A lithium battery direct current internal resistance detection method and system

Abstract

This invention provides a method and system for detecting the DC internal resistance of a lithium battery in the field of lithium battery performance testing technology. The method includes the following steps: S1, setting a threshold; S2, when the lithium battery is in a charging state, acquiring the real-time SOC and real-time current of the lithium battery; S3, when the real-time SOC < a second SOC threshold, proceeding to step S4; when the second SOC threshold ≤ real-time SOC < a third SOC threshold, proceeding to step S5; when the real-time SOC ≥ the third SOC threshold, proceeding to step S6; S4, when the real-time SOC ≥ a first SOC threshold, or the real-time current ≥ a second current threshold, proceeding to step S7; S5, determining whether the real-time current ≥ the second current threshold, proceeding to step S7; S6, determining whether the real-time current ≥ the first current threshold, proceeding to step S7; S7, calculating DCR1, DCR2, and DCR3 based on differential calculation and weighted averaging to obtain the DC internal resistance. The advantages of this invention are: it greatly improves the accuracy, safety, and efficiency of lithium battery DC internal resistance detection.

Description

Technical Field

[0001] This invention relates to the field of lithium battery performance testing technology, and in particular to a method and system for detecting the DC internal resistance of lithium batteries. Background Technology

[0002] DC internal resistance (DCR) is one of the key parameters for evaluating lithium battery performance. Research findings on DCR have wide applications in many fields such as engineering manufacturing and battery management, specifically in the following areas:

[0003] 1. Basis for assessing battery state of health (SOH): The DC internal resistance changes significantly with battery aging and has become a key indicator for many companies to assess SOH.

[0004] 2. Basis for cell sorting and grouping: The consistency of the internal resistance of individual cells directly affects the module capacity and service life. Therefore, DC internal resistance is widely used for cell sorting and grouping and is an important static screening indicator.

[0005] 3. Lithium plating phenomenon judgment index: In the application scenarios of retired batteries such as cascade utilization, DC internal resistance detection combined with parameters such as capacity loss can be used to determine whether the battery has the risk of lithium plating.

[0006] 4. Auxiliary parameters for State of Charge (SOC) estimation: DC internal resistance is closely related to battery charge, so it is used for SOC estimation in battery management system (BMS).

[0007] 5. Fault diagnosis indicators of power battery system: DC internal resistance is an important parameter characterizing potential battery faults and serves as a core evaluation indicator in the fault diagnosis system of power battery pack.

[0008] Given the crucial role of DC internal resistance in the multi-dimensional evaluation and control of lithium batteries, real-time online sampling and analysis are particularly important. However, existing DC internal resistance detection methods mainly rely on static evaluation, and the real-time online detection architecture is complex and difficult to implement practically, leading to the following common shortcomings in enterprise project management:

[0009] 1. Limited SOC evaluation range: Conventional methods typically perform single-point testing around 50% SOC, ignoring the nonlinear variation characteristics of DC internal resistance under low and high SOC conditions, resulting in evaluation results that deviate from actual usage scenarios.

[0010] 2. Insufficient current adaptability: Most of them use fixed high current detection schemes, which can easily damage low SOC batteries and cannot effectively simulate the dynamic current characteristics in the actual charging and discharging process, thus limiting the application value of the measurement results.

[0011] 3. Low detection efficiency: Wide-range (e.g., 0%-100% SOC) measurement takes a long time, which cannot meet the real-time requirements of application scenarios that require rapid response, such as battery swapping cabinets.

[0012] Therefore, how to provide a method and system for detecting the DC internal resistance of lithium batteries, so as to improve the accuracy, safety (especially the protection of low SOC batteries) and efficiency (shorten the detection time and meet the real-time requirements) of the detection of the DC internal resistance of lithium batteries, has become an urgent technical problem to be solved. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to provide a method and system for detecting the DC internal resistance of lithium batteries, thereby improving the accuracy, safety and efficiency of detecting the DC internal resistance of lithium batteries.

[0014] In a first aspect, the present invention provides a method for detecting the DC internal resistance of a lithium battery, comprising the following steps:

[0015] Step S1: Set a first SOC threshold, a second SOC threshold, a third SOC threshold, a first current threshold, a second current threshold, a first duration threshold, a second duration threshold, and a current loading threshold; the first SOC threshold is less than the second SOC threshold, the second SOC threshold is less than the third SOC threshold, and the first current threshold is less than the second current threshold.

[0016] Step S2: Monitor the operating status of the lithium battery. When the lithium battery is in the charging state, collect the real-time SOC and real-time current of the lithium battery.

[0017] Step S3: Determine the SOC range of real-time SOC based on the second SOC threshold and the third SOC threshold. If real-time SOC < second SOC threshold, proceed to step S4; if second SOC threshold ≤ real-time SOC < third SOC threshold, proceed to step S5; if real-time SOC ≥ third SOC threshold, proceed to step S6.

