Battery multi-stage fast discharge method based on thermal runaway risk constraint

Abstract

This invention provides a multi-stage rapid battery discharge method based on thermal runaway risk constraints, comprising: A) performing standard capacity calibration tests on the target cell and setting constraints; B) setting several constant current discharge stages, each with a different discharge rate; the constant current discharge stage ends when the voltage of a certain constant current discharge stage drops to a set cutoff voltage; C) setting a resting stage between adjacent constant current discharge stages; D) setting a constant voltage discharge stage after the last constant current discharge stage; the constant voltage discharge stage begins when the voltage of the last constant current discharge stage drops to a set cutoff voltage; E) terminating discharge when the current decays to a discharge rate of 0.02C; throughout the discharge process, thermal runaway parameters are monitored in real time, and subsequent discharge operations are determined based on the battery temperature T and the comprehensive temperature index C. This invention can effectively control the risk of thermal runaway, balancing discharge speed, capacity utilization, voltage rebound, and temperature rise safety.

Description

Technical Field

[0001] This invention relates to a multi-stage rapid discharge method for batteries based on thermal runaway risk constraints, applicable to power batteries, electrochemical energy storage systems, and retired battery cells. Background Technology

[0002] With the booming development of the new energy vehicle market, battery energy storage, drones, and other consumer electronics and power tools in recent years, the global lithium battery industry has experienced rapid growth. Benefiting from multiple strategic advantages, including policy support, market demand, technological breakthroughs, and collaboration across the entire industry chain, China's lithium battery industry has developed rapidly, with a growth rate significantly exceeding the global average. In 2024, China's lithium battery shipments reached 76.0% of the global total, making China's lithium battery industry a dominant force in the global market.

[0003] The working principle of a lithium-ion battery is as follows: During discharge, lithium ions are released from the negative electrode, pass through the electrolyte, and embed into the positive electrode material. Electrons flow from the negative electrode to the positive electrode via an external circuit, thus outputting electrical energy. The cell terminal voltage is determined by the potential difference between the positive and negative electrodes, and its macroscopic performance is influenced by multiple factors, including the properties of the electrode materials, ion diffusion / migration rates, polarization effects, and temperature distribution. On the one hand, rapid discharge technology can meet the high-power output requirements of electric vehicles, emergency power supplies, and power tools, and is used in scenarios such as power grid frequency and voltage regulation. On the other hand, rapid discharge also significantly increases the heat generation and stress levels inside the battery cell: under high-rate discharge, the current increases sharply, ohmic polarization and concentration polarization are enhanced, side reactions are aggravated, and the cell temperature rises rapidly. In extreme cases, it may trigger a series of exothermic reactions such as oxygen release at the positive electrode, electrolyte decomposition, and violent decomposition of the SEI film, thus evolving into a thermal runaway event, posing serious safety risks.

[0004] Currently, battery discharge often employs simple methods such as constant current discharge, constant voltage discharge, pulse discharge, constant resistance discharge, and constant power discharge. Constant current discharge is simple and easy to implement, but it can easily cause battery overheating; constant voltage discharge is suitable for high-power devices with high battery management requirements; pulse discharge releases a large amount of energy in a short time, but requires attention to battery thermal management; constant power discharge facilitates energy assessment and performance testing, but its battery capacity utilization and efficiency are relatively low.

[0005] Therefore, existing fast discharge methods often focus on discharge time or capacity utilization, lacking discharge strategies that take "thermal runaway risk" and "safety boundary" as core constraints in system design. There is still a lack of a fast discharge method and system with safety constraints that can comprehensively balance discharge speed, discharge depth, voltage rebound control, and temperature rise safety, and is optimized based on the internal mechanisms of the battery cell.

