JP2009199774A - Charging/discharging method for secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging/discharging method of a secondary battery, which can suppress the progress of deterioration in the capacity of the secondary battery. <P>SOLUTION: The secondary battery is charged and discharged after the secondary battery has been charged to a target capacity which is smaller than the total capacity of the secondary battery at the initial stage of usage. When a battery voltage at the end of charging the battery to the target capacity which is smaller than the total capacity of the secondary battery at the initial stage of usage reaches a predetermined voltage, it is determined that the service life of the secondary battery ends. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for charging and discharging a secondary battery.

  A method for detecting a deteriorated battery capacity is disclosed in the following patent document. In this publication, the following two methods are disclosed. One is disclosed that every time the cumulative amount of charge capacity of the battery reaches the learning capacity of the battery at that time, one cycle is counted, and the learning capacity is reduced as a specific cycle deterioration capacity per charge of one cycle. Also, the battery storage temperature and remaining capacity are used as parameters to specify the learning capacity decrease rate as storage deterioration capacity, and the learning capacity is reduced by the storage deterioration capacity specified from the battery storage temperature and remaining capacity. It is disclosed.

Here, as described in FIG. 2 and the corresponding description of the document, it is disclosed that the deterioration proceeds when the battery capacity is large.
JP 2002-236154 A

  In such a secondary battery, when the battery capacity is used in a range close to 100%, the capacity is likely to deteriorate.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a secondary battery charging / discharging method in which the capacity of the secondary battery is unlikely to deteriorate.

  The present invention is characterized in that the secondary battery is charged and discharged by charging to a target capacity smaller than the total capacity of the secondary battery in the initial stage of use. Further, when the battery voltage at the time of charging to a target capacity smaller than the total capacity of the secondary battery in the initial stage of use reaches a predetermined voltage, it is determined as the life.

  In the present invention, the secondary battery is charged and discharged by charging to a target capacity smaller than the total capacity of the secondary battery in the initial stage of use, so that the total capacity at that time is charged and discharged near full charge. And the progress of deterioration of the secondary battery is reduced.

  In addition, when the battery voltage when charging to a target capacity smaller than the total capacity of the secondary battery in the initial stage of use reaches a predetermined voltage, it can be determined that the battery life is reached. Therefore, it is possible to determine the life by simply detecting when the battery voltage at the time of charging to the target capacity has reached a predetermined voltage, so that it can be determined by a simple method. This method is a simple method because it is possible to determine the lifetime by measuring the battery voltage without performing detailed capacity learning.

  Embodiments of the present invention will be described in detail with reference to the drawings. First, the circuit configuration, operation, and function of the battery pack A according to the embodiment of the present invention will be described with reference to FIG. 1, and then the features of the present invention will be described. As shown in FIG. 1, the present embodiment includes a battery pack A and a portable device PC that is an electronic device including a power source for charging the battery pack A. The portable device PC is a portable personal computer such as a notebook computer. The battery pack A usually has a structure that is detachably attached to the portable device PC. The portable device PC is supplied with DC power output from an adapter (not shown) that converts AC commercial power from the outlet into DC power. S is provided. The power output from the control / power supply means S is used to charge the battery pack A or is supplied to the load L of the portable device PC. When power is not supplied from commercial power, power is supplied from the battery pack A to drive the power supply circuit S and the load L. Here, although a portable device is used as an electronic device using the battery pack A as a power source, an electric vehicle such as an electric vehicle can be used instead.

  In the battery pack A, a secondary battery 1 such as a lithium ion battery or a nickel metal hydride battery, a current detection unit 2 including a resistor or the like for detecting a current during charging / discharging of the battery 1, and charging / discharging of the battery 1 are monitored. And a microprocessor unit (hereinafter referred to as MPU) for control. In the battery pack A, a temperature detection unit 3 including a thermistor disposed in close contact with the battery 1 is provided.

  In the MPU, the total battery voltage (measurement point d), the analog voltage output from the current detection unit 2 and the analog voltage output from the temperature detection unit 3 are input, converted into digital values, and the actual voltage [mV] or actual current value [mA] ] A / D conversion section 4 for converting to the above is provided. Then, the output from the A / D conversion unit 4 is input to a charge / discharge control / calculation unit 5 as a control means, and calculation, comparison, determination, etc. are performed, and a signal from the control / calculation unit 5 is used. The control element 7 composed of a switching transistor or the like is on / off controlled.

