Charging strategy making method and charging control device for silicon-carbon negative electrode lithium ion battery

Abstract

This invention discloses a method for formulating a charging strategy and a charging control device for a silicon-carbon anode lithium-ion battery. The method includes: measuring the relationship between the charging rate and the anode potential of the target battery at different states of charge (SOCs) to determine the relationship between the limiting charging rate without lithium plating and the SOC, serving as an initial charging strategy; dividing the 0%~100% SOC of the target battery into multiple continuous SOC intervals; performing segmented cycle verification tests on each interval based on the initial charging strategy to determine the cycle performance parameters of each interval, thereby identifying outlier intervals with failure risk; for each outlier interval, performing segmented cycle verification tests by gradually reducing its charging rate until the corresponding cycle performance parameters meet preset conditions to obtain the target charging rate, thus forming the target charging strategy. This invention can maximize charging speed and extend battery life while ensuring safety.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and more specifically, relates to a method for formulating a charging strategy and a charging control device for a silicon-carbon anode lithium-ion battery. Background Technology

[0002] With the increasing energy density demands of electric vehicles and portable electronic devices, the chemical system of lithium-ion batteries is gradually evolving from liquid to semi-solid and all-solid state. To improve energy density, semi-solid batteries often employ silicon-carbon anode materials. Silicon-carbon anodes have a high theoretical specific capacity, but they face the following problems in practical applications: For traditional liquid lithium-ion batteries, charging strategies typically use lithium plating at the negative electrode as the boundary condition, controlling the charging rate to prevent the negative electrode potential from dropping below 0mV, thereby achieving the maximum charging current. However, when silicon is incorporated into the negative electrode, the lithium intercalation potential of silicon is higher than that of graphite, leading to a higher lithium intercalation potential in the hybrid negative electrode. This results in a significantly increased charging rate based on the lithium plating potential. However, excessively high charging rates cause severe volume expansion of the silicon-based material, deteriorating the contact between the active material and the current collector, leading to significant detachment of the active material and rapid capacity decay. Furthermore, high-rate charging exacerbates the continuous growth and reconstruction of the SEI film, further impacting battery life. Therefore, for silicon-carbon negative electrode batteries, charging strategies must not only avoid lithium plating at the negative electrode but also consider how to suppress negative electrode expansion failure at high rates to ensure stable battery performance.

[0003] To address the aforementioned issues, existing technologies have proposed several improvement solutions. For example, Chinese invention patent CN117810449A discloses a novel negative electrode active material and supporting technical solutions. This involves designing a composite negative electrode containing both carbon and silicon-based materials, combined with dual binders and specific conductive agents, to alleviate silicon expansion. It also proposes a stepped charging method based on SOC ranges, including pre-charging, constant current charging, and trickle charging. However, while this solution mitigates silicon expansion through material design, the cumulative effect of micro-expansion in the silicon-based material after long-term cycling may still affect battery performance. Furthermore, the patent does not explicitly provide a specific method for formulating the charging strategy, making it difficult to fully utilize the battery's maximum charging capacity.

[0004] Another Chinese invention patent, CN117913343A, designs a silicon-carbon lithium-ion stacked battery with a special structure. The negative electrode is divided into silicon and graphite negative electrodes, which are stacked alternately in a "positive electrode / silicon negative electrode / positive electrode / graphite negative electrode" configuration. It also includes a method for initial parallel constant current charging and subsequent individual constant current charging. This scheme avoids the expansion problem caused by the alloying of silicon followed by lithium intercalation in graphite in mixed electrodes by physically separating the silicon and graphite negative electrodes. However, this battery structure is complex, requires high assembly precision, has low production efficiency, and does not provide a clear method for formulating a charging strategy.

[0005] Therefore, there is a lack of a systematic and precise method for formulating charging strategies for silicon-carbon anode lithium-ion batteries that can simultaneously avoid lithium plating and suppress silicon expansion failure, thereby maximizing charging speed and extending cycle life while ensuring battery safety. Summary of the Invention

[0006] The purpose of this invention is to propose a charging strategy formulation method and charging control device for silicon-carbon anode lithium-ion batteries, solving the problem that existing silicon-carbon anode battery charging strategies only control the rate based on the lithium plating boundary and ignore the rapid degradation of cycle performance caused by silicon expansion failure. This invention achieves a target charging strategy and anode potential control boundary that balances avoiding lithium plating and suppressing silicon expansion through segmented cycle verification and iterative correction.

