Degradation state determination system and degradation state determination method for secondary battery

Abstract

To provide a degradation state determination system and a degradation state determination method that can appropriately determine whether there is abnormal degradation that causes an abnormal voltage drop when a secondary battery is discharged at a high C-rate.SOLUTION: A degradation state determination system 100 includes: a measuring section 101 that measures battery temperature Tbn(t), battery current Ib(t), and battery voltage Vbn(t); a storing section 102; a capacity estimating section 103 that estimates estimated charge capacity Cen(t); a suitable discharge period detecting section 104 that detects a suitable discharge period Dhn in which a high C-rate discharge that conforms to discharge conditions CD is performed; a measured voltage drop amount acquiring section 105 that obtains a measured voltage drop amount ΔVrnA that occurs during the suitable discharge period; an estimated voltage drop amount acquiring section 106 that obtains an estimated voltage drop amount ΔVen that is estimated to occur during the same period Dhn; and a determining section 107 that determines whether there is abnormal degradation in the battery from the measured voltage drop amount and the estimated voltage drop amount.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a degradation state determination system and a degradation state determination method for determining the degradation state of a secondary battery. [Background technology]

[0002] Secondary batteries such as lithium-ion secondary batteries deteriorate with use. For example, the battery capacity (charge capacity and discharge capacity) gradually decreases with use. This type of deterioration is normal and occurs normally in secondary batteries.

[0003] On the other hand, there are cases where deterioration progresses abnormally due to lithium deposition, etc. Patent Document 1 discloses a control system for dealing with such deterioration, taking into consideration the relationship with the amount of lithium deposition. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-73777 Summary of the Invention [Problem to be solved by the invention]

[0005] However, abnormal degradation may occur, which differs from the normal degradation described above and the degradation due to lithium precipitation described above. For example, the salt concentration in the electrolyte may decrease significantly depending on the usage conditions of the secondary battery, such as use at high temperatures or with a high discharge current. A secondary battery that has experienced a degradation phenomenon such as a decrease in the salt concentration in the electrolyte shows almost no difference in battery voltage change during charging compared to a normally deteriorated battery. However, when the secondary battery is discharged, especially when discharged with a high discharge current, the battery voltage during discharge decreases significantly compared to a normally deteriorated secondary battery with the same charge capacity, resulting in an abnormal voltage drop.

[0006] However, if the occurrence of such abnormal deterioration cannot be properly detected, in devices that use this secondary battery as a driving energy source, such as vehicles such as HEVs, PHEVs, and BEVs that use energy stored in the secondary battery for driving or flying, or battery-powered drones, when a high current is discharged due to sudden acceleration or sudden ascent, the battery voltage will drop significantly and reach the lower limit voltage early, which may result in problems such as the actual driving or flying distance being significantly shorter than the driving distance or cruising range estimated from the battery voltage and SOC.

[0007] It has been found that when a normally deteriorated secondary battery is discharged for a predetermined time at the same C-rate (the discharge current is calculated by dividing the battery current by the battery capacity (charge capacity) at that time) under the same starting conditions of the same battery temperature and the same battery voltage, the amount of decrease in battery voltage at the end of discharge relative to the battery voltage before the start of discharge is roughly the same regardless of the degree of normal deterioration.On the other hand, it has been found that when a secondary battery that has experienced the above-mentioned abnormal deterioration is discharged for a predetermined time at the same C-rate (the discharge current is calculated by dividing the battery current by the battery capacity (charge capacity) at that time) under the same starting conditions of the same battery temperature and the same battery voltage as a normally deteriorated secondary battery, the amount of decrease in battery voltage at the end of discharge relative to the battery voltage before the start of discharge is greater than that of a normally deteriorated secondary battery.

[0008] Note that, when discharging for the same period of time, the larger the discharge current, i.e., the higher the discharge C-rate, the greater the drop in battery voltage. Furthermore, in an abnormally deteriorated secondary battery, the higher the C-rate of the discharge current, the greater the drop in battery voltage compared to a normally deteriorated secondary battery. In particular, when a discharge current with a high discharge C-rate is applied—for example, in the case of an on-board secondary battery, when a discharge current 15 times or more larger than the discharge current discharged from the secondary battery when the vehicle is driven at a constant speed of 60 km / h on flat ground—the abnormally deteriorated secondary battery experiences a greater drop in battery voltage compared to a normally deteriorated secondary battery. This is thought to be because a large discharge current is likely to have an effect of increased diffusion resistance near the positive electrode plate within the secondary battery. Typically, when a discharge current of 100 A or more is applied from the secondary battery, the abnormally deteriorated secondary battery experiences a greater drop in battery voltage compared to a normally deteriorated secondary battery.

[0009] The present invention has been made in consideration of these problems and findings, and provides a degradation state determination system and a degradation state determination method that can appropriately detect the presence or absence of abnormal degradation that causes an abnormal voltage drop when a secondary battery is discharged. [Means for solving the problem]

[0010] (1) One aspect of the present invention for solving the above problem is a system for determining a state of deterioration of a secondary battery that houses an electrode assembly impregnated with an electrolyte solution, the system comprising: a measurement unit that measures a battery temperature, a battery current, and a battery voltage of the secondary battery; a memory unit that chronologically stores the measured battery temperature, the battery current, and the battery voltage; a capacity estimation unit that estimates a current estimated charge capacity of the secondary battery; a conformable discharge period detection unit that uses the battery temperature, the battery current, and the battery voltage to detect the occurrence of a conformable discharge period in which conformable discharge is performed according to predetermined discharge conditions; a measured voltage drop amount acquisition unit that uses the battery voltage to obtain a measured amount of voltage drop that occurred during the detected conformable discharge period; an estimated voltage drop amount acquisition unit that uses the estimated charge capacity, the duration of the conformable discharge period, the battery temperature during the conformable discharge period, and the battery current that flowed during the conformable discharge period to obtain an estimated amount of voltage drop that is estimated to occur during the conformable discharge period; and a determination unit that determines whether or not the secondary battery has abnormally deteriorated based on the measured voltage drop amount and the estimated voltage drop amount.

[0011] Even when a secondary battery experiences abnormal degradation, such as an abnormal decrease in the salt concentration of the electrolyte, the behavior of the secondary battery during charging is minimally affected. However, when an abnormally deteriorated secondary battery is discharged, a larger battery voltage drop occurs at the end of the discharge compared to when the battery is in a normally deteriorated state, compared to when the battery is in a normally deteriorated state before or immediately after the discharge begins. Therefore, this secondary battery degradation state determination system obtains the actual measured voltage drop that occurred during a conformal discharge period in which conformal discharge that satisfies predetermined discharge conditions is performed. In addition, the estimated voltage drop for normal deterioration is estimated using the current estimated charge capacity, and the presence or absence of an abnormal voltage drop in the secondary battery is determined based on the actual measured voltage drop and the estimated voltage drop. This allows for accurate determination of whether or not the secondary battery is experiencing abnormal degradation that causes an abnormal voltage drop.

[0012] Examples of secondary batteries include lithium ion secondary batteries and sodium ion secondary batteries. Examples of the electrolyte include nonaqueous solvent-based electrolytes obtained by dissolving electrolyte salts such as lithium salts and sodium salts in an organic solvent. Examples of the organic solvent include cyclic carbonates such as propylene carbonate and ethylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The electrode body may be a wound-type electrode body in which strip-shaped positive and negative electrode plates are wound with a separator interposed therebetween, or a flat wound-type electrode body obtained by flattening the wound-type electrode body. Alternatively, a stacked-type electrode body in which sheet-shaped positive and negative electrode plates are alternately stacked with a separator interposed therebetween may be used.

