A system and method for charging a battery with heat assistance

Abstract

A rapid pre-heat charging process for charging a rechargeable battery is disclosed. The process can be implemented by an integrated heating and battery system including a rechargeable battery, and a heating element in thermal contact with at least one cell of the battery and electrically connected in series with a switch, wherein the heating element and the switch form a switch-heater assembly. The switch-heater assembly can be electrically connected in parallel with the battery to form a battery-switch-heater circuit. Advantageously, the battery-switch-heater circuit is configured to be directly electrically engaged with a charger such that when the heating element is powered by the charger, the heating element is primarily powered by the charger and electrically connected with the battery. The system can be applied in a charging operation to pre-heat the battery to a predetermined charging temperature that can advantageously improve the kinetics of the charge and reduce the charging overpotential of the battery, thereby enabling rapid charging and charging at various temperatures.

Description

[0001] This invention is a divisional application filed on March 18, 2019, with application number 201980019497.2 (PCT / US2019 / 022690) and titled "A System and Method for Charging a Battery by Heating".

[0002] Cross-referencing of related patent applications

[0003] This application claims the benefit of U.S. Provisional Application No. 62 / 658,176, filed April 16, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0004] This invention generally relates to rechargeable electrochemical energy storage batteries. Specifically, this invention aims to improve the charging process of rechargeable batteries such as lithium-ion batteries. Background Technology

[0005] Rechargeable lithium-ion batteries are widely used in electric vehicles, consumer electronics, and stationary energy storage systems. A crucial aspect of using rechargeable batteries is the charging process, which, depending on the state of charge movement and the charging rate, generates overpotentials above the equilibrium potential. Therefore, during charging, the battery voltage rises and can potentially reach the upper voltage limit defined by significant degradation of the battery materials within the cell. This limits the permissible upper limit of overpotential, which in turn reduces the charging rate (or equivalently extends the charging time) and requires charging to be performed at near room temperature. Both of these factors cause significant inconvenience in battery use. Therefore, improving charge kinetics to reduce the charging overpotential of rechargeable batteries is essential.

[0006] Some published documents disclose charging systems with relatively complex configurations, including devices that electrically connect the rechargeable battery and the charger, such as DC-DC converters (e.g., documents with publication numbers US8779728 and US97999934). Other charging systems disconnect the electrical connection to the rechargeable battery when it is heated (e.g., US Patent Application 2013-0288089). However, further improvements in charging time and charging temperature range are needed. Summary of the Invention

[0007] One beneficial effect of this invention is the preheating charging process for rechargeable batteries. This process can be achieved through an integrated heating and battery system capable of rapid charging and charging at various temperatures. This process and system are extremely useful for battery charging in consumer electronics, transportation, aerospace, military, and stationary energy storage applications.

[0008] These and other advantages are at least partially achieved by a charging method for charging a battery, the charging method comprising: step one: heating the battery cell when the battery cell is below a predetermined charging temperature (T2); and step two: charging the battery cell using an external charger when the battery cell is at or above T2. Preferably, when the battery cell is below T2, the battery cell can be charged at at least 5... o C / min (e.g., at least 10) o C / min, at least 20, 30, 40 and 50 o The battery cells are heated at a rate of (C / min) to rapidly heat them. Under certain low-temperature conditions, such as temperatures that adversely affect the battery cells during charging, the battery cells are charged very little or not at all during the heating process in step one. The method also includes determining the temperature of the battery cells; if the temperature is below T2, step one is initiated to heat the battery cells; if the temperature is equal to or higher than T2, the battery cells are charged.

[0009] On the other hand, the present invention includes an integrated heating and battery system, the system comprising a rechargeable battery having at least one battery cell, and a heating element that is in thermal contact with at least one heating element and connected in series with a switch to form a switch-heater assembly. The switch-heater assembly is electrically connected in parallel with the battery to form a battery-switch-heater circuit, and the battery-switch-heater circuit is configured to be directly electrically connected to a charger. Preferably, the heating element is primarily powered by the charger, and when the heating element is primarily powered by the charger, it is electrically connected to at least one battery cell.

[0010] The battery configuration involved in this invention can be applied to a variety of electrochemical forms, such as, but not limited to, lithium-ion, lithium polymer, lead-acid, nickel metal hydride, lithium-sulfur, lithium-air, all-solid-state batteries, etc., and the at least one battery cell may include an anode, which may include metallic lithium, silicon, or silicon-carbon composite material.

[0011] In some embodiments, the heating element may be located inside the battery cell (exposed to the electrolyte) or in contact with the outer surface of the battery cell for thermal contact with the battery. Alternatively, if the system includes more than one heating element, the heating elements may be located both inside and outside the battery, each in thermal contact with the battery and electrically connected to a switch. Furthermore, the switch may be located within the battery cell. In some embodiments, the heating element comprises a flat resistive element.

