Method for determining infiltration time of battery cell after liquid injection
Through electrochemical impedance test and impedance spectral parameters extracted from transmission line model, the infiltration time of lithium-ion battery cells after injection is accurately determined, solving the problem of difficult to quantify the infiltration time in the prior art, and achieving high efficiency and cost reduction in cell production.
Patent Information
- Application Number
- CN202311074957.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-08-24
- Publication Date
- 2025-02-25
AI Technical Summary
In the production of lithium-ion batteries, the infiltration time of the battery cell after injection is difficult to accurately quantify, resulting in difficulty in setting the standstill time, which may lead to uneven cell performance and high production costs.
The impedance spectrum of the battery cell was obtained through electrochemical impedance test, and the Rs and Rpore values were extracted using the transmission line model, and the change curves of electron conduction and ion conduction were obtained respectively. The impedance change rate was obtained through differential treatment, and the infiltration time after the battery cell was injected was determined.
Accurate quantification of the battery cell infiltration process is achieved, significantly shortening the process cycle, reducing production costs, improving production capacity, and ensuring consistency of battery cell performance.
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Figure CN119511106A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of battery detection, and in particular to a method for determining the infiltration time of a battery cell after liquid injection. Background Art
[0002] At present, the lithium-ion battery production process mainly relies on the capillary force between pores and the flow characteristics of the electrolyte to complete the wetting process after liquid injection. Among them, the setting of the standing time is particularly critical. If the standing time is too long, although it can ensure good infiltration of the electrolyte, the long waiting time will lead to a sharp increase in production costs and reduced production capacity; on the contrary, if the standing time is too short, there will be problems with poor local infiltration of the battery cell, resulting in performance differences in the middle of the battery cell after formation, and serious problems such as lithium precipitation and black spots will occur. Although some product processes increase the standing temperature in order to better complete the infiltration of active materials and electrodes, there is still a lack of effective quantitative characterization methods for the actual time required for the infiltration of the battery cell after liquid injection and the degree of completion of the infiltration. Summary of the invention
[0003] In view of this, the present application provides a method for determining the wetting time after liquid injection of a battery cell. The determination method can be used to guide and / or optimize the determination of the standing time after liquid injection of the battery cell, and can also be used for comparative studies of the wetting differences (such as wetting rate, wetting completion status, etc.) after liquid injection under different DOE conditions.
[0004] A method for determining the soaking time after liquid injection of a battery cell, the determination method comprises the following steps: S100: injecting electrolyte into the battery cell to be injected, sealing and standing, performing electrochemical impedance test on the battery cell after injection at regular intervals to obtain the impedance spectrum of the battery cell changing with time, S200: extracting the Rs value and Rpore value in the impedance spectrum using a transmission line model to obtain a first change curve of the Rs value over time and a second change curve of the Rpore value over time, S300: performing differential processing on the change curve to obtain the impedance change rate, S400: determining the soaking time after liquid injection of the battery cell according to the impedance change rate. Among them, the Rs value is an ohmic impedance value, which is the intersection of the impedance spectrum and the X-axis (real part). The method for obtaining the Rpore value comprises: according to the transmission line model, in the impedance spectrum, the intersection of the ultra-high frequency zone and the real axis is taken as the starting point, the intersection of the oblique line in the medium and low frequency zone and the 45° straight line in the high frequency zone is taken as the end point, and the resistance value of the straight line segment connecting the starting point and the end point projected on the real part is the Rpore value.
[0005] This application extracts two key characterization parameters Rs and Rpore from the impedance spectrum, where Rs represents the change in electron conduction impedance (i.e., ohmic impedance) during the wetting process, such as factors of the active substance itself, electrode / electrolyte / diaphragm parameters, contact impedance between the active substance and the current collector, etc. Rpore represents the electrolyte ion diffusion impedance in the pores of the porous material (i.e., pore ion impedance). During the electrolyte infiltration process, both electron conduction and ion conduction show a certain change trend over time, and the two are independent of each other. Therefore, it is necessary to obtain the time-varying curves of the two separately. The curve obtained after smoothing is the quantitative expression of the actual wetting process of the battery cell. At the same time, according to the impedance change rate, it can be clearly concluded that the time required for the battery cell to complete the wetting under the current design level.
[0006] In some embodiments, the frequency range of the mid-low frequency region is 1 Hz to 100 Hz, the frequency range of the high frequency region is 100 Hz to 1000 Hz, and the frequency range of the ultra-high frequency region is 1000 Hz to 100000 Hz.
