Low-temperature charging method and low-temperature charging system for lithium battery

Abstract

The application discloses a low-temperature charging method and system for a lithium battery. The low-temperature charging method comprises the following steps: collecting the current temperature and the current voltage of the lithium battery in real time; if the current temperature is less than a preset first temperature threshold, entering a low-temperature charging mode; if the current temperature is greater than or equal to the first temperature threshold, entering a conventional constant-voltage charging mode; in the low-temperature charging mode, comparing the current temperature with a preset second temperature threshold, wherein the second temperature threshold is less than the first temperature threshold; if the current temperature is less than the second temperature threshold, querying a preset voltage-temperature relationship table according to the current voltage to obtain an initial alternating current amplitude and an initial alternating current frequency matched with the current voltage, and charging the lithium battery according to the initial alternating current amplitude and the initial alternating current frequency; and if the current temperature is greater than or equal to the second temperature threshold, performing alternating current and direct current superimposed charging. The technical scheme of the application can effectively improve the charging efficiency and the safety of the battery in a low-temperature environment.

Description

Technical Field

[0001] This invention relates to the field of battery charging technology, and more specifically to a low-temperature charging method and system for lithium batteries. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and excellent cycle performance, have been widely used in many fields such as new energy vehicles, energy storage devices, and portable electronic terminals. However, low-temperature environments below 0°C affect the electrochemical performance of lithium-ion batteries. The internal lithium-ion migration rate slows down, and the battery's internal resistance increases sharply, leading to a significant reduction in the allowable current intensity during charging. This not only results in low charging efficiency and excessively long charging times but also easily causes lithium plating at the negative electrode. Lithium plating leads to battery capacity decay, shortened cycle life, and in severe cases, can even puncture the separator, causing internal short circuits and inducing thermal runaway and other safety hazards. Existing charging technologies struggle to balance fast charging efficiency with battery safety, failing to meet the demands for fast and safe charging in low-temperature environments. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a low-temperature charging method for lithium batteries that can effectively improve charging efficiency and battery safety in low-temperature environments.

[0004] This application provides a low-temperature charging method for lithium batteries, the low-temperature charging method comprising:

[0005] During charging, the current temperature and voltage of the lithium battery are collected in real time.

[0006] If the current temperature is less than a preset first temperature threshold, then enter the low temperature charging mode; if the current temperature is greater than or equal to the first temperature threshold, then enter the normal constant voltage charging mode.

[0007] In the low-temperature charging mode, the current temperature is compared with a preset second temperature threshold, wherein the second temperature threshold is less than the first temperature threshold;

[0008] If the current temperature is less than the second temperature threshold, then the preset voltage-temperature relationship table is consulted according to the current voltage to obtain the initial AC amplitude and initial AC frequency that are compatible with the current voltage, and the lithium battery is charged according to the initial AC amplitude and the initial AC frequency.

[0009] If the current temperature is greater than or equal to the second temperature threshold, then AC / DC superposition charging is performed.

[0010] In one aspect, prior to the step of querying a preset voltage-temperature relationship table based on the current voltage, the following is included:

[0011] The internal resistance temperature coefficient, lithium-ion diffusion coefficient, and critical current density for lithium plating at the negative electrode of the lithium battery are provided to the electrochemical model. The simulation constructs a voltage-temperature relationship table, which stores the AC parameters that the lithium battery can be applied to under different temperature ranges and different voltage ranges. The AC parameters include AC amplitude and AC frequency.

[0012] In one aspect, the step of applying alternating current to the lithium battery based on the initial alternating current amplitude and the initial alternating current frequency includes:

[0013] The real-time temperature and real-time voltage of the lithium battery are continuously recorded according to a preset first time interval.

[0014] Monitor the real-time maximum voltage of the lithium battery. If the real-time maximum voltage is greater than a preset first voltage threshold and the duration is greater than a preset second time, then reduce the currently applied AC voltage amplitude to a predetermined proportion of the initial AC voltage amplitude.

[0015] If the real-time voltage maximum value is less than or equal to the first voltage threshold, or the duration of the voltage being greater than the first voltage threshold is less than the second time, then the lithium battery continues to be charged according to the initial AC amplitude and the initial AC frequency.

[0016] In one aspect, the steps of AC / DC superposition charging include:

[0017] Based on the current temperature and the current voltage, the voltage-temperature relationship table is queried to obtain the target AC amplitude, target AC frequency and target DC magnitude that are compatible with the current temperature and current voltage;

[0018] The lithium battery is powered according to the target AC amplitude, the target AC frequency, and the target DC magnitude, and the power supply continues for at least a preset third duration.

[0019] In one aspect, prior to the step of querying the voltage-temperature relationship table based on the current temperature and the current voltage, the method includes:

[0020] The constraints are established based on the condition that the rate of temperature rise during lithium battery charging is less than a specified rate and there is no risk of lithium plating.

