A charging and discharging control method for fast-charging lithium ion batteries
By monitoring the battery's internal resistance and polarization index in real time and dynamically adjusting the timing of charge and discharge switching, an adaptive pulse charge and discharge strategy is adopted to solve the problems of low charging efficiency and short lifespan in fast-charging lithium-ion batteries, achieving efficient and safe charge and discharge control.
Patent Information
- Application Number
- CN202611154948.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-31
- Publication Date
- 2026-11-03
AI Technical Summary
Existing fast-charging lithium-ion battery charging and discharging control methods fail to dynamically adjust according to the battery's real-time polarization state and aging degree, resulting in decreased charging efficiency, excessive battery temperature rise, and shortened cycle life.
By monitoring the battery's internal resistance and polarization index in real time, the timing of charge and discharge switching is dynamically adjusted. An adaptive pulse charge and discharge strategy is adopted, including standard and protective discharge pulse strategies. Combined with temperature rise rate correction and closed-loop adaptive adjustment, the sufficiency of polarization elimination and thermal safety are ensured.
It effectively suppresses polarization accumulation and temperature rise, extends battery cycle life, improves charging efficiency, and ensures long-term battery control accuracy and safety.
Smart Images
Figure CN123034589A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery management and control technology, specifically to a charging and discharging control method for fast-charging lithium-ion batteries. Background Technology
[0002] Fast-charging lithium-ion batteries refer to lithium-ion batteries with a high charging rate, which rely on the movement of lithium ions between the positive and negative electrodes to function. During high-rate fast charging, the rapid migration of lithium ions can easily cause concentration polarization and electrochemical polarization at the electrode interface. Accumulated polarization can cause the terminal voltage to reach the cutoff voltage earlier, shorten the constant current charging time, and even induce lithium plating at the negative electrode and thermal runaway.
[0003] Currently, alternating charge-discharge pulse charging is often used to alleviate polarization. However, existing pulse switching relies on fixed time control, which cannot adapt to the characteristic evolution of the battery throughout its entire life cycle: new batteries have low polarization internal resistance, and fixed charging time can easily reduce charging efficiency; aged batteries accumulate polarization quickly and dissipate slowly, and fixed time can lead to incomplete polarization elimination, exacerbating the risk of lithium plating.
[0004] Therefore, there is a need in the field for a control method that can dynamically adjust the timing of charge-discharge switching based on the real-time polarization state and aging degree of the battery. Summary of the Invention
[0005] To address this issue, the present invention provides a charging and discharging control method for fast-charging lithium-ion batteries. This method overcomes the problem in the prior art where the switching timing between the charging and discharging pulse stages in pulse-type fast charging is determined solely based on a fixed time or voltage, without considering the coupling effect of the battery's real-time polarization accumulation and aging state. This results in untimely polarization elimination during charging, a mismatch between the timing of the charging and discharging stage switching and the actual polarization state of the battery, leading to decreased charging efficiency, excessive battery temperature rise, and shortened cycle life, thus causing poor charging and discharging efficiency of fast-charging lithium-ion batteries.
[0006] To achieve the above objectives, the present invention provides a charging and discharging control method for fast-charging lithium-ion batteries, comprising: before the start of the current charging stage of pulse fast charging, acquiring the current internal resistance of the battery, and determining the internal resistance change rate based on the current internal resistance and the calibrated internal resistance of the battery; and determining the polarization fluctuation grade value of the current charging stage based on the internal resistance change rate. During the current charging phase, the polarization fluctuation ratio is calculated based on the polarization index rise rate and the polarization index fall rate, and the polarization fluctuation limit value is determined based on the polarization fluctuation ratio and the polarization fluctuation classification value. The polarization recovery requirement level is determined based on the polarization fluctuation exceeding the limit. The polarization recovery requirement levels include a low level that does not trigger a handover, a medium level that triggers a standard handover, and a high level that triggers an early handover. In response to the polarization recovery requirement level being medium or high, a discharge pulse switching strategy is determined based on the polarization rate reduction attenuation; the discharge pulse switching strategy includes a standard discharge pulse strategy and a protective discharge pulse strategy. Before executing the discharge pulse switching strategy, the battery temperature rise rate is obtained, and the discharge pulse switching strategy is modified according to the temperature rise rate. After the current discharge pulse phase ends, the polarization fluctuation grading value for the next charging phase is adjusted according to the rate of decrease of the polarization index.
