Passive equalization method and device for lithium battery pack

Abstract

The invention discloses a passive equalization method and device for a lithium battery pack. The method comprises the steps of judging whether the lithium battery pack is passively equalized or not according to whether a working condition environment of the lithium battery pack meets a set condition or not; after it is determined that the working condition environment meets the set conditions, whether abnormal cells exist in the lithium battery pack or not is recognized, if yes, a passive equalization process is executed on normal battery cells except the abnormal cells in the lithium battery pack, and if not, the passive equalization process is executed on the normal battery cells in the lithium battery pack; and gradually adjusting the voltage of each normal single battery to a balanced state. The equalization effect is ideal, excessive equalization is avoided, and the service life of the lithium battery is prolonged.

Description

Technical Field

[0001] This invention relates to the field of lithium battery packs, and in particular to a passive balancing method and apparatus for lithium battery packs. Background Technology

[0002] Lithium batteries have been widely used as a new energy source. Among them, passive balancing technology, with its advantages of simple circuitry and ease of implementation, has been widely adopted to balance the charge of individual cells, thereby improving battery pack performance, safety, extending service life, and enhancing overall efficiency.

[0003] Currently, passive balancing technology is often used to improve the problem of inconsistent voltage among individual cells in lithium batteries. Its strategy is mainly based on the voltage values ​​of each cell in the lithium battery pack, and consumes the high-voltage energy in the form of resistive discharge, so that the charge of each cell in the lithium battery pack is basically the same.

[0004] In existing technologies, one approach is to automatically identify and moderately discharge cells with voltages exceeding a preset voltage difference towards the end of the charging cycle. This ensures voltage balance between individual cells, thereby improving the overall capacity of the lithium battery pack and extending its lifespan. However, this method only works during charging and requires the lithium battery pack to be in charging mode for a charging time longer than a preset time. Therefore, its effectiveness is limited for lithium battery packs that are not frequently charged or have insufficient charging time.

[0005] Another approach involves optimizing the voltage consistency of individual lithium-ion cells within the battery pack during the final stages of charging or when it is at rest, using a specific equalization control strategy. This improves the overall performance and lifespan of the battery pack. While this approach proposes a specific equalization control strategy, it lacks solutions for handling special cases, thus affecting the effectiveness of the equalization process.

[0006] Another approach involves achieving passive balancing of the lithium battery pack by accurately estimating the capacity, remaining discharge capacity, and remaining charge capacity of each individual lithium battery cell, and calculating a balanced charge value based on these estimates. This ensures that the charge capacity of each individual lithium battery cell is consistent, improving the overall performance and capacity utilization of the lithium battery pack. This approach requires precise estimation of the capacity, remaining discharge capacity, and remaining charge capacity of each individual lithium battery cell, making the calculation process relatively complex and placing high demands on the system's computing power and real-time performance.

[0007] All three of the above solutions fall short in considering the actual operating conditions of lithium batteries during passive balancing, and lack protection for the lithium batteries. In addition, the current passive balancing strategy applies to all lithium battery cells. If the balancing strategy does not comprehensively consider some actual operating conditions and protect some special abnormal cells, it will affect the life of the lithium battery and even aggravate the damage to the lithium battery. Summary of the Invention

[0008] The main objective of this invention is to overcome the shortcomings of existing technologies in terms of inadequate consideration of actual operating conditions of lithium batteries and lack of protection for lithium batteries. It proposes a passive balancing method and device for lithium battery packs, which effectively protects abnormal cells, prevents over-balancing, and optimizes the strategy logic of the balancing stage, resulting in ideal balancing effect and greatly extending the service life of lithium batteries.

[0009] The present invention adopts the following technical solution:

[0010] A passive balancing method for a lithium battery pack includes: determining whether the lithium battery pack needs passive balancing based on whether the operating environment of the lithium battery pack meets set conditions; after determining that the operating environment meets the set conditions, identifying whether there are abnormal cells in the lithium battery pack; if there are abnormal cells, performing a passive balancing process on the normal cells in the lithium battery pack other than the abnormal cells; if there are no abnormal cells, performing a passive balancing process on the normal cells in the lithium battery pack, gradually adjusting the voltage of each normal cell to a balanced state.

