Formation method for positive electrode lithium supplement battery cell

Abstract

The invention relates to the technical field of batteries, in particular to a formation method for a positive electrode lithium supplement battery cell, which comprises the following steps: applying a first interval current to the battery cell injected with electrolyte at a first temperature and a first negative pressure to perform first-stage formation; applying a second interval current to the battery cell after the first-stage formation at a second temperature and a second negative pressure for second-stage formation until the voltage of the battery cell reaches a first set voltage; applying a third interval current to the battery cell after the second-stage formation at a third temperature and a third negative pressure for third-stage formation until the voltage of the battery cell reaches a second set voltage; wherein the first temperature, the second temperature and the third temperature are sequentially increased, the first negative pressure and the third negative pressure are respectively larger than the second negative pressure, and the magnitude of the first interval current and the magnitude of the third interval current are respectively smaller than the magnitude of the second interval current. The invention aims to solve the problem that the formation quality of an SEI (solid electrolyte interface) film is influenced by gas production of a lithium supplement agent in the formation process of a positive electrode lithium supplement cell.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a formation method for lithium-ion battery cells with positive electrodes. Background Technology

[0002] The formation process of lithium-ion batteries is the first charge-discharge process after battery manufacturing. Its core purpose is to form a stable and dense solid electrolyte interphase (SEI) film on the graphite surface of the negative electrode, while simultaneously activating the electrode materials. The quality of the SEI film directly affects the battery's cycle life, safety, and rate performance. However, if a lithium supplement is added to the positive electrode, it will release more lithium and generate oxygen, affecting the SEI film growth process. This significantly impacts the film quality of the cell. Therefore, more precise methods are needed to control the charging status at each stage of the lithium-supplemented cell formation process to regulate the SEI film growth.

[0003] Currently, mainstream formation methods generally involve simple constant current (CC) charging or multi-stage constant current-constant voltage (CC-CV) charging. The core idea is to use multiple small currents for staged formation in the early stages, then gradually increase the current to achieve the first full charge of the battery, and finally discharge to the specified state of charge (SOC). However, these traditional methods have significant drawbacks: the decomposition potential of the lithium replenishing agent in the cathode material (such as Li5FeO4) overlaps or intersects with the delithiation potential of traditional cathode materials (such as nickel-cobalt-manganese ternary materials NCM and lithium iron phosphate materials LFP). Therefore, the high current of traditional formation may cause the lithium replenishing agent to decompose too quickly in localized areas, generating a large amount of gas and heat, leading to gas expansion and even safety issues. Furthermore, this results in uneven thickness and unstable composition of the formed SEI film, leading to rapid degradation of the battery's long-term cycle performance and low initial coulombic efficiency. Summary of the Invention

[0004] The present invention aims to improve the problem that the gas generated by the lithium replenishing agent affects the quality of SEI film formation during the formation of positive electrode lithium-ion cells.

[0005] To solve or partially solve the above problems, the present invention provides a formation method for positive electrode lithium-ion battery cells, comprising: After the electrolyte is injected, the battery cell is subjected to a first-stage formation under a first temperature and a first negative voltage by applying a first-range current. The battery cell after the first stage of formation is subjected to a second interval current under a second temperature and a second negative pressure to perform a second stage of formation until the voltage of the battery cell reaches a first set voltage. The battery cell after the second stage formation is subjected to a third-stage formation under a third temperature and a third negative voltage with a third interval current until the voltage of the battery cell reaches the second set voltage. The first temperature, the second temperature, and the third temperature increase sequentially; the first negative pressure and the third negative pressure are respectively greater than the second negative pressure; and the magnitudes of the first interval current and the third interval current are respectively less than the magnitude of the second interval current.

[0006] Optionally, the first temperature ranges from 15 to 25°C, the second temperature ranges from 25 to 35°C, and the third temperature ranges from 35 to 45°C. And / or, the magnitude range of the first negative pressure and the third negative pressure is 60 to 80 kPa, and the magnitude range of the second negative pressure is 30 to 50 kPa; And / or, the magnitude of the current in the first interval ranges from 0.01C to 0.05C, the magnitude of the current in the second interval ranges from 0.25C to 0.5C, and the magnitude of the current in the third interval ranges from 0.02C to 0.3C.