[0012] In other embodiments, the switch includes an electromechanical relay and a temperature controller, or a solid-state relay with a temperature sensor, or a power MOSFET with a temperature sensor, or a high-current switch with a temperature sensor, or an insulated-gate bipolar transistor, or a bimetallic switch. In a further embodiment, the switch is configured to be driven by a temperature sensor to open when the battery cell temperature is below a first predetermined value, or to close when the battery cell temperature is at or above a second predetermined value. In other embodiments, the switch may be configured to pulse over time during charging and / or heating operations.

[0013] On the other hand, the present invention relates to a charging method for charging a battery, the charging method comprising the integrated heating and battery system described herein. The method includes a first step, which involves heating the battery cell by supplying power to a heating element via a charger when the battery cell temperature is below a predetermined charging temperature (T2). The method may further include determining a first temperature of the battery cell before charging, and initiating step one if the first temperature is below T2. The method may further include a second step, which involves charging the battery cell by the charger (without supplying power to the heating element) when the battery cell temperature is T2 or higher than T2.

[0014] Other advantages of the invention will become apparent to those skilled in the art from the following detailed description, in which preferred embodiments of the invention are shown and described only by illustrating the best mode for carrying out the invention. As will be realized, the invention can have other and different embodiments, and several details thereof can be modified in various obvious ways without departing from the invention. Therefore, the drawings and description are to be considered illustrative in nature and not restrictive. Attached Figure Description

[0015] Referring to the accompanying drawings, elements having the same reference numerals generally represent similar elements, wherein:

[0016] Figure 1A This illustration demonstrates a battery charging method that does not involve heating the battery.

[0017] Figure 1B A battery charging method according to an embodiment of the present invention is illustrated schematically.

[0018] Figure 2A This is a schematic diagram of a battery-switch-heater circuit according to an embodiment of the present invention.

[0019] Figure 2B This is a circuit diagram comprising multiple battery cells, a heater, and one or more switches according to an embodiment of the present invention.

[0020] Figure 3A and 3BThe diagrams illustrate battery charging methods with and without separate heating. Figure 3A This demonstrates a constant current constant voltage (CCCV) charging operation without heating. Figure 3B An embodiment of the present invention is shown, illustrating a constant current, constant voltage charging operation for preheating (h-cccv) of a battery cell.

[0021] Figure 4 A schematic diagram of pulse switch operation in the battery heating and charging operation according to the present invention is shown.

[0022] Figure 5A , 5B Figures 5C and 5D show experimental data on battery charging using the battery heating and charging method according to the present invention, using a charging rate of 3.5C and starting charging the battery from a temperature of -40°C. Figure 5A The changes in charging voltage during the charging operation are shown; Figure 5B The current flowing through the heating element (e.g., nickel foil) and the battery cell during charging operation is shown; Figure 5C It is a graph of the battery surface temperature during the charging operation; Figure 5D This is a diagram showing the state of charge (SOC) of the battery during the charging operation.

[0023] Figure 6A and Figure 6B The results of a series of preheating charging experiments according to an embodiment of the present invention are shown, wherein the ambient temperature of the preheating charging experiments was -50°C. o C, -40 o C, -20 o C and 0 o C. Figure 6A The voltage curves during the heating and charging steps are shown, as well as the changes in battery surface temperature during the heating step. Figure 6B The heating time and total charging time for all scenarios are summarized.

[0024] Figure 7 The relationship between battery capacity retention and cycle count was compared during a cyclic test at 0°C ambient temperature and a charging rate of 3.5C, with and without heating.

[0025] Figure 8 This is a graph showing the relationship between capacity retention and cycle number when four test battery cells are heated to different charging temperatures (T2) before charging, with a charging rate of 6C.

[0026] Figure 9 The effect of heating rate on battery cycle life is shown by the preheating charging method according to the present invention. Detailed Implementation

[0027] This invention relates to a battery system with an improved charging process, which enables rapid charging (saving time) and allows charging at virtually all ambient temperatures, including sub-freezing temperatures. The battery system of this invention can advantageously reduce charging overpotential, thereby improving the battery's energy efficiency during discharge and charge cycles.

[0028] As mentioned in the background section, a crucial aspect of using rechargeable batteries is the charging process, which, due to charge kinetics and the charging rate, generates overpotentials above the equilibrium battery potential. Consequently, the battery voltage increases during charging and typically reaches an upper voltage limit determined by significant degradation of the battery materials within the cell (see [link to relevant documentation]). Figure 1A Battery degradation limits the permissible overcharge potential (η). chg (i.e., the difference between the charging voltage and the open-circuit equilibrium potential Uo), which in turn reduces the charging rate (or equivalently prolongs the charging time) and requires near-room temperature to continue charging. These two factors—the lower charging rate and the requirement for near-room temperature charging—pose significant inconvenience to the practical use of the battery. However, advantageously, when the battery temperature is below T2, the configuration of the battery system according to the present invention allows for the addition of a preheating step before the battery charging operation to raise the battery temperature from a first temperature (T1) to at least a second temperature (T2) (i.e., the preferred charging temperature), such as... Figure 1B As shown. Before charging, a higher charging temperature (T2) thermally stimulates the electrochemical reactions and transport characteristics of the battery, thereby significantly improving charge kinetics and reducing the charge overpotential (η). chg The improved charge kinetics help the battery charge faster than an unheated battery, or reduce the overpotential under the same charging conditions, thus improving energy efficiency. See Figure 1B .

