JP6951666B2 - Deterioration estimation device for lithium ion capacitors - Google Patents

Description

The present invention relates to a deterioration estimation device for a lithium ion capacitor. More specifically, the present invention relates to a deterioration estimation device for lithium ion capacitors, which is used for a laminated body constructed by laminating a plurality of lithium ion capacitors.

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, one of the power sources that can be suitably used as the main power source or the auxiliary power source of these vehicles is a lithium ion capacitor (LiC). 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 has a lower internal resistance than a lithium ion secondary battery. It can be charged and discharged rapidly, and has advantages such as long life.

A lithium ion capacitor typically uses an activated carbon as the positive electrode active material and a carbon material capable of occluding or releasing lithium ions as the negative electrode active material. The positive and negative electrodes are arranged via a separator, and an electrolytic solution containing a lithium salt is used. Has a wet composition. In a lithium ion capacitor having such a configuration, anions and lithium ions in the electrolytic solution move during charging and discharging, and are adsorbed and desorbed on the positive electrode and the negative electrode. At this time, in the positive electrode of the lithium ion capacitor, the ion species that are adsorbed and desorbed change at a predetermined voltage (for example, 3 V). Due to the characteristics of the positive electrode of the lithium ion capacitor, the deterioration of the lithium ion capacitor is promoted by charging / discharging over the predetermined voltage (for example, 3V) or storing at the predetermined voltage (for example, 3V) or less. Sometimes. Prior arts relating to the deterioration of this type of lithium ion capacitor include those described in Patent Documents 1 and 2.

Japanese Unexamined Patent Publication No. 2013-187487 Japanese Unexamined Patent Publication No. 2013-96790

As a method of suppressing deterioration of the lithium ion capacitor, it is conceivable to measure the voltage of the lithium ion capacitor and control charging / discharging of the capacitor according to the voltage. However, for example, when the voltage sensor installed in the lithium ion capacitor fails and the voltage of the capacitor cannot be measured, the charging / discharging of the capacitor is controlled while suppressing the deterioration of the capacitor. It was difficult to do.

The present invention has been made in view of this point, and it is possible to preferably estimate whether or not the lithium ion capacitor is in a state of being easily deteriorated without measuring the voltage of the lithium ion capacitor. It is an object of the present invention to provide a deterioration estimation device.

According to the present invention, a deterioration estimation device for a lithium ion capacitor is provided. Here, the deterioration estimation device is used for the lithium ion capacitor in a laminated body in which a plurality of the lithium ion capacitors are laminated and a restraining load is applied in the stacking direction.

The deterioration estimation device includes a load measuring unit that measures the restraint load over time. Further, the deterioration estimation device includes a determination unit for determining the voltage region of the lithium ion capacitor from the time-dependent change of the restraint load measured by the load measurement unit. The determination unit determines the charge / discharge state of the lithium-ion capacitor, and further, when the lithium-ion capacitor is being charged and the restraint load is decreasing over time, and when the lithium-ion capacitor is discharged. When the restraining load is increasing with time, it is determined that the voltage of the lithium ion capacitor is equal to or less than a predetermined value.

According to the deterioration estimation device having such a configuration, it is possible to determine the voltage region of the lithium ion capacitor during charging / discharging (that is, whether or not the voltage of the lithium ion capacitor is equal to or less than a predetermined value) from the change in the restraint load. It is possible to estimate from the determined voltage range whether or not the lithium ion capacitor is in a state of being easily deteriorated.

It is a figure which shows typically the structure of the deterioration estimation apparatus and a laminated body which concerns on one Embodiment. It is a figure which shows typically the outer shape of the load sensor which concerns on one Embodiment. It is a graph which shows the relationship between the load change and SOC at the time of charging of the lithium ion capacitor which concerns on one Embodiment. It is a graph which shows the relationship between the load change and SOC at the time of discharge of the lithium ion capacitor which concerns on one Embodiment. It is a graph which schematically explains the relationship between the load change and voltage at the time of charging and discharging of the lithium ion capacitor which concerns on one Embodiment. It is a flowchart which shows the deterioration estimation method of the lithium ion capacitor which concerns on one Embodiment. It is a graph which shows the relationship between the charge resistance increase rate of the lithium ion capacitor which concerns on one Embodiment, and charge / discharge start SOC. It is a graph which shows the relationship between the discharge resistance increase rate of the lithium ion capacitor which concerns on one Embodiment, and charge / discharge start SOC. It is a graph which shows the relationship between the storage voltage of the lithium ion capacitor which concerns on one Embodiment, and the capacity retention rate.