[0013] Methods for estimating the estimated charge capacity in the capacity estimation unit include, for example, estimating the charge capacity using the battery temperature history of the secondary battery and the time it was held at each temperature, or estimating the charge capacity of the secondary battery based on the interval charge capacity when the secondary battery is partially charged (for example, interval charging from SOC 40% to 50%).

[0014] The conforming discharge period detection unit may determine whether a conforming discharge period has occurred by, for example, determining that a certain verification period is a conforming discharge period when discharge conditions CD are satisfied during a certain verification period, specifically, when all of the following sub-discharge conditions CDa to CDd that make up the discharge conditions CD are satisfied. CDa: The SOC of the secondary battery at the start of the verification period is within a predetermined range (e.g., SOC 60±5%). CDb: The average battery temperature during the verification period, including the start, is within a predetermined temperature range (e.g., 25±5°C). CDc: The average C rate, which is the average value of the C rate obtained by dividing the battery current discharged from the secondary battery during the verification period, including the start, by the estimated charge capacity, is within a predetermined range (e.g., +20 to +40°C). CDd: The length of the verification period that satisfies each of the discharge conditions CDa to CDc reaches a predetermined length (e.g., 10 seconds, 15 seconds, etc.).

[0015] The conforming discharge period detection unit may use a plurality of different discharge conditions (e.g., a plurality of sub-discharge condition sets, each of which has different condition contents among the sub-discharge conditions CDa to CDd) to detect a conforming discharge period that satisfies one of the discharge conditions (e.g., one of the sub-discharge condition sets CDa to CDd). The conforming discharge performed during the conforming discharge period is a discharge that satisfies a predetermined discharge condition (e.g., one of the sub-discharge condition sets CDa to CDd). The larger the battery current value (C rate) of the conforming discharge, the shorter the condition regarding the length of the conforming discharge period (see the sub-discharge condition CDd). When charge carriers such as Li ions are inserted from the electrolyte into the positive-electrode active material layer during discharge of the secondary battery, the charge carrier concentration, such as Li ion concentration, decreases in the electrolyte near the positive electrode plate, generating diffusion resistance and resulting in a voltage drop. This is because a large discharge current tends to increase this diffusion resistance early. The length of the conforming discharge period (corresponding to the predetermined length of the verification period under the sub-discharge condition CDd) is preferably at least 5 seconds. This is because an abnormal voltage drop due to a drop in salt concentration or the like occurs significantly when discharge continues for a certain period of time (for example, 5 seconds or more).

[0016] The measured voltage drop amount acquisition unit obtains the measured voltage drop amount using the battery voltage. Specifically, for example, the measured voltage drop amount is calculated by using the battery voltage at each time point stored in the memory unit and averaging the difference between the detected battery voltage at the start of the adaptive discharge period and the battery voltage occurring at each timing during the adaptive discharge period when the discharge current is flowing.

[0017] The estimated voltage drop amount acquisition unit estimates and acquires the "estimated voltage drop amount," which is the amount of voltage drop estimated to occur during the conforming discharge period when a secondary battery that is not degraded or has normally deteriorated, i.e., a secondary battery that has not deteriorated to the point of abnormal voltage drop, using the estimated charge capacity, the duration of the conforming discharge period, the battery temperature during the conforming discharge period, and the battery current flowing during the conforming discharge period. For example, for a number of secondary batteries that have been used or subjected to a forced deterioration test to cause normal deterioration and have different charge capacities, the amount of voltage drop that occurs in the secondary battery when conforming discharge is performed that satisfies the discharge conditions for the conforming discharge period determined by the conforming discharge period detection unit (e.g., the sub-discharge conditions CDa to CDd described above), is obtained in advance, and a graph, lookup table, function, etc. obtained from the results is then used to obtain the estimated voltage drop amount. The graph, lookup table, function, etc. can then be used to obtain the estimated voltage drop amount.

[0018] The determination unit may determine whether or not an abnormal voltage drop has occurred by calculating a deviation state index, such as the deviation amount (ΔVrnA-ΔVen), the deviation ratio (ΔVrnA / ΔVen), or the deviation rate ((ΔVrnA-ΔVen) / ΔVen), from the actually measured voltage drop ΔVrnA and the estimated voltage drop ΔVen, and determining that an abnormal voltage drop has occurred in the secondary battery, i.e., that deterioration that causes an abnormal voltage drop has occurred, if these values ​​are greater than a predetermined threshold. Note that the determination unit may further determine the degree and rank of the deterioration that causes an abnormal voltage drop, in addition to determining whether or not an abnormal voltage drop has occurred.

[0019] (2) In the system for determining the deterioration state of a secondary battery described in (1) above, the estimated voltage drop amount acquisition unit may obtain the estimated voltage drop amount using a linear function equation obtained in advance with an average C rate, which is obtained by dividing the battery current by the estimated charge capacity and averaging the C rate over the adapted discharge period, as a variable.

[0020] When a secondary battery undergoes normal degradation that typically occurs with use, the battery capacity (charge capacity and discharge capacity) decreases as the normal degradation progresses from the beginning of use. However, as described above, even for such normally deteriorated secondary batteries, if they are discharged for a predetermined discharge period (e.g., 10 seconds) at the same C-rate (battery current divided by battery capacity (charge capacity)) under the same starting conditions of battery temperature and battery voltage, the amount of battery voltage decrease will be approximately the same regardless of the degree of normal degradation. Note that in automotive and other secondary batteries, the magnitude of the battery current flowing over a predetermined discharge period is often not constant. Therefore, we consider the C-rate (battery current divided by estimated charge capacity) as the average C-rate over the discharge period. Even in this case, for a normally deteriorated secondary battery, if it is discharged for a predetermined discharge period at the same average C-rate under the same starting conditions of battery temperature and battery voltage, the amount of battery voltage decrease will be approximately the same regardless of the degree of normal degradation.

[0021] Furthermore, the higher the C rate or average C rate during a discharge period, the greater the amount of voltage drop that occurs during that discharge period. Therefore, if a secondary battery is undergoing normal degradation, the average C rate of the battery current flowing during a specified discharge period and the measured amount of voltage drop will have a relationship that generally satisfies the same linear function, regardless of the degree of normal degradation.

[0022] On the other hand, if the secondary battery is abnormally deteriorated due to an abnormal decrease in the salt concentration of the electrolyte, the relationship between the average C rate of the battery current flowing during a specified discharge period and the measured voltage drop will deviate from (not satisfy) the linear function formula described above. This is because the measured voltage drop will be larger than that of a secondary battery with normal deterioration.

[0023] Therefore, as described above, the estimated voltage drop amount acquisition unit obtains an estimated voltage drop amount using a predetermined linear function formula with the average C rate of the battery current flowing during the compatible discharge period that satisfies the discharge conditions as a variable. This makes it possible to easily determine whether or not the secondary battery is experiencing abnormal degradation based on the difference between the estimated voltage drop amount and the actually measured voltage drop amount.

[0024] (3) Furthermore, in the system for determining the deterioration state of a secondary battery described in (1) or (2), the determination unit may include a deviation state acquisition unit that acquires a deviation state index between the estimated voltage drop amount and the actually measured voltage drop amount, and a deviation state determination unit that determines whether or not abnormal deterioration has occurred based on the acquired deviation state index.

[0025] In this system, the abnormal degradation determination unit includes a deviation state acquisition unit that obtains a deviation state index, and a deviation state determination unit that determines whether or not abnormal degradation exists based on the deviation state index. Since the presence or absence of abnormal degradation is determined using the deviation state index in this way, the determination process is easy. The determination by the deviation state determination unit may include determining the degree and rank of abnormal degradation in addition to determining whether abnormal degradation exists.