[0007] To achieve the above objectives, in a first aspect, the present invention proposes a method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery, comprising: The relationship between the charging rate and the negative electrode potential of the target battery under different states of charge was determined to identify the relationship between the limiting charging rate without lithium plating and the state of charge, which can be used as an initial charging strategy. The target battery's 0%~100% state of charge is divided into multiple consecutive state of charge intervals. Based on the initial charging strategy, segmented cyclic verification tests are performed on each state of charge interval to determine the cyclic performance parameters of each state of charge interval. Based on the cycle performance parameters, outlier and non-outlier intervals with failure risk are identified in each of the charge state intervals. For each outlier interval, the segmented cyclic verification test is performed by gradually reducing its charging rate until the corresponding cyclic performance parameters meet the preset conditions, thereby obtaining the target charging rate. A target charging strategy is formed by combining the target charging rate corresponding to each outlier interval and the limit charging rate corresponding to each non-outlier interval in order of state of charge. The battery is charged according to the target charging strategy, and the lowest negative electrode potential corresponding to each of the states of charge intervals is monitored and recorded as the negative electrode potential control boundary of each of the states of charge intervals.

[0008] Optionally, the determination of the relationship between the charging rate and the negative electrode potential of the target battery under different states of charge, in order to determine the relationship between the limiting charging rate without lithium plating and the state of charge, includes the following as an initial charging strategy: At a preset temperature, the target battery containing the reference electrode is charged at multiple different charging rates, and the negative electrode potential is monitored using the reference electrode. Real-time monitoring and recording of the negative electrode potential and corresponding state of charge during the charging process, obtaining the state of charge-negative electrode potential curves at each charging rate; The limiting charging rate when the negative electrode potential is 0mV under each state of charge is obtained by extrapolation based on the fitting of the state of charge-negative electrode potential curves, and the relationship between the limiting charging rate and the state of charge is used as the initial charging strategy.

[0009] Optionally, the segmented cyclic verification test includes: For each of the stated state of charge intervals, the following operations are performed: Cyclic charge-discharge test: The target battery is adjusted to the initial state of charge of the state of charge range. Within the state of charge range, it is charged at a constant current according to the limit charging rate corresponding to the initial charging strategy. Then, it is discharged at a constant current at a preset discharge rate until the cutoff voltage. This process is repeated multiple times. Full capacity calibration: After completing the multiple charge-discharge cycles, the target battery is charged to 100% state of charge at a preset charging rate, and then discharged to the cutoff voltage at the preset discharging rate. The coulombic efficiency of this charge-discharge process is calculated. Benchmark test: Replace the charging rate within the state of charge range with the preset charging rate, re-execute the cycle charge-discharge test and the full capacity calibration to obtain the benchmark coulombic efficiency; Calculate the ratio: Calculate the ratio of the coulombic efficiency to the reference coulombic efficiency, and use the ratio as the cycle performance parameter of the state of charge range.

[0010] Optionally, the step of identifying outlier and non-outlier intervals with failure risk in each of the states of charge intervals based on each of the cycle performance parameters includes: The state of charge intervals where the cycle performance parameters are lower than a preset threshold are identified as outlier intervals, and the state of charge intervals where the cycle performance parameters are not lower than the preset threshold are identified as non-outlier intervals.

[0011] Optionally, for each outlier interval, the segmented cyclic verification test is performed by gradually reducing its charging rate until the corresponding cyclic performance parameters meet preset conditions to obtain the target charging rate, including: For each of the outlier intervals, perform the following iterative process: Reduce the current charging rate by one step and use it as the test charging rate; Replace the extreme charging rate corresponding to the outlier interval with the test charging rate, and re-execute the segmented cyclic verification test to obtain the cyclic performance parameters of the outlier interval under the test charging rate. Determine whether the cycle performance parameters meet the preset conditions; If not, the test charging rate is further reduced and the segmented cyclic verification test is repeated until the cyclic performance parameters meet the preset conditions. The test charging rate that meets the preset conditions is determined as the target charging rate of the outlier range.

[0012] Optionally, the preset conditions include: The cycle performance parameter is not less than 0.98.

[0013] Optionally, the range of the plurality of different charging rates is 0.1C to 4C.

[0014] Optionally, the preset discharge rate is 1C, the preset charge rate is 0.33C, and the number of multiple charge-discharge cycles is not less than 20.

