JP2021182474A - Determination device for determining decrease in electrolyte quantity of secondary battery, and determination method - Google Patents

Abstract

To provide a determination device capable of previously detecting a considerable reduction of battery capacity caused by a decrease in an electrolyte quantity of a secondary battery.SOLUTION: The present invention relates to a determination device for determining a decrease in an electrolyte quantity of a secondary battery employing graphite for a negative electrode. The determination device comprises sensors 11 and 12 each for detecting a voltage and/or a current of the secondary battery, and a controller 10. The controller 10 calculates a state of charge of a secondary battery 2 on the basis of values detected by the sensors 11 and 12, identifies a plurality of peaks of a ratio (dV/dSOC) of an amount of change in the voltage of the secondary battery 2 with respect to an amount of change in the state of charge from battery characteristics obtained by the ratio (dV/dSOC) and the state of charge and, in a case where a difference of the state of charge between the plurality of identified peaks is equal to or smaller than a predetermined determination threshold, determines that the electrolyte quantity of the secondary battery decreases.SELECTED DRAWING: Figure 1

Description

The present invention relates to a determination device and a determination method for determining a decrease in the amount of electrolytic solution in a secondary battery.

Conventionally, there has been known a battery system that alleviates a deterioration in the performance of a secondary battery cell by additionally injecting an electrolytic solution (Patent Document 1). In the battery system described in Patent Document 1, the maximum number of secondary batteries is larger than that of a secondary battery cell having a structure in which the battery case is sealed with the first electrolytic solution and the electrode assembly built in the battery case. When the capacity is reduced by 20% to 60%, a second electrolytic solution having a composition different from that of the first electrolytic solution is additionally injected into the battery case.

International Publication No. 2017/217646

However, the above-mentioned battery system has a problem that it is a coping method after a large decrease in the maximum capacity of the battery and cannot detect a large decrease in the battery capacity in advance.

An object to be solved by the present invention is to provide a determination device and a determination method capable of detecting in advance a large decrease in battery capacity due to a decrease in the amount of electrolytic solution.

The present invention calculates the charge state of a secondary battery using graphite for the negative electrode, and during charging or discharging of the secondary battery, the ratio of the change in the voltage of the secondary battery to the change in the charge state and charging. Multiple peaks of ratio (dV / dSOC) are specified from the battery characteristics obtained from the state, and when the difference in charge state between the specified peaks is equal to or less than a predetermined determination threshold, the amount of electrolyte in the secondary battery The above problem is solved by determining that the number of batteries is decreasing.

According to the present invention, it is possible to detect in advance a large decrease in battery capacity due to a decrease in the amount of electrolytic solution.

FIG. 1 is a block diagram showing a determination system for a secondary battery according to the present embodiment. FIG. 2 is a graph showing the analysis results of the durability test of the secondary battery. FIG. 3 is a graph showing the characteristics of the dV / dSOC battery. FIG. 4 is a graph showing the characteristics of the difference in charge state between peaks with respect to the number of cycles. FIG. 5 is a graph showing the characteristics of the difference in charge state between peaks with respect to the number of cycles. FIG. 6 is a flowchart showing a procedure of determination processing in a system for determining a decrease in the amount of electrolyte in a secondary battery. FIG. 7 is a flowchart showing a procedure of determination processing in a system for determining a decrease in the amount of electrolyte in a secondary battery. FIG. 8 (а) is a graph showing the characteristics of the positive electrode voltage with respect to the SOC, and FIG. 8 (b) is a graph showing the characteristics of the negative electrode voltage with respect to the SOC. FIG. 9 (а) is a graph showing the dV / dSOC battery characteristics of the secondary battery, and FIG. 9 (b) is a graph showing the characteristics of the negative electrode voltage with respect to the SOC. FIG. 10 is a graph of the discharge characteristics of the secondary battery.

<< First Embodiment >>
An embodiment of a determination device and a determination method for determining a decrease in the amount of electrolytic solution of the secondary battery according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a determination system including an embodiment of the determination device according to the present invention. As shown in FIG. 1, the determination system according to the present embodiment controls the charging / discharging of the secondary battery 2 and determines whether or not the amount of the electrolytic solution in the secondary battery 2 is decreasing. It is a system for notifying before the battery capacity is significantly reduced that the battery capacity may be significantly reduced due to the decrease in the amount. The determination system includes a determination device 1 and a secondary battery 2. The determination device 1 may include a charging device or the like (not shown in FIG. 1).

The determination device 1 includes a controller 10, a voltage sensor 11, a current sensor 12, a DCDC converter 13, and a display 14. The controller 10 is a battery control unit (BCU). The controller 10 manages the state of the secondary battery 2 based on the detected voltage detected by the voltage sensor 11 and / or the detected current detected by the current sensor 12, and before the battery capacity drops significantly. It is detected in advance that the battery capacity may be significantly reduced due to the decrease in the amount of electrolyte. The controller 10 is composed of a memory such as a ROM or RAM, a processor such as a CPU, and the like.

The voltage sensor 11 is a sensor for detecting the voltage between the terminals of the secondary battery 2. It is connected between the wiring connected to the positive electrode and the negative electrode of the secondary battery 2. The current sensor 12 is a sensor for detecting the input / output current of the secondary battery 2. The current sensor 12 is connected to the wiring connected to the positive electrode or the negative electrode of the secondary battery 2. The voltage sensor 11 and the current sensor 12 detect the state of the battery, and output the detected value to the controller 10.

The DCDC converter 13 is a power conversion device that converts the voltage input from the secondary battery 2 into a predetermined voltage and outputs the power to a load such as a motor. The DCDC converter 13 is also a power conversion device that converts a voltage input from a load such as a motor or a charging device into a predetermined voltage and outputs power to the secondary battery 2. The DCDC converter 13 is controlled by the controller 10.

The display 14 is a display device for notifying the user of the state of the secondary battery 2. The display 14 is controlled by the controller 10. When the controller 10 determines that the amount of the electrolytic solution of the secondary battery 2 is decreasing, the controller 10 displays a display screen for notifying that the battery capacity may be significantly reduced before the battery capacity is significantly reduced. By displaying the image on the display 14, the user is notified of the status of the secondary battery 2.

