Battery cell baking process and effectiveness judgment method

Abstract

The invention discloses a battery cell baking process and a baking effectiveness judgment method, and the method sequentially comprises the steps of equipment vacuum leakage rate testing, baking pretreatment, staged preheating heating, staged constant-temperature vacuum baking, staged nitrogen conversion baking, constant-temperature vacuum baking keeping and calculation of the vacuum leakage rate r1 of equipment in the baking process, and judging whether baking is finished. The time of the initial preheating stage of battery cell baking can be effectively shortened, the high-vacuum baking time proportion is increased, and the overall baking efficiency is improved; the method can automatically analyze the baking effectiveness of the battery cell on line in real time, and by monitoring the vacuum leakage rate and analyzing the evaporation rate and baking effect of the moisture and alcohol additives, the control consistency of the moisture and alcohol additives is improved, the influence of sampling testing of the moisture and alcohol additive content on the utilization rate of baking equipment is eliminated, the problem of re-baking and reworking is eliminated, and the product quality is improved. The production line efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of battery cell baking and effectiveness determination, and in particular to a battery cell baking process and effectiveness determination method. Background Art

[0002] Lithium-ion batteries are electrochemical systems. The water content and alcohol additives in the battery cells will participate in a series of side reactions, which will affect the quality reliability and safety reliability of the battery cells to a certain extent. Therefore, in the manufacturing process of lithium-ion batteries, battery cell baking is an extremely important process to remove the water content and alcohol additives in the battery cells. The monitoring of the water content and alcohol additive content after the battery cells are baked is also an important process semi-finished product control method.

[0003] The current conventional cell baking process uses a vacuum baking method, including contact baking and thermal radiation baking, etc. First, preheat in a high-purity inert gas N2 environment for a certain period of time, and then bake at a constant temperature vacuum for a certain period of time after reaching the set temperature. After the baking process is completed, the cell is extracted and sent to test the moisture and alcohol additive content results. After the moisture and alcohol additive tests are qualified, the baked cell is cooled and circulated to complete the cell baking process. There are two main methods for determining the effectiveness of the cell baking process in the existing technical solutions. One is the commonly used post-baking sampling test of moisture and alcohol additive content, and the determination is made based on the moisture and alcohol additive content results, such as the drying method of lithium-ion batteries disclosed in patent CN2023101638574; the second is to make a determination with the help of the voltage-time curve of the first charging process of the cell (patent CN2015109793713, the determination method of the effectiveness of the lithium-ion cell baking process disclosed in the disclosure).

[0004] The main deficiencies of the existing technology for determining the effectiveness of the cell baking process are as follows: in the initial preheating stage of the cell baking, the cell temperature rises slowly and takes a long time; in the initial preheating stage of the cell baking, the vacuum degree is low, and the boiling points of moisture and alcohol additives are high, which is not conducive to the vaporization and evaporation of moisture and alcohol additives; after the cell baking process is completed, the process of taking moisture samples to test moisture and alcohol additives takes 30 minutes to 60 minutes, the cells occupy the baking equipment, and the utilization rate of the baking equipment is low; based on the test results of moisture and alcohol additives, there is a certain proportion of re-baking and rework, which reduces the equipment capacity and production line efficiency; the cell baking effectiveness is determined by using the voltage-time curve of the cell first charging process, which has serious hysteresis, and can only evaluate the influence of moisture to a certain extent, and cannot evaluate the influence of alcohol additives; in addition, it usually takes at least 2 days from the end of baking to the first charge of formation, and even if there is a problem with the baking effectiveness, it has become a fact and cannot be remedied, so this method can only be used in the experimental research process. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings and defects of the prior art and provide a cell baking process with high cell baking efficiency and good consistency and a method for determining baking effectiveness. The process can effectively shorten the time of the initial preheating stage of cell baking, increase the proportion of high vacuum baking time, and improve the overall baking efficiency; the process can automatically analyze the baking effectiveness of the cell online in real time, monitor the vacuum leakage rate, analyze the evaporation rate of water and alcohol additives and the baking effect, improve the control consistency of water and alcohol additives, eliminate the influence of sampling test of water and alcohol additive content on the utilization rate of baking equipment, eliminate the problem of re-baking and rework, and improve the efficiency of the production line.

