JP6981208B2 - Battery deterioration judgment system - Google Patents

Description

The present disclosure relates to a battery deterioration determination system, and more particularly to a battery deterioration determination system for determining whether or not deterioration other than high rate deterioration has occurred in a secondary battery.

In general, a secondary battery deteriorates with the passage of time, and the capacity of the secondary battery decreases with the progress of deterioration. It is empirically known that the amount of decrease in the capacity of the secondary battery with the progress of deterioration is almost proportional to the square root of time. However, it has been confirmed that when the secondary battery deteriorates due to charging / discharging at a low temperature or charging / discharging at a high rate, the capacity of the secondary battery decreases at a speed higher than the above empirical rule. Hereinafter, the deterioration of the secondary battery at such a rapid speed is referred to as "rapid deterioration".

In general, from the viewpoint of system protection and the like, it is not preferable that the battery reaches the end of its life and the battery cannot be used while the secondary battery is being used. Therefore, it is required to determine whether or not the secondary battery is in the state of the end of its life. According to International Publication No. 2017/098686 (Patent Document 1), it is determined whether or not the above-mentioned rapid deterioration has occurred in the secondary battery, and if the secondary battery has sudden deterioration, the battery has been determined. Discloses a technique for determining a state at the end of life. In this technique, a linear regression analysis is performed on the history of the capacity retention rate of the secondary battery, and the amount of change in the capacity retention rate is calculated from the slope of the straight line obtained as a result of the analysis. Then, when the amount of change is larger than the threshold value, it is determined that sudden deterioration has occurred, and when the amount of change is smaller than the threshold value, it is determined that sudden deterioration has not occurred. If the secondary battery is suddenly deteriorated, the use of the battery is prohibited or the battery is replaced. The capacity retention rate used in this technology is expressed as a numerical value obtained by dividing the current full charge capacity by the initial full charge capacity.

International Publication No. 2017/098686

According to the above technique described in Patent Document 1, it is possible to determine whether or not the secondary battery is rapidly deteriorated. However, even if such a judgment is made, it is not known what causes the sudden deterioration.

One of the causes of sudden deterioration of the secondary battery is the deterioration of the secondary battery due to the above-mentioned charging / discharging at a high rate (so-called “high rate deterioration”). High-rate deterioration is a phenomenon in which the internal resistance of a secondary battery increases due to a bias in the ion concentration distribution in the electrolytic solution due to continuous charging / discharging at a large current (high rate). High-rate deterioration is recoverable deterioration, and when the capacity of the secondary battery is reduced due to high-rate deterioration, the capacity of the secondary battery can be recovered by performing recovery processing for the high-rate deterioration. .. For this reason, if it is determined that the battery is at the end of its life and the battery is replaced only because the secondary battery has suddenly deteriorated, the life of the battery is substantially shortened. There is a possibility that it will end up. This is because even if the secondary battery is suddenly deteriorated, if the cause is high-rate deterioration (that is, recoverable deterioration), the battery can be recovered and then used continuously. ..

The present disclosure has been made to solve the above-mentioned problems, and an object thereof is that when a secondary battery is rapidly deteriorated, the cause is high-rate deterioration or other deterioration. It is to judge appropriately. Another object of the present disclosure is to accurately detect when the use of the secondary battery should be stopped (and by extension, when the secondary battery in use should be replaced or discarded).

The battery deterioration determination system of the present disclosure includes a detection unit and a determination unit. The detection unit is configured to detect the peak position of the dQ / dV voltage characteristic line during charging of the secondary battery using the power of the external power source. The determination unit performs recovery processing for high-rate deterioration on the secondary battery, and the peak position of the dQ / dV voltage characteristic line before the recovery processing and the dQ / dV detected by the above-mentioned detection unit after the recovery processing. Using the degree of misalignment of the voltage characteristic line from the peak position (hereinafter, may be referred to as "degree of misalignment before and after recovery"), it is determined whether or not the secondary battery has deteriorated other than high-rate deterioration. It is configured as follows.

The above dQ / dV voltage characteristic line is dQ / dV, which is the ratio of the change amount dQ of the storage amount (Q) of the secondary battery to the change amount dV of the voltage (V) of the secondary battery, and the voltage of the secondary battery. It is a line showing the relationship with (V). Hereinafter, the voltage value indicating the peak position of the dQ / dV voltage characteristic line may be referred to as “Vp”. Further, the Vp before the recovery process may be referred to as "pre-recovery Vp". Further, Vp detected after performing the recovery process (for example, immediately after) may be referred to as "post-recovery Vp". The degree of deviation between the pre-recovery Vp and the post-recovery Vp corresponds to the degree of positional deviation before and after the recovery.

When the secondary battery is suddenly deteriorated and the cause is high rate deterioration, the capacity of the battery can be recovered by the recovery process. Therefore, the battery is used after the recovery process. It is preferable to continue. An example of the recovery process for high-rate deterioration is to alleviate the bias of the ion concentration distribution in the electrolytic solution by leaving the secondary battery for a long time without charging or discharging. On the other hand, if the cause of the sudden deterioration of the secondary battery is deterioration other than high-rate deterioration, it is considered difficult to recover the battery, and it is preferable to stop using the battery. Details will be described later, but examples of deterioration other than high-rate deterioration include precipitation of a charge carrier (lithium in a lithium ion battery) on the surface of the negative electrode.

As mentioned above, if the secondary battery is rapidly deteriorated due to irreparable (or difficult-to-recover) deterioration (that is, deterioration other than high-rate deterioration), the use of the secondary battery may be stopped. preferable. In order to accurately detect when to stop using the secondary battery (and by extension, when to replace or dispose of the secondary battery in use), whether or not the secondary battery has deteriorated other than high-rate deterioration. Is required to be properly determined.