[0007] In some embodiments, in step S100, the standing includes standing at room temperature and standing at high temperature, the standing temperature at room temperature is 25°C to 35°C, the standing time at room temperature is 16h to 26h, the standing temperature at high temperature is 60°C to 65°C, and the standing time at high temperature is 10h to 24h. It can be seen that the total standing time is 26h to 50h, for example, the standing time at room temperature is 20h, the total standing time is 35h, and the high temperature standing time is 15h. It should be noted that in this application, h and H both represent hours in time.
[0008] In some embodiments, in step S100, the time interval for performing electrochemical impedance test on the battery cell after liquid injection is 0.5h to 3h, and the test environment temperature should be consistent with the current infiltration temperature. The time interval can be a time interval that gradually increases within the above range, or it can be an equal interval time, which is specifically selected according to the actual situation. In this application, an equal interval time is preferred, especially an electrochemical impedance test is performed on the battery cell after liquid injection every 1h to obtain the corresponding point value. The equal interval time should not be too long (for example, more than 3h). If the equal interval time is too long, the time point when the infiltration is completed cannot be detected.
[0009] In some embodiments, in step S200, both the first change curve and the second change curve include a normal temperature section curve and a high temperature section curve, and in step S300, performing differential processing on the change curve to obtain the impedance change rate includes: performing first-order differential processing on the normal temperature section curve and the high temperature section curve of the first change curve, respectively, to obtain the impedance change rate A of the normal temperature section curve of the first change curve and the impedance change rate B of the high temperature section curve of the first change curve. Performing first-order differential processing on the normal temperature section curve and the high temperature section curve of the second change curve, respectively, to obtain the impedance change rate A′ of the normal temperature section curve of the second change curve and the impedance change rate B′ of the high temperature section curve of the second change curve.
[0010] In some embodiments, in step S400, determining the soaking time after the cell is injected with liquid according to the impedance change rate includes: when the impedance change rate A is less than the system measurement error, obtaining the corresponding standing time t1 on the first change curve, when the impedance change rate A′ is less than the system measurement error, obtaining the corresponding standing time t2 on the second change curve, when the impedance change rate B is less than the system measurement error, obtaining the corresponding standing time t3 on the first change curve, when the impedance change rate B′ is less than the system measurement error, obtaining the corresponding standing time t4 on the second change curve, determining the larger value of t1 and t2 as the soaking time of the cell at room temperature after the cell is injected with liquid, and determining the larger value of t3 and t4 as the soaking time of the cell at high temperature after the cell is injected with liquid. The system measurement error is measured by the GRR method, and the system measurement error of the system is determined by GRR according to different measurement systems. In this application, the range of the system measurement error is recorded as M, satisfying: M≤0.02mohm / H.
[0011] In some embodiments, in step S300, before differentiating the change curve, the step also includes: using a moving average smoothing algorithm to perform data smoothing on the first change curve and the second change curve respectively. When performing the data smoothing, the average number of the first change curve and / or the second change curve is 2 to 4.
[0012] In some embodiments, the perturbation voltage amplitude of the electrochemical impedance spectroscopy test is 5 mV to 8 mV, and the scanning frequency range is 0.05 Hz to 10000 Hz.
[0013] In some embodiments, the battery cell to be injected with liquid is a soft-pack laminated battery cell or a wound structure battery cell.
[0014] This application extracts two key characterization parameters Rs and Rpore from the impedance spectrum, where Rs represents the change in electron conduction impedance during the infiltration process, and Rpore represents the electrolyte ion diffusion impedance in the pores of the porous material. During the electrolyte infiltration process, both electron conduction and ion conduction show a certain change trend over time. This application simultaneously obtains the parameters Rs and Rpore, and by comparing the two, it is possible to accurately determine the time required for the battery cell to complete infiltration under the current design level. Compared with the standing time under the conventional empirical mode, the process cycle can be significantly shortened, which is beneficial to reducing production costs and increasing production capacity. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.
[0016] Figure 1 This is an electrochemical impedance test diagram of the battery cell after liquid injection in Example 1 of the present application;
[0017] Figure 2 for Figure 1 The characteristic parameter Rs in the electrochemical impedance test diagram is shown as a curve of changes over time;
[0018] Figure 3 for Figure 1 The electrochemical impedance test diagram shown is a curve of the characteristic parameter Rpore changing with time. DETAILED DESCRIPTION
[0019] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.
[0020] In the production process of lithium-ion batteries, in order to determine whether the battery is fully infiltrated, empirical parameters (such as 25℃_48H / 60℃_24H and other conditions) are usually used to produce the battery cell. The battery cell is indirectly judged to be fully infiltrated by disassembling the fully charged finished fresh battery cell and observing the electrode piece with the naked eye to see if the color is uniform and there is no abnormality, or the electrode piece is disassembled and the infiltration is judged by the weighing difference method. The whole process involves the disassembly of the battery cell. The destructive experiment determines that the operation is cumbersome and the consistency is poor. The link of visual judgment only supports qualitative comparison. The electrolyte is easy to volatilize, resulting in large errors in the weighing method, and the performance test cycle is long and costly.
