JPH09154239A - Charging of secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for charging by which quick charging can be done with the increase in temperature of the battery being held as low as possible. SOLUTION: By this method, a secondary battery is charged according to the increase in temperature during charging per unit time of the secondary battery. Quick charging is conducted with charging current of a first current value. When the rate of the increase in temperature reaches a first set value, the charging current is reduced to a second current value which is smaller than the first one and complementary charging is conducted. Then, when the rate of the increase in temperature reaches a second set value, charging is stopped.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a charging method for rapidly charging a secondary battery.

[0002]

2. Description of the Related Art Various methods have been proposed for rapid charging of secondary batteries. As a representative one, there is a system called -ΔV control and a system called dT / dt control.
6 and 7 are diagrams showing typical changes in battery voltage and battery temperature over time and charging current waveforms during constant current charging of a secondary battery, where 1 is a battery voltage change curve and 2 is a battery temperature change. Curve 3 is the charging current waveform.

The -ΔV control system utilizes the phenomenon that the battery voltage reaches a peak and then drops again at the end of charging, and as shown in FIG. 6, when the battery voltage reaches a peak and drops by ΔV. This is a method of stopping charging. This method has a drawback in that the battery is overcharged because the charging is stopped after the battery voltage reaches its peak.

On the other hand, the dT / dt control method utilizes the fact that the battery temperature rises sharply at the end of charging, and as shown in FIG. 7, the temperature rise rate dT per unit time of the secondary battery is dT / dt.
This is a method of stopping the charging when a time point A when / dt (also referred to as temperature differential) reaches a predetermined value. According to this method, charging is stopped before the battery voltage reaches its peak, so overcharging does not occur unlike in the -ΔV control method. However, in the case of performing the rapid charging such that the charging current exceeds 1C, the temperature rise rate d is reached before the full charging.
T / dt may reach the set value, resulting in insufficient charging.

As a method for solving these drawbacks, Japanese Patent Laid-Open No. 6-1216468 discloses that the current value of the charging current is, for example, 5C.fwdarw.3C.fwdarw.2C.fwdarw.1 at each change point of the slope of battery temperature rise.
A method of charging the battery by gradually reducing it to C is shown. However, in this method, the battery temperature continuously rises as the charging progresses, so there are problems that the charging efficiency is low and the life of the battery is impaired. May reach the temperature cutoff (TCO) and become unchargeable.

[0006]

As described above, in the conventional rapid charging method in which the charging current value is reduced each time the slope of the temperature rise of the battery changes, the charging efficiency increases because the battery temperature continuously rises. However, there is a problem in that the battery may reach the temperature cutoff and become unchargeable if the temperature of the battery continues to rise for a long time. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a secondary battery charging method capable of performing rapid charging while suppressing an increase in battery temperature as much as possible.

[0007]

In order to solve the above-mentioned problems, the present invention provides a method for charging a secondary battery, wherein a secondary battery is charged according to a temperature rise rate per unit time during charging of the secondary battery. When the temperature rise rate reaches the first set value, the charge current is reduced to the second current value that is smaller than the first current value and the charge is performed. The charging is stopped when a preset value of 2 is reached or after a predetermined time has elapsed after the charging current is reduced to the second current value.

Further, according to the present invention, after the charging by the charging current having the second current value is started, the temperature rise rate reaches the second set value and the charging current is reduced to the second current value. It is characterized in that charging is stopped at an earlier point in time after a predetermined time has elapsed.

Here, the second current value is 1 of the first current value.
It is desirable that it is / 2 or less. When the charging rate according to the first current value is C1, the charging rate according to the second current value is C2, the charging time according to the first current value is t1 (minutes), and the charging efficiency is η, the predetermined time is , T2 = {(60 / C1) -t1} × (C1 / C2) ×
The time is preferably represented by (2-η).

According to the present invention, after the rapid charging by the charging current having the first current value is performed until the temperature rising rate reaches the first set value, the charging current is lowered to the second current value to raise the temperature. By performing the auxiliary charging until the rate reaches the second set value or after the elapse of a predetermined time, the rapid charging is efficiently performed up to the charged amount near 100% while suppressing the increase in the battery temperature.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION First, the configuration of a charger in this embodiment will be described with reference to FIG. In FIG. 1, a charger 10 includes AC connection terminals 11 and 12, and a power transformer 13 whose primary side is connected to these AC input terminals 11 and 12.
A rectifying / smoothing circuit 14 connected to the secondary side of the power transformer 13 and a current control element 15 including a transistor.
And a control circuit 16 for controlling the current control element 15,
It comprises a temperature detection circuit 17, charging terminals 18, 19 and a temperature detection terminal 20. Both ends of a secondary battery 21 are connected to the charging terminals 18 and 19, and a temperature sensor 22 such as a thermistor arranged in contact with or close to the secondary battery 21 is connected to the temperature detecting terminal 20.

