WO2021214875A1

WO2021214875A1 - Secondary cell control system, battery pack, and control method for secondary cell

Info

Publication number: WO2021214875A1
Application number: PCT/JP2020/017216
Authority: WO
Inventors: 拳中村; 靖博 ▲高▼木; 佑輔久米; 英司遠藤
Original assignee: Tdk株式会社
Priority date: 2020-04-21
Filing date: 2020-04-21
Publication date: 2021-10-28

Abstract

This secondary cell control system is configured such that, while a secondary cell is being charged: where the second cell has a voltage of 3.65 V, a first inflection point is either the first inflection point at which a Q-dQ/dV curve turns from ascending to descending, or a point mathematically equivalent thereto, the q-dQ/dV curve indicating the relationship between an amount Q of charging of the secondary cell and dQ/dV, which is the proportion of an amount of change in the amount Q of charging with respect to an amount of change in a voltage V; where the secondary cell has a voltage of 3.75 V, a second inflection point is either the first inflection point at which the Q-dQ/dV curve turns from descending to ascending, or a point mathematically equivalent thereto; the control system calculates an insufficient amount of charging with respect to a reference amount of charging at the second inflection point on the basis of the difference between the value dQ/dV at the first inflection point and the value dQ/dV at the second inflection point; and the system corrects the SOC of the secondary cell to a reference SOC when this insufficient amount of charging has been supplied to the secondary cell. A battery pack using this secondary cell control system is highly stable, contributes to stable supply of energy, and contributes to sustainable development goals.

Description

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

The present invention relates to a secondary battery control system, 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 charge amount (remaining capacity) of the secondary battery, and SOH is an index showing the deterioration state of the battery. SOC is the ratio of the amount of charge to the full charge capacity. SOH is the ratio of the fully charged capacity at the time of deterioration to the initial fully charged capacity. Conventionally, various methods for estimating the SOC of a secondary battery have been proposed.

For example, Patent Document 1 discloses a method of estimating the charge state by integrating the charge / discharge currents of a secondary battery. Further, Patent Document 2 discloses a method of detecting an open circuit voltage of a secondary battery and estimating a charge state based on the open circuit voltage.

On the other hand, an estimation method that does not use charge / discharge current integration or open circuit voltage has also been proposed. For example, in Patent Document 3, the charge state of the secondary battery is estimated by using the feature point of dQ / dV, which is the ratio of the change amount dQ of the charge amount Q of the secondary battery to the change amount dV of the battery voltage V. The method of doing so is disclosed.

Japanese Patent No. 5989320 Japanese Patent No. 3669202 Japanese Patent No. 6295858

However, the estimation error still occurs in the charging state estimation method based on the charge / discharge current integration and the open circuit voltage as described above. This is because the error of the current sensor and the voltage sensor is large, and this error cannot be reset until it is fully charged and fully discharged. Therefore, the error cannot be reset when estimating between the fully charged state and the fully discharged state. .. Further, since the open circuit voltage depends on the deteriorated state of the secondary battery, there is a concern that the estimation accuracy will be further lowered.

In addition, in the charging state estimation method using the above dQ / dV feature points, the SOC estimated value may vary depending on the individual difference of the secondary battery, the deterioration state, the environmental temperature, and the like. For example, the characteristic points of the charge curve change depending on the deterioration state, and the mode of change due to high temperature deterioration and the mode of change due to low temperature deterioration are different. Therefore, it is difficult to estimate the charge state of the secondary battery with high accuracy even by using the feature points of the charge curve.

The present invention has been made in view of the above problems, and provides a control system for a secondary battery, a battery pack, and a control method for the secondary battery, which can correct the charge state of the secondary battery with high accuracy. With the goal.

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

(1) The control system for the secondary battery according to the first aspect is charging the secondary battery while charging the secondary battery.
The relationship between the charge amount Q of the secondary battery and dQ / dV, which is the ratio of the change amount of the charge amount Q to the change amount of the voltage V, when the voltage of the secondary battery is 3.65 V or more is shown. The first inflection point at which the Q-dQ / dV curve changes from rising to falling or a point mathematically equivalent to this is set as the first inflection point.
The first inflection point at which the voltage of the secondary battery is 3.75 V or higher and the QdQ / dV curve changes from falling to rising, or a point mathematically equivalent to this, is set as the second inflection point.
Based on the difference between the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point, the insufficient charge amount of the secondary battery with respect to the reference charge amount at the second inflection point is determined. Calculate and
Corrected that the SOC of the secondary battery has reached a predetermined reference SOC when the insufficient charge amount or the amount of electricity mathematically equivalent to the insufficient charge amount is supplied to the secondary battery. do.

(2) In the secondary battery control system according to the first aspect, the reference charge amount at the second inflection point is a value measured using a reference secondary battery having the same configuration as the secondary battery. It may be configured to be.

(3) In the secondary battery control system according to the first aspect, even if the reference SOC is a value measured using a reference secondary battery having the same configuration as the secondary battery. good.

