JP7078890B2 - Secondary battery controller - Google Patents

Description

The present disclosure relates to a technique for determining whether or not a secondary battery is in an overcharged state.

Japanese Unexamined Patent Publication No. 2013-118090 (Patent Document 1) discloses a monitoring device for monitoring the state of charge of a secondary battery. This monitoring device monitors the amount of potential change per unit time of the reference electrode placed outside the negative electrode plate of the secondary battery, and when the amount of potential change per unit time of the reference electrode exceeds the threshold value, it is secondary. It is determined that the battery is overcharged.

Japanese Unexamined Patent Publication No. 2013-118090

When the secondary battery is in an overcharged state, the positive electrode and the negative electrode are in a thermodynamically unstable state, so that the secondary battery may be in an overheated state. In order to suppress overheating due to overcharging without excessively restricting the use of the secondary battery, a threshold that serves as a reference for determining whether or not the secondary battery is in an overcharged state (hereinafter referred to as "overcharge criterion"). It is desirable to appropriately set the "threshold") and limit the charging of the secondary battery when the parameter indicating the charge state of the secondary battery exceeds the overcharge reference threshold.

The overcharge resistance of the secondary battery (difficulty of overheating due to overcharging) is affected by the reaction speed in the secondary battery. That is, when the reaction rate in the secondary battery decreases, the heat generation rate (heat generation amount per unit time) caused by the reaction decreases, so that overheating due to overcharging is less likely to occur. The reaction rate in the secondary battery may change depending on the temperature history of the secondary battery and the period of use. Therefore, the overcharge resistance of the secondary battery can change depending on the temperature history of the secondary battery and the period of use.

However, in Patent Document 1, the threshold value (overcharge reference threshold value) compared with the amount of potential change per unit time of the reference electrode is not a value determined by the temperature history and usage period of the secondary battery, but is inside the secondary battery. The value does not reflect the reaction rate of. Therefore, in the technique disclosed in Patent Document 1, it is not possible to accurately determine whether or not the battery is overcharged, and as a result, the use of the secondary battery is excessively restricted, or overheating due to overcharging occurs. There is concern that it will occur.

The present disclosure has been made to solve the above-mentioned problems, and an object thereof is to suppress overheating due to overcharging without excessively restricting the use of the secondary battery.

The control device according to the present disclosure is a control device for a secondary battery including a positive electrode, a negative electrode, and an electrolytic solution, and has a temperature detection unit configured to detect the temperature of the secondary battery and a charging state of the secondary battery. It is provided with a control unit for limiting the charging of the secondary battery when the parameter indicating the above exceeds the overcharge reference threshold. The control unit calculates a first parameter indicating the amount of the positive electrode film formed on the surface of the positive electrode and a second parameter indicating the salt concentration of the electrolytic solution by using the history of the temperature of the secondary battery and the period of use. The control unit sets the overcharge reference threshold value using the calculated first parameter and second parameter.

In the secondary battery, as the amount of the positive electrode film increases, the reaction rate between the positive electrode and the electrolytic solution (the heat generation rate due to the reaction between the positive electrode and the electrolytic solution) decreases, so that overheating due to overcharging is less likely to occur. Further, as the salt concentration of the electrolytic solution decreases, the decomposition rate of the electrolytic solution (heat generation rate due to the decomposition of the electrolytic solution) decreases, so that overheating due to overcharging is less likely to occur. In view of these points, in the above configuration, the overcharge reference threshold value is set by using the first parameter indicating the amount of the positive electrode film and the second parameter indicating the salt concentration of the electrolytic solution. Thereby, the overcharge reference threshold value can be set to a value that reflects the reaction rate between the positive electrode and the electrolytic solution and the decomposition rate of the electrolytic solution. Therefore, the overcharge reference threshold value can be set to an appropriate value in consideration of overcharge resistance (difficulty of overheating due to overcharge). As a result, overheating due to overcharging can be suppressed without excessively restricting the use of the secondary battery.

According to the present disclosure, overheating due to overcharging can be suppressed without excessively restricting the use of the secondary battery.