[0015] Optionally, the preset temperature range is -60℃ to 60℃.

[0016] Secondly, the present invention provides a charging control device for a silicon-carbon anode lithium-ion battery, comprising: A storage unit is used to store the target charging strategy formulated by the charging strategy formulation method of the silicon-carbon negative electrode lithium-ion battery according to any one of the first aspects, as well as the negative electrode potential control boundary corresponding to each state of charge interval. The control unit, connected to the storage unit, is used to control the charging current according to the target charging strategy during the charging process and monitor the negative electrode potential in real time. When the negative electrode potential in any state of charge interval is lower than its corresponding negative electrode potential control boundary, a protection operation is performed.

[0017] The beneficial effects of this invention are as follows: By measuring the relationship between the charging rate and the negative electrode potential of the target battery under different states of charge, the relationship between the limiting charging rate without lithium plating and the state of charge is determined as the initial charging strategy, avoiding the risk of silicon expansion failure caused by simply controlling the charging rate based on the lithium plating boundary; furthermore, by dividing the state of charge intervals and conducting segmented cycle verification tests, outlier intervals with failure risk are identified using the coulombic efficiency ratio as the cycle performance parameter, and the charging rate is iteratively reduced for the outlier intervals until the preset conditions are met, thereby obtaining a target charging strategy that takes into account both the lithium plating boundary and silicon expansion suppression, effectively solving the problem of rapid capacity decay caused by volume expansion at high rates in silicon-carbon anode batteries, and significantly improving the cycle stability of the battery; finally, charging according to the target charging strategy and recording the lowest negative electrode potential in each interval as the control boundary provides the battery management system with a precise and quantifiable real-time protection threshold, maximizing the charging speed and extending the battery life while ensuring safety.

[0018] The system of the present invention has other features and advantages that will be apparent from or will be set forth in detail in the accompanying drawings and following detailed description, which together serve to explain the particular principles of the invention. Attached Figure Description

[0019] The above and other objects, features and advantages of the present invention will become more apparent from the accompanying drawings, in which like reference numerals generally denote like parts.

[0020] Figure 1 A flowchart illustrating the steps of a method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery according to Embodiment 1 of the present invention is shown.

[0021] Figure 2 A flowchart illustrating the steps of a method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery according to Embodiment 2 of the present invention is shown.

[0022] Figure 3 A schematic diagram of negative electrode potential data at different charging rates according to Embodiment 2 of the present invention is shown.

[0023] Figure 4 A schematic diagram of the maximum charging rate curves for different SOCs according to Embodiment 2 of the present invention is shown.

[0024] Figure 5 A schematic diagram of the negative electrode potential curve of the charging strategy according to Embodiment 2 of the present invention and the comparative example is shown.

[0025] Figure 6A schematic diagram of the charging strategy cycle capacity curves of this embodiment and the comparative example according to Embodiment 2 of the present invention is shown. Detailed Implementation

[0026] The invention will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0027] Example 1

[0028] like Figure 1 As shown, this embodiment provides a method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery, including: S1. Measure the relationship between the charging rate and the negative electrode potential of the target battery under different states of charge to determine the relationship between the limiting charging rate without lithium plating and the state of charge, as an initial charging strategy. In this step, the relationship between the charging rate and the negative electrode potential of the target battery under different states of charge is determined to ascertain the relationship between the limiting charging rate without lithium plating and the state of charge. This serves as the initial charging strategy and specifically includes: At a preset temperature, the target battery containing the reference electrode is charged at multiple different charging rates, and the negative electrode potential is monitored using the reference electrode. Real-time monitoring and recording of the negative electrode potential and corresponding state of charge during the charging process, obtaining the state of charge-negative electrode potential curves at each charging rate; The limiting charging rate when the negative electrode potential is 0mV under each state of charge is obtained by fitting and extrapolating the curves of each state of charge and negative electrode potential. The relationship between the limiting charging rate and the state of charge is used as the initial charging strategy.

