BATTERY DIAGNOSTIC DEVICE

Abstract

A battery diagnostic device (12) of the present invention comprises a current source (40) configured to apply a pulsed current to a battery (10), a voltage sensor (42) configured to detect a voltage between terminals of the battery (10), and a controller (54). The controller (54) comprises one or more processors (60) and one or more memories (62) coupled to the one or more processors (60).The one or more processors (60) are configured to perform processing comprising: detecting a voltage response obtained by applying the pulse current from the power source (40) to the battery (10); deriving, based on the voltage response, an index indicative of a comparison between an ON-ATRF and an OFF-ATRF, wherein the ON-ATRF is a function of an apparent contact resistance of the battery (10) when the pulse current is turned on and the OFF-ATRF is a function of an apparent contact resistance of the battery (10) when the pulse current is turned off; and determining a lithium deposition level in the battery (10) based on the derived index.

Description

Technical FieldThe present invention relates to a battery diagnostic apparatus for diagnosing a state of a battery.Prior ArtFor example, PTL 1 discloses a battery diagnostic apparatus for determining a degree of deterioration of a battery. Such a battery diagnostic apparatus detects a resistance value from a current and a voltage measured when a pulse current is applied to the battery, and determines the degree of deterioration of the battery from the resistance value.List of ReferencesPatent LiteraturePTL 1: Japanese Patent No. JP 6 991 616 B2Summary of the InventionTechnical ProblemIn lithium ion batteries, for example, there is a phenomenon that lithium deposits on the negative electrode with time. The lithium deposition may promote degradation and, in some cases, may result in thermal runaway of the battery. In order to detect such lithium deposits, the battery must be disassembled and the lithium deposit visually checked. Determination of the degree of deterioration such as lithium deposition requires much time, labor and cost.Accordingly, it is an object of the present invention to provide a battery diagnostic apparatus that can easily diagnose the deterioration of a battery.Solution of the ProblemIn order to solve the above-described problem, a battery diagnostic apparatus according to an embodiment of the present invention is a battery diagnostic apparatus for diagnosing the state of a battery, including:a power source configured to apply a pulse current to the battery;a voltage sensor configured to detect a voltage between terminals of the battery; anda control device.The controller includes:one or more processors; andone or more memories coupled to the one or more processors.The one or more processors are configured to perform processing comprising:detecting a voltage response obtained by applying the pulse current from the power source to the battery;deriving, based on the voltage response, an index indicating a comparison between an ON-ATRF and an OFF-ATRF, wherein the ON-ATRF is a function of an apparent transition resistance of the battery when switching on the pulse current, and the OFF-ATRF is a function of an apparent transition resistance of the battery when switching off the pulse current; anddetermining a lithium deposition degree in the battery based on the derived index.Advantageous Effects of the InventionAccording to the present invention, deterioration of a battery can be easily diagnosed.Brief Description of the DrawingsThe drawings show in: FIG. 1 is a schematic diagram showing a configuration of a battery diagnostic system according to the present embodiment. FIG. 2 is a diagram showing an example of a pulse current and a voltage response when substantially no lithium is deposited. FIG. 3 is a diagram showing an example of a relation between a specific time and an ON-ATRF, and an example of a relation between a specific time and an OFF-ATRF when substantially no lithium is deposited. FIG. 4 is a diagram showing an example of a pulse current and a voltage response when a large amount of lithium is deposited. FIG. 5 is a diagram showing an example of a relation between a specific time and an ON-ATRF, and an example of a relation between a specific time and an OFF-ATRF when a large amount of lithium is deposited. FIG. 6 is a diagram showing an example of a determination criteria table. FIG. 7 is a flowchart illustrating a process flow of a battery diagnostic apparatus.DESCRIPTION OF THE EMBODIMENTSHereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Specific dimensions, materials, numerical values, and the like illustrated in the embodiment are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations will be denoted by the same reference numerals, and redundant descriptions thereof will be omitted. Further, elements not directly related to the present invention are not illustrated in the drawings.FIG. 1 is a schematic diagram of a configuration of a battery diagnostic system 1 according to the present embodiment. The battery diagnostic system 1 includes a battery 10 and a battery diagnostic device 12.The battery 10 is, for example, a lithium ion battery. The battery 10 is mounted and used in, for example but not limited to, an electric vehicle or a hybrid electric vehicle. The battery 10 may be used in any electric device or the like.The battery 10 has two power terminals 20 and two voltage terminals 21. A first power terminal of the two power terminals 20 and a first voltage terminal of the two voltage terminals 21 of the battery 10 are coupled to a positive electrode of the battery 10. A second power terminal of the two power terminals 20 and