Method and apparatus for optimizing fast battery charging

Abstract

The present application relates to methods and apparatus for optimizing fast battery charging. In the described example of a method and apparatus for fast charging a battery with optimized charging, a system (400) includes a battery charger (420) for applying a voltage to a rechargeable battery (430), and a controller (422) coupled to the battery charger (420) and monitoring at least one of a battery voltage, a battery temperature, and a current flowing into the battery (430). The system (400) is configured to apply a charging current from the battery charger (420) by calculating an open circuit cell anode voltage and anode resistance of the battery (430) and determining a charging current. In an additional arrangement, lithium ion plating is prevented by the charging current.

Description

[0001] This application is a divisional application of Chinese patent application 201680044260.6 (PCT / US2016 / 051025), entitled "Method and apparatus for optimizing fast battery charging," filed on September 9, 2016, with an international filing date of September 9, 2016, and entering the national phase on January 29, 2018. Technical Field

[0002] This application relates generally to battery charging, and more specifically to fast charging of rechargeable lithium batteries without battery degradation due to lithium plating. Background Technology

[0003] Recent developments in lightweight, rechargeable lithium-ion batteries, with their ability to store relatively large amounts of energy in relatively small packages, have made lithium-ion batteries the power source of choice for portable electronic devices. After manufacturing, the lifespan of a lithium-ion battery is largely determined by the type of use and the recharging method employed. While the use of lithium-ion batteries is primarily determined by the consumer, the type of recharging can be determined by the device manufacturer and / or charger manufacturer. Although battery manufacturers can provide recharging guidelines, these guidelines typically specify rather conservative charging rates to minimize any adverse battery charging effects. This results in battery recharging times ranging from 2 to 4 hours or even longer. In many cases, consumers naturally prefer to charge portable devices in shorter times, such as less than 1 hour. Therefore, there is a conflict between the conservative charging guidelines written to ensure long battery life and the actual practices and preferences in field battery use. Improper fast charging of lithium-ion battery packs can significantly shorten battery life and, in the worst case, may lead to battery pack swelling or rupture; in certain environments, fast charging can also pose a potential fire risk.

[0004] A battery's capacity, described as a "C" rating, is defined as the sum of the constant currents a rated battery cell can deliver during a 20-hour discharge cycle while remaining within its rated voltage limits at room temperature. For example, an ideal battery that can produce 50 mA for 20 hours while remaining within the described voltage window would have a C rating of 50 mA × 20H = 1000 mAh or 1 Ah. A "perfect" battery will have 100% efficiency during both charging and discharging. If a perfect battery has a 1 Ah C rating, then it can deliver 1A for 1 hour, or 0.5A for 2 hours, or 100 mA for 10 hours, or 50 mA for 20 hours, and so on. Furthermore, a perfect battery with a 1 Ah C rating can be recharged in 1 hour by charging at 1A for 1 hour, or 0.5A for 2 hours, or 100 mA for 10 hours. Other terms commonly used in the description of battery charging and capacity are State of Charge (SOC) and Depth of Discharge (DOD). Both SOC and DOD are expressed in percentage units and are flattering definitions. SOC represents the relative amount of energy stored in the battery compared to its fully charged state. DOD represents how much battery energy has been used compared to its fully charged state. For example, for a perfect 1Ah battery: if 0.25Ah is depleted, the battery will have 75% SOC and 25% DOD; and if 0.5Ah is depleted, the battery will have 50% SOC and 50% DOD. The battery voltage is typically specified as the Open Circuit Cell Voltage (OCV), where the cell voltage is measured without an external load. Full Charge Capacity (FCC), on the other hand, is the capacity of a cell at any given point in its life when fully charged. Using the example of the perfect battery above, when new, the FCC would be 1Ah. As the battery ages, the FCC decreases.

[0005] When battery capacity increases or decreases arbitrarily with the addition or reduction of battery materials, the voltage characteristics of a given battery chemistry remain independent of battery capacity. For this reason, the discharge and charge of a single cell are typically discussed in terms of the C rating. For example, if a perfect 1Ah battery is discharged at a maximum rate of 1C, then the maximum discharge rate will be 1A. Similarly, a perfect battery, charged at a maximum rate of 2C, will see a maximum discharge current of 2A.

[0006] In rechargeable lithium-ion batteries, energy is stored in chemical reactions and regained in chemical reactions through the migration of lithium ions between electrode pairs. Both the positive electrode (cathode) and the negative electrode (anode) can bind lithium ions. During discharge, lithium ions move from the anode to the cathode, releasing energy in the process. During a charging cycle, the electric field generated between the cathode and anode forces lithium ions back to the anode, absorbing energy in the process. In some cases, including charging at high C rates, a small fraction of the lithium ions form metallic lithium and is deposited on the anode during the recharging phase. This lithium material partially reacts with the electrolyte and is then no longer available for recharging, resulting in a reduction in battery capacity. This phenomenon is called "lithium plating." Lithium plating reduces battery capacity and lifespan.

[0007] Traditional battery charging methods involve two phases: a constant current (CC) phase followed by a constant voltage (CV) phase. During the CC phase, a current considered safe for the battery is applied until the cell voltage reaches a target voltage, such as 4.2 volts. The current is then reduced as the voltage remains in the CV phase until it reaches a minimum when charging stops. Traditional battery chargers also monitor conditions (such as temperature), and many traditional methods stop charging when the temperature drops below a minimum (such as 10°C or 0°C).

[0008] Figure 1A is a flowchart of a traditional two-stage constant current (CC) and constant voltage (CV) charging process, or "CC / CV". Figure 1B is a typical battery charging cycle curve using the CC / CV process.