  In other words, the control / calculation unit 5 calculates the remaining capacity by accumulating the charge / discharge current, detects the full charge of the battery 1, detects the abnormal current, abnormal temperature, abnormal voltage, etc. Control the discharge. The control element 7 composed of a switching transistor or the like is on / off controlled, and cuts off the current with a control signal from the control / calculation unit 5 when detecting an abnormal current, abnormal temperature, or abnormal voltage. Using a well-known technique, the control / calculation unit 5 integrates the value obtained by multiplying the charging / discharging current converted by the A / D conversion unit 4 by a measurement unit time (for example, 250 msec), and the value is satisfied at the time of discharging. The integrated amount is subtracted from the charge, or, at the time of charging, the integrated amount is added from the remaining capacity at the start of charging. By such calculation, the remaining capacity (Ah) of the battery 1 is calculated. Instead of such remaining current accumulated capacity, the accumulated power (Wh) obtained by multiplying the value obtained by multiplying the voltage, current, and measurement unit time at the time of measurement may be used as the remaining capacity.

  The control / calculation unit 5 records various data in a memory. A control / arithmetic unit 5 including a CPU (Central Processing Unit) includes various memories. A program memory for storing a program for controlling the operation of the battery pack A is provided, and the program memory is a nonvolatile storage medium. A ROM (Read Only Memory) stores data necessary for executing the program in advance. A RAM (Random Access Memory) temporarily stores a part of a program and various data. In addition, EEPROM (Electrically Erasable Programmable ROM) or FlashMemory is provided as non-volatile memory, and EEPROM or FlashMemory needs to be saved even if software or setting data executed by the CPU or MPU shuts down. Data (for example, learning capacity, number of cycles, data at the time of abnormality, etc.) and the like are stored before shutdown, and these can be rewritten as needed.

  Furthermore, the control / arithmetic unit 5 includes various timers and counters, and is used for time measurement, frequency measurement, and the like.

    In this embodiment, as will be described in detail later, up to a target capacity (800 mAH, initial rated capacity ratio 80%) smaller than the total capacity of the secondary battery in the initial stage of use (total capacity 1050 mAH, initial rated capacity ratio 105%). Charge the battery.

  On the other hand, in the conventional example, charging is stopped upon detection of full charge. That is, in the control / calculation unit 5, when the battery 1 is a nickel metal hydride battery or the like, the peak voltage is detected, the battery voltage −ΔV (= voltage drop) is detected, It is detected by a known method such as using the remaining capacity. When the battery 1 is a lithium ion battery, it uses constant current (MAX current 0.5-1C) / constant voltage (MAX4.2V / cell) charging with regulated current and voltage. When the condition is below the predetermined value, the battery is fully charged.

  Here, the control / arithmetic unit 5 is a control element 7 for cutting off the charging current and the discharging current, the charging FET element 71 being a p-channel FET as the charging control element, and the discharging control element. A signal for on / off control is issued to the discharging FET element 72 which is a p-channel FET. Instead of the p-channel FET, it is also possible to use an n-channel FET charging FET element and discharging FET element using a charge pump.

  In the control / arithmetic unit 5, when the voltage of the battery 1 becomes lithium ion or more and becomes an overcharge voltage or more (for example, 4.2 V or more), an off signal (element Since 71 is applied to the gate of the p-channel FET, the voltage of the off signal is equivalent to a high voltage signal) from the port CH. When the voltage of the battery 1 becomes equal to or lower than the overdischarge voltage (for example, 2.7 V / Cell or lower), an off signal (the element 72 is applied to the gate of the p-channel FET) to turn off the discharging FET element 72. In order to apply, the voltage of the off signal is equivalent to the signal of the high voltage) from the port DSC. As described above, since the voltage is applied to the gates of the p-channel FETs of the elements 71 and 72, the voltage of the off signal corresponds to a high voltage signal, and the voltage of the on signal corresponds to a low voltage signal. . In the overcharged state, charging is stopped by the control / calculation unit 5 issuing an off signal to the port CH. At this time, when the portable device PC is discharged, the DSC is an ON signal, so that the discharging FET element 72 can be discharged through the parasitic diode 71B of the charging FET element 71 in the OFF state. In the overdischarge state, the discharge is stopped by the control unit 5 issuing an off signal to the port DSC. At this time, when the portable device PC is charged, CH is an ON signal, so that the charging FET element 71 is in the ON state and can be charged via the parasitic diode 72B of the discharging FET element 72 in the OFF state.

