JPH05326018A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To improve self-discharging properties during the storage of a lithium secondary battery in high temperature environment wherein the lithium secondary battery has a structure composed of a positive electrode of vanadium pentoxide, a negative electrode of a compound of lithium and niobium pentoxide, and an organic electrolytic solution used as an electrolyte. CONSTITUTION:A case 1 is used also as a positive electrode terminal, a sealing plate 2 which works also as a negative electrode terminal is sealed and insulated by a gasket 3 made of polypropylene, and a positive electrode 4 composed of 90% of vanadium pentoxide, 5% of carbon black, and 5% of fluororein is set in touch with the case 1. The negative electrode 5 prepared by giving lithium dope to a mixture of niobium oxide 90%, carbon black 5%, and fluororesin 5% through a separator 5 is set in touch with the sealing plate 2. The self- discharging property in high temperature environment is improved, using lithium perfluoromethylsulfonylimide as a lithium self for an electrolytic solution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode made of vanadium pentoxide, a negative electrode made of a compound of lithium and niobium pentoxide, and a lithium battery made of an organic electrolyte, which are used as a direct current power source for mobiles, a backup power source and the like. It relates to the next battery.

[0002]

2. Description of the Related Art Lithium secondary batteries using lithium as a negative electrode have a high energy density in principle, and have been attracting attention in recent years and are being actively developed.

However, the dendritic and mossy lithium dendrites generated in the lithium negative electrode during charge and discharge bring the positive electrode and the negative electrode into conduction, which causes a so-called internal short circuit of the battery. Moreover, since the negative electrode itself gradually collapses from its original shape and deteriorates, it is very difficult to maintain a long-term charge / discharge cycle life.

Therefore, as one of the solutions, it has been attempted to use a compound of lithium and niobium pentoxide for the negative electrode, and especially when lithium perchlorate is used as the lithium salt in the electrolyte. It is expected as a battery system that has a significantly improved discharge cycle life.

[0005]

However, in such a battery system using lithium perchlorate, when it is stored in a high temperature atmosphere in a fully charged state, the voltage drop due to self-discharge is caused in other lithium battery systems. In comparison, it is observed significantly. Although the mechanism of self-discharge is not clear, it is considered as follows. That is, vanadium pentoxide, which is the positive electrode, is partly eluted as vanadate ions into the electrolytic solution due to the high potential. The dissolved vanadate ions oxidize the negative electrode lithium-doped niobium pentoxide electrode, so that lithium ions are released from the negative electrode. It is believed that the lithium ions react with vanadium pentoxide to cause self-discharge.

It is known that the above characteristics are closely related to the type of lithium salt in the electrolytic solution, and several types of lithium salts for improving self-discharge characteristics have been proposed. One of them is a battery system using lithium trifluoromethanesulfonate, but it is the current situation that it cannot be a drastic measure because it shows deterioration of discharge load characteristics due to decrease of conductivity of electrolyte.

The object of the present invention is to provide an optimal electrolyte for this type of battery system.

[0008]

In order to solve this problem, the present invention uses lithium perfluoromethylsulfonyl imide (CF ₃ SO ₂ ) ₂ NLi as a lithium salt.

[0009]

[Operation] After assembling a battery system using lithium perfluoromethylsulfonylimide as a lithium salt in the electrolytic solution and then storing it in a high temperature atmosphere in a fully charged state and examining the self-discharge rate, the characteristics are remarkably improved. I understood. Moreover, the discharge load characteristics are the same as those in the case of using lithium perchlorate, which is good.

