Battery diagnosis device, battery diagnosis method, battery pack, and electric vehicle

Abstract

A battery diagnostic apparatus according to the present application includes a voltage sensor that generates a voltage signal indicative of a battery voltage of a battery, a current sensor that generates a current signal indicative of a battery current flowing through the battery, and a control circuit. The control circuit determines a measured capacity curve within a predetermined set voltage range based on the voltage signal and the current signal collected per unit time within a constant current period in which the battery is charged or discharged at a predetermined current rate throughout the set voltage range. The control circuit determines a measured differential curve within the set voltage range based on the measured capacity curve. The control circuit compares the measured differential curve with a reference differential curve to determine whether a negative electrode curvature of the battery is abnormally increased.

Description

TECHNICAL FIELD

[0001] This application claims the benefit of Korean Patent Application No. 10-2020-0185698, filed December 29, 2020, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

[0002] The disclosure relates to a technology for diagnosing abnormal degradation of a battery. BACKGROUND

[0003] Recently, the demand for portable electronic products such as laptop computers, camcorders, and mobile phones has rapidly increased, and with the widespread development of electric vehicles, accumulators for energy storage, robots, and satellites, much research is being conducted on high-performance batteries that can be repeatedly recharged.

[0004] Currently, commercially available batteries include nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, lithium-ion batteries, and the like, and among them, lithium-ion batteries have little or no memory effect, and thus they are gaining more attention than nickel-based batteries because the advantages of lithium-ion batteries are that recharging can be performed at any time when it is convenient, the self-discharge rate is very low, and the energy density is high.

[0005] A battery gradually deteriorates over time due to charging, discharging, and resting since the product is released. The deterioration of the battery occurs in various aspects such as a decrease in the maximum allowable charge capacity and an increase in internal resistance.

[0006] One of the reasons for the increase in internal resistance is an increase in tortuosity of the negative electrode of the battery. The tortuosity of the negative electrode is a parameter indicating how much the flow path of the reactant ions in the negative electrode is bent. In the disclosure, when the reactant ions pass through the negative electrode active material layer, the tortuosity of the negative electrode can be defined as the ratio of the actual moving distance of the reactant ions to the shortest moving distance (the thickness of the negative electrode active material layer). When the battery is a lithium-ion battery, the reactant ions are lithium ions.

[0007] The deterioration of the battery causes the tortuosity of the negative electrode to increase, and as the tortuosity of the negative electrode increases, the battery deteriorates faster due to the non-uniform charging / discharging reaction at the negative electrode. SUMMARY

[0008] TECHNICAL PROBLEM

[0009] The inventors recognized that a capacity curve indicating the relationship between the voltage and the remaining capacity of the battery changes due to the increase in the tortuosity of the negative electrode of the battery.

[0010] The present disclosure is designed to solve the above problems, and relates to providing a battery diagnosis apparatus, a battery diagnosis method, a battery pack, and an electric vehicle, in which a capacity curve of a battery that has deteriorated from a fresh condition is obtained through a constant current process and / or a constant current charging process, and the capacity curve is used to determine whether a curvature of a negative electrode of the battery is abnormally increased.

[0011] These and other objects and advantages of the present disclosure can be understood from the following description, and will be apparent from the embodiments of the present disclosure. Also, it will be easily understood that the objects and advantages of the present disclosure can be realized by means recited in the claims and combinations thereof.

