JP3036018B2 - Organic electrolyte battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an organic electrolyte battery.

2. Description of the Related Art Conventionally, an organic electrolyte battery generally uses metallic lithium for a negative electrode and is superior in terms of high voltage and high energy density as compared with other aqueous batteries. However, since the organic solvent has a significantly lower conductivity than the aqueous solution, the high rate discharge characteristics of the organic electrolyte battery are extremely poor.

The electrolyte of a conventional organic electrolyte battery is dimethoxyethane (hereinafter referred to as DME) in propylene carbonate (hereinafter referred to as PC) or ethylene carbonate (hereinafter referred to as EC) or a mixture of both.
LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF ₆ , LiSb
F _6, LiCF ₃ SO ₃ or LiCF ₃ CO ₃ which was added alone or mixed solute is used.

PC or EC which is a high dielectric constant solvent and DM which is a low viscosity solvent
When E is mixed, the following effects can be obtained. That is, PC and EC are excellent in that their dielectric constants are as high as 64 and 89, respectively, but are problematic in that their viscosities are as high as 2.53 cp and 1.8 cp, respectively. On the other hand, DME is excellent in that the viscosity is as low as 0.45 cp, but has a problem in that the dielectric constant is as low as 5.5. When these are mixed, a solvent having both a high dielectric constant, a low viscosity, and a high conductivity can be obtained, having both advantages.

However, DME has the following disadvantages. That is,
_{Recently, LiCoO 2, LiNiO 2, LiFeO} 2, but LiMnO ₂ or a positive electrode showing a very noble potential of 3.5Vvs.Li/Li ⁺ more such carbon electrode has come to be discussed, DME is as this When a positive electrode having a high potential is used, it is easily oxidized and decomposed, so that it cannot be used as an electrolytic solution.

The inventor has studied acetonitrile (hereinafter referred to as AN) as a new low-viscosity solvent replacing DME. AN is
Has better oxidation resistance than DME, and has a viscosity of 0.34c
Even lower than p and DME. However, AN has a disadvantage that it easily reacts with metallic lithium. Thus, the inventor has prevented the reductive decomposition of AN by using another negative electrode plate having a potential nobler than lithium instead of metal lithium which has been generally used as a negative electrode plate of an organic electrolyte battery in the past. I thought that. Then, it was found that the use of a negative electrode having a noble potential of 0.2 V vs. Li ^/ Li ⁺ or more can suppress the reductive decomposition of AN, and made practical use of the AN-based electrolyte possible. (Japanese Patent Application No. 2-131685).

However, further improving the conductivity of the electrolytic solution and further increasing the stability of the electrolytic solution are issues that should always be considered in improving the high-rate discharge performance and the life performance of the organic electrolyte battery. .

Means for Solving the Problems The present invention includes a negative electrode plate having a potential of 0.2 V vs. more noble than Li ^/ Li ⁺ , and the organic solvent is composed of two types of solvents, a solvent A and a solvent B, The solvent A is valeronitrile (hereinafter abbreviated as VN), butyronitrile (hereinafter abbreviated as BN),
Acetonitrile (hereinafter abbreviated as AN) + VN, AN + BN, VN +
BN, AN + VN + BN, and the solvent B is N-methylacetamide (hereinafter abbreviated as NMAA), N
-Methylpropionamide (hereinafter abbreviated as NMPA), N-
Methylformamide (hereinafter abbreviated as NMFA) + NMAA, NMFA
An object of the present invention is to solve the above-mentioned problem by using an organic electrolyte battery including an organic solvent selected from the group of + NMPA, NMAA + NMPA, and NMFA + NMAA + NMPA as an electrolyte.

Further, the object of the present invention is further facilitated by using an organic electrolyte battery comprising an electrolyte solution obtained by adding ethylene carbonate to the electrolyte solution.

The inventors studied an organic solvent having a relatively low viscosity and a larger difference in oxidation-reduction potential than that of AN. As a result, valeronitrile (hereinafter referred to as VN) and butyronitrile (hereinafter referred to as VN) were used. BN).
These organic solvents have a slightly wider potential range from the oxidation potential to the reduction potential than AN. Therefore, VN or BN AN
When used in place of or mixed with AN, the electrochemical stability of the electrolytic solution can be improved.

