Power storage device and battery degradation estimation method

Abstract

A power storage device according to the present invention comprises: a secondary battery that can be charged and discharged; a control unit that controls charging and discharging of the secondary battery; a voltage detection unit that detects the voltage of the secondary battery; and a battery temperature detection unit that detects the temperature of the secondary battery. The control unit, during stoppage of charging of the secondary battery, calculates a first self-discharge amount of the secondary battery on the basis of an elapsed time from a time point at which charging of the secondary battery stopped and on the basis of the temperature detected by the battery temperature detection unit, calculates a second self-discharge amount of the secondary battery on the basis of a variation in the value of the voltage detected by the voltage detection unit during the elapsed time, and estimates the degree of degradation of the secondary battery on the basis of the first self-discharge amount and the second self-discharge amount.

Description

Energy storage device, battery deterioration estimation method

[0001] The present invention relates to a power storage device and a method for estimating a battery deterioration level.

[0002] A backup power storage device is known that is connected to a power supply device that supplies power to various electrical devices such as communication devices used in communication base stations, stores the power supplied from the power supply device, and, if the power supply from the power supply device is stopped, supplies power to the various electrical devices using the stored power instead of the power supply device. Such a backup power storage device can be realized using a secondary battery.

[0003] Generally, secondary batteries deteriorate with repeated charging and discharging and the passage of time, and the more the battery deteriorates, the less power it can store. Therefore, it is necessary to accurately estimate the degree of deterioration of the secondary battery and control charging and discharging according to the estimation results. For example, Patent Document 1 describes a battery management device that measures the open-circuit voltage (OCV) of a secondary battery at the start and end of charging, calculates a full charge capacity based on the difference in charge capacity calculated based on these measurement results and the integrated current value during charging, and estimates the ratio of the full charge capacity at the start of use to the current full charge capacity as an indicator of the degree of deterioration of the secondary battery.

[0004] Japanese Patent Application Publication No. 2021-144886

[0005] In the method of estimating the degree of deterioration of a secondary battery using a battery management device described in Patent Document 1, if the difference in OCV between the start and end of charging is small, the error in the calculation result of the full charge capacity becomes large, and as a result, the accuracy of estimating the degree of deterioration of the secondary battery decreases.

[0006] In view of the above-mentioned problems, an object of the present invention is to provide a power storage device and a method for estimating the degree of battery degradation that can estimate the degree of battery degradation with high accuracy.

[0007] A first aspect of the present invention provides an energy storage device that is connected to a power supply facility, stores power supplied from the power supply facility, and supplies power to other electrical devices connected to the power supply facility when the power supply facility is stopped. The energy storage device comprises a chargeable and dischargeable secondary battery, a control unit that controls charging and discharging of the secondary battery, a voltage detection unit that detects the voltage of the secondary battery, and a battery temperature detection unit that detects the temperature of the secondary battery. While charging of the secondary battery is stopped, the control unit calculates a first self-discharge amount of the secondary battery based on the elapsed time since charging of the secondary battery was stopped and the temperature detected by the battery temperature detection unit, calculates a second self-discharge amount of the secondary battery based on the amount of change in the voltage detected by the voltage detection unit over the elapsed time, and estimates the degree of deterioration of the secondary battery based on the first self-discharge amount and the second self-discharge amount. According to a second aspect of the present invention, a power storage device is connected to a power supply facility, stores power supplied from the power supply facility, and supplies power to other electrical devices connected to the power supply facility when the power supply facility is not operating, and includes a rechargeable secondary battery and a control unit that controls charging and discharging of the secondary battery, wherein the control unit estimates a degree of deterioration of the secondary battery based on a self-discharge amount during a charging suspension period from a time when charging of the secondary battery was stopped to a time when charging was resumed in each charging cycle from the time when operation of the secondary battery started to the present. According to a third aspect of the present invention, a battery deterioration estimation method is a method for estimating a degree of deterioration of a secondary battery, comprising: detecting a voltage and a temperature of the secondary battery while charging of the secondary battery is suspended; calculating a first self-discharge amount of the secondary battery based on the elapsed time since charging of the secondary battery was stopped and the detected temperature; calculating a second self-discharge amount of the secondary battery based on a variation in the detected voltage value over the elapsed time; and estimating a degree of deterioration of the secondary battery based on the first and second self-discharge amounts. A battery deterioration level estimation method according to a fourth aspect of the present invention is a method for estimating the deterioration level of a secondary battery, and estimates the deterioration level of the secondary battery based on the amount of self-discharge during the charging stop period from the point at which charging was stopped to the point at which charging was resumed in each charging cycle from the start of operation of the secondary battery to the present.

[0008] According to the present invention, it is possible to provide a power storage device and a method for estimating the degree of battery degradation that are capable of estimating the degree of battery degradation with high accuracy.

[0009] 8 is a schematic diagram of a communication base station including a power storage device according to one embodiment of the present invention. FIG. 9 is a schematic diagram of a power storage device according to one embodiment of the present invention. FIG. 10 is a graph showing a specific example of charge / discharge control of a secondary battery. FIG. 11 is a flowchart showing the flow of a deterioration level estimation process according to one embodiment of the present invention. FIG. 12 is a graph showing the relationship between the stop time during which charging of a secondary battery is stopped and the amount of self-discharge. FIG. 13 is a graph showing the relationship between coefficient α and the temperature of the secondary battery. FIG. 14 is a flowchart showing details of a deterioration level estimation process based on two types of self-discharge amounts. FIG. 15 is a graph showing the relationship between the number of charges and the SOH value when charging and discharging of a secondary battery are repeated. FIG. 16 is a graph showing the relationship between the slope of the graph of FIG. 8 and the amount of self-discharge. FIG. 17 is a flowchart showing details of a deterioration level estimation process based on a deterioration rate.

[0010] 1 is a schematic diagram of a communication base station including a power storage device according to an embodiment of the present invention. The communication base station 1 shown in Fig. 1 is a base station for wireless communication used in, for example, a mobile phone network, and includes a power supply facility 10, communication equipment 11, and one or more power storage devices 12.

[0011] The power supply facility 10 is connected to the power grid 2 via a circuit breaker 3, and converts AC power input from the power grid 2 into DC power, which is supplied to the communication equipment 11 and each power storage device 12. The power supply facility 10 is configured by combining, for example, a rectifier and a lead battery.

