JPH09117075A - Charging method for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the charging efficiency by applying a lithium ion secondary battery with a recommended voltage pulse and a higher voltage pulse alternate ly. SOLUTION: A switching circuit 4 switches a constant voltage/constant current control circuit 2 and a constant voltage control circuit 3 such that a lithium ion battery 1 is applied with a charging voltage pulse of 4.2V/cell recommended by the constant voltage/constant current control circuit 2 and a higher voltage pulse from the constant voltage control circuit 3. A unit 5 for monitoring the charging voltage level of the lithium ion battery 1 and a display section 6 for notifying the under charging and the end of charging of the lithium ion battery 1. The display section 6 flickers when the lithium ion battery 1 is being charged and it is lighted upon ending the charging operation. According to the constitution, charging efficiency can be enhanced while shortening the charging time by increasing the charging quantity per charging time of the lithium ion battery 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a method for charging a secondary battery, and more particularly, to a method for controlling the charging of a charger that charges a lithium-ion secondary battery that is lighter in weight and can be driven for a longer time than a nickel-cadmium battery.

[0002]

2. Description of the Related Art Lithium ion secondary batteries have been drawing attention because they can be made lighter in weight and can be driven for a longer time than nickel-cadmium batteries. The lithium-ion secondary battery is a battery that is usually charged by constant voltage control such as 4.2V. On the other hand, the lithium metal battery is charged by increasing the voltage by constant current control instead of constant voltage control to increase charging efficiency. A lithium metal battery has a smaller voltage value than a lithium ion secondary battery, is complicated in handling, and is rarely used in terminals and the like. A lithium-ion secondary battery can increase the charge amount when charged by constant current control like a lithium metal battery,
If the battery voltage is too high and lithium ions are metalized and adhere to the negative electrode such as carbon and the battery characteristics are deteriorated, constant voltage control is performed instead of constant current control so that the battery voltage does not increase too much. In the worst case, if lithium ions are metallized and adhere to the negative electrode and the metallized lithium extends toward the positive electrode, there is a risk of short-circuiting. Conventionally, the charging method of this lithium ion secondary battery is generally performed as follows. First, after starting charging, constant voltage control is performed when the battery voltage rises to 4.2V. After that, the charging is terminated when the charging current decreases to a certain value. Hereinafter, the conventional method for charging the lithium-ion secondary battery will be specifically described with reference to the drawings. FIG. 5 is a block diagram showing a configuration of a charging circuit used in a conventional lithium-ion secondary battery charging method. In FIG. 5, 101 is a recommended constant voltage of 4.2V, which is recommended so that the battery characteristics do not deteriorate during charging and the charging is fully charged (charge amount; 100%). Is a lithium-ion secondary battery that is charged by
02 is a lithium-ion secondary battery 101 having a battery voltage of 4.
A constant voltage / constant current control circuit performs constant current control until the voltage rises to 2V, and also performs constant voltage control when the battery voltage of the lithium ion secondary battery 101 rises to 4.2V, and 103 is a lithium ion secondary battery. Reference numeral 104 denotes a voltage monitoring device that monitors the charging voltage value of the battery 101, and reference numeral 104 denotes a charging display unit that notifies the charging of the lithium ion secondary battery 101 and the end of charging. The charging display unit 104 is configured to blink when the lithium-ion secondary battery 101 is charged and is turned on when the charging is finished, or is turned on when the lithium-ion secondary battery 101 is charged and the charging is finished. Some of them are configured to be turned off at times. Next, FIG. 6 is a diagram showing a method of charging a lithium ion secondary battery in the charging circuit shown in FIG. When the lithium-ion secondary battery 101 is used up to the discharge end voltage,
The battery voltage is 2.5 V / cell. When the constant voltage / constant current control circuit 102 starts charging and constant current control is performed from the state where the battery voltage of the lithium ion secondary battery 101 is 2.5 V / cell, as shown in period A of FIG. Then, the battery voltage gradually rises. If the lithium-ion secondary battery 101 is charged by the constant current control as it is, the battery voltage rises excessively. Therefore, the battery voltage is 4.2 V / which is the recommended charging voltage when the lithium-ion secondary battery 101 is charged. The constant voltage control is performed at the cell (point B) to control the increase in the battery voltage. In this way, when the lithium ion secondary battery 101 is subjected to constant voltage control, the charging current of the lithium ion secondary battery 101 decreases depending on the characteristics of the battery. Then, when the charging current finally stops flowing (point C: 0A), the charging ends. The lithium-ion secondary battery 101 is fully charged when the open circuit voltage reaches 4.2 V, and the charging is completed. In this conventional method for charging a lithium-ion secondary battery, charging is performed by constant voltage control with a recommended charging voltage of 4.2 V, so a constant current is merely used to increase the charging efficiency of the lithium-ion secondary battery. As compared with the case where charging is performed only by control, deterioration of the battery characteristics of the lithium ion secondary battery can be less likely to occur, and there is an advantage that charging can be performed with high reliability.