[0029] One aspect of the invention includes a preheating charging method to rapidly heat a battery and / or one or more battery cells thereon before charging. The method includes a first step, which involves heating the battery cells at a rapid heating rate when the battery cells are below a predetermined charging temperature (T2). Preferably, the heating rate is at least 5... o C / min (e.g., at least 10) o C / min, at least 20, 30, 40 and 50 o The battery cell is heated at a rate of (C / min). This rapid heating can be achieved by powering the heating element, which can also be used to charge the battery cell. The heating element is preferably in thermal contact with the battery cell.

[0030] Heating operations may include heating the battery cells to a temperature of T2 or higher before subjecting them to significant charging. Under certain low-temperature conditions, such as temperatures that adversely affect the battery cells during charging, the battery cells may receive very little or no charge during the heating operation in step one. At such low temperatures, the battery cells heat up rapidly but receive almost no charge, i.e., the charge is below 0.1C or below 0.05C, or the charge is unmeasurable.

[0031] The predetermined charging temperature (T2) can be selected as the value most favorable for the electrochemical and transport processes of charging the battery. For example, the charging temperature can be at least 35°C, 40°C, or significantly higher (e.g., close to or equal to 60°C).

[0032] The method may further include a second step, which involves charging the battery cell via a charger when the battery cell is at or above T2. When the battery cell is at or above T2, battery heating can be stopped; that is, the battery can be charged without using a separate heat source to heat the battery cell.

[0033] In some embodiments, the method may further include charging the battery at a temperature of T2 or higher with a constant current, constant voltage, constant power, or variable power, or any combination thereof. For example, the method may also include charging the battery with an external power source at a constant current at a temperature of T2 or higher until a voltage upper limit is reached, and then maintaining a constant voltage at the battery voltage upper limit until a predetermined current is reached. In other embodiments, the method may include determining the temperature of the battery cell, and if the temperature is below T2, initiating step one to heat the battery cell, and if the temperature is equal to or higher than T2, charging the battery cell. Further embodiments include a rest period between the heating and charging operations.

[0034] Another aspect of the invention includes an integrated battery heating and charging system comprising a rechargeable battery including at least one battery cell. The system also includes a heating element that is in thermal contact with the at least one battery cell and electrically connected in series with the switch to form a switch-heater assembly. The system further includes a battery-switch-heater circuit. The battery-switch-heater circuit can be configured to be directly electrically connected to a charger; for example, the battery-switch-heater circuit can be configured to be directly electrically engaged with the charger such that current from the charger flows directly into the battery-switch-heater circuit without interference from other devices, such as a DC / DC converter. As used herein, a charger refers to any external charging source, such as an external battery charger or external power supply that can charge the system's rechargeable battery.

[0035] Advantageously, the switching heater assembly is electrically connected in parallel with the battery. With this simple configuration, the heating element and battery can be powered by the same charger without requiring an additional power source, electronic control unit (ECU), or battery management system (BMS). The system of this invention differs fundamentally from other systems that disclose additional devices for electrical connection between the charger and battery, or the use of separate circuits for charging and heating, and control units and BMS for such separate circuits. In some respects, the system of this invention differs from other systems in that the battery and heater of this invention are connected in parallel, whereas in some systems they are connected in series. This difference allows the charger to operate within the same voltage window as in conventional cases.

[0036] Figure 2A A battery-switch-heater circuit configured for direct electrical connection to an external charger (30) is schematically shown. As shown, the circuit includes a battery cell 22 and a switch-heater assembly 24, wherein a heating element 26 is electrically connected in series with a switch 28. The figure also shows that the battery 22 and the switch-heater assembly 24 are directly connected in parallel with a charging source such as an external battery charger or an external power source (30). Although Figure 2A Not shown, but the heating element 26 will make thermal contact with the battery cell 22. In some embodiments, the heating element may be located inside the battery cell (exposed to the electrolyte) or may contact the outer surface of the battery cell for thermal contact with the battery. Alternatively, the switch may be placed inside the battery cell along with the heating element.