[0006] A battery cell baking process and effectiveness determination method, comprising:

[0007] Step 1: Vacuum leakage rate r1 test: The battery cell baking equipment is in a sealed state, and the vacuum is evacuated to the set value P1. The vacuum is maintained for t1, and the vacuum degree in the cavity is reduced from P1 to P1. t , the vacuum leakage rate r1 of the baking equipment is calculated: r1=(P1 t -P1)*V1 / t1;

[0008] The vacuum leakage rate r1 of the cell baking equipment in this step is tested regularly, and an alarm threshold C0 is set to detect the sealing of the equipment to ensure sufficient vacuum holding capacity and avoid the problem of insufficient baking capacity due to poor sealing of the baking equipment; when the vacuum leakage rate r1 exceeds the alarm threshold C0, the equipment automatically alarms and notifies the equipment personnel to perform sealing maintenance;

[0009] Step 2: Pre-baking treatment: Place the battery cell to be baked in the baking equipment, evacuate to the set value P2, and fill with high-purity inert gas N2 until the vacuum degree reaches the set value P3; before the baking starts and the temperature rises, the air in the equipment is evacuated and filled with inert gas N2 to avoid electrode oxidation problems during the temperature rise of the battery cell. At the same time, the inert gas N2 plays a role in protecting the heating metal plate and heat conduction during the baking process; the heating metal guides the electrical probe plate to connect the circuit to start heating. Nitrogen plays a role in heat conduction in the environment, and the temperature rise rate of the battery cell body is faster than that of the vacuum environment.

[0010] Step 3: Start preheating in stages, the temperature setting value of the first stage is T1, the duration is t1; the temperature setting value of the second stage is T2, the duration is t2;

[0011] In the first preheating stage, since the battery cell is heated from room temperature, it is not limited to heating by heat radiation and contact heating. The temperature of the battery cell body is much lower than the normal baking temperature. The temperature setting T1 is 10-20°C higher than T2. ​​By increasing the temperature difference between the oven and the battery cell body, the heating speed of the battery cell from room temperature is increased and the heating time is shortened. This step three is used to quickly complete the preheating of the battery cell, shorten the preheating time, and stabilize the temperature in a constant temperature vacuum baking state.

[0012] Step 4: Start the staged constant temperature vacuum baking, the first stage temperature setting value is T3, the vacuum setting value is P L1 ~P U1 , duration t3; second stage temperature setting value T4, vacuum setting value P L2 ~P U2 , duration t4;

[0013] In each stage of baking, when the vacuum degree reaches P U1 / P U2 Continue to evacuate until P L1 / P L2 , vacuum degree in vacuum holding stage is from P L1 / P L2 Reduce to P U1 / P U2 The corresponding time t U1 / t U2 , and then the vacuum leakage rate r of the current state is calculated t calculate;

[0014] In the first stage, due to the high moisture concentration in the oven environment, the moisture and alcohol additives inside the battery cell are quickly vaporized by heat, and the vacuum setting value P L1 ~P U1 Higher than P L2 ~P U2 , avoid too long vacuuming time, temperature T3 is higher than or equal to T4, and promote the shortening of the temperature rise time of the battery cell; at the same time, the water and alcohol additives inside the battery cell are quickly vaporized in a high temperature and high vacuum environment in this stage, and discharged through the vacuum pipeline, and no N2 filling operation is required; step four is the stage of rapid evaporation of water and alcohol additives;

[0015] Step 5: Start phased N2 replacement baking, temperature setting value T4, vacuum setting value P L3 ~P U3 In the first stage, the following steps are repeated: fill with inert gas N2 to break the vacuum to vacuum degree P4, duration t5, continue to evacuate to the set value P L3 ~P U3, duration t6, number of repetitions n1; in the second stage, repeat the following steps: fill with inert gas N2 to break the vacuum to vacuum degree P4, duration t5, continue to evacuate to the set value P L3 ~P U3 , duration t7, number of repetitions n2;

[0016] As the concentration of water and alcohol additives inside the battery cell decreases, the intermolecular forces between the water molecules and alcohol additive molecules and the active substances inside the gaps of the pole pieces significantly reduce the evaporation rate of water and alcohol additives, and N2 needs to be filled in for replacement baking. N2 enters the gaps of the pole pieces, weakens the intermolecular forces between the water molecules and alcohol additive molecules and the active substances, and discharges trace amounts of water and alcohol additives through high vacuum. In the second stage of N2 replacement baking, the frequency of N2 replacement is significantly higher than that in the first stage, so that at the end of baking, trace amounts of water and alcohol additive molecules are discharged to the greatest extent.