Although the reason for this effect is not clear, it is considered that when lithium perfluoromethylsulfonylimide is used as the lithium salt, the dissolution reaction of vanadium pentoxide, which is the positive electrode, was significantly suppressed during storage in a high temperature atmosphere. .. Further, the electrolytic solution containing lithium perfluoromethylsulfonyl imide as a lithium salt exhibits a conductivity similar to that of lithium perchlorate, and thus exhibits a good discharge load characteristic.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the structure of a coin-type lithium secondary battery of the present invention. As shown in the figure, a case 1 also serving as a positive electrode terminal and a sealing plate 2 also serving as a negative electrode terminal are insulated and sealed by a polypropylene gasket 3. The positive electrode 4 contains 90 wt% of vanadium pentoxide, 5 wt% of carbon black as a conductive agent, and 5 w of fluororesin as a binder.
The mixture is kneaded so as to have a weight ratio of t%, molded into pellets having a diameter of 15 mm and a thickness of 0.5 mm, dried at high temperature under vacuum, and dehydrated for adjustment. First, the negative electrode 5 is niobium pentoxide 9
0 wt%, carbon black 5 wt% as a conductive agent, and fluororesin a binder as a weight ratio of 5 wt% were kneaded and molded into pellets with a diameter of 15 mm and a thickness of 0.5 mm, and vacuumed at high temperature. Adjust by drying and dehydration.
A lithium foil having a diameter of 13 mm and a thickness of 0.1 mm was adhered to this mixture pellet, and a predetermined lithium salt was immersed in a propylene carbonate solution containing 1 mol / l to dope lithium into niobium pentoxide. .. Separator 6
Consists of a two-layer laminate of a polypropylene microporous membrane and a non-woven fabric. The electrolyte solution was prepared by dissolving lithium perfluoromethylsulfonyl imide at 1 mol / l in a solvent prepared by mixing propylene carbonate and 1,2 dimethoxyethane at a ratio of 1: 1 to prepare a battery (A) of the present invention. Battery size is diameter 2
The size is 0 mm and the thickness is 2.0 mm, and the capacity is 15 mAh in the voltage range of 2.0 V to 1.0 V. Next, as a comparative example, a comparative battery (B) using 1 mol / l of lithium perchlorate as a solute and a comparative battery (C) using 1 mol / l of lithium trifluoromethanesulfonate using the same battery structure and solvent. )made.

Next, the battery of the present invention (A) and the comparative battery (B),
Immediately after assembling (C), it was discharged at a constant current of 2 mA in a fully charged state, and the electric capacity up to 1.0 V was measured. Next, in the same way, each fully charged battery immediately after assembly is
Store in 60 ℃ atmosphere individually for 20 days, 40 days, 60
After four days, 80 days, and 100 days, four of each were taken out and discharged at a constant current of 2 mA, and the remaining capacity up to 1.0 V was measured and compared with the measured value immediately after assembly to determine the degree of self-discharge. I checked. The result is shown in FIG. As is clear from FIG. 2, by using lithium perfluoromethylsulfonylimide as the lithium salt, self-discharge is extremely suppressed and improved as compared with the case of using lithium perchlorate. Further, although the battery using lithium trifluoromethanesulfonate has good self-discharge characteristics, it was confirmed that the discharge capacity immediately after assembly was low and the discharge load characteristics tended to deteriorate.

[0013]

As is apparent from the above description of the embodiments, by using lithium perfluoromethylsulfonylimide as the lithium salt of the present invention, vanadium pentoxide can be used for the positive electrode and lithium and niobium pentoxide for the negative electrode. It is intended to provide a lithium secondary battery having excellent characteristics, in which the self-discharge characteristics of the used lithium secondary battery in a high temperature atmosphere can be improved without impairing the discharge load characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view of a coin-type lithium secondary battery according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the storage period at 60 ° C. and the remaining capacity.

[Explanation of symbols]

 1 case 2 Sealing plate 3 Gasket 4 Positive electrode 5 Negative electrode 6 Separator

Claims (1)

[Claims] 1. A structure in which an organic solvent in which a lithium salt is dissolved is used as an electrolytic solution, and vanadium pentoxide is used as a positive electrode and a compound of lithium and niobium pentoxide is used as a negative electrode in a charged state. - fluoromethyl sulfonyl imide (CF ₃ SO ₂₎ lithium secondary battery, which comprises using a ₂ NLi.