[0012] Technical Solution

[0013] A battery diagnosis apparatus according to one aspect of the present disclosure includes a voltage sensor configured to measure a battery voltage across a battery and to generate a voltage signal indicative of the measured battery voltage, a current sensor configured to measure a battery current flowing through the battery and to generate a current signal indicative of the measured battery current, and a control circuit configured to collect the voltage signal and the current signal at each unit time. The control circuit is configured to determine a measured capacity curve indicative of a relationship between the battery voltage and a remaining capacity in a predetermined set voltage range based on the voltage signal and the current signal collected at each unit time for a constant current period during which the battery is charged or discharged at a predetermined current rate in the set voltage range. The control circuit is configured to determine a measured differential curve indicative of a relationship between the battery voltage and a differential capacity in the set voltage range based on the measured capacity curve. The differential capacity is a ratio of a change in the remaining capacity per unit time to a change in the battery voltage per unit time. The control circuit is configured to determine whether a negative electrode curvature of the battery is abnormally increased by comparing the measured differential curve with a reference differential curve. The reference differential curve is given as a relationship between the battery voltage and the differential capacity in the set voltage range when the battery is in a fresh condition.

[0014] The control circuit can be configured to determine an approximate measured capacity curve by fitting the measured capacity curve to a polynomial function. The control circuit can be configured to determine the measured differential curve by differentiating the remaining capacity with respect to the battery voltage of the approximate measured capacity curve.

[0015] The control circuit can be configured to determine a first voltage of interest that is a voltage at which a magnitude of a difference in differential capacity between the measured differential curve and the reference differential curve is a maximum. The control circuit can be configured to determine a signal distance between the measured differential curve and the reference differential curve over a range of voltages of interest from the first voltage of interest to a second voltage of interest that is greater than the first voltage of interest. The control circuit can be configured to determine that the negative curvature of the battery is abnormally increased when the signal distance is equal to or greater than a reference distance.

[0016] The control circuit can be configured to determine the second voltage of interest to be equal to a lesser of a sum of the first voltage of interest and a reference voltage and an upper limit on voltage.

[0017] The control circuit can be configured to determine the signal distance using dynamic time warping.

[0018] The control circuit can be configured to determine a cumulative charge / discharge capacity of the battery over a total duration of use of the battery. The control circuit can be configured to determine the reference distance based on the cumulative charge / discharge capacity.

[0019] The control circuit can be configured to determine the reference distance using the following equation:

[0020] <equation>

[0021]

[0022] (where m is a predetermined natural number, C[i] is an ith predetermined positive coefficient, x is the cumulative charge / discharge capacity, and y is the reference distance).

[0023] A battery pack according to another aspect of the present disclosure includes a battery diagnostic device.

[0024] An electric vehicle according to yet another aspect of the present disclosure includes a battery pack.

[0025] A battery diagnosis method according to still another aspect of the disclosure can be performed by a battery diagnosis device. The battery diagnosis method includes the steps of determining a measured capacity curve indicating a relationship between a battery voltage and a remaining capacity at a predetermined set voltage range based on the voltage signal and the current signal collected per unit time during a constant current period during which the battery is charged or discharged at a predetermined current rate within the set voltage range; determining a measured differential curve indicating a relationship between the battery voltage and a differential capacity within the set voltage range based on the measured capacity curve, wherein the differential capacity is a ratio of a change in the remaining capacity per unit time to a change in the battery voltage per unit time; and determining whether a negative electrode curvature of the battery is abnormally increased by comparing the measured differential curve with a reference differential curve, wherein the reference differential curve is given as a relationship between the battery voltage and the differential capacity within the set voltage range when the battery is in a factory state.

[0026] Advantageous Effects

[0027] According to at least one of the embodiments of the disclosure, it can be determined whether the curvature of the negative electrode of the battery is abnormally increased using the capacity curve obtained through the constant current process and / or the constant current charging process for the battery that has deteriorated from the factory state.

[0028] According to at least one of the embodiments of the disclosure, it can be determined whether the curvature of the negative electrode of the deteriorated battery is abnormally increased based on similarity (meaning'signal distance' described below) between a differential curve corresponding to the capacity curve obtained from the deteriorated battery and another differential curve associated with the factory state within a certain voltage range.

[0029] According to at least one of the embodiments of the disclosure, a reference value (meaning'reference distance' described below) for determining whether the curvature of the negative electrode of the deteriorated battery is abnormally increased can be set based on the cumulative charge / discharge capacity of the deteriorated battery.

