JPH08203563A - Charging method for battery - Google Patents

Abstract

PURPOSE: To efficiently prevent lowering of a battery performance and quickly charge in a short time by setting a current switch voltage for switching charging current of constant current charge and a full charge voltage for detecting full charge of a battery to different voltage values. CONSTITUTION: After starting constant current charge, the charge is interrupted at a fixed cycle to detect the open voltage of a battery and a timer detects whether Ta is elapsed. Secondarily, when the charging voltage of the battery increases to a current switch voltage V1 (for example 4.5V/cell), a microcomputer controls a charging power supply so as to switch the charging current. Namely, the charging voltage of the battery is charged at constant current while comparing with the voltage V1, and when the battery voltage increases to the voltage V1, the charging current is changed to decrease gradually. And charge for charging at constant current is temporarily interrupted so as to detect the open voltage, it is compared with the full charge voltage V2 (for example 4.1V/cell) which is set lower than the voltage V1 so as to detect the full charge, and the voltage V1 is set lower as approaching to the full charge, so as to prevent lowering of the' performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery charging method which is most suitable for charging a non-aqueous secondary battery such as a lithium ion secondary battery.

[0002]

2. Description of the Related Art A non-aqueous secondary battery such as a lithium ion secondary battery is first charged with a constant current to raise the battery voltage to a set voltage. After that, it is fully charged by constant voltage charging.
The reason why the battery is charged to a constant voltage at the end to be fully charged is that the battery performance is significantly reduced when the battery voltage becomes higher than a certain voltage. This charging method has a drawback that it takes time to fully charge the battery. This is because if the battery is charged to a constant voltage and fully charged, the charging current gradually decreases as the battery approaches full charge. Further, the constant voltage charging in which the battery voltage is controlled and charged with high accuracy has a drawback that the charging circuit becomes expensive. This is because electronic parts with few errors are required to control the output voltage of the charging circuit with extremely high accuracy.

In order to prevent this adverse effect, a method has been developed in which the charging current for constant current charging is gradually reduced to fully charge the battery (Japanese Patent Laid-Open No. 61-26438). In the charging method described in this publication, as shown in FIG. 1, a constant current is first charged with a large current. When the battery voltage rises to the current switching voltage during constant current charging, the charging current for constant current charging is gradually reduced.

[0004]

As shown in FIG. 1, a constant current charging method in which the charging current is reduced each time the charging voltage of the battery rises to a current switching voltage is constant voltage charging followed by constant voltage charging. Compared with the conventional method, it has the feature that it can be fully charged in a short time. This is because the constant current charging does not reduce the charging current even when the battery approaches the full charge as in the constant voltage charging, and thus the charging capacity per hour can be increased. further,
Unlike the constant voltage charging circuit, the constant current charging circuit does not need to control the output voltage with high accuracy, so that the charging circuit can be designed at low cost.

However, the charging method shown in FIG. 1 has a drawback that when the battery approaches the full charge, the battery is adversely affected and the battery performance is deteriorated. This is because the substantial charging voltage applied to the battery being charged increases as the charging current decreases. The charging voltage of the battery is the voltage obtained by subtracting the voltage loss of the circuit impedance from the output voltage of the charging circuit. The voltage loss of the circuit impedance decreases as the charging current decreases. For this reason,
Even if the current switching voltage is set to be the same, if the charging current becomes small, the charging voltage of the battery will gradually increase. In particular, the problem is that the charging method shown in Fig. 1
Each time the charging voltage of the battery rises to the current switching voltage, the charging current for constant current charging is reduced, so that the charging voltage of the battery increases as the battery approaches full charge.

A non-aqueous secondary battery such as a lithium ion secondary battery has a characteristic that battery performance remarkably deteriorates when an overvoltage occurs in a state close to full charge. In order to prevent this adverse effect, it is necessary to set the current switching voltage low. However, if the current switching voltage is set low, the charging current becomes small, the charging time becomes long, and the feature of constant current charging that can be rapidly charged in a short time is lost. Therefore,
The charging method shown in FIG. 1 has a drawback that it is difficult to effectively prevent the battery performance from being deteriorated and to rapidly charge the battery in a short time.

