Uncharged capacity estimation method and fully charged capacity estimation method for secondary battery in battery module

Abstract

This uncharged capacity estimation method for secondary batteries (12) in a battery module (10) comprises acquiring charging master data indicating the relationship between an SOC and a voltage when charging a master secondary battery at a master charging rate. The estimation method comprises: performing constant current charging on the battery module (10) while lowering a charging rate in multiple stages; and, in a state in which the charging rate is lowered to the master charging rate and at a timepoint when the voltage of any one of the secondary batteries (10) has reached the voltage corresponding to the SOC of 100%, acquiring the voltages of the other remaining secondary batteries (10). The estimation method comprises estimating the SOC of each of the secondary batteries (10) from the acquired voltage by using the charging master data, and estimating the uncharged capacity of each of the secondary batteries (10) on the basis of the estimated SOC.

Description

Method for estimating remaining charge capacity and fully charged capacity of secondary battery in battery module

[0001] The present disclosure relates to a method for estimating the remaining charge capacity and the fully charged capacity of a secondary battery in a battery module.

[0002] A battery module has a plurality of secondary batteries connected in series. When such a battery module is charged, when any one of the secondary batteries is charged to a voltage corresponding to SOC (State Of Charge) 100%, in order to prevent overcharging of the secondary battery, charging of the battery module is stopped. Therefore, after charging is stopped, for the secondary batteries that have not been charged to the voltage corresponding to SOC 100%, an estimation of the remaining charge capacity is performed in order to estimate the fully charged capacity. As a method for estimating the capacity of each secondary battery of the battery module, for example, Patent Document 1 discloses a method for estimating the remaining capacity based on the voltage obtained from each secondary battery.

[0003] Japanese Patent Laid-Open No. 8-317572

[0004] One of the charging methods for secondary batteries is constant current-constant voltage charging. Constant current-constant voltage charging is a method in which a secondary battery is charged by constant current charging until a predetermined voltage is reached, and then the secondary battery is charged by constant voltage charging. However, when this method is used for a battery module having a plurality of secondary batteries connected in series, it is necessary to shift from constant current charging to constant voltage charging when the voltage of any one of the secondary batteries of the battery module reaches the voltage corresponding to SOC 100%, rather than when the battery module reaches the fully charged voltage. The fully charged capacity and the like of each secondary battery are different due to individual differences of the secondary batteries. Therefore, when constant current-constant voltage charging is adopted as the charging method of the battery module, when the charging current is changed in an attempt to maintain constant voltage charging, the voltage of each secondary battery fluctuates according to its respective SOC. Therefore, fluctuations caused by the voltage fluctuations specific to each secondary battery occur in the voltage of the entire battery module, so that constant voltage charging cannot be maintained.

[0005] Secondary batteries using olivine-type structured positive electrode active materials are known. In this type of secondary battery, it is known that a plateau region exists in the SOC-OCV curve, which represents the relationship between SOC and OCV (Open Circuit Voltage), where OCV remains approximately constant even when SOC changes. The plateau region extends to the end of charging, just before SOC reaches 100%. Therefore, in a battery module equipped with secondary batteries using olivine-type structured positive electrode active materials, when the voltage of one of the secondary batteries reaches the voltage corresponding to 100% SOC and charging of the battery module stops, the voltage of the remaining secondary batteries is often in the plateau region. In the plateau region, the rate of change of voltage is small relative to the rate of change of SOC. Therefore, even if the uncharged capacity of the secondary battery is estimated by referring to the SOC-OCV curve, the accuracy of the SOC estimation is low, which reduces the accuracy of the estimation of the uncharged capacity of the secondary battery.

[0006] A method according to one aspect of the present disclosure is a method for estimating the uncharged capacity of secondary batteries in a battery module in which a plurality of secondary batteries having an olivine-type structure positive electrode active material are connected in series. The uncharged capacity is the difference between the capacity charged up to the completion of charging and the fully charged capacity of each of the plurality of secondary batteries whose State of Charge (SOC) has not reached 100% when the battery module is fully charged. The method for estimating the uncharged capacity includes acquiring charging master data showing the relationship between the voltage obtained during the charging process in which a master secondary battery is charged at a specific master charging rate until the SOC reaches 100%, and the SOC. The method for estimating the uncharged capacity includes performing constant current charging of the battery module while lowering the charging rate in multiple steps, one step at a time, each time the voltage of any one of the plurality of secondary batteries reaches the voltage corresponding to the state where the SOC is 100%. The uncharged capacity estimation method includes, when the charging rate has decreased to the master charging rate, obtaining the voltage of each of the remaining secondary batteries that have not yet reached the voltage corresponding to the state of 100% SOC when the voltage of any one of the secondary batteries reaches the voltage corresponding to the state of 100% SOC. The uncharged capacity estimation method also includes, using the charging master data, estimating the state of OC of each of the remaining secondary batteries from the obtained voltages of each of the remaining secondary batteries, and estimating the uncharged capacity of each of the remaining secondary batteries based on the estimated SOC.

[0007] According to this method, the battery module is charged using constant current charging, which involves gradually lowering the charging rate in multiple stages. Therefore, unlike constant current constant voltage charging, voltage fluctuations caused by individual differences among the multiple secondary batteries in the battery module converge after the charging rate is changed. In other words, when the battery module is charged at a certain charging rate, even if the voltage of one of the secondary batteries reaches the voltage corresponding to 100% SOC, lowering the charging rate by one stage will cause the voltage of the secondary battery to decrease accordingly. As a result, it becomes possible to continue charging until one of the secondary batteries reaches the voltage corresponding to 100% SOC again.

[0008] The charging master data shows the relationship between the voltage of a secondary battery and its State of Charge (SOC) when the secondary battery is charged at the master charging rate. By charging a secondary battery at a sufficiently low charging rate, the voltage rise due to polarization can be moderated. Therefore, when a secondary battery is charged at a sufficiently low charging rate, the rate of change of voltage relative to the rate of change of SOC near 100% SOC becomes large. For this reason, when secondary batteries are charged at a master charging rate that is sufficiently low, the acquired voltages tend to differ significantly between secondary batteries. As a result, the SOC of each secondary battery can be estimated with high accuracy from the voltage acquired for each secondary battery. Therefore, the estimation accuracy regarding the uncharged capacity of the secondary batteries can be increased. Consequently, even if the voltage of one of several secondary batteries reaches the voltage corresponding to 100% SOC, and the voltages of many of the remaining secondary batteries are in the plateau region, the estimation accuracy regarding the uncharged capacity of each secondary battery can be increased.

[0009] Regarding the method for estimating the uncharged capacity of a secondary battery in a battery module, it is preferable that the secondary battery is equipped with a positive electrode active material formed from lithium iron phosphate. According to this method, the secondary battery, being equipped with a positive electrode active material formed from lithium iron phosphate, has a long plateau region. However, even for such a secondary battery, the estimation accuracy of the uncharged capacity of the secondary battery can be improved.