[0026] The deviation state index is an index that indicates how much the actual measured voltage drop amount ΔVrnA deviates from the estimated voltage drop amount ΔVen, and examples include the deviation amount (ΔVrnA-ΔVen), the deviation ratio (ΔVrnA / ΔVen), and the deviation rate ((ΔVrnA-ΔVen) / ΔVen).

[0027] (4) Further, in the system for determining the deterioration state of a secondary battery described in any one of (1) to (3), the conforming discharge performed during the conforming discharge period detected by the conforming discharge period detection unit is a high-current conforming discharge that flows an average battery current of 75 A or more.

[0028] In this system, a high current conformal discharge is performed during the conformal discharge period detected by the conformal discharge period detection unit, and a large battery current of 75 A or more is passed during the conformal discharge period. As a result, in this system, the "voltage drop ΔV" when abnormal degradation occurs in the secondary battery tends to be larger than the "voltage drop ΔV" when normal degradation occurs, making it easy to determine whether or not there is abnormal degradation.

[0029] (5) Another solution is a method for determining a degradation state of a secondary battery that houses an electrode assembly impregnated with an electrolyte solution, the method comprising: a measurement step of measuring a battery temperature, a battery current, and a battery voltage of the secondary battery; a measurement value storage step of storing the measured battery temperature, the battery current, and the battery voltage in chronological order; a capacity estimation step of estimating a current estimated charge capacity of the secondary battery; a conformable discharge period detection step of detecting the occurrence of a conformable discharge period in which conformable discharge is performed using the battery temperature, the battery current, and the battery voltage; a measured voltage drop amount acquisition step of obtaining an actual measured voltage drop amount that occurred during the detected conformable discharge period using the battery voltage; an estimated voltage drop amount acquisition step of obtaining an estimated voltage drop amount that is estimated to occur during the conformable discharge period using the estimated charge capacity, the duration of the conformable discharge period, the battery temperature during the conformable discharge period, and the battery current that flowed during the conformable discharge period; and a determination step of determining whether or not the secondary battery has abnormally deteriorated based on the actual measured voltage drop amount and the estimated voltage drop amount.

[0030] As described above, abnormal degradation of a secondary battery, such as an abnormal decrease in the salt concentration of the electrolyte, has little effect on the behavior of the secondary battery during charging. However, discharging the battery results in a significant drop in battery voltage compared to before or immediately after the discharge. Therefore, this method for determining the degradation state of a secondary battery obtains the actual voltage drop that occurred during a conformal discharge period in which conformal discharge that satisfies predetermined discharge conditions is performed. In addition, the estimated voltage drop for normal degradation is estimated using the current estimated charge capacity, and the presence or absence of an abnormal voltage drop in the secondary battery is determined based on the actual voltage drop and the estimated voltage drop. This allows for accurate determination of the presence or absence of abnormal degradation that causes an abnormal voltage drop in the secondary battery.

[0031] (6) Furthermore, in the method for determining the degradation state of a secondary battery described in (5), the estimated voltage drop amount acquisition step may be a method for determining the degradation state of a secondary battery in which a linear function is previously obtained using an average C rate obtained by dividing the battery current by the estimated charge capacity and averaging the average C rate over the adapted discharge period as a variable, and the estimated voltage drop amount is obtained using the linear function.

[0032] In this degradation state determination method, the estimated voltage drop amount acquisition step obtains the estimated voltage drop amount using a predetermined linear function with the average C rate of the battery current flowing during the conforming discharge period as a variable. Therefore, it is possible to easily determine whether or not the secondary battery is experiencing abnormal degradation based on the difference between the estimated voltage drop amount and the actually measured voltage drop amount.

[0033] (7) Furthermore, in the method for determining the degradation state of a secondary battery described in (5) or (6), the determination step may include a deviation state acquisition step of obtaining a deviation state index between the estimated voltage drop amount and the actually measured voltage drop amount, and a deviation state determination step of determining whether or not abnormal degradation has occurred based on the obtained deviation state index.

[0034] In this degradation state determination method, the determination step includes a deviation state acquisition step of obtaining a deviation state index, and a deviation state determination step of determining whether or not abnormal degradation exists based on the deviation state index. Since the presence or absence of abnormal degradation is determined using the deviation state index in this way, the determination process is easy.

[0035] (8) The method for determining the deterioration state of a secondary battery according to any one of (5) to (7), wherein the conforming discharge performed during the conforming discharge period detected in the conforming discharge period detection step is a high-current conforming discharge that flows an average battery current of 75 A or more.

[0036] In this method, a large battery current of 75 A or more is passed on average during the conformal discharge period detected in the conformal discharge period detection step by a high current conformal discharge. Therefore, in this method, the "voltage drop ΔV" when abnormal degradation of the secondary battery occurs tends to be larger than the "voltage drop ΔV" when normal degradation occurs, making it easy to determine whether or not abnormal degradation exists. [Brief explanation of the drawings]

[0037] [Figure 1] FIG. 1 is a longitudinal sectional view of a battery according to an embodiment. [Figure 2] 10 is a graph showing the relationship between the average C rate and current value of the discharge current flowing through the battery according to the embodiment and the estimated voltage drop amount and the actually measured voltage drop amount during the conforming discharge period. [Figure 3] 1 is a block diagram showing the configuration of a degradation state determination system for determining the degradation state of a battery that constitutes a battery pack according to an embodiment; [Figure 4] 2 is an explanatory diagram showing the connection state of each battery constituting a battery pack and a measurement unit that measures the battery temperature, battery voltage, and battery current of each battery in the degradation state determination system according to the embodiment. FIG. [Figure 5] 4 is a graph showing changes over time in battery temperature, C rate or battery current, and battery voltage when the battery is discharged according to the embodiment. [Figure 6] 4 is a flowchart showing steps of a measurement process in a procedure for determining a deterioration state of a battery according to an embodiment. [Figure 7] 10 is a flowchart showing the first half of the steps of an abnormal degradation detection process in the procedure for determining the degradation state of a battery according to an embodiment. [Figure 8] 10 is a flowchart showing the latter half of the steps of an abnormal degradation detection process in the procedure for determining the degradation state of a battery according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0038] (Embodiment) Hereinafter, a lithium ion secondary battery according to an embodiment of the present invention, that is, battery 1 (an example of a secondary battery), will be described with reference to Fig. 1. Battery 1 is a rectangular, sealed lithium ion secondary battery, and is installed in various devices such as vehicles, such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs), as well as drones.

[0039] The battery 1 of this embodiment is composed of a rectangular battery case 4, an electrode assembly 2 housed inside the battery case 4, and an electrolyte 3 housed in the battery case 4 and impregnating the electrode assembly 2. The battery case 4 is made of metal (aluminum in this embodiment) and has a rectangular box shape. It has a case body 4a in the shape of a rectangular cylinder with a bottom, and a lid 4b welded to an opening 4ao of the case body 4a to seal the opening 4ao. The electrode assembly 2 is covered by a rectangular bag-shaped insulating film 8 inside the battery case 4. The aforementioned electrolyte 3 is also housed inside the battery case 4, with a portion of the electrolyte 3 impregnated in the electrode assembly 2 and another portion pooling at the bottom of the battery case 4. A positive electrode terminal 5 and a negative electrode terminal 6 are fixed to the lid 4b of the battery case 4 via an insulating member 7, and the positive electrode terminal 5 is connected to a positive electrode current collector 2cp located at one end (the left end in Figure 1) of the electrode body 2, and the negative electrode terminal 6 is connected to a negative electrode current collector 2cn located at the other end (the right end in Figure 1) of the electrode body 2.

