JPH09149556A - Secondary battery charging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten charging time without lowering the performance of a battery by temporarily adopting a first set voltage as a set voltage to perform constant current-constant voltage charging, and after a battery is charged up to a predetermined capacity, performing constant voltage charging by a second set voltage compensated for temperature. SOLUTION: A central control part 3 computes a battery voltage inputted from a voltage detecting part 4 and a charging current inputted from a current detecting part 5 to control a charging control part 2, and the constant current- constant voltage charging of a secondary battery 8 is performed by adjusting an output voltage and an output current by the charging control part 2. The charging control part 2 performs constant current constant voltage charging by setting the maximum voltage as a first set voltage to the battery 8 at the initial stage in which charging is started, and when the battery 8 is charged up to a predetermined capacity, the first set voltage is changed over to a second set voltage to perform the constant current constant voltage charging. In that case, the first set voltage is set higher than the second set voltage, and the second set voltage is compensated for temperature to keep the set voltage an optimal voltage for the battery 8.

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 such as a nickel-cadmium battery, a nickel-hydrogen battery and a lithium ion secondary battery.

[0002]

2. Description of the Related Art Nickel-cadmium batteries and nickel-
Hydrogen batteries can be fully charged by constant current charging. When this type of battery is charged with constant current, the battery voltage rises to the peak voltage and then decreases by ΔV.
Fully charged by detecting V drop. However, the lithium-ion secondary battery has a higher battery voltage as it is charged. Since this battery does not have the property of lowering the battery voltage even when it is fully charged, it cannot detect the decrease of the battery voltage by ΔV like a nickel-cadmium battery and cannot detect the full charge. Further, the lithium-ion secondary battery has an adverse effect that the battery performance is significantly deteriorated when the battery voltage is abnormally increased due to overcharge. Therefore, the lithium-ion secondary battery cannot be fully charged by constant current charging, but is fully charged by constant voltage charging.

As described above, the nickel-cadmium battery and the nickel-hydrogen battery are charged with constant current to be fully charged, and the lithium-ion secondary battery is charged with constant voltage to be fully charged. Therefore, the lithium-ion secondary battery cannot be charged by the nickel-cadmium battery charging method in which constant current charging is performed. The constant current-constant voltage charging method that charges the battery by limiting the maximum value of the charging voltage and the maximum value of the charging current can fully charge both nickel-cadmium battery and lithium-ion secondary battery. . However, since the nickel-cadmium battery and the lithium-ion secondary battery have considerably different battery voltages, for example, a pack battery in which three nickel-cadmium batteries are connected in series and one lithium-ion secondary battery are connected. Must be charged at the same set voltage.

A method of charging a battery with a constant current and a constant voltage is described in Japanese Utility Model Laid-Open No. 5-60146. Further, the charging method described in this publication temperature-compensates a set voltage for constant voltage charging. The internal resistance of the battery increases when the temperature is low. In order to compensate for the voltage drop due to the large internal resistance, low temperature batteries are charged at a constant voltage with a high set voltage. If you charge the battery with this charging method,
The voltage and current curves change as shown in FIG. In the charging method shown in this figure, the set voltage for constant voltage charging at 50 ° C. is set to 4.2V, and the set voltage at 0 ° C. is 4.4V and 0.2V.
V is high. Since the battery at 0 ° C. has a larger internal resistance than the battery at 50 ° C., the constant current charging time can be extended by increasing the set voltage as shown in the figure. Therefore, it is possible to lengthen the time for charging the low temperature battery with constant current and shorten the time until the battery is fully charged.

[0005]

However, it is difficult to further shorten the charging time of the battery by this method. This is because if the set voltage is further increased in order to shorten the time for full charge, the charging current of the battery having a high temperature and a small internal resistance does not decrease, and the battery performance remarkably decreases.

The present invention was developed for the purpose of further shortening the charging time without lowering the battery performance.

[0007]

According to the method of charging a secondary battery of the present invention, the set voltage for charging the secondary battery 8 at a constant voltage is temperature-compensated, and the set voltage for constant voltage charging is compensated at a low temperature. This is an improved charging method.