[0010] Regarding the method for estimating the uncharged capacity of a secondary battery in a battery module, it is preferable that the secondary battery is equipped with a negative electrode active material formed from graphite. This allows for high accuracy in estimating the uncharged capacity of the secondary battery, even for secondary batteries with long plateau regions.

[0011] Regarding the method for estimating the uncharged capacity of secondary batteries in a battery module, the battery module comprises a stack of multiple secondary batteries, the size of the secondary batteries in a plan view when viewed in the stacking direction of the stack is 0.1 square meters or more, and the master charge rate is 0.01C or less.

[0012] Large secondary batteries, when viewed from above, experience uneven charging, leading to a greater voltage increase due to overvoltage during charging, causing them to reach the voltage corresponding to 100% SOC earlier. Therefore, towards the end of the charging period, the larger the secondary battery when viewed from above, the smaller the rate of change in voltage relative to the rate of change in SOC. With the above configuration, even with secondary batteries that are large when viewed from above, the SOC of each secondary battery can be estimated with high accuracy by lowering the charging rate.

[0013] Regarding the method for estimating the uncharged capacity of a secondary battery in a battery module, it is preferable that the charging rate be reduced in multiple stages such that the changed charging rate is 75% or less of the previous charging rate.

[0014] This makes it possible to achieve both a reduction in charging time and a highly accurate estimation of the uncharged capacity of each secondary battery 12 in the battery module 10. A method for estimating the full charge capacity of secondary batteries in a battery module in which a plurality of secondary batteries having an olivine-type structure positive electrode active material are connected in series, according to one aspect of the present disclosure, includes acquiring discharge master data showing the relationship between the voltage obtained during a discharge process in which a master secondary battery is discharged with a constant current until the SOC reaches 0%, and the SOC. The full charge capacity estimation method includes, during the discharge of the battery module, when the voltage of one of the secondary batteries, a first secondary battery, reaches the voltage corresponding to the SOC state of 0%, acquiring the voltages of the remaining secondary batteries that have not yet reached the voltage corresponding to the SOC state of 0%. The full charge capacity estimation method includes estimating the SOC of each of the remaining secondary batteries from the acquired voltages of each of the remaining secondary batteries using the discharge master data, and estimating the remaining capacity of each of the remaining secondary batteries based on the estimated SOC. The full charge capacity estimation method includes obtaining the cumulative charge capacity of the second secondary battery from the cumulative value of the current that flowed while charging the battery module, from the state in which the voltage of the first secondary battery of the battery module reaches the voltage corresponding to the state in which the SOC is 0%, until the voltage of the second secondary battery, which is either the same as or different from the first secondary battery, reaches the voltage corresponding to the state in which the SOC is 100%, or obtaining the cumulative discharge capacity of each of the first secondary batteries from the cumulative value of the current that flowed while discharging the battery module, from the state in which the voltage of the second secondary battery of the battery module reaches the voltage corresponding to the state in which the SOC is 100%, until the voltage of the first secondary battery reaches the voltage corresponding to the state in which the SOC is 0%. The method for estimating the full charge capacity includes adding the uncharge capacity of each of the remaining secondary batteries, estimated by the method for estimating the uncharge capacity of secondary batteries in the battery module described above, and the remaining capacity of each of the remaining secondary batteries to the acquired cumulative charge capacity or cumulative discharge capacity, in order to estimate the full charge capacity of each of the remaining secondary batteries.

[0015] According to this method, the estimation accuracy regarding the full charge capacity of secondary batteries can be improved.

[0016] This invention can improve the estimation accuracy of the uncharged capacity and fully charged capacity of a secondary battery.

[0017] Figure 1 is a cross-sectional view of the battery module. Figure 2 is a circuit diagram showing the battery module of Figure 1 and a secondary battery testing device. Figure 3 is a plan view of the battery module of Figure 1. Figure 4 is a graph showing the master data for discharge. Figure 5 is a graph showing the master data for charge. Figure 6 is a graph showing the relationship between the voltage during multi-stage charging of the secondary battery in the battery module of Figure 1 and the capacity charged to the secondary battery.

[0018] The following describes one embodiment of a method for estimating the uncharged capacity and the fully charged capacity of a secondary battery in a battery module. The "method for estimating the uncharged capacity of a secondary battery in a battery module" may also be simply referred to as "method for estimating the uncharged capacity of a secondary battery." The "method for estimating the fully charged capacity of a secondary battery in a battery module" may also be simply referred to as "method for estimating the fully charged capacity of a secondary battery."

[0019] <Battery Module> As shown in Figure 1, the battery module 10 includes a stacked body 11. The stacked body 11 includes a plurality of secondary batteries 12 connected in series. The plurality of secondary batteries 12 are stacked. In the following description, the direction in which the secondary batteries 12 are stacked will be referred to as the stacking direction.

[0020] The secondary battery 12 is rectangular when viewed in the stacking direction. The lower limit of the size of the secondary battery 12 in a plan view when viewed in the stacking direction can be set to, for example, 0.1 square meters, 0.5 square meters, 1 square meter, or 1.5 square meters. The upper limit of the size of the secondary battery 12 in a plan view can be set to, for example, 5 square meters, 4 square meters, 3 square meters, or 2 square meters. It is preferable that the secondary battery 12 is a large secondary battery 12 with a size of 0.1 square meters or more in a plan view. The size of the secondary battery 12 in a plan view can be arbitrarily set within the range of the upper and lower limits described above. The size of the secondary battery 12 in a plan view means the area of ​​the rectangle that defines the outer shape of the secondary battery 12, that is, the projected area of ​​the secondary battery 12 in a plan view.

[0021] The secondary battery 12 comprises a positive electrode 13, a negative electrode 19, and a separator 27. The positive electrode 13 comprises a positive electrode current collector 14 and a positive electrode active material layer 17. The positive electrode current collector 14 is in the form of a sheet. The positive electrode current collector 14 comprises a first surface 15 and a second surface 16. The first surface 15 and the second surface 16 are surfaces located on opposite sides of each other in the thickness direction of the positive electrode current collector 14.

[0022] The positive electrode active material layer 17 is provided on the first surface 15 of the positive electrode current collector 14. The positive electrode active material layer 17 contains a positive electrode active material capable of intercalating and releasing lithium ions as a charge carrier. The positive electrode active material is a polyanionic compound having an olivine-type structure. Examples of olivine-type structured positive electrode active materials include olivine-type lithium iron phosphate (LiFePO4). ４ ) and olivine-type manganese iron lithium (LiMnFePO) ４ ) are examples. In this embodiment, the positive electrode active material is olivine-type lithium iron phosphate (LiFePO) ４ Therefore, the secondary battery 12 is equipped with a positive electrode active material formed from lithium iron phosphate. The secondary battery 12 equipped with an olivine-type structured positive electrode active material has a long plateau region in the high SOC region. The change in voltage per 1 mAh / g discharge in the plateau region is, for example, 1 mV or less, 0.5 mV or less, or 0.2 mV or less.

