Method for in-vehicle condition estimation with regard to voltage decay

Abstract

A vehicle includes a system that performs a method for operating the vehicle.A processor receives an initial voltage fade state of a battery of the vehicle and a model of an initial state of the battery of the vehicle, starts a charging operation of the battery, measures a terminal voltage of the battery during charging, updates the model during the charging operation using the terminal voltage, ends the charging operation, receives measured values ​​of a cathode voltage after ending the charging operation, determines a maximum cathode voltage from the measured values, determines an updated voltage fade state of the battery based on the maximum cathode voltage, selects a relationship between the cathode voltage and the lithiation state based on the updated voltage fade state, calculates a lithiation state of a cathode from the maximum cathode voltage using the selected relationship, and operates the vehicle based on the updated voltage fade state.

Description

INTRODUCTION

[0001] The present disclosure relates to determining a condition of a battery pack for a vehicle, and more particularly to a system and method for determining battery pack voltage fade.

[0002] Electric vehicles use electric batteries as a power source. The electric batteries can be lithium-manganese-rich batteries, such as lithium manganese oxide (LiMnO) batteries. In lithium-manganese-rich batteries, the thermodynamic relationship between the equilibrium potential and the material state of lithiation changes over the lifetime. This change can be attributed to gradual structural changes of the active material over the lifetime of the battery. A battery capacity fade state indicates a remaining capacity of the battery and can be used to determine a remaining lifetime of the battery. Accordingly, it is desirable to provide a method for determining a battery fade state based on measurable battery parameters. SUMMARY

[0003] According to an exemplary embodiment, a method for operating a vehicle is disclosed. The method includes obtaining an initial voltage fade state of a battery of the vehicle and a model of an initial state of the battery of the vehicle, initiating a charging operation of the battery, measuring a terminal voltage of the battery during charging, updating the model of the battery during the charging operation using the terminal voltage, terminating the charging operation, obtaining a plurality of measured values ​​of a cathode voltage after terminating the charging operation, determining a maximum cathode voltage from the plurality of measured values, determining an updated voltage fade state of the battery based on the maximum cathode voltage, selecting a relationship between the cathode voltage and the lithiation state based on the updated voltage fade state,calculating a state of lithiation of a cathode from the maximum cathode voltage using the selected relationship and operating the vehicle based on the updated voltage fading state.

[0004] In addition to one or more of the features described herein, the model further includes a positive electrode model representing a cathode of the battery and a negative electrode model representing an anode of the battery, the method further including updating the positive electrode model and the negative electrode model during the charging operation.

[0005] In addition to one or more of the features described herein, the method further includes determining an open circuit voltage of the cathode from the terminal voltage and determining the lithiation state of the cathode from the open circuit voltage of the cathode using the selected relationship.

[0006] In addition to one or more of the features described herein, the positive electrode model or the negative electrode model includes a state variable, wherein the state variable includes an open circuit voltage and / or a hysteresis voltage and / or an ohmic resistance.

[0007] In addition to one or more of the features described herein, the positive electrode model or the negative electrode model includes a dynamic parameter, wherein the dynamic parameter includes a time constant indicating a response of the battery to an applied load.

[0008] In addition to one or more of the features described herein, the method further includes updating the state variable and the dynamic parameter using a Kalman filter.

[0009] In addition to one or more of the features described herein, operating the vehicle further includes limiting an amount of current supplied to the vehicle from the battery based on the updated voltage fade state or the state of lithiation.