AC input power from a commercial AC power supply (not shown) connected to the AC connection terminals 11 and 12 is transmitted to the rectifying / smoothing circuit 14 via the power supply transformer 13 and converted into DC. Then, the charging current is supplied from the output of the rectifying / smoothing circuit 14 to the secondary battery 21 through the current control element 15.

On the other hand, the temperature sensor 22 causes the secondary battery 21
Is detected as a resistance value change of the thermistor, and the resistance value change is converted into battery temperature information by the temperature detection circuit 17,
It is input to the control circuit 16. The control circuit 16 is configured by using a microcomputer. After the battery temperature information from the temperature detection circuit 17 is digitized by the A / D converter, the temperature rise rate of the secondary battery 21 per unit time (hereinafter, simply referred to as temperature A so-called temperature differential value, which is called a rate of increase) dT / dt, is calculated, and the resistance value of the current control element 15 is controlled based on the temperature increase rate dT / dt.

Next, the charging operation in this embodiment will be described with reference to FIG. FIG. 2 shows the control circuit 1 during charging.
It is a flow chart which shows a processing procedure of No. 6. First, the control circuit 16 controls the resistance value of the current control element 15 to a certain value to start the rapid charging of the secondary battery 21 with the charging current having the first current value I1 (step S11). At the time of this rapid charging, the control circuit 16 determines the temperature increase rate d per unit time based on the battery temperature information from the temperature detection circuit 17.
T / dt is calculated, and it is further determined whether or not the temperature increase rate dT / dt has reached the first set value TH1 (steps S12 to S13).

In step S13, the temperature rise rate dT /
When dt reaches the first set value TH1, the control circuit 16 increases the resistance value of the current control element 15 by a predetermined amount, thereby causing the secondary battery 21 to have the second current value I2 smaller than the first current value I1. It is charged with the charging current of (step S14).
That is, supplementary charging is performed. Also during this supplementary charging, the control circuit 16 calculates the temperature increase rate dT / dt, and further determines whether the temperature increase rate dT / dt has reached the second set value TH2 (steps S15 to S16). And
When the temperature increase rate dT / dt reaches the second set value TH2 in step S16, the control circuit 16 turns off the current control element 15 to stop charging (step S17).

Next, the charging operation in this embodiment will be described with reference to FIG.
This will be described in more detail with reference to FIG. FIG. 3 shows the secondary battery 21.
FIG. 3 is a diagram showing a temporal change of a battery voltage and a battery temperature at the time of charging and a charging current waveform. 1 is a battery voltage change curve, 2 is a battery temperature change curve, and 3 is a charging current waveform. First, rapid charging is performed with a charging current having a first current value I1 (for example, a current value of 1C or more). The battery temperature rises as the charging progresses. When the battery temperature passes the first inflection point A and the temperature increase rate dT / dt reaches the first set value TH1, the charging current is switched to the second current value I2 to perform supplementary charging. The second current value I2 is suitably 1/2 or less of the first current value I1.

When the charging current is reduced to the second current value I2, the battery temperature temporarily drops, then becomes flat for a short time, then rises again, and passes through the second inflection point B. After that, the temperature increase rate dT / dt is set to the second set value TH.
When it reaches 2, charging stops.

According to such a charging method, first, the rapid charging by the charging current having the first current value I1 is performed at the temperature increase rate dT.
/ Dt reaches the first set value TH1 and then the charging current is reduced to the second current value I2 to increase the temperature increase rate dT / d.
By performing the supplementary charge until t reaches the second set value TH2, 100% can be obtained without the increase of the battery temperature as shown by the broken line 2a in the case of performing the charge with a constant current value as in the conventional case. It is possible to efficiently charge up to a nearby charge level.

Next, the charging operation in another embodiment of the present invention will be described using the flowchart shown in FIG. 4, the processing of steps S21 to S24 is the same as the processing of steps S11 to S14 in FIG. In this embodiment, in step S24, the secondary battery 21 is supplementarily charged with the charging current having the second current value I2, and the charging is stopped after a predetermined time has elapsed. That is, the auxiliary charge is started and the timer count is performed in the control circuit 16 to obtain the count value t.
When (the elapsed time of supplementary charging) reaches the timer set value t2 corresponding to the above-mentioned predetermined time, the charging is stopped (step S2).
5 to S27).

The timer set value t2 at this time is roughly determined by the following equation. t2 = {(60 / C1) -t1} * (C1 / C2) * (2- [eta]) ... (1) where C1 is the charge rate (time rate) by the first current value I1, and C2 is the second. Is the charging rate (time rate) according to the current value I2, t1 is the charging time according to the first current value (rapid charging time), and η is the charging efficiency. As for C1, I1 is the secondary battery 2
It becomes 2 when the current value is twice the nominal capacity of 1.

At t2 of the equation (1), since the charging efficiency η is less than 100% only by the rapid charging by the charging current of the first current value I1, the shortage is caused by the charging current of the second current value I2. It is time to make up by supplementary charging. That is,
(60 / C1) -t1 represents the shortage time of the rapid charging due to the first current value I1. Further, the ratio of C1 / C2 is a conversion coefficient for converting this shortage time (60 / C1) -t1 into the time for supplementary charging by the second current value I2. Further, 2-η is a value obtained when 100% of the charging efficiency η is represented by 1.00, and the shortage time (60/60 /
C1) -t1 indicates a magnification for supplementing.

