JP7217538B2 - METHOD AND SYSTEM FOR MEASURING CHARACTERISTICS OF LITHIUM-ION BATTERY - Google Patents

Description

The present invention relates to a method and system for measuring the characteristics of lithium ion batteries, and more particularly to a method and system for connecting a plurality of lithium ion batteries in series and simultaneously measuring the characteristics of the plurality of lithium ion batteries.

Lithium-ion batteries (lithium cells), which consist of a separator sandwiched between a positive electrode and a negative electrode, have features such as high capacity, high safety, and long life. widely used in electronic devices. FIG. 1 shows an example of the external appearance of a lithium ion battery, which has an external configuration in which a positive electrode terminal 11 and a negative electrode terminal 12 are provided on the upper surface of a flat battery body 10 .

In recent years, in order to improve the characteristics of such lithium ion batteries, development of battery constituent members has been actively carried out. Therefore, it is essential to measure the characteristics of lithium-ion batteries. Lithium ion battery characteristic measurements include charge/discharge rate characteristics, charge/discharge capacity, charge/discharge cycle deterioration, and the like, and all measurements involve charging and discharging of the lithium ion battery.

FIG. 2 shows an example of characteristics of charge/discharge rate measurement, and shows an example of measurement of how the lithium ion battery voltage drops over time when the lithium ion battery is fully charged and then discharged at a constant current. As the magnitude of the constant current, in this example, 1C (current value that completely discharges the nominal capacity of the battery in 1 hour) and 0.2C (current value that completely discharges the nominal capacity of the battery in 5 hours) are shown. , and the current value is further changed to 0.5C, 2C, and 3C, and the voltage measurement is repeated to evaluate the overall characteristics.

Such a characteristic measurement system has the configuration shown in FIG. A charging/discharging power supply 2 having a current detection function as well as charging/discharging and a voltage measuring instrument 4 for measuring the voltage between terminals are connected, and one lithium ion battery ( positive electrode and negative electrode) 3 are connected.

In such a configuration, the basic operation will be described with reference to the flow chart of FIG. 4, taking CC (constant current) charging/CC (constant current) discharging as an example.

First, the controller 1A instructs the charging/discharging power supply 2 to output a constant current in the forward direction, whereby the charging/discharging power supply 2 charges the lithium ion battery 3 (step S1). During the charging period, the controller 1A measures the terminal voltage of the lithium ion battery 3 with the voltage meter 4, and measures the charging current value with the charging/discharging power supply 2 (step S2). The controller 1A continues the charging until the rated voltage is measured by the voltage meter 4 (step S3), and stops charging when the measured voltage reaches the rated voltage (step S4).

Next, the controller 1A instructs the charging/discharging power source 2 to output a constant current in the negative direction to discharge the lithium ion battery 3 (step S5). During the discharge period, the controller 1A measures the voltage across the terminals of the lithium ion battery 3 with the voltage measuring instrument 4, and measures the discharge current value with the charge/discharge power source 2 (step S6). The controller 1A continues the discharge until the end voltage is measured by the voltage measuring device 4 (step S7), and stops the discharge when the measured terminal voltage reaches the end voltage (step S8).

The charging and discharging are performed for a plurality of constant currents, and the characteristics of the lithium ion battery 3 are measured.

WO2017/187637 WO2018/187888 JP 2011-29139 A

The biggest problem with the conventional characteristic measurement method described above is that the cost increases. In other words, in a lithium-ion battery factory, for example, there is a need to measure more than 1000 cells at the same time. It is necessary to prepare the same number as the number of lithium-ion batteries. However, since charging/discharging power sources are expensive, if a plurality of power sources are to be prepared, the equipment cost will become enormous, which is a serious problem. Further, if the characteristics of each lithium ion battery are measured one by one, it takes time and labor to measure the characteristics of a large number of lithium ion batteries, which is extremely uneconomical.

