JP2020149880A - Secondary battery system - Google Patents

Abstract

To appropriately control high-rate deterioration of a lithium ion secondary battery.SOLUTION: A secondary battery system 2 comprises: a battery 21; a heater 23 which is configured to adjust the temperature of the battery 21; and an ECU 20 which controls the heater 23. If a state of charge (SOC) of the battery 21 is included in a resistance reduction region, then the battery 21 expands largely compared with the case where the SOC of the battery 21 is not included in the resistance reduction region. During the charging of the battery 21, if the SOC of the battery 21 is included in a predetermined region, then the ECU 20 controls the heater 23 in such a way that the temperature of the battery 21 becomes high compared with the case where the SOC of the battery 21 is not included in the resistance reduction region.SELECTED DRAWING: Figure 5

Description

The present disclosure relates to a secondary battery system, and more specifically, to a charging technique for suppressing deterioration of a lithium ion secondary battery.

In recent years, vehicles (hybrid vehicles, electric vehicles, etc.) equipped with assembled batteries made of lithium-ion secondary batteries have become widespread. For the purpose of fully exerting the performance of the lithium ion secondary battery, a technique for suppressing deterioration of the lithium ion secondary battery has been proposed.

For example, according to Japanese Patent Application Laid-Open No. 2016-123251 (Patent Document 1), the diffusion coefficient of lithium ions in the graphite negative electrode shows the maximum value in the SOC (State Of Charge) region of 0% or more and less than 40%, and is 40%. The minimum value is shown in the SOC region of 60% or more, and the intermediate value between the maximum value and the minimum value is shown in the SOC region where the SOC exceeds 60%. Therefore, in the method of charging the lithium ion secondary battery disclosed in Patent Document 1, the charging current is increased or decreased for each SOC region (see, for example, Tables 1 and 2 of Patent Document 1). As a result, heat generation of the lithium ion secondary battery due to charging can be minimized. As a result, deterioration of the lithium ion secondary battery (deterioration of battery characteristics such as charge / discharge cycle characteristics) can be suppressed.

JP-A-2016-123251 JP-A-2017-175758

In general, it is known that when a lithium ion secondary battery is charged with a large current (so-called high-rate charging), the concentration of lithium salt in the electrolytic solution (hereinafter, also abbreviated as "salt concentration") may be biased. ing. If the salt concentration is biased, the internal resistance of the lithium ion secondary battery increases, which may reduce the battery characteristics. Generally, such deterioration is also referred to as "high rate deterioration".

The present inventor has found that, for example, in a lithium ion secondary battery using a negative electrode containing soft carbon, the susceptibility to high-rate deterioration depends on SOC. The method for charging a lithium ion secondary battery disclosed in Patent Document 1 has room for improvement in that the SOC dependence of the susceptibility to high-rate deterioration is not particularly considered.

The present disclosure has been made to solve the above problems, and an object of the present disclosure is to appropriately suppress high-rate deterioration of a lithium ion secondary battery.

A secondary battery system according to an aspect of the present disclosure includes a battery, a temperature regulator configured to regulate the temperature of the battery, and a controller that controls the temperature regulator. The battery expands when the SOC of the battery is included in the predetermined area as compared with the case where the SOC of the battery is included in the predetermined area. When the SOC of the battery is included in the predetermined area during charging of the battery, the control device sets the temperature control device so that the temperature of the battery is higher than that when the SOC of the battery is not included in the predetermined area. Control.

When the battery is charged at a high rate, the salt concentration distribution is biased in the electrolytic solution inside the electrode body, and the internal resistance of the battery increases. The details will be described later, but as the temperature of the battery increases, the diffusion of the salt in the electrolytic solution is promoted, so that the bias of the salt concentration distribution in the electrolytic solution is easily alleviated. As a result, an increase in the internal resistance of the battery is suppressed. Therefore, according to the above configuration, high-rate deterioration of the battery can be appropriately suppressed.

According to the present disclosure, high-rate deterioration of a lithium ion secondary battery can be appropriately suppressed.

It is a figure which shows schematic the whole structure of the charging system which concerns on embodiment of this disclosure. It is a block diagram which shows schematic structure of a vehicle and a charger. It is a figure which shows the structure of a secondary battery system in more detail. It is a figure which shows the SOC dependence of the surface pressure between cells. It is a flowchart for demonstrating the temperature adjustment control in Embodiment 1. It is a figure which shows schematic the whole structure of the charging system which concerns on Embodiment 2 of this disclosure. It is a flowchart for demonstrating the temperature adjustment control in Embodiment 2.