The inventor has for the first time found that the addition of PC or EC to AN, VN or BN results in a decrease in conductivity. This is an unexpected result from the conventional knowledge that the conductivity is improved when PC or EC is added to DME. The inventor
The cause was considered as follows. That is, PC and EC are DM
Although it has a sufficiently high dielectric constant as compared to E, it cannot be said that the dielectric constant is so high as compared to AN. For this reason, when PC or EC is added to AN, it is considered that the electrical conductivity is rather reduced due to the effect of increasing the viscosity as compared with AN alone. (However, the conductivity at low temperatures is improved by mixing.) The inventor has studied a new organic solvent that can be added to AN, VN or BN to improve the conductivity. As a result, N-methylformamide (hereinafter referred to as NMFA), N-methylacetamide (hereinafter referred to as NMAA) or N-methylpropionamide (hereinafter referred to as NMFA)
PA). These electrolytes have the disadvantage of high viscosity, but have a very high dielectric constant of 150 or more. The inventors have found that the conductivity of the electrolyte can be improved by mixing these organic solvents with AN, VN or BN.

Further, the inventors have found that reduction resistance performance is improved by adding EC to an electrolytic solution obtained by mixing AN, VN or BN and NMFA, NMAA or NMPA. That is, as shown in detail in Examples, it was found that the addition of EC has an effect of suppressing the deterioration of the electrolytic solution.

Examples Hereinafter, the present invention will be described using preferred examples.

Using LiCoO ₂ as the positive electrode active material and an aluminum alloy as the negative electrode active material, a button type organic electrolyte battery having the internal structure shown in FIG. 1 was prototyped in the following manner.

70 wt% LiCoO ₂ , 20 wt% acetylene black and
10 wt% of polytetrafluoroethylene (PTFE) was mixed to prepare a positive electrode mixture. Then, 0.50 g of this positive electrode mixture was collected, wrapped in a 325 mesh stainless steel (SUS316) wire mesh, and a positive electrode plate pellet having a diameter of 12 mm and a thickness of 2.1 mm (1)
Was prototyped. The discharge capacity of the positive electrode plate pellet is 50 mAh, assuming that 0.5 mol of lithium is inserted and released.

Al (92wt%)-Li (2wt%)-Si (5wt%)-Mn (1wt
%) The alloy was processed into a powder having an average particle size of 8 microns by a gas atomizing method. Then, 0.20 g of this aluminum alloy powder was collected, wrapped in a 180 mesh nickel wire mesh, and a negative electrode plate pellet (2) having a diameter of 10 mm and a thickness of 1.9 mm was prototyped. The potential of this aluminum alloy is about 0.3 V higher than lithium.

A microporous separator (3) was prototyped by punching a polyethylene microporous membrane having an average thickness of 23 microns having a non-porous portion in the form of veins and a perforated portion in which holes were three-dimensionally arranged to a diameter of 14 mm. . Also, a nonwoven fabric separator (4) having an average thickness of 0.2 mm was punched out by punching a polypropylene nonwoven fabric into 12 mm. These are impregnated with the electrolyte solution described below under vacuum, and then laminated as shown in FIG. 2 to form a positive electrode can (5) and a negative electrode can (6) made of a contact-resistant stainless steel plate, and an insulating gasket made of polypropylene (7). A button-type organic electrolyte battery with a diameter of 15.4 mm and a thickness of 4.8 mm was housed in a battery case consisting of

The following seven types were used as electrolytes. That is, 1.2M
_{LiAsF 6 /BN+NMAA(1:1),1.2M LiAsF 6 / VN +} NMAA (1:
1), 1.2M LiAsF _{6 /} AN + BN + NMAA (1: 1: 2), 1.2M LiAsF
₆ / BN + NMPA (1: 1), 1.2M LiAsF ₆ / AN + VN + NMPA (1: 1:
2), 1.2M LiAsF ₆ / BN + NMAA + EC (2: 1: 1) or 1.2ML
iAsF ₆ / BN + NMFA + NMPA + EC (3: 1: 1: 1). Organic electrolyte batteries using these batteries are referred to as batteries 1, 2, 3, 4, 5, 6, and 7 according to embodiments of the present invention, respectively.

