JP2023030370A - Device for estimating deterioration of lithium ion secondary battery and method for estimating battery capacity of lithium ion secondary battery - Google Patents

Abstract

To estimate the deterioration index of a secondary battery with high accuracy while using a simple method.SOLUTION: A positive electrode of a lithium ion secondary battery contains at least a positive electrode active material having two or more inflection points that shift to a range, in which the amount of voltage change is relatively small with respect to changes in a charging rate, from a range, in which the amount of voltage change is relatively large, when the charging rate is changed in at least one of a charging direction and a discharging direction between charging rates within a continuous range. A device for estimating the deterioration of the battery of an embodiment includes: an acquisition part acquiring a first capacitance value at a first inflection point and a second capacitance value at a second inflection point at a voltage different from a voltage at the first inflection point; a calculation part calculating the current full charge capacity based on the first capacitance value and the second capacitance value; and an estimation part estimating the deterioration state of the battery based on the current full charge capacity and the value of full charge capacity in the initial state of the battery.SELECTED DRAWING: Figure 7

Description

The present invention relates to technology for estimating deterioration of a lithium ion secondary battery.

2. Description of the Related Art In recent years, mobile cordless products such as mobile phones, notebook personal computers, and video cameras are becoming more and more compact and portable. In addition, from the viewpoint of environmental problems such as air pollution and increased carbon dioxide, the development of electric vehicles such as hybrid vehicles, electric vehicles, electric ships, and small aircraft such as drones is progressing, and it is at the stage of practical use. It has become. These electronic devices and electric vehicles such as electric vehicles require excellent secondary batteries having characteristics such as high efficiency, high output, high energy density, and light weight. Furthermore, as a means for efficiently storing electricity generated by nighttime power or natural energy such as sunlight, the effective use of secondary batteries is attracting attention. Development and research on secondary batteries having such characteristics have been actively carried out, and various secondary batteries such as lithium batteries and lithium ion batteries have been put to practical use.

The lithium-ion battery described above tends to have a lower usable electrical capacity depending on the storage environment such as temperature, state of charge, and number of charge/discharge cycles. However, it is extremely important for the operation of a system using a secondary battery as a drive source. Therefore, various techniques have been proposed for estimating the state of deterioration of lithium ion batteries.
For example, a method has been attempted in which battery usage history information is stored and the state of deterioration (SOH) is estimated using a model created based on the usage history information.
In addition, by utilizing the fact that the shape of the differential curve with parameters of the battery capacity and battery voltage during charging and discharging of the secondary battery varies depending on the deterioration state of the secondary battery, the transition of characteristic points appearing on the differential curve and the A method of estimating the deterioration index of the secondary battery based on the amount of change has also been proposed.

JP 2016-184528 A

However, in the method of estimating the state of deterioration (SOH) of a lithium-ion battery using a model created based on usage history information, in order to store a huge amount of usage history information about the battery itself, Information stored in a large-scale storage device or in a system such as the cloud must be sent and received using communication means each time, considering the increase in the size of the device and the increase in the load on the communication means. Hard to say practical. In addition, since a huge amount of usage history information is handled, the calculation tends to be complicated, and there is a problem that the load on the processor increases and the calculation of the estimation result takes time.
On the other hand, in the method of estimating the deterioration index of the secondary battery based on the transition and the amount of change of the characteristic points appearing on the differential curve, the setting of ΔV when differentiating the measured value is inappropriate, and noise etc. Therefore, it is difficult to automatically determine the difference in the shape of the differential curve, and it is hard to say that it is a practical estimation means.

The present invention has been made to solve the above-described problems, and an object of the present invention is to estimate the deterioration index of a secondary battery with high accuracy using a simple method. It is to provide a system.

A first aspect of the present invention is a deterioration estimating device for estimating deterioration of a lithium ion secondary battery, wherein the lithium ion secondary battery includes a positive electrode having a positive electrode active material layer formed on a positive electrode current collector. a negative electrode having a negative electrode active material layer formed on a negative electrode current collector; A positive electrode having two or more inflection points where, when at least one of them is changed, a range in which the amount of voltage change is relatively large with respect to a change in the charging rate shifts to a range in which the amount of voltage change is relatively small. The device includes at least an active material, a first capacitance value at a first inflection point, a second capacitance value at a second inflection point different in voltage from the first inflection point, , a calculation unit that calculates the current full charge capacity based on the first capacity value and the second capacity value that the acquisition unit acquires, and the current current calculated by the calculation unit an estimating unit that estimates the state of deterioration of the lithium ion secondary battery based on the value of the full charge capacity and the value of the full charge capacity in the initial state of the lithium ion secondary battery. This is a device for estimating the deterioration of the next battery.