(4) In the secondary battery control system according to the first aspect, the insufficient charge amount of the secondary battery may be calculated by the following formula (I).
Insufficient charge = A + B × C (I)
In formula (I), A and B are dQ / dV values at the first inflection point and dQ / dQ / at the second inflection point measured using a reference secondary battery having the same configuration as the secondary battery. It was obtained by the minimum square method using the difference between the dV value and the charge amount at the initial second inflection point of the reference secondary battery and the measured charge amount at the second inflection point. Represents a constant, and C represents the difference between the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point of the secondary battery.

(5) The battery pack according to the second aspect may be configured to include a secondary battery, the above-mentioned control system for the secondary battery, and a charging means for supplying a current to the secondary battery. ..

(6) In the battery pack according to the second aspect, the secondary battery has a voltage of 3.65 V or more and 3.75 V in the Q-dQ / dV curve when charged from a fully discharged state. It may be configured to show a maximum peak within a range of less than.

(7) In the battery pack according to the second aspect, the secondary battery has a voltage of 3.80 V or more and 3.90 V in the Q-dQ / dV curve when charged from a fully discharged state. It may be configured to show a minimum peak within a range of less than.

(8) In the battery pack according to the second aspect, the secondary battery has a positive electrode and a negative electrode.
The positive electrode contains an oxide represented by the general formula LiMO ₂ (where M is at least one transition metal element selected from the group consisting of Co, Ni, Al, Mn and Fe).
The negative electrode may be configured to contain graphite.

(9) In the battery pack according to the second aspect, the positive electrode of the secondary battery may be configured to contain a lithium nickel cobalt manganese composite oxide or a lithium manganese oxide.

(10) The method for controlling the secondary battery according to the third aspect is to charge the secondary battery while charging the secondary battery.
The relationship between the charge amount Q of the secondary battery and dQ / dV, which is the ratio of the change amount of the charge amount Q to the change amount of the voltage V, when the voltage of the secondary battery is 3.65 V or more is shown. The first inflection point at which the Q-dQ / dV curve changes from rising to falling or a point mathematically equivalent to this is set as the first inflection point.
The first inflection point at which the voltage of the secondary battery is 3.75 V or higher and the QdQ / dV curve changes from falling to rising, or a point mathematically equivalent to this, is set as the second inflection point.
Based on the difference between the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point, the insufficient charge amount of the secondary battery with respect to the reference charge amount at the second inflection point is determined. Calculate and
Corrected that the SOC of the secondary battery has reached a predetermined reference SOC when the insufficient charge amount or the amount of electricity mathematically equivalent to the insufficient charge amount is supplied to the secondary battery. do.

According to the secondary battery control system, the battery pack, and the secondary battery control method according to the above aspect, the secondary battery can be efficiently charged based on the highly accurate estimation of the SOC.
Further, according to the present invention, it is possible to 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 a QV curve and a QdQ / dV curve when a secondary battery is charged using the battery pack according to the embodiment of the present invention. It is a graph which shows the change of the 1st inflection point and the 2nd inflection point of the QdQ / dV curve by the number of charge / discharge cycles of a secondary battery. It is a graph which shows the relationship between the difference between dQ / dV at the 1st inflection point and dQ / dV at the 2nd inflection point of a secondary battery, and the insufficient charge amount. It is a conceptual diagram explaining the method of calculating the insufficient charge amount of a secondary battery based on a correction formula. It is a flow chart of the control method of the secondary battery using the battery pack which concerns on 1st Embodiment. It is sectional drawing of the secondary battery which can be used in the battery pack which concerns on 1st Embodiment.

Hereinafter, the embodiment will be described in detail with reference to the drawings 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, a charging means 20, and a control system 30. Signal communication is performed between the secondary battery 10 and the control system 30 and between the charging means 20 and the control system 30. The signal communication may be wired or wireless.

The secondary battery 10 is, for example, a lithium ion secondary battery. The specific configuration of the secondary battery 10 will be described later. The number of secondary batteries 10 may be one or two or more. The two or more secondary batteries 10 may be connected in series or in parallel.

The charging means 20 supplies a current to the secondary battery 10 to charge the secondary battery 10. As the charging means 20, for example, a constant current charging device can be used. In the present embodiment, the charging means 20 is provided inside the battery pack 100, but may be provided outside the battery pack 100, for example, in an electric device to which the battery pack 100 is mounted.

The control system 30 is a control device (controller) that controls the state of charge of the secondary battery 10. The control system 30 is, for example, a microcomputer. The control system 30 includes a detection means 31, a dQ / dV calculation means 32, an insufficient charge amount calculation means 33, a correction means 34, and a storage means 35.

The detecting means 31 detects the amount of electricity supplied to the secondary battery 10, that is, the charge amount Q of the secondary battery 10 and the voltage V of the secondary battery 10. The charge amount Q is a value (I × t) obtained by multiplying the current value I supplied from the charging means 20 to the secondary battery 10 and the current supply time t. The detection interval between the charge amount Q and the voltage V varies depending on conditions such as the current value I supplied from the charging means 20 to the secondary battery 10, but is usually 1 second or more and 10 minutes or less.

The dQ / dV calculation means 32 calculates dQ / dV by differentiating the charge amount Q detected by the detection means 31 with the voltage V. dQ / dV is the ratio of the amount of change in the charge amount of the secondary battery 10 to the amount of change in the voltage V of the secondary battery 10.