[0009] Figure 1A flowchart shows the steps used in the controller to operate the CC / CV charging process. Step 110 begins this process. In step 111, the charging process begins. In this step, the maximum current is applied to the battery. In step 113, the constant current phase begins. In this phase, the charging process charges the battery at a predetermined maximum current. The current can be the maximum value available from the charger, or a maximum current considered safe according to the manufacturer's instructions, such as 1C. This process continues in step 113, and a test is performed to see if the maximum voltage "Max V" has been reached. Constant current charging continues by holding in step 113 until the maximum voltage is reached.

[0010] When the test in step 113 indicates that the maximum voltage Max V has been reached, in step 115, the charging process switches to "constant voltage" operating mode. During the constant voltage charging process, as the battery reaches full capacity, the current flowing into the battery is allowed to decrease. In step 117, the current flowing into the battery is tested to see if it has reached the cutoff limit (the current flowing into the battery is measured and found to be less than the minimum charging current), and when the cutoff is reached, the process transitions to step 119 ("stop" state).

[0011] In Figure 1B, the left vertical axis of the charging curve 120 depicts the charging voltage, represented by data line 124. The right vertical axis depicts the charging current, represented by data line 122. The unit on the right axis is labeled C, indicating the battery's C-rated value. The bottom axis represents the charging time in hours. Near the top of the curve are indicated two different stages of the CC / CV charger, with a CC stage as shown in 130 and a CV stage as shown in 132.

[0012] In this example, the maximum charging rate is 1C, represented by the peak value of the charging current line 122 in the constant current or CC phase 130. As the current line 122 transitions from the CC phase to the constant voltage of the CV phase, the cutoff current is approximately 0.15C at the final current value in the CV phase 132. The maximum charging voltage is indicated by the value of the voltage line 124 in the CV phase 132, and is approximately 4.2V. In this example charging scenario, the total charging time is approximately 1 hour and 10 minutes, as indicated by the termination of the charging current line 122.

[0013] To achieve shorter recharge times, the current in the common charge (CC) phase can be increased to 2C or higher. However, repeatedly charging at these higher rates significantly reduces the lifespan and capacity of the lithium battery compared to charging at lower rates (such as 0.5C). An ideal charging system would be able to charge the battery in the least amount of time without accelerating battery degradation.

[0014] Figure 2This is a graph illustrating the degradation of a cell's capacity as the charging rate (C-rate) increases. The data depicted in graph 200 shows that charging the battery at higher C-rates can have an adverse effect on the usable capacity of the cell, as described in the article "Factors that affect cycle-life and possible degradation mechanisms of a Li-ion cell based on LiCoO2" published by S.S. Choi et al. in the Journal of Power Sources, Vol. 111, No. 1, pp. 130-136, 2002. Figure 2 The graph shows that when using a CC / CV charger with a charging rate similar to 1.4C, the capacity of the cell illustrated in the graph has decreased to approximately 27% of its initial capacity after 500 charging cycles. A cell with the same chemistry, charged at 1C, still maintains approximately 800mA after 500 cycles. Figure 2 As shown in the graph, a higher constant current charging rate causes the battery to degrade rapidly and shorten its lifespan.

[0015] The open-circuit cell voltage (OCV) of a battery cell can be calculated as shown in equation (1) below:

[0016] V cell =V cathode -V anode (1)

[0017] Battery voltage V cathode (V 阴极 ) and V anode (V 阻极 Direct measurement of the anode and cathode potentials is typically accomplished by inserting a third reference electrode into the electrolyte region of the battery. Due to the delicate nature of the procedure, it is usually performed only by the battery manufacturer in a laboratory setting. When successful, the anode and cathode potentials are extracted from the battery, which has undergone very few cycles and is typically at room temperature. However, due to the lack of a third reference electrode, these voltages are not available for the battery in practical use.

[0018] Battery degradation is categorized into two basic types: loss of active materials and increase in internal impedance. In the first type (loss of active materials), the loss of materials reduces the amount of chemicals available for the ionization process to generate current. Although battery manufacturers seal the batteries, some electrolyte loss still occurs due to parasitic reactions within the cell. Improperly charged battery packs may exhibit swelling due to the generated gas. In extreme cases, this swelling can damage equipment containing the battery pack.

[0019] In the second category (increased impedance), the amount of energy available for an external load decreases due to increased internal resistance. Increased impedance is a common degradation experienced by lithium-ion battery cells. Internal resistance increases with battery aging and the number of charge / discharge cycles. Furthermore, internal resistance increases at lower temperatures. When internal impedance increases, lithium plating is more likely during charging because the increased internal impedance negatively impacts the internal potential. Due to the increased impedance at lower temperatures, some conventional chargers include cutoff temperature sensors and do not charge below certain temperatures (such as 10°C or 0°C). However, increased impedance also occurs at temperatures above these, and charging acceptable at room temperature can lead to lithium plating at lower temperatures, especially as the battery cell ages.

[0020] Lithium plating leads to two types of degradation: loss of active material and increased internal resistance. When lithium ions become lithium metal and react with the solvent, the number of lithium ions available for charge transport decreases. Furthermore, as lithium metal decomposition products accumulate at the anode, fewer sites remain for lithium ions to exchange their charge. Due to this dual degradation, conditions that accelerate lithium plating are desirable to avoid. Lithium plating reduces the capacity and lifespan of battery cells.