[0011] Furthermore, the operating environment includes operating parameter information and environmental information. When the operating parameter information or the environmental information of the lithium battery pack does not meet the set conditions, the lithium battery pack does not perform passive equalization; when both the operating parameter information and the environmental information of the lithium battery pack meet the set conditions, the lithium battery pack performs passive equalization.

[0012] Furthermore, the operating parameter information includes discharge state and discharge current. When the lithium battery pack is in a discharge state and the discharge current exceeds the first current threshold, the operating environment of the lithium battery pack does not meet the set conditions.

[0013] Furthermore, the operating parameter information includes a static state and a current value; when the lithium battery pack is in a static state and the current value is greater than the second current threshold, the operating environment of the lithium battery pack does not meet the set conditions.

[0014] Furthermore, the environmental information includes temperature information or humidity information. When the temperature information of the lithium battery pack environment does not exceed a set temperature threshold or the humidity information does not exceed a set humidity threshold, the lithium battery pack will not perform a passive equalization process.

[0015] Furthermore, the abnormal cells include aged battery cells. Identifying whether there are aged battery cells in the lithium battery pack includes the following:

[0016] During the discharge process of the lithium battery pack, the battery cells with the lowest voltage value are continuously monitored and recorded. If the lowest voltage value of the battery cell continues to exceed a set first time length, it is identified as the battery cell with the lowest voltage.

[0017] After the lithium battery pack is fully charged, the battery cells with the highest voltage value are continuously monitored and recorded. If the highest voltage value of a battery cell continues to exceed a set second time length, it is identified as the battery cell with the highest voltage.

[0018] If the lowest voltage battery cell and the highest voltage battery cell are the same battery cell, then the battery cell is identified as an aged battery cell.

[0019] Furthermore, the abnormal individual cell includes a battery cell with poor contact. Identifying whether there is a battery cell with poor contact in the lithium battery pack includes the following:

[0020] When the lithium battery pack is in a static state, it is determined whether the average voltage of the lithium battery pack is within a set voltage threshold range. If so, the battery cell whose absolute value of the difference between the voltage of the individual battery cell in the lithium battery pack and the average voltage is greater than a set first difference threshold and whose voltage duration is greater than a set third time length is identified as a battery cell with poor contact.

[0021] Furthermore, a passive balancing process is performed on the normal battery cells in the lithium battery pack, excluding the abnormal cell, to gradually adjust the voltage of each normal battery cell to an equal state. Specifically, this includes the following:

[0022] The voltage of the normal battery cell in the lithium battery pack is judged. When the difference between the highest voltage and the lowest voltage is greater than or equal to the set second difference threshold, equalization is started and run for a fourth time length, then paused for a fifth time length. This equalization is repeated until the difference between the highest voltage and the lowest voltage is less than or equal to the set third difference threshold, which is less than the second difference threshold.

[0023] Furthermore, a passive balancing process is performed on the normal battery cells in the lithium battery pack, excluding the abnormal cell, to gradually adjust the voltage of each normal battery cell to an equal state. Specifically, this includes the following:

[0024] Calculate the average voltage of the normal battery cells in the lithium battery pack, and look up the corresponding start and stop thresholds from the equalization threshold lookup table based on the average voltage. If the voltage of a single normal battery cell reaches or exceeds the start threshold, equalization is started. If the voltage of each normal battery cell is lower than the stop threshold, equalization is stopped.

[0025] During the balancing process, a cyclical pattern is adopted, in which the process runs for a sixth time period and then stops for a seventh time period, and the average voltage of the normal battery cells is periodically recalculated to query new on and off thresholds.