The insufficient charge amount calculation means 33 detects the first inflection point and the second inflection point. Then, based on the difference between the detected dQ / dV value at the first inflection point and the detected dQ / dV value at the second inflection point, the secondary battery with respect to the reference charge amount at the second inflection point. Calculate the insufficient charge amount of 10. The insufficient charge amount is the difference between the charge amount at the second inflection point of the secondary battery 10 being charged and the reference charge amount at the second inflection point of the secondary battery 10 in the initial state. The first inflection point and the second inflection point will be described with reference to FIG.

FIG. 2 is an example of the QV curve and the QdQ / dV curve of the secondary battery when the secondary battery is charged using the battery pack according to the embodiment of the present invention. In FIG. 2, the horizontal axis represents the charge amount Q of the secondary battery 10, and the vertical axis represents the voltage V and dQ / dV of the secondary battery 10. In FIG. 2, the QV curve is shown by a broken line and the QdQ / dV curve is shown by a solid line. The QV curve and the QdQ / dV curve are data when the secondary battery 10 is charged with a constant current from a fully discharged state.

As shown in FIG. 2, the Q-dQ / dV curve has a plurality of peaks. The plurality of peaks are the peak top (the inflection point where the Q-dQ / dV curve changes from rising to falling) indicated by the maximum points P1, P2, P3, and P4 in the figure, and the minimum points B1, B2, B3, and B4. Includes the peak bottom indicated by (the inflection point at which the Q-dQ / dV curve changes from falling to rising). The Q-dQ / dV curve shows a maximum peak in the range where the voltage V of the secondary battery is 3.65 V or more and less than 3.75 V, and shows a minimum peak in the range of 3.80 V or more and less than 3.90 V. .. The maximum points P1 to P4 and the minimum points B1 to B4 indicate that the stages of the positive electrode active material or the negative electrode active material that contribute to the charging reaction of the secondary battery 10 are switched. Therefore, the shape and position of the peak differ depending on the material of the positive electrode active material and the negative electrode active material of the secondary battery 10.

The first inflection point is the first inflection point at which the voltage of the secondary battery 10 is 3.65 V or higher and the QdQ / dV curve changes from rising to falling, or a point mathematically equivalent to this. .. The point at which the Q-dQ / dV curve changes from rising to falling is the point at which the continuously rising Q-dQ / dV curve changes so as to continuously fall. It should be noted that continuous is, for example, 1 minute or more, although it depends on the charging rate.

In the QdQ / dV curve shown in FIG. 2, the first inflection point is the maximum point P2. The point mathematically equivalent to the first inflection point is, for example, a point in the QV curve where the amount of change dV of the voltage V of the secondary battery with respect to the amount of change dQ of the amount of electricity changes from an increase to a decrease. Further, a V-dQ / dV curve is used instead of the Q-dQ / dV curve, and the V-dQ / dV curve changes from rising to falling.

The second inflection point is the first inflection point at which the voltage of the secondary battery 10 is 3.75 V or higher and the QdQ / dV curve changes from falling to rising, or a point mathematically equivalent to this. .. The point at which Q / dV changes from falling to rising is a point at which dQ / dV, which has been continuously falling, changes so as to continuously rise. It should be noted that continuous is, for example, 1 minute or more, although it depends on the charging rate.

In the QdQ / dV curve shown in FIG. 2, the second inflection point is the minimum point B2. The point mathematically equivalent to the second inflection point is, for example, that in the QV curve, the amount of change dV of the voltage V of the secondary battery with respect to the amount of change dQ of the amount of electricity changes from decreasing to increasing. Further, a V-dQ / dV curve is used instead of the Q-dQ / dV curve, and the V-dQ / dV curve changes from falling to rising.

Next, a method of calculating the insufficient charge amount of the secondary battery 10 will be described. The secondary battery 10 deteriorates by repeating the charge / discharge cycle, and the position and height of the peak of the QdQ / dV curve change. Due to this change, the charge amount when the charging secondary battery 10 reaches the second inflection point and the charge amount when the initial secondary battery 10 reaches the second inflection point are significantly different. There is. Therefore, the difference between the charge amount at the second inflection point of the secondary battery 10 being charged and the reference charge amount at the second inflection point of the initial secondary battery 10 is calculated as the insufficient charge amount. The reference charge amount may be, for example, a value measured using a reference secondary battery having the same configuration as the secondary battery 10. The reference secondary battery is a battery in which each material constituting the battery is the same as that of the secondary battery 10, and the QV curve and the QdQ / dV curve when the battery is charged are the same as those of the secondary battery 10. ..

The insufficient charge amount is calculated based on the difference between the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point of the secondary battery 10. The insufficient charge amount can be calculated by, for example, the insufficient charge amount calculation formula represented by the following formula (I).
Insufficient charge = A + B × C (I)
In formula (I), A and B are the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point measured using a reference secondary battery having the same configuration as the secondary battery. Represents a constant obtained by the minimum square method using the difference between the difference between , Represents the difference between the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point of the secondary battery. The formula for calculating the insufficient charge amount of the above formula (I) will be described with reference to FIGS. 3 to 5.