[0021] During the charging of a lithium-ion battery cell, lithium plating occurs when the voltage across the anode material drops, causing the potential of the graphite surface at the anode of the lithium cell to fall below the lithium potential. Figure 3 A graph 300 depicts the charging limitations exhibited by lithium-ion plating. In graph 300, the vertical axis is a graph of the anode potential (expressed in volts) compared to the lithium-ion potential. The horizontal axis illustrates the state of charge (SOC) of the charging cycle (expressed as a percentage). On the left side of the graph, the SOC is 0%, and charging begins. Charging ends when the SOC represents 100% full charge. Trace 305 illustrates the open-circuit cell voltage of the graphite anode in a lithium-ion cell. The anode OCV is greater than zero throughout the overall charging cycle. However, trace 307 depicts a comparison of the anode potential to the lithium-ion potential. For low temperatures, fast charging, or for aged battery cells, internal resistance can increase, causing the anode potential to drop to zero or become negative compared to the lithium-ion potential. This is... Figure 3The inner side of region 309 is shown, where lithium plating may occur. Therefore, lithium plating is a limitation on the charging rate that can be achieved without damaging the battery. Furthermore, the battery impedance changes with temperature. Since the battery impedance increases at lower temperatures, charging at lower temperatures, such as when charging outdoors or in a vehicle, can cause lithium plating, even when charging at a level that is suitable for room temperature.

[0022] A charging method is desired to avoid lithium plating and thus extend battery life while maintaining battery capacity. U.S. Patent Application Serial No. 14 / 014,195, published March 6, 2014, filed August 29, 2013, entitled "METHODAND APPARATUS OF CHARGING THE BATTERY WITH GLOBALLY MINIMIZED INTEGRALDEGRADATION POSSIBLE FOR PREDEFINED CHARGING DURATION," is jointly owned by Yevgen Barsukov et al., who are inventors, and is incorporated herein by reference in its entirety. The aforementioned patent application represents an improvement in reducing the recharge time of lithium-ion cells. Multiple charging profiles have been developed to adapt to battery aging, impedance, temperature, and state of charge (SOC) in laboratory testing and modeling of specific battery chemistry processes. By empirically characterizing lithium chemistry, a set of optimized constant current-constant voltage (CC / CV) charge profiles can be loaded into a battery charging device. These charge profiles can then be used to reduce overall charging time while avoiding charging conditions that degrade the battery, including degradation caused by lithium plating at high charging rates. The method described in the aforementioned patent application goes beyond conventional approaches to achieve the goal of rapid battery recharging without increasing cell degradation. This method requires considerable computation offline to characterize each specific battery cell and create a CC / CV charge profile for each battery pack. If materials or battery cells are modified, these calculations must be repeated, and new profiles are required. However, further optimization of the charging method is needed to reduce charging time without inducing additional battery degradation. Summary of the Invention

[0023] In the described example, a system includes: a battery charger for applying current to a rechargeable battery; and a controller coupled to the battery charger and monitoring at least one of battery voltage, battery temperature, and current flowing into the battery; wherein the system is configured to apply a charging current from the battery charger to the battery during a battery charging cycle, wherein the current is determined by the steps of: calculating the open-circuit cell anode voltage and calculating the anode resistance of the battery, and determining the charging current from the calculated open-circuit cell anode voltage and the calculated anode resistance.

[0024] In a further arrangement, the system further includes an application processor coupled to the controller, and the application processor is configured to control the battery charger. In another arrangement, the system is configured to calculate the anode resistance using parameters stored for the anode resistance. In yet another further arrangement, the system further includes an instruction store in the CPU and the controller containing instructions configured to cause the CPU to calculate a charging current proportional to the calculated open-circuit cell anode voltage divided by the anode resistance.

[0025] In an additional arrangement, the system further includes data storage containing parameters for battery storage, including anode resistance parameters for compensating for depth of discharge. In another arrangement, the controller further includes data storage containing parameters for battery storage, including resistance parameters for compensating for battery temperature. In a further alternative arrangement, the controller further includes an input configured to receive battery voltage, a temperature sensor for the battery, and a current sensor for the battery. Still in another arrangement, the controller is configured to control the battery charger to apply a charging current to the battery until a predetermined battery voltage is reached. In a further alternative arrangement, the controller is configured to control the battery charger to apply a constant voltage to the battery after the predetermined battery voltage is reached. In yet another arrangement, the system is provided, wherein the system further includes a lithium-ion battery coupled to the battery charger and a controller. In yet another alternative arrangement, the system is configured to apply a charging current from the battery charger calculated to avoid lithium plating within the lithium-ion battery.

[0026] In another arrangement, a method for charging a battery includes: providing a controller coupled to a battery charger; determining a charging current in the controller by the steps of: calculating the open-circuit cell anode voltage of the battery, and determining the charging current from the calculated open-circuit cell anode voltage and the anode resistance of the battery; and applying the charging current from the battery charger to the battery. In a further alternative arrangement, the above method further includes determining whether a predetermined battery voltage has been reached; if the predetermined battery voltage has not been reached, calculating the charging current from another calculated open-circuit cell anode voltage and the anode resistance of the battery; and dynamically adjusting the charging current and applying the adjusted charging current to the battery.

[0027] Still in an additional alternative arrangement, if a predetermined battery voltage has been reached, the method includes calculating the battery voltage from the open-cell anode voltage and applying the battery voltage from the battery charger. In a further alternative arrangement, in the above method, calculating the charging current further includes calculating a maximum charging current that can be applied without causing lithium plating. In an additional arrangement, the above method further includes determining the charging current by the steps of: calculating the open-cell anode voltage of the battery and determining the charging current from the calculated open-cell anode voltage, which further includes: retrieving stored data corresponding to the open-cell anode voltage parameterized by temperature. In another alternative arrangement, the above method is performed and further includes calculating the open-cell anode voltage by retrieving the stored open-cell anode voltage characterized by the depth of discharge of the battery. In another arrangement, in the above method, the controller further includes providing a battery gauge integrated circuit device coupled to the battery charger.

