JP7060332B2 - Control device - Google Patents

Description

The present invention relates to a control device for a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, which are lightweight and have high energy density, are preferably used as a power source for mounting on vehicles. In this type of secondary battery, a charge carrier (for example, in the case of a lithium ion secondary battery, lithium) is transferred between the positive electrode active material layer containing the positive electrode active material and the negative electrode active material layer containing the negative electrode active material. As a result, charging and discharging are performed. That is, during charging, the charge carrier is extracted from the positive electrode active material and released as ions into the electrolytic solution (electrolyte). At the time of charging, the charge carrier enters the structure of the negative electrode active material provided on the negative electrode side, where electrons that have passed through an external circuit are obtained from the positive electrode active material and are occluded. As a conventional technique relating to a control device for this type of secondary battery, for example, Patent Document 1 can be mentioned.

Patent Document 1 describes evaluation values for evaluating deterioration components that reduce the output performance of a secondary battery due to a bias in the ion concentration in the electrolyte due to the discharge of the secondary battery from the battery temperature, the amount of discharge current, and the like. A control device that calculates and controls to set a low upper limit value of the discharge power of the secondary battery when the calculated evaluation value exceeds the threshold value is disclosed. The document describes that such a configuration makes it possible to suppress deterioration due to high-rate discharge.

International Publication No. 2013/046263

By the way, in this kind of secondary battery, the battery temperature is generally measured by using a temperature sensor attached to the lid (typically the upper surface) of the battery case. According to the knowledge of the present inventor, a temperature difference may occur inside the battery depending on the cooling structure of the secondary battery. For example, when the secondary battery is cooled at the bottom of the can (typically the bottom), the temperature near the lid inside the battery tends to be higher than the temperature near the bottom of the can. When the above-mentioned evaluation value is calculated using the above-mentioned temperature sensor when the temperature difference occurs inside the battery in this way, the evaluation value tends to be calculated lower when the temperature is high, so that the evaluation value is the above-mentioned threshold value. As a result of misunderstanding the upper limit of the discharge power that should originally limit the output, it may not be possible to properly suppress the deterioration due to the high rate discharge (for example, the internal resistance of the battery increases). The present invention solves the above problems.

The control device proposed here is a control device that controls the discharge of the secondary battery so that the discharge power of the non-aqueous electrolyte secondary battery does not exceed the upper limit value. This control device includes a plurality of temperature sensors installed at different locations of the secondary battery, and a control unit electrically connected to each of the plurality of temperature sensors. The control unit detects the battery temperature of the secondary battery at different locations by the plurality of temperature sensors, selects the lowest temperature from the battery temperatures at the different locations, and uses the selected minimum temperature. In the step of calculating the evaluation value for evaluating the deterioration component which deteriorates the output performance of the secondary battery due to the bias of the ion concentration in the electrolyte due to the discharge of the secondary battery, and the calculated evaluation value. It is configured to execute the step of setting the upper limit value based on the above. According to such a configuration, when a temperature difference occurs inside the secondary battery, the evaluation value is calculated by selecting the lowest temperature from the battery temperatures detected at different locations of the secondary battery. Can be used to appropriately control the discharge of the secondary battery. Therefore, it is possible to more reliably suppress deterioration due to high-rate discharge.

It is a block diagram which shows the structure of the power-source system controlled by the control device of the secondary battery which concerns on this embodiment. It is a flowchart which shows an example of the input allowable current value setting processing routine. It is a graph which shows the relationship between the total energization amount and the resistance increase rate.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. The dimensional relationships (length, width, thickness, etc.) in each figure do not reflect the actual dimensional relationships. In addition, matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention (for example, configurations and manufacturing methods of positive electrodes and negative electrodes, general techniques for constructing secondary batteries and other batteries). Etc.) can be grasped as design matters of those skilled in the art based on the prior art in the field.

Although not intended to be particularly limited, a preferred embodiment according to the control device of the present invention will be described below by mainly taking a case of controlling a lithium ion secondary battery as an example. In the present specification, the "lithium ion secondary battery" is a secondary battery that uses lithium ion (Li ion) as an electrolyte ion and realizes charging and discharging by the transfer of electric charge accompanying the Li ion between the positive and negative electrodes. To say.

