WO2021186511A1 - Secondary battery control device, battery pack, and secondary battery control method - Google Patents

Abstract

In this secondary battery control device, a degree of deterioration SOH of the secondary battery is corrected to (1): SOH=AX+B when: X is the surface area of a triangle formed by two of a plurality of maximum points which appear on a curve V-dQ/dV, or two points which are mathematically equivalent to the two maximum points; and an arbitrary point on the horizontal axis, and A and B are constants which are calculated in advance from a relationship between the surface area of a calibration sample and a degree of deterioration of the calibration sample. A battery pack comprising this secondary battery control device exhibits excellent safety, and contributes to the stable supply of energy and sustainable development objectives.

Description

Secondary battery control device, battery pack and secondary battery control method

The present invention relates to a secondary battery control device, a battery pack, and a secondary battery control method.

SOC (State of Charge) and SOH (State of Health) are known as indicators of the state of the secondary battery. SOC is an index showing the remaining capacity of the secondary battery, and SOH is an index showing the deterioration state of the battery. SOC is the ratio of the remaining capacity to the fully charged capacity. SOH is the ratio of the discharge capacity from full charge to full discharge at the time of deterioration to the capacity from initial full charge to full discharge.

For example, Patent Document 1 describes the maximum of the V-dQ / dV curve obtained from dQ / dV, which is the ratio of the amount of change in the amount of stored electricity to the amount of change in the voltage, and the voltage V of the secondary battery when the secondary battery is charged. A method of estimating the capacity reduction rate (corresponding to SOH) from the voltage value of the point is described.

For example, Patent Document 2 describes a method of obtaining dQ / dV when the secondary battery is discharged and obtaining SOH from the maximum value of the amount of change in dQ / dV with respect to voltage.

Japanese Unexamined Patent Publication No. 2013-19709 Japanese Unexamined Patent Publication No. 2016-9569

When the secondary battery repeats the charge / discharge cycle, the SOH value estimated from the actual SOH value may deviate. With the methods described in Patent Documents 1 and 2, the error between the actual SOH value and the estimated SOH value cannot be sufficiently reduced.

The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a control device for a secondary battery, a battery pack, and a control method for the secondary battery, which can correct the deteriorated state of the secondary battery to an appropriate value. do.

To solve the above problems, the following means will be provided.

(1) In the secondary battery control device according to the first aspect, the vertical axis is dQ / dV, which is the ratio of the amount of change in the amount of stored electricity to the amount of change in the voltage of the secondary battery, and the voltage of the secondary battery is defined as the vertical axis. A triangle formed by two maximal points of a plurality of extremum points appearing on a V-dQ / dV curve on the horizontal axis or points mathematically equivalent to them and arbitrary points on the horizontal axis. Let X be the area
When the constants obtained in advance from the relationship between the area of the calibration sample and the deterioration degree of the calibration sample are A and B, the deterioration degree SOH of the secondary battery is corrected to SOH = AX + B ... (1). do.

(2) In the secondary battery control device according to the above aspect, the two maximum points and an arbitrary point on the horizontal axis are 0.4 ≦ (MPa) / (MPb) ≦ 2.4. (2) may be satisfied, and in the formula (2), MPa is the distance between the maximum point on the low voltage side and an arbitrary point on the horizontal axis, and MPb is the maximum point on the high voltage side and the above. The distance to any point on the horizontal axis.

(3) In the secondary battery control device according to the above aspect, the maximum point on the low voltage side may be a maximum point appearing in a voltage range of 3.55 V or more and 3.85 V or less.

(4) In the control device for the secondary battery according to the above aspect, the maximum point on the high voltage side may be a maximum point appearing in a voltage range of 3.95 V or more and 4.20 V or less.

(5) The secondary battery control device according to the above aspect includes the dQ / dV calculating means for calculating the dQ / dV and the two maximums among the plurality of extreme points appearing on the V−dQ / dV curve. An area calculation means for selecting a point, selecting the arbitrary point on the horizontal axis, and calculating the area of a triangle formed by the two selected maximum points and an arbitrary point on the horizontal axis. , A correction means for correcting the degree of deterioration of the secondary battery to a correction value based on the area.

(6) The battery pack according to the second aspect includes a secondary battery and a control device for the secondary battery according to the above aspect.

(7) In the battery pack according to the above aspect, the secondary battery may contain lithium nickel cobalt manganese composite oxide (NCM) and lithium manganese oxide (LMO) as active materials in the positive electrode.

(8) In the method for controlling a secondary battery according to the third aspect, the vertical axis is dQ / dV, which is the ratio of the amount of change in the amount of stored electricity to the amount of change in the voltage of the secondary battery, and the voltage of the secondary battery is used. A triangular shape formed by two maximum points of a plurality of extreme points appearing on a V-dQ / dV curve on the horizontal axis or points mathematically equivalent to the maximum points and arbitrary points on the horizontal axis. When the area is X and the constants obtained in advance from the relationship between the area in the calibration sample and the deterioration degree of the calibration sample are A and B, the deterioration degree SOH of the secondary battery is SOH = AX + B ... Correct to (1).

(9) In the secondary battery control device according to the fourth aspect, the vertical axis is dQ / dV, which is the ratio of the amount of change in the amount of stored electricity to the amount of change in the voltage of the secondary battery, and the voltage of the secondary battery is defined as the vertical axis. A triangular shape formed by two minimum points of a plurality of extreme points appearing on a V-dQ / dV curve on the horizontal axis or points mathematically equivalent to them and arbitrary points on the horizontal axis. Let the area be Y
When the constants obtained in advance from the relationship between the area of the calibration sample and the deterioration degree of the calibration sample are C and D, the deterioration degree SOH of the secondary battery is corrected to SOH = CY + D ... (3). do.

