JP3148470B2 - Rechargeable battery charging method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for charging a secondary battery, and particularly to a method for rapidly charging a non-aqueous secondary battery.

[0002]

2. Description of the Related Art Among secondary batteries that can be used repeatedly, a lithium ion secondary battery, which is one of nonaqueous secondary batteries, has a high battery voltage (eg, 4.2 V), a high energy density, and a high energy density. It has excellent cycle characteristics and has recently been spotlighted. As a method for charging such a non-aqueous secondary battery, there is a constant current (or quasi-constant current) / constant voltage charging method as disclosed in JP-A-2-192670.

According to such a charging method, first, when the battery voltage of the secondary battery is lower than the constant voltage value of the charging power source, constant current charging (or quasi-constant current charging) is performed, and then the battery voltage is reduced to a predetermined voltage. (E.g., 4.2 V), constant-voltage charging with this predetermined voltage is performed thereafter. As the constant voltage charging proceeds, the charging current gradually decreases, and when the charging current decreases to a predetermined value, charging ends.

In charging such a non-aqueous secondary battery,
When performing rapid charging, it is conceivable to increase the current value of constant current (or quasi-constant current) charging in the initial stage.

[0005]

However, when performing rapid charging by increasing the current value, it is necessary to increase the rated output on the charger side as the current value increases.
This causes an increase in the size and cost of the charger. Furthermore, adverse effects such as a decrease in the reliability of the charger and the secondary battery due to thermal factors also occur. In addition, application of a large current may cause performance degradation of the secondary battery.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to rapidly charge a secondary battery without increasing the size, cost, and reliability of the battery charger, and without reducing the reliability and performance of the secondary battery. And

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method for charging a secondary battery, wherein the secondary battery is repeatedly charged at a constant voltage with a first voltage and a second voltage higher than the first voltage. The ratio of the constant voltage charging time by the second voltage to the constant voltage charging time by the voltage is substantially proportional to the charging current at the time of constant voltage charging at either the first voltage or the second voltage. It is characterized by.

[0008]

According to the charging method of the present invention, first, constant-current charging (or quasi-constant-current charging) of the secondary battery is performed, and the battery voltage reaches a predetermined voltage (for example, the second voltage of 4.3 V). When it reaches, thereafter, the constant voltage charging with the second voltage and the constant voltage charging with the first voltage (for example, 4.2 V) smaller than this are repeatedly performed.

At this time, the charging current of the secondary battery is detected, and as the charging current decreases, the ratio of the constant voltage charging time by the second voltage to the constant voltage charging time by the first voltage decreases. Charge the battery repeatedly. Then, when the charging current decreases to a predetermined value, charging ends.

[0010]

FIG. 1 shows a secondary battery B using the charging method of the present invention.
FIG. 2 is a block circuit diagram showing a charging circuit for charging the power supply.

Reference numeral 1 denotes a power supply circuit, which includes an input filter for removing noise contained in a commercial AC power supply of 100 V AC;
A rectifier circuit that converts input AC to DC, a switching unit that converts DC of the rectifier circuit to high-frequency AC, a conversion transformer that converts high-frequency AC to a predetermined voltage, and rectifies an AC output of the conversion transformer. And a well-known DC power supply circuit such as a rectifying / smoothing circuit for converting into a smooth DC.

Reference numeral 2 denotes a charge control circuit for controlling the power supply from the power supply circuit 1 such as on / off, and includes a constant voltage circuit 11 for generating a predetermined constant voltage; an arithmetic circuit 12 comprising a microcomputer; A current detection circuit 13 for detecting
A voltage detection circuit 14 for detecting a battery voltage of the secondary battery B;
It comprises a charge control switch 15 provided between the power supply circuit 1 and the secondary battery B.

The differential amplifier 11 constituting the constant voltage circuit 11
A has a negative input terminal connected to a voltage dividing resistor for dividing the battery voltage of the secondary battery B, and a positive input terminal connected to a first voltage (4 in this embodiment) via a switch SW. .2
V) or the second reference voltage source E that generates a second voltage (4.3 V in this embodiment).
2 connected.

The differential amplifier 11A compares the voltage of the negative input terminal (that is, the battery voltage of the secondary battery B) with the voltage of the positive input terminal (the first voltage or the second voltage). When the battery voltage becomes higher than the first voltage or the second voltage, the output of the differential amplifier 11A becomes negative and the control transistor T
The base current of R1 is drawn. Therefore, the output supplied via the control transistor TR1 is reduced. Otherwise, the output of the differential amplifier 11A is + and does not draw in the base current of the control transistor TR1. With this operation, the constant voltage circuit 11 supplies the first voltage or the second voltage to the secondary battery B.

The arithmetic circuit 12 controls the charge control switch 15 and the changeover switch SW based on the outputs of the current detection circuit 13 and the voltage detection circuit 14. The arithmetic circuit 12 has a built-in timer for counting a predetermined time.

An embodiment of the charging method of the present invention will be described below.
This will be described with reference to the flowchart of FIG. 2 and the graph of FIG. In this embodiment, the secondary battery B to be charged is a lithium ion secondary battery having a capacity of 1000 mAh.