[0021] The target DC current magnitude is obtained through simulation based on the aforementioned constraints and recorded in the voltage-temperature relationship table.

[0022] In one aspect, following the step of continuously supplying power according to a preset third duration, the following is included:

[0023] Determine whether the current voltage is greater than a preset second voltage threshold, and obtain the current DC current, and determine whether the current DC current is lower than a preset first current threshold;

[0024] If all conditions are met, the low-temperature charging mode is terminated and the system is switched to the conventional constant-voltage charging mode.

[0025] If at least one condition is not met, the AC / DC superposition charging process will be repeated.

[0026] In one aspect, under the conventional constant voltage charging mode, if the current temperature of the lithium battery is detected to be lower than the first temperature threshold and the current voltage is lower than the second voltage threshold again within a specified time, the low temperature charging mode is automatically restarted.

[0027] In one aspect, prior to the step of real-time acquisition of the current temperature and voltage of the lithium battery during charging, the following steps are included:

[0028] Set a first initial threshold and a second initial threshold;

[0029] Based on the type of lithium battery and the usage scenario, the first initial threshold is fine-tuned by ±3℃ to obtain the first temperature threshold, and the second initial threshold is fine-tuned by ±3℃ to obtain the second temperature threshold.

[0030] In one aspect, the step of charging the lithium battery based on the initial AC amplitude and the initial AC frequency includes:

[0031] The alternating current impedance of the lithium battery is monitored in real time. If the sudden change in the alternating current impedance is greater than a set ratio, the alternating current is stopped, and the current temperature and voltage are used to determine whether to perform AC and DC superposition charging.

[0032] Furthermore, to address the aforementioned problems, this application also provides a low-temperature charging system for lithium batteries, the low-temperature charging system comprising:

[0033] The data acquisition module is used to collect the current temperature and voltage of the lithium battery in real time during charging.

[0034] The judgment module is used to enter a low-temperature charging mode if the current temperature is less than a preset first temperature threshold, and to enter a normal constant voltage charging mode if the current temperature is greater than or equal to the first temperature threshold.

[0035] A low-temperature charging module is used in the low-temperature charging mode to compare the current temperature with a preset second temperature threshold, wherein the second temperature threshold is less than the first temperature threshold; if the current temperature is less than the second temperature threshold, it queries a preset voltage-temperature relationship table based on the current voltage to obtain an initial AC amplitude and an initial AC frequency adapted to the current voltage, and charges the lithium battery according to the initial AC amplitude and the initial AC frequency; if the current temperature is greater than or equal to the second temperature threshold, it performs AC and DC superposition charging.

[0036] The beneficial effects of this invention are as follows: By real-time acquisition of the current temperature and voltage of the lithium battery, the low-temperature charging mode and the conventional constant-voltage charging mode are switched according to whether the temperature is lower than the first temperature threshold. In the low-temperature charging mode, the charging method is further distinguished according to the second temperature threshold. When the temperature is lower than the second temperature threshold, the initial AC parameters are matched with the current voltage. When the temperature is higher than or equal to the second temperature threshold, AC and DC superposition charging is used. This improves the lithium-ion migration rate of the lithium battery in low-temperature environment. At the same time, by selecting the appropriate charging parameters, the phenomenon of lithium plating on the negative electrode is avoided, and the safety hazards such as battery capacity decay, shortened cycle life and thermal runaway are reduced. This achieves improved lithium battery charging efficiency and improved safety in low-temperature environment. Attached Figure Description

[0037] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0038] Figure 1 This is a schematic diagram of the process steps of the low-temperature charging method for lithium batteries in this application;

[0039] Figure 2 This is a schematic diagram of the process steps for applying alternating current to the lithium battery in the low-temperature charging method of the lithium battery in this application.

[0040] Figure 3 A schematic diagram of the process steps for AC / DC superposition charging in the low-temperature charging method for lithium batteries of this application;

[0041] Figure 4 A schematic diagram of the process steps for deriving the target DC current in the low-temperature charging method of the lithium battery in this application;

[0042] Figure 5 This is a schematic diagram of the process steps for terminating the low-temperature charging mode in the low-temperature charging method for lithium batteries of this application.

[0043] Figure 6This is a schematic diagram of the process steps for forming the first temperature threshold and the second temperature threshold in the low-temperature charging method for lithium batteries of this application.

[0044] Figure 7 This is a functional structure diagram of the low-temperature charging system for the lithium battery of this application. Detailed Implementation

[0045] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0046] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0047] like Figure 1 As shown, this application provides a low-temperature charging method for lithium batteries, the low-temperature charging method comprising:

[0048] Step S10: In the charging state, the current temperature and voltage of the lithium battery are collected in real time; when the lithium battery is connected to the charging device and is in the charging state, the current temperature and voltage data of the lithium battery are continuously collected through temperature sensors, voltage detection elements and other related devices to ensure the continuity and accuracy of data collection.