[0006] Current common fast discharge strategies typically only focus on indicators such as voltage, current, and termination capacity, and do not adequately consider the internal thermo-electric coupling process, often resulting in the following problems: 1. During high-rate discharge, the migration rate of lithium ions at the electrode and electrolyte interface increases significantly, the local concentration gradient increases, polarization intensifies, and the internal heat generation power of the cell increases significantly. 2. Under high current density, the surface of the negative electrode is more prone to local oversaturation, which induces lithium plating, resulting in lithium source loss, increased internal resistance, capacity decay and safety hazards. 3. When the accumulated heat exceeds the heat dissipation capacity, the local temperature may rise further and trigger side reactions, forming a thermal runaway chain reaction; 4. High-rate rapid discharge also brings about a significant voltage relaxation / rebound effect, increasing the difficulty for the battery management system (BMS) to estimate SOC / SOH.

[0007] Therefore, it is necessary to propose a novel fast discharge method that takes thermal runaway risk control as a prerequisite constraint and takes into account discharge speed, capacity utilization, voltage rebound and temperature rise safety. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the main objective of this invention is to provide a multi-stage rapid discharge method for batteries based on thermal runaway risk constraints. This method can effectively control the risk of thermal runaway while taking into account discharge speed, capacity utilization, voltage rebound, and temperature rise safety.

[0009] To achieve the above-mentioned main objectives, the present invention provides a multi-stage rapid discharge method for batteries based on thermal runaway risk constraints, comprising: A. Perform standard capacity calibration tests on the target battery cell and set constraints; B. Set several constant current discharge stages, each with a different discharge rate; when the voltage of a certain constant current discharge stage drops to the set cutoff voltage, the constant current discharge stage ends. C. Set a resting phase between adjacent constant current discharge phases; D. Set a constant voltage discharge stage after the last constant current discharge stage; when the voltage of the last constant current discharge stage drops to the set cutoff voltage, switch to the constant voltage discharge stage. E. When the current decays to a discharge rate of 0.02C, the discharge is terminated; Throughout the discharge process, thermal runaway parameters are monitored in real time, and subsequent discharge operations are determined based on the battery temperature T and the comprehensive temperature index C.

[0010] The discharge strategy employed in this invention is a multi-stage stepped constant current discharge-constant current and constant voltage discharge (MSCC-CCCV), such as... Figure 1 As shown, it mainly includes several constant current discharge stages with different current ratios. The discharge cutoff voltage of each stage remains consistent, and finally a constant voltage discharge stage is connected as the end. The constant current discharge (CC) generally adopts a discharge ratio of 0.5C, and the constant voltage discharge voltage is set as the cutoff voltage. The termination condition of constant voltage discharge is that the discharge current decreases to 0.02C, which is regarded as the end of discharge.

[0011] In this invention, a short resting period (e.g., 30s) is inserted between adjacent constant current discharge stages, and this can be adjusted appropriately according to the cell type and health status. During the resting period, the current is zero, and this time window is used to allow the Li⁺ concentration gradient inside the electrolyte and electrode particles to relax through diffusion, thereby reducing concentration polarization.

[0012] In this invention, the multiplier and duration of several constant current discharge stages are determined, for example, the first stage is 2.5C, the second stage is 2.0C, and the third stage is 1.5C; the multiplier of the stages can be arranged in a large-medium-small, large-small-large or other non-monotonic order, as long as the temperature rise and termination conditions are met.

[0013] In this invention, the voltage during the constant voltage discharge stage is stabilized near the cutoff voltage, allowing the current to decay naturally until it reaches 0.02C to terminate the discharge.

[0014] In this invention, the control system executes each stage of discharge sequentially according to a preset current-time-rest sequence; it collects voltage, temperature, and current data in real time, and can dynamically shorten the current stage or reduce the rate of subsequent stages if the temperature approaches the threshold or the voltage drops abnormally.

[0015] Taking into account the risk of thermal runaway in lithium-ion batteries, this invention focuses on solving the following technical problems: 1. Achieve rapid discharge within a safe temperature window. How to enable more capacity to be released at high rates while shortening the "tail end time" at low rates or constant voltage, under the condition that the cell temperature does not exceed the preset safety temperature and temperature rise rate threshold, so as to achieve rapid discharge under the premise of safety.

[0016] 2. Suppress voltage rebound and shorten total time while controlling thermal risks. How can we utilize the voltage relaxation, ion diffusion redistribution, and polarization recovery during a short resting period without increasing the overall discharge risk, to both suppress the voltage rebound amplitude after the discharge ends and shorten the total discharge time, while avoiding failures and hidden dangers caused by high polarization and high temperature?