[0012] The communication device 11 operates using DC power supplied from the power supply facility 10, and performs processes such as transmitting and receiving, generating, and decoding wireless signals. The communication device 11 is configured by combining, for example, a modulator, a demodulator, an antenna, and the like.

[0013] The power storage device 12 is provided in the communication base station 1 as a backup for the power supply equipment 10 in the event of a power outage in the power grid 2. The power storage device 12 is connected to the power supply equipment 10, and stores the power supplied from the power supply equipment 10 when the power supply equipment 10 is operating. On the other hand, when the operation of the power supply equipment 10 stops due to a power outage in the power grid 2 or the like, the power storage device 12 supplies the power stored up to that point to the communication equipment 11. This allows the communication equipment 11 to continue operating even during a power outage.

[0014] The number of storage devices 12 installed in the communication base station 1 can be set arbitrarily depending on the power consumption of the communication equipment 11, the amount of electricity that can be stored per storage device 12, the maximum expected power outage duration during a power outage, etc.

[0015] Next, each of the power storage devices 12 will be described in detail below with reference to FIGS.

[0016] 2 is a schematic diagram of a power storage device according to one embodiment of the present invention. As shown in FIG. 2, the power storage device 12 according to this embodiment includes a secondary battery 20, a control unit 21, switches 22a and 22b, diodes 23a and 23b, a voltage detection unit 24, a current detection unit 25, a battery temperature detection unit 26, a communication unit 27, and a storage unit 28.

[0017] 1 via switches 22a and 22b. When power is supplied from power supply equipment 10, secondary battery 20 is charged under the control of control unit 21, thereby storing power in secondary battery 20. On the other hand, when the operation of power supply equipment 10 stops due to a power outage in power grid 2 or the like, secondary battery 20 is discharged under the control of control unit 21, and power is supplied from secondary battery 20 to communication equipment 11.

[0018] The switches 22a and 22b are provided between the secondary battery 20 and the power supply equipment 10 and the communication device 11, and are each switched between a conductive state and a cut-off state under the control of the control unit 21. The switches 22a and 22b are each configured using, for example, a relay, an insulated gate bipolar transistor (IGBT), a field effect transistor (FET), or the like. As shown in FIG. 2 , the switches 22a and 22b are connected in series. The series connection of the switches 22a and 22b constitutes a switching circuit in the power storage device 12 that can switch the electrical connection between the secondary battery 20 and the power supply equipment 10 and the communication device 11 between a conductive state and a cut-off state.

[0019] A diode 23a is connected in parallel to the switch 22a. As shown in Figure 2, the orientation of the diode 23a is set so that it conducts current in the direction (charging direction) flowing from the power supply equipment 10 to the secondary battery 20 and blocks current in the opposite direction.

[0020] A diode 23b is connected in parallel to the switch 22b. As shown in Figure 2, the direction of the diode 23b is opposite to that of the diode 23a, i.e., the direction of the diode 23b is set so that the current flows from the secondary battery 20 to the communication device 11 (discharge direction) and the current in the opposite direction is blocked.

[0021] When FETs are used for the switches 22 a and 22 b, the body diodes of the FETs may be used as the diodes 23 a and 23 b, respectively, which can reduce the number of components in the power storage device 12 and further reduce costs.

[0022] The voltage detection unit 24 detects the voltage between the positive and negative electrodes of the secondary battery 20 as the battery voltage and outputs the detection result to the control unit 21. The current detection unit 25 detects the charge / discharge current flowing through the secondary battery 20 and outputs the detection result to the control unit 21. The battery temperature detection unit 26 detects the surface temperature of the secondary battery 20 or the temperature of the members or space near the secondary battery 20 as the battery temperature and outputs the detection result to the control unit 21.

[0023] The control unit 21 controls charging and discharging of the secondary battery 20. The control unit 21 has the following functional blocks: a capacity management unit 211, a power outage control unit 212, a switching control unit 213, and a deterioration level estimation unit 214. The control unit 21 is configured using, for example, a microcomputer, and can realize these functional blocks by executing a predetermined program. Note that the control unit 21 may also be configured using a logic circuit such as an FPGA (Field Programmable Gate Array) instead of a microcomputer.

[0024] The capacity management unit 211 calculates an SOC value representing the state of charge (SOC) of the secondary battery 20 and outputs a switching command to the switching control unit 213 based on the SOC value, thereby managing the capacity of the secondary battery 20. The power outage control unit 212 outputs a switching command to the switching control unit 213 so that power is supplied from the secondary battery 20 to the communication device 11 instead of the power supply equipment 10 when the operation of the power supply equipment 10 stops due to a power outage or the like and power is not supplied from the power supply equipment 10. The switching control unit 213 controls the switching states of the switches 22a and 22b in response to commands from the capacity management unit 211 and the power outage control unit 212. The degradation level estimation unit 214 estimates the current degradation level of the secondary battery 20 relative to the start of operation and calculates an SOH value representing the state of health (SOH) of the secondary battery 20 based on the estimation result. Specific details of these processes will be described later.

[0025] The communication unit 27 communicates with a management center (not shown) that manages the communication base station 1, and notifies the management center of the state of the power storage device 12. The communication unit 27 can notify the management center of the state of the power storage device 12 by transmitting information such as the SOH value calculated by the deterioration level estimation unit 214 to the management center.

[0026] The storage unit 28 is configured using a storage medium such as a RAM or a flash memory, and stores various information used in the processing of the control unit 21. For example, the storage unit 28 stores the program executed by the control unit 21, the latest SOC value of the secondary battery 20 calculated by the capacity management unit 211, the SOH value of the secondary battery 20 calculated by the deterioration level estimation unit 214, and the like.

[0027] For example, a nickel-based battery (nickel-cadmium battery, nickel-metal hydride battery, nickel-zinc battery, etc.) or a lithium-ion battery can be used as the secondary battery 20. Any type of battery can be used as the secondary battery 20 as long as it is chargeable and dischargeable and its voltage decreases when the SOC value decreases due to self-discharge. In particular, a nickel-based battery with charge / discharge hysteresis characteristics is preferably used as the secondary battery 20, because the higher the rate of change in voltage relative to changes in the SOC value, the more accurate the capacity management becomes.

[0028] Next, a method for controlling charging and discharging of the secondary battery 20 by the control unit 21 will be described with reference to Fig. 3. Fig. 3 is a graph showing a specific example of charging and discharging control of the secondary battery 20. In the graph of Fig. 3, the horizontal axis represents time, and the vertical axis represents the SOC value of the secondary battery 20.