[0029] Specifically, at a preset temperature (e.g., room temperature 25°C), multiple different charging rates (e.g., 0.33C, 0.5C, 0.75C, 1C, etc.) are selected to perform constant current charging on the target battery with a reference electrode, while continuously monitoring the negative electrode potential using the reference electrode. During charging, the negative electrode potential and the corresponding state of charge (SOC) are recorded in real time, thus plotting a SOC-negative electrode potential curve for each charging rate. Since the negative electrode potential gradually decreases with charging, the lithium plating critical point is reached when the negative electrode potential drops to 0mV. Based on these curves at different rates, a fitting extrapolation method is used to calculate the charging rate corresponding to the negative electrode potential being exactly 0mV at each SOC. This rate is the limiting charging rate at which lithium plating does not occur at that SOC point. Connecting the limiting charging rates at each SOC point into a curve yields the relationship between the limiting charging rate and the state of charge, which is used as the initial charging strategy. This strategy only considers lithium plating as the boundary and needs to be corrected for silicon expansion failure in subsequent steps.

[0030] In this step, the range of different charging rates is 0.1C to 4C.

[0031] In this step, the preset temperature range is -60℃ to 60℃.

[0032] S2. Divide the target battery’s 0%~100% state of charge into multiple consecutive state of charge intervals, and perform segmented cycle verification tests on each state of charge interval based on the initial charging strategy to determine the cycle performance parameters of each state of charge interval. Specifically, the target battery's 0% to 100% state of charge (SOC) is divided into multiple consecutive SOC intervals (e.g., each interval is 5%). For each SOC interval, based on the obtained initial charging strategy (i.e., the maximum charging rate at each SOC), segmented cyclic verification tests are performed. In this test, the maximum charging rate corresponding to the initial strategy and a low rate are used as controls. Through multiple charge-discharge cycles and full-capacity calibration, the ratio of the coulombic efficiency at the maximum rate to the baseline coulombic efficiency for each interval is calculated. This ratio is used as the cyclic performance parameter for that SOC interval. This parameter can quantify the degree of irreversible damage to the battery caused by maximum rate charging, providing a basis for subsequent identification of outlier intervals.

[0033] In this step, the segmented loop verification test includes: For each state of charge interval, perform the following operations: Cyclic charge-discharge test: The target battery is adjusted to the initial state of charge in the state of charge range. Within the state of charge range, it is charged at a constant current according to the limit charging rate corresponding to the initial charging strategy. Then, it is discharged at a constant current to the cutoff voltage at a preset discharge rate. This process is repeated multiple times. Full capacity calibration: After completing multiple charge-discharge cycles, the target battery is charged to 100% state of charge at a preset charging rate, and then discharged to the cutoff voltage at a preset discharging rate. The coulombic efficiency of this charge-discharge process is calculated. Benchmark test: Replace the charging rate within the state of charge range with the preset charging rate, re-execute the cycle charge-discharge test and full capacity calibration to obtain the benchmark coulombic efficiency; Calculate the ratio: Calculate the ratio of the coulombic efficiency to the reference coulombic efficiency, and use the ratio as the cycle performance parameter in the state-of-charge range.

[0034] Specifically, for each defined state of charge interval, the segmented cyclic verification test is performed in the following order.

[0035] First, perform a cyclic charge-discharge test: adjust the target battery to the initial state of charge of the charge range, and then charge it at a constant current within the charge range according to the limit charging rate given by the initial charging strategy. After charging, discharge it at a constant current to the cutoff voltage at a preset discharge rate (e.g., 1C). Repeat this process multiple times (e.g., no less than 20 times) to subject the material within the charge range to multiple high-rate impacts to expose potential expansion damage.

[0036] Next, perform full capacity calibration: After completing the above multiple cycles, charge the battery to 100% state of charge using a smaller preset charging rate (e.g., 0.33C), and then discharge it to the cutoff voltage using the same preset discharge rate (1C). Record the charging capacity and discharging capacity of the entire charging and discharging process, and calculate its coulombic efficiency (discharging capacity / charging capacity). This value reflects the remaining reversibility after high-rate cycling. The preset charging rate is less than the limit charging rate.

[0037] Then, a benchmark test is performed: the charging rate in this range is replaced from the limit charging rate to the preset charging rate (0.33C) mentioned above, and a complete cycle charge-discharge test and full capacity calibration are re-executed to obtain the benchmark coulombic efficiency, which represents the ideal reversible level without high-rate damage.

[0038] Finally, the ratio is calculated: the coulombic efficiency obtained from full-capacity calibration is divided by the reference coulombic efficiency, and the resulting ratio is the cycle performance parameter for this state of charge range. The closer this ratio is to 1, the more likely that the extreme rate charging has not caused significant additional damage; a ratio significantly lower than 1 indicates the presence of failure risks such as silicon expansion.