(10) In the secondary battery control device according to the above aspect, the two minimum points and an arbitrary point on the horizontal axis are 0.7 ≦ (NBa) / (NBb) ≦ 1.3. (4) may be satisfied, and in the formula (4), NBa is the distance between the minimum point on the low voltage side and an arbitrary point on the horizontal axis, and NBb is the minimum point on the high voltage side and the above. The distance to any point on the horizontal axis.

(11) In the secondary battery control device according to the above aspect, the minimum point on the low voltage side may be a minimum point that appears in a voltage range of 3.40 V or more and 3.80 V or less.

(12) In the control device for the secondary battery according to the above aspect, the minimum point on the high voltage side may be a minimum point that appears in a voltage range of 3.65 V or more and 4.00 V or less.

(13) The control device for the secondary battery according to the above aspect is the dQ / dV calculating means for calculating the dQ / dV and the two minimums among the plurality of extreme value points appearing on the V−dQ / dV curve. An area calculation means for selecting a point, selecting an arbitrary point on the horizontal axis, and calculating the area of a triangle formed by the two selected minimum points and an arbitrary point on the horizontal axis. A correction means for correcting the degree of deterioration of the secondary battery to a correction value based on the area may be provided.

(14) The battery pack according to the fifth aspect includes a secondary battery and a control device for the secondary battery according to the above aspect.

(15) In the battery pack according to the above aspect, the secondary battery may contain lithium nickel cobalt manganese composite oxide (NCM) and lithium manganese oxide (LMO) as active materials in the positive electrode.

(16) In the method for controlling a secondary battery according to the sixth aspect, the vertical axis is dQ / dV, which is the ratio of the amount of change in the amount of stored electricity to the amount of change in the voltage of the secondary battery, and the voltage of the secondary battery is set. A triangular shape formed by two minimum points of a plurality of extreme points appearing on a V-dQ / dV curve on the horizontal axis or points mathematically equivalent to them and arbitrary points on the horizontal axis. When the area is Y and the constants obtained in advance from the relationship between the area in the calibration sample and the deterioration degree of the calibration sample are C and D, the deterioration degree SOH of the secondary battery is SOH = CY + D ... Correct to (3).

The secondary battery control device, the battery pack, and the secondary battery control method according to the above aspect can correct the deteriorated state of the secondary battery to an appropriate value.
Further, the secondary battery control device, the battery pack, and the secondary battery control method according to the above aspect enhance the safety of the secondary battery, contribute to the stable supply of energy, and contribute to the sustainable development goal.

It is a block diagram of the battery pack which concerns on 1st Embodiment. This is an example of the V-dQ / dV curve of the secondary battery. This is an example of a triangle formed by two maximum points (Pa and Pb) and an arbitrary point (M) on the horizontal axis. It is a V-dQ / dV curve which changes as the charge / discharge cycle of a calibration sample is repeated. It is a figure which shows the relationship between the degree of deterioration of a calibration sample, and a predetermined area. It is sectional drawing of the secondary battery which concerns on 1st Embodiment. This is an example of a triangle formed by two minimum points (Ba and Bb) and an arbitrary point (N) on the horizontal axis.

Hereinafter, the embodiment will be described in detail with reference to the figures as appropriate. In the drawings used in the following description, the featured portion may be enlarged for convenience in order to make the feature easy to understand, and the dimensional ratio of each component may be different from the actual one. The materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and the present invention can be appropriately modified without changing the gist thereof.

"Battery pack"
FIG. 1 is a block diagram of the battery pack 100 according to the first embodiment. The battery pack 100 includes a secondary battery 10 and a control device 20. Signal communication is performed between the secondary battery 10 and the control device 20. The signal communication may be wired or wireless.

The secondary battery 10 is, for example, a lithium secondary battery. The specific configuration of the secondary battery 10 will be described later. The secondary battery 10 deteriorates with use. The index of deterioration of the secondary battery 10 is SOH. SOH is represented by "capacity from full charge to full discharge at the time of deterioration (Ah) / capacity from initial full charge to full discharge (Ah) x 100". Appropriate evaluation of SOH leads to extension of battery life.

The control device 20 is a control device (controller) that controls the secondary battery 10. The control device 20 is, for example, a microcomputer.

The control device 20 has, for example, a control program that corrects the degree of deterioration of the secondary battery 10 to SOH = AX + B ... (1). Hereinafter, the control device 20 will be described with reference to a specific example of the control device 20.

The control device 20 includes, for example, a dQ / dV calculation means 21, an area calculation means 22, and a correction means 23. The dQ / dV calculation means 21, the area calculation means 22, and the correction means 23 are, for example, programs stored in the control device 20.

The dQ / dV calculation means 21 monitors the voltage and the amount of electricity stored in the secondary battery 10. The dQ / dV calculation means 21 calculates dQ / dV from the amount of change in voltage and the amount of change in storage amount per unit time. The calculation of dQ / dV may be performed at the time of charging or at the time of discharging. It is preferable to calculate dQ / dV at the time of charging.

The dQ / dV calculation means 21 draws a V−dQ / dV curve based on the calculated dQ / dV. The V-dQ / dV curve is obtained by differentiating the capacitance measured by the charge / discharge test with a voltage. FIG. 2 is an example of a V-dQ / dV curve. In the V−dQ / dV curve, the horizontal axis is the voltage of the secondary battery and the vertical axis is dQ / dV.

As shown in FIG. 2, the V-dQ / dV curve has a plurality of extremum points. The extremum point has a maximum point and a minimum point. The maximum point in the VdQ / dV curve corresponds to a portion where the potential is flat in the charge / discharge curve (QV curve) in which the horizontal axis is the amount of electricity stored and the vertical axis is the voltage. The minimum point on the V-dQ / dV curve corresponds to the portion of the charge / discharge curve where the potential fluctuation is large.

The V−dQ / dV curve data obtained by the dQ / dV calculation means 21 is sent to the area calculation means 22.

