Battery deterioration diagnosis device and battery deterioration diagnosis method

Abstract

A battery deterioration diagnosis device includes one or more processors. The one or more processors are configured to: perform discharging of each of a plurality of battery cells included in a battery pack while measuring a voltage of each of the plurality of battery cells; estimate a degree of deterioration of each of the plurality of battery cells using voltage data indicating a transition of the voltage of each of the plurality of battery cells from a voltage at the start of discharging to a predetermined discharging end voltage; and end the discharging when the voltage of all of the battery cells included in the battery pack reaches the predetermined discharging end voltage. The discharging end voltage is a battery cell voltage at which a degree of change in the battery cell voltage per unit amount of discharging starts to sharply rise while the battery cell voltage is decreasing due to the discharging.

Description

Technical Field

[0001] This disclosure relates to battery degradation diagnosis equipment and battery degradation diagnosis methods. Background Technology

[0002] A battery pack consists of multiple secondary batteries that are electrically connected to each other. By combining these secondary batteries, a high-capacity battery pack can be obtained. However, as the secondary batteries deteriorate, their full-charge capacity (the amount of electricity accumulated in the secondary battery when fully charged) decreases. For example, Japanese Patent Application Publication No. 2013-110906 (JP2013-110906A) discloses a method for diagnosing battery degradation. This method discharges the battery pack until its voltage (inter-terminal voltage) reaches a predetermined discharge end voltage, and uses data (discharge curves) representing the voltage transition of the battery pack from the discharge start voltage to the discharge end voltage to estimate the degree of degradation of the battery pack. Summary of the Invention

[0003] In the battery degradation diagnosis method described in JP 2013-110906 A, discharge is terminated when the voltage between the terminals of the battery pack reaches the discharge termination voltage during discharge. In this method, since the voltage of some of the secondary cells included in the battery pack does not reach the discharge termination voltage at the end of discharge, it is difficult to estimate the degree of degradation of each secondary cell included in the battery pack. Hereinafter, each secondary cell included in the battery pack will be referred to as a "cell".

[0004] Therefore, a degradation diagnosis method for batteries could be considered that terminates discharge when the voltage of all individual cells in the battery pack reaches the discharge termination voltage. However, in such a method, the discharge termination voltage needs to be set to an appropriate value. When the discharge termination voltage is too low, some individual cells in the battery pack may be over-discharged during discharge. Over-discharge of individual cells accelerates their degradation. On the other hand, when the discharge termination voltage is too high, sufficient data cannot be obtained during discharge, and the accuracy of estimating the degree of degradation of individual cells (e.g., full charge capacity) may decrease.

[0005] This disclosure provides a battery degradation diagnosis device and a battery degradation diagnosis method, which sets the discharge end voltage to an appropriate value and estimates the degree of degradation of each battery cell included in the battery pack with sufficient accuracy while limiting the degradation of individual battery cells during discharge.

[0006] The battery degradation diagnostic device according to a first aspect of this disclosure includes one or more processors. The one or more processors are configured to: simultaneously measure the voltage of each of a plurality of battery cells included in a battery pack, discharge each of the plurality of battery cells; estimate the degree of degradation of each of the plurality of battery cells included in the battery pack using voltage data indicating the transition of the voltage of each of the plurality of battery cells included in the battery pack from a discharge start voltage to a predetermined discharge end voltage; and terminate the discharge when the voltage of all battery cells included in the battery pack reaches the predetermined discharge end voltage. The discharge end voltage is the battery cell voltage at which the degree of change in battery cell voltage per unit discharge amount begins to rise sharply as the battery cell voltage decreases due to discharge.

[0007] In battery pack degradation diagnostic equipment, since discharge continues until the voltage of all battery cells in the battery pack reaches the discharge termination voltage, the degree of degradation of each battery cell in the battery pack can be estimated using voltage data indicating the transition of the voltage of each battery cell in the battery pack from the discharge start voltage to the predetermined discharge termination voltage. Furthermore, in the battery pack degradation diagnostic equipment, the discharge termination voltage is set to an appropriate value as described below. Hereinafter, the degree of change (absolute value) of the battery cell voltage per unit discharge is expressed as "|ΔV / ΔQ|". The discharge amount corresponds to the time integral value of the discharge current. A battery cell is a secondary battery that constitutes a battery pack. A battery pack consists of multiple battery cells electrically connected to each other.

[0008] During the discharge of a battery cell, the cell voltage decreases. In the initial stage of discharge, |ΔV / ΔQ| remains essentially constant. In the final stage of discharge, |ΔV / ΔQ| rises sharply due to the increase in reaction resistance. Specifically, during the discharge of a battery cell, |ΔV / ΔQ| begins to rise sharply immediately after the cell voltage reaches a predetermined voltage (hereinafter also referred to as the "voltage at the point of change"). Essentially, the longer the discharge period of a battery cell lasts, the higher the accuracy of degradation diagnosis becomes, but the more easily the battery cell deteriorates. Before |ΔV / ΔQ| begins to rise sharply, the advantage of improving diagnostic accuracy by continuously discharging the battery cell outweighs the disadvantage of easy degradation. On the other hand, after |ΔV / ΔQ| begins to rise sharply, the disadvantage of easy degradation outweighs the advantage of improving diagnostic accuracy by continuously discharging the battery cell. Therefore, by setting the cell voltage at the point where the change in cell voltage per unit of discharge begins to rise sharply while the cell voltage decreases due to discharge as the discharge ends, it is possible to promote both sufficient diagnostic accuracy and limit cell degradation. Thus, according to the above configuration, the degree of degradation of each battery cell in the battery pack can be estimated with sufficient accuracy while limiting the degradation of individual battery cells during discharge.

[0009] The voltage at the point of change can be the cell voltage at which the change in cell voltage per unit of discharge is the lowest during the discharge period. In the final stage of cell discharge, |ΔV / ΔQ| initially tends to decrease, then begins to rise sharply. The discharge termination voltage can be the voltage at the point of change or a voltage close to the point of change (e.g., a voltage slightly lower than the voltage at the point of change).

[0010] In the first aspect, each of the individual cells included in the battery pack can be a lithium-ion secondary battery. The predetermined discharge termination voltage can be higher than the voltage at which all lithium sites in the positive electrode active material of the lithium-ion secondary battery are occupied.

[0011] In lithium-ion secondary batteries, lithium sites exist in the positive electrode active material. These sites are crystallographically equivalent lattice positions. Atoms present at a lattice position are represented as occupying that site. A lithium site is a site occupied by lithium. In the following text, the voltage at which all lithium sites in the positive electrode active material of a lithium-ion secondary battery are occupied is also called the "lithium occupancy voltage." x Ni y Co z Mn (1-x-z) In the lithium-ion secondary battery (hereinafter also referred to as "ternary LIB") with a layered crystal structure positive electrode, the lithium occupancy voltage is 3.0V.

[0012] When estimating the degradation level of only one ternary lithium battery cell (LIB) in a battery pack comprising multiple ternary LIBs, the discharge of the battery pack ends when the voltage of at least one ternary LIB in the battery pack reaches the discharge termination voltage. In such a battery degradation diagnostic device, by setting the discharge termination voltage to 3.0V, the degradation level of each battery cell in the battery pack can be estimated with sufficient accuracy while limiting the degradation of individual cells during discharge.

[0013] On the other hand, in battery degradation diagnostic equipment, when diagnosing a battery pack comprising multiple ternary lithium batteries (LIBs), the battery pack discharges continuously until the voltage of all ternary lithium batteries in the pack reaches the discharge termination voltage, since the degree of degradation of each ternary lithium battery is estimated within the pack. In such a battery degradation diagnostic equipment, 3.0V is considered too low as the discharge termination voltage. Therefore, in the above configuration, the discharge termination voltage is set to be higher than the lithium occupation voltage.

[0014] In the first aspect, each of the multiple battery cells included in the battery pack can be of the general formula Li x Ni y Co z Mn (1-x-z) This describes a lithium-ion secondary battery with a layered crystal structure as the positive electrode. The predetermined discharge termination voltage can be above 3.1V and below 3.5V. With the above configuration, the degree of degradation of each battery cell in the battery pack can be estimated with sufficient accuracy while limiting the degradation of individual cells during discharge. In embodiments where each of the multiple battery cells in the battery pack is a ternary lithium-ion battery (LIB), the discharge termination voltage can be above 3.3V and below 3.4V.

[0015] In the first aspect, each of the multiple battery cells included in the battery pack can be of the general formula Li x This is a lithium-ion secondary battery with a positive electrode featuring an olivine-type crystal structure represented by FePO4. The predetermined discharge termination voltage can be above 2.0V and below 3.2V. With the above configuration, the degree of degradation of each battery cell in the battery pack can be estimated with sufficient accuracy while limiting the degradation of individual cells during discharge.

[0016] In a first aspect, the predetermined discharge termination voltage can be the battery cell voltage at which the degree of change in battery cell voltage per unit discharge amount becomes a predetermined value or higher while the individual cell voltage decreases due to discharge. One or more processors can be configured to determine whether the degree of change in battery cell voltage per unit discharge amount is a predetermined value or higher while the individual cell voltage decreases due to the discharge of each individual cell included in the battery pack, and to terminate the discharge when it is determined that the degree of change in battery cell voltage per unit discharge amount of all individual cells included in the battery pack has become a predetermined value or higher. Therefore, one or more processors can be configured to terminate the discharge when it is determined that the degree of change in battery cell voltage per unit discharge amount of all individual cells included in the battery pack is a predetermined value or higher.

