Operating voltage limiting for batteries

Abstract

Aspects of the present disclosure include a battery management system that actively limits an operating voltage of a battery cell in response to an indication of battery cell degradation to avoid battery cell pressure fluctuations. An exemplary battery management system may include a memory, computer readable instructions, and one or more processors that perform operations including measuring a first cell pressure of a battery cell of a battery pack at a reference voltage, and measuring a second cell pressure of the battery cell of the battery pack at the reference voltage. A moving average of the cell pressure series is determined from the first cell pressure and the second cell pressure. In response to the moving average of the cell pressure series exceeding a cell pressure series threshold, the cells of the battery pack are identified as degraded cells, and an estimate of remaining cycles of the degraded cells is determined.

Description

Technical Field

[0001] The present invention relates to battery cell technology and, more particularly, to operating voltage limits for batteries. Background Art

[0002] High voltage electrical systems are increasingly used to power onboard functions for both mobile and stationary systems. For example, in motor vehicles, the need to increase fuel economy and reduce emissions has led to the development of advanced electric vehicles (EVs). EVs rely on a rechargeable energy storage system (RESS), which typically includes one or more high voltage battery packs and an electric drive train to transmit the power from the batteries to the wheels. Depending on the power requirements of a given application, the battery pack may include any number of interconnected battery modules. Each battery module includes a collection of conductively coupled electrochemical cells. The battery pack is configured to provide a direct current (DC) output voltage at a level suitable for powering coupled electrical and / or mechanical loads (e.g., electric motors).

[0003] The capacity of a battery pack can be increased by increasing the number of modules and / or cells in the pack, and by increasing the number of parallel core rollers, the number of electrode layers, and the electrode surface area within each cell of the pack. The cell chemistry also affects the overall capacity. Two common battery chemistries are nickel-cobalt-manganese (NCM) and lithium-iron-phosphate (LFP). Summary of the invention

[0004] In an exemplary embodiment, a vehicle includes an electric motor, a battery pack electrically coupled to the electric motor, and a battery management system coupled to the battery pack. The battery management system actively limits the operating voltage of the battery cell to avoid battery cell pressure fluctuations in response to an indication of battery cell degradation. The battery management system includes a memory, computer-readable instructions, and one or more processors for executing the computer-readable instructions. The computer-readable instructions control the one or more processors to perform operations. The operations include measuring a first battery cell pressure of a battery cell of the battery pack at a reference voltage, and measuring a second battery cell pressure of a battery cell of the battery pack at the reference voltage. A moving average of a battery cell pressure level is determined from the first battery cell pressure and the second battery cell pressure. In response to the moving average of the battery cell pressure level exceeding a battery cell pressure level threshold, the battery cell of the battery pack is identified as a degraded battery cell, and an estimate of the remaining cycles of the degraded battery cell is determined.

[0005] In addition to one or more features described herein, in some embodiments, the battery management system is further configured to establish a lookup table. In some embodiments, the lookup table is configured to provide an estimate of the remaining useful cycle life of the battery cell as an output. In some embodiments, the lookup table is a four-dimensional (4D) lookup table that includes as inputs the battery cell voltage, the change in battery cell pressure between cycles, the battery cell temperature, and the operating voltage window.

[0006] In some embodiments, determining an estimate of remaining cycles for a degraded battery includes inputting a first battery cell voltage, a first change in battery cell pressure between cycles, a first battery cell temperature, and a first operating voltage window into a lookup table, and in response to the inputs, receiving the estimate of remaining cycles from the lookup table.

[0007] In some embodiments, the estimate of remaining cycles for the degraded cell includes an estimate of the number of cycles until a predetermined end-of-life condition for the degraded cell. In some embodiments, the predetermined end-of-life condition includes one of an estimated number of cycles until an expected cell pressure fluctuation exceeds a predetermined threshold and a number of cycles until a predetermined percentage of previous cells fail.

[0008] In some embodiments, the battery management system is further configured to determine one of a state of charge and a state of discharge of the battery pack. In some embodiments, the battery management system is further configured to use a lookup table to adjust one of a charging voltage limit and an operating voltage limit of a degraded battery cell.

[0009] In another exemplary embodiment, a battery management system may include a memory, computer-readable instructions, and one or more processors for executing the computer-readable instructions. The computer-readable instructions control the one or more processors to perform operations. The operations include measuring a first cell pressure of a battery cell of a battery pack at a reference voltage, and measuring a second cell pressure of a battery cell of the battery pack at the reference voltage. A moving average of a cell pressure level is determined from the first cell pressure and the second cell pressure. In response to the moving average of the cell pressure level exceeding a cell pressure level threshold, the battery cell of the battery pack is identified as a degraded cell, and an estimate of the remaining cycles of the degraded cell is determined.

[0010] In yet another exemplary embodiment, a method for reducing the risk of cell pressure fluctuations in a battery pack may include measuring a first cell pressure of a battery cell of the battery pack at a reference voltage, and measuring a second cell pressure of a battery cell of the battery pack at the reference voltage. A moving average of a cell pressure level is determined from the first cell pressure and the second cell pressure. In response to the moving average of the cell pressure level exceeding a cell pressure level threshold, a battery cell of the battery pack is identified as a degraded cell, and an estimate of remaining cycles of the degraded cell is determined.