[0018] Step S4: Determine whether the real-time SOC is less than the first SOC threshold or the real-time current is less than the second current threshold. If yes, proceed to step S3; otherwise, proceed to step S7.

[0019] Step S5: Determine whether the real-time current is less than the second current threshold. If yes, proceed to step S3; otherwise, proceed to step S7.

[0020] Step S6: Determine whether the real-time current is less than the first current threshold. If yes, proceed to step S3; otherwise, proceed to step S7.

[0021] Step S7: After the lithium battery continues to charge for the first time threshold, the first voltage value and the first current value of the lithium battery are collected. Then, the charging current of the lithium battery is superimposed with the current loading threshold. After the lithium battery continues to charge for the second time threshold, the second voltage value and the second current value of the lithium battery are collected.

[0022] Step S8: Calculate the segmented DC internal resistance based on the first voltage value, the first current value, the second voltage value, and the second current value. The segmented DC internal resistance calculated in the range where real-time SOC < second SOC threshold is taken as DCR1, the segmented DC internal resistance calculated in the range where second SOC threshold ≤ real-time SOC < third SOC threshold is taken as DCR2, and the segmented DC internal resistance calculated in the range where real-time SOC ≥ third SOC threshold is taken as DCR3.

[0023] Step S9: Calculate the DC internal resistance of the lithium battery by performing a weighted average calculation on DCR1, DCR2 and DCR3.

[0024] Furthermore, in step S1, the first SOC threshold is 5%; the second SOC threshold is 50%; the third SOC threshold is 90%; the first current threshold is 5A; and the second current threshold is 14A.

[0025] Furthermore, in step S1, the first duration threshold is set to 10 seconds; the second duration threshold is set to 3 seconds; and the current loading threshold is set to 0.5A.

[0026] Furthermore, in step S8, the formula for calculating the segmented DC internal resistance is:

[0027] Segmented DC internal resistance = (second voltage value - first voltage value) / (second current value - first current value).

[0028] Furthermore, in step S9, the formula for calculating the DC internal resistance is:

[0029] DCR = a*DCR1 + b*DCR2 + c*DCR3;

[0030] Where DCR represents the DC internal resistance of the lithium battery; a, b, and c all represent weighting coefficients.

[0031] Secondly, the present invention provides a lithium battery DC internal resistance detection system, comprising the following modules:

[0032] The threshold setting module is used to set a first SOC threshold, a second SOC threshold, a third SOC threshold, a first current threshold, a second current threshold, a first duration threshold, a second duration threshold, and a current loading threshold; the first SOC threshold is less than the second SOC threshold, the second SOC threshold is less than the third SOC threshold, and the first current threshold is less than the second current threshold.

[0033] The operating status monitoring module is used to monitor the operating status of the lithium battery. When the lithium battery is in the charging state, it collects the real-time SOC and real-time current of the lithium battery.

[0034] The SOC interval judgment module is used to judge the SOC interval of real-time SOC based on the second SOC threshold and the third SOC threshold. When real-time SOC < second SOC threshold, it enters the first verification module; when the second SOC threshold ≤ real-time SOC < third SOC threshold, it enters the second verification module; when real-time SOC ≥ third SOC threshold, it enters the third verification module.

[0035] The first verification module is used to determine whether the real-time SOC is less than the first SOC threshold or the real-time current is less than the second current threshold. If so, it enters the SOC range judgment module; otherwise, it enters the data acquisition module.

[0036] The second verification module is used to determine whether the real-time current is less than the second current threshold. If so, it enters the SOC range judgment module; otherwise, it enters the data acquisition module.

[0037] The third verification module is used to determine whether the real-time current is less than the first current threshold. If so, it enters the SOC range judgment module; otherwise, it enters the data acquisition module.

[0038] The data acquisition module is used to collect the first voltage value and the first current value of the lithium battery after the lithium battery continues to charge for the first time threshold. Then, the current loading threshold is added to the charging current of the lithium battery. After the lithium battery continues to charge for the second time threshold, the second voltage value and the second current value of the lithium battery are collected.

[0039] The differential calculation module is used to calculate the segmented DC internal resistance based on the first voltage value, the first current value, the second voltage value, and the second current value. The segmented DC internal resistance calculated in the range of real-time SOC < second SOC threshold is used as DCR1, the segmented DC internal resistance calculated in the range of second SOC threshold ≤ real-time SOC < third SOC threshold is used as DCR2, and the segmented DC internal resistance calculated in the range of real-time SOC ≥ third SOC threshold is used as DCR3.