[0028] In another arrangement, a system for charging a lithium-ion battery includes a battery charger integrated circuit having a battery output terminal for outputting a battery charging current and a battery charging voltage to the lithium-ion battery; and a battery metering integrated circuit coupled to the battery charger integrated circuit, the battery metering integrated circuit having an input terminal coupled to sense the battery voltage, a temperature sensor coupled to the battery, and a current sensor coupled to the battery; wherein the battery metering integrated circuit is further configured to determine the charging current for charging the battery by calculating the open-circuit cell anode voltage and anode resistance, and is configured to control the battery charger to output the charging current. In another arrangement, in the above system, the charging current is calculated as a maximum charging current, which results in an open-circuit cell anode voltage that avoids lithium plating. Attached Figure Description

[0029] Figure 1A illustrates the flowchart of the CC / CV process of the conventional method, and Figure 1B illustrates the curve of the battery charging process in Figure 1A.

[0030] Figure 2 It is a graph illustrating the capacity of a battery cell after 500 cycles using different charging rates.

[0031] Figure 3 It is a graph of the anodic potential during the battery's charging cycle.

[0032] Figure 4 It is a circuit diagram of a battery coupled to a battery charging device using multiple arrangements.

[0033] Figure 5 This is another circuit diagram of a battery coupled to a battery charging device using multiple arrangements.

[0034] Figure 6A It is a flowchart for the optimized charging arrangement of the battery, and Figure 6B Is using Figure 6A The battery charging cycle curve of the process, and Figure 6C This is a comparison graph of the charging time of the charging cycle in an example embodiment compared to the conventional method.

[0035] Figure 7 This is a simplified block diagram of a battery meter circuit using multiple arrangements.

[0036] Figure 8 It is a graph comparing the battery degradation rate measured in a traditional CC / CV battery charging process with an optimized charging process that includes these arrangements. Detailed Implementation

[0037] When charging a battery, an optimized charging current should charge the battery quickly while avoiding battery degradation due to lithium plating. In the examples of methods and systems described for charging batteries, the charging current is calculated in a way that avoids lithium plating problems using the calculation of the anode voltage of the open-circuit cell, and these arrangements can be used to charge the battery with optimized current.

[0038] By using the advantageous methods and apparatus of the example embodiments, rechargeable batteries or battery packs can be rapidly charged using a charging current optimized for recharging, while avoiding lithium plating. The method dynamically adjusts the charging current during charging cycles to avoid lithium plating conditions (which would otherwise occur), thus extending battery life and maintaining battery capacity over many cycles, in stark contrast to conventional charging methods.

[0039] The example embodiments include improvements in battery chargers and methods for charging lithium-ion batteries. Battery degradation during charging is avoided, maintaining a high level of battery cell capacity over a large number of cycles, while extending battery life. The example embodiments help prevent damage to battery cells and the equipment in which they are installed due to improper charging.

[0040] In different diagrams, corresponding numbers and symbols usually refer to corresponding parts unless otherwise specified. These diagrams are drawn to clearly illustrate relevant aspects of illustrative example arrangements and are not necessarily drawn to scale.

[0041] The manufacture and use of various examples of illustrative arrangements, including exemplary embodiments, are discussed in detail below. Furthermore, the disclosed illustrative examples provide numerous applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific examples and arrangements discussed are merely illustrative methods for making and using various arrangements, and the described examples do not limit the scope of the specification, nor do they limit the scope of the appended claims.

[0042] For example, when the term “coupled” is used herein to describe a relationship between components, the term as used in the specification and appended claims will be interpreted broadly, and the term “coupled” includes “connection”, and is not limited to “connection” or “direct connection”; however, the term “coupled” may include connections established with intermediate components, and additional components and various connections may be used between any components described as “coupled”.

[0043] The arrangements disclosed herein can be implemented in various ways. For example, these methods can be implemented and executed by a programmable device that executes instructions. These methods can be implemented in software or firmware or machine language instructions. Alternatively, programmable logic can be used to form a dedicated hardware solution. Devices that can be configured to execute these methods, including field-programmable gate arrays (FPGAs), complex logic programmable devices (CPLDs), and application-specific integrated circuits (ASICs), can be used to implement these arrangements. Processors such as CPUs, microcontroller units (MCUs), mixed-signal processors (MSPs), or digital signal processors (DSPs) and memories including RAM, ROM, flash memory, volatile and non-volatile types, EEPROMs, etc., can be used. These arrangements can be implemented using several commercially available integrated circuits that form a complete solution on a circuit board or module.

[0044] Example embodiments include a maximum-life battery charger and method. In this arrangement, the charging device is specifically configured to charge a lithium-ion battery using a charging algorithm, wherein the charging current is optimized to a maximum current level that can be used without lowering the anode electrode potential below the potential of lithium metal, and therefore without causing lithium plating. These methods include a constant anode potential (CAP) phase and a subsequent constant voltage (CV) phase. These arrangements allow the lithium-ion battery cell to be charged with an optimized charging current for the shortest possible time without accelerating battery degradation due to lithium plating. In stark contrast to conventional methods, the charging current is dynamically adjusted to provide an optimized maximum charging current on a continuous basis during the first part of the charging cycle, the CAP phase, which roughly corresponds to the preceding “constant current” phase. The charging current is adjusted to prevent lithium plating and battery degradation caused by overcharging. The method arrangement includes information about battery aging, depth of discharge, and temperature, and avoids overcharging at a given time by modeling the conditions within the battery and by performing calculations on a continuous basis and dynamically adjusting the charging current to reflect those conditions. The model includes information about the anode potential, thus avoiding lithium plating that can occur with conventional solutions.