The second problem is the low minimum voltage of lithium-ion batteries during discharge. When discharged with a charge/discharge power supply, the terminal voltage of the lithium ion battery gradually decreases with time, and finally reaches the terminal voltage. However, the final voltage is so low that it may fall below the minimum voltage that can be discharged depending on the power supply. In that case, accurate measurement can be performed only before complete discharge, and the reliability of characteristic measurement is impaired. On the other hand, there are power supplies with a low minimum voltage that can be discharged, but they are generally expensive, and concerns remain in terms of performance, such as current accuracy during low-voltage discharge and regenerative efficiency.

The present invention has been made based on the above circumstances, and an object of the present invention is to simultaneously measure the characteristics of a large number of lithium ion batteries without increasing the cost, improve accuracy on the low voltage side and An object of the present invention is to provide a method and system for measuring the characteristics of a lithium-ion battery that achieves improved regeneration efficiency.

The present invention relates to a method for measuring characteristics of lithium ion batteries, and the above object of the present invention is to connect N (≧2) lithium ion batteries in series, charge the N lithium ion batteries with a constant current, and perform constant current charging of the N lithium ion batteries. monitoring the total voltage of the N lithium ion batteries, switching the constant current charging to constant voltage charging when the total voltage reaches the rated voltage or more, and the voltage between each terminal of the N lithium ion batteries is a predetermined voltage balance control is performed to maintain the upper limit voltage of the constant voltage charge, and when the charging current of the constant voltage charge becomes equal to or less than the rated current, the constant voltage charge is stopped, and the N lithium ion batteries are charged at a constant current. Various constant current discharges are performed by discharging, measuring the voltage between the terminals of the N lithium ion batteries and the current of the series connection, and stopping the constant current discharge when the voltage between the terminals reaches the terminal voltage. This is accomplished by measuring the characteristics of the N lithium-ion batteries, run for current and various constant voltages.

Further, the present invention relates to a system for measuring characteristics of lithium ion batteries, and the above object of the present invention includes a controller for controlling the entire system, cell connection means for connecting N (≧2) lithium ion batteries in series, and the controller. a charging/discharging power supply for constant-current charging, constant-voltage charging, and constant-current discharging of the N lithium-ion batteries connected in series; a voltage measuring instrument that measures voltage ; and a balance circuit that performs balance control to maintain the voltage between terminals of the N lithium ion batteries at a predetermined upper limit voltage based on the balance command from the controller, When constant current charging is performed on the N lithium ion batteries by the charging/discharging power source, switching to constant voltage charging according to a first predetermined condition, and balance control by the balancing circuit satisfies a second predetermined condition. and the charging/discharging power supply performs constant current discharging, stops discharging when the voltage across the terminals of the N lithium ion batteries reaches a third predetermined condition, and determines the characteristics of the N lithium ion batteries. This is achieved by measuring

According to the present invention, characteristics of a large number of lithium ion batteries (cells) can be measured simultaneously, which is very efficient and economical. A balance circuit is added compared to the conventional one, and a current sensor is added in the case of charging/discharging capacity measurement.

Also, by connecting N lithium-ion batteries in series, the total voltage of the lithium-ion batteries is N times that of one cell. This makes it possible to solve the problem of the charge/discharge power supply caused by the low minimum voltage of the lithium ion battery during discharge. In other words, there is no need for an expensive power supply with a low dischargeable minimum voltage, and there is no need to worry about current accuracy, regeneration efficiency, etc. during low-voltage discharge.

1 is an external view showing an example of a lithium ion battery; FIG. FIG. 3 is a characteristic diagram showing an example of measurement of charge/discharge rate of a lithium ion battery; 1 is a block diagram showing a configuration example of a conventional characteristic measurement system for a lithium ion battery; FIG. 10 is a flow chart showing an operation example of a conventional characteristic measurement system; It is a block diagram which shows the structural example (1st Embodiment) of this invention. 1 is an external development view showing an example of cell connecting means for connecting a plurality of lithium ion batteries in series; FIG. FIG. 4 is an external view showing an example of dummy cells used in the present invention; 3 is a block diagram showing a configuration example of a controller; FIG. 3 is a block diagram showing a configuration example of a balance circuit; FIG. 3 is a block diagram showing a configuration example of a load circuit of balance circuit elements; FIG. It is a flowchart which shows the operation example (1st Embodiment) of this invention. It is a block diagram which shows the structural example (2nd Embodiment) of this invention. It is a flowchart which shows the operation example (2nd Embodiment) of this invention.

