JP7137760B2 - Charge/discharge control method for secondary battery - Google Patents

Description

The present invention relates to a charge/discharge control method for a secondary battery.

Non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are lightweight and have high energy density compared to existing batteries, so they have a large capacity and charge and discharge at a high rate. Electric vehicles (EV) and hybrid vehicles (HV), plug-in hybrid vehicles (PHV), etc., are preferably used as high-output power sources for driving vehicles. A secondary battery used as a power source for driving a vehicle is used in the form of an assembled battery in which a plurality of single cells are connected in series and/or in parallel.

For example, in a lithium ion secondary battery, when the negative electrode potential drops to the lithium reference potential, metallic lithium is deposited on the negative electrode surface, resulting in deterioration of the battery performance. Therefore, in this type of non-aqueous electrolyte secondary battery, an input voltage is applied to the secondary battery so that the negative electrode potential does not drop to a predetermined charge carrier deposition potential (here, the lithium reference potential) during charging and discharging based on the charging and discharging history. It is controlled to adjust the power (see, for example, Patent Literature 1).

International Publication No. 2010/005079

However, the inventors of the present invention actually performed the charge/discharge control described in Patent Document 1 for a hybrid vehicle, and examined in detail the charge/discharge state of the secondary battery under the control together with the characteristics of the secondary battery. As a result, it was found that there was a situation in which the input power was excessively limited. In other words, there have been cases where the charging/discharging control suppresses the input/output of the secondary battery too much and the performance of the secondary battery is not fully utilized.

The present invention was created based on such new findings, and an object thereof is to provide a charge/discharge control method capable of suppressing deterioration while exhibiting the performance of a secondary battery.

The technology disclosed herein provides a charge/discharge control method for a lithium ion secondary battery. This lithium ion secondary battery has a positive electrode and a negative electrode. In this control method, the first allowable charge current is set as the maximum current value at which metallic lithium is not deposited on the negative electrode, and is decreased according to the charge duration time and increased according to the discharge duration time. Current and a second allowable charge current set as a maximum current value at which metallic lithium that does not redissolve is deposited on the negative electrode, and is decreased according to the charge duration time and increased according to the discharge duration time. The allowable input power is determined based on at least one of the current and the charging/discharging is performed below the allowable input power.

In another aspect of the secondary battery charge/discharge control device disclosed herein, the allowable charging current is set as the maximum current value at which metallic lithium does not deposit on the negative electrode, and is reduced according to the charging duration time. , a first allowable charging current that increases according to the duration of discharge, and an allowable charging current that is set as a maximum current value at which metallic lithium that does not re-dissolve is deposited on the negative electrode, and decreases according to the duration of charging. , and a second allowable charging current that increases according to the discharge duration time.

In the above configuration, the stricter first allowable charging current and the more relaxed second allowable charging current are used as charging current standards for preventing deposition of metallic lithium. This allows, for example,
During normal power supply, the charging current is controlled based on the relatively relaxed second allowable charging current, and the first allowable charging current is relatively strict only in situations where deposition of metallic lithium that degrades battery performance may occur. The charging current is controlled based on the charging current. As a result, while suppressing the deposition amount of metallic lithium that causes performance deterioration, the battery performance can be fully exhibited without being subject to excessive restrictions in a situation where the original high output performance of the battery is required. In other words, deterioration can be suppressed while the performance of the secondary battery is exhibited.

1 is a diagram schematically showing the configuration of a charge/discharge control device according to an embodiment mounted on a hybrid vehicle; FIG. FIG. 4 is a flowchart of charge/discharge control of a secondary battery according to one embodiment; FIG. 4 is a diagram illustrating an input power limit value W _{in in} a charge/discharge control method according to one embodiment; 5 is a graph for explaining how charge/discharge control is performed according to one embodiment. 4 is a graph showing a line B corresponding to a first permissible charging current and a line A corresponding to a second permissible charging current;

Hereinafter, the control method according to the present invention will be described based on preferred embodiments with reference to the drawings as appropriate. Matters other than those specifically referred to in this specification that are necessary for the implementation of the present invention (for example, secondary batteries, vehicle structures, etc. that do not characterize the present invention) are conventional in the relevant field. It can be grasped as a design matter of a person skilled in the art based on technology. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. The expression "A to B" indicating a numerical range means "A or more and B or less".

As used herein, the term "lithium ion secondary battery" includes a secondary battery that utilizes lithium ions as charge carriers and repeatedly charges and discharges as the charge carriers move between the positive and negative electrodes. The electrolyte may be a solid electrolyte, a gel polymer electrolyte, or a liquid electrolyte (electrolytic solution). Secondary batteries generally called lithium ion batteries, lithium polymer batteries and the like are typical examples included in the non-aqueous electrolyte secondary battery in the present specification. Hereinafter, a case where the non-aqueous electrolyte secondary battery disclosed herein is a lithium ion battery will be described in detail as an example.