Hereinafter, the present embodiment 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.

[Embodiment]
<Overall configuration of charging system>
FIG. 1 is a diagram schematically showing an overall configuration of a charging system according to a first embodiment of the present disclosure. With reference to FIG. 1, the charging system 100 includes a vehicle 1 and a charger 5. FIG. 1 shows a situation during external charge control in which the vehicle 1 and the charger 5 are electrically connected by a charging cable 6 and power is supplied from the charger 5 to the vehicle 1.

The vehicle 1 is, for example, an electric vehicle. However, the vehicle 1 may be, for example, a plug-in hybrid vehicle as long as it is a vehicle configured to enable external charging. The charger 5 may be a dedicated charger provided in the user's home or the like, or may be a charger provided in a public charging stand (also referred to as a charging station).

FIG. 2 is a block diagram schematically showing the configurations of the vehicle 1 and the charger 5. With reference to FIG. 2, the charger 5 is a direct current (DC) charger, and the power supplied from the system power source 7 (AC power) is used as the charging power (AC power) of the battery 21 mounted on the vehicle 1. Convert to DC power). The charger 5 includes a power line ACL, an AC / DC converter 51, a voltage sensor 52, feed lines PL0 and NL0, and a control circuit 50.

The power line ACL is electrically connected to the system power supply 7. The power line ACL transmits AC power from the system power source 7 to the AC / DC converter 51.

The AC / DC converter 51 converts the AC power on the power line ACL into DC power for charging the battery 21 mounted on the vehicle 1. The power conversion by the AC / DC converter 51 may be performed by a combination of AC / DC conversion for improving the power factor and DC / DC conversion for adjusting the voltage level. The DC power output from the AC / DC converter 51 is supplied by the feeder line PL0 on the positive electrode side and the feeder line NL0 on the negative electrode side.

The voltage sensor 52 is electrically connected between the feeder line PL0 and the feeder line NL0. The voltage sensor 52 detects the voltage between the feeder line PL0 and the feeder line NL0, and outputs the detection result to the control circuit 50.

The control circuit 50 includes a CPU, a memory, and input / output ports (none of which are shown). The control circuit 50 controls the power conversion operation by the AC / DC converter 51 based on the voltage detected by the voltage sensor 52, the signal from the vehicle 1, and the map and the program stored in the memory.

The vehicle 1 includes an inlet 11, a charging line PL1, NL1, a voltage sensor 121, a current sensor 122, a charging relay 131, 132, a system main relay (SMR) 141, 142, and a power line PL2. It includes an NL 2, a PCU (Power Control Unit) 16, a motor generator 17, a power transmission gear 18, a drive wheel 19, and a secondary battery system 2. The secondary battery system 2 includes a battery 21, a voltage sensor 221 and a current sensor 222, a temperature sensor 223, a heater 23, and an ECU (Electronic Control Unit) 20.

The inlet (charging port) 11 is configured so that the connector 61 of the charging cable 6 can be inserted with mechanical connection such as fitting. With the insertion of the connector 61, an electrical connection between the feeder line PL0 and the contact on the positive electrode side of the inlet 11 is secured, and an electrical connection between the feeder line NL0 and the contact on the negative electrode side of the inlet 11 is secured. The connection is secured. Further, when the inlet 11 and the connector 61 are connected by the charging cable 6, the ECU 20 of the vehicle 1 and the control circuit 50 of the charger 5 communicate with each other according to a communication standard such as CAN (Controller Area Network) to obtain signals and commands. , Messages or data can be sent and received to and from each other.

The voltage sensor 121 is electrically connected between the charging line PL1 and the charging line NL1 on the inlet 11 side of the charging relays 131 and 132. The voltage sensor 121 detects the DC voltage between the charging line PL1 and the charging line NL1, and outputs the detection result to the ECU 20. The current sensor 122 is provided on the charging line PL1. The current sensor 122 detects the current flowing through the charging line PL1 and outputs the detection result to the ECU 20. The ECU 20 can also calculate the power supplied from the charger 5 (the amount of charge of the battery 21) based on the detection results of the voltage sensor 121 and the current sensor 122.

The charging relay 131 is connected to the charging line PL1, and the charging relay 132 is connected to the charging line NL1. The closing / opening of the charging relays 131 and 132 is controlled in response to a command from the ECU 20. When the charging relays 131 and 132 are closed and the SMRs 141 and 142 are closed, power can be transmitted between the inlet 11 and the battery 21.