[0040] The electrode assembly 2 housed in the battery case 4 is a known so-called flat wound electrode assembly, which is formed by winding a strip-shaped positive electrode plate 2P and a strip-shaped negative electrode plate 2N with a pair of strip-shaped separators 2S interposed between them and then pressing them in a direction perpendicular to the paper surface in Fig. 1 to make them flat. This electrode assembly 2 is housed in the battery case 4 with its winding axis 2X lying on its side.

[0041] Of the electrode body 2, the strip-shaped positive electrode plate 2P is formed by laminating positive electrode active material layers on both surfaces of a positive electrode current collector foil made of aluminum foil. The positive electrode active material layer is composed of positive electrode active material particles, conductive particles, and a binder. In this embodiment, the positive electrode active material particles are, for example, lithium transition metal composite oxide particles such as lithium nickel cobalt manganese composite oxide particles. Note that at one end of the strip-shaped positive electrode plate 2P in the width direction (the left side in FIG. 1), the exposed positive electrode current collector foil is spirally overlapped, forming the aforementioned positive electrode current collector part 2cp.

[0042] On the other hand, the strip-shaped negative electrode plate 2N of the electrode body 2 is formed by laminating negative electrode active material layers on both surfaces of a negative electrode current collector foil made of copper foil. The negative electrode active material layer is made of negative electrode active material particles and a binder. In this embodiment, graphite particles are used as the negative electrode active material particles. At the end of the other widthwise side (the right side in FIG. 1) of the strip-shaped negative electrode plate 2N, the exposed negative electrode current collector foil is spirally overlapped to form the aforementioned negative electrode current collector portion 2cn.

[0043] The positive electrode terminal 5 is formed by bending an aluminum plate. A positive electrode internal connection portion 5I forming one end of the positive electrode terminal 5 is welded to a positive electrode current collector portion 2cp of a positive electrode plate 2P constituting the electrode body 2. Meanwhile, the other end of the positive electrode terminal 5 is drawn out of the battery case 4 to form a positive electrode external terminal portion 5G.

[0044] The negative electrode terminal 6 is formed by bending a copper plate. A negative electrode internal connection portion 6I forming one end of the negative electrode terminal 6 is welded to the negative electrode current collecting portion 2cn of the negative electrode plate 2N constituting the electrode body 2. Meanwhile, the other end of the negative electrode terminal 6 is drawn out of the battery case 4 to form a negative electrode external terminal portion 6G.

[0045] The electrolyte solution 3 is a non-aqueous electrolyte solution containing an organic solvent and a fluorine-containing lithium salt as a supporting salt. In this embodiment, the organic solvent used is a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate. The fluorine-containing lithium salt used is LiPF6. The salt concentration of the lithium salt in the electrolyte solution 3 at the time of injection is 1.1M.

[0046] The characteristics of this battery 1 deteriorate as it is repeatedly discharged and charged during use. Therefore, the battery capacity (charge capacity and discharge capacity) of the battery 1 gradually decreases. However, if the battery 1 is deteriorating normally, that is, if the battery 1 is deteriorating normally, a voltage drop of approximately the same magnitude occurs during discharge when the battery is discharged at the same C rate from the same battery voltage at the same battery temperature, regardless of the degree of degradation. Furthermore, the larger the discharge current and its C rate, the greater the voltage drop. In other words, in a graph with the C rate of the discharge current on the horizontal axis and the voltage drop on the vertical axis, if the battery 1 is deteriorating normally, the magnitude of the discharge C rate and the voltage drop occurring during discharge will generally have the same upward-sloping relationship, as shown by the solid line in Figure 2, for example. Furthermore, this relationship is approximately the same regardless of the degree of normal degradation of the battery 1. In other words, when the C-rate is used as a variable, it has been found that the amount of voltage drop that occurs during discharge generally follows the same linear function FM when the battery 1 is undergoing normal degradation, regardless of the degree of normal degradation. Note that Figure 2 shows the characteristics of a high-output battery 1 with a charge capacity of 5 Ah. As shown in parentheses on the horizontal axis, for example, a battery current of 100 A during discharge corresponds to 20 C at the C-rate, and a battery current of 150 A corresponds to 30 C at the C-rate. Furthermore, the magnitude of the battery current flowing through an in-vehicle battery 1 during discharge is often not constant. Therefore, as mentioned above, Figure 2 uses an average C-rate, which is the average C-rate over the discharge period, instead of the C-rate.

[0047] On the other hand, it has been found that when a phenomenon such as a decrease in the salt concentration in the electrolyte 3 in the electrode assembly 2 occurs, for example, due to operating the battery 1 at high temperatures, the battery 1 enters a state of abnormal degradation, which differs from normal degradation. Furthermore, as described above, when the battery 1 is discharged at the same C rate from the same battery voltage at the same battery temperature, the abnormally deteriorated battery 1 exhibits a larger voltage drop during discharge than a normally deteriorated battery 1, compared to the battery voltage immediately after the start of discharge. That is, as shown by the open circle ○ in the graph of Figure 2, the amount of voltage drop during discharge for the abnormally deteriorated battery 1 is found to be above the solid line of the linear function FM, and is therefore larger than this graph. Conversely, it is possible to determine whether the battery 1 is abnormally deteriorated by determining whether the amount of voltage drop during discharge is larger than the solid line of the linear function FM. Although not shown in the graph in Figure 2, in abnormally deteriorated batteries, the deviation from the graph of the linear function formula FM increases as the discharge C rate increases and as the abnormal deterioration progresses. This is thought to be because the voltage drop due to diffusion resistance generated near the positive electrode during discharge due to abnormal deterioration increases.

[0048] Therefore, the following describes a degradation state determination system 100 (see FIGS. 3 to 5) and a degradation state determination method (see FIGS. 6 to 8) according to this embodiment, which detect whether or not abnormal degradation has occurred in a battery 1. In this embodiment, as shown in FIG. 4, m (e.g., m=24) batteries 1 (assuming batteries 11 to 1m) are connected in series to form a battery pack 10. This battery pack 10 is connected to an inverter INV and is used to drive a motor MT mounted on, for example, an electric vehicle (not shown) via this inverter INV. It is also possible to use the motor MT as a generator and regeneratively charge each battery 1 in the battery pack 10 via the inverter INV. This degradation state determination system 100 is configured as part of a control system for the battery pack 10, which includes a CPU, memory, etc. (not shown).

[0049] In the following, for the sake of simplicity, the symbol n will be used to indicate that the nth battery 1n from the low potential side of the m batteries 11 to 1m is representative of the batteries 11 to 1m, and in some cases, the explanation of battery 1n will be omitted for the sake of simplicity.

[0050] Each of the m batteries 11-1m constituting the battery pack 10 is connected to a measurement unit 101, allowing the battery voltages Vb1(t)-Vbm(t) to be detected at predetermined time intervals (e.g., every 100 msec). Temperature sensors ST1-STm are attached to each of the batteries 11-1m. The temperature sensors ST1-STm are also connected to the measurement unit 101, allowing the battery temperatures Tb1(t)-Tbm(t) to be detected at predetermined time intervals. A current sensor SI is connected in series between the battery pack 10 and the inverter INV. This current sensor SI detects the battery current Ib(t) flowing through each of the batteries 11-1m at predetermined time intervals due to charging and discharging of the batteries 11-1m, and inputs the detected current to the measurement unit 101. In this specification, a discharging battery current is considered to be a current with a positive sign, and a charging battery current is considered to be a current with a negative sign.