[0023] The negative electrode 19 comprises a negative electrode current collector 20 and a negative electrode active material layer 24. The negative electrode current collector 20 is in the form of a sheet. The negative electrode current collector 20 comprises a first surface 21 and a second surface 22. The first surface 21 and the second surface 22 are surfaces located on opposite sides of each other in the thickness direction of the negative electrode current collector 20.

[0024] The negative electrode active material layer 24 is provided on the first surface 21 of the negative electrode current collector 20. The negative electrode active material layer 24 contains a negative electrode active material capable of intercepting and releasing charge carriers such as lithium ions. The negative electrode active material is not particularly limited and can be used as long as it is a single element, alloy, or compound capable of intercepting and releasing charge carriers such as lithium ions. For example, examples of negative electrode active materials include Li, carbon, metal compounds, and elements or compounds thereof that can be alloyed with lithium. Examples of carbon include natural graphite, artificial graphite, hard carbon (carbon that is difficult to graphitize), and soft carbon (carbon that is easily graphitized). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. Examples of elements that can be alloyed with lithium include silicon and tin. In this embodiment, the negative electrode active material contains graphite. Therefore, the secondary battery 12 is equipped with a negative electrode active material formed from graphite.

[0025] The laminate 11 includes a bipolar electrode 25. The bipolar electrode 25 includes a current collector 26, a positive electrode active material layer 17 provided on one side of the current collector 26, and a negative electrode active material layer 24 provided on the other side of the current collector 26. The current collector 26 is formed by integrating a positive electrode current collector 14 and a negative electrode current collector 20 that are in contact with each other. For example, in the bipolar electrode 25, the current collector 26 is formed by joining the positive electrode current collector 14 and the negative electrode current collector 20 with the second surface 16 of the positive electrode current collector 14 and the second surface 22 of the negative electrode current collector 20 superimposed on each other. In the bipolar electrode 25, the positive electrode current collector 14 and the negative electrode current collector 20 that are in contact with each other are considered as one current collector 26.

[0026] The positive electrode 13 located at the first end of the stacking direction of the laminate 11 is designated as the positive electrode terminal electrode 13A. The negative electrode 19 located at the second end of the stacking direction of the laminate 11 is designated as the negative electrode terminal electrode 19A. Multiple bipolar electrodes 25 are arranged between the positive electrode terminal electrode 13A and the negative electrode terminal electrode 19A in the stacking direction. The second surface 16 of the positive electrode current collector 14 on the positive electrode terminal electrode 13A constitutes the outer surface of the laminate 11. The second surface 22 of the negative electrode current collector 20 on the negative electrode terminal electrode 19A constitutes the outer surface of the laminate 11. The secondary battery 12 located at the first end of the laminate 11 comprises a positive electrode active material layer 17 provided on the positive electrode terminal electrode 13A and a negative electrode active material layer 24 of a bipolar electrode 25 adjacent to the positive electrode terminal electrode 13A. The secondary battery 12 provided at the second end of the laminate 11 comprises a negative electrode active material layer 24 provided on the negative electrode terminal electrode 19A and a positive electrode active material layer 17 of a bipolar electrode 25 adjacent to the negative electrode terminal electrode 19A. Each of the secondary batteries 12 provided between the secondary battery 12 located at the first end of the laminate 11 and the secondary battery 12 located at the second end of the laminate 11 comprises a positive electrode active material layer 17 included in one of two adjacent bipolar electrodes 25 and a negative electrode active material layer 24 included in the other.

[0027] The separator 27 is positioned between the positive electrode active material layer 17 and the negative electrode active material layer 24. The separator 27 prevents short circuits caused by contact between the two electrodes by isolating the positive electrode active material layer 17 and the negative electrode active material layer 24 from each other, while allowing charge carriers such as lithium ions to pass through.

[0028] The battery module 10 includes a positive electrode conductive plate 31 and a negative electrode conductive plate 32. The positive electrode conductive plate 31 and the negative electrode conductive plate 32 are made of a metal material such as aluminum, copper, or stainless steel.

[0029] The positive electrode current-carrying plate 31 is electrically connected to the second surface 16 of the positive electrode current collector 14 provided on the positive electrode terminal electrode 13A. The negative electrode current-carrying plate 32 is electrically connected to the second surface 22 of the negative electrode current collector 20 provided on the negative electrode terminal electrode 19A. As shown in Figure 3, the battery module 10 performs charging and discharging through the positive electrode terminal 31a provided on the positive electrode current-carrying plate 31 and the negative electrode terminal 32a provided on the negative electrode current-carrying plate 32.

[0030] As shown in Figures 1 and 3, the battery module 10 includes a encapsulant 40. The encapsulant 40 is rectangular in shape. The encapsulant 40 comprises a first portion 41 and a second portion 42. The first portion 41 is located between adjacent current collectors 26, between the positive electrode current collector 14 of the positive terminal electrode 13A and the current collector 26 of the bipolar electrode 25 adjacent to the positive terminal electrode 13A, and between the negative electrode current collector 20 of the negative terminal electrode 19A and the current collector 26 of the bipolar electrode 25 adjacent to the negative terminal electrode 19A. The second portion 42 is located outside the peripheral edges of the current collectors 26, the positive electrode current collector 14 of the positive terminal electrode 13A, and the negative electrode current collector 20 of the negative terminal electrode 19A. The encapsulant 40 encapsulates the laminate 11.

[0031] The battery module 10 is equipped with voltage detection wires 51. The voltage detection wires 51 are, for example, long foil-like wires. One voltage detection wire 51 is provided for each of the current collectors 26 of the bipolar electrode 25, the positive electrode current collector 14 of the positive electrode terminal electrode 13A, and the negative electrode current collector 20 of the negative electrode terminal electrode 19A. For example, the voltage detection wires 51 are joined to each of the current collectors 26 of the bipolar electrode 25, the positive electrode current collector 14 of the positive electrode terminal electrode 13A, and the negative electrode current collector 20 of the negative electrode terminal electrode 19A by ultrasonic welding. This makes it possible to detect the voltage of the secondary battery 12 by two voltage detection wires 51 that are adjacent to each other in the stacking direction.

[0032] A portion of the voltage detection wire 51 is covered by the encapsulant 40. The voltage detection wire 51 extends outward from the encapsulant 40. A portion of the voltage detection wire 51 is exposed to the outside of the encapsulant 40. That is, the voltage detection wire 51 is brought out to the outside of the encapsulant 40 so that the voltage of the secondary battery 12 can be detected outside the encapsulant 40.

