Method for improving consistency of formation fluid loss
Patent Information
- Application Number
- CN202611133833.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-29
- Publication Date
- 2026-10-30
AI Technical Summary
化成前期产气速率急剧升高，气流扰动剧烈，电解液夹带流失集中在此阶段，恒定参数难以适配产气峰值，批次电芯失液离散度大，无法均衡两级电解液消耗
1、本发明通过依据产气速率曲线划分产气剧烈、平缓阶段，产气剧烈段采用低充电倍率、低负压，产气平缓段采用高充电倍率、高负压，区别于恒定倍率、恒定负压现有工艺；各恒流充电后设置破真空静置使缓存杯电解液回流电芯，从产气源头与电解液回流双维度控制流失，降低整体化成失液量，缩小批次电芯失液离散程度。
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Figure CN123018196A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery manufacturing technology, specifically a method for improving the consistency of liquid loss during formation. Background Technology
[0002] In lithium-ion battery manufacturing, formation is the core process for generating the SEI passivation film on the negative electrode. The uniformity of the SEI film directly determines the cell capacity, cycle life, and electrochemical stability. Currently, mass-produced cells generally adopt a step-by-step electrolyte injection process. The first injection of electrolyte completes the electrode wetting and basic film formation, while the second injection of electrolyte adds functional additives to optimize battery performance. This process has strict requirements for the uniformity of formation losses between the two electrolyte injections.
[0003] The formation process continuously generates side reaction gases. Under negative pressure formation conditions with an external buffer cup, the gas flow easily carries away electrolyte, causing physical loss. This, combined with the chemical consumption of electrolyte during SEI film formation, results in formation liquid loss. Excessive liquid loss reduces the cell's initial coulombic efficiency and accelerates capacity decay. In production, this loss can only be compensated for by overfilling the electrolyte, increasing electrolyte costs. If the difference in electrolyte loss between the first and second fills is too large, it will cause uneven SEI film thickness, exacerbating batch cell performance fluctuations and increasing the difficulty of mass production control.
[0004] Traditional formation processes use a fixed charging rate and constant negative pressure throughout the entire process, without dynamically differentiating reaction stages based on the gas production rate. In the early stages of formation, the gas production rate increases sharply, causing severe gas flow disturbances. Electrolyte entrainment and loss are concentrated in this stage, making it difficult for constant parameters to match the peak gas production. This results in large dispersion in electrolyte loss between batches of cells and an inability to balance electrolyte consumption in both stages.
[0005] Existing improvement solutions only adjust negative pressure or charging current, failing to integrate the gas generation stage, graded negative pressure rates, and electrolyte recirculation process. This prevents simultaneous control of liquid loss from multiple dimensions, including the gas generation source, gas entrainment, and liquid recovery. Simply reducing the charging rate significantly prolongs formation time and reduces production line efficiency, while merely adjusting negative pressure exacerbates electrolyte entrainment. Furthermore, the current process lacks a post-charging vacuum-breaking recirculation design, leading to liquid accumulation in the buffer cup, overflow, and contamination of pipelines. Some control methods can also damage the SEI film quality and degrade the cell's high and low temperature cycling performance. Summary of the Invention
[0006] The purpose of this invention is to provide a method for improving the consistency of liquid loss during formation, so as to solve the problems in the background art.
[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for improving the consistency of electrolyte loss during formation, the method being used for cell formation employing a step-by-step electrolyte injection method, wherein the electrolyte injection port of the cell is externally connected to a buffer cup and negative pressure vacuum formation is used, comprising the following steps: S1. Collect gas generation rate data for the entire cell formation process and plot the gas generation rate curve. Based on the gas generation rate, divide the formation process into a stage of intense gas generation and a stage of moderate gas generation. The gas generation rate of the intense gas generation stage is higher than that of the moderate gas generation stage. S2. During the constant current charging process in each stage of the violent gas production phase, the battery cell is charged with constant current at a first charging rate, and vacuum is performed at a first negative pressure. During the constant current charging process in each stage of the gas production smooth phase, the battery cell is charged with constant current at the second charging rate, while vacuuming is performed with the second negative pressure. Wherein, the first charging rate is less than the second charging rate, and the absolute value of the first negative voltage is less than the absolute value of the second negative voltage; S3. After each constant current charging step is completed, the vacuum is broken and the static pressure is adjusted to the first air pressure so that the electrolyte in the buffer cup connected to the cell's liquid injection port flows back into the cell.
