JP2013053943A - Device and method for estimation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve estimation accuracy for estimating a fully charged capacity of a secondary battery from a changing amount of the capacity of the secondary battery.SOLUTION: The estimation device includes a controller (30) for estimating the fully charged capacity of the secondary battery. The controller acquires a sectional capacity which is a battery capacity when an open circuit voltage of the secondary battery has changed from a first voltage to a second voltage, and identifies the fully charged capacity corresponding to the acquired sectional capacity by using information indicating a correspondence relation between the sectional capacity and the fully charged capacity that changes according to deterioration of the secondary battery. In this case, the first voltage and the second voltage are contained in a voltage range where the battery capacity tends to vary in response to a change in a negative electrode voltage accompanying the deterioration of the secondary battery.

Description

  The present invention relates to an estimation device that estimates the full charge capacity of a secondary battery from the amount of change in the capacity of the secondary battery, and to this estimation method.

  The full charge capacity of the secondary battery changes according to the deterioration of the secondary battery. For example, in a lithium ion secondary battery, the full charge capacity of the lithium ion secondary battery is reduced due to a decrease in lithium ions involved in charge / discharge.

JP 2010-085243 A

  When the full charge capacity of the secondary battery changes, the change amount of the capacity of the secondary battery also changes, so that the full charge capacity of the secondary battery can be estimated from the change amount of the capacity. The amount of change in capacity is the amount of change when the capacity of the secondary battery changes from the first capacity to the second capacity.

  Here, depending on the voltage (open circuit voltage) of the secondary battery, even if the full charge capacity of the secondary battery changes, the amount of change in the capacity may not easily change. In this case, even if the amount of change in capacity is specified, it is difficult to estimate the full charge capacity of the secondary battery, and the estimation accuracy is reduced.

  The estimation device according to the first invention of the present application includes a controller that estimates the full charge capacity of the secondary battery. The controller obtains a section capacity that is a battery capacity when the open circuit voltage of the secondary battery changes from the first voltage to the second voltage, and the section capacity and the full charge capacity that changes according to the deterioration of the secondary battery. Is used to identify the full charge capacity corresponding to the acquired section capacity. Here, the first voltage and the second voltage are included in a voltage range in which the battery capacity is likely to change according to the change in the negative electrode potential accompanying the deterioration of the secondary battery.

  According to the first invention of the present application, by setting the first voltage and the second voltage to a voltage within the voltage range described above, the section capacity is made different according to the full charge capacity of the secondary battery being different. be able to. Thereby, it becomes easy to specify the full charge capacity from the section capacity, and the estimation accuracy of the full charge capacity can be improved.

  The section capacity can be obtained by integrating the charge / discharge current of the secondary battery until the open circuit voltage of the secondary battery changes from the first voltage to the second voltage. Information about the voltage range can be stored in a memory. Further, information indicating the correspondence relationship can be stored in a memory. Examples of the information indicating the correspondence include a table indicating the correspondence between the section capacity and the full charge capacity, and an arithmetic expression using the section capacity and the full charge capacity as parameters (variables).

  When a lithium ion secondary battery is used as the secondary battery, the upper limit voltage defining the voltage range can be 3.6 [V] or less. Thereby, in a lithium ion secondary battery, according to a full charge capacity | capacitance differing, area capacity can be varied and it becomes easy to specify (estimate) full charge capacity from area capacity.

  A second invention of the present application is an estimation method for estimating a full charge capacity of a secondary battery, and an interval capacity that is a battery capacity when the open circuit voltage of the secondary battery changes from the first voltage to the second voltage. get. Next, the full charge capacity corresponding to the acquired section capacity is specified using information indicating a correspondence relationship between the section capacity and the full charge capacity that changes according to the deterioration of the secondary battery. Here, the first voltage and the second voltage are included in a voltage range in which the battery capacity is likely to change according to the change in the negative electrode potential accompanying the deterioration of the secondary battery. Also in the second invention of the present application, the same effect as that of the first invention of the present application can be obtained.