[0030] Effects of the disclosure are not limited to the above-mentioned effects, and these and other effects not mentioned herein will be clearly understood by those skilled in the art from the attached claims based on the disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings illustrate preferred embodiments of the disclosure and, together with the detailed description of the disclosure below, provide further understanding of the technical aspects of the disclosure, and therefore the disclosure should not be construed as being limited to the drawings.

[0032] Figure 1 is a schematic view showing an electric vehicle according to the disclosure.

[0033] Figure 2 is a schematic diagram showing a capacity curve obtained by a constant current process of the battery shown in Figure 1

[0034] Figure 3 is a schematic diagram showing a differential curve associated with the capacity curve shown in Figure 2 Figure 4 is a schematic diagram showing a differential capacity difference between the differential curves shown in Figure 3

[0035] Figure 5 is an exemplary flowchart showing a battery diagnosis method that can be executed by the battery diagnosis apparatus shown in Figure 1

[0036] Figure 6 is an exemplary flowchart showing a sub-step of step S540 of Figure 5 DETAILED DESCRIPTION

[0037] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Before the description, it is to be understood that the terminology or the word used in the specification and the appended claims should not be interpreted as being limited to commonly used meanings and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to define the terms appropriately based on the best possible interpretation. Accordingly, it should be understood that the terms or words should be interpreted on the basis of the technical meanings and concepts of the present disclosure.

[0038] Accordingly, the embodiments described herein and the diagrams shown in the accompanying drawings are merely the most preferred embodiments of the present disclosure, but are not intended to describe the technical aspects of the present disclosure completely, and thus it should be understood that various other equivalents and modifications can be made thereto at the time of filing the application.

[0039] The terms including ordinal numbers (such as "first," "second," etc.) are used to distinguish one element from another element among various elements, but are not intended to limit the elements by the terms.

[0040] Unless the context clearly indicates otherwise, it will be understood that the term "comprise" used in the present specification designates the presence of stated elements but does not exclude the presence or addition of one or more other elements. In addition, the term "control unit" as used herein refers to at least one processing unit of a function or operation, and can be implemented by hardware and software, individually or in combination.

[0041] In addition, throughout the specification, it will be further understood that when an element is referred to as being "connected to" another element, it can be directly connected to the other element, or there can be an intervening element.

[0042] Figure 1 ​​​​​is a schematic diagram showing an electric vehicle according to the present disclosure.

[0043] Reference Figure 1 The electric vehicle 1 includes a battery pack 2, an inverter 3, an electric motor 4, a charge / discharge circuit 5, and a vehicle controller 6.

[0044] The battery pack 2 includes a battery B, a switch SW, and a battery management system 100.

[0045] The battery B can be coupled to the inverter 3 and / or the charge / discharge circuit 5 through a pair of power terminals provided in the battery pack 2. The battery B is a rechargeable battery, and can be, for example, a lithium-ion battery.

[0046] The inverter 3 is provided to convert direct current (DC) from the battery B into alternating current (AC) in response to a command from the battery management system 100. The electric motor 4 can be, for example, a 3-phase AC motor. The electric motor 4 operates using the AC from the inverter 3.

[0047] The switch SW is connected in series with the battery B. The switch SW is installed on a current path for charge / discharge of the battery B. On / off control of the switch SW is performed in response to a switch signal from the battery management system 100. The switch SW can be a mechanical relay that is turned on / off by magnetic force through a coil or a semiconductor switching device such as a metal oxide semiconductor field effect transistor (MOSFET).

[0048] The charge / discharge circuit 5 is provided to regulate charge power and discharge power of the battery B in response to a command from a control circuit 230. When a battery voltage of the battery B is equal to or lower than a voltage lower limit V L of a set voltage range as described below, the control circuit 230 can command the charge / discharge circuit 5 to charge at a constant current. When the battery voltage of the battery B is equal to or higher than a voltage upper limit V U of the set voltage range, the control circuit 230 can command the charge / discharge circuit 5 to discharge at a constant current.