[0021] In recent years, ultrasonic testing has been mentioned repeatedly. This method uses the difference in the penetration ability of sound waves in gas and liquid phases to image the received signal, thereby determining the difference in wetting at different locations of the battery cell. Conventional ultrasonic testing equipment has poor measurement accuracy and cannot effectively identify subtle design differences or production fluctuations. In order to improve the resolution of ultrasonic imaging, different frequency probes are equipped, which requires high equipment investment and greatly increases the analysis cost of the test.
[0022] In order to solve the above problems, the present application provides a method for determining the wetting time of a battery cell after liquid injection. By using an electrochemical workstation to monitor the Nyquist impedance spectrum of the battery cell after liquid injection in real time, and using the LIBs transmission line model to extract Rs (ohmic impedance) and Rpore (pore impedance) to comprehensively evaluate the change process of electronic conduction and ion conduction over time, non-destructive and accurate evaluation of the completion process of the battery cell wetting after liquid injection can be achieved.
[0023] A method for determining the soaking time after liquid injection of a battery cell comprises the following steps: S100: injecting electrolyte into a battery cell to be injected, sealing and leaving it to stand, performing electrochemical impedance test on the battery cell after injection at regular intervals to obtain an impedance spectrum of the battery cell changing with time, S200: extracting the Rs value and Rpore value in the impedance spectrum using a transmission line model to obtain a first change curve of the Rs value over time and a second change curve of the Rpore value over time, S300: performing differential processing on the change curve to obtain an impedance change rate, and S400: determining the soaking time after liquid injection of the battery cell according to the impedance change rate. Among them, the Rs value is an ohmic impedance value, and the method for obtaining the Rpore value comprises: according to the transmission line model, in the impedance spectrum, the intersection point of the ultra-high frequency zone and the real axis is taken as the starting point, the intersection point of the oblique line in the medium and low frequency zone and the 45° straight line in the high frequency zone is taken as the end point, and the resistance value of the straight line segment connecting the starting point and the end point projected on the real part is the Rpore value.
[0024] In some embodiments, the frequency range of the mid-low frequency region is 1 Hz to 100 Hz, the frequency range of the high frequency region is 100 Hz to 1000 Hz, and the frequency range of the ultra-high frequency region is 1000 Hz to 100000 Hz.
[0025] In some embodiments, in step S100, the standing includes standing at room temperature and standing at high temperature. The standing temperature at room temperature is 25°C to 35°C, and the standing time at room temperature is 16h to 26h. The standing temperature at high temperature is 60°C to 65°C, and the standing time at high temperature is 10h to 24h.
[0026] Exemplarily, the room temperature static temperature is 25°C, 28°C, 30°C, 32°C, 33°C, 35°C or a range consisting of any two of the above values.
[0027] Exemplarily, the standing time at room temperature is 16 h, 18 h, 20 h, 22 h, 24 h, 26 h, or a range consisting of any two of the above values.
[0028] Exemplarily, the high temperature static temperature is 60° C., 61° C., 62° C., 63° C., 64° C., 65° C., or a range consisting of any two of the above values.
[0029] Exemplarily, the high temperature standing time is 10 h, 12 h, 14 h, 15 h, 16 h, 18 h, 20 h, 22 h, 24 h, 26 h, or a range consisting of any two of the above values.
[0030] In some embodiments, in step S100, the time interval for performing electrochemical impedance test on the battery cell after liquid injection is 0.5h to 3h.
[0031] Exemplarily, the time interval for performing electrochemical impedance testing on the battery cell after liquid injection is 0.5h, 0.8h, 1h, 1.5h, 2h, 2.5h, 3h or a range consisting of any two of the above values.
[0032] In some embodiments, in step S200, the first change curve and the second change curve both include a normal temperature section curve and a high temperature section curve. In step S300, the change curves are differentiated to obtain the impedance change rate, including: performing first-order differential processing on the normal temperature section curve in the first change curve and the high temperature section curve in the first change curve, respectively, to obtain the impedance change rate A of the normal temperature section curve in the first change curve and the impedance change rate B of the high temperature section curve in the first change curve; similarly, performing first-order differential processing on the normal temperature section curve in the second change curve and the high temperature section curve in the second change curve, respectively, to obtain the impedance change rate A′ of the normal temperature section curve in the second change curve and the impedance change rate B′ of the high temperature section curve in the second change curve.