a second voltage terminal of the two voltage terminals 21 of the battery 10 are coupled to a negative electrode of the battery 10.When lithium deposits on a negative electrode of a lithium ion battery, the deposited lithium prevents lithium ions in the solution from migrating into a graphite layer of the negative electrode or results in a side reaction on the surface of the graphite layer. Consequently, the performance of the lithium ion battery deteriorates. That is, the larger the amount of deposited lithium, the more deterioration of the battery 10 proceeds.The battery diagnostic device 12 is a device for diagnosing a state such as the degree of deterioration of the battery 10. For example, the battery diagnostic apparatus 12 is not mounted on a vehicle in which the battery 10 is mounted, and is managed by a mechanic repairing or inspecting the vehicle. However, the battery diagnostic apparatus 12 may be mounted in a vehicle in which the battery 10 is mounted.The battery diagnostic apparatus 12 includes two external power terminals 30, two external power terminals 31, two power cables 32, and two power cables 33.A first power cable of the two power cables 32 is coupled to a first external power terminal of the two external power terminals 30. An end of the first power cable that is farther from the first external power terminal may be electrically coupled to the first power terminal of the two power terminals 20 of the battery 10. A second power cable of the two power cables 32 is coupled to a second external power terminal of the two external power terminals 30. An end of the second power cable that is farther from the second external power terminal may be electrically coupled to the second power terminal of the two power terminals 20 of the battery 10.A first power cable of the two power cables 33 is coupled to a first external power terminal of the two external power terminals 31. An end of the first voltage cable that is farther from the first external voltage terminal may be electrically coupled to the first voltage terminal of the two voltage terminals 21 of the battery 10.A second power cable of the two power cables 33 is coupled to a second external power terminal of the two external power terminals 31. An end of the second voltage cable that is farther from the second external voltage terminal may be electrically coupled to the second voltage terminal of the two voltage terminals 21 of the battery 10.When the battery 10 is a battery that does not have voltage terminals 21, the voltage terminals 21 may be coupled to the same terminals as the power terminals 20.In this mode, the voltage terminals 21 are coupled to regions closer to the battery 10 than the power terminals 20, so that measurement accuracy equivalent in degree to that of the battery 10 having both the power terminals 20 and the voltage terminals 21 is achieved.The battery diagnostic apparatus 12 includes a power source 40, a voltage sensor 42, a temperature sensor 44, and an SOC adjuster 46. The SOC (State Of Charge) indicates a charge rate representing the ratio between the current charge capacity and the full charge capacity of the battery 10 and is expressed in percent.The power source 40 is electrically coupled to the two external power terminals 30. The current source 40 is configured to be able to generate a pulse current that is a pulsed current. The power source 40 is also configured to be able to change the current value of the pulse current to be generated.The power source 40 may apply a pulsed current to the battery 10 when the external power terminals 30 remain electrically coupled to the power terminals 20 of the battery 10 via the power cables 32.The voltage sensor 42 is electrically coupled to the two external voltage terminals 31. The voltage sensor 42 detects a voltage between the two external voltage terminals 31, that is, when the external voltage terminals 31 remain electrically coupled to the voltage terminals 21 of the battery 10 via the voltage cables 33, the voltage sensor 42 detects a voltage between the voltage terminals 21 of the battery 10.In the following description, the expression "the external power terminals 30 are electrically coupled to the power terminals 20 of the battery 10 via the power cables 32, and the external voltage terminals 31 are electrically coupled to the voltage terminals 21 of the battery 10 via the power cables 33" may be used as the expression "the battery diagnostic apparatus 12 is coupled to the battery 10" for convenience of description.The temperature sensor 44 detects the temperature of the battery 10. The temperature sensor 44 may be, for example, in contact with the battery 10 or disposed in close proximity to the battery 10 to appropriately detect the temperature of the battery 10.The SOC adjuster 46 is electrically connected between the two external power terminals 30. The SOC adjuster 46 is configured to be able to receive an output electric power from the battery 10 while the battery diagnostic apparatus 12 remains coupled to the battery 10. The SOC adjuster 46 is also configured to be able to supply electric power to the battery 10 while the battery diagnostic apparatus 12 remains coupled to the battery 10.That is, the SOC adjuster 46 may discharge the battery 10 to selectively reduce the SOC, and may also charge the battery 10 to selectively increase the SOC. The SOC adjuster 46 may be any electric device capable of charging and discharging the battery 10, such as a motor generator or a battery other than the battery 10.The battery diagnostic apparatus 12 includes an input / output device 50, a storage device 52, and a control device 54. The input / output device 50 includes an input device that receives an