[0037] This invention describes, in one aspect, that when the switch is on, the heating element is primarily powered by the charger (>50%, e.g., >51%), and when the switch is off, the battery is charged by the charger. The energization of the heating element heats the battery and raises its temperature. As is known to those skilled in the art, when the switch is on, the charging current tends to flow more through the heating element than the battery because the voltage of the heating element is significantly lower than the battery voltage. Therefore, in one respect, the battery cell receives almost no charge during the heating operation in this heat-charging method.

[0038] although Figure 2A A battery cell with a switchable heater assembly is shown, but the integrated heating and battery system of the present invention may include a battery with multiple electrochemical cell units, and / or multiple heating elements, and / or multiple switches. For example, in other embodiments, such as Figure 2B The exemplary circuit shown may include a system comprising multiple battery cells (22) 1-n ), and may optionally include a plurality of heater elements (26) in thermal contact with the plurality of battery cells. 1-n), and optionally one or more switches (28), wherein the heater element is connected in series with one or more switches to form multiple switch-heater assemblies. The battery cell and switch-heater assembly are directly connected in parallel to a charging source such as an external battery charger or an external power source (30).

[0039] In some embodiments of the invention, the integrated heating and battery system can be charged via step one, which includes heating the battery by powering a heating element with a charger when the battery is below a predetermined charging temperature (T2). The charging operation may further include determining the battery temperature using a component such as a temperature sensor before charging or heating the battery. If the determined temperature is below a predetermined value required for battery charging (e.g., less than T2), a switch in the integrated system is activated, and the heater is powered by a charging source, which may be the same charging source used to charge the battery. When the battery temperature determined by the temperature sensor reaches or exceeds the predetermined value, the switch is turned off, and battery charging can be powered by the same charger. Therefore, step two, the charging operation, includes charging the battery (without powering the heating element) by the charger when the battery is at or above T2.

[0040] Advantageously, the same charging source (battery charger or external power supply) in this system can seamlessly power the heater when the switch is on and charge the battery when the switch is off. For example, in implementation, the integrated heating and charging system of the present invention does not require a DC / DC converter, inverter, diode, or additional switch (except for the switch connected in series with the heater), ECU, or BMS to heat or charge the battery. Therefore, in some embodiments, the integrated heating and charging system of the present invention does not include any combination of DC / DC converters, inverters, diodes, additional switches, ECUs, or such devices between the charging source and the battery. A significant feature of this integrated heating and battery system according to certain embodiments of the present invention is its simplicity, resulting in lower cost compared to the more complex systems in conventional BMSs.

[0041] A predetermined charging temperature (T2) is a value that is most favorable for the electrochemical and transport processes of battery charging, and in some cases, it can be much higher than room temperature. For example, the charging temperature can be determined to be close to human body temperature (i.e., 35-40°C), or significantly higher (e.g., close to or equal to 60°C).

[0042] In some embodiments, step one of battery heating may include delivering energy from the charger at a constant current, constant voltage, constant power, or variable power. Furthermore, step one of battery heating may include heating the battery at a rapid rate, such as at a rate of at least 1 degree Celsius per minute. More preferably, step one of battery heating may include heating the battery at a rapid rate of at least 5°C / min (e.g., at least 10°C / min), such as at least 20°C, 30°C, 40°C, and 50°C / min.

[0043] Traditionally, batteries are... Figure 3A The constant current constant voltage (CCCV) charging method shown is used for charging. One embodiment of the invention is a novel charging mode called h-CCCV (see [link to invention]). Figure 3B This h-CCCV charging mode includes a battery preheating phase, a constant current phase until the upper voltage limit is reached, and then a constant voltage phase fixed at the upper limit until the charging current decreases to, for example, C / 20. The h-CCCV method can be implemented using the integrated heating and charging system of this invention. For example, in a battery with a switch-heater assembly, the switch can be configured to first turn on the heating until the battery temperature reaches a predetermined temperature optimal for charging. Subsequently, the switch is turned off, allowing the charger's power to be fully used to charge the preheated battery in CCCV mode. The h-CCCV method is particularly suitable for rapid charging from low temperatures to room temperature or the optimal charging temperature.

[0044] As used herein, the terms "rechargeable battery" or "battery" are used to refer to any rechargeable electrochemical energy storage device comprising one or more electrochemical battery cells. The basic components of a battery cell include an anode electrode coated on a current collector, a cathode electrode coated on another current collector, and an electrolyte.

[0045] The integrated heating and battery system described in this invention may include a variety of battery chemistry types, such as, but not limited to, lithium-ion, lithium polymer, lead-acid, nickel metal hydride, nickel manganese cobalt, lithium sulfur, lithium air and all solid-state batteries.

[0046] Batteries with an anode made of silicon or a silicon-graphite composite material can be improved by this invention. Experiments by Li et al. (J. Li, F. Yang, Y.T. Cheng, MW. Weber-Ruger, X. Shaw, J. Faith-Chen. C 116, 2012) found that the diffusion coefficient of lithium in silicon is two orders of magnitude lower than that in graphite, which is a problem for fast charging. This problem can now be solved by a preheating operation, resulting in a significant increase in the lithium diffusion coefficient in silicon during the high-temperature heating charging method of this invention.