A second aspect of the present invention is that when the charge rate or discharge rate in a continuous range of the battery is changed in a certain direction, the range in which the amount of change in voltage is relatively large with respect to the change in the charge rate or discharge rate From, a battery capacity estimation method for a lithium ion secondary battery containing a positive electrode active material having two or more inflection points where the amount of change in voltage shifts to a relatively small range, wherein the first at the first inflection point obtaining a first capacitance value and a second capacitance value at a second inflection point different in voltage from the first inflection point, and obtaining the first capacitance value and the second capacitance value; Based on the current full charge capacity is calculated, and based on the calculated current full charge capacity value and the full charge capacity value in the initial state of the lithium ion secondary battery, the lithium ion secondary battery and estimating the deterioration state of the lithium-ion secondary battery.

A third aspect of the present invention is a deterioration estimating device for estimating deterioration of a lithium ion secondary battery, wherein the lithium ion secondary battery includes a positive electrode having a positive electrode active material layer formed on a positive electrode current collector. a negative electrode having a negative electrode active material layer formed on a negative electrode current collector; A positive electrode having two or more inflection points where, when at least one of them is changed, a range in which the amount of voltage change is relatively large with respect to a change in the charging rate shifts to a range in which the amount of voltage change is relatively small. a first voltage value at a first inflection point; a second voltage value at a second inflection point different in voltage from the first inflection point; an acquisition unit that acquires the current full charge capacity calculated by the calculation unit based on the first voltage value and the second voltage value acquired by the acquisition unit; an estimating unit that estimates the state of deterioration of the lithium ion secondary battery based on the value of the full charge capacity and the value of the full charge capacity in the initial state of the lithium ion secondary battery. This is a device for estimating the deterioration of the next battery.

A fourth aspect of the present invention is a deterioration estimating device for estimating deterioration of a lithium ion secondary battery, wherein the lithium ion secondary battery includes a positive electrode having a positive electrode active material layer formed on a positive electrode current collector. a negative electrode having a negative electrode active material layer formed on a negative electrode current collector; A positive electrode having two or more inflection points where, when at least one of them is changed, a range in which the amount of voltage change is relatively large with respect to a change in the charging rate shifts to a range in which the amount of voltage change is relatively small. The device includes at least an active material, and the device has a first capacity value at a first inflection point and a second capacity value at a voltage different from the first inflection point when the lithium ion secondary battery is in use. A first acquisition unit that acquires a second capacitance value at an inflection point, a third capacitance value at the first inflection point in the initial state of the lithium ion secondary battery, and the second a fourth capacitance value at the point of inflection, a second acquisition unit that acquires a difference between the first capacitance value and the third capacitance value, and the second capacitance value and the fourth capacitance an estimating unit for estimating that the lithium ion secondary battery is in a more deteriorated state when the difference from the value is large than when the difference is small. .

According to one aspect of the present invention, the deterioration index of a secondary battery can be estimated with high accuracy using a simple method.

FIG. 4 is a diagram showing charge/discharge curves according to the number of cycles of the secondary battery cell of one embodiment; FIG. 2 is a diagram showing charge/discharge curves according to the number of cycles of the secondary battery cell of one embodiment at temperatures different from those in FIG. 1 ; FIG. 4 is a diagram showing discharge curves and charge curves of secondary battery cells when the LMFP content of the positive electrode active material is different. 4 is a diagram showing charge-discharge curves of a secondary battery cell using a positive electrode active material different from that in FIG. 3; FIG. It is a figure which shows the structure of the battery degradation estimation apparatus of one Embodiment. It is a figure which shows the map data stored in the battery degradation estimation apparatus of one Embodiment. It is a flow chart which shows operation of a battery degradation estimating device of one embodiment.

In a secondary battery (hereinafter referred to simply as “battery” as appropriate) using a phosphate-based positive electrode active material having an olivine structure (lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP)), discharge It is known that a plateau region appears in the vicinity of a voltage of 3.3 to 3.5 V, where there is almost no change in voltage with respect to a certain change in capacitance. Among them, batteries using lithium manganese iron phosphate as a positive electrode active material have a larger capacity than batteries using lithium iron phosphate, which similarly exhibits a plateau region during discharge, and are suitable for increasing the energy density of batteries. ing.

In a lithium-ion secondary battery that uses a mixture of a layered metal oxide and a phosphate-based positive electrode active material, the relationship between the cell capacity and the cell voltage in the initial stage of charging and the final stage of charging, and the initial stage of discharging and the final stage of discharging. An inflection point due to the above plateau region occurs on the charge-discharge curve showing .
Although the layered metal oxide is not limited, examples thereof include lithium nickel manganese cobalt oxide (hereinafter referred to as “NMC”), which is a lithium metal composite oxide having a layered structure. As a result of intensive research, the inventors of the present application have found that by using a mixture of a layered metal oxide and a phosphate-based positive electrode active material as a positive electrode active material, the charge-discharge cycle progress of a lithium ion secondary battery can be improved. Since the point of inflection moves along with , it was found that the state of deterioration of the battery can be estimated by monitoring this point of inflection.