[0011] The above features and advantages and other features and advantages of the present disclosure will become apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Other features, advantages and details appear, by way of example only, in the following detailed description, which refers to the accompanying drawings, in which:

[0013] Figure 1 is a vehicle configured according to one or more embodiments;

[0014] Figure 2 is a graph depicting a relationship between battery cell pressure and battery cell voltage over a plurality of charge-discharge cycles according to one or more embodiments;

[0015] Figure 3 is a graph depicting the relationship between state of charge and battery cell voltage as the battery cell undergoes multiple charge-discharge cycles according to one or more embodiments;

[0016] Figure 4 is a graph depicting example Coulombic efficiency versus cycling curves and example delta cell pressure versus cycling curves according to one or more embodiments;

[0017] Figure 5 is a process workflow for implementing operating voltage limits in response to battery cell degradation according to one or more embodiments;

[0018] Figure 6 is a computer system according to one or more embodiments; and

[0019] Figure 7 is a flow chart according to one or more embodiments. DETAILED DESCRIPTION

[0020] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or use. It should be understood that in all figures, corresponding reference numerals represent the same or corresponding parts and features. As used herein, the term module refers to a processing circuit, which may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated or group) and memory that executes one or more software or firmware programs, a combinational logic circuit and / or other suitable components that provide the described functions.

[0021] As mentioned earlier, two common battery chemistries are nickel-cobalt-manganese (NCM) batteries and lithium-iron-phosphate (LFP) batteries. While NCM and LFP batteries offer reasonable energy density and charge / discharge profiles, other battery chemistries, including lithium metal batteries (LMBs), are being used for next-generation battery solutions.

[0022] The main difference between lithium metal batteries and lithium ion batteries (such as LFP batteries) lies in the composition and behavior of their respective anodes (negative electrodes). Lithium metal batteries use metallic lithium as the anode material. During charging, lithium ions are deposited from the cathode (positive electrode) onto the lithium metal anode, forming a layer of metallic lithium. This deposition process is called lithium plating. During discharge, lithium ions are released from the anode and travel through the electrolyte to the cathode, generating an electric current.

[0023] Lithium metal batteries have several advantages over NCM and LFP batteries. For example, lithium metal batteries have the potential for relatively higher energy density compared to NCM and LFP batteries because of the high theoretical specific capacity achieved by using metallic lithium as the anode material. In short, lithium metal batteries can store more energy per unit weight or unit volume. Another advantage is the lower self-discharge rate. This means that lithium metal batteries can hold a charge for longer durations when not in use, making them more suitable for applications that require long-term storage. Another advantage is the potential for faster charging capabilities. The deposition of metallic lithium during the charging process can occur at a high rate, allowing for fast charging rates and reduced charging times compared to NCM and LFP batteries.

[0024] Lithium metal batteries experience significant volume changes (including expansion and contraction) during charge-discharge due to the host-free deposition and dissolution of lithium. During the charging process, lithium ions are deposited as lithium metal on the anode, causing the electrode to expand. This reversible expansion is a natural part of the operation of lithium metal batteries and is known as the lithium plating process. During discharge, lithium dissolves back into the electrolyte, causing the electrode to shrink. These volume changes can induce mechanical stresses within the battery cell, which can lead to electrode damage, loss of electrical connectivity, and ultimately reduce overall battery cell performance.

[0025] In addition to reversible expansion / contraction, lithium metal batteries also experience irreversible cell expansion when they age. Over time, repeated cycles of lithium deposition and dissolution lead to electrode degradation, resulting in the formation of a solid electrolyte interface (SEI) layer and other irreversible structural changes. These irreversible expansion phenomena are mainly caused by the gradual accumulation of side reactions, the formation of permanent dendrites, and the growth of lithium metal deposits in an uneven pattern.

[0026] The reversible expansion and contraction as well as the irreversible expansion of lithium metal batteries presents some challenges to battery pack design. For example, due to the continuous volume expansion, the battery cell pressure in a lithium metal battery at a fixed volume will gradually increase between cycles. In addition, as the battery cell approaches the end of its life, the battery cell pressure will begin to increase relatively quickly. This process is often referred to as battery cell pressure fluctuations, which can lead to, for example, separator breakdown, internal short circuits, and ultimately capacity failure of the battery cell and / or battery pack.

[0027] The present disclosure introduces a battery management system that actively limits the operating voltage of a battery cell in response to an indication of battery cell degradation to avoid battery cell pressure fluctuations. In some embodiments, the battery management system uses the monitored cycle-to-cycle battery cell pressure level to identify battery cell degradation. In lithium batteries and other batteries that require high pressure (e.g., greater than 1000 kPa) to operate properly, the battery cell pressure level can be a good indicator of battery cell degradation because it has been found that during the battery cell life of these batteries, the battery cell pressure exhibits two continuous behaviors. Initially, the battery cell pressure increases linearly, while the coulombic efficiency and battery cell capacity remain unchanged. This "linear" state runs through the initial life of the battery (i.e., from the first cycle to the Nth cycle), after which the battery cell pressure behavior transitions to an "exponential" state. During the exponential regime, the battery cell pressure increases exponentially between cycles, and the coulombic efficiency decreases significantly. Without wishing to be bound by theory, it should be understood that when the lithium-based or other high-voltage battery degradation exceeds a certain level—specifically, after a threshold level of Δ irreversibility—a transition from linear to exponential behavior occurs. In some embodiments, the battery management system detects the transition from linear to exponential behavior by monitoring the point at which the cell pressure at a given voltage begins to deviate from a linear relationship. In some embodiments, cell degradation is inferred when the difference between the cell pressures measured between cycles exceeds a predetermined threshold. In some embodiments, cell degradation is inferred when a moving average of the difference between the cell pressures measured between cycles exceeds a predetermined threshold.

[0028] Once cell degradation is detected (using, for example, cycle-to-cycle cell pressure levels or other means), the battery management system uses a 4-dimensional (4D) lookup table to determine the remaining useful cycle life of the corresponding battery. In some embodiments, the battery management system limits (reduces) the operating voltage of the degraded battery cell based on the output from the 4D lookup table to accommodate capacity degradation.