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

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

<Deterioration estimation device>
FIG. 1 schematically shows the configuration of a laminate 20 composed of a deterioration estimation device 50 and a lithium ion capacitor 10 according to an embodiment of the present invention. The deterioration estimation device 50 disclosed here determines whether or not the voltage of the lithium ion capacitor 10 is a predetermined value (for example, 3V) or less, and thereby whether or not the lithium ion capacitor 10 is in a state of being easily deteriorated. Estimate.

The lithium-ion capacitor 10 to which the present invention is applied is used in the form of a laminated body 20 in which a plurality of lithium-ion capacitors 10 are laminated in a predetermined direction and integrated. The laminated body 20 is constructed by fixing a plurality of lithium ion capacitors 10 by applying a restraining load in the laminated direction. The method of applying such a restraining load is not particularly limited. For example, a pair of end plates 30A and 30B facing each other are arranged on both outer sides of the laminated body 20 in the laminating direction, and the end plates 30A, with a predetermined restraining load applied to the laminated body 20 in the laminating direction. By fixing the 30B and the bridging member or the like connecting the end plates 30A and 30B to each other, a suitable restraining load can be applied to the lithium ion capacitor 10.

The deterioration estimation device 50 disclosed here includes a load measuring unit 52 and a determining unit 54. The load measuring unit 52 has a load sensor 56 arranged in the laminated body 20. The load sensor 56 preferably constantly detects the constraining load applied to the lithium ion capacitor 10. The load measuring unit 52 can continuously measure the change in the restraining load applied to the lithium ion capacitor 10 over time by continuously taking in the data of the restraining load detected by the load sensor 56. FIG. 2 schematically shows the outer shape of the load sensor 56 according to the embodiment. In the examples shown in FIGS. 1 and 2, the load sensor 56 includes a lithium ion capacitor 10A arranged on the outermost side of the stacking direction of the laminated body 20 and an end plate 30A arranged facing the lithium ion capacitor 10A. It is placed between. The load sensor 56 may be installed in a gap between the stacked adjacent lithium ion capacitors 10. The load sensor 56 is preferably a surface pressure sensor as shown in FIG. When a surface pressure sensor is used as the load sensor 56, it is possible to more preferably detect a change in the restraint load applied to the lithium ion capacitor 10.

The determination unit 54 estimates the voltage of the lithium ion capacitor 10 from the change in the restraint load measured by the load measurement unit 52. From the estimation of such a voltage, the deterioration state of the lithium ion capacitor 10 can be determined. Hereinafter, the reason why the deterioration state of the lithium ion capacitor 10 can be estimated from the change in the restraining load applied to the lithium ion capacitor 10 will be described.

FIG. 3 is an example showing the relationship between the magnitude of the restraint load applied to the lithium ion capacitor and the SOC of the lithium ion capacitor 10 when the lithium ion capacitor 10 according to the embodiment is charged. The vertical axis represents the constraining load (unit: kgf) applied to the lithium ion capacitor 10, and the horizontal axis represents the SOC (unit:%) of the lithium ion capacitor 10. Referring to FIG. 3, in the lithium ion capacitor 10 according to the present embodiment, the constraining load applied to the lithium ion capacitor 10 temporarily decreases while the SOC increases from 0% to 100% due to charging, and the SOC is said to be around 50%. The restraint load takes a minimum value. After that, it can be seen that the restraining load applied to the lithium ion capacitor 10 increases as the SOC increases.

FIG. 4 is an example showing the relationship between the magnitude of the restraining load applied to the lithium ion capacitor and the SOC of the lithium ion capacitor 10 when the lithium ion capacitor 10 according to the embodiment is discharged. What the vertical axis and the horizontal axis represent is the same as in FIG. Referring to FIG. 4, in the lithium ion capacitor 10 according to the present embodiment, the restraint load is temporarily reduced while the SOC is reduced from 100% to 0% by electric discharge, and a minimum value is taken in the vicinity of the SOC of 50%, and then. It can be seen that the restraining load applied to the lithium ion capacitor 10 increases as the SOC decreases.

FIG. 5 is a graph schematically explaining how the load applied to the lithium ion capacitor 10 changes during charging and discharging of the lithium ion capacitor 10 according to the embodiment shown in FIGS. 3 and 4. The arrow X in FIG. 5 indicates the direction of the voltage change of the lithium ion capacitor 10 during charging, and the arrow Y indicates the direction of the voltage change of the lithium ion capacitor 10 during discharging. As shown in FIG. 5, when the voltage of the lithium ion capacitor 10 is equal to or less than a predetermined value (3 V in this example) during charging (that is, when the voltage is changing in the direction of arrow X), the restraint load is It decreases over time. Further, when the voltage of the lithium ion capacitor 10 is equal to or less than a predetermined value (about 3 V in this example) at the time of discharging (that is, when the voltage is changing in the Y direction of the arrow), the restraint load is applied over time. To increase.