[0007] By employing the above technical solution, this invention obtains the current internal resistance of the battery, calculates the rate of change of internal resistance, and adaptively calibrates the polarization fluctuation classification value based on the aging state. This allows new batteries, moderately aged batteries, and severely aged batteries to each correspond to different switching thresholds, solving the problem that fixed switching strategies cannot adapt to the changes in polarization characteristics throughout the battery's life cycle. Furthermore, by calculating the polarization fluctuation ratio in real time during the current charging stage and comparing it with the classification value calibrated by the aging state, the switching timing during the charging and discharging stages can be adaptively adjusted according to the actual polarization state of the battery. This avoids the untimely polarization elimination caused by fixed-time switching. At the same time, the invention achieves the goal of adapting to the changes in polarization characteristics throughout the battery's life cycle by determining the low, medium, and high polarization recovery demand levels based on the polarization fluctuation exceeding the limit value. The graded response to the same degree of polarization accumulation ensures sufficient polarization elimination while maintaining charging efficiency. The degree of degradation of discharge recovery capability is assessed by the polarization decay rate. During degradation, protective strategies such as extending discharge time and reducing charging current are adopted to compensate for the decline in polarization recovery capability of aging batteries. Combined with the temperature rise rate correction before the strategy is implemented, the thermal safety risk is controlled within an acceptable range. After the discharge pulse ends, the graded value is adjusted in a closed loop according to the polarization index decrease rate to ensure long-term stable control accuracy. Thus, this invention realizes dynamic adaptive adjustment of battery polarization state and aging degree, effectively suppressing polarization accumulation and temperature rise while ensuring charging efficiency, and extending battery cycle life. Attached Figure Description
[0008] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments.
[0009] Figure 1 This is a flowchart of a charging and discharging control method for a fast-charging lithium-ion battery according to an embodiment of the present invention; Figure 2 This is a flowchart of the process for obtaining the polarization fluctuation ratio in an embodiment of the present invention; Figure 3 This is a comparison curve of the cycle life of the embodiments of the present invention with CC-CV charging and fixed-time pulse charging at 4C rate. Detailed Implementation
[0010] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0011] Example 1: Please see Figure 1 The charging and discharging control method for fast-charging lithium-ion batteries according to embodiments of the present invention includes: Before the current charging phase of pulse fast charging is started, the current internal resistance of the battery is obtained, and the rate of change of internal resistance is determined based on the current internal resistance and the calibrated internal resistance of the battery; the polarization fluctuation grade value of the current charging phase is determined based on the rate of change of internal resistance. During the current charging phase, the polarization fluctuation ratio is calculated based on the polarization index rise rate and the polarization index fall rate, and the polarization fluctuation limit value is determined based on the polarization fluctuation ratio and the polarization fluctuation classification value. The polarization recovery requirement level is determined based on the polarization fluctuation exceeding the limit. The polarization recovery requirement levels include a low level that does not trigger a handover, a medium level that triggers a standard handover, and a high level that triggers an early handover. In response to the polarization recovery requirement level being medium or high, a discharge pulse switching strategy is determined based on the polarization rate reduction attenuation; the discharge pulse switching strategy includes a standard discharge pulse strategy and a protective discharge pulse strategy. Before executing the discharge pulse switching strategy, the battery temperature rise rate is obtained, and the discharge pulse switching strategy is modified according to the temperature rise rate. After the current discharge pulse phase ends, the polarization fluctuation grading value for the next charging phase is adjusted according to the rate of decrease of the polarization index.
