JPH10257684A - Charge-discharge control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charge-discharge control device which can change a final voltage at the time of charging and discharging, according to a value of a charge-discharge current and can suppress lowering of a capacity once, even in the case of charging and discharging by a large current. SOLUTION: A load 16 is connected to a cell 10, through the intermediary of an on-off switch 14, and a discharging operation is conducted for the load 16. A voltage detector 12 is connected to the opposite ends of the cell 10, while a discharge current is detected by a current detector 18. Values of these detectors are inputted to a final voltage control circuit 20, and the value of a final discharge voltage is determined herein according to the current value detected by the current detector 18. In the case when a voltage between terminals of the cell detected by the voltage detector 12 is below the final discharge voltage, the final voltage control circuit 20 makes the on-off switch 14 open, thereby the discharging operation is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in a charge / discharge control device for a non-aqueous solvent secondary battery.

[0002]

2. Description of the Related Art As a non-aqueous solvent secondary battery, for example, a lithium ion secondary battery is known. Since such a non-aqueous solvent secondary battery has a high internal resistance, a difference is generated between the open voltage of the battery and the actual voltage between terminals when the battery is driven. This is because a voltage loss (IR drop) occurs due to the internal resistance R, and a potential difference occurs between the open circuit voltage and the inter-terminal voltage corresponding to the IR drop.

For example, in a battery discharging operation, a range of voltage Veff in which the battery can be driven is expressed by the following equation in consideration of the above-mentioned IR drop.

[0004]

(Equation 1) Here, Vop represents the open-circuit voltage of the battery at the beginning of discharge, I represents the discharge current, R represents the internal resistance of the battery, and Vcutd represents the discharge end voltage of the battery. The end-of-discharge voltage Vcutd in the above equation is determined for each battery.
Whether the voltage between terminals suddenly drops and no effective power can be taken out even if it is discharged below that voltage, and it is not expected that an increase in capacity can be expected. Or the like is set as a reference.

When charging a battery, the range of voltage Veff in which the battery can be driven is expressed by the following equation.

[0006]

(Equation 2) Here, Vop represents the open voltage of the battery at the initial stage of charging, I represents the charging current of the battery, R represents the internal resistance of the battery, and Vcutc represents the ending voltage of the battery. Again, in this case,
The end-of-charge voltage Vcutc is determined for each battery, and it is determined whether an increase in capacity cannot be expected even if the battery is charged to a voltage higher than the voltage, or whether deterioration occurs inside the battery when the battery is charged to the voltage or higher. Set as a reference.

As described above, when a battery is charged to a voltage higher than a predetermined terminal voltage or discharged to a voltage lower than a predetermined terminal voltage, the capacity cannot be expected to increase, and There is a problem that the battery is deteriorated. For this reason, a device for preventing overcharging or overdischarging of a battery is conventionally known. For example, JP-A-4-33
No. 1425 also discloses a device for preventing overcharge and overdischarge of a non-aqueous solvent secondary battery.

[0008]

However, in the above conventional example, the discharge end voltage Vcutd and the charge end voltage Vcutc have fixed values, respectively.
There was a problem that it was not possible to cope with changes in the discharge current and the charge current.

That is, for example, when the discharge is performed,
In a non-aqueous solvent battery having a high internal resistance, such as a lithium ion secondary battery, as shown in FIG. 5, the change in the voltage between the terminals of the battery varies greatly depending on the discharge current. This is because the internal resistance R is large and the IR drop greatly changes with an increase in current. Thus, when the discharge current is small, for example, at a 1 hour rate (1C), and when the discharge current is large, for example, at a 5 hour rate (5C), the open voltage Vo of the battery is low.
Even if p is the same, the voltage between terminals, that is, the value of Vop-IR becomes smaller in the case of large current discharge by the amount of IR drop. Therefore, the discharge end voltage Vcut at 1C
If d is applied to the discharge at 5C as it is, the discharge operation ends with the battery still having a discharge margin. For this reason, for example, when a large current discharge is required as in an electric vehicle, the range of the drive voltage Veff becomes smaller as compared with the small current discharge, and as a result, there is a problem that the capacity of the battery cannot be used sufficiently. .