input operation of a user. Examples of the input device include a keyboard, a mouse, and a touch panel. The input / output device 50 also includes an output device that presents various kinds of information to a user. Examples of the output device include a display device that displays a diagnosis result.The storage device 52 is realized as a nonvolatile memory element such as a hard disk drive or a flash memory. The storage device 52 may store a diagnostic result or the like.The controller 54 includes one or more processors 60 and one or more memories 62 coupled to the processor(s) 60. The memory (or memories) 62 includes a ROM storing programs and the like and a RAM serving as a work area. The processor (or processors) 60 controls (or controls) the entire battery diagnostic apparatus 12 according to a program included in the memory (or memories) 62.The processor(s) 60 executes (or execute) a program, and also serves (or serve) as a voltage response detector 70, an index deriver 72, a determiner 74, a determination criteria presenter 76, and an SOC adjuster 78.In the following description, it is assumed that the battery diagnostic apparatus 12 has been coupled to the battery 10.The voltage response detector 70 causes the power source 40 to apply a pulse current to the battery 10. In response to application of a pulse current to the battery 10, a voltage is generated between the voltage terminals 21 of the battery 10. The voltage sensor 42 detects the voltage between the voltage terminals 21 of the battery 10. The voltage response detector 70 detects the voltage response detected by the voltage sensor 42.FIG. 2 is a diagram showing an example of a pulse current and a voltage response when practically no lithium is deposited. In FIG. 2, the time "τ" of the pulse width "W" is set to be, for example, 10 seconds or the like. However, the time "τ" of the pulse width "W" may be set as an arbitrary time. The symbol "Ip" indicates a current value of the pulse current.The symbol "TBon" indicates a rising start time of the pulse stream, i.e., the time of a rising edge of the pulse stream. The symbol "TBoff" indicates a falling start time of the pulse current, i.e., the time of a falling edge of the pulse current. The time "τ" indicates an application time of the pulse current when the rise start time "TBon" of the pulse current is set as 0. The time "t" indicates a certain time when the rise start time "TBon" of the pulse current is set as 0.When practically no lithium has deposited, the time for decreasing the voltage in response to turning off the pulse current is approximately the same as the time for increasing the voltage in response to turning on the pulse current.The symbol "Ton" indicates a time at which a specific time "Ts" has elapsed from the time "TBon" of a rising edge of the pulse stream. The symbol "Toff" indicates a time at which a specific time "Ts" has elapsed from the time "TBoff" of a falling edge of the pulse current. In other words, the time "Toff" is obtained from the addition of the specific time "Ts" to the time "τ" measured with respect to the time "TBon". It is assumed that the specific time "Ts" between the times "TBon" and "Ton" and the specific time "Ts" between the times "TBoff" and "Toff" are substantially the same.When the time at which the certain time "t" has elapsed from the time "TBon" is "Ton", the specific time "Ts" between the times "TBon" and "Ton" is equal to the time "t". When the time at which the certain time "t" has elapsed from the time "TBon" is "Toff", the specific time "Ts" between the times "TBoff" and "Toff" is equal to the time "t-τ".The symbol "V 0" indicates an open circuit voltage value of the battery 10. Here, it is assumed that the voltage value at the rise start time "TBon" of the pulse current is "V 0". The symbol "Off" indicates a voltage value detected by the voltage sensor 42 at the time "Ton". The symbol "V T" indicates a voltage value detected by the voltage sensor 42 at the fall start time "TBoff" of the pulse current. The symbol "Voff" indicates a voltage value detected by the voltage sensor 42 at the time "Toff".The current value of the pulse current and the voltage response obtained by applying the pulse current may be used to calculate a function of a impedance transition resistance (ATRF). The ATRF is a function indicating a temporal change in the value of the impedance in response to the pulse current being turned on and off.The value "of" indicating a voltage response obtained when the pulse current is turned on may be defined as indicated in the following equation (1).That is, the value "of" is obtained by subtracting the open circuit voltage value "V 0" at the time "TBon" from a voltage value at the time when the certain time "t" has elapsed from the time "TBon", for example, the voltage value "of" at the time "Ton" at which the specific time "Ts" has elapsed from the time "TBon". The value "Von" differs from the time "TBon" depending on the certain time "t" or the specific time "Ts".The ATRF based on the voltage response obtained when the pulse current is turned on may be referred to as ON-ATRF. ON-ATRF may be represented by "ATRFon(t)".As indicated in the following equation (2), ON-ATRF "ATRFon(t)" is derived by dividing the voltage response "from" obtained when the pulse current is turned on by the current value "Ip" of the pulse current.As described above, since the value "of" differs from the time "TBon" depending on the certain time "t", ATRFon(t) differs depending on the time "t" and is a function whose variable is the time "t". Since the specific time "Ts" between the times "TBon" and "Ton" corresponds to the time "t", ATRFon(t) can be regarded as a function whose variable