[0012] The test object used in this embodiment is an NCM523 / graphite ternary lithium-ion power battery with a rated capacity of 50Ah, a nominal voltage of 3.7V, a charging cut-off voltage of 4.2V, and a discharging cut-off voltage of 2.8V. The calibrated internal resistance was obtained through battery factory testing and recorded in the non-volatile memory of the BMS. The above control method is executed by the charge / discharge control module in the battery management system (BMS). The BMS collects the battery's terminal voltage, charge / discharge current, and surface temperature data in real time through voltage sensors, current sensors, and temperature sensors at a sampling frequency of no less than 100Hz. The charge / discharge control module runs on an embedded processor (such as an ARM Cortex-M4 or equivalent processor), and the control cycle is set to 10ms to meet the real-time control requirements during fast charging.
[0013] The polarization index is determined by the absolute value of the difference between the terminal voltage and the open-circuit voltage. The open-circuit voltage is obtained by looking up the OCV-SOC lookup table based on the current state of charge (SOC).
[0014] To verify the technical effectiveness of the method of the present invention, a cycle life comparison test was conducted between the method of the present invention and the CC-CV charging strategy and the fixed-time pulse charging strategy under the same conditions. The test conditions were: 4C rate charging (charging range from 20% SOC to 80% SOC), 1C rate discharging (discharging range from 80% SOC to 20% SOC), and an ambient temperature of 25±2℃. Three sets of parallel samples were used for each strategy.
[0015] like Figure 3 As shown, within the 1600-cycle test range, the capacity retention rates of the three strategies exhibited significant differences. The CC-CV strategy showed the fastest capacity retention rate decay, dropping below 80% after 850 cycles; the fixed-time pulse strategy showed the second fastest decay rate, dropping below 80% after 1050 cycles; the method of this invention showed the slowest capacity retention rate decay, maintaining above 80% after 1500 cycles. These results demonstrate that this invention, through dynamic control of polarization levels, effectively suppresses polarization accumulation and capacity decay during fast charging, extending cycle life by approximately 76% compared to the CC-CV strategy and approximately 43% compared to the fixed-time pulse strategy.
[0016] In summary, this embodiment constructs a pulse-type fast charging control method based on real-time polarization state monitoring and aging state adaptation. It achieves adaptive adjustment of the timing of switching between charging and discharging stages by dynamically comparing the polarization fluctuation ratio and the grade value. The multi-level response strategy and closed-loop update mechanism ensure that the control accuracy remains stable as the battery ages.
[0017] Example 2: Please see Figure 2 The embodiments of the present invention provide a detailed calculation process for the polarization fluctuation ratio: During the current charging phase, the terminal voltage of the battery is collected at multiple sampling times according to a preset sampling period, and the open-circuit voltage of the battery at each of the multiple sampling times is obtained. The polarization index of each of the multiple sampling times is determined based on the absolute value of the difference between the terminal voltage and the corresponding open-circuit voltage. Based on the polarization index at multiple sampling times and the corresponding sampling times, a polarization index change curve for the current charging stage is constructed and linearly fitted to obtain the polarization index rise rate for the current charging stage. Retrieve multiple historical polarization indices and corresponding historical sampling times from the previous discharge pulse phase; Based on the multiple historical polarization indices and their corresponding historical sampling times, a polarization index change curve for the previous discharge phase is constructed and linearly fitted to obtain the polarization index decrease rate for the previous discharge pulse phase. The ratio of the rate of increase of the polarization index during the current charging phase to the rate of decrease of the polarization index during the previous discharge pulse phase is denoted as the polarization fluctuation ratio.
[0018] The preset sampling period is set to 100ms, meaning the terminal voltage is sampled and the corresponding polarization index is calculated every 100ms. During the current charging phase, after continuously sampling the polarization index for at least 10 sampling moments, a least-squares linear fit is performed with the sampling moment as the x-axis and the polarization index as the y-axis. The slope of the fitted line is the rate of increase of the polarization index. If the correlation coefficient R... 2 If the value is below 0.85, the sampling window is extended to 20 sampling times before refitting to ensure fitting accuracy.
[0019] During the previous discharge pulse phase, the polarization index was collected at a sampling period of 100ms. After collecting at least 5 sampling times, the least squares linear fitting method was performed, and the absolute value of the slope of the fitted line was the rate of decrease of the polarization index.