Also, at the time of charging, I
Due to the influence of the R drop, the charging end voltage Vcutc is faster when charged with a large current than when charged with a small current.
, And the charging operation ends when the open voltage Vop of the battery is still low. As a result, the range Veff of the driving voltage of the battery becomes smaller than that at the time of the small current charging,
There was a problem that the chargeable capacity was reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to change the end voltage at the time of charging / discharging in accordance with the value of charging / discharging current, so that the charging / discharging by a large current is performed. Another object of the present invention is to provide a charge / discharge control device capable of suppressing a decrease in capacity.

[0012]

In order to achieve the above object, the present invention provides a voltage detecting means for detecting a voltage between both ends of a battery whose battery voltage changes according to a charged amount, And a cut-off voltage control means for interrupting the discharge current when the voltage between them falls below a predetermined value, wherein the predetermined value of the voltage between both ends is variable according to the magnitude of the discharge current. It is characterized by.

Further, the present invention provides a voltage detecting means for detecting a voltage between both ends of a battery in which a battery voltage changes according to a charged amount, and a method for detecting when a voltage between both ends of the battery exceeds a predetermined value during charging.
A charge / discharge control device having a cut-off voltage control means for interrupting a charging current, wherein a predetermined value of a voltage between both ends is variable according to a magnitude of the charging current.

According to the above configuration, the charge / discharge end voltage can be changed according to the change in the charge / discharge current, and even if the charge / discharge current becomes large, a decrease in the battery capacity can be prevented.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 shows a block diagram of a first embodiment of a charge / discharge control device according to the present invention. FIG.
, A voltage detection circuit 12 for detecting a voltage between both ends of the battery 10 is connected to the battery 10. The battery 16 is connected to a load 16 via an open / close switch 14.
Is connected, and predetermined power is supplied from the battery 10 to the load 16. The current flowing through the load, that is, the discharge current of the battery 10 is detected by the current detector 18. The values detected by the voltage detector 12 and the current detector 18 are input to an end voltage control circuit 20. The end voltage control circuit 20 determines the optimum value of the discharge end voltage Vcutd corresponding to each discharge current, that is, the optimum value of the voltage for stopping the discharge operation, based on the input voltage value and current value. When the voltage between both ends of the battery 10 detected by the voltage detector 12 decreases to the final voltage, the final voltage control circuit 20 issues an instruction to the open / close switch 14 to open the open / close switch 14 to perform a discharging operation. Is stopped.

The discharge control operation of the charge / discharge control device according to the present embodiment shown in FIG. 1 is shown as a flowchart in FIG. In FIG. 2, the discharge current Idis of the battery 10
Is detected by the current detector 18 and input to the cut-off voltage control circuit 20 (S1). In the cutoff voltage control circuit 20, the magnitude of the input discharge current Idis is one
It is checked whether it is greater than the time rate (1C) (S2).

If the discharge current Idis is smaller than 1 C (S2), the discharge voltage V
The discharge voltage Vdis is 3.0 (S3).
It is checked whether it is larger or smaller than V (S4).

In S4, the discharge voltage Vdis becomes 3.0
If it is larger than volts, it means that the battery 10 still has a dischargeable capacity.
6 is continued, and the cut-off voltage control circuit 20
Step S4 is repeated. Note that the voltage value of 3.0 V adopted in S4 can be appropriately changed according to the type of the battery.

On the other hand, in S4, the discharge voltage Vdis
Is smaller than 3.0 V, the cut-off voltage control circuit 2
0 indicates that the voltage between the terminals of the battery 10 is a predetermined discharge end voltage Vc.
It is determined that the voltage has decreased to utd, and the open / close switch 14 is opened to terminate the discharge of the battery 10 (S5).

When the discharge current Idis is larger than 1 C in S2, the discharge voltage Vdis is checked (S6) in the same manner as in S3, and the value of Vdis is determined.

(Equation 3) Is determined (S7). Here, I _1C represents a one-hour rate discharge current value. That is, in the cut-off voltage control circuit 20, when the discharge current Idis is larger than 1C in S2, the discharge cut-off voltage Vcutd for stopping the discharging operation of the battery 10 is increased from 3.0 V to the discharge current Idis, and the IR drop is reduced. It is lowered by (Idis-I _1C ) · R, which is an increase.

In step S7, if Vdis is larger than the corrected discharge end voltage Vcutd, the process returns to step S1 to continue the discharge operation, and the end voltage control circuit 20 continues to monitor the terminal voltage. Further, the discharge end voltage Vcu obtained by correcting the discharge voltage Vdis in S7.
If it is smaller than td, the cut-off voltage control circuit 2
0 opens the open / close switch 14 to end the discharging operation (S5).