[0017] 3. Compatible with different types and health conditions (including retired battery cells) for safe and rapid discharge. Ultimately, a universal, safe, and fast discharge strategy is constructed that does not require complex real-time electrochemical modeling and can obtain control parameters through pre-calibration and empirical optimization. This strategy is applicable to different types of lithium-ion cells, different health states, and even retired lithium-ion cells, and can be integrated and compatible with existing BMS control strategies or discharge equipment systems.

[0018] According to a specific embodiment of the present invention, the formula for calculating the comprehensive temperature index C is as follows: ; Where t represents the value at a certain moment; A is the predicted internal temperature of the battery based on the coupling of voltage dynamics and thermal model, and B is the temperature assessment value based on the prediction of thermocouple surface temperature. w1 and w2 are weighting coefficients that satisfy: w 1+ w2=1, .

[0019] In this scheme, in order to simultaneously consider the internal thermal risk sensitivity and measurement stability, A and B are weighted and fused to construct a comprehensive temperature index C based on the fusion of multi-source temperature information.

[0020] The weighting coefficient can be dynamically adjusted according to the operating conditions. For example, w1 can be increased during the rapid discharge phase to enhance the response capability to the risk of internal thermal runaway.

[0021] The thermal runaway risk monitoring method of the present invention integrates the internal temperature prediction method based on thermal models with the surface temperature prediction method based on thermocouples, and constructs a comprehensive temperature evaluation index through multi-source temperature information.

[0022] 1) Predicted internal battery temperature A based on the coupling of voltage dynamics and thermal model • Dynamic model of battery terminal voltage Under constant current discharge conditions, the battery terminal voltage can be expressed as: V(t) = V OCV (z(t),T (t))-I (t)R0 (T, z) -V p (t) Where z(t) is the battery state of charge; V OCV V is the open-circuit voltage, which varies with SOC and temperature; R0 is the equivalent ohmic internal resistance; V p I(t) represents the polarization voltage. Taking the time derivative of the above voltage expression, neglecting the I(t) term under constant current discharge conditions, and treating the SOC variation as a disturbance within a short prediction window, we can obtain an approximate relationship between the rate of change of terminal voltage and the rate of change of internal temperature:

[0023] During the constant current discharge stage, there is Furthermore, within a short prediction window, the rate of change of SOC is relatively slow and can be incorporated into the modeling uncertainty term, thus obtaining an approximate expression directly related to the rate of temperature change:

[0024] Where ε(t) represents the perturbation term caused by polarization dynamics and SOC changes.

[0025] • Inversion of the rate of change of internal temperature Ignoring short-term disturbances ε(t), the rate of change of internal battery temperature can be deduced from the rate of change of voltage:

[0026] in: This refers to the battery entropy coefficient. Characterizes the sensitivity of internal resistance to temperature; The above parameters can be obtained through offline experimental calibration.

[0027] • Internal temperature prediction under thermal model constraints To avoid the cumulative error introduced by simple integration, a first-order lumped heat model is introduced to constrain the internal temperature evolution:

[0028] in For the core temperature change rate; C th Equivalent heat capacity (J / K) represents the cell's "heat storage capacity"; h represents the equivalent convective heat transfer coefficient between the battery and its surrounding environment, hA reflects how quickly heat "escapes"; Q gen Battery heating power (W) represents how much heat is generated inside the battery cell.

[0029] Battery heating power is expressed as:

[0030] The result obtained from the inversion of the voltage change rate Substituting these values ​​into the thermal model constraints and combining them with the initial temperature T0, the predicted internal temperature of the battery can be obtained:

[0031] 2) Temperature assessment value B based on thermocouple surface temperature prediction During the rapid discharge of lithium batteries, the battery surface temperature reflects the overall heat accumulation level and is an important basis for determining whether the discharge process has entered a high-heat-risk zone. Compared with internal temperature prediction methods based on voltage dynamics, the surface temperature change process is smoother and less affected by transient disturbances, making it suitable as a reference for assessing the average temperature rise and safety constraints during the discharge process.