[0026] A passive balancing device for a lithium battery pack, comprising:

[0027] The judgment module determines whether the lithium battery pack needs to be passively balanced based on whether the operating environment of the lithium battery pack meets the set conditions.

[0028] The abnormal cell identification module identifies abnormal cells in the lithium battery pack after determining that the operating environment meets the set conditions.

[0029] The balancing module is used to perform a passive balancing process on the normal battery cells in the lithium battery pack, excluding the abnormal cell, and gradually adjust the voltage of each normal battery cell to a balanced state.

[0030] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. In this invention, the suitability of the lithium battery pack for passive equalization is determined based on the working environment. During passive equalization, abnormal cells in the lithium battery pack are identified and effectively protected. Normal battery cells other than abnormal cells are subjected to passive equalization process, resulting in ideal equalization effect, avoiding over-equalization, and extending the service life of the lithium battery.

[0032] 2. In this invention, the variable and complex operating environment includes operating parameter information and environmental information. The operating parameter information includes discharge state and discharge current, static state and current value, etc. The environmental information includes temperature information or humidity information of the environment in which the lithium battery pack is located, etc. Combining these actual operating environment conditions, it is determined whether to perform passive equalization, so as to avoid the problem of operating environment affecting the acquisition of equalization voltage and the determination of equalization strategy, and protect the battery from potential damage.

[0033] 3. This invention possesses precise detection and identification capabilities for abnormal cells, enabling rapid and accurate identification of abnormal battery cells with performance degradation or potential problems, such as aging cells or cells with poor contact. Immediate protective measures are taken to effectively isolate and mitigate further damage to these cells during the equalization process. This not only prevents the passive equalization function from failing under specific circumstances but also significantly improves the overall stability and reliability of the lithium battery pack through refined cell management.

[0034] 4. In this invention, the strategy logic of the passive balancing stage is optimized. When executing the passive balancing process, by starting for a period of time and pausing for a period of time, the device can not only have time to dissipate heat and avoid overheating due to prolonged operation, thus protecting the safety of the battery, but also reduce wear and tear caused by continuous operation and extend the service life of the lithium battery.

[0035] 5. This invention is applicable to new energy lithium battery forklifts and can significantly improve the balancing efficiency and protection effect of the battery pack, thereby effectively extending the service life of the lithium battery. By reducing performance degradation caused by abnormally balanced cells, it extends the service life of the lithium battery pack by an additional one to two years, providing users with a more durable and reliable energy solution. Attached Figure Description

[0036] Figure 1 This is the main flowchart of the method of the present invention;

[0037] Figure 2 This is a flowchart of Embodiment 1 of the present invention;

[0038] Figure 3 This is a flowchart of Embodiment 2 of the present invention;

[0039] Figure 4 This is a table of equalization thresholds.

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Detailed Implementation

[0041] The present invention will be further described below through specific embodiments.

[0042] In practical applications, lithium battery packs face variable operating conditions and complex environments, such as usage frequency, environment, and usage habits. These factors may cause abnormalities in individual battery cells, thereby affecting the acquisition of equalization voltage and the determination of equalization strategies, further amplifying the inconsistency of lithium batteries, and consequently greatly reducing the usable capacity of the lithium battery pack.

[0043] This invention, by comprehensively considering the existence of variable operating conditions and environment, and addressing the inconsistencies between individual cells, adjusts the passive balancing logic and proposes a passive balancing method for lithium battery packs. (See [link to relevant documentation]). Figure 1 It includes:

[0044] S1 determines whether the lithium battery pack needs passive equalization based on whether the operating environment of the lithium battery pack meets the set conditions. If the conditions are not met, passive equalization is not performed, and this step is repeated to continuously detect. If the conditions are met, the process proceeds to step S2 to perform passive equalization.