It is a figure which shows the structure of a battery system. It is a flowchart which shows the estimation process of a full charge capacity. It is the schematic which shows the correspondence of a section capacity and a full charge capacity. It is a figure which shows the relationship between each of a battery voltage, a positive electrode potential, and a negative electrode potential, and battery capacity. It is a figure explaining the method of determining a voltage range. It is a figure explaining the method of determining a voltage range. It is a figure which shows the relationship between the maintenance rate of an area capacity | capacitance, and the deterioration rate of full charge capacity.

  Examples of the present invention will be described below.

  FIG. 1 is a diagram showing the configuration of the battery system of this example.

  The assembled battery 10 includes a plurality of unit cells 11 connected in series. As the cell 11, a secondary battery such as a nickel metal hydride battery or a lithium ion battery can be used. The number of unit cells 11 constituting the assembled battery 10 can be appropriately set in consideration of the required output of the assembled battery 10 and the like. In this embodiment, all the unit cells 11 constituting the assembled battery 10 are connected in series. However, the assembled battery 10 may include a plurality of unit cells 11 connected in parallel.

  The unit cell 11 includes a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate. The separator contains an electrolytic solution. A solid electrolyte (inorganic solid electrolyte or organic solid electrolyte) can be used instead of the separator containing the electrolytic solution. The positive electrode plate includes a current collector plate and a positive electrode active material layer formed on the surface of the current collector plate. The positive electrode active material layer includes a positive electrode active material, a conductive agent, a binder, and the like. The negative electrode plate has a current collector plate and a negative electrode active material layer formed on the surface of the current collector plate. The negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and the like.

When a lithium ion secondary battery is used as the unit cell 11, examples of the positive electrode active material include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFePO ₄ , Li ₂ FePO ₄ F, LiCo _1/3 Ni _1/3 Mn. _1/3 O ₂ or Li (Li _a Ni _x Mn _y Co _z ) O ₂ can be used. As the negative electrode active material, for example, carbon can be used. The current collector plate of the positive electrode plate can be made of, for example, aluminum, and the current collector plate of the negative electrode plate can be made of, for example, copper.

  The voltage sensor 21 detects the voltage between the terminals of the assembled battery 10 and outputs the detection result to the controller 30. Since the plurality of single cells 11 constituting the assembled battery 10 are connected in series, if the voltage detected by the voltage sensor 21 is divided by the number of the single cells 11 constituting the assembled battery 10, the voltage of the single cell 11 is can get. If a voltage sensor 21 is provided for each unit cell 11, the voltage detected by the voltage sensor 21 is the voltage of the unit cell 11.

  The controller 30 has a built-in memory 31, and various kinds of information are stored in the memory 31. The controller 30 can operate based on a program stored in the memory 31. The memory 31 may be disposed outside the controller 30.

  The current sensor 22 detects a charge / discharge current flowing through the assembled battery 10 (unit cell 11) and outputs the detection result to the controller 30. Here, the charging current can be a positive value and the discharging current can be a negative value. The temperature sensor 23 detects the temperature of the assembled battery 10 (unit cell 11) and outputs the detection result to the controller 30.

  The load 24 is connected to the assembled battery 10 via the relays 25a and 25b, and operates by receiving electric power from the assembled battery 10. When the relays 25a and 25b are on, the assembled battery 10 is connected to the load 24, and when the relays 25a and 25b are off, the connection between the assembled battery 10 and the load 24 is cut off.

  When the assembled battery 10 is mounted on a vehicle, a motor / generator can be used as the load 24. The motor / generator converts the electric energy supplied from the assembled battery 10 into kinetic energy for running the vehicle. The motor / generator converts kinetic energy generated during braking of the vehicle into electric energy. The electric energy generated by the motor / generator can be stored in the assembled battery 10.

  In the current path between the assembled battery 10 and the motor / generator, an inverter or a booster circuit can be arranged. If an inverter is used, an AC motor can be used as the motor / generator. If the booster circuit is used, the output voltage of the assembled battery 10 can be boosted. An inverter and a booster circuit are included in the load 24.

  The controller 30 estimates the full charge capacity of the unit cell 11 using the detection results of the voltage sensor 21 and the current sensor 22. The full charge capacity estimation process will be described with reference to the flowchart shown in FIG.

  In step S <b> 101, the controller 30 detects the open circuit voltage V <b> 1 of the cell 11 using the voltage sensor 21. In step S102, the controller 30 determines whether or not the open circuit voltage V1 detected in step S101 is included in a predetermined voltage range R.

