Healthy fast charge battery system and protocol

Abstract

Battery systems and protocols can include applying a first charge current, such as first constant-current (CC) or first constant-power (CP), to charge a battery until a voltage of the battery (Vc) reaches a predetermined safe voltage of the battery (Vsafe) which increases with battery temperature. The battery can be heated while applying a charge current and Vsafe can be updated based on increasing battery temperature.

Description

HEALTHY FAST CHARGE BATTERY SYSTEM AND PROTOCOLCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 522,655 filed 22 June 2023, the entire disclosure of which is hereby incorporated by reference herein.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under Contract No. FA864921P1486 awarded by the U.S. Air Force. The government has certain rights in the invention.TECHNICAL FIELD

[0003] The present disclosure generally relates to systems and methods of charging and heating a battery having one or more electrochemical cells at various voltages.BACKGROUND

[0004] The rate of charge and lifetime of electrochemical cells are factors in implementing battery powered systems and in particular in the implementation of battery-powered industrial equipment, electric vehicles, etc. For example, increasing battery temperature can reduce the time to charge a lithium ion (Li-ion) battery, but increasing the temperature of the battery can degrade the battery and reduces its cycle life. In addition, fast charging lithium ion batteries can induce lithium plating, which can lead to irreversible capacity loss. To avoid degradation and lithium plating, lithium-ion batteries are typically charged using a constant-current, constant voltage (CCCV) protocol. FIG. 1 shows the charging characteristics of a typical cylindrical lithium ion battery at 20 °C charged under a CCCV protocol. The protocol includes a first stage of charging at constant current to 4.2 Volts followed by a second stage of charging at a constant voltage at 4.2 Volts until a current cutoff limit is reached. This protocol takes over 2 hours and is too slow for many applications including for industrial equipment and electric vehicles.

[0005] One approach reported for fast charging lithium ion batteries involved rapidly preheating a Li-ion battery and charging the battery at elevated temperature. See, e.g., Wang et al., Fast charging of energy-dense lithium-ion batteries, Nature 2022(611):485-490; Yang, et al., Thermally modulated lithium iron phosphate batteries for mass-market electric vehicles,Nat Energy 2021(6): 176-185; Yang et al., Asymmetric temperature modulation for extreme fast charging of lithium-ion batteries, Joule 2019(3):3002-3019.

[0006] The design of fast-charge protocols, however, involves trade-offs between charging time and cell cycle life. Accordingly, a continuing need exists for developing systems and protocols for fast charging batteries.SUMMARY OF THE DISCLOSURE

[0007] Advantages of the present disclosure include charging systems and protocols that can charge a battery rapidly while maintaining high cycle life. Such a system can be included in electrically powered equipment, an electrically powered vehicle, e.g., an electric vehicle (EV), hybrid electric vehicle (HEV), and plug-in hybrid electric vehicle (PHEV), etc. Additionally, fast charging according to the systems and protocols of the present disclosure can enable use of relatively smaller battery packs, which reduces resources and costs.

[0008] These and other advantages are satisfied, at least in part, by a method for charging a battery, which includes applying a first charge current to the battery until a voltage of the battery (Vc) exceeds a predetermined safe voltage of the battery (Vsafe) based on a temperature of the battery (Tc). When Vc>Vsafe, applying heat to the battery via a heater to increase the battery temperature. The increased battery temperature (Ti) advantageously can be used to provide an updated Vsafe based on Ti, e.g., determine an new Vsafe value, which may be constant or increase with increasing temperature of the battery. The first charge current can be either a constant current or constant power.

[0009] The method can further include applying a second charge current to the battery while applying heat to the battery via the heater. The second charge current can also be applied as either a constant current or constant power and in some aspects, the second charge current has a magnitude less than the magnitude of the first charge current. Further, the method can include discontinuing applying heat to the battery via the heater. Heat can be discontinued when a preset condition is met. Advantageously, the steps of: (i) applying the first charge current to the battery; (ii) applying heat to the battery via the heater; (iii) updating Vsafe based on an increased temperature of the battery; and (iv) discontinuing applying heat to the battery; can be repeated until a cutoff criterion is reached.

[0010] In other implementations, a battery can be charged by charging the battery under a constant current (CC) or constant power (CP); and during charging under CC or CP, cycling a heater on and off to increase a temperature of the battery. The heater can be cycled on when avoltage of the battery is greater than a predetermined safe voltage (Vsafe), which may be constant or increase with increasing temperature of the battery. The heater can be cycled off when a preset condition is met.

[0011] Other implementations of the preset disclosure include battery charging system. The system can include one or more batteries; one or more heaters; and one or more controllers (e.g., electronic control units (ECUs)). The system can further include one or more sensors or monitors to determine battery voltage and temperature. The controller can be configured to execute the protocols and algorithms of the present disclosure. For example, the controller can be configured to monitor or determine a voltage (Vc) of the battery and a temperature of the battery (Tc) and to determine whether the voltage of the battery (Vc) exceeds a predefined safe voltage (Vsafe). The controller is also configured to charge the battery at a constant current, or at constant power, e.g., apply a first charge current to the battery, heat the battery when Vc exceeds Vsafe, and update Vsafe based on increasing temperature of the battery (e.g., Ti). Alternatively, or in combination, the controller can be configured to charge the battery under a constant current (CC) or constant power (CP) protocol; and during the CC or CP protocol, cycle the heater on and off to increase the battery temperature. The heater can be cycled on to heat the battery when Vc > Vsafe, which increases with increasing temperature of the battery, and the heater can be cycled off when a preset condition is met.

[0012] In accordance with the present disclosure, one or more of the following features, individually or combined, can be included in the subject technology. For example, the battery can be charged when the battery is below a predefined normal temperature of the battery (Tnorm), by heating the battery, and while heating the battery, charging the battery at a constant voltage set to an electrochemical potential of a cathode active material of the battery. In other examples, the first charge current can be at least 1.5C, 2C, 3C, 4C, 5C, 6C, etc. In some examples, the heater is discontinued, or cycled off, when a preset condition is met, such as one or more of: a predetermined period of time is reached, or a predetermined temperature of the battery is reached, or a temperature change of the battery is reached. In still further examples, heating can be applied to increase the battery temperature at a rate of at least 5 °C / min.