[0033] When the impedance change rate A is less than the system measurement error, the corresponding standing time t1 is obtained on the first change curve. When the impedance change rate A′ is less than the system measurement error, the corresponding standing time t2 is obtained on the second change curve. When the impedance change rate B is less than the system measurement error, the corresponding standing time t3 is obtained on the first change curve. When the impedance change rate B′ is less than the system measurement error, the corresponding standing time t4 is obtained on the second change curve. Determine the larger value of t1 and t2 as the soaking time of the battery cell at room temperature after liquid injection, and determine the larger value of t3 and t4 as the soaking time of the battery cell at high temperature after liquid injection. By mapping each point on the first change curve and / or the second change curve to the corresponding time coordinate axis, the time corresponding to the point can be obtained. Under normal circumstances, the standing is normal temperature standing and high temperature standing, respectively. Therefore, the time of normal temperature standing can be directly obtained by obtaining the corresponding time point value on the time coordinate. The high temperature standing starts after the normal temperature standing ends. Therefore, the high temperature standing time needs to be obtained by subtracting the normal temperature standing time from the time point value directly obtained on the time coordinate.
[0034] At the beginning of infiltration, the electrolyte first penetrates the surface area of the component in direct contact with the liquid, and begins to compress or replace the residual gas in the pores, which is manifested as a rapid decrease in impedance; secondly, the electrolyte is redistributed mainly by capillary attraction, which is manifested as a slowdown in the rate of impedance decrease. When the force balance is reached between all pores (such as capillary force, gas compression, gravity, etc.), the impedance remains basically unchanged, and the impedance change rate approaches 0. At this time, the corresponding standing time is determined as the completion time of electronic conduction and ion conduction after injection. Finally, the maximum value of Rs and Rpore is selected as the time required for complete infiltration of the battery cell. Relying on actual production conditions, this application can quickly, accurately and in situ obtain quantitative data of the battery cell infiltration process. The operation is simple, and the data is intuitive and reliable. It has great practical significance for optimizing the standing time after injection and comparing the difference in infiltration degree.
[0035] In some embodiments, in step S300, before performing differentiation processing on the change curve, the step further includes: performing data smoothing processing on the first change curve and the second change curve respectively using a moving average smoothing algorithm, and when performing the data smoothing processing, the average number of the first change curve and / or the second change curve is 2 to 4. At this time, an intuitive and quantitative infiltration process can be obtained.
[0036] In some embodiments, the perturbation voltage amplitude of the electrochemical impedance test is 5mV to 8mV, and the scanning frequency range is 0.05Hz to 10000Hz. Preferably, the perturbation voltage amplitude of the electrochemical impedance test is 5mV.
[0037] In some embodiments, the battery cell to be injected with liquid is a soft-pack laminated battery cell or a wound structure battery cell.
[0038] Technical principle: In the field of lithium-ion batteries, the unformed electrode is approximately regarded as a blocking electrode due to its extremely strong polarization resistance. Due to the existence of the "pseudo-CPE phenomenon", the low-frequency region of the impedance spectrum is shown as an inclined line less than 90°, representing the solid phase diffusion process; the high-frequency region of the impedance spectrum presents a 45° straight line segment, reflecting the ion diffusion in the solid active particles. The more developed the pore network, the easier it is for ion transmission to cross to nearby pores, and the easier it is to achieve multi-directional transfer, and the lower the overall impedance. Therefore, the 45° straight line segment in the high-frequency region is taken as the research object, and the intersection of the impedance spectrum and the horizontal axis (real part) is extracted as Rs (ohmic impedance), with the intersection of the ultra-high frequency region and the real axis Rs as the starting point, and the intersection of the oblique line in the low-frequency region and the 45° straight line in the high-frequency region as the end point. The resistance value of the line segment projected on the real part is Rpore, and the changes of the two over time after the lithium-ion battery is injected can be monitored in real time, which can effectively characterize its infiltration process.
[0039] Embodiment design:
[0040] Preparation of lithium-ion batteries
[0041] (1) Preparation of negative electrode sheet:
[0042] Graphite, conductive carbon (Super-P), styrene-butadiene rubber and sodium carboxymethyl cellulose (CMC) were mixed in a solvent deionized water at a mass ratio of about 95:2:2:1, and stirred evenly to obtain a negative electrode slurry. The slurry was coated on a copper foil with a thickness of about 12 μm, dried, cold pressed, and then cut and welded to obtain a negative electrode sheet.
[0043] (2) Preparation of positive electrode sheet:
[0044] Lithium cobalt oxide (LiCoO2), conductive carbon (Super-P) and polyvinylidene fluoride (PVDF) are mixed in a solvent N-methylpyrrolidone at a mass ratio of about 95:2:3, and stirred evenly to obtain a positive electrode slurry. The slurry is coated on an aluminum foil with a thickness of about 12 μm, dried, cold pressed, and then cut and welded to obtain a positive electrode sheet.
