JPS63205049A - Lithium battery - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to improving the safety of lithium batteries using non-aqueous solvents as electrolytes.

BACKGROUND OF THE INVENTION Lithium batteries using a non-aqueous solvent as an electrolyte have high energy density, excellent storage performance, and a wide operating temperature range, and are therefore used in many fields.

Among these batteries, a so-called lithium-thionyl chloride battery using thionyl chloride as an anode active material is attracting attention because of its high energy density.

By the way, this type of battery may be used as a single cell, or a plurality of cells may be connected in series or in parallel to form an assembled battery having the required voltage and capacity.

Unless there is a large variation in the capacity of the cells built into an assembled battery, the capacity of the assembled battery is usually dominated by the cell with the lowest capacity, or there are very few cells that are extremely over-discharged. be. However, since the capacity of such secondary batteries cannot be known in advance, batteries with extremely small capacities may occasionally get mixed up in assembled batteries. Depending on the number of cells connected in series in the assembled battery, or the device incorporating the assembled battery or the minimum voltage required for the battery, that is, the final voltage, the capacity may be extremely small or the cells may be mixed together. When discharging an assembled battery, the single cell is often over-discharged.

It is known that when a lithium-thionyl chloride battery is discharged, the battery temperature rises rapidly at the end of discharge. If the internal temperature of the battery exceeds 186"C, which is the melting point of lithium, the battery will react directly with lithium or thionyl chloride and explode. In order to prevent such explosions, conventional methods have been used to prevent such explosions, as shown in Figure 4.
Connect one diode L to each cell 2 in parallel, and if an extremely small capacity battery is mixed in, it will be over-discharged and the two-ener voltage of diode L will be about -0.8V. When it comes to below.

A method of reducing the amount of current flowing through this current by causing part of the current flowing through the battery to flow through the diode L, and connecting a resistor 3 in series with the cell 2 as shown in Figure 1. A method has been adopted in which only enough current is drawn out to prevent an explosion even if the single cell 2 with a small capacity is over-discharged, or a method in which the two are combined.

Problems to be Solved by the Invention Among the above problems, even if the method of connecting a diode l in parallel to each cell 2 is used, for example, a wound type D-type lithium
Discharge a thionyl chloride battery with a current of 0.30A! , the battery temperature rises rapidly at the end of discharge and reaches 120°C before reaching 10.8V, which is the voltage across diode 1. On the other hand, this temperature decreases below -0.8V. Since 120°C is the surface temperature of the battery, the internal temperature must be higher than that, so there is a high possibility of explosion, and safety remains a problem.

On the other hand, by connecting a resistor 3 in series with the cell 2 and reducing the current that can be applied, our experiments have confirmed that even if the assembled battery contains a battery with an extremely small capacity, it will not explode. In the case of a battery assembly consisting of four of the above-mentioned wound type D-type lithium-thionyl chloride batteries connected in series, 5.
Ω is the minimum value of this resistance, and if it becomes smaller than this value, the possibility of explosion increases if this resistance is small, although it depends on the resistance of the external load. The practical maximum load current of this assembled battery connected to a 5Ω resistor is about 0.5A, and it has the disadvantage that it cannot be used for applications requiring a larger current.

Means for Solving the Problems The present invention eliminates the above-mentioned drawbacks by connecting a humidity switch in series to each of a plurality of lithium cells connected in series to form a unit cell. A diode is connected in parallel with the battery.

Function: Even if a cell with an extremely small capacity is present in the assembled battery having the circuit of the present invention, the temperature that rises at the end of discharge of this cell can be detected by a temperature switch.

At the same time as this part is electrically disconnected, all of the current that previously flowed through this small capacity battery flows through the diode connected in parallel with this battery, preventing over-discharge of this battery and preventing an explosion. This will prevent such worst-case situations from happening.

Example: In a 24ViM cell in which eight wound-type D-type lithium-thionyl chloride batteries are connected in series, one of the eight batteries has a 7Ah capacity with the number of batteries intentionally reduced, and the remaining seven batteries have normal capacity. Using 10Ah batteries having 10Ah, each individual battery was connected in series with a 100°C temperature fuse in close contact with the battery, and a diode 1 was further connected in parallel to make a prototype battery. This is called assembled battery A. 7A with this prototype battery
The battery h corresponds to a particularly small capacity battery.

On the other hand, 8 batteries identical to those used in battery pack A were connected in parallel with each battery without using a temperature fuse, and a diode 1 was connected.
For comparison, we made a prototype of a conventional assembled battery connected to This is called assembled battery B.

A thermal lightning pair was attached to each assembled battery so that the temperature of the cell surface could be measured.

Typical results when battery pack A and battery pack B were discharged under a load of 50% are shown in FIGS. 2 and 3. In FIGS. 2 and 3, A is the voltage of the assembled battery, and B is the temperature of a single battery with a small capacity. FIG. 3 shows the results of an exploded battery, which will be described later.

In all of the battery packs, a snow field of 4.5 A flowed at the beginning of discharge, and the voltage suddenly decreased from 1 hour and 30 minutes after discharge, and decreased by 2.5 V or more at 1 hour and 50 minutes. This suggests that the discharge of a cell with low capacity has been completed. Assembled battery A no longer showed a sudden voltage drop at this point, while assembled battery B's voltage gradually decreased after that.
Ten rags exploded 2 hours and 10 minutes after the start of discharge.

Looking at the temperature on the battery surface, the temperature of the 7Ah battery rose rapidly as the voltage decreased, and rose to 100"C after 1 hour and 50 minutes. After that, the temperature of assembled battery A stopped rising, and the temperature tended to drop gradually. On the other hand, the temperature of assembled battery B was even higher, and one of the batteries exploded at 130°C.The surface temperature of the battery at the time of the explosion was 130°C, but the internal temperature was at the melting point of lithium. I think that it may have reached a certain 186°C.The temperature fuse was cut when the surface temperature of all the small capacity cells in the assembled battery AIO thin cloth reached 100°C, so over-discharging could not be more than that. Proceed (
It is assumed that the explosion was prevented. Note that 4 is a temperature switch.

Effects of the Invention As described above, according to the present invention, even if a cell with an extremely low capacity is mixed in an assembled battery in which a plurality of lithium cells are connected in series, explosion during high rate discharge can be prevented. Its industrial value is enormous.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an assembled battery having an explosion prevention circuit according to the present invention, and FIGS. 2 and 3 are curve diagrams showing discharge test results of assembled batteries having an explosion prevention circuit according to the present invention and a conventional explosion prevention circuit. , 4 and 5 are circuit diagrams of an assembled battery having a conventional explosion prevention circuit. l is a diode, 2 is a cell, 4 is a temperature switch

Claims (1)

[Claims] 1. In an assembled battery in which two or more cells using lithium as a cathode and a nonaqueous solution as an electrolyte are connected in series, a diode is connected in parallel with each cell, and at the same time the outer wall of each cell is It is characterized by having a circuit in which a temperature switch is provided in contact with the cell, and when the temperature switch is turned off due to an increase in the temperature of the outer wall of the cell, all of the current flowing through the cell flows through a diode connected in parallel with the temperature switch. Lithium battery. 2. The lithium battery according to claim 1, wherein the temperature switch is a temperature fuse. 3. The lithium battery according to claim 1, wherein the temperature switch is a bimetallic thermostat.