JP6889401B2 - Alkaline secondary battery state estimator - Google Patents

Description

The present disclosure relates to a technique for estimating the internal temperature of a cell (cell of an alkaline secondary battery) including a positive electrode having nickel hydroxide and a negative electrode having a hydrogen storage alloy.

Japanese Patent No. 4775524 (Patent Document 1) discloses an apparatus for estimating the internal temperature of a cell by using a heat conduction equation showing the relationship between the internal temperature and the external temperature of the cell of a lithium ion secondary battery. Has been done.

Japanese Patent No. 4775524

However, the heat conduction equation disclosed in Patent Document 1 is a heat conduction formula premised on a lithium ion secondary battery. Therefore, if the internal temperature of the cell of the alkaline secondary battery is estimated simply by using the heat conduction equation disclosed in Patent Document 1, the estimation accuracy of the internal temperature of the cell of the alkaline secondary battery deteriorates. Is a concern.

The present disclosure has been made to solve the above-mentioned problems, and an object thereof is to accurately estimate the internal temperature of a cell (cell) of an alkaline secondary battery.

The state estimation device according to the present disclosure is a state estimation device for a cell including a positive electrode having nickel hydroxide and a negative electrode having a hydrogen storage alloy, and includes a current sensor configured to detect the current of the cell and a current sensor configured to detect the current of the cell. A voltage sensor configured to detect the voltage of the cell, a temperature sensor configured to detect the temperature of the outer surface of the cell, and a control device configured to calculate the internal temperature of the cell. To be equipped. The control device calculates the positive electrode resistance, the negative electrode resistance, the positive electrode reaction resistance, and the negative electrode reaction resistance of the cell using the detection results of the current sensor, the voltage sensor, and the temperature sensor. The control device uses the detection results of the voltage sensor and the temperature sensor to calculate the oxygen evolution current, which is the current consumed in the oxygen evolution reaction at the positive electrode. The control device calculates the positive electrode main reaction current, which is the current consumed in the charge / discharge reaction at the positive electrode, using the detected value of the current sensor and the oxygen evolution current. The control device calculates the first calorific value due to the charge / discharge reaction of the cell using the detected value of the current sensor, the positive electrode main reaction current, the positive electrode resistance, and the negative electrode resistance. The control device calculates the second calorific value due to the oxygen evolution reaction at the positive electrode using the oxygen evolution current and the positive electrode reaction resistance. The control device uses the detected values of the voltage sensor and the temperature sensor to calculate the oxygen recombination current, which is the current consumed in the oxygen recombination reaction at the negative electrode. The control device uses the oxygen recombination current and the negative electrode reaction resistance to calculate the third calorific value due to the oxygen recombination reaction at the negative electrode. The control device calculates the amount of heat change accompanying the enthalpy change of the negative electrode using the detected value of the current sensor. The control device calculates the amount of heat change accompanying the entropy change due to the charge / discharge reaction, the oxygen generation reaction at the positive electrode, and the oxygen recombination reaction at the negative electrode using the detected value of the temperature sensor. The control device calculates the internal temperature of the cell using the detection value of the temperature sensor, the first to third calorific value, the amount of heat change accompanying the enthalpy change, and the amount of heat change accompanying the entropy change.

According to the above configuration, the first calorific value due to the charge / discharge reaction of the cell, the second calorific value due to the oxygen generation reaction at the positive electrode, the third calorific value due to the oxygen recombination reaction at the negative electrode, and the heat accompanying the change in enthalpy. The internal temperature of the cell of the alkaline secondary battery is estimated in consideration of the amount of change and the amount of heat change accompanying the change in entropy. Therefore, the internal temperature of the cell (cell) of the alkaline secondary battery can be estimated accurately.

It is a figure which shows an example of the whole structure of a battery system. It is a figure which shows typically the reaction which occurs inside a cell. It is a flowchart which shows an example of the processing procedure of an ECU.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals, and the description thereof will not be repeated.

<Overall configuration>
FIG. 1 is a diagram showing an example of the overall configuration of the battery system 1 to which the state estimation device for the alkaline secondary battery according to the present embodiment is applied.

The battery system 1 includes a cell 10, a voltage sensor 31, a current sensor 32, a temperature sensor 33, and an ECU (Electronic Control Unit) 100. The battery system 1 can be mounted on an electric vehicle (hybrid vehicle, electric vehicle, etc.) capable of traveling by using the electric power stored in the battery module including the plurality of cells 10.

