JP2957690B2 - Non-aqueous electrolyte battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte battery, and more particularly to a positive electrode thereof.

(B) Conventional technology Generally, non-aqueous electrolyte batteries are becoming widespread in a wide range of fields such as a memory backup power supply and a camera power supply because of their high voltage and high energy density. Such non-aqueous electrolyte electricity uses active lithium and organic electrolytes, and therefore, sufficient care is taken to ensure reliability.

Since the positive electrode of such a battery has a large resistance of an active material constituting the positive electrode, carbon powder has conventionally been added as a conductive agent. The material of the carbon powder is roughly classified into diamond, graphite, and amorphous carbon.
Here, diamond is an sp ³ type bond having four bonds in the direction of the apexes of the tetrahedron. On the other hand, graphite and amorphous carbon are composed of a plate-like body in which carbon atoms are firmly bonded in a ring and layers formed on a hexagonal mesh plane are stacked one on top of the other (sp ² type bonding). Graphite is a large parallel arrangement of the bodies, and amorphous carbon is extremely small in width and thickness of the plate-like bodies.

As the conductive agent of the positive electrode active material, graphite and carbon black, which is a kind of amorphous carbon, are widely used.

By the way, when graphite is used as a conductive agent, lithium enters into crystalline graphite when the battery is overdischarged, and a compound of lithium and carbon (C ₆ Li) is generated on the graphite surface. It is said that this compound becomes an active site and decomposes the electrolytic solution.

In addition, when carbon black is used as a conductive agent, lithium is not introduced because the carbon black is amorphous, but carbon black itself has a BET surface area based on the BET formula representing gas adsorption on a solid surface. Is as large as 50 to 5000 m ² / g, it is known that a terminal group of carbon (OH group, OOH group, etc.) becomes an active site and decomposes the electrolytic solution.

(C) Problems to be Solved by the Invention However, when the carbon powder is added to the positive electrode as in the above-described prior art, the battery becomes overdischarged and the potential of the positive electrode becomes
If the voltage is lower than 0.5 to 0.6 V (potential between Li ⁺ / Li), decomposition of the electrolytic solution on the carbon powder may occur, and gas may be generated. As a result, blistering or leakage of the battery may occur. There was a problem of inviting.

The problem to be solved by the present invention is to provide a non-aqueous electrolyte battery which is excellent in reliability at the time of overdischarge of a battery and further has excellent cycle characteristics when used as a secondary battery in view of the problems of the conventional technology. It is to be.

(D) Means for Solving the Problems The present invention provides a non-electrode comprising a negative electrode made of lithium or a material capable of storing and releasing lithium, a positive electrode, and an electrolytic solution made of an organic solvent and a solute. In the aqueous electrolyte battery, the positive electrode has a BET surface area of 1 as a conductive agent.
An amorphous carbon material of 0 m ² / g or less is added.

Preferably, the amorphous carbon material is coke.

(E) Action When an amorphous carbon material having a BET surface area of 10 m ² / g or less is used as a conductive agent for the positive electrode, decomposition of the electrolyte during overdischarge of the battery is suppressed, and the blister of the battery is suppressed. You.

(F) Example Hereinafter, an example of the nonaqueous electrolyte battery of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a nonaqueous electrolyte battery (primary battery) of the present invention.

In FIG. 1, a negative electrode 1 made of lithium metal is pressed against the inner surface of a negative electrode current collector 2. It is stuck to.

A peripheral end of the negative electrode can 3 is fixed inside a polypropylene insulating packing 4, and a positive electrode made of stainless steel and having a U-shaped cross section in a direction opposite to the negative electrode can 3 is provided on the outer periphery of the insulating packing 4. The 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 current collector 6.

A separator 8 impregnated and held with an electrolyte is interposed between the positive electrode 7 and the negative electrode 1.

In the above configuration, the positive electrode 7 uses manganese dioxide heat-treated in a temperature range of 350 to 430 ° C. as an active material,
This manganese dioxide, a carbon material powder as a conductive agent, and a fluororesin powder as a binder were mixed at a weight ratio of 85: 10: 5, and the mixture was pressed and then molded at 200 to 350 ° C.
And heat-treated.

On the other hand, the negative electrode 1 is made by punching a lithium plate having a thickness of 1 mm into a predetermined size.

The electrolyte was prepared by dissolving 1 mol / mol of LiCF ₃ SO ₃ as a solute in a mixed organic solvent obtained by mixing propylene carbonate (PC) and dimethoxyethane (DME) at a ratio of 5: 5. Using.

In addition, the battery diameter of the assembled battery is 20 mm, and the battery thickness is 2.
5 mm, the battery capacity was 130 mAH.

By the way, the battery A of the present invention and the comparative batteries X and Y were respectively manufactured using three kinds of carbon material powders as a conductive agent added to the positive electrode 7 in the following table.

<Table> After short-circuiting each of the batteries A, X, and Y at room temperature for one minute, the battery thickness of each of these batteries was measured. As a result, in the battery A of the present invention, the battery thickness did not change and no swelling of the battery was observed.
The increase was 0.3 mm and that of the comparative battery Y was 0.1 to 0.2 mm, and slight swelling was observed in each of the batteries.