[0007] Optionally, the step of applying a first interval current to the battery cell after electrolyte injection at a first temperature and a first negative pressure for a first stage of formation includes: first applying a first current to the battery cell after electrolyte injection at the first temperature and the first negative pressure for constant current charging, and then applying a second current for constant current charging after resting; wherein the first current and the second current are within the range of the first interval current, and the first current is less than the second current.

[0008] Optionally, the magnitude of the first current ranges from 0.01C to 0.03C, and the magnitude of the second current ranges from 0.03C to 0.05C; the application time of the first current and the second current is from 110min to 130min, respectively.

[0009] Optionally, the step of applying a second range current to the battery cell after the first stage of formation at a second temperature and a second negative pressure for the second stage of formation includes: applying a third current, a fourth current, and a fifth current sequentially to the battery cell after the first stage of formation at the second temperature and a second negative pressure for constant current charging; wherein the third current, the fourth current, and the fifth current are within the range of the second range of current values, and the third current and the fifth current are respectively less than the fourth current.

[0010] Optionally, the magnitudes of the third and fifth currents range from 0.25C to 0.4C, and the magnitude of the fourth current ranges from 0.4C to 0.5C. And / or, the application time of the third current is 50 to 70 minutes, and the application time of the fourth current is 10 to 20 minutes.

[0011] Optionally, the step of applying a third-range current to the battery cell after the second-stage formation at a third temperature and a third negative voltage for the third-stage formation includes: first applying a sixth current to the battery cell after the second-stage formation at the third temperature and the third negative voltage for constant current charging, until the voltage of the battery cell reaches an intermediate set voltage, and then applying a seventh current for constant current charging; wherein the sixth current and the seventh current are within the value range of the third-range current, and the sixth current is greater than the seventh current.

[0012] Optionally, the magnitude of the sixth current ranges from 0.1C to 0.3C, and the magnitude of the seventh current ranges from 0.02C to 0.1C.

[0013] Optionally, the first set voltage is 3.6 to 3.7V, the intermediate set voltage is 3.7 to 3.8V, and the second set voltage is 4.0 to 4.2V.

[0014] Optionally, the step of applying a third interval current to the battery cell after the second stage formation at a third temperature and a third negative pressure to perform a third stage formation until the voltage of the battery cell reaches a second set voltage further includes: venting the battery cell after the third stage formation and then discharging it at a constant current until the voltage of the battery cell reaches 50% SOC.

[0015] The advantages of this invention compared to related technologies include: The formation stage of the lithium-ion battery cell in this invention mainly includes three stages: The first stage is carried out under a low-temperature, high-negative-pressure environment to induce the formation of an initial reaction interface on the negative electrode surface under mild conditions. In this stage, a small current is applied to induce the initial formation of the SEI film. The lower temperature allows for control of the reaction rate, slowing down electrochemical behavior and reducing the impact of subsequent lithium-ion agent gas generation on the SEI film. Simultaneously, the higher negative pressure promotes tighter interfacial bonding between the electrodes. Therefore, the combination of low temperature and high negative pressure in the first stage contributes to a more dense and uniform initial film formation. The second stage is carried out under a high-temperature, low-negative-pressure environment. This stage is the main stage for lithium-ion agent gas generation. Since the SEI film is relatively unstable after formation, appropriately reducing the negative pressure value can avoid damage to the SEI film caused by lithium-ion agent gas generation. Applying a large current in this stage saves charging time and reduces production costs. Furthermore, the gas generation in this stage promotes further decomposition and recombination of the initially formed unstable SEI film components, fostering the formation of a more stable and dense SEI film with high content of inorganic substances such as Li2CO3 and LiF. Since the formation of the SEI film has been ensured in the first two stages, the specific capacity of the lithium replenishment can be fully utilized in the third stage by increasing the temperature and reducing the current, which is beneficial to stabilizing the battery state and eliminating polarization effects. At the same time, since the SEI film is already stable enough at this time, applying a higher negative pressure in the third stage can provide appropriate pressure to promote gas discharge, thereby alleviating the growth of gas production during subsequent storage. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the formation method for positive electrode lithium battery cells in an embodiment of the present invention; Figure 2 This is a schematic diagram showing the change in gas production volume during a 7-day / 28-day storage test at 60℃ and 100% SOC. Figure 3 This is a schematic diagram showing the change in DCR (direct current resistance) during 7d / 28d storage tests at 60℃ and 100% SOC. Detailed Implementation