It should be noted that mixing NMC with a phosphate-based positive electrode active material is convenient in the following respects.
The inflection point derived from the phosphate-based positive electrode active material is slightly lower than the voltage corresponding to the cell capacity set as the end-of-discharge state when using a positive electrode in which NMC and a phosphate-based positive electrode active material are mixed. Since it appears around high 3.2 to 3.5V, it is easy to monitor. again. Since the difference between the specific capacity of NMC and the specific capacity of lithium manganese phosphate is small, even if both are used in combination, the energy density does not decrease significantly.
Therefore, when NMC is mixed with a phosphate-based positive electrode active material, the effect of the present application is particularly exhibited. Among the phosphate-based positive electrode active materials, it is preferable to use lithium manganese iron phosphate as the positive electrode active material because a battery with a large capacity can be realized.

The lithium manganese iron phosphate contained in the positive electrode active material is preferably represented by the chemical formula (1).
[Chemical Formula 1] _{LiwFevMn (1-v) PO4} (0.5<w<1.5 _, 0.20≤v≤0.
55) Chemical formula (1)
Here, it is preferable that 0.5<w<1.5, considering the amount of lithium intercalated and deintercalated during charge and discharge.
The reason for setting 0.20≦v≦0.55 is that when v is within this range, it is easy to detect an inflection point on the charge/discharge curve, as will be described later.

FIG. 1 shows a battery cell using a positive electrode in which an active material layer is formed using lithium manganese iron phosphate (Li _w Fe _v Mn _(1-v) PO ₄ ) as a positive electrode active material under predetermined conditions. The measurement result of a charge-discharge curve is shown. In the lithium iron manganese phosphate used here, v=0.3 in Li _w Fe _v Mn _(1-v) PO ₄ .

FIG. 1 shows the characteristics in each of the 100th, 400th, 800th, and 1600th charge and discharge cycles in the charge/discharge cycle. From Fig. 1, in the charging curve, the "first inflection point (charging)" on the low voltage side and the "second inflection point (charging)" on the high voltage side occur at the beginning of charging and the end of charging, respectively. However, in the discharge curve, the “first inflection point (discharge)” on the high voltage side and the “second inflection point (discharge)” on the low voltage side occur at the beginning of the discharge and the end of the discharge, respectively. I understand. Moreover, it can be seen that these inflection points move as the charge/discharge cycle progresses. Specifically, both inflection points shift to the left in FIG. 1 as the cycle progresses.

Therefore, we monitor changes in the low-voltage side inflection point (“first stage inflection point (charging)”) and high-voltage side inflection point (“second stage inflection point (charging)”) on the charging curve. By doing so, the degree of deterioration of the battery cell can be estimated. For example, the capacitance value (Qc1 _INT ) at the low voltage side inflection point and the capacitance value (Qc2 _INT ) at the high voltage side inflection point in the initial state (for example, the first charging cycle) are stored, and the current The capacitance value (Qc1 _CUR ) at the low voltage side inflection point during charging and the capacitance value (Qc2 _CUR ) at the high voltage side inflection point are specified and compared. That is, when the difference between Qc1 _INT and Qc1 _CUR and the difference between Qc2 _INT and Qc2 _CUR are large, it can be determined that the battery cell is in a more deteriorated state than when the difference is small.
In the following description, the capacitance value at the point of inflection will be referred to as "inflection point capacitance value" as appropriate.

Similarly, the change in the high voltage side inflection point (“first stage inflection point (discharge)”) and the low voltage side inflection point (“second stage inflection point (discharge)”) in the discharge curve By monitoring , the degree of deterioration of the battery cell can be estimated.
It is preferable to monitor the capacity at the inflection point when the battery cells are being charged. This is because the measured inflection point capacity value tends to fluctuate depending on the environment such as the state of the load and the temperature when the battery cell is discharged, but a stable inflection point capacity value can be obtained during charging.

From another point of view, the current cycle number of the battery cell can be estimated by monitoring the change in the inflection point from the initial state. For example, the number of cycles (N), the relationship between the low-voltage side inflection point capacitance value Qc1 _N and the high-voltage side inflection point capacitance value Qc2 _N in the number of N-th charging cycles, and the number of cycles (N) and , the relationship between the inflection point capacitance value _Qd1N on the high voltage side and the inflection point capacitance value _Qd2N on the low voltage side at the N-th discharge cycle number is stored as map data. Then, the current low voltage side inflection point capacitance value Qc1 _CUR and the high voltage side inflection point capacitance value Qc2 _CUR during charging, and/or the current high voltage side inflection point capacitance value Qd1 during discharging By acquiring _CUR and the inflection point capacity value Qd2 _CUR on the low voltage side and referring to the map data, the current cycle number of the battery cell can be identified.
Since such processing is performed based on the current charge/discharge curve, the number of cycles can be specified even for a battery whose detailed usage history is unknown.

