JP3078058B2 - Lithium 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 lithium battery using lithium metal as a negative electrode and an organic electrolyte, and more particularly, to a technical improvement for preventing ignition caused by thermal runaway due to overheating of the battery.

[0002]

2. Description of the Related Art As is well known, in a lithium battery, if a short circuit occurs externally for some reason, a very large current flows, and the inside of the battery generates heat, resulting in an abnormally high temperature. Also, when the battery is heated by mistake, the internal pressure of the battery increases. If this abnormal heat generation / gas generation state continues for a long time, the internal pressure of the battery may increase and the battery may burst or ignite. Therefore, the following countermeasures have conventionally been taken to prevent such a phenomenon.

The most common type is a safety valve type explosion-proof structure. A safety valve of various structures is provided in a part of the case of the lithium battery, and when the pressure inside the battery becomes abnormally high, the safety valve operates to release the gas inside.

The following technique is known as a measure for preventing heat generation due to overcurrent of a battery. Insert a thermal fuse made of a low melting point alloy into the current path in the battery,
A temperature sensitive resistor made of a positive temperature coefficient thermistor is interposed. When a large current flows through the battery due to some abnormality, the thermal fuse is blown and the current path is cut off, thereby stopping the battery discharge. In the case of the temperature-sensitive resistor, the resistance value increases rapidly due to heat generation, the discharge current is narrowed down, and the exothermic reaction is suppressed.

[0005]

The measures against overcurrent by the explosion-proof structure of the safety valve type, the temperature fuse or the temperature sensitive resistor described above are effective to prevent the heat generation of the lithium battery. Heat generation may not be completely prevented. In particular, when heat is applied from the outside, even if the safety valve operates to release gas or electrolyte from the battery, the temperature of the battery does not stop rising and the melting point (180 ° C) of metallic lithium as the negative electrode When it reaches, lithium melts and comes into contact with outside air, causing ignition.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object to prevent the ignition of a battery which could not be stopped by a conventional safety valve type explosion-proof structure or overcurrent prevention circuit, and to provide a lithium battery. To increase the safety of the vehicle.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention relates to a lithium battery using an organic electrolyte and using a negative electrode made of metallic lithium in an aluminum powder coated with a resin having a low melting point and being insoluble in the organic electrolyte. The body was dispersed and arranged on the surface or inside of the lithium anode.

[0008]

In a lithium battery employing the above structure, if the temperature inside the battery rises abnormally for some reason, the resin coating the aluminum powder melts at a temperature considerably lower than the melting point of lithium, and the internal aluminum The powder is exposed and comes into direct contact with the lithium anode. When lithium and aluminum come into contact with each other, a lithium-aluminum alloy is quickly produced at the contact portion. The melting point of lithium is about 180 ° C., whereas the melting point of lithium-aluminum is much higher. Therefore, the alloyed negative electrode is less likely to be melted, and a fire accident due to the melting of lithium is less likely to occur.

[0009]

FIG. 1 shows an embodiment of a cylindrical lithium battery having a spiral electrode structure to which the present invention is applied. In this battery, a power generating element 5 having a spiral structure is hermetically sealed together with an organic electrolytic solution 11 and an insulating bottom plate 10 in a cylindrical battery case including a negative electrode can 1, a positive electrode terminal plate 7 and a gasket 6. The power generating element 5 includes a strip-shaped separator 2, a lithium negative electrode 3, and a positive electrode 4, each of which is overlapped so that the separator 2 is sandwiched between the lithium negative electrode 3 and the positive electrode 4, and wound in a spiral shape. ing. The negative electrode 3 is a sheet of metallic lithium, and the negative electrode can 1 is connected to the negative electrode can 1 by a negative electrode lead plate 9. Manganese dioxide or the like is used as the positive electrode 4, and the positive electrode terminal plate 7 is connected to the manganese dioxide by a positive electrode lead plate 8.
In this embodiment, the gasket 6 and the positive electrode terminal plate 7 were used.
Incorporates the safety valve explosion-proof structure described above, but will not be described here.