In the present invention, a large number of N (≧2) lithium ion batteries (hereinafter sometimes referred to as “cells”) connected in series are measured through a controller consisting of a CPU or the like, and the characteristics are measured using one charge/discharge power supply. At the same time, by providing a balance circuit that performs balance control for each of the N lithium-ion batteries, it is possible to improve the accuracy of the low voltage side and the efficiency of regeneration, enabling efficient and economical characteristic measurement. Realized.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 5 shows the first embodiment of the present invention corresponding to FIG. -1 to 3-N are accommodated in the cell connection means and electrically connected in series, and the charge/discharge power supply 2 charges and discharges the series-connected lithium ion batteries 3-1 to 3-N at a constant current or constant voltage. At the same time, the charge/discharge current is measured, and the total voltage at both ends (the positive electrode of the lithium ion battery 3-1 and the negative electrode of the lithium ion battery 3-N) is measured.

FIG. 6 shows an example of the configuration of the cell connecting means for connecting N lithium ion batteries 3-1 to 3-N in series, with four lithium ion batteries 3-1 to 3-4. The lithium ion batteries 3-1 to 3-4 are provided with positive terminals 3-1P to 3-4P and negative terminals 3-1N to 3-4N, respectively. has an alternating positive and negative relationship. The cell connecting means comprises a container 30 for containing a lithium ion battery for inspection, and a fixing member 20 for holding and fixing the contained lithium ion battery and for making electrical connection. . The storage body 30 is provided with storage holes 31 to 34 having a rectangular cross section for storing the lithium ion batteries 3-1 to 3-4. After each of 3-1 to 3-4 is accommodated, the fixing member 20 is attached to the container 30 from above and fixed.

The fixing member 20 has a flat cover plate 21 covering the upper surface of the container 30, and elongated guides are provided on the left and right sides of the cover plate 21 for sliding on the side surfaces of the container 30 for smooth mounting. Plates 22 and 23 are arranged, and a side plate 24 extends from the central portion of the cover plate 21 . A ball screw 25 is screwed into the side plate 24 , and by rotating the ball screw 25 , the cover plate 21 moves up and down via the side plate 24 . In addition, probes PR1 to PR8 made of a conductive material are provided on the lower surface of the lid plate 21, and the probes PR1 to PR8 are electrically connected to the voltage measuring instrument 4 and the balance circuit 5, and the probe PR1 charges and discharges. The positive terminal (+) of the power supply 2 and the probe PR7 are connected to the negative terminal (-) of the charging/discharging power supply 2, respectively. The probes PR2 and PR4 are connected by a conductor piece 26-1, the probes PR3 and PR5 by a conductor piece 26-2, and the probes PR6 and PR8 by a conductor piece 26-3.

The arrangement positions of the probes PR1 to PR8 are opposed to the positive terminals 3-1P to 3-4P and the negative terminals 3-1N to 3-4N of the lithium ion batteries 3-1 to 3-4 in the vertical direction. The probes PR1 to PR8 are formed at the same height. The shape of the probes PR1 to PR8 is not limited to the one shown in the drawing, and any shape can be used as long as it can be electrically connected while being in contact with or pressed against the positive terminal and the negative terminal.