According to the charging method of the present invention, the secondary battery 8 is charged with a constant voltage at the first set voltage and then with the second set voltage. The first set voltage is set to be equal to or higher than the second set voltage, and the second set voltage is changed according to the temperature.
The set voltage when the temperature is low is set higher than the set voltage when the temperature is high. That is, the charging method of the present invention is
The battery is characterized in that the battery is charged at a constant current-constant voltage with the first set voltage as a temporarily high set voltage, and after the battery is charged to a predetermined capacity, the battery is charged with a constant voltage at the temperature-compensated second set voltage. And The first set voltage can be temperature-compensated to change the set voltage, or can be set to a constant voltage without temperature compensation. In the method of temperature compensating the first set voltage, the set voltage when the temperature is low is set higher than when the temperature is high.

The timing of switching from the first set voltage to the second set voltage is, for example, when the battery voltage reaches the first set voltage, when the charging current of the battery decreases to a set value, or when the battery temperature changes. When the temperature rises to the set temperature.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. However, the examples described below exemplify the charging method of the secondary battery for embodying the technical idea of the present invention, and the present invention does not specify the charging method as the following method.

Further, in this specification, in order to facilitate understanding of the claims, the numbers corresponding to the members shown in the embodiments are referred to as "the claims column" and "to solve the problems. It is added to the members shown in "Means column".
However, the members described in the claims are not limited to the members of the embodiments.

FIG. 2 shows the voltage and current characteristics when the secondary battery is charged by the method of the embodiment of the present invention. The charging method in this figure shows the case of charging a lithium ion secondary battery.
However, the rechargeable secondary battery is not specified as a lithium ion secondary battery. For example, a secondary battery such as a nickel-cadmium battery or a nickel-hydrogen battery can be charged in the same manner. However, nickel-cadmium batteries and nickel-
Since the hydrogen battery has a low voltage, it is a battery pack in which three batteries are connected in series. This is because it is charged at the same voltage as the lithium ion secondary battery. In this charging method, in addition to the lithium-ion secondary battery, a nickel-cadmium battery and a nickel-hydrogen battery can be charged in the same manner in the same charger. The following examples show one lithium ion secondary battery, three nickel-cadmium batteries and a nickel-ion battery.
A method for charging a hydrogen battery will be shown, but the conditions for constant current-constant voltage charging are the type of secondary battery to be charged, the number of series connections,
Set to the optimum value depending on the capacity.

The charging method of FIG. 2 limits the maximum values of charging current and charging voltage, that is, constant current-constant voltage charging is performed to fully charge the secondary battery. The rechargeable battery that is charged with a constant current-constant voltage is set to the first set voltage during charging.
The set voltage is switched to the second set voltage. The secondary battery is
First, constant current-constant voltage charging is performed at the first setting voltage, and then constant current-constant voltage charging is performed at the second setting voltage.

The first set voltage is set to be equal to or higher than the second set voltage. In the charging method shown in the figure, the first set voltage is set to 4.4V. It is considered that when the battery voltage of the lithium-ion secondary battery exceeds 4.2 V during charging, metallic lithium is deposited and the battery performance deteriorates. In the charging method shown in FIG. 2, the first set voltage is set higher than 4.2V, but the battery voltage rises to the first set voltage in a very short time. That is also when the battery is not fully charged. When the maximum voltage of the battery is set to the first set voltage or less and the constant current-constant voltage charging is performed, the battery voltage of the secondary battery becomes the first set voltage because the constant current charge is performed at the first set voltage to charge. Is a short time until the first set voltage is switched to the second set voltage. For this reason, the first set voltage can be set as high as 4.4 V to reduce obstacles to the lithium ion secondary battery.

The secondary battery is charged by increasing the first set voltage to 4.4V and then switched to the second set voltage to be fully charged. The second set voltage is set equal to or lower than the first set voltage, and the set voltage is changed according to the temperature. The second set voltage is set so that the set voltage when the temperature is low is higher than the set voltage when the temperature is high. The reason why the second set voltage is increased when the temperature is low is that the secondary battery charged in an environment with a low temperature has a large internal resistance and a large voltage drop due to the internal resistance.