[0010] According to another exemplary embodiment, a system for operating a vehicle is disclosed. The system includes a processor. The processor is configured to obtain an initial voltage fade state of a battery of the vehicle and a model of an initial state of the battery of the vehicle, to begin a charging operation of the battery, to measure a terminal voltage of the battery during charging, to update the model of the battery during the charging operation using the terminal voltage, to terminate the charging operation, to obtain a plurality of measured values ​​of a cathode voltage after the charging operation has ended, to determine a maximum cathode voltage from the plurality of measured values, to determine an updated voltage fade state of the battery based on the maximum cathode voltage, to select a relationship between the cathode voltage and the lithiation state based on the updated voltage fade state,to calculate a state of lithiation of a cathode from the maximum cathode voltage using the selected relationship and to operate the vehicle based on the updated voltage fading state.,

[0011] In addition to one or more of the features described herein, the model further includes a positive electrode model representing a cathode of the battery and a negative electrode model representing an anode of the battery, and further includes updating the positive electrode model and the negative electrode model during the charging operation.

[0012] In addition to one or more of the features described herein, the processor is further configured to determine an open circuit voltage of the cathode from the terminal voltage and to determine the lithiation state of the cathode from the open circuit voltage of the cathode using the selected relationship.

[0013] In addition to one or more of the features described herein, the positive electrode model or the negative electrode model includes a state variable, wherein the state variable includes an open circuit voltage and / or a hysteresis voltage and / or an ohmic resistance.

[0014] In addition to one or more of the features described herein, the positive electrode model or the negative electrode model includes a dynamic parameter, wherein the dynamic parameter includes a time constant indicating a response of the battery to an applied load.

[0015] In addition to one or more of the features described herein, the processor is further configured to update the state variable and the dynamic parameter using a Kalman filter.

[0016] In addition to one or more of the features described herein, the processor is further configured to operate the vehicle by limiting an amount of current supplied to the vehicle from the battery based on the updated voltage fade state or the state of lithiation.

[0017] According to another exemplary embodiment, a vehicle is disclosed. The vehicle includes a processor. The processor is configured to obtain an initial voltage fade state of a battery of the vehicle and a model of an initial state of the battery of the vehicle, to begin a charging operation of the battery, to measure a terminal voltage of the battery during charging, to update the model of the battery during the charging operation using the terminal voltage, to terminate the charging operation, to obtain a plurality of measured values ​​of a cathode voltage after the charging operation has ended, to determine a maximum cathode voltage from the plurality of measured values, to determine an updated voltage fade state of the battery based on the maximum cathode voltage, to select a relationship between the cathode voltage and the lithiation state based on the updated voltage fade state,to calculate a state of lithiation of a cathode from the maximum cathode voltage using the selected relationship and to operate the vehicle based on the updated voltage fading state.,

[0018] In addition to one or more of the features described herein, the model further includes a positive electrode model representing a cathode of the battery and a negative electrode model representing an anode of the battery, and further includes updating the positive electrode model and the negative electrode model during the charging operation.

[0019] In addition to one or more of the features described herein, the processor is further configured to determine an open circuit voltage of the cathode from the terminal voltage and to determine the lithiation state of the cathode from the open circuit voltage of the cathode using the selected relationship.

[0020] In addition to one or more of the features described herein, the positive electrode model or the negative electrode model includes a state variable, wherein the state variable includes an open circuit voltage and / or a hysteresis voltage and / or an ohmic resistance.

[0021] In addition to one or more of the features described herein, the positive electrode model or the negative electrode model includes a dynamic parameter, wherein the dynamic parameter includes a time constant indicating a response of the battery to an applied load.

[0022] In addition to one or more of the features described herein, the processor is further configured to update the state variable and the dynamic parameter using a Kalman filter.