[0049] The battery management system 100 is provided to be in charge of overall control relating to charge / discharge of the battery B. The battery management system 100 includes a battery diagnosis device 200. The battery management system 100 can also include at least one of a temperature sensor 310 or a communication circuit 320. Hereinafter, it is assumed that the battery management system 100 includes the battery diagnosis device 200, the temperature sensor 310, and the communication circuit 320.

[0050] The battery diagnosis device 200 includes a voltage sensor 210, a current sensor 220, and the control circuit 230.

[0051] The voltage sensor 210 is connected in parallel to the battery B and is configured to detect a battery voltage across the battery B and generate a voltage signal indicative of the detected battery voltage.

[0052] The current sensor 220 is connected in series to the battery B through a current path. The current sensor 220 is configured to detect a battery current flowing through the battery B and generate a current signal indicative of the detected battery current.

[0053] The temperature sensor 310 is configured to detect a temperature of the battery B and generate a temperature signal indicative of the detected temperature.

[0054] The control circuit 230 can be implemented in hardware using at least one of an application specific integrated circuit (ASIC), a digital signal processor (DSP), a digital signal processing device (DSPD), a programmable logic device (PLD), a field programmable gate array (FPGA), a microprocessor, or an electrical unit for performing other functions.

[0055] The control circuit 230 can have a storage device. The storage device can include at least one type of storage medium such as a flash memory type, a hard disk type, a solid state drive (SSD) type, a silicon disk drive (SDD) type, a multimedia card micro type, a random access memory (RAM), a static random access memory (SRAM), a read only memory (ROM), an electrically erasable programmable read only memory (EEPROM), or a programmable read only memory (PROM). The storage device can store data and programs required for computation by the control circuit 230. The storage device can store data indicative of a result of computation by the control circuit 230.

[0056] The control circuit 230 can be operatively coupled to the switch SW, the charge / discharge circuit 5, the voltage sensor 210, the current sensor 220, the temperature sensor 310, and / or the communication circuit 320. The operative coupling refers to a connection to transmit and receive signals in one or both directions. The control circuit 230 can periodically or aperiodically collect sensing signals in a repetitive manner. The sensing signals are indicative of the synchronously detected voltage signal, the current signal, and / or the temperature signal.

[0057] The control circuit 230 can determine a state of charge (SOC) of the battery B based on the sensing signals at predetermined time intervals during charging / discharging of the battery B. Well-known algorithms such as ampere counting, SOC open circuit voltage (OCV) curve, and Kalman filter can be used to determine the SOC.

[0058] The communication circuit 320 can include a communication circuit configured to support wired or wireless communication between the control circuit 230 and the vehicle controller 6 (e.g., electronic control unit (ECU)). The wired communication can be, for example, controller area network (CAN) communication, and the wireless communication can be, for example, Zigbee or Bluetooth communication. The communication protocol is not limited to a specific type, and can include any communication protocol for supporting wired / wireless communication between the control circuit 230 and the vehicle controller 6.

[0059] The communication circuit 320 can include an output device (e.g., display, speaker) to provide information received from the vehicle controller 6 and / or the control circuit 230 in an identifiable form. The vehicle controller 6 can control the inverter 3 based on battery information (e.g., voltage, current, temperature, SOC) collected via communication with the battery management system 100.

[0060] Figure 2 is a schematic diagram showing a capacity curve obtained by a constant current process of the battery shown in Figure 1 is a schematic diagram showing a capacity curve obtained by a constant current process of the battery shown in

[0061] Referring to Figure 2 , the measured capacity curve 201 indicates a relationship between the battery voltage and the remaining capacity of the deteriorated battery B obtained by the constant current process. The reference capacity curve 202 indicates a relationship between the battery voltage and the remaining capacity of a sample battery in a factory state obtained by the constant current process. The sample battery is manufactured to have the same electrochemical specifications as the battery B. The factory state refers to a state that is brand new and free from defects.