[0051] As described above, the measurement unit 101 acquires the battery temperature Tbn(t), battery current Ib(t), and battery voltage Vbn(t) of battery 1n of the battery pack 10 at predetermined time intervals and stores them in chronological order in the memory unit 102. In parallel with the data storage in the memory unit 102, the capacity estimation unit 103 estimates the estimated charge capacity Cen(t) of battery 1n using the current and past data acquired by the measurement unit 101 and stored in the memory unit 102.

[0052] Note that the capacity estimation unit 103 can select an appropriate method for estimating the estimated charge capacity Cen(t) of the battery 1n. For example, the estimated charge capacity Cen(t) can be estimated using the change in the battery temperature Tbn(t) to which the battery 1n is exposed after the battery 1n is mounted on a vehicle (not shown) and powered on. This is because the deterioration of the battery 1n is more likely to progress when the battery temperature Tbn(t) is high. However, even for the same batteries 11-1m housed in a single battery pack 10, differences in the battery temperatures Tb1(t)-Tbm(t) occur depending on the location because the ease of heat input and heat dissipation from the outside differs. Therefore, the estimated charge capacities Ce1(t)-Cem(t) of each battery 11-1m may also differ between batteries. Therefore, in this embodiment, the estimated charge capacities Ce1(t)-Cem(t) are estimated individually for each battery 11-1m. However, although the estimated charge capacity Cen(t) of battery 1n gradually decreases due to deterioration, it is not expected to change in a short period of time, and therefore may be treated as constant during the adapted discharge period Dhn, etc., which will be described later. The reason why the capacity estimation unit 103 estimates the estimated charge capacity Cen(t) of battery 1n is that the magnitude of the charge capacity is less susceptible to the influence of the abnormal deterioration described above and is less likely to differ from that in the case of normal deterioration.

[0053] Separately, the capacity estimation unit 103 uses the past and present data measured by the measurement unit 101 and the estimated charge capacity Cen(t) to obtain the current SOC (State of Charge) CHn(t) of the battery 1n and the C rate Rin(t) of the flowing battery current Ib(t), and stores these in the storage unit 102. The C rate Rin(t) is calculated by dividing the battery current Ib(t) flowing through the battery 1n by the estimated charge capacity Cen(t) (Rin(t)=Ib(t) / Cen(t)).

[0054] Furthermore, the adaptive discharge period detection unit 104 uses the measured and stored current and past battery temperature Tbn(t), battery current Ib(t), and battery voltage Vbn(t) of the battery 1n to detect the occurrence of an adaptive discharge period Dhn in which adaptive discharge is performed in accordance with predetermined discharge conditions CD. Specifically, it detects the start (start time ts) and end (end time te) of the adaptive discharge period Dhn. More specifically, in this embodiment, when the battery 1n performs adaptive discharge in a verification period DTn under the discharge conditions CD, satisfying the following four sub-discharge conditions CDa to CDd, the verification period DTn is designated as the adaptive discharge period Dhn, and the occurrence of the adaptive discharge period Dhn is detected. CDa: SOCCHn(ts) of the battery 1n at the start time ts of the testing period DTn is within a predetermined range (for example, in this embodiment, CHn(ts)=60±5%). CDb: The average battery temperature TbnA of the battery temperatures Tbn(t) during the verification period DTn, including the start time ts, is within a predetermined temperature range (for example, in this embodiment, TbnA=25±5° C.). CDc: The average C rate RinA, which is the average value of the C rate Rin(t) of the battery current Ib(t) discharged from the battery 1n during the test period DTn, including the start time ts, is within a predetermined C rate range (for example, in this embodiment, RinA = +30 ± 10C). CDd: The length Ln of the test period DTn that satisfies the above-described sub-discharge conditions CDa to CDc has reached a predetermined duration DLn (for example, in this embodiment, Ln≧10 seconds=DLn). The time t when the length Ln of the test period DTn reaches the duration DLn is defined as the end time te.

[0055] That is, as shown in FIG. 5, for example, the time t of the verification period DTn begins when the SOCCHn(t) of battery In is 55-65%, the battery temperature Tbn(t) is 20-30°C, the magnitude of the discharge battery current Ib(t) increases, and the discharge C rate Rin(t) becomes +20°C or higher. This time t is set as the start time ts, and the verification period DTn begins. Thereafter, if the average battery temperature TbnA during the verification period DTn is 20-30°C and the average C rate RinA during the discharge is within the range of +20°C to +40°C, the verification period DTn continues. On the other hand, if the average battery temperature TbnA falls outside the range of 20-30°C or the average C rate RinA falls outside the range of +20°C to +40°C, the verification period DTn ends. The verification period DTn then ends at the end time te, when the length Ln of the verification period DTn reaches 10 seconds. Furthermore, it is assumed that this test period DTn is the conforming discharge period Dhn, and conforming discharge conforming to the discharge conditions CD is performed, and the occurrence of the conforming discharge period Dhn is detected, with the start time ts and the end time te.

[0056] Examples of vehicle operating conditions that satisfy the above-described discharge condition CD (sub-discharge conditions CDa to CDd) include climbing a slope and rapid acceleration to enter a highway from an interchange. Meanwhile, the discharge condition CD may be changed to increase opportunities to determine whether or not abnormal degradation is present during vehicle operation. For example, the range of the average C rate RinA specified in the sub-discharge condition CDc may be lowered, for example, to a range of 5 to 15 C, or even lower, such as a range of 3 to 8 C. Furthermore, in conjunction with this change, the contents of the other sub-discharge conditions CDa, CDb, and CDd may also be appropriately changed, such as by lengthening the duration DLn.

[0057] Meanwhile, the measured voltage drop amount acquisition unit 105 obtains the measured voltage drop amount ΔVrnA that occurred during the detected conforming discharge period Dhn. Specifically, the difference between the battery voltage Vbn(ts) at the start time ts and the battery voltage Vbn(t) at each time t is defined as the voltage drop amount ΔVrn(t) (ΔVrn(t) = Vrn(ts) - Vrn(t)). Furthermore, the voltage drop amount ΔVrn(t) obtained at each time t is used to obtain the average value of the voltage drop amount ΔVrn(t) over the entire conforming discharge period Dhn from the start time ts to the end time te, and this is defined as the measured voltage drop amount ΔVrnA. Note that this measured voltage drop amount ΔVrnA corresponds to the difference between the battery voltage Vrn(ts) at the start time ts and the average battery voltage VbnA, which is the average value of the battery voltage Vbn(t) during the conforming discharge period Dhn.

[0058] The estimated voltage drop amount acquisition unit 106 also uses the estimated charge capacity Cen(t), the duration DLn of the adaptive discharge period Dhn (DLn=10 seconds in this embodiment), the battery temperature Tbn(t) during the adaptive discharge period Dhn, and the battery current Ib(t) flowing during the adaptive discharge period Dhn to obtain an estimated voltage drop ΔVen that is estimated to occur during the adaptive discharge period Dhn if the detected battery 1n is not abnormally degraded. Specifically, in this embodiment, the estimated voltage drop ΔVen is obtained using the estimated charge capacity Cen(t) estimated by the capacity estimation unit 103, the average battery temperature TbnA of the battery temperatures Tbn(t) during the adaptive discharge period Dhn, and the average C-rate RinA obtained from the discharge battery current Ib(t) flowing during the adaptive discharge period Dhn. More specifically, the estimated voltage drop ΔVen corresponding to the average C-rate RinA is obtained using the previously obtained graph shown by the solid line in FIG. 2.