FIG. 3 is a graph showing changes in the first inflection point and the second inflection point of the QdQ / dV curve by the deterioration test. In FIG. 3, the maximum point P2 _i is the first inflection point in the secondary battery 10 with SOH = 100% (initial), and the maximum point P2 _m is the first inflection point in the secondary battery 10 with SOH = 93%. The maximum point P2 _f is the first inflection point in the secondary battery 10 with SOH = 87%. The minimum point B2 _i is the second inflection point in the secondary battery 10 with SOH = 100% (initial), and the minimum point B2 _m is the second inflection point in the secondary battery 10 with SOH = 93%. , The minimum point B2 _f is the second inflection point in the secondary battery 10 with SOH = 87%.
As shown in FIG. 3, as the SOH of the secondary battery 10 decreases (that is, deterioration progresses), the dQ / dV value of the first inflection point (maximum point P2) decreases, and the first inflection point Position shifts to the low charge side. Along with this, the position of the second inflection point (minimum point B2) shifts to the low charge amount side and becomes far from _{the second inflection point (minimum point B2 i) of the initial secondary battery 10.} Also, the slope of the QdQ / dV curve after the second inflection point becomes smaller. Therefore, it may be difficult for the secondary battery 10 to accurately detect the charge amount at the second inflection point by repeating the charge / discharge cycle.

FIG. 4 is a graph showing the relationship between the difference between dQ / dV at the first inflection point and dQ / dV at the second inflection point of the secondary battery and the insufficient charge amount. In FIG. 4, the horizontal axis is the difference [(P2-B2) dQ / dV] between the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point of the secondary battery 10. The vertical axis is the insufficient charge amount, that is, _{the difference between the charge amount Q at the initial second inflection point (B2 i} ) of the secondary battery 10 and the charge amount Q at the second inflection point (B2) at the time of measurement [( B2 _i- B2) Q]. From the graph shown in FIG. 4, it can be seen that (P2-B2) dQ / dV and (B2 _i- B2) Q have a linear correlation. Therefore, from the relationship between (P2-B2) dQ / dV and (B2 _i- B2) Q, a linear function formula with (P2-B2) dQ / dV as a variable is calculated using the least squares method. By substituting the measured (P2-B2) dQ / dV into a linear function formula, the insufficient charge amount at the time of measurement, that is, (B2 _i- B2) Q can be calculated accurately. The formula for calculating the insufficient charge amount in the above formula (I) is a linear function calculated by the least squares method using _{(P2-B2) dQ / dV and (B2 i-B2) Q of the reference secondary battery.} It is an expression.

FIG. 5 is a conceptual diagram illustrating a method of calculating the insufficient charge amount of the secondary battery based on the insufficient charge amount calculation formula. The curve shown in FIG. 5 is a QdQ / dV curve of the secondary battery 10 being charged. The insufficient charge amount of the secondary battery 10 is calculated as follows. First, the first inflection point (maximum point P2) and the second inflection point (minimum point B2) are detected, and the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point The difference [(P2-B2) dQ / dV] (X in FIG. 5) is calculated. Next, the obtained (P2-B2) dQ / dV is substituted into C of the undercharge amount calculation formula of the above formula (I) to calculate the undercharge amount. The obtained insufficient charge amount (Y in FIG. 5) is the difference between the charge amount _{at the second inflection point B2 and the charge amount at the initial second inflection point B2 i} _{of the reference secondary battery [(B2 i-).} B2) Corresponds to Q].

In the correction means 34, when the undercharge amount calculated by the undercharge amount calculation means 33 is supplied to the secondary battery 10 by the charging means 20, the SOC (charge rate) of the secondary battery 10 is set in advance. Correct as if the specified standard SOC has been reached. The charge amount of the secondary battery 10 when the amount of electricity corresponding to the insufficient charge amount is supplied corresponds to the charge amount at the initial second inflection point (minimum point B2 _i ) of the reference secondary battery. Therefore, the reference SOC is the charge rate (SOC) at _{the second inflection point (minimum point B2 i} ) of the initial Q-dQ / dV curve of the reference secondary battery. This reference SOC uses the charge amount when the reference secondary battery in the fully discharged state is fully charged by constant current constant voltage charging as the denominator, and the QdQ / dV curve obtained by the constant current constant voltage charging. It is a value calculated as a molecule of the charge amount at the second inflection point of.

The storage means 35 stores the insufficient charge amount calculation formula of the above formula (1) calculated using the reference secondary battery and the reference SOC. The storage means 35 may further store the reference charge amount.

Next, a method of controlling the secondary battery 10 using the battery pack 100 according to the first embodiment will be described with reference to FIG. The control method of the secondary battery 10 shown in FIG. 6 includes the following steps S1 to S8.

In step S1, the voltage value V of the secondary battery 10 is measured. When the voltage V of the secondary battery 10 is higher than 3.65 V (No), the secondary battery 10 is discharged. The discharge may be performed until the voltage value V of the secondary battery 10 is in a fully discharged state. The fully discharged state is, for example, a state in which the voltage V of the secondary battery 10 is 3.0 V or less. When the voltage V of the secondary battery 10 is lower than 3.65 V (Yes), the secondary battery 10 is charged (step S2).