[0023] The above features and advantages and other features and advantages of the disclosure will be readily apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further features, advantages and details appear only as examples in the following detailed description, which refers to the drawings; they show: Fig. 1 an embodiment of a vehicle according to an exemplary embodiment; Fig. 2 an electrical system of the vehicle; Fig. 3 is a view of a schematic representation of an electrochemical battery cell of the power source in a disassembled state; Fig. 4 a system model for the electrochemical battery cell; Fig. 5 a view of the system model containing a reference electrode; Fig. 6 is a detailed view of the positive electrode model according to an illustrative embodiment; Fig. 7 is a detailed view of the negative electrode model according to an illustrative embodiment; Fig. 8 is a flowchart of a method for determining a voltage fade condition of a battery cell after a charging operation according to one embodiment; Fig. 9 is a flowchart of a method for determining a voltage fade state of a battery cell from the maximum cathode voltage; Fig. 10 is a graph illustrating a difference between a capacity fade and a voltage fade; and Fig. 11 shows a graph relating the cathode potential to the reversible capacity of the battery cell. DETAILED DESCRIPTION

[0025] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or uses. It should be understood that corresponding reference numerals designate like or corresponding parts and features throughout the drawings. As used herein, the term module refers to processing circuitry that may include an application-specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory executing one or more software or firmware programs, combinational logic circuitry, and / or other suitable components that provide the described functionality.

[0026] Fig. 1 shows an embodiment of a vehicle 10 according to an exemplary embodiment, including a vehicle body 12 that at least partially defines an occupant compartment 14. Furthermore, the vehicle body 12 supports various vehicle subsystems, including a propulsion system 16 and other subsystems for supporting functions of the propulsion system 16, and other vehicle components such as a braking subsystem, a suspension system, a steering subsystem, and others.

[0027] The vehicle 10 may be an electric vehicle (EV), a hybrid vehicle, or any other vehicle. According to one embodiment, the vehicle 10 is an electric vehicle that includes multiple motors and / or drive systems. The vehicle 10 may be a passenger car, a truck, a van, a bus, a motorcycle, or another type of motor vehicle. Any number of drive units may be included, such as one or more drive units for applying torque to the front wheels (not shown) and / or to the rear wheels (not shown). The drive units are controllable to operate the vehicle 10 in various modes, such as a normal mode, a high-performance mode (in which additional torque is applied), all-wheel drive ("AWD"), front-wheel drive ("FWD"), rear-wheel drive ("RWD"), and others.

[0028] The propulsion system 16 is, for example, a multiple drive system that includes a front drive unit 20 for driving the front wheels and rear drive units for driving the rear wheels. The front drive unit 20 includes a front electric motor 22 and a front power converter 24 (e.g., a front power converter module or FPIM), as well as other components such as a cooling system. A left rear drive unit 30L includes a left rear electric motor 32L and a left rear power converter 34L. A right rear drive unit 30R includes a right rear electric motor 32R and a right rear power converter 34R. The front power converter 24, the left rear power converter 34L, and the right rear power converter 34R (e.g., power converter units or PIMs) each convert direct current (DC) power from a high-voltage (HV) battery system 40 into multi-phase alternating current (AC) power (e.g., two-phase, three-phase, six-phase, etc.).) alternating current (AC) power to drive the front electric motor 22, the left rear electric motor 32L and the right rear electric motor 32R.

[0029] As in Fig. As shown in Figure 1, the drive systems comprise separate electric motors. However, embodiments are not limited to this. For example, instead of separate motors, multiple drives may be provided by a single machine having multiple sets of physically independent windings.

[0030] As also in Fig. 1, the drive systems are configured such that the front electric motor 22 drives the front wheels (not shown) and the left rear electric motor 32L and the right rear electric motor 32R drive the rear wheels (not shown). However, embodiments are not limited to this, as there may be any number of drive systems and / or motors in different locations (e.g., one motor driving each wheel, two motors per axle, etc.). Furthermore, embodiments are not limited to a dual drive system, as embodiments may be used with a vehicle having any number of motors and / or power converters.

[0031] In the propulsion system 16, the front-wheel drive unit 20, the left rear-wheel drive unit 30L, and the right rear-wheel drive unit 30R are electrically connected to the battery system 40. The battery system 40 may also be electrically connected to other electrical components (also referred to as "electrical loads") such as vehicle electronics (e.g., via an auxiliary power module or APM 42), heating devices, cooling systems, and others. The battery system 40 may be configured as a rechargeable energy storage system (RESS).