[0032] Therefore, this invention introduces a surface temperature prediction method based on thermocouples to stably assess the temperature evolution trend during the discharge process, and complements the internal temperature prediction method based on thermal models.

[0033] Thermocouple surface temperature measurement model A thermocouple sensor is installed on the outer surface of the battery casing to collect the battery surface temperature signal T in real time. s (t) represents the battery surface temperature measured by the thermocouple at time t. To reduce the influence of environmental noise and measurement fluctuations, the acquired surface temperature signal can be filtered to obtain a smoothed surface temperature: .

[0034] Surface temperature change rate and short-term prediction During rapid discharge, the surface temperature typically exhibits a continuous upward trend. By time-differencing the smoothed surface temperature, the rate of surface temperature change can be obtained: .

[0035] Within a short-term prediction window, assuming the rate of change of surface temperature remains approximately constant, a linear extrapolation prediction of the surface temperature at future times can be made:

[0036] Where Δt is the prediction time window. Let B(t) be expressed as: B(t) = .

[0037] The above predictions are used to characterize the average upward trend of surface temperature, rather than to accurately characterize internal transient thermal behavior.

[0038] According to one specific embodiment of the present invention, if T exceeds the upper temperature limit, the discharge is immediately terminated; otherwise, the discharge continues as planned.

[0039] According to a specific embodiment of the present invention, the thermal runaway parameters include voltage V and its first derivative dV / dt, and battery temperature T and its first derivative dT / dt.

[0040] According to a specific embodiment of the present invention, if C > battery safety temperature threshold T lim If the discharge is stopped immediately and allowed to stand still, then the current is reduced and the discharge continues; if C <T limIf so, continue discharging as originally planned.

[0041] In this scheme, discharge judgment is based on comprehensive temperature indicators; a battery safety temperature threshold T is set. lim Different discharge strategies are executed when the overall temperature index meets the following criteria: • Criteria for safe and rapid discharge:

[0042] When the above conditions are met, the battery is determined to be in a safe temperature range, and the system maintains the current constant current rapid discharge strategy.

[0043] • Thermal risk suppression criterion (small current discharge):

[0044] When the comprehensive temperature index reaches or exceeds T lim If a risk of thermal runaway is detected, a low-current discharge mode is used to suppress the temperature rise, thereby avoiding the occurrence of thermal runaway.

[0045] According to a specific embodiment of the present invention, the cutoff voltage in both steps B and D is 1.5V.

[0046] According to one specific embodiment of the present invention, the standard capacity calibration test can obtain the rated capacity, internal resistance, and temperature rise / springback characteristics.

[0047] According to one specific embodiment of the present invention, the constraints include target discharge depth (termination voltage), maximum allowable temperature rise, maximum allowable voltage rebound amplitude, etc.

[0048] In this scheme, the constraints also include the maximum allowable operating temperature.

[0049] To address the shortcomings of existing rapid discharge methods for lithium-ion batteries in terms of safety, particularly in thermal runaway risk management, this invention proposes a safe and rapid discharge method for lithium batteries based on thermal runaway risk constraints.

[0050] Within the cell's permissible discharge capacity, safe temperature window, and thermal safety constraints, a multi-stage stepped constant current discharge-constant current and constant voltage (MSCC-CCCV) approach combined with an optimized rest window is employed. During discharge, this approach integrates predicted internal battery temperature based on voltage dynamics and a coupled thermal model, with temperature assessments based on thermocouple surface temperature predictions, introducing a comprehensive temperature index to dynamically monitor the risk of thermal runaway throughout the discharge process. At each specific stage of the discharge process, different constant currents are carefully configured, forming a complete discharge scheme across multiple stages. This scheme prevents lithium plating and thermal runaway risks during discharge. While increasing the discharge rate, it also reduces the voltage rebound amplitude after discharge, thereby optimizing the lithium battery's performance in different scenarios and balancing the relationship between discharge rate, battery safety performance, and stability.