[0017] One or more processors can determine whether |ΔV / ΔQ| begins to rise sharply based on whether |ΔV / ΔQ| becomes a predetermined value or higher as the cell voltage decreases due to discharge. With this configuration, the discharge of a cell can be easily terminated when |ΔV / ΔQ| begins to rise sharply as the cell voltage decreases due to discharge. The predetermined value is set such that the cell voltage at the point where |ΔV / ΔQ| becomes a predetermined value or higher as the cell voltage decreases due to discharge is the same as the cell voltage at the point where |ΔV / ΔQ| begins to rise sharply as the cell voltage decreases due to discharge.

[0018] In the first aspect, the battery pack can be mounted on a vehicle. One or more processors can be configured to use the vehicle's usage history to estimate the degree of degradation of the battery pack and to change a predetermined discharge termination voltage such that the predetermined discharge termination voltage becomes higher as the estimated degree of degradation of the battery pack increases.

[0019] As the individual cell voltage decreases due to discharge, the individual cell voltage at the point where |ΔV / ΔQ| begins to rise sharply tends to gradually increase with battery degradation. With the above configuration, the discharge termination voltage can be fine-tuned based on the change in individual cell voltage at the point where |ΔV / ΔQ| begins to rise sharply. One or more processors can fine-tune the discharge termination voltage within, for example, a variation range of 0.1V. Examples of parameters indicating the vehicle's usage history may include the vehicle's cumulative mileage, the battery pack's input / output capacity (cumulative value), the number of charge / discharge cycles of the battery pack, and the duration of battery pack usage (e.g., time elapsed since the start of usage). One or more processors can use the vehicle's usage history information to roughly determine the degree of battery pack degradation (e.g., major degradation / medium degradation / minor degradation).

[0020] In the first aspect, all the battery cells included in the battery pack can be connected in series. One or more processors can be configured to maintain a current value during the discharge of each of the multiple battery cells.

[0021] With the above configuration, it is easy to ensure that the current value of each battery cell in the battery pack is consistent during discharge. This allows for easy and highly accurate estimation of the battery pack's degradation level.

[0022] In the first aspect, the battery pack can be configured to supply power to onboard electrical loads. One or more processors can be configured to perform discharge by controlling the onboard electrical loads.

[0023] Based on the above configuration, degradation diagnostics for the vehicle's battery pack can be easily and appropriately performed. During discharge, the on-board electrical loads controlled by one or more processors may include at least one of air conditioning equipment, seat heaters, and lighting devices.

[0024] The battery degradation diagnostic device according to a second aspect of this disclosure includes a storage device and one or more processors. The storage device is configured to manage a discharge termination voltage indicating the end time of battery discharge. Battery discharge is performed to obtain data for estimating the degree of battery degradation. The one or more processors are configured to store the battery voltage in the storage device as the discharge termination voltage when the voltage change per unit discharge amount becomes a predetermined value or higher after the start of battery discharge.

[0025] With the above configuration, an appropriate discharge termination voltage can be managed. The battery degradation diagnostic device can provide an appropriate discharge termination voltage to the device performing battery discharge (discharge device) to obtain data for estimating the degree of battery degradation. Alternatively, the battery degradation diagnostic device can obtain data for estimating the degree of battery degradation by performing battery discharge itself. By discharging the battery based on an appropriate discharge termination voltage, the degree of battery degradation can be estimated with sufficient accuracy while limiting the degree of battery degradation during discharge. More specifically, by ending the discharge of the battery pack when the voltage of all battery cells in the battery pack reaches the discharge termination voltage, the degree of degradation of each battery cell in the battery pack can be estimated with sufficient accuracy while limiting the degradation of the battery cells during discharge. The storage device can manage the discharge termination voltage in association with the battery type. The battery type can be distinguished using at least one of the battery manufacturer, model, and serial number.

[0026] The battery degradation diagnosis method according to the third aspect of this disclosure is executed by one or more processors. The degradation diagnosis method includes: simultaneously measuring the voltage of each of a plurality of battery cells included in a battery pack and discharging each of the plurality of battery cells, and ending the discharge when the voltages of all battery cells included in the battery pack reach a predetermined discharge end voltage; and estimating the degree of degradation of each of the plurality of battery cells included in the battery pack using voltage data indicating the transition of the voltage of each of the plurality of battery cells included in the battery pack from a discharge start voltage to a predetermined discharge end voltage. The predetermined discharge end voltage is the battery cell voltage at which the degree of change in battery cell voltage per unit discharge amount begins to rise sharply while the battery cell voltage decreases due to discharge.

[0027] The battery pack degradation diagnosis method described above, in the same manner as the degradation diagnosis equipment described above, can estimate the degree of degradation of each battery cell in the battery pack with sufficient accuracy while limiting the degradation of individual battery cells during discharge.

[0028] Battery pack degradation can be diagnosed while the battery pack is mounted on the vehicle. The vehicle may include an internal combustion engine and a motor (hereinafter also referred to as a "first motor") that performs the starting process for the internal combustion engine. The battery pack whose degradation is diagnosed may be mounted on the vehicle and configured to supply power to the first motor. Hereinafter, the internal combustion engine mounted on the vehicle may be referred to as an "engine". The engine may be configured to generate driving power. In addition to the first motor, the vehicle may also include a second motor that receives power from the battery pack and generates driving power. The first motor may be configured to use the driving power output from the engine to generate electricity and supply the generated electricity to the battery pack. The starting process for the internal combustion engine is the process for starting the internal combustion engine. The internal combustion engine can be started by receiving assistance from the motor. The starting process may be starting. Starting is starting the internal combustion engine by rotating the crankshaft of the internal combustion engine.

[0029] The initial full-charge capacity of the battery pack can be less than 5 kWh. When the battery pack capacity is less than 5 kWh, the degradation diagnostic method using discharge described above can be used to perform diagnostics with sufficient throughput. The full-charge capacity of the battery pack to be diagnosed in the initial state can be more than 0.1 kWh and less than 5 kWh, or more than 0.3 kWh and less than 3 kWh. The battery pack to be diagnosed can be the drive battery installed in a hybrid electric vehicle (HEV). Attached Figure Description

[0030] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and in the drawings: Figure 1 This is a diagram illustrating the configuration of a vehicle according to an embodiment of the present disclosure; Figure 2 This is a diagram illustrating the configuration of a battery degradation diagnostic device according to an embodiment of the present disclosure; Figure 3 This is a flowchart illustrating a battery degradation diagnosis method according to an embodiment of the present disclosure; Figure 4 It shows Figure 2 A graph illustrating an example of the discharge characteristics of the individual cells included in the battery pack shown. Figure 5 It is a graph used to describe the problems that may occur when the lower discharge limit voltage is set to the discharge end voltage; Figure 6 It is a graph used to describe the advantages of increasing the discharge end voltage; Figure 7 It is a graph used to describe the disadvantages of increasing the discharge termination voltage; Figure 8 It is a graph used to describe the method for determining the discharge end voltage in embodiments of the present invention; Figure 9 This is a graph showing the discharge characteristics of a lithium-ion secondary battery (ternary LIB). Figure 10 It is a graph showing the relationship between the discharge termination voltage and the coverage rate; Figure 11 This is a flowchart illustrating a method for setting a discharge termination voltage according to a variant example of an embodiment of the present disclosure; Figure 12 It shows Figure 3 The flowchart shows a variant example of the processing shown; Figure 13 It is used to describe the settings Figure 12 A graph showing the thresholding method used in the processing shown; Figure 14 It shows Figure 2 A diagram illustrating a variant example of the service tool shown; Figure 15 It shows Figure 14 The flowchart shown illustrates the data acquisition-related processes performed by the maintenance tool. Figure 16 It is used to describe based on usage Figure 15The flowchart shown illustrates a method for processing acquired data to set the discharge termination voltage. Figure 17 It shows Figure 2 A diagram showing a variant example of the vehicle control device; and Figure 18 It shows Figure 2 A diagram showing a variant example of the battery pack. Detailed Implementation

[0031] Embodiments of this disclosure will be described in detail with reference to the accompanying drawings. In the drawings, the same or corresponding parts are indicated by the same reference numerals and will not be described again thereafter. Hereinafter, the electronic control unit is also referred to as "ECU".

[0032] Figure 1 This is a diagram illustrating the configuration of a vehicle according to an embodiment. (Refer to...) Figure 1 Vehicle 100 is a hybrid electric vehicle (HEV). In this embodiment, it is assumed that the vehicle is a front-wheel drive four-wheel vehicle (more specifically, an HEV), but the number of wheels and the drive system can be appropriately changed. For example, the drive system can be four-wheel drive.

[0033] The vehicle 100 includes a drive battery 11, a voltage sensor 12a, a current sensor 12b, a temperature sensor 12c, a system main relay (SMR) 14, a first motor generator 21a (hereinafter referred to as "MG 21a"), a second motor generator 21b (hereinafter referred to as "MG 21b"), a power control unit (PCU) 24, and an engine 31.

[0034] The drive battery 11 includes rechargeable secondary batteries. The drive battery 11 is configured to supply power to the PCU 24 (and therefore to MG 21a and MG 21b). In this embodiment, a battery pack comprising multiple secondary batteries electrically connected to each other is used as the drive battery 11. The fully charged capacity of the drive battery 11 in its initial state may be, for example, approximately 1.5 kWh. The secondary batteries included in the drive battery 11 may be modularized in a predetermined number. The battery pack can be constructed by combining multiple modules. The number of secondary batteries included in the drive battery 11 may be 10 or more and less than 100, or may be 100 or more. In this embodiment, the number of secondary batteries included in the drive battery 11 is approximately 50. The drive battery 11 is assembled in the form of a battery pack on, for example, the floor panel of the vehicle 100. In this embodiment, a battery pack is formed by installing accessories (voltage sensor 12a, current sensor 12b, temperature sensor 12c, battery ECU 13, SMR 14, etc.) in a battery box that houses the drive battery 11.