[0029] Limiting the operating voltage of a battery in response to cell degradation according to one or more embodiments provides several technical advantages over other battery management systems. Specifically, the battery management system described herein can utilize a 4D lookup table to quickly estimate the available cycle life of a battery cell under current conditions, and can decisively limit the operating voltage of the battery when the estimated available cycle life is below a target. Limiting the operating voltage in this manner can mitigate (if not eliminate) cell pressure fluctuations, thereby extending the overall cycle life of the battery pack. In addition, the battery management system described herein can utilize the estimated remaining cycle life to provide users (e.g., drivers) and systems (e.g., a vehicle's ECU) with a time window for taking action before a battery pack capacity failure.

[0030] According to an exemplary embodiment, the vehicle Figure 1 100. The vehicle 100 is shown in the form of an automobile having a body 102. The body 102 includes a passenger compartment 104, within which a steering wheel, front seats, and rear passenger seats (not shown separately) are arranged. A plurality of components are arranged within the body 102, including, for example, an electric motor 106 (shown by a projection under the front hood). The electric motor 106 is shown for ease of illustration and discussion only. It should be understood that the configuration, location, size, arrangement, etc. of the electric motor 106 are not meant to be particularly limited, and all such configurations (including multi-motor configurations) are within the intended scope of the present disclosure.

[0031] The electric motor 106 is powered by a battery pack 108 (shown by a projection near the rear of the vehicle 100). The battery pack 108 is shown merely for ease of illustration and discussion. It should be understood that the configuration, location, size, arrangement, etc. of the battery pack 108 is not meant to be particularly limited, and all such configurations (including separate configurations) are within the intended scope of the present disclosure. In addition, while the present disclosure is primarily discussed in the context of a battery pack 108 configured for the electric motor 106 of the vehicle 100, the various aspects described herein may be similarly incorporated into any system (vehicle, building, etc.) having an energy storage system (e.g., one or more battery packs), and all such configurations and applications are within the intended scope of the present disclosure.

[0032] As will be described in greater detail herein, battery pack 108 is monitored and controlled by battery management system 110 (illustrated by a projection adjacent to battery pack 108). While battery management system 110 may be included in, for example, a battery pack of an electric vehicle (e.g., battery pack 108 of vehicle 100), other energy storage applications (for vehicles, structures, etc.) are also within the contemplated scope of the present disclosure.

[0033] In some embodiments, the battery management system 110 monitors the battery cell pressure as a function of the battery cell voltage over multiple charge-discharge cycles (see Figure 2 ). The battery cell pressure may be measured using, for example, a pressure sensor (not shown separately) of the battery management system 110. Alternatively, the battery cell pressure may be measured using an upstream system, such as using an onboard electronic control unit (ECU, not shown separately) configured to provide battery cell pressure measurements to the battery management system 110. In other embodiments, the battery cell pressure may be estimated. For example, a physics-based or data-driven empirical model may be used to estimate the battery cell pressure, although other techniques for battery cell pressure estimation are also within the intended scope of the present disclosure.

[0034] Figure 2 A graph 200 is shown depicting the relationship between battery cell pressure and battery cell voltage over a plurality of charge-discharge cycles 202 according to one or more embodiments. Figure 2 As shown, the cell pressure (here measured in kPa) increases relatively slowly when proceeding from an initial cell voltage of about 2.5 volts to an intermediate cell voltage of about 3.4 volts. This relatively stable region is sometimes referred to as a high hysteresis region 204 .

[0035] like Figure 2 As further shown, further increases in the cell voltage beyond the high hysteresis region 204 result in a faster cell pressure response. It is observed that between about 3.7 volts and about 3.9 volts, the cell pressure increases rapidly, but somewhat linearly. This region may be referred to as the measurement region 206. In some embodiments, the battery management system 110 is configured to measure, poll, or otherwise receive cell pressure measurements within the measurement region 206. In some embodiments, the battery management system 110 is configured to measure, poll, or otherwise receive cell pressure measurements at the same reference voltage in multiple charge-discharge cycles 202. In some embodiments, the reference voltage is 3.7, 3.8, or 3.9 volts, although other reference voltages (including voltages outside the measurement region 206) are also within the intended scope of the present disclosure.

[0036] In some embodiments, the battery management system 110 is configured to perform cell pressure measurements at a single (e.g., 3.7 volt) reference voltage during multiple charge-discharge cycles 202. In some embodiments, the battery management system 110 is configured to perform cell pressure measurements at two or more reference voltages (e.g., 2.9 volts and 3.9 volts) during multiple charge-discharge cycles 202. In some embodiments, the battery management system 110 is configured to perform cell pressure measurements at a reference voltage while charging during one or more charge-discharge cycles 202. For example, a cell pressure measurement may be performed when the cell voltage increases (due to charging) to 3.7 volts. In some embodiments, the battery management system 110 is configured to perform cell pressure measurements at a reference voltage while discharging during one or more charge-discharge cycles 202. For example, a cell pressure measurement may be performed when the cell voltage decreases (due to driving) to 3.7 volts.

[0037] The charge-discharge cycle 202 may include a first (initial) cycle 208 and a last (most recent) cycle 210. It is observed that the cell pressure obtained at the same (reference) voltage increases along the progression between the first cycle 208 and the last cycle 210. For example, the cell pressure at 3.7 volts for the first cycle 208 is about 1425 kPa, while the cell pressure at 3.7 volts for the last cycle 210 is about 1810 kPa. This relationship holds true in both the high hysteresis region 204 and the measurement region 206. It is further observed that in the initial group of charge-discharge cycles 202, the difference (Δ) in the cell pressure obtained at the same reference voltage between consecutive cycles is relatively small, but increases rapidly as the charge-discharge cycle 202 approaches the last cycle 210.