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0018] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing particular embodiments only and is not intended to limit this application. The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0019] During the initial charge formation stage of lithium-ion batteries, the addition of a lithium replenishing agent to the cathode material causes overlap or intersection between the decomposition potential of the lithium replenishing agent and the delithiation potential of traditional cathode materials (such as NCM and LFP). While releasing more lithium, the lithium replenishing agent also generates oxygen, which in turn affects the growth process of the SEI film, significantly impacting the cell's film quality. Therefore, more precise methods are needed to regulate the charging process at each stage of lithium-replenished cell formation to control the SEI film growth.

[0020] An embodiment of the present invention provides a formation method for a positive electrode lithium battery cell, the formation method comprising the following steps: Step S1: Apply a first-range current to the battery cell after electrolyte injection at a first temperature and a first negative voltage to perform the first-stage formation.

[0021] Step S2: Apply a second-range current to the battery cell after the first stage of formation at the second temperature and the second negative pressure to perform the second stage of formation until the voltage of the battery cell reaches the first set voltage.

[0022] Step S3: Apply a third-range current to the battery cell after the second-stage formation at a third temperature and a third negative voltage to perform the third-stage formation until the voltage of the battery cell reaches the second set voltage.

[0023] Among them, the first temperature, the second temperature and the third temperature increase in sequence, the first negative pressure and the third negative pressure are greater than the second negative pressure, and the magnitude of the current in the first interval and the magnitude of the current in the third interval are less than the magnitude of the current in the second interval.

[0024] It should be noted that in the embodiments of the present invention, the first negative pressure, the second negative pressure, and the third negative pressure are all defined as the magnitude of vacuum or negative pressure, representing the value by which the actual air pressure is lower than atmospheric pressure. The first interval current, the second interval current, and the third interval current are respectively interpreted as: current values ​​within a certain interval range. For example, the first interval current may include one or more current values ​​within the first interval, and the second interval current and the third interval current are interpreted similarly. It should be understood that the selectable current values ​​within the first interval and the selectable current values ​​within the third interval should be less than the selectable current values ​​within the second interval.

[0025] As described above, the formation stage of the lithium-ion battery cell in this invention mainly includes three stages: The first stage is carried out under a low-temperature, high-negative-pressure environment to induce the formation of an initial reaction interface on the negative electrode surface under mild conditions. In this stage, a small current is applied to induce the initial formation of the SEI film. The lower temperature allows for control of the reaction rate, slowing down electrochemical behavior and reducing the impact of subsequent lithium-ion agent gas generation on the SEI film. Simultaneously, the higher negative pressure promotes tighter interfacial bonding between the electrodes. Therefore, the combination of low temperature and high negative pressure in the first stage contributes to a more dense and uniform initial film formation. The second stage is carried out under a high-temperature, low-negative-pressure environment. This stage is the main stage for lithium-ion agent gas generation. Since the SEI film is relatively unstable after formation, appropriately reducing the negative pressure value can prevent damage to the SEI film caused by lithium-ion agent gas generation. Applying a large current in this stage saves charging time and reduces production costs. Furthermore, the gas generation in this stage promotes further decomposition and recombination of the initially formed unstable SEI film components, fostering the formation of a more stable and dense SEI film with high content of inorganic substances such as Li2CO3 and LiF. Since the formation of SEI has been ensured in the first two stages, the specific capacity of the lithium replenishment can be fully utilized in the third stage by increasing the temperature and reducing the current, which is beneficial to stabilizing the battery state and eliminating polarization effects. At the same time, since the SEI is already stable enough at this time, applying a higher negative pressure in the third stage can provide appropriate pressure to promote gas discharge, thereby alleviating the growth of gas production during subsequent storage.