The secondary battery 2 is, for example, a lithium ion secondary battery. The secondary battery 2 of this type exemplifies a negative electrode active material using an active material having a plurality of charge / discharge regions in which the charge / discharge potential changes stepwise with the insertion / desorption of lithium ions. Can be done. A graphite-based active material containing a graphite structure is suitable as an active material having a plurality of charge / discharge regions in which the charge / discharge potential changes stepwise with the insertion / desorption of such lithium ions. Therefore, in the embodiment shown below, the present invention will be described by exemplifying a lithium ion secondary battery using graphite for the negative electrode. The positive electrode active material is not particularly limited, and a known positive electrode active material for a lithium ion secondary battery such as a lithium-transition metal composite oxide can be used. The secondary battery 2 has an electrolytic solution, a separator, and a tab in addition to the positive electrode and the negative electrode.

The secondary battery 2 is electrically connected to the charging device. The charging device connected to the secondary battery 2 is, for example, a device for charging the secondary battery 2 mounted on an electric vehicle or a hybrid vehicle. Charging of the in-vehicle secondary battery 2 is performed by taking out the charging cable of the charging device, attaching the charging gun at the tip of the charging cable to the connector of the charging port of the vehicle, and then operating the charging start switch. The controller 10 controls the DCDC converter 13 and the charging device, respectively, so that the charging state of the secondary battery 2 becomes the target charging state while managing the charging state (State of Charge: SOC) of the secondary battery 2. do.

The secondary battery 2 is electrically connected to a load such as a motor. The load is a device that operates using the electric power of the secondary battery 2, and is a motor that is a drive source of the vehicle, auxiliary equipment such as an air conditioner and a light, and the like. The discharge of the secondary battery 2 is executed under the control of the controller 10 by a power request from the outside. For example, when the time until the vehicle starts running can be grasped, such as by operating the air conditioner before the vehicle runs by setting a timer so that the temperature inside the vehicle becomes appropriate when the vehicle starts running, the discharge control of the secondary battery 2 is performed. Is executed. The controller 10 receives a discharge command signal for discharging the secondary battery 2 from the main controller (not shown) of the vehicle at a predetermined time before the vehicle use start time set in advance in response to a user request or the like. Then, the DCDC converter 13 is controlled so that the required power indicated by the discharge command signal is reached, and the secondary battery 2 is discharged.

Here, a usage pattern of the secondary battery 2 will be described. The secondary battery 2 is designed so that it can be tolerated even if the amount of the electrolytic solution of the secondary battery 2 is reduced by filling the secondary battery 2 in excess, assuming normal usage. On the other hand, in recent years, batteries for automobiles are being reused and effectively utilized. In particular, because the performance required for the secondary battery 2 for automobiles is high spec, even if the secondary battery 2 cannot be used for vehicles, it can be used for devices and systems other than vehicles such as power storage devices and solar systems. It can be effectively used as a consumer battery to be used. Further, it is possible that the secondary battery 2 of the vehicle can be mounted on another vehicle and reused. Such reuse is often not taken into consideration at the design stage of the secondary battery 2. Therefore, if the secondary battery 2 is used in a form not expected at the design stage and the capacity is significantly reduced due to a decrease in the amount of electrolytic solution, the system equipped with the secondary battery 2 may malfunction. There is also. As the amount of electrolyte in the lithium-ion battery decreases, the battery capacity decreases faster, so even if the system determines that the battery capacity is sufficient at this point, the battery may become unusable in a short time.

In order to prevent the system from malfunctioning due to such a decrease in battery capacity, the system according to the present embodiment determines a decrease in the amount of electrolytic solution before the battery capacity is significantly reduced. Further, by determining the decrease in the amount of the electrolytic solution before the battery capacity is significantly reduced, there are also the following advantages. Before the secondary battery 2 is mounted on the system (reuse destination system) (so-called off-board), for example, it is possible to sort out whether the battery to be reused is appropriate or inappropriate. Further, after the secondary battery 2 is mounted on the system (reuse destination system) (so-called on-board), the battery can be replaced before the battery capacity of the secondary battery 2 is significantly reduced. ..

Next, the battery characteristics when the battery capacity of the secondary battery 2 decreases due to the decrease in the amount of the electrolytic solution will be described with reference to FIG. FIG. 2 is a graph showing the analysis results of the durability test of the secondary battery 2. The vertical axis of FIG. 2 shows the ratio (dV / dQ) of the amount of change in the voltage of the secondary battery 2 to the amount of change in the discharge capacity of the secondary battery 2, and the horizontal axis shows the ratio of the amount of change in the voltage of the secondary battery 2 (dV / dQ). It shows the discharge capacity. FIG. 2 (а) is a graph showing battery characteristics when the number of cycles is (zero), and FIGS. 2 (b) to 2 (e) are batteries in the order of 250, 500, 750, and 1000 cycles, respectively. It is a graph which shows the characteristic. The secondary battery 2 used in the durability test is a lithium-ion battery containing an electrolytic solution using graphite as a negative electrode, similar to the battery included in the system according to the present embodiment. However, the secondary battery 2 used in the durability test is a battery in which the amount of electrolytic solution is reduced in the initial state, and a prototype battery that is likely to be affected by the decrease in the amount of electrolytic solution in obtaining the battery characteristics shown in FIG. 2 is prototyped. I am using it. In the following description, the ratio of the amount of change in the voltage of the secondary battery 2 to the amount of change in the discharge capacity of the secondary battery 2 will be simply referred to as dV / dQ.