[0051] • Throughout the discharge process, the cell temperature, temperature rise rate (dT / dt), and estimated thermal safety boundary are used as explicit constraints; • Insert short periods of rest between each constant current stage to reduce the polarization level and thermal stress in subsequent stages through voltage relaxation and concentration polarization recovery; • Use CCCV to terminate near the cutoff voltage and extract the remaining usable capacity under controlled temperature conditions; • Throughout the process, temperature, voltage, and current are monitored in real time, and threshold judgments are made to prevent the temperature from approaching the critical zone of thermal runaway.

[0052] This invention treats the rest time between each stage as an explicit optimization variable in the algorithm, rather than an additional "waiting time." Through experimental verification and mechanism analysis, it utilizes the natural relaxation of concentration polarization when the current is zero during the rest stage to reduce the polarization level at the beginning of subsequent stages. This achieves the following: while preventing the risks of lithium plating and thermal runaway, it increases the effective capacity released per unit time, shortens the total discharge time, and reduces the voltage rebound amplitude after the discharge ends, thus balancing safety, speed, and usable capacity utilization.

[0053] Compared with the traditional single-discharge-rate CC-CV lithium battery fast discharge method, the present invention has the following advantages: 1. Explicitly incorporate thermal runaway risk constraints to improve discharge safety. • By setting parameters such as the maximum operating temperature of a single cell, the allowable rate of temperature rise, and the temperature safety margin, the “thermal safety boundary” is taken as a prerequisite for the discharge strategy design. • Limit the peak rate and stage duration in multi-stage constant current discharge, and use a resting window to avoid excessively rapid temperature rise under continuous high load; • When the temperature approaches the preset threshold, measures such as reducing the discharge rate in subsequent stages, shortening the duration, or entering the CCCV stage earlier can be taken to prevent the temperature from rising further and significantly reduce the risk of thermal runaway.

[0054] 2. Achieve faster and more complete discharge under safety constraints. • By using a multi-stage constant current system with a rest window, more capacity can be released in the high-rate stage under controlled temperature rise conditions, significantly shortening the time of the final constant pressure tail section and the low-rate stage. • Under the same termination voltage and termination current conditions, compared with some single-rate operating conditions, the present invention can achieve higher available capacity release efficiency while shortening the total discharge time.

[0055] 3. Reduce polarization, improve termination state stability, and suppress voltage rebound. • During the settling phase, the natural relaxation of concentration polarization when the current is zero is utilized to significantly reduce the concentration polarization and ohmic polarization at the end. • The termination voltage is closer to the open-circuit voltage, which reduces the voltage rebound amplitude after the discharge ends. This is beneficial for subsequent charging strategy design and SOC / SOH estimation, and reduces BMS algorithm deviation.

[0056] 4. Wide range of applications, easy to implement in engineering projects. This invention does not rely on complex online electrochemical models. It only requires obtaining the capacity, internal resistance, temperature rise characteristics and voltage rebound characteristics of each cell / battery system through pre-calibration experiments to determine the multi-stage current and rest time parameters. It can be applied to power battery packs, electrochemical energy storage systems, and scenarios for safe and rapid discharge and condition assessment of retired battery cells; • Facilitates integration with existing BMS or discharge equipment control interfaces, enabling rapid deployment in engineering projects.

[0057] To more clearly illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0058] Figure 1 This is a diagram of the MSCC-CCCV discharge strategy in Example 1; Figure 2 This is a schematic diagram of the overall thermal runaway discharge strategy in Example 1; Figure 3 This is the current change curve of the experimental group in Experiment 1 of Example 1; Figure 4 This is the current change curve of the control group in Experiment 1 of Example 1; Figure 5This is the voltage change curve of the experimental group in Experiment 1 of Example 1; Figure 6 This is the voltage change curve of the control group in Experiment 1 of Example 1; Figure 7 This is the temperature change curve of the experimental group in Experiment 1 of Example 1; Figure 8 This is the temperature change curve of the control group in Experiment 1 of Example 1; Figure 9 This is an infrared thermal image (highest temperature) of the experimental group in Experiment 1 of Example 1. Figure 10 This is an infrared thermal image (highest temperature) of the control group in Experiment 1 of Example 1. Figure 11 This is a comparison graph of voltage change curves in Experiment 2 of Example 1 (conventional group (norest) and control group (rest)). Figure 12 This is a comparison graph of temperature change curves in Experiment 2 of Example 1 (conventional group (norest) and control group (rest)). Detailed Implementation

[0059] Many specific details are set forth in the following description in conjunction with embodiments in order to provide a full understanding of the invention. However, it should be understood that the following embodiments and detailed descriptions are for illustrative purposes only and do not limit the scope of protection of the invention.