In the first embodiment, the area calculation means 22 selects two maximum points out of a plurality of extreme value points appearing on the V−dQ / dV curve and an arbitrary point on the horizontal axis, and two selected points. Calculate the area of the triangle formed by the maximum point and any point on the horizontal axis.

The selection of the maximum point in the area calculation means 22 is arbitrary. The area calculation means 22 selects two maximum points. The two maximum points selected by the area calculation means 22 may be adjacent to each other, or another maximum point may exist between the two selected maximum points.

For example, the area calculation means 22 may select a maximum point appearing in a voltage range of 3.55 V or more and 3.85 V or less as the maximum point on the low voltage side of the two selected maximum points. For example, if there are multiple maxima within the voltage range, the largest main extremum is selected. The maximum point P2 in FIG. 2 is within this voltage range. The maximum point P2 is an extreme value point associated with the voltage stable region that appears second from the fully discharged state in the initial charge / discharge test of the secondary battery. In other words, as the maximum point on the low voltage side, the maximum point that appears second from the fully discharged state in the initial charge / discharge test of the secondary battery can be selected. Here, the initial term means a charge / discharge cycle within 10 times. The maximum point P2 is, for example, an extreme value point associated with a voltage stable region based on the coexistence state of the stage 2L and the stage 2 in the graphite stage structure of the negative electrode.

For example, the area calculation means 22 may select a maximum point appearing in a voltage range of 3.95 V or more and 4.20 V or less as the maximum point on the high voltage side of the two selected maximum points. For example, if there are multiple maxima within the voltage range, the largest main extremum is selected. The maximum point P4 in FIG. 2 is within this voltage range. The maximum point P4 is the extreme value point associated with the voltage stable region that appears fourth from the fully discharged state in the initial charge / discharge test of the secondary battery. In other words, as the maximum point on the high voltage side, the maximum point that appears fourth from the fully discharged state in the initial charge / discharge test of the secondary battery can be selected. The maximum point P4 is, for example, an extreme value point associated with a voltage stable region based on a two-phase coexistence reaction of two cubic crystals of lithium manganese oxide contained in the positive electrode active material of the secondary battery 10.

The area calculation means 22 calculates the area of a triangle formed by two selected maximum points and an arbitrary point on the selected horizontal axis. FIG. 3 shows an example of a triangle formed when Pa and Pb are selected as two maximum points and M is selected as an arbitrary point on the horizontal axis. The coordinates of the maximum point Pa on the low voltage side are (Pax, Pay), the coordinates of the maximum point Pb on the high voltage side are (Pbx, Pby), and the coordinates of any point M on the horizontal axis are (Mx, 0). Then, the area X of the triangle can be obtained by the following formula.
X = | (Pax-Mx) Pby- (Pbx-Mx) Pay | × 0.5

The area X obtained by the area calculation means 22 is sent to the correction means 23. The correction means 23 estimates the SOH of the secondary battery 10 based on the area X sent from the area calculation means 22. The correction means corrects the SOH of the secondary battery 10 using the estimated SOH as a correction value.

The correction value satisfies the following equation (1).
SOH = AX + B ... (1)
In the formula (1), SOH is an estimated degree of deterioration of the secondary battery and is a correction value. In the formula (1), X is the area calculated by the area calculation means 22. In equation (1), A and B are constants.

The constants A and B are obtained in advance from the relationship between the area of the calibration sample and the degree of deterioration of the calibration sample. The constants A and B differ depending on the combination of extreme points selected by the area calculation means 22. The constants A and B are obtained in advance by the calibration sample and are stored in the correction means 23 in advance.

Here, how to obtain the constants of A and B will be explained. First, prepare a calibration sample. The calibration sample is prepared with the same material and the same capacity as the actually used secondary battery 10. The deterioration behavior of the calibration sample prepared with the same material and the same capacity is similar to the deterioration behavior of the secondary battery 10 actually used.

Next, a charge / discharge test of the calibration sample is performed to obtain a V-dQ / dV curve. FIG. 4 shows a V-dQ / dV curve that changes as the charge / discharge cycle of the calibration sample is repeated. As shown in FIG. 4, when the charge / discharge cycle is repeated, the calibration sample deteriorates and the dQ / dV value at the extreme point changes.

Next, select two maximum points and arbitrary points on the horizontal axis in the V-dQ / dV curve of the calibration sample, and obtain the area of the triangle formed by these points. The two maximum points selected to determine the area of the triangle for the calibration sample and any point on the horizontal axis are the two selected to determine the area of the triangle for the secondary battery 10 actually used. It is the same point as the maximum point and any point on the horizontal axis. In other words, two maximas selected to determine the area of the triangle for the rechargeable battery 10 actually used and any point on the horizontal axis selected to determine the area of the triangle for the calibration sample. The two maximum points and the points on the horizontal axis are selected.

The area of the triangle is calculated every time the charge / discharge cycle is performed a predetermined number of times. In addition, the degree of deterioration (SOH) of the calibration sample at the time when the area of the triangle is obtained is also obtained. The degree of deterioration (SOH) of the calibration sample is obtained by dividing the capacity from full charge to full discharge (Ah) by the capacity from initial full charge to full discharge (Ah) in the number of cycles. FIG. 5 shows the relationship between the degree of deterioration of the calibration sample and the area of the triangle.

As shown in FIG. 5, there is a correlation between the degree of deterioration of the calibration sample and the area of the triangle. For example, the relationship between the degree of deterioration of the calibration sample and the area of the triangle is a linear correlation. Draw a regression line for the plot shown in FIG. The slope of the regression line is the constant A, and the intercept of the regression line is the constant B.