[0013] Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein certain embodiment of the subject technology is shown and described, simply by way of illustration. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention.Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent similar elements throughout and wherein:

[0015] FIG. 1 shows typical constant current, constant voltage (CCCV) charging characteristics of a 18650 lithium ion battery.

[0016] FIGS. 2 A, 2B, 2C, and 2D are flow diagrams illustrating various implementations of charging an battery according to one or more algorithms of the present disclosure.

[0017] FIG. 3 is a plot showing Vsafe versus battery cell temperature for four different relationships in which the slope of the line is varied.

[0018] FIGS. 4 A and 4B and 4C illustrate relationships including average battery cell temperature for batteries tested using a protocol according to the present disclosure. In particular, FIG. 4A is a plot of average cell temperature versus change in Vsafe over change in temperature; FIG. 4B is a plot of charge time versus average cell temperature; and FIG. 4C is a plot of average rate of capacity loss versus average cell temperature.

[0019] FIGS. 5A, 5B and 5C show plots of battery cell voltage and temperature evolutions for cells tested under one or more algorithms of the present disclosure.

[0020] FIGS. 6 A and 6B are additional plots of battery cell voltage and temperature evolutions for cells tested under one or more algorithms of the present disclosure.

[0021] FIGS. 7 A and 7B are additional plots of battery cell voltage and temperature evolutions for cells tested under one or more algorithms of the present disclosure.

[0022] FIGS. 8 A and 8B show plots of average charge time, average charge temperature and capacity retention and cycle number for battery cells tested under one or more algorithms of the present disclosure.

[0023] FIG. 9 shows a plot of E°cafor certain cathode active materials as a function of charge carrier concentration.DETAILED DESCRIPTION OF THE DISCLOSURE

[0024] The present disclosure relates to battery systems and protocols with improved charging that enable fast charging (saving time) while maintaining long lifetime of the battery, also referred to as a battery cell. As used herein a battery includes at least one electrochemicalcell and can also include multiple electrochemical cells that are electrically connected and assembled or packaged together. The batteries of the present disclosure further include configuration as a battery subassembly or battery module, which in turn can be arranged or packed together to form a battery pack.

[0025] The battery systems and protocols of the present disclosure can be applied to a single electrochemical cell or multiple cells electrically connected together in the battery and to a variety of cell chemistries such as, but not limited to, metal-ion, lithium-ion, lithiumpolymer, sodium-ion, lead-acid, nickel-metal hydride, lithium-sulfur, lithium-air and all solid- state batteries. The battery systems and charge protocols of the present disclosure can include electrochemical cells having individual capacities of at least 1 Ah, such as at least 5, 10, 20, 50, 100, 200, 500 Ah, etc. and batteries having capacities of at least 1 Ah, such as at least 5, 10, 20, 50, 100, 200, 500 Ah capacity. Such batteries and systems can be used for electrically powered equipment, electrically powered vehicle, etc.

[0026] In an implementation, a battery charging system and protocol can include applying a first charge current to a battery until a voltage of the battery (Vc) exceeds a predetermined safe voltage of the battery (Vsafe) based on a temperature of the battery (Tc). . The first charge current can be either a constant current or constant power and can be at a fast charge rate such as at least about 1.5C, e.g., at least about 2C, 2.5C, 3C, 3.5C, 4.5C, 5C, 5.5C, 6C, etc. and the equivalent rate for constant power.

[0027] In practicing aspects of the protocols of the present disclosure, the voltage of the battery can be the voltage of an individual electrochemical cell of the battery, or an average voltage of multiple electrochemical cells of a battery, or the total battery voltage. In addition, the voltage may be estimated based on a pre-determined algorithm without direct measurement. The algorithm may utilize, but is not limited to, methods considering the applied charge current and the internal resistance of the battery as a whole or individual electrochemical cells. In addition, a temperature of the battery can be a temperature of an individual electrochemical cell of the battery, or an average temperature of multiple electrochemical cells of a battery. In addition, the temperature of the battery can be estimated for a particular battery configuration based on a predetermined algorithm.

[0028] The battery charging system and protocol of the present disclosure further include when Vc>Vsafe, applying heat to the battery via a heater to increase the battery temperature (Ti) and updating Vsafe based on Ti. Heating the battery can include heating an individual electrochemical cell, or heating multiple electrochemical cells of a battery. To betterunderstand and to more fully implement the systems and protocols of the present disclosure, some background principals will be provided below.

[0029] BACKGROUND PRINCIPALS

[0030] Initially, background principals relating to the protocols of the present disclosure will be provided below. In certain aspects of a battery of the present disclosure, the anode storage (hosting) mechanism of the cation (e.g., Li+) is often intercalation and deintercalation. For example, during charging of a lithium ion battery, lithium ions (Li+) intercalate into the anode, and during discharge deintercalation occurs. To drive intercalation into the anode, the anode potential ((pan) must be reduced below its equilibrium electrochemical potential (E°an), and the difference between the two is referred to as anode overpotential (r|an= (pan - E°an). When the transport and / or reaction kinetics are insufficient in the anode, (pandecreases below the equilibrium potential of Li / Li+(E°Li / Li+) and formation of metallic Li on the surface of anode particles is thermodynamically feasible. Formation of metallic Li (lithium plating) can damage such a battery and cause loss of storage capacity and increase resistance. The prevention of lithium plating during charging is a factor for lithium-ion battery durability. Similarly, certain other battery chemistries may utilize intercalation-based anodes, and thus possess the ability to plate the metallic form of the charge carrier. For example, in the case of sodium-ion batteries, which utilize sodium ions as the charge carrier, metallic sodium can plate on the surface of an intercalation anode.

[0031] Advantageously, the charge protocols of the present disclosure can be applied to secondary batteries that utilize an anode in which the mechanism for hosting the charge carrier is intercalation such as metal-ion batteries, e.g., lithium-ion batteries such as lithium metal phosphate and sodium-ion batteries.