First, in step S1, the secondary battery B
It is determined whether or not is attached to the charging device. When the secondary battery B is mounted, charging of the secondary battery B is started in step S2. This charging is performed at 1 A until the battery voltage of the secondary battery B reaches the second voltage (that is, 4.3 V).
, The changeover switch SW is set to the second reference voltage source E2 side, and under the control of the constant voltage circuit 11,
Shift to constant voltage charging at 4.3V.

In step S3, the value of the charging current which decreases with the constant voltage charging at 4.3V is detected, and the constant voltage charging at 4.3V is continued until the value becomes 500 mA or less. And the charging current is 500 mA
When the following occurs, in step S4, the changeover switch S
With W as the first reference voltage source E1 side, switching to constant voltage charging at 4.2V is performed. This constant-voltage charging at 4.2 V is performed for 3 seconds in step S5, and thereafter, in step S5.
At 6, the mode is switched to the constant voltage charging at 4.3V again.

The constant voltage charging at 4.3 V is performed for 10 seconds in step S7, and thereafter, in step S8, switching to the constant voltage charging at 4.2 V is performed again. Then, in step S9, it is determined whether the charging current is equal to or less than 300 mA. If not, the process returns to step S5, and constant voltage charging at 4.2V is performed for 3 seconds.

In other words, steps S3 to S9
Then, in the range where the charging current is 500 mA to 300 mA, the constant voltage charging at 4.2 V and the constant voltage charging at 4.3 V are repeatedly performed in a cycle of 3 seconds and 10 seconds.

Next, when the charging current becomes 300 mA or less, in steps S10 to S14, the charging current becomes 20 mA.
3. Constant voltage charging at 4.2 V until the current becomes 0 mA or less;
Constant voltage charging at 3 V is repeated at a cycle of 8 seconds and 5 seconds.

Further, when the charging current becomes 200 mA or less, in steps S15 to S19, the charging current becomes 10 mA.
3. Constant voltage charging at 4.2 V until the current becomes 0 mA or less;
Constant voltage charging at 3 V is repeated at a cycle of 10 seconds and 3 seconds.

If it is determined in step S19 that the charging current has become equal to or less than 100 mA, in step S20, the charging is completed, that is, the charging control switch 15 is turned off, and the charging is terminated.

As described above, in the present embodiment, when the battery voltage of the secondary battery B reaches 4.3 V, the battery voltage becomes 4.
The constant voltage charging with 3 V and the constant voltage charging with 4.2 V are repeatedly performed. At this time, the charging current of the secondary battery is detected. The ratio of the constant voltage charging time at 4.3 V is reduced. Thus, in the first half of charging, the ratio of the constant voltage charging time at 4.3 V is increased, thereby shortening the charging time of the secondary battery B. By increasing the ratio of the constant voltage charging time by 0.2 V, overcharge deterioration of the secondary battery is prevented.

In the above embodiment, the charging current is 500
After constant voltage charging at 4.3 V is continuously performed until the current becomes mA or less, constant voltage charging at 4.3 V and constant voltage charging at 4.2 V are repeatedly performed. Battery B
May be recharged as soon as the battery voltage reaches 4.2 V.

The charging current of the secondary battery B is 4.2 V
Although it is detected at the time of constant voltage charging in the above, it may be detected at the time of constant voltage charging at 4.3V. Further, in step S20, the charging is terminated immediately when the charging current becomes 100 mA or less. However, the charging may be terminated after performing the constant voltage charging at 4.2 V for a predetermined time.

[0027]

According to the present invention, there is provided a method for charging a secondary battery, wherein the secondary battery is repeatedly charged at a constant voltage with a first voltage and a second voltage higher than the first voltage. Since the ratio of the constant voltage charging time by the second voltage to the constant voltage charging time is substantially proportional to the charging current of the secondary battery, at the beginning of charging, the constant voltage charging by the second voltage is performed. By increasing the time ratio to shorten the charging time,
At the end of charging, the ratio of the constant voltage charging time by the first voltage is increased to prevent deterioration due to overcharging. As a result, rapid charging of the secondary battery is prevented while preventing deterioration due to overcharging. It can be performed.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing one embodiment of the present invention.

FIG. 2 is a flowchart showing an embodiment of the present invention.

FIG. 3 is a characteristic diagram of a charging current and a battery voltage according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply circuit 2 Charge control circuit 11 Constant voltage circuit 12 Operation circuit

Continuation of front page (56) References JP-A-6-189465 (JP, A) JP-A-3-251504 (JP, A) JP-A-51-114646 (JP, A) JP-A-58-136241 (JP) JP-A-3-103036 (JP, A) JP-A-6-14473 (JP, A) JP-A-6-21343 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H02J 7/00-7/10 H01M 10/44

Claims (1)

(57) [Claims] 1. A method for charging a secondary battery, wherein the secondary battery is repeatedly charged at a constant voltage with a first voltage and a second voltage higher than the first voltage, wherein the charging method is performed for a constant voltage charging time with the first voltage. The ratio of the constant voltage charging time due to the second voltage is equal to the first voltage.
A method of charging a secondary battery, wherein the charging current is substantially proportional to a charging current at the time of constant-voltage charging at either the first voltage or the second voltage.