is the specific time "Ts" between the times "TBon" and "Ton".The value "voff" indicating a voltage response obtained when the pulse current is cut off may be defined as indicated in the following equation (3).As described above, the specific time "Ts" between the times "TBoff" and "Toff" can be expressed by "t-τ" using the certain time "t" and the application time "τ" of the pulse current. The value "Vτ - Voff" is a difference value obtained by subtracting the voltage value at the time "t - τ", e.g., the value "Voff", from the voltage value "V T" at the time "TBoff". That is, the value "voff" is a voltage value minus the difference value. The value "voff" differs from the time "TBon" or the specific time "Ts" depending on the certain time "t".The ATRF, which is based on the voltage response obtained when the pulse current is turned off, may be referred to as OFF-ATRF. Off-ATRF may be represented by "ATRFoff(t-τ)".As indicated in the following equation (4), OFF-ATRF "ATRFoff(t-τ)" is derived by dividing the voltage response "voff" obtained when the pulse current is turned off by the current value "Ip" of the pulse current.As described above, since the value "voff" differs from the time "TBon" depending on the certain time "t", ATRFoff(t-τ) differs from the time "TBon" depending on the certain time "t", more specifically, depending on the time "t-τ", and is a function whose variable is the time "t" or the time "t-τ". Since the specific time "Ts" between the times "TBoff" and "Toff" corresponds to the time "t-τ", ATRFoff(t-τ) can be regarded as a function whose variable is the specific time "Ts" between the times "TBoff" and "Toff".FIG. 3 is a diagram showing an example of a relation between a specific time and an ON-ATRF, and an example of a relation between a specific time and an OFF-ATRF when practically no lithium has deposited.In FIG. 3, the horizontal axis represents time "t" as a solid line 100 and time "t-τ" as a broken line 102, i.e., specific time "Ts", and is represented on a logarithmic scale. The vertical axis represents the ON-ATRF or the OFF-ATRF. The solid line 100 indicates the relationship between the specific time and the ON-ATRF. The dashed line 102 indicates the relationship between the specific time and the OFF-ATRF.As shown in FIG. 3, the ON-ATRF and the OFF-ATRF are almost the same when a common specific time is given when practically no lithium has deposited.FIG. 4 is a diagram showing an example of a pulse current and a voltage response when a large amount of lithium is deposited.As illustrated in FIG. 4, when a large amount of lithium has deposited as compared with FIG. 2, the time for decreasing the voltage in response to the turning off of the pulse current is longer than the time for increasing the voltage in response to the turning on of the pulse current.FIG. 5 is a diagram showing an example of a relation between a specific time and an ON-ATRF, and an example of a relation between a specific time and an OFF-ATRF when a large amount of lithium has deposited.A solid line 110 indicates the relation between the specific time and the ON-ATRF. A broken line 112 indicates the relation between the specific time and the OFF-ATRF.As shown in FIG. 5, when a large amount of lithium has deposited as compared with FIG. 3, the ON-ATRF and the OFF-ATRF deviate from each other when a common specific time is given.Accordingly, the index deriver 72 shown in FIG. 1 derives an index indicating a comparison between the ON-ATRF and the OFF-ATRF based on the voltage response.It is assumed that, as indicated in Equation (5) below, for example, the index described above is a resistance function ratio "RR(Ts)" indicating the ratio of the OFF-ATRF "ATRFoff(t-τ)" to the ON-ATRF "ATFRon(t)". It is assumed that the specific time "Ts" for "ATRFoff(t-T)" and the specific time "Ts" for "ATRFon(t)"used for deriving the resistance duty ratio "RR(Ts)" are the same.The index deriver 72 derives multiple indices having different specific times, e.g., multiple resistor function ratios. For example, the index deriver 72 derives the resistance function ratios "RR(0.05)", "RR(0.089)", "RR(0.16)", "RR(0.28)", and "RR(0.5)" for which the specific time "Ts" is "0.05 sec", "0.089 sec", "0.16 sec", "0.28 sec", and "0.5 sec", respectively. The specific time is not limited to the times shown in the above-described example, but may be set as any time within a range not exceeding the pulse width of the pulse current. Further, the number of resistance function ratios is not limited to the five mentioned in the above-described example, but may be any number.The determiner 74 determines the lithium deposition degree indicating the deterioration degree of the battery 10 based on an average value of the indices, e.g., an average value of the resistance function ratios. The averaged value of the resistance function ratios may be referred to as an averaged resistance function ratio below.The memory (or memories) 62 stores (or store) a determination criteria table in advance. The determination criteria table indicates determination criteria for determining the lithium deposition degree in the battery 10. The determiner 74 determines the lithium deposition degree in the battery 10 by using the determination criteria table and the average resistance function ratio.FIG. 6 is a diagram showing an example of a determination criteria table. In the determination criteria table, a range for the average resistance function ratio is associated with a numerical value of a SLDT (State of Li Deposition Latency). The SLDT represents the state of tendency to deposit lithium, and is an index for determining how easily lithium deposits.In the SLDT, the lithium deposition degree in the battery 