[0045] In this invention, the operating environment includes operating parameter information and environmental information. Operating parameters include the operating status and related parameters of the lithium battery pack, while environmental information refers to the relevant parameters of the environment in which the lithium battery pack operates. This information affects the equalization operation. Specifically, when either the operating parameter information or the environmental information of the lithium battery pack does not meet the set conditions (such as extreme temperature, severe vibration, etc.), the lithium battery pack will not undergo passive equalization to protect it from potential damage. The set conditions are determined by setting relevant thresholds, and the judgment is achieved by comparing the operating parameter information and environmental information with the corresponding thresholds.

[0046] In practical applications, the operating parameters include discharge state and discharge current. When the lithium battery pack is in a discharge state and the discharge current exceeds a first current threshold, the lithium battery pack does not undergo a passive equalization process. Alternatively, the operating parameters include resting state and current value; when the lithium battery pack is not in a resting state and the current value is greater than a second current threshold, the lithium battery pack does not undergo a passive equalization process. The first and second current thresholds can be set according to actual conditions and are different; for example, the first current threshold could be 9.8A and the second current threshold could be 3A.

[0047] Environmental information includes temperature and humidity data. If the temperature or humidity of the lithium battery pack's environment does not exceed the set temperature or humidity threshold (i.e., the temperature or humidity exceeds the limit), it may affect the equalization effect and battery safety. In this case, the lithium battery pack will not undergo a passive equalization process. The temperature and humidity thresholds can be set according to actual conditions, for example, a temperature threshold of 70℃ and a humidity threshold of 60% RH. Environmental information may also include other information that can affect the equalization of the lithium battery pack.

[0048] When both the operating parameters and environmental information of the lithium battery pack meet the set conditions, the lithium battery pack undergoes passive equalization. During time-based judgment, one or more of the operating parameters and environmental information can be selected for evaluation as needed.

[0049] After S2 determines that the operating environment meets the set conditions, it identifies whether there are abnormal cells in the lithium battery pack. If there are abnormal cells, it performs a passive equalization process on the normal cells in the lithium battery pack, gradually adjusting the voltage of each normal cell to an equal state. If there are no abnormal cells, it directly performs a passive equalization process on the cells in the lithium battery pack.

[0050] This step utilizes precise detection technology to identify any abnormal cells. These abnormal cells may exhibit inconsistencies due to aging, poor contact, damage, or specific usage patterns. Upon detection, protective measures are prioritized, such as temporary isolation and removal, to prevent further damage during the equalization process. Only after ensuring the abnormal cells are properly protected will the passive equalization process be safely initiated. This process gradually adjusts the voltage of each cell to a balanced state through passive equalization and other methods. If no abnormal cells are detected, the normal passive equalization process is initiated directly, quickly and effectively balancing the charge of each battery cell, improving the overall performance and lifespan of the lithium battery pack. This intelligent equalization strategy not only ensures the safety and effectiveness of the equalization operation but also significantly extends the lifespan of the lithium battery.

[0051] The identification of whether there are aged battery cells in the lithium battery pack includes the following:

[0052] During the discharge process of the lithium battery pack, the battery cells with the lowest voltage value are continuously monitored and recorded. If the lowest voltage value of a battery cell continues to exceed a set first time length, it is identified as the battery cell with the lowest voltage.

[0053] After the lithium battery pack is fully charged, the battery cells with the highest voltage value are continuously monitored and recorded. If the highest voltage value of a battery cell continues to exceed a set second time length, it is identified as the battery cell with the highest voltage.

[0054] If the lowest voltage battery cell and the highest voltage battery cell are the same battery cell, then the battery cell is considered to be an aged battery cell.

[0055] The specific values ​​of the first and second time lengths can be set according to the actual situation. They can be the same or different, for example, both can be 30 seconds.

[0056] Identifying whether there are poorly connected battery cells in a lithium battery pack includes the following:

[0057] When the lithium battery pack is in a static state, it is determined whether the average voltage of the lithium battery pack is within a set voltage threshold range. If so, battery cells whose absolute value of the difference between the voltage of a single cell and the average voltage is greater than a set first difference threshold, and whose voltage duration is greater than a set third time length, are identified as having poor contact. The specific values ​​of the first difference threshold and the third time length can be set according to actual conditions; for example, the first difference threshold could be 50mV and the third time length could be 5s.