[0047] Furthermore, batteries containing high-salt electrolytes (e.g., a salt concentration of at least about 4 mol / L (4 M)) or solid electrolytes can benefit from this invention. For example, battery cells with high-salt electrolytes tend to have high viscosity and low ionic conductivity. However, the preheating charging method according to embodiments of the invention can significantly reduce charge overpotential. Solid electrolytes such as polymer electrolytes, sulfide electrolytes, and oxide electrolytes have high interfacial charge transfer resistance and / or low ionic conductivity. The preheating charging method according to embodiments of the invention also helps to reduce the total charge overpotential of solid electrolyte batteries.

[0048] Another type of electrochemical battery that can benefit from this invention is the lithium-air battery, where the oxygen evolution reaction during charging is very slow. During discharge, the air cathode reacts with lithium ions and oxygen in the air to form their oxides, such as Li₂O₂. During charging, lithium oxide (such as Li₂O₂) decomposes into lithium ions and electrons, releasing oxygen. The charge overpotential of the air cathode is typically very high; therefore, the thermal stimulation used in this invention is particularly effective in reducing the charge overpotential, thereby significantly improving the energy efficiency of the lithium-air battery.

[0049] In one embodiment of the invention, the heating element includes at least one resistive element that can be located either inside a battery cell (exposed to the electrolyte) or between two battery cells, or a combination of several resistive elements inside and outside the battery cells. The resistance of the resistive element is preferably a value in ohms, equal to a value between 0.1 and 5 divided by the battery capacity in ampere-hours (Ah), such as a value between approximately 0.5 and 2 divided by the battery capacity (Ah). For example, a 20 Ah battery resistive element is preferably between approximately 0.005 ohms (0.1 divided by 20) and approximately 0.25 ohms (5 divided by 20), such as between approximately 0.025 ohms (0.5 divided by 20) and approximately 0.1 ohms (2 divided by 20).

[0050] The resistive sheet of the present invention can be made of graphite, highly ordered pyrolytic graphite (HOPG), stainless steel, nickel, chromium, nickel-chromium, copper, aluminum, titanium, or combinations thereof. If used outside a battery cell or between two adjacent battery cells within a module, the resistive sheet does not require corrosion protection; therefore, other materials can be used as the resistive sheet of the present invention. In some embodiments, the resistive sheet of this disclosure preferably has two main surfaces, such as a flat plate with a large surface area, to facilitate good heat transfer with the battery assembly. The thickness of the resistive sheet of the present invention can range from about 1 micrometer to about 200 micrometers, preferably from about 5 to about 100 micrometers. A resistive sheet with high resistance, high thermal conductivity, and low cost is useful for some embodiments of the present invention.

[0051] The resistance of a resistor can be adjusted by patterning it, which involves removing material from the resistor. Patterning gives the resistor sufficient thickness to achieve mechanical strength and solderability, but reduces resistance. Patterns with rounded corners have the advantage of reducing heat buildup at the corners. Patterned resistors can be manufactured using methods such as photolithography, electrical discharge machining, waterjet cutting, laser cutting, and stamping.

[0052] In some embodiments, if the resistive element is inserted into the battery cell, a large portion of the surface of the resistive element can be coated to prevent unwanted chemical reactions or electrical contact with the electrolyte. The protective coating of the resistive element should be thermally conductive, electrically insulating, and chemically stable. It can be made of polymers, metal oxides, and other materials. Examples of polymeric materials for the protective coating include polyethylene, polypropylene, chlorinated polypropylene, polyester, polyimide, polyvinylidene fluoride, polytetrafluoroethylene, nylon, or copolymers thereof. Examples of metal oxide materials for the protective coating include oxides of magnesium, aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, and combinations thereof. The protective coating preferably has a high dielectric constant. In some embodiments, an adhesive may be used between the resistive element and the protective coating. The thickness of the protective coating can be between 10 nm and 100 µm, preferably between 10 nm and 50 µm. The coating should be thin enough to achieve good thermal transfer but not so thin as to prevent the resistive element from contacting the electrolyte within the battery. Protective coatings can be applied to resistor sheets by methods such as adhesive bonding, lamination, dip coating, spin coating, spraying, chemical vapor deposition, atomic layer deposition, solution casting, electrodeposition, self-assembled monolayers, photocuring, and surface oxidation.

[0053] The switch in the switch-heater assembly described in this invention can be composed of an electromechanical relay and temperature controller, a solid-state relay with a temperature sensor, a power MOSFET (metal-oxide-semiconductor field-effect transistor) with a temperature sensor, or a high-current switch with a temperature sensor, or an IGBT (insulated-gate bipolar transistor). The switch described in this invention can be placed inside or outside the battery cell. When the switch is placed inside the battery cell, the switch (e.g., a MOSFET) can be combined with a resistive element to form a planar substrate, wherein the gate line extends from the battery cell to control the switch from outside the battery cell.