  The voltage range R is a voltage range defined by the upper limit voltage Vmax and the lower limit voltage Vmin. Information regarding the voltage range R can be stored in the memory 31. Details of the voltage range R will be described later. When the open circuit voltage V1 is included in the voltage range R, the process proceeds to step S103. When the open circuit voltage V1 is out of the voltage range R, the process returns to step S101.

  In step S103, the controller 30 charges or discharges the unit cell 11. Specifically, the cell 11 is charged or discharged so that the open circuit voltage of the cell 11 changes in the voltage range R. Here, if the open circuit voltage V1 is closer to the lower limit voltage Vmin than the upper limit voltage Vmax, the unit cell 11 is preferably charged. If the open circuit voltage V1 is closer to the upper limit voltage Vmax than the lower limit voltage Vmin, the cell 11 is preferably discharged.

  In step S <b> 104, the controller 30 calculates the capacity by integrating the current value acquired from the current sensor 22 while charging or discharging the unit cell 11. By charging or discharging the cell 11, the capacity of the cell 11 changes. The capacity calculated in step S <b> 104 is a change amount of the capacity of the single battery 11.

  In step S <b> 105, the controller 30 detects the open circuit voltage V <b> 2 of the unit cell 11 using the voltage sensor 21. The open circuit voltage V2 is an open circuit voltage after the cell 11 is charged or discharged, and is different from the open circuit voltage V1 detected in step S101.

  In step S106, the controller 30 determines whether or not the open circuit voltage V2 detected in step S105 is included in the voltage range R. When the open circuit voltage V2 is included in the voltage range R, the process proceeds to step S107. When the open circuit voltage V2 is out of the voltage range R, the process returns to step S103.

  When the process returns from the process of step S106 to the process of step S103, the controller 30 charges and discharges the unit cell 11 so that the open circuit voltage of the unit cell 11 returns to the voltage range R. Specifically, when the open circuit voltage V2 is higher than the upper limit voltage Vmax of the voltage range R, the controller 30 discharges the cell 11 in step S103, thereby changing the open circuit voltage of the cell 11 to the voltage range R. Can be returned to. Further, when the open circuit voltage V2 is lower than the lower limit voltage Vmin of the voltage range R, the controller 30 returns the open circuit voltage of the single cell 11 to the voltage range R by charging the single cell 11 in step S103. Can do.

  In step S107, the controller 30 specifies the capacity (referred to as section capacity) until the open circuit voltage of the unit cell 11 changes from V1 to V2. The section capacity corresponds to the difference between the capacity of the single battery 11 corresponding to the open circuit voltage V1 and the capacity of the single battery 11 corresponding to the open circuit voltage V2. As described in step S104, the controller 30 can specify the section capacity by integrating the current values acquired from the current sensor 22 until the open circuit voltage reaches V2 from V1.

  In step S108, the controller 30 specifies (estimates) the full charge capacity corresponding to the section capacity specified in step S107 with reference to the table indicating the correspondence relationship between the section capacity and the full charge capacity. A table indicating the correspondence relationship between the section capacity and the full charge capacity can be prepared in advance and stored in the memory 31.

  FIG. 3 shows a schematic diagram of a table showing the correspondence between the section capacity and the full charge capacity. The table shown in FIG. 3 shows the correspondence between the section capacity and the full charge capacity when the open circuit voltages V1 and V2 are predetermined voltages.

  The table shown in FIG. 3 differs depending on the values of the open circuit voltages V1 and V2. That is, as many tables as shown in FIG. 3 need to be prepared in advance according to the number of combinations of the open circuit voltages V1 and V2. When the process of step S108 is performed, a table corresponding to the open circuit voltages V1 and V2 detected in steps S101 and S105 among a plurality of tables can be used.

  On the other hand, if the open circuit voltages V1 and V2 are set in advance when the full charge capacity of the cell 11 is estimated, the table shown in FIG. 3 is a table corresponding to the set open circuit voltages V1 and V2. You just have to prepare. The open circuit voltages V1 and V2 are set to values included in the voltage range R. In this case, the processes of steps S102 and S106 can be omitted in the flowchart shown in FIG.