[0059] Instead of the graph shown by the solid line in Figure 2, the estimated voltage drop ΔVen corresponding to the average C rate RinA may be calculated using a linear function FM (ΔVen = a RinA + b) with the average C rate RinA shown in the graph as a variable. By using this linear function FM, it is possible to easily determine whether or not the battery 1n is abnormally degraded. The coefficient a in the linear function FM corresponds to the magnitude of the resistance component, such as the diffusion resistance, generated in the battery 1n.

[0060] The graph and linear function FM shown by the solid line in Figure 2 can be obtained in advance as follows: A battery 1 at the beginning of use or a battery 1 that has undergone normal degradation is discharged at each C-rate (e.g., +20C, +30C, +40C) for 10 seconds (corresponding to the duration DLn of the adapted discharge period Dhn) at a specific battery temperature (e.g., 25°C) and a specific SOC (e.g., 60% SOC). Then, the battery voltage immediately after the start of discharge (corresponding to the start time ts) is used as a reference, and the amount of voltage drop relative to the average battery voltage that occurs thereafter is obtained. This is plotted, for example, as shown by the black circle ● in Figure 2, and these are connected to obtain the graph and linear function FM shown by the solid line. Note that the same procedure as described above may be carried out for cases where the battery temperature is different or the discharge duration is different, to obtain a graph or a linear function. Alternatively, these may be compiled in the form of a lookup table.

[0061] The determination unit 107 determines whether or not there is an abnormal voltage drop in the battery 1n based on the measured voltage drop amount ΔVrnA obtained by the measured voltage drop amount obtaining unit 105 and the estimated voltage drop amount ΔVen obtained by the estimated voltage drop amount obtaining unit 106. Specifically, first, the deviation state obtaining unit 107A obtains a deviation state index between the estimated voltage drop amount ΔVen and the measured voltage drop amount ΔVrnA. In this embodiment, specifically, the deviation amount Sren is obtained. Note that this deviation amount Sren is the difference between the measured voltage drop amount ΔVrnA and the estimated voltage drop amount ΔVen (Sren = ΔVrnA - ΔVen).

[0062] As the deviation state index, in addition to the deviation amount Sren, an index indicating the degree to which the measured voltage drop amount ΔVrnA deviates from the estimated voltage drop amount ΔVen is used. For example, a deviation ratio (=ΔVrnA / ΔVen) obtained by dividing the measured voltage drop amount ΔVrnA by the estimated voltage drop amount ΔVen, or a deviation rate ((ΔVrnA-ΔVen) / ΔVen) obtained by dividing the deviation amount Sren by the estimated voltage drop amount ΔVen, etc. may be used.

[0063] Next, the deviation state determination unit 107B determines the presence or absence of abnormal degradation based on the acquired deviation state index (in this embodiment, the deviation amount Sren). That is, when it can be determined that the actually measured voltage drop amount ΔVrnA deviates significantly from the estimated voltage drop amount ΔVen, it is determined that abnormal degradation has occurred in the battery 1n. Specifically, when the deviation state index exceeds a preset threshold value, it is determined that abnormal degradation has occurred. In this embodiment, it is determined based on whether the deviation amount Sren is equal to or greater than a preset threshold deviation amount Sth (Sren≧Sth).

[0064] When the deviation amount Sren is less than the threshold deviation amount Sth (Sren < Sth), it is determined that no abnormal degradation has occurred in the battery 1n, the process is stopped, and the process returns to the compatible discharge period detection unit 104 to wait for the occurrence of the compatible discharge period Dhn.

[0065] On the other hand, when the deviation amount Sren is equal to or greater than the threshold deviation amount Sth (Sren≧Sth), it can be determined that abnormal degradation has occurred that causes an abnormal voltage drop in the battery 1n.

[0066] Among the compatible discharges that satisfy each sub-discharge condition CDa to CDd forming the discharge condition CD, a discharge in which the battery current Ib(t) is 75 A or more on average (in this example, corresponding to +15C or more at the C rate) is defined as a high-current compatible discharge. As described above, in this embodiment, in the sub-discharge condition CDc, the range of the average C rate RinA is set to +30±10C, so the discharge that satisfies the above discharge condition CD corresponds to a high-current compatible discharge. In a high-current compatible discharge, since a large battery current of 75 A or more flows on average during the compatible discharge period, the "actually measured voltage drop amount ΔVrnA" when abnormal degradation has occurred in the battery 1 is likely to be larger than the "estimated voltage drop amount ΔVen" corresponding to the case of normal degradation, and it is easy to discriminate the presence or absence of abnormal degradation using the above deviation amount Sren and the like.

[0067] Therefore, the subsequent abnormal degradation processing unit 108 performs predetermined processing to deal with abnormal degradation. Examples of such processing include corrections to decrease the SOC, remaining battery charge, and vehicle mileage. When abnormal degradation occurs, even if the remaining battery charge is high and the vehicle mileage is still displayed as sufficient, discharging at a high C-rate, such as during sudden acceleration or climbing a steep slope, can significantly reduce the battery voltage Vbn(t) of battery 1n and fall below the lower limit voltage of battery 1n, causing the battery to run out of power and making it virtually impossible to drive the vehicle. Processing to deal with abnormal degradation can also include displaying a warning lamp to the vehicle driver, notifying a service center via communication of the occurrence of abnormal degradation, and changing the vehicle's driving mode to one that avoids high C-rate discharge or one that reduces the power consumption of the air conditioning.

[0068] Thus, the degradation state determination system 100 of this embodiment can appropriately determine whether or not the battery 1n has experienced degradation that causes an abnormal voltage drop. Furthermore, in this embodiment, the deviation state acquisition unit 107A and deviation state determination unit 107B of the determination unit 107 calculate the deviation state index (deviation amount Sren) and use this to determine whether or not abnormal degradation exists, making the determination process easy.

[0069] In the present embodiment, the deviation state determination unit 107B determines whether or not abnormal degradation occurs using the deviation amount Sren. However, in addition to determining whether or not abnormal degradation occurs, the degree of abnormal degradation may also be determined. That is, multiple types of threshold deviation amount Sth to be compared with the deviation amount Sren may be set, and the level of abnormal degradation may be determined in multiple stages, for example, levels 1, 2, and 3.

[0070] Next, the procedure of the method for determining the degradation state of a battery In according to this embodiment will be described with reference to the flowcharts of Figures 6 to 8. First, the procedure of the measurement process shown in Figure 6 will be described. This procedure of the measurement process mainly corresponds to the processes performed by the measurement unit 101, storage unit 102, and capacity estimation unit 103 of the degradation state determination system 100 described above.

[0071] First, in measurement step S11, the measurement unit 101 measures the battery temperature Tbn(t) of battery 1n at predetermined time intervals using a temperature sensor STn attached to battery 1n. The measurement unit 101 also measures the battery voltage Vbn(t). Furthermore, the measurement unit 101 measures the charging / discharging battery current Ib(t) flowing through battery 1n using a current sensor SI. This allows the battery temperature Tbn(t), battery voltage Vbn(t), and battery current Ib(t) of battery 1n to be obtained at predetermined time intervals. These are then stored in the storage unit 102 in chronological order in storage step S12.

[0072] In parallel with the storage step S12, in a capacity step S13, the current battery temperature Tbn(t), battery voltage Vbn(t), and battery current Ib(t) of battery 1n obtained and the stored past data are used to obtain an estimated charge capacity Cen(t) of battery 1n.