[0062] The constant current process is a discharge or charge event of the battery B using a predetermined current rate (e.g., 0.1C rate) for a constant current period from a time when the battery voltage is equal to either a voltage upper limit V U or a voltage lower limit V L to a time when the battery voltage reaches the other of the voltage upper limit V U or the voltage lower limit V L . The voltage upper limit V U (e.g., 4.2V) is preset to be lower than a predetermined charge end voltage that allows the battery B to be charged. The voltage lower limit V L (e.g., 3.0V) is preset to be higher than a predetermined discharge end voltage that allows the battery B to be discharged.

[0063] Figure 2Two capacity curves 201, 202 obtained by a discharge event at a constant current period are shown. The control circuit 230 can determine the measured capacity curve 201 based on the voltage signal and the current signal collected and recorded at each unit time within the constant current period. As the battery B deteriorates, the full charge capacity decreases, and thus the measured capacity curve 201 reaches the lower voltage limit V L at a time t B earlier than the reference capacity curve 202 reaches the lower voltage limit V L at a time t C . As the battery B deteriorates, the shape of the measured capacity curve 201 changes, and thus the difference between the reference capacity curve 202 and the measured capacity curve 201 gradually increases.

[0064] Figure 3 is a schematic diagram showing the differential curves associated with the capacity curves shown in Figure 2 , and Figure 4 is a schematic diagram showing the differential capacity difference between the differential curves shown in Figure 3 .

[0065] Referring to Figure 3 , the measured differential curve 301 is a dataset that can be obtained from the measured capacity curve 201 of Figure 2 , and indicates a relationship between (i) the battery voltage V and (ii) the differential capacity dQ / dV, including a time series that defines the measured capacity curve 201. The differential capacity dQ / dV is a ratio of a change dQ in the remaining capacity Q per unit time to a change dV in the battery voltage V per unit time. For example, the control circuit 230 can determine an approximate capacity curve that is a result of fitting the relationship between the battery voltage and the remaining capacity of the measured capacity curve 201 of Figure 2 to a polynomial function by curve fitting. By converting the measured capacity curve 201 to the approximate capacity curve, a noise component existing in the measured capacity curve 201 is removed. Subsequently, as a result of differentiating the approximate capacity curve with respect to an input variable (i.e., the battery voltage), the control circuit 230 can obtain the measured differential curve 301.

[0066] The reference differential curve 302 is a time series dataset that can be obtained from the reference capacity curve 202 of Figure 2 , and indicates a relationship between (i) the battery voltage and (ii) the differential capacity, including a time series that defines the reference capacity curve 202. That is, the reference differential curve 302 can be given as a result of differentiating the remaining capacity of the reference capacity curve 202 with respect to the battery voltage.

[0067] Each of the curves 201, 202, 301, and 302 described above can be considered a type of signal (time series). Control circuit 230 can determine whether the negative electrode curvature of battery B has increased abnormally by comparing the measured differential curve 301 with the reference differential curve 302. Control circuit 230 can determine whether the negative electrode curvature of battery B has increased abnormally by comparing the measured differential curve 301 with the reference differential curve 302. U to the lower voltage limit V L Calculate the differential capacity difference between differential curves 301 and 302 within the set voltage range. Figure 4 The result is shown by subtracting the differential capacity of the reference differential curve 302 from the differential capacity of the measured differential curve 301 within a set voltage range.