The inventor of the present application has focused on the fact that the peak position of the dQ / dV voltage characteristic line detected during charging of the secondary battery using the power of the external power source changes according to the degree of deterioration of the secondary battery. It was confirmed by experiments that as the deterioration of the secondary battery progressed, the peak position (Vp) of the dQ / dV voltage characteristic line deviated from the Vp of the secondary battery in the initial state (state in which deterioration did not occur). It was also confirmed by experiments that Vp changes by performing a recovery treatment (recovery treatment for high-rate deterioration) on a secondary battery in which high-rate deterioration has occurred. In the battery deterioration determination system of the present disclosure, the peak position (Vp before recovery) of the dQ / dV voltage characteristic line before the recovery process is stored in the Vp of the secondary battery in the initial state (for example, in advance in a storage device). It may be a value), or it may be a Vp detected by the above-mentioned detection unit before (for example, immediately before) the recovery process.

When the above recovery process is performed on a secondary battery with high rate deterioration, Vp approaches the Vp of the secondary battery in the initial state, but the above recovery is performed on the secondary battery with deterioration other than high rate deterioration. When the treatment is performed, Vp does not approach the Vp of the secondary battery in the initial state. Therefore, when the Vp of the secondary battery in the initial state is adopted as the Vp before recovery, if the degree of deviation between the Vp before recovery and the Vp after recovery is larger than a predetermined threshold value, the secondary battery has a high rate deterioration other than the deterioration. If the degree of deviation between the pre-recovery Vp and the post-recovery Vp is smaller than the above threshold value, it is determined that the secondary battery has not deteriorated other than the high rate deterioration. It is possible to appropriately determine whether or not the secondary battery has deteriorated other than the high rate deterioration.

Further, Vp changes when the above recovery treatment is performed on a secondary battery in which high rate deterioration has occurred, but when the above recovery treatment is performed on a secondary battery in which deterioration other than high rate deterioration has occurred. Does not change Vp. Therefore, when the Vp detected before the recovery process is adopted as the pre-recovery Vp, if the degree of deviation between the pre-recovery Vp and the post-recovery Vp is smaller than a predetermined threshold value, the secondary battery has a high rate. It is determined that deterioration other than deterioration has occurred, and if the degree of deviation between the pre-recovery Vp and the post-recovery Vp is larger than the above threshold value, it is determined that the secondary battery has not deteriorated other than the high rate deterioration. Therefore, it is possible to appropriately determine whether or not the secondary battery has deteriorated other than the high rate deterioration.

When the battery deterioration determination system is mounted on the vehicle, the power supply outside the vehicle corresponds to the above-mentioned external power supply.

The degree of deviation between the pre-recovery Vp and the post-recovery Vp is the difference (| pre-recovery Vp-post-recovery Vp |) or ratio (pre-recovery Vp / post-recovery Vp, or recovery) between the pre-recovery Vp and the post-recovery Vp. Post-Vp / Pre-recovery Vp) and the like can be adopted. The larger the difference, the larger the degree of misalignment. Further, the closer the ratio is to 1, the smaller the degree of misalignment.

According to the present disclosure, when a secondary battery is suddenly deteriorated, it is possible to appropriately determine whether the cause is high-rate deterioration or other deterioration. To. Further, according to the present disclosure, in place of or in addition to this effect, it is possible to accurately detect when the use of the secondary battery should be stopped (and by extension, when the secondary battery in use should be replaced or discarded). The effect of being able to do it is achieved.

It is a figure which shows schematically the whole structure of the vehicle to which the battery deterioration determination system according to the embodiment of this disclosure is applied. It is a figure which showed in detail the structure of an example (combination battery) of a battery in a battery pack. FIG. 3 is an enlarged view showing a set of cells and spacers in the assembled battery shown in FIG. 2. It is a figure which shows an example of the dQ / dV voltage characteristic line and the peak position thereof. It is a flowchart which showed the processing procedure of the battery deterioration determination executed by the battery deterioration determination system according to embodiment. It is a flowchart which showed the processing procedure of the peak position detection in the battery deterioration determination. It is a figure for demonstrating the calculation method of the difference value ΔdQ / dV. It is a figure which shows an example of the capacity reduction amount calculation information. It is a figure which shows an example of the dQ / dV voltage characteristic line which was detected before performing the recovery process for high rate deterioration. It is a figure which shows the dQ / dV voltage characteristic line which was detected after the recovery process for the high rate deterioration was performed about the example of the battery which has a high rate deterioration.

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 a schematic configuration of a vehicle to which a battery deterioration determination system according to an embodiment of the present disclosure is applied. With reference to FIG. 1, the vehicle 10 includes a battery pack 100, a battery monitoring unit 101, a charger 102, an inlet 103, a power control unit (PCU) 12, and a motor generator (MG: Motor). A generator) 13, a drive wheel 14, an electronic control unit (ECU) 15, a storage unit 16, and a communication line 18. The ECU 15 and the storage unit 16 are connected by a communication line 18 and are configured to be able to send and receive information to and from each other.

The vehicle 10 is configured to travel using the electric power stored in the battery pack 100. Further, the vehicle 10 is configured to be able to charge the battery in the battery pack 100 with the electric power of the power source outside the vehicle connected to the inlet 103. Hereinafter, charging the battery in the battery pack 100 with the electric power of the power source outside the vehicle is referred to as "external charging". The vehicle 10 is an external charging compatible vehicle in which the battery pack 100 is mounted in a manner capable of external charging. The vehicle 10 may be an electric vehicle that can run using only the electric power stored in the battery pack 100, or uses both the electric power stored in the battery pack 100 and the output of the engine (not shown). It may be a plug-in hybrid vehicle that can run on the vehicle. The power supply method for external charging may be a method in which the external power supply supplies power to the vehicle via a cable, or a method in which the external power supply supplies power to the vehicle in a non-contact manner without using a cable (wireless power supply method). ) May be.

The battery pack 100 includes a secondary battery (rechargeable battery) as a power storage device and a housing for accommodating the secondary battery. As the secondary battery, for example, a lithium ion battery or a nickel hydrogen battery can be adopted. The battery pack 100 may include an assembled battery composed of a plurality of cells (secondary batteries) connected in series and / or in parallel. The battery pack 100 supplies electric power for the MG 13 to drive the drive wheels 14 to the PCU 12.