[0032] According to one embodiment, battery system 40 includes multiple separate battery assemblies, in which each battery assembly can be independently charged and used to independently supply power to one or more propulsion systems. For example, battery system 40 includes a first battery assembly, such as a first battery pack 44 connected to front-end power converter 24, and a second battery pack 46. First battery pack 44 includes multiple battery modules 48, and second battery pack 46 includes multiple battery modules 50. Each battery module 48, 50 includes a number of individual cells (not shown).

[0033] Both the front electric motor 22 and the left rear electric motor 32L and the right rear electric motor 32R are three-phase motors with three-phase motor windings. However, the embodiments described here are not limited to this. For example, the motors can be any multi-phase machines powered by multi-phase converters, and the drive units can be implemented using a single machine with independent sets of windings.

[0034] The battery system 40 and / or the propulsion system 16 include a switching system with various switching devices for controlling the operation of the first battery pack 44 and the second battery pack 46 and for selectively connecting the first battery pack 44 and the second battery pack 46 to the front drive unit 20, to the left rear drive unit 30L, and to the right rear drive unit 30R. The switching devices are also operable to selectively connect the first battery pack 44 and the second battery pack 46 to a charging system. The charging system may be used to charge the first battery pack 44 and the second battery pack 46 and / or to supply power from the first battery pack 44 and / or the second battery pack 46 to charge another energy storage system (e.g., vehicle-to-vehicle (V2V) charging and / or vehicle-to-all (V2X) charging). The charging system contains one or more charging modules.For example, a first on-board charging module (OBCM) 52 is electrically connected to a charging port 54 for charging to and from an AC system or device, such as a utility's AC power supply. A second OBCM 53 may be included for DC charging (e.g., DC fast charging or DCFC). As shown in FIG. Fig. 1, the AC power supply of an electric utility is a charging station 110 connected to the charging port 54 via a cable 112.

[0035] According to one embodiment, the switching system includes a first switching device 60 that selectively connects the first battery pack 44 to the front power converter 24, to the left rear power converter 34L, and to the right rear power converter 34R, and a second switching device 62 that selectively connects the second battery pack 46 to the front power converter 24, to the left rear power converter 34L, and to the right rear power converter 34R. The switching system also includes a third switching device 64 (also referred to as a "battery switching device") for selectively connecting the first battery pack 44 to the second battery pack 46 in series.

[0036] Any of various controllers may be used to control functions of the vehicle's electrical system, including the battery system 40, the switching system, the drive units, etc. A controller 65 includes any suitable processing device or processing unit and may utilize an existing controller such as a drive system controller, a RESS controller, and / or controllers within the drive system. For example, a controller 65 may be included to control switching and drive control operations as discussed herein.

[0037] The controller 65 may include processing circuitry, which may include an application-specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory executing one or more software programs, combinational logic circuitry, and / or other suitable components that provide the described functionality. The controller 65 may include a non-transitory computer-readable medium storing instructions that, when processed by one or more processors of the controller 65, implement a method for determining a voltage fade condition of a battery pack during a charging operation, in accordance with one or more embodiments detailed herein.

[0038] The vehicle 10 also includes a computer system 55 that includes one or more processing devices 56 and a user interface 58. The computer system 55 can communicate with the charging system controller, for example, to provide commands thereto in response to user input. The various processing devices, modules, and units can communicate with each other via a communication device or system, such as a controller area network (CAN) bus or a transmission control protocol (TCP) bus.