In such a configuration, after the lithium ion batteries 3-1 to 3-4 are respectively accommodated in the accommodation holes 31 to 34 of the container 30, the fixing member 20 is attached to the container 30 along the guide plates 22 and 23 from above. Put it on and fix it. After that, by rotating the ball screw 25 by a motor or the like, the lid plate 21 is gradually lowered via the side plate 24, and finally the tips of the probes PR1, PR2, PR3, PR4, PR5, PR6, PR7 and PR8 are Contact the positive terminal 3-1P, negative terminal 3-1N, negative terminal 3-2N, positive terminal 3-2P, positive terminal 3-3P, negative terminal 3-3N, negative terminal 3-4N, positive terminal 3-4P, respectively. Or it is pressed, so it stops in that state. By maintaining this state, a series connection of lithium ion batteries 3-1 to 3-4 as shown in FIG. 5 can be formed. That is, charge/discharge power supply 2 (+) → probe PR1 → positive terminal 3-1P → lithium ion battery 3-1 → negative terminal 3-1N → probe PR2 → conductor piece 26-1 → probe PR4 → positive terminal 3-2P → Lithium ion battery 3-2→negative terminal 3-2N→probe PR3→conductor piece 26-2→probe PR5→positive terminal 3-3P→lithium ion battery 3-3→negative terminal 3-3N→probe PR6→conductor piece 26 -3→probe PR8→positive terminal 3-4P→lithium ion battery 3-4→negative terminal 3-4N→probe PR7→charging/discharging power source 2 (−+) can form a series connection path.

Further, when defective products are excluded from the cell connection means based on characteristic measurement to be described later, a dummy cell 40 whose positive and negative terminals are short-circuited by a conductor piece 41 as shown in FIG. Store in Since the dummy cell 40 is a simulated product in which the positive and negative terminals are simply short-circuited by the conductor piece 41 , the controller 1 disables balance control and voltage measurement for the dummy cell 40 .

In the cell connection means described above, four lithium ion batteries 3-1 to 3-4 are described, but the number is not limited to four, and any number of series connection configurations are possible. be. That is, when N (≧2) lithium ion batteries 3-1 to 3-N are accommodated in the accommodation holes, they are electrically connected in series via probes and conductor pieces, and the lithium ion batteries Any structure can be used as long as the positive and negative electrodes of 3-1 to 3-N can be electrically connected to the charging/discharging power source 2, the voltage measuring device 4 and the balance circuit 5.

FIG. 8 shows an example of the functional configuration of the controller 1. A CPU 1-1 performs overall control, etc., and a charging/discharging power supply 2, a voltage measuring instrument 4, and a balance circuit 5 are connected to the CPU 1-1. , a charge command unit 1-2, a discharge command unit 1-3, a voltage determination unit 1-4, a current determination unit 1-5, a total voltage monitoring unit 1-6, a switching unit 1-7, and a balance command unit 1-8. interconnected.

Further, the positive and negative electrodes of the lithium ion batteries 3-1 to 3-N are connected to the balance circuit elements 5-1 to 5-N constituting the balance circuit 5 and to the voltage measuring device 4. there is

All of the balance circuit elements 5-1 to 5-N have the same configuration. For example, the configuration of the balance circuit element 5-1 connected to the lithium ion battery 3-1 is as shown in FIG. That is, a voltage detection unit 5-11 that detects the terminal voltage Vt of the lithium ion battery 3-1 and outputs a current command CM corresponding to the terminal voltage Vt, and a voltage detection unit 5-11 that outputs a current command CM corresponding to the voltage Vt between the terminals, and "A→B" or "B" according to the current command CM. →A″ It is composed of a load circuit 5-12 capable of flowing a specified value of current in either direction, thereby adjusting the inter-terminal voltage Vt. A terminal voltage Vt of the lithium ion battery 3-1 is detected by a voltage detector 5-11, and a current command CM is output as a detection result and input to a load circuit 5-12. When the terminal voltage Vt is equal to or higher than the upper limit voltage _VH , the voltage detection unit 5-11 outputs a current command CM to flow a current in the direction of "A→B" to suppress the rise of the terminal voltage Vt. . Further, when the terminal voltage Vt is lower than the lower limit voltage _VL , the current command CM is output to flow the current in the direction of "B→A" to suppress the drop of the terminal voltage Vt.

The configuration of the load circuit 5-12 is, for example, a resistance switching system shown in FIG. 10(A) or a constant current control system shown in FIG. 10(B). The resistance switching method shown in FIG. 10(A) turns ON/OFF (opens and closes) a switch 5-122 connected in series with a resistor R by a drive circuit 5-121 based on a current command CM. is a method of obtaining a desired average current by controlling the ON/OFF frequency of the switch 5-122. Further, in the constant current control method shown in FIG. 10B, an FET (Field-Effect Transistor) connected in series with the current sensor 5-124 is controlled according to the current detected by the current sensor 5-124 based on the current command CM. It is a constant current control system, and is a high-performance system that obtains a desired current smoothly and accurately.