In step S2, it is preferable to charge the secondary battery 10 by constant current charging. The charging rate is preferably in the range of 0.1C or more and 2C or less, where 1C is the charging rate when the secondary battery 10 is charged from the fully discharged state to the fully charged state in 1 hour.

In step S2, while charging the secondary battery 10, the voltage V of the secondary battery 10 and the charge amount Q (the amount of electricity supplied to the secondary battery 10) are measured, and dQ / dV is calculated. A Q-dQ / dV curve is created accordingly. Then, in step S2, the following steps S3 and S4 are performed.

In step S3, the voltage V of the secondary battery 10 is 3.65 V or more, and the first inflection point at which the Q-dQ / dV curve changes from rising to falling is detected. Then, this inflection point is recognized as the first inflection point (maximum point P2).

In step S4, an inflection point at which the voltage of the secondary battery is 3.75 V or higher and the Q-dQ / dV curve changes from rising to falling is detected. Then, this inflection point is recognized as the second inflection point (minimum point B2).

In step S5, the difference (P2-B2) dQ / dV between the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point is calculated.

In step S6, the (P2-B2) dQ / dV calculated in step S5 is substituted into C in the undercharge amount calculation formula (A + B × C) of the above formula (I) to calculate the undercharge amount.

In step S7, the amount of electricity corresponding to the insufficient charge amount calculated in step S6 is supplied to the secondary battery 10.

In step S8, when the amount of electricity corresponding to the insufficient charge amount is supplied to the secondary battery 10, it is corrected that the charge rate (SOC) of the secondary battery 10 has reached the reference SOC.

FIG. 7 is a cross-sectional view of the secondary battery 10 that can be used in the battery pack 100 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 from both sides with a polymer film (resin layer 5B). 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 _{preferably contains an oxide represented by the general formula LiMO 2} (where M is a transition metal element containing at least one of Co, Ni, Al, Mn, and Fe). Further, the positive electrode active material may contain a phosphate. Specific examples of the positive electrode active material include lithium cobalt oxide (LCO), lithium nickel cobalt manganese composite oxide (NCM), lithium nickel cobalt aluminum composite oxide (NCA), lithium manganese oxide (LMO), and phosphoric acid. Lithium iron phosphate (LFP) can be mentioned. 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. As the electrolytic solution, one in a public land can be used.

The secondary battery 10 is configured so that the voltage of the secondary battery 10 shows a maximum peak within a range of 3.65 V or more and less than 3.75 V in the QdQ / dV curve when charged from a fully discharged state. It is preferable to have. Further, the secondary battery 10 is preferably configured so that the voltage of the secondary battery 10 shows a minimum peak within a range of 3.80 V or more and less than 3.90 V.

According to the battery pack 100 according to the first embodiment, the first inflection point (maximum point P2) and the second inflection point (minimum point) in the control system 30 while charging the secondary battery 10 by the charging means 20. B2) is detected, and the insufficient charge amount with respect to the reference charge amount at the second inflection point is calculated based on the difference between the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point. Then, when this insufficient charge amount is supplied to the secondary battery, the SOC of the secondary battery 10 is corrected to the reference SOC. The difference between the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point has a high correlation with the insufficient charge amount. Therefore, according to the control system 30, even if the positions of the first inflection point and the second inflection point and the dQ / dV value of the secondary battery 10 greatly fluctuate due to the charge / discharge cycle, the secondary battery is being charged. 10 SOCs can be corrected with high accuracy.

Further, in the battery pack 100 according to the first embodiment, when the reference charge amount at the second inflection point is a value measured using the reference secondary battery having the same configuration as the secondary battery 10, the battery is being charged. The SOC of the secondary battery 10 can be corrected with higher accuracy. Further, in the battery pack 100 according to the first embodiment, when the reference SOC is a value measured using a reference secondary battery having the same configuration as the secondary battery 10, the SOC of the secondary battery 10 being charged Can be corrected with higher accuracy.

Further, when the insufficient charge amount of the secondary battery 10 is calculated from the insufficient charge amount of the above formula (I), the insufficient charge amount can be measured more accurately. Therefore, the SOC of the secondary battery 10 being charged can be corrected with higher accuracy.

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, in the present embodiment, the reference charge amount, the reference SOC, and the insufficient charge amount calculation formula of the above formula (1) are obtained by using the reference secondary battery, but the present invention is not limited to this. The reference charge amount, the reference SOC, and the insufficient charge amount calculation formula may be obtained in the initial state of the secondary battery 10 incorporated in the battery pack 100, and the obtained values may be stored in the storage means 35. The initial state of the secondary battery 10 is a state in which the number of charge / discharge cycles is 10 or less.

[Example 1]
(1) Preparation of Lithium Ion Secondary Battery A lithium ion secondary battery was manufactured as a secondary battery. First, a positive electrode was prepared. NCM (composition formula: Li _1.0 Ni _1/3 Co _1/3 Mn _1/3 O ₂ ) was prepared as the positive electrode active material, carbon black was prepared as the conductive auxiliary 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 auxiliary material, and the binder was 95: 2: 3. After coating, the solvent was removed. A positive electrode sheet having a basis weight of the positive electrode active material layer of 10.0 mg / cm ^{3 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 basis weight of 6.0 mg / cm ^{3 of the negative electrode active material layer.}

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 (DMC) were mixed.