[0068] Control circuit 230 can determine a first voltage of interest, which is the voltage at which the difference in differential capacitance reaches its maximum value. The first voltage of interest can be determined within a voltage range where the measured differential curve 301 has a smaller differential capacitance than the reference differential curve 302. Figure 4 In the measurement, the differential capacity difference between the differential curve 301 and the reference differential curve 302 is minimized at voltage V1 within the set voltage range, and therefore the control circuit 230 can determine voltage V1 as the first voltage of interest. Furthermore, the control circuit 230 determines a second voltage of interest V2 based on the first voltage of interest V1. The second voltage of interest V2 can be equal to (i) the first voltage of interest V1 and the reference voltage V1. ref The sum of (ii) voltage upper limit V U The smaller one.

[0069] Reference voltage V ref The optimal width of the voltage range of interest (e.g., 0.3V) required to measure the similarity of two differential curves can be given.

[0070] Alternatively, the control circuit 230 can determine the reference voltage V based on the cumulative charge / discharge capacity of battery B. ref The storage device can pre-record a lookup table that defines a predetermined correlation between accumulated charge / discharge capacity and a reference voltage. In the lookup table, the reference voltage can have a linear or non-linear inverse relationship with the accumulated charge / discharge capacity. That is, in the lookup table, a larger accumulated charge / discharge capacity can be associated with a smaller reference voltage. When battery B deteriorates, the measured differential curve 301 differs significantly from the reference differential curve 302. Therefore, when the reference voltage V... ref (The width of the voltage range of interest) decreases as the cumulative charge / discharge capacity of battery B increases. The measured differential curve 301 and the reference differential curve 302 can be compared with sufficient accuracy and low computational complexity for similarity measurement.

[0071] The control circuit 230 can determine the signal distance between the measured differential curve 301 and the reference differential curve 302 within the range of interest voltages from the first voltage of interest V1 to the second voltage of interest V2. The signal distance decreases as the measured differential curve 301 and the reference differential curve 302 are more similar to each other within the range of interest voltages. The signal distance can be determined using at least one of various well-known similarity calculation methods, such as a Pearson correlation coefficient. In connection therewith, as the battery B deteriorates, the battery voltage during discharging shifts toward a low voltage bias and the battery voltage during charging shifts toward a high voltage bias due to the internal resistance of the battery B. Therefore, when determining the signal distance, dynamic time warping, which is a function that outputs the signal distance between two signals having different patterns, can be used to offset the shift of the battery voltage during charging / discharging.

[0072] As a result of comparing the signal distance with the reference distance, the control circuit 230 can determine that the negative curvature of the battery B is abnormally increased when the signal distance is found to be equal to or greater than the reference distance. The abnormal increase in the negative curvature of the battery B indicates that the negative curvature of the battery B is equal to or greater than the upper limit value of the negative curvature corresponding to the cumulative charge / discharge capacity of the battery B. The cumulative charge / discharge capacity can be the sum of the cumulative value of the discharge current and the cumulative value of the charge current that flow through the battery B within the total usage duration from the release time of the battery B to the start time (or end time) of the constant current period. The signal distance corresponds to the negative curvature of the battery B, and the reference distance corresponds to the upper limit value of the negative curvature corresponding to the cumulative charge / discharge capacity of the battery B. To compare the signal distance with the reference distance, the control circuit 230 can determine the reference distance using the following equation, which is pre-recorded in a storage.

[0073] < Equation >

[0074]

[0075] In the above equation, m denotes a predetermined natural number, C[i] denotes the ith predetermined positive coefficient, x denotes the cumulative charge / discharge capacity, and y denotes the reference distance. The above equation can be preset by testing (or calculation simulation) to obtain the relationship between the cumulative charge / discharge capacity and the negative curvature of a sample battery having the same electrochemical specifications as the battery B.

[0076] When it is determined that the negative electrode curvature of the battery B is abnormally increased, the control circuit 230 can execute a predetermined safety function. In one example, the control circuit 230 can transmit a warning message to the vehicle controller 6 through the communication circuit 320. In another example, the control circuit 230 can reduce the maximum allowable value of the charging current and / or the discharging current. The reduction of the maximum allowable value can be proportional to the difference between the signal distance and the reference distance.