[0033] <Capacity Inspection of Secondary Batteries> The battery module 10 is inspected after it is manufactured. In the inspection of the battery module 10, for example, each secondary battery 12 that makes up the battery module 10 is inspected. This is done to evaluate the performance of the battery module 10 or to check for any defects. Specifically, the battery module 10 is inspected before shipment.

[0034] The inspection of the battery module 10 includes inspection of the capacity of each secondary battery 12 that makes up the battery module 10. This capacity inspection of the secondary battery 12 is performed using a secondary battery 12 inspection device 60. The effective capacity of the secondary battery 12 can be set by the upper and lower voltage limits of the secondary battery 12. Each of the upper and lower voltage limits of the secondary battery 12 is arbitrarily set based on the design value of the secondary battery 12, etc. Each of the upper and lower voltage limits can be set as a common value for all secondary batteries 12 that make up the battery module 10. When the voltage of the secondary battery 12 is at the upper voltage limit, the charge level of the secondary battery 12 is set to 100% SOC. The upper voltage limit is, for example, 3.75V. When the voltage of the secondary battery 12 is at the lower voltage limit, the charge level of the secondary battery 12 is set to 0% SOC. The lower voltage limit is, for example, 3V.

[0035] During the charging of the battery module 10, when any one of the secondary batteries 12 forming the battery module 10 is charged to reach 100% SOC, charging of the battery module 10 is terminated to prevent overcharging of that secondary battery 12. This state of the battery module 10 being terminated is the state when the battery module 10 has been charged until the SOC of any one of the secondary batteries 12 forming the battery module 10 reaches 100%. This state is described as the [module charging stopped state]. The state in which any one of the secondary batteries 12 of the battery module 10 has reached 100% SOC is defined as the 100% SOC state of the battery module 10. In the module charging stopped state, other secondary batteries 12 that are different from the one that has reached 100% SOC include secondary batteries 12 that have not been charged to reach 100% SOC and still have chargeable capacity.

[0036] Assuming that secondary batteries 12 that have not reached SOC 100% are individually charged to SOC 100% after the battery module 10 has been charged, the remaining capacity that can be charged to each secondary battery 12 is called the "uncharged capacity." In other words, the uncharged capacity is the difference between the capacity of a secondary battery 12 that has not reached SOC 100% at the time the module charging stops, and the full charge capacity of that secondary battery 12. Differences in uncharged capacity occur among the secondary batteries 12 that make up the battery module 10 due to differences in the basis amount of positive electrode active material in the positive electrode 13. Differences in uncharged capacity also occur among the secondary batteries 12 that make up the battery module 10 due to individual differences in the secondary batteries 12.

[0037] During the discharge of the battery module 10, if one of the secondary batteries 12 is discharged to reach 0% SOC, the discharge of the battery module 10 is terminated to prevent over-discharge of that secondary battery 12. This state of termination of the battery module 10's discharge is the state reached when the battery module 10 has been discharged until the SOC of any one of the secondary batteries 12 forming the battery module 10 reaches 0%. This state is described as the [module discharge stopped state]. The state in which any one of the secondary batteries 12 in the battery module 10 has reached 0% SOC is defined as the SOC 0% state of the battery module 10. In the module discharge stopped state, other secondary batteries 12, different from the one whose SOC has reached 0%, may not have been discharged to reach 0% SOC and may still have dischargeable capacity.

[0038] Assuming that after the battery module 10 has been discharged, the secondary batteries 12 that have not yet reached SOC 0% are individually discharged to SOC 0%, the remaining capacity that each secondary battery 12 can discharge is called the "remaining capacity." Among the secondary batteries 12 that make up the battery module 10, there are differences in the amount of self-discharge due to individual differences in the secondary batteries 12, etc. Therefore, the remaining capacity of each secondary battery 12 increases or decreases according to the amount of self-discharge. Consequently, among the secondary batteries 12 that make up the battery module 10, there are differences in the remaining capacity according to the amount of self-discharge.

[0039] The method for estimating the uncharged capacity of the secondary battery 12 is a method for estimating the uncharged capacity of the secondary battery 12 that was not charged until the State of Charge (SOC) reached 100% after the battery module 10 had finished charging, that is, when the module charging was stopped. The method for estimating the uncharged capacity of the secondary battery 12 includes obtaining the cumulative charge capacity of the secondary battery 12 from the cumulative value of the current that flowed while charging the battery module 10, from the state in which the voltage of the first secondary battery, which is one of the secondary batteries 12 of the battery module 10, reached the voltage corresponding to the state in which the SOC is 0%, until the voltage of the second secondary battery, which is either the same as or different from the first secondary battery, reached the voltage corresponding to the state in which the SOC is 100%.

[0040] The method for estimating the full charge capacity of the secondary battery 12 includes estimating the remaining capacity of the secondary battery 12 that has not been discharged until the SOC reaches 0% after the discharge of the battery module 10 is complete, that is, in the module discharge stop state. The method for estimating the full charge capacity of the secondary battery 12 also includes obtaining the integrated discharge capacity of the secondary battery 12 from the integrated value of the current that flowed while the battery module 10 was being discharged, from the state in which the voltage of the second secondary battery of the battery module 10 reached the voltage corresponding to the SOC state of 100% until the voltage of the first secondary battery reached the voltage corresponding to the SOC state of 0%.

[0041] The method for estimating the full charge capacity of the secondary battery 12 includes adding the estimated uncharged capacity and remaining capacity for each secondary battery 12 to the calculated cumulative charge capacity or cumulative discharge capacity to estimate the full charge capacity of each secondary battery 12.

[0042] As shown in Figure 2, the secondary battery inspection device 60 includes a capacity estimation device 61. The capacity estimation device 61 includes a voltage detection circuit 62. The voltage detection circuit 62 is, for example, an integrated circuit. The voltage detection circuit 62 has multiple ports, and a voltage detection line 51 corresponding to each port is connected to it. The voltage detection circuit 62 detects the voltage of each secondary battery 12 from the potential input from the voltage detection line 51.

[0043] The capacity estimation device 61 includes an estimation device 63. The estimation device 63 is a device that estimates the uncharged capacity, remaining capacity, integrated charge capacity, integrated discharge capacity, full charge capacity of the secondary battery 12, and the full charge capacity of the battery module 10. The estimation device 63 includes a processor 64 and a storage unit 65. The processor 64 is, for example, a CPU (Central Processing Unit), GPU (Graphics Processing Unit), or DSP (Digital Signal Processor). The storage unit 65 includes a RAM (Random Access Memory) and a ROM (Read Only Memory). The storage unit 65 stores a program for performing a capacity inspection of the secondary battery 12, and charge master data and discharge master data, which will be described later.