[0039] Fig. 2 shows an electrical system 200 of the vehicle 10. The electrical system 200 includes a power source 202 that is discharged while supplying power to a load 204. The load includes a propulsion system load. The power source 202 is comprised of an array of electrochemical battery cells. The battery cells are recharged by the charging station 110. The operation of the charging station 110 is controlled by a switch 206. A controller 208 controls the operation of the switch 206. Sensors 210 measure various parameters of the battery cells, such as the terminal voltage signal (V T), a temperature (T) of the battery, etc. The controller 208 processes the measured parameters according to the methods disclosed herein to determine a state of lithiation of the battery cells and / or a lifetime state of the battery cells of the power source 202. The controller 208 controls the operation of the battery pack based on the state of lithiation and / or the voltage fade state.

[0040] Fig. 3 shows a view 300 of a schematic representation of an electrochemical battery cell 302 of the power source 202 in a disassembled state. The electrochemical battery cell 302 includes one or more cathodes 304, one or more separators 306, and one or more anodes 308. Each separator 306 is disposed between a cathode 304 and an anode 308. The one or more cathodes 304, the one or more separators 306, and the one or more anodes 308 are arranged in a stack. Each cathode 304 consists of a first set of electroactive materials, and the anode 308 consists of a second set of electroactive materials. An electroactive material is a material that can accept charged particles and release charged particles. A set of electroactive materials can be a single material or a mixture of materials. The one or more anodes 308 can, for example, B.a mixture of graphite and silicon. The one or more cathodes 304 may be a mixture of a cobalt cathode (NMC) and a cobalt-free manganese-rich cathode (LMR). According to one embodiment, a cathode 304 may be made of a lithium-manganese-rich material such as lithium manganese oxide or another suitable material, and an anode 308 may be made of graphite. The cathode 304 is connected to a first terminal A, and the anode 308 is connected to a second terminal B. A terminal voltage V may be applied across the battery cell between the first terminal A and the second terminal B. Tmeasured. The terms "cathode" and "positive electrode" can be used interchangeably, and the terms "anode" and "negative electrode" can be used interchangeably. A battery capacity fade state measures a degree of battery degradation or remaining capacity. A voltage fade state is related to voltage fade during normal battery use, while a capacity fade state is related to a loss of battery active material during various side reactions or mechanical stresses in the active material. The voltage fade state is linked to the lifetime state. The voltage fade state and the lifetime state are numbers between 0 and 1, and the sum of the voltage fade state and the lifetime state is defined as equal to 1. A battery state of charge indicates an amount of lithiation of the cathode 304 and the anode 308.

[0041] Fig. 4 shows a system model 400 for the electrochemical battery cell 302. The system model 400 includes a positive electrode model 402 representing the cathode 304 and a negative electrode model 404 representing the anode 308. A system resistance value 406 (R sys ) includes a resistance value of the battery cell due to internal welds, connecting leads, current collectors, etc. The system resistance value 406 is shown between the positive electrode model 402 and a first terminal node A. Between the first terminal node A and a second node B connected to the negative electrode model 404, a terminal voltage V T the battery cell can be measured

[0042] Fig. 5 shows a view 500 of the system model 400, which includes a reference electrode 502. The reference electrode 502 includes a third terminal node C and the positive electrode model 402 includes a fourth terminal node D. Between the third terminal node C and the fourth terminal node D, a cathode voltage V P,sense be measured. As in Fig. As shown in Figure 5, the reference electrode 502 may be arranged in contact with the cathode. Alternatively, the reference electrode 502 may be arranged in contact with the anode. When the reference electrode 502 is arranged in contact with the anode, it is used to explicitly measure the anode potential, and the cathode potential is calculated by adding the anode potential to the battery terminal voltage.