The battery 21 is an assembled battery including a plurality of cells 3. The battery 21 supplies electric power for generating the driving force of the vehicle 1. Further, the battery 21 stores the electric power generated by the motor generator 17.

The positive electrode of the battery 21 is electrically connected to the node ND1 via the SMR 141. The node ND1 is electrically connected to the charging line PL1 and the power line PL2. Similarly, the negative electrode of the battery 21 is electrically connected to the node ND2 via the SMR 142. The node ND2 is electrically connected to the charging line NL1 and the power line NL2. The closing / opening of the SMRs 141 and 142 is controlled in response to a command from the ECU 20.

The voltage sensor 221 detects the voltage of the battery 21. The current sensor 222 detects the current input / output to / from the battery 21. The temperature sensor 223 detects the temperature TB of the battery 21. Each sensor outputs the detection result to the ECU 20. The ECU 20 can estimate the SOC of the battery 21 based on the detection results of the voltage sensor 221 and / or the current sensor 222.

The heater 23 is, for example, an electric heating device such as a PTC (Positive Temperature Coefficient) heater, and raises the temperature of the battery 21 according to the control by the ECU 20. The heater 23 corresponds to an example of the "temperature adjusting device" according to the present disclosure.

The PCU 16 is electrically connected between the power lines PL2 and NL2 and the motor generator 17. The PCU 16 includes a converter and an inverter (neither of which is shown), and drives the motor generator 17 according to a command from the ECU 20.

The motor generator 17 is an AC rotating electric motor, for example, a permanent magnet type synchronous motor including a rotor in which a permanent magnet is embedded. The output torque of the motor generator 17 is transmitted to the drive wheels 19 through the power transmission gear 18 to drive the vehicle 1. Further, the motor generator 17 can generate electricity by the rotational force of the drive wheels 19 during the braking operation of the vehicle 1. The electric power generated by the motor generator 17 is converted into the charging electric power of the battery 21 by the PCU 16.

Like the control circuit 50, the ECU 20 includes a CPU 201, a memory 202 such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and an input / output port 203. The ECU 20 controls the devices so that the vehicle 1 is in a desired state in response to signals from each sensor or the like. The ECU 20 may be divided into a plurality of ECUs for each function.

As the main controls executed by the ECU 20 in the first embodiment, "external charge control" for charging the vehicle-mounted battery 21 with the electric power supplied from the charger 5 and "battery temperature" for raising the temperature of the battery 21 with the heater 23. "Control". In this embodiment, battery temperature control is performed during external charge control. The battery temperature control will be described in detail later.

<Cell configuration>
FIG. 3 is a diagram for explaining the configuration of each cell 3 in more detail. In FIG. 3, the cell 3 is shown through the inside thereof. The cell 3 has a battery case 41 having a substantially rectangular parallelepiped shape. The upper surface of the battery case 41 is sealed by the lid 42. One end of each of the positive electrode terminal 43 and the negative electrode terminal 44 projects outward from the lid body 42. The other ends of the positive electrode terminal 43 and the negative electrode terminal 44 are connected to the internal positive electrode terminal and the internal negative electrode terminal (neither of them is shown) inside the battery case 41, respectively.

The electrode body 45 is housed inside the battery case 41. The electrode body 45 is formed by laminating a positive electrode 46 and a negative electrode 47 via a separator 48 and winding the laminated body. The electrolytic solution (not shown) is held in the positive electrode 46, the negative electrode 47, the separator 48, and the like.

Soft carbon (easily graphitized carbon) is used for the negative electrode 47. As the material of the positive electrode 46, the separator 48, and the electrolytic solution, various conventionally known materials can be used. As an example, lithium cobalt oxide or lithium manganate is used for the positive electrode 46. Polyolefin is used for the separator 48. The electrolytic solution contains an organic solvent, lithium ions, and an additive. It is not essential that the electrode body 45 is a wound body, and the electrode body 45 may be a laminated body that is not wound.

<SOC dependency of high rate deterioration>
The present inventor carried out the following measurements in order to investigate the SOC dependence of the likelihood of high rates occurring in the battery 21. A battery of the same type as the battery 21 was prepared, and a surface pressure sensor (not shown) was installed between two adjacent cells. Then, the SOCs of these cells were adjusted to various values, and the surface pressure between the cells was measured after the steady state was reached.