With the above, the control operation at the time of discharging of the charge / discharge control device according to the present embodiment ends.

Hereinafter, an example in which a Li-ion secondary battery is actually manufactured and a discharge ending operation is performed using the charge / discharge control device according to the present embodiment will be described as an example.

Embodiment. A lithium ion secondary battery was manufactured according to the following procedure.

Active material capable of reversibly removing and inserting Li ions (LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ )
And a conductive material (graphite or carbon black) in NMP (N-methyl-2-) in which a binder (PVDF) is dissolved.
(Pyrrolidone) into a paste by mixing and kneading in the solution. After applying this paste on aluminum current collector foil,
A positive electrode sheet is obtained by heating, drying and pressing.

Similarly, a paste is prepared by mixing and kneading an active material (a carbon material such as natural graphite) capable of reversibly inserting and removing Li ions into an NMP solution in which a binder (PVDF) is dissolved. Shape. This paste is applied on a copper current collector foil, and then heated, dried and pressed to obtain a negative electrode sheet.

Next, a positive electrode, a porous polyethylene film, and a negative electrode sheet are stacked in this order and wound in a spiral shape.
Put it in the battery case. After the electrolyte is injected, the lid of the battery case is sealed by laser welding.

The discharge capacity of the battery thus manufactured was evaluated by setting the discharge end voltage to 3.0 V. As a result, the discharge capacity was 1.5 Ah. The discharge current at this time is 0.5
A (3 hour rate). The internal resistance of this battery is 4
It was 0 mΩ.

The lithium ion secondary battery produced as described above is connected to the charge / discharge control device shown in FIG.
The discharge capacity was measured according to the flow shown in FIG. The results are shown in Table 1.

[0031]

[Table 1] As shown in Table 1, the discharge current Idis is 1C,
The discharge capacity was measured in three stages of 3C and 5C.

Comparative Example A lithium ion secondary battery manufactured in the same manner as in the above embodiment was charged to a discharge end voltage Vcutd.
Was fixed to 3.0 V, and the discharge capacity was measured. The results are shown in Table 2.

[0033]

[Table 2] As shown in Tables 1 and 2, in this example,
Even when the discharge current Idis increases, the decrease in the discharge capacity of the battery is smaller than in the comparative example. This is because, by changing the discharge end voltage Vcutd according to the value of the discharge current Idis, even when the discharge current Idis increases, the range Veff of the drive voltage of the battery can be increased. That is, as shown in FIG. 5, the discharge end voltage Vcutd in the case of 5C is set to 1C
Is set to a value lower than the discharge end voltage Vcutd in the case of
You can recover the increase in drop.

When the discharge was performed at a discharge current of 5 C, there was no difference in the change of the inter-terminal voltage shown in FIG. 5 between the embodiment and the comparative example. Even if the voltage Vcutd is lowered, it is considered that the battery has not deteriorated.

Embodiment 2 FIG. FIG. 3 shows a block diagram of a second embodiment of the charge / discharge control device according to the present invention. The same elements as those in the first embodiment shown in FIG. The present embodiment is an example in which the battery 10 is charged. The difference from FIG. 1 is that a charger 22 is connected instead of the load 16.

In FIG. 3, the cut-off voltage control circuit 20
During the charging operation of the battery 10, the battery 22 is
The charging current flowing to 0 is received from the current detector 18, and the charging voltage at that time is received from the voltage detector 12. Thereby, according to the charging current detected by the current detector 18,
The value of the charge end voltage Vcutc is changed. As in the case of discharging, the voltage between the terminals of the battery 10 is detected by the voltage detector 12 as a value higher than the open-circuit voltage Vop by the IR drop due to the internal resistance of the battery 10. Accordingly, when the charging current increases, the value of the IR drop increases, and as a result, the chargeable capacity decreases. Therefore, the charge end voltage Vcutc is increased by the amount of the IR drop to prevent a decrease in the charge capacity. ing.

FIG. 4 shows a flowchart in the case where the charging operation is performed by the charge / discharge control device shown in FIG. In FIG. 4, when the charging operation is started, the charging current Icha is detected by the current detector 18, and this value is input to the end voltage control circuit 20 (S10). Next, in the termination voltage control circuit 20, the charging current Icha is
It is checked whether the battery is larger than 1C (S1).
1).