[0077] Figure 5 is an exemplary flowchart illustrating a battery diagnosis method that can be executed by the battery diagnosis apparatus 1 shown in Figure 1 Figure 6 is an exemplary flowchart illustrating a sub-step of the step S540 of Figure 5

[0078] Referring to Figures 1 to 5 In the step S500, the control circuit 230 commands the charging / discharging circuit 5 to start a constant current period. The constant current period is a period in which the battery B is charged or discharged at a predetermined current rate within a predetermined set voltage range V L ~ V U .

[0079] In the step S510, the control circuit 230 collects the voltage signal and the current signal at every unit time within the constant current period. That is, the control circuit 230 generates a time series of the battery voltage and a time series of the battery current within the constant current period.

[0080] In the step S520, the control circuit 230 determines a measured capacity curve 201 indicating a relationship between the battery voltage and the remaining capacity within the set voltage range, based on the voltage signal and the current signal collected in the constant current period.

[0081] In the step S530, the control circuit 230 determines a measured differential curve 301 indicating a relationship between the battery voltage and the differential capacity within the set voltage range, based on the measured capacity curve 201. The differential capacity is a ratio dQ / dV of a change in the remaining capacity per unit time to a change in the battery voltage per unit time.

[0082] In the step S540, the control circuit 230 determines whether the negative electrode curvature of the battery B is abnormally increased by comparing the measured differential curve 301 with the reference differential curve 302. When the value of the step S540 is “Yes”, the step S550 can be executed.

[0083] In the step S550, the control circuit 230 executes a predetermined safety function.

[0084] Referring to Figure 6 ​​In step S610, the control circuit 230 determines a first voltage of interest V1 that is a voltage at which the size of the differential capacity difference between the measurement differential curve 301 and the reference differential curve 302 is maximized.

[0085] In step S620, the control circuit 230 determines a second voltage of interest V2 based on the first voltage of interest V1. The second voltage of interest can be equal to one of (i) the sum of the first voltage of interest V1 and the reference voltage V ref (ii) the upper limit voltage V U , for example, the smaller one.

[0086] In step S630, the control circuit 230 determines the signal distance between the measurement differential curve 301 and the reference differential curve 302 in a voltage of interest range between the first voltage of interest V1 as a lower limit and the second voltage of interest V2 as an upper limit.

[0087] In step S640, the control circuit 230 determines a reference distance based on the cumulative charge / discharge capacity of the battery B (see Equation). Alternatively, when the reference voltage V ref is determined based on the cumulative charge / discharge capacity, step S640 can be omitted, and a predetermined value can be used as the reference distance.

[0088] In step S650, the control circuit 230 determines whether the signal distance is equal to or greater than the reference distance. The signal distance equal to or greater than the reference distance indicates that the negative curvature of the battery B is abnormally increased beyond an expected upper limit value according to the cumulative charge / discharge capacity of the battery B.

[0089] The above-described embodiments of the present disclosure are not only implemented by the apparatus and the method, and can be implemented by a program that performs functions corresponding to the configuration of the embodiments of the present disclosure or a recording medium having the program recorded thereon, and such implementation can be easily achieved by those skilled in the art from the disclosure of the above-described embodiments.

[0090] Although the present disclosure has been described with respect to a limited number of embodiments and drawings, the present disclosure is not limited thereto, and it will be obvious to those skilled in the art that various modifications and changes can be made thereto within the technical aspects of the present disclosure and the equivalent scope of the appended claims.

[0091] In addition, those skilled in the art can make many substitutions, modifications, and changes to the present disclosure described above without departing from the technical aspects of the present disclosure, the present disclosure is not limited by the above-described embodiments and drawings, and all or some of the embodiments can be selectively combined to allow various modifications.