[0058] In this embodiment, abnormal cells are protected and not included in the equalization process to avoid further damage during the equalization process. Specifically, a passive equalization process is performed on the normal cells in the lithium battery pack, excluding the abnormal cells, to gradually adjust the voltage of each normal cell to an equalized state. This includes the following:

[0059] The voltage of normal battery cells in the lithium battery pack is assessed. When the difference between the highest and lowest voltages is greater than or equal to a set second threshold, equalization is initiated and runs for a fourth time period, then paused for a fifth time period. This equalization process is repeated until the difference between the highest and lowest voltages is less than or equal to a set third threshold. At this point, equalization is considered complete, and the equalization function is deactivated to protect the battery pack from the potential effects of over-equalization. The third threshold is lower than the second threshold, and the fifth time period is shorter than the fourth time period.

[0060] The specific values ​​of the second difference threshold, the third difference threshold, the fourth time length, and the fifth time length can be set according to the actual situation. For example, the second difference threshold is 10mV, the third difference threshold is 5mV, the fourth time length is 9 minutes, and the fifth time length is 3 minutes.

[0061] In practical applications, the passive balancing process is not limited to this; the following methods can also be used:

[0062] The average voltage of each normal cell in the lithium battery pack is calculated. Based on the average voltage, the corresponding on and off thresholds are looked up from the equalization threshold lookup table. If the voltage of a single normal cell reaches or exceeds the on threshold, equalization is initiated; if the voltage of any normal cell is below the off threshold, equalization is deactivated. The equalization threshold lookup table records the average voltage and its corresponding on and off thresholds. (See [link to table]). Figure 4 .

[0063] Furthermore, during the balancing process, a cyclical mode is adopted, in which the process runs for a sixth time period and then stops for a seventh time period. The average voltage of normal battery cells is recalculated periodically to query new on and off thresholds, ensuring the balancing effect while protecting battery health.

[0064] The specific values ​​for the sixth and seventh time lengths can be set according to the actual situation. For example, the sixth time length is 4 minutes and the seventh time length is 1 minute.

[0065] This invention ensures the safety and effectiveness of equalization operations by continuously monitoring the operating environment of the lithium battery pack and the status of individual cells. The operating parameter information and environmental information in step 1), as well as the abnormal cell identification and passive equalization process in step 2), can be combined according to actual needs.

[0066] Examples are given below:

[0067] See Figure 2 The system determines whether the lithium battery pack needs passive equalization based on whether the operating environment meets the set conditions. When the lithium battery pack is not in a discharging state, the discharge current does not exceed the first current threshold (e.g., 9.8A), and the temperature does not exceed the set temperature threshold (e.g., 70℃), the lithium battery pack is suitable for equalization. The system then identifies whether there are aged battery cells in the lithium battery pack. If there are no aged battery cells, the system directly performs the passive equalization process on the normal battery cells. If there are aged battery cells, these aged battery cells are protected and do not participate in the equalization process, while the remaining normal battery cells undergo the passive equalization process.

[0068] The passive equalization process includes: judging the voltage of normal battery cells in the lithium battery pack; when the difference between the highest and lowest voltages is less than the set second difference threshold (e.g., 10mV), the equalization ends; when the difference between the highest and lowest voltages is greater than or equal to the set second difference threshold (e.g., 10mV), equalization is started and continues for a fourth time period (e.g., 9 minutes), then paused for a fifth time period (e.g., 3 minutes), and so on, until the difference between the highest and lowest voltages is less than or equal to the set third difference threshold (5mV), at which point the equalization is considered complete and the equalization ends.