10 is divided into, for example, a plurality of stages. The larger the numerical value of the SLDT, the larger the amount of depositing lithium, i.e., the higher the rate of use of the charging current associated with the deposition reaction of lithium. The numerical value "0" of the SLDT means that practically no lithium deposition occurs in response to application of a charging pulse current value having a certain value.As illustrated in FIG. 6, in the determination criteria table, ranges for the average resistance function ratio and numerical values of the SLDT are associated with each other such that the numerical value of the SLDT increases as the average resistance function ratio decreases. For example, when the average resistance function ratio "0.68" is obtained, the determiner 74 determines the SLDT "3" from the determination criteria table.Further, the voltage response detector 70 applies a plurality of pulse currents having different current values to the battery 10 in a stepwise manner to detect voltage responses for the corresponding current values. For example, the voltage response detector 70 increases the current value of the pulse current in stages to obtain pulse currents of "0.1 C", "0.3 C", "0.5 C", and "1 C" in this order. A C rate "C" indicates the ratio of the charge / discharge current value to the battery capacity (charge / discharge current value (A) / battery capacity (Ah)).The index deriver 72 derives indices for the respective current values based on the voltage responses for the respective current values. For example, the index deriver 72 derives the average resistance function ratio for "0.1 C", the average resistance function ratio for "0.3 C", the average resistance function ratio for "0.5 C", and the average resistance function ratio for "1 C".The determiner 74 determines the lithium deposition degrees in the battery 10 based on the corresponding indices for the current values. For example, the determiner 74 determines the SLDT corresponding to the averaged resistance function ratio for "0.1 C", the SLDT corresponding to the averaged resistance function ratio for "0.3 C", the SLDT corresponding to the averaged resistance function ratio for "0.5 C", and the SLDT corresponding to the averaged resistance function ratio for "1 C". The SLDT for each current value may be referred to as a current value specific SLDT hereinafter for convenience of description.The determiner 74 combines the determined current value specific SLDTs to determine the SLDT of the lithium deposition degree in the battery as a final determination result. The SLDT as a final determination result may be referred to as an overall SLDT below for convenience of description. For example, the determiner 74 may specify an averaged value of the current value-specific SLDTs as the total SLDT. Alternatively, the determiner 74 may set a median value of the current value-specific SLDTs as a total SLDT.In the battery diagnostic apparatus 12 according to the present embodiment, the lithium deposition degree in the battery is determined based on an index indicating a comparison between an ON-ATRF and an OFF-ATRF. Consequently, the lithium deposition degree can be easily recognized.The resistance function ratio derived from the voltage response depends on the temperature of the battery 10. For example, when the temperature of the battery 10 is relatively low, the resistance function ratio is lower than that at a relatively high temperature of the battery 10.Accordingly, the determination criteria presenter 76 illustrated in FIG. 1 obtains the temperature of the battery 10 from the temperature sensor 44 before the pulse current is applied to the battery 10.In the memory (or memories) 62, for example, respective determination criteria tables for each temperature of the battery 10 are stored in advance. The determination criteria presenter 76 selects a determination criteria table corresponding to the detected temperature of the battery 10 from the determination criteria tables.The determiner 74 compares the determined determination criterion with the index indicating the comparison between the ON-ATRF and the OFF-ATRF to determine the lithium deposition degree in the battery. For example, the determiner 74 uses the determination criteria table selected by the determination criteria presenter 76 and the averaged resistance function ratio derived by the index deriver 72 to determine the SLDT.Since an appropriate determination criterion is determined based on the temperature of the battery 10, the battery diagnostic apparatus 12 can more accurately determine the lithium deposition degree.The resistance function ratio derived from the voltage response changes depending on the SOC of the battery. Accordingly, the SOC of the battery is set to be approximately the same at each diagnosis.More specifically, when the SOC of the battery 10 is outside a predetermined range predetermined in advance, the SOC adjuster 78 causes the SOC adjuster 46 to adjust the SOC of the battery 10 so that the SOC of the battery 10 falls within the predetermined range before applying the pulse current to the battery 10. The predetermined range is, for example, but not limited to, a range of predetermined faults including an SOC of 50%. The predetermined range may be any range.For example, when the SOC of the battery 10 is greater than the upper limit of the predetermined range, the SOC adjuster 78 causes the SOC adjuster 46 to serve as a load and transfers the electric power of the battery 10 to the SOC adjuster 46 to reduce the SOC of the battery 10. When the SOC of the battery 10 is lower than the lower limit of the predetermined range, the SOC adjuster 78 causes the SOC adjuster 46 to serve