In the charging method shown in the figure, the second set voltage is set to the following voltage. 0 ° C …… 4.4V 25 ° C …… 4.3V 50 ° C …… 4.2V

When the second set voltage is set high, the capacity that can charge the secondary battery can be increased and the energy capacity can be increased. However, if the set voltage is too high, the battery performance will be degraded. Therefore, the second set voltage is adjusted to an optimum value in consideration of the battery type, capacity, usage environment and the like.

In the charging method shown in FIG. 2, first, the maximum voltage is set to the first set voltage to charge the secondary battery with constant current-constant voltage, and when the battery voltage reaches the first set voltage, the second set voltage is set. Switch to voltage and charge with constant current-constant voltage. The secondary battery charged in the state shown in this figure is initially charged with a constant current because the battery voltage is equal to or lower than the first set voltage. When the battery voltage rises as the charging progresses and the battery voltage reaches the first set voltage, the maximum voltage of the battery is switched to the second set voltage, so that the constant current charging is switched to the constant voltage charging.

In the charging method shown in this figure, the switching timing for switching the set voltage from the first set voltage to the second set voltage is
It is assumed that the battery voltage rises to the first set voltage. The charging method of the present invention does not specify the switching timing as this timing. The switching timing is not only the battery voltage,
The charging current may be detected or the battery temperature may be detected to determine. The method of detecting the charging current and determining the switching timing is as follows:
The set voltage is switched from the first set voltage to the second set voltage. The set current for specifying the switching timing is preferably smaller than the charging current for constant current charging the secondary battery, but is set to a current value substantially equal to the current value for constant current charging.

When the maximum voltage is set to the first set voltage and the secondary battery is charged with the constant current-constant voltage, when the battery voltage rises to the first set voltage, the battery voltage is limited to the first set voltage. , The charging current gradually decreases. Therefore, it is possible to detect the charging current and switch from the first set voltage to the second set voltage. Furthermore, when the secondary battery is charged, the battery temperature also rises. Therefore, it is possible to detect the battery temperature and switch the set voltage from the first set voltage to the second set voltage.

In the charging method shown in FIG. 2, the first set voltage is fixed and the second set voltage is changed according to the ambient temperature of the battery.
This method has the advantage that the secondary battery can be charged with a simple circuit because the first set voltage is not changed. However, in the charging method of the present invention, the first set voltage can be changed depending on the ambient temperature of the battery. For example, the first set voltage and the second set voltage can be set to the following voltages, and the first set voltage can be set higher than the second set voltage by a certain voltage. Ambient temperature 1st setting voltage 2nd setting voltage 0 ° C 4.4V 4.3V 25 ° C 4.3V 4.2V 50 ° C 4.2V 4.1V

A circuit for charging the secondary battery as described above is shown in FIG. The charging circuit shown in this figure is a power supply 1 for converting an input alternating current into a voltage capable of charging the secondary battery 8.
Then, the output of the power supply 1 is adjusted to keep the secondary battery 8 at a constant current-
A charging control unit 2 that performs constant voltage charging, a central control unit 3 that controls the charging control unit 2, a voltage detection unit 4 that inputs a battery voltage to the central control unit 3, and a charging current of the secondary battery 8 is detected. The central controller 3 is provided with a current detector 5, a temperature detector 6 for detecting the ambient temperature, and a timer 7 for controlling the charging time of the secondary battery 8.

The power supply 1 comprises a diode bridge for rectifying an input alternating current and converting it into a direct current, and an electrolytic capacitor smoothing circuit for smoothing the output of the diode bridge. As the power supply, a DC-DC converter that converts input alternating current into direct current, converts direct current into alternating current, and steps down can also be used.