The initial high-rate discharge characteristics of the batteries A, X, and Y and the high-rate discharge characteristics after short-circuiting for one hour were measured. These results are shown in FIGS. 2 and 3, respectively. Note that the discharge conditions were through a constant resistance (load: 300Ω) at 25 ° C.

Referring to FIG. 2, there is no difference between the battery A of the present invention immediately after charging and the comparative batteries X and Y, and the discharge time until the battery voltage reaches 2.0 V is 10.7 hours. However, as shown in FIG. 3, the battery of the present invention after a short circuit for one hour has a battery voltage of 2.
It can be seen that the discharge time until the voltage drops to 0 V is 10.5 hours, which is longer than the comparative battery X of 8.5 hours and the comparative battery Y of 9.9 hours.

The BET surface area of amorphous carbon materials was also studied. Batteries were assembled using amorphous carbon materials having various BET surface areas, and each battery was measured for discharge time until the battery voltage dropped to 2.0 V in a discharge after short-circuiting for one hour. The result is shown in FIG. A battery having a BET surface area of 10 m ² / g has a long life of 10.5 hours even after a short circuit, but a battery having a BET surface area of more than 20 m ² / g has a life of 10.2 hours. Moreover, it was found that the decrease was remarkable as the surface area increased. Thus, a battery using an amorphous carbon material having a BET surface area of 10 m ² / g or less is most desirable in terms of discharge characteristics.

Therefore, as described above, it is amorphous and has a BET surface area of 10 m ² /
When coal coke is used as a conductive agent for the positive electrode 7 as a carbon material having a capacity of less than g, almost no deterioration in discharge characteristics is observed in the discharge after short-circuiting for one hour as compared with a battery immediately after assembly, and a highly reliable battery is obtained. It is understood that it can be done.

Next, a non-aqueous electrolyte battery (secondary battery) will be described. The structure of this battery is the same as that of the flat battery shown in FIG.

In the case of such a battery, a chargeable / dischargeable manganese oxide is used as an active material of the positive electrode 7. In addition, propylene carbonate (PC) and ethylene carbonate (E
C) was mixed at a ratio of 5: 5, and a mixed organic solvent obtained by dissolving 1 mol / mol of LiPF ₆ as a solute was used. Further, a lithium-aluminum alloy was used for the negative electrode 1.

Here, as the conductive agent added to the positive electrode 7, batteries were assembled using coal coke, graphite, and carbon black in the same manner as in the case of the primary battery, and these were assembled with the battery B of the present invention, the comparative batteries P and Q, respectively. did.

Immediately after assembly and at room temperature (25
C.) for 1 hour, and a cycle test was performed, respectively, and the results shown in FIGS. 5 and 6 were obtained. The conditions in this cycle test were 3 hours at a charge / discharge current of 2 mA, and the time when the battery voltage reached 2.0 V within the discharge time was defined as the life of the battery.

As shown in FIG. 5, the batteries B, P, and Q immediately after assembly have almost the same life, and reach the battery voltage of 2.0 V at the 270th cycle. On the other hand, in the battery after short-circuiting for one hour, the battery B of the present invention reaches the battery voltage of 2.0 V at the 255th cycle, whereas the comparative battery P has the 205th cycle and the comparative battery Q has the 235th cycle. Life has been shortened.

As described above, the battery B of the present invention using coal coke as a conductive agent did not deteriorate in cycle characteristics even immediately after assembling even after short-circuiting for one hour, and a highly reliable secondary battery was obtained.

(G) Effect of the Invention As described above, the present invention is intended to prevent the deterioration of discharge characteristics during overdischarge in a primary battery by adding amorphous carbon having a BET surface area of 10 m ² / g or less to the conductive agent of the positive electrode. In addition, the effect of suppressing the deterioration of the cycle characteristics at the time of overdischarge is expected in the secondary battery, and any of the batteries has the effect of providing a highly reliable non-aqueous electrolyte battery.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the non-aqueous electrolyte battery of the present invention, FIG. 2 is a discharge characteristic diagram immediately after assembly, FIG. 3 is a discharge characteristic diagram after short-circuit, and FIG. FIG. 5 is a diagram showing the surface area and discharge time, FIG. 5 is a cycle characteristic diagram immediately after assembly, and FIG. 6 is a cycle characteristic diagram after a short circuit. 1 ... Anode, 2 ... Anode collector, 3 ... Anode can, 4 ...
Insulation packing, 5: positive electrode can, 6: positive electrode current collector, 7
... positive electrode, 8 ... separator.

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-60-258860 (JP, A) JP-A-63-218161 (JP, A) JP-A-62-17951 (JP, A) JP-A-4-171677 (JP, A) A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01M 4/02 H01M 4/06 H01M 4/62 H01M 6/16

Claims (2)

(57) [Claims] 1. A non-aqueous electrolyte battery comprising: a negative electrode made of lithium or a material capable of storing and releasing lithium; a positive electrode; and an electrolyte solution comprising an organic solvent and a solute. Is a non-aqueous electrolyte battery characterized by adding an amorphous carbon material having a BET surface area of 10 m ² / g or less as a conductive agent. 2. The non-aqueous electrolyte battery according to claim 1, wherein said amorphous carbon material is coke.