[0049] Step S20: If the current temperature is less than a preset first temperature threshold, enter the low-temperature charging mode; if the current temperature is greater than or equal to the first temperature threshold, enter the conventional constant-voltage charging mode. The first temperature threshold is generally set to 0℃. 0℃ is the critical temperature at which the electrochemical performance of lithium batteries undergoes significant changes. Below 0℃, the lithium-ion migration rate slows down significantly, the internal resistance increases sharply, the efficiency of conventional constant-voltage charging decreases drastically, and lithium deposition is easy. In addition, the first temperature threshold can also be adjusted according to different batteries. For example, lithium iron phosphate batteries have slightly poor low-temperature performance and can be lowered to -2℃ or -5℃, while ternary lithium batteries have slightly better low-temperature adaptability and can be raised to 2℃ or 5℃. After obtaining the current temperature data of the lithium battery, it is compared with the preset first temperature threshold. When the current temperature is lower than the first temperature threshold, it indicates that the battery is in a low-temperature environment, and the conventional charging mode cannot balance efficiency and safety, so switch to the low-temperature charging mode; if the current temperature reaches or exceeds the first temperature threshold, it indicates that the ambient temperature of the battery is suitable, and there is no need to adopt a low-temperature charging strategy. Directly adopt the conventional constant-voltage charging mode to ensure the stability of the charging process and the charging efficiency under normal conditions.

[0050] The low-temperature charging mode is suitable for low-temperature environments where the current temperature is below the first temperature threshold. It further distinguishes between extremely low-temperature and general low-temperature scenarios by using a second temperature threshold. In extremely low-temperature environments, it queries a preset voltage-temperature relationship table based on the current voltage to charge with an appropriate initial AC amplitude and frequency. In this application, AC and DC superposition charging is used in low-temperature environments. Temperature, voltage, and AC impedance need to be monitored in real time and parameters dynamically adjusted throughout the process. The conventional constant-voltage charging mode is suitable for conventional environments where the current temperature is greater than or equal to the first temperature threshold. It does not require superposition of AC power or complex parameter adjustments. It completes charging with a constant voltage output, providing stable energy replenishment and avoiding overcharging in conventional scenarios. The two modes can be switched between each other according to changes in temperature and voltage.

[0051] Step S30: In low-temperature charging mode, compare the current temperature with a preset second temperature threshold, where the second temperature threshold is lower than the first temperature threshold. The second temperature threshold is generally set to -10℃. Below -10℃ is considered an extremely low-temperature environment, where the battery's internal resistance is extremely high and the risk of lithium plating is extremely high. Therefore, AC power is prioritized for heating, rather than DC power charging. Furthermore, to match the low-temperature limits of different usage scenarios, the size of the second temperature threshold can be adjusted. For example, batteries for high-latitude outdoor equipment can be lowered to -12℃, while indoor backup energy storage batteries can be raised to -8℃, thus better reflecting actual operating conditions. After entering low-temperature charging mode, the current temperature of the lithium battery is further analyzed and compared with the second temperature threshold to determine the specific low-temperature range in which the battery is located. This ensures that an appropriate charging strategy can be adopted in different low-temperature scenarios, avoiding the inability of a single low-temperature charging method to adapt to the entire low-temperature range.

[0052] Step S40: If the current temperature is lower than the second temperature threshold, a preset voltage-temperature relationship table is consulted based on the current voltage to obtain the initial AC amplitude and frequency that match the current voltage. The lithium battery is then charged according to the initial AC amplitude and frequency. When the current temperature is lower than the second temperature threshold, the appropriate AC current is used to achieve heating and initial charging. Based on the collected current voltage data, a preset voltage-temperature relationship table is consulted to select the initial AC amplitude and frequency that match the current voltage. AC current is applied to the lithium battery according to these two parameters. The AC current generates heat under the battery's internal resistance to raise the battery temperature. If the voltage at the positive terminal of the battery is relatively high when the AC current is connected, initial charging can also be performed simultaneously. This relatively high voltage can also be obtained from the voltage-temperature relationship table, such as 3.7V for the lithium battery.

[0053] Step S50: If the current temperature is greater than or equal to the second temperature threshold, then AC / DC superimposed charging is performed. If the current temperature is greater than or equal to the second temperature threshold, it indicates that the battery temperature has reached a certain level through prior adjustments or its own characteristics, meeting the conditions for superimposed DC charging. In this case, an AC / DC superimposed charging method is used. The AC power continuously maintains the battery temperature and reduces internal resistance, while the DC power undertakes the main charging task. The two work together to reduce the risk of lithium plating on the negative electrode while significantly improving charging efficiency and shortening charging time in low-temperature environments.