[0020] If the current charge is the first charge or historical discharge pulse data has not yet been stored (cold start scenario), the preset initial polarization index decrease rate will be used as the polarization index decrease rate of the previous discharge pulse phase. The preset initial polarization index decrease rate is estimated based on the ratio of the battery's factory-calibrated DC internal resistance (DCIR) to the time constant τ, i.e., initial decrease rate ≈ DCIR / τ, where DCIR is obtained through battery factory testing, and τ is the time constant of the battery polarization process, typically taken as 1-3s.
[0021] Example 3: This invention provides a calibration process for polarization fluctuation classification values: If the rate of change of internal resistance is less than the first preset rate of change of internal resistance of 1.15, then the polarization fluctuation classification value is determined to be the first calibration value. If the rate of change of internal resistance is greater than or equal to the first preset rate of change of internal resistance and less than the second preset rate of change of internal resistance of 1.35, then the polarization fluctuation classification value is determined to be the second calibration value. If the rate of change of internal resistance is greater than or equal to the second preset rate of change of internal resistance, then the polarization fluctuation classification value is determined to be the third calibration value. Wherein, the first preset internal resistance change rate is less than the second preset internal resistance change rate; the first calibration value is greater than the second calibration value, and the second calibration value is greater than the third calibration value.
[0022] In this embodiment, the first preset internal resistance change rate is set to 1.15, and the second preset internal resistance change rate is set to 1.35; the first calibration value is set to 1.2 (corresponding to a new battery, SOH≥95%), the second calibration value is set to 1.0 (corresponding to a moderately aged battery, 80%≤SOH<95%), and the third calibration value is set to 0.8 (corresponding to a severely aged battery, SOH<80%). The internal resistance change rate is calculated by the ratio of the currently measured DCIR to the factory-calibrated DCIR. It should be noted that the above preset values are all results obtained through previous experimental verification of this invention. Each preset value can be adjusted according to the specific battery model and usage, as long as it satisfies the requirement that the method described in this invention can effectively calibrate the grading value through the internal resistance change rate.
[0023] If this is the first charge and the BMS has not yet stored polarization index data for historical discharge pulse phases, a cold start process is performed: First, the DCIR at the current battery temperature is measured. The internal resistance change rate is determined based on the ratio of DCIR to the calibrated DCIR, and the initial polarization fluctuation grade value is obtained by looking up a table. Simultaneously, the ratio of DCIR to τ is used as the preset initial polarization index decrease rate for calculating the polarization fluctuation ratio during the first charge phase. After the cold start is completed, subsequent charging cycles will retrieve historical data for calculations as normal.
[0024] Example 4: This invention provides a strategy for determining the polarization recovery requirement level and switching discharge pulses: If the polarization fluctuation limit is less than the preset polarization limit start threshold 0, then the polarization recovery demand level is determined to be low, the switching is not triggered, and the current charging phase continues. If the polarization fluctuation limit is greater than or equal to the preset polarization limit start threshold and less than the preset polarization limit upper threshold of 0.5, then the polarization recovery requirement level is determined to be medium level, and standard switching is triggered. If the polarization fluctuation limit is greater than or equal to the preset polarization limit threshold, the polarization recovery requirement level is determined to be high, triggering an early switch. Wherein, the polarization fluctuation limit value is the difference between the polarization fluctuation ratio and the polarization fluctuation grade value.
[0025] In this embodiment, the preset polarization over-limit start threshold is set to 0, and the preset polarization over-limit upper limit threshold is set to 0.5.
[0026] The standard switching is to switch to the discharge pulse stage after the current charging stage lasts for a first duration. The first duration is determined according to the polarization fluctuation limit value, and the rate of change of the first duration with the polarization fluctuation limit value is a first change slope. The early switching is to switch to the discharge pulse stage after the current charging stage lasts for a second duration, the second duration is determined according to the polarization fluctuation limit value, and the rate of change of the second duration with the polarization fluctuation limit value is the second change slope; The second duration is shorter than the first duration, and the absolute value of the second slope is greater than the absolute value of the first slope.