FIG. 2 is a diagram showing in detail the configuration of an example of a battery (an assembled battery composed of a plurality of lithium ion batteries) in the battery pack 100. FIG. 3 is an enlarged view showing a set of cells and spacers in the assembled battery shown in FIG. In FIGS. 2 and 3, the arrangement direction D1 indicates the direction in which the plurality of cells 110 constituting the assembled battery are arranged, and the width direction D2 indicates the direction orthogonal to the arrangement direction D1.

With reference to FIG. 2, this assembled battery is configured by alternately stacking a plurality of cells 110 and a plurality of spacers 120 in the arrangement direction D1. That is, the assembled battery includes a plurality of cells 110 arranged in the arrangement direction D1 and a spacer 120 interposed between the cells 110. The number of cells 110 is, for example, 2 or more and 20 or less. However, the number of cells 110 can be appropriately changed according to the output required for the assembled battery and the like.

The cell 110 is a non-aqueous electrolyte secondary battery (for example, a lithium ion battery). The cell 110 includes a positive electrode terminal 131 and a negative electrode terminal 132. Further, a gas discharge valve 130 is provided between the positive electrode terminal 131 and the negative electrode terminal 132.

The plurality of cells 110 shown in FIG. 2 are electrically connected in series. Specifically, the plurality of cells 110 constituting the assembled battery are arranged one by one while being reversed in direction. The positive electrode terminal 131 of one cell 110 and the negative electrode terminal 132 of another adjacent cell 110 are electrically connected by a connecting member 140 (bus bar). Restraint plates 141 and 142 are arranged at both ends of the battery assembly direction D1. Further, the restraint plate 141 and the restraint plate 142 are connected to each other via a restraint band 151. The restraint band 151 and the restraint plates 141 and 142 are connected by a screw 152. By tightening the screw 152, the plurality of cells 110 and the spacer 120 can be fixed by the restraint band 151 and the restraint plates 141 and 142. Further, by tightening the screw 152, pressure (binding force) is applied to the cell 110 and the spacer 120.

With reference to FIG. 3, the spacer 120 has a plate-shaped main body portion 122 and a protrusion 121 (for example, a rib) protruding from the main body portion 122 toward the cell 110. FIG. 3 shows an example in which the protrusions 121 are formed only on one side of the main body 122, but the protrusions 121 may be formed on both sides of the main body 122.

Of the two main surfaces F1 and F2 (surfaces at both ends of the arrangement direction D1) of the cell 110, the protrusion 121 comes into contact with the main surface F1. Further, the main body portion 122 of the spacer 120 (not shown in FIG. 3) comes into contact with the main surface F2. A refrigerant flow path is formed in the gap between the main surface F1 of the cell 110 and the main body portion 122. The spacer 120 is made of, for example, a resin.

The cell 110 includes an electrode group 114 and a case 115 (battery case). The electrode group 114 is housed in the case 115. Further, although not shown, an electrolytic solution is also housed in the case 115. By immersing the electrode group 114 in the electrolytic solution, the electrolytic solution also enters the inside of the electrode group 114.

The electrode group 114 is a winding type electrode group formed by winding a laminate of a positive electrode plate 111, a separator 113, and a negative electrode plate 112. The positive electrode plate 111 and the negative electrode plate 112 are laminated with the separator 113 interposed therebetween. The electrode group 114 is not limited to the winding type electrode group, but may be a stack type electrode group.

The positive electrode plate 111 includes a positive electrode current collector (for example, aluminum foil) and a positive electrode active material layer. The positive electrode active material layer is formed on both sides of the positive electrode current collector, for example, by applying a positive electrode mixture containing the positive electrode active material to the surface of the positive electrode current collector. The negative electrode plate 112 includes a negative electrode current collector (for example, a copper foil) and a negative electrode active material layer. The negative electrode active material layer is formed on both sides of the negative electrode current collector, for example, by applying a negative electrode mixture containing the negative electrode active material to the surface of the negative electrode current collector. The separator 113 is, for example, a microporous membrane. The presence of pores in the separator 113 facilitates the retention of the electrolytic solution in the pores.

Examples of the positive electrode active material include lithium transition metal oxides (specifically, lithium nickel cobalt manganese composite oxides and the like). The positive electrode active material layer may contain a conductive material (for example, acetylene black) and a binder (for example, polyvinylidene fluoride) in addition to the positive electrode active material. Examples of the negative electrode active material include carbon-based materials (specifically, graphite and the like). The negative electrode active material layer may contain a thickener (for example, carboxymethyl cellulose) and a binder (for example, styrene-butadiene rubber) in addition to the negative electrode active material.

Examples of the material of the separator 113 include a polyolefin resin (specifically, polyethylene, polypropylene, etc.). Further, the separator 113 may be a separator with an HRL (Heat Resistance Layer). Examples of separators with HRL include a first polypropylene (PP) layer, a polyethylene (PE) layer, a second polypropylene (PP) layer, and a porous heat-resistant layer (HRL) having higher heat resistance than these layers. Examples thereof include an insulating film in which polyethylene is laminated and integrated. For example, HRL is formed on both sides of a long sheet-shaped separator base material composed of a PP layer / PE layer / PP layer.

The electrolytic solution contains an aprotic solvent and a lithium salt dissolved in the solvent (for example, LiPF ₆ ). Examples of aprotic solvents include ethylene carbonate (EC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), or diethyl carbonate (DEC). Two or more kinds of solvents may be mixed and used. Further, the electrolytic solution may further contain an additive. Examples of additives include lithium difluorophosphate (LiPO ₂ F ₂ ) and lithium bis (oxalate) borate (LiBOB).

The case 115 is, for example, a square case. The outer shape of the square case is a rectangular parallelepiped (for example, a flat rectangular parallelepiped). An example of the material of the case 115 is an aluminum alloy.

