine molecules are preferentially adsorbed on the surface of the negative electrode containing lithium as an active material, and an inert film tends to be easily formed on the negative electrode. As a result, the internal impedance of the battery is increased.

On the other hand, as in the present invention, a compound containing no fluorine, particularly an aryl group such as phenyl and tolyl has high stability due to a resonance effect and hardly forms an inert film.
As a result, it greatly contributes to the improvement of the cycle characteristics and storage characteristics of the battery.

[0014]

Embodiments of the present invention will be described below in detail. Embodiment 1 Nonaqueous Electrolyte Secondary Battery FIG. 1 is a half sectional view of a flat nonaqueous electrolyte secondary battery as an embodiment of the present invention. Here, the negative electrode 1 made of lithium metal is pressed against the inner surface of the negative electrode current collector 2, and the negative electrode current collector 2 is made of a negative U-shaped can 3 made of ferritic stainless steel (SUS430) and having a substantially U-shaped cross section. It is fixed to the inner bottom surface. The peripheral end of the negative electrode can 3 is fixed inside a polypropylene insulating packing 4. The outer periphery of the insulating packing 4 is made of stainless steel and has a substantially U-shaped cross section in a direction opposite to the negative electrode can 3. The positive electrode can 5 is fixed. A positive electrode current collector 6 is fixed to the inner bottom surface of the positive electrode can 5, and a positive electrode 7 is fixed to the inner surface of the positive electrode current collector 6. A separator 8 is interposed between the positive electrode 7 and the negative electrode 1, and is impregnated with an electrolytic solution in which an electrolyte characteristic of the present invention is dissolved.

The positive electrode 7 is composed of a manganese oxide containing lithium in advance, acetylene black as a conductive agent, and a fluororesin as a binder:
It was prepared by mixing and using a weight ratio of 10: 5, press-molding and heat-treating at 250 to 350 ° C. The negative electrode 1 is manufactured by stamping a rolled lithium plate into a predetermined size.

Here, the electrolyte solution is a mixture of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) (50:50 in volume ratio) and LiC (C ₆ H ₅ SO ₂ )
₃ Add [ lithium tris (benzenesulfone) methide ]
What was melt | dissolved by the ratio of mol / liter was used.

Thus, Battery A of the present invention having an outer diameter of 24.0 mm and a thickness of 3.0 mm was produced.

As a comparative example, LiC (CF ₃ S) was used as a solute in a mixed solvent of PC and DME (50:50 by volume).
O ₂ ) ₃ [lithium tris (trifluoromethane sulfone)
The above-mentioned battery was prepared using an electrolytic solution in which methide], LiClO ₄ [lithium perchlorate], LiBF ₄ [lithium tetrafluoroborate], and LiPF ₆ [lithium hexafluorophosphate] were each dissolved at a ratio of 1 mol / liter. Batteries similar to A were prepared, and these were set as comparative batteries (a1, a2, a3, a4).

Table 1 shows the battery A of the present invention and comparative batteries a1 to a
4 shows the cycle life. The charge / discharge conditions at this time are as follows: charge / discharge current is 2 mA for 4 hours each;
The battery which reached V was regarded as the life. Here, the results of averaging the results of five batteries are shown.

[0020]

[Table 1]

As apparent from this, the battery A of the present invention
Indicates that the cycle life is longer and the cycle characteristics are improved as compared with the comparative batteries a1 to a4. (Example 2: Non-aqueous electrolyte secondary battery) Ethylene carbonate (EC), PC and D
A battery was prepared in the same manner as in Example 1 except that a mixed solvent of ME (40:40:20 in volume ratio) was used, and a battery B of the present invention was obtained.

On the other hand, as a comparative example, LiC (CF ₃ SO ₂ ) ₃ , LiClO ₄ , LiBF ₄ , LiPF ₆
And a comparative battery b1, b2, b3, b
And 4.

Table 2 shows the cycle life of these batteries. As is clear from Table 2, the battery B of the present invention has an increased cycle life and improved cycle characteristics as compared with the comparative batteries b1 to b4. This difference is due to the fact that LiC (C ₆ H ₅ SO ₂ ) ₃ [ Li
[Tritium (benzenesulfone) methide ].

[0024]

[Table 2]

Example 3 Nonaqueous Electrolyte Secondary Battery A mixed solvent of EC and 2-methyl-tetrahydrofuran (2Me-THF) (50:50 by volume) as a solvent constituting the electrolyte.
And LiC (CH ₃ C ₆ H ₄ SO ₂ ) ₃ [ lithium tri
(Toluenesulfone) methide ] was used in the same manner as in Example 1 to produce a battery. Thus, the battery C of the present invention was obtained.

On the other hand, as a comparative example, instead of LiC (CH ₃ C ₆ H ₄ SO ₂ ) ₃ as a solute in the battery C of the present invention, LiC (CF ₃ S
Batteries using O ₂ ) ₃ , LiClO ₄ , LiBF ₄ , and LiPF ₆ were produced, and were referred to as comparative batteries c1, c2, c3, and c4.

Table 3 shows the cycle life of these batteries. As is clear from Table 3, the battery C of the present invention has an increased cycle life and improved cycle characteristics as compared with the comparative batteries c1 to c4.

[0028]

[Table 3]

Example 4 Nonaqueous Electrolyte Primary Battery A flat nonaqueous electrolyte primary battery having the same structure as the flat nonaqueous electrolyte secondary battery shown in FIG. 1 was produced.

The positive electrode 7 uses manganese dioxide heat-treated at a temperature of 350 to 430 ° C. as an active material. The manganese dioxide, carbon powder as a conductive agent, and fluororesin powder as a binder are used. 85:10:
After mixing at a weight ratio of 5 and then press-molding this mixture, the mixture was heat-treated at 250 to 350 ° C. to produce a mixture.