[0040] The DC internal resistance calculation module is used to calculate the DC internal resistance of the lithium battery by performing a weighted average calculation on DCR1, DCR2 and DCR3.

[0041] Furthermore, in the threshold setting module, the first SOC threshold is set to 5%; the second SOC threshold is set to 50%; the third SOC threshold is set to 90%; the first current threshold is set to 5A; and the second current threshold is set to 14A.

[0042] Furthermore, in the threshold setting module, the first duration threshold is set to 10 seconds; the second duration threshold is set to 3 seconds; and the current loading threshold is set to 0.5A.

[0043] Furthermore, in the differential calculation module, the calculation formula for the segmented DC internal resistance is as follows:

[0044] Segmented DC internal resistance = (second voltage value - first voltage value) / (second current value - first current value).

[0045] Furthermore, in the DC internal resistance calculation module, the formula for calculating the DC internal resistance is:

[0046] DCR = a*DCR1 + b*DCR2 + c*DCR3;

[0047] Where DCR represents the DC internal resistance of the lithium battery; a, b, and c all represent weighting coefficients.

[0048] The advantages of this invention are:

[0049] 1. By setting a first SOC threshold, a second SOC threshold, a third SOC threshold, a first current threshold, a second current threshold, a duration threshold, and a current loading threshold, the operating status of the lithium battery is monitored. When the lithium battery is charging, the real-time SOC and real-time current of the lithium battery are collected. Then, based on the second and third SOC thresholds, the SOC range of the real-time SOC is judged, and different branches are entered based on different SOC ranges. After the lithium battery continues to charge for a duration threshold to stabilize the current, the first voltage value and the first current value of the lithium battery are collected. Then, the current loading threshold is superimposed on the charging current of the lithium battery. After the lithium battery continues to charge for a duration threshold to stabilize the current, the second voltage value and the second current value of the lithium battery are collected. Finally, based on the first voltage value, the first current value, the second voltage value, and the second current value, DCR1, DCR2, and D are calculated using a differential algorithm. CR3 calculates the DC internal resistance of the lithium battery by weighted averaging DCR1, DCR2, and DCR3. Specifically, by setting three SOC thresholds (first / second / third), the battery state is divided into three typical ranges: low, medium, and high. During charging, detection is dynamically triggered based on real-time SOC and adaptive current thresholds (first / second current thresholds). Different triggering conditions are used for different SOC ranges. Combined with a small-amplitude current load (0.5A) and short-time sampling (3 seconds), this method protects the safety of low-charge batteries while accurately capturing the segmented internal resistance (DCR1 / DCR2 / DCR3) across the entire SOC range. Finally, by weighted averaging and integrating the nonlinear characteristics of different ranges, high-precision, low-damage internal resistance detection is completed within 3 seconds, significantly improving measurement efficiency and applicability under various operating conditions. Ultimately, this greatly enhances the accuracy, safety, and efficiency of lithium battery DC internal resistance detection.

[0050] 2. By dividing the SOC (State of Charge) of lithium batteries into three intervals—low (<50%), medium (50%–90%), and high (≥90%)—and independently calculating the segmented DC internal resistance (DCR1, DCR2, DCR3) for each interval, this segmentation takes into account the non-linear characteristics of lithium battery internal resistance changing with SOC (e.g., internal resistance is usually higher at low SOC), avoiding errors caused by single-point measurements. The final DCR is calculated by weighted averaging (formula: DCR=a*DCR1+b*DCR2+c*DCR3), and the weighting coefficients a, b, and c can be adjusted according to battery type or application scenario, ensuring that the results better reflect the overall battery performance. Compared with traditional methods (such as single-pulse testing), this improves the reliability and repeatability of internal resistance measurement, helping to more accurately assess the battery's state of health (SOH).

[0051] 3. Measurements are actively triggered during lithium battery charging, eliminating the need to stop charging or perform dedicated test cycles. By setting current thresholds (e.g., a second current threshold of 14A) and SOC thresholds (e.g., a first SOC threshold of 5%), measurement steps are performed only under specific conditions (e.g., when the current is high), avoiding unnecessary operations. This reduces the total detection time (e.g., setting a first duration threshold of 10 seconds and a second duration threshold of 3 seconds), saving energy and computing resources. The application of a current loading threshold (0.5A) allows for small-scale controllable current changes, ensuring stable voltage difference measurement and simplifying the data acquisition process. The overall process is automated and easily integrated into the battery management system (BMS), improving the efficiency of real-time monitoring.

[0052] 4. By designing multiple safety judgment logics, such as requiring high current conditions to perform measurements only when the SOC is low (<50%), or only allowing low current (first current threshold of 5A) to trigger measurements when the SOC is high (≥90%), excessive current is prevented from being introduced under battery sensitive conditions (such as deep discharge or full charge), reducing the risk of overheating, short circuit or performance degradation; by controlling the duration threshold (such as the second duration threshold of 3 seconds), the duration of current loading is limited, reducing the impact of electrochemical stress on battery life. This preventive design is more suitable for high safety requirements scenarios such as electric vehicles.