[0043] Fig. 6 shows a detailed view 600 of the positive electrode model 402 according to an illustrative embodiment. The positive electrode model 402 includes various state variables and dynamic parameters. The state variables include voltages present at the cathode 304 during operation of the battery cell, such as an open circuit voltage 602 (V OCV,P ) of the positive electrode, an ohmic resistance of 604 (V ohmic,P ) of the positive electrode (i.e. a voltage loss at the positive electrode due to an ohmic resistance) and a hysteresis voltage (V hys,P ) 606 of the positive electrode. The ohmic resistance 604 of the positive electrode is related to an ohmic resistance of the cathode 304, and the hysteresis voltage 606 of the positive electrode results from hysteresis effects in the cathode. The open-circuit voltage 602 V OCV,P the positive electrode can be determined by measuring the cathode potential V Pwith respect to the reference electrode 502 under an open-load equilibrium condition. The dynamic parameters may represent responses of the cathode 304 to a load applied during charging. The responses may result from electrochemical processes occurring during charging. For illustrative purposes, the dynamic parameters are time constants represented by resistor-capacitor pairs 608, 610, and 612.

[0044] Fig. Figure 7 shows a detailed view 700 of the negative electrode model 404 according to an illustrative embodiment. The negative electrode model 404 includes various state variables and dynamic parameters. The state variables include voltages present at the anode 308 during operation of the battery cell, such as an open circuit voltage 702 (V OCV,N ) of the negative electrode, an ohmic resistance of 704 (V ohmic,N) of the negative electrode (i.e. a voltage loss at the negative electrode due to an ohmic resistance) and a hysteresis voltage (V hys,N ) 706 of the negative electrode. The ohmic resistance 704 of the negative electrode is related to an ohmic resistance of the anode 308, and the hysteresis voltage 706 of the negative electrode results from hysteresis effects in the anode. The dynamic parameters can represent a response of the anode 308 to an applied load. For illustrative purposes, dynamic parameters are time constants represented by resistor-capacitor pairs 708, 710, 712.

[0045] A state of the electrochemical battery cell is determined by individually determining the state of the cathode 304 using the positive electrode model 402 and the state of the anode 308 using the negative electrode model 404. The battery model relates a state of lithiation of the battery (or cathode) to a terminal voltage of the battery. During charging, a state prediction model can be applied to the positive electrode model to predict a next state of the cathode in a next (k+1) time step based on the current (k) state variables and the charging operations. Various measurable parameters are then predicted from the state variables in the next time step. Measurements are then taken in the next time step and compared to the measurable parameters.The result of the comparison is used to update the positive electrode model for the next time step. This method may include the use of a Kalman filter. Thus, this method predicts the state of the cathode after the charging operation. Similarly, the state prediction model can be used on the negative electrode model to predict the state of the anode after the charging operation.

[0046] Fig. 8 is a flowchart 800 of a method for determining a voltage fade state of a battery cell after a charging operation, according to one embodiment. The method begins in box 802. In box 802, the vehicle or system operating on the battery cell may be in any state, including at rest, driving, discharging, etc. In box 804, data regarding the initial state of the battery cell is uploaded from memory to a processor. The data includes an initial voltage fade state of the battery cell and electrical models of the battery, including state variables and dynamic parameters of both the positive electrode model and the negative electrode model. In box 806, a charging process for the battery cell is initiated. In box 808, a terminal voltage of the battery is measured at one or more time steps during the charging process. In box 810, the model of the battery (i.e.The cathode and anode state variables and dynamic parameters are updated using the predictive model over the one or more time steps using the terminal voltage and temperature. In block 812, the charging operation is monitored to determine whether charging is still in progress or whether the charging operation has ended. If the charging operation is still in progress, the method returns to block 808. Otherwise, the method proceeds to block 814.

[0047] In field 814, a cathode potential is measured after the charging operation has ended. In field 816, a timer is compared to a selected time period, with the time starting at zero when the charging operation is completed. If the timer is less than the selected time period, the method returns to field 814 to obtain another measurement of the cathode potential. Otherwise, the method proceeds to field 818 if the selected time period has elapsed.