FIG. 4 is a diagram showing the SOC dependence of the surface pressure between cells. In FIG. 4, the horizontal axis represents the SOC of the battery 21. The vertical axis represents the surface pressure between cells [unit: Pa (= N / m ² )].

In the example shown in FIG. 4, in the low SOC region of 20% or less or the high SOC region of 60% or more, the surface pressure between cells is larger than that in the intermediate SOC region of more than 20% and less than 60%. A large surface pressure between cells means that the volume of each cell is large. That is, in the low SOC region or the high SOC region, each cell expands even when it is not being charged, as compared with the intermediate SOC region.

When the battery 21 is charged at a high rate, the electrode body 45 expands. However, in the low SOC region or high SOC region of the battery 21, since each cell 3 is expanded before the start of high-rate charging as compared with the intermediate SOC region, there is room for the electrode body 45 to expand with high-rate charging. small. When the expansion of the electrode body 45 is hindered, the salt concentration distribution tends to be biased in the electrolytic solution inside the electrode body 45 with high-rate charging, which tends to increase the internal resistance R of the battery 21. That is, high-rate deterioration of the battery 21 is likely to occur. Therefore, the measurement result shown in FIG. 5 means that the resistance of the battery 21 to high rate deterioration is lower in the low SOC region or the high SOC region than in the intermediate SOC region. Therefore, in the following, a low SOC region having an SOC of 20% or less and a high SOC region having an SOC of 60% or more will also be referred to as a “resistance reduction region”. The area of reduced resistance corresponds to the "predetermined area" according to the present disclosure.

In the first embodiment, in view of the fact that the ease of progress of high-rate deterioration shows SOC dependence as shown in FIG. 4, the SOC of the battery 21 is included in the resistance reduction region, and the SOC of the battery 21 is The heating mode of the battery 21 by the heater 23 is different depending on whether the battery 21 is not included in the resistance reduction region. More specifically, in the first embodiment, when the SOC of the battery 21 is included in the resistance reduction region, the heater 23 is controlled as compared with the case where the SOC of the battery 21 is not included in the resistance reduction region. Increases the temperature TB of the battery 21.

Generally, the higher the temperature, the easier it is for the substance to diffuse. Therefore, when the temperature TB of the battery 21 is raised, the salt in the electrolytic solution tends to diffuse. As a result, the bias of the salt concentration distribution in the electrolytic solution is alleviated (eventually eliminated). As a result, an increase in the internal resistance R of the battery 21 is suppressed. That is, it becomes possible to suppress the high rate deterioration of the battery 21.

<Temperature adjustment control flow>
FIG. 5 is a flowchart for explaining the temperature adjustment control according to the first embodiment. The processes included in the flowcharts shown in FIGS. 5 and 7 to be described later are called from the main routine (not shown) and executed every time a predetermined control cycle elapses during the external charge control of the vehicle 1. Further, each step (hereinafter, abbreviated as "S") included in this flowchart is basically realized by software processing by the ECU 20, but is realized by dedicated hardware (electric circuit) manufactured in the ECU 20. May be done.

With reference to FIG. 5, in S11, the ECU 20 estimates the SOC of the battery 21. For SOC estimation, various known methods such as a method of referring to an OCV-SOC curve or a current integration method can be used.

In S12, the ECU 20 determines whether the SOC of the battery 21 estimated in S11 is within the resistance reduction region. When the SOC of the battery 21 is within the resistance reduction region, that is, when the SOC of the battery 21 is 20% or less or 60% or more (YES in S12), the ECU 20 advances the process to S13.

In S13, the ECU 20 heats the battery 21 by controlling the heater 23. As a result, the temperature of the battery 21 rises.

On the other hand, when the SOC of the battery 21 is outside the resistance reduction region in S12, that is, when the SOC of the battery 21 is more than 20% and less than 60% (NO in S12), the ECU 20 uses the battery 21. The treatment proceeds without heating (S14). When the processing of S13 and S14 is completed, the processing is returned to the main routine, and when the next control cycle comes, a series of processing is executed again.

Note that, in FIG. 5, an example in which the battery 21 is not heated in S14 has been described, but this does not mean that heating of the battery 21 is prohibited. When the SOC of the battery 21 is within the reduced resistance region and the SOC of the battery 21 is outside the reduced resistance region, the battery 21 is heated, but when the SOC of the battery 21 is outside the reduced resistance region, The heater 23 may be controlled so that the heating amount of the battery 21 is smaller than that in the case where the SOC of the battery 21 is within the resistance reduction region.