The lithium-ion secondary battery 10 generally has the form of an assembled battery in which a plurality of cells (hereinafter sometimes referred to as "cells") are connected. In the cell, as the charged state continues, the average positive electrode potential increases, the average negative electrode potential decreases, and the potential difference (Vav) between the positive and negative electrodes increases. Here, it is known that metallic lithium (Li) is deposited on the surface of the negative electrode when the negative electrode potential becomes equal to or lower than the Li reference potential. Therefore, conventionally, when charging a lithium ion secondary battery, the terminal voltage between the positive and negative electrodes, which is the potential difference of the average potential between the positive and negative electrodes, is suppressed within a predetermined potential (for example, 4.1 V), and the negative electrode surface The deposition of metallic lithium is suppressed. The Li reference potential is the Li ⁺ /Li equilibrium potential of the lithium metal electrode, and the electrode potential of the lithium ion secondary battery 10 is defined with this Li reference potential as 0 V (vs Li ⁺ /Li).

However, in an assembled battery, there may be variations in performance from cell to cell. In addition, there may be variations in reactivity inside the cells of the battery (for example, the surfaces of the positive and negative electrodes). Therefore, even if the potential difference between the positive and negative electrode average potentials of the assembled battery is equal to or less than a predetermined potential (for example, the current is equal to or less than an allowable input current value _Vlim , which will be described later), the negative electrode potential (hereinafter referred to as local potential of the negative electrode) reaches the Li reference potential or less, and metallic lithium may be deposited on the surface of the negative electrode. Such deposition of metallic lithium is caused by charging at a high rate (for example, 20 C or higher), charging from a high state of charge (high SOC, State of Charge: SOC), continuous charging for a long time, low temperature (internal resistance of battery cell) high voltage). The cell potential is the potential difference between the positive electrode and the negative electrode in the cell of the lithium ion secondary battery, and the negative electrode potential and the positive electrode potential are grasped as the potential difference with respect to the Li reference electrode. Here, it is conceivable to lower the average potential of the positive electrode so that the negative electrode potential does not fall below the Li reference potential. .

Therefore, the charge/discharge control device 20 for a secondary battery disclosed herein has input permission power adjustment means 40 in order to suppress the negative electrode potential from locally reaching the Li reference potential. This input permission power adjustment means 40 adjusts the input permission power to the secondary battery based on the charge/discharge history so that the negative electrode potential of the lithium ion secondary battery does not drop to the lithium reference potential during charge/discharge.

The configuration and operation of the secondary battery charging/discharging control device 20 and the input permission power adjusting means 40 will be described below based on an example of an automobile 100 equipped with the charging/discharging control device 20 shown in FIG. A vehicle 100 in FIG. 1 is a so-called hybrid vehicle (HV), and is a preferred example of the vehicle 100 disclosed herein. In this specification, the term "hybrid vehicle" means a vehicle equipped with both an internal combustion engine and an electric motor (motor) as power sources. However, the vehicle 100 may be a vehicle without an internal combustion engine, such as a so-called electric vehicle (EV) or a fuel cell electric vehicle (FCEV).

A hybrid vehicle (HV) 100 includes an engine 58 , a motor 52 , and a rechargeable secondary battery 10 . The engine 58 is an internal combustion engine that converts thermal energy into mechanical energy by burning hydrocarbon fuel such as gasoline or light oil to output power. The motor 52 is a power device or a prime mover that converts electrical energy into mechanical energy, and enables power generation by converting mechanical energy into electrical energy. The output shafts of the motor 52 and the engine 58 are connected to a three-shaft power distribution/integration mechanism 56, which rotates driving wheels 60 of the automobile 100. FIG. The vehicle 100 also includes a generator 54 connected to the power distribution integration mechanism 56 for generating power, and a boost converter/inverter 50 that connects the secondary battery 10 to the motor 52 and the generator 54 . The secondary battery 10 exchanges electric power with the motor 52 via the boost converter/inverter 50 to be charged and discharged. In addition, secondary battery 10 stores electric power and regenerated energy generated from generator 54 via boost converter/inverter 50 . Note that the secondary battery 10 may be detachably provided. The boost converter controls the inverter input voltage, and controls the inverter input voltage according to the output torque of the motor 52 and the like. The inverter controls the drive current to the motor 52 and also controls regenerative braking. The power generated by generator 54 is supplied to secondary battery 10 via boost converter/inverter 50 . It should be noted that it is not always necessary to provide the generator 54 separately from the motor 52 .

The automobile 100 further includes a charge/discharge control device 20 for a secondary battery. The charge/discharge control device 20 includes a secondary battery electronic control unit (hereinafter referred to as "secondary battery ECU") 22, an SOC estimation means 24, an engine electronic control unit (hereinafter referred to as "engine ECU") 26, It has a motor electronic control unit (hereinafter referred to as “motor ECU”) 28 , a hybrid electronic control unit (hereinafter referred to as “HVECU”) 30 , and input permission power adjusting means 40 . In order to calculate the power value that can be input to the secondary battery by the input permission power adjusting means 40, the charge/discharge control device 20 includes a temperature sensor 12 for detecting the temperature of the secondary battery and a It may have a current sensor 14 for detecting current and a voltage sensor 16 . _A current sensor 14 is attached to the power line connected to the output terminal of the secondary battery 10 and detects the current IB of the secondary battery. A temperature sensor 12 is provided inside the secondary battery 10 and detects a temperature _TB of the secondary battery. A voltage sensor 16 is attached to the secondary battery 10 and measures the voltage across the terminals of the secondary battery 10 . In FIG. 1, the voltage sensor 16 is installed so as to measure the voltage of the entire secondary battery 10 (battery assembly), but the voltage sensor 16 is installed so as to measure the cell voltage of each cell. good too.