  The MPU also includes a communication unit 9 that transmits various battery information such as battery voltage, remaining capacity, charge / discharge current value, and various command information to the control / power supply means S of the portable device PC. Communication processing between the battery pack A and the portable device PC is performed by the communication unit 9 as follows. The communication unit 9 includes a communication data generation unit that generates various battery information such as a battery voltage, a remaining capacity, and a charge / discharge current value as signal data that can be received by the portable device PC, and a driver unit that performs actual communication. The memory in the control / arithmetic unit 5 for storing various parameters for calculating the remaining capacity and various data is used. In addition, the driver unit receives a request for transmission of various information of the battery pack from the electronic device, and transmits the data created by the communication data creation unit to the electronic device from the driver unit. As a communication system, a well-known technique such as the SMBus system can be used, and it has a function of transmitting and receiving data signals and the like via two communication lines, a data line SDA and a clock line SCL.

  In general, the control / arithmetic unit 5 performs the following processing to obtain the remaining capacity. The control / arithmetic unit 5 discharges the battery 1 and subtracts the discharge capacity from the total discharge amount (= learning capacity), which is the total capacity of the battery 1 to be described later. Calculated as the integrated amount (Ah). Further, the control / calculation unit 5 calculates the remaining capacity ratio (%) of the battery 1 from the relational expression of (total capacity−integrated amount) / (total capacity) = remaining capacity ratio during discharging. The charge capacity is calculated by the integrated amount of the charge current of the battery 1 or by multiplying this by the charge efficiency. The discharge capacity is calculated in consideration of the integrated amount of discharge current or discharge efficiency. The integrating unit 5 can calculate the remaining amount by the integrated amount of electric power (Wh) instead of integrating the current. The integrated value of power is calculated by subtracting discharge power from charge power.

  Here, as the total capacity (= learning capacity) of the battery at that time, the battery 1 is completely discharged even with the accumulated capacity (Ah or Wh) of the discharge from the fully charged state to the fully discharged state. The accumulated capacity (Ah or Wh) of charging from full charge to full charge may be used. When a battery voltage corresponding to a predetermined remaining capacity (for example, 8%) described later is reached, a value (1-predetermined remaining capacity value, here, 0.92) is divided by the capacity discharged from full charge. Learning capacity. If the total capacity can be obtained by other methods, the total capacity of the battery at that time may be used.

  Then, as the discharge proceeds, the control / calculation unit 5 corrects the remaining amount by the voltage signal input from the A / D conversion unit 4. When a signal indicating that the voltage of the battery 1 has reached or dropped from the A / D conversion unit 4 is input, the control / calculation unit 5 causes the first voltage (for example, a lithium ion battery 3.6V / The calculated remaining capacity rate is corrected by a first remaining capacity (rate) Ya1 (for example, 8%) set in advance corresponding to the cell.

  That is, assuming that the first remaining capacity Ya1 is a predetermined remaining capacity 8%, the control / calculation unit 5 causes the battery voltage of the secondary battery 1 to decrease to the first voltage V1 when the calculated remaining capacity reaches 9%. 9% is retained as the remaining capacity. On the other hand, when the calculated remaining capacity is 9% or more and the battery voltage of the secondary battery 1 decreases to the first voltage V1, the control / calculation unit 5 sets the calculated remaining capacity value to 8%. To correct.

  Further, when the discharge progresses and a signal indicating that the voltage of the battery 1 has decreased to a predetermined discharge end voltage is input, the control / calculation unit 5 corrects the calculated remaining amount to zero. This is because when the battery voltage decreases to the discharge end voltage, the actual capacity of the battery 1 becomes 0 as the lower limit capacity. Then, the control / calculation unit 5 calculates and stores the discharge current integrated amount from the start of discharge to the discharge end voltage as a total discharge amount (= total capacity).