[0003]

However, in the above-mentioned conventional method for charging a lithium ion secondary battery, the battery voltage does not rise excessively during charging in order to prevent deterioration of the battery characteristics of the lithium ion secondary battery. Since constant voltage control is performed at the recommended charging voltage as described above, deterioration of battery characteristics during charging can be suppressed, but as shown in FIG. 6, the amount of charge during constant voltage control particularly at the end of charging is significantly reduced. Resulting in. Therefore, there is a problem that the charging efficiency of the lithium ion secondary battery during constant voltage control is reduced and the charging time is long.

Therefore, according to the present invention, when charging a lithium ion secondary battery by constant voltage control, the charging efficiency of the lithium ion secondary battery can be increased and the charging time of the lithium ion secondary battery can be shortened. An object is to provide a method of charging an ion secondary battery.

[0005]

The present invention provides a method for charging a lithium ion secondary battery, which comprises:
It is characterized in that the secondary battery is charged by alternately applying a recommended charging voltage recommended when charging the lithium ion secondary battery and a voltage equal to or higher than the recommended charging voltage in a pulsed manner.

The charging method for the lithium ion secondary battery is characterized in that the pulse frequency is fixed when the lithium ion secondary battery is charged by applying a pulse.

The charging method for the lithium ion secondary battery is characterized in that the pulse frequency is changed when the lithium ion secondary battery is charged by applying a pulse.

The above-mentioned method for charging a lithium ion secondary battery is characterized in that when the lithium ion secondary battery is charged by applying a pulse, the application duty of the recommended charging voltage is changed.

The above-mentioned method for charging a lithium ion secondary battery is characterized in that when the lithium ion secondary battery is charged by applying a pulse, the applied duty of a voltage higher than the recommended charging voltage is changed.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a charging circuit used in a method for charging a lithium ion secondary battery according to an embodiment of the present invention. In FIG. 1, 1 is a recommended charging voltage of 4.2 V / cell which is recommended so that the battery characteristics do not deteriorate during charging and the charging is fully charged (charging amount; 100%). The lithium-ion secondary battery 2 is charged with a voltage, and 2 performs constant current control until the battery voltage of the lithium-ion secondary battery 1 rises to the recommended charging voltage of 4.2 V / cell. The battery voltage of Battery 1 is 4.2, which is the recommended charging voltage.
The recommended charging voltage 4.2 for the lithium ion secondary battery 1 is periodically increased to V / cell for a certain period of time (10 ms).
A constant voltage / constant current control circuit for applying the voltage of V / cell in a pulsed manner, 3 is a fixed time (10 ms) cycle when the battery voltage of the lithium ion secondary battery 1 has risen to the recommended voltage of 4.2 V / cell A constant voltage control circuit that pulse-applies a voltage of 4.35 V / cell, which is a recommended charging voltage of 4.2 V / cell or more, to the lithium-ion secondary battery 1.