  The correspondence relationship between the section capacity and the full charge capacity will be described with reference to FIG. FIG. 4 shows changes in the positive electrode potential, the negative electrode potential, and the battery voltage (open circuit voltage) with respect to the capacity of the unit cell 11. The capacity shown on the horizontal axis of FIG. 4 corresponds to the SOC (State of Charge) of the unit cell 11. The voltage (battery voltage) of the unit cell 11 is obtained by subtracting the negative electrode potential from the positive electrode potential. If a reference electrode is disposed between the positive electrode and the negative electrode, the positive electrode potential and the negative electrode potential can be measured.

  When the unit cell 11 deteriorates, as shown in FIG. 4, the curve indicating the negative electrode potential shifts to the high capacity side. The capacity deterioration of the unit cell 11 is greatly influenced by the deactivation of lithium ions in the negative electrode. For this reason, the capacity | capacitance degradation of the cell 11 can be prescribed | regulated by shifting the curve which shows a negative electrode electric potential.

  Here, it is assumed that the positive electrode potential does not change, and the curve indicating the positive electrode potential is not shifted. By subtracting the shifted negative electrode potential from the positive electrode potential, the voltage (battery voltage) of the unit cell 11 after deterioration is obtained. FIG. 4 shows curves (one example) of the negative electrode potential and the battery voltage before and after the deterioration of the unit cell 11.

  The shift amount of the curve indicating the negative electrode potential corresponds to the deterioration amount of the unit cell 11, and as the deterioration amount of the unit cell 11 increases, in other words, as the capacity retention rate decreases, the shift of the curve indicating the negative electrode potential decreases. The amount increases. The capacity maintenance rate is represented by a ratio (C2 × 100 / C1) between the full charge capacity C1 of the single battery 11 in the initial state and the full charge capacity C2 of the single battery 11 after deterioration. As the full charge capacity of the unit cell 11 decreases, the curve indicating the negative electrode potential shifts to the high capacity side.

  When the unit cell 11 is in a state before deterioration, the section capacity can be obtained by specifying two arbitrary voltages (open circuit voltages) V1 and V2 located on the curve indicating the battery voltage before deterioration. . That is, the section capacity is a difference between the battery capacity corresponding to the voltage V1 and the battery capacity corresponding to the voltage V2. Since this section capacity has a corresponding relationship with the full charge capacity in the unit cell 11 before deterioration, this corresponding relationship becomes a part of the table described above.

  When the unit cell 11 is in a deteriorated state, the section capacity can be obtained by specifying two arbitrary voltages V1, V2 located on the curve indicating the battery voltage after deterioration. Since this section capacity has a corresponding relationship with the full charge capacity in the unit cell 11 after deterioration, this corresponding relationship becomes a part of the table described above.

  In this way, in different full charge capacities, in other words, in the case where the curves indicating the negative electrode potentials are different from each other, if the section capacities corresponding to the respective full charge capacities are obtained in advance, the section capacities can be determined by specifying the section capacities. The full charge capacity corresponding to can be specified. If the section capacities are different from each other, it becomes easy to specify the full charge capacity corresponding to the section capacities.

  In this embodiment, the full charge capacity corresponding to the section capacity is specified using a table (see FIG. 3) indicating the correspondence relationship between the section capacity and the full charge capacity, but the present invention is not limited to this. Specifically, an arithmetic expression using the section capacity and the full charge capacity as parameters (variables) is determined, and the full charge capacity can be specified from the section capacity using the arithmetic expression. In this case, information related to the arithmetic expression can be stored in the memory 31. The above-described table and calculation formula are information indicating the correspondence relationship between the section capacity and the full charge capacity.

  As shown in FIG. 4, in the first voltage range R1, the battery voltage curve before deterioration and the battery voltage curve after deterioration are shifted from each other. That is, when the battery voltage is an arbitrary voltage included in the first voltage range R1, the battery capacity of the single battery 11 before deterioration is lower than the battery capacity of the single battery 11 after deterioration. On the other hand, in the second voltage range R2, the curve of the battery voltage before deterioration and the curve of the battery voltage after deterioration almost overlap. For this reason, when the battery voltage is an arbitrary voltage included in the second voltage range R2, the battery capacity in the single battery 11 before deterioration and the battery capacity in the single battery 11 after deterioration are almost the same.