  After obtaining the total discharge amount (= learning capacity), the control / calculation unit 5 uses this total discharge amount until the next total discharge amount is obtained. Further, in addition to the first voltage corresponding to the first remaining capacity (rate), the calculated remaining capacity is also calculated with the second voltage corresponding to the second remaining capacity (rate) with a smaller capacity (for example, 3%). The rate may be corrected. In addition, the first voltage, discharge end voltage, etc. corresponding to the above-mentioned remaining capacity (rate) depend on the current and temperature, so it is possible to use a voltage corrected based on the current and temperature in use. is there.

  Here, as described above, in order to obtain the learning capacity (= total capacity), it corresponds to a predetermined remaining capacity (for example, 8%) until it is completely discharged from a fully charged state (predetermined remaining capacity is zero). It is necessary to discharge until the battery voltage is reached.

  Depending on how the battery pack A is used, in this case, the control / calculation unit 5 may charge the battery pack A up to the predetermined remaining capacity. It is also possible to notify that the battery is discharged and used (calibration function). Such notification is communicated from the battery pack A to the portable device PC by communication processing, and is notified to the user by turning on the display screen of the portable device PC having a charging function as a charger or a separately provided LED. Is done. Thus, the user uses the portable device PC with only the battery pack A without supplying commercial power until the predetermined remaining capacity or the battery pack A is completely discharged. Alternatively, a discharge resistor for discharging the power of the battery pack A is built in the portable device PC, a switch for discharging the power of the battery pack A is provided in the discharge resistor, and the user presses this switch. Thus, the battery pack A can be used until a predetermined remaining capacity or the battery pack A is completely discharged. Thereby, the control / calculation unit 5 of the battery pack A can obtain the learning capacity (= total capacity) at that time. Specifically, the learning capacity (= total capacity) at that time is discharged to a predetermined voltage at the lower limit, and in the battery pack, the discharge capacity from the previous full charge to the charger and the charger The discharge capacity up to the lower limit voltage at is added to obtain the discharge capacity (= the learning capacity at that time).

(When notifying)
・ When the capacity at the start of charging is less than a predetermined value (for example, 10%) as a percentage of the total capacity (= learning capacity) at that time ・ The number of charge / discharge cycles, the number of charges or the number of full charge detections When the learning capacity is obtained a predetermined number of times (in the range of 20 to 100 times, for example, 90 times) or more, by using a timer in the control / calculation unit 5, When the predetermined time (in the range of 30 to 100 days, for example, 90 days) or more is reached. ・ When the user wants to obtain the learning capacity at the start of charging and presses the above discharge switch. The features of this embodiment will be described. This embodiment will be described with reference to FIG. FIG. 2 is a graph showing the relationship between the initial total capacity, the rated capacity, the total capacity in each deteriorated state, the target capacity, etc. in each deteriorated state. The vertical axis direction indicates the capacity.

  FIGS. 2 (1) and 2 (2) show an initial state at the initial stage of use. As an example, the secondary battery has an initial total capacity of 1050 mAH (105% when an initial rated capacity described later is 100%, which is referred to as an initial rated capacity ratio). Here, in such a secondary battery, in consideration of variations in the total capacity of secondary batteries that are mass-produced, in terms of guaranteed capacity, (initial) rated capacity 1000 mAH (initial rated capacity) The ratio is 100%). As shown in FIG. 2 (2), in the initial use, the target capacity (800 mAH, initial rated capacity ratio 80%) smaller than the total capacity of the secondary battery in the initial use (total capacity 1050 mAH, initial rated capacity ratio 105%). The secondary battery is used and utilized by charging and discharging the secondary battery with the target capacity as the upper limit. Such a target capacity is desirably set to 60 to 90% (= 630 to 945 mAH = the above-mentioned initial rated capacity ratio of 63 to 94.5%) with respect to the total capacity in the initial stage of use. More desirably, such a target capacity is preferably set to 70 to 81% (= 730 to 850 mAH = the above-mentioned initial rated capacity ratio of 73 to 85%) with respect to the total capacity in the initial use.

  FIG. 2 (3) shows a case where the secondary battery has deteriorated due to use and neglect, and the total capacity becomes 900 mAH. In other words, at this time, the total capacity is deteriorated, and the initial rated capacity ratio is reduced by 15%. At this time, the secondary battery is used and used by charging up to the target capacity (800 mAH, initial rated capacity ratio 80%) and charging / discharging the secondary battery with this target capacity as the upper limit.

