JP2019145564A - Control device for lithium ion capacitor - Google Patents

Abstract

To provide a control device for a lithium ion capacitor that performs charge/discharge control in which a decrease in the energy input output amount of the lithium ion capacitor in a low temperature environment can be suppressed.SOLUTION: There is provided a control device for a lithium ion capacitor according to the present invention. The control apparatus is provided with a temperature measurement portion which measures the temperature in a cell of the lithium ion capacitor, and a charge/discharge control portion which controls charging/discharging of the lithium ion capacitor. The charge/discharge control portion prohibits discharge of the lithium ion capacitor in a region below a discharge lower limit SOC corresponding to the temperature measured by the temperature measurement portion.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a control device for a lithium ion capacitor.

  In a vehicle (for example, an automobile) that uses electric energy as a power source, a power supply device that combines a plurality of power sources having different characteristics may be used in order to improve adaptability to various energy requirements. For example, a lithium ion capacitor (LiC) is mentioned as one of the electric power sources which can be used suitably as the main power supply or auxiliary power supply of these vehicles. A lithium ion capacitor typically has a configuration in which a positive electrode of an electric double layer capacitor and a negative electrode of a lithium ion secondary battery (LiB) are combined, and the internal resistance is low compared to a lithium ion secondary battery, There are advantages such as rapid charge and discharge and long life. The prior art relating to this type of lithium ion capacitor includes the one described in Patent Document 1.

JP 2013-78235 A

  However, in general, a lithium ion capacitor has a small energy capacity compared to a lithium ion secondary battery, and thus it is difficult to increase the energy input / output amount. In particular, the internal resistance of the lithium ion capacitor tends to increase under a low temperature environment (for example, an environment in which the cell temperature of the lithium ion capacitor is about 0 ° C. or less). In a low temperature environment showing resistance, when the lithium ion capacitor is charged and discharged using a conventional control method, the energy input / output amount tends to be further reduced.

  This invention is made in view of this point, and provides the control apparatus of a lithium ion capacitor which performs charging / discharging control which can suppress the energy input / output amount fall of the lithium ion capacitor in a low-temperature environment. With the goal.

  According to the present invention, a control device for a lithium ion capacitor is provided. The said control apparatus is provided with the temperature measurement part which measures the temperature in the cell of the said lithium ion capacitor, and the charging / discharging control part which controls charging / discharging of this lithium ion capacitor.

  Here, when the lithium ion capacitor is charged with a constant power P with respect to the lithium ion capacitor having a predetermined charge start SOC (State of charge) under a predetermined temperature environment, the lithium ion capacitor starts from the charge start. For the input energy E defined by the product of the time T until the SOC reaches 100% and the power P, the charge start SOC at which the input energy E takes a maximum value is defined as a discharge lower limit SOC. In this case, the charge / discharge control unit prohibits the discharge of the lithium ion capacitor in a region below the discharge lower limit SOC corresponding to the temperature measured by the temperature measurement unit.

  According to the control device having such a configuration, the lithium ion capacitor to be controlled is charged / discharged in a low temperature environment (for example, an environment in which the temperature inside the cell of the lithium ion capacitor is about 0 ° C. or lower). However, since it is suppressed to start charge from the area | region below the said discharge minimum SOC, the fall of energy input-output amount (energy capacity) can be suppressed.

It is explanatory drawing which shows typically the structure of the control apparatus which concerns on one Embodiment. It is a graph which shows the relationship between the in-cell temperature of the lithium ion capacitor which concerns on one Embodiment, and discharge minimum SOC. It is a flowchart which shows the charging / discharging control method which concerns on one Embodiment. It is a flowchart which shows the measuring method of the input energy in the predetermined temperature environment of the lithium ion capacitor of control object. It is a graph which shows a time-dependent voltage change when it charges from predetermined charging start SOC in a -30 degreeC environment about the lithium ion capacitor which concerns on one Embodiment. It is a graph which shows a time-dependent voltage change when it charges from predetermined | prescribed charge start SOC in a 25 degreeC environment about the lithium ion capacitor which concerns on one Embodiment. It is a graph which shows the relationship between the input energy in -30 degreeC environment, and charge start SOC about the lithium ion capacitor which concerns on one Embodiment. It is a graph which shows the relationship between the input energy in 25 degreeC environment, and charge start SOC about the lithium ion capacitor which concerns on one Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings as appropriate. Matters other than the matters specifically mentioned in the present specification (for example, the structure of LIC that does not characterize the present invention) and the matters necessary for carrying out the present invention are those of ordinary skill in the art based on the prior art in this field. It can be grasped as a design matter. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  In this specification, SOC (State of Charge) represents the state of charge of a lithium ion capacitor. When the upper limit voltage of the lithium ion capacitor is normal, the SOC is 100%, and when the lower limit voltage is normal, the SOC is 0%. Suppose that