The correction means 23 sends the obtained correction value to the secondary battery 10. The SOH value of the secondary battery 10 is replaced with the correction value. The replacement with the correction value is performed, for example, after passing through all the extreme points selected at the time of charging. The replacement with the correction value is performed, for example, every time the extremum points selected at the time of charging are passed. The correction may be performed when the correction value is obtained. Further, the correction may be performed by adding the difference between the possessed value (value before correction) and the correction value at the correction point after the correction value is obtained. In addition, the correction gradually corrects the value from the correction point to the correction completion point so that the value corresponding to the difference between the possession value at the correction point and the correction value is added to the possession value at the correction point at the correction completion point. You may do it.

When SOH is replaced with a correction value, for example, the continuously changing SOH value changes discontinuously. The fact that the SOH value read out changed discontinuously can be presumed to have been corrected. Further, when the correction value at the time of correction satisfies the above relational expression (1), it can be estimated that the method for controlling the secondary battery according to the first embodiment has been performed.

For example, in the area calculation means 22, the two selected maximum points and an arbitrary point on the horizontal axis satisfy 0.4 ≦ (MPa) / (MPb) ≦ 2.4 ... (2). Select any point on the horizontal axis. In the equation (2), MPa is the distance between the maximum point on the low voltage side and an arbitrary point on the horizontal axis, and MPb is the distance between the maximum point on the high voltage side and an arbitrary point on the horizontal axis.

FIG. 6 is a schematic diagram of the secondary battery according to the first embodiment. The secondary battery 10 includes, for example, a power generation element 4, an exterior body 5, and an electrolytic solution (not shown). The exterior body 5 covers the periphery of the power generation element 4. The exterior body 5 is, for example, a metal laminate film in which a metal foil 5A is coated with a polymer film (resin layer 5B) from both sides. The power generation element 4 is connected to the outside by a pair of connected terminals 6. The electrolytic solution is housed in the exterior body 5 and impregnated in the power generation element 4.

The power generation element 4 includes a positive electrode 2, a negative electrode 3, and a separator 1. The separator 1 is sandwiched between the positive electrode 2 and the negative electrode 3. The separator 1 is, for example, a film having an electrically insulating porous structure. A known separator 1 can be used.

The positive electrode 2 has a positive electrode current collector 2A and a positive electrode active material layer 2B. The positive electrode active material layer 2B is formed on at least one surface of the positive electrode current collector 2A. The positive electrode active material layer 2B may be formed on both surfaces of the positive electrode current collector 2A. The positive electrode current collector 2A is, for example, a conductive plate material. The positive electrode active material layer 2B has, for example, a positive electrode active material, a conductive auxiliary material, and a binder.

The positive electrode active material reversibly proceeds with the occlusion and release of lithium ions, the desorption and insertion (intercalation) of lithium ions, or the doping and dedoping of lithium ions and counter anions. The positive electrode active material is, for example, lithium cobalt oxide (LCO), lithium nickel cobalt manganese composite oxide (NCM), lithium nickel cobalt aluminum composite oxide (NCA), lithium manganese oxide (LMO), lithium iron phosphate (LFP). ). The positive electrode active material layer 2B may contain a plurality of these positive electrode active materials. The positive electrode active material is not limited to these, and known materials can be used. Known conductive auxiliary materials and binders can be used.

The negative electrode 3 has a negative electrode current collector 3A and a negative electrode active material layer 3B. The negative electrode active material layer 3B is formed on at least one surface of the negative electrode current collector 3A. The negative electrode active material layer 3B may be formed on both surfaces of the negative electrode current collector 3A. The negative electrode current collector 3A is, for example, a conductive plate material. The negative electrode active material layer 3B has, for example, a positive electrode active material, a conductive auxiliary material, and a binder.

The negative electrode active material may be any compound that can occlude and release ions, and a known negative electrode active material used in a lithium ion secondary battery can be used. The negative electrode active material is, for example, graphite. The negative electrode active material may be metallic lithium, a silicon compound or the like.

The electrolytic solution is sealed in the exterior body 5 and impregnated in the power generation element 4. A known electrolytic solution can be used.

The battery pack 100 according to the first embodiment can correct the SOH of the secondary battery 10 to an appropriate value by the control device 20.

The control device 20 according to the first embodiment selects two maximum points in the V-dQ / dV curve and arbitrary points on the horizontal axis, and utilizes the area of the triangle formed by these three points. And make corrections. The maximum point on the V-dQ / dV curve corresponds to the portion where the potential is flat on the charge / discharge curve, and the minimum point corresponds to the portion where the potential fluctuates greatly on the charge / discharge curve. That is, the maximum point in the V-dQ / dV curve is a state in which the charge / discharge reaction of a certain stage is in progress, and the minimum point is a state in which the charge / discharge reaction is shifting from a certain stage to a different stage.

The area of the triangle reflects not only the change in the vertical axis (dQ / dV) direction of the selected maximum point, but also the change in the horizontal axis (V) direction. By correcting the SOH using the area of the triangle, the deteriorated state of the secondary battery 10 can be accurately grasped, and as a result, the SOH of the secondary battery 10 can be accurately estimated.

In the second embodiment, the area calculation means 22 selects two minimum points from the plurality of minimum points appearing on the V−dQ / dV curve, selects an arbitrary point on the horizontal axis, and selects two. Calculate the area of a triangle formed by one minimum point and an arbitrary point on the horizontal axis.

The selection of the minimum point in the area calculation means 22 is arbitrary. The area calculation means 22 selects two minimum points. The two minimum points selected by the area calculation means 22 may be adjacent to each other, or another minimum point may exist between the two selected minimum points.

For example, the area calculation means 22 may select a minimum point appearing in a voltage range of 3.40 V or more and 3.80 V or less as the minimum point on the low voltage side of the two selected minimum points. For example, if there are a plurality of minimum points within the voltage range, the smallest main minimum point is selected. The minimum point B1 in FIG. 2 is within this voltage range. The minimum point B1 is the minimum point that appears first from the fully discharged state in the initial charge / discharge test of the secondary battery. For example, the minimum point B1 is an extreme value point associated with a voltage fluctuation region based on the single-phase reaction of stage 4 in the graphite stage structure of the negative electrode. In other words, as the minimum point on the low voltage side, the minimum point that appears first from the fully discharged state in the initial charge / discharge test of the secondary battery can be selected.