In such a configuration, the basic operation will be described with reference to the flow chart of FIG. 11, taking CC (constant current)-CV (constant voltage) charging/CC (constant current) discharging as an example. Perform the following characteristic measurements at various constant currents and constant voltages, and if there is a cell whose terminal voltage Vt does not reach the rated voltage even after a certain period of time has passed, the cell is judged to be defective and eliminated. , the dummy cells 40 described above are accommodated, and then the determination of characteristic measurement is continued with the remaining cells.

First, N lithium ion batteries are accommodated in the cell connection means as described in FIG. 6 to form a series connection of the lithium ion batteries. The controller 1 instructs the charge command unit 1-2 to output a positive constant current to the charge/discharge power source 2, and the charge/discharge power source 2 simultaneously controls all the series-connected lithium ion batteries 3-1 to 3-N. Charge (step S10). During the charging period, the controller 1 measures the voltage Vt between the terminals of the lithium ion batteries 3-1 to 3-N with the voltage measuring device 4, and measures the charging current flowing through the series connection with the charging/discharging power supply 2 (step S11). In addition, the charging/discharging power supply 2 detects the total voltage of the lithium ion batteries 3-1 to 3-N connected in series (step S12), and the total voltage is equal to or higher than the rated voltage by the total voltage monitoring unit 1-6. It is determined whether or not (step S13). The total voltage can also be obtained by adding the terminal-to-terminal voltages of the cells measured by the voltage meter 4 .

If it is determined in step S13 that the total voltage is lower than the rated voltage, the constant current charging is continued, and if the total voltage is equal to or higher than the rated voltage, the constant current charging is performed by the switching unit 1-7. is switched to constant voltage charging (step S14). At the same time, the controller 1 outputs a balance command BC from the balance command unit 1-8, and controls the balance circuit 5 (balance circuit elements 5-1 to 5-N) to balance the lithium ion batteries 3-1 to 3-N, respectively. (step S20).

The balance circuit 5 supplies current to the positive side (in the direction of A→B) so that the voltage Vt across the terminals of each cell maintains the specified upper limit voltage _VH by the balance circuit elements 5-1 to 5-N. flush. As charging progresses to the positive side, the charging current gradually decreases, but the current determination unit 1-5 of the controller 1 determines whether or not the charging current has become equal to or less than the rated current (step S30). If it is determined in step S30 that the charging current is greater than the rated current, the balance control is continued. stops charging (step S31).

Next, the controller 1 instructs the charge/discharge power source 2 to output a negative (B→A direction) constant current through the discharge command unit 1-3, and the series-connected lithium ion batteries 3-1 to 3-N is discharged (step S40). During the discharge period, the controller 1 measures the voltage Vt between the terminals of the lithium ion batteries 3-1 to 3-N with the voltage measuring device 4, and measures the discharge current of the series connection with the charge/discharge power supply 2 (step S41). . The controller 1 continues the discharge until the terminal voltage Vt measured by the voltage measuring device 4 by the voltage determination unit 1-4 reaches the final voltage (step S42), and the measured terminal voltage Vt reaches the final voltage. When it reaches the discharge command section 1-3, the discharge is stopped (step S43). The controller 1 stops discharging when the terminal voltage Vt of even one of the N cells reaches the terminal voltage.

The charging and discharging are performed at a plurality of constant currents and constant voltages, and the characteristics of the lithium ion batteries 3-1 to 3-N are simultaneously measured.

Next, an embodiment (second embodiment) of the present invention for measuring the charge/discharge capacity of a lithium ion battery will be described with reference to FIG. 12 corresponding to FIG.

