WO2017179347A1

WO2017179347A1 - Secondary battery system

Info

Publication number: WO2017179347A1
Application number: PCT/JP2017/009581
Authority: WO
Inventors: 耕平本蔵
Original assignee: 株式会社日立製作所
Priority date: 2016-04-11
Filing date: 2017-03-09
Publication date: 2017-10-19

Abstract

This secondary battery system comprises: a retaining unit for retaining an internal resistance first reference value in a first state-of-charge that is lower than a predetermined state-of-charge, and an internal resistance second reference value in a second state-of-charge that is higher than the first state-of-charge, in the initial state of the secondary battery; a measurement unit for measuring, in an in-use state of the secondary battery, a first internal resistance of the secondary battery in the first state-of-charge, and a second internal resistance of the secondary battery in the second state-of-charge; and a detection unit detecting a deterioration of the secondary battery on the basis of a comparison between the first reference value and the first internal resistance in the first state-of-charge measured by the measurement unit, and a comparison between the second reference value and the second internal resistance in the second state-of-charge measured by the measurement unit.

Description

Secondary battery system

The present invention relates to a secondary battery system.

In recent years, efforts have been made to efficiently use energy by using secondary batteries such as lithium-ion batteries for power storage power sources for vehicles and smart houses. It is known that the secondary battery is deteriorated in characteristics by charging / discharging and storage. Since the above power storage power source is assumed to be used for a long time, it is important to suppress deterioration of the characteristics of the secondary battery. It is also important to continue to use the secondary battery safely.

The characteristic deterioration of the secondary battery is mainly regarded as a decrease in battery capacity and an increase in battery internal resistance. Usually, the internal resistance continues to rise gradually with use. When the internal resistance of the secondary battery rises above a certain level, it becomes difficult for the secondary battery to obtain the required output. For this reason, it is common to determine the rate of increase of the internal resistance of the secondary battery and reflect it in the control on the power supply destination device side. Also, a method for predicting the rate of increase of the internal resistance of the battery has been studied. For example, Patent Document 1 proposes a mathematical expression and a method for estimating an increase rate of internal resistance with respect to an initial state of a secondary battery. This Patent Document 1 describes a method for estimating the rate of increase in internal resistance by substituting appropriate values of elapsed time and coefficient into a predetermined mathematical expression. By estimating the rate of increase of the internal resistance in this way, it becomes possible to optimize the control of the apparatus.

Japanese Unexamined Patent Publication No. 2013-057576

However, the method for estimating the rate of increase of the internal resistance described in Patent Document 1 is effective only when the normal internal resistance continues to increase gradually. It was not applicable when rising.

In the secondary battery system according to the present invention, in the initial state of the secondary battery, the first reference value of the internal resistance in the first charge state lower than the predetermined charge state, and the second charge state higher than the first charge state. A holding unit that holds a second reference value of an internal resistance; in a use state of the secondary battery; a first internal resistance of the secondary battery in the first charge state; and the second charge of the secondary battery. A measuring unit that measures the second internal resistance in the state, a comparison between the first internal resistance and the first reference value in the first charging state measured by the measuring unit, and a second charging that is measured by the measuring unit A detector that detects deterioration of the secondary battery based on a comparison between the second internal resistance in the state and the second reference value.

According to the present invention, a rapid increase in the internal resistance of the secondary battery can be detected at an early stage.

It is a schematic block diagram of a secondary battery system. It is a flowchart which shows the processing operation of the battery management part concerning 1st Embodiment. It is a figure which shows the relationship between charge condition SOC and internal resistance R in an initial state and a state after deterioration. It is a figure which shows the relationship between the charge condition of a secondary battery, and the raise rate of internal resistance. It is the figure which showed each SOC of 1st charge state SOC1, and the ratio of the raise rate of internal resistance. It is a flowchart which shows the processing operation of the battery management part concerning 2nd Embodiment. It is a flowchart which shows the processing operation of the battery management part concerning 3rd Embodiment.

(First embodiment)
First, the structure of the secondary battery 21 used for the secondary battery system of this embodiment is demonstrated.
The secondary battery 21 is configured such that an electrode group including a positive electrode, a separator, and a negative electrode is installed in a battery case. The electrode group has a configuration in which positive electrodes, separators, negative electrodes, and separators are alternately stacked and wound, or a configuration in which positive electrodes, separators, negative electrodes, and separators are alternately stacked. The shape of the secondary battery 21 is a cylindrical shape, a flat oval shape, or a square shape when the electrode group is wound, and a square shape, a laminate shape, or the like when the electrode group is wound. Yes, any shape may be selected.