[0054] In this embodiment, by real-time acquisition of the current temperature and voltage of the lithium battery, the low-temperature charging mode and the conventional constant-voltage charging mode are switched according to whether the temperature is lower than a first temperature threshold. In the low-temperature charging mode, the charging method is further distinguished according to a second temperature threshold. When the temperature is lower than the second temperature threshold, the initial AC parameters are matched with the current voltage. When the temperature is higher than or equal to the second temperature threshold, AC and DC superposition charging is used to improve the lithium-ion migration rate of the lithium battery in low-temperature environment. At the same time, by selecting adaptive charging parameters, the phenomenon of lithium plating on the negative electrode is reduced, and the safety hazards such as battery capacity decay, shortened cycle life and thermal runaway are reduced. This achieves improved lithium battery charging efficiency and improved safety in low-temperature environment.

[0055] In one embodiment of this application, before the step of querying a preset voltage-temperature relationship table based on the current voltage, the following steps are included:

[0056] Step S01: Provide the internal resistance temperature coefficient, lithium-ion diffusion coefficient, and critical current density for lithium plating at the negative electrode to the electrochemical model. Simulate and construct a voltage-temperature relationship table, which stores the allowable AC parameters for the lithium battery under different temperature and voltage ranges. These AC parameters include AC amplitude and frequency. Before performing low-temperature charging, input the key parameters—internal resistance temperature coefficient, lithium-ion diffusion coefficient, and critical current density for lithium plating at the negative electrode—into the electrochemical model. Through electrochemical model simulation, simulate the working state of the lithium battery under different temperature and voltage ranges, and screen out the safe AC parameters that ensure charging performance in each range. These parameters include AC amplitude and frequency. Organize these verified parameters according to their corresponding temperature and voltage ranges to construct the voltage-temperature relationship table.

[0057] The electrochemical model in this application integrates the lithium-ion migration rate model, internal resistance temperature correlation function, lithium plating risk judgment function, temperature rise rate control function, and charging parameter optimization function. It inputs inherent parameters such as the internal resistance temperature coefficient of the lithium battery, the lithium-ion diffusion coefficient, and the critical current density for lithium plating at the negative electrode, and combines them with operating parameters such as ambient temperature and real-time battery temperature and pressure to construct a voltage-temperature relationship table.

[0058] The lithium-ion migration rate model is as follows: , k1 represents the migration rate of lithium ions in the battery electrode material; k1 is a proportionality constant determined by the characteristics of the battery electrode material. ΔU is the lithium-ion diffusion coefficient, reflecting the diffusion ability of lithium ions in the electrode material; ΔU is the voltage difference between the positive and negative electrodes of the battery, driving lithium-ion migration; d is the thickness of the electrode material, affecting the path length of lithium-ion migration; Ea is the activation energy of lithium-ion migration, which requires higher energy at low temperatures to drive lithium-ion migration; R is the gas constant, a fixed value, approximately 8.314 J / (mol・K); T is the absolute temperature of the battery (in K).

[0059] The internal resistance temperature correlation function is R(T) represents the battery internal resistance at temperature T; R0 is the initial internal resistance of the battery at the reference temperature T0; α T It is the internal resistance temperature coefficient, which reflects the proportion of change in internal resistance when the temperature changes by 1°C; T is the current actual temperature of the battery (in °C); T0 is the set reference temperature (usually 25°C).

[0060] The lithium plating risk assessment function is: J Li Represents the lithium plating risk coefficient, if J Li If J > 0, there is a risk of lithium plating; if J Li ≤0 indicates no risk of lithium plating; k2 is a correction factor determined by the characteristics of the battery negative electrode material; I is the charging current; A is the effective reaction area of ​​the battery negative electrode; J lim (T,U) is the critical current density for lithium plating.

[0061] Temperature rise rate control function:

[0062] dT represents the rate of temperature rise of the battery (unit: °C / min); k3 is the heat generation coefficient, which is related to the thermal conductivity of the battery; I is the charging current; R(T) is the internal resistance of the battery at the current temperature; k3·I 2 R(T): Represents the Joule heat generated by the current passing through the internal resistance during charging; k4 is the heat dissipation coefficient, which is related to the heat dissipation conditions of the charging environment; T is the current battery temperature; T env It refers to the ambient temperature.

[0063] Charging parameter optimization function:

[0064] argmin: means "find the parameter that minimizes the value of the function within the parentheses"; This represents the deviation between the rate of temperature increase and the safety threshold; the smaller the deviation, the more precise the temperature control. This represents the actual rate of temperature increase of the battery during charging. This represents the maximum permissible safe rate of temperature rise during charging; λ is a weighting coefficient, adjusted according to battery characteristics, typically taken as 0.5-1; abs(J Li The value represents the absolute value of the lithium plating risk coefficient; the smaller the value, the lower the risk of lithium plating.