[0054] To avoid damaging the battery materials inside the battery cell, it is best to keep the battery operating voltage V... cell Maintain a value above the predetermined value, such as 2V. Figure 4 The configuration is shown as follows Figure 2A The diagram shows the charging current of a battery cell in a switch-heater assembly. When the switch is on, i.e., in heating mode, the battery voltage is equal to I. h R hIf we assume the current I flowing through the battery b If it is very small, the battery voltage is approximately equal to I. chg R h Therefore, I chg R h The voltage must be equal to or greater than 2V. This condition can be met at higher charging rates. For example, for a 10Ah battery with a heater resistance of 0.06 Ohm, the above condition is met when the charging current is higher than 35A (i.e., 3.5C), allowing the switch to be turned on as long as the battery temperature is below the predetermined charging temperature without the risk of damaging the battery materials. However, for low charging currents or I... chg R h When the voltage is <2V, we can use a pulse switching procedure instead of continuous conduction to keep the battery voltage above 2V. For example, as Figure 4 As shown, during the period when the switch is off, the battery will receive I chg t off The total charge. Once the switch is turned on, the battery will release the same amount of charge received during the off period to the heater, releasing a charge of I. chg t off =I b t on Therefore, it is converted into battery discharge current I. b = I chg t off / t on Therefore, it can be deduced that when the switch is turned on, the heating current I... h =I chg +I b =I chg (1+t off / t on Therefore, as shown in Figure 3, the total heating current is actually equal to I. b and I chg The sum of. Therefore, V cell =I h R h =I chg R h (1+t off / t on If t > 2V, then t must be greater than 2V. off / t on >2 / (I chg R h -1. For example, for a low charging current (such as 0.3C or 3A) of the same 10Ah battery, the ratio of off time to on time needs to be greater than 10.11 or rounded to 11 so that the battery voltage always remains above the 2V threshold. When the switch is configured to t on =1s and t off=11sec combination, or t off =0.1s and t off The condition can be satisfied when there is another combination of =1.1s.

[0055] The switch described in this invention can be activated to preheat the battery cell from its initial temperature. This is a preferred method for ultra-fast charging of high-energy-density power batteries with high load capacity and thick electrodes, for example, reaching 80% state of charge in 10 minutes or less. This is because fast charging of some electric vehicle batteries benefits from the significantly enhanced electrolyte transport capacity through a thick electrode at high temperatures, thus avoiding lithium plating, a process that severely reduces battery life. We note that battery degradation may be exacerbated at higher charging temperatures (T2) due to the accelerated growth of the solid electrolyte membrane (SEI). However, the growth of the SEI depends on the exposure time. In practical applications, the charging process typically lasts less than 5% of the total charge-discharge cycle time, making the impact of battery degradation accelerated during high-temperature charging on the overall battery life negligible. For example, for a vehicle with a cruising range of 200 miles, if using a power battery with a 100,000-mile / 10-year warranty, 500 charge cycles are required to reach 100,000 miles. Assuming all 500 charges are completed using the 30-minute fast charging method of this invention, the total charging time is 250 hours. In a 10-year battery lifespan, less than 0.3% of the time will be spent charging at the high temperature of T2, resulting in accelerated battery degradation.

[0056] The preferred preheating rate before battery charging is at least 5 minutes. o C / min, more preferably at least 10 o C / min, for example, at least 20, 30, 40 and 50 o C / min. For example, if a battery is charged for one hour, and the initial temperature rises by 20°C, the heating time is less than 4 minutes, which has a negligible impact on the battery charging time. The faster the battery charges, the faster the heating rate is preferred, so that the heating process is negligible compared to the total battery charging process. In some embodiments, the heating operation takes less than 10% of the total time required to charge the battery to 80% state of charge, for example, less than 5% of the total time.