[0032] For an electrochemical battery, the battery voltage (Vc, measured between the positive and negative terminals) is the difference between the electrochemical potential of the cathode and anode. Thus, during charging, metallic plating can be minimized by setting a battery voltage upper limit equal to the approximate equilibrium potential of the cathode with respect to the charge carrier (E°ca). Under this condition, the anode potential remains at or above the potential of the charge carrier (e.g., Li / Li+) and formation of metallic plating (e.g., Li plating) on the surface of anode particles is not thermodynamically feasible.

[0033] In addition to a decrease in anode potential, charging induces an increase in cathode potential (cathode overpotential, (r|ca)). Thus, metallic plating avoidance can be minimized, while allowing a faster charge rate by adding the expected r|cato E°ca, thereby defining an uppercell voltage limit of Vsafe (the cathode overpotential corresponding to the cell condition in which the anode has an electrochemical potential greater than or equal to that of the charge carrier). An expression for Vsafe which can be determined empirically for an individual electrochemical cell or battery can be defined by Equation 1 below.

[0034] Vsafe(Cion.ca, Tc) = E°ca(Cion,ca) + r|safe(Tc) (1)

[0035] In Equation (1), E°ca(cion) is the cathode equilibrium potential corresponding to the concentration of the charge carrying ion in the cathode (cion,ca) of the battery - which is an underlying indicator of battery state of charge (SOC) - and r|safe(Tc) is an allowable overpotential evaluated at a given cell temperature (Tc) to minimize cell degradation such as from metallic plating or degradation from other mechanisms. It is believed that the first term of Equation (1) (E°ca(cion,ca)) enables safe (e.g., plating-free) charging at any cell temperature and the second term (r|safe(Tc)) permits safe charging at rates equal to or faster than the first term alone.

[0036] Charging a battery according to Equation (1) can be implemented in several ways. For example, r|safe(Tc) can be set to zero and consequently Vsafe is simply a function of charge carrier concentration in the cathode (E°ca). Hence, in one aspect of the present disclosure, a battery can be charged by applying a first charging current until a voltage of the battery (Vc) reaches E°ca, e.g., until Vcequals E°ca. The applied first charging current can be a constantcurrent or constant power charging current and applied until the battery reaches E°ca. A second charging current can then be applied, e.g., a constant voltage charge, when Vcequals E°ca. Charging proceeds at E°cauntil a predefined cutoff criterion is reached, e.g., a charge capacity limit is reached or a minimum charge current limit is reached. An advantage of such a charging protocol is that it would tend to increase cycle life generally and substantially longer if charging the battery below its normal operating temperature.

[0037] Another background principal relating to the protocols of the present disclosure involves relationships between a voltage of the battery and its temperature. In particular, we have found that Vsafe can strongly depend on a temperature of a battery during charging of the cell. Hence, in some implementations of the present disclosure, a battery can be charged by applying a first charging current until a voltage of the battery cell (Vc) reaches Vsafe in which case Vsafe is updated to higher values as the temperature of the battery increases. The temperature of the battery can be increased either by native heat generation from the inefficiencies of charge, or by the supply of supplemental thermal energy, or both. However, heating the battery when needed to update Vsafe advantageously allows the battery to be chargedwith a high charge current during the entire charging process thereby shortening the charge time while lowering the overall average temperature of the battery during charge.

[0038] For a given battery temperature, the cell overpotential (r|ca- r|an) increases with the rate of charge. For a given charge rate, the overpotential shrinks in near-exponential fashion with increasing temperature. Thus, a coupling between maximum safe charge rate and temperature exists. That is, minimizing plating of the metallic form of the charge carrier under a fast charge rate (e.g., at least 1.5C) can be carried out by increasing temperature to reduce overpotential. A charge rate, C-rate, is defined as the charge / discharge current divided by the nominally rated battery capacity. For example, a 5,000 mA charge on a 2,500 mAh rated battery would be a 2C rate.

[0039] An aspect of the subject technology incorporates the fundamental understanding of the fact that the proportional relationship between r|caand r|anhas strong temperature dependence. Particularly, in lithium-ion batteries, r|ancan have a significantly stronger dependence on temperature than r|ca. Because both obey Arrhenius (exponential) relationships with temperature, the change of r|ca° with temperature is effectively linear across a wide temperature range. We can derive from this an implication to a charging protocol wherein the voltage limit (e.g., Vsafe) has a strong temperature dependence. Therefore, under a Vsafevs Tclimit, maximizing charge rate requires increasing cell temperature, either by native heat generation from the inefficiencies of charge, or by the supply of supplemental thermal energy. The former case requires non-zero charge current, while the latter case can be achieved by simultaneously heating and charging the battery or by temporarily pausing charging to heat the battery. The supply of heat, for example, can be achieved with a heater utilizing resistive heat generation, inductive heat generation, convective heat transfer, conductive heat transfer, radiative heat transfer, or any combination thereof. In one aspect, the battery can be heated by resistive heaters located inside the battery enclosure or by resistive heaters located within individual cells of the battery. After a temperature rise is achieved, charging proceeds with a new voltage limit based on Vsafeevaluated at the new battery temperature and the present concentration of the charge carrier in the cathode.

[0040] BATTERY SYSTEMS AND PROTOCOLS

[0041] Aspects of the present disclosure include battery systems and charge protocols that employ Vsafebased on a temperature of the battery and the concentration of the charge carrier in the cathode, e.g., where T|safe(Tc) is greater than zero. Such systems and protocols areadvantageous when the temperature of the battery is at or above its normal operating temperature.