[0044] The storage unit 65 stores program codes or instructions configured to cause the processor 64 to execute processing. The storage unit 65, that is, the computer-readable medium, includes any available medium accessible by a general-purpose or dedicated computer. The estimation device 63 may be configured by a hardware circuit such as an ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array). The estimation device 63, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or FPGA, or a combination thereof.

[0045] The inspection device 60 includes a charge and discharge device 71. The charge and discharge device 71 charges each secondary battery 12 of the battery module 10 by applying a DC voltage to the battery module 10. The charging of the battery module 10 is performed with the charge and discharge device 71 connected to the positive terminal 31a and the negative terminal 32a. When charging the battery module 10 with a constant current, as described above, not all the secondary batteries 12 are charged to the same SOC at the same time. When charging the battery module 10, if one of the secondary batteries 12 is charged until it reaches 100% SOC, the charge and discharge device 71 stops charging the battery module 10 to prevent overcharging of that secondary battery 12. That is, the battery module 10 enters a module charge stop state. As described above, the estimation device 63 of the inspection device 60 estimates the uncharged capacity for each secondary battery 12 that has not been charged until it reaches 100% SOC, and estimates the full charge capacity for each of those secondary batteries 12.

[0046] The discharge of the battery module 10 is performed by discharging with a constant current in a state where the charge and discharge device 71 is connected to the positive terminal 31a and the negative terminal 32a. When discharging the battery module 10, as described above, not all the secondary batteries 12 are discharged to the same SOC at the same time. When discharging the battery module 10, if one of the secondary batteries 12 is discharged until it reaches 0% SOC, the charge and discharge device 71 stops discharging the battery module 10 to prevent over-discharge of that secondary battery 12. That is, the battery module 10 enters a module discharge stop state. The estimation device 63 of the inspection device 60 estimates the remaining capacity for each secondary battery 12 that has not been discharged until it reaches 0% SOC, and estimates the full charge capacity for each of those secondary batteries 12.

[0047] <Discharge master data> As shown in FIG. 4, the discharge master data is a curve showing the relationship between the voltage and the SOC obtained during the discharge process of discharging the master secondary battery with a constant current until the SOC reaches 0%. Specifically, the discharge master data is an SOC-OCV curve. The SOC-OCV curve is a curve showing the correlation between the SOC and the OCV of the secondary battery 12.

[0048] When obtaining the SOC-OCV curve, a secondary battery 12 with a full charge capacity close to the design specification value is prepared as the master secondary battery. After each discharge of the master secondary battery from SOC 100% by a predetermined amount of SOC at a constant current, the voltage of the master secondary battery is obtained after being left for a predetermined time. Specifically, in the master secondary battery, after each discharge of a predetermined amount of SOC at a constant current from the voltage corresponding to SOC 100%, i.e., the upper limit voltage of 3.75V, down to the voltage corresponding to SOC -1%, i.e., 2.9V, i.e., after being left for a predetermined time (e.g., 30 minutes), the voltage (OCV) of the master secondary battery is obtained. The voltage corresponding to SOC -1% is the voltage at which the charge rate of the master secondary battery drops by 1% from the charge rate at the lower limit voltage of 3V, i.e., SOC 0%. The master secondary battery is discharged at a predetermined SOC, for example, by 0.1% at a time, but is not limited to this. A State of Charge (SOC) - OCV curve is obtained from the acquired voltage, the cumulative discharge capacity, and the fully charged capacity approximated by the standard value. This SOC - OCV curve is stored in the storage unit 65 as discharge master data. When acquiring discharge master data, the temperature of the master secondary battery is maintained at a constant temperature. The constant temperature is, for example, 25°C, but the constant temperature may be appropriately selected from between 20°C and 25°C. The constant temperature may also be selected according to the temperature of the secondary battery 12 when estimating the remaining capacity of each secondary battery 12 in the battery module 10. For example, a constant temperature chamber can be used to maintain the temperature of the master secondary battery.

[0049] Discharge master data only needs to be acquired within the range necessary for estimating the remaining capacity. The range necessary for estimating the remaining capacity is, for example, from 15% SOC to 0% SOC, or from 10% SOC to 0% SOC. The discharge rate when acquiring the discharge master data can be set in the range of, for example, 0.1C to 0.001C. The discharge rate is, for example, 0.1C, 0.01C, or 0.005C.

[0050] <Charging Master Data> As shown in Figure 4, it is generally known that in secondary batteries 12 using olivine-type structured positive electrode active material, a plateau region R exists for a long time in the high SOC region, where the voltage remains approximately constant even when the SOC changes. In other words, in the plateau region R, the rate of change of voltage with respect to the rate of change of SOC is small. The plateau region R extends to the end of charging, just before the SOC reaches 100%. For this reason, in the battery module 10, when the SOC of one of the secondary batteries 12 reaches 100%, the voltage of the remaining secondary batteries 12 is often in the plateau region R. When the voltage of the remaining secondary batteries 12 in the plateau region R is obtained, there is little difference in the voltage values ​​among those secondary batteries 12. Therefore, even if the uncharged capacity of the secondary batteries 12 is estimated by referring to the SOC-OCV curve, the estimation accuracy of the uncharged capacity of the secondary batteries 12 decreases because the estimation accuracy of the SOC is low.

[0051] The inventors have devised a method for estimating the uncharged capacity of a secondary battery 12 using charging master data. The charging master data is a charging curve (SOC-CCV curve) that associates the CCV (Closed Circuit Voltage) obtained when a master secondary battery is charged at a specific master charging rate with the SOC.

[0052] Next, we will explain how to obtain the master data for charging. First, prepare a secondary battery 12 whose full charge capacity is close to the design specification value as the master secondary battery.

[0053] Next, a master charging rate is set, and the master secondary battery is charged at the set master charging rate. The charging master data is a charging curve obtained when the master secondary battery is charged at the set master charging rate, increasing the SOC by a predetermined amount in the process from a lower limit voltage, which is the OCV corresponding to 0% SOC, to an upper limit voltage, which is the OCV corresponding to 100% SOC. In this embodiment, the lower limit voltage, which is the OCV corresponding to 0% SOC, is set to 3V, and the upper limit voltage, which is the OCV corresponding to 100% SOC, is set to 3.75V. However, the lower limit voltage and upper limit voltage may be changed as appropriate. The master secondary battery is charged so that the SOC increases by, for example, 0.1% SOC, but this value of 0.1% SOC may be changed as appropriate. The charging curve of the charging master data is obtained from the voltage (CCV) acquired in the above charging process, the accumulated charging capacity, and the full charging capacity approximated by the standard value. The acquired charging master data is stored in the storage unit 65.

[0054] To explain the method for acquiring charging master data in more detail, a charge / discharge device 71 is connected to the master secondary battery, and constant current charging is performed on the master secondary battery at a set master charging rate. During charging, the voltage (CCV) of the master secondary battery is acquired every time the SOC rises by 0.1%. The SOC is calculated from the accumulated charging capacity and the full charging capacity approximated by the standard value. The acquired voltage and the calculated SOC are linked to acquire charging master data at the master charging rate.