When graphite is used for the negative electrode of the secondary battery 2, the potential of the negative electrode fluctuates when the stage structure is switched during charging / discharging of the battery. Then, this potential fluctuation appears as a peak of dV / dQ. In the initial state of the secondary battery 2 (number of cycles = 0), as shown in FIG. 2 (а), the peak of dV / dQ appears when the discharge capacities are 13.3 mAh and 30.2 mAh. As shown in FIGS. 2 (b) to 2 (d), the peak of dV / dQ appears even when the number of cycles of the secondary battery 2 is 250, 500, and 750. The difference in discharge capacity between the peaks of dV / dQ is Δ16.9 [mAh] (= 30.2-13.3) in the initial state (number of cycles = 0). Further, when the number of cycles of the secondary battery 2 is 250, 500, 750, the difference in discharge capacity between the peaks of dV / dQ is Δ16.0 [mAh] (= 27.2-11.2). It is Δ15.6 [mAh] (= 25.3-9.7) and Δ14.8 [mAh] (= 23.6-8.8). That is, as the number of cycles increases and the battery capacity decreases, the difference in discharge capacity between the peaks of dV / dQ gradually decreases. That is, the interval corresponding to the difference in the discharge capacity between the peaks of dV / dQ (hereinafter, also simply referred to as the inter-peak capacity) is gradually narrowed. Then, when the number of cycles is further increased to 1000 cycles, the peak of dV / dQ disappears as shown in FIG. 2 (e).

According to the inventor's knowledge, the change in battery characteristics as shown in FIGS. 2 (а) to 2 (e) can be explained as follows. The decrease in battery capacity with an increase in the number of cycles is mainly caused by a decrease in lithium operation due to a film (Solid Electrolyte Interphase: SEI) formed mainly at the interface between the negative electrode and the electrolyte during charging. It is considered that the peak shape of dV / dQ becomes broad because the SOC in the electrode is distributed due to the decrease in the amount of the electrolytic solution. Further, it is considered that the decrease in the inter-peak volume is caused by the isolation of a part of the active material in the electrode due to the decrease in the amount of the electrolytic solution.

When the electrolytic solution is re-injected into the secondary battery 2 having a narrow peak-to-peak capacity, the peak-to-peak capacity becomes a state close to the initial state, and the peak shape of dV / dQ also becomes a state close to the initial state. From this point, it can be confirmed that the cause of the change in battery characteristics as shown in FIGS. 2 (а) to 2 (e) is a decrease in the amount of electrolytic solution.

Further, according to the inventor's knowledge, the reason why it is possible to detect in advance that the battery capacity is significantly reduced by determining whether or not the amount of the electrolytic solution is reduced can be explained as follows. As the amount of electrolytic solution decreases, some active materials are isolated in the electrode. Even if the route to the active material is narrow, it can be charged and discharged as long as it remains, so there is no significant decrease in battery capacity. Then, when the amount of the electrolytic solution is further reduced and the path leading to many active materials is completely interrupted, the battery capacity is greatly reduced. In the battery characteristics of dV / dQ, the isolation of some active materials due to the decrease in the amount of electrolytic solution is reflected in the inter-peak capacity. Further, when a part of the active material is isolated, the capacity of the electrode is reduced by the amount of the active material that does not contribute to charging / discharging, so that the battery characteristics of dV / dQ are in the left-right direction (direction along the horizontal axis in FIG. 2). Shrink to. As a result, the peak capacity is reduced. Further, in the battery characteristics of dV / dQ, when the path to the active material becomes narrow and the SOC distribution is formed due to the decrease in the amount of the electrolytic solution, the peak shape of dV / dQ becomes broad. Therefore, it is possible to determine whether or not the amount of electrolytic solution is decreasing based on the inter-peak capacity, and by determining whether or not the amount of electrolytic solution is decreasing, it is detected in advance that the battery capacity is significantly reduced. can.

That is, due to the change in the battery characteristics represented by the peak of dV / dQ, there is a possibility that the battery capacity of the secondary battery 2 may be significantly reduced due to the decrease in the amount of the electrolytic solution before the battery capacity of the secondary battery 2 is significantly reduced. Can be detected. In the present embodiment, such a battery characteristic is used to determine a decrease in the amount of electrolytic solution, and it is detected in advance that the capacity of the secondary battery 2 may be significantly reduced due to the decrease in the amount of electrolytic solution. The controller 10 included in the determination device 1 shown in FIG. 1 identifies a plurality of dV / dQ peaks, and compares the difference in charge state between the specified plurality of peaks with a predetermined determination threshold value. Therefore, it is determined whether or not the amount of the electrolytic solution of the secondary battery is reduced.

Here, dV / dQ and dV / dSOC will be described. dV / dSOC indicates the ratio of the amount of change in the voltage of the secondary battery 2 to the amount of change in the state of charge of the secondary battery 2. The relationship between the cell voltage (voltage between terminals) of the secondary battery 2 and the amount of electric charge changes depending on the size of the battery capacity. For example, when compared with a battery having a battery capacity of 10 times that of a certain secondary battery 2, in order to make the cell voltage the same, it is necessary to charge a battery having a battery capacity of 10 times 10 times. On the other hand, the state of charge is represented by the ratio of the current charge amount (remaining charge capacity) to the battery capacity. Therefore, in the present embodiment, dV / dSOC is used in order to make the battery characteristics common among batteries having different battery capacities. As with the peak of dV / dQ, the peak of dV / dSOC appears during charging / discharging of the battery. Further, when the electrolytic solution decreases and the battery capacity decreases, the peak shape of dV / dSOC changes, and the difference in SOC between the peaks of dV / dSOC gradually decreases.

A method of calculating the difference in charge state between peaks of dV / dSOC (dV / dQ) by the controller 10 will be described. The controller 10 discharges the secondary battery 2 from a state in which the secondary battery 2 is fully charged or nearly fully charged. The controller 10 acquires a detected value from the voltage sensor 11 and / or the current sensor 12 while the secondary battery 2 is discharging, and calculates the charge state of the secondary battery 2 based on the detected value. The controller 10 calculates the current charge amount of the secondary battery 2 by integrating the discharge current of the secondary battery 2 and subtracting the current integrated value from the battery capacity (capacity when fully charged) of the secondary battery 2. do. Then, the controller 10 calculates the charge state by dividing the current charge amount (Q) by the battery capacity of the secondary battery 2. The controller 10 measures the cell voltage of the secondary battery 2 and calculates the SOC in accordance with a predetermined control cycle.

ただし、ｔは時間を示し、ｔ−１は、時間（ｔ）に対して１制御周期前の時間を表す。 Next, the controller 10 calculates dV / dSOC according to the following equation (1) according to the control cycle.

However, t represents a time, and t-1 represents a time one control cycle before the time (t).