[0017] Step 6: After completing the N2 replacement baking in step 5, continue to maintain constant temperature vacuum baking for a duration of t8;

[0018] Step 7: Calculate the vacuum leakage rate r1 of the equipment during the baking process, and determine whether to end the baking: The system automatically calculates the vacuum leakage rate r1 of the battery cell baking process from step 4 to step 6 above t , and automatically generate the vacuum leakage rate r t -Time t curve based on vacuum leak rate r t -Time t curve to analyze and determine the vacuum leakage rate r of more than 3 consecutive times before the end of step 6 constant temperature vacuum baking t result:

[0019] When 3 consecutive r t If both meet the threshold value C1, the baking is judged to be effective, the baking process ends normally, and the battery cell is taken out of the baking equipment for cooling and automatic circulation; otherwise, the second stage of step 5 N2 replacement baking and step 6 constant temperature vacuum baking will be automatically executed once, for 3 consecutive r t When all the conditions are below the threshold C1, the baking is determined to be effective, the process ends, and the battery cell is taken out of the baking equipment for cooling and automatic circulation; if it still does not meet the requirements, the effectiveness is determined by sampling and testing the moisture and alcohol additive content, and the vacuum leak rate r1 test in step 1 is repeated.

[0020] According to the vacuum leakage rate r t -Time t curve, when the baking process time is over, the vacuum leakage rate r t会 If the evaporation rate of the water in the battery cell is reduced to a certain level and meets a certain threshold range, it can be determined that the evaporation rate of the water in the current battery cell has reached an extremely low level and the baking process is terminated; if the baking process time is over, the vacuum leakage rate of the last three times r tIf it is still relatively high and exceeds a certain threshold range, it is considered that the moisture content of the battery cell has not reached the baking effect.

[0021] Preferably, in step 1, P1 is 20-80 Pa, t1 is 10-60 min, V1 is the volume of the inner cavity of the device in an unloaded state, and the time accuracy of the device data collection is 1-5 S.

[0022] Preferably, in step 2, P2 is 20-100 Pa, and P3 is 50000-90000 Pa.

[0023] Preferably, in step three, T1 is 100-120° C., T2 is 90-105° C., t1 is 30-60 min, and t2 is 5-10 min.

[0024] Preferably, in step 4, T3 is 90-105°C, T4 is 90-100°C, t3 is 30-300min, t4 is 30-300min, P L1 50~80Pa, P U1 70~100Pa, P L2 30~50Pa, P U2 It is 60~80Pa.

[0025] Preferably, in step 4, the vacuum leakage rate r of the current state t Including the vacuum leakage rate r of the current state of the first stage t1， The vacuum leakage rate of the second stage is r t2 , r t2 =(P U2 -P L2 )*V2 / t U2 , r t1 =(P U1 -P L1 )*V2 / t U1 , V2 is the volume of the inner cavity of the device in the loaded state.

[0026] Preferably, in step 5, the nitrogen filled is high purity ≥ 99.9%, P4 is 80000-90000Pa, t5 is 2-5min, t6 is 30-60min, t7 is 20-40min, P L 30~50Pa, P U It is 60~80Pa, and the number of replacement times n is 2~10 times.

[0027] Preferably, in step six, t8 is 20 to 60 min.

[0028] Preferably, in the step 7, during the first cell baking process, the water content and alcohol additive sampling test results are used as the basis for determining the effectiveness, and the vacuum leakage rate r of the last three consecutive tests is t Only record and upload the vacuum leak rate r t Average value, starting from the second battery cell baking process, the device automatically determines the effectiveness based on the threshold value by the program.

[0029] The threshold C1 is the vacuum leakage rate r of the last three consecutive times of each battery cell baking process. t The weighted average of the average value*coefficient K, K is 1.01~1.10, and the coefficient K needs to be dynamically updated according to the test results of moisture and alcohol additive content.

[0030] In each baking process, there will be three consecutive vacuum leakage rates rt to obtain an average value; each subsequent baking process will increase the average value, and the average value of the last three vacuum leakage rates rt of each baking process will be used as the data source for continuing to calculate the average value, and will be updated in a rolling manner.

[0031] The method of the present invention increases the temperature rise rate of the battery core, compresses the baking preheating time, increases the high vacuum baking time ratio, improves the overall baking efficiency, and shortens the baking time.