[0035] Each secondary battery included in the battery pack is referred to as a "cell battery". In this embodiment, all the cell battery included in the battery pack are connected in series (for example, see below). Figure 2 In this embodiment, a product with the general formula Li is used. x Ni y Co z Mn (1-x-z) The lithium-ion secondary battery (ternary LIB) with a layered crystal structure cathode (ternary cathode) is used as a battery cell. However, examples of battery cells are not limited to lithium-ion secondary batteries and may include other secondary batteries (e.g., nickel-metal hydride batteries). Furthermore, all-solid-state secondary batteries may be used as battery cells. Examples of the form in which the drive battery 11 is assembled in the vehicle 100 are not limited to battery packs and may include packless forms.

[0036] Voltage sensor 12a detects the voltage of each cell in the drive battery 11. Current sensor 12b detects the current flowing through the drive battery 11. Temperature sensor 12c detects the temperature of each cell in the drive battery 11. Each sensor outputs its detection result to the battery ECU 13. The battery ECU 13 uses the detection results from each sensor to calculate the State of Charge (SOC) of each cell and the SOC of the drive battery 11. SOC indicates the remaining accumulated charge and is expressed as, for example, the ratio of the current accumulated charge to the accumulated charge in a fully charged state, from 0% to 100%. Current sensor 12b is located in the current path of the drive battery 11. In this embodiment, one voltage sensor 12a and one temperature sensor 12c are provided for each cell.

[0037] SMR 14 is configured to switch between connecting and disconnecting the current path connecting PCU 24 to drive battery 11. For example, an electromechanical relay can be used as SMR 14. When SMR 14 is in the closed state (connected state), power can be sent and received between drive battery 11 and PCU 24. On the other hand, when SMR 14 is in the open state (disconnected state), the current path connecting drive battery 11 to PCU 24 is disconnected. SMR 14 is controlled by HVECU 50. For example, when vehicle 100 is in motion, SMR 14 is switched to the closed state.

[0038] Each of MG 21a and MG 21b is a motor-generator that functions as a motor outputting torque by receiving a supply of drive power and as a generator producing power by receiving torque. Each of MG 21a and MG 21b uses an AC motor (e.g., a permanent magnet synchronous motor or an induction motor). Each of MG 21a and MG 21b is electrically connected to the drive battery 11 via PCU 24. MG 21a and MG 21b each have rotor shafts 43a and 43b. Rotor shafts 43a and 43b correspond to the rotation shafts of MG 21a and MG 21b, respectively.

[0039] Vehicle 100 also includes a single-pinion planetary gear 431. The output shaft 41 of engine 31 is connected to the planetary gear 431. Any internal combustion engine can be used as engine 31, but in this embodiment, a spark-ignition internal combustion engine comprising multiple cylinders (e.g., four cylinders) is used. Engine 31 generates driving force by burning fuel (e.g., gasoline) in each cylinder and uses the generated driving force to rotate a crankshaft (not shown) common to all cylinders. The crankshaft of engine 31 is connected to output shaft 41 via a torsional damper (not shown). As the crankshaft rotates, output shaft 41 also rotates. Examples of engine 31 are not limited to gasoline engines and may include diesel engines or hydrogen engines.

[0040] The output shaft 41 of the engine 31 is connected to the input shaft 42 of the planetary gear 431. The planetary gear 431 has three rotating elements: an input element, an output element, and a reaction element. More specifically, the planetary gear 431 has a sun gear, a ring gear arranged coaxially with the sun gear, a pinion meshing with the sun gear and the ring gear, and a planet carrier that holds the pinion so that it can rotate and revolve. The planet carrier corresponds to the input element, the ring gear corresponds to the output element, and the sun gear corresponds to the reaction element. The input shaft 42 of the planetary gear 431 is connected to the planet carrier.

[0041] The rotor shaft 43a of MG 21a is connected to the sun gear of planetary gear 431. Torque is input from engine 31 to the planet carrier of planetary gear 431. Planetary gear 431 is configured to divide and transmit the torque output by engine 31 to the sun gear (and therefore MG 21a) and the ring gear. When the torque output by engine 31 is output to the ring gear, the reaction torque output by MG 21a acts on the sun gear.

[0042] Planetary gears 431 and MG 21b are configured to combine the driving force output from planetary gear 431 (i.e., the driving force output to the ring gear) and the driving force output from MG 21b (i.e., the driving force output to the rotor shaft 43b) and transmit the combined power to drive wheels 45a, 45b. More specifically, an output gear (not shown) meshing with driven gear 432 is mounted at the ring gear of planetary gear 431. Furthermore, a drive gear (not shown) mounted at the rotor shaft 43b of MG 21b also meshes with driven gear 432. The driven gear 432 combines the torque output from MG 21b to rotor shaft 43b with the torque output from the ring gear of planetary gear 431. The combined driving torque is transmitted to differential gear 44 and further to drive wheels 45a, 45b via drive shafts 44a, 44b extending to the left and right of differential gear 44.

[0043] A transmission mechanism (not shown) may be located downstream of planetary gear 431 (e.g., between driven gear 432 and differential gear 44). The transmission mechanism includes clutches and brakes and is configured to change the gear ratio (i.e., the ratio of the rotational speed of the input shaft to the rotational speed of the output shaft of the transmission mechanism) based on the state (engagement / disengagement) of each of the clutches and brakes. The vehicle 100 may also include a hydraulic circuit (not shown) supplying hydraulic pressure to each of the clutches and brakes included in the transmission mechanism. The HVECU 50 can switch the state (engagement / disengagement) of each of the clutches and brakes included in the transmission mechanism by controlling the hydraulic circuit. The transmission mechanism may be located upstream of the power splitter (planetary gear 431) (e.g., between engine 31 and planetary gear 431).

[0044] Vehicle 100 also includes a shift lever 101 and a P position switch 102. Each of the shift lever 101 and the P position switch 102 is configured to switch between gear positions based on the user's shifting operation. The user can select any of the following gears by moving the shift lever 101 to a predetermined position: neutral (N), reverse (R), drive (D), and brake (B). Additionally, the user can select the parking (P) gear by stopping the vehicle 100 and pressing the P position switch 102. The HVECU 50 shifts the vehicle 100 to the gear selected by the user. The HVECU 50 controls the hydraulic circuit according to, for example, the shift gear.

[0045] The vehicle 100 also includes a battery ECU 13, a motor ECU 23, an engine ECU 33, and an HVECU 50. In this embodiment, a computer (e.g., a microcomputer) is used for each of the battery ECU 13, motor ECU 23, engine ECU 33, and HVECU 50. The ECUs are connected to each other in a manner that enables them to perform CAN communication.

[0046] The HVECU 50 includes a processor 51, random access memory (RAM) 52, and a storage device 53. The processor 51 may be, for example, a central processing unit (CPU). The RAM 52 serves as working memory for temporary storage of data processed by the processor 51. The storage device 53 is configured to retain the stored information. In addition to the program, the storage device 53 also stores information used in the program (e.g., maps, mathematical formulas, and various parameters). When the processor 51 executes the program stored in the storage device 53, various processes are performed in the HVECU 50.

[0047] Although Figure 1 The detailed configuration of HVECU 50 is shown only, but each of the other ECUs also includes a processor, RAM, and storage devices. The number of processors included in each ECU is arbitrary, and any ECU may include multiple processors. Furthermore, the various processes in each ECU are not limited to being executed by software, but can be executed by dedicated hardware (electronic circuitry).

[0048] Motor sensors 22a and 22b, which detect the status (e.g., current, voltage, temperature, and speed) of MG 21a and MG 21b, are respectively installed in MG 21a and MG 21b. Each of the motor sensors 22a and 22b outputs its detection result to the motor ECU 23. Engine sensor 32, which detects the status (e.g., intake air volume, intake air pressure, intake air temperature, exhaust pressure, exhaust temperature, catalyst temperature, engine coolant temperature, and speed) of engine 31, is installed in engine 31. Engine sensor 32 outputs its detection result to engine ECU 33. HVECU 50 receives the detection values ​​from motor ECU 23 and engine ECU 33 as needed. In addition, HVECU 50 receives the status (e.g., cell voltage, current, temperature, and SOC) of drive battery 11 from battery ECU 13 as needed.

[0049] Vehicle 100 includes a monitoring unit 80a that detects the state of auxiliary battery 80 (described later). Monitoring unit 80a includes various sensors that detect the state of auxiliary battery 80 (e.g., temperature, current, and voltage) and outputs the detection results to HVECU 50. HVECU 50 can obtain the state of auxiliary battery 80 (e.g., temperature, current, voltage, and SOC) based on the output of monitoring unit 80a. Furthermore, although not shown, other sensors indicating the state of vehicle 100 (e.g., vehicle speed sensor, fuel gauge, odometer, throttle position sensor, and atmospheric pressure sensor) are also mounted on vehicle 100. HVECU 50 can obtain information about vehicle 100 based on the outputs of various sensors mounted on vehicle 100 (on-board sensors).

[0050] HVECU 50 is configured to output commands (control commands) to engine ECU 33 for controlling engine 31. Engine ECU 33 is configured to control various actuators of engine 31 (e.g., throttle, ignition, and injectors, none of which are shown) according to the commands from HVECU 50. HVECU 50 can control the engine through engine ECU 33.

[0051] HVECU 50 is configured to output commands (control commands) to Motor ECU 23 for controlling each of MG 21a and MG 21b. Motor ECU 23 is configured to generate a current signal (e.g., a signal indicating the magnitude and frequency of the current) corresponding to the target torque of each of MG 21a and MG 21b, based on the commands from HVECU 50, and output the generated current signal to PCU 24. HVECU 50 can control the motor via Motor ECU 23.

