JP2000270491A - Lithium ion battery charging method and lithium ion battery charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion battery charging technique which can secure enough capacity extending for a full period of use, and moreover can elongate the exchange cycle. SOLUTION: A charging monitor means 4 monitors the charged capacity by the charge as specified voltage to a lithium battery 1, and a life time point reach determining means 5 determines whether this charged capacity exceeds a prescribed life point. Then, when the life time point reach determining means 5 does not determines the passage of the life time point, even if the specified life time passes, a charge setting means 6 sets charging voltage anew by raising the charging voltage by a prescribed value, and a charging means 10 charges the lithium ion battery 1 with this charging voltage set anew. Hereby, the charging voltage at the initial stage of the start of use of the lithium ion battery 1 is set a slightly low to charge it, and the charging voltage is raised gradually, accompanying the passage of use, to charge it, and enough capacity be secured extending the full period of use of the lithium ion battery 1, and besides the exchange cycle can be elongated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and a device for charging a lithium ion battery.

[0002]

2. Description of the Related Art For example, large-capacity lithium-ion (secondary) batteries used in electric vehicles have a substantially 1: 1 relationship between the charging voltage and the obtained capacity, and the charging voltage must be set high. With this, a large capacity can be obtained.

On the other hand, when the charging voltage is increased, the degree of deterioration of the lithium ion battery is increased, and after a certain period of use, the capacity is shorter than when the charging is repeated while setting the charging voltage at a lower level. It tends to fall below the point.

[0004]

Since the lithium ion battery has the above-mentioned characteristics, the battery is charged by setting the charging voltage at the beginning of use to a relatively low value, and gradually increases as the use period elapses. By increasing the charge, a sufficient capacity can be charged by recharging, and the service life can be prolonged and the replacement cycle can be prolonged.

[0005] The present invention has been made in view of such technical problems, and an object of the present invention is to provide a lithium ion battery charging technique capable of securing a sufficient capacity over the entire period of use and extending the replacement cycle. Aim.

[0006]

According to a first aspect of the present invention, there is provided a method for charging a lithium ion battery, wherein a charging voltage is set at a low level at the beginning of use, and the charging voltage is gradually increased with use. Things.

As a result, a sufficient capacity can be ensured over the entire period of use of the lithium ion battery, and the replacement cycle can be lengthened.

According to a second aspect of the present invention, there is provided a method for charging a lithium ion battery, wherein the degree of deterioration is estimated by measuring the internal resistance of the lithium ion battery, and when the degree of deterioration is low, the battery is charged at a lower charging voltage. The charging is performed by increasing the charging voltage as the process proceeds.

In this way, the lithium ion battery is charged with a relatively low charging voltage at the beginning of use when the degree of deterioration is small and the internal resistance is low. You can charge it to get the required capacity by setting the voltage high,
Sufficient capacity can be secured over the entire period of use of the lithium ion battery, and the replacement cycle can be lengthened.

According to a third aspect of the present invention, there is provided a lithium ion battery charger, wherein charge monitoring means for monitoring a charge capacity of the lithium ion battery by charging at a predetermined charge voltage, and wherein the charge capacity monitored by the charge monitor means is a predetermined charge capacity. A life point reaching determination means for determining whether the life point has been exceeded, and when the life point reaching determination means does not determine that the life point has been exceeded even after a predetermined charging time has elapsed, the charging voltage is increased by a predetermined value. A charging voltage setting unit that sets a new charging voltage; and a charging unit that charges the lithium ion battery with the charging voltage set by the charging voltage setting unit.

According to a third aspect of the present invention, the charge monitoring means monitors the charge capacity of the lithium ion battery by charging at a predetermined charge voltage, and determines whether the charge capacity exceeds a predetermined life point. Is determined by the life point reaching determination means. If the life point reaching determination means does not determine that the life point has been exceeded even after the predetermined charging time has elapsed, the charging setting means increases the charging voltage by a predetermined value to set a new charging voltage, and the charging means sets the new charging voltage. The lithium ion battery is charged by the newly set charging voltage.

Thus, the charging voltage at the beginning of use of the lithium-ion battery can be set at a low level, and the charging voltage can be gradually increased as the battery is used. Sufficient capacity can be secured over the entire period, and the replacement cycle can be lengthened.