For example, the area calculation means 22 may select a minimum point appearing in a voltage range of 3.65 V or more and 4.00 V or less as the minimum point on the high voltage side of the two selected minimum points. For example, if there are a plurality of minimum points within the voltage range, the smallest main minimum point is selected. The minimum point B2 in FIG. 2 is within this voltage range. The minimum point B2 is the minimum point that appears second from the fully discharged state in the initial charge / discharge test of the secondary battery. For example, the minimum point B2 is a minimum point associated with the completion of the hexagonal / monoclinic two-phase coexistence reaction of nickel cobalt manganese oxide contained in the positive electrode active material of the secondary battery 10. In other words, as the minimum point on the high voltage side, the minimum point that appears second from the fully discharged state in the initial charge / discharge test of the secondary battery can be selected.

The area calculation means 22 calculates the area of a triangle formed by two selected minimum points and an arbitrary point on the selected horizontal axis. FIG. 7 shows an example of a triangle formed when Ba and Bb are selected as two minimum points and N is selected as an arbitrary point on the horizontal axis. The coordinates of the minimum point Ba on the low voltage side are (Bax, Bay), the coordinates of the minimum point Bb on the high voltage side are (Bbx, Bby), and the coordinates of any point N on the horizontal axis are (Nx, 0). Then, the area Y of the triangle can be obtained by the following formula.
Y = | (Bax-Nx) Bby- (Bbx-Nx) Bay | × 0.5

The area Y obtained by the area calculation means 22 is sent to the correction means 23. The correction means 23 estimates the SOH of the secondary battery 10 based on the area Y sent from the area calculation means 22. The correction means corrects the SOH of the secondary battery 10 using the estimated SOH as a correction value.

The correction value satisfies the following equation (3).
SOH = CY + D ... (3)
In the formula (3), SOH is an estimated degree of deterioration of the secondary battery and is a correction value. In the formula (3), Y is the area calculated by the area calculation means 22. In equation (3), C and D are constants.

Similar to the first embodiment, the constants C and D are obtained in advance from the relationship between the area of the calibration sample and the degree of deterioration of the calibration sample, and are stored in advance in the correction means 23.

For example, in the area calculation means 22, the two selected minimum points and an arbitrary point on the horizontal axis satisfy 0.7 ≦ (NBa) / (NBb) ≦ 1.3 ... (4). Select any point on the horizontal axis. In equation (4), NBa is the distance between the minimum point on the low voltage side and an arbitrary point on the horizontal axis, and NBb is the distance between the minimum point on the high voltage side and an arbitrary point on the horizontal axis.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the configurations and combinations thereof in the respective embodiments are examples, and the configurations are added or omitted within the range not deviating from the gist of the present invention. , Replacements, and other changes are possible.

For example, instead of the area of a triangle formed by two maximum points or two minimum points and an arbitrary point on the horizontal axis, a value mathematically equivalent to this area may be used. For example, instead of two local maximum points or two local minimum points, mathematically equivalent points may be used. For example, since the VdQ / dV curve is obtained by exchanging the X-axis and the Y-axis of the QV curve and differentiating Q by V, the extreme point of dQ / dV is in the normal QV curve. It is mathematically equivalent to the inflection point. For example, in the QV curve, select two inflection points where the reciprocal of the slope is the maximum or minimum, and use the area of the triangle formed by these two inflection points and any point on the horizontal axis. The correction value (SOH) may be calculated. In this case, only the index used for calculating the correction changes, and the correction value (SOH) estimated by the same procedure as when using the extreme value point in the V-dQ / dV curve can be calculated.

"Example 1"
A lithium ion secondary battery was produced as the secondary battery of Example 1. First, a positive electrode was prepared. NCA (composition formula: Li _1.0 Ni _0.78 Co _0.19 Al _0.03 O ₂ ) was prepared as the positive electrode active material, carbon black was prepared as the conductive material, and polyvinylidene fluoride (PVDF) was prepared as the binder. These were mixed in a solvent to prepare a paint, which was applied onto a positive electrode current collector made of aluminum foil. The mass ratio of the positive electrode active material, the conductive material, and the binder was 95: 2: 3. After coating, the solvent was removed. A positive electrode sheet having a loading of the positive electrode active material layer of 10.0 mg / cm ^{2 was prepared.}

Then the negative electrode was prepared. Graphite was prepared as the negative electrode active material, styrene-butadiene rubber (SBR) was prepared as the binder, and carboxymethyl cellulose (CMC) was prepared as the thickener. These were dispersed in distilled water to prepare a paint, which was applied onto a negative electrode current collector made of copper foil.
The mass ratio of the negative electrode active material, the binder and the thickener was 95: 3: 2. After coating, it was dried to prepare a negative electrode sheet having a loading of the negative electrode active material layer of 6.0 mg / cm ^2.

The positive electrode and the negative electrode prepared above were laminated via a separator. A laminate of polyethylene and polypropylene was used as the separator. The obtained power generation unit was impregnated with the prepared electrolytic solution, sealed in the exterior body, and then vacuum-sealed to prepare a lithium secondary battery for evaluation. The electrolytic solution was prepared by dissolving 1.5 MOL / L of _{lithium hexafluorophosphate (LiPF 6} ) in a solvent in which equal amounts of ethylene carbonate (EC) and dimethyl carbonate (DEC) were mixed.

While repeating the charge / discharge cycle of the lithium secondary battery, the measured SOH and the estimated SOH were obtained. The measured and estimated SOH was determined in 100 cycles, 200 cycles, and 300 cycles, respectively. The results are shown in Tables 1 and 2.