The current full charge capacity of the battery cell can be obtained by applying the specified number of cycles to known methods. By storing the initial full charge capacity in a memory, for example, the SOH of the battery cell can be estimated based on the initial full charge capacity and the current full charge capacity.
Such a method of estimating the SOH of a battery cell can be performed with high accuracy by detecting an inflection point in a charge/discharge curve, and does not require complicated calculations.

In the example shown in FIG. 1, at the inflection points on the low voltage side (“1st stage inflection point (charge)” and “2nd stage inflection point (discharge)”), the monitor voltage increases as the cycle progresses. It's getting harder. However, when estimating the state of deterioration of the battery, the low voltage side inflection point and the high voltage side inflection point in the charge curve illustrated in FIG. It is sufficient if at least part of the four inflection points of the curve point can be monitored. Therefore, even if some of the four inflection points become difficult to monitor, this does not impede the estimation of the state of deterioration of the battery.

FIG. 2 shows measurement results of charge-discharge curves under the same conditions as in FIG. 1 for a battery cell using a positive electrode in which an active material layer is formed using the same lithium manganese iron phosphate as the positive electrode active material as in FIG. However, the temperature conditions (battery temperature is 25° C. in FIG. 1 and 45° C. in FIG. 2) are different from FIG. In addition, FIG. 2 shows the characteristics in each of the 100th and 800th charge and discharge cycles in the charge/discharge cycle.
As shown in FIG. 2, even in an environment with a temperature higher than that in FIG. 1, a low voltage side inflection point and a high voltage side inflection point occur in the charging curve, It can be seen that an inflection point occurs on the low voltage side, and the inflection point shifts to the left in FIG. 2 as the charge/discharge cycle progresses.

Comparing FIG. 1 and FIG. 2, it can be seen that cycle deterioration is greater in a high temperature (45° C.) environment than in a relatively low temperature (25° C.) environment. Therefore, when calculating the deterioration index such as SOH of the battery cell from the charge/discharge curve, it is preferable to consider the temperature of the battery cell.

FIG. 3 shows measurement results of charge/discharge curves of battery cells using positive electrodes in which active material layers are formed using different positive electrode active materials.
In FIG. 3, as a battery cell according to the comparative example, a battery cell using a positive electrode in which an active material layer is formed using only NMC532 (LiNi _0.5 Mn _0.3 Co _0.2 O ₂ ) as a positive electrode active material is shown. Discharge curves and charge curves (NMC532 only) are shown as solid lines. In FIG. 3, as a battery cell according to one embodiment, when the total weight of the positive electrode active material is 100 parts by weight, 80 parts by weight of NMC532 and 20 parts by weight of lithium manganese iron phosphate (LMFP) are mixed to form an active material. Discharge and charge curves (NMC532:LMFP=80:20) of a battery cell with a layered positive electrode are shown by dashed lines. In FIG. 3, when the total weight of the positive electrode active material is 100 parts by weight, 60 parts by weight of NMC532 and 40 parts by weight of lithium manganese iron phosphate (LMFP) are mixed as an active material in a battery cell according to an embodiment. Discharge and charge curves (NMC532:LMFP=60:40) of a battery cell using a layered positive electrode are indicated by dashed lines.

As shown in FIG. 3, in a battery cell using a positive electrode in which an active material layer that does not contain lithium manganese iron phosphate (LMFP) is used as a positive electrode active material, none of the four inflection points occurs. It becomes difficult to estimate the state of deterioration of the battery based on the discharge curve.
On the other hand, in a battery cell using a positive electrode in which an active material layer containing lithium manganese iron phosphate (LMFP) is formed as a positive electrode active material, the low voltage side inflection point, the high voltage side inflection point, Also, four inflection points, a high-voltage side inflection point and a low-voltage side inflection point, occur in the discharge curve. Therefore, it is possible to estimate the state of deterioration of the battery by monitoring the change in the inflection point with the lapse of charge/discharge cycles. As shown in FIG. 3, the inflection point capacity value varies depending on the ratio of lithium manganese iron phosphate (LMFP) contained in the active material layer.

FIG. 4 shows charge-discharge curves for lithium manganese iron phosphate (LFMP) with different Mn content ratios. In FIG. 4, the horizontal axis represents the specific capacity, and the vertical axis represents the cell voltage. In FIG. 4, in Li _w Fe _v Mn _(1-v) PO ₄ , the case where the Mn content ratio is 70% is indicated by a solid line, and the case where the Mn content ratio is 45% is indicated by a dotted line.
As shown in FIG. 4, at any content ratio of Mn, at least a high voltage side inflection point occurs in the discharge curve, and a low voltage side inflection point and a high voltage side inflection point occur in the charge curve. do. Although not shown, it has been confirmed that there is an inflection point in the charge/discharge curve when the Mn content ratio is in the range of at least 45 to 80%.