It is a figure which shows an example of the whole structure of a vehicle. It is a figure which shows typically the internal state of a battery in the state before use of a battery. It is a figure which shows typically the internal state of a battery in the state after use of a battery. It is a figure which shows typically the characteristic that the battery temperature Tb rises by charging. It is a flowchart which shows an example of the processing procedure which is executed when the ECU sets an overcharge reference threshold value V.

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.

FIG. 1 is a diagram showing an example of an overall configuration of a vehicle 1 to which a control device according to the present embodiment is applied. In the following, an example in which the control device according to the present embodiment is mounted on the vehicle 1 will be described, but the control device according to the present embodiment is not necessarily limited to being mounted on the vehicle 1.

The vehicle 1 includes a battery 10, a load 20, and an ECU (Electronic Control Unit) 100. The vehicle 1 is an electric vehicle (hybrid vehicle, electric vehicle, etc.) that can travel by using the electric power stored in the battery 10.

The battery 10 is a lithium ion secondary battery that is electrically connected to the load 20 and stores the driving power of the load 20. Inside the battery 10, a positive electrode, a negative electrode, and an electrolytic solution that ionically bonds them are provided.

The load 20 includes a traveling electric motor that generates a driving force for driving the vehicle 1 by using the electric power from the battery 10. Further, the load 20 can charge the battery 10 by the regenerative power of the traveling electric motor.

The battery 10 has a voltage sensor 11 for detecting the voltage between terminals of the battery 10 (hereinafter, also referred to as “battery voltage Vb”) and a current flowing through the battery 10 (hereinafter, also referred to as “battery current Ib”). A current sensor 12 and a temperature sensor 13 for detecting the temperature of the battery 10 (hereinafter, also referred to as “battery temperature Tb”) are provided. The detected values of the sensors 11 to 13 are transmitted to the ECU 100.

The ECU 100 incorporates a CPU (Central Processing Unit) and a memory (not shown). The ECU 100 executes a predetermined arithmetic process based on the information from the sensors 11 to 13 and the information stored in the memory.

<Suppression of overheating due to overcharging>
When the battery 10 is in an overcharged state, the positive electrode and the negative electrode of the battery 10 become thermodynamically unstable, and the positive electrode material is easily decomposed to release oxygen or the electrolytic solution is oxidized. As the internal temperature of the battery 10 rises, the battery 10 may become overheated.

The ECU 100 according to the present embodiment has a voltage value as a reference for determining whether or not the battery 10 is in an overcharged state in order to suppress overheating due to overcharging (hereinafter, also referred to as “overcharge reference threshold value V”). ) Is set. Then, when the battery voltage Vb exceeds the overcharge reference threshold V, the ECU 100 limits the charging of the battery 10 in order to suppress overheating due to overcharging (or lowers the charging current when charging is in progress). (Stop charging, etc.) Perform processing.

<Setting of overcharge reference threshold>
The ECU 100 according to the present embodiment sets the overcharge reference threshold value V to be overcharge resistant (difficulty of overheating due to overcharge) by setting the above-mentioned overcharge reference threshold value V variably according to the reaction speed in the battery 10. ) Is taken into consideration and set to an appropriate value.

FIG. 2 is a diagram schematically showing an internal state of the battery 10 in a state before use (almost new state) of the battery 10. As described above, the inside of the battery 10 is provided with a positive electrode, a negative electrode, and an electrolytic solution that ionically binds them. Before the use of the battery 10, a film or the like was hardly formed on the surface of the positive electrode, and the salt concentration of the electrolytic solution did not decrease.

FIG. 3 is a diagram schematically showing an internal state of the battery 10 in a state after the battery 10 is used. As shown in FIG. 3, by using (charging or discharging) the battery 10, a positive electrode film can be formed on the positive electrode surface. In addition, the salt concentration of the electrolytic solution may decrease due to the decomposition of the electrolytic solution.

When the amount of the positive electrode film increases due to the use of the battery 10, even if the battery voltage Vb is the same, the reaction rate between the positive electrode and the electrolytic solution decreases, so that the heat generation rate (unit time) due to the reaction between the positive electrode and the electrolytic solution The amount of heat generated per unit) decreases. Therefore, as the amount of the positive electrode film increases, overheating due to overcharging is less likely to occur.