The present invention was developed with the object of solving this drawback. An important object of the present invention is to provide a battery charging method that can effectively prevent a decrease in battery performance and can be rapidly charged in a short time.

[0008]

The battery charging method of the present invention has the following constitution in order to achieve the above object.
The method for charging a battery according to claim 1 of the present invention charges the battery with constant current, and when the charging voltage of the battery rises to a preset current switching voltage, the charging current is reduced to perform constant current charging, Further, the charging method of detecting the full charge voltage of the battery and ending the charging of the battery is improved.

In this charging method, the current switching voltage for switching the charging current for constant current charging and the full charge voltage for detecting full charge of the battery are set to different voltage values. That is, the full charge voltage is set lower than the current switching voltage. This method
The battery voltage detected while charging the battery with constant current is compared with the current switching voltage to change the current value for constant current charging. The full charge of the battery is not detected by the current switching voltage. The battery open circuit voltage is detected when the battery is temporarily interrupted at a predetermined cycle during constant current charging and the charging is interrupted. When it reaches the charging voltage, it is determined that the battery is fully charged and the constant current charging is terminated.

Further, the battery charging method according to the second aspect of the present invention is such that the overcharge protection circuit built in the battery pack to be charged does not operate even if the battery voltage temporarily rises. When performing constant current charging, pulse charging is performed in which the charging current of the battery is set to 0 in a pulse form in a short cycle. In pulse charging, the cycle for setting the charging current to 0 is, for example, 1 to
It is set to 100 msec.

Furthermore, a battery charging method according to a third aspect of the present invention is to charge the battery at a constant current, and decrease the charging current when the charging voltage of the battery rises to a preset current switching voltage. The charging method for constant current charging is further improved. This charging method is characterized in that the set voltage of the current switching voltage for reducing the charging current of the constant current charging is set low as the battery approaches full charge.

[0012]

In the battery charging method according to claim 1 of the present invention, as shown in FIG. 2, the current switching voltage for switching the charging current for constant current charging and the full charging voltage for detecting full charging of the battery are different voltages. It is set to a value. When the battery is charged with a constant current and the charging voltage rises to the current switching voltage, the charging current is gradually reduced. In order to detect the full charge of the battery, the constant current charge is temporarily interrupted at a constant cycle to detect the open circuit voltage of the battery. The open-circuit voltage is compared with the full-charge voltage, and when the open-circuit voltage of the battery reaches the full-charge voltage, it is determined that the battery has reached the full-charge voltage and the constant current charging is terminated. Since the open circuit voltage is detected by interrupting the constant current charging, it is not affected by the charging current of the constant current charging.

Therefore, the method of the present invention can accurately detect the full charge of the battery regardless of the charging current of the constant current charging. Therefore, it is not necessary to lower the current switching voltage in order to prevent the deterioration of the battery performance, and it is possible to prevent the deterioration of the battery performance and perform rapid charging in a short time.

Further, in the battery charging method according to the second aspect of the present invention, when the constant current charging is performed, the charging current of the battery is pulse-charged to zero in a short cycle. Therefore, the battery can be fully charged in a short time without operating the overcharge protection circuit built in the battery pack.

In the battery charging method according to the third aspect of the present invention, the set voltage of the current switching voltage is changed to a lower value as the battery approaches the full charge, so that the battery approaches the full charge. It is possible to prevent the battery performance from being lowered due to overvoltage. In particular, if the rate at which the current switching voltage is lowered is designed in consideration of the voltage loss due to the impedance of the circuit, there is a feature that the charging voltage of the battery can be the same and constant charging can be performed as different charging currents.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. However, the following examples illustrate a charging method for embodying the technical idea of the present invention,
The present invention does not specify the battery charging method as follows. Hereinafter, charging of the lithium ion secondary battery, which is a non-aqueous secondary battery, will be described in detail.