The positive electrode and the negative electrode are arranged away from each other through the electrolytic solution. As the electrolytic solution, for example, a non-aqueous solution in which 1 mol / l of lithium hexafluorophosphate as a lithium salt is dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate having a volume ratio of 1: 1 is injected.

The positive electrode includes a positive electrode active material made of a lithium-containing oxide that can reversibly insert and desorb lithium ions. Examples of the positive electrode active material include layered transition metal oxides with or without substitution elements, lithium transition metal phosphates, and spinel type transition metal oxides. For example, as the layered transition metal oxide, lithium nickelate LiNiO ₂ or lithium cobaltate LiCoO ₂ , as the transition metal lithium phosphate lithium iron phosphate LiFePO ₄ , manganese phosphate lithium LiMnPO ₄ , spinel type transition metal oxide Examples thereof include lithium manganate LiMn ₂ O ₄ . One kind or two or more kinds of the above materials may be contained as the positive electrode active material. In the positive electrode active material in the positive electrode, lithium ions are desorbed in the charging process, and lithium ions desorbed from the negative electrode active material in the negative electrode are inserted in the discharging process.

The negative electrode is, for example, a carbon material capable of reversibly inserting and extracting lithium ions, silicon-based material Si, SiO, lithium titanate with or without a substitution element, lithium vanadium composite oxide, lithium and metal, for example, The negative electrode active material which consists of an alloy with tin, aluminum, antimony, etc. is included. As a carbon material, as a raw material, natural graphite, a composite carbonaceous material obtained by forming a film on natural graphite by a dry CVD method or a wet spray method, a resin material such as epoxy or phenol, or a pitch-based material obtained from petroleum or coal Examples thereof include artificial graphite and non-graphitizable carbon material produced by firing. The above materials may be contained singly or in combination of two or more as the negative electrode active material. The negative electrode active material in the negative electrode undergoes insertion / extraction reaction or conversion reaction of lithium ions during the charge / discharge process.

For example, a polypropylene separator is used as the separator used between the positive electrode and the negative electrode. In addition to polypropylene, a microporous film or non-woven fabric made of polyolefin such as polyethylene can be used.

FIG. 1 is a schematic configuration diagram of a secondary battery system according to the first embodiment. The secondary battery system includes a battery management unit 10, a plurality of battery systems 20 connected in parallel to the battery management unit 10, and a memory 30 connected to the battery management unit 10.

The battery system 20 detects a plurality of secondary batteries 21 connected in series, a voltage detection unit 22 provided for each secondary battery 21, and a current flowing through the plurality of secondary batteries 21 connected in series. And a current control unit 24 that controls the current flowing through the plurality of secondary batteries 21 connected in series.

The voltage detector 22 detects the battery voltage of the secondary battery 21 and is constituted by a voltage sensor such as a voltmeter. Although the voltage detection part 22 demonstrates in the example which measures the battery voltage of each secondary battery 21, you may make it measure the whole battery voltage which connected the some secondary battery 21 in series. The voltage value detected by the voltage detection unit 22 is input to the battery management unit 10.

The current detection unit 23 detects the charge / discharge current of the secondary battery 21 and is configured by a current sensor such as an ammeter. As the ammeter used in the current detection unit 23, for example, a galvanometer, an ammeter using a shunt resistor, a clamp meter, and the like are conceivable. Note that the current detection method in the current detection unit 23 is not limited to this, and any method can be used as long as it detects the value of the current flowing in the secondary battery 21. The current value detected by the current detection unit 23 is input to the battery management unit 10.

The current control unit 24 is a part for controlling the charge / discharge current of the secondary battery 21, and its operation is controlled by the battery management unit 10. For example, the current control unit 24 can be realized by controlling opening and closing of a switch such as a semiconductor switch or a mechanical switch according to the magnitude of the charge / discharge current. Further, a power conversion device such as an inverter or a DC-DC converter may be used as the current control unit 24. In addition, the current control unit 24 is not limited to these as long as the current value when the secondary battery 21 is charged / discharged can be controlled from the battery management unit 10.