[0065] like Figure 2 As shown, the steps of applying AC current to the lithium battery based on the initial AC current amplitude and the initial AC current frequency include:

[0066] Step S410: Continuously record the real-time temperature and voltage of the lithium battery according to a preset first time interval. The first time interval is generally set to 1-10 seconds; for example, it can be set to 2 seconds for lithium batteries in small portable electronic devices and 5 seconds for lithium batteries in new energy vehicles. During the initial AC charging process, the real-time temperature and voltage data of the battery are recorded uninterruptedly according to the preset first time interval. The recording process maintains continuity and accuracy, comprehensively capturing the dynamic changes in the battery state during charging and providing complete and reliable data. The electrochemical model is a mathematical model built based on the internal electrochemical reaction mechanism of the lithium battery. It mainly simulates the electrochemical behavior of the battery under different temperature, voltage, and current conditions by quantifying key physicochemical parameters of the battery, such as the internal resistance temperature coefficient, lithium-ion diffusion coefficient, and critical current density for lithium deposition at the negative electrode.

[0067] Step S420: Monitor the real-time maximum voltage of the lithium battery. If the real-time maximum voltage exceeds a preset first voltage threshold and the duration exceeds a preset second time, reduce the currently applied AC current amplitude to a specified proportion of the initial AC current amplitude. The first voltage threshold can be set according to the lithium battery. Taking a 3.7V nominal voltage lithium battery as an example, the first voltage threshold can be set to 4.0V to reduce damage to the battery due to excessive voltage during charging. The second time is set to 5-30 seconds, for example, 10 seconds, to ensure that the voltage exceeding the threshold is a stable state rather than an instantaneous fluctuation, avoiding incorrect adjustment of charging parameters. The specified proportion is usually set to 70%~90%, for example, 80%. When the voltage exceeds the threshold and the duration meets the standard, the initial AC current amplitude is reduced to 80%, which reduces safety risks without affecting charging efficiency. While continuously recording real-time battery data, the focus is on monitoring changes in the real-time maximum voltage. When the real-time maximum voltage value is detected to exceed the preset first voltage threshold, and the duration of the over-threshold state is greater than the preset second time, it indicates that the current applied AC voltage amplitude exceeds the battery's current tolerance range. The current AC voltage amplitude is then adjusted to a specified proportion of the initial AC voltage amplitude to reduce the damage to the battery caused by excessively high voltage.

[0068] In step S430, if the real-time maximum voltage is less than or equal to the first voltage threshold, or the duration of the voltage exceeding the first voltage threshold is less than the second time, then continue charging the lithium battery according to the initial AC amplitude and initial AC frequency. If the monitoring results show that the real-time maximum voltage is less than the first voltage threshold, or although it exceeds the first voltage threshold, the duration does not reach the second time, it indicates that the currently applied initial AC amplitude and frequency are compatible with the current state of the battery and will not cause safety risks. At this time, there is no need to adjust the charging parameters, and continue charging the lithium battery according to the original initial AC amplitude and initial AC frequency to ensure stable progress of the charging process.

[0069] like Figure 3 As shown, the steps for performing AC / DC superposition charging include:

[0070] Step S510: Based on the current temperature and voltage, consult the voltage-temperature relationship table to obtain the target AC amplitude, target AC frequency, and target DC magnitude that are compatible with the current temperature and voltage. After entering the AC / DC superposition charging stage, combine the continuously collected current temperature and voltage data of the lithium battery and perform a precise query in the preset voltage-temperature relationship table. Directly obtain the corresponding target AC amplitude, target AC frequency, and target DC magnitude to ensure that the selected parameters not only conform to the current operating conditions of the battery but also avoid the risk of lithium plating and ensure charging efficiency.

[0071] Step S520: Power is supplied to the lithium battery according to the target AC amplitude, target AC frequency, and target DC magnitude, and the power supply is maintained for at least a preset third duration. The third duration is set to 5-15 minutes, for example, 8 minutes, to ensure that the AC and DC superposition charging can fully utilize the heating and charging effects and avoid frequent switching of charging states. After determining the target AC amplitude, target AC frequency, and target DC magnitude, AC and DC currents are applied to the lithium battery simultaneously according to these three sets of parameters. During the charging process, the stability of the power supply must be ensured, and the power supply duration must not be less than the preset third duration. Through the continuous synergistic effect of AC and DC currents, a suitable battery temperature is maintained, internal resistance is reduced, and the charge is efficiently replenished, achieving a balance between safety and efficiency in low-temperature environments.

[0072] like Figure 4 As shown, before the step of querying the voltage-temperature relationship table based on the current temperature and current voltage, the following steps are included:

[0073] Step S501 establishes constraints based on the premise that the temperature rise rate during lithium battery charging is less than a specified rate and there is no risk of lithium plating. Before constructing the relevant data for the target DC current in the voltage-temperature relationship table, two constraints are defined: First, the temperature rise rate during lithium battery charging is limited to ensure it does not exceed a specified rate, preventing rapid temperature increases from damaging the battery structure and performance. The specified rate is generally between 0.1℃ / min and 0.5℃ / min. Second, the risk of lithium plating at the negative electrode is strictly avoided to prevent lithium plating from causing battery capacity decay, shortening cycle life, or even safety hazards. These two requirements are integrated into a unified constraint, defining a safety boundary for simulation calculations.