[0045] Figure 4 This illustration shows a typical schematic diagram of a battery charging and monitoring apparatus that can be used with an example embodiment. In circuit 400, an application processor 410 is coupled to a battery cell meter 422. For example, the battery cell meter 422 may be a standalone integrated circuit. The battery cell meter 422 may also be implemented as a circuit board or system, or, in an alternative arrangement, as firmware including instructions for a programmable microprocessor. The battery cell meter 422 is coupled to a lithium battery cell 430 and a charger 420. Again, the charger 420 may be a standalone integrated circuit in a typical example. Alternatively, the charger 420 may be a circuit board or system. The charger 420 is coupled to the meter 422 and the battery cell 430. In this example arrangement, the battery cell meter 422 monitors the battery voltage at an input labeled "voltage sensing," the battery temperature at an input labeled "temperature sensing," and the battery current at an input labeled "current sensing." During operation in this arrangement, for example, the battery cell meter 422 may be implemented as an integrated circuit or circuit board, operating the charger 420 using an interface labeled I2C during charging cycles. When the system operates at battery power, the battery charger 420 supplies power from the battery 430 to the system load, while the battery meter 422 can provide the system with information about the battery status, such as remaining operating time. When power is applied to the VBUS input of the charger 420, the system load is powered by the provided DC power supply, and the charger 420 is used to charge the battery 430.

[0046] Figure 5 This describes another arrangement of the battery charging and monitoring device used in the example embodiment. In arrangement 500, application processor 510 is coupled to charger 520 and meter 522. Meter 522 is coupled to processor 510 and lithium-ion battery pack 530. Charger 520 is coupled to application processor 510 and lithium-ion battery pack 530. Meter 522 monitors battery voltage, battery current, and battery temperature. Figure 5 In this configuration, application processor 510 uses an I2C interface bus to control charger 520 using information provided by battery meter device 522. A range of products implementing fuel meters and battery chargers to form a battery management solution are commercially available from Texas Instruments, Inc. An example commercially available battery meter device is the BQ27530 Battery Management Unit Impedance Track Fuel Gauge; an example battery charger device is the BQ24161. Additional battery meter and battery charger ICs are also available from Texas Instruments, Inc.

[0047] In both arrangements 400 and 500, numerous battery parameters (such as the number of charge and discharge cycles, full charge capacity, impedance, voltage, temperature, SOC, and calendar life) are captured and stored in the memory within meter 422 or processor 510, enabling battery pack 430 or 530 to be charged efficiently and safely. Furthermore, during battery-powered operation, the battery meter and / or application processor can provide the system with an estimate of remaining operating time for display to the user. For example, using battery parameters, meter 422 or 522 can sense temperature, current, and voltage.

[0048] An aspect of the example embodiment describes the configuration of a system including a charging device to calculate the maximum charging current (I0). CH_MAX The optimized level of ) continuously provides charging current, as shown in equation (2) below:

[0049] I CH_MAX =OCV AN (DOD, T) / R AN (DOD, T) (2)

[0050] Among them: I CH_MAX This is the maximum charging current, which is transferred to the cell unit; OCV AN This is the estimated open-circuit cell voltage at the anode electrode at the current temperature and discharge level; R AN It represents the resistance of the anode; DOD is the depth of discharge; and T is the temperature in degrees Celsius (°C).

[0051] OCV AN =OCV AN 25(DOD)+OCV B (DOD)*(T-25) (2A)

[0052] Among them: OCV AN The estimated open-circuit cell voltage of the anode electrode in equation (2); OCV AN 25 is the OCV at 25℃. AN ; and OCV B It is the temperature compensation coefficient for the open-circuit cell voltage at a given temperature;

[0053] R AN (DOD, T) = (R) A (DOD,T)-R TRACE )*F ANODE (2B)

[0054] Where: R AN It is the resistance of the anode electrode from equation (2), compensating for the depth of discharge (DOD) and temperature (T); R A It is the resistance of the anode of DOD and T to compensate; R TRACE It is the sum of all parasitic resistances present in the measurement of the cell impedance; and F ANODE It is the anode factor, the ratio between the total cell resistance and the anode resistance;

[0055]

[0056] Wherein: F ANODE It is the anode factor from equation (2B); AN SHARE It is the contribution of the anode to the total impedance of the cell; R PRESENT This is the last recorded impedance value of the cell; R NEW This is the cell impedance value when the cell is new; RT RACE It is the impedance value of the entire anode trace; F ANODE0 It is F ANODE The initial value; and using data collected from offline cell characteristic descriptions, F ANODE0 The value and AN SHARE The value is provided to the charger.

[0057] Equations (2), (2A), (2B), and (2C) have been found to provide the ability to dynamically adjust the charging current applied to the battery on a continuous basis to ensure that the open-circuit cell voltage at the anode (OCVan) is maintained at a positive voltage and using a constant anode potential (CAP). In the example embodiment, a method incorporating these calculations is performed to charge the battery with an optimized charging current while avoiding lithium plating, thereby preventing premature battery degradation. Charging can be performed as quickly as possible while maintaining a healthy battery pack, and therefore the battery pack life can be extended to "maximum life," i.e., many more cycles than battery life obtained using conventional methods.

[0058] Using these equations requires certain parameter information. In one example aspect of the exemplary embodiment, the open-circuit cell anode voltage, depth of discharge, and temperature dependence are obtained by performing direct measurements using a three-electrode cell including a reference electrode, a cathode electrode, and an anode electrode.

[0059] In another alternative arrangement, the anode factor is obtained by performing direct measurement of the full cell impedance and direct measurement of the anode impedance using a three-electrode cell including a reference electrode, a cathode electrode, and an anode electrode.

[0060] In yet another alternative arrangement, the open-cell voltage anode, depth of discharge, and temperature dependence parameters are obtained by performing a decomposition of the full-cell open-cell voltage profile for depth of discharge (DOD) into known anode and cathode open-cell voltage profiles. This decomposition is accomplished by optimizing the state of charge of the anode, the state of charge of the cathode, and the ratio of anode to cathode material in the cell to achieve the closest match between the open-cell voltage profile OCV(DOD) for depth of discharge and the following relationship: open-cell voltage cathode for depth of discharge (OCV cathode(DOD)) minus open-cell voltage anode for depth of discharge (OCV anode(DOD)).