[0055] Generally, when charging a secondary battery 12, the higher the charging rate, the greater the voltage rise of the secondary battery 12 due to polarization (overvoltage). As a result, the CCV of the secondary battery 12 reaches its upper limit voltage of 3.75V at an earlier stage (for example, when it reaches about 95% SOC). On the other hand, the OCV of the secondary battery 12 is not affected by polarization, so it remains in the plateau region R even when it is close to 100% SOC (for example, 99.5% SOC).

[0056] Therefore, by charging the secondary battery 12 at a sufficiently low charging rate, for example, the master charging rate in this embodiment, the voltage rise due to polarization can be made gentler, and the rate of change of voltage relative to the rate of change of SOC becomes large near 100% SOC, for example, between 99% and 100% SOC, and especially between 99.5% and 100% SOC. Therefore, the method for estimating the uncharged capacity of the secondary battery 12 according to this embodiment can accurately estimate the SOC of the secondary battery 12 by using a charging curve with a large rate of change of voltage relative to the rate of change of SOC near 100% SOC as the charging master data.

[0057] The larger the area of ​​the positive electrode active material layer 17 and the negative electrode active material layer 24 of the secondary battery 12, that is, the larger the size of the secondary battery 12 in a plan view, the more likely uneven charging is to occur within the plane during charging of the secondary battery 12. Within the uneven charging, the voltage in the areas where charging progresses easily becomes relatively higher, increasing the voltage value obtained from the secondary battery 12. As a result, similar to when charging at a high charge rate, the difference in the obtained voltages between multiple secondary batteries 12 becomes less pronounced. For this reason, it is preferable to estimate the State of Charge (SOC) by charging secondary batteries 12 with a large shape in a plan view at a lower charge rate.

[0058] On the other hand, if the charging rate becomes too low, it will take time to acquire the master data for charging. Therefore, the master charging rate, which is a specific charging rate when acquiring the master data for charging, is preferably set in the range of 0.001C to 0.1C. For example, the master charging rate is 0.01C or less, or 0.005C or less. If the size of the secondary battery 12 in plan view is 0.1 square meters or more, the master charging rate is preferably 0.01C or less, and if it is 1 square meter or more, the master charging rate is preferably 0.005C or less. In other words, the larger the secondary battery 12, the smaller the master charging rate is preferable in order to improve the estimation accuracy of the State of Charge (SOC).

[0059] The dashed line in Figure 5 represents the charging master data when the master charging rate is 0.01C in the range of SOC 97% to SOC 100%. The solid line in Figure 5 represents the charging master data when the master charging rate is 0.005C in the same range. Although there is a difference in the voltage values ​​shown by the two, both are smooth curves.

[0060] The charging master data shows the relationship between voltage and SOC obtained during the charging process when the charging master secondary battery is charged to a predetermined voltage (3.75V, which is the OCV corresponding to 100% SOC) at a sufficiently low charging rate, the same as when all secondary batteries 12 are charged simultaneously when charging the battery module 10.

[0061] Master data for charging only needs to be acquired within the range necessary for estimating the uncharged capacity. The range necessary for estimating the uncharged capacity is, for example, from 85% to 100% SOC, from 90% to 100% SOC, from 95% to 100% SOC, or from 97% to 100% SOC. When acquiring master data for charging, the temperature of the master secondary battery is maintained at a constant temperature. The constant temperature is, for example, 25°C, but it may be appropriately selected from a range between 20°C and 25°C. The constant temperature may be selected according to the temperature of the secondary battery 12 when estimating the uncharged capacity of each secondary battery 12 in the battery module 10. For example, a constant temperature chamber can be used to maintain the temperature of the master secondary battery.

[0062] [Method for Estimating Remaining Capacity After Discharge] To estimate the remaining capacity of the secondary battery 12 after discharge of the battery module 10, the battery module 10 is connected to the charge / discharge device 71 and the battery module 10 is discharged. The battery module 10 is discharged with a constant current while decreasing the discharge rate in multiple stages. Each time the voltage of any one of the secondary batteries 12 in the battery module 10 reaches a predetermined voltage, the discharge rate is decreased by one stage. The predetermined voltage is 3V, which is the voltage corresponding to SOC 0%. In this embodiment, the discharge rate, which is changed in multiple stages, is changed in the order of 0.33C → 0.2C → 0.05C → 0.01C → 0.005C. When the battery module 10 is discharged at a discharge rate of 0.005C, the discharge is terminated when the voltage of any one of the secondary batteries 12 reaches 3V, which is the voltage corresponding to SOC 0%. At this time, the battery module 10 enters a module discharge stop state. Thirty minutes after the battery module 10 has finished discharging, the OCV of each of the remaining secondary batteries 12 that have not reached the voltage corresponding to SOC 0% is obtained from the voltage detection circuit 62.

[0063] The estimation device 63 estimates the State of Charge (SOC) for each secondary battery 12 whose voltage has been acquired, using the discharge master data, and also estimates the remaining capacity from the estimated SOC. When discharging each secondary battery 12 of the battery module 10, the temperature of the secondary battery 12 is maintained at a constant temperature. The constant temperature is, for example, 25°C, but the constant temperature may be appropriately selected from a range between 20°C and 25°C. A constant temperature chamber can be used to maintain the temperature of the secondary battery 12, for example.

[0064] [Method for Estimating Uncharged Capacity After Charging] The method for estimating the uncharged capacity of the secondary batteries 12 in the battery module 10 is a method for estimating the uncharged capacity of each of the multiple secondary batteries 12 when the battery module 10 is fully charged (when the module charging is stopped). This method for estimating the uncharged capacity of the secondary batteries 12 includes performing constant current charging of the battery module 10 while lowering the charging rate in multiple stages. Specifically, each time the voltage of any one of the secondary batteries 12 reaches the voltage corresponding to SOC 100%, the charging rate is lowered by one stage. The smallest charging rate among the multiple charging rates is equal to the master charging rate when the master data for charging was acquired. The method for estimating the uncharged capacity of the secondary batteries 12 includes acquiring the voltage of the remaining secondary batteries 12 when the voltage of any one of the secondary batteries 12 reaches the voltage corresponding to SOC 100% at the master charging rate. The method for estimating the uncharged capacity of secondary battery 12 includes using charging master data to estimate the State of Charge (SOC) of each of the remaining secondary batteries 12 from the voltage of the remaining secondary batteries 12 obtained, and estimating the uncharged capacity of each of the remaining secondary batteries based on the estimated SOC.