[0039] In this step, the preset discharge rate is 1C, the preset charge rate is 0.33C, and the number of charge-discharge cycles is no less than 20.

[0040] S3. Based on the performance parameters of each cycle, identify the outlier and non-outlier intervals with failure risk in each state of charge interval; In this step, based on the performance parameters of each cycle, the outlier and non-outlier intervals with failure risk in each state of charge interval are identified, specifically including: The state of charge intervals where the cyclic performance parameters are below a preset threshold are identified as outlier intervals, and the state of charge intervals where the cyclic performance parameters are not below the preset threshold are identified as non-outlier intervals.

[0041] Specifically, the cycle performance parameters calculated for each state of charge (i.e., the ratio of coulombic efficiency at the limiting rate to the baseline coulombic efficiency) are compared with a pre-set threshold (e.g., 0.98). If the ratio for a certain state of charge is lower than the preset threshold, it indicates that high-rate charging and discharging at the initial limiting charge rate within that state of charge will lead to significant irreversible damage (such as capacity loss caused by silicon expansion). Therefore, this state of charge is identified as an outlier with a risk of failure. Conversely, if the ratio is not lower than the preset threshold, it indicates that the limiting charge rate within that state of charge has not caused significant damage and is safe to use. Therefore, this state of charge is identified as a non-outlier. Through this comparison process, all state of charge are clearly distinguished into outliers that require charging rate adjustment and non-outliers that can retain the original limiting charge rate.

[0042] S4. For each outlier interval, a segmented cyclic verification test is conducted by gradually reducing its charging rate until the corresponding cyclic performance parameters meet the preset conditions and the target charging rate is obtained. In this step, for each outlier interval, segmented cyclic verification tests are conducted by gradually reducing its charging rate until the corresponding cyclic performance parameters meet preset conditions. The specific steps to obtain the target charging rate include: For each outlier interval, perform the following iterative process: Reduce the current charging rate by one step and use it as the test charging rate; Replace the extreme charging rate corresponding to the outlier interval with the test charging rate, and re-execute the segmented cyclic verification test to obtain the cyclic performance parameters of the outlier interval under the test charging rate. Determine whether the cycle performance parameters meet the preset conditions; If not, continue to reduce the test charging rate and repeat the segmented cyclic verification test until the cyclic performance parameters meet the preset conditions. The test charging rate that meets the preset conditions is determined as the target charging rate for the outlier range.

[0043] Specifically, for each state-of-charge interval identified as an outlier, iterative optimization is performed by gradually reducing the charging rate. Initially, the current charging rate is the original limiting charging rate for that interval. First, the current charging rate is reduced by one step (e.g., a fixed value of 0.2C or a fixed percentage of the current rate) to obtain the test charging rate. Then, the original limiting charging rate of the outlier interval is replaced with this test charging rate, and the complete segmented cyclic verification test (including cyclic charge-discharge test, full capacity calibration, and benchmark test) is re-executed to calculate the cyclic performance parameters (i.e., the ratio of coulombic efficiency to benchmark coulombic efficiency) of the outlier interval at this test charging rate. Next, it is determined whether the cyclic performance parameters meet the preset conditions (e.g., the ratio is not less than 0.98). If they do, the iteration stops, and the test charging rate is determined as the target charging rate for the outlier interval; if they do not, the current test charging rate is further reduced (again by one step), and the segmented cyclic verification test and judgment steps are repeated until the cyclic performance parameters meet the preset conditions. Through this iterative process of gradually reducing and verifying, the target charging rate that can both avoid lithium plating and suppress silicon expansion failure in each outlier range is finally obtained.

[0044] In this step, the preset conditions include: Cyclic performance parameters are not less than 0.98.

[0045] S5. Based on the target charging rate corresponding to each outlier interval and the limit charging rate corresponding to each non-outlier interval, the target charging strategy is formed by combining them in order of state of charge. Specifically, for each outlier interval, the target charging rate was obtained after iterative testing with progressively decreasing rates. For each non-outlier interval, the maximum charging rate corresponding to that interval in the initial charging strategy was directly retained. These charging rates were arranged sequentially according to the state of charge (SOC) intervals from 0% to 100%, forming a complete SOC interval-charging rate correspondence table (e.g., 0-5% corresponds to one rate, 5%-10% to another rate, ..., 95%-100% to yet another rate). This correspondence constitutes the final target charging strategy, which maintains the initial maximum fast charging capability in non-outlier intervals while reducing the rate in outlier intervals to suppress silicon expansion failure, thus achieving the optimal balance between safety and performance.