[0026] In summary, the embodiments of the present invention achieve the formation of a stable SEI film in the positive electrode lithium-filled cell by dynamically controlling the temperature, pressure and current of the three formation stages, and provide protection for the subsequent lithium-filling agent reaction through the low temperature and low current formation process in the first stage, thereby minimizing the impact of the gas generated by the lithium-filling agent reaction on the SEI film.

[0027] In some optional embodiments, the first temperature ranges from 15 to 25°C, specifically 15°C, 20°C, and 25°C; the second temperature ranges from 25 to 35°C, specifically 25°C, 30°C, and 35°C; and the third temperature ranges from 35 to 45°C, specifically 35°C, 40°C, and 45°C. The first and third negative pressures range from 60 to 80 kPa, specifically 60 kPa, 65 kPa, 70 kPa, 75 kPa, and 80 kPa; and the second negative pressure ranges from 30 to 50 kPa, specifically 30 kPa. a. 35 kPa, 40 kPa, 45 kPa, 50 kPa; the current range in the first interval is 0.01 C to 0.05 C, specifically 0.01 C, 0.02 C, 0.03 C, 0.04 C, 0.05 C; the current range in the second interval is 0.25 C to 0.5 C, specifically 0.25 C, 0.3 C, 0.33 C, 0.4 C, 0.45 C, 0.5 C; the current range in the third interval is 0.02 C to 0.3 C, specifically 0.02 C, 0.05 C, 0.1 C, 0.2 C, 0.3 C.

[0028] In this embodiment of the invention, a small current is used for initial film formation, while the stepped temperature gradient allows for appropriate increases in charging current in the second and third stages, thus reducing the formation time. Simultaneously, adjusting the negative pressure throughout the process contributes to a more dense and uniform film formation.

[0029] In some optional embodiments, the first stage of formation in step S1 above specifically includes: firstly, applying a first current to the battery cell after electrolyte injection at a first temperature and a first negative pressure for constant current charging, and then applying a second current for constant current charging after standing; wherein the first current and the second current are within the range of values ​​of the first interval current, and the first current is less than the second current.

[0030] Specifically, the magnitude of the first current ranges from 0.01C to 0.03C, such as 0.01C, 0.02C, and 0.03C; the magnitude of the second current ranges from 0.03C to 0.05C, such as 0.03C, 0.04C, and 0.05C; the application time of the first current and the second current is from 110min to 130min, such as 110min, 120min, and 130min; and the settling time between the first current and the second current is from 5min to 10min, such as 5min, 8min, and 10min.

[0031] In the first stage of formation, the battery is first charged with a small, constant current, and then, after a certain period of rest, it is recharged with a slightly larger current. This approach allows for gentle and uniform nucleation and growth of the initial SEI film on the negative electrode surface using a very small current, minimizing side reactions. Based on this stable initial SEI film, appropriately increasing the current allows for more orderly and rapid deposition and reaction, resulting in a uniform and strengthened SEI film. This avoids the problem of an excessively thin or uneven film that might occur with a single small current.

[0032] It should be understood that since the first stage of formation mainly serves as pre-activation and provides the initial reaction interface, the cell voltage is relatively low after the first stage, which is not limited here.

[0033] In some optional embodiments, the second stage of formation in step S2 specifically includes: applying a third current, a fourth current and a fifth current sequentially to the battery cell after the first stage of formation at a second temperature and a second negative pressure for constant current charging until the voltage of the battery cell reaches a first set voltage; wherein the third current, the fourth current and the fifth current are within the range of the second interval current, and the third current and the fifth current are respectively less than the fourth current.

[0034] Specifically, the magnitude range of the third and fifth currents is 0.25C to 0.4C, such as 0.25C, 0.3C, and 0.33C; the magnitude range of the fourth current is 0.4C to 0.5C, such as 0.4C, 0.45C, and 0.5C; the application time of the third current is 50 to 70 minutes, such as 50 minutes, 60 minutes, and 70 minutes; and the application time of the fourth current is 10 to 20 minutes, such as 10 minutes, 15 minutes, and 20 minutes.