[0053] 5. With configurable threshold parameters (such as SOC thresholds of 50% and 90%, and current thresholds of 5A and 14A), it can be adapted to different battery types and operating conditions (such as charging speed); the introduction of weights allows for optimization for specific application scenarios (such as assigning greater weight to high SOC batteries in automobiles), enhancing versatility; the segmented calculation formula (segmented DC internal resistance = (second voltage value - first voltage value) / (second current value - first current value)) is simple and easy to implement, based on the principle of Ohm's law, but effectively handles the problem of dynamic changes in the battery through segmented processing, making the method easy to deploy in laboratory or industrial environments.

[0054] 6. By independently outputting DCR1, DCR2, and DCR3, internal resistance data for each SOC range is provided, helping to identify specific problems (such as increased internal resistance in the low SOC range may indicate aging). Combined with weighted DCR, predictive maintenance capabilities are enhanced, enabling early detection of battery faults. The entire system is based on software algorithms, with low hardware requirements (only existing charging equipment and sensors are needed), and can be easily applied to existing BMS through software upgrades, reducing implementation costs.

[0055] 7. By dividing the SOC into three intervals (<50%, 50%-90%, ≥90%) and combining them with dynamic current thresholds (e.g., 5A / 14A) to trigger measurements, the system intelligently captures the battery state during charging. It calculates the internal resistance of each interval by using segmented loading current and collecting voltage / current values, and finally integrates the results using a weighted average algorithm. This not only significantly improves the accuracy of internal resistance detection (especially solving the error caused by nonlinear changes in SOC), but also greatly optimizes the detection efficiency (no need to interrupt charging, only a short measurement of 13 seconds is required). At the same time, it achieves safety protection by intelligently avoiding sensitive states (such as low SOC with high current or high SOC with forced loading). Ultimately, it provides a highly reliable internal resistance evaluation solution that is suitable for different battery types at a low hardware cost, providing strong support for battery health management. Attached Figure Description

[0056] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0057] Figure 1 This is a flowchart of a method for detecting the DC internal resistance of a lithium battery according to the present invention.

[0058] Figure 2 This is a schematic diagram of the structure of a lithium battery DC internal resistance detection system according to the present invention. Detailed Implementation

[0059] The overall concept of the technical solution in this application is as follows: By setting three SOC thresholds, the battery state is divided into three typical ranges: low, medium, and high. During the charging process, detection is dynamically triggered based on real-time SOC and adaptive current thresholds. Different triggering conditions are used for different SOC ranges. By combining small-amplitude current loading and short-time sampling, the accurate capture of segmented internal resistance across the entire SOC range is achieved while protecting the safety of low-charge batteries. Finally, by calculating the nonlinear characteristics of different ranges using weighted average, high-precision, low-damage internal resistance detection is completed within 3 seconds, thereby improving the accuracy, safety, and efficiency of lithium battery DC internal resistance detection.

[0060] Please refer to Figures 1 to 2 As shown, a preferred embodiment of the method for detecting the DC internal resistance of a lithium battery according to the present invention includes the following steps:

[0061] Step S1: Set a first SOC threshold, a second SOC threshold, a third SOC threshold, a first current threshold, a second current threshold, a first duration threshold, a second duration threshold, and a current loading threshold; the first SOC threshold is less than the second SOC threshold, the second SOC threshold is less than the third SOC threshold, and the first current threshold is less than the second current threshold.

[0062] Step S2: Monitor the operating status of the lithium battery. When the lithium battery is in the charging state, collect the real-time SOC and real-time current of the lithium battery.

[0063] Step S3: Determine the SOC range of real-time SOC based on the second SOC threshold and the third SOC threshold. If real-time SOC < second SOC threshold, proceed to step S4; if second SOC threshold ≤ real-time SOC < third SOC threshold, proceed to step S5; if real-time SOC ≥ third SOC threshold, proceed to step S6.

[0064] Step S4: Determine whether the real-time SOC is less than the first SOC threshold or the real-time current is less than the second current threshold. If yes, proceed to step S3; otherwise, proceed to step S7.

[0065] Step S5: Determine whether the real-time current is less than the second current threshold. If yes, proceed to step S3; otherwise, proceed to step S7.

[0066] Step S6: Determine whether the real-time current is less than the first current threshold. If yes, proceed to step S3; otherwise, proceed to step S7.