Reference numeral 4 denotes a lithium ion secondary battery 1 with a recommended charging voltage of 4.2 V / cell by the constant voltage / constant current control circuit 2 and a voltage 4.
A switching circuit for switching between the constant voltage / constant current control circuit 2 and the constant voltage control circuit 3 so as to alternately apply 35 V / cell pulse, and 5 is a voltage for monitoring the charging voltage value of the lithium ion secondary battery Reference numeral 6 denotes a monitor device, and reference numeral 6 denotes a charge display unit for notifying that the lithium ion secondary battery is being charged or has been charged. The charging display unit 6 is configured to blink when the lithium-ion secondary battery 1 is charged and is turned on when the charging is finished, or the lithium-ion secondary battery 1
It is possible to cite that the light is turned on when the battery is charged and turned off when the battery is charged.

Next, FIG. 2 is a diagram showing a method of charging a lithium ion secondary battery in the charging circuit shown in FIG. 1, and FIG. 3 is a charging time and charging voltage from the start of charging to the completion of charging in the charging circuit shown in FIG. It is a figure which shows the relationship of. An embodiment of the present invention will be described based on experimental data. Here, the case of charging the 2-cell series-connected pack of the lithium-ion secondary battery 1 will be described. Note that FIG. 2 shows data per cell of the lithium ion secondary battery 1, and FIG. 3 shows data per two cells of the lithium ion secondary battery 1.

First, a two-cell series-connected pack of the lithium-ion secondary battery 1 (nominal voltage 7.2V, charging voltage 8.4).
V, nominal capacity 1000mAh) at 0.2C, 5V / 2
After discharging to a cell (the end-of-discharge voltage of 2.5 V per cell), 1 hour later, charging was started at 1C (1A).
The constant voltage / constant current control circuit 2 starts charging to perform constant current control. At this time, as shown in the period A of FIG. 2, the battery voltage gradually increases. If the lithium-ion secondary battery 1 is charged by the constant current control as it is, the battery voltage will rise excessively. Therefore, the battery voltage is 4.2 V / which is the recommended charging voltage when the lithium-ion secondary battery 1 is charged. When a cell is formed, as shown in a period B of FIG. 2, a recommended charging voltage of 4.2 V / cell and a voltage 4.3 higher than the recommended charging voltage are set.
Pulses of 5 V / cell are applied alternately. This pulse application is performed by switching the switching circuit 4 between the constant voltage / constant current control circuit 2 for 4.2V / cell application and the constant voltage control circuit 3 for 4.35V / cell application. Then, as shown in period C of FIG. 2, in order to measure the electromotive voltage of the battery, a charge stop period of 30 seconds is provided every 5 minutes after 45 minutes have elapsed from the start of charging, and the open circuit voltage of the battery is 8. 4V /
The time until it became 2 cells was measured. When the open circuit voltage of this battery reaches 4.2 V, it is fully charged and the charging is completed.

Charging after the 2-cell series-connected pack of the lithium-ion secondary battery 1 reaches the recommended charging voltage is specifically performed as follows. 7. The recommended charging voltage is the battery voltage of the 2-cell series connection pack of the lithium-ion secondary battery 1.
From the time when it becomes 4V / 2 cells or more, the constant voltage charging of 8.7V / 2 cells which is higher than the recommended charging voltage and the constant voltage charging of 8.4V / 2 cells which is the recommended charging voltage are repeated for each 10ms time. Then, a charge stop period of 30 seconds was provided every 5 minutes after the lapse of 45 minutes, and the time until the open circuit voltage of the battery reached 8.4 V / 2 cells was measured. As a result, as shown in FIG. 3, until the open circuit voltage of the battery reaches 8.4 V / 2 cells,
It took a minute.

On the other hand, in the charging method in which the constant voltage control is simply performed after the constant current control of the comparative example (conventional) of FIGS. 5 and 6 described above, two cells of lithium ion secondary batteries are connected in series as in this embodiment. 60 after charging the pack and starting charging
A charge stop period of 30 seconds is provided every 5 minutes after the lapse of minutes.
When the time required for the open circuit voltage of the battery to reach 8.4 V / 2 cells was measured, it took 68 minutes to reach the open circuit voltage of the battery of 8.4 V / 2 cells. From this result, in the present embodiment, the charging efficiency is accelerated by temporarily setting the constant voltage charging state of 8.4 V / 2 cells or more to accelerate the current inflow to the lithium ion secondary battery 1 as compared with the conventional case. It was found that the charging time can be increased and the charging time can be significantly shortened.