[0027] In this embodiment, the baseline value for the first duration is set to 8 seconds, and the first change slope is -4 seconds per unit exceeding the limit, meaning that for every 1 increase in the polarization fluctuation exceeding the limit, the first duration decreases by 4 seconds. The baseline value for the second duration is set to 6 seconds, and the second change slope is -8 seconds per unit exceeding the limit, meaning that for every 1 increase in the polarization fluctuation exceeding the limit, the second duration decreases by 8 seconds. The lower limit for the second duration is 3 seconds to avoid excessively frequent switching.
[0028] Example 5: This invention provides a process for determining a discharge pulse switching strategy based on the polarization rate reduction decay rate: If the polarization rate reduction decay rate is less than 20% of the preset aging threshold, it is determined that the discharge recovery capability of the battery has not significantly degraded, and a standard discharge pulse switching strategy is adopted. The standard discharge pulse switching strategy includes executing the discharge pulse phase for a preset standard duration. If the polarization rate reduction decay rate is greater than or equal to the preset aging threshold, it is determined that the battery's discharge recovery capability has degraded, and a protective discharge pulse switching strategy is adopted. The protective discharge pulse switching strategy includes extending the duration of the discharge pulse phase based on the preset standard duration, and reducing the charging current of the next charging phase by a preset number of levels. The extension of the duration is positively correlated with the difference between the polarization rate reduction decay rate and the preset aging threshold.
[0029] In this embodiment, the preset aging threshold is set to 20%. The polarization decay rate is calculated as (polarization index decrease rate in the previous discharge pulse phase - polarization index decrease rate in the current discharge pulse phase) / polarization index decrease rate in the previous discharge pulse phase × 100%.
[0030] In the standard discharge pulse strategy, the preset standard duration is set to 2 seconds, and the discharge current is -1.5C. It can be understood that the extension of the duration in the protective discharge pulse strategy is positively correlated with the difference between the polarization rate reduction decay rate and the preset aging threshold. The extension duration = standard duration × (1 + (polarization rate reduction decay rate - 20%) / 20%), meaning that when the decay rate is 40%, the extension duration is 3 seconds. The preset number of charging levels is 1, with each level reducing the charging current by 0.5C, meaning the next charging current will decrease from 4C to 3.5C.
[0031] The process of obtaining the polarization rate reduction decay rate includes: During the current discharge pulse phase, the terminal voltage of the battery is collected at multiple sampling times according to a preset sampling period of 100ms, and the open circuit voltage of the battery at each of the multiple sampling times is obtained. The polarization index of each of the multiple sampling times is determined based on the absolute value of the difference between the terminal voltage and the corresponding open-circuit voltage. Based on the polarization index at multiple sampling times and the corresponding sampling times, a polarization index change curve for the current discharge pulse stage is constructed. A linear fit is performed on the current discharge pulse stage polarization index change curve, the slope of the fitted curve is calculated, and the absolute value of the slope is determined as the polarization index decrease rate V for the current discharge pulse stage. current ; Retrieve multiple historical polarization indices and corresponding historical sampling times from the previous discharge pulse phase; Based on the multiple historical polarization indices and their corresponding historical sampling times, a polarization index change curve for the previous discharge pulse phase is constructed and linearly fitted. The slope of the fitted curve is calculated, and the absolute value of the slope is determined as the polarization index decrease rate V for the previous discharge pulse phase. last ; Polarization deceleration rate = (V last -V current ) / V last ×100%, where V last V represents the rate of decrease in polarization index during the previous discharge pulse phase. current This represents the rate of decrease in the polarization index during the current discharge pulse phase. It can be understood that a positive polarization rate decrease indicates a degradation in the polarization elimination capability of the current discharge pulse phase compared to the previous one; a negative polarization rate decrease indicates an improvement in the polarization elimination capability.
[0032] In this embodiment, the polarization rate reduction decay rate is calculated as follows: Assuming the polarization index decrease rate during the previous discharge pulse phase is 4.0 mΩ / s and the current discharge pulse phase has a polarization index decrease rate of 3.0 mΩ / s, then the polarization rate reduction decay rate = (4.0 - 3.0) / 4.0 × 100% = 25%. Since 25% is greater than the preset aging threshold of 20%, it is determined that the battery's discharge recovery capability has degraded. Therefore, a protective discharge pulse switching strategy is adopted, extending the preset standard duration from 2s to 3s and reducing the charging current of the next charging phase from 4C to 3.5C.