[0067] Step S7: After the lithium battery continues to charge for the first time threshold (i.e., after the current stabilizes), collect the first voltage value and the first current value of the lithium battery. Then, add the current loading threshold to the charging current of the lithium battery. After the lithium battery continues to charge for the second time threshold (i.e., after the current stabilizes), collect the second voltage value and the second current value of the lithium battery.

[0068] Step S8: Calculate the segmented DC internal resistance based on the first voltage value, the first current value, the second voltage value, and the second current value. The segmented DC internal resistance calculated in the range where real-time SOC < second SOC threshold is taken as DCR1, the segmented DC internal resistance calculated in the range where second SOC threshold ≤ real-time SOC < third SOC threshold is taken as DCR2, and the segmented DC internal resistance calculated in the range where real-time SOC ≥ third SOC threshold is taken as DCR3.

[0069] Step S9: Calculate the DC internal resistance of the lithium battery by performing a weighted average calculation on DCR1, DCR2 and DCR3.

[0070] This invention covers the DC internal resistance change curve of the entire life cycle of lithium batteries through segmented SOC testing, which reduces the error compared with traditional methods and effectively improves the detection accuracy; it avoids the risk of battery overcurrent by dynamically configuring the current through SOC threshold, and extends the battery cycle life; and it reduces the invalid test time by 70% through the conditional skip test mechanism, which effectively improves the detection efficiency.

[0071] In step S1, the first SOC threshold is set to 5%; the second SOC threshold is set to 50%; the third SOC threshold is set to 90%; the first current threshold is set to 5A; and the second current threshold is set to 14A. In practice, each threshold can be flexibly set based on the actual scenario. At different SOC stages, an appropriate current is dynamically configured for testing to avoid overcharging and ensure data accuracy.

[0072] In step S1, the first duration threshold is 10 seconds; the second duration threshold is 3 seconds; and the current loading threshold is 0.5A.

[0073] In step S8, the formula for calculating the segmented DC internal resistance is:

[0074] Segmented DC internal resistance = (second voltage value - first voltage value) / (second current value - first current value). That is, DCR is calculated differentially by ΔV / ΔI to eliminate interference and improve data accuracy.

[0075] In step S9, the formula for calculating the DC internal resistance is:

[0076] DCR = a*DCR1 + b*DCR2 + c*DCR3;

[0077] Where DCR represents the DC internal resistance of the lithium battery; a, b, and c all represent weighting coefficients.

[0078] A preferred embodiment of the lithium battery DC internal resistance detection system of the present invention includes the following modules:

[0079] The threshold setting module is used to set a first SOC threshold, a second SOC threshold, a third SOC threshold, a first current threshold, a second current threshold, a first duration threshold, a second duration threshold, and a current loading threshold; the first SOC threshold is less than the second SOC threshold, the second SOC threshold is less than the third SOC threshold, and the first current threshold is less than the second current threshold.

[0080] The operating status monitoring module is used to monitor the operating status of the lithium battery. When the lithium battery is in the charging state, it collects the real-time SOC and real-time current of the lithium battery.

[0081] The SOC interval judgment module is used to judge the SOC interval of real-time SOC based on the second SOC threshold and the third SOC threshold. When real-time SOC < second SOC threshold, it enters the first verification module; when the second SOC threshold ≤ real-time SOC < third SOC threshold, it enters the second verification module; when real-time SOC ≥ third SOC threshold, it enters the third verification module.

[0082] The first verification module is used to determine whether the real-time SOC is less than the first SOC threshold or the real-time current is less than the second current threshold. If so, it enters the SOC range judgment module; otherwise, it enters the data acquisition module.

[0083] The second verification module is used to determine whether the real-time current is less than the second current threshold. If so, it enters the SOC range judgment module; otherwise, it enters the data acquisition module.

[0084] The third verification module is used to determine whether the real-time current is less than the first current threshold. If so, it enters the SOC range judgment module; otherwise, it enters the data acquisition module.

[0085] The data acquisition module is used to collect the first voltage value and the first current value of the lithium battery after the lithium battery continues to charge for the first time threshold (i.e., after waiting for the current to stabilize), and then to add the current loading threshold to the charging current of the lithium battery, and after the lithium battery continues to charge for the second time threshold (i.e., after waiting for the current to stabilize), to collect the second voltage value and the second current value of the lithium battery.

[0086] The differential calculation module is used to calculate the segmented DC internal resistance based on the first voltage value, the first current value, the second voltage value, and the second current value. The segmented DC internal resistance calculated in the range of real-time SOC < second SOC threshold is used as DCR1, the segmented DC internal resistance calculated in the range of second SOC threshold ≤ real-time SOC < third SOC threshold is used as DCR2, and the segmented DC internal resistance calculated in the range of real-time SOC ≥ third SOC threshold is used as DCR3.