[0069] See Figure 3 The system determines whether passive equalization of the lithium battery pack should be performed based on whether the operating environment meets the set conditions. When the lithium battery pack is in a static state, the current value is less than or equal to the second current threshold (e.g., 3A), and the humidity does not exceed the humidity threshold (e.g., 60% RH), it is suitable for equalization. The system then identifies whether there are any battery cells with abnormal contact in the lithium battery pack. If there are no battery cells with abnormal contact, the passive equalization process is directly performed on the normal battery cells; if there are battery cells with abnormal contact, these abnormal battery cells are protected and do not participate in the equalization process, while the remaining normal battery cells undergo passive equalization.

[0070] The passive balancing process includes: calculating the average voltage of normal battery cells in the lithium battery pack; looking up the corresponding on and off thresholds from the balancing threshold lookup table based on the average voltage; if the voltage of a single normal battery cell is less than the on threshold, balancing ends; if the voltage of a single normal battery cell reaches or exceeds the on threshold, balancing is started and continues for a sixth time period (e.g., 4 minutes), then pauses for a seventh time period (e.g., 1 minute), and repeats this process until the voltage of each normal battery cell is lower than the off threshold, at which point balancing ends.

[0071] Based on this, the present invention also proposes a passive balancing device for lithium battery packs, which is used to implement the above-mentioned passive balancing method for lithium battery packs, comprising:

[0072] The judgment module determines whether the lithium battery pack should undergo passive balancing based on whether the operating environment meets the set conditions. Passive balancing is performed when the operating environment meets the set conditions; otherwise, it is not performed. This module executes step 1 above.

[0073] The abnormal cell identification module identifies abnormal cells in the lithium battery pack after confirming that the operating environment meets the set conditions. This module can identify various abnormal cells, including aged abnormal cells, abnormal cells with poor contact, or damaged abnormal cells, etc. This module is used to perform the abnormal cell identification part in step 2) above.

[0074] The balancing module is used to perform a passive balancing process on the normal battery cells in the lithium battery pack, excluding abnormal cells, gradually adjusting the voltage of each normal battery cell to a balanced state. This module is used to execute the passive balancing process part of step 2).

[0075] The method and apparatus of this invention are applicable to new energy lithium battery forklifts, and can significantly improve the balancing efficiency and protection effect of the battery pack, thereby effectively extending the service life of the lithium battery. By reducing the performance degradation caused by abnormally balanced individual cells, it brings an additional one to two years of service life extension to the lithium battery pack, providing users with a more durable and reliable energy solution.

[0076] In this invention, the terms "first," "second," and "third," etc., are used only to distinguish similar objects and are not necessarily used to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. The use of terms such as "upper," "lower," "left," "right," "front," and "rear" to indicate orientation or positional relationships is based on the orientation or positional relationships shown in the accompanying drawings and is only for the convenience of describing the invention, not to indicate or imply that the device referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation on the scope of protection of this invention. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0077] Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0078] The above are merely specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the protection scope of the present invention.

Claims

1. A passive balancing method for lithium battery packs, characterized in that, include: Whether the lithium battery pack needs to be passively balanced depends on whether the operating environment of the lithium battery pack meets the set conditions. After confirming that the operating environment meets the set conditions, the system identifies whether there are any abnormal cells in the lithium battery pack. If there are abnormal cells, the system performs a passive balancing process on the normal cells in the lithium battery pack, excluding the abnormal cells. If there are no abnormal cells, the system performs a passive balancing process on the normal cells in the lithium battery pack, gradually adjusting the voltage of each normal cell to a balanced state.

2. The passive balancing method for a lithium battery pack as described in claim 1, characterized in that, The operating environment includes operating parameter information and environmental information. When the operating parameter information or the environmental information of the lithium battery pack does not meet the set conditions, the lithium battery pack does not perform passive equalization; when both the operating parameter information and the environmental information of the lithium battery pack meet the set conditions, the lithium battery pack performs passive equalization.