With reference to FIG. 1 again, the battery monitoring unit 101 includes various sensors and is configured to monitor the state of the batteries in the battery pack 100. The battery monitoring unit 101 includes, for example, a voltage sensor, a current sensor, and a temperature sensor. The voltage sensor detects the voltage of the battery in the battery pack 100 and outputs it to the ECU 15. The current sensor detects the current of the battery in the battery pack 100 and outputs it to the ECU 15. The temperature sensor detects the temperature of the battery in the battery pack 100 and outputs it to the ECU 15.

A charging cable connector (not shown) is connected to the inlet 103. By connecting the connector to the inlet 103, it becomes possible to supply electric power from an external power source (not shown) of the charging equipment to the battery pack 100 via the charging cable.

The charger 102 includes a rectifier circuit and a converter (neither shown). The AC power from the external power source is sent to the charger 102 through the charging cable and the inlet 103, and is converted into DC power by the rectifier circuit of the charger 102. Further, the DC power converted by the rectifier circuit is boosted or stepped down by the converter of the charger 102 and supplied to the battery pack 100. Further, the charger 102 is provided with a sensor for detecting the state (voltage and the like) of the charger 102.

The MG 13 is a rotary electric machine, for example, a three-phase AC motor generator. The MG 13 is driven by the PCU 12 to rotate the drive wheels 14. Further, the MG 13 can also generate regenerative power generation when the vehicle 10 is braked or the like. The electric power generated by the MG 13 is rectified by the PCU 12 and charged into the battery in the battery pack 100.

The PCU 12 is configured to include an inverter and a converter (neither of them is shown), and drives the MG 13 according to a drive signal from the ECU 15. The PCU 12 converts the electric power stored in the battery in the battery pack 100 into AC electric power and supplies it to the MG 13 when the MG 13 is driven by force, and when the MG 13 is regenerated (such as when the vehicle 10 is braked), the MG 13 is used. The generated electric power is rectified and supplied to the battery in the battery pack 100.

The ECU 15 includes a CPU (Central Processing Unit) as an arithmetic unit, a storage device, and input / output ports for inputting / outputting various signals (none of which are shown). The storage device includes a RAM (Random Access Memory) as a work memory and a storage (ROM (Read Only Memory), etc.) for storage. Signals from various sensors (sensors of the battery monitoring unit 101, etc.) are input to the ECU 15. Then, the ECU 15 functions as a control device. The ECU 15 controls each device (charger 102, etc.) using the signals of each sensor. Various controls are executed by the CPU executing the program stored in the storage device. The various controls performed by the ECU 15 are not limited to software processing, but can also be processed by dedicated hardware (electronic circuits).

The ECU 15 outputs information to be stored (calculation result, etc.) to a storage unit 16 (for example, a rewritable non-volatile memory) and stores it in the storage unit 16. The storage unit 16 may store information used for detecting the battery state and controlling the vehicle 10 in advance. For example, the storage unit 16 may store the initial information of the battery pack 100 (battery type, capacity, internal resistance, electrode thickness, basis weight, etc.) in advance.

In this embodiment, the storage unit 16 stores the dQ / dV voltage characteristic line of the secondary battery in the initial state (state in which deterioration has not occurred) and its peak position (Vp) as the initial information of the battery pack 100. ing. Hereinafter, the Vp of the secondary battery in the initial state may be referred to as "initial Vp".

FIG. 4 is a diagram showing an example of a dQ / dV voltage characteristic line and its peak position (Vp). In the graph of FIG. 4, the horizontal axis represents the voltage (V) of the secondary battery, and the vertical axis is the ratio of the change amount dQ of the storage amount Q of the secondary battery to the change amount dV of the voltage V of the secondary battery ( dQ / dV) is shown. The solid line k10 in FIG. 4 shows the dQ / dV voltage characteristic line. Vp in FIG. 4 is a voltage value indicating the position of the main peak of the dQ / dV voltage characteristic line. The dQ / dV voltage characteristic line can be obtained from, for example, the current and voltage of the secondary battery detected during charging.

Although the details will be described later, the storage unit 16 may further store the corresponding information (for example, the map used for calculating the stored amount Q) used for determining the deterioration of the battery. Correspondence information is information indicating the relationship between a plurality of correlated parameters. The correspondence information may be a map, a table, a mathematical formula, or a model. Further, the correspondence information may be configured by combining a plurality of maps and the like.

By the way, from the viewpoint of system protection and the like, it is not preferable that the battery reaches the end of its life while the secondary battery is being used and the battery cannot be used. Therefore, it is required to determine whether or not the secondary battery is in the state of the end of its life.

It is known that when the secondary battery reaches the end of its life, the secondary battery deteriorates rapidly. Therefore, when the secondary battery is suddenly deteriorated, it is conceivable to determine that the battery is at the end of its life. However, if it is determined that the secondary battery is at the end of its life and the battery is replaced only because the secondary battery has suddenly deteriorated, the life of the battery will be substantially shortened. there is a possibility. High-rate deterioration, which is one of the causes of sudden deterioration of the secondary battery, is recoverable deterioration, and if the capacity of the secondary battery is reduced due to high-rate deterioration, recovery processing is performed for the high-rate deterioration. This is because the capacity of the secondary battery can be restored.

When the secondary battery is suddenly deteriorated and the cause is high rate deterioration, the capacity of the battery can be recovered by the recovery process. Therefore, the battery is used after the recovery process. It is preferable to continue. On the other hand, if the cause of the sudden deterioration of the secondary battery is deterioration other than high-rate deterioration, it is considered difficult to recover the battery, and it is preferable to stop using the battery. That is, it is preferable to determine that the secondary battery is in the end of life when the secondary battery has deteriorated other than the high rate deterioration.

Here, examples of deterioration other than high-rate deterioration include precipitation of charge carriers on the surface of the negative electrode. For example, if lithium precipitates on the surface of the negative electrode of a lithium ion battery (secondary battery), the capacity of the battery decreases. If the precipitated lithium can be removed from the negative electrode, the capacity of the battery will be restored, but it is not easy to remove the lithium from the negative electrode. Generally, lithium is removed by removing the lithium ion battery from the battery pack and cleaning the negative electrode of the battery with a chemical (that is, dissolving the precipitated lithium with a chemical). Therefore, if the secondary battery suddenly deteriorates due to such precipitation of lithium, it is difficult to continue using the battery.