[0087] The DC internal resistance calculation module is used to calculate the DC internal resistance of the lithium battery by performing a weighted average calculation on DCR1, DCR2 and DCR3.

[0088] This invention covers the DC internal resistance change curve of the entire life cycle of lithium batteries through segmented SOC testing, which reduces the error compared with traditional methods and effectively improves the detection accuracy; it avoids the risk of battery overcurrent by dynamically configuring the current through SOC threshold, and extends the battery cycle life; and it reduces the invalid test time by 70% through the conditional skip test mechanism, which effectively improves the detection efficiency.

[0089] In the threshold setting module, the first SOC threshold is set to 5%; the second SOC threshold is set to 50%; the third SOC threshold is set to 90%; the first current threshold is set to 5A; and the second current threshold is set to 14A. In practice, each threshold can be flexibly set based on the actual scenario. At different SOC stages, an appropriate current is dynamically configured for testing to avoid overcharging and ensure data accuracy.

[0090] In the threshold setting module, the first duration threshold is set to 10 seconds; the second duration threshold is set to 3 seconds; and the current loading threshold is set to 0.5A.

[0091] In the differential calculation module, the calculation formula for the segmented DC internal resistance is:

[0092] Segmented DC internal resistance = (second voltage value - first voltage value) / (second current value - first current value). That is, DCR is calculated differentially by ΔV / ΔI to eliminate interference and improve data accuracy.

[0093] In the DC internal resistance calculation module, the formula for calculating the DC internal resistance is:

[0094] DCR = a*DCR1 + b*DCR2 + c*DCR3;

[0095] Where DCR represents the DC internal resistance of the lithium battery; a, b, and c all represent weighting coefficients.

[0096] In summary, the advantages of this invention are:

[0097] 1. By setting a first SOC threshold, a second SOC threshold, a third SOC threshold, a first current threshold, a second current threshold, a duration threshold, and a current loading threshold, the operating status of the lithium battery is monitored. When the lithium battery is charging, the real-time SOC and real-time current of the lithium battery are collected. Then, based on the second and third SOC thresholds, the SOC range of the real-time SOC is judged, and different branches are entered based on different SOC ranges. After the lithium battery continues to charge for a duration threshold to stabilize the current, the first voltage value and the first current value of the lithium battery are collected. Then, the current loading threshold is superimposed on the charging current of the lithium battery. After the lithium battery continues to charge for a duration threshold to stabilize the current, the second voltage value and the second current value of the lithium battery are collected. Finally, based on the first voltage value, the first current value, the second voltage value, and the second current value, DCR1, DCR2, and D are calculated using a differential algorithm. CR3 calculates the DC internal resistance of the lithium battery by weighted averaging DCR1, DCR2, and DCR3. Specifically, by setting three SOC thresholds (first / second / third), the battery state is divided into three typical ranges: low, medium, and high. During charging, detection is dynamically triggered based on real-time SOC and adaptive current thresholds (first / second current thresholds). Different triggering conditions are used for different SOC ranges. Combined with a small-amplitude current load (0.5A) and short-time sampling (3 seconds), this method protects the safety of low-charge batteries while accurately capturing the segmented internal resistance (DCR1 / DCR2 / DCR3) across the entire SOC range. Finally, by weighted averaging and integrating the nonlinear characteristics of different ranges, high-precision, low-damage internal resistance detection is completed within 3 seconds, significantly improving measurement efficiency and applicability under various operating conditions. Ultimately, this greatly enhances the accuracy, safety, and efficiency of lithium battery DC internal resistance detection.

[0098] 2. By dividing the SOC (State of Charge) of lithium batteries into three intervals—low (<50%), medium (50%–90%), and high (≥90%)—and independently calculating the segmented DC internal resistance (DCR1, DCR2, DCR3) for each interval, this segmentation takes into account the non-linear characteristics of lithium battery internal resistance changing with SOC (e.g., internal resistance is usually higher at low SOC), avoiding errors caused by single-point measurements. The final DCR is calculated by weighted averaging (formula: DCR=a*DCR1+b*DCR2+c*DCR3), and the weighting coefficients a, b, and c can be adjusted according to battery type or application scenario, ensuring that the results better reflect the overall battery performance. Compared with traditional methods (such as single-pulse testing), this improves the reliability and repeatability of internal resistance measurement, helping to more accurately assess the battery's state of health (SOH).

[0099] 3. Measurements are actively triggered during lithium battery charging, eliminating the need to stop charging or perform dedicated test cycles. By setting current thresholds (e.g., a second current threshold of 14A) and SOC thresholds (e.g., a first SOC threshold of 5%), measurement steps are performed only under specific conditions (e.g., when the current is high), avoiding unnecessary operations. This reduces the total detection time (e.g., setting a first duration threshold of 10 seconds and a second duration threshold of 3 seconds), saving energy and computing resources. The application of a current loading threshold (0.5A) allows for small-scale controllable current changes, ensuring stable voltage difference measurement and simplifying the data acquisition process. The overall process is automated and easily integrated into the battery management system (BMS), improving the efficiency of real-time monitoring.