[0008] Based on the above technical solutions, the present invention also provides the following optional technical solutions: In one alternative approach: the method for obtaining gas generation rate data of the battery cell during the formation process in step S1 includes: Connect the cell's electrolyte inlet to a battery gas generation test instrument via a hose to perform a formation test on the cell, collect gas generation data, and plot a gas generation rate curve.
[0009] In one alternative approach: the formation test of the battery cell includes: performing the formation test on the battery cell using a baseline charging step and a low-rate experimental charging step respectively, obtaining two gas production rate curves, comparing the two curves, and taking the period when the gas production rate is higher than a preset threshold or in the gas production peak range as the period of intense gas production.
[0010] In one alternative: the reference charging step consists of two constant current charging stages at 0.1C and 0.2C; the low-rate experimental charging step consists of two constant current charging stages at 0.05C and 0.05C; the formation temperature of both the reference charging step and the low-rate experimental charging step is 45±5℃.
[0011] In one alternative: the first charging rate is 0.03C to 0.08C; the second charging rate is 0.1C to 0.3C.
[0012] In one alternative: the first negative pressure is -30 kPa to -60 kPa, and the second negative pressure is -70 kPa to -90 kPa.
[0013] In one alternative: in step S3, the first air pressure is -5kPa to 5kPa; the duration of the vacuum breaking and settling is 1 to 5 minutes.
[0014] In one alternative: the formation process includes a pre-settling step, one or more constant current charging steps during the intense gas production stage, and one or more constant current charging steps during the gradual gas production stage. A vacuum breaking and static setting step is set between every two constant current charging steps.
[0015] In one alternative: the pre-static step lasts for 1 to 3 minutes, and the negative pressure during the pre-static stage is controlled at -85 kPa to -75 kPa.
[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention divides the gas production process into intense and gradual stages based on the gas production rate curve. The intense gas production stage uses a low charging rate and low negative pressure, while the gradual gas production stage uses a high charging rate and high negative pressure, which is different from the existing constant rate and constant negative pressure process. After each constant current charge, a vacuum breaking and static setting is set to allow the electrolyte in the buffer cup to flow back to the cell. This controls the loss from both the gas production source and the electrolyte return, reducing the overall liquid loss during formation and minimizing the dispersion of liquid loss in batches of cells.
[0017] 2. This invention can complete the process switching by simply adjusting the formation program parameters, without the need for hardware modification of the negative pressure formation equipment. The overall formation time increment is low, and the interference with the production line cycle is small. Compared with a single control scheme that only optimizes the charging rate or negative pressure, this invention has a multi-process coordinated control, which has a better effect on improving the balance of electrolyte consumption in the two stages of the step-by-step electrolyte injection cell.
[0018] 3. The cell capacity, initial coulombic efficiency, self-discharge characteristics, and electrode interface state prepared by the process of this invention are not significantly different from those of the benchmark process. The degradation trend of room temperature and high temperature cycling is consistent, and the SEI film formation quality is not negatively affected. It can avoid the problems of buffer cup overflow and electrolyte contamination in negative pressure pipeline, reduce equipment maintenance and cell scrapping losses, and is suitable for the large-scale mass production of cells with step-by-step liquid injection. Attached Figure Description
[0019] Figure 1 This is a comparison chart of gas production rate curves at different oxidation ratios of the present invention.
[0020] Figure 2 This is a 25°C cycle curve diagram of the present invention.
[0021] Figure 3 This is a schematic diagram of the 45°C cycling curve structure of the present invention. Detailed Implementation
[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.
[0023] When collecting gas generation rate data, the cell's liquid injection port is connected to the battery gas generation test instrument through a hose. The test instrument continuously records the gas generation at a sampling frequency of no less than once per second to ensure that the plotted gas generation rate curve can accurately reflect the instantaneous change in the gas generation rate, thereby providing a high-precision data basis for stage division.
[0024] Meanwhile, in order to eliminate interference from the initial unstable phase, the data for the first 60 seconds after the formation begins can be used as a transition period and not be adopted. Effective data collection can only begin after the gas production rate enters a stable range.