[0074] Step S502: Based on the constraints, the target DC current magnitude is obtained through simulation and recorded in the voltage-temperature relationship table. The constraints are then substituted into a preset electrochemical model for simulation calculation. The impact of the DC current magnitude on battery temperature changes and lithium plating risk under different operating conditions is simulated, and the target DC current magnitude that satisfies both the temperature rise rate requirement and reduces lithium plating is selected. The target DC current magnitudes verified by simulation are then categorized into corresponding temperature and voltage ranges and recorded in the voltage-temperature relationship table.

[0075] like Figure 5 As shown, after the step of continuously supplying power according to the preset third duration, the process includes:

[0076] Step S530: Determine if the current voltage is greater than a preset second voltage threshold, and obtain the current DC current, determining if the current DC current is lower than a preset first current threshold. The second voltage threshold is usually set to a value close to the battery's full charge voltage. For a 3.7V lithium battery, the second voltage threshold can be set to 4.2V, serving as the voltage judgment standard for switching to the conventional constant voltage charging mode. After completing the AC / DC superimposed power supply for a preset third duration, two key judgments are performed simultaneously: first, detect the current voltage of the lithium battery and determine if it exceeds the preset second voltage threshold; second, obtain the current DC current value applied to the battery and determine if this value is lower than the preset first current threshold. Through these two judgments, the charging state and charge saturation level of the lithium battery are determined. The first current threshold is a key parameter for determining whether the AC / DC superimposed charging has reached the switching condition, and is usually set to 0.05C-0.1C (C is the battery's rated capacity). For example, for a lithium battery with a rated capacity of 20Ah, the first current threshold can be set to 1A (0.05C) or 2A (0.1C).

[0077] Step S531: If all conditions are met, terminate the low-temperature charging mode and switch to the regular constant-voltage charging mode. If the current voltage exceeds the second voltage threshold and the current DC current is lower than the first current threshold, it indicates that the battery has approached or reached the ideal charging state, and there is no need to continue using the low-temperature charging mode. Terminate the operation of the low-temperature charging mode and switch to the regular constant-voltage charging mode to complete the subsequent charging process in a stable and safe manner, ensuring the stability of battery charging.

[0078] Step S532: If at least one condition is not met, the AC / DC superposition charging process is restarted. If the current voltage is less than the second voltage threshold or the current DC current is greater than the first current threshold, it indicates that the battery has not yet reached a suitable charging state, and the AC / DC superposition charging method must be maintained to continuously replenish the battery's power.

[0079] In one embodiment of this application, under the conventional constant-voltage charging mode, if the current temperature of the lithium battery is detected to be lower than a first temperature threshold and the current voltage is detected to be lower than a second voltage threshold again within a specified time, the low-temperature charging mode is automatically restarted. The specified time is generally set to 3-10 minutes, for example, 5 minutes, to promptly respond to abnormal drops in battery temperature and voltage and ensure charging continuity. Even after switching to conventional constant-voltage charging, the temperature and voltage status of the lithium battery still need to be continuously monitored. If, within a preset specified time, the current battery temperature is detected to drop below the first temperature threshold and the current voltage is also lower than the second voltage threshold, it indicates that the battery is again in a special low-temperature, low-voltage condition, and the conventional constant-voltage charging mode can no longer guarantee charging efficiency and safety. At this time, the low-temperature charging mode is automatically restarted, and the battery continues to be charged through an adapted low-temperature charging strategy to ensure the safety and efficiency of the entire charging process.

[0080] like Figure 6 As shown, before the step of real-time acquisition of the current temperature and voltage of the lithium battery during charging, the following steps are included:

[0081] Step S11: Set the first initial threshold and the second initial threshold. Before starting the low-temperature charging process for lithium batteries, two basic temperature judgment criteria must be defined, namely, setting the first initial threshold and the second initial threshold. These two initial thresholds are the benchmarks for dividing charging modes and subdividing low-temperature ranges, ensuring that there is a clear initial reference basis for switching charging modes.

[0082] Step S12: Based on the type of lithium battery and the usage scenario, the first initial threshold is fine-tuned by ±3℃ to obtain the first temperature threshold, and the second initial threshold is fine-tuned by ±3℃ to obtain the second temperature threshold. Different types of lithium batteries have different electrochemical characteristics, and their application scenarios, charging environments, and requirements vary, such as new energy vehicles, portable electronic terminals, and energy storage devices. The preset first and second initial thresholds are fine-tuned according to the specific battery type and usage scenario. Specifically, the first initial threshold can be adjusted by ±3℃ from its original value to determine the first temperature threshold; the second initial threshold is also fine-tuned by ±3℃ to obtain the second temperature threshold. The first and second temperature thresholds better reflect actual operating conditions, ensuring the accuracy of charging mode switching.