[0061] In a further arrangement, the resistance factor is determined by fitting cycling data obtained at the battery's standard charging rate and increased charging rate to a battery degradation model, the degradation model including lithium plating degradation effects dependent on the resistance factor.

[0062] In another arrangement, the resistance factor is found by performing a pulse scan test on the battery, wherein a combination of charging pulses, relaxation pulses, discharging pulses, and relaxation pulses is applied to the battery at different rates until the rate at which the effective impedance derived from the response to the charging pulse differs from the impedance derived from the discharging pulse is determined. Subsequently, after finding the limiting charging rate, the resistance factor is found using the known total cell impedance, the open-circuit cell voltage anode for the depth of discharge, and the tested battery temperature.

[0063] Figure 6A This is a flowchart of an example method for battery charging, layout 600, along with corresponding graphs depicting the charging voltage and current. The method uses a two-stage CAP / CV approach. As shown, method 600 has a start block 610 coupled to the following consecutive blocks: 618, 620, 622, 630, 632, 636, and 640. Block 612 is coupled to blocks 618 and 632. Blocks 614 and 616 are coupled to block 620. Block 616 is also coupled to block 632. Block 634 is coupled to decision block 636. The first part of the flowchart, from start block 610 to block 622, executes the process... Figure 6B The constant anode potential optimized charging (CAP) phase of the charging operation is indicated by bracket 646 in graph 602. In the second part of the flowchart, the stop at block 630 to block 640 is executed, performing the constant voltage (CV) phase of the charging operation indicated by bracket 648 in graph 602.

[0064] exist Figure 6B The curve in Figure 602 depicts Figure 6A CAP / CV charging. The charging current is shown in curve 638, and the charging voltage is shown in curve 634. The left vertical line or Y-axis indicates the cell voltage, and the right Y-axis indicates the charging current in units of cell capacity (C) or “C” rating. The horizontal line or X-axis indicates the charging time in hours (hr). Section 646 of curve 602 illustrates the constant anode potential (CAP) charging phase, and the conventional CV phase is shown in section 648. Figure 6B The time brackets 646 and 648 in the text correspond to... Figure 6A The flowchart 600 contains brackets with the same numbers.

[0065] Before the charging process begins, the maximum charging current capacity of the charging circuit is available for the process represented by block 614 (device maximum amperes (Amp)). Although in the example arrangement shown here, the maximum current applied during the optimized current charging process, obtained from equation (2), is dynamically and continuously calculated in the charging method of the example embodiment, this calculated current may exceed the amount of current that a particular charger can actually provide in certain parts of the process, in which case the current is limited to the device maximum ampere value at that time. Similarly, the maximum cell voltage of the lithium battery chemistry process is available for the process represented by block 616 (battery maximum voltage). The initial FCC (full charge capacity) is available in block 634 (full charge capacity), and this value is updated and maintained during the life of the lithium battery cell by charging the battery and by monitoring devices that store data in read / write memory. Battery data describing the cell characteristics at the factory and additional "real-time" data (such as temperature, cathode voltage, and current) are available in block 612 (battery data).

[0066] Various storage methods for retrieving and updating stored data utilize battery charging devices. For example, battery data from the manufacturer or factory can be provided as a lookup table (LUT) in ROM, EPROM, or flash memory, which retains the data when no power is available. For instance, data needed to calculate the maximum current is provided by, for example,... Figure 4 and Figure 5 The battery metering circuit shown provides, or draws from, values ​​stored in memory, which can be used by the battery charging device for calculations in equations (2), (2A), and (2B). Additionally, for example, the anode factor Fanode is stored based on measurements taken by the battery or charger manufacturer and can be stored as a lookup table.

[0067] exist Figure 6AIn the flowchart, the charging process begins at step 610 and proceeds to block 618 for the calculation of the open-circuit cell anode voltage (OCVAN). The calculation is performed using equations (2A) and (2B). This equation takes into account information at battery data 612, including cell impedance, battery life, DOD, and cell temperature, which are recorded by the charging device for that particular lithium-ion battery cell. In block 620 of the flowchart, equation (2) is executed using the open-circuit cell anode voltage OCVAN to determine the maximum charging current (ICH_MAX) that can be applied when charging in a certain manner to prevent lithium plating. The charging current during the charging process is limited by ICH_MAX. In one example, if the charger can only provide a lower current (device maximum amperes) based on the charger's maximum current capacity 614, then this lower current will be the maximum charging current for that period of time. Block 620 also understands the maximum charging voltage and will limit the charging current to ensure that it does not exceed the maximum battery voltage 616. After setting the charging current 620, a test and determination are formed in block 622. The test performed in block 622 determines whether the cell voltage is now equal to or has exceeded the maximum cell voltage. If false, the continuous estimation of the charging current continues back to block 618. Otherwise, if the maximum voltage has been reached, the charging process exits the CAP phase and proceeds to block 630, where the constant voltage or CV phase begins. During CAP process steps 618 to 622, the charging device (such as...) Figure 4 400 or Figure 5 The 500) continues to update various battery data 612, including DOD, battery aging, battery voltage, and temperature. This allows for the calculation of new anode voltage and anode resistance to maintain a constant anode potential (CAP) since OCV cannot be measured. 阳极 And therefore it must be calculated as shown in equation (2).