[0052] PCU 24 includes, for example, two inverters (not shown) corresponding to MG 21a and MG 21b, and a converter (not shown) arranged between each inverter and the drive battery 11. PCU 24 is configured to supply power accumulated in the drive battery 11 to each of MG 21a and MG 21b, and to supply power generated by each of MG 21a and MG 21b to the drive battery 11. PCU 24 is configured to independently control the state of MG 21a and MG 21b, i.e., for example, it can switch MG 21b to a power operation state while switching MG 21a to a power generation state.

[0053] MG 21a is configured to perform the starting process of engine 31. Specifically, when engine 31 is started, MG 21a, which receives power from the drive battery 11, performs the starting of engine 31.

[0054] MG 21a is configured to generate electricity using the driving force output from engine 31 (i.e., engine-generated electricity). HVECU 50 uses the electricity generated by the engine-generated electricity to charge drive battery 11, ensuring that the state of charge (SOC) of drive battery 11 does not become too low while vehicle 100 is in motion. Furthermore, drive battery 11 is also charged by electricity generated by MG 21b through regenerative braking.

[0055] Vehicle 100 is configured to perform both HV (High-Voltage) and EV (Electric Vehicle) driving. HV driving is performed by engine 31 and MG 21b while engine 31 is providing driving force. EV driving is performed by MG 21b when engine 31 is stopped. When engine 31 is stopped, combustion in each cylinder is not performed. When combustion in each cylinder ceases, no combustion energy is generated in engine 31 (and therefore no driving force is generated).

[0056] The vehicle 100 also includes an auxiliary battery 80, DC / DC converters 81 and 82, an auxiliary relay 83, a high-voltage load 91, and a low-voltage load 92. The full-charge capacity of the auxiliary battery 80 is less than that of the drive battery 11. The full-charge capacity of a battery is the amount of electricity accumulated in the battery when it is fully charged, and it decreases as the battery deteriorates. For example, a lead-acid battery can be used as the auxiliary battery 80. However, a secondary battery other than a lead-acid battery (e.g., a nickel-metal hydride battery) can also be used as the auxiliary battery 80. The DC / DC converters 81 and 82, the auxiliary relay 83, the high-voltage load 91, and the low-voltage load 92 are controlled by an HVECU 50. The HVECU 50 can control these components via a battery ECU 13.

[0057] High-voltage load 91 is an auxiliary device for the high-voltage system. Low-voltage load 92 is an auxiliary device for the low-voltage system. The drive voltage of low-voltage load 92 is lower than that of high-voltage load 91. Auxiliary battery 80 is an on-board battery for the low-voltage system (e.g., a 12V system) and is configured to supply power to low-voltage load 92. In this embodiment, high-voltage load 91 includes air conditioning equipment, and low-voltage load 92 includes lighting equipment. The air conditioning equipment is configured to heat and cool the passenger compartment of vehicle 100. The lighting equipment includes interior lighting for illuminating the vehicle and exterior lighting for illuminating the vehicle (e.g., headlights). At least one of high-voltage load 91 and low-voltage load 92 may also include a seat heater for heating the seats of vehicle 100.

[0058] DC / DC converter 81 is disposed between drive battery 11 and high-voltage load 91, stepping down the power supplied from drive battery 11 and outputting it to high-voltage load 91. DC / DC converter 82 steps down the power supplied from drive battery 11 and outputs it to each of auxiliary battery 80 and low-voltage load 92. When SMR 14 is in the open circuit state (disconnected state), power from drive battery 11 is not supplied to any of high-voltage load 91, low-voltage load 92, and auxiliary battery 80. Auxiliary relay 83 is arranged in the current path connecting DC / DC converter 82 to low-voltage load 92. When auxiliary relay 83 is in the open circuit state (disconnected state), no power is supplied to low-voltage load 92.

[0059] When SMR 14 is in the closed state (connected state), power can be supplied from the drive battery 11 to the auxiliary battery 80 via the DC / DC converter 82. For example, when the SOC of the auxiliary battery 80 is lower than a predetermined value, the HVECU 50 uses the power from the drive battery 11 to charge the auxiliary battery 80. Furthermore, the HVECU 50 performs degradation diagnosis on the battery pack described below (refer to...). Figure 3 According to maintenance tool 200 (see S16), Figure 2 The HVECU 50, upon receiving the instruction from the drive battery 11, uses power from the drive battery 11 to drive the high-voltage load 91 and the low-voltage load 92. At this time, the HVECU 50 controls the SMR 14, DC / DC converters 81 and 82, and auxiliary relay 83, so that power from the drive battery 11 is supplied to each of the high-voltage load 91 and the low-voltage load 92.

[0060] HVECU 50 is configured to perform SOC limiting control on the drive battery 11. SOC limiting control is a control used to limit the SOC of the drive battery 11 to a predetermined SOC range. HVECU 50 limits the input / output of the drive battery 11 so that the SOC of the drive battery 11 does not leave the SOC range. Specifically, HVECU 50 controls MG 21a, MG 21b, engine 31, and DC / DC converters 81, 82 to keep the SOC of the drive battery 11 within the SOC range. The SOC range can be variably set according to the state of the vehicle 100. HVECU 50 can use, for example, a mapping stored in storage device 53 to set the SOC range for protecting the drive battery 11 and its peripheral components.

[0061] Vehicle 100 also includes a power switch 103. Power switch 103 is used to switch between starting and stopping the vehicle system (HVECU 50, etc.). Power switch 103 is operated by the user.

[0062] Vehicle 100 also includes a notification device 104. Notification device 104 is configured to send a notification to a user of vehicle 100 in response to a request from HVECU 50. Examples of notification device 104 may include a dashboard, head-up display, navigation display, warning lights, or a speaker. Notification device 104 can be used as an input device to receive input from a user. Notification device 104 may include a touch panel display or a smart speaker that receives voice input. Notification device 104 may be mounted on a portable device such as a tablet terminal, smartphone, or wearable device (i.e., an electronic device that can be carried by the user).

[0063] Figure 2 This is a diagram illustrating the configuration of a battery degradation diagnostic device according to this embodiment. Figure 1 Refer to together Figure 2 In this embodiment, the maintenance tool 200 serves as a battery degradation diagnostic device. The maintenance tool 200 includes a computer having a processor 201, RAM 202, and a storage device 203. The storage device 203 stores diagnostic programs. When the processor 201 executes the diagnostic program stored in the storage device 203, a battery degradation diagnostic method according to this embodiment is executed (see the description below). Figure 3 ).

[0064] Maintenance tool 200 also includes a Human Machine Interface (HMI) 204. HMI 204 includes input devices and a display device. HMI 204 may be a touch panel display. HMI 204 may include a smart speaker that receives voice input.

[0065] The HVECU 50 also includes a Data Link Connector (DLC) 55a and an interface 55b for the DLC 55a. The DLC 55a is a connector capable of connecting to the connector 250 of the maintenance tool 200 and is, for example, configured near the driver's seat of the vehicle 100. The maintenance tool 200 is an external diagnostic tool used by, for example, a worker in a repair shop (such as a mechanic) to monitor the vehicle's condition. Examples of the maintenance tool 200 may include a General Scan Tool (GST). By connecting the connector 250 of the maintenance tool 200 to the DLC 55a, the maintenance tool 200 can read vehicle data stored in the storage device 53.

[0066] In the battery degradation diagnosis method according to this embodiment, the maintenance tool 200 discharges each battery cell while measuring the voltage of each individual cell included in the drive battery 11 (battery pack). Then, when the voltage of all the battery cells included in the drive battery 11 reaches a predetermined discharge end voltage (hereinafter referred to as "V"), the battery is discharged. end When the discharge is complete, the maintenance tool 200 stops discharging. After discharging, the maintenance tool 200 uses the voltage of each cell included in the drive battery 11 from the discharge start voltage to V. end The voltage data of the transition is used to estimate the degree of degradation of each cell included in the drive battery 11.

[0067] However, when V end When V is too low, some individual cells in the battery pack may be over-discharged during the battery pack's discharge process. On the other hand, when V... end If the value is too high, sufficient data cannot be obtained during the discharge of the battery pack, and the accuracy of estimating the degree of degradation of individual battery cells (e.g., full charge capacity) may decrease. Therefore, in the battery degradation diagnosis method according to this embodiment, the battery cell voltage at the point where |ΔV / ΔQ| (i.e., the degree of change in battery cell voltage per unit discharge) begins to rise sharply while the battery cell voltage decreases due to discharge is set to V. end The following will describe how to determine V. end The method and its technical significance (see below) Figures 5 to 10 ).

[0068] The maintenance tool 200 according to this embodiment includes a discharge unit 211 and an estimation unit 212. The discharge unit 211 is configured to discharge each battery cell while measuring the voltage of each battery cell included in the drive battery 11 mounted on the vehicle 100, and to discharge when the voltage of all battery cells included in the battery pack reaches V. endThe discharge ends at the specified time. The estimation unit 212 is configured to use the voltage of each individual cell included in the battery pack from the discharge start voltage to V. end The voltage data of the transition is used to estimate the degree of degradation of each cell in the battery pack.

[0069] Figure 3 This is a flowchart illustrating a battery degradation diagnosis method according to this embodiment. The process shown in this flowchart is executed when, for example, after the connector 250 of the maintenance tool 200 is connected to the DLC 55a of the vehicle 100 in a parked state, a predetermined command is input from the user to the HMI 204. However, the process begins... Figure 3 The conditions for the processing shown are not limited to these and can be set arbitrarily. In the following text, each step in the flowchart will be simply referred to as "S". The discharge unit 211 of the maintenance tool 200 sends control commands to the HVECU 50, thereby... Figure 3 S10 to S18 are executed.