[0025] When dividing the gas production stage into the intense gas production stage and the slow gas production stage, the point where the second derivative of the gas production rate curve crosses zero or the moment when the gas production rate first exceeds 60% of the maximum gas production rate of the baseline step can be used as the starting point of the preset threshold. The point where the gas production rate falls back below the threshold and continues to stably exceed the set time (e.g., 30 seconds) can be used as the ending point, thereby defining the time window of the intense gas production stage.
[0026] If the gas production rate curve has multiple peaks, the intervals of each peak can be merged into the same intense gas production stage to avoid frequent switching of charging rate and negative pressure due to short-term fluctuations.
[0027] Regarding the selection of the first charging rate and the second charging rate, the first charging rate during the intense gas production stage is preferably 0.03C to 0.08C. This range can effectively reduce the peak gas production without excessively prolonging the charging time. The second charging rate during the gradual gas production stage is preferably 0.1C to 0.3C. It can be gradually increased in stages according to the cell's state of charge to balance the formation efficiency and the gas discharge requirements.
[0028] In actual operation, the absolute value of the first negative pressure is controlled between 30 kPa and 60 kPa, and the absolute value of the second negative pressure is controlled between 70 kPa and 90 kPa. The process of switching from the first negative pressure to the second negative pressure is carried out in a gradual manner. For example, a transitional static step is set between adjacent steps to gradually adjust the negative pressure and avoid sudden pressure changes from impacting the inside of the battery cell.
[0029] During the vacuum breaking and settling step after each constant current charging cycle, the negative pressure is slowly raised from the first negative pressure or the second negative pressure to the first air pressure by adjusting the opening of the vacuum valve. The rate of increase is controlled to be no more than 10 kPa per second to avoid impact on the internal structure of the battery cell due to sudden pressure increase. The settling time is 1 to 5 minutes to ensure that the electrolyte collected in the buffer cup is fully returned.
[0030] During the vacuum breaking process, the connecting pipe between the cell's liquid injection port and the buffer cup is kept unobstructed, so that the reflux process is carried out entirely by gravity without the need to apply additional positive pressure, so as to prevent external gas or impurities from being forced into the cell.
[0031] For cells that use a step-by-step electrolyte injection method, this method balances the formation losses of the first and second electrolyte injections by controlling the amount of electrolyte loss during the intense gas generation stage and the gentle stage, thus avoiding uneven SEI film thickness due to excessive differences in electrolyte loss between the two injections and ensuring the consistency of performance of batch cells.
[0032] Specifically, since the intense gas production phase is mainly concentrated in the early formation stage, the electrolyte injected in the first injection dominates at this time. By reducing the charging rate and negative pressure in this stage and cooperating with vacuum breaking and reflux, the electrolyte loss in this stage can be significantly reduced, making the consumption of one injection of electrolyte closer to the design value. In the stage of slow gas production, the electrolyte injected in the second injection begins to play a role. A higher charging rate and a higher negative pressure are used to ensure the formation efficiency. At the same time, vacuum breaking and reflux can still recover some of the entrained electrolyte from the second injection, so that the overall loss of the two injections tends to be balanced.
[0033] The constant current charging step in the formation process can be segmented according to the fluctuation of the gas production rate curve. The stage of intense gas production is divided into 1 to 3 segments, and the stage of slow gas production is divided into 1 to 2 segments. The charging capacity of each segment is allocated according to the proportion of the total charging capacity. After each segment of charging, a vacuum breaking and settling step is set to realize multiple recovery of electrolyte.
[0034] If the period of intense gas production is long or the gas production rate curve shows multiple peaks, the period can be further divided into multiple charging steps. Each step uses the same first charging rate and first negative pressure, but the charging capacity of each step can be adjusted according to the distribution of peaks. For example, the charging capacity of a single step can be appropriately reduced in the sub-interval with the highest gas production rate to shorten the charging time of that step and avoid gas production from being in the peak range for a long time.
[0035] The negative pressure control of the pre-standing step is -85kPa to -75kPa, lasting 1 to 3 minutes. This negative pressure range can effectively remove residual gas inside the cell without causing the electrolyte to be drawn out too early due to excessive negative pressure, ensuring that the electrolyte fully wets the electrode and provides stable initial conditions for the subsequent formation reaction.
[0036] After the pre-static setting is completed, the first stage of constant current charging, which is the stage of intense gas production, is directly started without additional venting operations, so as to avoid unnecessary loss of electrolyte during the venting process.