なお、ｎはノイズの影響や測定精度等に合わせて実験的に設定すればよい。 The controller 10 may calculate dV / dSOC from the slope of the approximate straight line using a plurality of measurement points in order to further suppress the influence of noise. The controller 10 may calculate dV / dSOC by obtaining the slope by the method of least squares using the following equation (2).

It should be noted that n may be set experimentally according to the influence of noise, measurement accuracy, and the like.

The charge state can be calculated using the characteristics of SOC-OCV (open circuit voltage), but when the change in charge state calculated from the characteristics of SOC-OCV is small with respect to the control cycle, , The state of charge may be obtained by using current integration or the like.

The controller 10 calculates dV / dSOC according to the control cycle while the secondary battery 2 is being discharged. The controller 10 calculates the battery characteristics obtained from the state of charge and the dV / dSOC (hereinafter, the battery characteristics that can be expressed by dV / dSOC with respect to the SOC are also referred to as dV / dSOC battery characteristics). FIG. 3 is a graph showing the characteristics of the dV / dSOC battery. The vertical axis of FIG. 3 shows dV / dSOC, and the horizontal axis shows the depth of discharge (DOD). In the example of FIG. 3, the discharge depth at the end of discharge is less than 100%, but the DOD on the horizontal axis is represented by a value converted into SOC based on the battery capacity in the initial state, so that the battery is discharged. The discharge depth at the end is a value lower than 100% due to the deterioration of the battery.

The controller 10 acquires the dV / dSOC battery characteristics as shown in FIG. 3 by using the dV / dSOC-SOC data obtained in time series by calculation. As shown in FIG. 3, the dV / dSOC battery characteristics include the peak of dV / dSOC and are represented by a steeply shaped graph with the peak value as the apex. In the example of FIG. 3, since there are two peaks of dV / dSOC, the dV / dSOC battery characteristics have two convex shapes with the peak of dV / dSOC as the apex. After acquiring the dV / dSOC battery characteristics, the controller 10 identifies a plurality of dV / dSOC peaks. In order to identify the peak of dV / dSOC, the controller 10 calculates the amount of change in dV / dSOC per control cycle during the discharge of the secondary battery 2, and dV / dSOC is increasing in the section where dV / dSOC is increasing. Identify the section where dSOC is decreasing. As shown in FIG. 3, when the dV / dSOC changes repeatedly in a short time, the amount of change in the dV / dSOC can be calculated using the average value of the dV / dSOC per predetermined time. good. Then, the controller 10 specifies the value at the point where the dV / dSOC is inverted from the increase to the decrease as the peak of the dV / dSOC. The method for specifying the peak of dV / dSOC may be another method. Further, the controller 10 does not necessarily have to obtain the dV / dSOC battery characteristics from the start to the end of discharge, and during the calculation of dV / dSOC, the amount of change in dV / dSOC is calculated in time series, and based on the calculation result. , The peak of dV / dSOC may be specified.

Next, the controller 10 calculates the difference in charge state between a plurality of peaks of dV / dSOC (hereinafter, simply referred to as inter-peak SOC) in the dV / dSOC battery characteristics as shown in FIG. In the example of FIG. 3, the controller 10, the peak of the dV / dSOC take vertex _{P 1,} identify each peak in dV / dSOC taking vertex _{P 2,} and DOD _L at vertex _{P 1,} DOD at vertex _{P 2 The difference from H} (ΔDOD = DOD _H −DOD _L ) is calculated as the peak-to-peak SOC.

After calculating the peak-to-peak SOC, the controller 10 compares the calculated peak-to-peak SOC with a predetermined determination threshold value, and determines whether or not the amount of electrolytic solution in the secondary battery 2 is reduced according to the comparison result. judge. When the calculated peak-to-peak SOC is equal to or less than a predetermined determination threshold value, the controller 10 determines that the amount of electrolytic solution is decreasing. When the calculated peak-to-peak SOC is higher than a predetermined determination threshold value, the controller 10 determines that the amount of electrolytic solution has not decreased.

A method of setting the determination threshold value will be described with reference to FIGS. 4 and 5. FIG. 4 is a graph showing the characteristics of inter-peak SOC (ΔSOC) with respect to the number of cycles. In FIG. 4, the horizontal axis indicates the number of cycles, and the vertical axis indicates the peak-to-peak SOC (ΔSOC).

An evaluation experiment was conducted on a certain secondary battery 2, and dV / dSOC battery characteristics were obtained every 250 cycles from the initial state to 1000 cycles from the experimental data, and the dV / dSOC battery characteristics had multiple peaks of dV / dSOC. Suppose it is identified. Then, when the difference in the state of charge between the peaks is calculated while observing every 250 cycles, the peak-to-peak SOC changes as shown in FIG.

In the secondary battery 2 in the initial state, the peak-to-peak SOC is about 46.7 [%]. As the number of cycles increases, the peak-to-peak SOC gradually decreases, and the peak-to-peak SOC becomes about 45.0 [%] in the number of cycles (250) and about 43.9 [%] in the number of cycles (500). At (750), it becomes about 43.1 [%].

For example, when the determination threshold value is set between 43 [%] and 44 [%], when the number of cycles of the secondary battery 2 used in the example of FIG. 4 exceeds about 500 to 750, Since the peak-to-peak SOC (ΔSOC) is lower than the determination threshold value, the controller 10 determines that the amount of the electrolytic solution is decreasing.

The graph of FIG. 5 shows the ratio of the peak-to-peak SOC to the initial peak-to-peak SOC every 250 cycles when the peak-to-peak SOC (hereinafter, also referred to as the initial peak-to-peak SOC) in the secondary battery 2 in the initial state is 100%. It is shown.

The ratio of dV / dSOC peak-to-peak SOC to initial peak-to-peak SOC gradually decreases as the number of cycles increases. The determination threshold is preferably set in the range of 92% or more to 94% or less with respect to the initial peak-to-peak SOC. In FIG. 5, the range of 92% or more to 94% or more with respect to the initial peak-to-peak SOC is the range of the dotted line T _{th_L} or more and the dotted line T _{th_H} or less. When the determination threshold is set in the range of 92% or more to 94% or more of the initial peak-to-peak SOC, the dV / dSOC peak occurs when the number of cycles of the secondary battery 2 exceeds about 500 to 750. Since the SOC is lower than the determination threshold value, the controller 10 determines that the amount of the electrolytic solution is decreasing.