According to a fourth aspect of the present invention, there is provided a lithium-ion battery charging device, comprising: an internal resistance detecting means for detecting an internal resistance of the lithium-ion battery; and a battery charger for the lithium-ion battery based on the internal resistance detected by the internal resistance detecting means. Deterioration degree monitoring means for determining the degree of deterioration, charging voltage setting means for variably setting a charging voltage in accordance with the degree of deterioration determined by the deterioration degree monitoring means, and the lithium ion based on the charging voltage set by the charging voltage setting means. Charging means for charging the battery.

[0014] In the lithium ion battery charger according to the fourth aspect of the present invention, the internal resistance detecting means detects the internal resistance of the lithium ion battery, and based on the detected internal resistance, the deterioration monitoring means determines the deterioration degree of the lithium ion battery. Obtain the degree of deterioration. Then, the charging voltage setting means variably sets the charging voltage according to the obtained degree of deterioration, and the charging means charges the lithium ion battery with the set charging voltage.

Thus, the lithium ion battery is charged with a relatively low charging voltage in the early stage of use when the degree of deterioration is small and the internal resistance is low.
As the internal resistance increases, a charging method can be realized in which the charging voltage is gradually set higher to obtain the required capacity,
Sufficient capacity can be secured over the entire period of use of the lithium ion battery, and the replacement cycle can be lengthened.

[0016]

According to the method for charging a lithium ion battery according to the first aspect of the present invention, it is possible to secure a sufficient capacity over the entire period of use of the lithium ion battery and extend the replacement cycle.

According to the method of charging a lithium ion battery according to the second aspect of the present invention, the lithium ion battery is charged with a relatively low charging voltage at the beginning of use when the degree of deterioration is small and the internal resistance is low. As the internal resistance increases, the charging voltage can be gradually set higher to obtain the required capacity, and sufficient capacity can be secured over the entire period of use of the lithium-ion battery. Can be lengthened.

According to the lithium ion battery charger of the third aspect, the lithium ion battery is charged with a relatively low charging voltage in the early stage of use when the degree of deterioration is small and the internal resistance is low. As the internal resistance increases, a charging method can be realized in which the required capacity is obtained by gradually setting the charging voltage to a higher value, and a sufficient capacity can be secured over the entire period of use of the lithium ion battery. The replacement cycle can be lengthened.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

First, the characteristics of the lithium ion battery will be described. FIG. 1 is a graph of charging voltage-discharging capacity / deterioration rate characteristics showing the effect of charging voltage on capacity / life. An electric vehicle uses a lithium-ion battery with a charging voltage of 4.2V.
The curve A shows the cycle deterioration rate characteristics at each charging voltage when charging at 4.4 V. Also,
Curve B shows the discharge capacity characteristics when charging is performed at each charging voltage.

From the characteristics of FIG. 1, when the charging voltage is set to a lower value, the discharge capacity is reduced, but the deterioration rate is also reduced, and therefore, the number of times of repetition of charging and discharging can be increased. Conversely, if you set the charging voltage to a higher value,
Although the discharge capacity is increased, the deterioration rate is increased, and therefore, the number of times charge and discharge can be repeated and used can be reduced.

For example, when charged at a charging voltage of 4.2 V, the capacity is about 93 Ah, and the deterioration rate is about 0.0025.
(That is, it means that the life is obtained in about 400 cycles). On the other hand, when the battery is charged at a lower charging voltage of 4.15 V, the capacity is about 78 Ah, the deterioration rate is about 0.0023 (the cycle life is about 435 times), and the charging voltage is 4.2 V. Although the discharge capacity is lower than in the case of, the life is extended.

Therefore, as shown in FIG. 2, the discharge capacity life line C = 70% at the beginning of use of the lithium ion battery.
In FIG. 2, the charging voltage is set to 4.15 V, and the charging voltage is set to one stage (= T1) at the time T1 at which charging beyond the life line C becomes impossible due to repeated charging and discharging. Reset to 4.16V, which is higher by 0.01V). Then, the battery is used at this charge voltage of 4.16 V. At time T2 when the battery cannot be charged again to a capacity exceeding the life line C due to repetition of charge and discharge, the charge voltage is again set to 4.17 V which is higher by one stage, I do. Hereinafter, in the same manner, this charging method is repeated until time point T3 at which charging with a capacity exceeding the life line C becomes impossible even when charging is performed at a charging voltage of 4.2V.