The condition of one charge / discharge was that at 25 ° C., the battery was charged to a final voltage of 4.4 V with a constant current corresponding to 0.1 C, and then discharged to 3.0 V with a constant current corresponding to 0.1 C. 1C represents the current value for discharging the reference capacity of the battery in 1 hour, and 0.1C represents the current value of 1/10 of the current value. The measured SOH was obtained by dividing the capacity from full charge to full discharge in each cycle by the capacity from the first full charge to full discharge and multiplying by 100. The estimated SOH is a correction value obtained from the above-mentioned relational expression (1). Further, as described above, the estimated SOH may be a correction value obtained by using the inflection point in the QV curve. In this example, the extreme points of dQ / dV were used in order to capture the inflection point more clearly.

In Example 1, two maximum points were selected when obtaining the correction value. Select the maximum point on the low voltage side from the voltage range of 3.35V to 3.75V, select the maximum point on the high voltage side from the voltage range of 3.75V to 4.20V, and use it as an arbitrary point on the horizontal axis. , 0V point was selected. As the maximum points, a maximum point (P1) associated with the voltage stabilizing region that appears first from the fully discharged state and a maximum point (P3) associated with the voltage stabilizing region that appears third from the fully discharged state were selected.

"Example 2"
In Example 2, two maximum points were selected when obtaining the correction value. Select the maximum point on the low voltage side from the voltage range of 3.40V to 3.75V, select the maximum point on the high voltage side from the voltage range of 3.85V to 4.20V, and use it as an arbitrary point on the horizontal axis. A point of 4.0 V was selected. As the maximum points, a maximum point (P1) associated with the voltage stabilizing region that appears first from the fully discharged state and a maximum point (P3) associated with the voltage stabilizing region that appears third from the fully discharged state were selected. Other conditions were the same as in Example 1, and the measured and estimated SOH was obtained in each of 100 cycles, 200 cycles, and 300 cycles. The results are shown in Tables 1 and 2.

"Example 3"
In Example 3, two maximum points were selected when obtaining the correction value. Select the maximum point on the low voltage side from the voltage range of 3.55V to 3.85V, select the maximum point on the high voltage side from the voltage range of 3.90V to 4.20V, and use it as an arbitrary point on the horizontal axis. A point of 4.0 V was selected. As the maximum points, a maximum point (P2) associated with the voltage stabilizing region appearing second from the fully discharged state and a maximum point (P3) associated with the voltage stabilizing region appearing third from the fully discharged state were selected. Other conditions were the same as in Example 1, and the measured and estimated SOH was obtained in each of 100 cycles, 200 cycles, and 300 cycles. The results are shown in Tables 1 and 2.

"Example 4"
In Example 4, two maximum points were selected when obtaining the correction value. Select the maximum point on the low voltage side from the voltage range of 3.60V to 3.85V, select the maximum point on the high voltage side from the voltage range of 3.95V to 4.20V, and use it as an arbitrary point on the horizontal axis. A point of 4.0 V was selected. As the maximum points, a maximum point (P2) associated with the voltage stabilizing region appearing second from the fully discharged state and a maximum point (P4) associated with the voltage stabilizing region appearing fourth from the fully discharged state were selected. Other conditions were the same as in Example 1, and the measured and estimated SOH was obtained in each of 100 cycles, 200 cycles, and 300 cycles. The results are shown in Tables 1 and 2.

"Example 5"
_{In Example 5, a mixture of LiNi 0.33} Mn _0.33 Co _0.33 O ₂ (NCM) and LiMn ₂ O ₄ (LMO) was used as the positive electrode active material for the positive electrode of the lithium ion secondary battery. .. The ratio of NCM to LMO was 8: 2.
In Example 5, two maximum points were selected when obtaining the correction value. Select the maximum point on the low voltage side from the voltage range of 3.60V to 3.80V, select the maximum point on the high voltage side from the voltage range of 4.00V to 4.20V, and use it as an arbitrary point on the horizontal axis. A point of 4.0 V was selected. As the maximum points, a maximum point (P2) associated with the voltage stabilizing region appearing second from the fully discharged state and a maximum point (P4) associated with the voltage stabilizing region appearing fourth from the fully discharged state were selected. Other conditions were the same as in Example 1, and the measured and estimated SOH was obtained in each of 100 cycles, 200 cycles, and 300 cycles. The results are shown in Tables 1 and 2.

"Example 6"
In Example 6, two minimum points were selected when obtaining the correction value. Select the minimum point on the low voltage side from the voltage range of 3.40V to 3.80V, select the minimum point on the high voltage side from the voltage range of 3.75V to 4.20V, and use it as an arbitrary point on the horizontal axis. A point of 4.0 V was selected. As the minimum points, the minimum point (B1) associated with the voltage fluctuation region appearing first from the fully discharged state and the minimum point (B3) associated with the voltage fluctuation region appearing third from the fully discharged state were selected. Other conditions were the same as in Example 1, and the measured and estimated SOH was obtained in each of 100 cycles, 200 cycles, and 300 cycles. The results are shown in Tables 1 and 2.

"Example 7"
In Example 7, two minimum points were selected when obtaining the correction value. Select the minimum point on the low voltage side from the voltage range of 3.45V to 3.80V, select the minimum point on the high voltage side from the voltage range of 3.80V to 4.20V, and use it as an arbitrary point on the horizontal axis. , 0V point was selected. As the minimum points, the minimum point (B1) associated with the voltage fluctuation region appearing first from the fully discharged state and the minimum point (B3) associated with the voltage fluctuation region appearing third from the fully discharged state were selected. Other conditions were the same as in Example 1, and the measured and estimated SOH was obtained in each of 100 cycles, 200 cycles, and 300 cycles. The results are shown in Tables 1 and 2.