The HVECU 30 controls the entire power output device. For example, the HVECU 30 is connected to the engine ECU 26, the motor ECU 28, and the secondary battery ECU 22 via communication ports, and can transmit and receive various control signals and data to and from the engine ECU 26, the motor ECU 28, and the secondary battery ECU 22. is configured to The HVECU 30 also receives signals from various sensors that detect the operating state of the automobile 100 . For example, the HVECU 30 receives an ignition signal from an ignition switch (not shown), a signal from an accelerator sensor (not shown), and signals from other sensors, and inputs information such as accelerator opening, brake depression amount, and vehicle speed. Here, the HVECU 30 determines a torque command based on information such as accelerator opening, brake depression amount, and vehicle speed. The determined torque command is output from the HVECU 30 to the motor ECU 28 and the engine ECU 26 . For example, the HVECU 30 determines whether or not the motor 52 is regenerating, and if it determines that it is regenerating, determines a motor torque command from these pieces of information. The HVECU 30, for example, determines a motor torque command, controls the boost converter/inverter 50 via the motor ECU 28, and controls the charging current of the secondary battery.

The HVECU 30 is configured as a microprocessor centering on a CPU 32. In addition to the CPU 32, a ROM 34 for storing processing programs, a RAM 36 for temporarily storing data, input/output ports and communication ports (not shown) are provided. and Here, the ROM 34 stores a program for calculating the allowable input current value I _lim calculated by the input permission power adjusting means 40 and the secondary battery input power limit value W _in . The RAM 36 stores a secondary battery current value _IB and a secondary battery temperature value _TB output from the secondary battery ECU 22, which will be described later, an allowable input current value _Ilim calculated by the allowable input power adjusting means 40, and The secondary battery input power limit value W _in and other data necessary for various calculations can be temporarily stored.

The engine ECU 26 controls driving of the engine 58 . The engine ECU 26 receives signals from various sensors that detect the operating state of the engine 58 and controls driving of the engine 58 . The engine ECU 26 is also connected to the HVECU 30 and controls the driving of the engine 58 so as to match the torque command sent from the HVECU 30 . The engine ECU 26 performs operational control such as fuel injection control, ignition control, and intake air amount adjustment control on the engine 58, for example. The engine ECU 26 also transmits data regarding the operating state of the engine 58 to the HVECU 30 as necessary.

The motor ECU 28 drives and controls the motor 52 . The motor ECU 28 receives signals from various sensors that detect the operating state of the motor 52 . The motor ECU 28 controls the step-up converter/inverter 50 according to the signal to control the driving of the motor 52 . In addition, the motor ECU 28 is communicably connected to the HVECU 30 and receives a torque command sent from the HVECU 30 . The motor ECU 28 controls the step-up converter/inverter 50 according to the motor torque command, for example, and adjusts the drive of the motor 52 . do. The motor ECU 28 outputs data regarding the operating state of the motor 52 to the HVECU 30 as necessary.

The secondary battery ECU 22 monitors the state of the secondary battery 10 . The secondary battery ECU 22 receives signals necessary for managing the secondary battery 10, such as a voltage across terminals from a voltage sensor 16 installed between the positive and negative terminals of the secondary battery 10, and a charge signal from a current sensor 14. A discharge current (hereinafter referred to as "secondary battery current I _B "), a battery temperature T _B from the temperature sensor 12, and the like are input and stored. The secondary battery ECU 22 outputs the secondary battery current value IB and the battery temperature _TB at time t to the RAM 36 of the _HVECU 30 for temporary storage.

The SOC estimating means 24 estimates the state of charge (State of Chare: SOC, here corresponding to the remaining capacity) of the secondary battery 10 . The SOC estimator 24 estimates the charge capacity value SOC at time t by accumulating the secondary battery current value _IB input to the secondary battery ECU 22 . It is preferable to use the estimated current value corrected by the actually measured secondary battery temperature value _TB for the integration, and other information such as the secondary battery electromotive voltage can be used to estimate the SOC more accurately. may be adopted. As a method of estimating the charge capacity value SOC considering the temperature of the secondary battery, various known SOC calculation methods can be adopted. In estimating the SOC, in addition to the battery temperature, one or more factors such as the age of the battery, operation mode, area of use, season, outside temperature, etc. may be considered.

The input permission power adjustment means 40 calculates, for example, a limit value _Win that limits the input power of the secondary battery at predetermined time intervals (for example, every 100 msec), and based on this limit value _Win , the power supplied to the secondary battery 10 is is adjusting the allowable input power of The allowable input power adjusting means 40 includes, for example, allowable input current value calculating means 42 and input power limit value calculating means 44 . These means may be configured by hardware such as integrated circuits and microprocessors, or may be functionally implemented by the CPU executing a computer program. The technology disclosed herein includes providing a computer program for causing the processor to function as each of the means 42 and 44, and a computer-readable recording medium in which this computer program is recorded. The recording medium does not include propagating signals that do not retain their form such as signals or carriers.