[0083] In one embodiment of this application, the step of charging the lithium battery based on the initial AC amplitude and the initial AC frequency further includes:

[0084] Step S401: Monitor the AC impedance of the lithium battery in real time. If the sudden change in AC impedance exceeds a set percentage, stop applying AC power and determine whether to perform AC / DC superimposed charging based on the current temperature and voltage. The set percentage is generally set between 20% and 50%, for example, 30%. When the detected sudden change in AC impedance exceeds 30%, it is determined that there may be an abnormality inside the battery, and the application of AC power is stopped immediately. During the charging process of the lithium battery with the initial AC power parameters, monitor the changes in the battery's AC impedance in real time. If the detected sudden change in AC impedance exceeds the preset set percentage, it indicates that there may be an abnormal condition inside the battery, such as increased local polarization or potential lithium plating risk. The application of AC power must be stopped immediately to avoid safety hazards. Combine the currently collected battery temperature and voltage data for comprehensive judgment to determine whether the conditions for switching to AC / DC superimposed charging are met, ensuring that the subsequent charging process always conforms to the actual state of the battery and ensures charging safety.

[0085] like Figure 7 As shown, this application also provides a low-temperature charging system for lithium batteries, which includes: a data acquisition module 10, a judgment module 20, and a low-temperature charging module 30.

[0086] The data acquisition module 10 is used to collect the current temperature and voltage of the lithium battery in real time during charging. When the battery is connected to the charging device and is charging, the acquisition module 10 continuously and accurately collects the current temperature and voltage data of the lithium battery through its built-in temperature sensing element and voltage detection component. The acquisition process must ensure continuity and data accuracy, and provide real-time feedback on the dynamic operating condition of the battery, providing reliable basic data support for the mode switching decision of the subsequent judgment module 20 and the charging parameter adaptation of the low-temperature charging module 30.

[0087] The judgment module 20 is used to enter a low-temperature charging mode if the current temperature is lower than a preset first temperature threshold, and to enter a normal constant-voltage charging mode if the current temperature is greater than or equal to the first temperature threshold. The judgment module 20 compares and analyzes the current temperature data of the lithium battery transmitted by the acquisition module 10 with the preset first temperature threshold. When it is determined that the current temperature is lower than the first temperature threshold, it indicates that the battery is in a low-temperature environment, and the normal charging mode is difficult to balance efficiency and safety, triggering an instruction to enter the low-temperature charging mode; if the current temperature is greater than or equal to the first temperature threshold, it indicates that the ambient temperature of the battery is suitable, and there is no need to activate the low-temperature charging strategy, directly entering the normal constant-voltage charging mode to ensure the stability and efficiency of the charging process in normal scenarios.

[0088] The low-temperature charging module 30 is used in low-temperature charging mode to compare the current temperature with a preset second temperature threshold, where the second temperature threshold is less than a first temperature threshold. If the current temperature is less than the second temperature threshold, it queries a preset voltage-temperature relationship table based on the current voltage to obtain the initial AC amplitude and frequency suitable for the current voltage, and charges the lithium battery according to the initial AC amplitude and frequency. If the current temperature is greater than or equal to the second temperature threshold, it performs AC / DC superposition charging. In low-temperature charging mode, the low-temperature charging module 30 compares the current temperature obtained by the acquisition module with the preset second temperature threshold. When the current temperature is less than the second temperature threshold, it queries a preset voltage-temperature relationship table based on the current battery voltage to select the initial AC amplitude and frequency suitable for it, and applies AC with these parameters to the lithium battery to achieve coordinated heating and charging. If the current temperature is greater than or equal to the second temperature threshold, it switches to AC / DC superposition charging, using AC to maintain the battery temperature and reduce internal resistance, while using DC to perform the main charging task, reducing the risk of lithium plating and significantly improving charging efficiency in low-temperature environments.

[0089] The implementation method of the low-temperature charging system for lithium batteries in this application refers to the low-temperature charging method for lithium batteries described above, and will not be repeated here.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A low-temperature charging method for lithium batteries, characterized in that, The low-temperature charging method includes: During charging, the current temperature and voltage of the lithium battery are collected in real time. If the current temperature is less than a preset first temperature threshold, then enter the low temperature charging mode; if the current temperature is greater than or equal to the first temperature threshold, then enter the normal constant voltage charging mode. In the low-temperature charging mode, the current temperature is compared with a preset second temperature threshold, wherein the second temperature threshold is less than the first temperature threshold; If the current temperature is less than the second temperature threshold, then the preset voltage-temperature relationship table is consulted according to the current voltage to obtain the initial AC amplitude and initial AC frequency that are compatible with the current voltage, and the lithium battery is charged according to the initial AC amplitude and the initial AC frequency. If the current temperature is greater than or equal to the second temperature threshold, then AC / DC superposition charging is performed.