Next, a battery deterioration estimating device 1 for a lithium ion secondary battery (hereinafter simply referred to as "battery deterioration estimating device 1") according to one embodiment will be described with reference to FIG. A battery deterioration estimation device 1 is connected to a battery module 2 and configured to estimate SOH, which is an example of a deterioration index of the battery module 2 .
The battery module 2 is, for example, a module formed by connecting a plurality of battery cells in series and/or in parallel. Each battery cell uses a positive electrode active material in which lithium manganese iron phosphate is mixed with NMC532, and has the inflection point described above. Note that the charge/discharge curves of the battery cells included in the battery module 2 are generally the same, and it can be assumed that the deterioration characteristics of the battery cells are also the same.

As shown in FIG. 5 , the battery deterioration estimating device 1 includes a processor 11 , a storage device 12 , a cell monitoring section 13 and a communication section 14 .
The processor 11 controls the operation of the battery deterioration estimation device 1 by executing a predetermined program.
The storage device 12 (an example of a storage unit) is a non-volatile memory and stores map data and values of full charge capacity of battery cells. The value of the full charge capacity is recorded in the storage device 12, for example, when the battery module 2 is manufactured.

The map data includes the number of cycles (N), the low voltage side inflection point capacitance value Qc1 _N and the high voltage side inflection point capacitance value Qc2 _N in the Nth charge cycle number, and the Nth discharge cycle number. , the inflection point capacitance value Qd1 _N on the high voltage side and the inflection point capacitance value Qd2 _N on the low voltage side are described. The capacity values described in the map data are, for example, representative values measured in advance for battery cells.
In one embodiment, the map data is cycled from each inflection point capacitance value (same as Qc1 _INT , Qc2 _INT , Qd1 _INT , Qd2 _INT described above) in the initial state when N=1, as shown in FIG. Includes data on the amount of change (decrease) of each inflection point capacitance value when the number advances.

The storage device 12 stores the value (FCC _INT ) of the full charge capacity in the initial state of the battery cell. The value of this full charge capacity is obtained, for example, at the time of manufacture of the battery cell and recorded in the storage device 12 .

The cell monitoring unit 13 is a part that monitors the state of each battery cell of the battery module 2 and includes a voltage sensor 131 and a current sensor 132 .
The voltage sensor 131 is configured to detect the charging voltage (closed circuit voltage) of the battery cell. Current sensor 132 is configured to detect the current flowing through the battery cell.
Detection signals from the voltage sensor 131 and the current sensor 132 are sent to the processor 11 sequentially.

The communication unit 14 communicates with a charging device (not shown) during charging of the battery module 2 using a communication protocol conforming to a predetermined charging specification. It functions as a communication interface that communicates with a communication protocol.

The processor 11 executes the programs to function as the following units (i) to (iii).
(i) an acquisition unit for acquiring the current low voltage side and high voltage side inflection point capacitance values (ii) based on the current low voltage side and high voltage side inflection point capacitance values acquired by the acquisition unit, Calculation unit for calculating the current full charge capacity (iii) The current full charge capacity value (FCC _CUR ) calculated by the calculation unit and the value of the full charge capacity in the initial state of the battery cell stored in the storage device 12 An estimating unit that estimates SOH (=FCC _CUR /FCC _INT ) as the deterioration state of the battery cell based on (FCC _INT )

In (i), the processor 11 has an A/D converter that receives detection signals from the voltage sensor 131 and the current sensor 132 and converts each detection signal into a digital signal. The processor 11 calculates the inflection point capacitance values on the low voltage side and the high voltage side based on the digital signal of each detection signal.
For example, when specifying an inflection point while charging the battery module 2, the elapsed time (t) from the start of charging, the voltage (V) of the battery cell, and the current (I) flowing through the battery cell are monitored. In the charging curve as illustrated in FIG. 1, the cell capacity on the horizontal axis is equivalent to It. Therefore, by monitoring the elapsed time (t) and the voltage (V) and current (I) of the battery cell, it is possible to discretely reproduce the charging curve when performing processing by the processor 11 .
Here, since the inflection point occurs when the sign of the second order differential of the charge curve or the discharge curve changes, the inflection point can be detected at the timing when the sign changes. In other words, the point of inflection can be detected at the timing when the sign of the rate of change of the slope V/(I·t) in the charge curve or the discharge curve changes. The value of I·t when the inflection point occurs is the inflection point capacitance value.

When acquiring the inflection point capacitance value, whether the inflection point is the low voltage side inflection point or the high voltage side inflection point is determined based on the cell voltage V when the inflection point occurs. can be discriminated. For example, when the cell voltage V when the inflection point occurs is in the range of 4.0 V to 4.2 V, the inflection point is determined to be the high voltage side inflection point, and the inflection point occurs When the cell voltage V at that time is in the range of 3.3V to 3.5V, it is determined that the inflection point is the low voltage side inflection point.
In addition, for each of the low-voltage side inflection point and the high-voltage side inflection point, depending on the charge curve or the discharge curve, there may be cases where two or more inflection points are detected. The point of inflection to be determined may be specified as the point of inflection on the low voltage side or the point of inflection on the high voltage side.