Therefore, the determination unit 54 first determines the charge / discharge state of the lithium ion capacitor 10 (that is, whether the lithium ion capacitor 10 is being charged or being discharged). Next, when the lithium ion capacitor 10 is being charged and the restraint load measured by the load measuring unit 52 decreases with time, the voltage of the lithium ion capacitor is equal to or less than a predetermined value (3 V in this example). Is determined to be. Further, when the lithium ion capacitor 10 is being discharged, the voltage of the lithium ion capacitor 10 is a predetermined value (in this example, about) even when the restraint load measured by the load measuring unit 52 increases with time. It is determined that the voltage is 3V) or less.

Next, the voltage of the lithium ion capacitor 10 and the susceptibility to deterioration of the lithium ion capacitor 10 will be briefly described. It is known that in the lithium ion capacitor 10, the ion species that adsorb and desorb to the positive electrode active material (typically, activated carbon) during charging and discharging change at a predetermined voltage. For example, in the lithium ion capacitor 10 according to one embodiment, when the lithium ion capacitor 10 is larger than 3V, an anion (for example, PF ₆ ⁻ ) is attached to and detached from the positive electrode active material, and when it is 3V or less, the positive electrode active material is absorbed and desorbed. The cation (Li ⁺ ) is absorbed and desorbed. Here, since the positive electrode active material ^{tends to have low durability against Li +} , charging / discharging the lithium ion capacitor 10 at a voltage of 3 V or less can accelerate the deterioration of the lithium ion capacitor 10.

7 and 8 are graphs showing the relationship between the charge resistance increase rate or the discharge resistance increase rate of the lithium ion capacitor 10 according to the embodiment and the charge / discharge start SOC, respectively. The vertical axis shows the resistance increase rate, and the horizontal axis shows the SOC (unit:%) at the start of charging / discharging. As shown in FIGS. 7 and 8, the lithium ion capacitor 10 according to the embodiment is charged / discharged from a charge / discharge start SOC of 50% or less (voltage 3 V or less), and is in an overcharged state (that is, charge / discharge). , Charging / discharging in a state where the charging rate is higher than the discharging rate) causes high rate deterioration and the resistance increase rate greatly increases. As can be seen from this example, when the lithium ion capacitor 10 according to one embodiment is charged / discharged at a voltage of 3 V or less (particularly, high-speed charging / discharging in an overcharged state), deterioration of the lithium ion capacitor 10 can be accelerated. ..

FIG. 9 shows a graph showing the relationship between the storage voltage (storage voltage) of the lithium ion capacitor 10 according to the embodiment and the capacity retention rate. The vertical axis shows the capacity retention rate (unit:%), and the horizontal axis shows the storage voltage (unit: V). As shown in FIG. 9, the lithium ion capacitor 10 according to the embodiment tends to have a reduced capacity retention rate when stored at a voltage of 3 V or less. As described above, when the lithium ion capacitor 10 is stored at a voltage of 3 V or less for a predetermined period of time, the deterioration of the lithium ion capacitor 10 can be accelerated.

As described above, when the lithium ion capacitor 10 is used (charge / discharge or the like) at a voltage at which the ion species adsorbed and desorbed on the positive electrode changes, deterioration can be accelerated. Here, the voltage region that the determination unit 54 can determine from the change in the constraining load applied to the lithium ion capacitor 10 substantially coincides with the voltage region in which the ion species that adsorb and desorb to the positive electrode changes. Therefore, when the determination unit 54 determines that the voltage of the lithium ion capacitor 10 is equal to or less than a predetermined value (about 3 V in this example) from the change in the restraint load, the lithium ion capacitor 10 is in a state of being easily deteriorated. It can be estimated that.

<Deterioration estimation method>
FIG. 6 shows a flowchart showing a method of estimating deterioration of the lithium ion capacitor according to the embodiment. As shown in FIG. 6, in this method, first, the voltage of each cell of the lithium ion capacitor 10 is measured by a voltage sensor or the like, and it is determined whether or not the measured value is normal (S10). When it is determined that the voltage measurement value by the voltage sensor or the like is normal (S10: Yes), normal control is performed on the lithium ion capacitor 10 (S12). On the other hand, when it is determined that the measured value of the voltage is abnormal (S10: No), the load value P applied to the lithium ion capacitor 10 is measured by the load measuring unit 52 (S14). Here, in the following description, the load values measured at _{arbitrary times t 1} and t ₂ (where t ₁ <t ₂ ) are referred to as P _{t 1 and P t 2, respectively.}