Also according to this embodiment, the first current value I1
After the rapid charging by the charging current is performed until the temperature increase rate dT / dt reaches the set value TH1, the charging current is reduced to the second current value I2 and the timer count value t is set to the timer set value t.
By performing supplemental charging until the secondary battery 21
It is possible to efficiently charge up to a charge amount close to 100% while suppressing the temperature rise.

Next, the charging operation in still another embodiment of the present invention will be described using the flowchart shown in FIG. The present embodiment is a combination of the operations of FIG. 2 and FIG.

In FIG. 5, the processing of steps S31 to S36 is the same as the processing of steps S11 to S26 in FIG. In the present embodiment, when supplementary charging is performed with the charging current having the second current value I2 in step S34, the temperature increase rate dT / dt is calculated (step S35), and dT / dt is compared with the second threshold value TH2 ( In parallel with step S36), the timer count (step S37) and the comparison between the count value t and the timer setting value t2 (step S38) are performed, and the time point at which dT / dt = TH2 is reached after the start of supplementary charging and t = t2. The charging is stopped at an earlier point of time when the temperature reaches (step S39).

According to this embodiment, when the temperature rise of the battery is slow after the shift to the auxiliary charge and the time until the temperature rise rate reaches the second set value TH2 is long, the timer count value t becomes the timer. Since the charging can be stopped by reaching the set value t2, it is possible to perform efficient charging while preventing overcharging.

[0026]

As described above, according to the present invention, the rapid charging by the charging current of the first current value is performed until the temperature rise rate reaches the first set value, and then the charging current is changed to the second value. Whether the temperature rise rate reaches the second set value by decreasing to the current value,
Alternatively, by performing supplementary charging until a time point after a lapse of a predetermined time, efficient rapid charging can be performed while suppressing an increase in battery temperature.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a charger according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining a charging operation in the same embodiment.

FIG. 3 is a diagram showing a time change of a battery voltage and a battery temperature during charging and a charging current waveform for explaining a charging operation in the embodiment.

FIG. 4 is a flowchart illustrating a charging operation according to another embodiment of the present invention.

FIG. 5 is a flowchart for explaining a charging operation in still another embodiment of the present invention.

FIG. 6 is a diagram showing a time variation of a battery voltage and a battery temperature and a charging current waveform for explaining a conventional −ΔV control method.

FIG. 7 is a diagram showing a time change of a battery voltage and a battery temperature and a charging current waveform for explaining a conventional dT / dt control method.

[Explanation of symbols]

 1 ... Battery voltage change curve 2 ... Battery temperature change curve 3 ... Charging current waveform 10 ... Charger 11, 12 ... AC input terminal 13 ... Power supply transformer 14 ... Rectifying / smoothing circuit 15 ... Current control element 16 ... Control circuit 17 ... Temperature detection Circuits 18 and 19 ... Charging terminal 20 ... Temperature detection terminal 21 ... Secondary battery 22 ... Temperature sensor

Claims (5)

[Claims] 1. A method of charging a secondary battery, wherein the secondary battery is charged according to a temperature increase rate per unit time when the secondary battery is charged, wherein charging is performed with a charge current having a first current value, and the temperature increase rate is When the set value of 1 is reached, the charging current is reduced to a second current value smaller than the first current value to perform charging, and when the temperature increase rate reaches the second set value, the charging is stopped. And a method for charging a secondary battery. 2. A method of charging a secondary battery, wherein the secondary battery is charged in accordance with a temperature increase rate per unit time when the secondary battery is charged, wherein charging is performed with a charge current having a first current value, and the temperature increase rate is set. When the value is reached, the charging current is reduced to a second current value smaller than the first current value to perform charging, and the charging current is reduced to the second current value, and then the charging is stopped after a predetermined time has elapsed. And a method for charging a secondary battery. 3. A method of charging a secondary battery, wherein the secondary battery is charged according to a temperature rise rate per unit time when the secondary battery is charged, wherein charging is performed with a charging current having a first current value, and the temperature rise rate is When the set value of 1 is reached, the charging current is reduced to a second current value smaller than the first current value to perform charging, and the time at which the temperature increase rate reaches the second set value and the charging current are set to A method for charging a secondary battery, comprising: stopping the charging at an earlier time point after a predetermined time has elapsed after the current value is reduced to 2. 4. The method for charging a secondary battery according to claim 1, wherein the second current value is ½ or less of the first current value. 5. The charging rate according to the first current value is C1, the charging rate according to the second current value is C2, and the predetermined time is C2.
When the charging time by the first current value is t1 (min) and the charging efficiency is η, t2 = {(60 / C1) -t1} × (C1 / C2) ×
The method for charging a secondary battery according to claim 1 or 3, which is represented by (2-η).