[0029] First, when operation of the power storage device 12 begins in the communication base station 1, the control unit 21 starts charging the secondary battery 20 using power supplied from the power supply equipment 10. As a result, the charge / discharge state of the secondary battery 20 becomes "charging," and power is stored in the secondary battery 20. As a result, as shown by arrow 31, the SOC value of the secondary battery 20 gradually increases over time. At this time, the control unit 21 causes the capacity management unit 211 to successively calculate the SOC value of the secondary battery 20 based on the integrated value of the current flowing through the secondary battery 20 during charging, and uses this SOC value to manage the capacity of the secondary battery 20.

[0030] After that, at time t1, the SOC value of the secondary battery 20 reaches a predetermined upper limit S Ｈ (For example, S Ｈ= 95%), the control unit 21 stops charging the secondary battery 20. As a result, the charge / discharge state of the secondary battery 20 changes from "charging" to "stopped," and the power supply from the power supply equipment 10 to the secondary battery 20 stops. As a result, as shown by arrow 32, the SOC value of the secondary battery 20 gradually decreases due to self-discharge. At this time, the control unit 21 causes the capacity management unit 211 to successively calculate the SOC value of the secondary battery 20 based on the open circuit voltage (OCV) of the secondary battery 20, and manages the capacity of the secondary battery 20 using this SOC value.

[0031] After that, at time t2, the SOC value of the secondary battery 20 reaches a predetermined lower limit S Ｌ (For example, S Ｌ = 90%), the control unit 21 resumes charging of the secondary battery 20. As a result, the charge / discharge state of the secondary battery 20 changes from "stopped" to "charging", and power is stored in the secondary battery 20. As a result, as indicated by arrow 33, the SOC value of the secondary battery 20 gradually increases over time. At this time, the control unit 21, as in the period up to time t1, causes the capacity management unit 211 to successively calculate the SOC value of the secondary battery 20 based on the integrated value of the current flowing through the secondary battery 20 during charging, and uses this SOC value to manage the capacity of the secondary battery 20.

[0032] After that, at time t3, the SOC value of the secondary battery 20 again reaches the upper limit value S Ｈ , the control unit 21 stops charging the secondary battery 20. As a result, the charge / discharge state of the secondary battery 20 changes from "charging" to "stopped," and the power supply from the power supply equipment 10 to the secondary battery 20 stops. As a result, as shown by arrow 34, the SOC value of the secondary battery 20 gradually decreases due to self-discharge. At this time, the control unit 21, as in the period from time t1 to time t2, causes the capacity management unit 211 to sequentially calculate the SOC value of the secondary battery 20 based on the open circuit voltage (OCV) of the secondary battery 20, and uses this SOC value to manage the capacity of the secondary battery 20.

[0033] After that, at time t4, the SOC value of the secondary battery 20 again reaches the lower limit value S Ｌ When the battery voltage reaches 10V, the control unit 21 resumes charging the secondary battery 20.

[0034] If the power supply equipment 10 is in operation, the same control is repeated thereafter. Ｌ to the upper limit S Ｈ The charging of the secondary battery 20 is controlled so as to maintain the charge within the range.

[0035] At time t5, a power outage occurs in the power grid 2, and the power supply from the power grid 2 to the power supply equipment 10 is interrupted, causing the power supply equipment 10 to stop operating. The power storage device 12 immediately starts supplying power to the communication device 11 in place of the power supply equipment 10. At this time, the control unit 21 discharges the power stored in the secondary battery 20, so that the power storage device 12 can cover the power supplied to the communication device 11. As a result, the charge / discharge state of the secondary battery 20 becomes "discharging," and the SOC value of the secondary battery 20 gradually decreases over time, as shown by arrow 36.

[0036] Thereafter, when the SOC value of the secondary battery 20 drops to 0% (discharge end SOC) at time t6, the control unit 21 stops discharging the secondary battery 20. As a result, the charge / discharge state of the secondary battery 20 changes from "discharging" to "stopped," and the supply of power from the power storage device 12 to the communication device 11 stops. Thereafter, as indicated by arrow 37, the SOC value of the secondary battery 20 is maintained at 0% until the power outage is resolved.

[0037] At time t7, the power outage is resolved, the power grid 2 is restored, and power supply from the power supply equipment 10 is resumed. The control unit 21 then resumes charging the secondary battery 20. As a result, the charge / discharge state of the secondary battery 20 changes from "stopped" to "charging," and power is stored in the secondary battery 20. As a result, as indicated by arrow 38, the SOC value of the secondary battery 20 gradually increases over time. At this time, the control unit 21, as in the period up to time t1 and the period from time t2 to time t3, sequentially calculates the SOC value of the secondary battery 20 using the capacity management unit 211 based on the integrated value of the current flowing through the secondary battery 20 during charging, and uses this SOC value to manage the capacity of the secondary battery 20.

[0038] After that, at time t8, the SOC value of the secondary battery 20 reaches the upper limit value S Ｈ, the control unit 21 stops charging the secondary battery 20. As a result, the charge / discharge state of the secondary battery 20 changes from "charging" to "stopped," and the power supply from the power supply equipment 10 to the secondary battery 20 stops. As a result, as shown by arrow 39, the SOC value of the secondary battery 20 gradually decreases due to self-discharge. At this time, the control unit 21 sequentially calculates the SOC value of the secondary battery 20 based on the open circuit voltage (OCV) of the secondary battery 20 using the capacity management unit 211, as in the period from time t1 to time t2 and the period from time t3 to time t4, and performs capacity management of the secondary battery 20 using this SOC value.

[0039] After that, at time t9, the SOC value of the secondary battery 20 reaches the lower limit S Ｌ When the time t1 reaches the predetermined time, the control unit 21 resumes charging the secondary battery 20. The same applies to the control after time t9.