The memory 30 includes a first reference value R01 of internal resistance in the first charge state SOC1 lower than the predetermined charge state of the secondary battery 21 and a second reference of internal resistance in the second charge state SOC2 higher than the first charge state SOC1. Holds the value R02. The first reference value R01 and the second reference value R02 are read from the battery management unit 10.

The battery management unit 10 controls charging / discharging of the secondary battery 21 according to a command from the host controller, and includes a microcomputer that operates according to a predetermined program, a CPU, a ROM, a RAM, and the like.
In addition, the battery management unit 10 is based on a process for obtaining a state of charge (SOC) of the secondary battery 21 from the voltage value measured by the voltage detection unit 22 and the current value measured by the current detection unit 23. Either or both of the processes for obtaining the state of charge of the secondary battery 21 from the accumulated charge / discharge electricity amount are included. Further, the open circuit voltage V1 of the secondary battery 21 corresponding to the first charge state SOC1 and the open circuit voltage V2 of the secondary battery 21 corresponding to the second charge state SOC2 are held in the memory 30.

In addition, the battery management unit 10 calculates the internal resistance of the secondary battery 21 based on the voltage value and the current value measured by the voltage detection unit 22 and the current detection unit 23, and at the same time, the secondary battery 21 at the present time. Has a function of determining the state of charge. Furthermore, it has the function as the measurement part 11 which calculates (measures) the internal resistance R1 in the 1st charge state SOC1 and the internal resistance R2 in the 2nd charge state SOC2 from the combination data group of a some charge state and internal resistance. Then, the deterioration of the secondary battery 21 is performed based on the comparison between the internal resistance R1 and the first reference value R01 in the first charge state SOC1 and the comparison between the internal resistance R2 and the second reference value R02 in the second charge state SOC2. It has a function as the detection part 12 to detect.

FIG. 2 is a flowchart showing the processing operation of the battery management unit 10 in the present embodiment.
In step S11, in the usage state of the secondary battery 21, the internal resistances R1 and R2 are measured with respect to the two charged states SOC1 and SOC2 in the relationship of the first charged state SOC1 <the second charged state SOC2. At this time, the first charge state SOC1 is preferably a predetermined charge state, for example, 50% or less, and more preferably 20% or less. Further, the second charging state SOC2 is higher than the first charging state SOC1, for example, preferably 30% or more, and more preferably 40% or more. The usage state of the secondary battery 21 is a state after the use of the secondary battery 21 is started.

Here, a method for measuring the internal resistances R1 and R2 by the battery management unit 10 will be described. In order to measure the internal resistance R1, the battery management unit 10 first charges or discharges the secondary battery 21 until the open circuit voltage V1 of the secondary battery 21 corresponding to the first charge state SOC1 is reached. Thereafter, the battery is allowed to stand for a certain period of time, and then a predetermined current value I0 is discharged, and the closed circuit voltage V of the battery at that time is measured. Similarly, in order to measure the internal resistance R2, the battery management unit 10 first charges or discharges the secondary battery 21 until the open circuit voltage V2 of the secondary battery 21 corresponding to the second charge state SOC2 is reached. Thereafter, the battery is allowed to stand for a certain period of time and then a predetermined current value I0 is discharged, and the closed circuit voltage V of the battery at that time is measured. Based on these measurement results, the battery management unit 10 obtains internal resistances R1 and R2 from the following equation (1). In the measurement method described above, measurement by the voltage detection unit 22 and current detection unit 23 and current control by the current control unit 24 are performed.
R1 = (V-V1) / I0, R2 = (V-V2) / I0 (1)

Further, another method for measuring the internal resistances R1 and R2 by the battery management unit 10 will be described. For example, the battery management unit 10 detects the battery voltage Vi, the current Ii, and the state of charge SOCi at a certain moment, and uses these detection results and the open circuit voltage Voi corresponding to the state of charge SOCi. The internal resistance Ri = (Vi−Voi) / Ii is calculated. Then, the obtained combination data of the state of charge SOCi and the internal resistance Ri is held in the memory 30. After that, when a certain amount of data is accumulated in the memory 30, the battery management unit 10 performs an averaging process of data and a complementary process by interpolation and extrapolation, and the internal resistance R1 corresponding to the first charge state SOC1 and the first resistance. 2. Calculate the internal resistance R2 corresponding to the state of charge SOC2. In this way, the internal resistances R1 and R2 may be measured.
In any case, when the secondary battery 21 is in use, the battery management unit 10 measures the internal resistance R1 in the first charge state SOC1 and the internal resistance R2 in the second charge state SOC2 of the secondary battery 21. It functions as the unit 11.