[0035] In this embodiment, the second-stage formation process further employs a three-stage current charging method. The first and last stages use relatively small currents for longer charging times, the middle stage uses the maximum current of the entire formation stage for a shorter charging time, and finally, a relatively small current is used to charge to the first set voltage. The advantage of this charging process is that since the first stage of formation uses a small current, directly jumping to the maximum design current could result in an excessive current jump, impacting the battery's internal interface. Therefore, the first stage of the second-stage formation uses a moderately small current as a transition, allowing the electrode interface to smoothly enter a higher reaction rate state. A gentle increase in current helps the battery's internal temperature rise evenly, avoiding a sudden surge of large current that could cause localized overheating. The middle stage efficiently completes the main capacity formation by applying the designed maximum safe current, significantly shortening the formation time. Finally, switching back to a smaller current allows ions sufficient time to diffuse and migrate, eliminating polarization effects, and the smaller current ensures the cell voltage steadily reaches the first set voltage.

[0036] It should be noted that in step S2 above, the first set voltage is 3.6 to 3.7V, which reaches the decomposition voltage of the lithium replenishing agent. Therefore, in the second stage of formation, the lithium replenishing agent begins to decompose and produce gas, which promotes the further decomposition and recombination of the initially formed unstable SEI film components, thereby forming a more stable and dense SEI film with high content of inorganic substances such as Li2CO3 and LiF.

[0037] In some optional embodiments, step S3 above, the third stage of formation specifically includes: applying a sixth current for constant current charging of the battery cell after the second stage formation at a third temperature and a third negative voltage until the voltage of the battery cell reaches an intermediate set voltage, and then applying a seventh current for constant current charging; wherein the sixth current and the seventh current are within the value range of the third interval current, and the sixth current is greater than the seventh current. Specifically, the magnitude range of the sixth current is 0.1C to 0.3C, such as 0.1C, 0.2C, 0.3C, and the magnitude range of the seventh current is 0.02C to 0.1C, such as 0.02C, 0.05C, 0.08C, 0.1C.

[0038] It is understandable that the third stage of formation, as the final stage of formation charging, still requires controlling the current to decrease in a relatively smooth transition trend. Therefore, a relatively large current is first applied to charge to an intermediate set voltage, and then the current is reduced to charge to a second set voltage. Optionally, the intermediate set voltage is 3.7 to 3.8V, and the second set voltage is 4.0 to 4.2V.

[0039] It should be noted that after electrolyte injection into the lithium-ion battery cell, it should first be allowed to stand at a certain temperature to allow the electrolyte to fully impregnate the cell, promoting uniform distribution of the electrolyte within the cell and thus facilitating the uniformity of SEI film formation in the subsequent formation stage. The impregnation time can be 24 to 48 hours, such as 24h, 30h, 40h, or 48h, and the impregnation temperature can be 30 to 50℃, such as 30℃, 35℃, 40℃, 45℃, or 50℃. During the intervals between the first, second, and third formation stages, the battery cell should also be allowed to stand for 5 to 10 minutes, during which time the temperature should be slowly increased.

[0040] In some optional embodiments, after step S3, the process further includes: venting the cell after the third-stage formation, followed by constant-current discharge until the cell voltage reaches 50% SOC. Since a certain amount of gas generated by the lithium replenishing agent still exists inside the cell after the three-stage formation, a negative pressure can be set to expel the generated gas inside the cell, and then constant-current discharge is performed until the set voltage is reached to end the cell formation. The constant-current discharge current can be 0.5C. Furthermore, after formation, the cell can be aged in a 45°C oven for 48 hours to fully expel the gas from the formation process, followed by a secondary vacuum sealing.

