JPS61206179A - Series connection circuit of lithium secondary battery - Google Patents

Abstract

PURPOSE:To stabilize battery performance when batteries are connected in series by connecting a diode in parallel for stabilizing voltage to each battery connected in series. CONSTITUTION:A plurality of rechargeable batteries B having lithium as negative active material are connected in series, and a diode D such as Zener diode or light emitting diode is connected in parallel to each battery for stabilizing voltage. Even when voltage is concentrated on one battery by some accidents, current corresponding to excessive voltage branches to the diode and overcharge is prevented. At the same time, an action to charge battery is applied to other battery and both batteries are charged all together. Therefore, charging characteristics of each battery are stabilized and life of batteries are increased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a circuit configuration using rechargeable lithium secondary batteries connected in series.

Conventional technology Generally, when using secondary batteries connected in series.

Directly connect the ■terminal and eterminal of battery B by welding them with a lead plate.
It was customary to use it as shown in Figure 8. However, with this method of use, the voltage of the battery with the smallest electric capacity drops first at the end of discharge, exceeding OV, and enters a negative region, resulting in a so-called polarity inversion state. Also, when charging, the battery with the smallest electric capacity will finish charging faster,
The battery becomes overcharged until all the batteries are fully charged.

Since these phenomena significantly shorten the life of the battery, the following measures have been taken for N1-cd storage batteries and the like.

In other words, it is necessary to check the electrical capacity of the batteries in advance and combine batteries with almost the same electrical capacity, and to equip batteries with an undercut circuit to prevent over-discharging. charge,
It used the so-called trickle charging method.

These countermeasures are very troublesome in terms of battery manufacturing and circuit configuration, and increase the cost of the battery, which is not a desirable situation, but it is an unavoidable measure.0 Also, as a charging method, there is a constant voltage charging method. However, this is to prevent overvoltage charging at the end of charging. However, this is fine for single batteries, but when multiple batteries are connected in series, the charging voltage is not necessarily distributed evenly to each battery, especially at the end of charging.
There was a tendency to become unbalanced.

On the other hand, recently, rechargeable batteries with lithium as an anode, that is, lithium secondary batteries, have been attracting attention, but because they use a non-aqueous electrolyte, they have a high decomposition voltage, and their storage characteristics and charging efficiency are lower than that of conventional batteries. It is expected that it will be much better than the next battery. Additionally, since it is extremely sensitive to moisture, it is completely sealed. For these reasons, when lithium secondary batteries are connected in series, the above-mentioned problems are more likely to occur, and voltage balance at the end of charging becomes a problem, requiring more sophisticated control than υ.

Problems to be Solved by the Invention Among lithium secondary batteries, battery systems that use activated carbon for the positive electrode and lithium alloy for the negative electrode are particularly affected, so this system will be specifically explained.

The discharge characteristics of this battery are as shown in FIG. 2, and when charging this battery, it can be charged using a constant voltage method.

For example, if you charge with a charging voltage of 3V, after charging is completed the voltage will be 3V.
Start the discharge. Also, when charging at 2.7V, discharging starts at 2.7V. Therefore, in the case of a single battery, the battery voltage can be accurately defined by setting the charging voltage. However, when two cells of this battery are connected in series and charged at 6V, each battery v'
It is not necessarily divided equally by c3V. This may vary slightly due to differences in internal resistance and capacitance of each battery.
As ab and ab are repeatedly charged and discharged, the difference between the two becomes greatly expanded, and eventually an overvoltage is applied to one of the batteries, leading to deterioration of battery performance.

The present invention aims to solve such problems during charging and to stabilize battery performance even when lithium secondary batteries are connected in series.

In order to solve the problem, in the present invention, a diode element for voltage regulation is connected in parallel to each battery connected in series.

A Zener diode, a light emitting diode, or the like may be used as the diode element for voltage constantization here.

FIG. 1 shows the circuit configuration, where B is a lithium secondary battery and C is a diode element connected in parallel to each battery.

The charging/discharging circuit when the functional lithium secondary batteries B are connected in series is as shown in Figure 7, but if no constant voltage is provided, the charging/discharging characteristics of each battery become unbalanced, as shown in Figure 6C ,■
However, if a constant voltage circuit is installed, Figure 6, B
As a result, the charging and discharging characteristics of each battery are uniform and stabilized.

This means that even if the charging voltage tries to concentrate on one battery due to some effect during charging, the current corresponding to the excess voltage is shunted to the diode element to prevent overcharging, and in the meantime, the other uncharged battery is sufficiently charged. This is because the charging action works, and as a result, all the batteries are charged together.

The voltage set by the diode element must be set to a voltage below which the battery characteristics do not deteriorate (hereinafter referred to as withstand voltage), and must be selected to match the operating voltage of the circuit in use.