FIG. 1 is a block diagram showing a configuration of a control device for the lithium ion secondary battery 10 according to the present embodiment. The control device 1 of the lithium ion secondary battery 10 is suitably used for a vehicle (typically, an automobile, particularly an automobile equipped with an electric motor such as a hybrid automobile, an electric vehicle, and a fuel cell vehicle).

The control device 1 includes a load 20 connected to the lithium ion secondary battery 10, temperature sensors 40 and 42 for detecting the temperature of the secondary battery 10, and a current sensor for detecting the current flowing in and out of the secondary battery 10 (FIG. (Not shown), a voltage sensor (not shown) for detecting the voltage of the secondary battery, and an electronic control unit (ECU) 30 electrically connected to each of the sensors 40, 42 and the secondary battery 10. It can be a configuration. The ECU 30 is configured to control the operation of the lithium ion secondary battery 10 connected to the load 20, and drives and controls the load 20 based on predetermined information. The load 20 connected to the lithium ion secondary battery 10 may include a power consuming machine (for example, a motor) that consumes the power stored in the battery 10. Further, the load 20 may include a power supply device (charger) that supplies electric power capable of charging the battery 10.

The lithium ion secondary battery 10 is composed of a positive electrode and a negative electrode facing each other via a separator, and a non-aqueous electrolyte containing lithium ions supplied between the positive and negative electrodes. The positive and negative electrodes contain active materials that can occlude and release lithium ions. When the battery 10 is charged, lithium ions are released from the positive electrode active material of the positive electrode, and the lithium ions are stored in the negative electrode active material of the negative electrode through the electrolyte. On the contrary, when the secondary battery 10 is discharged, the lithium ions stored in the negative electrode active material of the negative electrode are released, and the lithium ions are stored in the positive electrode active material again through the electrolyte. With the movement of lithium ions between the positive electrode active material and the negative electrode active material, electrons flow from the active material to the external terminal. As a result, the load 20 is discharged.

Here, in order to suppress deterioration of the secondary battery 10 due to high-rate discharge, the present inventor determines the output performance of the secondary battery 10 from the battery temperature detected by the temperature sensor according to the deviation of the ion concentration in the electrolyte. It is considered to calculate an evaluation value for evaluating the deterioration component to be lowered and set an upper limit value of the discharge power of the secondary battery 10 based on the calculated evaluation value. However, according to the knowledge of the present inventor, a temperature difference may occur inside the battery depending on the cooling structure of the secondary battery 10. For example, when the secondary battery 10 is cooled at the bottom of the can, the temperature near the lid inside the battery tends to be higher than the temperature near the bottom of the can. When the above evaluation value is calculated when the temperature difference occurs inside the battery in this way, the evaluation value tends to be calculated lower when the temperature is high, so the upper limit of the discharge power that should be originally limited in output. There is a possibility that the value will be misunderstood and deterioration due to high-rate discharge cannot be suppressed appropriately (for example, the internal resistance of the battery will increase).

In the technique disclosed here, attention is paid to such a temperature difference that may occur inside the battery, and when a temperature difference occurs inside the battery, the lowest battery temperature detected at different points of the secondary battery is obtained. By selecting the temperature, calculating the above evaluation value, and appropriately setting the upper limit of the discharge power, deterioration due to high-rate discharge is surely suppressed.

That is, the control device 1 is a device that controls the discharge of the secondary battery 10 so that the discharge power of the secondary battery 10 does not exceed the upper limit value. The control device 1 includes a plurality of temperature sensors 40 and 42 installed at different locations of the secondary battery 10, and a control unit 30 electrically connected to each of the plurality of temperature sensors 40 and 42. The control unit 30 detects the battery temperature of the secondary battery 10 at different locations by the plurality of temperature sensors 40 and 42, and selects the lowest temperature from the battery temperatures at the different locations (minimum temperature selection step). Using the selected minimum temperature, a step (evaluation) for calculating an evaluation value for evaluating a deterioration component that deteriorates the output performance of the secondary battery due to a bias in the ion concentration in the electrolyte due to the discharge of the secondary battery 10. The value calculation step) and the step of setting the upper limit value based on the calculated evaluation value (upper limit value setting step) are configured to be executed.