FIG. 2 is a flow chart of the charge/discharge control of the secondary battery by the charge/discharge control device 20 for the secondary battery. The operation of the charge/discharge control device 20 will be described below.
In the charge/discharge control device 20, the temperature sensor 12 measures the secondary battery temperature T _B (t) at time t at predetermined measurement intervals (for example, every 100 msec). Further, the current sensor 14 measures the secondary battery current I _B (t) at time t (S10). The secondary battery temperature value T _B (t) and the secondary battery current value I _B (t) measured by each sensor are sent to the secondary battery ECU 22 and stored in the secondary battery ECU 22 .

The secondary battery ECU 22 also outputs the secondary battery temperature value T _B (t) and the secondary battery current value I _B (t) at time t to the SOC estimation means 24 and the HVECU 30 . The HVECU 30 temporarily stores the secondary battery temperature value T _B (t) and the secondary battery current value I _B (t) in the RAM 36 . The SOC estimating means 24 estimates the charge capacity SOC(t) at time t based on the input secondary battery temperature value T _B (t) and secondary battery current value I _B (t) (S20). .

Next, the HVECU 30 determines whether or not the motor is regenerating from the accelerator opening, the amount of brake depression, the vehicle speed, etc. (S30). When the HVECU 30 determines that the motor is regenerating, the HVECU 30 starts charging the secondary battery 10 in order to store the regenerated energy (S40). That is, the HVECU 30 determines a motor torque command and controls the boost converter/inverter 50 via the motor ECU 28 . At this time, _HVECU 30 charges secondary battery 10 using power limit value Win so that the input power to secondary battery 10 does not become excessive. This power limit value W _in is calculated by the input permission power adjusting means 40 in the following procedure.

In the allowable input power adjusting means 40, the allowable input current value calculating means 42 first calculates the allowable input current value I _lim (t) to the secondary battery (S50). A method for calculating the allowable input current value I _lim (t) is not particularly limited. Allowable input current value calculation means 42 calculates, for example, secondary battery current value I _B (t) and secondary battery temperature value T _B (t) at time t temporarily stored in RAM 36 and estimated by SOC estimation means 24 . The allowable input current value I _lim (t) can be calculated based on the program stored in the ROM 34 using the charging capacity value SOC(t) at time t. The allowable input current value calculation means 42 calculates, for example, the _allowable input current value I _lim (t _n ) is referenced to the known calculated allowable input current value I _lim (t _n−1 ) at t=t _n−1 and the decrease in allowable input current value per unit time due to continued charging is It can be calculated by subtracting F or f from the allowable current amount recovery amount G or g due to being left as it is per unit time.

Here, the measurement start time is t ₀ =0. Further, when there is no charge/discharge history, that is, for the first time (t ₀ ), the initial allowable input current value I _lim (t ₀ ) is set as the allowable input current value I _lim ( 0) can be used. As described above, the allowable input current value I _lim is calculated from the allowable input current value I _lim (0) in a state where there is no charge/discharge history, the decrease F in the allowable input current value due to continuation of charge/discharge, and the secondary battery It is calculated by subtracting the recovery amount G of the allowable input current value due to leaving.

Each term in formulas (I) and (II) indicates the following. Note that the initial set allowable input current value I _lim (0) is, for example, the maximum value at which metal Li does not precipitate within a unit time when the target secondary battery is charged from a state where there is no influence of the charge/discharge history. It can be obtained as a current value. Regarding this initial set allowable input current value I _lim (0), the "maximum current value at which metallic lithium does not precipitate" is measured in advance for each battery temperature, and the battery temperature and the initial set allowable input current For example, it can be stored in the RAM 36 of the HVECU 30 as a map or the like showing the relationship with the value I _lim (0). Such a map may also be prepared as a plurality of patterns that are changed in consideration of any one or more factors such as battery age, operation mode, area of use, season, outside temperature, etc. . The same is true for the maps described below.

Here, when the allowable input current value I _lim =0, it indicates that Li ions are fully charged (saturated) in the negative electrode active material of the secondary battery, so I _lim (0)−I _lim (t) indicates the amount of Li ions occluded in the negative electrode active material of the secondary battery. On the other hand, since spontaneous discharge occurs in the secondary battery, the amount of Li ions in the negative electrode active material decreases, and the allowable input current value I _lim recovers with time, and the magnitude is proportional to the amount of decrease in Li ions. . Therefore, the amount of decrease in Li ions at time t _{n -1} , which is the unit time (dt) before I _lim (t _n ) at time t n, is I _lim (0) and I _lim (t _n-1 ). is proportional to the difference between Now, to make the difference dimensionless, we can get the recovery by dividing the difference by I _lim (0).