[0042] In addition, Equation 1 can be simplified when the temperature of the battery is above a normal operating temperature and re-written as Equation (1.1) below.Vsafe = X + Y* (Tc-Tnorm) (1.1 )

[0043] In Equation (1.1) above, X is E°ca(cion) (the cathode equilibrium potential) in a unit of voltage (e.g., Volts (V)), for example. The X term can be estimated or determined from established cathode potentials. Tcis the temperature of the battery during charging (in units of degrees such as Celsius) and TnOrm is a predetermined normal operating temperature of the battery (in the same units as Tc, e.g., °C). Y is a predetermined value in units of voltage per degree temperature such as mV / °C and can be established experimentally or calculated. That is, the relationship between Vsafeand Tc(e.g., the Y-term) can be determined empirically by evaluating charging-induced battery degradation under various values for Y. Such an empirically determined Vsafeis provided in the Examples below. The Y-term in Equation (1.1) represents a trade-off for a given fast charge-heating protocol in terms of lithium plating based degradation on the one hand, and high temperature induced calendar degradation of the battery on the other hand. For example, higher values for the Y-term results in a lower average temperature of the battery after a charging protocol employing Vsafebut a higher propensity for lithium plating. In contrast, however, lower values for the Y-term results in a higher average temperature of the battery after the protocol but a higher propensity for calendar degradation. A charging-heating protocol employing Equation (1) or (1.1) in which the value for Vsafeincreases with increasing temperature can be referred to as a Temperature-Limited Voltage (“TLV”) charging protocol.

[0044] To reduce overall charge time, the battery can be heated rapidly during the charging protocols of the present disclosure. Such rapid heating can be achieved by powering a heater (e.g., a heater having one or more heating elements in thermal contact with the battery) with a power source external to the battery system such as by an external charger. To simplify the battery system, such an external charger can also be configured to charge the battery in addition to heating the battery. In some implementations, the battery can be heated by applying heat to the battery to increase the battery temperature at a rate of about 5 °C / min or higher, e.g., at least 10 °C / min, such as at least 20, 30, 40, 50 °C / min, etc. Battery systems that can heat electrochemical cells at such rates are disclosed in WO 2019 / 203969, for example. Heatingthe battery includes heating an individual electrochemical cell or heating multiple electrochemical cells of a battery.

[0045] Various methods for charging a battery are described below. In the description of the methods, statements that the method is performing some task or function refers to a controller or a processor such as a general purpose processor executing programmed instructions stored in non-transitory computer readable storage media operatively connected to the controller or processor to manipulate data or to operate one or more components in a system to perform the task or function. For example a charge controller and / or a battery controller can be such a controller or processor and the executed program instructions can be stored in memory. Alternatively, the controller can be implemented with more than one processor and associated circuitry and components, each of which is configured to perform one or more tasks or functions described herein. Additionally, the steps of the methods can be performed in any feasible chronological order, regardless of the order shown in the figures or the order in which the steps are described.

[0046] In implementations of the present disclosure and as described above, T|safe(Tc) (e.g. Y (mV / °C)) can be set to zero and consequently Vsafe is simply a function of charge carrier concentration in the cathode (E°ca). For certain cathodes, E°cais a strong function of charge carrier concentration. For example, E°cafor a lithium -nickel -manganese cathode active material, such as Li(Nio.8Coo.iMno.i)02 (NCM811), can vary by hundreds of millivolts over the concentration range typical in lithium-ion cells containing NCM811, as shown in FIG. 9. In this and other similar cases, the implementation of Eoca(cion,ca) in Equation (1) and X in Equation (1.1) can factor the charge carrier concentration-dependence of the cathode, and thus state-of- charge dependence (SOC-dependence). In the case of certain other cathodes, the cathode equilibrium potential is approximately constant over a wide range of Li+ concentration. For example, the equilibrium potential corresponding to lithium iron phosphate (LFP) is approximately 3.43 Volts across greater than 80% of the Li+concentration range typical in lithium-ion batteries with a LFP cathode (FIG. 9). In such a case, the implementation of E°ca(cion,ca) in Equation (1) and X in Equation (1.1) can be simplified to a single value, removing the dependence of E°caon concentration (i.e., SOC).

[0047] A practical advantage of using a charging protocol employing Vsafeas simply a function of charge carrier concentration in the cathode (E°ca) by setting r|safe(Tc) (e.g. Y (mV / °C)) to zero is that such a method can minimizing metal (e.g., lithium) plating baseddegradation without having to perform any empirical study of the battery being charged once the cathode equilibrium potential has been determined.

[0048] Such a charge protocol is advantageous when a temperature of the battery (Tc) is below a normal operating temperature of the battery (TnOrm) and the battery is heated. Below a normal operating temperature of the battery (TnOrm) can include when Tcis below 30° C, e.g., below about 20° C, 15° C, 10° C, 5° C, or even at or below water freezing temperatures, e.g., at or below about 0° C, -5° C, etc. In addition to charging the battery, even below TnOrm, the battery can be heated. Heating via a heater can start approximately concurrently (i.e., no more than about 1 second such as less than about 100 msec.) with application of either a first or second charge current and heating can continue during the application of the first or second charge current continuously until a cutoff criterion, e.g., the battery reaches a predetermined battery temperature, predefined voltage, predefined state-of-charge, minimum charge current, etc.

[0049] An additional advantage of the battery systems and protocols of the present disclosure is that they do not require instrumentation for in operando measurement of the anode potential. For example, a reference electrode could permit the direct measurement of anode potential to avoid conditions favorable to metal (e.g., lithium) plating, but such instrumentation would add significant cost and complexity to a battery or battery system.

[0050] Various charging protocols of the present disclosure and that can be used in battery systems can be illustrated and are exemplified in figures 2A-2D. The protocols illustrated in the figures can be implemented by a battery system having a battery, heater and a controller. The control can include a processor with suitable logic, circuitry, and / or code that enables processing data and / or controlling operations of the battery system. The battery system can also include a temperature sensor to determine a temperature of the battery and voltage sensor to determine a voltage of the battery.