In a typical configuration of the ECU 30, at least a ROM (Read Only Memory) that stores a program for performing such control, a CPU (Central Processing Unit) that can execute the program, and data are temporarily stored. A RAM (random access memory) and an input / output port (not shown) are included. A plurality of temperature sensors 40 and 42, a current sensor (not shown), a voltage sensor (not shown), and a temperature sensor are attached to the secondary battery 10. The current sensor is configured to detect the current flowing in and out of the secondary battery 10 and output it to the ECU 30. The voltage sensor is configured to detect the voltage of the secondary battery 10 (typically the voltage between terminals) and output it to the ECU 30. The plurality of temperature sensors 40 and 42 are installed at different locations of the secondary battery 10, respectively. In this embodiment, the plurality of temperature sensors 40, 42 are the first temperature sensor 40 attached to the lid (typically the upper surface) of the secondary battery 10 and the can bottom (typically) of the secondary battery 10. Is composed of a second temperature sensor 42 attached to the bottom surface). The first temperature sensor 40 detects the temperature near the lid of the secondary battery 10 and outputs it to the ECU 30. The second temperature sensor 42 detects the temperature near the bottom of the can bottom of the secondary battery 10 and outputs it to the ECU 30. The number of temperature sensors installed in the secondary battery 10 is not limited to two, and may be, for example, three to ten. The output signal of each sensor is input to the ECU 30 via the input port. Then, the ECU 30 acquires information on the current value, the voltage value, and the battery temperature that enter and exit the secondary battery 10 based on the output signals from each sensor. The control unit of the present embodiment is configured by the ECU 30.

The operation of the control device 1 configured in this way will be described. FIG. 2 is a flowchart showing a part (minimum temperature selection step) of the processing routine executed by the ECU 30 of the control device 1 according to the present embodiment. This routine is repeated at preset time intervals (cycle times).

When the process shown in FIG. 2 is executed, the CPU of the ECU 30 first detects the battery temperature of the lithium ion secondary battery 10 to be controlled by a plurality of temperature sensors 40 and 42 at different points of the secondary battery 10. (Step S10). In this embodiment, the temperature near the lid of the secondary battery 10 (hereinafter, also referred to as “cover temperature”) is acquired by the first temperature sensor 40. Further, the temperature near the can bottom of the secondary battery 10 (hereinafter, also referred to as “can bottom temperature”) is acquired by the second temperature sensor 42. Next, in step S20, the lowest temperature is selected from the battery temperatures at different locations of the secondary battery 10 detected by the first temperature sensor 40 and the second temperature sensor 42. In this embodiment, the ECU 30 determines whether or not the can bottom temperature acquired by the second temperature sensor 42 is lower than the lid temperature acquired by the first temperature sensor 40. When the can bottom temperature is lower than the lid temperature (when "YES"), it is determined that the can bottom temperature is the lowest temperature, and the can bottom temperature is selected as the lowest temperature. Then, the subsequent control (control of the discharge of the secondary battery) is continued using the selected can bottom temperature (step S30). On the other hand, when the can bottom temperature is equal to or higher than the lid temperature (in the case of "NO"), it is determined that the lid temperature is the lowest temperature, and the lid temperature is selected as the lowest temperature. Then, the subsequent control (control of the discharge of the secondary battery) is continued using the selected can bottom temperature (step S40).

Next, a step of calculating an evaluation value using the above-selected minimum temperature will be described. In the evaluation value calculation step, the minimum temperature selected above (the lid temperature or the can bottom temperature in the example of FIG. 2) is used, and the secondary battery 10 is accompanied by a bias in the ion concentration in the electrolyte due to the discharge of the secondary battery 10. The evaluation value for evaluating the deterioration component which deteriorates the output performance of is calculated. As a method of calculating the above evaluation value, the evaluation value for evaluating the deterioration component that deteriorates the output performance of the secondary battery due to the bias of the ion concentration in the electrolyte due to the discharge of the secondary battery using the battery temperature. Is not particularly limited as long as it can be calculated. Techniques for such evaluation values are disclosed, for example, in International Publication No. 2013/046263. The calculation of the evaluation value can be performed with reference to the above document. Therefore, with respect to the disclosed part, detailed description is omitted with reference to the above-mentioned document, and only a brief description is given.