Next, the process of estimating the SOH of the battery module 2 in the battery deterioration estimation device 1 of one embodiment will be described with reference to the flowchart of FIG.
The flowchart of FIG. 7 is executed by the processor 11 of the battery deterioration estimation device 1 when charging the battery module 2 as an example.

Referring to FIG. 7, the processor 11 obtains the closed circuit voltage (V) and current (I) values of the battery cells from the voltage sensor 131 and the current sensor 132, respectively, during charging of the battery module 2, and calculates the charge/discharge curve. It is determined that an inflection point is detected at the timing when the sign of the rate of change of V/(I·t), which is the slope of , changes.
When charging the battery module 2, the low voltage side inflection point is first detected (step S2: YES), and the inflection point capacity value (Qc1 _CUR ) corresponding to the low voltage side inflection point is acquired and recorded in the memory. (step S4). As described above, in order to more reliably detect the low-voltage side inflection point, it is preferable to set the cell voltage within a predetermined range as a detection condition.
Next, when charging progresses and the cell voltage increases, the processor 11 detects the high voltage side inflection point (step S6: YES), and the inflection point capacitance value (Qc2 _CUR ) is obtained and recorded in the memory (step S8). As described above, in order to more reliably detect the inflection point on the high voltage side, it is preferable to set the condition for detection that the cell voltage is within a predetermined range.

After acquiring the low voltage side inflection point capacitance value Qc1 _CUR and the high voltage side inflection point capacitance value Qc2 _CUR , the processor 11 calculates the SOH of the battery cells of the battery module 2 as follows.
First, the processor 11 refers to the map data (FIG. 6), and corresponds to the acquired inflection point capacitance value (Qc1 _CUR ) on the low voltage side and the acquired inflection point capacitance value (Qc2 _CUR ) on the high voltage side. The number of cycles (current number of cycles) is estimated (step S10). That is, in the map data (FIG. 6) stored in the storage device 12, the decrease in each inflection point capacitance value when the number of cycles progresses from each inflection point capacitance value in the initial state when N=1. Contains quantity data. Therefore, the processor 11 calculates the difference between the inflection point capacitance value in the initial state and the inflection point capacitance values acquired in steps S4 and S8 ((Qc1 _INT −Qc1 _CUR ) and (Qc2 _INT −Qc2 _CUR )). The corresponding number of cycles is specified by referring to the map data (FIG. 6).

Next, the processor 11 calculates the current full charge capacity value (FCC _CUR ) based on the current cycle number estimated in step S10 (step S12). A known method can be adopted as a method of calculating the full charge capacity from the number of cycles. For example, the number of cycles may be calculated by referring to a lookup table showing the relationship between the number of cycles and the full charge capacity. The number of cycles may be calculated from a model formula assuming that there is a relationship of

The processor 11 acquires the full charge capacity value (FCC _INT ) in the initial state of the battery cell from the storage device 12 by reading it (step S14), and calculates the SOH (=FCC _CUR /FCC _INT ) of the battery cell ( step S16).

Although the process when the battery module 2 is charged has been described with reference to FIG. 7, the same process can be performed when the battery module 2 is discharged. That is, when the battery module 2 discharges, the processor 11 detects the high-voltage side inflection point and the low-voltage side inflection point in this order to determine the high-voltage side inflection point capacity value (Qd1 _CUR ). and the inflection point capacitance value (Qd2 _CUR ) on the low voltage side. The processor 11 refers to the map data (FIG. 6) based on the difference between the obtained inflection point capacitance value and the initial state value ((Qd1 _INT −Qd1 _CUR ) and (Qd2 _INT −Qd2 _CUR )). , to identify the corresponding cycle numbers.

As described above, according to the battery deterioration estimating device of one embodiment, two inflection points occurring in the charge curve or the discharge curve during charging or discharging of the battery cell are detected, and corresponding to the two inflection points Get the inflection point capacitance value. The current full charge capacity of the battery cell is calculated based on the acquired inflection point capacity value, and the deterioration state of the battery cell such as SOH is determined based on this current full charge capacity and the initial state full charge capacity. presume.
That is, the battery degradation estimation device of one embodiment can estimate the SOH of a battery cell using an inflection point appearing in a charge curve or a discharge curve, and information on the usage history of the battery cell is necessary when estimating the SOH of the battery cell. do not have. Therefore, the SOH of the battery cell can be estimated even if the usage history of the battery cell is unknown.
Since the calculation load for calculating the inflection point capacity value is low, the battery deterioration estimation apparatus does not require a high-performance processor, and can estimate the SOH at high speed.
In addition, since the inflection point is not easily affected by measurement noise, it is possible to calculate the SOH with high accuracy as a result.

In FIG. 6, the map data includes data on the variation (decrease amount) of each inflection point capacitance value when the cycle number advances from each inflection point capacitance value in the initial state when N=1. However, it is not limited to that. If the same type of battery cells are used, the inflection point capacity values corresponding to each cycle are considered to have almost no variation. You can also try to When the map data is configured in such a manner, the map data is referenced to identify the cycle number corresponding to the inflection point capacitance value that approximately matches the detected inflection point capacitance value.