A determination flow for determining a decrease in the amount of the electrolytic solution of the secondary battery 2 will be described with reference to FIG. The control flow shown in FIG. 6 is a control flow for determining whether or not there is a decrease in the amount of electrolytic solution during offboarding. The controller 10 can execute a control flow for determining whether or not the amount of the electrolytic solution is decreasing at an arbitrary timing.

In step S1, the controller 10 determines whether or not to end the determination flow with the secondary battery 2 charged. As will be described later, since the determination of the decrease in the amount of electrolytic solution can be performed both during charging and discharging, for example, the determination is made in the state where the secondary battery 2 is charged according to the needs of the secondary battery 2 after the determination. Whether to end the flow or to end the determination flow with the secondary battery 2 discharged can be appropriately selected. For example, when the secondary battery 2 is used after the determination is completed, the secondary battery 2 can be used immediately after the determination flow is completed in a charged state. On the other hand, when the secondary battery 2 is stored after the determination is completed, the deterioration of the secondary battery can be suppressed by storing the secondary battery 2 in a discharged state. The selection of whether to make the secondary battery 2 charged or discharged after the determination is completed is predetermined by the user. When the determination flow is terminated when the secondary battery 2 is discharged, the determination flow in step S1 proceeds to "NO", and when the determination flow is terminated when the secondary battery 2 is charged, the determination flow proceeds to "NO". The determination flow in step S1 proceeds to "YES".

In step S2, the controller 10 charges the secondary battery 2 until it is fully charged. In step S3, the controller 10 discharges the secondary battery 2 at the first discharge C rate until the peak of the second dV / dSOC is measured, and acquires the dV / dSOC battery characteristics. Specifically, the dV / dSOC battery characteristics are acquired by the following method. The controller 10 starts discharging from the state where the secondary battery 2 is fully charged. The controller 10 discharges the secondary battery 2 at the first discharge C rate. Regarding the first discharge C rate, if the C rate is too high, the variation in SOC in the battery becomes large, so that the calculation accuracy when specifying the peak of dV / dSOC becomes low. On the contrary, if the C rate is too low, it takes time to determine. Therefore, the optimum value of the first discharge C rate is set in an experiment or the like, and may be set to, for example, about 0.1 C.

ただし、Ｑ_ｃは二次電池２の電池容量（満充電時の電荷量）を示す。 While the secondary battery 2 is being discharged, the controller 10 acquires the detected voltage and the detected current of the secondary battery 2 detected by the voltage sensor 11 and the current sensor 12 in a predetermined control cycle. The controller 10 calculates the charge amount and the charge state of the secondary battery 2 in a predetermined control cycle based on the detected values of the voltage sensor 11 and / or the current sensor 12. The controller 10 calculates the charge amount by adding the value obtained by multiplying the discharge current by the time for one control cycle to the previous value of the charge amount calculated at the time of the previous control cycle. The initial value of the amount of electric charge (Q) is zero. Further, the controller 10 calculates the charging state by using the following equation (3).

However, Q _c indicates the battery capacity (the amount of charge when fully charged) of the secondary battery 2.

The controller 10 stores the value of the cell voltage (V) for each SOC in the memory while calculating the dV / dSOC. Further, the controller 10 identifies the peak of dV / dSOC from the calculation result of dV / dSOC. When the second peak of dV / dSOC can be specified from the calculation result of dV / dSOC, the controller 10 stops the processing such as the calculation of dV / dSOC. This makes it possible to acquire dV / dSOC battery characteristics.

In step S4, the controller 10 discharges the secondary battery 2 at the second discharge C rate until the state of charge becomes zero. The second discharge C rate is higher than the first discharge C rate.

If the determination flow in step S2 is "YES", in step S5, the controller 10 discharges the secondary battery 2 until the state of charge of the secondary battery 2 becomes zero. In step S6, the controller 10 charges the secondary battery 2 at the first charging C rate until the peak of the second dV / dSOC is measured, and acquires the dV / dSOC battery characteristics. The calculation process for acquiring the dV / dSOC battery characteristics is the same as the calculation process in step S3 after changing the calculation method of the charging state according to the charging of the secondary battery 2 in the calculation process in step S3. Just do it. As with the first discharge C rate, the first charge rate is set to an optimum value for specifying the peak of dV / dSOC, and may be set to, for example, about 0.1 C.

In step S7, the controller 10 charges the secondary battery 2 at the second charging C rate until the secondary battery 2 is fully charged. The second charge C rate is higher than the first charge C rate.

After the control flow in step S4 or after the control flow in step S7, the controller 10 calculates the peak-to-peak SOC from the acquired dV / dSOC battery characteristics and compares the peak-to-peak SOC with the determination threshold value (step S8). ). When the peak-to-peak SOC is higher than the determination threshold value, the controller 10 determines in step S9 that the amount of the electrolytic solution has not decreased. When the peak-to-peak SOC is equal to or less than the determination threshold value, the controller 10 determines in step S10 that the amount of the electrolytic solution has decreased. Since the determination flow in step S8 is performed before the battery capacity of the secondary battery 2 is significantly reduced, the controller 10 causes a decrease in the amount of electrolytic solution before the battery capacity of the secondary battery 2 is significantly reduced. It can be detected that the battery capacity may be significantly reduced.

In step S11, the controller 10 executes limit control in order to protect the secondary battery 2. The limit control is, for example, lowering the upper limit voltage of the secondary battery 2, raising the lower limit voltage of the secondary battery, lowering the upper limit value of the charge / discharge current, and the like. The various restriction controls may be a combination of a plurality of controls. Further, the controller 10 may pass the current battery state to the user in combination with the limit control. The notification to the user is, for example, a notification for requesting the user to replace the secondary battery 2. Then, the controller 10 ends the control flow shown in FIG.