In the evaluation value calculation step, the ECU 30 first acquires the discharge current value I based on the output signal of the current sensor. Next, the SOC (State Of Charge) of the secondary battery 10 is calculated (estimated) based on the acquired discharge current value I. SOC is the ratio of the current charge capacity to the full charge capacity of the secondary battery 10. The SOC can be calculated by integrating the current values when the secondary battery 10 is charged and discharged, for example. Alternatively, the SOC may be calculated from the voltage between the terminals of the secondary battery 10 detected by the voltage sensor. Next, the ECU 30 calculates the forgetting coefficient A by using the selected minimum temperature and the SOC calculated above. Here, the forgetting coefficient A is a coefficient corresponding to the diffusion rate of ions in the electrolytic solution of the secondary battery 10. The forgetting coefficient A is expressed in the range of 0 <A × Δt <1 (Δt: cycle time). The forgetting coefficient A can be determined by using a map showing the relationship between the temperature of the secondary battery and the forgetting coefficient A acquired in advance by a preliminary experiment or the like.

Next, the ECU 30 calculates the reduction amount D (−) of the evaluation value. The evaluation value D (N) is a value for evaluating the deterioration state (high rate deterioration described later) of the secondary battery 10. That is, when the high-rate discharge of the secondary battery 10 is continuously performed, the ion concentration in the electrolytic solution is biased, the internal resistance of the secondary battery 10 increases, and the output voltage starts to drop sharply. Can occur. Therefore, it is necessary to suppress high-rate discharge before high-rate deterioration occurs. Here, the evaluation value D (N) is set as the value for evaluating the high rate deterioration.

The amount of decrease in the evaluation value D (-) is the ion associated with the diffusion of ions from the time when the evaluation value D (N-1) of the previous time (immediately before) was calculated to the time when one cycle time Δt elapses. Calculated according to the decrease in concentration bias. For example, the ECU 30 can calculate the reduction amount D (−) of the evaluation value based on D (−) = A × Δt × D (N-1). Here, D (N-1) indicates the evaluation value calculated last time (immediately before). D (0) as an initial value can be, for example, 0.

Next, the ECU 30 determines the limit value C from the calculated SOC and the selected minimum temperature with reference to the map showing the relationship between the SOC, the battery temperature, and the limit value C acquired in advance by a preliminary experiment or the like. do. The map may be set so that, for example, if the temperature (minimum temperature) of the secondary battery 10 is the same, the higher the SOC of the secondary battery 10, the larger the limit value C. Further, if the SOC of the secondary battery 10 is the same, the higher the temperature (minimum temperature) of the secondary battery 10, the larger the limit value C can be set.

Next, the ECU 30 calculates the increase amount D (+) of the evaluation value. The increase amount D (+) of the evaluation value is the ion concentration associated with the discharge from the time when the evaluation value D (N-1) of the previous time (immediately before) is calculated to the time when one cycle time Δt elapses. Calculated according to the increase in bias. For example, the ECU 30 can calculate the increase amount D (+) of the evaluation value based on D (+) = B / C × I × Δt. Here, B indicates a current coefficient. The current coefficient may be stored in a memory such as a ROM in advance.

Next, the ECU 30 calculates the evaluation value D (N) at the current cycle time Δt. The evaluation value D (N) can be calculated based on D (N) = D (N-1) −D (−) + D (+). Here, D (N) is an evaluation value at the current cycle time Δt, and D (N-1) is an evaluation value at the previous (immediately before) cycle time Δt. D (0) as an initial value can be set to 0, for example. In this way, the evaluation value D (N) can be calculated in consideration of the increase in the bias of the ion concentration and the decrease in the bias of the ion concentration.

Next, a step of setting an upper limit value of the discharge power based on the calculated evaluation value will be described. In the discharge power upper limit setting step, the upper limit value of the discharge power is set based on the evaluation value calculated above. The method for setting the upper limit value of the discharge power is not particularly limited as long as the upper limit value of the discharge power can be set based on the evaluation value calculated above. A technique for setting such an upper limit value of discharge power is disclosed in, for example, International Publication No. 2013/046263. The setting of the upper limit value of the discharge power can be executed with reference to the above document. Therefore, with respect to the disclosed part, detailed description is omitted with reference to the above-mentioned document, and only a brief description is given.