<Control device>
FIG. 1 schematically shows a configuration of a control device 50 according to an embodiment of the present invention. Further, a lithium ion capacitor (LIC) 10 that is a control target of the control device 50 is shown. The control device 50 of the lithium ion capacitor 10 disclosed herein includes a temperature measurement unit 20 and a charge / discharge control unit 30. The temperature measurement unit 20 includes a casing (exterior body) of the lithium ion capacitor 10 and a temperature sensor 22 installed in at least one place inside thereof. The temperature measurement unit 20 measures (calculates) the temperature in the cell of the lithium capacitor 10 based on the data detected by the temperature sensor 22. The temperature sensor 22 may be installed in a lid portion that constitutes a part of the casing (exterior body) of the lithium ion capacitor 10 from the viewpoint of manufacturability and the like. The charge / discharge control unit 30 controls charge / discharge of the lithium ion capacitor 10 by a charge / discharge control method described later while referring to the temperature in the cell of the lithium ion capacitor 10 measured by the temperature measurement unit 20.

  Here, charging and discharging of the lithium ion capacitor 10 is performed using a conventional control method in a low temperature environment (for example, in an environment where the temperature in the cell of the lithium ion capacitor 10 is about 0 ° C. or lower). The reason why the energy input / output amount (energy capacity) tends to decrease when this is done will be briefly described.

  Generally, when the lithium ion capacitor 10 becomes low temperature, the internal resistance tends to increase. Here, if charging (input) is performed with respect to the lithium ion capacitor 10 in a state where the internal resistance is relatively high, the lithium ion capacitor 10 is likely to be in an overvoltage state, and as a result, the lithium ion capacitor 10 is charged. There may be restrictions (input restrictions). For this reason, when the lithium ion capacitor 10 is charged / discharged in a low temperature environment, the energy input / output amount (capacity) tends to be lower than originally expected.

  According to the study by the present inventors, such a decrease in the energy input / output amount is caused by the SOC (State of when starting charging (input) of the lithium ion capacitor 10 in addition to the in-cell temperature of the lithium ion capacitor 10 described above. charge) (hereinafter also referred to as “charging start SOC”). In other words, in a low temperature environment (for example, the temperature inside the cell is 0 ° C. or lower), the lithium ion capacitor 10 that has been discharged until the low SOC (for example, less than 40% SOC) is started to be charged. It has been found that when the charge start SOC of the lithium ion capacitor 10 is low (for example, the charge start SOC is less than 40%), the energy input / output amount of the lithium ion capacitor 10 is greatly reduced. This is considered to be because when the charging is performed from a low SOC under a low temperature environment, the voltage of the lithium ion capacitor 10 easily reaches the upper limit voltage in a shorter period and is more easily subjected to the charging restriction. For these reasons, by prohibiting charging from a low SOC region below a predetermined value in a low temperature environment, inefficient charging and discharging of the lithium ion capacitor 10 can be suppressed. As a result, the lithium ion capacitor 10 The decrease in the energy input / output amount can be suppressed.

<Lower discharge SOC>
According to the control device 50 disclosed herein, the charge / discharge control unit 30 prohibits the discharge of the lithium ion capacitor 10 in a region below a predetermined SOC (hereinafter also referred to as “discharge lower limit SOC”). Thereby, since the charge start SOC is limited to be less than the discharge lower limit SOC, inefficient charging of the lithium ion capacitor 10 in a low temperature environment can be suppressed. Here, the lower discharge limit SOC can be defined as a value that varies depending on the temperature in the cell of the lithium ion capacitor 10. Therefore, the charge / discharge control unit 30 refers to the temperature in the cell of the lithium ion capacitor 10 measured by the temperature measurement unit 20, and discharges the lithium ion capacitor 10 in a region below the discharge lower limit SOC corresponding to the temperature. Is preferably prohibited.

  In the technology disclosed herein, for the lithium ion capacitor 10 to be controlled, a specific value of the discharge lower limit SOC under a predetermined temperature environment can be calculated by the following method. First, the lithium ion capacitor 10 having a predetermined in-cell temperature and a predetermined charging start SOC is charged with a constant power P. Then, a time T from the start of charging until the SOC of the lithium ion capacitor 10 reaches 100% is measured. Next, an input energy E that is a product of the measured time T and power P is calculated. At this time, when the input energy E takes a maximum value with respect to the charge start SOC, the charge start SOC when the input energy E takes the maximum value is set as the discharge lower limit SOC of the lithium ion capacitor 10 at the above temperature.