When the open circuit voltages V1 and V2 are included in the second voltage range R2, the interval capacities ΔC _S3 and ΔC _S4 during the change of the open circuit voltage from V1 to V2 are the same as the unit cell 11 before degradation and the unit cell after degradation. The battery 11 is approximately the same. The section capacity ΔC _S3 is a section capacity when the unit cell 11 is in a state before deterioration, and the section capacity ΔC _S4 is a section capacity when the unit cell 11 is in a state after deterioration. The full charge capacities of the cells 11 corresponding to the section capacities ΔC _S3 and ΔC _S4 are different from each other.

  When the open circuit voltages V1 and V2 are included in the second voltage range R2, even if the full charge capacities of the cells 11 are different from each other, the section capacities are equal. In such a case, it is difficult to specify the full charge capacity corresponding to this section capacity even if the section capacity is specified by the process of step S107 shown in FIG. Therefore, the estimation accuracy when the full charge capacity is estimated from the section capacity is likely to be lowered.

When the open circuit voltages V1 and V2 are included in the first voltage range R1, if the full charge capacities are different from each other, the section capacities are also different according to the full charge capacities. As shown in FIG. 5, the interval capacities ΔC _S1 and ΔC _S2 while the open circuit voltage changes from V1 to V2 are different between the unit cell 11 before degradation and the unit cell 11 after degradation. The section capacity ΔC _S1 is a section capacity when the unit cell 11 is in a state before deterioration, and the section capacity ΔC _S2 is a section capacity when the unit cell 11 is in a state after deterioration.

If the section capacity is different depending on the full charge capacity, the full charge capacity corresponding to the section capacity can be specified by specifying the section capacity. Specifically, the section capacity ΔC _S1 has a correspondence relationship with the full charge capacity of the single battery 11 before deterioration, and the section capacity ΔC _S2 has a correspondence relation with the full charge capacity of the single battery 11 after deterioration. If the section capacity ΔC _S1 is specified in the process of step S107 shown in FIG. 2, it can be estimated that the current full charge capacity of the unit cell 11 is the full charge capacity of the unit cell 11 before deterioration. If the section capacity ΔC _S2 is specified, it can be estimated that the current full charge capacity of the single battery 11 is the full charge capacity of the single battery 11 after deterioration. The full charge capacity of the unit cell 11 after deterioration changes according to the deterioration state of the unit cell 11.

  As shown in FIG. 6, when the battery capacity is smaller than the reference capacity Cref, the amount of change in the negative electrode potential with respect to the change in battery capacity is relatively large. On the other hand, when the battery capacity is larger than the reference capacity Cref, the amount of change in the negative electrode potential with respect to the change in battery capacity is relatively small. In other words, the change rate of the negative electrode potential in a range where the battery capacity is smaller than the reference capacity Cref is larger than the change rate of the negative electrode potential in a range where the battery capacity is larger than the reference capacity Cref.

  In consideration of such negative electrode characteristics, if the voltages V1 and V2 are set to be equal to or lower than the battery voltage Vref corresponding to the reference capacity Cref, different section capacities can be easily obtained when the full charge capacities are different from each other. That is, if the section capacity is specified, it becomes easy to specify the full charge capacity corresponding to the section capacity, and the estimation accuracy when the full charge capacity is estimated from the section capacity can be improved. The upper limit voltage Vmax of the voltage range R can be set to a value equal to or lower than the battery voltage Vref.

  Since the curve indicating the negative electrode potential varies depending on the type of the unit cell 11, a curve indicating the negative electrode potential is obtained according to the type of the unit cell 11, and from the viewpoint described above (rate of change in the negative electrode potential), the reference Capacitance Cref can be determined. If the reference capacity Cref is determined, the battery voltage Vref can be determined, and the voltage range R can also be determined.

  FIG. 7 is an experimental result showing the relationship between the section capacity maintenance rate and the full charge capacity deterioration rate. The maintenance rate of the section capacity and the deterioration rate of the full charge capacity are expressed by the following formulas (1) and (2).

Section capacity maintenance rate = ΔC2 × 100 / ΔC1 (1)
Degradation rate of full charge capacity = (C1-C2) × 100 / C1 (2)

  In the equation (1), ΔC1 indicates a section capacity obtained when the single battery 11 before deterioration is used, and ΔC2 indicates a section capacity obtained when the single battery 11 after deterioration is used. In Expression (2), C1 represents the full charge capacity of the single battery 11 before deterioration, and C2 represents the full charge capacity of the single battery 11 after deterioration.