[0051] FIG. 2A is a flow diagram that illustrates implementation of TLV charging protocol when Vsafe equals E°ca. Such a charging protocol can be advantageous when the battery is below a normal operating temperature of the battery (TnOrm). As shown in the diagram, the protocol starts (202) by determining a state of charge of the battery (SOC) and a temperature of the battery (Tc). When the state of charge (SOC) of the battery is below a maximum state of charge (SOCmax)(204) and below a normal operating temperature (TnOrm)(210), the battery can be charged by applying a first charging current at a constant voltage (CV) set at Vsafe (206), which in this example can be set to E°ca, e.g., Vsafe can be equal to E°ca, which can beset to 3.4V for a battery with a LiFePCE cathode. Heating can be applied to the battery (208). Heating can start approximately concurrently (i.e., no more than about 1 second) with application of the first charging current (206). Heating and the first charging current continue until a predefined cutoff criterion is reached, e.g., a state of charge is reached (204), in which case the protocol ends, or the battery is heated to at least its normal operating temperature (210). When the battery reaches at least its normal operating temperature, a separate charging protocol can be employed (212). Steps 210, 206, and 208 together form a constant-voltage heating (CV- Heat) protocol or algorithm (205).

[0052] FIG. 2B is another flow diagram that illustrates implementation of a TLV charging protocol according to Equation (1) or Equation (1.1) above. A battery having an initial temperature (Tc or first temperature Tl) and an initial state of charge below a predetermined threshold can be charged by the protocol of FIG. 2B. As shown in the diagram, such a battery can be charged by applying a first charging current (222), which can be either a constant current (CC) or constant power (CP) charge current. Under this protocol, the first charge current can be at a fast charge rate such as at least about 1.5C, e.g., at least about 2C, 2.5C, 3C, 3.5C, 4.5C, 5C, 5.5C, 6C, etc. and the equivalent rate for measuring constant power. The first charge current continues until a voltage of the battery (Vc) reaches a predetermined safe voltage (Vsafe) (224).

[0053] As provided in Equation (1) or (1.1), Vsafe can be determined based on the temperature of the battery Tcand the current state of charge of the battery. Alternatively, Vsafe can be approximated simply based on the temperature of the battery Tc. Such an approximation is more accurate when the voltage of the battery does not vary significantly across the state of charge during the interval of charge. For example, a battery configured with a lithium metal phosphate (e.g., LiFePCU) cathode active material does not vary significantly between approximately 10% <SOC< 90%.

[0054] When Vcexceeds Vsafe (224), a heater is activated (226) and heat is applied to the battery for an increased battery temperature (Ti), e.g., the battery is heated to a second temperature of the battery (T2). The battery can be heated by a heater located inside or outside of the battery enclosure and even within an enclosure of individual cells. The battery can be heated by employing resistance heating, inductive heating, inductive, convective, conductive, or radiative heat transfer, or any combination thereof. In one aspect, the battery is heated by a resistive heater located inside one or more electrochemical cells. The battery can be heated until a preset condition is met, e.g., a predetermined period of time is reached, or until apredetermined temperature of the battery is reached, or until a temperature change of the battery is reached. As illustrated in FIG. 2B and step 228 for this example, heat can be applied to increase the battery temperature by applying heat for a predetermined period of time (At). Once the predetermined period of time for heating the battery is reached (At>tset), the heater is shut off (230a) to discontinue applying heat to the battery via the heater. During or after the battery is heated, an updated Vsafe is determined based on the increased temperature of the battery (e.g., Vsafe is updated based on Ti or in this case the second temperature of the battery T2). The battery can be continuously charged with the first charge current (222) during or after heating the battery. Alternatively, while heating the battery, the battery can be charged with a second charge current (232), e.g., a constant current or constant power charge current, which can have a magnitude lower than the magnitude of the first charge current (e.g., a magnitude that is 10%, 20%, 30%, 40-%, 50%. 60% or more lower than the first charge current). Charging with a second charge current can be practical when, for example, an external charger is configured to supply power to charge the battery and power the heater and such external charger cannot supply sufficient current to charge the battery and simultaneously power the heater on the same circuit to heat the battery. The optional second charge current (232) can start approximately concurrently (i.e., no more than about 1 second such as <100 ms) with application of heating (226) and can continue until the first charge current is reactivated (222). Steps 222, 224, 226, 228, 230a and optionally 232, together form a constant-current or constant-power, thermal modulation (CC / CP-TM) protocol or algorithm (221).

[0055] The CC / CP-TM protocol can be repeated until a cutoff criterion is reached. That is, steps 222, 224, 226, 228, 230 and optionally step 232, are repeated until a cutoff criterion is met (234b). Such a cutoff criterion can be, for example: (a) a predefined maximum temperature of the battery is reached, or (b) a predefined maximum voltage of the battery is reached, or (c) a predefined state of charge is reached. The predefined maximum temperature (Tmax), maximum voltage (Vmax), or predefined maximum state of charge (SOCmax) can depend on the battery chemistry and can be, for example: Tmax > 50° C, 55° C, 60° C, 65° C, 70° C, 75° C, 80° C etc., Vmax > Vsafe at Tmax, SOCmax > 70%, 75%, 80%, 85%, 90%, etc.

[0056] As illustrated in the example of FIG. 2B, the CC / CP-TM protocol 221 is repeated until Tmax or a cutoff criterion (234a, 234b) is reached and the heater is deactivated (230a or 230b). If the system reaches Tmax or SOCmax and Vc < Vsafe, charging continues at the first charging current, if or when Vc > Vsafe, charging proceeds at the second charging rate.

[0057] In addition to the CC / CP-TM charge protocol illustrated in FIG. 2B, when the battery meets a cutoff criterion in the CC / CP-TM charge protocol, rather than end charging, charging of the battery can continue by deactivating the CC / CP-TM protocol and applying a constant-voltage (CV) charge current at a predetermined maximum voltage. For example, when the battery exceeds Tmax or SOCmax (234a, 234b), charging of the battery can continue by deactivating the CC / CP-TM protocol and applying a constant-voltage (CV) charge current at a predetermined maximum voltage. As illustrated by FIG. 2C, when a cutoff criteria is met in the CC / CP-TM protocol (221) and the battery has not exceed a predetermined full state of charge (SOCfull) (238a) or a predetermined full voltage (Vfull) (238b), charging the battery can continue by applying a constant-voltage (CV) charge current at a predetermined maximum voltage of the battery (Vfull) (240). The CV charge can be applied at a predetermined voltage such as Vsafe based on the temperature of the battery (240), e.g., based on Ti. The CV charge can continue until a cutoff criterion is reached (242) such as when a predetermined full state of charge is reached or a limited current is reached, etc. Steps 240 and 242 together form a constant-voltage (CV) charge protocol or algorithm (239).