[0040] Note that, while FIG. 3 shows an example in which the secondary battery 20 is discharged during a power outage and its SOC value drops to 0%, there are cases in which the power outage is resolved and the power grid 2 is restored before the SOC value of the secondary battery 20 drops to 0%. In this case, it is preferable to resume charging of the secondary battery 20 regardless of the SOC value of the secondary battery 20. Alternatively, a predetermined SOC value greater than 0% may be set as the discharge end SOC, and if the SOC value of the secondary battery 20 reaches this discharge end SOC during discharging, discharging of the secondary battery 20 may be stopped even if the power outage is not resolved. In either case, when charging of the secondary battery 20 is resumed after power is restored to the power grid 2, the SOC value of the secondary battery 20 may be set to the upper limit value S Ｈ Charging continues until the upper limit S Ｈ It is preferable to stop charging when the

[0041] Next, the details of the degradation level estimation of the secondary battery 20 by the degradation level estimation unit 214 will be described. In the power storage device 12 of this embodiment, when the charge / discharge state of the secondary battery 20 is "suspended," the degradation level estimation unit 214 can estimate the degradation level of the secondary battery 20 using one of two degradation level estimation methods. One of the methods calculates the amount of stored power decrease due to self-discharge of the secondary battery 20 (hereinafter referred to as "self-discharge amount") using two different methods, and estimates the degradation level of the secondary battery 20 based on the difference between the calculated values. Hereinafter, this degradation level estimation method will be referred to as "degradation level estimation based on two types of self-discharge amount." The other method estimates the degradation rate during charging suspension periods in each charging cycle from the start of operation of the secondary battery 20 to the present, and estimates the degradation level of the secondary battery 20 based on the estimation results. Hereinafter, this degradation level estimation method will be referred to as "degradation level estimation based on degradation rate." The deterioration level estimation unit 214 can estimate the deterioration level of the secondary battery 20 by calculating the SOH value of the secondary battery 20 using one of these deterioration level estimation methods, taking into account the state of the storage device 12.

[0042] 4 is a flowchart showing the flow of a degradation level estimation process according to one embodiment of the present invention. In the power storage device 12 of this embodiment, the control unit 21 estimates the degradation level of the secondary battery 20 by causing the degradation level estimation unit 214 to execute the process shown in the flowchart of FIG. 4 at predetermined processing intervals.

[0043] In step S10, the control unit 21 determines whether charging of the secondary battery 20 has stopped. This determination can be made, for example, based on the current value of the secondary battery 20 obtained from the current detection unit 25. If the result of the determination in step S20 is that charging of the secondary battery 20 has stopped, the process proceeds to step S20. On the other hand, if the secondary battery 20 is being charged, the process shown in the flowchart in FIG. 4 ends. In this case, the degradation level estimation unit 214 does not estimate the degradation level of the secondary battery 20 in this process.

[0044] In step S20, the control unit 21 determines whether the deterioration level of the secondary battery 20 has been estimated during the current charging suspension period. If the processing of step S40 or step S50 described below has been performed during the current charging suspension period and the deterioration level of the secondary battery 20 has been estimated by these processing, the processing shown in the flowchart of Fig. 4 is terminated. On the other hand, if the processing of step S40 or step S50 has not been performed and the deterioration level of the secondary battery 20 during the current charging suspension period has not yet been estimated, the process proceeds to step S30.

[0045] In step S30, the control unit 21 determines whether the power storage device 12 is in a predetermined peculiar condition. Here, the control unit 21 determines that the power storage device 12 is in a peculiar condition, for example, when the power supply equipment 10 is stopped or when charging of the secondary battery 20 is resumed before the degradation estimation process based on the two types of self-discharge amounts described above is performed. Otherwise, the control unit 21 determines that the power storage device 12 is not in a peculiar condition. If the control unit 21 determines that the power storage device 12 is not in a peculiar condition, the process proceeds to step S40. If the control unit 21 determines that the power storage device 12 is in a peculiar condition, the process proceeds to step S50. Note that the above-described peculiar condition is merely an example. The control unit 21 may also determine that the power storage device 12 is in a peculiar condition under any other circumstances depending on the difference in estimation accuracy obtained by the two degradation estimation methods described above.

[0046] In step S40, the control unit 21 performs the degradation level estimation process based on two types of self-discharge amounts from the two degradation level estimation methods described above. The specific processing methods will be described later.

[0047] In step S50, the control unit 21 performs the degradation level estimation process based on the degradation rate, one of the two degradation level estimation methods described above. The specific processing method will be described later.

[0048] Once the deterioration level of secondary battery 20 has been estimated by the process of either step S40 or S50, the process proceeds to step S60. In step S60, control unit 21 transmits the deterioration level of secondary battery 20 estimated in step S40 or S50, i.e., the SOH value of secondary battery 20 calculated in step S40 or S50, to the management center using communication unit 27. This allows power storage device 12 to notify the management center of the current deterioration level of secondary battery 20.

[0049] After executing the process of step S60, the control unit 21 ends the process shown in the flowchart of FIG.

[0050] Next, the degradation level estimation process based on two types of self-discharge amounts, which is performed in step S40 of FIG. 4, will be described below with reference to FIGS.

[0051] Fig. 5 is a graph showing the relationship between the suspension time and the self-discharge amount when charging of the secondary battery 20 is suspended. In Fig. 5, each of the curves 51 to 54 shows the relationship between the suspension time and the self-discharge amount for each temperature condition of the secondary battery 20. Specifically, graph 51 shows the relationship between the suspension time and the self-discharge amount of the secondary battery 20 at 25°C, graph 52 at 45°C, graph 53 at 55°C, and graph 54 at 65°C. In these graphs, the horizontal axis shows the suspension time, and the vertical axis shows the self-discharge amount.

[0052] Graphs 51 to 54 in Fig. 5 show that the self-discharge amount of the secondary battery 20 increases as the stop time passes while charging is stopped, and the slope becomes steeper as the temperature increases and decreases as the stop time becomes longer. Here, the degree of decrease in the slope of graphs 51 to 54 according to the stop time can be approximated by the square root of the stop time. That is, if the self-discharge amount of the secondary battery 20 while charging is stopped is D, this can be expressed by the following equation (1). In equation (1), α represents a coefficient according to the temperature, and H represents the elapsed time since charging was stopped. D = α × √H (1)

[0053] 6 is a graph showing the relationship between the coefficient α in equation (1) and the temperature of the secondary battery 20. In FIG. 6, plot points 61 to 64 represent the values ​​of the coefficient α obtained from the graphs 51 to 54 in FIG. 5, respectively. When a graph 60 is obtained by connecting these plot points 61 to 64, this graph 60 has a parabolic shape. In other words, it can be seen that the coefficient α can be approximated by a value proportional to the square of the temperature (provided that the temperature is 0°C or higher).

[0054] It is also known that the self-discharge rate of a secondary battery generally varies depending on the amount of charge stored at the time when charging stops (when self-discharge starts). However, the amount of charge stored at the time when charging stops has a smaller effect on the self-discharge rate than the elapsed time or temperature.