[0033] Example 6: This invention provides a temperature rise rate correction process: If the temperature rise rate is less than the first preset temperature rise threshold of 1℃ / s, the thermal safety state is determined to be normal, and the discharge pulse switching strategy is directly executed. If the temperature rise rate is greater than or equal to the first preset temperature rise threshold and less than the second preset temperature rise threshold of 3℃ / s, then the thermal safety state is determined to be too high, and the discharge pulse switching strategy is executed after reducing the charging current. If the temperature rise rate is greater than or equal to the second preset temperature rise threshold, the thermal safety state is determined to be a dangerous state, charging is stopped and heat dissipation is initiated.
[0034] In this embodiment, the temperature rise rate is calculated by the change in surface temperature within a 1-second time window. The first preset temperature rise threshold is set to 1°C / s, and the second preset temperature rise threshold is set to 3°C / s. When the temperature rise rate is greater than or equal to 1°C / s but less than 3°C / s, the charging current is reduced by one level (0.5C), and a discharge pulse switching strategy is executed. When the temperature rise rate is greater than or equal to 3°C / s, charging is immediately stopped and the cooling fan is started. Charging resumes after the temperature drops to a safe range.
[0035] Example 7: Based on Example 1, this embodiment of the invention provides a closed-loop adaptive update process: The absolute value of the difference between the current polarization index decrease rate during the discharge pulse phase and the previously recorded polarization index decrease rate is defined as the decrease rate deviation. If the deviation of the descent rate is less than the preset deviation threshold for a preset number of consecutive preset number of times, the polarization fluctuation classification value is not changed. If the descent rate deviation is greater than or equal to a preset deviation threshold for a consecutive preset number of times, the polarization fluctuation classification value is reduced according to the difference between the descent rate deviation and the preset deviation threshold.
[0036] In this embodiment, the preset number of times is set to 3, and the preset deviation threshold is set to 15% of the previously recorded polarization index decrease rate. When the decrease rate deviation is ≥15% for 3 consecutive times, the reduction in the polarization fluctuation grade value is = (decline rate deviation - 15%) × 0.01. The polarization fluctuation grade value after each adjustment is not lower than 80% of the third calibration value (0.8), i.e., 0.64, to prevent the polarization fluctuation grade value from being excessively downgraded, which would cause the switching to be too sensitive.
[0037] The retrieval of multiple historical polarization indices and corresponding historical sampling times within the previous discharge pulse phase includes: If the current charging cycle is the first charging cycle or there is no historical polarization index and corresponding historical sampling time stored for a historical discharge pulse phase, then no retrieval is performed. Instead, the preset initial polarization index decrease rate is used as the polarization index decrease rate for the previous discharge pulse phase. In this embodiment, the first charging cycle refers to the charging cycle after the BMS is powered on without storing any historical discharge pulse data. The preset initial polarization index decrease rate is determined according to the DCIR / τ estimation method described in Embodiment 2. For example, when the battery's factory DCIR is 1.75mΩ and τ is 2s, the preset initial polarization index decrease rate is 0.875mΩ / s.
[0038] If multiple historical polarization indices and corresponding historical sampling times from the previous discharge pulse phase are already stored, then the retrieval will be performed.
[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A charging and discharging control method for a fast-charging lithium-ion battery, characterized in that, Before the current charging phase of pulse fast charging is started, the current internal resistance of the battery is obtained, and the rate of change of internal resistance is determined based on the current internal resistance and the calibrated internal resistance of the battery; the polarization fluctuation grade value of the current charging phase is determined based on the rate of change of internal resistance. During the current charging phase, the polarization fluctuation ratio is calculated based on the polarization index rise rate and the polarization index fall rate, and the polarization fluctuation limit value is determined based on the polarization fluctuation ratio and the polarization fluctuation classification value. The polarization recovery requirement level is determined based on the polarization fluctuation exceeding the limit. The polarization recovery requirement levels include a low level that does not trigger a handover, a medium level that triggers a standard handover, and a high level that triggers an early handover. In response to the polarization recovery requirement level being medium or high, a discharge pulse switching strategy is determined based on the polarization rate reduction attenuation; the discharge pulse switching strategy includes a standard discharge pulse strategy and a protective discharge pulse strategy. Before executing the discharge pulse switching strategy, the battery temperature rise rate is obtained, and the discharge pulse switching strategy is modified according to the temperature rise rate. After the current discharge pulse phase ends, the polarization fluctuation grading value for the next charging phase is adjusted according to the rate of decrease of the polarization index.