[0048] In field 818, a maximum value of the cathode potential is determined from the cathode potential measurements obtained after the charging operation has ended. In field 820, the maximum cathode voltage V P,sense_max and a voltage fade state of the cathode is determined from the updated model of the battery cell. In field 822, based on the open circuit voltage (V OCV,P ) of the positive electrode and the open circuit voltage (V OCV,N) of the negative electrode, the lithiation state of the battery is updated. In field 824, the processor operates the vehicle based on the updated voltage fade state of the battery. Operating the vehicle may include limiting an amount of current supplied by the battery cell to the vehicle. The current limit may be based on the fade state and / or the lithiation state of the battery cell. In field 826, the method ends.

[0049] Fig. 9 is a flowchart 900 of a method for determining a voltage fade condition of a battery cell from a maximum cathode voltage. The flowchart 900 is an extension of the method shown in box 820 of Fig. 8. The method begins in field 902. In field 904, a peak voltage is measured during charging. In field 906, a voltage fading lifetime change is made based on the maximum charge reached at the end of the charging process. It should be understood that the maximum charge at the end of the charging process is not necessarily 100%. Some users may charge to a lower state of charge, especially when charging using DC fast charging. In field 908, the voltage fading parameters for the open circuit voltage V OCV,P updated using the voltage fade lifetime change. The procedure ends in field 910.

[0050] Fig. Figure 10 shows a graph 1000 illustrating a difference between capacity fade and voltage fade. Along the abscissa, the reversible capacity (indicating the lithiation state) is shown in milliampere-hours per gram (mAh / g), and along the ordinate, the cathode potential is shown in volts (V). Curve 1002 shows a relationship between the cathode potential and the reversible capacity for a battery in an early-life state. Curve 1004 shows the relationship for a battery for which capacity fade is present. Curve 1006 shows a relationship for a battery for which voltage fade is present.Voltage fade is a result of structural changes that affect the energy of the battery's active material during normal battery use, while capacity fade is a result of the loss of accessibility to the battery's active material, often due to damage or excessive use. Voltage fade is reflected in curve 1004 with lower voltage (indicated by voltage fade line 1008). Capacity fade is reflected in curve 1004 with less capacity density (indicated by capacity fade line 1010).

[0051] Fig.Figure 11 shows a graph 1100 relating the cathode potential to the reversible capacity of the battery cell. Along the abscissa, the reversible capacity (indicating the lithiation state) is shown in milliampere-hours per gram (mAh / g), and along the ordinate, the cathode potential is shown in volts (V). The curves shown in graph 1100 show a combination of both voltage fade and capacity fade. A first curve 1102 shows a relationship between the cathode potential and the reversible capacity for a battery with a first fade state. A second curve 1104 shows a relationship between the cathode potential and the reversible capacity for a battery with a second fade state. A third curve 1106 shows a relationship between the cathode potential and the reversible capacity for a battery with a third fade state.The third fade state is greater than the second fade state, which is greater than the first fade state. According to an illustrative embodiment, the voltage fade of the first curve 1102 is 0. The graph shows that the relationship changes as the voltage fade state increases. The curve of graph 1100 can be used to determine the cathode lithiation state from the maximum cathode voltage. This involves first determining the voltage fade state for the battery, selecting an appropriate curve for the voltage fade state, and determining the lithiation state from the maximum cathode voltage using the selected curve.

[0052] The estimation of the lithiation state can be performed at a voltage where the selected curve is not too steep (i.e., nearly non-differentiable). Thus, a suitable estimate can be obtained using voltages, e.g., in the range of 3.5 V to 4.0 V. On the other hand, using a voltage of approximately 4.5 V exploits a portion of the curve that is highly vertical.

[0053] The terms "a" and "an" do not imply a limitation on the quantity, but rather denote the presence of at least one of the mentioned objects. Unless the context clearly indicates otherwise, the term "or" means "and / or." Reference throughout the application to "an aspect" means that a particular element described in connection with the aspect (e.g., feature, structure, step, or property) is included in at least one aspect described herein and may or may not be included in other aspects. Furthermore, it is to be understood that the described elements may be combined in any suitable manner according to the various aspects.