If Icha is smaller than 1C, the cut-off voltage detection circuit 20 checks the value of the charging voltage Vcha detected by the voltage detector 12 (S12).
It is confirmed whether or not it is larger than 2V (S13). When the charging voltage Vcha is not higher than 4.2 V, the charging operation is continued, and the cut-off voltage control circuit 20 performs S10 to S
Step 13 is repeated. When the charging voltage Vcha becomes higher than 4.2 V (S13), the end voltage control circuit 20 opens the open / close switch 14, and ends the charging operation (S14). In this case, the charging end voltage 4.2
The value of V can be appropriately changed according to the battery.

Further, at S11, the charging current Icha
Is larger than 1C, the termination voltage control circuit 20 checks the charging voltage Vcha input from the voltage detector 12 (S15), and checks whether this value is higher or lower than a predetermined charging termination voltage (S16). ).

That is, as described above, when the charging current increases, the voltage between the terminals of the battery 10 increases by the amount of the IR drop.
The value of the charge end voltage Vcutc is increased by an amount corresponding to the increase in the IR drop. Specifically, the following equation is used.

[0041]

(Equation 4) According to the above equation, the charging current Icha is 1C by a larger amount, i.e., is set high (Icha-I _1C) · R by the charging end voltage Vcutc charge. This allows
In comparison with the case where the charging current Icha is equal to or less than 1 C, the adjustment of the charge end voltage Vcutc by the amount corresponding to the IR drop is performed.
The charging voltage Vc is higher than the charging end voltage Vcutc.
If ha is low, the charging is continued, and the termination voltage control circuit 20 continues to monitor the charging voltage in steps S10 to S16. When the charging voltage Vcha becomes higher than the above-mentioned charging end voltage Vcutc, S
Similarly to the case of 13, the end voltage control circuit 20 opens the on-off switch 14 and ends the charging operation (S14).

Table 3 shows the results when the charging operation was performed on the same lithium ion secondary battery as that of the above-described example using the above-described charge / discharge control device according to the present embodiment. As a comparative example, Table 4 shows the results when the charge end voltage was kept constant at 4.2 V.

[0043]

[Table 3]

[Table 4] As can be seen from Tables 3 and 4, when the charge / discharge control device according to the present embodiment is used, the charge capacity is larger at any charge current than when the charge end voltage is kept constant. . This is similar to the case of the discharging operation, in accordance with the change in the value of the charging current, the charging end voltage Vcu.
This is because by changing the value of tc, the range Veff of the driving voltage in charging is increased.

[0044]

As described above, according to the present invention,
When the charge / discharge current increases, the voltage attributable to the voltage loss due to the internal resistance of the battery increases, that is, the discharge end voltage and the charge end voltage are corrected by the change in the apparent voltage between both ends. Can be widened. As a result, even when the charge / discharge current becomes large, it is possible to prevent a decrease in the capacity of the battery.

[Brief description of the drawings]

FIG. 1 is a first embodiment of a charge / discharge control device according to the present invention.
FIG. 3 is a block diagram showing the configuration of FIG.

FIG. 2 is a flowchart showing an operation of the charge / discharge control device shown in FIG. 1 at the time of discharging.

FIG. 3 is a second embodiment of a charge / discharge control device according to the present invention;
FIG. 3 is a block diagram showing the configuration of FIG.

FIG. 4 is a flowchart showing an operation of the charge / discharge control device shown in FIG. 3 during charging.

FIG. 5 is a graph showing a relationship between a discharge current and a change in voltage between terminals of a battery.

[Explanation of symbols]

10 battery, 12 voltage detector, 14 open / close switch,
16 load, 18 current detector, 20 cut-off voltage control circuit, 22 charger.

Claims (2)

[Claims] 1. A voltage detecting means for detecting a voltage between both ends of a battery in which a battery voltage changes according to a charged amount, and interrupting a discharge current when a voltage between both ends of the battery falls below a predetermined value during discharging. A charge / discharge control device having a cut-off voltage control means that performs a predetermined value of the voltage between both ends according to a magnitude of a discharge current. 2. A voltage detecting means for detecting a voltage between both ends of a battery in which a battery voltage changes according to a charged amount, and interrupting a charging current when a voltage between both ends of the battery exceeds a predetermined value during charging. A charging / discharging control device comprising: a charge / discharge control device comprising: