JP2012122817A - Reversible capacity estimation method of nonaqueous electrolyte secondary battery, life prediction method, reversible capacity estimation method, life prediction device and power storage system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible capacity estimation method of a nonaqueous electrolyte secondary battery capable of precisely and easily measuring a deteriorated state of the nonaqueous electrolyte secondary battery such as a lithium ion secondary battery in the long term.SOLUTION: In the reversible capacity estimation method, the reversible capacity which is a capacity capable of charging and discharging a secondary battery 200 is estimated by a computer. This method includes: an acquisition step of acquiring an AC impedance at a predetermined frequency in the secondary battery 200 (S204); and an estimation step (S206) of estimating the reversible capacity by using the acquired AC impedance and a linear relational expression showing the relationship between the AC impedance and the reversible capacity (S206).

Description

  The present invention relates to a reversible capacity estimation method and a reversible capacity estimation apparatus for estimating a reversible capacity that is a chargeable / dischargeable capacity of a nonaqueous electrolyte secondary battery, a life prediction method and a life prediction to predict the life of a nonaqueous electrolyte secondary battery. The present invention relates to a power storage system including a device and a nonaqueous electrolyte secondary battery and a reversible capacity estimation device or a life prediction device.

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used as power sources for mobile devices such as notebook computers and mobile phones, but in recent years they have been used in a wide range of fields such as electric vehicle power sources and backup power sources. It has come to be. In particular, when a lithium ion secondary battery is used as a backup power source, it is important to improve the reliability of the lithium ion secondary battery so as to cope with a sudden power failure.

  For this reason, it is extremely important to accurately grasp the deterioration state of the lithium ion secondary battery. Here, conventionally, techniques for estimating a deterioration state of a lithium ion secondary battery have been proposed (see, for example, Patent Documents 1 to 3).

  In Patent Document 1, regarding a lithium ion secondary battery for an electric vehicle, a direct current resistance is calculated by measuring a current flowing through the battery and an open circuit voltage during an engine start period, and the remaining life of the battery is calculated based on the internal resistance. A technique for calculating the value is disclosed. Moreover, in patent document 2, the arithmetic expression showing the relationship between the deterioration rate in the regular temperature range of the battery of object and time is determined beforehand, the temperature change to which the battery was actually exposed is recorded, A technique for estimating a deterioration state of a battery based on an arithmetic expression from a time exposed to a temperature range is disclosed. Patent Document 3 discloses a technique for estimating battery capacity based on complex impedance measurement.

Japanese Patent Laid-Open No. 15-129927 Japanese Patent Laid-Open No. 15-161768 Japanese Patent Laid-Open No. 10-082843

  However, the above conventional technique has the following problems.

  That is, in the technique disclosed in Patent Document 1, the remaining life of the battery is calculated using the maximum load terminal voltage and current value when the engine of the electric vehicle is started, so that the measurement cycle, starter, engine state, etc. The magnitude of the impedance measured varies depending on the environmental conditions. In addition, since a plurality of internal resistances are calculated and the remaining life of the battery is calculated from the plurality of internal resistances, the processing is complicated. For this reason, in the technique disclosed in Patent Document 1, in order to estimate the deterioration state of the lithium ion secondary battery, the process is complicated and it is difficult to maintain high estimation accuracy.

  Further, in the technique disclosed in Patent Document 2, errors are likely to accumulate, and there is a risk that the accuracy of estimation of the deterioration state may be reduced in the long term. Further, the technique disclosed in Patent Document 3 requires a sophisticated device such as a frequency analyzer in order to measure the complex impedance, so that the process of estimating the deterioration state of the lithium ion secondary battery is complicated.

  As described above, in the conventional technique, it is difficult to accurately estimate the deterioration state of the lithium ion secondary battery in the long term, and the process for estimating the deterioration state is complicated.

  The present invention has been made to solve the above-described problems, and can provide a non-aqueous electrolyte secondary that can accurately and easily estimate the deterioration state of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery over a long period of time. An object of the present invention is to provide a reversible capacity estimation method and a reversible capacity estimation device for a secondary battery, a life prediction method and a life prediction device, and a power storage system.

  In order to achieve the above object, a reversible capacity estimation method according to an aspect of the present invention is a reversible capacity estimation method in which a computer estimates a reversible capacity that is a chargeable / dischargeable capacity of a nonaqueous electrolyte secondary battery. Using the acquisition step of acquiring AC impedance at a predetermined frequency in the non-aqueous electrolyte secondary battery, the acquired AC impedance, and a linear relational expression indicating the relationship between the AC impedance and the reversible capacity, Estimating the reversible capacity.

  According to this, the AC impedance indicating the internal resistance of the nonaqueous electrolyte secondary battery is acquired, and using the acquired AC impedance and the linear relational expression indicating the relationship between the AC impedance and the reversible capacity, the nonaqueous electrolyte is obtained. Estimate the reversible capacity of the secondary battery. As a result, the reversible capacity can be estimated based on a linear relational expression indicating the relationship between the AC impedance and the reversible capacity, so that the error is not accumulated and the reversible capacity is accurately estimated in the long term. Can do. Moreover, since the reversible capacity at that time can be estimated by only obtaining the AC impedance at the time of estimation once using the simple linear relational expression, the estimation process is simple. For this reason, the reversible capacity which shows the deterioration state of a nonaqueous electrolyte secondary battery can be estimated easily accurately in the long term.

  Preferably, in the estimation step, the reversible capacity is calculated by calculating the reversible capacity by multiplying the AC impedance acquired in the acquisition step by a predetermined first constant and adding a predetermined second constant. Estimate capacity.

  According to this, the reversible capacity of the nonaqueous electrolyte secondary battery is estimated by calculating the reversible capacity by multiplying the AC impedance by the first constant and adding the second constant. Here, the first constant and the second constant are numerical values derived based on experimental results, and are numerical values representing a linear relational expression that accurately indicates the relationship between the AC impedance and the reversible capacity. That is, since the reversible capacity is calculated by a linear relational expression using the numerical value, the reversible capacity can be estimated accurately over the long term. Further, by using the linear relational expression, the reversible capacity can be easily estimated from the AC impedance. For this reason, the reversible capacity which shows the deterioration state of a nonaqueous electrolyte secondary battery can be estimated easily accurately in the long term.

  Preferably, in the acquisition step, the AC impedance is measured by applying an AC voltage or an AC current having the predetermined frequency to the non-aqueous electrolyte secondary battery, and the measured AC impedance is acquired.

  According to this, the AC impedance is measured by applying an AC voltage or an AC current having a predetermined frequency to the non-aqueous electrolyte secondary battery, and the measured AC impedance is obtained. As a result, the AC impedance can be easily and accurately acquired, and therefore the reversible capacity indicating the deterioration state of the nonaqueous electrolyte secondary battery can be easily and accurately estimated over the long term using the AC impedance. .

  In order to achieve the above object, a life prediction method according to an aspect of the present invention is a life prediction method in which a computer predicts the life of a nonaqueous electrolyte secondary battery, and is included in the reversible capacity estimation method. Referring to each step, a storage step for storing a value indicating the reversible capacity estimated in the estimation step in a storage unit, and a value indicating the reversible capacity stored in the storage unit, the non-aqueous electrolyte 2 A life prediction step for predicting the life of the secondary battery.

  According to this, the lifetime of the nonaqueous electrolyte secondary battery is predicted using a value indicating the reversible capacity estimated by the reversible capacity estimation method. For this reason, predicting the lifetime of a nonaqueous electrolyte secondary battery by predicting the lifetime of the nonaqueous electrolyte secondary battery using the reversible capacity estimated accurately and simply over the long term by the reversible capacity estimation method. Can be estimated accurately over a long period of time with high accuracy.

  The present invention can be realized not only as a reversible capacity estimation method or a life prediction method of such a nonaqueous electrolyte secondary battery, but also as a processing unit that performs steps included in the reversible capacity estimation method or the life prediction method. Can also be realized as a reversible capacity estimation device or a life prediction device. The present invention can also be realized as an integrated circuit including a characteristic processing unit included in such a reversible capacity estimation device or life prediction device.

  The present invention can also be realized as a power storage system including a nonaqueous electrolyte secondary battery and a reversible capacity estimation device or a lifetime prediction device that estimates a deterioration state of the nonaqueous electrolyte secondary battery.

  The present invention can also be realized as a program that causes a computer to execute characteristic processing included in the life prediction method or the reversible capacity estimation method. Needless to say, such a program can be distributed via a recording medium such as a CD-ROM and a transmission medium such as the Internet.

  According to the present invention, the deterioration state of a non-aqueous electrolyte secondary battery can be estimated easily and accurately over the long term.

It is an external view of an electrical storage system provided with the lifetime prediction apparatus which concerns on embodiment of this invention. It is a block diagram which shows the functional structure of a lifetime prediction apparatus provided with the reversible capacity | capacitance estimation apparatus which concerns on embodiment of this invention. It is a figure which shows an example of the reversible capacity | capacitance data based on embodiment of this invention. It is a figure explaining the mechanism in which a secondary battery charges / discharges. It is a figure explaining the mechanism in which a secondary battery deteriorates. It is a figure which shows the relationship between the alternating current impedance which concerns on embodiment of this invention, and a reversible capacity | capacitance. It is a flowchart which shows an example of the process in which the lifetime prediction apparatus which concerns on embodiment of this invention estimates the lifetime of a secondary battery. It is a flowchart which shows an example of the process in which the reversible capacity | capacitance estimation apparatus which concerns on embodiment of this invention estimates a reversible capacity | capacitance. It is a block diagram which shows the structure of the electrical storage system which concerns on other embodiment of this invention. It is a block diagram which shows the structure which implement | achieves the lifetime prediction apparatus or reversible capacity | capacitance estimation apparatus which concerns on embodiment of this invention with an integrated circuit.

  Hereinafter, a reversible capacity estimation device according to an embodiment of the present invention, a life prediction device including the reversible capacity estimation device, and a power storage system including the life prediction device will be described with reference to the drawings.

First, the configuration of the power storage system 10 will be described.
FIG. 1 is an external view of a power storage system 10 including a life prediction apparatus 100 according to an embodiment of the present invention.

  As shown in the figure, the power storage system 10 includes a life prediction apparatus 100, a plurality (six in the figure) secondary batteries 200, and a housing case 300 that houses the life prediction apparatus 100 and the plurality of secondary batteries 200. And.

  The life prediction apparatus 100 is a circuit board on which a circuit that is disposed above the plurality of secondary batteries 200 and predicts the life of the plurality of secondary batteries 200 is mounted. Specifically, the life prediction apparatus 100 is connected to a plurality of secondary batteries 200, acquires information from the plurality of secondary batteries 200, and has a chargeable / dischargeable capacity of the plurality of secondary batteries 200. By estimating the reversible capacity, the lifetimes of the plurality of secondary batteries 200 are predicted. The detailed functional configuration of the life prediction apparatus 100 will be described later.

  Here, the life prediction apparatus 100 is disposed above the plurality of secondary batteries 200, but the life prediction apparatus 100 may be disposed anywhere.

  The secondary battery 200 is a non-aqueous electrolyte secondary battery having a positive electrode and a negative electrode, for example, a lithium ion secondary battery. That is, the secondary battery 200 is, for example, a secondary battery in which the positive electrode is a lithium transition metal oxide such as lithium cobalt oxide and the negative electrode is a carbon material. In FIG. 6, six rectangular secondary batteries 200 are arranged in series to form an assembled battery. In addition, the number of the secondary batteries 200 is not limited to six, and may be another plural number or one. Further, the shape of the secondary battery 200 is not particularly limited.

Next, a detailed functional configuration of the life prediction apparatus 100 will be described.
FIG. 2 is a block diagram illustrating a functional configuration of the life prediction apparatus 100 including the reversible capacity estimation apparatus 110 according to the embodiment of the present invention.

  The life prediction apparatus 100 is an apparatus that predicts the life of the secondary battery 200. As shown in the figure, the life prediction device 100 includes a reversible capacity estimation device 110, a life prediction unit 120, and a storage unit 130.

  The reversible capacity estimation device 110 is a device that estimates a reversible capacity that is a chargeable / dischargeable capacity of the secondary battery 200. Here, the reversible capacity estimation device 110 includes an acquisition unit 111 and an estimation unit 112.

  The acquisition unit 111 acquires AC impedance at a predetermined frequency in the secondary battery 200. Specifically, the acquisition unit 111 measures AC impedance by applying an AC voltage or AC current having the predetermined frequency to the secondary battery 200, and acquires the measured AC impedance.

  The estimation unit 112 estimates the reversible capacity using the AC impedance acquired by the acquisition unit 111 and the linear relational expression indicating the relationship between the AC impedance and the reversible capacity. Specifically, the estimating unit 112 estimates the reversible capacity by calculating the reversible capacity by multiplying the AC impedance acquired by the acquiring unit 111 by a predetermined first constant and adding a predetermined second constant. . The predetermined first constant and the predetermined second constant in the linear relational expression indicating the relationship between the AC impedance and the reversible capacity will be described later. Then, the estimation unit 112 causes the storage unit 130 to store a value indicating the estimated reversible capacity.

  The storage unit 130 is a memory for storing information for estimating the reversible capacity and predicting the lifetime. Specifically, the storage unit 130 stores a linear relational expression indicating the relationship between the AC impedance and the reversible capacity, and a value indicating the reversible capacity estimated by the estimation unit 112 of the reversible capacity estimation device 110. Here, the storage unit 130 stores reversible capacity data 131 including a value indicating the reversible capacity. Details of the reversible capacity data 131 will be described later.

  The life prediction unit 120 refers to the value indicating the reversible capacity stored in the storage unit 130 and predicts the life of the secondary battery 200.

FIG. 3 is a diagram showing an example of the reversible capacity data 131 according to the embodiment of the present invention.
The reversible capacity data 131 is a collection of data indicating the reversible capacity for each date and time. That is, as shown in the figure, the reversible capacity data 131 is a data table in which “date and time” and “reversible capacity” are associated with each other. In “date and time”, the date and time when the estimation unit 112 estimates the reversible capacity is stored. In the “reversible capacity”, a value indicating the reversible capacity estimated by the estimation unit 112 at “date and time” is stored.

  Next, a linear relational expression indicating the relationship between the AC impedance and the reversible capacity used when the estimating unit 112 estimates the reversible capacity will be described in detail below.

First, the mechanism in which the secondary battery 200 is charged and discharged and deteriorates will be described.
FIG. 4 is a diagram illustrating a mechanism in which the secondary battery 200 performs charging and discharging.

  As shown in FIG. 2A, the secondary battery 200 includes a positive electrode P, a negative electrode N, and a separator between the positive electrode P and the negative electrode N. Here, the case where the secondary battery 200 is a lithium ion secondary battery will be described. That is, for example, the positive electrode P is a lithium transition metal oxide such as lithium cobalt oxide, and the negative electrode N is a carbon material. Further, the positive electrode P contains a lot of lithium ions x.

  And when the secondary battery 200 is charged, it changes from the state shown to (a) of the figure to the state shown to (b) of the figure. That is, lithium ions x move from the positive electrode P to the negative electrode N. By the movement of the lithium ions x, the amount of electricity for the moved capacity can be charged.

  Similarly, when the secondary battery 200 is discharged, a transition is made from the state shown in FIG. 5B to the state shown in FIG. That is, lithium ions x move from the negative electrode N to the positive electrode P. Due to the movement of the lithium ions x, it is possible to discharge an amount of electricity corresponding to the moved capacity.

  Thus, the lithium ion x reciprocates between the positive electrode P and the negative electrode N, whereby the secondary battery 200 can be charged / discharged. And when this charging / discharging is continued and repeated, secondary battery 200 deteriorates by side reactions other than charging / discharging reaction, and reversible capacity | capacitance reduces.

FIG. 5 is a diagram illustrating a mechanism in which the secondary battery 200 deteriorates.
Specifically, (a) of the figure shows a state of lithium ions x in an initial state before the secondary battery 200 repeats charging and discharging, and (b) of the figure shows a secondary battery. It is a figure which shows the state of the lithium ion x when 200 repeats charging / discharging and deteriorates.

  That is, when the charge / discharge described in FIG. 4 is repeatedly performed from the initial state shown in FIG. 4A, a lithium-containing coating X is formed on the negative electrode N as shown in FIG. ,grow up. Specifically, the lithium ion x contained in the positive electrode P is accumulated and grown on the negative electrode N by reciprocating between the positive electrode P and the negative electrode N, whereby the lithium-containing coating X is generated.

  Here, both the amount of decrease in the reversible capacity of the secondary battery 200 due to the generation of the lithium-containing coating X and the amount of increase in the internal resistance of the secondary battery 200 are both in the route of the charge / discharge period of the secondary battery 200. The so-called “root rule” is established.

  Since the growth rate of the lithium-containing coating X is proportional to the root of the charge / discharge period, the amount of increase in the thickness l of the lithium-containing coating X shown in FIG. Proportional to period root. For these reasons, the increase amount of the thickness l is proportional to the decrease amount of the reversible capacity of the secondary battery 200 and the increase amount of the internal resistance of the secondary battery 200.

  That is, when the thickness l increases and the number of lithium ions x that can reciprocate between the positive electrode P and the negative electrode N decreases, the reversible capacity of the secondary battery 200 decreases. Further, as the thickness l increases, the internal resistance of the secondary battery 200 increases.

  From the above, the reversible capacity Q of the secondary battery 200 due to the generation of the lithium-containing coating X is expressed by the following formula 1 using the thickness l of the lithium-containing coating X. In the following formula 1, M represents the lithium density in the lithium-containing coating X, and S represents a break when the lithium-containing coating X is cut along the YY line shown in FIG. The area is shown.

      Q = M × l × S (Formula 1)

Here, the internal resistance of the battery is composed of a plurality of types of resistances such as an electrolyte resistance, a charge transfer resistance, and a diffusion resistance in addition to the resistance corresponding to the lithium-containing coating X. The resistance component can change. When the influence of the resistance component that changes depending on the degree of deterioration of the battery other than the resistance corresponding to the lithium-containing coating X can be eliminated by selecting the predetermined frequency, the internal resistance R _AC of the secondary battery 200 is The negative electrode film resistance R _film indicating the resistance value of the lithium-containing film X and the other resistance R ₀ are expressed by the following formula 2.

R _AC = R _film + R ₀ (Formula 2)

Here, R _AC is the AC impedance of the secondary battery 200 measured when, for example, an AC voltage or AC current of 1 kHz is applied to the secondary battery 200. R ₀ is a constant.

Therefore, in order to measure the internal resistance R _AC in the above formula 2, it is necessary to select a predetermined frequency corresponding to the lithium-containing coating X. For example, a frequency as low as 0.1 Hz is not preferable because it is strongly influenced by the diffusion resistance in the solid phase. Here, the predetermined frequency is preferably 10 Hz to 5 kHz, more preferably 500 Hz to 2 kHz, and more preferably 1 kHz. The predetermined frequency does not need to be measured while changing a specific frequency range, and can be a fixed value such as 1 kHz.

  By selecting a predetermined frequency in this way, the measured impedance can effectively exclude most of the charge transfer resistance component and diffusion resistance component that change depending on the degree of deterioration, and the lithium-containing Impedance composed of a component corresponding to the coating X and an electrolyte resistance component considered to hardly change can be measured. It should be noted that the above preferred frequency range is at room temperature.

Further, the negative electrode film resistance R _film is expressed by the following formula 3 using the resistivity ρ of the lithium-containing film X, the thickness l of the lithium-containing film X, and the cross-sectional area S of the lithium-containing film X.

R _film = ρ · l / S (Formula 3)

Then, a linear relational expression indicating a relation between the _AC impedance R _AC and the reversible capacity Q of the secondary battery 200 as in the following Expression 4 is derived from the above Expressions 1 to 3. The following A and B are constants.

R _AC = A × Q + B (Formula 4)

  As described above, the inventors of the present application have derived the above-described Expression 4 as a result of intensive studies.

Next, a method for calculating the constants A and B by an experiment is illustrated by an example. First, a plurality of 600 mAh-class lithium ion secondary batteries using a mixture of LiMn ₂ O ₄ and Li [Co _1/3 Ni _1/3 Mn _1/3 ] O ₂ for the positive electrode and graphite for the negative electrode are prepared. did. Then, using the lithium ion secondary battery, a float charge life test at 45 ° C. is performed, and a plurality of lithium ions are in various deterioration states and in a 100% charge state (a charge state equivalent to the float test). A secondary battery was prepared, and a value of 1 kHz AC impedance and a value of reversible capacity were measured.

  Then, the relationship between 1 kHz AC impedance and reversible capacity was examined. In addition, 1 kHz alternating current impedance is alternating current impedance when measuring with the alternating voltage or alternating current whose frequency is 1 kHz.

  FIG. 6 is a diagram showing the relationship between the AC impedance and the reversible capacity according to the embodiment of the present invention.

That is, the figure is a graph showing experimental results in the experiment described above. Specifically, this figure is a graph showing the measured value of 1 kHz AC impedance R _{AC and} the value of reversible capacity Q for three lithium ion secondary batteries of the same type having different reversible capacities. It is a thing.

The inventors of the present application have found from this graph that the 1 kHz AC impedance R _AC and the reversible capacity Q are in a proportional relationship represented by the following Equation 5. That is, the following expression 5 indicates that the values of A and B in the above expression 4 are A = −0.32 and B = 260.

R _AC = −0.32Q + 260 (Formula 5)

In addition, the inventors of the present application have confirmed through experiments that the linear relational expression shown in Equation 5 above is substantially the same regardless of the test temperature in the normal temperature range (−20 ° C. to 60 ° C.). Therefore, the relationship of the above formula 5 is established between the 1 kHz AC impedance R _AC and the reversible capacity Q regardless of the test temperature. Therefore, the following expression 6 is derived from the above expression 5.

Q = −3.125R _AC +812.5 (Formula 6)

In this way, the reversible capacity Q is obtained by multiplying the 1 kHz AC impedance R _AC by the predetermined first constant (−3.125) and adding the predetermined second constant (812.5) using the above Equation 6. Therefore, the reversible capacity can be estimated without discharging the lithium ion secondary battery. Further, since the reversible capacity can be calculated by measuring the 1 kHz AC impedance, complicated measurement such as impedance measurement in a wide frequency range is unnecessary.

  Here, the linear relational expression shown in Expression 5 above is determined in advance by the user and stored in the storage unit 130. Note that the linear relational expression may not be stored in the storage unit 130, and the estimation unit 112 may be configured to perform the calculation of the expression 5 using a circuit configuration or a program.

  Note that the constants A and B in the linear relational expression shown in Equation 5 above are values that can be applied to the lithium ion secondary battery designed in the experiment, In other types of lithium ion secondary batteries, these values may be different. For this reason, it is applicable to various types of lithium ion secondary batteries by conducting the experiment for each type of lithium ion secondary battery and determining a mathematical expression corresponding to the above formula 5.

Next, the process in which the lifetime prediction apparatus 100 predicts the lifetime of the secondary battery 200 will be described.
FIG. 7 is a flowchart illustrating an example of a process in which the lifetime prediction apparatus 100 according to the embodiment of the present invention predicts the lifetime of the secondary battery 200.

  As shown in the figure, first, the reversible capacity estimation device 110 acquires a linear relational expression indicating the relationship between the AC impedance and the reversible capacity from the storage unit 130 (S102). For example, the reversible capacity estimation device 110 acquires the linear relational expression of Expression 5 stored in the storage unit 130.

  Then, the reversible capacity estimation device 110 estimates the reversible capacity, and stores the value indicating the estimated reversible capacity in the storage unit 130, thereby updating the reversible capacity data 131 (S104). A detailed description of the process in which the reversible capacity estimation apparatus 110 estimates the reversible capacity will be described later.

  Next, the life prediction unit 120 determines whether to predict the life (S106). For example, the life prediction unit 120 determines to predict the life when receiving an instruction to predict the life from the user. Moreover, you may determine with the lifetime prediction part 120 predicting a lifetime after progress of a fixed period so that a lifetime may be estimated regularly.

  If the life prediction unit 120 does not determine that the life is predicted (NO in S106), the reversible capacity estimation device 110 estimates the reversible capacity again and stores a value indicating the estimated reversible capacity in the storage unit 130. The reversible capacity data 131 is stored and updated (S104). Thus, the value indicating the reversible capacity is stored in the reversible capacity data 131 together with the date and time when the reversible capacity is estimated.

  If the life prediction unit 120 determines that the life is predicted (YES in S106), the life prediction unit 120 refers to the value indicating the reversible capacity of the reversible capacity data 131 stored in the storage unit 130, and Predict life.

  For example, the life prediction unit 120 generates a mathematical expression indicating the relationship between the date and time and the reversible capacity from the change over time in the value indicating the reversible capacity accumulated in the reversible capacity data 131, and calculates the date and time when the reversible capacity falls below a predetermined threshold. Thus, the lifetime of the secondary battery 200 is predicted. The life prediction unit 120 may predict the life by any method.

  Thus, the process of predicting the lifetime of the secondary battery 200 by the lifetime predicting apparatus 100 ends.

  Next, the process (S104 in FIG. 7) in which the reversible capacity estimation apparatus 110 estimates the reversible capacity will be described in detail.

  FIG. 8 is a flowchart showing an example of processing in which the reversible capacity estimation apparatus 110 according to the embodiment of the present invention estimates reversible capacity.

  As shown in the figure, first, the acquisition unit 111 applies an AC voltage or an AC current having a predetermined frequency to the secondary battery 200 (S202).

  And the acquisition part 111 acquires the alternating current impedance in the predetermined frequency in the secondary battery 200 (S204). Specifically, the acquisition unit 111 measures AC impedance obtained by applying an AC voltage or AC current having a predetermined frequency to the secondary battery 200, and acquires the measured AC impedance.

  Next, the estimation unit 112 estimates the reversible capacity (S206). Specifically, the estimation unit 112 reads a linear relational expression indicating the relationship between the AC impedance and the reversible capacity that is determined in advance and stored in the storage unit 130 from the storage unit 130. And the estimation part 112 calculates a reversible capacity | capacitance from the alternating current impedance which the acquisition part 111 acquired using the said numerical formula.

  Then, the estimation unit 112 stores a value indicating the estimated reversible capacity in the storage unit 130, and updates the reversible capacity data 131 illustrated in FIG. 3 (S208). Specifically, the estimation unit 112 updates the reversible capacity data 131 by writing the date and time when the reversible capacity is estimated and the value indicating the estimated reversible capacity in association with each other to the reversible capacity data 131.

  Thus, the process of reversible capacity estimation apparatus 110 estimating the reversible capacity (S104 in FIG. 7) ends.

  As described above, according to the reversible capacity estimation device 110 according to the embodiment of the present invention, the AC impedance indicating the internal resistance of the secondary battery 200 is acquired, and the acquired AC impedance, AC impedance, and reversible capacity are obtained. The reversible capacity of the secondary battery 200 is estimated using a linear relational expression indicating the above relationship. As a result, the reversible capacity can be estimated based on a linear relational expression indicating the relationship between the AC impedance and the reversible capacity, so that the error is not accumulated and the reversible capacity is accurately estimated in the long term. Can do. Moreover, since the reversible capacity at that time can be estimated by only obtaining the AC impedance at the time of estimation once using the simple linear relational expression, the estimation process is simple. For this reason, the reversible capacity which shows the deterioration state of the secondary battery 200 can be estimated easily accurately in the long term.

  Further, the reversible capacity of the secondary battery 200 is estimated by calculating the reversible capacity by multiplying the AC impedance by the first constant and adding the second constant. Here, the first constant and the second constant are numerical values derived based on experimental results, and are numerical values representing a linear relational expression that accurately indicates the relationship between the AC impedance and the reversible capacity. That is, since the reversible capacity is calculated by a linear relational expression using the numerical value, the reversible capacity can be estimated accurately over the long term. Further, by using the linear relational expression, the reversible capacity can be easily estimated from the AC impedance. For this reason, the reversible capacity which shows the deterioration state of the secondary battery 200 can be estimated easily accurately in the long term.

  Further, the AC impedance is measured by applying an AC voltage or AC current having a predetermined frequency to the secondary battery 200, and the measured AC impedance is obtained. Thereby, since AC impedance can be acquired simply and accurately, the reversible capacity indicating the deterioration state of the secondary battery 200 can be estimated easily and accurately over the long term using the AC impedance.

  Moreover, according to the lifetime prediction apparatus 100 according to the embodiment of the present invention, the lifetime of the secondary battery 200 is predicted using the value indicating the reversible capacity estimated by the reversible capacity estimation apparatus 110. For this reason, by predicting the lifetime of the secondary battery 200 using the reversible capacity estimated by the reversible capacity estimation device 110 accurately and easily in the long term, the predicted lifetime indicating the deterioration state of the secondary battery 200 is determined in the long term. It can be estimated easily with high accuracy.

  For example, a secondary battery as an emergency power source installed in a building or the like always stands by in a fully charged state in preparation for an emergency, but such an emergency secondary battery is subject to deterioration over time. The reversible capacity decreases. The degree of this aging deterioration is difficult to estimate because it varies depending on the environment such as the ambient temperature where the emergency secondary battery is installed. However, in order to confirm the current reversible capacity, the emergency secondary battery cannot be discharged. Therefore, the reversible capacity is estimated by the reversible capacity estimation device 110 according to the present invention, or the life is predicted by the life prediction device 100, thereby grasping the degree of deterioration of the secondary battery over time and the replacement time of the secondary battery. For example, it is possible to predict the lifetime for the future.

  The power storage system 10, the life prediction apparatus 100, and the reversible capacity estimation apparatus 110 according to the embodiment of the present invention have been described above, but the present invention is not limited to this embodiment.

  That is, the embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  For example, in the present embodiment, the power storage system 10 includes the life prediction apparatus 100. However, as illustrated in FIG. 9, the power storage system may include a reversible capacity estimation device 110 instead of the life prediction device 100. FIG. 9 is a block diagram showing a configuration of a power storage system 11 according to another embodiment of the present invention. As shown in the figure, the power storage system 11 includes a secondary battery 200 and a reversible capacity estimation device 110 that estimates the reversible capacity of the secondary battery 200.

  In addition, the present invention can be realized not only as the power storage system 10, the life prediction apparatus 100, or the reversible capacity estimation apparatus 110, but also as a characteristic processing unit included in the life prediction apparatus 100 or the reversible capacity estimation apparatus 110. It can also be realized as a life prediction method or a reversible capacity estimation method using the steps.