(2) Setting of standard SOC and insufficient charge amount calculation formula (setting of standard SOC)
The secondary battery (reference secondary battery) produced in (1) above is charged to a final voltage of 4.2 V with a constant current value of 0.2 C in a temperature environment of 25 ° C., and then 3 at 0.2 C. It was discharged to 0.0V. After that, the reference secondary battery was charged to a final voltage of 4.2 V by constant current and constant voltage charging to bring it into a fully charged state. The current supply amount at this time was set as the fully charged amount of the secondary battery, and the SOC of the secondary battery in the fully charged state was set as 100%, which was used as the reference for the subsequent evaluation. The QV curve and the QdQ / dV curve obtained by this charging were the same as those shown in FIG. As a result of reading the charge amount (reference charge amount) at the second inflection point (minimum point B2) from the Q-dQ / dV curve and calculating the ratio of the reference charge amount at the second inflection point to the full charge amount, 50 %Met. Therefore, in this embodiment, the reference SOC is set to 50%.

(Setting of insufficient charge calculation formula)
The reference secondary battery used to set the reference SOC is charged to a final voltage of 4.2 V with a constant current value of 0.5 C under a temperature environment of 25 ° C, and terminates at a constant current value of 0.5 C. The charge / discharge cycle of discharging to a voltage of 3.0 V was set as one cycle, and 3000 cycles were performed. Every 50 cycles, the reference secondary battery was charged to a final voltage of 4.2 V by constant current and constant voltage charging to bring it into a fully charged state. From the Q-dQ / dV curve at the time of charging, the dQ / dV value at the first inflection point, the dQ / dV value at the second inflection point, and the electric energy Q were read. Then, the insufficient charge amount calculation formula (approximate formula of the linear function) was obtained by the least squares method. As a result, the obtained insufficient charge amount calculation formula was A + B × C (however, A is 100 and B is 0.005).

(3) Preparation of Battery Pack A battery pack was produced by connecting the lithium ion secondary battery produced in (1) above, a constant current charging / discharging device, and a control system, respectively. The control system includes a detection means having a coulomb counter and a voltage measuring instrument, a dQ / dV calculation means, a shortage charge amount calculation means, a correction means, a storage means, and an SOC display means. The reference SOC and the insufficient charge amount calculation formula obtained in (2) above were stored in the storage means.

(4) Evaluation of battery pack The difference between the controlled SOC and the measured SOC was measured by the following method for the battery pack at the initial stage and after the charge / discharge cycle processing. The results are shown in Table 1 below.
(A) Difference between the control SOC of the initial battery pack and the measured SOC The lithium ion secondary battery was charged under a temperature environment of 25 ° C. at a constant current value of 0.2 C until the voltage became 4.2 V. Then, it was discharged to a final voltage of 3.0 V at a constant current value of 0.2 C. The difference between the controlled SOC after the end of discharge and the measured SOC was calculated. The results are shown in the "Initial" column of Table 1 below. The control SOC is an internal SOC control value when the discharge end voltage is reached. If the SOC during charging is correctly corrected, it will be 0. The measured SOC is the SOC of the lithium ion secondary battery when the discharge end voltage is reached, that is, 0.

(B) Difference between control SOC of battery pack after charge / discharge cycle processing and measured SOC The lithium ion secondary battery after the end of discharge in (a) above is terminated at a constant current value of 0.5 C in an environment of 45 ° C. After charging to a voltage of 4.2 V, a charge / discharge cycle of discharging to a final voltage of 3.0 V at a constant current value of 0.5 C was set as one cycle, and 100 cycles were performed. Next, the lithium ion secondary battery is charged to a final voltage of 4.2 V at a constant current value of 0.5 C under a temperature environment of 25 ° C., and then discharged to a final voltage of 3.0 V at a constant current value of 0.5 C. The charge / discharge cycle was set as one cycle, and 400 cycles were performed. For the battery pack subjected to the above charge / discharge cycle processing, the control SOC at the time of discharge and the measured SOC were measured, and the difference was calculated.
The charge / discharge cycle process was performed three times, and the difference between the control SOC of the battery pack and the measured SOC after each charge / discharge cycle process was calculated.

[Comparative Example 1]
(3) In the production of the battery pack, the battery pack was produced and evaluated in the same manner as in Example 1 except that the storage means did not store the insufficient charge amount calculation formula. The results are shown in Table 1 below.

[Comparative Example 2]
In the preparation of the battery pack of (3), the SOC-OCV (open circuit voltage) characteristics of the initial battery pack were stored in the storage means. Then, the energization was stopped in the middle of charging, the terminal voltage after a one-hour pause was used as the open circuit voltage, and the SOC was estimated and corrected from the obtained open circuit voltage and the stored SOC-OCV characteristics (OCV). Law). Except for the above points, a battery pack was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

[Comparative Example 3]
In the setting of the above (2) reference SOC and insufficient charge amount calculation formula, the charge amount at the first inflection point (maximum point P2) in the QdQ / dV curve is read, and the reference SOC is set to the first change with respect to the full charge amount. The ratio of the amount of charge at the inflection point (30%) was used. Then, in the production of the battery pack (3), the first turning point (first changing point) in which the lithium ion secondary battery voltage V is 3.65V or more and the QdQ / dV curve changes from rising to falling. A battery pack was prepared in the same manner as in Example 1 except that the SOC of the lithium ion secondary battery was set to be corrected to reach the reference SOC (30%) when the point) was reached. evaluated. The results are shown in Table 1 below.