[0054] When an element, such as a layer, film, region, or substrate, is referred to herein as being "on" another element, it may be directly on top of the other element or may also have intervening elements present. In contrast, when an element is referred to as being "directly on" another element, no intervening elements are present.

[0055] Unless otherwise specified herein, all examination standards are the most recent examination standards in effect as of the filing date of this application or the filing date of the earliest priority application in which the examination standard appears, if priority is claimed.

[0056] Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0057] Although the above disclosure has been described with reference to exemplary embodiments, those skilled in the art will understand that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope thereof. Furthermore, many changes may be made to adapt a particular situation or material to the teachings of the disclosure without departing from its essential scope. Thus, the present disclosure is not intended to be limited to the particular embodiments disclosed, but is intended to include all embodiments within its scope.

Claims

[1] A method of operating a vehicle, the method comprising: Obtaining an initial voltage fading state of a battery of the vehicle and a model of an initial state of the battery of the vehicle; Starting a battery charging operation; Measuring a battery terminal voltage during charging; Updating the battery model during the charging operation using the terminal voltage; End the loading operation; Obtaining multiple cathode voltage measurements after the charging operation has ended; Determining a maximum cathode voltage from the multiple measured values; Determining an updated battery voltage fade state based on the maximum cathode voltage; Selecting a relationship between the cathode voltage and the lithiation state based on the updated voltage fading state; Calculating a state of lithiation of a cathode from the maximum cathode voltage using the selected relationship; and Operate the vehicle based on the updated voltage fade status. [2] The method of claim 1, wherein the model further comprises a positive electrode model representing a cathode of the battery and a negative electrode model representing an anode of the battery, further comprising updating the positive electrode model and the negative electrode model during the charging operation. [3] The method of claim 2, further comprising determining an open circuit voltage of the cathode from the terminal voltage and determining the lithiation state of the cathode from the open circuit voltage of the cathode using the selected relationship. [4] The method of claim 2, wherein the positive electrode model or the negative electrode model includes a state variable, the state variable including at least one of the following: (i) an open circuit voltage; (ii) a hysteresis voltage; and (iii) an ohmic resistance. [5] The method of claim 4, wherein the positive electrode model or the negative electrode model includes a dynamic parameter, the dynamic parameter including a time constant indicative of a response of the battery to an applied load. [6] System for operating a vehicle, comprising: a processor configured to: Obtaining an initial voltage fading state of a battery of the vehicle and a model of an initial state of the battery of the vehicle; Starting a battery charging operation; Measuring a battery terminal voltage during charging; Updating the battery model during the charging operation using the terminal voltage; End the loading operation; Obtaining multiple cathode voltage measurements after the charging operation has ended; Determining a maximum cathode voltage from the multiple measured values; Determining an updated battery voltage fade state based on the maximum cathode voltage; Selecting a relationship between the cathode voltage and the lithiation state based on the updated voltage fading state; Calculating a state of lithiation of a cathode from the maximum cathode voltage using the selected relationship; and Operate the vehicle based on the updated voltage fade status. [7] The system of claim 6, wherein the model further comprises a positive electrode model representing a cathode of the battery and a negative electrode model representing an anode of the battery, further comprising updating the positive electrode model and the negative electrode model during the charging operation. [8] The system of claim 7, wherein the processor is further configured to determine an open circuit voltage of the cathode from the terminal voltage and to determine the lithiation state of the cathode from the open circuit voltage of the cathode using the selected relationship. [9] The system of claim 8, wherein the positive electrode model or the negative electrode model includes a state variable, the state variable including at least one of the following: (i) an open circuit voltage; (ii) a hysteresis voltage; and (iii) an ohmic resistance. [10] The system of claim 9, wherein the positive electrode model or the negative electrode model includes a dynamic parameter, the dynamic parameter including a time constant indicative of a response of the battery to an applied load.

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