The cell 10 stores electric power for supplying a load (for example, a motor generator that generates a driving force of an electric vehicle) (not shown). The cell 10 is an alkaline secondary battery (nickel-metal hydride secondary battery: NiMH) having nickel hydroxide as a positive electrode and a hydrogen storage alloy as a negative electrode.

The voltage sensor 31 detects the voltage between the terminals of the cell 10. The current sensor 32 detects the current flowing through the cell 10. The temperature sensor 33 is attached to the outer surface of the case 13 (see FIG. 2) of the cell 10 and detects the external temperature of the cell 10. In the following, the value detected by the voltage sensor 31 is also described as “battery voltage V”, the value detected by the current sensor 32 is also described as “battery current I”, and the value detected by the temperature sensor 33 is also described as “battery external temperature T”. To do.

The ECU 100 incorporates a CPU (Central Processing Unit) and a memory (not shown). The ECU 100 executes a predetermined calculation process based on the information (battery voltage V, battery current I, battery external temperature T) from the sensors 31 to 33 and the information stored in the memory, and the cell 10 is based on the calculation result. Estimate the internal temperature of the battery.

<Estimation of internal temperature of alkaline secondary battery>
As described in Patent Document 1 described above, the difference between the internal temperature and the external temperature of the cell 10 can be estimated by the heat conduction equation shown in the following equation (1).

In the formula (1), "T _p " indicates the internal temperature of the cell 10, "T _s " indicates the external temperature of the cell 10 (value detected by the temperature sensor 33), "t" indicates the time, and "Δt". "" Indicates the time step, "λ" indicates the thermal conductivity, "ρ" indicates the density, "c" indicates the specific heat, "x" indicates the thermal diffusion distance, and "q _p " indicates the cell 10. Indicates the amount of heat generated per unit volume inside the above, and "k1" and "k2" indicate correction coefficients, respectively.

Further, the equation (1) can be expressed by the following equation (2).

“Α” and “β” in the formula (2) are represented by the following formulas (3) and (4), respectively.

Here, the internal temperature T _p of the cell 10, by adjusting the correction coefficients k1, k2, the maximum temperature and the internal cells (hereinafter also referred to as "capability temperature") at which reflects the internal resistance of the cell and be considered Can be done.

The internal temperature T _p of the cell 10 can be estimated by using a thermal conduction represented by the above formula (1) or Equation (2) to (4).

However, the above equations (1) to (4) disclosed in Patent Document 1 are thermal conduction equations premised on a lithium ion secondary battery. Therefore, the internal temperature T _{p (maximum} temperature or performance the temperature inside the cell) of the cell 10 of the nickel-hydrogen secondary battery, the above equation (1) assuming a lithium ion secondary battery simply using to (4) simply by estimation Te, estimation accuracy of the internal temperature T _p is a concern that deteriorated. In particular, the side reaction is large under the conditions of use of the nickel-hydrogen secondary battery (e.g. SOC (if continuously discharged or charged in a high state of State Of Charge)), the estimated accuracy of the internal temperature T _p is significantly deteriorated obtain. This point will be described in detail below.

FIG. 2 is a diagram schematically showing a reaction occurring inside the cell 10 of a nickel-metal hydride secondary battery. The cell 10 is covered with a metal case 13. Inside the cell 10, a positive electrode 11 having nickel hydroxide, a negative electrode 12, and an alkaline electrolytic solution that ionicly binds them are provided.

Inside the cell 10 of the nickel-metal hydride secondary battery, first, the main reaction (charge / discharge reaction) of the battery occurs as in the case of the lithium ion secondary battery. Further, inside the cell 10, as a side reaction peculiar to the nickel-metal hydride secondary battery, a self-discharge (oxygen generation) reaction at the positive electrode and a recombination reaction at the negative electrode (oxygen generated at the positive electrode moves to the negative electrode, and the negative electrode is moved. Reaction with hydrogen ^{to return to OH −} ) occurs. Therefore, the calorific value generated inside the cell 10 includes the calorific value q _{main due to the main reaction, the calorific value q gen} due to the oxygen evolution reaction at the positive electrode, _{and the calorific value q comb} due to the oxygen recombination reaction at the negative electrode. Will be included.

Here, the current consumed for the main reaction of the positive electrode (hereinafter _{, also referred to as “positive electrode main reaction current I main, p} ”) and the current consumed for the side reaction (oxygen generation) of the positive electrode (hereinafter, “oxygen generation current I _gen”). The relationship between the total current of the cell 10 (the battery current I detected by the current sensor 32) is expressed by the following equation (5).