[0037] The aforementioned supplementary process parameter selection and operational details enable liquid loss control and consistency improvement through parameter adjustments in the formation process without increasing hardware modification costs. In actual mass production, process switching can be completed simply by setting the corresponding charging rate, negative pressure value, and vacuum breaking settling time in the formation equipment according to the defined stages. This does not affect the existing production line layout, nor does it require replacement of buffer cups or piping structures, demonstrating excellent industrial applicability.
[0038] The experimental subject of this invention is a 228Ah prismatic lithium iron phosphate battery cell. The battery cell adopts a mass production process of adding different components of electrolyte in one-fill and two-fill steps. The formation equipment is equipped with a negative pressure suction structure with an external buffer cup connected to the liquid injection port. The formation is completed at a constant temperature of 45±5℃ throughout the process. Each group of 180 cells is tested in parallel. The advantages and disadvantages of the process are compared from multiple dimensions such as formation time, liquid loss, dispersion, electrical performance, thickness, self-discharge, and high and low temperature cycling.
[0039] Appendix Figure 1 The horizontal axis represents the formation time (in seconds), and the vertical axis represents the gas production rate (in mL / min). The black curve represents the gas production curve of the baseline 0.1C / 0.2C mass production process, and the red curve represents the gas production curve of the 0.05C low-rate process of this invention.
[0040] Baseline black curve: The gas production rate rises rapidly in the early stage of charging, with a peak value close to 2.3 mL / min. The first 2000s is the stage of intense gas production. During this stage, the gas flow rate is high, and when the negative pressure is used for gas extraction, it is very easy to entrain electrolyte into the buffer cup, which is the main source of liquid loss during formation. Low-rate red curve: The overall peak gas production is only 1.5 mL / min, the gas production rate is significantly reduced, and the gas production in the intense gas production range is greatly reduced, thus reducing electrolyte entrainment and loss from the source; The interval division is based on the peak gas production interval of the two curves to define the intense gas production stage, and the remaining time period is defined as the slow gas production stage, which provides data support for the segmented multiplier and stepped negative pressure process of this invention.
[0041] Take a battery cell of the same specification that has been allowed to stand before high temperature, seal the injection port hose and connect it to a gas generation tester. Collect the total gas generation during the entire charging process using two sets of charging steps: a baseline of 0.1C / 0.2C and a low-rate of 0.05C / 0.05C. Plot the results in the attached diagram. Figure 1 The curves were used to determine the range of intense gas production with high liquid loss, and six control synthesis schemes were designed accordingly.
[0042] Example 1 (Baseline Group)
[0043] Example 2 (Only one vacuum breaking operation is added; no optimization of magnification or negative pressure)
[0044] Example 3 (Reduced gas production rate, uniform negative pressure throughout, and single vacuum breaking)
[0045] Example 4 (Multi-stage low-rate gas production, uniform negative pressure, multiple vacuum breaking)
[0046] Example 5 (Low magnification + two-stage negative pressure, multiple vacuum breaking, and gradual low-pressure pumping in stages)
[0047] Example 6 (Low-rate gas production section + three-stage stepped negative pressure + multi-stage vacuum breaking + high-rate acceleration in the later stage)
[0048] After the battery cells were allowed to stand at high temperature, they were tested according to the formation process described above. Each group tested 180ea battery cells, and the collected data are summarized below: Table 1. Formation time, liquid loss, and core electrical properties
[0049] Table 2 Cell thickness, self-discharge K-value, and electrode interface condition
[0050] room temperature Figure 2 In the 0-500 cycle range, the two capacity decay curves completely overlap, and the decrease in capacity retention rate is no different. High temperature Figure 3 Under high-temperature accelerated aging conditions, the degradation trend and capacity retention of the six-year standard are highly consistent with those of the benchmark. Conclusion: The stepped negative pressure + low rate + vacuum breaking combination process of this invention only optimizes the control of electrolyte loss and will not damage the SEI film formation quality. The cell's room temperature and high temperature cycle life are on par with the traditional mass production benchmark process, with no risk of performance degradation.