  When the in-cell temperature is higher than the predetermined temperature, the input energy E of the lithium ion capacitor 10 tends to increase as the charging start SOC decreases, and there is a tendency that the maximum value does not exist. In such a case, the discharge lower limit SOC is not set.

FIG. 2 shows the relationship between the discharge lower limit SOC of the lithium ion capacitor 10 according to one embodiment and the in-cell temperature. In the lithium ion capacitor 10 according to the present embodiment, when the temperature in the cell is higher than 0 ° C., the input energy E does not take a maximum value, and therefore, the discharge lower limit SOC is set to 0% for convenience.
When the in-cell temperature is 0 ° C. or less, the input energy E has a maximum value. At this time, the discharge lower limit SOC, which is the SOC when taking the maximum value, tends to increase as the temperature in the cell decreases, as shown in FIG. When the present invention is applied to the lithium ion capacitor 10 according to the present embodiment, the discharge lower limit SOC is preferably set as follows. That is, when the cell internal temperature is over -10 ° C and below 0 ° C, the lower limit of discharge is SOC 0% to 5%, and when the cell internal temperature is over -20 ° C and below -10 ° C, the lower limit of discharge is SOC 5% to 10%. When the internal temperature is above -30 ° C and below -20 ° C, the lower discharge limit SOC is 10% to 40%, and when the internal temperature is -40 ° C to -30 ° C, the lower discharge limit SOC is 40% to 55%. It is preferable to set to.

<Charging / discharging control method>
Next, an embodiment of a method of controlling the lithium ion capacitor 10 by the control device 50 disclosed herein will be described with reference to the flowchart of FIG. In the example shown in FIG. 3, the lithium ion capacitor (LIC) 10 is used in the form of a power supply system that is used together with a lithium ion secondary battery (LIB).

  In the control method of this embodiment, the temperature of the lid portion of the lithium ion capacitor 10 is measured by the temperature sensor 22 installed on the lid portion of the cell of the lithium ion capacitor 10 (S10). Based on the temperature data, the temperature measurement unit 20 calculates the temperature in the cell of the lithium ion capacitor 10 while referring to a cell temperature estimation map that is prepared in advance to estimate the temperature in the cell of the lithium ion capacitor 10. Calculate (S12). Next, the charge / discharge control unit 30 determines whether or not the temperature in the cell of the lithium ion capacitor 10 is equal to or lower than a predetermined temperature (0 ° C. in this example) (S14).

  Here, when the temperature in the cell of the lithium ion capacitor 10 is higher than a predetermined temperature (in this example, higher than 0 ° C.) (S14: No), the charge / discharge control unit 30 Then, normal charge / discharge control is performed (S16). Conversely, when the temperature in the cell of the lithium ion capacitor 10 is equal to or lower than a predetermined temperature (in this example, 0 ° C. or lower) (S14: Yes), the charge / discharge control unit 30 It is determined whether or not the stacked body (stack) is being discharged (S18).

  Here, when the stack of the lithium ion capacitors 10 is not being discharged (S18: No), normal charge / discharge control is performed on the lithium ion capacitors 10 (S20). However, when the stack of the lithium ion capacitor 10 is being discharged (S18: Yes), the charge / discharge control unit 30 performs discharge below the discharge lower limit SOC corresponding to the temperature in the cell of the lithium ion capacitor 10. Discharge control to be prohibited is performed (S22). Such discharge control restricts the charge start SOC from being lower than the discharge lower limit SOC, so that inefficient charge (that is, charge that can reduce the energy input / output amount) can be suppressed.

  When the above discharge control is performed, with respect to charging / discharging limited by the SOC use limitation of the lithium ion capacitor 10, control for increasing the input / output distribution to the lithium ion secondary battery connected to the lithium ion capacitor 10 is performed. It can be compensated by performing (S24). Thereby, it becomes easy to maintain the total input / output amount as the whole power supply system including the lithium ion capacitor 10 and the lithium ion secondary battery.

  Next, the process returns to the step of measuring the temperature of the lithium ion capacitor 10 again (S10), and the above steps are repeated thereafter. Thereby, when the temperature in the cell again becomes higher than a predetermined temperature (0 ° C. in this example), the discharge control is canceled and normal charge / discharge control is performed (return control). By such return control, the energy capacity of the lithium ion capacitor 10 can be used more efficiently.