In the discharge power upper limit setting step, the ECU 30 first determines whether or not the calculated evaluation value D (N) exceeds the predetermined target values Dtar + and Dtar−. The target values Dtar + and Dtar- are set to values smaller than the evaluation value D (N) at which high rate deterioration starts to occur, and can be set in advance. The target value Dtar + is a positive value, and the target value Dtar-is a negative value. When the evaluation value D (N) does not exceed the target values Dtar + and Dtar-, the evaluation value D (N) is stored in the memory and the change of the evaluation value D (N) is monitored. If the evaluation value D (N) exceeds the target values Dtar + and Dtar-, the evaluation value D (N) is integrated. Specifically, among the evaluation values D (N), the portions exceeding the target values Dtar + and Dtar- are integrated. In this way, the integrated value ΣDex (N) is calculated. ΣDex (N) is a value obtained by accumulating the differences between the evaluation value D and the respective target values Dtar + and Dtar- in the cycle time up to this time. The integrated value ΣDex (N) can be corrected by referring to, for example, International Publication No. 2013/046263, if necessary.

Next, the ECU 30 determines whether or not the integrated value ΣDex (N) is larger than the threshold value K. The threshold value K is a value for allowing high rate deterioration. The threshold value K may be a fixed value or may be changed according to the deterioration state of the secondary battery 10. The determination of the threshold value K can be made, if necessary, with reference to, for example, International Publication No. 2013/046263.

When the integrated value ΣDex (N) is equal to or less than the threshold value K, the ECU 30 sets the output limit value used for charge / discharge control of the secondary battery 10 to the maximum value. The output limit value is an upper limit value (power [kW]) that allows the secondary battery 10 to be discharged. The ECU 30 controls the discharge of the secondary battery 10 so that the output power of the secondary battery 10 does not exceed the output limit value. The output limit value as the maximum value can be determined in advance.

When the integrated value ΣDex (N) is larger than the threshold value K, the ECU 30 sets the output limit value to a value smaller than the maximum value. The lower the output limit value is, the more the output of the secondary battery 10 is limited. The amount of reducing the output limit value may be changed with respect to the maximum value according to the difference between the integrated value ΣDex (N) and the threshold value K. The amount of decrease in the output limit value can be determined, for example, with reference to International Publication No. 2013/046263.

The ECU 30 transmits a command regarding discharge control of the secondary battery 10 to the load 20. This directive contains information about the output limit values set above. As a result, the discharge of the secondary battery 10 is controlled so that the discharge power of the secondary battery 10 does not exceed the output limit value.

According to the above embodiment, when a temperature difference occurs inside the secondary battery 10, the lowest temperature is selected from the battery temperatures detected at different locations of the secondary battery to calculate the evaluation value D (N). The discharge of the secondary battery can be appropriately controlled by using the evaluation value D (N). For example, the evaluation value D (N) was calculated by detecting a battery temperature higher than the minimum temperature inside the battery even though the output limit value needs to be set to a value smaller than the maximum value. Therefore, the integrated value ΣDex (N) does not exceed the threshold value K, and it is unlikely that the discharge power (setting of the upper limit value), which originally requires the output limitation, is misunderstood. Therefore, it is possible to more reliably suppress deterioration due to high-rate discharge.

Hereinafter, test examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the following test examples.

A positive and negative electrode sheet in which a positive electrode active material and a negative electrode active material are held in a sheet-shaped positive electrode current collector and a negative electrode current collector, respectively, is wound through a separator sheet and housed in a case together with an electrolyte. I prepared two secondary batteries.