[0046] S6. Charge the battery according to the target charging strategy, monitor and record the lowest negative electrode potential corresponding to each state of charge interval, and use it as the negative electrode potential control boundary for each state of charge interval.

[0047] Specifically, following the finalized target charging strategy (i.e., the charging rate table corresponding to each state of charge (SOC) interval), a complete charging process is performed using a three-electrode battery including a reference electrode. During charging, the change in negative electrode potential is monitored in real time using the reference electrode, and for each SOC interval (e.g., every 5% interval), the lowest value of the negative electrode potential reached within that interval (i.e., the potential closest to 0mV) is recorded. Since the target charging strategy has already undergone outlier correction, this lowest negative electrode potential is always higher than the lithium plating critical point (0mV), but the value may differ between different intervals. For example, the potential is higher in the low SOC interval (e.g., 380mV), and lower in the medium-high SOC interval (e.g., 15mV). These lowest negative electrode potentials are recorded in order of SOC interval, thus forming the negative electrode potential control boundary corresponding to each SOC interval. This boundary can serve as a real-time protection threshold for the subsequent battery management system (BMS): during actual charging, the BMS monitors the negative electrode potential, and once the potential of any state of charge interval is lower than the corresponding control boundary, it triggers protection operations (such as reducing the charging current or stopping charging), thereby ensuring safe and fast charging without lithium plating or silicon expansion failure.

[0048] Example 2

[0049] like Figure 2 As shown, this embodiment provides a method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery, including: 1. Battery fabrication and three-electrode system: This embodiment takes an 18Ah semi-solid-state lithium-ion battery as an example. The positive electrode material is LiNi0.8Co0.1Mn0.1O2, the silicon doping ratio of the negative electrode is 10%, and a lithium-plated copper wire with a diameter of 100μm is used as a reference electrode to prepare a three-electrode battery.

[0050] 2. Limiting charging rate determination and initial charging strategy: At 25℃, the three-electrode battery was constant-current charged at different charging rates of 0.33C, 0.5C, 0.75C, and 1C, while the negative electrode potential was monitored in real time using a reference electrode. The change in negative electrode potential with state of charge (SOC) at each charging rate was recorded, resulting in a negative electrode potential data graph for different charging rates. Figure 3 Charging stops when the negative electrode potential drops to 0mV.

[0051] Based on the curves at different rates, the limiting charging rate when the negative electrode potential is exactly 0mV at each SOC is obtained by fitting and extrapolating, and the maximum charging rate curves for different SOCs are plotted. Figure 4The SOC was divided into 20 intervals of 5% from 0% to 100%, and the limit charging rate corresponding to each interval was read to obtain the initial charging strategy (Table 1). This strategy only considers lithium plating as the boundary and does not consider silicon expansion failure.

[0052] Table 1 Initial charging strategy (charging rate corresponding to different SOCs)

[0053] 3. Segmented cyclic verification test and outlier interval identification: At room temperature, discharge the battery at 0.33C to the cutoff voltage as the initial state. For each SOC range (taking 5%~45% range as an example), perform the following operations in sequence: Cyclic charge-discharge test: Adjust the battery to the initial SOC of this range (e.g., 5% SOC), charge it at the maximum charging rate of the initial strategy (e.g., 8C) within this range, and then discharge it at a constant current of 1C to the cutoff voltage. Repeat this 100 times.

[0054] Full capacity calibration: After completing 100 cycles, charge the battery to 100% SOC at 0.33C, and then discharge it to the cutoff voltage at 1C. Calculate the coulombic efficiency (discharge capacity / charge capacity) of this process, and denot it as E1.

[0055] Benchmark Test: Replace the charging rate in this range with 0.33C, and re-perform the above cycle charge-discharge test and full-capacity calibration to obtain the benchmark coulombic efficiency, denoted as E1. .

[0056] Calculate the ratio η1 = E1 / E1 .

[0057] The above test was repeated for all SOC ranges (5% to 100%) to obtain E1 and E2 for each range at different charging rates. The values ​​of η are shown in Table 2. Table 2 shows that the η values ​​for the SOC 5%–45% range are all below 0.98, while the η values ​​for the range of 50% and above are all greater than 0.98. Therefore, the SOC 5%–45% range is identified as an outlier, and the 50%–100% range is considered a non-outlier.