[0065] When estimating the uncharged capacity of the secondary battery 12, the battery module 10 is connected to the charge / discharge device 71 and the battery module 10 is charged. The battery module 10 is charged with a constant current while gradually decreasing the charging rate in multiple stages. To shorten the charging time, charging is performed at a relatively high charging rate in the initial stages, and the charging rate is gradually decreased each time the voltage of any one of the secondary batteries 12 in the battery module 10 reaches a predetermined voltage. The amount of change in the rate (current) when decreasing the charging rate is set so that the new charging rate is 75% or less of the previous charging rate. For example, the amount of change in the charging rate is 75% or 50% of the previous charging rate. The charging of the battery module 10 in this embodiment is different from control that gradually decreases the charging rate while maintaining a constant voltage, such as constant voltage charging in constant current constant voltage charging. The predetermined voltage that triggers the decrease in the charging rate is 3.75V, which is the voltage corresponding to 100% SOC. In charging using the master charge rate, charging is terminated when the voltage of any one of the secondary batteries 12 reaches the voltage corresponding to 100% SOC. As shown in Figure 6, the charge rate, which is changed in multiple stages, is changed in the order of 0.1C → 0.05C → 0.01C → 0.005C in this embodiment. Therefore, in charging using the master charge rate of 0.005C, charging is terminated when the voltage of any one of the secondary batteries 12 reaches 3.75V, which is the voltage corresponding to 100% SOC.

[0066] The charging method for the battery module 10 will be explained in more detail below. When charging the battery module 10, the charge / discharge device 71 is connected to the secondary battery 12. As shown in Figure 6, constant current charging is performed on the secondary battery 12 at a charge rate of 0.1C, and the voltage of each secondary battery 12 is acquired by the voltage detection circuit 62. When the voltage of any one of the secondary batteries 12 reaches the upper limit voltage of 3.75V, the charge / discharge device 71 is controlled to change the charge rate from 0.1C to 0.05C. As the overvoltage decreases in accordance with the decrease in charge rate, the voltage of the secondary battery 12 temporarily drops, making further charging at a charge rate of 0.05C possible. In other words, it is possible to continue charging until the voltage of any one of the secondary batteries 12 of the battery module 10 reaches the voltage corresponding to 100% SOC again. Next, while charging at a charge rate of 0.05C, when the voltage of any one of the secondary batteries 12 reaches 3.75V, the charge / discharge device 71 is controlled to change the charge rate from 0.05C to 0.01C. At this time, as the overvoltage decreases in accordance with the decrease in charge rate, the voltage of the secondary battery 12 temporarily drops, making further charging at a charge rate of 0.01C possible. In other words, it becomes possible to continue charging until the voltage of any one of the secondary batteries 12 of the battery module 10 reaches the voltage corresponding to 100% SOC again. Furthermore, while charging at a charge rate of 0.01C, when the voltage of any one of the secondary batteries 12 reaches 3.75V, the charge / discharge device 71 changes the charge rate from 0.01C to 0.005C. At this time, as the overvoltage decreases in accordance with the decrease in charge rate, the voltage of the secondary battery 12 temporarily drops, making further charging at a charge rate of 0.005C possible. In other words, charging can be continued until the voltage of any one of the secondary batteries 12 in the battery module 10 reaches the voltage corresponding to 100% SOC again. Then, during charging at the master charging rate of 0.005C, charging is terminated when the voltage of any one of the secondary batteries 12 reaches 3.75V.

[0067] When charging each secondary battery 12 of the battery module 10, the temperature of the secondary battery 12 is maintained at a constant temperature. The constant temperature is, for example, 25°C, but the constant temperature may be appropriately selected from a range between 20°C and 25°C. A constant temperature chamber can be used to maintain the temperature of the secondary battery 12, for example.

[0068] After the battery module 10 has finished charging at the master charging rate, the estimation device 63 obtains the voltage of each of the other secondary batteries 12 that have not reached the voltage corresponding to SOC 100% from the voltage detection circuit 62.

[0069] The estimation device 63 estimates the State of Charge (SOC) for each secondary battery 12 whose voltage has been acquired after charging at the master charging rate, using the charging master data, and also estimates the uncharged capacity from the estimated SOC.

[0070] [Method for estimating the full charge capacity of each secondary battery and battery module] Among the secondary batteries 12 forming the battery module 10, the capacity of the secondary battery 12 that has not reached the voltage corresponding to SOC 0% in the module discharge stop state is the same as the cumulative discharge capacity, corresponding to the amount of electricity discharged up to the module discharge stop state. Among the secondary batteries 12 forming the battery module 10, the capacity of the secondary battery 12 that has not reached the voltage corresponding to SOC 100% in the module charge stop state is the same as the cumulative charge capacity, corresponding to the amount of electricity charged up to the module charge stop state. The cumulative discharge capacity and the cumulative charge capacity are estimated to be the same value.

[0071] The estimation device 63 adds the estimated uncharged capacity and remaining capacity to the accumulated discharge capacity or accumulated charge capacity to estimate the full charge capacity of each secondary battery 12 that has not reached the voltage corresponding to SOC 100% in the module charging stopped state.

[0072] This allows the fully charged capacity of each secondary battery 12 forming the battery module 10 to be estimated. The estimation device 63 adds up the fully charged capacities of all secondary batteries 12 forming the battery module 10 to estimate the total fully charged capacity of the battery module 10.

[0073] [Effects of the Embodiment] According to the above embodiment, the following effects can be obtained. (1) Charging of the battery module 10 is performed while maintaining a constant current and lowering the charging rate in multiple stages. Therefore, unlike the constant current constant voltage charging method, voltage changes caused by individual differences in the secondary batteries 12 converge after the charging rate is changed. That is, when the battery module 10 is charged at a certain charging rate, even if the voltage of one of the secondary batteries 12 reaches the voltage corresponding to SOC 100%, when the charging rate is lowered by one stage, the voltage of the secondary battery 12 decreases accordingly. Therefore, it becomes possible to continue charging until one of the secondary batteries 12 reaches the voltage corresponding to SOC 100% again.

[0074] The uncharged capacity is estimated using charging master data. The charging master data shows the relationship between voltage and SOC when the master secondary battery is charged at a sufficiently low master charging rate. By charging the secondary battery 12 at a sufficiently low charging rate, the voltage rise due to polarization can be kept moderate. Therefore, when the secondary battery 12 is charged at a sufficiently low charging rate, the rate of change of voltage relative to the rate of change of SOC near 100% SOC becomes large. For this reason, when the secondary battery 12 is charged at a sufficiently low master charging rate, the acquired voltages tend to differ significantly between secondary batteries 12. Therefore, using the charging master data, the SOC of each secondary battery 12 can be estimated with high accuracy from the voltage acquired for each secondary battery 12. As a result, the uncharged capacity can be estimated with high accuracy. Therefore, when the voltage of one of the multiple secondary batteries 12 reaches the voltage corresponding to SOC 100%, even if the voltages of many of the remaining secondary batteries 12 are in the plateau region R, the estimation accuracy of the uncharged capacity of each secondary battery 12 can be increased.