2. The charging and discharging control method for fast-charging lithium-ion batteries according to claim 1, characterized in that, The process of obtaining the polarization fluctuation ratio includes: During the current charging phase, the terminal voltage of the battery is collected at multiple sampling times according to a preset sampling period, and the open-circuit voltage of the battery at each of the multiple sampling times is obtained. The polarization index of each of the multiple sampling times is determined based on the absolute value of the difference between the terminal voltage and the corresponding open-circuit voltage. Based on the polarization index at multiple sampling times and the corresponding sampling times, a polarization index change curve for the current charging stage is constructed and linearly fitted to obtain the polarization index rise rate for the current charging stage. Retrieve multiple historical polarization indices and corresponding historical sampling times from the previous discharge pulse phase; Based on the multiple historical polarization indices and their corresponding historical sampling times, a polarization index change curve for the previous discharge phase is constructed and linearly fitted to obtain the polarization index decrease rate for the previous discharge pulse phase. The ratio of the rate of increase of the polarization index during the current charging phase to the rate of decrease of the polarization index during the previous discharge pulse phase is denoted as the polarization fluctuation ratio.
3. The charging and discharging control method for fast-charging lithium-ion batteries according to claim 1, characterized in that, The process of determining the polarization fluctuation classification value of the current charging stage based on the internal resistance change rate includes: If the rate of change of internal resistance is less than the first preset rate of change of internal resistance, then the polarization fluctuation classification value is determined to be the first calibration value. If the rate of change of internal resistance is greater than or equal to the first preset rate of change of internal resistance and less than the second preset rate of change of internal resistance, then the polarization fluctuation classification value is determined to be the second calibration value. If the rate of change of internal resistance is greater than or equal to the second preset rate of change of internal resistance, then the polarization fluctuation classification value is determined to be the third calibration value. Wherein, the first preset internal resistance change rate is less than the second preset internal resistance change rate; the first calibration value is greater than the second calibration value, and the second calibration value is greater than the third calibration value.
4. The charging and discharging control method for fast-charging lithium-ion batteries according to claim 1, characterized in that, The process of determining the polarization recovery requirement level based on the polarization fluctuation limit includes: If the polarization fluctuation limit is less than the preset polarization limit start threshold, the polarization recovery requirement level is determined to be low, the switching is not triggered, and the current charging phase continues. If the polarization fluctuation limit is greater than or equal to the preset polarization limit start threshold and less than the preset polarization limit upper threshold, then the polarization recovery requirement level is determined to be medium level, and standard switching is triggered. If the polarization fluctuation limit is greater than or equal to the preset polarization limit threshold, the polarization recovery requirement level is determined to be high, triggering an early switch. Wherein, the polarization fluctuation limit value is the difference between the polarization fluctuation ratio and the polarization fluctuation grade value.
5. The charging and discharging control method for fast-charging lithium-ion batteries according to claim 4, characterized in that, The standard switching is to switch to the discharge pulse stage after the current charging stage lasts for a first duration. The first duration is determined according to the polarization fluctuation limit value, and the rate of change of the first duration with the polarization fluctuation limit value is a first change slope. The early switching is to switch to the discharge pulse stage after the current charging stage lasts for a second duration, the second duration is determined according to the polarization fluctuation limit value, and the rate of change of the second duration with the polarization fluctuation limit value is the second change slope; The second duration is shorter than the first duration, and the absolute value of the second slope is greater than the absolute value of the first slope.