[0058] Table 2. Coulombic efficiency and η value at different charging rates in the 5%~45% SOC range.

[0059] 4. Outlier interval maximization iterative correction: For each outlier interval, the charging rate is progressively reduced and segmented cyclic verification tests are repeated until η ≥ 0.98. Taking the SOC 5% interval as an example: the initial limiting rate is 8C, η = 82.64%; after reducing to 4.8C, η = 93.56%; after reducing to 4.2C, η = 98.09%, meeting the condition, and the target rate is determined to be 4.2C. Similarly, the rate is progressively reduced for other outlier intervals to obtain the corrected target charging rate (Table 3). The original limiting rates in Table 1 are retained for non-outlier intervals.

[0060] Table 3. Corrected target charging strategy

[0061] 5. Determination of negative electrode potential control boundary: A three-electrode battery was used, and a full charge was performed according to the target charging strategy in Table 3. The negative electrode potential was monitored in real time, and the lowest negative electrode potential within each SOC range was recorded to obtain the corresponding negative electrode potential control boundary for each range (Table 4).

[0062] Table 4. Negative electrode potential control boundaries for each SOC range

[0063] 6. Cyclic performance comparison and verification: Two charging strategies were used to conduct 100 cycles of "charging (according to their respective strategies) + 1C discharging": Strategy A: The comparative example only uses the initial limit strategy (Table 1), which is the strategy without outlier interval correction.

[0064] Strategy B: The target charging strategy obtained in this embodiment (Table 3).

[0065] The charging data for the examples and comparative examples are shown in Table 5 below.

[0066] Table 5. Comparison of equivalent rate of charge and cycle capacity retention for different charging strategies

[0067] The negative electrode potential curves of the comparative example and this embodiment are as follows: Figure 5 As shown, the cycle capacity retention curves of the comparative example and this embodiment are as follows: Figure 6 As shown in the table, Strategy A maintained a capacity retention of 90.42% after 100 cycles, while Strategy B maintained a capacity retention of 98.85% after 100 cycles. Furthermore, although the negative electrode potential of Strategy A remained above 0mV throughout, the excessively high rate of change in the low SOC range led to severe silicon expansion, active material shedding, and rapid capacity decay. In contrast, the negative electrode potential of Strategy B consistently exceeded the control boundaries shown in Table 4, indicating a stable silicon-carbon negative electrode structure and excellent cycling performance.

[0068] This embodiment successfully obtained a target charging strategy that balances avoiding lithium plating and suppressing silicon expansion failure by measuring the maximum charge rate, segmented cycle verification, outlier interval identification, and iterative correction, and established the negative electrode potential control boundary for each SOC range. Compared with the initial strategy that only uses lithium plating as the boundary, the strategy in this embodiment significantly improves the cycle stability of the battery (capacity retention after 100 cycles increases from 90.42% to 98.85%), while ensuring charging safety, providing a systematic and precise method for formulating charging strategies for silicon-carbon anode lithium-ion batteries.

[0069] Example 3

[0070] This embodiment provides a charging control device for a silicon-carbon anode lithium-ion battery, including: The storage unit is used to store the target charging strategy formulated by the charging strategy formulation method of the silicon-carbon negative electrode lithium-ion battery described in Example 1, as well as the negative electrode potential control boundary corresponding to each state of charge interval. The control unit, connected to the storage unit, is used to control the charging current according to the target charging strategy during the charging process and monitor the negative electrode potential in real time. When the negative electrode potential in any state of charge interval is lower than its corresponding negative electrode potential control boundary, a protection operation is performed.

[0071] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery, characterized in that, include: The relationship between the charging rate and the negative electrode potential of the target battery under different states of charge was determined to identify the relationship between the limiting charging rate without lithium plating and the state of charge, which can be used as an initial charging strategy. The target battery's 0%~100% state of charge is divided into multiple consecutive state of charge intervals. Based on the initial charging strategy, segmented cyclic verification tests are performed on each state of charge interval to determine the cyclic performance parameters of each state of charge interval. Based on the cycle performance parameters, outlier and non-outlier intervals with failure risk are identified in each of the charge state intervals. For each outlier interval, the segmented cyclic verification test is performed by gradually reducing its charging rate until the corresponding cyclic performance parameters meet the preset conditions, thereby obtaining the target charging rate. A target charging strategy is formed by combining the target charging rate corresponding to each outlier interval and the limit charging rate corresponding to each non-outlier interval in order of state of charge. The battery is charged according to the target charging strategy, and the lowest negative electrode potential corresponding to each of the states of charge intervals is monitored and recorded as the negative electrode potential control boundary of each of the states of charge intervals.

