JPH114549A - Battery charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a discharging capacity to a minimum and provide a longer life of a battery, by controlling the charging capacity when a lithium ion secondary battery is charged under a constant current and constant voltage control. SOLUTION: A constant current and constant voltage circuit 1 generates a charging voltage of 3.85 V lower than the charging voltage of 4.2 V for charging full a lithium ion secondary battery BT. A voltage of the battery is detected by a voltage detecting circuit. In a voltage comparing circuit 4, whether the battery voltage reaches 3.85 V or not is monitored. If the battery voltage reaches 3.85 V, a switch signal for commanding the stop of charging is fed to a charging stop/start switch circuit 2. Then, the continuity between the constant current and constant voltage circuit 1 and the lithium ion secondary battery is broken.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery charger for charging a lithium ion secondary battery.

[0002]

2. Description of the Related Art In general, a method of charging a lithium ion secondary battery is a constant current constant voltage charge. FIG. 9 illustrates the charge characteristics thereof. FIG. 9 (A) shows a charge voltage (V) / charge amount (%). ) And time (h), and (B) shows the relationship between charging current (A) and time (h). Here, the lithium-ion secondary battery was charged at a maximum charging voltage of 4.2 V,
When charging at a constant current of 1A, the charge amount reaches about 80% of the full charge in about one hour from the start of charging, and then shifts to constant voltage charging, the charging current decreases, and the charging starts. After about 2.5 hours from the charging, the charged amount reaches 100%, and the charging is completed. FIG. 9 illustrates the case of single cell / approximately 1C charging. By the way, one of the features of the lithium ion secondary battery is that the memory effect seen in the Ni battery system does not occur, and the discharge characteristics do not change even if shallow discharge and charge are repeated. However, if a physically high voltage state (such as a fully charged state) is continued, the reaction inside the battery proceeds, and the discharge capacity decreases. FIG. 10 is a graph showing the relationship between the discharge capacity (%) and the period (year), and is a discharge capacity deterioration characteristic during rated continuous charging. Such a decrease in the discharge capacity is irreversible deterioration of the battery discharge capacity, and the discharge capacity does not recover even when recharging is performed. In general, the rate of decrease at 100% charge is about 8% every half year.

[0003]

As described above, the charge amount is 10
The use method in which 0% continuous charge is performed or the discharge period is long has a disadvantage that the discharge capacity decreases and the actual use time becomes extremely short.
That is, FIG. 11A shows the capacity ratio (%) and the period (yea).
r), and (B) shows the relationship between the actual usage time rate and the period (year). The aging of the capacity rate and the aging of the actual usage rate by 100% charging are shown in FIG. Lower. Note that, in FIG. 11B, the values in parentheses in the figure indicate the time when the use time at 100% capacity is assumed to be 40 hours. The object of the present invention is to
By controlling the amount of charge when charging a lithium ion secondary battery by constant current and constant voltage control, it is possible to reduce the discharge capacity to a minimum and achieve a longer battery life. .

[0004]

The means of the present invention are as follows. According to a first aspect of the present invention, in a battery charger for charging a lithium ion secondary battery by constant current and constant voltage control, a predetermined voltage lower than a charging voltage when the lithium ion secondary battery is fully charged is generated as a charging voltage. A voltage generating means for detecting the terminal voltage of the lithium ion secondary battery, and a voltage monitoring means for monitoring whether or not the detected terminal voltage has reached the predetermined voltage. Charge control means for stopping charging of the lithium ion secondary battery when it has been detected that the voltage has reached the predetermined voltage, by stopping charging before the lithium ion secondary battery is fully charged. It is characterized in that the charge amount is suppressed. In addition,
The voltage monitoring means detects a terminal voltage of the lithium ion secondary battery, monitors whether the detected terminal voltage has reached the predetermined voltage, and has reached a predetermined charging start voltage. The charging control means stops charging the lithium ion secondary battery when the voltage monitoring means detects that the terminal voltage has reached a predetermined voltage, and sets the charging start voltage , The charging of the lithium ion secondary battery may be started. The output means generates and outputs a charging voltage at the time of fully charging the lithium ion secondary battery or a predetermined voltage lower than the charging voltage as a first charging voltage, and outputs a predetermined voltage lower than the first charging voltage. Generating and outputting a voltage as a second charging voltage;
Selecting means for selecting either one of the charging voltage and the second charging voltage, and charging the lithium-ion secondary battery with the charging voltage selected by the selecting means, in accordance with the selected charging voltage. You may make it charge a lithium ion secondary battery by the charge amount. In this case, the selection means may select one of the first charging voltage and the second charging voltage in response to a switching operation of the external switch means.