[0038] Figure 3 A graph 300 depicting the relationship between state of charge (SOC, %) and battery cell voltage (V) as the battery cell undergoes multiple charge-discharge cycles according to one or more embodiments is shown. Figure 3 As shown, the operating range 302 of battery cell voltages between 0% SOC (empty battery) and 100% SOC (full battery) decreases as the battery ages. In other words, as the number of cycles increases, the voltage range covered by a full charge decreases.

[0039] For illustration, consider three example curves 304, 306, and 308 obtained at the (i), (i+j), and (i+j+k)th cycles of the charge-discharge cycle 202, respectively, where i, j, and k are positive constants. The three example curves 304, 306, and 308 are provided merely to illustrate the relative change in the operating range 302 of the battery cell voltage over multiple charge-discharge cycles. The exact operating range 302 for a given battery cell will vary depending on many factors, such as battery chemistry, temperature (ambient temperature and battery pack temperature), number of current cycles, battery pack capacity, SOC limit, etc. The operating range 302 for the (i)th cycle is the widest, ranging from a battery cell voltage of 2.5 volts to a battery cell voltage of 4.3 volts. The operating range 302 for the (i+j)th cycle is relatively narrow, ranging from a battery cell voltage of 2.5 volts to a battery cell voltage of 4.2 volts. The operating range 302 of the (i+j+k)th cycle is the narrowest, from a battery cell voltage of 2.5 volts to a battery cell voltage of 4.1 volts.

[0040] It is observed that for SOC close to 100% (i.e., fully charged state), the actual battery cell voltage decreases from cycle (i) to cycle (i+j), and again to cycle (i+j+k). This decrease in battery cell voltage at maximum SOC represents a loss in total battery capacity (i.e., capacity degradation).

[0041] In some embodiments, the battery management system 110 is configured to reduce the operating voltage of the battery cells and / or battery packs (e.g., battery pack 108) to accommodate this capacity loss. For example, the battery management system 110 may reduce the operating voltage of the battery cells and / or battery packs from 4.3 volts to 4.2 volts in the (i+j)th cycle. The battery management system 110 may again reduce the operating voltage of the battery cells and / or battery packs from 4.2 volts to 4.1 volts in the (i+j+k)th cycle. Advantageously, reducing the operating voltage in this manner can prevent overcharging, and due to the relationship between battery cell pressure and battery cell voltage, over-pressurization of degraded battery cells and / or battery packs can be prevented. The result is reduced battery cell pressure fluctuations. Otherwise, overcharging would occur when, for example, a degraded cell at the (i+j+k)th cycle is forced to the same maximum cell voltage (e.g., 4.3 volts) corresponding to 100% SOC at the (i+j)th cycle or (i)th cycle, while, due to cell degradation, 100% SOC is actually achieved at a lower cell voltage of 4.1 volts, representing an overcharge of 0.2 volts. This degree of overcharging is merely illustrative, and in practice may be greater (and will continue to increase with increasing cycle number due to further degradation of the battery).

[0042] Figure 4A graph 400 depicting an example coulombic efficiency versus cycle curve 402 and an example delta cell pressure versus cycle curve 404 according to one or more embodiments is shown. In some embodiments, the coulombic efficiency versus cycle curve 402 is constructed by measuring the coulombic efficiency (capacity) at each cycle at the same reference voltage. In some embodiments, the reference voltage is 3.7 volts, although other reference voltages are within the contemplated scope of the present disclosure. Similarly, in some embodiments, the delta cell pressure versus cycle curve 404 is constructed by taking cell pressure measurements (reference voltage) at each cycle at the same reference voltage. Figure 2 ) and then determining the difference (Δ) between the two cell pressure measurements to construct. The coulombic efficiency versus cycle curve 402 and the Δ cell pressure versus cycle curve 404 are merely illustrative and will vary for a given application and conditions.

[0043] like Figure 4 As shown in the Coulombic efficiency-cycle curve 402, the efficiency (e.g. Figure 1 ) of the battery pack 108 is relatively stable until the capacity conversion cycle 406 (here, the 21st cycle). For example, in the first 20 cycles, the deviation of the coulombic efficiency between cycles remains within about 3%. After the capacity conversion cycle 406, the efficiency drops rapidly. For example, at the 22nd cycle, the coulombic efficiency drops to about 90%. After the capacity conversion cycle 406, the reduction in efficiency accelerates. For example, at the 23rd cycle, the coulombic efficiency drops from about 90% (at the 22nd cycle) to about 60%.

[0044] like Figure 4 As shown in the Δ cell pressure-cycle curve 404, the cell pressure change (Δ CP ) remains relatively stable until the cell pressure conversion cycle 408 (here the 19th cycle). For example, during the first 18 cycles, the cycle-to-cycle ΔCP remains below about 20 kPa. It is observed that the capacity conversion cycle 406 lags behind the cell pressure conversion cycle 408 (here about 2 cycles).

[0045] The change in cell pressure between any two cycles N and M can be calculated directly from the generalized equation (1):

[0046]

[0047] Where Pr(.) is the pressure measured at the reference voltage, N>M (i.e., N is the current cycle and M is the previous cycle).

[0048] like Figure 4As further shown in FIG. 4 , the cycle-to-cycle increase in the cell pressure begins to accelerate after the cell pressure transition cycle 408. For example, ΔCP is about 25 kPa at the 19th cycle, about 52 kPa at the 20th cycle, about 90 kPa at the 21st cycle, and about 165 kPa at the 22nd cycle.

[0049] In some embodiments, the battery management system 110 identifies the degraded battery cell by finding the corresponding battery cell pressure transition cycle 408 in the battery cell pressure progression obtained during the charge-discharge cycle 202. This process can be repeated to find any number of degraded battery cells.