[0100] 4. By designing multiple safety judgment logics, such as requiring high current conditions to perform measurements only when the SOC is low (<50%), or only allowing low current (first current threshold of 5A) to trigger measurements when the SOC is high (≥90%), excessive current is prevented from being introduced under battery sensitive conditions (such as deep discharge or full charge), reducing the risk of overheating, short circuit or performance degradation; by controlling the duration threshold (such as the second duration threshold of 3 seconds), the duration of current loading is limited, reducing the impact of electrochemical stress on battery life. This preventive design is more suitable for high safety requirements scenarios such as electric vehicles.

[0101] 5. With configurable threshold parameters (such as SOC thresholds of 50% and 90%, and current thresholds of 5A and 14A), it can be adapted to different battery types and operating conditions (such as charging speed); the introduction of weights allows for optimization for specific application scenarios (such as assigning greater weight to high SOC batteries in automobiles), enhancing versatility; the segmented calculation formula (segmented DC internal resistance = (second voltage value - first voltage value) / (second current value - first current value)) is simple and easy to implement, based on the principle of Ohm's law, but effectively handles the problem of dynamic changes in the battery through segmented processing, making the method easy to deploy in laboratory or industrial environments.

[0102] 6. By independently outputting DCR1, DCR2, and DCR3, internal resistance data for each SOC range is provided, helping to identify specific problems (such as increased internal resistance in the low SOC range may indicate aging). Combined with weighted DCR, predictive maintenance capabilities are enhanced, enabling early detection of battery faults. The entire system is based on software algorithms, with low hardware requirements (only existing charging equipment and sensors are needed), and can be easily applied to existing BMS through software upgrades, reducing implementation costs.

[0103] 7. By dividing the SOC into three intervals (<50%, 50%-90%, ≥90%) and combining them with dynamic current thresholds (e.g., 5A / 14A) to trigger measurements, the system intelligently captures the battery state during charging. It calculates the internal resistance of each interval by using segmented loading current and collecting voltage / current values, and finally integrates the results using a weighted average algorithm. This not only significantly improves the accuracy of internal resistance detection (especially solving the error caused by nonlinear changes in SOC), but also greatly optimizes the detection efficiency (no need to interrupt charging, only a short measurement of 13 seconds is required). At the same time, it achieves safety protection by intelligently avoiding sensitive states (such as low SOC with high current or high SOC with forced loading). Ultimately, it provides a highly reliable internal resistance evaluation solution that is suitable for different battery types at a low hardware cost, providing strong support for battery health management.

[0104] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for detecting the DC internal resistance of a lithium battery, characterized in that: Includes the following steps: Step S1: Set a first SOC threshold, a second SOC threshold, a third SOC threshold, a first current threshold, a second current threshold, a first duration threshold, a second duration threshold, and a current loading threshold; the first SOC threshold is less than the second SOC threshold, the second SOC threshold is less than the third SOC threshold, and the first current threshold is less than the second current threshold. Step S2: Monitor the operating status of the lithium battery. When the lithium battery is in the charging state, collect the real-time SOC and real-time current of the lithium battery. Step S3: Determine the SOC range of real-time SOC based on the second SOC threshold and the third SOC threshold. If real-time SOC < second SOC threshold, proceed to step S4; if second SOC threshold ≤ real-time SOC < third SOC threshold, proceed to step S5; if real-time SOC ≥ third SOC threshold, proceed to step S6. Step S4: Determine whether the real-time SOC is less than the first SOC threshold or the real-time current is less than the second current threshold. If yes, proceed to step S3; otherwise, proceed to step S7. Step S5: Determine whether the real-time current is less than the second current threshold. If yes, proceed to step S3; otherwise, proceed to step S7. Step S6: Determine whether the real-time current is less than the first current threshold. If yes, proceed to step S3; otherwise, proceed to step S7. Step S7: After the lithium battery continues to charge for the first time threshold, the first voltage value and the first current value of the lithium battery are collected. Then, the charging current of the lithium battery is superimposed with the current loading threshold. After the lithium battery continues to charge for the second time threshold, the second voltage value and the second current value of the lithium battery are collected. Step S8: Calculate the segmented DC internal resistance based on the first voltage value, the first current value, the second voltage value, and the second current value. The segmented DC internal resistance calculated in the range where real-time SOC < second SOC threshold is taken as DCR1, the segmented DC internal resistance calculated in the range where second SOC threshold ≤ real-time SOC < third SOC threshold is taken as DCR2, and the segmented DC internal resistance calculated in the range where real-time SOC ≥ third SOC threshold is taken as DCR3. Step S9: Calculate the DC internal resistance of the lithium battery by performing a weighted average calculation on DCR1, DCR2 and DCR3.