[0075] (2) The secondary battery 12 comprises a positive electrode active material formed from lithium iron phosphate. The secondary battery 12 uses graphite as the negative electrode active material. Therefore, the secondary battery 12 has a long plateau region R. In this embodiment, even with a secondary battery 12 having a long plateau region R, the accuracy of estimating its uncharged capacity can be increased.

[0076] (3) The secondary battery 12 is a large secondary battery with a size of 0.1 square meters or more in a plan view in the stacking direction. In a large secondary battery 12, the voltage rise due to overvoltage during charging is large due to charging unevenness, so the upper limit voltage of 3.75V corresponding to 100% SOC is reached earlier. For this reason, at the end of the charging period, the larger the size of the secondary battery 12 in a plan view, the smaller the rate of change of voltage with respect to the rate of change of SOC. Even with a secondary battery 12 that is large in a plan view, the SOC of each secondary battery 12 can be estimated with high accuracy by lowering the charging rate. As a result, even in a battery module 10 in which large secondary batteries 12 are stacked, the estimation accuracy of the uncharged capacity of each secondary battery 12 can be increased.

[0077] (4) In the method for estimating the uncharged capacity of the secondary battery 12, the charging rate when charging the battery module 10 is reduced in multiple stages so that the changed charging rate is 75% or less of the previous charging rate. This makes it possible to achieve both a reduction in charging time and a highly accurate estimation of the uncharged capacity of each secondary battery 12 in the battery module 10.

[0078] (5) In the method for estimating the full charge capacity of the secondary battery 12, the uncharged capacity and remaining capacity of the secondary battery 12 are estimated. By adding the estimated uncharged capacity and remaining capacity to either the cumulative charge capacity or the cumulative discharge capacity estimated for each secondary battery 12, the full charge capacity of each secondary battery 12 can be estimated. Therefore, the accuracy of estimating the full charge capacity of each secondary battery 12 that has not reached the voltage corresponding to 100% SOC in the module charging stopped state can be increased.

[0079] [Example of modification] The above embodiment may be modified as follows: ○ When charging the secondary battery 12 while lowering the charging rate in multiple stages, the magnitude of the charging rate at each stage can be changed as appropriate.

[0080] ○When acquiring master data for charging, the master secondary battery may be charged while gradually decreasing the charging rate in multiple stages. In this case, a charging curve may be acquired during the charging process at each charging rate.

[0081] ○When performing constant-current charging of the battery module 10, the timing of lowering the charging rate by one step may be changed as appropriate. For example, the charging rate may be lowered by one step each time the voltage of any one of the secondary batteries 12 reaches a voltage corresponding to 95%, 98%, or 99% of the State of Charge (SOC).

[0082] 10...Battery module, 11...Laminate, 12...Secondary battery, 17...Positive electrode active material layer, 24...Negative electrode active material layer.

Claims

1. A method for estimating the uncharged capacity of secondary batteries in a battery module comprising multiple secondary batteries connected in series, each having an olivine-type positive electrode active material, wherein the uncharged capacity is the difference between the capacity charged up to the completion of charging and the fully charged capacity of each of the multiple secondary batteries whose State of Charge (SOC) has not reached 100% at the time of completion of charging of the battery module, and the uncharged capacity estimation method comprises: acquiring charging master data showing the relationship between the voltage obtained during the charging process in which a master secondary battery is charged at a specific master charging rate until the SOC reaches 100%, and performing constant current charging of the battery module while lowering the charging rate in multiple steps, one step at a time, each time the voltage of any one of the multiple secondary batteries reaches the voltage corresponding to the state where the SOC is 100%. A method for estimating the uncharged capacity of secondary batteries in a battery module, comprising: when the charging rate has decreased to the master charging rate, obtaining the voltage of each of the remaining secondary batteries that have not yet reached the voltage corresponding to the state of 100% SOC when the voltage of any one of the secondary batteries reaches the voltage corresponding to the state of 100% SOC; and using the charging master data, estimating the state of OC of each of the remaining secondary batteries from the obtained voltages of each of the remaining secondary batteries, and estimating the uncharged capacity of each of the remaining secondary batteries based on the estimated SOC.

2. A method for estimating the uncharged capacity of a secondary battery in a battery module according to claim 1, wherein the secondary battery comprises a positive electrode active material formed from lithium iron phosphate.

3. A method for estimating the uncharged capacity of a secondary battery in a battery module according to claim 1 or 2, wherein the secondary battery comprises a negative electrode active material formed from graphite.

4. The battery module comprises a laminate formed by stacking a plurality of the secondary batteries, the size of the secondary batteries in a plan view when viewed in the stacking direction of the laminate is 0.1 square meters or more, and the master charge rate is 0.01C or less, a method for estimating the uncharged capacity of secondary batteries in a battery module according to claim 1 or claim 2.

5. The method for estimating the uncharged capacity of a secondary battery in a battery module according to claim 1 or 2, wherein the charging rate is reduced in multiple steps such that the changed charging rate is 75% or less of the immediately preceding charging rate.

6. A method for estimating the full charge capacity of secondary batteries in a battery module in which multiple secondary batteries having an olivine-type structure positive electrode active material are connected in series, comprising: acquiring discharge master data showing the relationship between the voltage obtained during the discharge process in which a master secondary battery is discharged with a constant current until the SOC reaches 0%; acquiring the voltages of the remaining secondary batteries that have not yet reached the voltage corresponding to the SOC 0% state when the voltage of one of the secondary batteries, a first secondary battery, reaches the voltage corresponding to the SOC 0% state during the discharge of the battery module; estimating the SOC of each of the remaining secondary batteries from the acquired voltages of each of the remaining secondary batteries using the discharge master data, and estimating the remaining capacity of each of the remaining secondary batteries based on the estimated SOC. The cumulative charge capacity of the second secondary battery is obtained from the cumulative value of the current that flowed while charging the battery module, from the state in which the voltage of the first secondary battery of the battery module reaches the voltage corresponding to the state of SOC of 0%, until the voltage of the second secondary battery, which is either the same as or different from the first secondary battery, reaches the voltage corresponding to the state of SOC of 100%, or the cumulative discharge capacity of the first secondary battery is obtained from the cumulative value of the current that flowed while discharging the battery module, from the state in which the voltage of the second secondary battery of the battery module reaches the voltage corresponding to the state of SOC of 100%, until the voltage of the first secondary battery reaches the voltage corresponding to the state of SOC of 0%, A method for estimating the full charge capacity of secondary batteries in a battery module, comprising: adding the uncharged capacity of each of the remaining secondary batteries estimated by the method of claim 1 or claim 2, and the remaining capacity of each of the remaining secondary batteries to the acquired cumulative charge capacity or cumulative discharge capacity, to estimate the full charge capacity of each of the remaining secondary batteries.

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