The first temperature sensor was installed on the lid of each lithium ion secondary battery prepared above, and the second temperature sensor was installed on the bottom of the can. Then, each lithium ion secondary battery was mounted on the vehicle as a power source for mounting on the vehicle, and the transition of the resistance increase rate (= IV resistance / initial IV resistance) when the vehicle was driven according to the LA # 4 mode was measured. .. At that time, in the embodiment, the evaluation value D (N) and the integrated value ΣDex are used by using the lower temperature of the lid temperature acquired by the first temperature sensor and the can bottom temperature acquired by the second temperature sensor. (N) is calculated, and when the calculated integrated value ΣDex (N) is equal to or less than the threshold value K, the output limit value used for charge / discharge control of the secondary battery is set to the maximum value, and the integrated value ΣDex (N) is set. When it was larger than the threshold value K, the output limit value was set to a value smaller than the maximum value, and the discharge of the secondary battery was controlled so that the output power of the secondary battery did not exceed the output limit value. Further, in the comparative example, the evaluation value D (N) and the integrated value ΣDex (N) were calculated using only the lid temperature acquired by the first temperature sensor. The discharge of the secondary battery was controlled by the same method as in the embodiment except that the evaluation value D (N) and the integrated value ΣDex (N) were calculated using only the lid temperature acquired by the first temperature sensor. The results are shown in FIG. FIG. 3 shows the change in the resistance increase rate corresponding to the total energization amount of the battery.

As shown in FIG. 3, the battery of the example in which the evaluation value D (N) and the integrated value ΣDex (N) were calculated by selecting the lower temperature of the lid temperature and the can bottom temperature uses only the lid temperature. Compared with the comparative example in which the evaluation value D (N) and the integrated value ΣDex (N) were calculated, the increase in the resistance increase rate was suppressed. In the embodiment, the lowest temperature is selected from the battery temperatures detected at different points of the secondary battery to calculate the evaluation value D (N). Therefore, the evaluation value D (N) is used to appropriately discharge the secondary battery. It is presumed that the deterioration due to high-rate discharge could be suppressed more reliably. From this result, the lowest temperature is selected from the battery temperatures of different parts of the secondary battery, the evaluation value D (N) and the integrated value ΣDex (N) are calculated, and the resistance is increased by controlling the discharge of the secondary battery. It was confirmed that the increase in the rate could be suppressed.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above.

For example, the location where the plurality of temperature sensors are installed is not limited to the vicinity of the lid and the vicinity of the can bottom as described above. For example, a positive and negative electrode sheet in which a positive electrode active material and a negative electrode active material are held in a sheet-shaped positive electrode current collector and a negative electrode current collector, respectively, is wound through a separator sheet and housed in a case together with an electrolyte. In a lithium ion secondary battery, a temperature difference may occur between the inner peripheral portion and the outer peripheral portion of the wound body (electrode body). In such a case, temperature sensors are installed on the inner peripheral portion and the outer peripheral portion of the wound body (electrode body) inside the battery, and the lowest temperature is selected from the battery temperature detected by the temperature sensor to evaluate the evaluation value. It may be configured to calculate D (N). Even in such a case, the above-mentioned action and effect can be obtained.

1 Control device 10 Lithium-ion secondary battery 20 Load 30 ECU
40 1st temperature sensor 42 2nd temperature sensor

Claims (1)

The discharge power of the lithium-ion secondary battery in which the electrode body including the positive and negative electrode sheets and the separator sheet is housed in a case having two surfaces, a lid and a can bottom, together with a non-aqueous electrolyte, has an upper limit. It is a control device for controlling the discharge of the lithium ion secondary battery so as not to exceed it and suppressing deterioration due to high rate discharge .
A plurality of temperature sensors attached to the lid and the bottom of the can bottom of the lithium ion secondary battery, respectively .
A control unit electrically connected to each of a plurality of temperature sensors attached to the lid and the bottom of the can is provided.
The control unit
The plurality of temperature sensors detect the temperature near the lid of the lithium ion secondary battery and the temperature near the bottom of the can, and the lowest temperature among the temperature near the lid and the temperature near the bottom of the can. Steps to select the temperature and
Using the selected minimum temperature, for evaluating a deterioration component that deteriorates the output performance of the lithium ion secondary battery due to a bias in the ion concentration in the non- aqueous electrolyte due to the discharge of the lithium ion secondary battery. Steps to calculate the evaluation value and
A control device configured to perform a step of setting the upper limit value based on the calculated evaluation value.

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