[0050] In some embodiments, the battery management system 110 compares the change (Δ) in the battery cell pressure data between cycles with a predetermined Δ pressure threshold (Δ C ). In some embodiments, the predetermined Δ pressure threshold represents a critical (or maximum allowable) increase in cell pressure between cycles at the reference voltage. The predetermined Δ pressure threshold may vary from application to application. In some embodiments, the predetermined Δ pressure threshold is calibrated based on test data specific to the cell. In some embodiments, when the measured change (Δ) in the cell pressure data exceeds Δ C When the battery management system 110 identifies the battery cell degradation condition. For example, assuming a predetermined Δ pressure threshold of 20 kPa, the battery management system 110 may identify the battery cell degradation condition at cycle 19.

[0051] In some embodiments, the battery management system establishes a lookup table configured to provide as an output an estimate of the remaining useful cycle life of the battery cell. In some embodiments, the lookup table is a calibratable 4-dimensional lookup table that is empirically constructed from previous battery cell data using four inputs: (1) battery cell voltage (e.g., 4.0 volts), (2) cycle-to-cycle change in battery cell pressure (e.g., 20 kPa), (3) battery cell temperature (e.g., 10 degrees Celsius), and (4) a corresponding operating voltage window (e.g., 3.0 to 4.1 volts). In some embodiments, the battery management system configures the 4D lookup table to output the useful cycle life (e.g., 8 cycles remaining) as a function of the four inputs.

[0052] In some embodiments, the usable cycle life is an estimate of the number of cycles until a predetermined end-of-life condition. For example, the predetermined end-of-life condition may include an estimated number of cycles until the expected cell pressure fluctuation is above a predetermined threshold and / or the number of cycles until a predetermined percentage of previous similar cells fail. As used herein, "similar" cells refer to cells with the same chemistry, same capacity, same temperature, same operating conditions, same battery pack layout, etc., or these parameters within a specified tolerance (e.g., ±5% of rated capacity, ±10 degrees Celsius operating temperature, etc.).

[0053] Tables 1, 2, 3, and 4 represent example entries in a 4-dimensional lookup table using battery cell voltage, changes in battery cell pressure between cycles, battery cell temperature, and operating voltage windows. Tables 1, 2, 3, and 4 are descriptive, but are only used to illustrate the construction of the 4D lookup table. It should be understood that although the 4-dimensional lookup table is shown as including specific tables 1, 2, 3, and 4, additional (or fewer) tables may be included. In addition, although specific tables 1, 2, 3, and 4 are shown as spanning specific temperature ranges (here -20°C and 50°C) and operating voltage windows (here 2.5 to 4.3 volts and 3.0 to 4.1 volts), a four-dimensional lookup table can be constructed from any number of tables that divide the temperature and / or operating voltage window at any desired resolution. For example, the temperature range in the table is between -20°C (or colder) and 50°C (or hotter), in increments of 1 degree, 5 degrees, 10 degrees, etc. Similarly, the operating voltage windows in the table can span any desired range (e.g., 3.5 to 3.9 volts, 2.0 to 5.0 volts, etc.), with any resolution (e.g., 0.01, 0.05 volts, etc., such as from 2.5-4.3 volts and 2.51-4.25 volts).

[0054] Table 1 - Operating voltage window (2.5V to 4.3V); battery cell temperature (-20°C)

[0055]

[0056] Table 2 - Operating voltage window (2.5V to 4.3V); battery cell temperature (50°C)

[0057]

[0058]

[0059] Table 3 - Operating voltage window (3.0V to 4.1V); battery cell temperature (-20°C)

[0060]

[0061] Table 4 - Operating voltage window (3.0V to 4.1V); battery cell temperature (50°C)

[0062]

[0063] Figure 5 A process workflow 500 for implementing operating voltage limits in response to battery cell degradation according to one or more embodiments is shown. The workflow 500 may be implemented using, for example, the battery management system 110 of the vehicle 100 (see FIG. Figure 1 ) to be performed. It should be understood that although the process workflow 500 is primarily discussed with respect to a single battery cell for convenience and ease of illustration, the basic techniques can be repeated for any number of battery cells in a battery pack. For example, the process workflow 500 for implementing operating voltage limits in response to battery cell degradation according to one or more embodiments can be repeated for each parallel-connected battery cell group in a battery pack. In some embodiments, a battery cell (or battery pack, or module, etc.) failure can be determined by the corresponding battery cell in the battery pack, module, etc., which is predicted to have a capacity failure first.

[0064] Workflow 500 begins at step 502, where battery cell pressure monitoring is initiated (eg, cycle N=1), and various thresholds are set, including, for example, Δ CP ,Δ C and the reference battery cell voltage (V REF ), and make initial cell pressure measurements at a reference cell voltage and / or target state of charge (e.g., 25%, 50%, 75% SOC).

[0065] At step 504 , the battery management system 110 reads and / or receives the current battery cell pressure P from the i-th cycle. i In some embodiments, the battery management system 110 reads and / or receives the current battery cell pressure P from the i-th cycle at 50% SOC. i In some embodiments, the battery management system 110 proceeds to step 506 after making, retrieving, and / or recording the battery cell pressure measurements.

[0066] At step 506, the current battery cell pressure measurement (P i ) and previous cell pressure measurements (P i-1 ) between the battery cell pressure changes (Δ CP ). In some embodiments, the battery management system 110 proceeds to step 508 after calculating the change in the battery cell pressure. In some embodiments, before proceeding to step 508, the battery management system 110 increments a cycle counter (eg, i=i+1).

[0067] At step 508, the battery management system 110 checks the moving average of the battery cell pressure (i.e., the battery cell pressure level) within a window of multiple cycles. In some embodiments, the battery management system 110 checks the moving average of the battery cell pressure within a window of a predetermined number of cycles (e.g., 2 cycles, 3 cycles, 5 cycles, 10 cycles, etc.).