Further, when the salt concentration of the electrolytic solution decreases due to the use of the battery 10, even if the battery voltage Vb is the same, the decomposition rate of the electrolytic solution decreases, so that the heat generation rate due to the decomposition of the electrolytic solution decreases. Therefore, the lower the salt concentration of the electrolytic solution, the less likely it is that overheating will occur due to overcharging.

FIG. 4 is a diagram schematically showing an increase characteristic of the battery temperature Tb due to charging. In FIG. 4, the horizontal axis indicates the charging duration, and the vertical axis indicates the battery temperature Tb. Further, in FIG. 4, the solid line shows the rising characteristic of the battery temperature Tb in the pre-use state (the state shown in FIG. 2), and the broken line shows the rising characteristic of the battery temperature Tb in the post-use state (the state shown in FIG. 3). The thermal runaway region shown in FIG. 4 is a region where overheating occurs due to overcharging. The permissible temperature Tb0 shown in FIG. 4 is an upper limit value of the battery temperature Tb that can avoid overheating due to overcharging.

After the battery 10 is used, the heat generation rate and the heat generation amount are reduced by increasing the amount of the positive electrode film, and the heat generation rate and the heat generation amount are reduced by reducing the salt concentration of the electrolytic solution. Therefore, as shown in FIG. 4, the rate of increase of the battery temperature Tb (inclination of the broken line) when charging the battery 10 after use is the battery temperature Tb when charging the battery 10 before use (new state). It is smaller than the ascending speed (slope of the solid line).

Due to this effect, the battery voltage Vb when the battery temperature Tb reaches the allowable temperature Tb0 is the initial voltage V1 in the battery 10 before use, but becomes a predetermined voltage V2 higher than the initial voltage V1 in the battery 10 after use. It turned out to be. In this case, it is necessary to set the overcharge reference threshold value V to the initial voltage V1 in the battery 10 before use, but in the battery 10 after use, the overcharge reference threshold value V is set to a predetermined voltage higher than the initial voltage V1. It can be set to V2.

Therefore, the ECU 100 according to the present embodiment has a positive electrode film amount M (first parameter indicating the positive electrode film amount) and an electrolytic solution salt concentration C (electrolyte solution) based on the usage history of the battery 10 (temperature history and usage period of the battery 10). The second parameter) indicating the salt concentration of the above is calculated. Then, the ECU 100 sets the overcharge reference threshold value V using the calculated positive electrode film amount M and the electrolytic solution salt concentration C.

FIG. 5 is a flowchart showing an example of a processing procedure executed when the ECU 100 sets the overcharge reference threshold value V. This flowchart is repeatedly executed, for example, at a predetermined cycle.

First, the ECU 100 acquires the history of the battery temperature Tb and the usage period t for each temperature from the memory (step S10). Specifically, the ECU 100 constantly stores the history of the battery temperature Tb detected by the temperature sensor 13 in the memory together with the usage period t for each temperature. The ECU 100 reads this information from the memory in step S10.

Next, the ECU 100 calculates the positive electrode film amount M (Tb, t) using the history of the battery temperature Tb acquired in step S10 and the usage period t for each temperature (step S12). For example, the ECU 100 stores a map showing the relationship between the battery temperature Tb, the usage period t, and the positive electrode film amount M, which is obtained by an experiment or the like, in a memory, and refers to this map to store the battery temperature Tb and the usage period. The positive electrode film amount M (Tb, t) corresponding to t is calculated.

Next, the ECU 100 calculates the electrolyte salt concentration C (Tb, t) using the history of the battery temperature Tb acquired in step S10 and the usage period t for each temperature (step S14). For example, the ECU 100 stores a map showing the relationship between the battery temperature Tb, the usage period t, and the electrolyte salt concentration C, which is obtained by experiments or the like, in the memory, and refers to this map for the battery temperature Tb and use. The electrolyte salt concentration C (Tb, t) corresponding to the period t is calculated.

Next, the ECU 100 calculates the overcharge reference threshold value V using the positive electrode film amount M (Tb, t) calculated in step S12 and the electrolyte salt concentration C (Tb, t) calculated in step S14 (. Step S16). For example, the ECU 100 calculates the overcharge reference threshold value V using the following equation (1).