The feature of this embodiment is that an aluminum powder 12 which is insoluble in the organic electrolytic solution 11 and whose entire surface is coated with a resin 13 having a low melting point is dispersed on the surface of the lithium anode 3. is there. Although the melting point of metallic lithium is about 180 ° C., a resin material having a melting point of about 120 ° C., which is much lower than the melting point of lithium, is used as the resin 13 for coating the aluminum powder 2. The aluminum powder 12 coated with the resin 13 is dispersed at an appropriate density on the surface of the lithium negative electrode 3 and spirally wound together with the separator 2 and the positive electrode 4 as described above.

When the lithium battery thus constructed generates heat or is heated and the temperature gradually rises, the resin coating 13 of the aluminum powder 12 starts to melt at about 120 ° C., and is covered with the resin coating 13. The exposed aluminum powder 12 comes into direct contact with the lithium anode 3. Then, a lithium-aluminum alloy is quickly generated at the contact portion between lithium and aluminum.

As shown in FIG. 2, the melting point of metallic lithium is about 180 ° C., but its melting point is higher than that of lithium alone due to lithium-aluminum alloying. As shown in detail in FIG. 2, for example, in an alloy of lithium 80 and aluminum 20 in atomic percent, the melting point is about
become. Therefore, even if the temperature of the battery becomes higher than the melting temperature of the coating resin film 13 and exceeds the melting point of metallic lithium, the surface of the lithium negative electrode 3 is formed into a lithium-aluminum alloy, and the melting point becomes significantly higher. Therefore, the negative electrode is hardly melted. As a result, ignition can be prevented.

The lithium battery of the embodiment of FIG. 1 described in detail above and the lithium battery of the prior art except for the aluminum powder 12 coated with the resin 13 in the embodiment of the present invention are the same as those of the conventional lithium battery. A heating test was performed as follows. A total of 20 test batteries were placed in a thermostat at 180 ° C. for 10 minutes. As a result, eight out of ten conventional batteries ignited, but the battery of this example did not ignite at all.

Next, another embodiment of the present invention will be described. In the embodiment of FIG. 3, an aluminum powder 12 coated with a resin 13 is dispersed at an appropriate density between two sheets of lithium and sandwiched in a sandwich shape, and a resin-coated aluminum powder is placed inside the lithium anode 3. 12 are distributed. Further, in the embodiment of FIG. 4, the punched metal 14 as a current collector is pressed on one side of the lithium anode 3, but in this case, the resin-coated aluminum powder 12 is embedded in the hole of the punched metal 14. Are distributed. Note that this method can also be used when a wire mesh or the like is used instead of the punched metal 14. Further, the present invention is not limited to the lithium battery having the spiral electrode structure as shown in FIG. 1, but can be applied to various lithium batteries such as an inside-out electrode structure.

[0015]

According to the lithium battery to which the present invention is applied,
When the battery temperature rises due to heat generation or heating, the coating resin of the aluminum powder melts at a temperature sufficiently lower than the melting point of metallic lithium as the negative electrode, the aluminum powder directly contacts the lithium negative electrode, and lithium- An aluminum alloy is produced. The melting point of the lithium-aluminum alloy is significantly higher than that of metallic lithium, and the negative electrode is hardly melted. As a result, the risk of ignition caused by the melting of lithium metal can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a cylindrical lithium battery having a spiral electrode structure according to an embodiment of the present invention.

FIG. 2 is a graph showing melting point characteristics of a lithium-aluminum alloy.

FIG. 3 is a sectional view showing a second embodiment of a method of dispersing and disposing an aluminum powder having a resin coating on a lithium negative electrode.

FIG. 4 is a sectional view showing a third embodiment of a method of dispersing and disposing an aluminum powder with a resin coating on a lithium anode.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Negative electrode can 2 Separator 3 Lithium negative electrode 4 Positive electrode 5 Power generation element 6 Gasket 7 Positive electrode terminal plate 8 Positive electrode lead plate 9 Negative electrode lead plate 10 Insulating bottom plate 11 Organic electrolyte 12 Aluminum powder 13 Coating resin film 14 Punched metal

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hidenori Nakura 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd. (72) Inventor Minoru Inagaki 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01M 19/40 H01M 4/02 H01M 4/62 H01M 6/16

Claims (1)

(57) [Claims] In a lithium battery using an organic electrolyte and using a negative electrode made of metallic lithium, an aluminum powder whose entire surface is coated with a resin having a low melting point which is insoluble in the organic electrolyte is used to remove the surface of the lithium anode or A lithium battery, which is dispersed and disposed inside.