Also, as the first charging state SOC1 and the second charging state SOC2, a charging state in an appropriate range may be set instead of a single charging state. In that case, as the internal resistance R1 and the internal resistance R2, the average value of the internal resistance in the range set as the first charging state SOC1 and the second charging state SOC2 is used. As an appropriate state of charge SOC, for example, the first state of charge SOC1 is 0 to 20%, and the second state of charge SOC2 is 40 to 100%.

Next, in step S12, the battery management unit 10 stores the first reference value R01 of the internal resistance in the first charging state SOC1 and the second reference value R02 of the internal resistance in the second charging state SOC2 stored in the memory 30. Is read. The first reference value R01 and the second reference value R02 are previously measured or calculated in advance in the initial state of the secondary battery 21. The initial state of the secondary battery 21 is an initial state before or after using the secondary battery 21. Further, the first charging state SOC1 and the second charging state SOC2 used in step S11 and step S12 are specific values determined in the above-described range.

In step S13, battery management unit 10 calculates internal resistance increase rate R1 / R01 in first charge state SOC1 and internal resistance increase rate R2 / R02 in second charge state SOC2.
In step S <b> 14, the battery management unit 10 calculates the ratio r of the increase rates of the two internal resistances according to the equation (2).
r = (R1 / R01) / (R2 / R02) (2)
Note that the difference r ′ between the ratios of the two internal resistances may be calculated by equation (3).
r '= (R1 / R01)-(R2 / R02) (3)

In step S15, the battery management unit 10 determines whether the ratio r of the rate of increase in internal resistance is greater than a predetermined value r0. The predetermined value r0 may be arbitrarily set to 1 or more, but is preferably set to 1.03 or more. In step S15, it may be determined whether the difference r ′ between the two internal resistances is greater than a predetermined value r′0. Thus, the battery management unit 10 functions as the detection unit 12 that detects the deterioration of the secondary battery 21.

When the ratio r of the increase rate of the internal resistance is larger than r0, the process proceeds to the next step S16. Alternatively, if the difference r ′ between the two internal resistances is larger than the predetermined value r′0 in step S15, the process proceeds to the next step S16.
In step S16, the battery management unit 10 transmits a warning signal to the host controller. As a result, the host controller can take measures corresponding to the deterioration of the secondary battery 21.

Here, the rapid increase in internal resistance of the secondary battery 21 and its detection will be described below.
FIG. 3 is a diagram showing a relationship between the charge state and the internal resistance in the initial state and the deteriorated state in the secondary battery 21 in which the internal resistance has rapidly increased. In FIG. 3, the horizontal axis indicates the state of charge, and the vertical axis indicates the internal resistance. Even in the initial state of the secondary battery 21, the internal resistance tends to increase as the state of charge is lower, but the tendency becomes more prominent after the secondary battery 21 is deteriorated.

FIG. 4 is a diagram showing the relationship between the state of charge of the secondary battery 21 and the rate of increase in internal resistance. In FIG. 4, the horizontal axis represents the value of the state of charge, and the vertical axis represents the value of the rate of increase in internal resistance. As can be seen from this figure, when the state of charge is 25% or more, the increase rate of the internal resistance is about 1.5, but when the state of charge is 25% or less, the increase rate of the internal resistance increases as the state of charge decreases. .

FIG. 5 is a diagram showing the relationship between the first charge state SOC1 and the ratio r of the increase rate of the internal resistance, assuming that the second charge state SOC2 is 50%. In FIG. 5, the horizontal axis indicates the value of the first state of charge SOC1, and the vertical axis indicates the value of the ratio r of the rate of increase in internal resistance. In the example of FIG. 5, when the first state of charge SOC1 is 30% or less, a rapid increase in internal resistance can be detected when the predetermined value r0 = 1.03 or more. If the first state of charge SOC1 is made lower, a rapid increase in internal resistance can be detected earlier.
According to the present embodiment, a rapid increase in the internal resistance of the secondary battery can be detected at an early stage, prompting the user to replace the battery early, or taking measures corresponding to the deterioration of the secondary battery 21. be able to.