[0058] FIG. 2D illustrates another example of implementing an TLV protocol. FIG. 2D combines certain protocols of FIGS. 2A, 2B and 2C. As shown in FIG. 2D, the protocol starts by determining a state of charge of the battery (SOC) and a temperature of the battery (Tc). When the state of charge (SOC) of the battery is below a predetermined full state of charge (SOCfull)(250) and below a normal operating temperature (TnOrm)(252), the battery can be charged by the CV-Heat protocol (205) described for FIG. 2A. When the state of charge (SOC) of the battery is below a predetermined full state of charge (SOCfull)(250) but at or above a normal operating temperature (TnOrm)(252), the battery can be charged by the CC / CP-TM protocol (221) described for FIG. 2B. When a cutoff criteria is met in the CC / CP-TM protocol (221), charging the battery continues by applying a constant-voltage (CV) charge protocol (239 described for FIG. 2C. The CV charge can continue until a cutoff criterion is reached (242) such as when a predetermined full state of charge is reached or a limited current is reached, etc. As such FIGS. 2A-2D illustrate various TLV charging protocols.

[0059] A principal advantage of an TLV charging protocol is that it significantly extends the period of constant current (or constant power) during fast charging (e.g., > 1.5C) while maintaining a metal (e.g., lithium) plating free condition and minimizing temperature related calendar degradation. For example, the period of constant current (or constant power) charging can be extended from ending at 40% SOC to ending at 80% SOC.

[0060] An additional advantage of the TLV protocol applying the CC / CP-TM algorithm is that it can reduce the overall average temperature of a battery compared to a protocol that simply heats the battery to a predetermined temperature followed by charging, thus extending lifetime of the battery. Moreover, as battery degradation ensues, it is commonly accompanied by an increase in the internal resistance of the battery, in many cases. The lower average battery temperature, and thus, slower degradation achieved with TLV subdues internal resistance growth attendant to battery capacity loss.

[0061] Additionally, the increased internal resistance of an aged battery will induce a higher voltage for a given state of charge, temperature, and charge rate. In a charge protocol in which a single voltage limit is applied, the voltage limit will be reached sooner, and the subsequent tapering of current will slow the average charge rate. In certain cases, the TLV protocol can compensate for this issue by driving the battery temperature higher to increase the voltage limit, allowing fast charging to continue and maximizing the average charge rate.

[0062] Another advantage of the TLV protocol of the present disclosure is that it can reduce or eliminate a delay in initiating charging to heat a battery. TLV protocol can allow a portion of the total charge throughput to be delivered earlier, as the heating time is distributed throughout the charge process.

[0063] As explained in describing FIG.s 2A-2D, battery systems can be configured to implement the various TLV protocols. For example, battery management systems of the present disclosure include, without limitation, one or more batteries, each of which can have one or more electrochemical cells; one or more heaters; one or more controllers (e.g., electronic control units (ECUs), which can each include a processor and optionally memory; one or more voltage sensors; and one or more temperature sensors. The system can further include a charging circuit configured to use an external power source to both charge and heat the one or more batteries.

[0064] Battery of the present disclosure can include electrodes having electrode active materials (e.g., an anode active material and a cathode active material), a separator, electrolyte, container and terminals. For example, a battery of the present disclosure can include an anode electrode coated on a current collector, a cathode electrode coated on another current collector and an electrolyte which can be a solid or liquid. The battery can include a separator between the cathode electrode and anode electrode. In certain aspects, battery of the present disclosure can comprise a metal ion cathode active material such as a lithium or sodium ion cathode active material.

[0065] Additional cathode active materials useful for a battery of the present disclosure can include, for example, a metal oxide such as lithium metal oxide, e.g., lithium cobalt oxide, lithium manganese oxide, lithium nickel -cob alt-manganese oxides, lithium-rich layered oxides, sodium metal oxide, a metal phosphate such as lithium iron phosphate, lithium manganese phosphate, or combinations thereof, etc. Anode active materials useful for a battery of the present disclosure can include, for example, carbonaceous material, e.g., graphite, silicon, silicon alloys, alkali metals such as lithium metal, lithium alloys such as lithium titanate, or combinations thereof, etc.EXAMPLES

[0066] The following examples are intended to further illustrate certain aspects of the subject technology and are not limiting in nature. Those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances and procedures described herein.

[0067] Batteries. Lithium ion pouch cells of approximate 11-Ah were fabricated using LiFePCU (LFP) as cathodes and graphite as anodes with LiFSI salt in ethylene carbonate / ethyl methyl carbonate (3:7 by weight) + 2% vinylene carbonate as electrolyte (Soulbrain, Michigan). The negative-to-positive capacity ratio was about 1.1. The 11-Ah pouch cells used a stacked electrode design with 28 anode layers and 26 cathode layers. A ceramic-coated separator (Celgard 2325) of 25 pm thickness was used. A 25-pm-thick nickel foil sized at 90 m was coated with a thin layer of polyethylene terephthalate (25 pm, each side) for electrical insulation and sandwiched in the center of the cell stack adjacent to two single-sided anodes. One tab of the nickel foil was welded with the anode tabs, and the second tab of the nickel foil extended out of the pouch to form a third tab for internal heater connection. Electrochemical cells with an internal resistor sheet have been described in published patent applications W02016018830 and WO US2019 / 203969, which are incorporated herein by reference. Such a configured cell can be heated at a rate of at least about 5° C / min, such as at least about 60° C / min and higher.

[0068] The cathodes were prepared by coating N-methylpyrrolidone-based slurry onto 13 pm Al foil, whose dry material consisted of 96.3 wt.% LFP. The anodes were prepared by coating deionized water-based slurry onto 8 pm Cu foil, whose dry weight consisted of 95.7 wt.% graphite. The mass loadings of NMC811 and graphite were 17.65 and 9.07 mg cm’2,respectively. Each pouch cell had a 157 mm x 75 mm footprint area, a thickness of 10.1 mm, weighed 220 g, and had a discharge capacity of 11 Ah at 3.7A.