[0070] and Figure 1 and Figure 2 Refer to together Figure 3 In S10, the maintenance tool 200 removes the SOC range associated with the SOC limit control. Thus, the SOC limit (SOC limit control) of the drive battery 11 becomes invalid.

[0071] Subsequently, in S11, the maintenance tool 200 drives the engine 31 and uses the electricity generated by the engine generator to charge the drive battery 11. Through the processing in S11, the electricity generated by the MG 21a using the driving force output from the engine 31 is input to the drive battery 11 via the PCU 24 and SMR 14.

[0072] In S12, the maintenance tool 200 determines whether the voltage of all the individual battery cells included in the drive battery 11 has changed to the predetermined start-up voltage (hereinafter referred to as "V"). start (V) or higher voltage. The voltage of each cell included in the drive battery 11 is measured by voltage sensor 12a. start This could be the cell voltage indicating that the battery cell has reached a fully charged state, or it could be the upper limit voltage for charging the battery cell. The upper limit voltage corresponds to the upper end of the recommended voltage range. If a battery cell continues to charge until its voltage exceeds the upper limit voltage, the cell may be overcharged. Overcharging accelerates battery degradation. start The voltage can be above 3.6V and below 3.9V, or it can be approximately 3.6V. Furthermore, the maintenance tool 200 can determine whether the voltage of all individual cells included in the drive battery 11 has changed to V based on the SOC of the drive battery 11. startOr higher. For example, when the SOC of the drive battery 11 becomes a predetermined SOC value (e.g., 70%) or higher, the maintenance tool 200 can determine that the voltage of all battery cells included in the drive battery 11 has become V. start Or higher.

[0073] Repeat steps S11 and S12 until the voltage of all individual cells in the drive battery 11 becomes V. start Or higher (No in S12). When the voltage of all battery cells becomes V start If the voltage is higher (Yes in S12), in S13, the maintenance tool 200 stops the engine 31. Then, in S14, the maintenance tool 200 determines whether the voltage of all battery cells included in the drive battery 11 has stabilized. This process remains in standby mode in S14 until the voltage of each battery cell included in the drive battery 11 stabilizes, and when the voltage of each battery cell included in the drive battery 11 stabilizes (Yes in S14), the process proceeds to S15.

[0074] In S15, the maintenance tool 200 measures the state (voltage, current, and temperature) of each battery cell included in the drive battery 11 and records the measurement results in the storage device 203. Subsequently, in S16, the maintenance tool 200 discharges the drive battery 11 by controlling the electrical load of the vehicle 100. The drive battery 11 is configured to supply power to the electrical load mounted on the vehicle 100.

[0075] Specifically, in S16, the maintenance tool 200 controls the electrical load of the vehicle 100 (e.g., at least one of the high-voltage load 91 and the low-voltage load 92) such that the discharge current of each battery cell included in the drive battery 11 becomes a predetermined value (hereinafter referred to as "Vd"). In this embodiment, the air conditioning unit (high-voltage load 91) and the lighting unit (low-voltage load 92) are driven by power supplied from the drive battery 11. The maintenance tool 200 uses DC / DC converters 81 and 82 to regulate the power supplied from the drive battery 11 to the high-voltage load 91 and the low-voltage load 92, respectively. Then, the maintenance tool 200 maintains a current value during the discharge of each battery cell included in the drive battery 11. Vd can be more than 1A and less than 10A, or it can be about 5A. In this embodiment, the current value during the discharge of each battery cell is maintained at Vd. In this embodiment, Vd is set to a fixed value (e.g., 5A), but Vd can also be changed depending on the conditions.

[0076] In S17, the maintenance tool 200 determines whether the voltage of all individual cells included in the drive battery 11 has reached the predetermined discharge end voltage (V). end ).

[0077] Figure 4 This is a graph illustrating an example of the discharge characteristics of the individual cells included in the drive battery 11. Figure 4 Each of lines L1 to L3 in the diagram illustrates when execution Figure 3 Examples of the changes in current and voltage of the drive battery 11 (battery pack) during S10 to S16 and when discharge (S16) continues for a predetermined time. Line L1 shows the change in current of the drive battery 11. Lines L2 and L3 show the discharge characteristics (more specifically, the changes in cell voltage during discharge) of the first and second cell included in the drive battery 11, respectively. The full-charge capacity of the first cell is greater than that of the second cell.

[0078] Reference Figure 4 In the comparison between the voltage transition of the first cell (line L2) and the voltage transition of the second cell (line L3), the voltage of the second cell begins to decrease earlier than that of the first cell, and decreases to a voltage lower than that of the first cell. Thus, during discharge, cell voltage tends to decrease more easily as the full charge capacity decreases. When the cell voltage decreases too much due to discharge, cell degradation is accelerated. The fact that a cell voltage continues to discharge until it drops too much is called "over-discharge."

[0079] In the following text, refer to Figures 5 to 9 The description will determine the discharge termination voltage (V). end The method. Figure 5 It is used to describe when the discharge lower limit voltage is set to V end A graph showing potential problems that may arise. Figure 5 Line L11 shows the voltage distribution of all the cells in the first battery pack (hereinafter referred to as the "first cell voltage distribution"). Line L12 shows the voltage distribution of all the cells in the second battery pack (hereinafter referred to as the "second cell voltage distribution"). The second cell voltage distribution (line L12) has a wider range of cell voltage variations than the first cell voltage distribution (line L11). The first and second cell voltage distributions are determined by continuous discharge until the voltages of all the cells in the first and second battery packs reach their respective lower discharge limits (V). end Distribution at time ).

[0080] exist Figure 5In this embodiment, the lower discharge limit voltage corresponds to the lower limit of the recommended voltage range. Continuing to discharge a battery cell until its voltage falls below the lower discharge limit voltage may accelerate battery degradation. The fact that continuous discharge of a battery cell may accelerate its degradation corresponds to the aforementioned "over-discharge." The discharge prohibition voltage corresponds to the discharge limit value. When a battery cell continues to discharge until its voltage falls below the discharge prohibition voltage, an anomaly (e.g., malfunction or failure) may occur in the battery cell. In the vehicle 100 according to this embodiment, the HVECU 50 has a warning sign for self-diagnosis (OBD) in the storage device 53, and the HVECU 50 is configured to raise the warning sign (e.g., the value of the sign changes from "0" to "1") when the voltage of any of the battery cells included in the drive battery 11 falls below the discharge prohibition voltage. The lower discharge limit voltage and discharge prohibition voltage of each battery cell included in the drive battery 11 according to this embodiment are 3.0V and 1.6V, respectively.

[0081] Reference Figure 5 When the lower limit voltage of discharge is set to V end In battery pack degradation diagnostic equipment, when the voltage of individual battery cells fluctuates significantly (e.g., reference line L12), the degradation of some battery cells within the battery pack may progress excessively, potentially shortening the battery pack's lifespan. Furthermore, when starting the engine using power supplied by the battery pack, the overall battery pack voltage decreases, as shown by line L13. Consequently, the voltage of some individual battery cells within the battery pack may fall below the discharge prohibition voltage, potentially triggering warning indicators.

[0082] Figure 6 It is used to describe the increase of V end The advantages are shown in the graph. Figure 6 Line L12 and Figure 5 The line L12 in the middle is the same. Figure 6 Line L14 in the diagram shows the V end In an embodiment where the voltage is set to be higher than the lower discharge limit voltage, the voltage distribution of the second cell at the end of discharge is shown.

[0083] Reference Figure 6 By V end Raising the voltage to a level higher than the lower discharge limit (e.g., see line L14) increases the margin of the discharge prohibition voltage, making it less likely for warning signs to rise. Furthermore, the number of battery cells in an over-discharged state decreases. Therefore, the reduction in battery pack life is limited, and insufficient battery pack voltage during engine start-up is also limited. Additionally, the range of variation in battery cell voltage tends to widen with longer discharge periods. Therefore, by increasing V... end The variation range of battery cell voltage is reduced.

[0084] Figure 7 It is used to describe the increase of V end The graph shows the disadvantages. Figure 7 Line L21 in the diagram illustrates an example of the voltage transition of the individual cells included in the drive battery 11 during discharge. The voltage transition during discharge varies slightly for each individual cell, but the general trend is the same.

[0085] Reference Figure 7 As a battery cell begins to discharge, its voltage gradually decreases. The value ΔV / ΔQ, obtained by differentiating the battery cell voltage (vertical axis) with respect to the discharge amount (horizontal axis) (corresponding to the slope of the curve), remains essentially constant after the initial discharge, but increases on the negative side after a period of continuous discharge. In the battery pack degradation diagnosis method according to this embodiment, voltage data (i.e., data indicating the voltage transition of the battery cells) of each battery cell in the battery pack is acquired during the discharge period (from the start to the end of discharge), and the degree of degradation of each battery cell is estimated based on the voltage data. Figure 7 The "Q" in end "Showing the relationship with V" end The corresponding discharge quantity (the discharge quantity at the end of the discharge). When V end As voltage increases, the discharge ends earlier and the discharge period becomes shorter. When the discharge period becomes shorter, the number of voltage data points used for battery pack degradation diagnosis decreases, reducing the accuracy of the estimation of the degradation degree of individual battery cells.