2. The method for detecting the DC internal resistance of a lithium battery as described in claim 1, characterized in that: In step S1, the first SOC threshold is 5%; the second SOC threshold is 50%; the third SOC threshold is 90%; the first current threshold is 5A; and the second current threshold is 14A.

3. The method for detecting the DC internal resistance of a lithium battery as described in claim 1, characterized in that: In step S1, the first duration threshold is 10 seconds; the second duration threshold is 3 seconds; and the current loading threshold is 0.5A.

4. The method for detecting the DC internal resistance of a lithium battery as described in claim 1, characterized in that: In step S8, the formula for calculating the segmented DC internal resistance is: Segmented DC internal resistance = (second voltage value - first voltage value) / (second current value - first current value).

5. The method for detecting the DC internal resistance of a lithium battery as described in claim 1, characterized in that: In step S9, the formula for calculating the DC internal resistance is: DCR = a*DCR1 + b*DCR2 + c*DCR3; Where DCR represents the DC internal resistance of the lithium battery; a, b, and c all represent weighting coefficients.

6. A lithium battery DC internal resistance detection system, characterized in that: Includes the following modules: The threshold setting module is used to set a first SOC threshold, a second SOC threshold, a third SOC threshold, a first current threshold, a second current threshold, a first duration threshold, a second duration threshold, and a current loading threshold; the first SOC threshold is less than the second SOC threshold, the second SOC threshold is less than the third SOC threshold, and the first current threshold is less than the second current threshold. The operating status monitoring module is used to monitor the operating status of the lithium battery. When the lithium battery is in the charging state, it collects the real-time SOC and real-time current of the lithium battery. The SOC interval judgment module is used to judge the SOC interval of real-time SOC based on the second SOC threshold and the third SOC threshold. When real-time SOC < second SOC threshold, it enters the first verification module; when the second SOC threshold ≤ real-time SOC < third SOC threshold, it enters the second verification module; when real-time SOC ≥ third SOC threshold, it enters the third verification module. The first verification module is used to determine whether the real-time SOC is less than the first SOC threshold or the real-time current is less than the second current threshold. If so, it enters the SOC range judgment module. If not, proceed to the data acquisition module; The second verification module is used to determine whether the real-time current is less than the second current threshold. If so, it enters the SOC range judgment module; otherwise, it enters the data acquisition module. The third verification module is used to determine whether the real-time current is less than the first current threshold. If so, it enters the SOC range judgment module; otherwise, it enters the data acquisition module. The data acquisition module is used to collect the first voltage value and the first current value of the lithium battery after the lithium battery continues to charge for the first time threshold. Then, the current loading threshold is added to the charging current of the lithium battery. After the lithium battery continues to charge for the second time threshold, the second voltage value and the second current value of the lithium battery are collected. The differential calculation module is used to calculate the segmented DC internal resistance based on the first voltage value, the first current value, the second voltage value, and the second current value. The segmented DC internal resistance calculated in the range of real-time SOC < second SOC threshold is used as DCR1, the segmented DC internal resistance calculated in the range of second SOC threshold ≤ real-time SOC < third SOC threshold is used as DCR2, and the segmented DC internal resistance calculated in the range of real-time SOC ≥ third SOC threshold is used as DCR3. The DC internal resistance calculation module is used to calculate the DC internal resistance of the lithium battery by performing a weighted average calculation on DCR1, DCR2 and DCR3.

7. The lithium battery DC internal resistance detection system as described in claim 6, characterized in that: In the threshold setting module, the first SOC threshold is set to 5%; the second SOC threshold is set to 50%; the third SOC threshold is set to 90%; the first current threshold is set to 5A; and the second current threshold is set to 14A.

8. The lithium battery DC internal resistance detection system as described in claim 6, characterized in that: In the threshold setting module, the first duration threshold is set to 10 seconds; the second duration threshold is set to 3 seconds; and the current loading threshold is set to 0.5A.

9. A lithium battery DC internal resistance detection system as described in claim 6, characterized in that: In the differential calculation module, the calculation formula for the segmented DC internal resistance is: Segmented DC internal resistance = (second voltage value - first voltage value) / (second current value - first current value).

10. A lithium battery DC internal resistance detection system as described in claim 6, characterized in that: In the DC internal resistance calculation module, the formula for calculating the DC internal resistance is: DCR = a*DCR1 + b*DCR2 + c*DCR3; Where DCR represents the DC internal resistance of the lithium battery; a, b, and c all represent weighting coefficients.

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