It should be noted that the battery performance of the secondary battery may deteriorate with use. In this case, the allowable input current value calculation means 42 may calculate the allowable input current value I _lim ' in consideration of deterioration of the secondary battery over time. The allowable input current value calculation means 42 of the present embodiment further calculates the allowable input current value I _lim ' in consideration of the deterioration of the secondary battery over time in order to suppress metal lithium deposition over time (S52 ). The allowable input current value I _lim ' can be obtained by multiplying I _lim obtained in S50 by a deterioration coefficient η, as shown in the following equation (III).

Here, the deterioration coefficient η may be a constant value or a variable. For example, the relationship between the charging/discharging frequency and the deterioration coefficient of the target secondary battery may be prepared as a map in advance and stored in the RAM 36 of the HVECU 30 or the like. By accessing the RAM 36 according to the charge/discharge frequency of the secondary battery, the allowable input current value calculation means 42 can obtain a more appropriate deterioration coefficient corresponding to the charge/discharge frequency. As a result, it is possible to calculate the allowable input current value considering the deterioration of the secondary battery.

By the way, the allowable input current value I _lim (0) is set as the maximum current C _maxB such that metallic lithium does not deposit on the negative electrode when the battery is charged for a unit time. In particular, the allowable input current value I _lim (0)=C _maxB , as described above, takes into consideration the variation in performance of each cell, and is determined by high-rate charging of the secondary battery, charging from a high SOC, and continuous charging for a long time. , the maximum current C is set such that metallic lithium does not deposit on the negative electrode even during low-temperature charging. Here, the metallic lithium deposited on the surface of the negative electrode contains active lithium and inactive lithium. Active lithium can be re-dissolved in the electrolytic solution depending on the potential of the negative electrode. In other words, even metallic lithium once deposited can be dissolved in the electrolytic solution by discharging the battery if it is active lithium. The dissolution of active lithium proceeds in order from the most recently deposited active lithium, that is, active lithium closer to the surface of the negative electrode. Also, the active lithium reacts with the surrounding electrolytic solution to gradually become inactive and transform into inactive lithium. Once active lithium becomes inactive lithium, it cannot be dissolved in the electrolyte and does not contribute to the electrochemical reaction. However, the re-dissolved metallic lithium can contribute to the electrochemical reaction again, and it can be said that there is no problem in terms of battery performance and durability. In other words, it can be said that there is no problem with the charging/discharging mode of the secondary battery in which metallic lithium that redissolves is deposited. In addition, unless the secondary battery is charged and discharged in such a manner that inert lithium is deposited, the limitation by the allowable input current value I _lim is excessive, and there is a possibility that the secondary battery cannot satisfy the required output performance. .

For these reasons, in the technology disclosed herein, the allowable input current value I _lim is expressed as "I _limB " for distinction. Then, when the lithium-ion secondary battery 20 is not short-circuited and can be remelted, the _HVECU 30 sets the allowable input current value I _lim to an allowable input current value I _limA (here, I _limB < _IlimA ) is prepared. Then, the allowable input power is determined based on at least one of the allowable input current value _IlimB and the allowable input current value _IlimA , and charging/discharging is performed below this allowable input power. The permissible input current value _IlimB is an example of a first permissible charging current in the present invention. The allowable input current value _IlimA is an example of the second allowable charging current in the present invention. The allowable input current value _IlimA and the allowable input current value _IlimB form an allowable input current line A and an allowable input current line B in relation to time t, as shown in FIG.

Here, _IlimA can be calculated by the allowable input current value calculating means 42 based on the above equations (I) and (II) (S60). However, the initial set allowable input current value I _limA (0) is such that, for example, when the target secondary battery is charged from a state where there is no influence of the charge/discharge history, active lithium is deposited within a unit time. However, it can be obtained as the maximum current value at which inert lithium is not deposited. Regarding this initial set allowable input current value I _limA (0), the "maximum current value at which metallic lithium does not precipitate" is measured in advance for each battery temperature. For example, it can be stored in the RAM 36 of the HVECU 30 as a map or the like showing the relationship with the value I _limA (0). Note that the method for calculating I _limA is not limited to the above example, and can be modified without departing from the essence of the technology disclosed herein. As an example, another calculation method proposed by the present applicant (see, for example, Japanese Unexamined Patent Application Publication No. 2017-103896) may be employed.

In addition, the allowable input current value calculation means 42 of the present embodiment calculates the allowable input current value I _lim ' in consideration of the deterioration of the secondary battery over time in order to further suppress the deposition of metallic lithium over time ( S62). The allowable input current value calculation means 42 considers the deterioration of the secondary battery over time, and _{replaces IlimB} ' with _IlimA ' as the allowable input current value _Ilim ' (where _IlimB '< _IlimA ' (there is). The allowable input current value I _lim ′ can be calculated, for example, by multiplying I _limA obtained in S60 by the deterioration coefficient η, as shown in the above equation (III).

Here, the deterioration coefficient η may be a constant value or a variable. For example, the relationship between the charging/discharging frequency and the deterioration coefficient of the target secondary battery may be prepared as a map in advance and stored in the RAM 36 of the HVECU 30 or the like. By accessing the RAM 36 according to the charge/discharge frequency of the secondary battery, the allowable input current value calculation means 42 can obtain a more appropriate deterioration coefficient corresponding to the charge/discharge frequency.