Here, the first discharge C rate and the second discharge C rate will be described with reference to FIG. When acquiring the dV / dSOC battery characteristics while the secondary battery 2 is being discharged, the secondary battery starts discharging from a fully charged state. The secondary battery 2 is charged at the first discharge C rate. The dV / dSOC battery characteristics are plotted from the low DOD side to the high DOD side. During the secondary battery 2 discharges, depth of discharge, when it is DOD _L, the peak of the first dV / dSOC is identified. Further, when the discharge of the secondary battery 2 progresses and the discharge depth becomes DOD _H , the second peak of dV / dSOC is specified. Then, after the second dV / dSOC peak is identified, the secondary battery 20 is discharged at the second discharge rate. That is, the discharge current is suppressed in the range of DOD required to acquire the peak-to-peak SOC, and the discharge current is not suppressed in the other range. As a result, the determination time can be shortened.

Further, the first charge C rate and the second charge C rate will be described with reference to FIG. Although the horizontal axis of FIG. 3 is represented by the discharge depth (DOD), it will be described after being replaced with the state of charge (SOC) (for example, 70% of DOD corresponds to 30% of SOC). Charging is started from the state where the charging state of the secondary battery 2 is zero. The secondary battery 2 is discharged at the first charge C rate. The dV / dSOC battery characteristics are plotted from the low SOC side (high DOD side in FIG. 3) to the high SOC side (low DOD side in FIG. 3). During charging of the secondary battery 2, when the state of charge becomes _{SOC corresponding to DOD H} , the first peak of dV / dSOC is specified. Further, when the charging of the secondary battery 2 progresses and the charged state becomes _{the SOC corresponding to DOD L} , the second peak of dV / dSOC is specified. Then, after the second dV / dSOC peak is identified, the secondary battery 20 is charged at the second charging rate. That is, the charging current is suppressed in the range of the charging state required to acquire the peak-to-peak SOC, and the charging current is not suppressed in the other range. As a result, the determination time can be shortened.

Next, with reference to FIG. 7, a control flow for determining whether or not there is a decrease in the amount of electrolytic solution at the time of onboarding will be described.

In step S71, the controller 10 measures the voltage and current of the secondary battery 2 by using the voltage sensor 11 and the current sensor 12. In step S72, the controller 10 calculates the state of charge (SOC) of the secondary battery 2. The controller 10 refers to a map showing the correlation between the open circuit voltage of the secondary battery 2 and the state of charge, and calculates the state of charge corresponding to the measured battery voltage. Further, the controller 10 may calculate the charging state from the current integration. In step S73, the controller 10 determines whether or not the secondary battery 2 is being charged. If the secondary battery 2 is not being charged, in step S74, the controller 10 ends the control flow of FIG. 7 without determining whether or not the amount of the electrolytic solution has decreased.

When the secondary battery 2 is being charged, in step S75, the controller 10 determines whether or not the current charging state is less than a predetermined charging state. In order to identify the two dV / dSOC peaks in the dV / dSOC battery characteristics, charging is started from the charged state where the peak on the low SOC side appears among the two dV / dSOC peaks. There is a need to. Therefore, in the present embodiment, the predetermined charging state is set to a charging state lower than the charging state in which the peak on the low SOC side appears. If the current charging state is equal to or higher than the predetermined charging state, the determination flow proceeds to "NO".

When the current charging state is less than the predetermined charging state, in step S76, the controller 10 ends the flow of determining whether or not the amount of the electrolytic solution is reduced by the scheduled start time of the vehicle. Determine if it can be done. The scheduled travel start time is determined by, for example, a timer setting by the user, or an operation end time of the air conditioner when the air conditioner is operated before the vehicle travels by the timer setting. The time required for the determination flow can be predicted by calculation from the C rate. For example, when charging from SOC (0%) to SOC (50%) at a charging C rate (1C), the determination time is 30 minutes. If the determination flow cannot be completed by the scheduled start time of the vehicle, the determination flow proceeds to "NO".

If the determination flow can be completed by the scheduled start time of the vehicle, in step S77, the controller 10 starts the determination flow as to whether or not the amount of the electrolytic solution is reduced, and dV / dSOC. Acquire battery characteristics. The method of acquiring the dV / dSOC battery characteristics is the same as the method acquired during offboarding and charging of the secondary battery 2, that is, the method in step S6 of FIG. In order to determine whether or not there is a decrease in the amount of electrolyte, it is necessary to identify two dV / dSOC peaks. Therefore, the dV / dSOC battery characteristics are acquired until the charge state of the secondary battery 2 becomes a charge state higher than the charge state in which the peak on the high SOC side appears among the two dV / dSOC peaks.

In step S78, the controller 10 determines whether or not there is a dV / dSOC peak in the dV / dSOC battery characteristics. As shown in FIG. 2 (e), when the charge / discharge cycle increases and the battery capacity decreases significantly due to the decrease in the amount of electrolytic solution, the peak of dV / dSOC disappears in the dV / dSOC battery characteristics. In such a case, the determination flow proceeds to "YES", and the control process of step S81 is executed.

When there is a peak of dV / dSOC, in step S79, the controller 10 calculates the peak-to-peak SOC from the dV / dSOC battery characteristics and compares the peak-to-peak SOC with the determination threshold value. When the peak-to-peak SOC is higher than the determination threshold value, the controller 10 determines in step S80 that the amount of the electrolytic solution has not decreased. When the peak-to-peak SOC is equal to or less than the determination threshold value, the controller 10 determines in step S81 that the amount of the electrolytic solution has decreased. Since the determination flow in step S79 is performed before the battery capacity of the secondary battery 2 is significantly reduced, the controller 10 causes a decrease in the amount of electrolytic solution before the battery capacity of the secondary battery 2 is significantly reduced. It can be detected that the battery capacity may be significantly reduced.

In step S82, the controller 10 executes limit control in order to protect the secondary battery 2. The limit control is the same as the limit control in the control process of step S9. Further, the controller 10 may pass the current battery state to the user in combination with the limit control. The notification to the user is, for example, a notification for requesting the user to replace the secondary battery 2. Then, the controller 10 ends the control flow shown in FIG. 7.

In step S77, when charging the secondary battery 2 in order to acquire the dV / dSOC battery characteristics, the charging state required for acquiring the peak-to-peak SOC is the same as the charging at the time of off-board. In the range of, the charging C rate may be lowered, and in the other range, the charging C rate may be increased.