[0073] In the SOC calculation step S14, the SOCCHn(t) of battery 1n is obtained. Furthermore, in the C rate calculation step S15, the battery current Ib(t) flowing through battery 1n is converted into a C rate Rin(t). Specifically, the C rate Rin(t) is obtained by dividing the battery current Ib(t) by the estimated charge capacity Cen(t) of battery 1n. In this embodiment, these steps S11 to S15 are repeated at predetermined time intervals to measure the battery temperature Tbn(t), battery voltage Vbn(t), and battery current Ib(t) of battery 1n, and to obtain the estimated charge capacity Cen(t) and C rate Rin(t).

[0074] Next, the procedure for the abnormal deterioration detection process will be described with reference to the flowcharts of Figures 7 and 8. This procedure for abnormal deterioration detection is performed at predetermined time intervals, separate from the measurement process described above. Note that the steps S21 to S2A described below together constitute a conforming discharge period detection step S20 that detects the occurrence of a conforming discharge period Dhn during which conforming discharge conforming to predetermined discharge conditions CD has occurred.

[0075] First, the SOC check step S21 corresponds to the sub-discharge condition CDa, and determines whether the current SOCCH(t) of the battery 1n obtained in the SOC calculation step S14 is within a predetermined range (CH(t)=60±5% in this embodiment). If the result is No, i.e., outside the range, the process returns to the SOC check step S21. On the other hand, if the result is Yes, i.e., within the range, the process proceeds to the subsequent battery temperature check step S22.

[0076] In the battery temperature check step S22, it is determined whether the current battery temperature Tbn(t) of the battery 1n obtained in the measurement step S11 is within a predetermined range (in this embodiment, Tbn(t)=25±5°C). If the result is No, i.e., outside the range, the process returns to the SOC check step S21. On the other hand, if the result is Yes, i.e., within the range, the process proceeds to the subsequent discharge rate check step S23.

[0077] In the discharge rate check step S23, it is determined whether the current C rate Rin(t) of the battery In obtained in the C rate calculation step S15 is within a predetermined C rate range for discharge (in this embodiment, Rin(t) = +30 ± 10 C). If the result is No, i.e., outside the range, the process returns to the SOC check step S21. On the other hand, if the result is Yes, i.e., within the range, the process proceeds to the subsequent test start step S24.

[0078] In the test start step S24, the current time t is stored as the start time ts and the timing of the test period DTn is started. However, if the timing of the test period DTn has already started, this test start step S24 is skipped.

[0079] In the subsequent average battery temperature calculation step S25, the average battery temperature TbnA, which is the average value during the verification period DTn, is calculated using the battery temperatures Tbn(t) obtained at each time point during the verification period DTn.

[0080] In the next average battery temperature check step S26, it is determined whether the obtained average battery temperature TbnA is within a predetermined temperature range (in this embodiment, TbnA = 20 to 30°C). If the answer is No, that is, if the average battery temperature TbnA is outside the temperature range, the verification period DTn is terminated and the process returns to the SOC check step S21. This is because the battery temperature is too low or too high, making it impossible to properly determine whether abnormal degradation has occurred. On the other hand, if the answer is Yes, that is, if it is within the range, the process proceeds to the next average C rate calculation step S27.

[0081] In the subsequent average C rate calculation step S27, the C rates Rin(t) obtained at each time point during the validation period DTn are used to calculate an average C rate RinA, which is the average value of these rates.

[0082] In the next average C rate check step S28, it is determined whether the obtained average C rate RinA is within a predetermined discharge C rate range (in this embodiment, RinA = +30 ± 10 C). If the result is No, i.e., outside the range, the calibration period DTn is terminated and the process returns to the SOC check step S21. This is because the discharge was not continued within the predetermined C rate range, making it impossible to properly determine whether abnormal degradation has occurred. On the other hand, if the result is Yes, i.e., within the range, the process proceeds to the next calibration period check step S29 via the connection point P1.

[0083] In the verification period check step S29, it is determined whether the length Ln of the verification period DTn from the start time ts has reached a predetermined duration DLn (in this embodiment, Ln≧10 sec=DLn). If the result is No, i.e., the predetermined duration DLn has not yet elapsed, the process returns to the average battery temperature calculation step S25 via the connection point P2. This is to continue the verification period DTn. On the other hand, if the result is Yes, i.e., the predetermined duration DLn has elapsed, the process proceeds to the subsequent verification end step S2A.

[0084] In the test termination step S2A, the current time t is stored as the end time te, and timing of the test period DTn is stopped. This test period DTn is set as the adapted discharge period Dhn, and it is assumed that the occurrence of the adapted discharge period Dhn, which begins at the start time ts and ends at the end time te, has been detected.

[0085] In the subsequent measured voltage drop amount acquisition step S31, the measured voltage drop amount ΔVrnA occurring during the detected adapted discharge period Dhn is obtained. Specifically, the measured voltage drop amount ΔVrnA is obtained in the same manner as the measured voltage drop amount acquisition unit 105 obtains the measured voltage drop amount ΔVrnA.

[0086] In the subsequent estimated voltage drop amount acquisition step S32, an estimated voltage drop amount ΔVen that is estimated to occur during the compatible discharge period Dhn if the detected battery 1n is not abnormally deteriorated is obtained using the estimated charge capacity Cen(t), the duration DLn of the compatible discharge period Dhn (DLn=10 seconds in this embodiment), the battery temperature Tbn(t) during the compatible discharge period Dhn, and the battery current Ib(t) that flowed during the compatible discharge period Dhn. Specifically, in the same way as the estimated voltage drop amount ΔVen was obtained by the estimated voltage drop amount acquisition unit 106, the estimated voltage drop amount ΔVen corresponding to the average C-rate RinA is obtained using the graph shown by the solid line in Figure 2.

[0087] Note that instead of the graph shown by the solid line in Figure 2, the estimated voltage drop ΔVen corresponding to the average C rate RinA may be calculated using a linear function FM (ΔVen = a RinA + b) in which the average C rate RinA shown in the graph is used as a variable. By using this linear function FM, it is possible to easily determine whether or not the battery In is abnormally degraded.

[0088] In the subsequent determination step S33, it is determined whether or not there is an abnormal voltage drop in the battery 1n from the measured voltage drop ΔVrnA obtained in the measured voltage drop amount obtaining step S31 and the estimated voltage drop ΔVen obtained in the estimated voltage drop amount obtaining step S32. First, in determination step S33, in deviation state acquisition step S33A, a deviation state index of the estimated voltage drop amount ΔVen and the measured voltage drop amount ΔVrnA is obtained. Specifically, a deviation amount Sren which is the difference between the measured voltage drop amount ΔVrnA and the estimated voltage drop amount ΔVen is obtained.

[0089] Subsequently, in deviation state determination step S33B, based on the deviation amount Sren which is the deviation state index obtained in deviation state acquisition step S33A, the presence or absence of abnormal degradation is determined. In the present embodiment, it is determined whether the deviation amount Sren is greater than or equal to a preset threshold deviation amount Sth. Here, if No, that is, when the deviation amount Sren is less than the threshold deviation amount Sth (Sren < Sth), the process proceeds to non-degradation processing step S34. On the other hand, if Yes, that is, when the deviation amount Sren is greater than or equal to the threshold deviation amount Sth (Sren ≧ Sth), the process proceeds to subsequent abnormal degradation processing step S35.

[0090] In non-degradation processing step S34, assuming that there is no abnormal degradation in battery 1n, the process returns to SOC check step S21 via connection point P3 to wait for the occurrence of a new adaptation discharge period Dhn.