[0032] The method of the present invention improves the effect of removing moisture and alcohol additives inside the battery core, and improves the ability to control the content of moisture and alcohol additives after baking.

[0033] The method of the present invention can view and analyze the evaporation rate of water and alcohol additives inside the battery cell in real time through the vacuum leakage rate time curve, which is more convenient for comparing the effects of different baking process designs.

[0034] According to the method of the present invention, after the cell baking process is completed, online determination is performed through vacuum leakage rate data, thereby avoiding the waiting time for sampling and testing the moisture and butanediol content, and greatly improving production efficiency and equipment utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of a battery cell baking process and effectiveness determination method of the present invention.

[0036] Figure 2 It is a vacuum leakage rate-time curve diagram obtained in the baking process of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] See also Figure 1 As shown in the embodiment of the present application, the cell baking process and effectiveness determination method include the following steps:

[0039] Step 1: Vacuum leakage rate r1 test: When the battery cell baking equipment is sealed, evacuate to the set value P1, and maintain the vacuum for t1. The vacuum degree in the cavity is reduced from P1 to P1. t , calculate the vacuum leakage rate r1 of the battery cell baking equipment, r1=(P1 t -P1)*V1 / t1, V1 is the inner cavity volume of the equipment in the no-load state. When the vacuum leakage rate r1 exceeds the threshold C0, the equipment alarms;

[0040] Step 2: Pre-baking treatment: Place the battery cell to be baked in the battery cell baking equipment, evacuate to the set value P2, and fill with high-purity inert gas N2 until the vacuum degree reaches the set value P3, where P3 is greater than P2; before the baking starts to rise in temperature, evacuate the air in the battery cell baking equipment and fill with inert gas N2;

[0041] Step 3: Start preheating in stages: the first stage temperature setting value is T1, the duration is t1; the second stage temperature setting value is T2, the duration is t2; t1 is greater than t2, T1 is higher than T2;

[0042] Step 4: Start the staged constant temperature vacuum baking: the first stage temperature setting value is T3, the first vacuum setting value is P L1 ~P U1 , duration t3; second stage temperature setting value T4, second vacuum setting value P L2 ~P U2 , duration t4; in staged baking, when the vacuum degree reaches P U1 / P U2 Continue to evacuate until P L1 / P L2 , vacuum degree in vacuum holding stage is from P L1 / P L2 Reduce to P U1 / P U2 The corresponding time t U1 / t U2 , the vacuum leakage rate r of the current state t Calculation: The first vacuum setting value P L1 ~P U1 Higher than the second vacuum setting value P L2 ~P U2 , temperature T3 is higher than / equal to T4;

[0043] Step 5: Start phased N2 replacement baking: temperature setting value T4, vacuum setting value P L3 ~P U3The first stage is N2 replacement baking. Repeat the following steps: fill the inert gas N2 to break the vacuum to the vacuum degree P4, duration t5, continue to evacuate to the set value P L3 ~P U3 , duration t6, number of repetitions n1; in the second stage, N2 replacement baking, repeat the following steps: fill with inert gas N2 to break the vacuum to vacuum degree P4, duration t5, continue to evacuate to the set value P L3 ~P U3 , duration t7, number of repetitions n2;

[0044] Step 6: Continue to maintain constant temperature vacuum baking for a duration of t8;

[0045] Step 7: Calculate the vacuum leakage rate r1 of the equipment during the baking process, and determine whether to end the baking: Automatically calculate the vacuum leakage rate r1 of the battery cell during the above steps 4 to 6 t , and automatically generate the vacuum leakage rate r t r with time t t- t curve, through r t- t curve analysis and judgment step 6: vacuum leakage rate r for at least 3 times in a row before the end of constant temperature vacuum baking t result;

[0046] At least 3 consecutive vacuum leak rates r t If both meet the threshold value C1, it is judged as valid and the baking process ends normally; otherwise, the second stage N2 replacement baking in step 5 and the constant temperature vacuum baking in step 6 are automatically executed once, and then the vacuum leakage rate r is kept constant for at least 3 consecutive times. t When all the conditions are lower than the threshold value C1, it is determined to be effective and the process ends; if it is still not satisfied, the effectiveness is determined by sampling and testing the water and alcohol additive content, and the vacuum leakage rate r1 test in step 1 is repeated.