[0055] As explained above, it can be seen that the self-discharge amount of the secondary battery 20 while charging is stopped is determined by two factors: the product of the square root of the elapsed time since charging was stopped and the square of the temperature, and the amount of charge stored at the time charging was stopped. Therefore, by determining a calculation formula for the self-discharge amount using these factors by multiple regression analysis, the self-discharge amount D of the secondary battery 20 while charging is stopped can be expressed by the following formula (2). In formula (2), H represents the elapsed time since charging was stopped, T represents the temperature, A represents the amount of charge stored at the time charging was stopped, and a and b represent predetermined constants. D = (a x A - b) x (√H x T ２ ) ... (2)

[0056] However, while the above formula (2) is applicable when the temperature T is constant, it is not applicable when the temperature T fluctuates while charging of the secondary battery 20 is stopped. Therefore, when the temperature T fluctuates, the following formula (3), which is obtained by time-differentiating formula (2), is used to calculate the self-discharge amount D' per predetermined unit time (for example, one hour) for each unit time, and this self-discharge amount D' per unit time is integrated to calculate the self-discharge amount D of the secondary battery 20 while charging is stopped. Note that the self-discharge amount D' per unit time calculated by formula (3) corresponds to the self-discharge current of the secondary battery 20. D' = (a × A - b) × (½ × H －１／２ ×T ２ ) ... (3)

[0057] Hereinafter, the self-discharge amount of the secondary battery 20 calculated by integrating the above formula (2) or the above formula (3) will be referred to as the "first self-discharge amount." This first self-discharge amount decreases as the deterioration of the secondary battery 20 progresses. In other words, the degree of deterioration of the secondary battery 20 is reflected in the first self-discharge amount.

[0058] On the other hand, the self-discharge amount of the secondary battery 20 while charging is stopped can also be determined from the amount of change in the open circuit voltage (OCV). That is, the amount of OCV decrease while charging is stopped is determined by calculating the difference between the voltage value detected by the voltage detection unit 24 immediately after charging is stopped and the voltage value detected by the voltage detection unit 24 while charging is stopped. Then, the amount of self-discharge of the secondary battery 20 while charging is stopped can be determined based on a predetermined relationship between the amount of OCV decrease and the amount of self-discharge of the secondary battery 20. Hereinafter, the amount of self-discharge of the secondary battery 20 determined in this manner will be referred to as the "second self-discharge amount." This second self-discharge amount is determined corresponding to the initial state of the secondary battery 20 and is constant regardless of the degree of deterioration.

[0059] In the degradation level estimation process based on two types of self-discharge amounts, the first self-discharge amount and the second self-discharge amount described above are calculated, and the ratio between these is calculated to estimate the degradation level of the secondary battery 20. Furthermore, when the first self-discharge amount reaches a predetermined value while charging of the secondary battery 20 is stopped, the second self-discharge amount is calculated to estimate the degradation level of the secondary battery 20. This makes it possible to keep the value of the self-discharge amount used to estimate the degradation level constant, making it possible to determine the degradation level of the secondary battery 20 with higher accuracy than the method described in Patent Document 1.

[0060] FIG. 7 is a flowchart showing the details of the degradation level estimation process based on two types of self-discharge amounts.

[0061] In step S110, the control unit 21 acquires the voltage value of the secondary battery 20 from the voltage detection unit 24. Here, the open circuit voltage (OCV) of the secondary battery 20 is acquired.

[0062] In step S120, control unit 21 determines whether charging has just been stopped. If charging has just been stopped, i.e., if this is the first time the deterioration level estimation process is performed after charging of secondary battery 20 has been stopped, control proceeds to step S130. On the other hand, if charging has not just been stopped, i.e., if this is the second or subsequent time the deterioration level estimation process is performed after charging of secondary battery 20 has been stopped, control proceeds to step S150.

[0063] In step S130, the control unit 21 acquires the amount of stored power in the secondary battery 20 at the time when charging was stopped. Here, for example, the amount of stored power in the secondary battery 20 at the time when charging was stopped can be acquired by integrating the current value detected by the current detection unit 25 while charging the secondary battery 20.

[0064] In step S140, the control unit 21 stores the voltage value acquired in step S110 and the amount of stored power acquired in step S130 in the storage unit 28 as the voltage value and amount of stored power at the time when charging was stopped. The voltage value and amount of stored power at the time when charging was stopped stored here are used in the calculation process of the second self-discharge amount performed in step S220 (described later) and the calculation process of the first self-discharge amount performed in step S180 or S200 (described later). After performing the process of step S140, the control unit 21 ends the process shown in the flowchart of FIG. 7.

[0065] In step S150, the control unit 21 acquires the elapsed time from the time when charging was stopped.

[0066] In step S160 , the control unit 21 acquires the temperature of the secondary battery 20 from the battery temperature detection unit 26 .

[0067] In step S170, the control unit 21 determines whether the temperature of the secondary battery 20 is constant while charging is stopped, based on the temperature acquired in step S160. If the temperature change while charging is stopped is within a predetermined range and the temperature of the secondary battery 20 from the time charging was stopped to the present can be considered constant, the process proceeds to step S180; otherwise, the process proceeds to step S190.

[0068] In step S180, the control unit 21 calculates the first self-discharge amount of the secondary battery 20 using an arithmetic expression for when the temperature of the secondary battery 20 is constant. Here, the control unit 21 calculates the first self-discharge amount of the secondary battery 20 using the above-mentioned expression (2) based on the elapsed time acquired in step S150, the temperature acquired in step S160, and the amount of stored power at the time of stopping charging stored in the storage unit 28 in step S140.

[0069] In step S190, the control unit 21 calculates the self-discharge current of the secondary battery 20 using an arithmetic expression for when the temperature of the secondary battery 20 is inconstant. Here, the control unit 21 calculates the self-discharge current of the secondary battery 20, i.e., the self-discharge amount per unit time, using the above-mentioned expression (3) based on the elapsed time acquired in step S150, the temperature acquired in step S160, and the amount of stored power at the time of stopping charging stored in the storage unit 28 in step S140.

[0070] In step S200, the control unit 21 calculates a first self-discharge amount of the secondary battery 20 from the integrated value of the self-discharge current calculated in step S190. Here, for example, the value of the self-discharge current obtained in the current process is multiplied by the elapsed time since the previous process, i.e., the execution cycle of the process shown in the flowchart of Fig. 7, and the result is added to the first self-discharge amount obtained in the previous process for integration. In this way, even if the temperature of the secondary battery 20 is unstable, the first self-discharge amount of the secondary battery 20 can be calculated.