Next, the determination unit 54 determines the charge / discharge state of the lithium ion capacitor 10 (S16). As a result, when it is determined that the lithium ion capacitor 10 is being charged (S18), _{it is determined whether or not the following equation: P t1-} P _t2 >0; is satisfied (S20), and when it is satisfied (S20:). Yes), it is determined that the lithium ion capacitor 10 is below a predetermined voltage (3 V in this example) (S30), and if it is not satisfied (S20: No), the lithium ion capacitor 10 has a predetermined voltage (in this example). It is determined that it is larger than 3V) (S32). On the other hand, when it is determined that the lithium ion capacitor 10 is being discharged (S22), _{it is determined whether or not the following equation: P t1-} P _t2 ≤ 0; is satisfied (S24), and when it is satisfied (S24: Yes). ) Is determined that the lithium ion capacitor 10 is equal to or less than a predetermined voltage (3 V in this example) (S30), and if it is not satisfied (S24: No), the lithium ion capacitor 10 has a predetermined voltage (3 V in this example). ) Is larger than (S32). When it is determined that the lithium ion capacitor 10 is at a predetermined voltage (3 V in this example) or less (S30), it is presumed that the lithium ion capacitor 10 is in a state of being easily deteriorated. When it is determined that the lithium ion capacitor 10 is larger than a predetermined voltage (3 V in this example) (S32), it is presumed that the lithium ion capacitor 10 is not in a state of being easily deteriorated.

According to the deterioration estimation device 50 or the deterioration estimation method disclosed herein, it is possible to determine whether or not the lithium ion capacitor 10 is in the voltage region where the deterioration described above can be promoted without directly measuring the voltage. .. Therefore, for example, even when the voltage sensor that measures the voltage of the lithium ion capacitor 10 fails, it is possible to preferably determine whether or not the lithium ion capacitor 10 is in a state of being easily deteriorated.

The configuration of the deterioration estimation device 50 and the lithium ion capacitor 10 targeted by the deterioration estimation method disclosed here is not particularly limited, and the same ones as those usually used can be used. Hereinafter, the lithium ion capacitor 10 to which the technique 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 aspect, 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 contains at least the positive electrode active material, and may further contain other optional components (for example, a conductive material, a binder, etc.). As the positive electrode active material, a carbon material having a relatively large specific surface area (for example, activated carbon) is suitable. By using a material having a relatively large specific surface area, the adsorption / desorption ability of the charge carrier is enhanced, 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 aspect, 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 made of a metal having good conductivity (for example, copper punching metal) can be preferably adopted. By using the punched (perforated) conductive member, the lithium ion predoping operation can be suitably performed, and the capacity can be increased. The negative electrode active material layer may contain at least the negative electrode active material and may further contain other optional components (eg, binder, thickener, etc.). As the negative electrode active material, for example, carbon materials such as graphite (graphite), non-graphitized carbon (hard carbon), and easily graphitized 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. Further, as the thickener, polymer compounds such as celluloses such as carboxymethyl cellulose (CMC) and methyl cellulose (MC) are suitable.

The non-aqueous electrolyte of the lithium ion capacitor 10 typically comprises 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. Among them, carbonates, for example, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and the like 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. As the case of the lithium ion capacitor 10, a case made of a lightweight metal such as aluminum is preferable.

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 can 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 × 50 to 80 mm in height). ..
Further, the normal upper limit voltage of the lithium ion capacitor 10 can be, for example, 2.8 to 4.5 V (typically 3.6 to 4.2 V). The working lower limit voltage of the lithium ion capacitor 10 can be, for example, 1.3 to 3.0 V (typically 1.8 to 2.4 V). The capacitance of the lithium ion capacitor 10 in the normal voltage range can be, for example, about 1000 to 7000F (typically 2000 to 5500F).

The deterioration estimation device and deterioration estimation method of 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 a vehicle include a hybrid vehicle (HV), a plug-in hybrid vehicle (PHV), an electric vehicle (EV), a hybrid railroad vehicle, a forklift, an electric wheelchair, an electrically assisted bicycle, an electric scooter and the like.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above.

10 Lithium-ion capacitor 20 Laminated body 30A, 30B End plate 50 Deterioration estimation device 52 Load measurement unit 54 Judgment unit 56 Load sensor

Claims (1)

It is a deterioration estimation device of the lithium ion capacitor in a laminated body formed by laminating a plurality of lithium ion capacitors and applying a restraining load in the laminating direction.
The deterioration estimation device is
A load measuring unit that measures the restraint load over time,
It is provided with a determination unit that determines the voltage region of the lithium ion capacitor from the time course of the restraint load measured by the load measurement unit.
The determination unit
The charge / discharge state of the lithium ion capacitor is determined, and further
When the lithium ion capacitor is being charged and the restraining load is decreasing with time, and when the lithium ion capacitor is being discharged and the restraining load is increasing with time, the above. Lithium-ion capacitors determine that the voltage is below a predetermined value,
A deterioration estimation device for a lithium ion capacitor.

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