In order to accurately detect when to stop using the secondary battery (and by extension, when to replace or dispose of the secondary battery in use), whether or not the secondary battery has deteriorated other than high-rate deterioration. Is required to be properly determined. In the battery deterioration determination system according to this embodiment, the dQ / dV voltage characteristic line is obtained when a recovery process (a process for alleviating the bias of the ion concentration distribution in the electrolytic solution) is performed on the secondary battery in which high rate deterioration has occurred. Utilizing the change in the peak position (Vp), it is appropriately determined whether or not the secondary battery has deteriorated other than the high rate deterioration.

Specifically, the ECU 15 (detection unit) detects the peak position of the dQ / dV voltage characteristic line during charging of the secondary battery using the power of the external power source in cooperation with the battery monitoring unit 101, the charger 102, and the like. It is configured to do. Further, the ECU 15 (determination unit) performs a recovery process for high-rate deterioration on the secondary battery, and detects the peak position of the dQ / dV voltage characteristic line detected before the recovery process and the recovery process after the recovery process. Use the degree of misalignment of the dQ / dV voltage characteristic line with the peak position (for example, the difference in voltage value indicating each peak position) to determine whether the secondary battery has deteriorated other than high rate deterioration. It is composed of. With such a configuration, it becomes possible to appropriately determine whether or not the secondary battery has deteriorated other than the high rate deterioration. Hereinafter, the deterioration determination of the battery performed by the ECU 15 will be described in detail with reference to FIGS. 5 to 10.

FIG. 5 is a flowchart showing a battery deterioration determination processing procedure executed by the ECU 15. The process shown in this flowchart is called from the main routine and executed when there is a deterioration determination execution request for the battery in the battery pack 100. This request may be an instruction from the user, or may be the arrival of a start time by a timer or the like.

By executing the process shown in FIG. 5, it is determined whether or not the battery in the battery pack 100 has deteriorated other than the high rate deterioration. In the process of FIG. 5, the state of the battery is first detected, and then it is determined whether or not the battery has suddenly deteriorated. Then, when the battery is rapidly deteriorated, the recovery process for the high rate deterioration is performed, and the above-mentioned sudden deterioration is performed based on the peak position of the dQ / dV voltage characteristic line detected after the recovery process. It is determined whether the cause is high-rate deterioration or other deterioration.

As an example, the battery in the battery pack 100 is an assembled battery including a cell (lithium ion battery) having the following configuration. Further, as deterioration other than high-rate deterioration, precipitation of lithium on the negative electrode surface of the lithium ion battery is assumed.
[Construction of lithium-ion battery]
-Positive electrode: Layered ternary system (NCM: LiNiComnO ₂ )
・ Negative electrode: Graphite type ・ Separator: PP / PE / PP + HRL
-Lithium salt: LiPF ₆ = 1.2M
-Solvent: EC / DMC / EMC = 30/40/30
-Additives: LiPO ₂ F ₂ = 0.08M, LiBOB = 0.023M
With reference to FIG. 5, the ECU 15 calculates the dQ / dV voltage characteristic line of the battery in the battery pack 100 and detects the peak position (Vp) of the dQ / dV voltage characteristic line (step S11). Hereinafter, a method for detecting Vp will be described with reference to FIG. FIG. 6 is a flowchart showing a processing procedure of Vp detection executed by the ECU 15.

With reference to FIG. 6, the ECU 15 determines whether or not the battery in the battery pack 100 is ready to be charged (step S21). The ECU 15 is, for example, when the external power supply of the charging equipment (not shown) and the battery in the battery pack 100 are electrically connected and the voltage of the battery in the battery pack 100 is equal to or less than a predetermined value. , Judge that the battery is ready for charging. By connecting the connector of the charging cable connected to the external power supply to the inlet 103, the external power supply and the battery in the battery pack 100 are electrically connected. The ECU 15 can detect whether or not the external power supply and the battery in the battery pack 100 are electrically connected based on the state (voltage or the like) of the charger 102. Further, the ECU 15 can detect whether or not the voltage (cell voltage) of the battery in the battery pack 100 is equal to or less than a predetermined value based on the signal (detected value of the voltage sensor) from the battery monitoring unit 101. In this embodiment, the predetermined value is 3.2V.

When the voltage of the battery in the battery pack 100 is not 3.2 V or less, the ECU 15 discharges the battery so that the voltage of the battery in the battery pack 100 is 3.2 V or less. At this time, the discharge current value is preferably 1C or less (for example, 1C). For example, when the rated capacity of the battery is 4.0 Ah, 1C = 4.0 A, so it is preferable to discharge at a current value of 4.0 A or less. The electric power discharged from the battery in the battery pack 100 may be supplied to another battery mounted on the vehicle 10 (for example, a spare battery (not shown)) or consumed by an electronic device mounted on the vehicle 10. You may try to do it. The above discharge may be automatically executed when the ECU 15 determines that the voltage of the battery is not equal to or lower than a predetermined value, or may be executed by the ECU 15 based on a user's instruction.

The conditions for completing the charging preparation are not limited to the above and can be set arbitrarily. For example, when a signal notifying the completion of charging preparation is input to the ECU 15, the ECU 15 may determine that the charging preparation is completed.

If it is determined in step S21 that the preparation for charging is not completed (NO in step S21), the determination in step S21 is repeated until the preparation for charging is completed. However, if the preparation for charging is not completed even after a lapse of a predetermined time from the time when step S21 is first executed, or if the user inputs a request to stop the deterioration determination of the battery to the ECU 15, the process of FIG. 5 is performed. And the process of FIG. 6 is stopped and the process is returned to the main routine.

When it is determined in step S21 that the preparation for charging is completed (YES in step S21), the ECU 15 controls the charger 102 and the like to start external charging of the battery in the battery pack 100 (step S22). ). As a result, electric power is supplied from the external power source to the batteries in the battery pack 100 through the charging cable. At this time, the charging current value is preferably 1 C or less (for example, 0.5 C).