as a power source and transmits the electric power of the SOC adjuster 46 to the battery 10 to increase the SOC of the battery 10.Since the SOC of the battery 10 is adjusted selectively before diagnosis is performed, the battery diagnostic device 12 can determine the lithium deposition degree more accurately.FIG. 7 is a flowchart illustrating a process flow in the battery diagnostic device 12. When the battery diagnostic apparatus 12 is coupled to the battery 10 and receives an input operation to give an instruction to start diagnosis, a series of processing operations illustrated in FIG. 12 is started.First, the SOC adjuster 78 derives the current SOC value of the battery 10 (S 10). For example, the SOC adjuster 78 acquires the current voltage from the voltage sensor 42 and estimates the current SOC value of the battery 10 from the acquired current voltage.Then, the SOC adjuster 78 determines whether the current SOC value is within a predetermined range (S 11). When the current SOC value is outside the predetermined range (NO in S 11), the SOC adjuster 78 causes the SOC adjuster 46 to selectively adjust the SOC value so that the SOC value of the battery falls within the predetermined range (S 12).Then, the SOC adjuster 46 proceeds to the processing of step S 13. When the current SOC value is within the predetermined range (YES in S 11), the SOC adjuster 46 directly proceeds to the processing of step S 13.In step S 13, the determination criteria presenter 76 acquires the temperature of the battery 10 from the temperature sensor 44 (S 13). The determination criteria presenter 76 presents a determination criterion based on the detected temperature of the battery (S 14).Then, the voltage response detector 70 determines the current value of the pulse current to be applied from candidate current values (S 15). The voltage response detector 70 causes the current source 40 to apply a pulse current having the determined voltage value to the battery (S 16).The voltage response detector 70 detects a voltage response detected by the voltage sensor 42 in parallel with application of the pulse current (S 17). The voltage response detector 70 may store the detected voltage response in the memory (or the memories) 62 or the storage device 52.Then, the index deriver 72 derives an ON-ATRF based on the voltage response obtained when the pulse current is turned on (S 18). The index diverter 72 also derives an OFF-ATRF based on the voltage response obtained when the pulse current is turned off (S 19). At this time, the index deriver 72 may check whether the ON-ATRF and the OFF-ATRF are obviously abnormal values.When it is determined that the ON-ATRF or the OFF-ATRF is an abnormal value, the derivation of the resistance function ratio, the determination of the current value specific SLDT, and the like may be omitted, and the ON-ATRF or the OFF-ATRF, which is an abnormal value, may be excluded from the target value from which the total SLDT is to be derived.Then, the index deriver 72 divides the OFF-ATRF by the ON-ATRF to derive a resistance function ratio (S 20). At this time, the index deriver 72 uses the OFF-ATRF and the ON-ATRF having a common specific time to derive the resistance function ratio at the specific time.Further, the index deriver 72 derives resistance function ratios for a plurality of specific times to derive a plurality of resistance function ratios. Then, the index deriver 72 averages the plurality of resistance function ratios by the number of resistance function ratios to derive an averaged resistance function ratio (S 21).Then, the determiner 74 determines a current value specific SLDT for the current current current value determined in step S 15, based on the determination criterion predetermined in step S 14 and the averaged resistance function ratio derived in step S 21 (S 22). The determiner 74 may store the determined current value specific SLDT in the memory (or the memories) 62 or the storage device 52.Then, the determiner 74 determines whether a measurement completion condition is satisfied (S 23). For example, when the determination of the current value specific SLDT for all the candidate current values is completed, the determiner 74 determines that the measurement completion condition is satisfied. The measurement completion condition is not limited to this example, and any condition may be set.When the measurement completion condition is not satisfied (NO in S 23), the determiner 74 returns to step S 15, and determines any current value among the candidate current values for which the determination of the current value specific SLDT is not completed (S 15). Then, the battery diagnostic apparatus 12 executes the processing of step S 16 and the subsequent steps again.When the measurement completion condition is satisfied (YES in S 23), the determiner 74 combines the current value specific SLDTs determined for the respective current values and determines a total SLDT (S 24). The total SLDT is notified from the determiner 74 as a diagnosis result (S 25).Then, the series of processing operations ends. For example, the determiner 74 causes the display device of the input / output device to display the whole SLDT as a diagnosis result. The notification method is not limited to this example. Any method that allows the user to recognize the diagnostic result appropriately may be used.As described above, in the battery diagnostic apparatus 12 according to the present embodiment, the lithium deposition degree in the battery 10 is determined based on an index indicating a comparison between an ON-ATRF obtained when the pulse current is turned on and an OFF-ATRF obtained when the pulse current is turned off.For the above-described determination, the