  In addition, each processing unit included in the life prediction apparatus 100 or the reversible capacity estimation apparatus 110 according to the present invention may be realized as an LSI (Large Scale Integration) that is an integrated circuit. That is, as shown in FIG. 10, the present invention can be realized as an integrated circuit 140 including an acquisition unit 111 and an estimation unit 112 or an integrated circuit 150 further including a life prediction unit 120. FIG. 10 is a block diagram illustrating a configuration in which the life prediction apparatus 100 or the reversible capacity estimation apparatus 110 according to the embodiment of the present invention is realized by an integrated circuit.

  Each processing unit included in the integrated circuit 140 or the integrated circuit 150 may be individually made into one chip, or may be made into one chip so as to include a part or all of them.

  The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

  Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI, or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.

  Furthermore, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. There is a possibility of adaptation of biotechnology.

  The present invention can also be realized as a program that causes a computer to execute characteristic processing included in the life prediction method or the reversible capacity estimation method. Needless to say, such a program can be distributed via a recording medium such as a CD-ROM and a transmission medium such as the Internet.

  The present invention can be applied to a reversible capacity estimation device, a life prediction device, and the like that can easily and accurately estimate the deterioration state of a nonaqueous electrolyte secondary battery over a long period of time.

DESCRIPTION OF SYMBOLS 10, 11 Power storage system 100 Life prediction apparatus 110 Reversible capacity estimation apparatus 111 Acquisition part 112 Estimation part 120 Life prediction part 130 Storage part 131 Reversible capacity data 140,150 Integrated circuit 200 Secondary battery 300 Storage case

Claims (9)

A reversible capacity estimation method in which a computer estimates a reversible capacity, which is a chargeable / dischargeable capacity of a nonaqueous electrolyte secondary battery,
An acquisition step of acquiring AC impedance at a predetermined frequency in the non-aqueous electrolyte secondary battery;
A reversible capacity estimation method comprising: an estimating step of estimating the reversible capacity using the acquired AC impedance and a linear relational expression indicating a relationship between the AC impedance and the reversible capacity. In the estimating step, the reversible capacity is estimated by calculating the reversible capacity by multiplying the AC impedance acquired in the acquiring step by a predetermined first constant and adding a predetermined second constant. Item 2. The reversible capacity estimation method according to Item 1. The said acquisition step measures the said alternating current impedance by applying the alternating voltage or alternating current of the said predetermined frequency to the said nonaqueous electrolyte secondary battery, and acquires the measured said alternating current impedance. Reversible capacity estimation method. A computer is a life prediction method for predicting the life of a non-aqueous electrolyte secondary battery,
Each step included in the reversible capacity estimation method according to any one of claims 1 to 3,
A storage step of storing a value indicating the reversible capacity estimated in the estimation step in a storage unit;
A life prediction method including a life prediction step of predicting a life of the non-aqueous electrolyte secondary battery with reference to a value indicating the reversible capacity stored in the storage unit. A reversible capacity estimation device for estimating a reversible capacity, which is a chargeable / dischargeable capacity of a nonaqueous electrolyte secondary battery,
An acquisition unit that acquires AC impedance at a predetermined frequency in the nonaqueous electrolyte secondary battery;
A reversible capacity estimation device comprising: an estimation unit that estimates the reversible capacity using the acquired AC impedance and a linear relational expression indicating a relationship between the AC impedance and the reversible capacity. A life prediction apparatus for predicting the life of a non-aqueous electrolyte secondary battery,
Reversible capacity estimation device according to claim 5,
A storage unit for storing a value indicating the reversible capacity estimated by the estimation unit;
A life prediction apparatus comprising: a life prediction unit that predicts a life of the non-aqueous electrolyte secondary battery with reference to a value indicating the reversible capacity stored in the storage unit. A non-aqueous electrolyte secondary battery;
The reversible capacity estimation apparatus according to claim 5 that estimates a reversible capacity that is a chargeable / dischargeable capacity of the nonaqueous electrolyte secondary battery, or the life of the nonaqueous electrolyte secondary battery according to claim 6. A power storage system comprising a life prediction device. An integrated circuit for estimating a reversible capacity, which is a chargeable / dischargeable capacity of a nonaqueous electrolyte secondary battery,
An acquisition unit that acquires AC impedance at a predetermined frequency in the nonaqueous electrolyte secondary battery;
An integrated circuit comprising: the obtained AC impedance; and an estimation unit that estimates the reversible capacity using a linear relational expression indicating a relationship between the AC impedance and the reversible capacity. further,
The integrated circuit according to claim 8, further comprising a life prediction unit that predicts a life of the non-aqueous electrolyte secondary battery using a value indicating the reversible capacity estimated by the estimation unit.

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