During the execution of the external charging, the ECU 15 detects the state (current and voltage) of the battery in the battery pack 100 (step S23). The ECU 15 calculates the amount of electricity (storage amount Q) stored in the battery based on the voltage of the battery at the start of external charging (for example, the voltage value of the battery at the start of external charging detected in step S21). , The calculated storage amount Q (storage amount Q at the start of external charging) is stored in the storage unit 16. Further, the ECU 15 continuously detects and records the current and voltage of the battery in the battery pack 100 based on the signals (detected values of the current sensor and the voltage sensor) from the battery monitoring unit 101 during the external charging of the battery. do. Specifically, the ECU 15 detects the current and voltage of the battery every time a predetermined time (for example, 1 second) elapses, and stores the detected value at each timing (timing each time a predetermined time elapses). Output to 16. As a result, the storage unit 16 stores data indicating changes in the current and voltage of the battery during charging.

By executing the external charge, the SOC (State Of Charge) of the battery in the battery pack 100 becomes high. Then, the higher the SOC of the battery (that is, the longer the charging time), the higher the voltage of the battery tends to be. The SOC is defined as the ratio of the current charge capacity to the full charge capacity (for example, a percentage).

When the predetermined charging end condition is satisfied, the ECU 15 controls the charger 102 and the like to end the above-mentioned external charging (step S24). In this embodiment, the charging end condition is satisfied when the SOC of the battery in the battery pack 100 reaches 100%. The ECU 15 can calculate the SOC based on the battery voltage (signal from the battery monitoring unit 101). However, the present invention is not limited to this, and the ECU 15 may end the above-mentioned external charging based on the instruction of the user.

After the charging is completed, the ECU 15 calculates the dQ / dV voltage characteristic line of the battery in the battery pack 100 using the data detected during charging (step S25).

The ECU 15 can calculate data indicating a transition of the stored amount Q of the battery by using the current value of the battery continuously detected during the execution of the external charging. Specifically, the ECU 15 can calculate the amount of electricity charged to the battery during the execution of the external charging by integrating the current value flowing through the battery during the execution of the external charging. Therefore, the ECU 15 is executing external charging based on the stored amount Q (stored amount Q at the start of external charging) stored in the storage unit 16 at the start of external charging and the above-mentioned current integrated value (charging electricity amount). It is possible to calculate the stored amount Q at each timing (timing each time a predetermined time elapses).

The data showing the transition of the battery voltage during the execution of external charging is stored in the storage unit 16 in the above-mentioned step S23. The ECU 15 uses data indicating the transition of the stored amount Q during charging calculated as described above and data indicating the transition of the voltage V of the battery during charging stored in the storage unit 16 for external charging. Correspondence information (map, mathematical formula, etc.) showing the relationship between the stored amount Q of the battery and the voltage V in the battery can be created. Further, the ECU 15 can create a dQ / dV voltage characteristic line by calculating the value of dQ / dV corresponding to each voltage value during external charging by differentiating the stored amount Q by the voltage V.

Next, the ECU 15 detects the peak position (Vp) of the dQ / dV voltage characteristic line created as described above (step S26). Then, after the peak position is detected, the process returns to step S12 of FIG.

The calculation of the dQ / dV voltage characteristic line (step S25) and the detection of the peak position (step S26) may be performed in parallel with the acquisition of data (step S23) during charging.

Next, the ECU 15 uses the difference value ΔdQ / dV shown below to determine whether or not the battery in the battery pack 100 has suddenly deteriorated.

With reference to FIG. 5, the ECU 15 calculates the difference value ΔdQ / dV (step S12). The difference value ΔdQ / dV corresponds to the difference between the maximum value of dQ / dV and the minimum value of dQ / dV within a predetermined battery voltage range. In this embodiment, the lower limit of the boundary value defining the predetermined battery voltage range is 3.2 V (the voltage value used for the determination before the start of charging in step S21 of FIG. 6), and the upper limit is the initial value. Let it be Vp. That is, the battery voltage range is from 3.2 V to the initial Vp.

FIG. 7 is a diagram for explaining a method of calculating the difference value ΔdQ / dV. In FIG. 7, the solid line k11 shows the dQ / dV voltage characteristic line of the battery in the initial state (hereinafter referred to as “state A”). The solid line k12 shows the dQ / dV voltage characteristic line of the battery in the state where the deterioration is more advanced than the state A (hereinafter, referred to as “state B”). The solid line k13 shows the dQ / dV voltage characteristic line of the battery in the state where the deterioration is more advanced than the state B (hereinafter, referred to as “state C”). The Vp of the dQ / dV voltage characteristic line (solid line k11) of the battery in the state A corresponds to the initial Vp. In the example shown in FIG. 7, the initial Vp is 3.37V.

With reference to FIG. 7, the minimum value of dQ / dV in the battery voltage range “3.2V to initial Vp” is 1.0 for the batteries in any of the states A to C, and the battery voltage range “3”. The maximum value of dQ / dV in ".2V to initial Vp" is dQ / dV of initial Vp. The initial Vp dQ / dV tends to decrease as the deterioration of the battery progresses. Therefore, as shown in FIG. 7, the dQ / dV voltage characteristic line of the battery in the state C (d-dV voltage characteristic line) is larger than the difference value ΔdQ / dV calculated from the dQ / dV voltage characteristic line (solid line k12) of the battery in the state B. The difference value ΔdQ / dV calculated from the solid line k13) is smaller. Therefore, the degree of deterioration of the battery (and thus the amount of decrease in the capacity of the battery) can be estimated from the difference value ΔdQ / dV.

With reference to FIG. 5 again, the ECU 15 calculates the battery capacity reduction rate X using the difference value ΔdQ / dV calculated as described above (step S13). First, the ECU 15 obtains the amount of decrease in battery capacity (that is, a numerical value indicating how much the capacity of the current battery is reduced from the capacity of the battery in the initial state) based on the above difference value ΔdQ / dV.