  Here, with respect to the total capacity of 900 mAH (capacity in a fully charged state) at this time, charging is stopped with the target capacity of 800 mAH being fully charged, and charging and discharging is performed as an upper limit, so the total capacity at this time ( It is used at about 89% (= 800 mAH / 900 mAH) with respect to the (full charge capacity). Since the battery is used with a smaller capacity than the fully charged capacity, it is not used when the capacity is large unlike the fully charged capacity, so that the progress of deterioration of the secondary battery is reduced.

  FIG. 2 (4) shows a case where the deterioration proceeds due to the use and leaving of the secondary battery, and the total capacity becomes 800 mAH. In other words, at this time, the total capacity is deteriorated and the initial rated capacity ratio is reduced by 25%. Also at this time, the secondary battery is used and utilized by charging and discharging the secondary battery with the target capacity (800 mAH, initial rated capacity ratio 80%) as the upper limit.

  Here, with respect to the total capacity of 800 mAH at this time (capacity in a fully charged state), charging is stopped with the target capacity of 800 mAH being fully charged, and charging and discharging is performed as an upper limit. Therefore, the total capacity at this time ( It will be used at 100% (= 800 mAH / 800 mAH) with respect to the full charge capacity. In addition, when the capacity | capacitance of a secondary battery deteriorates any more, a secondary battery is used and utilized by charging / discharging a secondary battery by making the total capacity at that time into an upper limit.

  As shown in FIG. 3, the change in the battery voltage with respect to the discharge time in the deteriorated state of each capacity is shown. The symbol x indicates the battery voltage at the target capacity (800 mAH, initial rated capacity ratio 80%) in the deteriorated state. Is shown. Here, the battery voltage indicates a battery voltage (= open circuit voltage) when charging is temporarily stopped. The control / calculation unit 5 stores a battery voltage corresponding to the target capacity in each deterioration state, that is, each total capacity (= learning capacity), and when the battery voltage is detected, the control / calculation unit 5 performs charging. Control to stop.

In place of such a charge stop by detecting the battery voltage, the charge may be stopped when the accumulated battery capacity reaches 800 mAH. In this case, the degree of deterioration of the battery can be determined by reading the battery voltage value after charging the target capacity (for example, 800 mAh) using the fact that the charging depth of the battery increases as it deteriorates. Actual measurement data is shown in FIG. Charged / discharged cycle in which 50% of the rated capacity is charged at 1CA and discharged at 1CA from the fully discharged state. Has been implemented. Specifically, 100% charge / discharge (charge at 1CA, discharge at 0.2CA) is performed every 100 cycles, the capacity is learned, the degree of deterioration is confirmed, and the open circuit voltage after 50% charge is plotted It is. As can be seen from the figure, the open circuit voltage after charging increases as the cycle progresses. Thereafter, after 2700 cycles, the open circuit voltage has also increased significantly when the total capacity has dropped significantly. As shown in the data of FIG. 5, after charging the target capacity, the open circuit voltage of the battery is measured, and in the example shown in FIG. 5, in the range of about 3.95 to 4.15 V, for example, If 4.0V / cell) is detected, the life can be determined. (In FIG. 5, DOD indicates depth of discharge.)
For example, as shown in FIG. 2 (4), when the deterioration progresses and the total capacity becomes 800 mAH, the voltage after charging of the target capacity (800 mAH, initial rated capacity ratio 80%) is a predetermined voltage (for example, 4.2V per cell). When the control / calculation unit 5 measures the battery voltage (open circuit voltage) after charging the target capacity (800 mAH, initial rated capacity ratio 80%), and detects that the battery voltage has reached 4.2 V per cell. It is determined that it is a lifetime. Here, the life includes a state close to the life (= deterioration is progressing). From this determination, the control / calculation unit 5 can output a signal for prompting battery life or battery replacement. By transmitting such a signal from the communication unit 9, a display for prompting battery life or battery replacement can be separately presented to the user in the mobile device PC that has received the signal. In addition, the battery (A LED display) for prompting battery life or battery replacement can be provided on the battery pack A by the above determination.

  FIG. 4 is a graph showing the relationship between the initial total capacity in each deteriorated state, the rated capacity, the total capacity in each deteriorated state, the target capacity and the like when using the conventional charge / discharge method, in contrast to FIG. It is. The vertical axis direction indicates the capacity.