[0068] During the CV charging phase, from Figure 6AStep 630 begins, in which, in one example, the open-circuit cell anode voltage (OCVAN) is calculated using equations (2A) and (2B). These equations take into account battery data 612, which includes battery impedance, battery aging and DOD, and cell temperature, as recorded by the charging device for this particular lithium-ion cell. With OCVAN determined along with the maximum battery voltage 616 and battery data 612, the charging voltage is set to a lower voltage in block 632. To meet the lower charging voltage, the charging current 638 is typically reduced, as indicated by the current data 638 in CV stage 648 shown in graph 602. A charging current test is performed in block 636. The final charging current ICUTOFF can be determined as a portion of the full charge capacity 634, typically 5% to 10%. Charging is terminated in block 640 when the charging current is less than the predetermined ICUTOFF. Otherwise, the process loops back to block 630, where OCVAN is recalculated.

[0069] exist Figure 6B Graph 602 depicts the operation of the CAP / CV charger described in the example embodiment by displaying sampled charging voltage and charging current data of the CAP / CV charger. In graph 602, the CAP phase is indicated by time frame 646, the CV phase by time frame 648, and these two time frames are aligned with the data lines in graph 602. Dashed lines indicate the charging voltage of the CAP / CV charger, with the CAP / CV charging current represented by curve 638 and the CAP / CV charging voltage by curve 634. In this example, the charger's maximum charging current capacity is 1.35C, and the maximum battery charging voltage is 4.20V.

[0070] Utilizing various aspects of the current application, the CAP charging current 632 begins at the charger's maximum current of 1.35C, as shown in curve 602. The current is limited by the maximum capacity of the charging device. After the charging current data line 632, near the 0.5A mark on the right, the current level drops below the maximum current of 1.35A, thereby protecting the battery from lithium plating that would otherwise occur. The charging current is reduced to below the 1C charging level, close to 0.9C, and then gradually rises back to near 1.0C at the end of CAP stage 646. For the final portion of charging (CV stage 648), the maximum battery voltage has been reached, so the charging current is continuously reduced until it falls below the cutoff current. At that point, charging terminates.

[0071] The CAP / CV charging profile depicted in this example depends on battery aging, SOC, temperature, and charger capacity, and is therefore not the only charging profile that can be generated by the arrangement. Furthermore, it is preferable to incorporate a guard band, such as 10% to 20%, into the calculation of equation (2) to ensure that lithium plating does not occur due to measurement tolerances or calculation rounding errors.

[0072] Figure 6C The results obtained using the example CAP / CV charging arrangement of the example embodiment are compared with the constant current / constant voltage (CC / CV) charging cycle of the conventional method. Graph 650 is a graph comparing the charging current (current) plotted on the vertical axis (C rate) with the charging time, expressed in hours, on the horizontal axis. Line 653 depicts the charging current and charging time of the CAP / CV method of the example embodiment, while line 655 depicts the results obtained by the conventional CC / CV charging method. In this example, the total time required by the CAP / CV method is just over 1 hour. The total time required for the CC / CV cycle of the conventional method is approximately 1.75 hours. The CAP / CV method begins charging at time 0 with a relatively high current level, which is initially increased to above the 2C rate. However, as a dynamically adjusted current is determined, the charging current is reduced to avoid the possibility of lithium plating. After reaching the maximum voltage, the current continues to decrease until the end of the charging time (the final stage is the constant voltage stage). In contrast, the conventional method starts with a constant current, which is reduced to less than 1C and maintained for a long time (more than 1 hour) in curve 650, and then (after reaching the maximum voltage) the current drops until the end of the charging cycle.

[0073] like Figure 6C As shown in graph 650, the use of the CAP / CV method with optimized charging current in the example embodiment results in a significantly reduced charging time, while avoiding lithium plating, increasing battery life and maintaining charging capacity throughout battery life (because it also avoids an increase in internal resistance).

[0074] Figure 7 A simplified circuit diagram of an apparatus (such as a battery meter) for implementing the method arrangement of Figure 6 is described. Figure 7In the simplified circuit diagram, circuit 700 can be implemented as a standalone integrated circuit, as part of a larger integrated circuit, or as a board or module. Inputs from a battery voltage (BAT), a temperature sensor (Temp), and a state of charge (SOC) are fed to a multiplexer 701. The output of multiplexer 701 is fed to at least one analog-to-digital converter (ADC) 703. The ADC outputs digital data for use by a CPU 705. The CPU 705 is further coupled to a memory labeled instruction store 709, which stores instructions. For example, these instructions may include configurations for the CPU 705 to execute... Figure 6A The program code for the CAP / CV method. Furthermore, CPU 705 is coupled to a data bus DATA, which is coupled to static RAM 711 and non-volatile memory data storage 713 for storing battery parameters such as anode factor Fanode, Ranode, and battery aging and cycle count, used to calculate the potential OCV. 阳极 The temperature compensation factor of Ranode, and other parameters of the equations shown above. For example, data storage 713 may include data stored as a lookup table (LUT). As above Figure 4 and Figure 5 As shown, the battery meter circuit 700 can be coupled to a battery charger and / or application processor, for example, using I2C to interface with I2CA 717 and I2CB719.

[0075] Figure 8 Plot a comparison curve of battery degradation, showing percentage / second on the vertical axis and time on the horizontal axis. Optimized charging profiles (such as those that can be used...) Figure 6A (Method Implementation) Compared to conventional constant current / constant voltage or CC / CV methods, the degradation of conventional methods peaks between approximately 0.4 and 0.6 hours. This peak degradation of the battery indicates that lithium plating is occurring for that portion of the charging cycle. For optimized charge profiles, such as those implemented using the example embodiments described herein, the battery degradation profile is fairly constant and does not indicate a lithium plating problem. This occurs because the charge profile used is arranged to avoid conditions that cause lithium plating. The example embodiments use continuous dynamic adjustment of the charging current in the first portion of the charge profile, thus maintaining a constant anodic potential (CAP). This phase of the arrangement roughly corresponds to the "constant current" portion of the conventional method. However, in the example embodiments, charging is performed in a defined manner to avoid the lithium plating phenomenon of conventional methods.