For example, information indicating the relationship between the difference value ΔdQ / dV and the capacity reduction amount of the battery (hereinafter referred to as “capacity reduction amount calculation information”) may be obtained in advance by an experiment or the like and stored in the storage unit 16. FIG. 8 is a diagram showing an example (map) of the capacity reduction amount calculation information.

With reference to FIG. 8, as shown by the solid line k20, this map defines a relationship in which the smaller the difference value ΔdQ / dV, the greater the decrease in battery capacity. In the example shown in FIG. 8, the difference value ΔdQ / dV and the amount of decrease in battery capacity have a substantially proportional relationship. The ECU 15 can obtain the battery capacity reduction amount from the difference value ΔdQ / dV calculated in step S12 by referring to the map as shown in FIG. 8, for example.

Next, the ECU 15 calculates the capacity reduction rate X of the battery in the battery pack 100 from the battery capacity reduction amount obtained as described above. The capacity reduction rate X (%) is calculated according to the following equation (1).

X = 100 × (reduced battery capacity) / (initial battery capacity) ... (1)
The initial capacity of the battery in the above formula (1) is stored in the storage unit 16 as initial information of the battery pack 100.

The calculation of the difference value ΔdQ / dV (step S12) and the calculation of the capacity reduction rate X (step S13) are performed in parallel with the acquisition of data (step S23 in FIG. 6) during the above-mentioned external charging. May be good. Further, the stored amount Q and SOC of the battery may be calculated in consideration of the battery temperature and the like in addition to the battery voltage.

The ECU 15 determines whether or not the battery in the battery pack 100 has suddenly deteriorated based on whether or not the capacity reduction rate X calculated as described above is larger than the threshold value Th. That is, when the capacity reduction rate X is larger than the threshold value Th, it is determined that the battery has suddenly deteriorated. On the other hand, when the capacity decrease rate X is smaller than the threshold value Th, it is determined that the battery has not deteriorated suddenly.

With reference to FIG. 5 again, the ECU 15 determines whether or not the capacity reduction rate X is larger than the threshold value Th (step S14). The threshold value Th can be set arbitrarily. The threshold value Th may be a fixed value or may be variable depending on the situation of the vehicle and the like. In this embodiment, the threshold Th is set to 25%.

When it is determined that the capacity decrease rate X is equal to or less than the threshold value Th (NO in step S14), it is determined that the battery has not suddenly deteriorated, and the process is returned to the main routine. On the other hand, when it is determined that the capacity decrease rate X is larger than the threshold value Th (YES in step S14), it is determined that the battery has suddenly deteriorated, and the ECU 15 executes the recovery process for the high rate deterioration. (Step S15). Specifically, the ECU 15 alleviates the bias of the ion concentration distribution in the electrolytic solution of the battery by leaving the battery in the battery pack 100 for a predetermined time (for example, 72 hours) in a state where neither charging nor discharging is performed. The recovery process for high-rate deterioration is not limited to the stop of charging / discharging as described above, and is arbitrary. good.

When the recovery process for high rate deterioration is completed, the ECU 15 again calculates the dQ / dV voltage characteristic line of the battery in the battery pack 100 according to the procedure shown in FIG. 6, and the peak position of the dQ / dV voltage characteristic line ( Vp) is detected (step S16). Then, the ECU 15 compares the Vp detected before the recovery process with the Vp detected after the recovery process, and whether the Vp has changed by performing the above recovery process (returning to the initial Vp side). It is determined whether or not (step S17). Further, the ECU 15 determines whether the cause of the sudden deterioration is high-rate deterioration or other deterioration based on the determination result in step S17. Hereinafter, the deterioration determination of this battery will be described with reference to FIGS. 9 and 10.

FIG. 9 is a diagram showing a dQ / dV voltage characteristic line (solid line k2) detected before the recovery process is performed (step S11). FIG. 10 is a diagram showing a dQ / dV voltage characteristic line (solid line k3) detected after performing the above recovery process (step S16) for a battery in which high rate deterioration has occurred. In FIGS. 9 and 10, the broken line k1 indicates the dQ / dV voltage characteristic line of the battery in the initial state.

The peak position (Vp) of the dQ / dV voltage characteristic line of the battery in which the sudden deterioration has occurred is higher than the initial Vp as shown by the solid line k2 in FIG. However, if the cause of the sudden deterioration is high rate deterioration, the battery capacity is recovered by performing the above recovery process (step S15). The peak position (Vp) of the dQ / dV voltage characteristic line of the battery whose capacity has been recovered by the recovery process is as shown by the solid line k3 in FIG. 10 from before the recovery process (see the solid line k2 in FIG. 9). Also approaches the initial Vp. In the example shown in FIG. 10, the Vp of the dQ / dV voltage characteristic line (solid line k3) substantially coincides with the initial Vp.

On the other hand, if the cause of the sudden deterioration is deterioration other than high-rate deterioration (for example, precipitation of lithium on the surface of the negative electrode), the capacity of the battery is hardly recovered even if the above recovery treatment (step S15) is performed. Therefore, in a battery that has deteriorated other than high-rate deterioration, a dQ / dV voltage characteristic line that is almost the same as the dQ / dV voltage characteristic line shown by the solid line k2 in FIG. 9 is detected even after the above recovery process. Will be done.

With reference to FIG. 5 again, in step S17, the Vp detected by the ECU 15 before the recovery process (step S11) and the Vp (Vp after recovery) detected after the recovery process (step S16) are performed. It is determined whether or not the difference (absolute value) of is larger than the predetermined value. When the difference in Vp is larger than the predetermined value, it is determined that Vp has returned to the initial Vp side by the recovery process. On the other hand, when the difference in Vp is smaller than the predetermined value, it is determined that Vp has not returned to the initial Vp side by the recovery process. However, the present invention is not limited to this, and in addition to the above difference in Vp, the initial Vp in the storage unit 16 may be taken into consideration to determine whether or not the Vp has returned to the initial Vp side by the above-mentioned recovery process. ..