FIG. 3 shows a charging circuit used in the charging method of the present invention. This charging circuit includes a charging power source 1, a charging control switch SW1 connected between the charging power source 1 and a battery to be charged, and a detection circuit 2 for detecting a battery voltage.
And a microcomputer 3 for calculating the detection voltage of the detection circuit 2 and controlling the charging power source 1 and the charging control switch SW1.

The charging power source 1 includes a power supply circuit for converting an input alternating current into a predetermined voltage and converting it into a direct current, and a constant current charging circuit for controlling an output current of the power supply circuit to charge a battery with a constant current. Built in. The constant current charging circuit is controlled by the microcomputer 3 to control the charging current for charging the battery with a constant current.

The charge control switch SW1 is turned on when the battery is charged and turned off when the battery is not charged. The charge control switch SW1 is controlled by the microcomputer 3. The charge control switch SW1 is most preferably a semiconductor switching element such as a transistor or FET, but a relay or the like can also be used.

The microcomputer 3 arithmetically processes the voltage signal input from the voltage detection circuit 2 to control the charging control switch SW1 and the charging power source 1. The microcomputer 3 turns on the charge control switch SW1 when charging the battery, and turns off the charge control switch SW1 when the battery is fully charged and charging is completed. Further, the microcomputer 3 calculates the voltage signal input from the voltage detection circuit 2 and controls the charging power source 1 so as to reduce the charging current for constant current charging every time the battery voltage becomes the current switching voltage. . Further, the microcomputer 3 is
In order to detect the open circuit voltage of the battery to be charged, a timer (not shown) for interrupting constant current charging at a constant cycle is incorporated. Further, the microcomputer 3 also includes a timer (not shown) for setting the charging current of the battery to zero in a short cycle in a pulsed manner when the constant current charging is performed.

The charging circuit shown in FIG. 3 charges the battery with the voltage-current characteristics shown in FIG. 2 as follows in the flowchart of FIG. [Step S1] The microcomputer 3 controls the charging power source 1 to set the charging current for constant-current charging the battery to I1. I1 is set to 1.2 A, for example. [Step S2] The microcomputer 3 controls the charge control switch SW1 to turn on the charge control switch SW1. In this state, the charging power source 1 is connected to the battery and constant current charging of the battery is started.

[Step S3] After the constant current charging is started, in order to interrupt the charging at a constant cycle and detect the open circuit voltage of the battery, it is determined whether or not Ta has elapsed. The set time Ta of the timer is a cycle for interrupting charging and detecting the open circuit voltage of the battery, and is, for example, 10 seconds to 3 seconds.
Minutes, preferably 15 seconds to 2 minutes, more preferably 20 to
It is set to 60 seconds. [Step S4] When the timer set time Ta has not elapsed, in other words, until the timer set time Ta elapses after the constant current charging is started, the battery charge voltage is detected and the detected charge voltage is detected. Is compared with the current switching voltage V1. When the charging voltage of the battery does not rise to the current switching voltage V1, the process loops to step S2. In the case of a lithium ion secondary battery, the current switching voltage of the battery is, for example, 4.
It is set to 5V / cell.

[Step S5] When the charging voltage of the battery rises to the current switching voltage V1, the microcomputer 3
Controls the charging power supply 1 to switch the charging current. When the charging current is I1, it is switched to I2, and when it is I2, it is switched to I3. For example, I2 is set to 0.6A and I3 is set to 0.3A. The battery is charged with a constant current by looping the steps of S2 to S5. In the battery which is charged with constant current in these steps, the charging current is gradually reduced as I1 → I2 → I3 every time the charging voltage of the battery rises to the current switching voltage V1.

[Step S6] When constant current charging has elapsed Ta, which is the time set by the timer, the microcomputer 3 controls the charge control switch SW1 to temporarily turn it off. This is to detect the open circuit voltage of the battery.

[Step S7] The microcomputer 3 determines whether the built-in timer has elapsed Tb, and loops this step until Tb elapses. The set time of the timer Tb is a time for interrupting the charging of the battery to detect the open circuit voltage, and is set to, for example, 1 to 5 seconds.