In the second embodiment, current sensors 6-1 to 6-N for measuring the respective balance currents of the lithium ion batteries 3-1 to 3-N during balance control by the balance circuit 5 are connected to the negative electrode of each cell. It is connected to the. Note that the current sensors 6-1 to 6-N may be connected to the positive electrode of each cell.
Taking discharge as an example, the basic operation will be described with reference to the flow chart of FIG. The following characteristics are measured, the cell capacity is calculated from the measured current value and time, and if there is a cell that does not meet the specified capacity, the cell is determined to be defective and excluded, and the dummy cell 40 described above is housed instead. After that, the characterization determination continues with the remaining cells.

First, N lithium ion batteries are accommodated in the cell connection means as described in FIG. 6 to form a series connection of the lithium ion batteries. The controller 1 instructs the charge command unit 1-2 to output a positive constant current to the charge/discharge power source 2, and the charge/discharge power source 2 simultaneously controls all the series-connected lithium ion batteries 3-1 to 3-N. Charge (step S10). During the charging period, the controller 1 measures the voltage Vt between the terminals of the lithium ion batteries 3-1 to 3-N with the voltage measuring device 4, and measures the charging current flowing through the series connection with the charging/discharging power supply 2 (step S11). In addition, the charging/discharging power supply 2 detects the total voltage of the lithium ion batteries 3-1 to 3-N connected in series (step S12), and the total voltage monitoring unit 1-6 determines whether the total voltage is equal to or higher than the rated voltage. (step S13).

If it is determined in step S13 that the total voltage is lower than the rated voltage, the constant current charging is continued, and if the total voltage is equal to or higher than the rated voltage, the constant current charging is performed by the switching unit 1-7. is switched to constant voltage charging (step S14). At the same time, the controller 1 outputs a balance command BC from the balance command unit 1-8 to cause the balance circuit 5 (balance circuit elements 5-1 to 5-N) to control the balance of the lithium ion batteries 3-1 to 3-N. (step S20).

The balance circuit 5 supplies current to the positive side (in the direction of A→B) so that the voltage Vt across the terminals of each cell maintains the specified upper limit voltage _VH by the balance circuit elements 5-1 to 5-N. flush. At this time, the balance current of each cell is measured by the current sensors 6-1 to 6-N for capacity calculation later (step S20A). As charging progresses to the positive side, the charging current gradually decreases, but the charging determination section 1-5 of the controller 1 determines whether or not the charging current has become equal to or less than the rated current (step S30). If it is determined in step S30 that the charging current is greater than the rated current, the balance control is continued. stops charging (step S31) and starts measuring the discharge time (step S32).

Next, the controller 1 instructs the charge/discharge power source 2 to output a negative (B→A direction) constant current through the discharge command unit 1-3, and the series-connected lithium ion batteries 3-1 to 3-N is discharged (step S40). During the discharge period, the controller 1 measures the voltage Vt between the terminals of the lithium ion batteries 3-1 to 3-N with the voltage measuring device 4, and measures the discharge current of the series connection with the charge/discharge power supply 2 (step S41). . The controller 1 continues the discharge until the terminal voltage Vt measured by the voltage measuring device 4 by the voltage determination unit 1-4 reaches the final voltage (step S42), and the measured end voltage Vt reaches the final voltage. When it reaches the discharge command section 1-3, the discharge is stopped (step S43). The controller 1 stops discharging when the terminal voltage Vt of even one of the N cells reaches the terminal voltage.

Then, when the measured discharge time reaches the specified time or more, the discharge is terminated (step S43). However, since the cells that reach the final voltage before the specified time have insufficient discharge capacity, they are excluded as defective cells, and dummy cells 40 are excluded. (step S44).

The charging and discharging are performed at a plurality of constant currents and constant voltages, and the characteristics of the lithium ion batteries 3-1 to 3-N are measured.

In the present invention, one charging/discharging power source is sufficient for N (plural) lithium ion batteries, so a significant cost reduction is possible. Although the present invention requires more balance circuits and current sensors (required only for charging/discharging capacity measurement) than the conventional method, these are much cheaper than the charging/discharging power supply, so the total cost remains low. Also, by connecting N lithium-ion batteries in series, the total cell voltage is N times that of one cell. This solves the problem of the charging/discharging power supply due to the low minimum voltage of the cell during discharging. In other words, there is no need for an expensive power supply with a low minimum voltage that can be discharged, and there is no need to worry about current accuracy, regeneration efficiency, etc. during low-voltage discharge.