[0045] (3) Preparation of electrolyte:
[0046] In a dry argon environment, EC, PC and DEC (weight ratio of about 1:1:1) were mixed, and LiPF6 was added and mixed evenly to form an electrolyte.
[0047] (4) Preparation of isolation membrane
[0048] PE porous polymer film is used as the isolation membrane.
[0049] (5) Preparation of lithium-ion batteries
[0050] The obtained positive electrode sheet, negative electrode sheet and separator are wound in order and placed in the outer packaging foil, leaving a liquid injection port. The electrolyte is poured from the liquid injection port, packaged, and then the lithium-ion battery is obtained through the formation, capacity and other processes, wherein the formation, capacity and other processes can refer to the conventional methods in the art. The bare cell in this application refers to the cell to be filled with liquid and packaged. The bare cells in the following embodiments and comparative examples, unless otherwise specified, are all prepared by the above method.
[0051] Example 1
[0052] A method for determining the wetting time of a battery cell after liquid injection, comprising the following steps:
[0053] S100: injecting electrolyte into the bare battery cell (LiCoO2 / Graphite system-winding process) with positive and negative electrodes assembled and completing the battery cell sealing, and then leaving it to stand after sealing;
[0054] During the static immersion process of the battery cell, the electrochemical impedance test (such as Figure 1 shown).
[0055] S200: extract key characterization parameters Rs (ohmic impedance) and Rpore (pore ionic impedance) in the impedance spectrum, obtain the change curves of Rs and Rpore over time, respectively, and use a moving average smoothing algorithm to perform data smoothing on the change curves, with an average number of 3.
[0056] Figure 2 is the variation curve of Rs over time (the first variation curve), Figure 3 This is the change curve of Rpore over time (the second change curve).
[0057] S300: Perform first-order differential processing on the curve of Rs changing with time and the curve of Rpore changing with time respectively to obtain corresponding impedance change rates.
[0058] S400: According to the impedance change rate, the time RT (wetting time at room temperature) and HT (wetting time at high temperature) required for the cell to complete wetting under the current design level can be clearly obtained;
[0059] Specifically, the measurement system used in this application is Gamry Interface 1010E. The measurement error of the system is 0.02mohm / H as measured by the GRR method. Figure 2It can be seen that the impedance change rate corresponding to the position marked by arrow a is less than 0.02mohm / H, and the corresponding normal temperature static time t1=5H is obtained, that is, the time corresponding to the first impedance change rate in the normal temperature section is less than the system measurement error (the same below). Similarly, the impedance change rate corresponding to the position marked by arrow b is less than 0.02mohm / H, and the corresponding high temperature static time t3=3H is obtained, that is, the time corresponding to the first impedance change rate in the high temperature section is less than the system measurement error (the same below). Figure 3 It can be seen that the impedance change rate corresponding to the position marked by arrow a′ is less than 0.02mohm / H, and the corresponding normal temperature standing time t2=4H is obtained. The impedance change rate corresponding to the position marked by arrow b′ is less than 0.02mohm / H, and the corresponding high temperature standing time t4=3H is obtained. It can be determined that the normal temperature standing immersion time RT1 of the battery cell after liquid injection is 5H, and its high temperature standing immersion time HT1 is 3H.
[0060] Another bare cell (LCO / Graphite system) was prepared according to the test results of Example 1. The preparation process was as follows: after the bare cell was injected and sealed, it was infiltrated under static conditions of 25°C for 5H and 60°C for 3H, and then the cell was formed.
[0061] Example 2
[0062] A method for determining the wetting time of a battery cell after liquid injection, comprising the following steps:
[0063] S100: injecting electrolyte into the bare cell (LiCoO2 / Graphite system-lamination process) with positive and negative electrodes assembled and completing the cell sealing, and then leaving it to stand after sealing;
[0064] During the static immersion process of the battery cell, the electrochemical impedance spectroscopy was performed on the battery cell after injection using an electrochemical workstation and fixed parameters (the disturbance voltage amplitude was 5 mV and the scanning frequency range was 0.05 Hz to 10000 Hz) once per hour.
[0065] S200: extract key characterization parameters Rs (ohmic impedance) and Rpore (pore ionic impedance) in the impedance spectrum, obtain the change curves of Rs and Rpore over time, respectively, and use the moving average smoothing algorithm to perform data smoothing on the change curves, with an average number of 2.
[0066] S300: Perform first-order differential processing on the Rs versus time curve and the Rpore versus time curve respectively to obtain corresponding impedance change rates.
[0067] S400: According to the impedance change rate, the time RT2 (wetting time at room temperature) and HT2 (wetting time at high temperature) required for the cell to complete the wetting under the current design level can be clearly obtained. The calculation process is shown in Example 1, and the calculation results are shown in Table 1.