[0071] After calculating the first self-discharge amount in step S180 or S200, the control unit 21 determines in the following step S210 whether the value of the first self-discharge amount is equal to or greater than a predetermined value. Here, the calculated first self-discharge amount is compared with a predetermined value of a discharge amount set in advance within the range of the amount of stored power in the charge cycle of the secondary battery 20. As a result, if the first self-discharge amount is equal to or greater than the predetermined value, the process proceeds to step S220, and if it is less than the predetermined value, the process shown in the flowchart of FIG. 7 is terminated.

[0072] In step S220, control unit 21 calculates a second self-discharge amount of secondary battery 20. Here, by calculating the difference between the voltage value at the time when charging was stopped that was stored in storage unit 28 in step S140 and the voltage value acquired in step S110, the amount of change in open circuit voltage (OCV) from the time when charging was stopped to the present is calculated, and the second self-discharge amount of secondary battery 20 is calculated based on this amount of change. This makes it possible to calculate the second self-discharge amount when the first self-discharge amount reaches a predetermined value.

[0073] In step S230, the control unit 21 estimates the deterioration level of the secondary battery 20 based on the first self-discharge amount calculated in step S180 or S200 and the second self-discharge amount calculated in step S220. Here, the deterioration level can be estimated by calculating the SOH value according to the deterioration level of the secondary battery 20 using the following formula (4): SOH (%) = {(first self-discharge amount) / (second self-discharge amount)} × 100 (4)

[0074] In step S240, control unit 21 calculates a moving average of the degradation level for each charging suspension period. Here, the moving average is calculated between the SOH value calculated in step S230 for the current charging suspension period and the SOH values ​​calculated in step S230 for the previous charging suspension periods up to a predetermined number of times. This allows the SOH values ​​calculated when the first self-discharge amount reaches a predetermined value during each charging suspension period when secondary battery 20 is repeatedly charged and discharged to be averaged over the most recent predetermined number of times. This makes it possible to determine the degradation level of secondary battery 20 with even less error.

[0075] After executing the process of step S240, the control unit 21 ends the process shown in the flowchart of FIG.

[0076] In the energy storage device 12 of this embodiment, the deterioration level estimation process based on the two types of self-discharge amounts described above is performed during each charging stop period, and the deterioration level of the secondary battery 20 can be estimated for each charging stop period by utilizing the self-discharge characteristics of the secondary battery 20 during each charging stop period when the secondary battery 20 is repeatedly charged and discharged.

[0077] Next, the deterioration rate-based deterioration degree estimation process performed in step S50 of FIG. 4 will be described below with reference to FIGS.

[0078] 8 is a graph showing the relationship between the number of charges and the SOH value when charging and discharging are repeated so that the SOC value of secondary battery 20 falls within a predetermined range according to the method described in FIG. 3. In FIG. 8, each of the graphs shown by lines 81 to 84 shows the relationship between the number of charges and the SOH value for each self-discharge amount of secondary battery 20 during each charging suspension period. Specifically, graph 81 shows the relationship between the number of charges and the SOH value for secondary battery 20 when the self-discharge amount is 10 Ah, graph 82 shows the relationship between the number of charges and the SOH value for secondary battery 20 when the self-discharge amount is 15 Ah, graph 83 shows the relationship between the number of charges and the SOH value for secondary battery 20 when the self-discharge amount is 20 Ah, and graph 84 shows the relationship between the number of charges and the SOH value for secondary battery 20 when the self-discharge amount is 25 Ah. In these graphs, the horizontal axis shows the number of charges, and the vertical axis shows the SOH value.

[0079] 8, it can be seen that the SOH value of secondary battery 20 decreases in proportion to the number of times it is charged and discharged as the charge / discharge cycle is repeated, and the slope of this slope increases in the negative direction as the amount of self-discharge increases. In other words, the SOH value of secondary battery 20 can be expressed by a linear equation with a slope according to the amount of self-discharge and with the number of times it is charged as a variable.

[0080] 9 is a graph showing the relationship between the slope of graphs 81 to 84 in FIG. 8 and the amount of self-discharge. In FIG. 9, plot points 91 to 94 represent the slopes of graphs 81 to 84 in FIG. 8, respectively. When graph 90 is obtained by connecting these plot points 91 to 94, this graph 90 has a parabolic shape. In other words, it can be seen that the slopes of graphs 81 to 84 can be approximated by a quadratic expression of the amount of self-discharge.

[0081] The slopes of the graphs 81 to 84 correspond to the amount of decrease in the SOH value per charge / discharge, i.e., the degradation rate, of the secondary battery 20. In other words, the degradation rate when the secondary battery 20 is repeatedly charged / discharged varies depending on the amount of self-discharge during the charging stop period, and this value can be calculated using a quadratic equation for the amount of self-discharge.

[0082] As described above, the SOH value of secondary battery 20 can be calculated by integrating the deterioration rate determined according to the amount of self-discharge during charging stop periods in each charging cycle, i.e., the amount of deterioration per charging cycle, from the start of operation of secondary battery 20 to the present. This makes it possible to estimate the degree of deterioration of secondary battery 20 even when power storage device 12 is under the above-mentioned special condition.

[0083] However, the degradation level estimation process based on the degradation rate described above has the disadvantage that, compared to the degradation level estimation process based on the two types of self-discharge amounts described above, errors due to past estimation results are accumulated, resulting in a larger error in the resulting SOH value. Therefore, in this embodiment, the degradation level estimation process based on the degradation rate is performed only under specific conditions in which the degradation level estimation process based on the two types of self-discharge amounts cannot be applied.

[0084] FIG. 10 is a flowchart showing the details of the degradation level estimation process based on the degradation rate.

[0085] In step S310, control unit 21 acquires the voltage values ​​of secondary battery 20 at the time when charging was stopped during the previous charging suspension period and immediately before charging was resumed. Here, the voltage value of secondary battery 20 detected first by voltage detection unit 24 during the previous charging suspension period and the voltage value of secondary battery 20 detected last by voltage detection unit 24 are acquired as the voltage values ​​at the time when charging was stopped and immediately before charging was resumed, respectively. Note that these voltage values ​​can be acquired in step S310 by, for example, reading from memory unit 28 the values ​​stored in memory unit 28 during the previous charging suspension period.