[0041] The present invention will be described in detail below through specific embodiments and comparative examples: Example 1 LiFePO4 (positive electrode material), Li5FeO4 (lithium supplement material), PVDF, and conductive carbon black were dispersed in NMP dispersant at a ratio of 95:1:2:2 to form the positive electrode material. Simultaneously, graphite was used as the negative electrode. The positive electrode material, negative electrode, and separator were then assembled to form a lithium iron phosphate battery cell. After electrolyte injection, the cell was immersed at 45°C for 48 hours. The immersed cell then underwent a multi-stage formation process. (1) First stage of formation: First, under an environment of 15℃ and 60kPa negative pressure, the lithium battery cell is charged with constant current at the first current I1 = 0.02C, and the charging time is set to 120min. After the charging is completed, it is left to stand for 5min, and then the constant current is continued at the second current I2 = 0.05C, and the charging time is set to 120min.

[0042] (2) Second stage formation: After the first stage formation, the cell is left to stand for 10 minutes, while the formation temperature is increased to 35°C and the negative voltage is set to 45 kPa. The cell is charged with the third current I3 = 0.25C for 60 minutes, then charged with the fourth current I4 = 0.5C for 15 minutes, and finally charged with the fifth current I5 = 0.33C to the first set voltage of 3.7V.

[0043] (3) Third stage formation: After the second stage formation, the cell is left to stand for 10 minutes, while the formation temperature is raised to 45°C and the negative pressure is set to 60 kPa. The cell is charged with a constant current of I6 = 0.1C to the intermediate set voltage of 3.8V and left to stand for 5 minutes; then the cell is charged with a constant current of I7 = 0.05C to the second set voltage of 4.1V.

[0044] (4) After the third stage of formation, the cell was left to stand for 5 minutes, and then the cell was vented under a negative pressure of 60 kPa for 10 minutes. Finally, it was discharged at a constant current of 0.5C until 50% SOC was reached, which marked the end of the formation process. Then, it was aged in an oven at 45℃ for 48 hours to fully remove the gas from the formation process, and then a second vacuum sealing was performed.

[0045] Example 2 The difference between this embodiment and Embodiment 1 is that the multi-stage formation process includes: (1) First stage of formation: First, under an environment of 20℃ and 80kPa negative pressure, the lithium battery cell is charged with constant current with the first current I1 = 0.01C and the charging time is set to 130min. After the charging is completed, it is left to stand for 5min, and then the constant current charging is continued with the second current I2 = 0.04C and the charging time is set to 130min.

[0046] (2) Second stage formation: After the first stage formation, the cell is left to stand for 10 minutes, while the formation temperature is increased to 30°C and the negative voltage is set to 50 kPa. The cell is charged with the third current I3 = 0.3C for 60 minutes, then charged with the fourth current I4 = 0.4C for 20 minutes, and finally charged with the fifth current I5 = 0.3C to the first set voltage of 3.6V.

[0047] (3) Third stage formation: After the second stage formation, the cell is left to stand for 10 minutes, while the formation temperature is raised to 40℃ and the negative pressure is set to 80kPa. The cell is charged with a constant current of I6 = 0.2C to the intermediate set voltage of 3.7V and left to stand for 5 minutes; then the cell is charged with a constant current of I7 = 0.02C to the second set voltage of 4.1V.

[0048] (4) After the third stage of formation, the cell was left to stand for 5 minutes, and then the cell was vented under a negative pressure of 60 kPa for 10 minutes. Finally, it was discharged at a constant current of 0.5C until 50% SOC was reached, which marked the end of the formation process. Then, it was aged in an oven at 45℃ for 48 hours to fully remove the gas from the formation process, and then a second vacuum sealing was performed.

[0049] Example 3 The difference between this embodiment and Embodiment 1 is that the multi-stage formation process includes: (1) First stage formation: First, under an environment of 25℃ and 70kPa negative pressure, the lithium battery cell is charged with constant current at a first current I1 = 0.03C, and the charging time is set to 110min. After the charging is completed, it is left to stand for 5min, and then the constant current is continued at a second current I2 = 0.05C, and the charging time is set to 110min.