Thus, the charging voltage 4.2 in FIG.
In the curve D showing the change in the discharge capacity when the charge at a constant V is repeated, the life line C is reached in L0 = 431 cycles, but the charge voltage is changed as the use period elapses as described above. If the method is gradually increased, the life line C reaches L1 = 466 as shown by the curve E.
Cycle, and the usable cycle can be extended by about 8%.

Furthermore, even if the life line C with the charging voltage of 4.2 V is reached, the lithium ion battery is at the time of replacement at that point and cannot be reused as it is, so that current damage is caused. It is also possible to continue using the charging voltage while increasing the charging voltage stepwise to a higher voltage (for example, about 4.25 V) within a range in which no generation occurs.

Thus, according to the present invention, a lithium ion battery having the same characteristics can be used for a longer period of time depending on the charging method.

FIG. 3 shows a first embodiment of a lithium ion battery charger for realizing such a charging method. The lithium ion battery charger of this embodiment is
A voltage detector 2 for detecting a voltage of the lithium ion battery 1;
A current detecting unit 3 for detecting a charging / discharging current; a remaining capacity monitoring unit 4 for monitoring a charging capacity of the lithium ion battery 1 at a predetermined charging voltage by a charger 10;
The charging capacity monitored by the battery is at a predetermined life point (here, 70%
When the life point reaching determination unit 5 does not determine that the life point has been exceeded even after a predetermined charging time has elapsed, the charger 10
Is provided with a charging voltage setting unit 6 which raises the charging voltage by a predetermined value to set a new charging voltage.

The lithium ion battery charger of the first embodiment operates as follows. When charging the lithium ion battery 1 from the charger 10, the remaining capacity monitoring unit 4
Monitors the charge capacity from the voltage data of the lithium ion battery 1 detected by the voltage detection unit 2 and the current data detected by the current detection unit 3. When the battery is fully charged at the current charging voltage, the completion of charging is determined by the life point reaching determination unit 5 and the charger 10.
To stop charging, and inform the completion of charging by buzzer and lamp lighting.

However, even if the remaining capacity monitoring unit 4 outputs the charge completion signal, the charge capacity at that time is the charge capacity set as the life point (here, it is set to 70%).
If the battery life has not reached, the life point reaching determination unit 5 determines that the life point has not been reached and outputs it to the charging voltage setting unit 6, and the charging voltage setting unit 6 sets the charging voltage of the charger 10 to a predetermined range. (For example, 4.25 V or less at the maximum), the voltage is raised by one step (set to 4.15 V at the beginning as described above, and then 0.01 V, and then recharged).

As a result, it is possible to realize a method of charging while gradually increasing the charging voltage as time elapses from the start of use shown in FIG. 2, thereby extending the life of the battery.

Next, a lithium ion battery charger according to a second embodiment of the present invention will be described with reference to FIG. The lithium ion battery charger according to the second embodiment includes a voltage detector 12 that detects a voltage of the lithium ion battery 11,
A current detection unit 13 for detecting a charge / discharge current; an internal resistance detection unit 14 for detecting an internal resistance from these voltage detection values and current detection values; and a battery deterioration based on a correlation between the internal resistance value and the deterioration rate of the battery. A deterioration rate monitoring unit 15 for estimating the rate, a charging voltage setting unit 16 for variably setting the charging voltage of the charger 10 based on the battery deterioration rate calculated by the deterioration rate monitoring unit 15, and There is provided a remaining capacity monitoring unit 17 for monitoring the charge of the lithium ion battery 11 based on the set charging voltage, and for monitoring the remaining capacity of the lithium ion battery 11 during use.

Next, the operation of the above-described lithium ion battery charger will be described. When charging the lithium ion battery 11 from the charger 10, the internal resistance detection unit 14 determines the voltage-current based on the voltage data of the lithium ion battery 11 detected by the voltage detection unit 12 and the current data detected by the current detection unit 13. (VI) The characteristic is obtained, and the internal resistance r is calculated by the calculation of ΔV / ΔI = r.