"Example 8"
In Example 8, two minimum points were selected when obtaining the correction value. Select the minimum point on the low voltage side from the voltage range of 3.45V to 3.75V, select the minimum point on the high voltage side from the voltage range of 3.85V to 4.20V, and use it as an arbitrary point on the horizontal axis. , 0V point was selected. As the minimum points, the minimum point (B1) associated with the voltage fluctuation region appearing first from the fully discharged state and the minimum point (B3) associated with the voltage fluctuation region appearing third from the fully discharged state were selected. Other conditions were the same as in Example 1, and the measured and estimated SOH was obtained in each of 100 cycles, 200 cycles, and 300 cycles. The results are shown in Tables 1 and 2.

"Example 9"
In Example 9, two minimum points were selected when obtaining the correction value. Select the minimum point on the low voltage side from the voltage range of 3.50V to 3.75V, select the minimum point on the high voltage side from the voltage range of 3.65V to 4.20V, and use it as an arbitrary point on the horizontal axis. , 0V point was selected. As the minimum points, the minimum point (B1) associated with the voltage fluctuation region that appears first from the fully discharged state and the minimum point (B2) associated with the voltage fluctuation region that appears second from the fully discharged state were selected. Other conditions were the same as in Example 1, and the measured and estimated SOH was obtained in each of 100 cycles, 200 cycles, and 300 cycles. The results are shown in Tables 1 and 2.

"Example 10"
In Example 10, two minimum points were selected when obtaining the correction value. Select the minimum point on the low voltage side from the voltage range of 3.50V to 3.70V, select the minimum point on the high voltage side from the voltage range of 3.70V to 4.00V, and use it as an arbitrary point on the horizontal axis. , 0V point was selected. As the minimum points, the minimum point (B1) associated with the voltage fluctuation region that appears first from the fully discharged state and the minimum point (B2) associated with the voltage fluctuation region that appears second from the fully discharged state were selected. Other conditions were the same as in Example 1, and the measured and estimated SOH was obtained in each of 100 cycles, 200 cycles, and 300 cycles. The results are shown in Tables 1 and 2.

"Comparative Example 1"
In Comparative Example 1, one maximum point and one minimum point were selected when obtaining the correction value. Select the maximum point from the voltage range of 3.25V to 3.75V, select the minimum point from the voltage range of 3.60V to 4.10V, and select the 4.0V point as an arbitrary point on the horizontal axis. bottom. Other conditions were the same as in Example 1, and the measured and estimated SOH was obtained in each of 100 cycles, 200 cycles, and 300 cycles. The results are shown in Tables 1 and 2.

"Comparative Example 2"
In Comparative Example 2, no correction was performed. Other conditions were the same as in Example 1, and the measured and estimated SOH was obtained in each of 100 cycles, 200 cycles, and 300 cycles. The results are shown in Tables 1 and 2.

As shown in Tables 1 and 2, based on the area of the triangle formed by the two maxima and the points on the horizontal axis or the area of the triangle formed by the two local maxima and the points on the horizontal axis. In all of Examples 1 to 10 in which the SOH was corrected, the error between the actually measured SOH and the estimated SOH was smaller than in Comparative Examples 1 and 2 in which the correction using such an area was not performed.

(Actual machine verification)
A storage battery in which the SOH estimation process according to the present invention is incorporated in a control unit (control device) is prepared. The storage battery (battery pack) is mainly composed of a battery management system including a control unit and a safety mechanism, and 10 lithium-ion secondary battery cells. The prepared storage battery was fully discharged at a rate of 0.2 C at room temperature and then fully charged at a rate of 0.2 C at room temperature to bring the storage battery into the initial state of actual use. At the time of this charging, the dQ / dV value at each voltage was obtained to obtain the V-dQ / dV curve, and the SOH on the software of the control unit was recorded.

In order to intentionally deteriorate the storage battery in the initial state in the above process, a 100-cycle charge / discharge step was performed. Here, the 100-cycle charge / discharge process is
1) The cycle of fully discharging at a rate of 0.5C in a temperature environment of 45 ° C. and then fully charging at a rate of 0.5C is repeated 100 times.
2) After the final full discharge (that is, the 100th cycle full discharge), the battery is fully charged again at room temperature at a rate of 0.2C, and the dQ / dV value at each voltage during charging is obtained to obtain V-dQ. Get the / dV curve.
3) The obtained V-dQ / dV curve after the 100-cycle charge / discharge step is compared with the V-dQ / dV curve in the above initial state.
4-1) If a change in the shape of the extreme point is observed, it is determined that the lithium ion secondary battery in the storage battery has deteriorated, and the SOH value on the software of the control unit is recorded.
4-2) If no change in the extremum point shape is observed, repeat the above steps 1) to 3) again.
It refers to an evaluation process configured to include at least the above elements. In this actual machine verification, three V-dQ / dV curves different from the initial state and three SOH values can be obtained by performing the 100-cycle charge / discharge steps (1) to 4-2) above. Repeated until. As a result, the V-dQ / dV curves and SOH values in each of the three deteriorated states of the lithium ion secondary battery (hereinafter referred to as the first deteriorated state, the second deteriorated state, and the third deteriorated state) are obtained. Got

The first deteriorated V-dQ / dV curve, the second deteriorated V-dQ / dV curve, and the third deteriorated V-dQ / dV curve are output as maximum points. The extreme value point (P2) associated with the voltage stable region appearing second from the fully discharged state and the extreme value point (P4) associated with the voltage stabilizing region appearing fourth from the fully discharged state were adopted. A point of 4.0 V was selected as an arbitrary point on the horizontal axis, and the area of the triangle in each deteriorated state was calculated. When each obtained area was taken on the X-axis and the SOH value output from the control unit in each deteriorated state was taken on the Y-axis and plotted, a good linear relationship represented by the formula Y = AX + B was obtained. rice field. From this, it was confirmed that the SOH correction by the method of the present invention is functioning in the storage battery prepared in the verification of the actual machine.