According to the first aspect of the present invention, lithium is charged at a predetermined voltage (for example, 3.85 V) lower than a charging voltage (for example, 4.2 V) when the lithium ion secondary battery is fully charged (100% charged). When it is detected that the terminal voltage of the lithium ion secondary battery has reached a predetermined voltage while charging the ion secondary battery, the charging is stopped at that point, thereby charging the lithium ion secondary battery. The amount is suppressed as compared with the time of full charge, and becomes, for example, 50% charge.
Therefore, by controlling the amount of charge when charging the lithium ion secondary battery by constant current and constant voltage control,
The life of the battery can be extended by minimizing the decrease in the discharge capacity.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIGS. FIG. 1 is a block circuit diagram conceptually showing a configuration of a battery charger for charging a lithium ion secondary battery by constant current and constant voltage control. The constant current / constant voltage circuit 1 charges the lithium ion secondary battery BT by constant current / constant voltage control based on the output of the power supply source PW. Assuming that the voltage is 4.2 V, a voltage of 3.85 V lower than this charging voltage is generated and output as the maximum charging voltage. That is, when the charging voltage is reduced by 0.1 V as a characteristic of the lithium ion secondary battery BT, the charging amount becomes 1
The maximum charge voltage is set to 3.85 so that the final charge amount does not exceed 50% at the time of full charge by utilizing the decrease of 0% or less.
V, and the maximum charging voltage is 3.85 V, 1
The lithium ion secondary battery BT is charged with the constant current A. A charge stop / start switching circuit 2 is connected between the constant current / constant voltage circuit 1 and the lithium ion secondary battery BT, and the charge stop / start switching circuit 2 is a charging circuit for the lithium ion secondary battery BT. It has a switching element for connecting and disconnecting, and controls switching of charging stop / start. The voltage detection circuit 3 detects a terminal voltage (battery voltage) of the lithium ion secondary battery BT. The voltage comparison circuit 4 compares the battery voltage detected by the voltage detection circuit 3 with the preset charge stop voltage and charge start voltage, and determines whether the battery voltage has reached the charge stop voltage or the charge start voltage. To monitor. Here, the charging stop voltage is 3.8
The voltage is set to 5 V, the charging start voltage is set to 3.2 V, and the voltage comparing circuit 4 outputs a switching signal for instructing charging to stop when the battery voltage reaches 3,85 V. The switching signal is given to the start switching circuit 2, and when the battery voltage reaches 3.2V, a switching signal instructing the start of charging is given to the charging stop / start switching circuit 2.

Next, the operation of the battery charger will be described with reference to a time chart shown in FIG. Here, FIG.
(A) shows the change over time in the battery voltage, and FIG. 2 (B) shows the change over time in the charge amount. Stop charging /
The switching elements constituting the start switching circuit 2 are turned on, and the constant current / constant voltage circuit 1 and the lithium ion secondary battery BT
Is in a chargeable state in which is connected. When charging of the lithium ion secondary battery BT is started in this state, charging is performed according to a charging curve as shown in FIG. Here, FIG. 3 shows the same charging characteristics as FIG. 9, and FIG. 3A shows the relationship between the charging amount (%), the charging voltage (V) and the time (h). 3 (B)
Shows the relationship between the charging current (A) and the time (h), and the charge amount is approximately 50% after about 0.5 hour from the start of charging.
And the charging voltage becomes 3.85V. Here, since the battery voltage of 3.85 V is detected by the voltage detection circuit 3,
The voltage comparison circuit 4 detects the coincidence with the charging stop voltage, outputs a switching signal for instructing the charging stop, and supplies the switching signal to the charging stop / start switching circuit 2. Then, the switching element in the charge stop / start switching circuit 2 is turned off, and the connection between the constant current / constant voltage circuit 1 and the lithium ion secondary battery BT is cut off. As a result, a charging prevention state is set. As described above, the battery is in a chargeable state until the battery voltage reaches 3.85 V and the charged amount reaches 50% of the fully charged state. Stop assuming charging. In such a charging stop state, the charging amount gradually decreases, and when the battery voltage decreases to 3.2 V, the voltage comparison circuit 4 detects a match with the charging start voltage of 3.2 V and instructs to start charging. Output a switching signal for
This is given to the charge stop / start switching circuit 2. Then, the switching element in the charge stop / start switching circuit 2 is turned on, and the constant current / constant voltage circuit 1 and the lithium ion secondary battery BT are connected, so that the charging is possible again.