[0086] Figure 8 It is used to describe and determine V end The graph represents the method's curves. The vertical axis of the graph represents -ΔV / ΔQ, and the horizontal axis represents the discharge quantity. Since the individual cell voltage decreases as the discharge quantity increases, ΔV / ΔQ becomes negative, and -ΔV / ΔQ becomes positive. -ΔV / ΔQ indicates the degree of change in individual cell voltage per unit of discharge quantity. -ΔV / ΔQ has the same value as |ΔV / ΔQ|. Figure 8 Line L22 in the diagram illustrates an example of the -ΔV / ΔQ transition of the individual cells included in the drive battery 11 during discharge. The -ΔV / ΔQ transition during discharge varies slightly for each individual cell, but the general trend is the same.

[0087] For reference Figure 8 In the initial stage of a battery cell's discharge, -ΔV / ΔQ remains essentially constant. Subsequently, in the final stage of discharge, -ΔV / ΔQ rises sharply due to the increased reaction resistance. In the final stage of discharge, once -ΔV / ΔQ decreases, it reaches its lowest point during discharge (the voltage at the point of change) and then begins to rise sharply. As -ΔV / ΔQ increases, V... endThe reduction in discharge duration due to the increase in voltage (more specifically, the reduction in discharge duration for each increase in voltage) becomes wider. Before |ΔV / ΔQ| begins to rise sharply, the increase in V... end The advantages outweigh the increase in V end The drawback is that after |ΔV / ΔQ| begins to rise sharply, the increase in V... end The disadvantages outweigh the advantages of increasing V. end Advantages. In the battery degradation diagnosis method according to this embodiment, the battery cell voltage at the point where the battery cell voltage drops due to discharge and -ΔV / ΔQ (i.e., the degree of change in battery cell voltage per unit discharge) begins to rise sharply is set as V. end Such a V end This can be obtained in advance through experiments or simulations. Figure 7 and Figure 8 In the example shown, the length of the discharge period is represented by the amount of discharge, but the length of the discharge period can be represented by time.

[0088] Figure 9 This is a graph showing the discharge characteristics of a lithium-ion secondary battery. Figure 9 Lines L31, L32, and L33 illustrate the voltage transitions during discharge of the first lithium-ion secondary battery (hereinafter referred to as "first LIB"), the second lithium-ion secondary battery (hereinafter referred to as "second LIB"), and the third lithium-ion secondary battery (hereinafter referred to as "third LIB"), respectively. The first LIB through the third LIB are lithium-ion secondary batteries (more specifically, ternary LIBs) with varying degrees of degradation, ordered from the battery with the highest degradation level as the third LIB (high degradation), the second LIB (medium degradation), and the first LIB (low degradation).

[0089] Reference Figure 9 When the lithium-ion secondary battery in each cell of the driving battery 11 used in this embodiment has been discharged, |ΔV / ΔQ| begins to rise sharply when the voltage of the lithium-ion secondary battery becomes 3.4V. Therefore, in the battery degradation diagnosis method according to this embodiment, 3.4V is set as V. end In lithium-ion secondary batteries, the voltage at which all lithium sites in the positive electrode active material are occupied is 3.0V. In other words, V end The voltage is set to be higher than the voltage at which all lithium sites in the positive electrode active material of the lithium-ion secondary battery (cell) are occupied. Thus, discharge ends before all lithium sites in the positive electrode active material are occupied.

[0090] The discharge characteristics of lithium-ion secondary batteries change with battery degradation (see lines L31 to L33). However, the battery voltage (the voltage of the lithium-ion secondary battery) at which |ΔV / ΔQ| begins to rise sharply during discharge does not change significantly even as degradation progresses. Figure 9 In the example shown, the variation is within 0.1V.

[0091] As described above, in this embodiment, 3.4V is set as V. end Again with Figure 1 and Figure 2 Refer to together Figure 3 The voltage of any single cell included in the driving battery 11 is higher than V. end If (no in S17), repeat the processes from S15 to S17, and continue discharging the drive battery 11. Then, the voltage of all the battery cells included in the drive battery 11 becomes V. end When the discharge rate is lower (as in S17), in S18, the maintenance tool 200 stops the discharge of the drive battery 11.

[0092] After the drive battery 11 finishes discharging in S18, the maintenance tool 200 restarts the SOC limit control. Thus, the SOC of the drive battery 11 is once again limited to the predetermined SOC range.

[0093] By repeating the processes described in S15 to S17, data indicating the state of the drive battery 11 (especially the degree of degradation) is recorded in the storage device 203 of the maintenance tool 200. After the discharge ends in S18, in S19, the estimation unit 212 of the maintenance tool 200 uses the recorded data of the drive battery 11 to estimate the degree of degradation of each battery cell included in the drive battery 11.

[0094] Specifically, the maintenance tool 200 uses the data acquired in S15 (including voltage data indicating the transition from the discharge start voltage to the discharge end voltage of each battery cell) to obtain the voltage from the discharge start voltage to V for each battery cell. end The discharge quantity (Ah) within a given interval (discharge termination voltage) corresponds to the time integral of the discharge current (A). When the discharge current fluctuates within an interval, the discharge quantity can be obtained by integrating the discharge current per unit time with respect to time. When the discharge current is constant within the interval, the value obtained by multiplying the discharge current (A) by the discharge time (h) corresponds to the discharge quantity.

[0095] As described above, maintenance tool 200 calculates the range discharge amount of a single battery cell (i.e., from the discharge start voltage to V). endThe temperature of a battery cell, its range of discharge values, and its full charge capacity are mapped using a predetermined mapping. A mapping showing the relationship between the temperature of a battery cell, its range of discharge values, and its full charge capacity can be used to obtain the full charge capacity of a battery cell. When the temperature of a battery cell and its range of discharge values ​​are given to the mapping, the full charge capacity of the battery cell is output from the mapping. The temperature of the battery cell used can be the average temperature during discharge or the temperature at the start of discharge. This mapping can be pre-stored in storage device 203. The mapping can be a mapping common to all battery cells included in the drive battery 11. Maintenance tool 200 can obtain the mapping from an external server (e.g., a server that manages information about various batteries) or from vehicle 100.

[0096] As described above, in S19, the estimation unit 212 of the maintenance tool 200 estimates the full-charge capacity of each battery cell included in the drive battery 11. The full-charge capacity of a battery cell (the amount of electricity accumulated in the battery cell when fully charged) indicates the degree of degradation of the battery cell. The smaller the full-charge capacity of a battery cell, the higher the degree of degradation of the battery cell. When the process of S19 is performed, Figure 3 The series of processes shown here has ended.

[0097] exist Figure 3 Following the processing shown, the maintenance tool 200 can send diagnostic results (i.e., information indicating the full charge capacity of each battery cell included in the drive battery 11) to the vehicle 100. The diagnostic results received by the vehicle 100 can be stored in the storage device 53 of the HVECU 50. The notification device 104 can send a notification of the diagnostic results in response to a request from a user.

[0098] exist Figure 3 Following the processing described above, the HVECU 50 can start the engine 31 via the aforementioned start-up and charge the drive battery 11 using the electricity generated by the engine. The HVECU 50 can restore the SOC of the drive battery 11 to the SOC value prior to diagnosis. Alternatively, the HVECU 50 can charge the drive battery 11 until the vehicle 100 becomes capable of EV driving.

[0099] As described above, the battery degradation diagnosis method according to this embodiment includes: Figure 3 The series of processes shown.

[0100] exist Figure 3 In the process shown, while measuring the voltage of each individual battery cell included in the battery pack (drive battery 11), each individual battery cell is discharged, and the voltage of all battery cells included in the battery pack reaches a predetermined discharge end voltage (V). endDischarge ends when the signal is applied (S15 to S18). Discharge end voltage (V) end The value of a single cell is the cell voltage at which |ΔV / ΔQ| (i.e., the change in cell voltage per unit of discharge) begins to rise sharply as the cell voltage decreases due to discharge (e.g., 3.4V). (See [reference]). Figure 7 and Figure 8 ).exist Figure 3 In the process shown, the voltage of each cell in the battery pack is used from the discharge start voltage to the discharge end voltage (V). end The voltage data of the change in the battery pack (drive battery 11) is used to estimate the degree of degradation of each battery cell included in the battery pack (S19).

[0101] Figure 10 This shows the discharge termination voltage (V). end A graph showing the relationship between coverage and coverage rate. Figure 10 Lines L41, L42, and L43 in the diagram respectively indicate when the passage has been completed. Figure 3 The processing shown is used to perform the degradation diagnosis of the first LIB, second LIB, and third LIB described above, with coverage. Specifically, at the discharge end voltage (V end Coverage was measured when the voltage varied from 3.0V to 3.5V. Coverage corresponds to the ratio of the discharge capacity to the full charge capacity within the range. Coverage is determined by adjusting the voltage within the range of 3.0V to 3.5V. Figure 3 The coverage is obtained by dividing the interval discharge amount calculated in S19 by the full charge capacity. The coverage can be expressed as a percentage. The battery degradation levels are ranked from highest to lowest as follows: third LIB (degradation level: high), second LIB (degradation level: medium), and first LIB (degradation level: low).

[0102] Referring to 10, when V end Coverage drops sharply above 3.4V (see lines L41 to L43). At V... end In the degradation diagnosis method for 3.4V, the coverage is approximately 70%, and the degradation level of individual battery cells (ternary LIBs) can be estimated with sufficient accuracy. Furthermore, by using V... end As voltage increases to 3.4V, degradation of the individual battery cells (ternary lithium-ion batteries) is limited during discharge (see [link to relevant documentation]). Figure 6 Thus, by using the battery degradation diagnosis method according to this embodiment, the degradation degree of each battery cell included in the battery pack can be estimated with sufficient accuracy while limiting the degradation of individual battery cells during discharge.