10 Secondary battery 20 Control device 21 dQ / dV calculation means 22 Average value calculation means 23 Correction means 100 Battery pack

Claims (16)

1. A plurality of extremum points appearing in a V−dQ / dV curve with dQ / dV, which is the ratio of the amount of change in the amount of electricity stored to the amount of change in the voltage of the secondary battery, as the vertical axis and the voltage of the secondary battery as the horizontal axis. Let X be the area of the triangle formed by the two maximum points or points mathematically equivalent to them and any point on the horizontal axis.
   When the constants obtained in advance from the relationship between the area of the calibration sample and the degree of deterioration of the calibration sample are A and B,
   The degree of deterioration SOH of the secondary battery is corrected to SOH = AX + B ... (1).
   Secondary battery control device.
2. The two maximum points and an arbitrary point on the horizontal axis satisfy 0.4 ≦ (MPa) / (MPb) ≦ 2.4 (2).
   In the formula (2), MPa is the distance between the maximum point on the low voltage side and an arbitrary point on the horizontal axis, and MPb is the distance between the maximum point on the high voltage side and an arbitrary point on the horizontal axis. The secondary battery control device according to claim 1, which is a distance.
3. The secondary battery control device according to claim 1 or 2, wherein the maximum point on the low voltage side is a maximum point that appears in a voltage range of 3.55 V or more and 3.85 V or less.
4. The secondary battery control device according to any one of claims 1 to 3, wherein the maximum point on the high voltage side is a maximum point that appears in a voltage range of 3.95 V or more and 4.20 V or less.
5. The dQ / dV calculation means for calculating the dQ / dV, and the dQ / dV calculation means.
   Among the plurality of extreme points appearing in the V-dQ / dV curve, the two maximum points are selected, the arbitrary points are selected on the horizontal axis, and the selected two maximum points and the horizontal are selected. An area calculation means for calculating the area of a triangle formed by an arbitrary point on the axis,
   The control device for a secondary battery according to any one of claims 1 to 4, further comprising a correction means for correcting the degree of deterioration of the secondary battery to a correction value based on the area.
6. A battery pack including a secondary battery and a control device for the secondary battery according to any one of claims 1 to 5.
7. The battery pack according to claim 6, wherein the secondary battery contains lithium nickel cobalt manganese composite oxide (NCM) and lithium manganese oxide (LMO) as active materials in the positive electrode.
8. A plurality of extremum points appearing in a V−dQ / dV curve with dQ / dV, which is the ratio of the amount of change in the amount of electricity stored to the amount of change in the voltage of the secondary battery, as the vertical axis and the voltage of the secondary battery as the horizontal axis. Let X be the area of the triangle formed by the two maximum points or points mathematically equivalent to them and any point on the horizontal axis.
   When the constants obtained in advance from the relationship between the area of the calibration sample and the degree of deterioration of the calibration sample are A and B,
   A method for controlling a secondary battery, in which the degree of deterioration SOH of the secondary battery is corrected to SOH = AX + B ... (1).
9. A plurality of extreme points appearing in a V−dQ / dV curve with dQ / dV, which is the ratio of the amount of change in the amount of electricity stored to the amount of change in the voltage of the secondary battery, as the vertical axis and the voltage of the secondary battery as the horizontal axis. Let Y be the area of the triangle formed by the two local minimum points or points mathematically equivalent to them and any point on the horizontal axis.
   When the constants obtained in advance from the relationship between the area of the calibration sample and the degree of deterioration of the calibration sample are C and D,
   The degree of deterioration SOH of the secondary battery is corrected to SOH = CY + D ... (3).
   Secondary battery control device.
10. The two minimum points and an arbitrary point on the horizontal axis satisfy 0.7 ≦ (NBa) / (NBb) ≦ 1.3 ... (4).
    In the formula (4), NBa is the distance between the minimum point on the low voltage side and an arbitrary point on the horizontal axis, and NBb is the distance between the minimum point on the high voltage side and an arbitrary point on the horizontal axis. The secondary battery control device according to claim 9, which is a distance.
11. The secondary battery control device according to claim 9 or 10, wherein the minimum point on the low voltage side is a minimum point that appears in a voltage range of 3.40 V or more and 3.80 V or less.
12. The secondary battery control device according to any one of claims 9 to 11, wherein the minimum point on the high voltage side is a minimum point that appears in a voltage range of 3.65 V or more and 4.00 V or less.
13. The dQ / dV calculation means for calculating the dQ / dV, and the dQ / dV calculation means.
    Among the plurality of extreme value points appearing in the V−dQ / dV curve, the two minimum points are selected, an arbitrary point is selected on the horizontal axis, and the selected two minimum points and the horizontal axis are selected. An area calculation means for calculating the area of a triangle formed by any of the above points,
    The control device for a secondary battery according to any one of claims 9 to 12, further comprising a correction means for correcting the degree of deterioration of the secondary battery to a correction value based on the area.
14. A battery pack including a secondary battery and a control device for the secondary battery according to any one of claims 9 to 13.
15. The battery pack according to claim 14, wherein the secondary battery contains lithium nickel cobalt manganese composite oxide (NCM) and lithium manganese oxide (LMO) as active materials in the positive electrode.
16. A plurality of extreme points appearing in a V−dQ / dV curve with dQ / dV, which is the ratio of the amount of change in the amount of electricity stored to the amount of change in the voltage of the secondary battery, as the vertical axis and the voltage of the secondary battery as the horizontal axis. Let Y be the area of the triangle formed by the two local minimum points or points mathematically equivalent to them and any point on the horizontal axis.
    When the constants obtained in advance from the relationship between the area of the calibration sample and the degree of deterioration of the calibration sample are C and D,
    The degree of deterioration SOH of the secondary battery is corrected to SOH = CY + D ... (3).
    How to control the secondary battery.

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