As described above, in this battery charging device, when the maximum charging voltage when the lithium ion secondary battery BT is fully charged is 4.2 V, the battery voltage is 3.85.
V, when the charged amount reaches 50% of the full charge, the charging is stopped, and the charging control is performed so that the charging is not started unless the battery voltage decreases to the charging start voltage of 3.2 V. The discharge deterioration characteristics due to aging are as shown in FIG. Here, in comparison with the conventional discharge deterioration characteristics shown in FIG. 10, in the first embodiment, the discharge capacity decreases by about 5% every half year, but the discharge capacity after three years is 52%. On the other hand, since it is 72% in the past,
This embodiment is better by about 20%. This is due to the characteristics of the battery that occur because the battery voltage at the time of 50% charge is lower than the battery voltage at the time of full charge. FIG.
FIG. 11 shows the aging of the capacity ratio and the change of the actual use time ratio at the time of 0% charging. When the battery is fully charged as in the related art, the actual use time ratio changes as shown in FIG. However, in this embodiment, only 50% is charged, so that the actual use time rate does not change apparently, and the user who uses this apparently does not. , Always seem to use 100% battery.

[0009] In the first embodiment described above,
The voltage for 50% charge was set to 3.85 V, but this value differs depending on the battery manufacturer or the type (part number) of the battery.
It does not matter to 85V. Although the charging current is set to 1 A, any charging current may be used as long as the battery is within the allowable range.
Furthermore, although 50% charge was taken as an example, 60% charge or 70% charge may be used.

(Second Embodiment) Hereinafter, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, in the operation of a device using a lithium ion secondary battery, the battery capacity may be insufficient with only 50% charging. The charge amount is appropriately switched. In other words, in a device that always connects and operates the device body incorporating the lithium ion secondary battery and the charging device, the lithium ion secondary battery is in a continuous charge state,
In order to avoid deterioration of the battery capacity at the time of full charge, 50% charge is desirable. Conversely, in the case of operating the charging device separately from the device body incorporating the lithium-ion secondary battery BT, charging is performed when the lithium-ion secondary battery BT is consumed. The usage time may be shorter. As described above, the discharge capacity is greatly reduced when the battery voltage is high (close to full charge) and the time is long, and the operation method of charging when the lithium ion secondary battery BT is exhausted is used. Then, 100% charging is desirable. Here, the second embodiment has a 50% charge and a 100% charge depending on the operation of the device.
% Charge can be switched.

FIG. 6 is a block diagram showing a main configuration of a battery charging device according to a second embodiment. The battery charger includes two types of constant current / constant voltage circuits 11 for 100% charging,
A constant current / constant voltage circuit 12 for 50% charge is provided.
The 100% charging constant current / constant voltage circuit 11 and the 50% charging constant current / constant voltage circuit 12 charge the lithium ion secondary battery by constant current / constant voltage control based on the output of the power supply source PW. The charging constant current / constant voltage circuit 11 performs charging of the lithium ion secondary battery at the maximum charging voltage of 4.2 V and 1 A as usual, but the 50% charging constant current / constant voltage circuit 12 is the same as in the first embodiment. 3.8 maximum charging voltage
The switching devices 13 and 14 are connected to a 100% charging constant current / constant voltage circuit 11 and a 50% charging constant current / constant voltage circuit 12, respectively. ing. This changeover switch 13,
14 is an ON / OF signal of the charging voltage switching control unit 15
When the changeover switches 13 and 14 are turned ON, the corresponding 100% charging constant current / constant voltage circuit 11 and 50% charging constant current / constant voltage circuit 12 are connected to the lithium ion secondary battery. However, when turned off, the connection is cut off. The charging voltage switching control unit 15 selectively turns on the changeover switches 13 and 14 by software or the like. In addition, the constant current constant voltage circuit 1 for 50% charge
Although the output side of 2 is not shown, it has the same configuration as that of FIG.

As described above, since the changeover switches 13 and 14 are selectively turned on in accordance with the operation of the device, the constant current / constant voltage circuit connected to the lithium ion secondary battery is switched, and 100% charging is performed. When switched to the constant current / constant voltage circuit 11, the lithium ion secondary battery is charged 100% at 4.2 V and 1 A, but when switched to the constant current / constant voltage circuit 12 for 50% charge; 85V,
50% charge of lithium ion secondary battery by 1A
It can be reduced to charging. In this way, the amount of charge can be controlled by operating the device.