[Steps S8 and S9] The microcomputer 3 detects the open circuit voltage of the battery and compares the detected open circuit voltage with the full charge voltage V2 stored in the memory. The full charge voltage V2 is, for example, in the case of a lithium ion secondary battery,
Set to 4.1V / cell. When the open circuit voltage of the battery rises to the full charge voltage V2, it is determined that the battery is fully charged and the charging is terminated. When the open circuit voltage of the battery has not risen to the full charge voltage V2, the step jumps to the step S2 to continue the constant current charging.

Further, as shown in the enlarged view of FIG. 2, the charging circuit shown in FIG. 3 can be pulse-charged so that the charging current of the battery is set to 0 in a pulsed manner in a short cycle. A flowchart of this charging method is shown in FIG. In the flowchart of this figure, the battery is charged in the same manner as the flowchart of FIG. 4 except that the step S2 is pulse charging in the flowchart of FIG. In pulse charging, as shown in the enlarged view of FIG. 2, the charging current is set to 0 in a pulsed manner at a constant short cycle.

In pulse charging, the cycle in which the charging current is set to 0 in a pulsed manner is shorter than the cycle in which the overcharge protection circuit incorporated in the battery pack operates, for example, 1 to 300 m.
sec, preferably 10 to 100 msec.

The battery pack containing the overcharge protection circuit is
When charging the battery, if the battery voltage becomes higher than the set voltage, the overcharge protection circuit operates to forcibly stop the charging of the battery. In the charging method of the present invention, the current switching voltage, which is the voltage for switching the charging current for constant current charging,
If the voltage is set higher than the voltage at which the overcharge protection circuit for the battery pack operates, the overcharge protection circuit operates before the battery voltage rises to the current switching voltage, and the battery cannot be charged. In order to prevent this, as shown in the enlarged view of FIG.
The constant current charging is pulse charging, and the charging current is set to 0 in a pulsed manner in a short cycle. The overcharge protection circuit for the battery pack is designed to operate only when the battery voltage becomes higher than the set voltage for a certain period of time or longer. Therefore, in the pulse charging, if the short cycle for setting the charging current to 0 is set to a time shorter than the operation of the overcharge protection circuit, the operation of the overcharge protection circuit can be prevented.

When the operation of the overcharge protection circuit is stopped and the battery pack is charged, there is a concern that the battery will be overcharged and the performance will deteriorate. However, the charging method of the present invention is
We solve this problem in a unique way. That is, unlike the conventional charging method, the charging method of the present invention does not perform constant voltage charging of a battery that is close to full charge, but performs constant current charging until it reaches a predetermined voltage, so the battery voltage becomes high. However, it is only temporarily high, which prevents the degradation of battery performance.

Further, according to the charging method of the present invention, the battery can be charged with the voltage and current characteristics shown in FIG. A flow chart of this charging method is shown in FIG. The voltage and current characteristics shown in FIG. 6 show that as the battery approaches full charge,
The charging current for constant current charging is reduced, and the current switching voltage for switching the charging current is set gradually lower. The current switching voltage is preferably determined in consideration of the voltage loss of the circuit impedance caused by the charging current for constant current charging.

For example, the current switching voltage under the following conditions is set to the following voltages in order as the battery approaches full charge. V1 = 8.44V (1.2A → 0.6A) V2 = 8.32V (0.6A → 0.3A) V3 = 8.26V (0.3A → 0A) Circuit impedance …… 0.2Ω, constant current Charging currents I1, I2 and I3 are charged in order, I1 = 1.2A I2 = 0.6A I3 = 0.3A The battery pack to be charged has two lithium ion secondary batteries connected in series.