As described above, in the present embodiment, the charging state of the secondary battery 2 is calculated based on the value detected by the voltage sensor 11 and / or the current sensor 12, and the charging state is calculated while the secondary battery 2 is being charged or discharged. From the ratio of the amount of change in the voltage of the secondary battery (dV / dSOC) to the amount of change in the battery and the battery characteristics obtained from the charged state, a plurality of peaks of the ratio (dV / dSOC) are specified, and between the specified peaks. When the difference in charging state is equal to or less than a predetermined value (determination threshold value), it is determined that the amount of electrolytic solution in the secondary battery has decreased. When graphite is used for the negative electrode, two dV / dSOC peaks appear in the dV / dSOC battery characteristics. Both of these peaks are caused by structural changes when graphite is in a specific charged state, so when the amount of electrolyte decreases and some of the active material of the negative electrode cannot contribute to the battery capacity, these two peaks The capacity between peaks also decreases. When Li is consumed to form a film such as SEI, which is the main cause of deterioration of the battery, the peak-to-peak capacity does not change, so it can be determined separately from the capacity deterioration due to other than the decrease in the electrolyte. In the present embodiment, it is determined whether or not the amount of the electrolytic solution is reduced by utilizing such properties of the secondary battery 2. As a result, the decrease in the capacity of the secondary battery caused by the decrease in the amount of the electrolytic solution can be detected before the battery capacity decreases significantly.

Further, in the present embodiment, the dV / dSOC battery characteristic has a peak within a specific range of the charged state, and the controller 10 charges or discharges the secondary battery when the charged state is outside the specific range. Is higher than the predetermined current. For example, in the control flow of step S3, the DOD from the start of discharge to the identification of the second peak of dV / dSOC corresponds to the specific range. Further, for example, in the control flow of step S6, the charging state from the start of charging until the second peak of dV / dSOC is specified corresponds to the specific range. As a result, since the necessary data is only the part used for specifying the peak, the measurement time can be shortened and the necessary data can be acquired by suppressing the current to a small amount and acquiring the data.

Further, in the present embodiment, the controller 10 switches between charging and discharging at the time of determination according to the intended use of the secondary battery 2 after the determination result. As described above, the determination of the decrease in the amount of the electrolytic solution can be carried out at the time of charging or at the time of discharging, and therefore which one should be selected may be appropriately selected. As a result, unnecessary charging / discharging can be prevented by selecting whether to charge or discharge the battery after the determination according to the intended use after the determination.

Further, in the present embodiment, the predetermined value (determination threshold value) is set within the range of 92% or more and 94% or less with respect to the difference in the initial peak-to-peak charge state. This prevents erroneous determination due to noise and individual variation, and can detect in advance that the battery capacity is significantly reduced due to a decrease in the amount of electrolytic solution.

Further, in the present embodiment, when the controller 10 determines that the amount of the electrolytic solution of the secondary battery 2 is decreasing, the controller 10 notifies the user of the state of the secondary battery 2. When the amount of the electrolytic solution decreases, it is difficult to recover the battery by means other than processing the battery such as injecting the electrolytic solution. When the electrolyte is low, it is basically replaced with another battery except for a special battery. Therefore, by notifying the user of the state of the secondary battery 2, it is possible to urge the user to replace the battery before the battery capacity drops significantly.

Further, in the present embodiment, when the controller 10 determines that the amount of the electrolytic solution of the secondary battery 2 is decreasing, the controller 10 executes a limitation control for limiting the use of the secondary battery 2. Thereby, when the amount of the electrolytic solution is reduced, the use of the battery can be restricted so as to suppress the further decrease in the amount of the electrolytic solution.

Further, in the present embodiment, as limiting control, the controller 10 lowers the upper limit voltage of the secondary battery 2, raises the lower limit voltage of the secondary battery 2, and lowers the upper limit value of the charge / discharge current, at least one of them. Do one. When the amount of electrolytic solution decreases, the active material in the electrode cannot be partially used. Therefore, a dissociation occurs between the state of charge and the current assumed for the entire battery and the actual state of charge of the active material and the current flowing through the active material. Therefore, by limiting the use of the secondary battery 20 as in the present embodiment, further deterioration of the battery and consumption of the electrolytic solution can be suppressed.

Further, in the present embodiment, the controller 10 determines whether or not the amount of the electrolytic solution of the secondary battery 2 is decreasing while the secondary battery 2 is being charged. As a result, in addition to the normal charging of the secondary battery 2, the determination of the decrease in the amount of the electrolytic solution can be performed at the same time. Therefore, it is possible to prevent the secondary battery 2 from being charged or discharged only for the determination, and to make the determination. There is no need to set a separate time.

<< Second Embodiment >>
Next, the determination system according to the second embodiment will be described. In the second embodiment, the system can handle not only the case where the dV / dSOC peak is caused by the graphite contained in the negative electrode but also the case where the dV / dSOC peak is caused by the positive electrode material. It should be noted that the configuration is the same as that of the first embodiment except that the determination system is different from the determination system according to the first embodiment in the points described below, and the same control as that of the first embodiment is performed. It operates in the same manner as the above, and the description of the first embodiment is appropriately incorporated.

FIG. 8 is a graph showing the characteristics of the voltage of each pole with respect to the SOC, where (а) shows the positive electrode characteristics and (b) shows the negative electrode characteristics. The vertical axis shows voltage and the horizontal axis shows SOC. With the same SOC, the difference between the positive electrode voltage on the graph in FIG. 8 (а) and the negative electrode voltage on the graph in FIG. 8 (b) becomes the cell voltage (voltage between terminals) of the secondary battery 2. Equivalent to.

FIG. 9 shows a side-by-side graph of the battery characteristics shown in FIG. 8B and the graph of the dV / dSOC battery characteristics of the secondary battery 2. FIG. 9 (а) shows the dV / dSOC battery characteristics of the secondary battery 2, and FIG. 9 (b) is a graph in which the high voltage side of the battery characteristics shown in FIG. 8 (b) is cut off. The vertical axis of FIG. 9 (а) indicates dV / dQ, and the horizontal axis indicates SOC. The positive electrode of the secondary battery 2 having the battery characteristics as shown in the graph of FIG. 9 has the characteristics as shown in the graph of FIG. 8 (а), and the negative electrode has the characteristics as shown in the graph of FIG. 8 (b). Have.