[0047] Example 1

[0048] A battery cell baking process and effectiveness determination method comprises the following steps:

[0049] Step 1: The battery cell baking equipment is in a sealed state, and the vacuum is evacuated to the set value of 50Pa, and the vacuum is maintained for 30 minutes. The vacuum degree in the cavity is reduced from P1 to P1 t , the vacuum leakage rate r1 of the baking equipment is calculated: r1=(P1 t -50)*V1 / 30;

[0050] Step 2: Place the battery cell to be baked in the baking equipment, evacuate to the set value of 50Pa, and fill with high-purity inert gas N2 until the vacuum degree reaches the set value of 80000Pa;

[0051] Step 3: Start preheating in stages. The temperature setting value of the first stage is 110℃, and the duration is 60min; the temperature setting value of the second stage is 100℃, and the duration is 5min.

[0052] Step 4: Start the staged constant temperature vacuum baking. The temperature setting value of the first stage is 100°C, the vacuum setting value is 50Pa~100Pa, and the duration is 60min; the temperature setting value of the second stage is 100°C, the vacuum setting value is 30Pa~80Pa, and the duration is 180min;

[0053] Step 5: Start phased N2 replacement baking, temperature setting value 100℃, vacuum setting value 30Pa~80Pa; in the first stage, repeat the following steps: fill inert gas N2 to break vacuum to 90000Pa, duration 3min, continue to vacuum to the set value 30Pa~80Pa, duration 60min, repeat 2 times. In the second stage, repeat the following steps: fill inert gas N2 to break vacuum to 90000Pa, duration 3min, continue to vacuum to the set value 30Pa~80Pa, duration 30min, repeat 5 times.

[0054] Step 6: After completing the N2 replacement baking in step 5, continue to maintain constant temperature vacuum baking for 30 minutes.

[0055] Step 7: The system automatically calculates the vacuum leakage rate r of the cell baking process from step 4 to step 6 above t According to the vacuum leakage data during vacuum baking, the vacuum leakage rate r is obtained. t -Time t curve, and through the last three consecutive vacuum leakage rate data before the end of constant temperature vacuum baking in step 6, determine whether the baking process is effective and whether the baking test bench is ended. That is, the vacuum leakage rate data is used to characterize the evaporation rate of moisture and alcohol additives inside the battery cell, which is used to determine the level of moisture and alcohol additives after the battery cell baking is completed, so as to determine the effectiveness of the process, and then conduct benchmark analysis in combination with the offline sampling test results.

[0056] Example 2

[0057] A battery cell baking process and effectiveness determination method comprises the following steps:

[0058] Step 1: The battery cell baking equipment is in a sealed state, and the vacuum is evacuated to the set value of 50Pa, and the vacuum is maintained for 30 minutes. The vacuum degree in the cavity is reduced from P1 to P1 t , the vacuum leakage rate r1 of the baking equipment is calculated: r1=(P1 t -50)*V1 / 30;

[0059] Step 2: Place the battery cell to be baked in the baking equipment, evacuate to the set value of 50Pa, and fill with high-purity inert gas N2 until the vacuum degree reaches the set value of 80000Pa;

[0060] Step 3: Start preheating in stages. The temperature setting value of the first stage is 110℃, and the duration is 60min; the temperature setting value of the second stage is 108℃, and the duration is 5min.

[0061] Step 4: Start the staged constant temperature vacuum baking. The temperature setting value of the first stage is 105°C, the vacuum setting value is 50Pa~100Pa, and the duration is 30min; the temperature setting value of the second stage is 100°C, the vacuum setting value is 30Pa~80Pa, and the duration is 210min;

[0062] Step 5: Start phased N2 replacement baking, temperature setting value 100℃, vacuum setting value 30Pa~80Pa, repeat the following steps in the first stage: fill inert gas N2 to break vacuum to 90000Pa, duration 3min, continue to vacuum to the set value 30Pa~80Pa, duration 60min, repeat 2 times. In the second stage, repeat the following steps: fill inert gas N2 to break vacuum to 90000Pa, duration 3min, continue to vacuum to the set value 30Pa~80Pa, duration 30min, repeat 5 times.

[0063] Step 6: After completing the N2 replacement baking in step 5, continue to maintain constant temperature vacuum baking for 30 minutes.