[0068] Another bare cell (LCO / Graphite system) was prepared according to the test results of Example 2. The preparation process was as follows: after the bare cell was filled with liquid and sealed, it was infiltrated under static conditions of 25°C_RT2 and 60°C_HT2, and then the cell was formed.
[0069] Example 3
[0070] A method for determining the wetting time of a battery cell after liquid injection, comprising the following steps:
[0071] S100: injecting electrolyte into the bare cell (LiCoO2 / Graphite+Si system) with positive and negative electrodes assembled and sealing the cell, and letting it stand after sealing;
[0072] During the static immersion process of the battery cell, the electrochemical impedance spectroscopy was performed on the battery cell after injection using an electrochemical workstation and fixed parameters (the disturbance voltage amplitude was 5 mV and the scanning frequency range was 0.05 Hz to 10000 Hz) once per hour.
[0073] S200: extract key characterization parameters Rs (ohmic impedance) and Rpore (pore ionic impedance) in the impedance spectrum, obtain the change curves of Rs and Rpore over time respectively, and use the moving average smoothing algorithm to perform data smoothing on the change curves, with an average number of 4.
[0074] S300: Perform first-order differential processing on the Rs versus time curve and the Rpore versus time curve respectively to obtain corresponding impedance change rates.
[0075] S400: According to the impedance change rate, the time RT3 (wetting time at room temperature) and HT3 (wetting time at high temperature) required for the cell to complete the wetting under the current design level can be clearly obtained. The calculation process is shown in Example 1, and the calculation results are shown in Table 1.
[0076] Another bare cell (LiCoO2 / Graphite+Si system) was prepared according to the test results of Example 3. The preparation process was as follows: after the bare cell was filled with liquid and sealed, it was infiltrated under static conditions of 25°C_RT3 and 60°C_HT3, and then the cell was formed.
[0077] Example 4
[0078] A method for determining the wetting time of a battery cell after liquid injection, comprising the following steps:
[0079] S100: injecting electrolyte into the bare cell (NCM system, i.e. replacing the positive electrode active material LiCoO2 in the above-mentioned positive electrode sheet preparation process with LiNiCoMnO2) after the positive and negative electrodes are assembled, and sealing the cell, and then leaving it to stand;
[0080] During the static immersion process of the battery cell, the electrochemical impedance spectroscopy was performed on the battery cell after injection using an electrochemical workstation and fixed parameters (the disturbance voltage amplitude was 5 mV and the scanning frequency range was 0.05 Hz to 10000 Hz) once per hour.
[0081] S200: extract key characterization parameters Rs (ohmic impedance) and Rpore (pore ionic impedance) in the impedance spectrum, obtain the change curves of Rs and Rpore over time, respectively, and use a moving average smoothing algorithm to perform data smoothing on the change curves, with an average number of 3.
[0082] S300: Perform first-order differential processing on the Rs versus time curve and the Rpore versus time curve respectively to obtain corresponding impedance change rates.
[0083] S400: According to the impedance change rate, the time RT4 (wetting time at room temperature) and HT4 (wetting time at high temperature) required for the cell to complete the wetting under the current design level can be clearly obtained. The calculation process is shown in Example 1, and the calculation results are shown in Table 1.
[0084] Another bare cell (NCM system) was prepared according to the test results of Example 4. The preparation process was as follows: after the bare cell was filled with liquid and sealed, it was infiltrated under static conditions of 25°C_RT4 and 60°C_HT4, and then the cell was formed.
[0085] Example 5
[0086] A method for determining the wetting time of a battery cell after liquid injection, comprising the following steps:
[0087] S100: injecting electrolyte into the bare battery cell (LFP system, i.e. replacing the positive electrode active material LiCoO2 in the above positive electrode sheet preparation process with LiFePO4) after the positive and negative electrodes are assembled, and sealing the battery cell, and then leaving it to stand;
[0088] During the static immersion process of the battery cell, the electrochemical impedance spectroscopy was performed on the battery cell after injection using an electrochemical workstation and fixed parameters (the disturbance voltage amplitude was 5 mV and the scanning frequency range was 0.05 Hz to 10000 Hz) once per hour.
[0089] S200: extract key characterization parameters Rs (ohmic impedance) and Rpore (pore ionic impedance) in the impedance spectrum, obtain the change curves of Rs and Rpore over time, respectively, and use a moving average smoothing algorithm to perform data smoothing on the change curves, with an average number of 3.
[0090] S300: Perform first-order differential processing on the Rs versus time curve and the Rpore versus time curve respectively to obtain corresponding impedance change rates.