As shown in FIG. 9, the state of charge having a dV / dQ peak corresponds to the state of charge having a change point of the negative electrode voltage (see the portion indicated by the arrow in FIG. 9). That is, the structural change when the graphite of the negative electrode is in a specific charged state appears in the dV / dQ peak. If the dV / dQ peak appears not as a positive electrode factor but as a result of graphite contained in the negative electrode as in the example of FIG. 9, the specified dV / dQ peak is used to reduce the amount of electrolytic solution. You just have to judge.

On the other hand, when the dV / dQ peak caused by graphite on the negative electrode overlaps with the peak on the positive electrode, the accuracy of determining the decrease in the amount of electrolytic solution may be lowered by selecting the dV / dSOC peak to be determined. ..

FIG. 10 is a graph showing the discharge curve of the secondary battery 2. In FIG. 10, graph а indicates the characteristics of the cell, b indicates the characteristics of the cathode (positive electrode), and c indicates the characteristics of the anode (negative electrode). The vertical axis of FIG. 10 shows dV / dQ, and the horizontal axis shows SOC. The secondary battery 2 is a lithium ion battery, and the positive electrode is a mixed system of spinel-type lithium manganate and a ternary layered rock salt-type oxide (0.25 Li _1-x Mn ₂ O ₄ , 0.75 _{Li 1). -Y} Ni _0.5 Co _0.2 Mn _0.3 O ₂ ) is used, and graphite is used for the negative electrode.

With reference to FIG. 10, “A” and “C” are peaks caused by the positive electrode, and “B” and “D” are peaks caused by the negative electrode. In the example of FIG. 10, the peak of "B" is close to the peaks "A" and "C" on both sides. The peak of "D" is located away from the peaks "A" and "C" of the positive electrode factor. When calculating the inter-peak SOC, the peak of "D" can be used without any problem because it is located away from the peaks "A" and "C" of the positive electrode factor. On the other hand, since the peak of "B" is located near the peaks "A" and "C" of the positive electrode factor, if the peak of "B" can be separated from the peak of the positive electrode factor, it is "B". And the peak of "D" can be used to calculate the inter-peak SOC. If it cannot be separated from the peak of the positive electrode factor, it will be difficult to calculate the inter-peak SOC using the peaks of "B" and "D".

In the determination system according to the present embodiment, when the dV / dSOC battery characteristics include the peak of the positive electrode factor and the peak of the graphite factor, the peak of the graphite factor is used instead of the peak of the positive electrode factor. , It is determined whether or not the amount of the electrolytic solution of the secondary battery 2 is reduced. This makes it possible to prevent erroneous determination due to the influence of the peak of the positive electrode factor.

Although the embodiments of the present invention have been described above, these embodiments have been described for facilitating the understanding of the present invention, and have not been described for the purpose of limiting the present invention. Therefore, each element disclosed in the above-described embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

1 ... Judgment device 2 ... Secondary battery 10 ... Controller 11 ... Voltage sensor 12 ... Current sensor 13 ... DCDC converter 14 ... Display

Claims (10)

It is a judgment device that determines the decrease in the amount of electrolyte in a secondary battery that uses graphite for the negative electrode.
A sensor that detects the voltage and / or current of the secondary battery,
Equipped with a controller
The controller
Based on the value detected by the sensor, the charge state of the secondary battery is calculated.
The ratio (dV) is based on the ratio of the change in the voltage of the secondary battery to the change in the charge state (dV / dSOC) and the battery characteristics obtained from the charge state during charging or discharging of the secondary battery. Identify multiple peaks of / dSOC) and
A determination device for determining that the amount of electrolytic solution in the secondary battery is decreasing when the difference in the state of charge between the specified plurality of peaks is not more than a predetermined value. The determination device according to claim 1.
The battery characteristics have the peak within a specific range of the state of charge.
The controller is a determination device that makes the charging or discharging current of the secondary battery higher than a predetermined current when the charging state is outside the specific range. The determination device according to claim 1 or 2.
A determination device that switches between charging and discharging at the time of determination according to the intended use of the secondary battery after the determination result by the determination device. The determination device according to any one of claims 1 to 3.
The predetermined value is set within the range of 92% or more and 94% or less with respect to the difference in the initial peak-to-peak charge state.
The determination device in which the difference in the initial charge state between peaks is the difference in the charge state between the peaks of the ratio (dV / dSOC) in the secondary battery in the initial state. The determination device according to any one of claims 1 to 4.
The controller is a determination device that notifies the user of the state of the secondary battery when it is determined that the amount of the electrolytic solution of the secondary battery is decreasing. The determination device according to any one of claims 1 to 5.
The controller is a determination device that executes limit control for limiting the use of the secondary battery when it is determined that the amount of the electrolytic solution of the secondary battery is decreasing. The determination device according to claim 6.
The limit control is a control for executing at least one of lowering the upper limit voltage of the secondary battery, raising the lower limit voltage of the secondary battery, and lowering the upper limit value of the charge / discharge current. A judgment device. The determination device according to any one of claims 1 to 7.
The battery characteristics are
It has the peak that appears due to the positive electrode material contained in the secondary battery and the peak that appears due to the graphite.
The controller is a determination device for determining whether or not the amount of electrolytic solution in the secondary battery is decreasing by using the peak that appears due to the graphite without using the peak that appears due to the positive electrode material. .. The determination device according to any one of claims 1 to 8.
The controller is a determination device for determining whether or not the amount of electrolyte in the secondary battery is decreasing while the secondary battery is being charged. It is a judgment method for determining a decrease in the amount of electrolytic solution of a secondary battery using graphite for the negative electrode.
Obtain the detected value from the sensor that detects the voltage and / or current of the secondary battery.
Based on the detected value, the charge state of the secondary battery is calculated.
From the value expressed by the ratio (dV / dSOC) of the change in the voltage of the secondary battery to the change in the charge state during charging or discharging of the secondary battery and the battery characteristics obtained from the charge state. , Multiple peaks of the above ratio (dV / dSOC) were identified.
A method for determining that the amount of electrolytic solution in the secondary battery is decreasing when the difference in the state of charge between the specified plurality of peaks is not more than a predetermined value.

Images