[0060] Example 1

[0061] like Figure 1 and 2 As shown in the figure, this embodiment provides a multi-stage rapid discharge method for batteries based on thermal runaway risk constraints, and its specific steps are as follows: 1) Collect initial battery information Perform standard capacity calibration tests on the target cell to obtain its rated capacity, internal resistance, and temperature rise / springback characteristics; set constraints such as target discharge depth (termination voltage), maximum allowable operating temperature, maximum allowable temperature rise, and maximum allowable voltage springback amplitude, while simultaneously measuring its current voltage and temperature.

[0062] 2) Basic parameter settings Set the number of constant current discharge stages, n, where n represents the number of constant current discharge rounds; reset the discharge stage count i to zero; set the initial constant current discharge stage discharge current a; set the discharge cutoff voltage V1; and set the battery safety temperature threshold T. lim .

[0063] 3) Initial constant current discharge stage Perform the first discharge with current a, and during the discharge process, detect the thermal runaway parameters in real time, including voltage V, the first derivative of voltage dV / dt, temperature T, and the first derivative of temperature dT / dt.

[0064] If the battery temperature T exceeds the upper temperature limit, immediately end the discharge to prevent accidents; if the battery temperature does not exceed the upper limit, continue the current-stage discharge and monitor it using the comprehensive temperature index C.

[0065] If C>T lim , it is considered that the current battery state exceeds the safety threshold, and there is a risk trend of thermal runaway. Immediately stop the discharge and let it stand for a period of time, then discharge with a small current b (b < a), and continue to detect the thermal runaway parameters in real time; If C<T lim , the battery is in the safe temperature range. The system maintains the current constant-current discharge strategy until the battery is discharged to the set cut-off voltage V1; stop the discharge, let it stand for a period of time, then enter the next discharge stage, increment the count i by one, and set the discharge current c for the next stage.

[0066] 4) Multi-stage cycle of constant-current discharge When the stage count i = n, the set number of multi-stage constant-current discharge cycles is completed.

[0067] 5) CCCV end After the multi-stage constant-current discharge is completed, enter the CCCV end; first, discharge the battery at a constant current of 0.5C to the cut-off voltage V1, and then switch to the constant-voltage discharge stage; in the constant-voltage discharge stage, stabilize the voltage near the cut-off voltage and allow the current to decay naturally until the current reaches 0.02C to terminate the discharge.

[0068] Taking one of the schemes as an example, apply a high-rate constant-current discharge in the first stage, such as 2.5C (i.e., a current of 2.5 times the rated capacity), to quickly release a large amount of electricity when the voltage is relatively high; when the voltage drops to the cut-off voltage, enter the standing stage, and then switch to a lower constant current (such as 2.0C) in the second stage to reduce the premature voltage drop caused by the internal resistance effect; further reduce the current in the third stage (such as 1.5C) to ensure that the battery can still maintain the discharge when approaching the cut-off voltage without premature termination. Finally, when the voltage drops to the set cut-off voltage of 1.5V, the discharge strategy switches from constant current to constant voltage mode: stabilize the voltage near 1.5V and allow the current to decay freely until the current value is very small (0.02C) to end the discharge. The constant-voltage tail section can extract the small amount of available capacity remaining in the low-voltage area of the battery to ensure that the battery core is almost completely discharged when the discharge terminates.