[Comparative Example 4]
In the setting of the above (2) reference SOC and insufficient charge amount calculation formula, the charge amount at the second inflection point (minimum point B2) in the QdQ / dV curve is read, and the reference SOC is set to the second variation with respect to the full charge amount. The ratio of the amount of charge at the inflection point (45%) was used. Then, in the production of the battery pack (3), the first turning point (second turning point) in which the lithium ion secondary battery voltage V is 3.75V or more and the QdQ / dV curve changes from falling to rising. A battery pack was prepared and evaluated in the same manner as in Example 1 except that the SOC of the lithium ion secondary battery was set to be corrected to reach the reference SOC (45%) when the point) was reached. bottom. The results are shown in Table 1 below.

[Comparative Example 5]
(3) In the production of the battery pack, the battery pack was produced and evaluated in the same manner as in Example 1 except that the storage means stored the insufficient charge amount calculation formula as +50 (unit: mAh). The results are shown in Table 1 below.

Compared with the battery packs produced in Comparative Examples 1 to 5, the battery packs produced in Example 1 had a smaller difference between the controlled SOC and the actually measured SOC of the lithium ion secondary battery after deterioration due to the charge / discharge cycle. ..
The height and position of the first inflection point (P2) and the second inflection point (B3) of the secondary battery change as the lithium ion secondary battery deteriorates due to the charge / discharge cycle process. Therefore, in Comparative Example 3 in which the correction is made based only on the first inflection point, the difference between the control SOC and the actually measured SOC becomes large due to the influence of the change of the first inflection point. Similarly, in Comparative Example 4 in which the correction is made based only on the second inflection point, the difference between the controlled SOC and the actually measured SOC becomes large due to the large influence of the change in the second inflection point. On the other hand, the difference between the dQ / dV of the first inflection point (P2) and the second inflection point (B2) [(P2-B2) dQ / dV] and the insufficient charge amount, that is, the initial stage of the secondary battery. _{The difference [(B2 i-} B2) Q] between the charge amount Q at the second inflection point (B2 _i ) and the charge amount Q at the second inflection point (B2) after deterioration has a linear correlation. .. Therefore, in the battery pack of the first embodiment, the insufficient charge amount can be obtained with high accuracy. Then, since the SOC is corrected after charging this insufficient charge amount, the SOC of the lithium ion secondary battery of the deteriorated SOC can be corrected with high accuracy, and the difference between the controlled SOC and the actually measured SOC becomes small.

(Actual machine verification)
A battery pack in which the SOC correction function according to the present embodiment is incorporated in the control unit (control system) is prepared. The battery pack mainly consisted of a battery management system including a control unit and a safety mechanism, and 10 lithium-ion secondary batteries. Ten lithium-ion secondary batteries were connected in parallel. In the lithium ion secondary battery, a so-called NCM ternary active material of nickel-cobalt-manganese was used as the positive electrode active material, and carbon was used as the negative electrode active material. The prepared battery pack 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 lithium ion secondary battery into the initial state of actual use. At the time of this charging, the dQ / dV value at each voltage was obtained to calculate Q, and the Q−dQ / dV curve in the initial state was acquired and recorded in the storage means of the control unit.

In order to intentionally deteriorate the lithium ion secondary batteries (10 lithium ion secondary batteries connected in parallel) that were in the initial state in the above process, a 1000 cycle charge / discharge step was performed. Here, the 1000-cycle charge / discharge process refers to an evaluation process including the following elements.
1) In a temperature environment of 45 ° C., after full discharge at a rate of 0.5 C, charge / discharge is performed 1000 times at a rate of 0.2 C so that the cell voltage is always 4.0 V or higher. After that, it is fully discharged at a rate of 0.5C.
2) After the final full discharge (that is, the 1000th cycle full discharge), the battery is fully charged again at room temperature at a rate of 0.2 C. In this charging operation, the SOC value (this SOC value is referred to as "internal SOC value") and the capacity are continuously read from the control unit inside the battery pack. After full charge, a Q-dQ / dV curve is obtained from the dQ / dV value at each voltage during charging.
3) When the internal SOC value shows a peculiar fluctuation in the charging operation of 2) above, the capacity Y1 of the lithium ion secondary battery when the fluctuation is confirmed is read from the value of the continuous capacity change.
4) The Q-dQ / dV curve obtained after the 1000-cycle charge / discharge step and the Q-dQ / dV curve in the above initial state are all in the range of 3.65-3.90V. Confirm that the maximum value (maximum point P2, first inflection point) and the minimum value (minimum point B2, second inflection point) of dQ / dV are shown, and the peaks related to the maximum value and the minimum value of both. Compare the shapes and check for any differences. 3.65-3.90V was selected as the voltage range because the positive electrode active material of the lithium ion secondary battery used in this actual machine verification is the NCM ternary active material and the negative electrode active material is carbon. This is because the practical working voltage range of the secondary battery is naturally determined.