1, 1A Controller 1-1 CPU
1-2 Charge command unit 1-3 Discharge command unit 1-4 Voltage determination unit 1-5 Current determination unit 1-6 Total voltage monitoring unit 1-7 Switching unit 1-8 Balance command unit 2 Charge/discharge power supply 3, 3- 1 to 3-N Lithium ion battery (cell)
4 Voltage measuring instrument 5 Balance circuits 5-1 to 5-N Balance circuit elements 6-1 to 6-N Current sensor 10 Battery body 11 Positive terminal 12 Negative terminal 20 Fixing member 21 Lid 22, 23 Guide 30 Container 31 ~ 34 storage hole 40 dummy cell

Claims (7)

connecting N (≧2) lithium-ion batteries in series,
constant-current charging the N lithium-ion batteries;
monitoring the total voltage of the N lithium ion batteries;
when the total voltage becomes equal to or higher than the rated voltage, switching the constant current charging to constant voltage charging;
Performing balance control, which is control for maintaining the voltage between terminals of the N lithium ion batteries at a predetermined upper limit voltage ,
stopping the constant voltage charging when the charging current of the constant voltage charging becomes equal to or less than the rated current;
Constant current discharge of the N lithium ion batteries,
Measuring the voltage between each terminal of the N lithium ion batteries and the current of the series connection,
Stopping the constant current discharge when the voltage between the terminals reaches the final voltage,
A method for measuring characteristics of a lithium ion battery, characterized in that the characteristics of the N lithium ion batteries are measured by applying various constant currents and various constant voltages. 2. The method for measuring characteristics of a lithium ion battery according to claim 1 , wherein said constant current charge , said constant voltage charge and said constant current discharge are performed for various currents and various voltages. 3. The method of measuring characteristics of a lithium ion battery according to claim 1 , wherein each balance current of the N lithium ion batteries is measured during the balance control, and the characteristics are measured based on the capacity based on each of the balance currents. a controller that controls the whole
cell connecting means for connecting N (≧2) lithium ion batteries in series;
a charging/discharging power supply connected to the controller for constant-current charging, constant-voltage charging, and constant-current discharging of the N lithium-ion batteries connected in series;
a voltage measuring instrument connected to the controller and measuring a voltage across each terminal of the N lithium ion batteries;
a balance circuit that performs balance control such that the voltage across each terminal of the N lithium ion batteries maintains a predetermined upper limit voltage based on the balance command from the controller;
wherein constant current charging is performed on the N lithium ion batteries by the charge/discharge power supply, switching to constant voltage charging under a first predetermined condition, and balance control by the balance circuit is performed under a second predetermined condition , the charging/discharging power supply performs constant current discharging, stops discharging when the voltage between the terminals of the N lithium ion batteries reaches a third predetermined condition, and discharges the N lithium ion batteries A characteristic measurement system for a lithium ion battery characterized by measuring the characteristics of the battery. the balance circuit is composed of balance circuit elements corresponding to each of the N lithium ion batteries;
the balance circuit element comprising:
a voltage detection unit that detects a voltage between terminals of the lithium ion battery and outputs a current command;
a load circuit capable of passing current in the positive direction according to the current command and adjusting the voltage between the terminals;
5. The system for measuring characteristics of a lithium ion battery according to claim 4 , comprising: 6. The system for measuring characteristics of a lithium ion battery according to claim 5 , wherein said load circuit is of a resistance switching type or a constant current control type. The first predetermined condition is whether or not the total voltage of the N lithium ion batteries is equal to or higher than the rated voltage,
The second predetermined condition is whether or not the charging current is equal to or less than the rated current,
7. The system for measuring characteristics of a lithium ion battery according to claim 4 , wherein the third predetermined condition is whether or not the voltage between the terminals is the final voltage.

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