For example, if the withstand voltage of the battery is 3.5V"li, then 3.sV
The following constant voltage is used, and the circuit used is 5. If it is Ov, it is desirable to use a two-cell battery and a constant voltage circuit of 2.6V or more, which is half the voltage per battery.

When using a Zener diode as a diode element for voltage regulation, in the above example, a 3V type is used, and when using a light emitting diode, it is 1.6 volts per light emitting diode.
Since it has a constant voltage effect at ~1.7V, two connected in series can be used.

In this way, by connecting the constant voltage circuit to each battery in parallel, battery charging characteristics can be stabilized and battery life can be improved.

Example The present invention will be explained in detail below.

(Example 1) FIG. 3 shows a half-cut sectional view of a lithium secondary battery used in the present invention.

In the figure, 1 is a battery case made of stainless steel with a thickness of 0.25 mm and an outer diameter of 20 mm, 2 is a sealing plate made of stainless steel with a thickness of 0.25 mm, 3 is an alloy containing lithium as an active material, and 4 is activated carbon. 5 is a separator which is placed in a pot shape in a sealing plate and then impregnated with an organic electrolyte. 06 is an insulating sealing gasket that is insulated and sealed by caulking the battery case 2. .

The size of the battery is 20 mm in outer diameter and approximately 2.0 mm in height.

Using this battery B, a charging/discharging circuit shown in FIG. 4 is used to connect each battery in parallel with a Zener voltage of 3. OV zener diode 2
．． ．． 22 was connected. Of course, the same Zener diode is used for each battery. Let's call this a person.

In this charging/discharging circuit, the charging resistor R1 is set to 1Ω, and the discharging resistor R
The charging and discharging characteristics of each cell were measured for the 200th time under the conditions of charging voltage s, oV, charging time 4 hours, and discharging time 6 hours, with 2 okΩ.

(Example 2) In Example 1, a Zener diode was used, but instead, two light emitting diodes LED were connected in series and connected in parallel to each battery B, as shown in FIG. It was the same as 1, and the same test as humans was conducted. Let this be B.

For comparison, as shown in FIG. 7, the diode element was not used, and the other aspects were exactly the same as in Examples 1 and 2, and a person was tested.

I made the same comparison as B. Let this be C.

The results are shown in FIG. As is clear from Figure 6, the characteristics of batteries M and B are well matched and fall within the range of the solid line, whereas the characteristics of batteries C, which do not use diode elements,
In this case, the voltages of both batteries are largely separated during charging, and one battery (2) has a withstand voltage of 3.6V, which is much higher than that of the other battery, and its discharge characteristics are also deteriorated. In addition, since the charging voltage of battery (2) is low, it is not sufficiently charged and its discharge characteristics are deteriorated.

For these reasons, parallel connection of constant voltage circuits can stabilize battery charging.

Also, depending on the purpose of use, a resistor can be connected in series or parallel with the voltage regulator diode as a constant voltage circuit.Although activated carbon was used for the positive electrode in the example, titanium disulfide may also be used for the positive electrode. It is also effective for those using manganese oxide, etc.

Effects of the Invention As is clear from the above, according to the present invention, even when lithium secondary batteries are connected in series, stable and long-life charge/discharge cycles can be achieved.

[Brief explanation of drawings]

Fig. 1 is a series connection circuit diagram of the battery of the present invention, Fig. 2 is a diagram showing the discharge characteristics of the lithium secondary battery, Fig. 3 is a block diagram of the lithium secondary battery used in the present invention, and Fig. 4 is a diagram showing the discharge characteristics of the lithium secondary battery. A charging/discharging circuit diagram of the present invention when using a Zener diode, FIG. 6 is a charging/discharging circuit diagram of the present invention when using a light emitting diode,
FIG. 6 is a charging/discharging characteristic diagram of the present invention and a conventional case, FIG. 7 is a conventional charging/discharging circuit diagram, and FIG. 8 is a conventional battery series connection circuit. B...Battery, D...Diode element s
R1+ "2...Resistance, 1...Case, 2...Sealing plate, 3...Negative'hs
4...Positive electrode, 5...Separator, 6
・Old gasket. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Unexamined VJ B Figure 1 Food 4 Figure 4 Figure 5 LED-11 Death Guide

Claims (3)

[Claims] (1) A series connection circuit of lithium secondary batteries in which a plurality of rechargeable batteries each using lithium as a negative electrode active material are connected in series, and a diode element is connected in parallel to each battery. (2) A series connection circuit for lithium secondary batteries according to claim 1, wherein the diode element is a Zener diode. (3) A series connection circuit for lithium secondary batteries according to claim 1, wherein the diode element is a light emitting diode.