A battery using 1.2 M LiAsF ₆ / AN + EC as the electrolyte is referred to as Battery A for comparison. Battery B for comparison is the same battery as battery 1 according to the present invention except that lithium metal having a diameter of 10 mm and a thickness of 2 mm was used for the negative electrode plate.

FIG. 2 shows the results of comparing the discharge current density-dependent performances of the discharge capacities of these batteries. As is clear from the figure, the battery according to the present invention has a larger capacity at the time of high-rate discharge than the battery A. That is, AN, VN or BN and NMFA, NMAA or
Electrolyte mixed with NMPA or these electrolytes
Organic electrolyte battery with electrolyte mixed with EC is AN + EC
High rate discharge performance is superior to a battery provided with an electrolytic solution. The battery of the present invention is superior in the high-rate discharge performance as compared with the battery B. This is because the effective working area of the negative electrode is increased by using the powdered negative electrode plate. It is thought that there is.

Next, after charging the above battery to 4.0 V at 2 mA,
It was subjected to a cycle life test of discharging to V. FIG. 3 shows the change in the discharge capacity with the progress of the cycle.

As is clear from the figure, the battery B has a significantly shorter cycle life than the battery of the example and the battery A for comparison. This is considered to be due to the fact that the metal lithium of the negative electrode reacted with the AN, resulting in a decrease in the capacity of the battery.

Also, the batteries 2 and 3 according to the examples of the present invention have a smaller tendency to decrease in capacity as compared to 1. This is considered to be due to the fact that the electrochemical stability of the electrolyte solution to which VN or BN is added is superior to the electrolyte solution not using these.

Also, the batteries 6 and 7 have an excellent cycle life as compared with other batteries. This is considered to be due to the fact that reductive decomposition of the electrolytic solution is suppressed by the addition of EC.

From the above results, it is understood that the organic electrolyte battery of the present invention is significantly superior in high-rate discharge performance and cycle life performance as compared with the conventional battery.

In the present invention, an electrode having a potential 0.2 V or more noble than lithium is used for the negative electrode. This may be an aluminum alloy negative electrode as in the embodiment, or may be a carbon negative electrode, a lithium lead alloy negative electrode. Alternatively, a tungsten dioxide negative electrode or the like may be used. Further, a negative electrode plate in which polyparaphenylene is added to the negative electrode may be used. Further, in the embodiment of the present invention, LiCoO ₂ is used for the positive electrode active material,
LiNi showing a high potential of 3.5 V vs. Li ^/ Li ⁺ or more like LiCoO ₂
O ₂ , LiNi _1-x Co _x O ₂ , LiFeO ₂ , LiMn ₂ O ₃ or a carbon positive electrode plate may be used. Of course, a relatively low-potential positive electrode active material such as MnO ₂ , V ₂ O ₅ , or TiS ₂ may be used. In the examples, all the electrolytes use LiAsF ₆ for the electrolyte.
ClO ₄ , LiPF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ or LiCF ₃ CO ₃ may be used alone or in combination.

Effect of the Invention The present invention can significantly improve the high rate discharge performance and cycle life performance of an organic electrolyte battery, and its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a schematic view of the internal structure of a battery according to an embodiment of the present invention. FIG. 2 is a diagram comparing the high-rate discharge performance between the battery of the present invention and a conventional battery. FIG. 3 is a diagram comparing the cycle life performance of the battery of the present invention and a conventional battery.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 10/40 H01M 6/16

Claims (2)

(57) [Claims] 1. A negative electrode plate having a potential nobler than 0.2 V vs. Li ^/ Li ⁺ , wherein an organic solvent is composed of two kinds of solvents, a solvent A and a solvent B, wherein the solvent A is valeronitrile (Hereinafter abbreviated as VN), butyronitrile (hereinafter abbreviated as BN),
Acetonitrile (hereinafter abbreviated as AN) + VN, AN + BN, VN +
BN, AN + VN + BN, and the solvent B is N-methylacetamide (hereinafter abbreviated as NMAA), N
-Methylpropionamide (hereinafter abbreviated as NMPA), N-
Methylformamide (hereinafter abbreviated as NMFA) + NMAA, NMFA
An organic electrolyte battery comprising an organic solvent selected from the group of + NMPA, NMAA + NMPA, and NMFA + NMAA + NMPA as an electrolyte. 2. An organic electrolyte battery comprising the electrolyte according to claim 1 and ethylene carbonate added thereto.