[0103] Using a battery degradation diagnosis method, the full-charge capacity of each battery cell included in the battery pack (drive battery 11) is obtained. Therefore, the battery pack can be rebuilt by replacing only the most degraded battery cells in the battery pack. However, this disclosure is not limited to this; the battery pack including drive battery 11 can be replaced. Whether the battery pack needs to be replaced can be determined based on the full-charge capacity of the battery cell with the smallest capacity (the battery cell with the smallest full-charge capacity in the battery pack).

[0104] In this embodiment, 3.4V is set as the discharge termination voltage (V). end However, the discharge termination voltage is not limited to this and can be appropriately changed. For example, each of the battery cells included in the battery pack (drive battery 11) has a general formula Li x In embodiments of lithium-ion secondary batteries (LFP cells) using a cathode with an olivine-type crystal structure represented by FePO4 (cobalt-free iron phosphate cathode), a voltage selected from the range of 2.0V to 3.2V can be set as the discharge termination voltage. Using this discharge termination voltage, the degree of degradation of each cell in the battery pack can be estimated with sufficient accuracy while limiting battery degradation during discharge. Furthermore, in the battery degradation diagnosis method according to the embodiments, the discharge termination voltage (V... end The voltage is a fixed value (3.4V). However, this disclosure is not limited to this, and the discharge unit 211 can be configured to use the usage history of the vehicle 100 to estimate the degree of degradation of the drive battery 11, and change V. end Make V end The value increases as the estimated degree of degradation of the drive battery 11 increases.

[0105] Figure 11 This is a flowchart illustrating a method for setting the discharge termination voltage according to a variant example. Figure 3 The processes shown in the flowchart are executed before the processes shown in the diagram begin. For example, when the connector 250 of the maintenance tool 200 is connected to the DLC 55a of the parked vehicle 100, a predetermined command is input from the user to the HMI 204, the processes shown in the flowchart are executed. Figure 11 The process shown is then initiated by the process described below in S38. Figure 3 The processing shown.

[0106] and Figure 1 and Figure 2 Refer to together Figure 11In S31, the HVECU 50 sends vehicle history information (i.e., information indicating the usage history of vehicle 100) to the maintenance tool 200. The vehicle history information is sequentially acquired by various sensors mounted on vehicle 100 while the user is using vehicle 100 and is stored in storage device 53. In one example, the vehicle history information sent in S31 includes the cumulative mileage of vehicle 100.

[0107] In S32, the maintenance tool 200 receives vehicle history information. Thereafter, the discharge unit 211 of the maintenance tool 200 performs the processes described below in S33 to S38.

[0108] In S33, the maintenance tool 200 uses vehicle history information to estimate the degree of degradation of the drive battery 11. Specifically, it estimates that the longer the cumulative mileage of the vehicle 100, the higher the degree of degradation of the drive battery 11. Subsequently, in S34, the maintenance tool 200 determines whether the degree of degradation of the drive battery 11 is high, medium, or low.

[0109] When the estimated degradation level of the drive battery 11 is low ("low" in S34), in S35, the maintenance tool 200 sets 3.40V as the discharge termination voltage (V). end When the estimated degradation level of the drive battery 11 is approximately moderate (“medium” in S34), in S36, the maintenance tool 200 sets 3.42V as the discharge termination voltage (V). end When the estimated degradation level of the drive battery 11 is high (“high” in S34), in S37, the maintenance tool 200 sets 3.44V as the discharge termination voltage (V). end ).

[0110] When any of processes S35 to S37 are executed, in S38, the maintenance tool 200 generates a discharge control trigger for battery pack degradation diagnosis. Thus, the process begins. Figure 3 The processing shown.

[0111] Thus, according to Figure 11 The process shown, V end It was changed so that as the estimated degree of degradation of the drive battery 11 increases, V end The higher it becomes. Through such an embodiment, the cell voltage at which |ΔV / ΔQ| begins to rise sharply (the cell voltage at which |ΔV / ΔQ| begins to rise sharply varies depending on the degree of degradation of the drive battery 11) (see...) Figure 9 and Figure 10 To fine-tune the discharge termination voltage (V) end ).

[0112] Figure 3The processing shown can be modified appropriately. For example, the discharge termination voltage (V) end The cell voltage can be such that, at this cell voltage, the change in cell voltage per unit discharge amount becomes a predetermined value or higher as the cell voltage decreases due to discharge. Then, the discharge unit 211 can be configured to determine whether |ΔV / ΔQ| has become a predetermined value or higher as the cell voltage decreases due to the discharge of each cell in the battery pack, and to end the discharge when it is determined that |ΔV / ΔQ| of all cells in the battery pack has become a predetermined value or higher.

[0113] Figure 12 It shows Figure 3 The flowchart shows a variant example of the processing shown. Besides replacing S17 with S17A and S17B (… Figure 3 In addition to, Figure 12 The processing shown is in Figure 3 The processing shown is the same. It will be described below. Figure 12 The processing shown focuses on... Figure 3 The differences in the processing shown.

[0114] and Figure 1 and Figure 2 Refer to together Figure 12 In S17A, the maintenance tool 200 calculates |ΔV / ΔQ| for each battery cell by differentiating the cell voltage with respect to the discharge amount during the voltage transition mapped (plotted) during the discharge of each battery cell. In S17B, the maintenance tool 200 determines whether |ΔV / ΔQ| for all battery cells included in the drive battery 11 has become a predetermined value (hereinafter referred to as "Th") or a higher value.

[0115] Figure 13 It is a graph used to describe the method of setting Th. Figure 13 Line L22 and Figure 8 The line L22 in the middle is the same. For example... Figure 13 As shown, Th is set such that the cell voltage at which |ΔV / ΔQ| becomes Th or higher as the cell voltage decreases due to discharge becomes the cell voltage at which |ΔV / ΔQ| begins to rise sharply as the cell voltage decreases due to discharge.

[0116] When the |ΔV / ΔQ| of any battery included in the drive battery 11 is lower than Th, the maintenance tool 200... Figure 12In S17B, a negative judgment is made, and the processing from S15 to S17B is repeated, and the drive battery 11 is continuously discharged. Then, when the |ΔV / ΔQ| of all the battery cells included in the drive battery 11 becomes Th or higher (yes in S17B), in S18, the maintenance tool 200 ends the discharge of the drive battery 11.

[0117] Thus, the discharge unit 211 can determine whether |ΔV / ΔQ| begins to rise sharply based on whether |ΔV / ΔQ| has become a predetermined value or higher while the cell voltage decreases due to discharge. Figure 12 The process shown allows for easy determination of whether |ΔV / ΔQ| begins to rise sharply as the cell voltage decreases due to discharge. Then, when |ΔV / ΔQ| begins to rise sharply, the discharge unit 211 can terminate the discharge of the cell.

[0118] Figure 14 It shows Figure 2 A diagram illustrating a variant example of the maintenance tool 200 shown. (Refer to...) Figure 14 In addition to the discharge unit 211 and the estimation unit 212, the maintenance tool 200A also includes a management unit 213 and a data acquisition unit 214. The management unit 213 is configured to manage V... end V end The battery discharge is performed to obtain data for estimating the degree of battery degradation, corresponding to the discharge termination voltage indicating the time when the battery discharge ends. The data acquisition unit 214 stores the battery voltage in the management unit 213 as the discharge termination voltage when |ΔV / ΔQ| (the degree of voltage change per unit of discharge) becomes a predetermined value (Th) or higher after the start of discharge. The management unit 213 in the maintenance tool 200A is embodied by the storage device 203A. The data acquisition unit 214 in the maintenance tool 200A is embodied by the processor 201 and the diagnostic program stored in the storage device 203A.

[0119] Figure 15 It is shown that it is related to... Figure 14 The flowchart illustrates the data acquisition-related processing performed by the maintenance tool 200A. The data acquisition unit 214 of the maintenance tool 200A sends control commands to the HVECU 50 while the vehicle 100 is connected to the maintenance tool 200A in an unused state (e.g., before shipment), thereby executing… Figure 15 S41 to S47.

[0120] Reference Figure 15 as well as Figure 14 In step S41, maintenance tool 200A prepares to discharge drive battery 11. In step S41, maintenance tool 200A can perform the above-described... Figure 3 The processing of S10 to S14.

[0121] Subsequently, in S42, maintenance tool 200A discharges the drive battery 11. The processing in S42 is compatible with... Figure 3 The processing is the same as that of S16.

[0122] Subsequently, in S43, the maintenance tool 200A measures the state (voltage, current, and temperature) of each cell included in the drive battery 11 and records the measurement results in the storage device 203A. The processing in S43 is compatible with... Figure 3 The processing is the same as that of S15.

[0123] Subsequently, in S44, the maintenance tool 200A calculates |ΔV / ΔQ| for each battery cell by differentiating the cell voltage with respect to the discharge amount during the voltage transition of each battery cell included in the drive battery 11 during discharge. Then, in S45, the maintenance tool 200A determines whether |ΔV / ΔQ| for all battery cells included in the drive battery 11 has become Th or a higher value. The processing in S44 and S45 can be compared with... Figure 12 The processing of S17A and S17B is the same.

[0124] When the |ΔV / ΔQ| of all the battery cells included in the drive battery 11 becomes Th or higher (yes in S45), in S46, the maintenance tool 200A specifies the discharge amount (Q) when the |ΔV / ΔQ| of all the battery cells included in the drive battery 11 becomes Th or higher. end The maintenance tool 200A determines the specified battery voltage as V, where the battery voltage decreases due to discharge and |ΔV / ΔQ| begins to rise sharply. end V end It can be the voltage of the drive battery 11 when |ΔV / ΔQ| of all the battery cells included in the drive battery 11 has become Th or higher (e.g., the average battery cell voltage).