[0064] Step 7: The system automatically calculates the vacuum leakage rate r of the cell baking process from step 4 to step 6 above t According to the vacuum leakage data during vacuum baking, the vacuum leakage rate r is obtained. t -Time t curve, and use the last three consecutive vacuum leakage rate data to determine whether the baking process is effective and whether the baking is completed. That is, the vacuum leakage rate data is used to characterize the evaporation rate of moisture and alcohol additives inside the battery cell, which is used to determine the moisture and alcohol additive content levels after the battery cell is baked to determine the effectiveness of the process, and then conduct benchmark analysis combined with offline sampling test results.

[0065] The following is a comparison of the baking effects of the same product using the baking process of Example 1 and the traditional baking process:

[0066] Note: The traditional baking process is: preheating at 100℃ for 120min, baking at 30Pa vacuum for 700min, replacing N2 once every 1h for 5min.

[0067]

[0068] The method of the present invention collects the vacuum leakage rate data of the oven in no-load and loaded states, timely identifies the sealing state of the oven, and improves the reliability of the vacuum leakage rate analysis of the oven in loaded state.

[0069] The method of the present invention adopts staged preheating, in which the temperature setting value in the initial stage is 10-20°C higher than the normal baking temperature, thereby increasing the temperature gradient, improving the temperature rise rate of the battery cell, shortening the preheating time of the battery cell, and gradually restoring the temperature to the normal baking temperature through the second stage preheating, thereby preventing the temperature of the battery cell body from exceeding the controllable range of the constant temperature baking temperature.

[0070] The method of the present invention adopts staged constant temperature baking. In the initial baking stage, the water and alcohol additives evaporate quickly, and the matching vacuum setting value is slightly higher to avoid baking timeout caused by continuous vacuuming failing to reach the set value. In the second stage, the vacuum setting value is further reduced to reduce the boiling point of water and alcohol additives and promote vaporization and evaporation.

[0071] The method of the present invention adopts staged N2 replacement baking and designs an N2 replacement frequency gradient. In the baking process where the evaporation rate of moisture and alcohol additives is reduced, the N2 replacement frequency is low in the initial stage, and in the process where the evaporation rate of moisture and alcohol additives is further reduced, the N2 replacement frequency is increased to promote the replacement of N2 with moisture and alcohol additives, which helps to improve the removal effect of moisture and alcohol additives in the later stage of the baking process.

[0072] The method of the present invention adopts online collection and calculation of vacuum leakage rate, and establishes a characterization relationship between the vacuum leakage rate and the evaporation rate of water and alcohol additives inside the battery cell, which can be used to compare the baking effects of different baking processes, and can also determine the levels of water and alcohol additive content in the baking of the battery cell online, assist in determining the baking results, and compare with the offline measurement results, eliminating the waiting time for sampling and testing the water and alcohol additive content, which helps to improve the utilization rate of baking equipment.

[0073] The basic principles and main features of the present invention and the advantages of the present invention are shown and described above. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0074] Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is therefore intended that all changes falling within the meaning and range of equivalent elements of the claims are included in the present invention.