The deterioration rate monitor 15 is provided with the lithium ion battery 1
The current deterioration rate η is determined based on the internal resistance r of 1. The relationship between the internal resistance r of the battery 11 and the deterioration rate η is approximately 1: 1, and table data indicating the correlation between the internal resistance r and the deterioration rate η is incorporated in advance, or an approximate expression is registered. Thus, the deterioration rate is calculated.

The deterioration rate η calculated by the deterioration rate monitoring unit 15 is given to the charging voltage setting unit 16, and the charging voltage setting unit 16
An appropriate charging voltage is calculated for the given deterioration rate η. For the calculation of the charging voltage here, the curve A shown in FIG. 1 is stored as table data, or an approximate expression of the curve A is registered, and the charging voltage corresponding to the given deterioration rate η is designated.

For example, when the deterioration rate η is 0.0023 to 0.0
In the range of 027, the deterioration rate is set to 0.0002 in increments of 0.0002.
In the case of 0023, the charging voltage is set to 4.15 V, and when the deterioration rate advances to 0.0025, the charging voltage is set to 4.2 V. Further, when the deterioration rate becomes 0.0027, the charging voltage is set to 4 V. .25V. In addition,
When it becomes impossible to fully charge the battery at a charging voltage of 4.25 V at the maximum, it is determined that the replacement time has come.

As a result, the lithium ion battery is charged with a relatively low charging voltage at the beginning of use when the degree of deterioration is small and the internal resistance is low.
As the internal resistance increases, a charging method can be realized in which the charging voltage is gradually set higher to obtain the required capacity,
Sufficient capacity can be secured over the entire period of use of the lithium ion battery, and the replacement cycle can be lengthened.

It should be noted that the numerical values shown in the above embodiment are all examples, and are not particularly limited, and vary depending on the characteristics of the lithium ion battery used, and are experimentally determined in practical use. Is done.

[Brief description of the drawings]

FIG. 1 is a graph showing charge voltage-discharge capacity / deterioration rate characteristics of a general lithium ion battery.

FIG. 2 is a graph showing a method for charging a lithium ion battery according to one embodiment of the present invention.

FIG. 3 is a circuit block diagram of a lithium ion battery charger according to one embodiment of the present invention.

FIG. 4 is a circuit block diagram of a lithium ion battery charger according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lithium-ion battery 2 Voltage detection part 3 Current detection part 4 Remaining capacity monitoring part 5 Life point reaching judgment part 6 Charge voltage setting part 10 Charger 11 Lithium ion battery 12 Voltage detection part 13 Current detection part 14 Internal resistance detection part 15 Deterioration Rate monitoring unit 16 Charge voltage setting unit 17 Remaining capacity monitoring unit

Claims (4)

[Claims] 1. A method for charging a lithium-ion battery, comprising: setting a charging voltage at an early stage of use at a low level, charging the battery; and gradually increasing the charging voltage with use. 2. A method for measuring the internal resistance of a lithium ion battery to estimate the degree of deterioration, charging the battery with a lower charging voltage when the degree of deterioration is low, and increasing the charging voltage as the degree of deterioration progresses. A method for charging a lithium ion battery. 3. A charge monitoring means for monitoring a charge capacity of a lithium ion battery by charging at a predetermined charge voltage, and reaching a life point for determining whether the charge capacity monitored by the charge monitor means exceeds a predetermined life point. Determining means; and charging voltage setting means for increasing the charging voltage by a predetermined value and setting the charging voltage to a new charging voltage when the life point reaching determination means does not determine that the life point has been exceeded even after a predetermined charging time has elapsed. And a charging means for charging the lithium ion battery with the charging voltage set by the charging voltage setting means. 4. An internal resistance detecting means for detecting an internal resistance of the lithium ion battery; a deterioration monitoring means for obtaining a deterioration degree of the lithium ion battery based on the internal resistance detected by the internal resistance detecting means; Charging voltage setting means for variably setting a charging voltage according to the degree of deterioration determined by the degree of deterioration monitoring means; and charging means for charging the lithium ion battery with the charging voltage set by the charging voltage setting means. Lithium-ion battery charger.