5-1) If there is a difference in the peak shape of the maximum point and the minimum point of the Q-dQ / dV curve, it is judged that the lithium ion secondary battery in the battery pack has deteriorated, and the following data Perform processing.
i) The capacity Y2 at the minimum point is recorded, and the additional charge capacity Y = Y1-Y2 [(B2 _i- B2) Q added from the minimum point to the point where the SOC value shows a specific fluctuation. ] Is calculated.
ii) Read the dQdV maximum value Xmax at the maximum point and the dQdV minimum value Xmin at the minimum point.
iii) Calculate the dQ / dV intensity difference X = Xmax-Xmin [(P2-B2) dQ / dV].
5-2) If no difference in peak shape is observed, the above steps 1) to 4) are repeated again.

In this actual machine verification, this 1000-cycle charge / discharge process (work 1) to 5-2) is performed by three Q-dQ / dV curves that are different from the initial state and three additional charge capacities Y. Repeated until obtained. As a result, the Q-dQ / dV curves and capacities 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. , DQ / dV intensity difference X and insufficient charge amount Y were calculated. When the difference in dQ / dV intensity in each deteriorated state was taken on the X-axis and the additional charge capacity Y was taken on the Y-axis and plotted, a good linear relationship represented by the equation Y = AX + B was obtained. From this, it was confirmed that the SOC correction by the method according to the present embodiment is functioning in the battery pack in the verification of the actual machine.

10 Secondary battery 20 Charging means 30 Control system 31 Detecting means 32 dQ / dV calculating means 33 Insufficient charging amount calculating means 34 Correcting means 35 Storage means 100 Battery pack

Claims

While charging the secondary battery
The relationship between the charge amount Q of the secondary battery and dQ / dV, which is the ratio of the change amount of the charge amount Q to the change amount of the voltage V, when the voltage of the secondary battery is 3.65 V or more is shown. The first inflection point at which the Q-dQ / dV curve changes from rising to falling or a point mathematically equivalent to this is set as the first inflection point.
The first inflection point at which the voltage of the secondary battery is 3.75 V or higher and the QdQ / dV curve changes from falling to rising, or a point mathematically equivalent to this, is set as the second inflection point.
Based on the difference between the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point, the insufficient charge amount of the secondary battery with respect to the reference charge amount at the second inflection point is determined. Calculate and
A secondary battery control system that corrects that the SOC of the secondary battery has reached a predetermined reference SOC when the insufficient charge is supplied to the secondary battery.
The secondary battery control system according to claim 1, wherein the reference charge amount at the second inflection point is a value measured using a reference secondary battery having the same configuration as the secondary battery.
The secondary battery control system according to claim 1 or 2, wherein the reference SOC is a value measured using a reference secondary battery having the same configuration as the secondary battery.
The secondary battery control system according to any one of claims 1 to 3, wherein the insufficient charge amount of the secondary battery is calculated by the following formula (I).
Insufficient charge = A + B × C (I)
In formula (I), A and B are dQ / dV values at the first inflection point and dQ / dQ / at the second inflection point measured using a reference secondary battery having the same configuration as the secondary battery. It was obtained by the minimum square method using the difference between the dV value and the charge amount at the initial second inflection point of the reference secondary battery and the measured charge amount at the second inflection point. Represents a constant, and C represents the difference between the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point of the secondary battery.
A battery pack comprising a secondary battery, a control system for the secondary battery according to any one of claims 1 to 4, and a charging means for supplying a current to the secondary battery.
According to claim 5, the secondary battery shows a maximum peak in the range of 3.65 V or more and less than 3.75 V in the Q-dQ / dV curve when the secondary battery is charged from a fully discharged state. Described battery pack.
5. The battery pack according to 6.
The secondary battery has a positive electrode and a negative electrode, and has a positive electrode and a negative electrode.
The positive electrode contains an oxide represented by the general formula LiMO 2 (where M is at least one transition metal element selected from the group consisting of Co, Ni, Al, Mn and Fe).
The battery pack according to any one of claims 5 to 7, wherein the negative electrode contains graphite.
The battery pack according to claim 7, wherein the positive electrode contains a lithium nickel cobalt manganese composite oxide.
While charging the secondary battery
The relationship between the charge amount Q of the secondary battery and dQ / dV, which is the ratio of the change amount of the charge amount Q to the change amount of the voltage V, when the voltage of the secondary battery is 3.65 V or more is shown. The first inflection point at which the Q-dQ / dV curve changes from rising to falling or a point mathematically equivalent to this is set as the first inflection point.
The first inflection point at which the voltage of the secondary battery is 3.75 V or higher and the QdQ / dV curve changes from falling to rising, or a point mathematically equivalent to this, is set as the second inflection point.
Based on the difference between the dQ / dV value at the first inflection point and the dQ / dV value at the second inflection point, the insufficient charge amount of the secondary battery with respect to the reference charge amount at the second inflection point is determined. Calculate and
A method for controlling a secondary battery, in which when the insufficient charge amount is supplied to the secondary battery, it is corrected that the SOC of the secondary battery has reached a predetermined reference SOC.