(Second Embodiment)
A second embodiment will be described with reference to FIG. The schematic configuration diagram of the secondary battery system is the same as that of FIG. 1, and the configuration of the secondary battery 21 is also the same as that of the first embodiment. Further, the relationship between the state of charge and the internal resistance is the same as that in the first embodiment described with reference to FIGS.

FIG. 6 is a flowchart showing the processing operation of the battery management unit 10 according to the second embodiment. In FIG. 6, Steps S21 to S24 are the same as Steps S11 to S14 of FIG. 2 shown in the first embodiment, and thus description thereof is omitted.

In step S25, the battery management unit 10 records the current date and time t and the calculated ratio r in the memory 30. Every time the current date and time t is updated, the process from step S21 to step S24 is executed, and the date and time t and the calculated ratio r are accumulated and recorded in the memory 30. Instead of the current date and time t, the total operating time of the apparatus and the accumulated charge / discharge electricity amount may be recorded. Alternatively, the previous ratio r may be recorded, and thereafter the difference from this ratio r may be recorded. Further, a plurality of these may be combined as appropriate and recorded. Hereinafter, a case where the current date and time is recorded will be described.

In step S26, the battery management unit 10 calculates the date and time t0 at which the ratio r exceeds the predetermined value r0 based on the accumulated data of the date and time t and the ratio r recorded in the memory 30. When the difference r 'between the two internal resistances is obtained in step S24, the date and time t0 when the difference r' between the two internal resistances exceeds the predetermined value r'0 is calculated.

The calculation method may be arbitrary.For example, the date and time t is converted into the elapsed time t ′ from the reference date and time such as the device manufacturing date and the operation start date and time. Regress to an appropriate function, such as a power function at time t '.
For example, a case will be described in which the ratio r returns to a power function represented by the following equation (4) that increases in proportion to the 0.5th power of the elapsed time t ′.
r = 100 + k x t ' ^0.5 (4)

First, a data group composed of a combination of the ratio r and the elapsed time t ′ is regressed to the mathematical expression (4) to determine the coefficient k. Next, t ′ = t′0 where r = r0 is obtained by Expression (5) obtained by modifying Expression (4).
t'0 = [(r0-100) / k] ^{1 / 0.5} (5)
Next, the reference date and time is added to t′0 to obtain the date and time t0.

In step S27, the battery management unit 10 compares the calculated date and time t0 with the current date and time t. That is, it is determined whether the time (t0-t) until the date and time t0 is smaller than the predetermined value t1. When the time (t0-t) until the date and time t0 is smaller than the predetermined value t1, the process proceeds to step S28. The predetermined value t1 may be arbitrary, but may be, for example, one year or less.
In step S28, the battery management unit 10 transmits a warning signal to the host controller. As a result, the host controller can take measures corresponding to the deterioration of the secondary battery 21.

According to the present embodiment, it is possible to estimate in advance the time until a sudden increase in the internal resistance of the secondary battery 21 occurs, and to prompt the user to replace the battery. Thereby, it is possible to prevent unexpected performance degradation of the apparatus and improve reliability.

(Third embodiment)
A third embodiment will be described with reference to FIG. The schematic configuration diagram of the secondary battery system is the same as that of FIG. 1, and the configuration of the secondary battery 21 is also the same as that of the first embodiment. Further, the relationship between the state of charge and the internal resistance is the same as that in the first embodiment described with reference to FIGS.

FIG. 7 is a flowchart showing the processing operation of the battery management unit 10 according to the third embodiment. In FIG. 7, Steps S31 to S35 are the same as Steps S11 to S15 of FIG. 2 shown in the first embodiment, and thus description thereof is omitted.

In step S35, it is determined whether the ratio r of the increase rate of the internal resistance is greater than a predetermined value r0. If the ratio r of the increase rate of the internal resistance is greater than r0, the process proceeds to step S36.
In step S <b> 36, the battery management unit 10 changes the operation condition of the secondary battery 21. That is, by restricting charging / discharging of the secondary battery 21, a rapid increase in internal resistance is suppressed. The inventor has a situation in which the lower limit of the state of charge when operating the secondary battery 21 is low, a situation in which the current value is large, a situation in which the battery temperature is low, or the amount of electricity continuously charged without interruption, or continuous In the situation where the amount of electricity discharged is large, it was found that the internal resistance tends to increase rapidly. Therefore, in changing the operating conditions, for example, changing the lower limit of the charging state when operating the secondary battery 21, changing the current value, changing the battery temperature or the ambient temperature around the battery, continuously charging Change to suppress the amount of electricity to be discharged or the amount of electricity to be discharged continuously.