When the current switching voltage is set to the above voltage value, the voltage which substantially acts on the two batteries, in other words, the voltage value obtained by subtracting the voltage drop due to the circuit impedance from the current switching voltage is exactly 8 Can be set to 20V. Since the above battery pack contains two lithium ion secondary batteries, when converted into one battery, the current switching voltages V1, V2, and V3 are, in order, as shown in FIG. Become. V1 = 4.22V / cell (1.2A → 0.6A) V2 = 4.16V / cell (0.6A → 0.3A) V3 = 4.13V / cell (0.3A → 0A)

The method of charging with the voltage and current characteristics shown in FIG.
When the battery voltage of the battery pack to be charged rises to the third current switching voltage V3, it is determined that the battery is fully charged, and the charging is completed. However, the full charge detection of the battery can be performed in the same manner as the method shown by the flowcharts in FIGS. 4 and 5. That is, the charging of the battery may be temporarily stopped at a constant cycle to detect the open circuit voltage of the battery, and when the open circuit voltage reaches the full charge voltage, the battery may be fully charged and the charging may be terminated.

Furthermore, the method of charging the battery pack with the voltage-current characteristics shown in FIG. 6 is also applicable when charging is performed by setting the current switching voltage higher than the voltage at which the overcharge protection circuit built into the battery pack operates. As shown in the enlarged view of FIG. 2, constant current charging may be pulse charging so that the overcharge protection circuit does not operate.

FIG. 7 is a flow chart for charging the battery with the voltage-current characteristics of FIG. This flow chart uses the charging circuit of FIG. 3 to fully charge the battery in the following steps. [Step S1] The microcomputer 3 controls the charging power source 1 to set the charging current for constant current charging of the battery to I
Set to 1. I1 is 1.2 A, for example. further,
The microcomputer 3 controls the charging power source 1,
Current switching voltage V1 for switching the current of constant current charging
Is set to 4.22V, for example. [Step S2] The microcomputer 3 controls the charge control switch SW1 to turn on the charge control switch SW1. In this state, the charging power source 1 is connected to the battery and constant current charging of the battery is started.

[Step S3] The microcomputer 3 detects the charging voltage of the battery being charged with a constant current.
The detected charging voltage is compared with the current switching voltage V1.
This step is looped until the charging voltage becomes the current switching voltage V1. [Step S4] When the charging voltage of the battery rises to V1, the microcomputer 3 controls the charging power supply 1 to change the charging current for constant-current charging the battery from I1 to I2. I2 is, for example, 0.6 A. Further, the microcomputer 3 controls the charging power source 1 to change the current switching voltage V2 for switching the current for constant current charging to, for example, 4.16V.

[Step S5] The microcomputer 3 detects the charging voltage of the battery which is being charged with a constant current.
The detected charging voltage is compared with the current switching voltage V2.
This step is looped until the charging voltage reaches the current switching voltage V2. [Step S6] When the charging voltage of the battery rises to V2, the microcomputer 3 controls the charging power source 1 to change the charging current for constant-current charging the battery from I2 to I3. I3 is 0.3 A, for example. Further, the microcomputer 3 controls the charging power supply 1 to change the current switching voltage V3 for switching the current for constant current charging to, for example, 4.13V.

[Step S7] The microcomputer 3 detects the charging voltage of the battery being charged with a constant current.
The detected charging voltage is compared with the current switching voltage V3.
This step is looped until the charging voltage becomes the current switching voltage V3. [Steps S8 and S9] When the charging voltage of the battery rises to the current switching voltage V3, the microcomputer 3 turns off the charging control switch SW1 to end the charging of the battery.

[0040]

EFFECT OF THE INVENTION The battery charging method of the present invention has the excellent feature that it can effectively prevent deterioration of battery performance and can be charged rapidly in a short time. In particular, there is an extremely excellent feature that a non-aqueous secondary battery such as a lithium-ion secondary battery, which has the property that the performance is remarkably deteriorated by the increase of the battery voltage, can be rapidly charged to effectively prevent the deterioration of the battery performance. That is, the charging method of the present invention performs constant current charging while comparing the charging voltage of the battery with the current switching voltage, and gradually changes the charging current to a smaller value when the battery voltage rises to the current switching voltage. Discontinue the charge temporarily and detect the open circuit voltage and compare it with the full charge voltage that is set lower than the current switching voltage to detect the full charge of the battery, or the battery approaches the full charge. According to the above, the current switching voltage is set to a low value to prevent deterioration of battery performance due to overvoltage.