On the other hand, the negative electrode 1 is produced by punching a rolled lithium plate into a predetermined size.

As an electrolytic solution, EC is used as a solvent.
And a mixture solvent of butylene carbonate (BC) and DME (volume ratio 20:20:60), and LiC (C ₆ H ₅ SO
₂ ) ₃ [ Lithium tris (benzenesulfone) methide ] dissolved at a rate of 1 mol / liter is used.
Thus, Battery D of the present invention was produced.

On the other hand, as a comparative example, the solute LiC (C ₆ H ₅ SO ₂ ) ₃ used in the battery D of the present invention was replaced with LiCF ₃ SO ₃
Comparative Battery d was prepared in the same manner except that (lithium trifluoromethanesulfonate) was used.

FIG. 2 shows the initial discharge characteristics of the battery D of the present invention and the comparative battery d, and FIG. 3 shows the discharge characteristics after storing them in a thermostat at 60 ° C. for 3 months. Each of these discharges is a constant resistance discharge of 300Ω.

As is clear from FIGS. 2 and 3, the battery of the present invention has a small capacity deterioration after storage and has excellent storage characteristics. In addition, as a result of measuring the internal impedance of the battery before and after storage at this time, as shown in Table 4, it was found that the battery D of the present invention showed a small increase in impedance due to storage.

[0036]

[Table 4]

(Embodiment 5) Here, the case where the solute concentration is changed in the non-aqueous electrolyte secondary battery will be described in detail.

First, as a solvent, a solute is dissolved in a mixed solvent (volume ratio: 50:50) of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) at a ratio of 1 mol / l. It was evaluated with the one that was made. The solute used here is Nmol / liter LiC (C ₆ H ₅ SO ₂ ) ₃ [ Li
Tritium (benzenesulfone) methide ] and 1-N
A mole / liter mixture of LiClO ₄ [lithium perchlorate] is used. Then, a non-aqueous electrolyte secondary battery similar to the battery A of the present invention was produced using these, and the cycle characteristics were compared. The charging and discharging conditions at this time were the same as those in Example 1. The result is shown in FIG.

Thus, LiC (C ₆ H ₅ SO ₂ ) as a solute
₃ [ Lithium tris (benzenesulfone) methide ]
It can be understood that the addition effect is exhibited at 0.05 mol / liter or more. This addition range was the same for other compounds represented by the formula of the present invention: LiC (RYOn) m .

In the examples of the present invention, various batteries have been described. As is clear from these results, the effect of the present invention can be obtained by the formula: LiC (RSO _n ) _m regardless of the type of the solvent used.
Wherein R is an alkyl group, an aryl group or a substituted product thereof (except that all hydrogen atoms to be substituted are fluorine atoms), and n and m are each an integer of 2 or more. It is based on using the compound as a solute.

[0041]

As described in detail above, in the nonaqueous electrolyte battery of the present invention, in the formula: LiC (RSO _n ) _m , R is
A kill group, an aryl group or a substituted product thereof (except that all hydrogen atoms to be substituted are fluorine atoms)
And a compound in which n and m are each represented by an integer of 2 or more is used as a solute, and the anion of this compound is excellent in stability as an ion, so that a radical having high reactivity even under a high voltage is used. And the like are not easily generated, which is effective in suppressing the decomposition reaction of the electrolytic solution. Therefore, an increase in the internal impedance of the battery due to storage can be suppressed, and storage characteristics can be improved. In addition, the cycle characteristics of the secondary battery can be improved, so that its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a battery of the present invention.

FIG. 2 is a discharge characteristic diagram before storage of a primary battery.

FIG. 3 is a discharge characteristic diagram after storage of a primary battery.

FIG. 4 is a charge / discharge cycle characteristic diagram of a secondary battery in which a solute concentration is changed.

[Explanation of symbols]

 Reference Signs List 1 negative electrode 2 negative electrode current collector 3 negative electrode can 4 insulating packing 5 positive electrode can 6 positive electrode current collector 7 positive electrode 8 separator D battery of the present invention d comparative battery

Continued on the front page (72) Inventor Ryuji Oshita 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Nobuhiro Furukawa 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric (56) References JP-A-2-37673 (JP, A) JP-A-5-74491 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 6/16

Claims (5)

(57) [Claims] 1. A non-aqueous electrolyte battery comprising a positive electrode, a negative electrode using lithium as an active material, and a non-aqueous electrolyte, wherein a compound represented by the formula (1) is added to a solute of the non-aqueous electrolyte. A non-aqueous electrolyte battery characterized by using at least one kind. Li C (RSO _n ) _m ‥‥‥‥‥ (1) where R is an alkyl group, an aryl group, or a substituted product thereof (however, all hydrogen atoms to be substituted are fluorine atoms) n , M: integer of 2 or more 2. In the above formula (1), R is CH ₃ , C ₂
H _5, phenyl, nonaqueous electrolyte battery according to claim 1, wherein the at least one selected from the group consisting of tolyl. 3. The non-aqueous electrolyte battery according to claim 1, wherein the compound represented by the formula (1) is lithium tris (benzenesulfone) methide or lithium tris (toluenesulfone) methide. . 4. The non-aqueous electrolyte battery according to claim 1, wherein the positive electrode is an oxide of at least one metal selected from the group consisting of manganese, nickel, cobalt, chromium, and vanadium. . 5. The non-aqueous electrolyte battery according to claim 1, wherein the negative electrode is made of lithium metal or an alloy, oxide, or carbon material capable of inserting and extracting lithium.