[0125] Subsequently, in S47, maintenance tool 200A terminates the discharge of drive battery 11. The processing in S47 can be compared with... Figure 3 The processing is the same as that of S18.

[0126] Subsequently, in S48, the data acquisition unit 214 of the maintenance tool 200A will output the discharge termination voltage (V). endInformation indicating the type of battery constituting the drive battery 11 is stored in the management unit 213 in association with the battery type. The maintenance tool 200A can obtain this battery type information from the vehicle 100. This battery type information may be pre-stored in the storage device 53. In one example, the battery type information includes the battery manufacturer and model. The maintenance tool 200A can identify the type of battery constituting the drive battery 11 (e.g., lithium-ion rechargeable battery / nickel-metal hydride rechargeable battery) based on the battery manufacturer and model. For batteries installed in vehicles other than the vehicle 100, this can be achieved by performing... Figure 15 The series of processes shown are used to reduce the discharge end voltage (V) end The data is stored in the management unit 213. The management unit 213 manages the discharge termination voltage (V) of various battery types. end The management unit 213 manages the discharge end voltage (V) in association with information indicating the type of battery in each cell. end When processing S48 is executed, the process ends. Figure 15 The series of processes shown.

[0127] Figure 16 It is used to describe based on usage Figure 15 The flowchart shown illustrates a method for processing acquired data to set the discharge termination voltage. Figure 3 The processes shown in the flowchart are executed before the processes shown in the diagram begin. For example, when a predetermined command is input from the user to the HMI 204 after the maintenance tool 200A is connected to the vehicle 100 that has been put into use, the processes shown in the flowchart are executed. Figure 16 The process shown is then initiated by the process described below in S54. Figure 3 The processing shown.

[0128] and Figure 14 Refer to together Figure 16 In S51, HVECU 50 sends information to maintenance tool 200A indicating the type of battery constituting drive battery 11 (e.g., the battery manufacturer and model of the battery constituting drive battery 11).

[0129] In S52, the maintenance tool 200A receives information indicating the type of battery. Thereafter, the discharge unit 211 of the maintenance tool 200A performs the processes described below in S53 and S54.

[0130] In S53, the maintenance tool 200A uses information indicating the type of battery to obtain from the management unit 213 the discharge end voltage (V) corresponding to the type of battery constituting the drive battery 11. end Then, in S54, the maintenance tool 200A generates a discharge control start trigger for battery pack degradation diagnosis. Thus, the process begins. Figure 3 The processing shown is in... Figure 3 In the process shown, the appropriate discharge termination voltage (i.e., V set in S53) is based on the type of battery installed in the vehicle 100. end Discharge the battery. In this way, the degree of degradation of individual battery cells during discharge can be estimated with sufficient accuracy while limiting the extent of degradation.

[0131] The functions of the discharge unit 211 and the estimation unit 212 can be implemented in the vehicle 100. Figure 17 It shows Figure 2 A diagram illustrating a variant example of the HVECU 50 is shown. (Refer to...) Figure 17 The HVECU 50A mounted on the vehicle 100 may include a discharge unit 211 and an estimation unit 212. In such an embodiment, the HVECU 50A mounted on the vehicle 100 performs... Figure 3 The processing is shown in the diagram. The discharge unit 211 and estimation unit 212 in the HVECU 50A can be embodied by the processor 51 and the program executed by the processor 51 (e.g., a diagnostic program stored in the storage device 53A). However, each of the above-described discharge unit 211, estimation unit 212, and data acquisition unit 214 can be embodied by dedicated hardware (electronic circuitry).

[0132] In the above embodiments, the battery pack mounted on an HEV that does not include a plug-in port is the target of degradation diagnosis. However, this disclosure is not limited thereto, and the battery pack mounted on a plug-in hybrid electric vehicle (PHEV) that includes a plug-in port can also be the target of degradation diagnosis. Furthermore, the battery pack mounted on other xEVs (e.g., BEVs, FCEVs, range-extended EVs) can also be the target of degradation diagnosis. xEVs are vehicles that use electricity as a complete or partial driving power source.

[0133] In battery packs where degradation is diagnosed using any of the methods described above, it is not necessary to connect all individual battery cells in series (see [reference]). Figure 2 The structure of the battery pack whose degradation is being diagnosed is arbitrary. Figure 18 It shows Figure 2 A diagram illustrating a variant example of the battery pack shown. For example, Figure 18 The battery pack 500 shown can be a target for degradation diagnosis. The battery pack 500 includes N parallel battery cell blocks (i.e., parallel battery cell blocks CB-1 to CB-N). Each of the parallel battery cell blocks CB-1 to CB-N includes multiple battery cells connected in parallel. The number of battery cells connected in parallel in each parallel battery cell block is arbitrary, but... Figure 18In the example shown, there are three battery cells connected in parallel. The parallel battery cell blocks CB-1 to CB-N are connected in series via power lines.

[0134] The embodiments disclosed herein should be considered exemplary in all respects and not restrictive. The scope of the invention is shown not by the description of the above embodiments but by the claims, and is intended to include equivalents to the claims and all modifications within the scope of the claims.

Claims

1. A battery degradation diagnostic device, characterized in that, The degradation diagnostic device includes one or more processors, the one or more processors being configured to: After removing the SOC range limitation on each of the multiple battery cells included in the battery pack, each of the multiple battery cells included in the battery pack is charged using the electricity generated by the engine until the voltage of each of the multiple battery cells included in the battery pack has become a predetermined starting voltage or a higher voltage. Discharging of each of the plurality of battery cells included in the battery pack is performed while measuring the voltage of each of the plurality of battery cells; Using voltage data indicating the transition of the voltage of each of the plurality of battery cells included in the battery pack from the discharge start voltage to a predetermined discharge end voltage, the degree of degradation of each of the plurality of battery cells included in the battery pack is estimated. The predetermined discharge end voltage is the battery cell voltage at which the degree of change of the battery cell voltage per unit discharge begins to rise sharply as the battery cell voltage decreases due to discharge. The degree of change of the battery cell voltage per unit discharge is determined to begin to rise sharply based on the fact that the degree of change of the battery cell voltage per unit discharge has become a predetermined value or higher as the battery cell voltage decreases due to discharge. The discharge ends when the voltage of all the individual cells in the battery pack reaches the predetermined discharge end voltage; and After the discharge ends, the SOC range of each of the multiple battery cells included in the battery pack is restricted again.

2. The degradation diagnostic equipment according to claim 1, characterized in that, Each of the multiple battery cells included in the battery pack is a lithium-ion secondary battery; and The predetermined discharge termination voltage is higher than the voltage at which all lithium sites in the positive electrode active material of the lithium-ion secondary battery are occupied.

3. The degradation diagnostic equipment according to claim 1, characterized in that, Each of the multiple battery cells included in the battery pack has a general formula. The lithium-ion secondary battery represents a positive electrode with a layered crystal structure; and The predetermined discharge termination voltage is above 3.1V and below 3.5V.

4. The degradation diagnostic equipment according to claim 1, characterized in that, Each of the multiple battery cells included in the battery pack has a general formula. The lithium-ion secondary battery with a positive electrode representing an olivine-type crystal structure; and The predetermined discharge termination voltage is above 2.0V and below 3.2V.

5. The degradation diagnostic device according to any one of claims 1 to 4, characterized in that, The one or more processors are configured to determine whether the degree of change in the voltage per unit discharge of the battery cell is a predetermined value or higher when the voltage of the battery cell decreases due to the discharge of each battery cell included in the battery pack, and to terminate the discharge when it is determined that the degree of change in the voltage per unit discharge of all the battery cells included in the battery pack has become a predetermined value or higher.

6. The degradation diagnostic device according to any one of claims 1 to 4, characterized in that, The battery pack is mounted on the vehicle; and The one or more processors are configured to use the vehicle's usage history to estimate the degree of degradation of the battery pack and to change the predetermined discharge end voltage such that the predetermined discharge end voltage becomes higher as the estimated degree of degradation of the battery pack increases.

7. The degradation diagnostic device according to any one of claims 1 to 4, characterized in that, All the individual battery cells included in the battery pack are connected in series; and The one or more processors are configured to maintain a current value during the discharge of each of the plurality of battery cells.

8. The degradation diagnostic device according to any one of claims 1 to 4, characterized in that, The battery pack is configured to supply power to onboard electrical loads; and The one or more processors are configured to perform the discharge by controlling the on-board electrical load.

9. A method for diagnosing battery degradation, wherein the method is executed by one or more processors, characterized in that, The degradation diagnosis method includes: After removing the SOC range limitation on each of the multiple battery cells included in the battery pack, each of the multiple battery cells included in the battery pack is charged using the electricity generated by the engine until the voltage of each of the multiple battery cells included in the battery pack has become a predetermined starting voltage or a higher voltage. While measuring the voltage of each of the plurality of battery cells included in the battery pack, the discharge of each of the plurality of battery cells is performed, and the discharge ends when the voltage of all the battery cells included in the battery pack reaches a predetermined discharge end voltage. The predetermined discharge end voltage is the battery cell voltage at which the degree of change of the battery cell voltage per unit discharge begins to rise sharply as the battery cell voltage decreases due to discharge. The degree of change of the battery cell voltage per unit discharge is determined to begin to rise sharply based on the fact that the degree of change of the battery cell voltage per unit discharge has become a predetermined value or higher as the battery cell voltage decreases due to discharge. Using voltage data indicating the voltage transition of each of the plurality of battery cells included in the battery pack from the discharge start voltage to the predetermined discharge end voltage, the degree of degradation of each of the plurality of battery cells included in the battery pack is estimated; and After the discharge ends, the SOC range of each of the multiple battery cells included in the battery pack is restricted again.

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