In one embodiment, cell monitor 13 may comprise a temperature sensor.
As shown in FIGS. 1 and 2, the higher the temperature, the more likely the battery cells are to deteriorate. In other words, the higher the temperature, the greater the amount of change in the inflection point capacitance value from the initial state even if the number of cycles is the same. may be corrected. For example, a plurality of map data of temperature differences are stored in the storage device 12, and based on the temperature obtained from the temperature sensor, the map data corresponding to the temperature in the typical usage environment of the battery cell is referred to, and the number of cycles is determined. identify. As a result, the number of cycles is specified in consideration of the temperature environment of the battery cell, so that the accuracy of the SOH calculated by the battery deterioration estimating device 1 is further improved.

In the battery deterioration estimating device of one embodiment, the inflection point voltage value may be obtained instead of the inflection point capacity value, and the deterioration state of the battery cell may be estimated based on the obtained inflection point capacity value. As shown in Figures 1 to 4, as the number of cycles progresses, the cell voltage corresponding to the inflection point in the charge/discharge curve also changes, so obtaining the inflection point voltage value can also estimate the state of deterioration of the battery cell. can.
In that case, the processor of the battery deterioration estimation device may be configured to function as the following units (iv) to (vi) by executing the program.
(iv) an acquisition unit for acquiring the current low-voltage side and high-voltage side inflection point voltage values; (v) based on the current low-voltage side and high-voltage side inflection point voltage values acquired by the acquisition unit, Calculation unit for calculating the current full charge capacity (vi) The current full charge capacity value (FCC _CUR ) calculated by the calculation unit and the full charge capacity value in the initial state of the battery cell stored in the storage device ( FCC _INT ) and an estimating unit that estimates SOH (=FCC _CUR /FCC _INT ) as the deterioration state of the battery cell

As described above, in the charging cycle, the low voltage side inflection point capacitance value (Qc1 _INT ; an example of the third capacitance value) in the initial state and the current low voltage side inflection point capacitance value (Qc1 _CUR ; An example of the first capacitance value) is large, it can be determined that the battery cell is more deteriorated than when the difference is small. In the charging cycle, the initial high-voltage side inflection point capacitance value (Qc2 _INT ; an example of a fourth capacitance value) and the current high-voltage side inflection point capacitance value (Qc2 _CUR ; second capacitance value For example), if the difference is large, it can be determined that the battery cell is more deteriorated than if the difference is small.
Similarly, in the discharge cycle, the high voltage side inflection point capacitance value in the initial state (Qd1 _INT ; an example of the fourth capacitance value) and the current high voltage side inflection point capacitance value (Qd1 _CUR ; second (an example of the capacitance value of ) is large, it can be determined that the battery cell is in a state of deterioration more than when the difference is small. In the discharge cycle, the initial low-voltage side inflection point capacitance value (Qd2 _INT ; an example of a third capacitance value) and the current low-voltage side inflection point capacitance value (Qd2 _CUR ; first capacitance value For example), if the difference is large, it can be determined that the battery cell is more deteriorated than if the difference is small.
That is, by monitoring the difference between the inflection point capacity value in the initial state of the battery cell and the inflection point capacity value in the current use state of the battery cell, the relative degree of deterioration can be determined.

Therefore, in the battery degradation estimation device of one embodiment, the processor may be configured to function as the following units (vii) to (ix) by executing a program.
(vii) Acquiring the low voltage side inflection point capacity value (first capacity value) and the high voltage side inflection point capacity value (second capacity value) in the usage state of the battery cell First acquisition unit (viii) Low-voltage side inflection point capacity value (third capacity value) in the initial state of the battery cell and High-voltage side inflection point capacity value (third capacity value) in the initial state of the battery cell (ix) the difference between the first capacitance value and the third capacitance value and the difference between the second capacitance value and the fourth capacitance value are large , the estimation unit estimates that the battery cell is in a state of deterioration compared to when

Although the embodiments of the lithium ion secondary battery degradation estimation device and the lithium ion secondary battery battery capacity estimation method of the present invention have been described above, the present invention is not limited to the above embodiments. Also, the above embodiments can be modified and modified in various ways without departing from the gist of the present invention. For example, individual technical features described in each of the embodiments and modifications described above can be appropriately combined as long as there is no technical contradiction.