V = α ・ M (Tb, t) + β ・ C (Tb, t)… (1)
In the formula (1), “α” is a coefficient for reflecting the positive electrode film amount M (Tb, t) in the overcharge reference threshold value V. The coefficient α is adjusted so that the overcharge reference threshold value V increases as the positive electrode film amount M (Tb, t) increases. As a result, the reaction speed between the positive electrode and the electrolytic solution decreases as the amount of the positive electrode film M increases (that is, the overcharge resistance is improved), and the overcharge reference threshold V is increased to increase the battery voltage. It is possible to make it difficult for Vb to exceed the overcharge reference threshold V (make it difficult to intervene in the charge limit). Therefore, overheating due to overcharging can be suppressed without excessively limiting the charging of the battery 10.

In the formula (1), “β” is a coefficient for reflecting the electrolytic solution salt concentration C (Tb, t) in the overcharge reference threshold value V. The coefficient β is adjusted so that the overcharge reference threshold value V increases as the electrolytic solution salt concentration C decreases. As a result, the overcharge reference threshold V is increased and the battery voltage Vb is overcharged as the decomposition rate of the electrolyte increases (that is, the overcharge resistance is improved) in response to the decrease in the electrolyte salt concentration C. It is possible to make it difficult to exceed the reference threshold V (make it difficult to intervene in the charge limit). Therefore, overheating due to overcharging can be suppressed without excessively limiting the charging of the battery 10.

As described above, the ECU 100 according to the present embodiment calculates the positive electrode film amount M and the electrolytic solution salt concentration C of the battery 10 from the history of the battery temperature Tb and the usage period t for each temperature, and the calculated positive electrode film amount. The overcharge reference threshold V is set using M and the electrolyte salt concentration C. Thereby, the overcharge reference threshold value V can be set to a value that reflects the reaction rate between the positive electrode and the electrolytic solution and the decomposition rate of the electrolytic solution. Therefore, the overcharge reference threshold value V can be set to an appropriate value in consideration of the overcharge resistance of the battery 10 (difficulty of overheating due to overcharge). As a result, overheating due to overcharging can be suppressed without excessively limiting the charging of the battery 10.

<Modification example>
In the above-described embodiment, an example is shown in which "battery voltage Vb" is used as a parameter indicating the charge state of the battery 10 and charging of the battery 10 is restricted when the battery voltage Vb exceeds the "overcharge reference threshold V". rice field. However, the parameter indicating the state of charge of the battery 10 is not limited to the "battery voltage Vb".

For example, in consideration of the rising characteristic of the battery temperature Tb shown in FIG. 4, the "charging duration" shown on the horizontal axis of FIG. 4 is set as a parameter indicating the charging state of the battery 10, and the charging duration is the "overcharge reference threshold". The charging of the battery 10 may be restricted when T ”(charging duration as a reference for determining whether or not the battery is overcharged) is exceeded. In this case, the overcharge reference threshold value T may be lengthened as the positive electrode film amount M increases and the electrolytic solution salt concentration C decreases. Thereby, the overcharge reference threshold value T can be set to an appropriate value in consideration of the overcharge resistance of the battery 10 (difficulty of overheating due to overcharge). As a result, as in the above-described embodiment, overheating due to overcharging can be suppressed without excessively limiting the charging of the battery 10.

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 shown 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 vehicle, 10 batteries, 11 voltage sensor, 12 current sensor, 13 temperature sensor, 20 load.

Claims (1)

A control device for a secondary battery including a positive electrode, a negative electrode, and an electrolytic solution.
A temperature detector configured to detect the temperature of the secondary battery,
It is provided with a control unit that limits the charging of the secondary battery when the parameter indicating the charge state of the secondary battery exceeds the overcharge reference threshold value.
The control unit
Using the history of the temperature of the secondary battery and the period of use, a first parameter indicating the amount of the positive electrode film formed on the surface of the positive electrode and a second parameter indicating the salt concentration of the electrolytic solution were calculated.
The overcharge reference threshold is set using the calculated first parameter and the second parameter .
The control unit of the secondary battery increases the overcharge reference threshold as the amount of the positive electrode film indicated by the first parameter increases and the salt concentration of the electrolytic solution indicated by the second parameter decreases . Control device.

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