[0068] At step 510, the battery management system 110 determines the moving average value (Δ AVG ) is greater than (or equal to) a predetermined threshold. In some embodiments, the predetermined threshold is a predetermined Δ pressure threshold (Δ C ). In other words, the battery management system 110 determines whether Δ AVG ≥Δ C .

[0069] In some embodiments, the predetermined Δ pressure threshold (Δ C ) is a static predetermined threshold. In some embodiments, the predetermined Δ pressure threshold (Δ C ) is a dynamic variable. In some embodiments, the predetermined Δ pressure threshold (Δ C ) is the current moving average of the battery cell pressure (Δ AVG ). For example, a predetermined Δ pressure threshold (Δ C ) can be calculated as the current moving average of the battery cell pressure (Δ AVG ), 101%, 105%, 110%, 115%, 150%, etc. In some embodiments, the predetermined Δ pressure threshold (Δ C ) can be calculated as the current moving average of the battery cell pressure (Δ AVG ), where "m" is a function of the battery cell chemistry and design for a particular application. In some embodiments, "m" is a value learned from empirical data of previously failed battery cells.

[0070] In some embodiments, if Δ AVG <Δ C (ie, no), the battery management system 110 may indicate that the change in cell pressure between cycles remains below the critical cell pressure threshold, and the process may return to step 504. In some embodiments, if Δ AVG ≥Δ C(i.e., yes), the battery management system 110 may indicate that the cycle-to-cycle cell pressure change has exceeded the critical cell pressure threshold (i.e., indicating cell degradation of the corresponding cell), and the process may proceed to step 512. In some embodiments, when cell degradation is detected in one or more cells of the battery pack, the battery management system 110 may take one or more of a number of actions to mitigate the problem and ensure safe and optimal operation of the battery pack.

[0071] At step 512 , the battery management system 110 determines whether the battery cell and / or the vehicle (eg, Figure 1 In some embodiments, the battery management system 110 responds to battery cell degradation based on the charge / discharge state of the battery cell. If the battery cell and / or vehicle is in a charging state (i.e., "C"), the process proceeds to step 514. If the battery cell and / or vehicle is in a discharging state (i.e., "D"), the process proceeds to step 516.

[0072] At box 514 (during the charging state), the battery management system 110 indicates to a user (e.g., a driver) and / or an external system (e.g., a vehicle ECU) that the corresponding battery cell has degraded. In some embodiments, the battery management system 110 issues (flags) a capacity fault warning for the corresponding battery cell. In some embodiments, the battery management system 110 reports an estimated number of remaining life cycles of the corresponding battery cell to the user and / or external system using a calibratable lookup table (see Tables 1 to 4). In some embodiments, the battery management system 110 inputs the current battery cell voltage, the change in battery cell pressure between cycles, the battery cell temperature, and the operating voltage window into the calibratable lookup table, and receives the corresponding estimated number of remaining life cycles as output.

[0073] In some embodiments, the battery management system 110 uses a calibrable lookup table to set a new charging voltage limit (i.e., a new SOC window) for a battery cell, a battery module including the battery cell, and / or a battery pack including a battery module including the battery cell. For example, the battery management system 110 can limit the battery cell voltage during charging to adjust the SOC window to 10% (or more or less) to 90% (or more or less) of the original SOC window.

[0074] In some embodiments, a new charge voltage limit is selected from a calibrable lookup table to avoid an estimated cell pressure fluctuation within a predetermined number of cycles. For example, if a cell pressure fluctuation is predicted within the next cycle (or 2, 3, etc.), a new charge voltage limit may be selected that extends the cell pressure fluctuation prediction by 5 cycles (or 3, 4, 8, 12 cycles, etc.). In some embodiments, the battery management system 110 reports to a user and / or external system the estimated number of cycles available at the new charge voltage limit before a cell pressure fluctuation (battery failure) is expected. In short, the estimated number of cycles available at the new charge voltage limit acts as an additional time window for a user (e.g., a driver or system) to take action before an expected cell and / or battery pack failure.

[0075] At box 516 (during the discharge state), the battery management system 110 indicates to a user (e.g., a driver) and / or an external system (e.g., a vehicle ECU) that the corresponding battery cell has degraded. In some embodiments, the battery management system 110 issues (flags) a capacity fault warning for the corresponding battery cell. In some embodiments, the battery management system 110 reports an estimated number of remaining life cycles of the corresponding battery cell to the user and / or external system using a calibrable lookup table (see Tables 1 to 4). In some embodiments, the battery management system 110 inputs the current battery cell voltage, the change in battery cell pressure between cycles, the battery cell temperature, and the operating voltage window into the calibrable lookup table, and receives the corresponding estimated number of remaining life cycles as output.

[0076] In some embodiments, the battery management system 110 uses a calibrable lookup table to set a new operating voltage limit (i.e., a new SOC window) for a battery cell, a battery module including the battery cell, and / or a battery pack including a battery module including the battery cell. For example, the battery management system 110 can limit the battery cell voltage during driving to adjust the SOC window to 10% (or more or less) to 90% (or more or less) of the original SOC window.

[0077] In some embodiments, a new operating voltage limit is selected from a calibrable lookup table to avoid an estimated cell pressure fluctuation within a predetermined number of cycles. For example, if a cell pressure fluctuation is predicted within the next cycle (or 2, 3, etc.), a new operating voltage limit may be selected that extends the cell pressure fluctuation prediction by 5 cycles (or 3, 4, 8, 12, etc.). In some embodiments, the battery management system 110 reports to a user and / or external system the estimated number of cycles available at the new operating voltage limit before a cell pressure fluctuation (cell failure) is expected. In short, the estimated number of cycles available at the new operating voltage limit acts as an additional time window for a user (e.g., a driver or system) to take action before an expected cell and / or battery pack failure.