  The configuration of the lithium ion capacitor 10 to be controlled by the control device 50 and the control method disclosed herein is not particularly limited, and the same configuration as that normally used can be used. Hereinafter, the lithium ion capacitor 10 to which the technology disclosed herein can be applied will be briefly described.

  The positive electrode of the lithium ion capacitor 10 may be the same as the positive electrode of a general electric double layer capacitor. In a typical embodiment, a positive electrode current collector and a positive electrode active material layer fixed on the positive electrode current collector are provided. As the positive electrode current collector, a conductive member (for example, an aluminum etching foil) made of a metal having good conductivity is suitable. The positive electrode active material layer includes at least a positive electrode active material, and may further include other optional components (for example, a conductive material and a binder). As the positive electrode active material, a carbon material (for example, activated carbon) having a relatively large specific surface area is suitable. By using a material having a relatively large specific surface area, the ability to absorb and desorb charge carriers is increased, and the capacitance as a capacitor is improved. As the conductive material, for example, carbon black (typically acetylene black or ketjen black) is suitable. As the binder, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyethylene oxide (PEO) and the like are suitable.

  The negative electrode of the lithium ion capacitor 10 may be the same as the negative electrode of a general lithium ion secondary battery. In a typical embodiment, a negative electrode current collector and a negative electrode active material layer fixed on the negative electrode current collector are provided. As the negative electrode current collector, a conductive member (for example, copper punching metal) made of a metal having good conductivity can be suitably used. By using a punched (perforated) conductive member, lithium ion pre-doping can be suitably performed, and the capacity can be increased. The negative electrode active material layer includes at least a negative electrode active material, and may further include other optional components (such as a binder and a thickener). As the negative electrode active material, for example, carbon materials such as graphite (graphite), non-graphitizable carbon (hard carbon), and graphitizable carbon (soft carbon) are suitable. As the binder, for example, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polyethylene oxide (PEO) and the like are suitable. As the thickener, polymer compounds such as celluloses such as carboxymethylcellulose (CMC) and methylcellulose (MC) are suitable.

In a typical embodiment, the non-aqueous electrolyte of the lithium ion capacitor 10 includes a non-aqueous solvent and a supporting salt. As the non-aqueous solvent, for example, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones and lactones are suitable. Of these, carbonates such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) are preferable. As the supporting salt, LiPF ₆ , LiBF _{4 and the} like are suitable.

  In a typical configuration of the lithium ion capacitor 10, a separator is interposed between the positive electrode and the negative electrode. As the separator, for example, a porous sheet made of a resin such as polyethylene (PE) or polypropylene (PP) is suitable. The case of the lithium ion capacitor 10 is preferably a lightweight metal such as aluminum.

The weight of the lithium ion capacitor 10 can be, for example, 100 to 300 g (typically 130 to 220 g). The size of the lithium ion capacitor 10 may be, for example, 60 to 200 mm in length, 8 to 30 mm in width, 40 to 90 mm in height (typically 80 to 150 mm in length, 10 to 20 mm in width, and 50 to 80 mm in height). .
Moreover, the upper limit voltage in common use of the lithium ion capacitor 10 may be, for example, 2.8 to 4.5 V (typically 3.6 to 4.2 V). The common lower limit voltage of the lithium ion capacitor 10 may be, for example, 1.3 to 3.0 V (typically 1.8 to 2.4 V). The electrostatic capacity in the normal voltage range of the lithium ion capacitor 10 can be, for example, about 1000 to 7000 F (typically 2000 to 5500 F).

  The control device and control method for the lithium ion capacitor 10 disclosed herein can be suitably used for a vehicle that uses electric energy for all or part of a power source. Examples of such vehicles include hybrid vehicles (HV), plug-in hybrid vehicles (PHV), electric vehicles (EV), hybrid railway vehicles, forklifts, electric wheelchairs, electric assist bicycles, electric scooters, and the like.

  Test examples relating to the present invention will be described below, but the following description is not intended to limit the present invention.

  According to the flowchart shown in FIG. 4, the input energy of the lithium ion capacitor under a predetermined temperature environment was measured, and the relationship between the input energy of the lithium ion capacitor and the charge start SOC was examined.

<Construction of lithium ion capacitor>
The test method will be described with reference to FIG. First, a lithium capacitor was constructed in a thermostat maintained at a predetermined temperature (S30). In this test example, the positive electrode active material is activated carbon, graphene, and a conductive polymer, the positive electrode current collector foil is an aluminum foil, the negative electrode active material is carbon and activated carbon, and the negative electrode current collector foil is a copper foil. A lithium ion capacitor including a negative electrode using a separator and a separator containing polyethylene (PE) and polypropylene (PP) was constructed. The constructed lithium ion capacitor was subjected to normal initial processing including initial charging.