As the degree of deviation of Vp, a ratio may be adopted instead of the above difference. Further, the predetermined value used in step S17 is a threshold value that can be arbitrarily set, and is stored in, for example, a storage unit 16. A threshold value suitable for deterioration determination may be obtained in advance by an experiment or the like and stored in the storage unit 16.

When it is determined that Vp has returned to the initial Vp side by the above-mentioned recovery process (NO in step S17), it is determined that the battery in the battery pack 100 has not deteriorated other than the high rate deterioration, and the ECU 15 determines that the battery has not deteriorated. Perform an additional recovery process to continue using (step S182). This recovery process is a recovery process for high rate deterioration. However, if the capacity of the battery is sufficiently recovered by the recovery process of step S15, the battery may be continued to be used without performing the recovery process of step S182.

On the other hand, when it is determined that Vp has not returned to the initial Vp side by the above-mentioned recovery process (YES in step S17), the battery in the battery pack 100 cannot be recovered (or is difficult to recover) deterioration (that is, high rate). It is determined that deterioration other than deterioration) has occurred. That is, in order to prohibit the use of the battery in the battery pack 100, the ECU 15 records in the storage unit 16 that the battery has deteriorated other than the high rate deterioration and notifies the user (step S181). For example, the ECU 15 turns on the diagnosis (self-diagnosis) flag in the storage unit 16 (changes the value of the flag from 0 to 1), so that the storage unit 16 indicates that the battery has deteriorated other than the high rate deterioration. Record in. As a result, the batteries in the battery pack 100 cannot be used. The method of notifying the user is arbitrary, and may be notified by display (text or image, etc.), by sound (including voice), or by turning on the lamp (including blinking). .. After recording and notifying as described above, the process is returned to the main routine.

As described above, in the above battery deterioration determination, the ECU 15 performs a recovery process for high rate deterioration on the secondary battery (step S15). Further, the ECU 15 detects the peak position (Vp) of the dQ / dV voltage characteristic line before and after the recovery process. The ECU 15 determines whether or not the degree of deviation between the Vp detected before the recovery process (step S11) and the Vp detected after the recovery process (step S16) is larger than a predetermined value (step S17). When the degree of deviation of Vp is larger than the predetermined value, it is determined that the secondary battery has not deteriorated other than the high rate deterioration, and the use of the secondary battery is permitted (step S182). Further, when the degree of deviation of Vp is smaller than a predetermined value, it is determined that the battery has deteriorated other than the high rate deterioration, and the use of the secondary battery is prohibited (step S181).

According to the above-mentioned battery deterioration determination, when a secondary battery is suddenly deteriorated, it is possible to appropriately determine whether the cause is high-rate deterioration or other deterioration. .. Further, by the above battery deterioration determination, it becomes possible to more accurately detect the time when the use of the secondary battery should be stopped (and by extension, the time when the used secondary battery should be replaced or discarded). That is, according to the above-mentioned battery deterioration determination, it is possible to suppress the replacement or disposal of the secondary battery that can still be used and extend the usage period of the secondary battery.

In step S14 of FIG. 5, when the capacity reduction rate X and the threshold value Th are the same, NO is determined. However, the present invention is not limited to this, and step S14 may be changed so that when the capacity reduction rate X and the threshold value Th are the same, it is determined to be YES and the process proceeds to step S15.

The method of determining whether or not Vp has returned to the initial Vp side by the recovery process for high rate deterioration is not limited to the method of step S17. For example, it may be determined whether or not the degree of deviation between the initial Vp and the recovered Vp is larger than a predetermined value. When the degree of deviation of Vp is smaller than the predetermined value, it is determined that Vp has returned to the initial Vp side by the recovery process, and when the degree of deviation of Vp is larger than the predetermined value, Vp is initially determined by the recovery process. It may be determined that the Vp side has not returned. As described above, when the initial Vp is used instead of the Vp detected before the recovery process, it is not necessary to detect the Vp before the recovery process.

The ECU 15 performs determination of whether or not deterioration other than high-rate deterioration has occurred in the secondary battery and output of the result, and the user performs post-determination processing (additional recovery processing, etc.) according to the determination result. You may.

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

10 vehicles, 12 PCUs, 13 MGs, 14 drive wheels, 15 ECUs, 16 storage units, 18 communication lines, 100 battery packs, 101 battery monitoring units, 102 chargers, 103 inlets, 110 cells, 111 positive electrode plates, 112 negative electrode plates. , 113 separator, 114 electrode group, 115 case, 120 spacer, 121 protrusion, 122 main body, 131 positive electrode terminal, 132 negative electrode terminal, 130 gas discharge valve, 140 connection member, 141,142 restraint plate, 151 restraint band, 152 Screw.

Claims (2)

A detector that detects the peak position of the dQ / dV voltage characteristic line during charging of the secondary battery using the power of the external power supply, and
The secondary battery is subjected to a recovery process for high-rate deterioration , and the first Vp , which is the peak position of the dQ / dV voltage characteristic line detected by the detection unit before the recovery process, and the recovery process are performed. If the degree of misalignment with the second Vp, which is the peak position of the dQ / dV voltage characteristic line detected by the detection unit , is smaller than the predetermined first threshold value, the secondary battery has deteriorated other than the high rate deterioration. If the degree of misalignment between the first Vp and the second Vp is larger than the predetermined first threshold value, the determination unit determines that the secondary battery has not deteriorated other than the high rate deterioration. ,
Equipped with
The dQ / dV voltage characteristic line shows the relationship between dQ / dV, which is the ratio of the change amount dQ of the stored amount of the secondary battery to the change amount dV of the voltage of the secondary battery, and the voltage of the secondary battery. A battery deterioration judgment system that represents a line. After detecting the first Vp, the determination unit determines whether or not the capacity reduction rate of the secondary battery is larger than a predetermined second threshold value, and the capacity reduction rate of the secondary battery is the predetermined value. If it is larger than the second threshold value, the recovery process is executed, and if the capacity reduction rate of the secondary battery is equal to or less than the predetermined second threshold value, the recovery process is not executed. , The battery deterioration determination system according to claim 1.

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