[0057] Example

[0058] As an example, we constructed a 9.5 Ah polymer battery using lithium-nickel-manganese-cobalt (NMC622) as the cathode, graphite as the anode, and 1 M LiPF6 dissolved in ethylene carbonate / ethyl carbonate (EC / EMC) (weight ratio 3:7) + 2 wt% vinylene carbonate (VC) as the electrolyte, with a Celgard-2325 microporous trilayer membrane as the separator. The cathode was prepared by coating a 15 μm thick aluminum foil with an N-methylpyrrolidone (NMP)-based slurry. The dried materials of the aluminum foil included NMC622 (91.5 wt%), conductive agent Super-C65 (4.4 wt%), and polyvinylidene fluoride (PVdF) (Hitachi) (4.1 wt%) as the binder. The anode was prepared by coating a 10 μm thick copper foil with a deionized (DI) aqueous slurry. The dried materials of the copper foil included graphite (95.4 wt%), conductive agent Super-C65 (1.0 wt%), styrene-butadiene rubber (SBR) (JSR Corporation) (2.2 wt%), and CMC fiber (Nippon Paper Corporation) (1.4 wt%). The mass loadings of the NMC622 cathode and the graphite anode were 10.574 mg / cm³, respectively. 2 and 6.678 mg / cm 2 These correspond to 1.85mAh / cm³. 2 and 2.23mAh / cm 2 After rolling, the thicknesses (single-sided) of the positive and negative electrodes are 40.75 μm and 48.7 μm, respectively. The polymer battery comprises 34 anode layers and 33 cathode layers, covering an area of ​​152 × 75 mm, with a rated capacity of 9.5 Ah (all charge rates are defined by this standard), and specific energy of 170 Wh / kg and 334 Wh / L. Two nickel foils were placed inside the polymer battery as heating elements, one located at the top 1 / 4 of the battery thickness and the other at the top 3 / 4 of the battery thickness. Each nickel foil is 30 μm thick and has a resistance of 80.2 mΩ at 25°C. One end of the nickel foil is connected to the negative terminal, and the other end is connected to a MOSFET switch, which is then connected to the positive terminal, as shown below. Figure 2A As shown.

[0059] At -40 o A heating and charging experiment was conducted on a 9.5Ah battery at an ambient temperature of C. The experimental data are shown in the figure. Figure 5A Indicates the charging voltage. Figure 5B Indicates the charging current. Figure 5C Indicates battery temperature. Figure 5D This indicates the battery's state of charge. Before the test, the fully discharged battery was kept at -40°C. oThe battery was placed in the environmental chamber for more than 12 hours. For the initial heating step, electrical energy from the charging source can be transferred using constant current, constant voltage, constant power, or variable power. In this experiment, we provided a constant voltage of 3.15V, slightly lower than the battery's open-circuit voltage (~3.2V), and closed the switch for the heating step (see [link]). Figure 5A Thus, virtually all the current from the charging source flows to the nickel foil heater rather than the battery (see...). Figure 5B Therefore, the battery materials will not be damaged while the battery is still at a low temperature. The battery is heated rapidly (see...). Figure 5C Once the battery surface temperature reaches 20°C... o C, then turn on the MOSFET switch to terminate the heating step, and then let the battery rest for 10 seconds to allow the internal temperature gradient to relax. Figure 5C Subsequently, the battery was charged using a constant current constant voltage (CCCV) protocol at a current of 3.5C and a cutoff voltage of 4.2V until it reached 80% state of charge (SOC). Figure 5D The entire heating process took 894.8 seconds (14.91 minutes), including a 61.6-second heating step and a 10-second thermal relaxation process.

[0060] In the above experiment, since the set voltage can be controlled near the battery's open-circuit voltage, a constant voltage is applied during the heating step to precisely ensure that no current flows into the battery before the heating step is completed and the battery is preheated. Constant current or constant power also applies to the heating step because the unique circuitry in this invention always results in a very small portion of the current flowing through the battery (after overcoming the open-circuit voltage potential), while the majority of the current flows through the heater (due to the absence of voltage potential).

[0061] According to the disclosure of this invention, Figure 6A and 6B Successful preheating and charging experiments were demonstrated at ambient temperatures of 0°C, -20°C, -40°C, and even -50°C. Heating times at various initial temperatures were shown below. Figure 6B As shown. Transfer the battery from -50... o Heat to 20°C o C (~60) o (C / min) took 69 seconds, from 0 o C to 20 o C (~40) o (C / min) took 30.2 seconds. Even at the most extreme -50 o In case C, the heating step accounts for only 7.6% of the total time for the heating and charging steps. In all four cases, the total time to charge the battery to 80% SOC is similar. Figure 6B -50o C is 905.7 seconds, 0 o C is 863.2 seconds, a difference of 5%.

[0062] Figure 7 The capacity retention data of batteries cycled at 0 degrees Celsius using the preheating charge method (h-CCCV) of this invention and the conventional constant current, constant voltage (CCCV) method were compared between those using a 3.5C charging rate. It can be seen that the battery using the CCCV method lost 20% of its capacity in just 50 cycles. In contrast, the h-CCCV method unexpectedly achieved 4500 cycles with the same capacity retention, representing a 90-fold increase in cycle life.

[0063] Figure 8 This graph shows the relationship between capacity retention and cycle life for various batteries heated to different charging temperatures before charging at a 6C rate. The results indicate that the cycle life at 80% capacity retention significantly increased from less than 100 cycles at 34°C to over 1200 cycles at 61°C. The data shows an astonishing 12-fold improvement in cycle life. This significant improvement in cycle life is surprising because it's not always intuitive to see such a beneficial effect on battery cell life from rapid heating before charging.