FIG. 7 is a diagram showing how the section capacity changes when the full charge capacity of the unit cell 11 changes (deteriorates). In the experiment in which the results shown in FIG. 7 were obtained, a lithium ion secondary battery was used as the single battery 11. Here, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ was used as the positive electrode active material, and graphite was used as the negative electrode active material.

  In FIG. 7, if the maintenance ratio of the section capacity is not changed, the section capacity does not change even if the full charge capacity is different. Therefore, even if the section capacity is specified, it is difficult to specify the full charge capacity from the section capacity. On the other hand, if the maintenance rate of the section capacity changes, the section capacity also varies due to the different full charge capacity. Therefore, it becomes easy to specify the full charge capacity corresponding to the section capacity by specifying the section capacity.

  In the experiment in which the result shown in FIG. 7 was obtained, a plurality of voltage ranges R (3.0 to 3.5 [V], 3.0 to 3.6 [V], 3.6 to 4.1 [V] ), And in each voltage range R, the section capacitance when the open circuit voltage was changed from V1 to V2 was measured. The section capacity was measured while changing the deterioration rate of the full charge capacity.

  As shown in FIG. 7, when the voltage range R is in the range of 3.6 to 4.1 [V], even if the deterioration rate of the full charge capacity changes, the section capacity maintenance ratio does not change. When the voltage range R is in the range of 3.0 to 3.6 [V], the section capacity maintenance rate changes in accordance with the change in the deterioration rate of the full charge capacity. Even when the voltage range R is in the range of 3.0 to 3.5 [V], the maintenance rate of the section capacity changes according to the change of the deterioration rate of the full charge capacity.

  In the lithium ion secondary battery used in the experiment shown in FIG. 7, if the upper limit voltage Vmax of the voltage range R is set to 3.6 [V] or less, it becomes easy to specify the full charge capacity according to the section capacity. .

10: assembled battery 11: cell 21: voltage sensor 22: current sensor 23: temperature sensor 24: load 25a, 25b: relay 30: controller 31: memory

Claims (8)

An estimation device for estimating the full charge capacity of a secondary battery,
Obtaining a section capacity that is a battery capacity when the open circuit voltage of the secondary battery changes from a first voltage to a second voltage, and the section capacity and a full charge capacity that changes according to deterioration of the secondary battery, A controller that specifies the full charge capacity corresponding to the acquired section capacity using information indicating the correspondence relationship of
The estimation device according to claim 1, wherein the first voltage and the second voltage are included in a voltage range in which a battery capacity is likely to change according to a change in a negative electrode potential accompanying a deterioration of the secondary battery.   The controller obtains the section capacity by integrating the charge / discharge current of the secondary battery until the open circuit voltage of the secondary battery changes from the first voltage to the second voltage. The estimation apparatus according to claim 1.   The estimation apparatus according to claim 1, further comprising a memory that stores information related to the voltage range.   The estimation apparatus according to claim 1, further comprising a memory that stores information indicating the correspondence relationship. The secondary battery is a lithium ion secondary battery,
The estimation device according to claim 1, wherein an upper limit voltage that defines the voltage range is 3.6 [V] or less. An estimation method for estimating a full charge capacity of a secondary battery,
Obtaining a section capacity which is a battery capacity when the open circuit voltage of the secondary battery changes from the first voltage to the second voltage;
Using information indicating the correspondence relationship between the section capacity and the full charge capacity that changes according to the deterioration of the secondary battery, the full charge capacity corresponding to the acquired section capacity is identified,
The estimation method, wherein the first voltage and the second voltage are included in a voltage range in which battery capacity is likely to change according to a change in negative electrode potential accompanying deterioration of the secondary battery.   The interval capacity is obtained by integrating the charge / discharge current of the secondary battery until the open circuit voltage of the secondary battery changes from the first voltage to the second voltage. The estimation method according to claim 6. The secondary battery is a lithium ion secondary battery,
The estimation method according to claim 6 or 7, wherein the upper limit voltage defining the voltage range is 3.6 [V] or less.

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