DESCRIPTION OF SYMBOLS 1... Battery deterioration estimation apparatus 2... Battery module 11... Processor 12... Storage device 13... Cell monitoring part 131... Voltage sensor 132... Current sensor 14... Communication part

Claims (9)

A deterioration estimation device for estimating deterioration of a lithium ion secondary battery,
The lithium ion secondary battery includes at least a positive electrode having a positive electrode active material layer formed on a positive electrode current collector, a negative electrode having a negative electrode active material layer formed on a negative electrode current collector, and an electrolytic solution,
The positive electrode has a range in which the amount of voltage change is relatively large with respect to the change in the charging rate when the charging rate is changed in at least one of the charging direction and the discharging direction between charging rates in a continuous range. From, at least a positive electrode active material having two or more inflection points where the amount of change in voltage shifts to a relatively small range,
The device comprises:
an acquisition unit that acquires a first capacitance value at a first inflection point and a second capacitance value at a second inflection point having a different voltage from the first inflection point;
a calculation unit that calculates a current full charge capacity based on the first capacitance value and the second capacitance value obtained by the obtaining unit;
an estimating unit for estimating the deterioration state of the lithium ion secondary battery based on the current full charge capacity value calculated by the calculation unit and the full charge capacity value in the initial state of the lithium ion secondary battery; ,
A device for estimating deterioration of a lithium-ion secondary battery, comprising: The positive electrode active material is manganese iron lithium phosphate,
The deterioration estimating device for a lithium ion secondary battery according to claim 1 . The lithium manganese iron phosphate is represented by the chemical formula (1),
3. The apparatus for estimating deterioration of a lithium ion secondary battery according to claim 2.
[Chemical Formula 1] _{LiwFevMn (1-v) PO4} (0.5<w<1.5 _, 0.20≤v≤0.
55) Chemical formula (1) further comprising at least one or more positive electrode active materials different from the positive electrode active material;
The device for estimating deterioration of a lithium ion secondary battery according to any one of claims 1 to 3. The acquisition unit acquires the first capacitance value and the second capacitance value during charging of the lithium ion secondary battery.
The deterioration estimating device for a lithium ion secondary battery according to any one of claims 1 to 4. When the charge rate or discharge rate in a continuous range of the battery is changed in a certain direction, the amount of change in voltage is relatively large from the range in which the amount of change in voltage is relatively large with respect to the change in the charge rate or discharge rate. A battery capacity estimation method for a lithium ion secondary battery containing a positive electrode active material having two or more inflection points that shift to a small range,
Obtaining a first capacitance value at a first inflection point and a second capacitance value at a second inflection point having a different voltage from the first inflection point,
calculating a current full charge capacity based on the acquired first capacity value and the second capacity value;
estimating the deterioration state of the lithium ion secondary battery based on the calculated current full charge capacity value and the initial full charge capacity value of the lithium ion secondary battery;
A method for estimating a battery capacity of a lithium-ion secondary battery, comprising: obtaining the first capacitance value and the second capacitance value is performed when the lithium ion secondary battery is charged;
The method for estimating battery capacity of a lithium ion secondary battery according to claim 6. A deterioration estimation device for estimating deterioration of a lithium ion secondary battery,
The lithium ion secondary battery includes at least a positive electrode having a positive electrode active material layer formed on a positive electrode current collector, a negative electrode having a negative electrode active material layer formed on a negative electrode current collector, and an electrolytic solution,
The positive electrode has a range in which the amount of voltage change is relatively large with respect to the change in the charging rate when the charging rate is changed in at least one of the charging direction and the discharging direction between charging rates in a continuous range. From, at least a positive electrode active material having two or more inflection points where the amount of change in voltage shifts to a relatively small range,
The device comprises:
an acquisition unit that acquires a first voltage value at a first inflection point and a second voltage value at a second inflection point that is different in voltage from the first inflection point;
a calculation unit that calculates a current full charge capacity based on the first voltage value and the second voltage value obtained by the obtaining unit;
an estimating unit for estimating the deterioration state of the lithium ion secondary battery based on the current full charge capacity value calculated by the calculation unit and the full charge capacity value in the initial state of the lithium ion secondary battery; ,
A device for estimating deterioration of a lithium-ion secondary battery, comprising: A deterioration estimation device for estimating deterioration of a lithium ion secondary battery,
The lithium ion secondary battery includes at least a positive electrode having a positive electrode active material layer formed on a positive electrode current collector, a negative electrode having a negative electrode active material layer formed on a negative electrode current collector, and an electrolytic solution,
The positive electrode has a range in which the amount of voltage change is relatively large with respect to the change in the charging rate when the charging rate is changed in at least one of the charging direction and the discharging direction between charging rates in a continuous range. From, at least a positive electrode active material having two or more inflection points where the amount of change in voltage shifts to a relatively small range,
The device comprises:
A first capacity value at a first inflection point and a second capacity value at a second inflection point different in voltage from the first inflection point in the usage state of the lithium ion secondary battery a first acquiring unit that acquires ,
a second acquiring unit that acquires a third capacity value at the first inflection point and a fourth capacity value at the second inflection point in the initial state of the lithium ion secondary battery; ,
When the difference between the first capacity value and the third capacity value and the difference between the second capacity value and the fourth capacity value are large, the lithium ion secondary battery deteriorates more than when the difference is small. an estimating unit for estimating that the
A device for estimating deterioration of a lithium-ion secondary battery, comprising:

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