The oxygen evolution current I _gen is known to have properties that depend on the OCV (Open Circuit Voltage) and temperature of the cell 10. Therefore, for example, a map showing the correspondence between OCV and temperature and oxygen evolution current I _gen is obtained in advance by experiments or the like, and the oxygen evolution current I corresponding to the OCV and temperature of the actual cell 10 is referred to with reference to this map. _{The gen} can be calculated.

Alternatively, based on the electrochemical reaction formula (Tafel equation) as shown in the following equation (6), oxygen is input from the sensors 31 to 33 (battery voltage V, battery current I, battery external temperature T). It is also possible to sequentially calculate the generated current I _gen.

In equation (6), "α" indicates the transfer coefficient of the electrode reaction, "F" indicates the Faraday constant, "U _{eq, gen} " indicates the reference voltage for oxygen evolution, and "i _{0, gen} " indicates oxygen. The exchange current density of occurrence is shown.

The “V” in the formula (6) is a value obtained by removing the influence of the ohm loss derived from the DC resistance and the overvoltage derived from the negative electrode reaction resistance from the battery voltage V. The DC resistance and the negative electrode reaction resistance can be stored in advance as a map or function of temperature and OCV. Further, as the electrochemical reaction formula, the Butler-Volmer equation may be used.

From the above, the positive electrode _{main reaction current I main, p} is I _{main, p} = I-I _gen . In the voltage region where the side reaction (oxygen evolution) on the positive electrode is negligible, the oxygen evolution current I _gen can be approximated to zero.

Similarly, the current consumed for a side reaction (oxygen absorption) on the negative electrode (hereinafter _{also referred to as "oxygen recombination current Icomb} ") is known to have characteristics depending on the OCV and temperature of the cell 10. There is. Therefore, for example, a map showing the correspondence between OCV and temperature and the oxygen recombination current _Icomb is obtained in advance by experiments or the like, and oxygen recombination corresponding to the OCV and temperature of the actual cell 10 is referred to with reference to this map. The current I _comb can be calculated.

Alternatively, based on the electrochemical reaction formula (Tafel equation) as shown in the following equation (7), oxygen is input from the sensors 31 to 33 (battery voltage V, battery current I, battery external temperature T). It is also possible to sequentially calculate the recombination current I _comb.

In the formula (7), "U _{eq, comb} " indicates the reference voltage for oxygen absorption, and "i _{0, comb} " indicates the exchange current density for oxygen absorption. Here, the reference voltage U _{eq, comb} and the exchange current density i _{0, comb for} oxygen absorption may be the same values as when oxygen is generated, or may be different values.

Note that "V" in the formula (7) is a value obtained by removing the influence of the ohm loss derived from the DC resistance and the overvoltage derived from the negative electrode reaction resistance from the battery voltage V, as in the formula (6). The present disclosure presupposes that there is a time delay in the transfer of oxygen from the positive electrode to the negative electrode. Further, when the amount of oxygen in the cell 10 becomes zero, the reaction of the formula (7) does not occur, and the model is constructed.

On the other hand, when hydrogen is occluded in the hydrogen storage alloy of the negative electrode, it is desirable to consider the _{amount of heat change q h} accompanying the enthalpy change (ΔH [kJ / mol]) of the negative electrode according to the following formula (8). .. Since the number of hydrogen moles stored in the hydrogen storage alloy of _{the negative electrode can be calculated from the oxygen recombination current I comb} and the Faraday constant, the amount of heat change q _h due to the enthalpy change of the negative electrode can also be calculated sequentially ( See equation (14) below).

Furthermore, the positive and negative electrode entropy changes in lithium-ion secondary batteries are generally small and negligible, but the positive and negative electrode entropy changes in nickel-metal hydride secondary batteries are relatively small compared to lithium-ion secondary batteries. large. Therefore, when calculating the amount of heat generated inside the cell 10 of the nickel-metal hydride secondary battery, it is _{necessary to consider the amount of heat change q s} (see equation (15) described later) that accompanies the change in entropy due to each reaction. desirable.

From the above, the ECU 100 according to the present embodiment has a calorific value q _{main due to the main reaction, a calorific value q gen} due to the oxygen evolution reaction at the positive electrode, a _{calorific value q comb} due to the oxygen recombination reaction at the negative electrode, and an enthalpy change at the negative electrode. The internal temperature of the cell 10 of the nickel hydrogen secondary battery is estimated in consideration of five heat changes, that is, the amount of heat change q _h accompanying and the amount of heat change q _{s associated with the enthalpy change of each reaction.} Therefore, the internal temperature of the cell 10 of the nickel-metal hydride secondary battery can be estimated accurately.