2. The method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery according to claim 1, characterized in that, The determination of the relationship between the charging rate and the negative electrode potential of the target battery under different states of charge is used to determine the relationship between the limiting charging rate without lithium plating and the state of charge, which serves as the initial charging strategy. At a preset temperature, the target battery containing the reference electrode is charged at multiple different charging rates, and the negative electrode potential is monitored using the reference electrode. Real-time monitoring and recording of the negative electrode potential and corresponding state of charge during the charging process, obtaining the state of charge-negative electrode potential curves at each charging rate; The limiting charging rate when the negative electrode potential is 0mV under each state of charge is obtained by extrapolation based on the fitting of the state of charge-negative electrode potential curves, and the relationship between the limiting charging rate and the state of charge is used as the initial charging strategy.

3. The method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery according to claim 1, characterized in that, The segmented loop verification test includes: For each of the stated state of charge intervals, the following operations are performed: Cyclic charge-discharge test: The target battery is adjusted to the initial state of charge of the state of charge range. Within the state of charge range, it is charged at a constant current according to the limit charging rate corresponding to the initial charging strategy. Then, it is discharged at a constant current at a preset discharge rate until the cutoff voltage. This process is repeated multiple times. Full capacity calibration: After completing the multiple charge-discharge cycles, the target battery is charged to 100% state of charge at a preset charging rate, and then discharged to the cutoff voltage at the preset discharging rate. The coulombic efficiency of this charge-discharge process is calculated. Benchmark test: Replace the charging rate within the state of charge range with the preset charging rate, re-execute the cycle charge-discharge test and the full capacity calibration to obtain the benchmark coulombic efficiency; Calculate the ratio: Calculate the ratio of the coulombic efficiency to the reference coulombic efficiency, and use the ratio as the cycle performance parameter of the state of charge range.

4. The method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery according to claim 1, characterized in that, The outlier and non-outlier intervals with failure risk identified in each of the charge state intervals based on the cycle performance parameters include: The state of charge intervals where the cycle performance parameters are lower than a preset threshold are identified as outlier intervals, and the state of charge intervals where the cycle performance parameters are not lower than the preset threshold are identified as non-outlier intervals.

5. The method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery according to claim 1, characterized in that, For each outlier interval, the segmented cyclic verification test is performed by gradually reducing its charging rate until the corresponding cyclic performance parameters meet preset conditions to obtain the target charging rate, including: For each of the outlier intervals, perform the following iterative process: Reduce the current charging rate by one step to use as the test charging rate; Replace the extreme charging rate corresponding to the outlier interval with the test charging rate, and re-execute the segmented cyclic verification test to obtain the cyclic performance parameters of the outlier interval under the test charging rate. Determine whether the cycle performance parameters meet the preset conditions; If not, the test charging rate is further reduced and the segmented cyclic verification test is repeated until the cyclic performance parameters meet the preset conditions. The test charging rate that meets the preset conditions is determined as the target charging rate of the outlier range.

6. The method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery according to claim 1, characterized in that, The preset conditions include: The cycle performance parameter is not less than 0.

98.

7. The method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery according to claim 2, characterized in that, The range of the various charging rates is 0.1C to 4C.

8. The method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery according to claim 3, characterized in that, The preset discharge rate is 1C, the preset charging rate is 0.33C, and the number of multiple charge-discharge cycles is not less than 20.

9. The method for formulating a charging strategy for a silicon-carbon anode lithium-ion battery according to claim 2, characterized in that, The preset temperature range is -60℃ to 60℃.

10. A charging control device for a silicon-carbon negative electrode lithium-ion battery, characterized in that, include: A storage unit is used to store the target charging strategy formulated by the charging strategy formulation method of the silicon-carbon negative electrode lithium-ion battery according to any one of claims 1 to 9, and the negative electrode potential control boundary corresponding to each state of charge interval. The control unit, connected to the storage unit, is used to control the charging current according to the target charging strategy during the charging process and monitor the negative electrode potential in real time. When the negative electrode potential in any state of charge interval is lower than its corresponding negative electrode potential control boundary, a protection operation is performed.

Images