[0051] In summary: 1. Combined with the appendix Figure 1The gas generation pattern reveals that simultaneously reducing the charging rate and negative pressure during periods of intense gas generation, coupled with 0±5kPa vacuum reflux after each charging stage, can simultaneously suppress electrolyte entrainment and balance electrolyte consumption in the first / second charge stages. Compared to baseline implementation one, the average electrolyte loss decreased from 13.2g to 5.3g, a reduction of approximately 60%; the standard deviation of electrolyte loss decreased from 11.8 to 1.9, and the electrolyte loss distribution range for the entire batch of cells was less than 15g, significantly improving batch consistency. Implementations two through five, which only individually added vacuum breaking, reduced the charging rate, or implemented segmented negative pressure, all showed weaker improvement effects than the synergistic solution of the three elements presented in this invention.
[0052] 2. The total conversion time of the six-component process is 115 minutes, which is only 3 minutes longer than the baseline and much shorter than Examples 3, 4 and 5. While significantly reducing liquid loss, it hardly affects the production line operating efficiency and has strong industrial applicability.
[0053] 3. There were no significant differences in the capacity, initial coulombic efficiency, thickness, self-discharge K value, and electrode interface state of the six groups of cells. All cells showed no black spots or poor lithium plating. The cycling curves in Figures 2 and 3 confirm that the film formed by this process is uniform and does not sacrifice the long-cycle performance of the cells.
[0054] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.
Claims
1. A method for improving the consistency of electrolyte loss during formation, the method being used for cell formation employing a step-by-step electrolyte injection method, wherein the electrolyte injection port of the cell is externally connected to a buffer cup and negative pressure vacuum formation is used, characterized in that, Includes the following steps: S1. Collect gas generation rate data for the entire cell formation process and plot the gas generation rate curve. Based on the gas generation rate, divide the formation process into a stage of intense gas generation and a stage of moderate gas generation. The gas generation rate of the intense gas generation stage is higher than that of the moderate gas generation stage. S2. During the constant current charging process in each stage of the violent gas production phase, the battery cell is charged with constant current at a first charging rate, and vacuum is performed at a first negative pressure. During the constant current charging process in each stage of the gas production smooth phase, the battery cell is charged with constant current at the second charging rate, while vacuuming is performed with the second negative pressure. Wherein, the first charging rate is less than the second charging rate, and the absolute value of the first negative voltage is less than the absolute value of the second negative voltage; S3. After each constant current charging step is completed, the vacuum is broken and the static pressure is adjusted to the first air pressure so that the electrolyte in the buffer cup connected to the cell's liquid injection port flows back into the cell.
2. The method for improving the consistency of liquid loss during formation according to claim 1, characterized in that, In step S1, the method for obtaining the gas generation rate data of the battery cell during the formation process includes: Connect the cell's electrolyte inlet to a battery gas generation test instrument via a hose to perform a formation test on the cell, collect gas generation data, and plot a gas generation rate curve.
3. The method for improving the consistency of liquid loss during formation according to claim 2, characterized in that, The formation test of the battery cell includes: performing formation tests on the battery cell using the baseline charging step and the low-rate experimental charging step respectively, obtaining two gas production rate curves, comparing the two curves, and taking the period when the gas production rate is higher than the preset threshold or in the gas production peak range as the stage of intense gas production.
4. The method for improving the consistency of liquid loss during formation according to claim 3, characterized in that, The reference charging step consists of two constant current charging stages at 0.1C and 0.2C; the low-rate experimental charging step consists of two constant current charging stages at 0.05C and 0.05C; the formation temperature for both the reference charging step and the low-rate experimental charging step is 45±5℃.
5. The method for improving the consistency of liquid loss during formation according to claim 1, characterized in that, The first charging rate is 0.03C to 0.08C; the second charging rate is 0.1C to 0.3C.
6. The method for improving the consistency of liquid loss during formation according to claim 1, characterized in that, The first negative pressure is -30 kPa to -60 kPa, and the second negative pressure is -70 kPa to -90 kPa.
7. The method for improving the consistency of liquid loss during formation according to claim 1, characterized in that, In step S3, the first air pressure is -5kPa to 5kPa; the duration of the vacuum breaking and settling is 1 to 5 minutes.
8. The method for improving the consistency of liquid loss during formation according to claim 1, characterized in that, The formation process includes a pre-settling step, one or more constant current charging steps during the intense gas production stage, and one or more constant current charging steps during the gradual gas production stage. A vacuum breaking and static setting step is set between every two constant current charging steps.
9. The method for improving the consistency of liquid loss during formation according to claim 8, characterized in that, The pre-static step lasts for 1 to 3 minutes, and the negative pressure during the pre-static stage is controlled at -85 kPa to -75 kPa.