[0091] In abnormal degradation processing step S35, assuming that abnormal degradation has occurred in battery 1n, predetermined processing for abnormal degradation is performed, such as processing similar to the processing in abnormal degradation processing unit 108, for example, correction processing in the direction of decreasing the SOC, remaining battery amount, and vehicle travelable distance. After that, the process returns to SOC check step S21 via connection point P3 to wait for the occurrence of a new adaptation discharge period Dhn.

[0092] Thus, according to the degradation state determination method of the present embodiment, it is possible to appropriately determine the presence or absence of degradation that causes an abnormal voltage drop in battery 1n. Also, in the present embodiment, in deviation state acquisition step S33A and deviation state determination step S33B of determination step S33, a deviation state index (deviation amount Sren) is calculated and used to determine the presence or absence of abnormal degradation, so the determination process is easy.

[0093] Although the present invention has been described above in accordance with the embodiments, it goes without saying that the present invention is not limited to the embodiments, and can be modified and applied as appropriate within the scope of the gist of the present invention. For example, in the embodiment, the estimated charge capacity Cen(t) is estimated by the capacity estimation unit 103, but it is also possible to first estimate the estimated charge capacity maintenance rate and then obtain the estimated charge capacity Cen(t) using the obtained estimated charge capacity maintenance rate.

[0094] In the above-described embodiment, an example was shown in which the battery 1 is a high-output battery 1 with a charge capacity of 5 Ah, which is primarily used in hybrid cars. However, the present invention can also be applied to cases in which a battery with a charge capacity (battery capacity) greater or less than this is used. The present invention can also be applied to cases in which a high-capacity battery primarily used in plug-in hybrid cars and battery-powered vehicles is used. Even when a high-capacity battery is used, the range of the average C rate RinA specified in the sub-discharge condition CDc should be set taking into account the magnitude of the discharge current that flows during, for example, sudden acceleration, and should be, for example, a range of 0.5 to 1.5 C. [Explanation of symbols]

[0095] 1,11,1n,1m battery (secondary battery) 2 Electrode body 3 Electrolyte Ce1(t),Cen(t),Cem(t) Estimated charging capacity Tb1(t),Tbn(t),Tbm(t) Battery temperature TbnA Average battery temperature Ib(t) Battery current Ri1(t),Rin(t),Rim(t) C-rate RinA Average C Rate FM linear function Vb1(t),Vbn(t),Vbm(t) Battery voltage VbnA Average battery voltage ΔVrn(t) Voltage drop ΔVrnA Actual voltage drop ΔVen Estimated voltage drop Sren deviation amount Sth Threshold deviation amount Dhn compatible discharge period DLn duration 100 Deterioration state determination system 101 Measuring section 102 Storage section 103 Capacity estimation part 104 Appropriate discharge period detection unit CD, CDa to CDd Discharge conditions 105 Actual voltage drop amount acquisition unit 106 Estimated voltage drop amount acquisition unit 107 Judgment section 107A Deviation state acquisition unit 107B Deviation state determination unit 108 Abnormal Deterioration Processing Unit S11 Measurement step S12 Measurement value storage step S13 Capacity estimation step S20 Compatible discharge period detection step S31: Step to obtain actual voltage drop S32 Estimated voltage drop amount acquisition step S33 Judgment step S33A Deviation state acquisition step S33B Deviation state judgment step S35 Abnormal Deterioration Treatment Step

Claims

1. A system for determining a deterioration state of a secondary battery that houses an electrode assembly impregnated with an electrolytic solution, a measurement unit for measuring a battery temperature, a battery current, and a battery voltage of the secondary battery; a memory unit that stores the measured battery temperature, battery current, and battery voltage in chronological order; a capacity estimation unit that estimates a current estimated charge capacity of the secondary battery; an adaptive discharge period detection unit that detects the occurrence of an adaptive discharge period during which adaptive discharge conforming to predetermined discharge conditions is performed using the battery temperature, the battery current, and the battery voltage; an actual voltage drop amount acquisition unit that acquires an actual voltage drop amount that occurred during the detected adapted discharge period using the battery voltage; an estimated voltage drop amount acquisition unit that acquires an estimated voltage drop amount that is estimated to occur during the adaptive discharge period using the estimated charge capacity, the duration of the adaptive discharge period, the battery temperature during the adaptive discharge period, and the battery current that flows during the adaptive discharge period; a determination unit that determines whether or not the secondary battery has abnormally deteriorated based on the actually measured voltage drop amount and the estimated voltage drop amount. A system for determining the deterioration state of secondary batteries.

2. 2. The secondary battery deterioration state determination system according to claim 1, The estimated voltage drop amount acquisition unit The estimated voltage drop amount is obtained by using a linear function obtained in advance with an average C rate obtained by dividing the battery current by the estimated charge capacity and averaging the C rate over the conforming discharge period as a variable. A system for determining the deterioration state of secondary batteries.

3. 3. The system for determining a deterioration state of a secondary battery according to claim 1, The determination unit a deviation state acquisition unit that acquires a deviation state index between the estimated voltage drop amount and the actually measured voltage drop amount; and a deviation state determination unit that determines whether or not the abnormal deterioration exists based on the acquired deviation state index. A system for determining the deterioration state of secondary batteries.

4. 3. The system for determining a deterioration state of a secondary battery according to claim 1, The conforming discharge performed during the conforming discharge period detected by the conforming discharge period detection unit is a high-current conforming discharge that causes an average battery current of 75 A or more to flow. A system for determining the deterioration state of secondary batteries.

5. A method for determining a deterioration state of a secondary battery containing an electrode assembly impregnated with an electrolytic solution, comprising: a measuring step of measuring a battery temperature, a battery current, and a battery voltage of the secondary battery; a measurement value storage step of storing the measured battery temperature, battery current, and battery voltage in chronological order; a capacity estimation step of estimating a current estimated charge capacity of the secondary battery; a conforming discharge period detection step of detecting the occurrence of a conforming discharge period in which conforming discharge conforming to predetermined discharge conditions is performed using the battery temperature, the battery current, and the battery voltage; an actual voltage drop amount acquisition step of acquiring an actual voltage drop amount that occurred during the detected adapted discharge period using the battery voltage; an estimated voltage drop amount acquisition step of acquiring an estimated voltage drop amount that is estimated to occur during the adaptive discharge period using the estimated charge capacity, the duration of the adaptive discharge period, the battery temperature during the adaptive discharge period, and the battery current that flows during the adaptive discharge period; and a determining step of determining whether or not the secondary battery has abnormally deteriorated based on the actually measured voltage drop amount and the estimated voltage drop amount. A method for determining the deterioration state of a secondary battery.

6. 6. The method for determining a deterioration state of a secondary battery according to claim 5, The estimated voltage drop amount acquisition step includes: A linear function is previously obtained using an average C rate obtained by dividing the battery current by the estimated charge capacity over the conforming discharge period as a variable, and the estimated voltage drop amount is obtained using the linear function. A method for determining the deterioration state of a secondary battery.

7. 7. The method for determining a deterioration state of a secondary battery according to claim 5 or 6, The determining step a deviation state acquisition step of acquiring a deviation state index between the estimated voltage drop amount and the actually measured voltage drop amount; and a deviation state determination step of determining whether or not the abnormal deterioration exists based on the obtained deviation state index. A method for determining the deterioration state of a secondary battery.

8. 7. The method for determining a deterioration state of a secondary battery according to claim 5 or 6, The conforming discharge performed during the conforming discharge period detected in the conforming discharge period detection step is a high-current conforming discharge that causes an average battery current of 75 A or more to flow. A method for determining the deterioration state of a secondary battery.

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