When raising the lower limit of the state of charge when operating the secondary battery, it is desirable to raise it by 5% or more. For example, when the operating range of the original state of charge is 30-70%, a sudden increase in internal resistance can be suppressed by setting the operating range of the new state of charge to 40-70%.
According to the present embodiment, it is possible to prevent a sudden increase in internal resistance of the secondary battery 21 and to extend the life of the secondary battery.

According to the embodiment described above, the following operational effects can be obtained.
(1) In the secondary battery system according to the present embodiment, in the initial state of the secondary battery 21, the first reference value R01 of the internal resistance in the first charge state SOC1 lower than the predetermined charge state and the first charge state SOC1 The memory 30 that holds the second reference value R02 of the internal resistance in the second charge state SOC2 that is higher, and the first internal resistance R1 in the first charge state SOC1 of the secondary battery 21 when the secondary battery 21 is in use. The battery management unit 10 (measurement unit 11, step S11) for measuring the second internal resistance R2 in the second charge state SOC2 of the secondary battery 21 and the first charge state measured by the battery management unit 10 (step S11). For comparison between the first internal resistance R1 and the first reference value R01 in SOC1, and the comparison between the second internal resistance R2 and the second reference value R02 in the second charge state SOC2 measured by the battery management unit 10 (step S11). On the basis of Comprising a battery management unit 10 (detecting unit 12, steps S12 ~ S15) for detecting the deterioration of the following cell 21 and, a. Thereby, a rapid increase in the internal resistance of the secondary battery can be detected at an early stage.

The present invention is not limited to the above-described embodiment, and other forms conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention as long as the characteristics of the present invention are not impaired. . Moreover, it is good also as a structure which combined the above-mentioned embodiment.

The disclosure of the following priority application is hereby incorporated by reference.
Japanese Patent Application No. 78740 in 2016 (filed on April 11, 2016)

DESCRIPTION OF SYMBOLS 10 Battery management part 11 Measurement part 12 Detection part 20 Battery system 21 Secondary battery 22 Voltage detection part 23 Current detection part 24 Current control part 30 Memory

Claims

In the initial state of the secondary battery, the first reference value of the internal resistance in the first charging state lower than the predetermined charging state, and the second reference value of the internal resistance in the second charging state higher than the first charging state Holding part to hold;
A measurement unit that measures a first internal resistance of the secondary battery in the first charging state and a second internal resistance of the secondary battery in the second charging state in the usage state of the secondary battery;
Comparison between the first internal resistance and the first reference value in the first charge state measured by the measurement unit, and the second internal resistance and the second reference value in the second charge state measured by the measurement unit And a detector that detects deterioration of the secondary battery based on the comparison.
The secondary battery system according to claim 1,
The detection unit includes a first ratio that is a ratio between the first internal resistance and the first reference value in the first charge state measured by the measurement unit, and the second ratio in the second charge state that is measured by the measurement unit. A secondary battery system that detects deterioration of the secondary battery based on a second ratio that is a ratio of two internal resistances to the second reference value.
The secondary battery system according to claim 1,
The detection unit includes a first ratio that is a ratio between the first internal resistance and the first reference value in the first charge state measured by the measurement unit, and the second ratio in the second charge state that is measured by the measurement unit. A second ratio, which is a ratio between the two internal resistances and the second reference value, is accumulated in time, and the difference between the first ratio and the second ratio, or the first ratio and the second ratio, A secondary battery system that determines and outputs the time until the ratio exceeds a predetermined value.
In the secondary battery system according to any one of claims 1 to 3,
A secondary battery system that restricts charging and discharging of the secondary battery when the detection unit detects deterioration of the secondary battery.
In the secondary battery system according to any one of claims 1 to 3,
A voltage sensor for measuring the voltage of the secondary battery; and a current sensor for measuring a current flowing in the secondary battery,
The holding unit is a secondary battery system that is a memory that holds the first reference value and the second reference value.
In the secondary battery system according to any one of claims 1 to 3,
The secondary battery system in which the first charging state is any charging state of 20% or less, and the second charging state is any charging state of 40% or more.