6. The charging and discharging control method for fast-charging lithium-ion batteries according to claim 5, characterized in that, The process of determining the discharge pulse switching strategy based on the polarization rate reduction attenuation includes: If the polarization rate reduction decay rate is less than the preset aging threshold, it is determined that the discharge recovery capability of the battery has not significantly degraded, and a standard discharge pulse switching strategy is adopted. The standard discharge pulse switching strategy includes executing the discharge pulse phase for a preset standard duration. If the polarization rate reduction decay rate is greater than or equal to the preset aging threshold, it is determined that the battery's discharge recovery capability has degraded, and a protective discharge pulse switching strategy is adopted. The protective discharge pulse switching strategy includes extending the duration of the discharge pulse phase based on the preset standard duration, and reducing the charging current of the next charging phase by a preset number of levels. The extension of the duration is positively correlated with the difference between the polarization rate reduction decay rate and the preset aging threshold.
7. The charging and discharging control method for fast-charging lithium-ion batteries according to claim 6, characterized in that, The process of obtaining the polarization rate reduction decay rate includes: During the current discharge pulse phase, the terminal voltage of the battery is collected at multiple sampling times according to a preset sampling period, and the open-circuit voltage of the battery at each of the multiple sampling times is obtained. The polarization index of each of the multiple sampling times is determined based on the absolute value of the difference between the terminal voltage and the corresponding open-circuit voltage. Based on the polarization index at multiple sampling times and the corresponding sampling times, a polarization index change curve for the current discharge pulse stage is constructed. The polarization index change curve for the current discharge pulse stage is linearly fitted, the slope of the fitted curve is calculated, and the absolute value of the slope is determined as the rate of decrease of the polarization index for the current discharge pulse stage. Retrieve multiple historical polarization indices and corresponding historical sampling times from the previous discharge pulse phase; Based on the multiple historical polarization indices and the corresponding historical sampling times, a polarization index change curve for the previous discharge pulse phase is constructed and linearly fitted. The slope of the fitted curve is calculated, and the absolute value of the slope is determined as the polarization index decrease rate for the previous discharge pulse phase. The polarization decay rate is determined based on the polarization index decrease rate during the previous discharge pulse phase and the polarization index decrease rate during the current discharge pulse phase.
8. The charging and discharging control method for fast-charging lithium-ion batteries according to claim 7, characterized in that, The process of modifying the discharge pulse switching strategy according to the temperature rise rate includes: If the temperature rise rate is less than the first preset temperature rise threshold, the thermal safety state is determined to be normal, and the discharge pulse switching strategy is executed directly. If the temperature rise rate is greater than or equal to the first preset temperature rise threshold and less than the second preset temperature rise threshold, then the thermal safety state is determined to be too high, and the discharge pulse switching strategy is executed after reducing the charging current. If the temperature rise rate is greater than or equal to the second preset temperature rise threshold, the thermal safety state is determined to be a dangerous state, charging is stopped and heat dissipation is initiated.
9. The charging and discharging control method for fast-charging lithium-ion batteries according to claim 8, characterized in that, The process of adjusting the polarization fluctuation classification value for the next charging phase based on the polarization index decrease rate includes: The absolute value of the difference between the current polarization index decrease rate during the discharge pulse phase and the previously recorded polarization index decrease rate is defined as the decrease rate deviation. If the deviation of the descent rate is less than the preset deviation threshold for a preset number of consecutive preset number of times, the polarization fluctuation classification value is not changed. If the descent rate deviation is greater than or equal to a preset deviation threshold for a consecutive preset number of times, the polarization fluctuation classification value is reduced according to the difference between the descent rate deviation and the preset deviation threshold.
10. The charging and discharging control method for a fast-charging lithium-ion battery according to claim 2 or claim 7, characterized in that, The retrieval of multiple historical polarization indices and corresponding historical sampling times within the previous discharge pulse phase includes: If the current charging is the first charging or the historical polarization index and corresponding historical sampling time of the historical discharge pulse stage have not yet been stored, the retrieval will not be performed. Instead, the preset initial polarization index decrease rate will be used as the polarization index decrease rate of the previous discharge pulse stage. If multiple historical polarization indices and corresponding historical sampling times from the previous discharge pulse phase are already stored, then the retrieval will be performed.