[0092] [REFERENCE NUMERALS]

[0093] 1: electric vehicle

[0094] 2: battery pack

[0095] B: battery

[0096] 100: battery management system

[0097] 200: battery diagnostic device

[0098] 210: voltage sensor

[0099] 220: current sensor

[0100] 230: control circuit

Claims

1. A battery diagnostic device comprising: a voltage sensor configured to measure a battery voltage across a battery and generate a voltage signal indicative of the measured battery voltage; a current sensor configured to measure a battery current flowing through the battery and generate a current signal indicative of the measured battery current; and a control circuit configured to collect the voltage signal and the current signal at each unit time, wherein the control circuit is configured to: determine, based on the voltage signal and the current signal collected at each unit time over a constant current period during which the battery is charged or discharged at a predetermined current rate within a predetermined set voltage range, a measured capacity curve indicative of a relationship between the battery voltage and a remaining capacity within the set voltage range, determine, based on the measured capacity curve, a measured differential curve indicative of a relationship between the battery voltage and a differential capacity within the set voltage range, wherein the differential capacity is a ratio of a change in the remaining capacity per unit time to a change in the battery voltage per unit time, and determine whether a negative curvature of the battery is abnormally increased by comparing the measured differential curve with a reference differential curve, wherein the reference differential curve is defined as a relationship between the battery voltage and the differential capacity within the set voltage range when the battery is in a factory state. the control circuit is configured to:

2. The battery diagnostic device according to claim 1, wherein determine an approximate measured capacity curve by fitting the measured capacity curve to a polynomial function; and determine the measured differential curve by differentiating the remaining capacity with respect to the battery voltage of the approximate measured capacity curve. the control circuit is configured to:

3. The battery diagnostic device according to claim 1, wherein determine a first voltage of interest at which a magnitude of a difference in the differential capacity between the measured differential curve and the reference differential curve is a maximum value, determine a signal distance between the measured differential curve and the reference differential curve within a voltage of interest range from the first voltage of interest to a second voltage of interest greater than the first voltage of interest, and determine that the negative curvature of the battery is abnormally increased when the signal distance is equal to or greater than a reference distance. the control circuit is configured to determine the second voltage of interest as a smaller one of a sum of the first voltage of interest and a reference voltage and an upper limit of voltage.

4. The battery diagnostic device according to claim 3, wherein the control circuit is configured to determine the signal distance using dynamic time warping.

5. The battery diagnostic device according to claim 3, wherein the control circuit is configured to:

6. The battery diagnostic device according to claim 3, wherein determine a cumulative charge / discharge capacity of the battery over a total usage duration of the battery; and determine the reference distance based on the cumulative charge / discharge capacity. the control circuit is configured to determine the reference distance using the following equation:

7. The battery diagnostic device according to claim 6, wherein where m is a predetermined natural number, C[i] is an ith predetermined positive coefficient, x is the cumulative charge / discharge capacity, and y is the reference distance. ​ 8. The battery diagnostic device of claim 1, wherein, The control circuit executes a predetermined safety function when it is determined that the negative electrode curvature of the battery is abnormally increased.

9. A battery pack including the battery diagnosis device according to any one of claims 1 to 8.

10. An electric vehicle including the battery pack according to claim 9.

11. A battery diagnosis method executable by the battery diagnosis device according to any one of claims 1 to 7, the battery diagnosis method including the steps of: determining a measured capacity curve indicating a relationship between the battery voltage and the remaining capacity in a predetermined set voltage range based on the voltage signal and the current signal collected per unit time in a constant current period during which the battery is charged or discharged at a predetermined current rate in the set voltage range; determining a measured differential curve indicating a relationship between the battery voltage and a differential capacity in the set voltage range based on the measured capacity curve, wherein the differential capacity is a ratio of a change in the remaining capacity per unit time to a change in the battery voltage per unit time; and determining whether the negative electrode curvature of the battery is abnormally increased by comparing the measured differential curve with a reference differential curve, wherein the reference differential curve is defined as a relationship between the battery voltage and the differential capacity in the set voltage range when the battery is in a factory state.

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