Even when the HVECU 30 determines in S30 that the motor is not regenerating, the secondary battery ECU 22 may issue a charge request to the secondary battery 10 based on the SOC of the secondary battery 10. . In such a case, the HVECU 30 starts charging the secondary battery 10 . Therefore, in S116, it is determined that the secondary battery 10 is being charged even if it is not being regenerated (S40). In such a case, the charge/discharge control device 20 executes the operations from S50 to S62 described above. In this case, instead of the regenerated energy by the motor 52 , the power generated by the generator 54 is supplied to the secondary battery 10 .

On the other hand, in S30, there is a case where the HVECU 30 determines that the motor is not regenerating, and the secondary battery ECU 22 does not request charging, and the secondary battery 10 is not in a charging state. In other words, the secondary battery 10 is not used (hereinafter referred to as "left") or discharged as the vehicle runs. In such a case, the allowable input current value calculation means 42 calculates the allowable input current value _IlimB using the following formula (I') or (II') instead of the above formula (I) or formula (II). and _IlimA are calculated (S54, S64). That is, in the case of leaving or discharging instead of charging, the decrease F or f can be considered as recovery amount F' or f' of the allowable input current value per unit time. Therefore, the allowable input current values I _limB and I _limA are obtained by adding the allowable input current value recovery amount F′ or f′ due to neglect or continued charge/discharge, and the allowable input current value recovery amount due to the leave of the secondary battery G is calculated by subtracting In other words, the allowable input current value _Ilim can be calculated by changing the sign of the function of F and the function of f in the above formulas (I) and (II) from minus to plus. Note that formula (I') or formula (II') is the same as formulas (I) and (II) except that the F function and f function indicate the allowable current recovery term per unit time due to neglect or discharge. is. Therefore, description of other terms and the like is omitted here.

Next, the allowable input current value calculating means 42 calculates the allowable input current values I _limB ' and I _limA ' in consideration of the aging deterioration of the secondary battery by the above formula (III) (S56, S66). That is, the increase in allowable input current value _Ilim due to neglect (recovery by G term) or the recovery of allowable input current value _Ilim due to continuation of discharge (recovery by F term) is updated. Accordingly, the allowable input current value calculation means 42 calculates the allowable input current values I _limB ' and I _limA ' in consideration of deterioration over time.

The allowable input current value calculation means 42 calculates allowable input current values I _limB and I _limA and allowable input current values I _limB ' and I _limA ' considering deterioration over time. Here, the HVECU 30 relaxes the allowable input current value _Ilim in order to allow deposition of active lithium out of metallic lithium. That is, the allowable input current value I _lim (t) at time t is allowed to satisfy the relationship I _lim (t)>I _limB ' (S70).

In the charge/discharge control of the secondary battery, the secondary battery current _{IB may flow over the allowable input current value Ilim or Ilim} ' due to a delay in feedback control or the like. In the present embodiment, the input power limit value calculation means 44 sets the input power limit value W _in that limits the allowable input power to the secondary battery 10 in order to suppress deposition of metallic lithium based on the delay in feedback control. I am trying to stipulate.

Here, as shown in FIG. 3, when the actual secondary battery current value I _B (t) at time t approaches the allowable input current value I _lim ′(t), the input power limit value W _in is It is an input power (W) limit value that serves as a guideline for starting a limit so that the secondary battery current value I _B (t) does not reach the allowable input current value I _lim ′(t). For the input power limit value W _in , for example, when a current target value I _tag that is an input current that does not exceed I _lim ′ is set, the actual secondary battery current value I _B (t) is equal to this current target value I _tag can be grasped as an input power value that reaches

Specifically, the input power limit value calculation means 44 can calculate the input power limit value W _in as follows. That is, first, for example, an input current limit target value I _tag is once calculated by offsetting I _lim ′ by a predetermined amount. Next, based on the secondary battery current value I _B (t) at time t temporarily stored in the RAM 36 and the obtained I _tag , the input power limit value W _in is calculated by the following equation (IV). Note that I _tag1 and I _tag2 can be obtained by the following formula (V).

In equation (V), I _tag1 and I _tag2 are obtained as amounts offset from I _lim ' by a predetermined amount as described above. That is, I _tag1 and I _tag2 update the decrease in allowable input current value I _lim due to continued charging (decrease term by F function) in equation (I). Therefore, the relationship between I _tag1 , I _tag2 and I _lim ′ should be stored in advance as a map in the RAM 36 of the HVECU 30, and I _tag1 and I _tag2 may be obtained by referring to this map. By creating a map in consideration of the deterioration of the secondary battery and the control of the secondary battery, it is possible to further suppress deposition of metallic lithium due to a local decrease in the potential of the negative electrode.

The input power limit value calculation means 44 calculates the allowable input current value I _lim ' in which the recovering amount at the time of leaving or the increase at the time of discharging is updated, which is output by the allowable input current value calculating means 42, and the actual value at the time t. The input power limit value W _in is calculated using the formulas (IV) and ( _V ) based on the secondary battery current value IB (S100). Further, based on the calculated input power limit value _Win , the allowable input power to the secondary battery 10 is limited (S110). Here, charging of the secondary battery 10 is not performed when the battery is left standing or discharged. Therefore, only the input power limit value _Win is updated, and motor drive (output torque) control is performed regardless of the input power limit value _Win .