[0091] S400: According to the impedance change rate, the time RT5 (wetting time at room temperature) and HT5 (wetting time at high temperature) required for the cell to complete the wetting under the current design level can be clearly obtained. The calculation process is shown in Example 1, and the calculation results are shown in Table 1.
[0092] Another bare cell (LFP system) was prepared according to the test results of Example 5. The preparation process was as follows: after the bare cell was filled with liquid and sealed, it was infiltrated under static conditions of 25°C_RT5 and 60°C_HT5, and then the cell was formed.
[0093] Comparative Example 1
[0094] After the lithium-ion battery (LiCoO2 / Graphite system-winding process) is filled and packaged, it is placed vertically at room temperature 25°C for 24 hours, and at high temperature 60°C for 16 hours, with the air bag facing up. Then the battery cell is formed.
[0095] Comparative Example 2
[0096] After the lithium-ion battery (LiCoO2 / Graphite system-stacking process) is filled and packaged, it is placed vertically at room temperature 25°C for 24 hours, and at high temperature 60°C for 16 hours, with the air bag facing up. Then the battery cell is formed.
[0097] Comparative Example 3
[0098] After the lithium-ion battery (LiCoO2 / Graphite+Si system) is filled and packaged, it is placed vertically at room temperature of 25°C for 24 hours, and at high temperature of 60°C for 16 hours, with the air bag facing upward. Then the battery cell is formed.
[0099] Comparative Example 4
[0100] After the lithium-ion battery (NCM system) is filled and packaged, it is placed vertically at room temperature of 25°C for 24 hours, and at high temperature of 60°C for 16 hours, with the air bag facing upward. Then the battery cell is formed.
[0101] Comparative Example 5
[0102] After the lithium-ion battery (LFP system) is filled and packaged, it is placed vertically at room temperature of 25°C for 24 hours, and at high temperature of 60°C for 16 hours, with the air bag facing upward. Then the battery cell is formed.
[0103] Test method:
[0104] For each embodiment, an EIS test is required to confirm the time required for infiltration. The test conditions are: a Gamry electrochemical workstation is used to perform a constant potential EIS test under the same temperature environment as the infiltration conditions, with an amplitude of 0.5 mV and a frequency of 0.1 Hz to 100000 Hz.
[0105] The cells formed in each embodiment and comparative example were subjected to DCR test, rate test, cycle test and high temperature storage in turn to characterize the kinetic differences caused by different immersion times.
[0106] For the DCR test, the test conditions are as follows: (1) the battery cell is discharged at a constant current of 0.5C0 to 3.0V and left for 10 minutes; (2) the battery cell is charged at a constant current and constant voltage of 0.5C0 to 4.5V, then cut off at 0.05C0 and left for 10 minutes; (3) the battery cell is discharged at a constant current of 1C0 for 1 second and left for 10 minutes; (4) the battery cell is discharged at a constant current of 0.2C0 for 0.5h, then discharged at a constant current of 1C0 for 1 second and left for 10 minutes, and the cycle is repeated until the voltage is <3.0V.
[0107] For the rate test, the test conditions are as follows: (1) the battery cell is discharged at a constant current of 0.5C0 to 3.0V and left for 10 minutes; (2) the battery cell is charged at a constant current and constant voltage of 0.5C0 to 4.5V, and then cut off at 0.05C0 and left for 10 minutes; (3) the battery cell is discharged at a constant current of 3.0V at a discharge rate of 0.2C0 / 0.5C0 / 1C0 / 1.5C0 / 2C0, and the discharge capacities C1, C2, C3, C4, and C5 are recorded.
[0108] For the cycle test, the test conditions are as follows: (1) the battery cell is discharged at a constant current of 0.5C0 to 3.0V and left for 10 minutes; (2) the battery cell is charged at a constant current and constant voltage of 0.5C0 to 4.5V, and then the cell is cut off at 0.05C0 and left for 10 minutes; (3) steps 1-2 are cycled for 800 cycles, and the cycle capacity retention rate is calculated.
[0109] For high-temperature storage, the test conditions are as follows: after formation, the battery cell is subjected to a constant current and voltage test at 0.5C0 to 4.5V, and a cutoff of 0.05C0. It is then stored in a high-temperature environment of 60°C for 14 days, and its capacity recovery and retention capabilities are calculated.