battery 10 does not need to be disassembled, and thus the battery diagnostic apparatus 12 according to the present embodiment can easily diagnose a lithium deposit indicative of deterioration of the battery 10.The index indicating the comparison between the ON-ATRF and the OFF-ATRF changes according to the lithium deposition in the lithium ion battery. The battery diagnostic apparatus 12 according to the present embodiment is configured to perform diagnosis by using an index related to lithium deposition. Thus, the lithium deposition degree can be clearly indicated.Further, the battery diagnostic apparatus 12 according to the present embodiment can non-destructively diagnose the battery 10 and can save the labor and cost for disassembling the battery 10. Further, with the battery diagnostic apparatus 12 according to the present embodiment, the battery 10 in which the lithium deposition degree is low can be easily reused, for example.Further, in the battery diagnostic apparatus 12 according to the present embodiment, the time required for the diagnosis of the battery 10 is short because the time required for the pulse current to be turned on and off is short. Consequently, a diagnostic result can be obtained quickly.Further, in the battery diagnostic apparatus 12 according to the present embodiment, a resistance function ratio indicating the ratio between the OFF-ATRF and the ON-ATRF is used as an index indicating the comparison between the ON-ATRF and the OFF-ATRF. Thus, the battery diagnostic apparatus 12 according to the present embodiment can easily and accurately diagnose the lithium deposition in the battery 10.In the battery diagnostic apparatus 12 according to the present embodiment, the index indicates a comparison between an ON-ATRF at a time when a specific time has elapsed from the time of a rising edge of the voltage in response to the pulse current being turned on and an OFF-ATRF at a time when a specific time has elapsed from the time of a falling edge of the voltage in response to the pulse current being turned off.That is, the battery diagnostic apparatus 12 according to the present embodiment compares the ON-ATRF and the OFF-ATRF at a time when the specific time for the ON-ATRF and the specific time for the OFF-ATRF are substantially equal. Thus, the battery diagnostic apparatus 12 according to the present embodiment can accurately determine the lithium deposition degree in the battery 10.In the battery diagnostic apparatus 12 according to the present embodiment, the lithium deposition degree in the battery 10 is further determined based on an averaged value of indices having different specific times. Thus, the battery diagnostic apparatus 12 according to the present embodiment can reduce an error between the indexes and more accurately determine the lithium deposition degree in the battery 10.In the battery diagnostic apparatus 12 according to the present embodiment, the lithium deposition degree in the battery 10 is further determined based on respective indices for current values of the pulse current. Thus, the battery diagnostic apparatus 12 according to the present embodiment can more accurately determine the lithium deposition degree in the battery 10.Further, in the battery diagnostic apparatus 12 according to the present embodiment, the SOC is adjusted so that the SOC falls within a predetermined range before the application of the pulse current. Thus, the battery diagnostic apparatus 12 according to the present embodiment can more accurately determine the lithium deposition degree in the battery 10.In the battery diagnostic apparatus 12 according to the present embodiment, a determination criterion is further determined based on the temperature of the battery before the application of the pulse current. Thus, the battery diagnostic apparatus 12 according to the present embodiment can more accurately determine the lithium deposition degree in the battery 10.In the above-described embodiment, the resistance function ratio, i.e., the ratio between the OFF-ATRF and the ON-ATRF is used as an index indicating the comparison between the ON-ATRF and the OFF-ATRF. However, the index is not limited to the resistance function ratio.For example, in the above-described embodiment, the equations (2) and (4) have the common feature that the voltage response is divided by the pulse current Ip.In view of this, the lithium deposition degree in the battery 10 may also be determined based on a voltage ratio that is the ratio between the voltage response "voff" obtained when the pulse current is turned off and the voltage response "off" obtained when the pulse current is turned on, instead of based on the resistance duty ratio.As described with reference to FIG. 5, when a large amount of lithium has deposited, the ON-ATRF and the OFF-ATRF deviate from each other. This divergence may be represented by an absolute value of the difference between the ON-ATRF and the OFF-ATRF, rather than the resistance function ratio. That is, the index indicating the comparison between the ON-ATRF and the OFF-ATRF may be the absolute value of the difference between the ON-ATRF and the OFF-ATRF when a common specific time is given.However, when the absolute value of the difference between the ON-ATRF and the OFF-ATRF is used as an index, the error caused by a change in the ON-ATRF or the OFF-ATRF may be larger than when the resistance duty ratio is used. That is, the mode in which the resistance function ratio is used offers more accurate determination than the mode in which the absolute value of the difference is used.Further, in the above-described embodiment, a plurality of resistance function ratios are averaged to derive an averaged resistance function