[0069] Empirically Deriving Vsafe: As an example of empirically determining Vsafe, four identical lithium iron phosphate battery cells were charged starting at 30° C according to an TLV charging protocol using four different relationships for Vsafe according to Equation (1.2) below:Vsafe = X(V) + Y(mV / °C)* (Te-Tnorm) (1.2)

[0070] In Equation (1.2) above, X is E°ca(cion) (the cathode equilibrium potential) and in this case was set to 3.4V for a lithium iron phosphate, Y was either 8, 6, 5, or 4; Tcis the temperature of the cell during charging; and TnOrm is the normal operating temperature of the cell and in this case was set to 30° C.

[0071] FIG. 3 is a plot showing Vsafe vs battery cell temperature for four different relationships in which the slope of the line is varied, e.g., Y changes from 8 to 4. As further shown in FIG. 3, the steeper the slope for the Vsafe vs. Tcrelationship (e.g., Y=8) results in a lower average temperature of the cell after the charge protocol but a higher propensity for lithium plating. In contrast, a flatter slope for the Vsafe vs. Tcrelationship, (e.g., Y=2) results in a higher average temperature of the cell after the charge protocol but a higher propensity for cell calendar degradation. FIGS. 4A and 4B are plots showing the effect of varying the slope (Y-term) with either average cell temperature (FIG. 4 A) or with charge time (FIG. 4B). The significant impact of Y on the average cell temperature provides great flexibility with TLV charging, allowing for the empirical identification of the optimal Vsafe that balances high temperature-induced calendar degradation while avoiding lithium plating (FIG. 4A). Simultaneously, such flexibility is achieved with negligible impact on charge time, which varied by only 25 seconds in these experiments (FIG. 4B). Further, FIG. 4C shows the average rate of capacity loss versus average cell temperature for certain cells tested under an TLV charging protocol. As illustrated in FIG. 4C an optimal average cell temperature can be determined to balance cell capacity loss due to metal plating and cell capacity loss due to calendar degradation due to higher temperatures. The average cell temperature during charging is controlled by modifying Vsafe function as it depends on temperature, as illustrated in FIG. 3. Thus, these experiments represent an example of the empirical optimization of Vsafe by changing Y in Equation (1.2) to achieve the maximum lifetime of a battery repeatedly undergoing a fast charging TLV protocol of the present disclosure.

[0072] From our experiments, it appeared that a value of 6 mV / °C for the slope of the line provided the better results for the cells that were tested.

[0073] Alternatively, or in addition to empirical evaluation, a battery cell outfitted with a reference electrode can enable measurement of the anode potential, thus permitting the determination of Vsafe. Measuring the anode potential of such a cell at various temperatures and a high charge rate can also establish an effective Vsafevs Tcand SOC, when applicable. For example, a Li / Li+reference electrode can be embedded in a lithium-ion cell. The voltage measured between the negative terminal and the reference electrode represents the anode potential. Then, the maximum charge current or power can be applied at a given cell temperature until the anode potential reaches zero. The cell voltage corresponding to this condition is a maximum Vsafefor the present temperature and SOC, when SOC dependence applies. Repeating this experiment across an applicable temperature range and SOC range, when applicable, yields the Vsafeprofile.

[0074] Battery Cells Tested Under TLV Protocol

[0075] Several battery cells were tested with the following protocol: (1) A battery cell initially at To, and an initial state of charge, corresponding to an initial charge carrier concentration in the cathode(cion,ca°), is subjected to constant-current (CC) or constant-power (CP) charging at a predefined maximum rate until Vc> Vsafe(ciOn,ca, Tc) (Vsafeevaluated at Tcand the current state of charge). (2) At least one heater is activated to raise the battery cell temperature for a period of theat or until a temperature rise (ATheat) is achieved. The charging current or power is less than or equal to the prescribed maximum CC or CP setting, respectively. (3) After heating is terminated, charging proceeds at the prescribed maximum CC or CP setting until Vc> VLPF(TC). Steps 2-3 are repeated until a predefined charge capacity limit is reached unless a predefined maximum temperature (Tmax) is reached first. In the latter case, all active heating is terminated and the battery cell is charged at a constant voltage corresponding to Vsafe(Tc) until the predefined capacity limit is reached.

[0076] Experimental results during implementation of the above charge protocol are provided in FIGS. 5A, 5B and 5C. In this experiment, cells were charged with a first current at a constant-current rate of 3C from a fully discharged cell to 80% state of charge in a 22 °C ambient environment to a maximum temperature of 70 °C. Vsafewas defined as 3.4V + 6mV / °C*(Tc-30°C). FIGS. 5A-5B plot cell voltage, cell current, heating current, and temperature evolutions. The cell is initially near room temperature when charging is initiated. Following an initial heating step to 30 °C (TnOrm in this experiment), cell voltage rises rapidlyto the Vsafe limit. Heating is then initiated to raise the cell temperature and establish a new, higher Vsafe. This cycle continues until Tmax is reached, and a short constant voltage charging phase is executed to finish charging to 80% SOC. FIG. 5C compares the charge time of the cell under the TLV protocol to a theoretical cell charged at a 3C rate, showing that TLV charging allows the SOC to increase at an approximately constant rate throughout the charging process, with minor deviation from the theoretical maximum evolving from short intermittent heating phases.

[0077] Additional experimental results during implementation of the above charge protocol are provided in FIGS. 6A-6B. In this experiment, battery cells were charged with a first current at a constant-current rate of 6C from a fully discharged cell to 80% state of charge in a 22 °C ambient environment to a maximum temperature of 70 °C. Vsafewas defined as 3.4V + 6mV / °C*(Tc-30°C). Similar to charging at 3C rate (FIG. 5), a 6C charging rate induces a rapid rise in cell voltage, after which a temperature rise from heating allows 6C charging to continue with cell voltage below a new, higher Vsafe. When compared to the 3C example (FIG. 5), the cell overpotential is greater when charging at 6C. Avoiding lithium plating thus requires higher temperature. With the same Vsafeprofile, TLV charging automatically compensates for that by inducing heating earlier in the 6C charge process. The end result is a higher average cell temperature for 6C charging compared to 3C charging.