[0086] In step S320, control unit 21 calculates the amount of self-discharge during the previous charging suspension period based on the voltage values ​​of secondary battery 20 at the time when charging was stopped and immediately before charging was restarted, respectively, acquired in step S310. Here, similar to step S220 in Fig. 7 , the difference between the acquired voltage values ​​of secondary battery 20 at the time when charging was stopped and immediately before charging was restarted is calculated, i.e., the amount of change in the voltage detected by voltage detection unit 24 during the previous charging suspension period, and a second amount of self-discharge during the previous charging suspension period is calculated based on this difference, thereby making it possible to calculate the amount of self-discharge during the previous charging suspension period.

[0087] In step S330, the control unit 21 estimates the deterioration rate of the secondary battery 20 based on the self-discharge amount during the previous charging suspension period calculated in step S320. Here, the deterioration rate of the secondary battery 20 during the previous charging suspension period can be estimated using, for example, a quadratic equation that expresses the relationship between the self-discharge amount and the deterioration rate of the secondary battery 20 that is set in advance.

[0088] In step S340, the control unit 21 estimates the degree of deterioration of the secondary battery 20 based on the deterioration rate of the secondary battery 20 estimated in step S330. Here, for example, the deterioration rate for each charge suspension period in each charge cycle from the start of operation of the secondary battery 20 to the present is integrated using the following equation (5), and the integrated value is subtracted from the SOH value in the initial state to calculate an SOH value corresponding to the degree of deterioration of the secondary battery 20, thereby enabling the degree of deterioration to be estimated. Note that in equation (5), N represents the number of charge cycles (number of charge suspension periods) from the start of operation of the secondary battery 20 to the present.

[0089] After executing the process of step S340, the control unit 21 ends the process shown in the flowchart of FIG.

[0090] In the energy storage device 12 of this embodiment, the deterioration level estimation process based on the deterioration rate described above is performed during each charging stop period, thereby estimating the deterioration rate of the secondary battery 20 during each charging stop period when the secondary battery 20 is repeatedly charged and discharged, and accumulating the estimated deterioration rates for each charging stop period to estimate the deterioration level of the secondary battery 20.

[0091] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0092] (1) The power storage device 12 is connected to the power supply equipment 10, stores power supplied from the power supply equipment 10, and supplies power to a communication device 11, which is another electrical device connected to the power supply equipment 10, when the power supply equipment 10 is stopped. The power storage device 12 includes a rechargeable secondary battery 20, a control unit 21 that controls charging and discharging of the secondary battery 20, a voltage detection unit 24 that detects the voltage of the secondary battery 20, and a battery temperature detection unit 26 that detects the temperature of the secondary battery 20. While charging of the secondary battery 20 is stopped, the control unit 21 calculates a first self-discharge amount of the secondary battery 20 based on the elapsed time since charging of the secondary battery 20 was stopped and the temperature detected by the battery temperature detection unit 26 (steps S180 and S200), and calculates a second self-discharge amount of the secondary battery 20 based on the amount of change in the voltage detected by the voltage detection unit 24 over the elapsed time since charging was stopped (step S220). Then, the deterioration level of secondary battery 20 is estimated based on the calculated first self-discharge amount and second self-discharge amount (step S230). In this manner, it is possible to provide power storage device 12 and a method for estimating the battery deterioration level of secondary battery 20 that can estimate the battery deterioration level with high accuracy.

[0093] (2) When the first self-discharge amount reaches a predetermined value (step S210: Yes), the control unit 21 performs the process of step S230 to estimate the deterioration level of the secondary battery 20. In this manner, the value of the self-discharge amount used to estimate the deterioration level is kept constant, and the deterioration level of the secondary battery 20 can be determined with high accuracy.

[0094] (3) The control unit 21 performs the process of step S230 to estimate the degradation level during each charging stop period when the secondary battery 20 is repeatedly charged and discharged. Then, the control unit 21 calculates a moving average of the degradation level estimated for each charging stop period (step S240). This makes it possible to obtain the degradation level of the secondary battery 20 with further reduced error.

[0095] (4) The control unit 21 can calculate the first self-discharge amount (step S180) using equation (2), which is an arithmetic expression including a first factor based on the product of the square root of the elapsed time since charging of the secondary battery 20 was stopped and the square of the temperature, and a second factor based on the amount of stored power at the time charging of the secondary battery 20 was stopped. In this way, when the temperature of the secondary battery 20 is constant, it is possible to calculate the first self-discharge amount of the secondary battery 20 with high accuracy through simple arithmetic processing.

[0096] (5) The control unit 21 also calculates the first self-discharge amount for each predetermined unit time (step S190) and can calculate the current first self-discharge amount by integrating the first self-discharge amounts per unit time calculated from the time charging was stopped until the present (step S200). Specifically, in step S190, the first self-discharge amount per unit time can be calculated using the above-mentioned formula (3). In this way, even if the temperature of the secondary battery 20 is unstable, it is possible to calculate the first self-discharge amount of the secondary battery 20 with high accuracy.

[0097] (6) The control unit 21 estimates the deterioration level of the secondary battery 20 based on the self-discharge amount during the charge suspension period from the time when the charge was stopped to the time when the charge was resumed in each charge cycle from the start of operation of the secondary battery 20 to the present (step S340). Specifically, the control unit 21 estimates the deterioration rate of the secondary battery 20 during each charge suspension period when the secondary battery 20 is repeatedly charged and discharged based on a predetermined relationship between the self-discharge amount of the secondary battery 20 and the deterioration rate (step S330). The control unit 21 then estimates the deterioration level based on a value obtained by integrating the deterioration rates estimated for each charge suspension period (step S340). This also makes it possible to provide the power storage device 12 and the method for estimating the battery deterioration level for the secondary battery 20 with high accuracy.

[0098] (7) The control unit 21 calculates the self-discharge amount of the secondary battery 20 based on the amount of fluctuation in the voltage detected by the voltage detection unit 24 during the charging stop period (step S320). This allows the self-discharge amount of the secondary battery 20 during the charging stop period to be accurately determined.

[0099] (8) The control unit 21 determines whether the power storage device 12 is under a predetermined peculiar condition (step S30). If it is determined that the power storage device 12 is under the peculiar condition (step S30: Yes), the control unit 21 estimates the deterioration level of the secondary battery 20 based on the self-discharge amount during the charging stop period of each charging cycle (step S50). On the other hand, if it is determined that the power storage device 12 is not under the peculiar condition (step S30: No), the control unit 21 estimates the deterioration level of the secondary battery 20 based on the first self-discharge amount and the second self-discharge amount (step S40). In this case, for example, in step S30, the control unit 21 determines that the power storage device 12 is under the peculiar condition if the power supply equipment 10 is stopped or if charging of the secondary battery 20 is resumed before the deterioration level is estimated based on the first self-discharge amount and the second self-discharge amount in step S40. This allows the control unit 21 to switch the method for estimating the deterioration level of the secondary battery 20 depending on the situation, thereby enabling the control unit 21 to accurately estimate the deterioration level of the secondary battery 20 under any situation.