<Measurement of input energy>
<Test Example 1>
The lithium ion capacitor was placed in an environment of −30 ° C. (S32), and the following tests were performed. First, discharging was performed at a low current until the predetermined SOC was reached, and the SOC was adjusted until the predetermined charge start SOC was reached (S34). In this way, charging is started at a constant power P (W) for the lithium ion capacitor adjusted to a predetermined charging start SOC, and charging is performed until the SOC of the lithium ion capacitor reaches 100% (voltage 3.8 V). The time T and the voltage (V) change over time of the lithium ion capacitor were measured (S36). Input energy E (Wh) was calculated from the product of the obtained charging time T and power P (W) (S38). This measurement was repeated while changing the charge start SOC in the range of 0 to 80%.

<Test Example 2>
A lithium ion capacitor input energy measurement test was performed in the same manner as in Test Example 1 except that the lithium ion capacitor was tested in an environment of 25 ° C.

  The results of the input energy measurement test in Test Examples 1 and 2 are shown in FIGS. Here, FIGS. 5 and 6 are graphs showing the relationship between a change in voltage over time when a lithium ion capacitor is charged in a −30 ° C. environment or a 25 ° C. environment, and the charging start SOC, and the vertical axis is The voltage (V) indicates the measurement time (second) on the horizontal axis. FIGS. 7 and 8 are graphs showing the relationship between the input energy E of the lithium ion capacitor and the charge start SOC in a −30 ° C. environment or a 25 ° C. environment, and the vertical axis represents the input energy (Wh). The axis indicates the charge start SOC (%).

  As is apparent from the results shown in FIG. 6, in the charging of the lithium ion capacitor in an environment of 25 ° C., the voltage of the lithium ion capacitor increases with the lapse of the charging time. It was found to be less dependent on the starting SOC.

  On the other hand, as is apparent from the results shown in FIG. 5, in the charging of the lithium ion capacitor in the environment of −30 ° C. (low temperature), the charging start SOC is low (for example, the charging start SOC is 0%), and the voltage increase rate. It has been found that the voltage reaches the upper limit voltage subject to charging restrictions within a relatively short time.

  Referring to the results shown in FIG. 8, when charging the lithium ion capacitor in an environment of 25 ° C., the input energy tended to increase as the charge start SOC decreased. Moreover, it turned out that the value of the input energy with respect to charge start SOC does not have a maximum value.

  On the other hand, as is clear from the results shown in FIG. 7, when the lithium ion capacitor is charged in an environment of −30 ° C. (low temperature), the input energy decreases as the charge start SOC decreases in the region where the charge start SOC is 40% or more. However, in the region where the charge start SOC is less than 40%, the input energy tends to decrease as the charge start SOC decreases. That is, it became clear that the value of the input energy with respect to the charge start SOC has a maximum value at about SOC 40%. This is considered to be because in the charging of the lithium ion capacitor in an environment of −30 ° C. (low temperature), the voltage reached the upper limit voltage within a relatively short time, and the charging was restricted.

  As is apparent from these results, the lithium ion capacitors according to Test Examples 1 and 2 are the charge start SOC at which the input energy becomes maximum in an environment where the in-cell temperature of the lithium ion capacitor is −30 ° C. By adopting a charge / discharge control method in which SOC 40% is set as a discharge lower limit SOC and discharge is prohibited in a region less than the discharge lower limit SOC (SOC 40%), a decrease in capacity reduction (energy input / output amount) of the lithium ion capacitor can be suppressed. It became clear.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

10 Lithium ion capacitor (LIC)
20 Temperature Measurement Unit 22 Temperature Sensor 30 Charge / Discharge Control Unit 50 Control Device

Claims (1)

A control device for a lithium ion capacitor,
A temperature measuring unit for measuring the temperature in the cell of the lithium ion capacitor;
A charge / discharge control unit for controlling charge / discharge of the lithium ion capacitor;
With
here,
From the start of charging when the lithium ion capacitor is charged with a constant power P to the lithium ion capacitor having a predetermined charging start SOC under a predetermined temperature environment, until the SOC of the lithium ion capacitor reaches 100% For the input energy E defined by the product of the time T and the power P, when the charge start SOC at which the input energy E takes a maximum value is the discharge lower limit SOC,
The charge / discharge control unit prohibits the discharge of the lithium ion capacitor in a region below the discharge lower limit SOC corresponding to the temperature measured by the temperature measurement unit;
A control device characterized by.

Images