As described above, in the first embodiment, considering that the ease of progress of high-rate deterioration has an SOC dependence, the heating amount of the battery 21 when the SOC of the battery 21 is within the resistance reduction region is determined. , The amount of heating of the battery 21 when the SOC of the battery 21 is outside the resistance reduction region is made larger. By raising the temperature of the battery 21, the diffusion of the salt in the electrolytic solution is promoted, so that the bias of the salt concentration distribution can be easily eliminated. As a result, according to the first embodiment, it is possible to suppress an increase in the internal resistance R of the battery 21. In other words, the high rate deterioration of the battery 21 can be appropriately suppressed.

[Embodiment 2]
Although the configuration for heating the battery 21 has been described in the first embodiment, the cooling of the battery 21 may be controlled.

FIG. 6 is a diagram schematically showing the overall configuration of the charging system according to the second embodiment of the present disclosure. With reference to FIG. 6, the secondary battery system 2A of the charging system 200 is different from the secondary battery system 2 (see FIG. 2) in the first embodiment in that the cooling device 24 is provided instead of the heater 23.

The cooling device 24 is an air-cooled or liquid-cooled cooling device, and cools the battery 21 according to the control by the ECU 20. The cooling device 24 corresponds to another example of the “temperature adjusting device” according to the present disclosure.

FIG. 7 is a flowchart for explaining the temperature adjustment control according to the second embodiment. First, the ECU 20 estimates the SOC of the battery 21 with reference to FIG. 7 (S1). Then, the ECU 20 determines whether or not the SOC of the battery 21 is within the resistance reduction region (S22). The processing of S21 and S22 is the same as the processing of S11 and S12 in the first embodiment (see FIG. 5), respectively.

When the SOC of the battery 21 is outside the resistance reduction region (NO in S22), the ECU 20 advances the process to S24. In S24, the ECU 20 controls the cooling device 24 so as to cool the battery 21.

On the other hand, when the SOC of the battery 21 is within the resistance reduction region (YES in S22), the ECU 20 advances the process to S23. In S23, the ECU 20 controls the cooling device 24 so as not to cool the battery 21. That is, the ECU 20 causes the cooling device 24 to stop the cooling of the battery 21 when the battery 21 is being cooled, and causes the cooling device 24 to maintain that state when the cooling of the battery 21 has already stopped.

As described above, in consideration of the fact that the ease of progress of high-rate deterioration also has an SOC dependence in the second embodiment, the amount of cooling of the battery 21 when the SOC of the battery 21 is within the resistance reduction region is determined. The SOC of the battery 21 is set to be smaller than the cooling amount of the battery 21 when it is outside the resistance reduction region. By suppressing the cooling of the battery 21, the diffusion of the salt in the electrolytic solution is less likely to be hindered, so that the elimination of the bias in the salt concentration distribution is less likely to be hindered. As a result, according to the second embodiment, it is possible to suppress an increase in the internal resistance R of the battery 21.

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

100,200 charging system, 1 vehicle, 11 inlets, 12 AC / DC converters, 121 voltage sensors, 122 current sensors, 131, 132 SMRs, 141,142 charging relays, 15 PCUs, 16 motor generators, 17 power transmission gears, 18 drive wheels, 2,2A secondary battery system, 20 ECU, 201 CPU, 202 memory, 203 input / output port, 21 battery, 221 voltage sensor, 222 current sensor, 223 temperature sensor, 23 heater, 24 cooling device, 3 cells , 41 Battery case, 42 lid, 43 positive electrode terminal, 44 negative electrode terminal, 45 electrode body, 46 positive electrode, 47 negative electrode, 48 separator, 5 charger, 50 control circuit, 51 AC / DC converter, 52 voltage sensor, 6 Charging cable, 61 connector, 7 system power supply, ACL, NL2, PL2 power line, ND1, ND2 node, NL0, PL0 power supply line, NL1, PL1 charging line.

Claims (1)

With the battery
A temperature regulator configured to regulate the temperature of the battery,
A control device for controlling the temperature control device is provided.
When the SOC of the battery is included in the predetermined region, the battery expands as compared with the case where the SOC of the battery is included in the predetermined region.
In the control device, when the SOC of the battery is included in the predetermined region during charging of the battery, the temperature of the battery is higher than when the SOC of the battery is not included in the predetermined region. A secondary battery system that controls the temperature control device so as to be.

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