As described above, in the present embodiment, the lithium-ion secondary battery 1 is alternately pulsed with the recommended charging voltage recommended when the lithium-ion secondary battery 1 is charged and a voltage higher than the recommended charging voltage. By applying and charging, the voltage is periodically charged at a voltage higher than the recommended charging voltage for a short period of time. Therefore, compared with the conventional case where the lithium ion secondary battery is charged only under the recommended charging voltage, the lithium ion secondary battery is charged. There is an effect that the charging efficiency can be increased by increasing the charging amount with respect to the charging time of the secondary battery, and the charging time can be shortened.

Further, not only the charging is performed at a voltage higher than the recommended charging voltage, but also the charging is periodically performed for a short time at the recommended charging voltage. Therefore, this may occur when charging at a voltage higher than the recommended charging voltage for a long time. It is possible to suppress deterioration of the battery.

In the present embodiment, when the lithium-ion secondary battery 1 is pulse-charged and charged, the pulse frequency is fixed, so that a simple circuit configuration can be realized and the device cost can be reduced. It can be reduced.

In the present embodiment, when the lithium-ion secondary battery 1 is pulse-charged and charged, a charge stop period of 30 seconds is provided every 5 minutes after 45 minutes have elapsed from the start of charging. The electromotive voltage of the secondary battery 1 can be measured, and the full charge can be easily known.

In the above embodiment, the recommended charging voltage and the voltage equal to or higher than the recommended charging voltage are alternately pulsed from reaching the recommended charging voltage to the end of charging, and 5 minutes after 45 minutes have elapsed from the start of charging. Although the case where the charging stop period of 30 seconds is provided for each time has been described, the present invention is not limited to this, and the point is that the recommended charging is performed during a certain period from reaching the recommended charging voltage to the end of charging. It suffices to alternately apply a voltage and a voltage equal to or higher than the recommended charging voltage, for example, the recommended charging voltage and the voltage equal to or higher than the recommended charging voltage during the entire period from reaching the recommended charging voltage to the end of charging without providing a charging stop period. Alternatively, pulses may be applied alternately.

In the above embodiment, the case where the pulse frequency is fixed to, for example, 100 Hz when the lithium ion secondary battery 1 is pulse-charged and charged, but the present invention is not limited to this. The pulse frequency may be appropriately changed when the lithium-ion secondary battery 1 is charged by applying a pulse. In this case, charging can be performed in a shorter time by changing the pulse frequency as appropriate so that the charging efficiency is further increased. Further, the battery deterioration can be further suppressed by appropriately changing the pulse frequency so as to further suppress the battery deterioration. Therefore, the charging time and battery deterioration can be adjusted.

In the above embodiment, when the lithium ion secondary battery 1 is charged by applying a pulse, both the applied duty of the recommended charging voltage and the applied duty of the voltage higher than the recommended charging voltage are fixed, and both voltages are fixed. The case has been described where the application duty ratio of is fixed at 50%.
The present invention is not limited to this, and when the lithium-ion secondary battery is pulse-charged, at least one of the applied duty of the recommended charging voltage and the applied duty of the voltage equal to or higher than the recommended charging voltage is appropriately selected. The configuration may be changed. In this case, by appropriately increasing the applied duty of the voltage equal to or higher than the recommended charging voltage with respect to the applied duty of the recommended charging voltage, the charging amount is increased and the charging efficiency is increased as compared with the case where the applied duty of both voltages is the same. Can be raised. In addition, by appropriately increasing the applied duty of the recommended charging voltage with respect to the applied duty of the voltage equal to or higher than the recommended charging voltage, the battery deterioration can be suppressed more efficiently than in the case where the applied duties of both voltages are the same. it can. Therefore, the charging time and battery deterioration can be adjusted.