2. The low-temperature charging method according to claim 1, characterized in that, Before the step of querying the preset voltage-temperature relationship table based on the current voltage, the following steps are included: The internal resistance temperature coefficient, lithium-ion diffusion coefficient, and critical current density for lithium plating at the negative electrode of the lithium battery are provided to the electrochemical model. The simulation constructs a voltage-temperature relationship table, which stores the AC parameters that the lithium battery can be applied to under different temperature ranges and different voltage ranges. The AC parameters include AC amplitude and AC frequency.

3. The low-temperature charging method according to claim 1, characterized in that, The step of applying alternating current to the lithium battery based on the initial alternating current amplitude and the initial alternating current frequency includes: The real-time temperature and real-time voltage of the lithium battery are continuously recorded according to a preset first time interval. Monitor the real-time maximum voltage of the lithium battery. If the real-time maximum voltage is greater than a preset first voltage threshold and the duration is greater than a preset second time, then reduce the currently applied AC voltage amplitude to a predetermined proportion of the initial AC voltage amplitude. If the real-time voltage maximum value is less than or equal to the first voltage threshold, or the duration of the voltage being greater than the first voltage threshold is less than the second time, then the lithium battery continues to be charged according to the initial AC amplitude and the initial AC frequency.

4. The low-temperature charging method according to claim 1, characterized in that, The steps for performing AC / DC superposition charging include: Based on the current temperature and the current voltage, the voltage-temperature relationship table is queried to obtain the target AC amplitude, target AC frequency and target DC magnitude that are compatible with the current temperature and current voltage; The lithium battery is powered according to the target AC amplitude, the target AC frequency, and the target DC magnitude, and the power supply continues for at least a preset third duration.

5. The low-temperature charging method according to claim 4, characterized in that, Before the step of querying the voltage-temperature relationship table based on the current temperature and the current voltage, the following steps are included: The constraints are established based on the condition that the rate of temperature rise during lithium battery charging is less than a specified rate and there is no risk of lithium plating. The target DC current magnitude is obtained through simulation based on the aforementioned constraints and recorded in the voltage-temperature relationship table.

6. The low-temperature charging method according to claim 4, characterized in that, After the step of continuously supplying power according to the preset third duration includes: Determine whether the current voltage is greater than a preset second voltage threshold, and obtain the current DC current, and determine whether the current DC current is lower than a preset first current threshold; If all conditions are met, the low-temperature charging mode is terminated and the system is switched to the conventional constant-voltage charging mode. If at least one condition is not met, the AC / DC superposition charging process will be repeated.

7. The low-temperature charging method according to claim 6, characterized in that, In the conventional constant voltage charging mode, if the current temperature of the lithium battery is found to be lower than the first temperature threshold and the current voltage is lower than the second voltage threshold again within a specified time, the low temperature charging mode will be automatically restarted.

8. The low-temperature charging method according to claim 1, characterized in that, Before the step of real-time acquisition of the current temperature and voltage of the lithium battery during charging, the following steps are included: Set a first initial threshold and a second initial threshold; Based on the type of lithium battery and the usage scenario, the first initial threshold is fine-tuned by ±3℃ to obtain the first temperature threshold, and the second initial threshold is fine-tuned by ±3℃ to obtain the second temperature threshold.

9. The low-temperature charging method according to claim 1, characterized in that, The step of charging the lithium battery according to the initial AC amplitude and the initial AC frequency includes: The alternating current impedance of the lithium battery is monitored in real time. If the sudden change in the alternating current impedance is greater than a set ratio, the alternating current is stopped, and the current temperature and voltage are used to determine whether to perform AC and DC superposition charging.

10. A low-temperature charging system for a lithium battery, characterized in that, The cryogenic charging system includes: The data acquisition module is used to collect the current temperature and voltage of the lithium battery in real time during charging. The judgment module is used to enter a low-temperature charging mode if the current temperature is less than a preset first temperature threshold, and to enter a normal constant voltage charging mode if the current temperature is greater than or equal to the first temperature threshold. A low-temperature charging module is used in the low-temperature charging mode to compare the current temperature with a preset second temperature threshold, wherein the second temperature threshold is less than the first temperature threshold; if the current temperature is less than the second temperature threshold, it queries a preset voltage-temperature relationship table based on the current voltage to obtain an initial AC amplitude and an initial AC frequency adapted to the current voltage, and charges the lithium battery according to the initial AC amplitude and the initial AC frequency; if the current temperature is greater than or equal to the second temperature threshold, it performs AC and DC superposition charging.

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