[0110] Effect comparison:
[0111] Table 1 Time required for completion of infiltration obtained in Examples 1 to 5
[0112] RT HT Original RT time Original HT time Time reduction percentage Example 1 5H 3H 24H 16H 80.0％ Example 2 7H 4H 16H 16H 65.6％ Example 3 16H 6H 24H 20H 50.0％ Example 4 9H 4H 16H 16H 40.6％ Example 5 13H 9H 16H 24H 55.0％
[0113] Table 2 Battery performance results of Examples 1 to 5 and Comparative Examples 1 to 5
[0114]
[0115] Through the data of the embodiments and comparative examples, it can be seen that the determination method described in the present application can obtain a reliable infiltration completion time by quantifying the infiltration process after liquid injection. By preparing a battery cell with optimized infiltration time and comparing the dynamic performance of the battery cell under the original empirical infiltration conditions, it is confirmed that there is no significant difference in DCR, 2C high-rate discharge and long-term tests of cycle / storage. It can be seen that the present application proposes a reliable quantitative determination method for the infiltration time required after liquid injection of the battery cell. The determination method significantly shortens the standing time under the empirical mode, which helps to further reduce production costs and effectively improve production capacity.
[0116] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.
Claims
1. A method for determining the infiltration time of a battery cell after liquid injection, characterized in that: The following steps are involved: S100: injecting electrolyte into the battery cell to be injected, sealing it and letting it stand, and performing electrochemical impedance test on the injected battery cell at regular intervals to obtain the impedance spectrum of the battery cell changing with time; S200: extracting the Rs value and the Rpore value in the impedance spectrum by using a transmission line model, and obtaining a first variation curve of the Rs value over time and a second variation curve of the Rpore value over time; S300: Differentiate the change curve to obtain the impedance change rate; S4 00: Determine the soaking time of the battery cell after liquid injection according to the impedance change rate; The Rs value is the ohmic impedance value, and the method for obtaining the Rpore value includes: According to the transmission line model, the impedance spectrum takes the intersection of the ultra-high frequency region and the real axis as the starting point, the intersection of the oblique line in the medium and low frequency region and the 45° straight line in the high frequency region as the end point, and the resistance value of the straight line segment connecting the starting point and the end point projected on the real part is the Rpore value.
2. The determination method according to claim 1, characterized in that: The frequency range of the medium and low frequency area is 1 Hz to 100 Hz, the frequency range of the high frequency area is 100 Hz to 1000 Hz, and the frequency range of the ultra-high frequency area is 1000 Hz to 100000 Hz.
3. The determination method according to claim 1, characterized in that: In the step S100, the standing includes standing at room temperature and standing at high temperature; The room temperature is 25℃ to 35℃, and the room temperature is 16h to 26h; The high temperature standing temperature is 60°C to 65°C, and the high temperature standing time is 10h to 24h.
4. The determination method according to claim 1, characterized in that: In the step S100, the time interval for performing electrochemical impedance test on the battery cell after liquid injection is 0.5h to 3h.
5. The determination method according to claim 1, characterized in that: In the step S200, the first change curve and the second change curve both include a normal temperature section curve and a high temperature section curve; In step S300, the change curve is differentiated to obtain the impedance change rate, which includes: Performing first-order differential processing on the normal temperature section curve and the high temperature section curve in the first change curve respectively, to obtain an impedance change rate A of the normal temperature section curve and an impedance change rate B of the high temperature section curve in the first change curve; The normal temperature section curve and the high temperature section curve in the second change curve are respectively subjected to first-order differential processing to obtain the impedance change rate A′ of the normal temperature section curve and the impedance change rate B′ of the high temperature section curve in the second change curve.
6. The determination method according to claim 5, characterized in that: In the step S400, determining the soaking time of the battery cell after liquid injection according to the impedance change rate includes: When the impedance change rate A is less than the system measurement error, the corresponding rest time t1 is obtained on the first change curve; When the impedance change rate A′ is less than the system measurement error, the corresponding rest time t2 is obtained on the second change curve; When the impedance change rate B is less than the system measurement error, the corresponding rest time t3 is obtained on the first change curve; When the impedance change rate B′ is less than the system measurement error, the corresponding rest time t4 is obtained on the second change curve; Determine the larger value of t1 and t2 as the soaking time of the battery cell at room temperature after filling; The larger value of t3 and t4 is determined as the soaking time of the battery cell at high temperature after liquid filling.
7. The determination method according to claim 6, characterized in that: The system measurement error is denoted as M, and the value range of M is M≤0.02mohm / H.
8. The determination method according to claim 1, characterized in that: In the step S300, before the variation curve is differentiated, the following steps are further included: Using a moving average smoothing algorithm to perform data smoothing processing on the first change curve and the second change curve respectively; When performing the data smoothing process, the average number of the first change curve and / or the second change curve is 2 to 4.
9. The determination method according to claim 1, characterized in that: The perturbation voltage amplitude of the electrochemical impedance test is 5 mV to 8 mV, and the scanning frequency range is 0.05 Hz to 10000 Hz.
10. The determination method according to claim 1, characterized in that: The battery cell to be injected with liquid is a soft-package laminated battery cell or a wound structure battery cell.