[0078] The specific responses described above regarding the charge and discharge states of the corresponding battery cells are provided as examples and are not meant to be particularly limiting. In some embodiments, the battery management system 110 may take one or more of a number of additional or alternative actions. Some possible responses are provided below.

[0079] Warnings / Alarms: In some embodiments, the battery management system 110 issues battery cell degradation warnings to the user of the vehicle and / or the vehicle's internal systems (eg, the ECU).

[0080] Cell Balancing: In some embodiments, the battery management system 110 can initiate cell balancing to equalize the state of charge (SOC) of the battery cells in the battery pack. Cell balancing can minimize performance differences between battery cells and can mitigate the effects of cell degradation in a single battery cell. In some embodiments, cell balancing involves redistributing energy and / or charge between battery cells in the battery pack to achieve a more consistent SOC.

[0081] Current Limitation: In some embodiments, if a particular battery cell shows signs of degradation, the battery management system 110 can limit the current flowing into or out of the corresponding battery cell during charging and / or discharging. For example, the current can be limited between an upper and lower threshold (i.e., between 15% and 85%, etc.). By limiting the current, the battery management system 110 can reduce the stress on the degraded battery cell and can minimize the rate at which the battery cell further degrades.

[0082] Temperature Management: In some embodiments, the battery management system 110 can actively monitor and / or control the temperature of the battery pack. In some embodiments, the battery management system 110 can adjust the charge and / or discharge current and / or can activate a passive or active cooling system to maintain target temperature conditions in the corresponding battery cells.

[0083] Fault Isolation and Cell Replacement: In some embodiments, the battery management system 110 can isolate a faulty cell by electrically disconnecting the cell from the system and / or battery pack. In some embodiments, the battery management system 110 can initiate a cell replacement process by identifying a degraded cell to be replaced and / or by replacing the cell with a new (backup) cell.

[0084] System Shutdown: In some embodiments, the battery management system 110 can initiate an automatic shutdown and / or limit the operation of the battery pack in response to identification of battery cell degradation. In some embodiments, the battery management system 110 can request another system (e.g., an ECU) to initiate an automatic shutdown in response to identification of battery cell degradation.

[0085] Figure 6 600, which can perform various aspects of the embodiments described herein. In some embodiments, the computer system 600 can be used as a system (e.g., Figure 1 The battery management system 110 of the battery pack (eg Figure 1 In some embodiments, the computer system 600 may be configured to receive signals (e.g., battery cell pressure signals, battery cell voltage signals, charge status signals, temperature signals, etc.) from one or more battery cells of the battery pack.

[0086] Computer system 600 includes at least one processing device 602, which typically includes one or more processors for performing various functions, such as controlling an electric motor (e.g. Figure 1 The electric motor 106 of the embodiment of the present invention is used to transmit power to one or more wheels of a vehicle (e.g., vehicle 100), control one or more batteries (e.g., Figure 1 The computer system 600 may also include the logic necessary to detect battery cell degradation and take appropriate action based on the data (see Figure 5 ).

[0087] Components of computer system 600 include a processing device 602 (such as one or more processors or processing units), a system memory 604, and a bus 606 that couples various system components including system memory 604 to processing device 602. System memory 604 may include various computer system readable media. Such media may be any available media that can be accessed by processing device 602, and includes both volatile and non-volatile media, and removable and non-removable media.

[0088] For example, system memory 604 includes nonvolatile memory 608 such as a hard drive, and may also include volatile memory 610 such as random access memory (RAM) and / or cache memory. Computer system 600 may also include other removable / non-removable, volatile / nonvolatile computer system storage media.

[0089] The system memory 604 may include at least one program product having a set (e.g., at least one) of program modules configured to perform the functions of the embodiments described herein. For example, the system memory 604 stores various program modules that generally perform the functions and / or methods of the embodiments described herein. One or more modules 612, 614 may be included to perform functions related to the monitoring and / or control of the battery pack 108, such as determining one or more current battery cell temperatures, the current state of charge of the battery pack 108 and / or any battery cell of the battery pack 108, the charging duration, the charging current and / or the voltage, etc. The computer system 600 is not limited thereto, as other modules may be included according to the desired functions of the vehicle 100. As used herein, the term "module" refers to a processing circuit, which may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and a memory that executes one or more software or firmware programs, a combinational logic circuit, and / or other suitable components that provide the functions. For example, a module may be configured by software, hardware, and / or firmware to stop charging and / or isolate one or more battery cells of the battery pack of the vehicle 100.

[0090] The processing device 602 may also be configured to communicate with one or more external devices 616, such as a keyboard, a pointing device, and / or any device that enables the processing device 602 to communicate with one or more other computing devices (e.g., a network card, a modem, a vehicle ECU, etc.). Communication with various devices may occur through input / output (I / O) interfaces 618 and 620.

[0091] The processing device 602 may also communicate with one or more networks 622, such as a local area network (LAN), a general wide area network (WAN), a bus network, and / or a public network (e.g., the Internet) via a network adapter 624. In some embodiments, the network adapter 624 is or includes an optical network adapter for communicating over an optical network. It should be understood that, although not shown, other hardware and / or software components may be used in conjunction with the computer system 600. Examples include, but are not limited to, microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, and data archival storage systems, etc.

[0092] Reference now Figure 7, generally shows a flowchart 700 for implementing operating voltage limiting in response to battery cell degradation according to an embodiment. Figures 1 to 6 A flowchart 700 is described and may include Figure 7 Although depicted in a particular order, Figure 7 The blocks depicted in the drawings may be rearranged, subdivided, and / or combined.

[0093] At block 702, a first cell pressure of a battery cell of a battery pack is measured at a reference voltage. At block 704, a second cell pressure of a battery cell of the battery pack is measured at the reference voltage.

[0094] At block 706, a moving average of the cell pressure progression is determined from the first cell pressure and the second cell pressure. A moving average of the cell pressure progression may be determined in this manner over any desired number of cell pressure measurements.