[0078] Additional experimental results during implementation of the above charge protocol are provided in FIGS. 7A and 7B. In this experiment, the battery cell was charged with a first current at a constant-current rate of 6C from a fully discharged cell to 80% state of charge starting at -51 °C ambient environment. In this experiment, Vsafewas defined as a constant value of 3.4V for Tc< 30°C and 3.4 + 6mV / °C*(Tc-30°C) for Tc> 30°C. Tmaxwas set to 70°C. FIGS. 7A and 7B plot cell voltage and temperature evolutions. At the extremely low initial cell temperature, the cell voltage immediately rises to the 3.4V limit, after which CV charging is applied at 3.4V and heating is initiated until Tcreaches 30°C. Then, the CC-heat loop in FIG. 2D is implemented until the cell reaches 80%SOC. By utilizing rapid active heating and TLV charging, the healthy 0-80% charge in -51°C requires less than ten minutes.

[0079] FIGS. 8A and 8B show plots of average charge time, average charge temperature and capacity retention and cycle number corresponding to repeated cycles of the charge process shown in FIG. 6. The charge time is stable throughout these 800 cycles, showing a slight decrease as the capacity of cell slowly decreases moderately. After 800 cycles, the cell retained 93.8% capacity. Additionally, the average and maximum cell temperature during chargingshows a slow increase with cycle number. This increase corresponds to a moderate increase in cell internal resistance, which TLV charging automatically compensates for.

[0080] While the aforementioned test results are shown for a Li-ion battery with LFP and graphite electrodes, the TLV protocols are expected to have the similar advantages for other battery chemistries.

[0081] Only certain features and aspects of the subject technology and examples of its versatility are shown and described in the present disclosure. It is to be understood that the technology disclosed herein is capable of use in various other combinations and environments and is capable of changes or modifications. Thus, for example, those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances, procedures and arrangements described herein. Such equivalents are considered to be within the scope of the invention, and are covered by the following claims.

Claims

WHAT IS CLAIMED IS1. A method of charging a battery, the method comprising: applying a first charge current to the battery until a voltage of the battery (Vc) exceeds a predetermined safe voltage of the battery (Vsafe) based on a temperature of the battery (Tc); and when Vc>Vsafe, applying heat to the battery via a heater to an increased battery temperature (Ti) and updating Vsafe based on Ti; wherein the first charge current is either a constant current or constant power.

2. The method of claim 1, further comprising applying a second charge current to the battery while applying heat to the battery; wherein the second charge current is either a constant current or constant power.

3. The method of claim 2, wherein the magnitude of the second charge current is less than the magnitude of the first charge current.

4. The method of claim 1, further comprising, when Tc is below a predefined normal temperature of the battery (Tnorm), heating the battery, and while heating the battery, charging the battery at a constant voltage set to an electrochemical potential of a cathode active material of the battery.

5. The method of claim 1, wherein the magnitude of the first charge current is at least 1.5C.

6. The method of any one of claims 1-5, further comprising discontinuing applying heat to the battery via the heater after a predetermined period of time is reached, or until a predetermined temperature of the battery is reached, or until a temperature change of the battery is reached.

7. The method of claim 6, further comprising: after discontinuing applying heat to the battery via the heater, applying the first charge current to the battery until Vc exceeds the updated Vsafe based on Ti;when Vc>Vsafe based on Ti, applying heat to the battery via the heater to increase the battery temperature and updating Vsafe based on the increased battery temperature Ti; and until a cutoff criterion is reached, repeatedly applying the first charge current to the battery, applying heat to the battery, updating Vsafe and discontinuing applying heat to the battery.

8. The method of any one of claims 1-5, wherein applying heat to the battery increases the battery temperature at a rate of at least 5 °C / min.

9. The method of any one of claims 1-5, wherein the battery comprises a lithium iron phosphate cathode active material.

10. A method of charging a battery, the method comprising: charging the battery under constant current (CC), or under constant power (CP); and during charging under the CC or CP, cycling a heater on and off to increase a temperature of the battery; wherein the heater is cycled on when a voltage of the battery is greater than a predetermined safe voltage (Vsafe), wherein a value for Vsafe increases with increasing temperature of the battery.

11. The method of claim 10, wherein the heater is cycled off when a preset condition is met, wherein the preset condition is one or more of: a predetermined period of time, or a predetermined temperature of the battery is reached, or a temperature change of the battery is reached.

12. The method of any one of claims 10 to 11, wherein Vsafe increases with increasing temperature according to Equation (1.1):Vsafe = X + Y * (Tc-Tnorm) (1.1) wherein X is a predetermined minimum voltage, Y is a predetermined value in units of volts per degrees in temperature, Tc is the temperature of the battery and Tnorm is a normal operating temperature of the battery.

13. A battery charging system, comprising:a battery; a heater; and a controller configured to: determine a voltage of the battery and a temperature of the battery; determine whether the voltage of the battery (Vc) exceeds a predefined safe voltage (Vsafe); charge the battery at a constant current, or at constant power; heat the battery when Vc exceeds Vsafe; and update Vsafe based on an increased temperature of the battery (Ti); wherein a value for Vsafe increases with increasing temperature of the battery.

14. The battery charging system of claim 13, wherein the controller is further configured to cycle the heater on and off; and the heater is cycled on when Vc exceeds Vsafe based on an increased temperature of the battery (Ti); and the heater is cycled off when a preset condition is met.

15. The battery charging system of any one of claims 13 to 14, wherein the controller is configured to determine Vsafe according to Equation (1.1):Vsafe = X + Y * (Tc-Tnorm) wherein X is a predetermined minimum voltage, Y is a predetermined value in units of volts per degrees in temperature, Tc is the temperature of the battery and Tnorm is a normal operating temperature of the battery.

Images