[0076] As described above, in some arrangements, the battery meter can control the battery charger. In other arrangements, the battery meter can provide sensed and stored data parameters to an application processor, which can then control the battery charger. In yet another example arrangement, the battery charger and battery meter circuitry can be implemented as a single integrated circuit.

[0077] Various modifications can be made in the order and number of steps to form additional arrangements incorporating aspects of the example embodiments, and these modifications will form additional alternative arrangements.

[0078] Modifications are possible in the described embodiments, and other embodiments are possible within the scope of the claims.

[0079] Furthermore, the scope of the exemplary embodiments is not intended to be limited to the specific illustrative example arrangements of the processes, machines, manufactures, and combinations of things described herein. As will be readily apparent to those skilled in the art from this disclosure, currently existing or future processes, machines, manufactures, combinations of things, means, methods, or steps that perform substantially the same function or achieve substantially the same result as the corresponding example arrangements described herein can be used based on the illustrated arrangements and the described, suggested, or disclosed alternative arrangements. Therefore, the appended claims are intended to include such processes, machines, manufactures, combinations of things, means, methods, or steps within their scope.

Claims

1. A circuit for controlling a charger to charge a battery, comprising: The controller is configured as follows: Determine the voltage signal of the battery; Determine the anode potential of the first open-circuit cell of the battery; The maximum charging current value is determined based on the anode potential and anode resistance of the first open-circuit cell of the battery. Based on the maximum charging current value, a first control signal is generated to control the charger to charge the battery; Determine whether the voltage signal has reached a specific voltage; In response to the fact that the specific voltage has not yet been reached, Determine the anode potential of the second open-circuit cell of the battery; The maximum charging current value is adjusted based on the anode potential of the second open-circuit unit battery. as well as Based on the adjusted maximum charging current value, the first control signal used to control the charger to charge the battery is adjusted.

2. The circuit according to claim 1, wherein the controller is configurable as: In response to the fact that the specific voltage has been reached, Determine the anode potential of the third open-circuit cell of the battery; The charging voltage value is calculated based on the anode potential of the third open-circuit cell; and Based on the charging voltage value, a second control signal is generated to control the charger to charge the battery.

3. The circuit of claim 1, wherein the controller is configured to determine the maximum charging current value based on the anode potential of the first open-circuit cell of the battery divided by the anode resistance of the battery.

4. The circuit of claim 1, wherein the circuit is configured to sense the temperature of the battery, and the controller is configured to determine the anode potential of the first open-circuit cell based on the depth of discharge of the battery and the temperature of the battery.

5. The circuit of claim 4, wherein the controller is configured to determine the anode resistance based on the depth of discharge of the battery, the temperature of the battery, and the anode factor of the battery.

6. A method for operating a controller to control a charger to charge a battery, comprising: Determine the voltage signal of the battery; Determine the anode potential of the first open-circuit cell of the battery; The maximum charging current value is determined based on the anode potential and anode resistance of the first open-circuit cell of the battery. Based on the maximum charging current value, a first control signal is generated to control the charger to charge the battery; Determine whether the voltage signal has reached a specific voltage; In response to the fact that the specific voltage has not yet been reached, Determine the anode potential of the second open-circuit cell of the battery; The maximum charging current value is adjusted based on the anode potential of the second open-circuit unit battery. as well as Based on the adjusted maximum charging current value, the first control signal used to control the charger to charge the battery is adjusted.

7. The method of claim 6, further comprising: In response to the fact that the specific voltage has been reached, Determine the anode potential of the third open-circuit cell of the battery; The charging voltage value is calculated based on the anode potential of the third open-circuit cell; and Based on the charging voltage value, a second control signal is generated to control the charger to charge the battery.

8. The method of claim 6, further comprising: The maximum charging current value is determined by dividing the anode potential of the first open-circuit cell of the battery by the anode resistance of the battery.

9. The method of claim 6, further comprising: determining the anode potential of the first open-circuit cell based on the depth of discharge of the battery and the temperature of the battery.

10. The method of claim 8, further comprising: determining the anode resistance based on the depth of discharge of the battery, the temperature of the battery, and the anode factor of the battery.

11. A system for charging a battery, comprising: A charger configured to charge the battery; and A circuit, coupled between the charger and the battery, and including a controller configured to: Determine the voltage signal of the battery; Determine the anode potential of the first open-circuit cell of the battery; The maximum charging current value is determined based on the anode potential and anode resistance of the first open-circuit cell of the battery. Based on the maximum charging current value, a first control signal is generated to control the charger to charge the battery; Determine whether the voltage signal has reached a specific voltage; In response to the fact that the specific voltage has not yet been reached, Determine the anode potential of the second open-circuit cell of the battery; The maximum charging current value is adjusted based on the anode potential of the second open-circuit unit battery. as well as Based on the adjusted maximum charging current value, the first control signal used to control the charger to charge the battery is adjusted.

12. The system of claim 11, wherein the controller is configurable to: In response to the fact that the specific voltage has been reached, Determine the anode potential of the third open-circuit cell of the battery; The charging voltage value is calculated based on the anode potential of the third open-circuit cell; and Based on the charging voltage value, a second control signal is generated to control the charger to charge the battery.

13. The system of claim 11, wherein the controller is configured to determine the maximum charging current value based on the anode potential of the first open-circuit cell of the battery divided by the anode resistance of the battery.

14. The system of claim 11, wherein the controller is configured to determine the anode potential of the first open-circuit cell based on the depth of discharge of the battery and the temperature of the battery.

15. The system of claim 13, wherein the circuitry is configured to sense the temperature of the battery, and the controller is configured to determine the anode resistance based on the depth of discharge of the battery, the temperature of the battery, and the anode factor of the battery.

16. The system of claim 12, wherein the charger is configured to charge the battery based on the first control signal or the second control signal.

Images