In the above embodiment, the recommended charging voltage is 4.2.
The case of using the lithium-ion secondary battery 1 charged by V has been described, but the present invention is not limited to this, and the point is that the battery characteristics do not deteriorate during charging and the charging is performed. A lithium ion secondary battery having a recommended charging voltage that is recommended in consideration of fully charging the battery may be used, for example, a lithium ion secondary battery having a recommended charging voltage of 4.1 V may be used. .

[0024]

According to the present invention, a lithium ion secondary battery is charged by alternately applying a pulse of a recommended charging voltage recommended when charging the lithium ion secondary battery and a voltage higher than the recommended charging voltage. By doing so, since the battery is charged periodically at a voltage higher than the recommended charging voltage for a short period of time, it is possible to charge the lithium ion secondary battery more than the conventional case where the lithium ion secondary battery is charged only under the recommended charging voltage. There is an effect that the charging efficiency can be increased by increasing the charging amount with respect to the charging time and the charging time can be shortened. In addition to charging at a voltage higher than the recommended charging voltage, it also periodically charges at the recommended charging voltage for a short period of time.
It is possible to suppress the deterioration of the battery that would occur when the battery is charged at a voltage higher than the recommended charging voltage for a long time.

When the lithium-ion secondary battery is charged by applying a pulse, the pulse frequency is fixed, so that the circuit structure can be simplified and the device cost can be reduced.

Further, when charging the lithium ion secondary battery by applying a pulse, there is an effect that the charging time and the battery deterioration can be adjusted by changing the pulse frequency.

Further, when charging the lithium ion secondary battery, there is an effect that the charging time and battery deterioration can be adjusted by changing the applied duty of the recommended charging voltage.

Further, when charging the lithium ion secondary battery, there is an effect that the charging time and battery deterioration can be adjusted by changing the applied duty of a voltage higher than the recommended charging voltage.

[Brief description of the drawings]

FIG. 1 is a lithium ion 2 according to an embodiment of the invention.
It is a figure which shows the structure of the charging circuit used for the charging method of a secondary battery.

FIG. 2 is a diagram showing a method of charging a lithium ion secondary battery in the charging circuit shown in FIG.

FIG. 3 is a diagram showing the relationship between the charging time and the charging voltage from the start of charging to the end of charging in the charging circuit shown in FIG.

FIG. 4 is a diagram showing the relationship between the charging time and the charging voltage from the start of charging to the end of charging in the charging circuit of the comparative example shown in FIGS.

FIG. 5 is a block diagram showing a configuration of a charging circuit used in a conventional lithium-ion secondary battery charging method.

6 is a diagram showing a method of charging a lithium ion secondary battery in the charging circuit shown in FIG.

[Explanation of symbols]

1 lithium-ion secondary battery, 2 constant voltage / constant current control circuit, 3 constant voltage control circuit, 4 switching circuit, 5 voltage monitoring device, 6 charge display section.

Claims (5)

[Claims] 1. A method of charging a lithium ion secondary battery, wherein a recommended charging voltage recommended when charging the lithium ion secondary battery and a voltage equal to or higher than the recommended charging voltage are alternately applied to the lithium ion secondary battery. A method for charging a lithium ion secondary battery, which comprises charging by applying a pulse. 2. The charging method for a lithium ion secondary battery according to claim 1, wherein a pulse frequency is fixed when the lithium ion secondary battery is charged by applying a pulse. 3. The method for charging a lithium ion secondary battery according to claim 1, wherein the pulse frequency is changed when the lithium ion secondary battery is charged by applying a pulse. 4. The lithium ion secondary battery according to claim 1, wherein when the lithium ion secondary battery is charged by applying a pulse, the application duty of the recommended charging voltage is changed. How to charge the battery. 5. The charging duty of a voltage equal to or higher than the recommended charging voltage is changed when charging the lithium ion secondary battery by applying a pulse.
5. The method for charging the lithium ion secondary battery according to any one of 4 above.