[0069] Meanwhile, experiments have shown that the current selected for each stage of the constant current discharge does not need to have a strict magnitude relationship, i.e., it does not need to strictly decrease from large to small. When a "small current followed by large current" switch is performed (e.g., from 2C to 2.5C), although the voltage rebounds during the rest period, the voltage drops quickly and falls below the previous level after re-discharge due to the larger current in the second stage. If the switch is performed directly without a rest period, the instantaneous effect of the large current will cause the voltage to continue to drop along the original trend. It can be seen that regardless of the current switching sequence, as long as there is an open-circuit rest (rest period) between the constant current discharge stages, the voltage will definitely rebound, while continuous discharge without a rest period can be considered to have virtually no significant rebound.

[0070] Whether a short interval is needed between each discharge stage will be explained in the subsequent experimental analysis. The experimental results show that a short rest can effectively increase the discharge speed and reduce voltage rebound, that is, a short rest can reduce the overall discharge time.

[0071] Experiment and Results Analysis The batteries used in the experiment were 21700 type ternary lithium-ion cells. All cells underwent standard capacity calibration tests before rapid discharge to determine their actual usable capacity and ensure consistency in their initial state. ARBIN battery testing equipment was used for the experiment. During the experiment, each cell was fully charged and then allowed to rest for 30 minutes as the initial discharge state (t=0s) to eliminate the influence of surface voltage from the previous charging history. Rapid discharge was then immediately initiated.

[0072] In the rapid discharge experiment, a series of indicators characterizing battery performance and state changes were monitored and recorded: (1) Voltage rebound: refers to the phenomenon of the battery voltage rising and recovering over time (within half an hour observed in this experiment) after the discharge ends or is interrupted; (2) Battery temperature change: including temperature-time curves during discharge and infrared thermal images of cell surface temperature distribution before and after discharge, to assess the overall and local thermal effects caused by rapid discharge. (3) Discharge time: The time required to complete the predetermined depth of discharge, which is also a direct indicator of efficiency; The aforementioned observation indicators cover multiple aspects such as the battery's electrical performance (voltage, current) and thermal response (temperature) under rapid discharge conditions, providing data support for a comprehensive evaluation of the effectiveness of the rapid discharge strategy of this invention.

[0073] Based on the above, the following two experiments demonstrate the superiority of the discharge strategy of this invention.

[0074] Experiment 1: Comparison between the present invention and conventional discharge The three controllable discharge (CC) stages of this invention can employ different current rates, thus allowing for several different combinations. This experiment lists three strategies with particularly significant effects (Table 1), comparing them with conventional single-discharge-rate discharge strategies (Table 2), thereby demonstrating the superiority and feasibility of this invention.

[0075] Table 1 Operating Conditions of Four MSCC-CCCV Strategies

[0076] Table 2. Conventional single-discharge-rate discharge strategies

[0077] Experimental results are as follows Figure 3-10 As shown.

[0078] The discharge time comparisons are shown in Table 3: Table 3 Comparison of discharge time

[0079] In summary, compared with conventional single-stage discharge, the MSCC-CCCV strategy of the present invention, under the premise of meeting the same termination voltage and termination current conditions, has a significantly shorter total discharge time than low-rate single operating condition, and is close to or better than some high-rate single operating conditions; under the same or shorter discharge time, the maximum temperature of the cell under the MSCC-CCCV strategy is significantly lower than that under high-rate single constant current operating condition, the temperature rise curve is smoother, and there is no severe temperature rise segment approaching the thermal runaway boundary; Experiment 2: Proof of the Necessity and Feasibility of the Settling Stage Since this invention involves multiple stages and multiple discharge rates, it is necessary to discuss whether a rest period is needed between each stage. Two experimental groups were set up with identical MSCC-CCCV discharge rates. In the control group, a 30-second rest period (rest_time) was added between each stage. The experimental results are as follows: Figure 11 and 12 As shown.

[0080] It is evident that appropriately adding a resting period between each stage helps to shorten the overall discharge time and has a significant effect on suppressing voltage rebound; at the same time, it also effectively reduces the battery temperature.

[0081] The following section further explains the mechanism by which the multi-stage discharge and resting stages lead to performance improvements: 1. During the high-rate phase, "surface capacity" is released; during the static phase, "diffusion replenishment" is achieved. The high-rate constant current stage mainly consumes the active Li near the surface of the electrode particles. +Internal Li + The inability to diffuse and replenish in time leads to increased local concentration polarization and a rapid drop in voltage; The current is zero during the static phase, and the internal Li + As it diffuses towards the surface, the concentration gradient decreases, and the equivalent internal resistance decreases. Therefore, in the subsequent constant current stage, more effective capacity can be released under the same cutoff voltage conditions.