The central control unit 3 is a microprocessor,
The battery voltage input from the voltage detection unit 4 and the current detection unit 5 and the charging current are calculated to control the charging control unit 2, and the charging control unit 2 adjusts the output voltage and the output current to recharge the secondary battery. 8 is charged with constant current-constant voltage. As shown in FIG. 2, the charge control unit 2 controlled by the central control unit 3 sets the maximum voltage of the battery to the first set voltage and performs constant current-constant voltage charging at the beginning of charging, and Is charged to a predetermined capacity, the set voltage is switched from the first set voltage to the second set voltage to perform constant current-constant voltage charging. When the secondary battery 8 is fully charged, charging is stopped.

The voltage detector 4 detects the battery voltage, converts the detected battery voltage into a digital value, and inputs it to the central controller 3. The current detection unit 5 detects the charging current of the battery, converts it into a digital value, and inputs it to the central control unit 3. The temperature detecting unit 6 detects the ambient temperature of the secondary battery 8, converts the detected temperature into a digital value, and inputs the digital value to the central control unit 3. The temperature detector 6 can also detect both the ambient temperature and the battery temperature and input them to the central controller 3. The voltage detection unit 4, the current detection unit 5, and the temperature detection unit 6 have built-in A / D converters that convert the detected analog signals of voltage, current, and temperature into digital signals.

The timer section 7 stores the total time for charging the secondary battery 8. The timer unit 7 starts counting when charging is started. When the timer unit 7 finishes counting, the central control unit 3 controls the charging control unit 2 to finish charging the secondary battery 8. The timer unit 7 can also store the switching timing for switching the set voltage from the first set voltage to the second set voltage. The timer unit 7 is the first
The charging method for determining the timing of switching from the set voltage to the second set voltage is suitable for, for example, a method of detecting that the secondary battery 8 is sufficiently discharged and fully charging it. This is because it takes a certain amount of time for the battery voltage of the fully discharged secondary battery 8 to rise to the first set voltage. The switching timing stored in the timer unit 7 is set to a time that does not have a bad influence by setting the set voltage of the secondary battery 8 to the first set voltage, for example, 10 minutes to 1 hour.

[0027]

The secondary battery charging method of the present invention is characterized in that it can be fully charged in a short time without degrading the battery performance. That is, the charging method of the present invention switches the battery voltage from the first set voltage to the second set voltage to charge the battery by constant current-constant voltage, and increases the first set voltage to the second set voltage or higher, and This is because the second set voltage is temperature-compensated and the set voltage is controlled to an optimum voltage for the battery. At the beginning of charging, the secondary battery is charged at a constant current / constant voltage by setting the first set voltage having a high set voltage. Since the constant voltage-constant voltage charging is performed by increasing the set voltage, the battery is charged with the constant current for a longer time, and the charging capacity per hour in this process can be increased. Therefore, the charging time for full charge can be shortened. Since the first set voltage is increased, the battery voltage is somewhat increased, but the time for which the battery voltage exceeds the second set voltage is extremely short. Therefore, the charging method of the present invention realizes an extremely excellent feature that the battery can be fully charged in a short time without adversely affecting the secondary battery.

[Brief description of the drawings]

FIG. 1 is a graph showing voltage-current characteristics when a secondary battery is charged by a conventional method.

FIG. 2 is a graph showing voltage-current characteristics when a secondary battery is charged by the method of the embodiment of the present invention.

FIG. 3 is a block circuit diagram showing a circuit for charging a secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Power supply 2 ... Charge control part 3 ... Central control part 4 ... Voltage detection part 5 ... Current detection part 6 ... Temperature detection part 7 ... Timer part 8 ... Secondary battery

Claims (1)

[Claims] 1. A method for charging a secondary battery, wherein a set voltage for charging a secondary battery (8) with a constant voltage is temperature-compensated, and a set voltage for charging a constant voltage when a temperature is low is highly compensated. ) Is charged at a constant voltage with the first set voltage, and then is charged at a constant voltage with the second set voltage to set the first set voltage to the second set voltage or higher, and the second set voltage changes the set voltage according to the temperature. A method for charging a secondary battery, wherein the set voltage when the temperature is low is set higher than the set voltage when the temperature is high.