ratio for a current value. The index deriver 72 may also easily derive at least one resistance function ratio for a current value, and the derivation of an averaged resistance function ratio may be omitted. In this case, the index deriver 72 may determine a current value specific SLDT from a resistance function ratio and a determination criteria table.Further, in the above-described embodiment, an average resistance function ratio for a plurality of current values is derived. However, the index deriver 72 may derive an average resistance function ratio or a resistance function ratio for only one current value.Further, in the above-described embodiment, the SOC of the battery 10 is adjusted before the application of the pulse current. However, respective determination criteria tables may be prepared for a plurality of SOCs to omit the adjustment of the SOC.Although an embodiment of the present invention has been described with reference to the accompanying drawings, the present invention is by no means limited to this embodiment. It will be apparent to those skilled in the art that changes and modifications can be made unless they depart from the scope defined by the appended claims, and that such changes and modifications also fall within the technical scope of the present invention.List of reference characters10 Battery 12 Battery diagnostic apparatus 40 Power source 42 Voltage sensor 46 SOC adjuster 54 Controller 60 Processor 62 Memory 70 Voltage response detector 72 Index deriver 74 Determiner 76 Determination criteria presenter 78 Soc adjusterReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 6 991 616 B2

[0003]

Claims

A battery diagnostic apparatus for diagnosing the state of a battery, the battery diagnostic apparatus comprising: - a power source configured to apply a pulse current to the battery; - a voltage sensor configured to detect a voltage between terminals of the battery; and - a controller, wherein the controller comprises: - one or more processors; and - one or more memories coupled to the one or more processors, and wherein the one or more processors are configured to perform processing comprising: - detecting a voltage response obtained by applying the pulse current from the power source to the battery; deriving, based on the voltage response, an index indicating a comparison between an ON-ATRF and an OFF-ATRF, wherein the ON-ATRF is a function of an apparent transition resistance of the battery when switching on the pulse current and the OFF-ATRF is a function of an apparent transition resistance of the battery when switching off the pulse current; and determining a lithium deposition level in the battery based on the derived index.The battery diagnostic apparatus according to claim 1, wherein the index is a resistance function ratio indicating a ratio of the OFF-ATRF to the ON-ATRF.The battery diagnostic apparatus according to claim 1 or 2, wherein the index indicates a comparison between the ON-ATRF at a time when a specific time has elapsed from a time of a rising edge of a voltage in response to the turning-on of the pulse current and the OFF-ATRF at a time when the specific time has elapsed from a time of a falling edge of the voltage in response to the turning-off of the pulse current.The battery diagnostic apparatus according to claim 3, wherein the one or more processors are configured to, when deriving the index, execute processing including deriving a plurality of the indices having different specific times, and wherein the one or more processors are configured to, when determining the lithium deposition degree in the battery, execute processing including determining the lithium deposition degree in the battery based on an averaged value of the plurality of indices.The battery diagnostic apparatus according to claim 1 or 2, wherein the one or more processors are configured to, when detecting the voltage response, execute processing including applying a plurality of pulse currents having different current values to the battery in stages to detect the voltage response for each of the current values, wherein the one or more processors are configured to, when deriving the index, execute processing including deriving the index for each of the current values based on the voltage response for the current value, and wherein the one or more processors are configured to, when determining the lithium deposition degree in the battery, execute processing including determining the lithium deposition degree in the battery based on a plurality of the corresponding indices for the current values.The battery diagnostic apparatus according to claim 1 or 2, further comprising an SOC adjuster configured to adjust an SOC value of the battery, wherein the one or more processors are configured to perform processing comprising: causing, when the SOC of the battery is outside a predetermined range predetermined in advance, the SOC adjuster to adjust the SOC of the battery such that the SOC of the battery falls within the predetermined range before applying the pulse current to the battery.The battery diagnostic apparatus according to claim 1 or 2, wherein the one or more processors are configured to execute processing including determining a determination criterion for determining the lithium deposition degree in the battery based on a temperature of the battery before applying the pulse current to the battery, and wherein the one or more processors are configured to, when determining the lithium deposition degree in the battery, execute processing including comparing the determined determination criterion with the index to determine the lithium deposition degree in the battery.

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