As a result, the input power to the secondary battery 10 is subjected to feedback control according to the secondary battery current _IB with respect to _SWin , which is the base power value of the input power limit specified value. In this feedback control, I _tag 1 or I _tag 2 obtained by adding a predetermined offset (control margin) to the allowable input current value I _lim for preventing the deposition of metallic lithium or I _lim ' considering the deterioration of the battery. It is according to As a result, it is possible to effectively prevent the secondary battery current _IB from exceeding I _tag1 or I _tag2 due to a control delay due to feedback control or the like. Furthermore, I _tag1 (or I _tag2 ) takes into account the history of charging and discharging. That is, as shown in formulas (I), (II), (I'), (II'), and (III), the allowable input current decreases or recovers based on the charging/discharging duration, and the allowable input current increases due to neglect. Considering recovery. Therefore, it is possible to prevent deposition of metallic lithium according to the state of the secondary battery 10 at that time.

(1) Here, when the allowable input current value I _lim (t) is not I _lim (t)≧I _limB '(t), that is, when I _lim (t)<I _limB '(t), the allowable Even if the input current value I _lim (t) is input, metallic lithium is not deposited on the negative electrode. Therefore, the input power limit value calculation means 44 does not need to limit the allowable input power to the secondary battery 10, for example.

(2) However, when the allowable input current value I _lim (t) exceeds I _limB ', that is, when I _lim (t)≧I _limB ', metallic lithium can be deposited on the negative electrode surface. Therefore, the input power limit value calculation means 44 first limits the allowable input power to the secondary battery 10 based on the allowable input current value I _limA (t). Then, I×t exceeding I _limB ′ is integrated by the following formula (VI). In other words, ΣI _lim (t) corresponding to the deposition amount of metallic lithium is calculated (S80). Then, the input power limit value calculating means 44 determines that ΣI _lim (t) corresponding to the calculated deposition amount of metallic lithium is a predetermined threshold value corresponding to the deposition amount of metallic lithium at which active lithium reacts with inert lithium. In comparison with ΣI _limit , it is checked whether ΣI _lim (t)>ΣI _limit (S90). Then, when the relationship ΣI _lim (t)>ΣI _limit is satisfied, that is, when ΣI _lim (t) exceeds the threshold value, the decrease of the allowable input current value I _limB ' (decrease term by F function) , the input power limit value W _inB (t) is calculated according to the above procedure (S120).

(3) On the other hand, if the relationship ΣI _lim (t)>ΣI _limit is not satisfied in S90, that is, if ΣI _lim (t) is equal to or less than the threshold ΣI _limit , the precipitated active lithium is redissolved during discharge. Conceivable. Therefore, deposition of metallic lithium on the negative electrode is allowed within a range in which the metallic lithium deposited on the negative electrode does not reach the threshold value ΣI _limit that reacts with the electrolyte and becomes inactive lithium. Therefore, when ΣI _lim (t)≦ΣI _limit , the input power limit value calculation means 44 calculates a more relaxed input power limit value W _inA (t). Specifically, the input power limit value calculation means 44 calculates the input power limit value W _inA (t) according to the above procedure based on the decrease in the allowable input current value I _limA ' (decrease term by the F function). (S100).

The HVECU 30 limits the input power to the secondary battery 10 based on the input power limit value W _in calculated by the input power limit value calculation means 44 in this way (S124). More specifically, the _HVECU 30 adjusts the motor torque command (negative torque command for charging) so that the input power to the secondary battery 10 is equal to or less than the input power limit value Win, send. The motor ECU 28 limits the input power to the secondary battery 10 from the boost converter/inverter 50 according to the motor torque command controlled based on the input power limit value _Win .

FIG. 4 shows (a) charging/discharging current, (b) deposition amount ΣI _lim (t) of metallic lithium, (c) allowable input current value I _limmax , (d) input 7 is a graph showing an example of a change over time of a power limit value W _inmax ; In (a), the discharge current of the secondary battery is indicated by one line, but the input current is indicated by three lines during the time period when the input is limited. In this example, the top line (small charge) is I _limB (t), the middle line (medium charge) is I _limA (t), and the bottom line (large charge) is the unlimited represents the charging current. For example, as shown in the left half of FIG. 4A, when the time t was early, the relationship ΣI _lim (t)≦ΣI _limit was established in S90. may exceed the tighter allowable input current value I _limB or I _limB ′, but not the looser allowable input current value I _limA or I _limA ′ shown as line A, so that the input power limit W _inA (t) is limited (S130). No limit is imposed if I _limB or I _limB ' is not exceeded. Then, as shown in FIG. 4(b), in the time period (indicated by the double arrow) in which the relationship ΣI _lim (t)>ΣI _limit holds in S90, the HVECU 30 directs the input current to the secondary battery to the line B (S110) based on the input power limit value W _inB (t) so as not to exceed the stricter allowable input current value I _limB or I _limB ′ indicated as . As a result, the relationship ΣI _lim (t)≦ΣI _limit is maintained, and the charging current I _B to the secondary battery is maintained below I _limB ′. As a result, deposition of metallic lithium on the negative electrode can be suitably suppressed. Considering the service life of the secondary battery (for example, 10 years), the input current is limited by the allowable input current value I _limA (line A in FIG. 5) until the service life expires. The F-function and G-function may be designed to limit the input current by the allowable input current value I _limB (line B in FIG. 5).