3. The passive balancing method for a lithium battery pack as described in claim 2, characterized in that, The operating parameter information includes discharge state and discharge current. When the lithium battery pack is in discharge state and the discharge current exceeds the first current threshold, the operating environment of the lithium battery pack does not meet the set conditions.

4. The passive balancing method for a lithium battery pack as described in claim 2, characterized in that, The operating parameter information includes the static state and the current value; when the lithium battery pack is in the static state and the current value is greater than the second current threshold, the operating environment of the lithium battery pack does not meet the set conditions.

5. The passive balancing method for a lithium battery pack as described in claim 2, characterized in that, The environmental information includes temperature information or humidity information. When the temperature information of the lithium battery pack environment does not exceed the set temperature threshold or the humidity information does not exceed the set humidity threshold, the lithium battery pack will not perform a passive equalization process.

6. The passive balancing method for a lithium battery pack as described in claim 1, characterized in that, The abnormal cells include aged battery cells. Identifying whether there are aged battery cells in the lithium battery pack includes the following: During the discharge process of the lithium battery pack, the battery cells with the lowest voltage value are continuously monitored and recorded. If the lowest voltage value of the battery cell continues to exceed a set first time length, it is identified as the battery cell with the lowest voltage. After the lithium battery pack is fully charged, the battery cells with the highest voltage value are continuously monitored and recorded. If the highest voltage value of a battery cell continues to exceed a set second time length, it is identified as the battery cell with the highest voltage. If the lowest voltage battery cell and the highest voltage battery cell are the same battery cell, then the battery cell is identified as an aged battery cell.

7. The passive balancing method for a lithium battery pack as described in claim 1, characterized in that, The abnormal cells include battery cells with poor contact. Identifying whether there are battery cells with poor contact in the lithium battery pack includes the following: When the lithium battery pack is in a static state, it is determined whether the average voltage of the lithium battery pack is within a set voltage threshold range. If so, the battery cell whose absolute value of the difference between the voltage of the individual battery cell in the lithium battery pack and the average voltage is greater than a set first difference threshold and whose voltage duration is greater than a set third time length is identified as a battery cell with poor contact.

8. The passive balancing method for a lithium battery pack as described in claim 1, characterized in that, A passive balancing process is performed on the normal battery cells in the lithium battery pack, excluding the abnormal cell, to gradually adjust the voltage of each normal battery cell to an equal state. Specifically, this includes the following: The voltage of the normal battery cell in the lithium battery pack is judged. When the difference between the highest voltage and the lowest voltage is greater than or equal to the set second difference threshold, equalization is started and run for a fourth time length, then paused for a fifth time length. This equalization is repeated until the difference between the highest voltage and the lowest voltage is less than or equal to the set third difference threshold, which is less than the second difference threshold.

9. The passive balancing method for a lithium battery pack as described in claim 1, characterized in that, A passive balancing process is performed on the normal battery cells in the lithium battery pack, excluding the abnormal cell, to gradually adjust the voltage of each normal battery cell to an equal state. Specifically, this includes the following: Calculate the average voltage of the normal battery cells in the lithium battery pack, and look up the corresponding start and stop thresholds from the equalization threshold lookup table based on the average voltage. If the voltage of a single normal battery cell reaches or exceeds the start threshold, equalization is started. If the voltage of each normal battery cell is lower than the stop threshold, equalization is stopped. During the balancing process, a cyclical pattern is adopted, in which the process runs for a sixth time period and then stops for a seventh time period, and the average voltage of the normal battery cells is periodically recalculated to query new on and off thresholds.

10. A passive balancing device for a lithium battery pack, characterized in that, include: The judgment module determines whether the lithium battery pack needs to be passively balanced based on whether the operating environment of the lithium battery pack meets the set conditions. The abnormal cell identification module identifies abnormal cells in the lithium battery pack after determining that the operating environment meets the set conditions. The balancing module is used to perform a passive balancing process on the normal battery cells in the lithium battery pack, excluding the abnormal cell, and gradually adjust the voltage of each normal battery cell to a balanced state.

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