[0064] Based on the measurement data of battery degradation rate at various charging temperatures (T2), Figure 9 The relationship between battery cycle life and charging temperature (T2) at a 20% capacity loss under various heating rates (curve parameters) was summarized. It can be seen that at 0.5°C / min, the battery cycle life decreases sharply. This decrease is due to the battery cells operating at higher charging temperatures (i.e., 60°C). o This is caused by excessive exposure time under condition C). On the other hand, by increasing the heating rate of the rechargeable battery to at least 5... o A heating rate of at least 5°C / min minimizes the battery's exposure time to elevated charging temperatures, thus suppressing battery degradation. In the optimal heating charging method of this invention, a heating rate of at least 5°C / min is considered a lower threshold rate for suppressing battery degradation.

[0065] This disclosure only shows and describes preferred embodiments of the present disclosure and examples of its versatility. It should be understood that this disclosure can be used in various other combinations and environments, and can be changed or modified within the scope of the inventive concept expressed herein. Therefore, for example, those skilled in the art will recognize or be able to determine many equivalents of the specific substances, procedures, and arrangements described herein using no more than conventional experiments. Such equivalents are considered to be within the scope of this disclosure and are covered by the appended claims.

Claims

1. A charging method for charging a battery, the method comprising: Step 1: When the battery cell is below the predetermined charging temperature (T2), the charger provides electrical energy to heat the battery cell at a rate of at least 5°C / min; Step 2: When the battery cell is at or above T2, the charger charges the battery cell, wherein T2 is at least 35°C.

2. The charging method according to claim 1, wherein step one includes heating the battery cell by supplying power to a heating element in thermal contact with the battery cell via a charger.

3. The charging method according to claim 2, wherein step one includes heating the battery cell by using a charger to provide constant current, constant voltage, constant power or variable power to the heating element.

4. The charging method according to claim 1, wherein step one includes heating the battery at a rate of at least 10°C / min.

5. The charging method according to claim 1, wherein T2 is at least 40°C.

6. The charging method according to claim 1, wherein step two includes charging the battery with a constant current until the upper voltage limit is reached, and then maintaining a constant voltage at the upper voltage limit of the battery until a predetermined current is reached.

7. The charging method according to claim 1, further comprising determining the temperature of the battery cell, and if the temperature is lower than T2, initiating step one to heat the battery cell, and if the temperature is equal to or higher than T2, charging the battery cell.

8. An integrated heating and battery system, the system comprising: A rechargeable battery, the rechargeable battery comprising at least one battery cell; A heating element is thermally contacted with at least one battery cell and connected in series with a switch to form a switch-heater device; the switch-heater device is connected in parallel with a battery to form a battery-switch-heater circuit; the battery-switch-heater circuit is directly connected to a charger; the heating element is primarily powered by the charger, and when the heating element is primarily powered by the charger, the heating element is electrically connected to at least one battery cell.

9. An integrated heating and battery system according to claim 8, wherein the at least one battery cell includes an anode comprising lithium metal.

10. An integrated heating and battery system according to claim 8, wherein the at least one battery cell includes an anode, the anode comprising silicon or silicon-carbon composite material.

11. An integrated heating and battery system according to claim 8, wherein the at least one battery cell comprises an anode and a cathode, wherein the anode comprises lithium metal and the cathode uses air as a reactant.

12. An integrated heating and battery system according to any one of claims 8-11, wherein the at least one battery cell comprises a solid electrolyte.

13. An integrated heating and battery system according to any one of claims 8-11, wherein the at least one battery cell comprises an electrolyte containing a salt with a concentration greater than 4 moles per liter.

14. An integrated heating and battery system according to any one of claims 8-11, wherein the heating unit is located within at least one battery cell or in contact with the outer surface of at least one battery cell.

15. An integrated heating and battery system according to any one of claims 8-11, wherein the heating element comprises a resistive sheet having two large surfaces and a thickness of 1-200 micrometers.

16. An integrated heating and battery system according to claim 15, wherein the resistive element comprises graphite, highly ordered pyrolytic graphite (HOPG), stainless steel, nickel, chromium, nickel-chromium alloy, copper, aluminum, titanium, or a combination thereof.

17. An integrated heating and battery system according to any one of claims 8-11, wherein the switch comprises an electromechanical relay and a temperature controller, or a solid-state relay with a temperature sensor, or a power switch with a temperature sensor, or a high-current switch with a temperature sensor, or an insulated-gate bipolar transistor, or a bimetallic switch.

18. An integrated heating and battery system according to any one of claims 8-11, wherein the switch is located within at least one battery cell.

19. An integrated heating and battery system according to any one of claims 8-11, wherein the switch pulses over time during charging operation.

20. An integrated heating and battery system according to any one of claims 8-11, wherein the heating element and the switch are both located within the battery cell.

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