In addition, in the secondary battery charge/discharge control device 20 according to the present embodiment, the upper limit voltage of the lithium ion secondary battery does not exceed a preset upper limit voltage in order to suppress deterioration in performance due to use of the secondary battery. You may further have an upper limit voltage control means to control. As the upper limit voltage control means, for example, in the HVECU 30, a preset upper limit voltage value is compared with an actual secondary battery voltage value output from a voltage sensor (not shown) to control the charging amount. By setting the upper limit of the charging voltage in this manner, it is possible to prevent application of an unreasonably high voltage to the cell.

[degradation factor η]
As described above, the allowable input current value calculation means 42 shown in FIG. 1 uses the above formula (III) in consideration of deterioration in performance of the secondary battery 10 due to use, and I _lim ' is asking. Here, the degree of deterioration of a secondary battery such as a lithium ion secondary battery may change as it is used over time. Therefore, it is preferable to change the above-mentioned input power limit value W _{in in} order to suppress deposition of lithium metal according to the degree of deterioration while maximizing the input/output of the lithium ion secondary battery.

Therefore, the allowable input current value calculation means 42 may determine the deterioration coefficient η by obtaining the deterioration parameter D based on a known battery deterioration degree calculation method. As the battery deterioration degree calculation method, for example, (A) battery deterioration degree calculation method from electromotive voltage, (b) battery deterioration degree calculation method from internal resistance, (c) full charge capacity disclosed in Patent Document 1 and the like. According to this battery deterioration degree calculation method, the deterioration coefficient η can be obtained according to the deterioration parameter D using a map stored in advance in the ROM 34 of the HVECU 30 . This makes it possible to calculate I _lim ' that reflects the deterioration over time of the secondary battery and takes into account deterioration over time. That is, in the case of a secondary battery with a relatively small degree of deterioration, the degree of increase in the input power limit value W _in when charging is continued is relatively moderated, but in the case of a secondary battery with a large degree of deterioration, Therefore, it is desirable to limit the input power limit W _in relatively large (eg, to zero) to reduce the charging current to a smaller value. In addition, the threshold ΣI _limit may be determined as a deposition amount of metallic lithium that does not affect the performance of the secondary battery, or as a deposition amount that does not affect safety. These can be determined, for example, by taking into consideration the characteristics of the user who actually uses the secondary battery and the vehicle, such as battery performance, number of cells, and battery deterioration characteristics. In the battery deterioration degree calculation method described above, the timer 38 additionally provided in the HVECU 30 cumulatively counts the period of use from the time when the secondary battery 10 is installed. From the viewpoint of sharing timer information in consideration of parts replacement, for example, the timer provided in the secondary battery ECU 22 or the engine ECU 26 cumulatively counts the usage period from the time when the secondary battery 10 is installed. It is also preferable to count at multiple locations.

The above configuration is preferably applied, for example, to a control method for a relatively large-capacity secondary battery (for example, a battery capacity of 20 Ah or more, typically 25 Ah or more, for example 30 Ah or more) that charges and discharges at a high rate. can do. Therefore, taking advantage of such features, the technology disclosed herein includes secondary batteries for applications requiring high energy density, high input/output density, cycle characteristics, etc., and applications requiring high reliability. It can be particularly preferably applied to the control method. Such uses include, for example, power supplies for driving vehicles such as plug-in hybrid vehicles (PHV), hybrid vehicles (HV), and electric vehicles (EV). This secondary battery may typically be in the form of an assembled battery in which a plurality of batteries are connected in series and/or in parallel.

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 technology described in the claims of the present application includes various modifications and changes of the specific examples illustrated above. For example, according to the charge/discharge control described above, it is possible to suppress deterioration in performance due to the use of a lithium-ion secondary battery used as a secondary battery, and stably obtain output from the secondary battery. Such a secondary battery is not limited to charge/discharge control of a secondary battery in a vehicle, and can be applied to lithium ion secondary batteries for other uses.

10 secondary battery 20 charge/discharge control device 22 secondary battery ECU
30 HV ECU
40 Input permission power adjustment means 100 Automobile

Claims (1)

A method for controlling charging and discharging of a lithium ion secondary battery, the lithium ion secondary battery comprising a positive electrode and a negative electrode,
a first allowable charging current that is set as a maximum current value at which metallic lithium does not deposit on the negative electrode, that decreases according to the duration of charging and increases according to the duration of discharging;
a second allowable charge current that is set as the maximum current value at which metallic lithium that does not redissolve is deposited on the negative electrode, that is decreased according to the duration of charging and increased according to the duration of discharge ;
A charge/discharge control method for a secondary battery , comprising: determining an allowable input electric power based on the above;

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