  4 (1) and (2) show the initial state at the initial stage of use. As an example, the secondary battery has an initial total capacity of 1050 mAH and has an (initial) rated capacity of 1000 mAH (initial rated capacity ratio of 100%).

  As shown in FIG. 4 (2), in the initial stage of use, the target capacity (800 mAH, initial rated capacity ratio 80%) smaller than the total capacity of the secondary battery in the initial stage of use (total capacity 1050 mAH, initial rated capacity ratio 105%). Is used and used by charging and discharging the secondary battery.

  FIG. 4 (3) shows a case where the deterioration has progressed due to the use and leaving of the secondary battery, and the total capacity becomes 900 mAH. In other words, at this time, the total capacity is deteriorated, and the initial rated capacity ratio is reduced by 15%. Conventionally, the secondary battery is used and used by charging and discharging the secondary battery at a total capacity of 900 mAH (capacity in a fully charged state) at this time. Since the battery is used when the capacity is large like the full charge capacity, the secondary battery is further deteriorated.

  FIG. 4 (4) shows a case where the deterioration has progressed due to the use and leaving of the secondary battery, and the total capacity becomes 800 mAH. In other words, at this time, the total capacity is deteriorated and the initial rated capacity ratio is reduced by 25%. Conventionally, a secondary battery is used and used by charging / discharging the secondary battery at a total capacity of 800 mAH (capacity in a fully charged state) at this time.

  Further, as a reference example, it is also possible to provide a remaining amount display function of a fuel gauge as follows.

When calculating the battery capacity by integrating the charge / discharge current, if the battery is charged and fully charged (for example, -ΔV detection) is detected, the capacity is corrected to 100%. Thereafter, discharging is performed and the remaining capacity decreases (see FIG. 6A).
On the other hand, in order to prevent the charging time from becoming long, when a predetermined charging time has elapsed since the start of charging (timer detection), charging is stopped for the main purpose of safety, and the capacity is corrected to 100% as a full charge. ing. In this case, the battery may not be fully charged, and in the subsequent discharge, a predetermined lower limit voltage is reached, the remaining capacity becomes zero, and a phenomenon in which the remaining capacity suddenly decreases occurs (see FIG. 6B). ).

  In order to solve such a problem, at the time of discharging, a certain capacity (discharge coefficient) is multiplied by a discharge current so that the remaining capacity is displayed as a dotted line in FIG. Do. In addition, when it is considered that the accuracy of the capacity display is lowered as described above, a signal indicating a warning that the accuracy of the capacity display is lowered is transmitted from the battery pack A to the portable device PC which is an electronic device. The user can be alerted to the user by sending the message to the user. Further, a separately provided LED or the like can be turned on by a signal indicating the alert from the battery pack A.

It is a circuit block diagram of the battery pack of one Example of this invention. In this invention, it is a graph which shows the relationship between the initial total capacity | capacitance in each degraded state, a rated capacity, the total capacity | capacitance in each degraded state, a target capacity | capacitance, etc. As shown in FIG. 3, it is a graph which shows the change of the battery voltage with respect to the discharge time in the deterioration state of each capacity | capacitance. It is a graph which shows the relationship between the initial total capacity | capacitance in each deterioration state, a rated capacity, the total capacity | capacitance in each deterioration state, a target capacity | capacitance, etc. conventionally. It is a graph which shows the relationship between the total capacity | capacitance when charging and discharging to a target capacity | capacitance, the battery voltage in a target capacity | capacitance, and the number of cycles. It is a graph explaining the remaining amount display function as a reference example.

Explanation of symbols

A Battery pack PC Mobile device (= electronic device)
S control / power supply means L load MPU microprocessor unit 1 battery 2 resistance (current detection unit)
3 Temperature Detection Unit 4 A / D Conversion Unit 5 Control / Calculation Unit 7 Control Element 71 Charging FET Element 72 Discharging FET Element 9 Communication Unit

Claims (2)

  A charging / discharging method of a secondary battery, wherein the secondary battery is charged and discharged by charging to a target capacity smaller than the total capacity of the secondary battery in the initial use.   The secondary battery charging / discharging method according to claim 1, wherein when the battery voltage when charging to a target capacity smaller than the total capacity of the secondary battery in the initial stage of use reaches a predetermined voltage, the battery is determined to have a lifetime. .