<< Estimated flow of cell internal temperature >>
FIG. 3 is a flowchart showing an example of a processing procedure executed when the ECU 100 estimates the internal temperature of the cell 10. First, the ECU 100 acquires the battery voltage V, the battery current I, and the battery external temperature T from the sensors 31 to 33, respectively (step S10).

Next, the ECU 100 _{calculates the DC resistance R d} , the positive electrode resistance R _p , the negative electrode resistance R _n , the positive electrode reaction resistance R _{c, p} , and the negative electrode reaction resistance R _{c, n} (step S12). The DC resistance R _d is a resistance component related to electron resistance and ion resistance. The positive electrode resistance R _p is the sum of the resistance components derived from the positive electrode in the battery. The negative electrode resistance R _n is the sum of the resistance components derived from the negative electrode in the battery. The positive electrode reaction resistances R _{c and p} are resistance components related to charge transfer at the interface between the positive electrode active material and the electrolytic solution. The negative electrode reaction resistances R _{c and n} are resistance components related to charge transfer at the interface between the negative electrode active material and the electrolytic solution.

In the ECU 100, for example, the state of the cell 10 (battery voltage V, battery current I and battery external temperature T) and each resistance (DC resistance R _d , positive resistance R _p , negative negative resistance R _n , positive reaction resistance R _{c, p} , Read and read from the memory a plurality of maps (R _d map, R _p map, R _n map, R _{c, p} map, R _{c, n} map) that define the correspondence with the negative electrode reaction resistance R _{c, n).} The value of each resistor corresponding to the current state of the cell 10 is calculated with reference to the map. It should be noted that these maps can be obtained in advance by experiments or the like and stored in the memory.

Next, the ECU 100 _{calculates the oxygen evolution current I gen} on the positive electrode (step S14). For example, as described above, the ECU 100 has a map that defines the correspondence between the OCV (battery voltage V) and temperature (battery external temperature T) and the oxygen evolution current I _gen , or as shown in the above equation (6). _{The oxygen evolution current I gen} is calculated from the above electrochemical reaction formula.

Next, the ECU 100 _{calculates the value obtained by subtracting the oxygen evolution current I gen} on the positive electrode from the battery current I as the positive electrode _{main reaction current I mine, p} (step S16).

Next, the ECU 100 _{calculates the calorific value q mine} due to the main reaction (step S18). First, the ECU 100 calculates the calorific value q _{main, p due to} the positive electrode main reaction and the calorific value q _{main, n} due to the negative electrode main reaction using the following equations (9) and (10), respectively.

Then, ECU 100, as shown in the following equation (11), the heating value _{q main} by Seikyokunushi _reaction, the amount of heat generated by _p and the negative main reaction _{q main,} the sum of _n, as the heating value _{q main} by the main reaction calculate.

_{Next, the ECU 100 calculates the calorific value q gen} due to the oxygen evolution reaction at the positive electrode using the following formula (12) (step S20).

Next, the ECU 100 _{calculates the oxygen recombination current I comb} at the negative electrode (step S22). For example, as described above, the ECU 100 is shown in the map that defines the correspondence between the OCV (battery voltage V) and temperature (battery external temperature T) and the oxygen recombination current _Icomb , or in the above equation (7). _{The oxygen recombination current Icomb} is calculated from such an electrochemical reaction formula.

_{Next, the ECU 100 calculates the calorific value q comb} due to the oxygen recombination reaction at the negative electrode using the following formula (13) (step S24).

_{Next, the ECU 100 calculates the amount of heat change q h} associated with the enthalpy change at the negative electrode using the following equation (14) (step S26).

In the formula (14), "ΔH" indicates the amount of change in enthalpy (unit: kJ / mol), and "M" indicates the number of reaction moles.

Next, it is desirable _{that the ECU 100 considers the amount of heat change q s} accompanying the entropy change due to each reaction by using the following equation (15).
(Step S28).

In the formula (15), "T · ΔS _main " indicates the amount of heat change accompanying the entropy change due to the main reaction, and "T · ΔS _gen " indicates the amount of heat change accompanying the entropy change due to the oxygen evolution reaction at the positive electrode. The amount is shown, and "T · ΔS _comb " indicates the amount of heat change accompanying the change in entropy due to the oxygen recombination reaction at the negative electrode. _{The amount of heat change T · ΔS main} associated with the change in entropy due to the main reaction is the sum of the amount of heat change accompanying the change in entropy of the positive electrode and the amount of heat change accompanying the change in entropy of the negative electrode.