(Third Embodiment) A third embodiment of the present invention will be described below with reference to FIGS. FIG. 7 is a block diagram showing the main configuration of the battery charger. The battery charger of the second embodiment shown in FIG. 6 is different from the battery charger of FIG. 6 in that a 100% charge start switch 16 is added. It has a configuration. That is, the user can arbitrarily instruct the switching of the charge amount by a switch operation in accordance with the operation of the device. When the 100% charge start switch 16 is turned on, the charge voltage switch control unit 15 switches the switch 13 Is turned on and the switch 14 is turned off, thereby switching from 50% charging to 100% charging. FIG. 8 shows the charging characteristics by such charge switching. Usually, 50% charging is performed, and the charging voltage is 3.85 V. However, when the 100% charging start switch 16 is turned on, 100% charging is performed. Since the voltage is switched to 4.2 V for charging, the charging current increases, and the battery voltage gradually increases.
In this case, it takes about 1 hour until the charged amount reaches about 90%, and about 2 hours before fully charged. The second embodiment configured as described above has the same effects as the first embodiment described above, and also allows the user to switch the charge amount. In the above-described second and third embodiments, switching between the two charging methods of 100% charging and 50% charging is performed, but the charging amount may be, for example, 70% charging, 80% charging, or the like. The number of switching may be three or more. In addition, the present invention is not limited to a device in which the device main body and the charging device are separated from each other, and may have a built-in charging device in the device main body. May go.

[0014]

According to the present invention, when a lithium ion secondary battery is charged by constant current and constant voltage control, the amount of charge is controlled, so that a decrease in discharge capacity can be suppressed to a minimum and the battery length can be reduced. The service life can be extended, and the user who actually uses the battery does not feel the deterioration of the battery.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram conceptually showing a configuration of a battery charger for charging a lithium ion secondary battery by constant current and constant voltage control.

FIGS. 2A and 2B are time charts for explaining the operation of the battery charger, in which FIG. 2A shows a change over time in battery voltage, and FIG. 2B shows a change over time in the amount of charge.

3A and 3B are diagrams showing charging characteristics, in which FIG. 3A shows a relationship between a charging amount and a charging voltage and time, and FIG. 3B shows a relationship between a charging current and time.

FIG. 4 is a diagram showing discharge deterioration characteristics due to aging.

FIGS. 5A and 5B are diagrams showing a change in a capacity ratio with time and a change in an actual use time ratio at the time of 50% charging.

FIG. 6 is a block diagram showing a main configuration of a battery charging device according to a second embodiment.

FIG. 7 is a block diagram showing a main configuration of a battery charging device according to a third embodiment.

FIG. 8 is a diagram illustrating charging characteristics by switching charging in the third embodiment.

9A and 9B show a conventional charging characteristic, in which FIG. 9A shows a relationship between a charging amount and a charging voltage and time, and FIG. 9B shows a relationship between a charging current and time.

FIG. 10 is a diagram showing a conventional discharge capacity deterioration characteristic during rated continuous charging.

FIGS. 11A and 11B are diagrams showing a change over time in a capacity ratio and a change in an actual use time ratio at the time of conventional 100% charging.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Constant current constant voltage circuit 2 Charge stop / start switching circuit 3 Voltage detection circuit 4 Voltage comparison circuit 11 100% charging constant current constant voltage circuit 12 50% charging constant current constant voltage circuit 13, 14 Changeover switch 15 Charge voltage switching Control unit 16 100% charge start switch PW Power supply source BT Lithium ion secondary battery

Claims (4)

[Claims] 1. A battery charging device for charging a lithium ion secondary battery by constant current and constant voltage control, wherein a voltage generation for generating a predetermined voltage lower than a charging voltage when the lithium ion secondary battery is fully charged as a charging voltage. Means for detecting the terminal voltage of the lithium ion secondary battery,
Voltage monitoring means for monitoring whether or not the detected terminal voltage has reached the predetermined voltage; and when the electronic monitoring means detects that the terminal voltage has reached the predetermined voltage, the voltage is supplied to the lithium ion secondary battery. And a charge control means for stopping the charging of the battery, wherein the charging is stopped by stopping the charging before the lithium ion secondary battery is fully charged, thereby suppressing the charge amount. 2. The voltage monitoring means detects a terminal voltage of the lithium ion secondary battery, monitors whether the detected terminal voltage has reached the predetermined voltage, and determines a predetermined charging time. Monitoring whether or not the start voltage has been reached, the charge control means stops charging the lithium ion secondary battery when the voltage monitoring means detects that the terminal voltage has reached a predetermined voltage. 2. The battery charging device according to claim 1, wherein when it is detected that the charging start voltage has been reached, charging of the lithium ion secondary battery is started. 3. The output means generates and outputs a charging voltage when the lithium ion secondary battery is fully charged or a predetermined voltage lower than the charging voltage as a first charging voltage, and outputs the charging voltage based on the first charging voltage. A predetermined voltage, which is lower than the predetermined voltage, as a second charging voltage. A selecting means for selecting one of the first charging voltage and the second charging voltage is provided, and lithium is selected by the charging voltage selected by the selecting means. 2. The battery charger according to claim 1, wherein the lithium ion secondary battery is charged with a charge amount corresponding to the selected charging voltage by charging the ion secondary battery. 4. The apparatus according to claim 3, wherein said selecting means selects one of a first charging voltage and a second charging voltage in response to a switching operation of an external switch means. Battery charger.