[0095] At block 708 , in response to the moving average of the cell pressure level exceeding the cell pressure level threshold, a cell of the battery pack is identified as a degraded cell, and an estimate of remaining cycles of the degraded cell is determined.

[0096] In some embodiments, the battery management system is further configured to establish a lookup table configured to provide as an output an estimate of the remaining useful cycle life of the battery cell. In some embodiments, the lookup table is a four-dimensional (4D) lookup table having as inputs the battery cell voltage, the change in battery cell pressure between cycles, the battery cell temperature, and the operating voltage window.

[0097] In some embodiments, determining an estimate of remaining cycles for a degraded battery cell includes inputting a first battery cell voltage, a first change in battery cell pressure between cycles, a first battery cell temperature, and a first operating voltage window into a lookup table, and in response to the inputs, receiving the estimate of remaining cycles from the lookup table.

[0098] In some embodiments, the estimate of remaining cycles for the degraded cell is an estimate of the number of cycles until a predetermined end-of-life condition for the degraded cell. In some embodiments, the predetermined end-of-life condition includes one of an estimated number of cycles until an expected cell pressure fluctuation exceeds a predetermined threshold and a number of cycles until a predetermined percentage of previous cells fail.

[0099] In some embodiments, the battery management system is further configured to determine one of a state of charge and a state of discharge of the battery pack. In some embodiments, the battery management system is further configured to use a lookup table to adjust one of a charging voltage limit and an operating voltage limit of a degraded battery cell.

[0100] The terms "one" and "an" do not indicate a limitation of quantity, but rather indicate the presence of at least one of the referenced items. The term "or" means "and / or", unless the context clearly indicates otherwise. References to "an aspect" throughout the specification mean that a particular element (e.g., feature, structure, step, or characteristic) described in conjunction with that aspect is included in at least one aspect described herein, and may or may not be present in other aspects. In addition, it should be understood that the described elements may be combined in any suitable manner in various aspects.

[0101] When an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

[0102] Unless otherwise indicated herein, all test standards are the most recent standards in effect as of the filing date of the present application or, if priority is claimed, the filing date of the earliest priority application in which the test standards appear.

[0103] Unless defined otherwise, 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.

[0104] Although the above disclosure has been described with reference to exemplary embodiments, it will be appreciated by those skilled in the art that various changes may be made and equivalents may be substituted for its elements without departing from the scope thereof. In addition, many modifications may be made to adapt specific situations or materials to the teachings of the disclosure without departing from the essential scope of the disclosure. Therefore, it is intended that the disclosure is not limited to the specific embodiments disclosed, but will include all embodiments falling within its scope.

Claims

1. A vehicle comprising: Electric motor; a battery pack electrically coupled to the electric motor; as well as A battery management system coupled to the battery pack, the battery management system comprising a memory, computer readable instructions, and one or more processors for executing the computer readable instructions, the computer readable instructions controlling the one or more processors to perform operations including: measuring a first cell pressure of a battery cell of the battery pack at a reference voltage; measuring a second cell pressure of a battery cell of the battery pack at a reference voltage; determining a moving average of a cell pressure level from the first cell pressure and the second cell pressure; as well as In response to a moving average of the cell pressure level exceeding a cell pressure level threshold, a battery cell of the battery pack is identified as a degraded battery cell, and an estimate of remaining cycles of the degraded battery cell is determined.

2. The vehicle according to claim 1, wherein: The battery management system is also configured to establish a lookup table configured to provide as an output an estimate of a remaining useful cycle life of the battery cell.

3. The vehicle according to claim 2, wherein: The lookup table comprises a four-dimensional (4D) lookup table that includes as inputs a battery cell voltage, a change in battery cell pressure between cycles, a battery cell temperature, and an operating voltage window.

4. The vehicle according to claim 3, wherein: Determining the estimate of remaining cycles for the degraded battery cell includes inputting a first battery cell voltage, a first change in battery cell pressure between cycles, a first battery cell temperature, and a first operating voltage window into the lookup table and receiving the estimate of remaining cycles from the lookup table in response to the inputs.

5. The vehicle according to claim 4, wherein: The estimate of remaining cycles for the degraded battery cell includes an estimate of a number of cycles until a predetermined end-of-life condition for the degraded battery cell, wherein the predetermined end-of-life condition includes one of an estimated number of cycles until an expected battery cell pressure fluctuation exceeds a predetermined threshold and a number of cycles until a predetermined percentage of previous battery cells fail.

6. The vehicle according to claim 2, wherein: The battery management system is also configured to determine one of a state of charge and a state of discharge of the battery pack.

7. The vehicle according to claim 6, wherein: The battery management system is further configured to adjust one of a charging voltage limit and an operating voltage limit of the degraded battery cell using the lookup table.

8. A battery management system comprising a memory, computer readable instructions, and one or more processors for executing the computer readable instructions, the computer readable instructions controlling the one or more processors to perform operations including: measuring a first cell pressure of a battery cell of the battery pack at a reference voltage; measuring a second cell pressure of a battery cell of the battery pack at a reference voltage; determining a moving average of a cell pressure level from the first cell pressure and the second cell pressure; and In response to a moving average of the cell pressure level exceeding a cell pressure level threshold, a battery cell of the battery pack is identified as a degraded battery cell, and an estimate of remaining cycles of the degraded battery cell is determined.

9. The battery management system according to claim 8, wherein: The battery management system is further configured to establish a lookup table configured to provide as an output an estimate of a remaining useful cycle life of the battery cell.

10. The battery management system according to claim 9, wherein: The lookup table comprises a four-dimensional (4D) lookup table that includes as inputs a battery cell voltage, a change in battery cell pressure between cycles, a battery cell temperature, and an operating voltage window.

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