[0082] 2. Reduce the "inefficient time" at the end of the constant pressure stage. Traditional single-rate operating conditions typically spend a lot of time in the constant voltage stage at the end, slowly releasing the residual capacity with extremely low current. This invention, by rationally allocating the duration and rest window of the high-rate phase, releases more capacity in advance during the high-rate phase, significantly shortening the overall time of the constant-voltage tail section, thereby shortening the total discharge time.

[0083] 3. Voltage rebound suppression mechanism The main source of voltage rebound is the polarization voltage that remains at the time of termination; Multiple constant current-static cycles significantly reduce both concentration polarization and ohmic polarization at termination, thus the termination voltage is closer to the actual open circuit voltage, and the rebound amplitude is naturally reduced. This effect is more pronounced for retired battery cells with higher internal resistance, therefore this invention is particularly suitable for rapid discharge and condition assessment of retired battery cells.

[0084] As can be seen from the above mechanism analysis, the multi-stage MSCC-CCCV strategy proposed in this invention is not a simple superposition of existing operating conditions, but rather a system design and optimization based on lithium-ion diffusion / migration and polarization relaxation characteristics, thereby achieving a better comprehensive balance between discharge rate, discharge depth, safety and voltage rebound control.

[0085] Although the present invention has been described above by way of embodiments, the above embodiments are only used to exemplify possible implementations of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent substitutions or changes made by those skilled in the art in accordance with the present invention should also be covered by the scope of protection defined by the claims of the present invention.

Claims

1. A multi-stage rapid discharge method for batteries based on thermal runaway risk constraints, characterized in that, The multi-stage rapid discharge method for the battery includes: A. Perform standard capacity calibration tests on the target battery cell and set constraints; B. Several constant current discharge stages are set, and the discharge rate of each constant current discharge stage is different; when the voltage of a certain constant current discharge stage drops to the set cutoff voltage, the constant current discharge stage ends. C. A resting phase is provided between adjacent constant current discharge phases; D. A constant voltage discharge stage is set after the last constant current discharge stage; when the voltage of the last constant current discharge stage drops to the set cutoff voltage, the constant voltage discharge stage is entered. E. When the current decays to a discharge rate of 0.02C, the discharge is terminated; Throughout the discharge process, thermal runaway parameters are monitored in real time, and subsequent discharge operations are determined based on the battery temperature T and the comprehensive temperature index C.

2. The multi-stage rapid discharge method for batteries according to claim 1, characterized in that, The formula for calculating the comprehensive temperature index C is as follows: ; Where t represents the value at a certain moment; A is the predicted internal temperature of the battery based on the coupling of voltage dynamics and thermal model, and B is the temperature assessment value based on the prediction of thermocouple surface temperature. w1 and w2 are weighting coefficients that satisfy: w1 + w2 = 1. .

3. The multi-stage rapid discharge method for batteries according to claim 2, characterized in that, If T exceeds the upper temperature limit, the discharge will end immediately; otherwise, the discharge will continue as planned.

4. The multi-stage rapid discharge method for batteries according to claim 3, characterized in that, The thermal runaway parameters include voltage V and its first derivative dV / dt, and battery temperature T and its first derivative dT / dt.

5. The multi-stage rapid discharge method for batteries according to claim 4, characterized in that, If C > battery safety temperature threshold T lim If the discharge is stopped immediately and allowed to stand still, then the current is reduced and the discharge continues; if C <T lim If so, continue discharging as originally planned.

6. The multi-stage rapid discharge method for batteries according to claim 1, characterized in that, The standard capacity calibration test obtains the rated capacity, internal resistance, and temperature rise / springback characteristics.

7. The multi-stage rapid discharge method for batteries according to claim 6, characterized in that, The constraints include the target discharge depth, the maximum allowable temperature rise, and the maximum allowable voltage rebound amplitude.

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