The constant current charging is interrupted to detect the open circuit voltage,
In this method of comparing the open circuit voltage with the full charge voltage, the full charge voltage for detecting the full charge of the battery and the current switching voltage for switching the charging current for constant current charging can be set to different voltage values. Therefore, the full charge voltage is set to a voltage that can accurately detect that the battery is fully charged, and the current switching voltage is set to a voltage value that can quickly charge the battery in a short time without degrading the battery performance. can do.

Further, in the method of setting the current switching voltage to be lower as the battery approaches full charge, the current switching voltage can be set to lower as the battery voltage becomes higher and battery performance tends to decrease. , Effectively prevent the battery performance from decreasing due to the battery overvoltage,
It has the feature that it can be rapidly charged. Particularly, in the charging method of the present invention in which the charging current for constant current charging of the battery is controlled to be gradually lower, the voltage drop due to the circuit impedance becomes smaller when the charging current is made smaller, and the voltage actually applied to the battery becomes higher. However, as the battery approaches full charge, the charging method of the present invention in which the current switching voltage is changed to a low value is extremely effective in preventing such adverse effects, and can reliably prevent deterioration of battery performance. It has excellent features.

Furthermore, the charging method of the present invention does not require a high-precision constant voltage power source, and can realize the feature that a battery can be rapidly charged with an inexpensive charging circuit. This is because the battery is fully charged by constant current charging while detecting the battery voltage. A circuit for charging a battery with a constant current does not require extremely high-precision electronic parts, unlike a charging circuit for controlling an output voltage with high accuracy and charging with a constant voltage. The constant current charging circuit does not significantly reduce the battery performance even if there is some error in the current that charges the battery. On the other hand, the circuit for charging the battery with a constant voltage has a drawback that the battery performance is significantly deteriorated if the output voltage has a slight error.

[Brief description of drawings]

FIG. 1 is a graph showing voltage and current characteristics of a conventional charging method.

FIG. 2 is a voltage for charging a battery according to the method of the embodiment of the present invention,
Graph showing current characteristics

FIG. 3 is a block diagram of a charging circuit used in the method of the embodiment of the present invention.

FIG. 4 is a flowchart showing steps of charging a battery by the method according to the embodiment of the present invention.

FIG. 5 is a flowchart showing steps of charging a battery by a method according to another embodiment of the present invention.

FIG. 6 is a graph showing voltage / current characteristics for charging a battery by a method according to another embodiment of the present invention.

FIG. 7 is a flowchart showing steps of charging a battery by a method according to another embodiment of the present invention.

[Explanation of symbols]

 1 ... Charging power supply 2 ... Detection circuit 3 ... Microcomputer SW1 ... Charging control switch

Claims (3)

[Claims] 1. A battery is charged with a constant current, and when the charging voltage of the battery rises to a preset current switching voltage, the charging current is reduced to perform the constant current charging, and the full-charge voltage of the battery is detected. In the charging method that terminates battery charging, the full-charge voltage that determines that the battery is fully charged is set lower than the current switching voltage that switches the charging current for constant-current charging, and the battery was detected while constant-current charging. Change the current value for constant current charging by comparing the charging voltage with the current switching voltage, and temporarily interrupt the charging of the battery at a predetermined cycle during constant current charging to detect the battery A method for charging a battery, characterized in that an open circuit voltage is compared with a full charge voltage and constant current charging is terminated when the open circuit voltage rises to the full charge voltage. 2. The battery charging method according to claim 1, wherein when the constant current charging is performed, pulse charging is performed so that the charging current of the battery is set to 0 in a pulsed manner in a short cycle. 3. A charging method in which a battery is charged with a constant current, and when the charging voltage of the battery rises to a preset current switching voltage, the charging current is reduced to perform the constant current charging, as the battery approaches full charge. A method of charging a battery, characterized in that a set voltage of a current switching voltage for reducing a charging current of constant current charging is set low.