[0100] In the present embodiment, an example has been described in which the degradation level estimation process based on two types of self-discharge amounts is performed when the power storage device 12 is not under a specific condition, and the degradation level estimation process based on the degradation rate is performed when the power storage device 12 is under a specific condition, but only one of these degradation level estimation processes may be performed regardless of whether the power storage device 12 is under a specific condition. Even in this way, it is possible to provide the power storage device 12 and the battery degradation level estimation method that can estimate the battery degradation level of the secondary battery 20 with high accuracy.

[0101] The present invention is not limited to the above-described embodiment, and can be implemented using any components without departing from the spirit of the present invention.

[0102] The above-described embodiments and modifications are merely examples, and the present invention is not limited to these details as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these details. Other aspects that can be considered within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention.

[0103] 1: Communication base station 2: Power system 3: Circuit breaker 10: Power supply equipment 11: Communication equipment 12: Power storage device 20: Secondary battery 21: Control unit 22a, 22b: Switches 23a, 23b: Diodes 24: Voltage detection unit 25: Current detection unit 26: Battery temperature detection unit 27: Communication unit 28: Memory unit 211: Capacity management unit 212: Power outage control unit 213: Switching control unit 214: Deterioration level estimation unit

Claims

1. A power storage device that is connected to a power supply facility, stores power supplied from the power supply facility, and supplies power to other electrical devices connected to the power supply facility when the power supply facility is stopped, the power storage device comprising: a rechargeable secondary battery; a control unit that controls charging and discharging of the secondary battery; a voltage detection unit that detects the voltage of the secondary battery; and a battery temperature detection unit that detects the temperature of the secondary battery, wherein, while charging of the secondary battery is stopped, the control unit calculates a first self-discharge amount of the secondary battery based on the elapsed time since charging of the secondary battery was stopped and the temperature detected by the battery temperature detection unit; calculates a second self-discharge amount of the secondary battery based on the amount of change in the voltage detected by the voltage detection unit over the elapsed time; and estimates a degree of deterioration of the secondary battery based on the first self-discharge amount and the second self-discharge amount.

2. The power storage device according to claim 1, wherein the control unit estimates the degree of deterioration when the first self-discharge amount reaches a predetermined value.

3. A power storage device according to claim 1, wherein the control unit estimates the degree of deterioration during each charging stop period when the secondary battery is repeatedly charged and discharged, and calculates a moving average of the degree of deterioration estimated for each charging stop period.

4. A power storage device according to claim 1, wherein the control unit calculates the first self-discharge amount using an arithmetic expression including a first factor based on the product of the square root of the elapsed time and the square of the temperature, and a second factor based on the amount of stored electricity in the secondary battery at the time charging is stopped.

5. A power storage device according to claim 1, wherein the control unit calculates the first self-discharge amount for each predetermined unit time, and calculates the current first self-discharge amount by integrating the first self-discharge amount per unit time calculated from the time when charging was stopped until the present.

6. The power storage device according to claim 5, wherein the control unit calculates the first self-discharge amount per unit time using the following equation: D'=(a×A−b)×(½×H －１／２ ×T ２ where D' represents the first self-discharge amount per unit time, A represents the amount of charge stored in the secondary battery at the time when charging is stopped, H represents the elapsed time, T represents the temperature, and a and b represent predetermined constants.

7. A storage device according to claim 1, wherein the control unit estimates the degree of deterioration of the secondary battery based on the amount of self-discharge during the charging stop period from the point at which charging was stopped to the point at which charging was restarted in each charging cycle from the start of operation of the secondary battery to the present.

8. A power storage device according to claim 7, wherein the control unit estimates the rate of deterioration of the secondary battery during each charge stop period when the secondary battery is repeatedly charged and discharged, based on a predetermined relationship between the self-discharge amount of the secondary battery and the rate of deterioration, and estimates the degree of deterioration based on a value obtained by accumulating the rate of deterioration estimated for each charge stop period.

9. The power storage device according to claim 7, wherein the control unit calculates the self-discharge amount based on the amount of fluctuation in the voltage detected by the voltage detection unit during the charging stop period.

10. A storage device according to claim 7, wherein the control unit determines whether the storage device is under a predetermined peculiar condition, and if it determines that the storage device is under the peculiar condition, estimates the degree of deterioration based on the amount of self-discharge during the charging stop period of each charging cycle, and if it determines that the storage device is not under the peculiar condition, estimates the degree of deterioration based on the first amount of self-discharge and the second amount of self-discharge.

11. A power storage device according to claim 10, wherein the control unit determines that the power storage device is under the special condition when charging of the secondary battery is resumed while the power supply equipment is out of operation or before the degree of deterioration is estimated based on the first self-discharge amount and the second self-discharge amount.

12. A power storage device that is connected to a power supply facility, stores the power supplied from the power supply facility, and supplies power to other electrical devices connected to the power supply facility when the power supply facility is stopped, the power storage device comprising: a rechargeable secondary battery; and a control unit that controls the charging and discharging of the secondary battery, wherein the control unit estimates the degree of deterioration of the secondary battery based on the amount of self-discharge during the charging stop period from the point at which charging was stopped to the point at which charging was restarted in each charging cycle from the start of operation of the secondary battery to the present.

13. A method for estimating the degree of deterioration of a secondary battery, comprising: detecting the voltage and temperature of the secondary battery while charging of the secondary battery is stopped; calculating a first self-discharge amount of the secondary battery based on the elapsed time since charging of the secondary battery was stopped and the detected temperature; calculating a second self-discharge amount of the secondary battery based on the amount of change in the detected voltage value over the elapsed time; and estimating the degree of deterioration of the secondary battery based on the first self-discharge amount and the second self-discharge amount.

14. A method for estimating the degree of deterioration of a secondary battery, which estimates the degree of deterioration of the secondary battery based on the amount of self-discharge during the charging stop period from the point at which charging was stopped to the point at which charging was restarted in each charging cycle from the start of operation of the secondary battery to the present.

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