[0075] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A cell baking process and a method for determining effectiveness, characterized in that: The following steps are involved: Step 1: Vacuum leakage rate r1 test: When the battery cell baking equipment is sealed, evacuate to the set value P1, and maintain the vacuum for t1. The vacuum degree in the cavity is reduced from P1 to P1. t , calculate the vacuum leakage rate r1 of the battery cell baking equipment, r1=(P1 t -P1)*V1 / t1, V1 is the inner cavity volume of the equipment in the no-load state. When the vacuum leakage rate r1 exceeds the threshold C0, the equipment alarms; Step 2: Pre-baking treatment: Place the battery cell to be baked in the battery cell baking equipment, evacuate to the set value P2, and fill with high-purity inert gas N2 until the vacuum degree reaches the set value P3, where P3 is greater than P2; before the baking starts to rise in temperature, evacuate the air in the battery cell baking equipment and fill with inert gas N2; Step 3: Start staged preheating: the first stage temperature setting value is T1, and the duration is t1; The second stage temperature setting value is T2, and the duration is t2; t1 is greater than t2, and T1 is higher than T2; Step 4: Start the staged constant temperature vacuum baking: the first stage temperature setting value is T3, the first vacuum setting value is P L1 ~P U1 , duration t3; The second stage temperature setting value T4, the second vacuum setting value P L2 ~P U2 , duration t4; in staged baking, when the vacuum degree reaches P U1 / P U2 Continue to evacuate until P L1 / P L2 , vacuum degree in vacuum holding stage is from P L1 / P L2 Reduce to P U1 / P U2 The corresponding time t U1 / t U2 , the vacuum leakage rate r of the current state t Calculation: The first vacuum setting value P L1 ~P U1 Higher than the second vacuum setting value P L2 ~P U2 , temperature T3 is higher than / equal to T4; Step 5: Start phased N2 replacement baking: temperature setting value T4, vacuum setting value P L3 ~P U3 The first stage is N2 replacement baking. Repeat the following steps: fill the inert gas N2 to break the vacuum to the vacuum degree P4, duration t5, continue to evacuate to the set value P L3 ~P U3 , duration t6, number of repetitions n1; in the second stage, N2 replacement baking, repeat the following steps: fill the inert gas N2 to break the vacuum to the vacuum degree P4, duration t5, continue to evacuate to the set value P L3 ~P U3 , duration t7, number of repetitions n2; Step 6: Continue to maintain constant temperature vacuum baking for a duration of t8; Step 7: Calculate the vacuum leakage rate r1 of the equipment during the baking process, and determine whether to end the baking: Automatically calculate the vacuum leakage rate r1 of the battery cell during the above steps 4 to 6 t , and automatically generate the vacuum leakage rate r t r with time t t- t curve, through r t- t curve analysis and judgment step 6: vacuum leakage rate r for at least 3 times in a row before the end of constant temperature vacuum baking t result; At least 3 consecutive vacuum leak rates r t If both meet the threshold value C1, it is judged as valid and the baking process ends normally; otherwise, the second stage N2 replacement baking in step 5 and the constant temperature vacuum baking in step 6 are automatically executed once, and then the vacuum leakage rate r is kept constant for at least 3 consecutive times. t When all the conditions are lower than the threshold value C1, it is determined to be effective and the process ends; if it is still not satisfied, the effectiveness is determined by sampling and testing the water and alcohol additive content, and the vacuum leakage rate r1 test in step 1 is repeated.

2. The cell baking process and effectiveness determination method according to claim 1, characterized in that: In the step 1, P1 is 20-80 Pa, t1 is 10-60 min, and the equipment collects data with a time accuracy of 1-5 s.

3. The cell baking process and effectiveness determination method according to claim 1, characterized in that: In the step 2, P2 is 20-100 Pa, and P3 is 50000-90000 Pa.

4. The cell baking process and effectiveness determination method according to claim 1, characterized in that: In the step 3, T1 is 100-120° C., T2 is 90-105° C., t1 is 30-60 min, and t2 is 5-10 min.

5. The cell baking process and effectiveness determination method according to claim 1, characterized in that: In the step 4, T3 is 90-105°C, T4 is 90-100°C, t3 is 30-300min, t4 is 30-300min, P L1 50~80Pa, P U1 70~100Pa, P L2 30~50Pa, P U2 It is 60~80Pa.

6. The cell baking process and effectiveness determination method according to claim 1, characterized in that: In step 4, the vacuum leakage rate r of the current state t Including the vacuum leakage rate r of the current state of the first stage t1， The vacuum leakage rate of the second stage is r t2 , r t2 =(P U2 -P L2 )*V2 / t U2 , r t1 =(P U1 -P L1 )*V2 / t U1 , V2 is the volume of the inner cavity of the device in the loaded state.

7. The cell baking process and effectiveness determination method according to claim 1, characterized in that: In the step 5, the purity of N2 is ≥99.9%, P4 is 80000-90000Pa, t5 is 2-5min, t6 is 30-60min, t7 is 20-40min, P L3 / P L4 30~50Pa, P U3 / P U4 It is 60~80Pa, and the number of replacement times n1 / n2 is 2~10 times.

8. The cell baking process and effectiveness determination method according to claim 6, characterized in that: In the step six, t8 is 20 to 60 min.

9. The cell baking process and effectiveness determination method according to claim 7, characterized in that: In step 7, during the first cell baking process, the results of the water and alcohol additive sampling tests are used as the basis for determining the effectiveness. The vacuum leakage rate r t Only record and upload the vacuum leak rate r t Average value, starting from the second battery cell baking process, the equipment program automatically determines the effectiveness according to the threshold.

10. The cell baking process and effectiveness determination method according to claim 1, characterized in that: In step 7, the threshold C1 is the vacuum leakage rate r of at least three consecutive times in each battery cell baking process. t The average value is weighted average * coefficient K, K is 1.01 ~ 1.10, and coefficient K is dynamically updated according to the test results of moisture and alcohol additive content.

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