Then, ECU 100 calculates the internal temperature _{T p} of the cell 10 (step S30).
First, ECU 100 is a heating value _{q p} per unit volume in the interior of the cell 10 is calculated using equation (16) below. That is, in the ECU 100, the calorific value q _{main due to the main reaction, the calorific value q gen} due to the oxygen generation reaction at the positive electrode, the _{calorific value q comb} due to the oxygen recombination reaction at the negative electrode, and the thermal change amount due to the enthalpy change at the negative electrode. The sum of the five thermal changes of q _{h and the thermal change q s} accompanying the enthalpy change of each reaction is calculated as _{the calorific value q p} per unit volume inside the cell 10.

_{Then, by substituting the calorific value q p} (t) calculated using the above formula (16) and the external temperature T (T _s ) detected by the temperature sensor 33 into the above formula (1), to calculate the internal temperature _{T p} of the cell 10.

As described above, in the ECU 100 according to the present embodiment, the calorific value q _{mine due to the main reaction, the calorific value q gen} due to the oxygen evolution reaction at the positive electrode, the _{calorific value q comb} due to the oxygen recombination reaction at the negative electrode, and the enthalpy at the negative electrode The internal temperature of the cell 10 of the nickel hydrogen secondary battery is estimated in consideration of the five thermal changes, that is, the thermal change q _h associated with the change and the thermal change q _{s associated with the enthalpy change of each reaction.} To do. Therefore, the internal temperature of the cell 10 of the nickel-metal hydride secondary battery can be estimated accurately.

<Modification example>
In the cell 10 according to the above-described embodiment, since the case 13 is made of a metal having high thermal conductivity, it can be assumed that the surface temperature of the cell 10 is always substantially constant regardless of the mounting position of the temperature sensor 33. .. Therefore, in step S30 in FIG. 3, the external temperature T (T _s) detected by the temperature sensor 33, had it as substituted into the above equation (1).

However, in a nickel-metal hydride secondary battery, it is assumed that a resin is used for the outer body of the cell. When resin is used for the outer body of the cell, the thermal resistance (temperature difference) of the outer body of the cell may be taken into consideration depending on the mounting position of the temperature sensor 33. That is, the value of the temperature sensor 33 may be corrected in consideration of the thermal resistance derived from the outer body of the cell, and then substituted into the above equation (1).

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present disclosure is indicated by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 battery system, 10 cells, 11 positive electrode, 12 negative electrode, 13 cases, 31 voltage sensor, 32 current sensor, 33 temperature sensor.

Claims (1)

A state estimation device for a cell including a positive electrode having nickel hydroxide and a negative electrode having a hydrogen storage alloy.
A current sensor configured to detect the current of the cell and
A voltage sensor configured to detect the voltage of the cell and
A temperature sensor configured to detect the temperature of the outer surface of the cell and
A control device configured to calculate the internal temperature of the cell is provided.
The control device is
Using the detection results of the current sensor, the voltage sensor, and the temperature sensor, the positive electrode resistance, the negative electrode resistance, the positive electrode reaction resistance, and the negative electrode reaction resistance of the cell are calculated.
Using the detection results of the voltage sensor and the temperature sensor, the oxygen evolution current, which is the current consumed in the oxygen evolution reaction at the positive electrode, is calculated.
Using the detected value of the current sensor and the oxygen evolution current, the positive electrode main reaction current, which is the current consumed in the charge / discharge reaction at the positive electrode, is calculated.
Using the detected value of the current sensor, the positive electrode main reaction current, the positive electrode resistance, and the negative electrode resistance, the first calorific value due to the charge / discharge reaction of the cell is calculated.
Using the oxygen evolution current and the positive electrode reaction resistance, the second calorific value due to the oxygen evolution reaction at the positive electrode was calculated.
Using the detected values of the voltage sensor and the temperature sensor, the oxygen recombination current, which is the current consumed in the oxygen recombination reaction at the negative electrode, is calculated.
Using the oxygen recombination current and the negative electrode reaction resistance, the third calorific value due to the oxygen recombination reaction at the negative electrode was calculated.
The amount of heat change accompanying the change in enthalpy of the negative electrode was calculated using the detected value of the current sensor.
The amount of heat change accompanying the change in entropy due to the charge / discharge reaction, the oxygen generation reaction at the positive electrode, and the oxygen recombination reaction at the negative electrode was calculated using the detected value of the temperature sensor.
The internal temperature of the cell is calculated using the detected values of the temperature sensor, the first to third calorific value, the amount of heat change accompanying the enthalpy change, and the amount of heat change accompanying the entropy change. , Alkaline secondary battery state estimation device.

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