[0050] (2) Second stage formation: After the first stage formation, the cell is left to stand for 10 minutes, while the formation temperature is increased to 35°C and the negative voltage is set to 45 kPa. The cell is charged with the third current I3 = 0.33C for 60 minutes, then charged with the fourth current I4 = 0.5C for 10 minutes, and finally charged with the fifth current I5 = 0.33C to the first set voltage of 3.7V.

[0051] (3) Third stage formation: After the second stage formation, let the cell stand for 10 minutes, while raising the formation temperature to 45°C and setting the negative pressure to 70 kPa. Charge the cell with the sixth current I6 = 0.3C at a constant current to the intermediate set voltage of 3.8V, and let it stand for 5 minutes; then charge the cell with the seventh current I7 = 0.1C at a constant current to the second set voltage of 4.2V.

[0052] (4) After the third stage of formation, the cell was left to stand for 5 minutes, and then the cell was vented under a negative pressure of 60 kPa for 10 minutes. Finally, it was discharged at a constant current of 0.5C until 50% SOC was reached, which marked the end of the formation process. Then, it was aged in an oven at 45℃ for 48 hours to fully remove the gas from the formation process, and then a second vacuum sealing was performed.

[0053] Comparative Example 1 Comparative Example 1 used the same lithium-ion battery cell as the Example, except for the formation process: the formation temperature was set to 25°C and the negative pressure to 45 kPa throughout the process. The formation process was as follows: first, the cell was charged at a constant current of 0.05C for 110 minutes; then, it was charged at a current of 0.2C for 75 minutes; subsequently, it was charged at a current of 0.3C to the intermediate set voltage of 3.8V; and finally, it was charged at a constant current of 0.1C to the cutoff voltage of 4.2V.

[0054] The performance test results of Examples 1 to 3 and Comparative Example 1 are shown in Table 1. Figures 2 to 3 As shown: Table 1 Performance test results of Examples 1 to 3 and Comparative Example 1

[0055] The test process for 28-day storage DCR in Table 1 is as follows: After the cell has completed the formation and capacity testing, the SOC of the cell is adjusted to 50%, and then a 2C current is used to discharge for 30 seconds. The DC resistance (DCR) of the cell is calculated by dividing the voltage difference before and after discharge by the current.

[0056] The K-value test process is as follows: Measure the open-circuit voltage OCV1 of the offline battery cell, and after leaving it at room temperature for 3 days, test the open-circuit voltage OCV2 again. Calculate the K-value = (OCV1-OCV2) / leave time h.

[0057] In addition, after charging to 100% SOC, a glass clamp was attached, and storage tests were conducted at 60°C. Gas production volume and DCR were also tested at 7 and 28 days. The test results are as follows: Figure 2 and Figure 3 As shown. By Figure 2 and Figure 3It can be seen that, compared with Comparative Example 1, the storage gas production of the cells after formation in Examples 1 to 3 of the present invention is reduced after 28 days, the DCR growth is reduced, and the total formation time is reduced.

[0058] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A formation method for a positive electrode lithium supplementing battery cell, characterized in that, The application comprises: applying a first interval current to the battery cell after injecting electrolyte at a first temperature and a first negative pressure to perform a first stage formation; applying a second interval current to the battery cell after the first stage formation at a second temperature and a second negative pressure to perform a second stage formation until the voltage of the battery cell reaches a first set voltage; applying a third interval current to the battery cell after the second stage formation at a third temperature and a third negative pressure to perform a third stage formation until the voltage of the battery cell reaches a second set voltage; wherein the first temperature, the second temperature and the third temperature increase in turn, the first negative pressure and the third negative pressure are greater than the second negative pressure respectively, and the size of the first interval current and the size of the third interval current are less than the size of the second interval current respectively. 2.The formation method for the positive lithium supplement cell of claim 1, wherein, The size of the first temperature ranges from 15 to 25℃, the size of the second temperature ranges from 25 to 35℃, and the size of the third temperature ranges from 35 to 45℃; and / or, the size of the first negative pressure and the third negative pressure ranges from 60 to 80kpa, and the size of the second negative pressure ranges from 30 to 50kpa; and / or, the size of the first interval current ranges from 0.01C to 0.05C, the size of the second interval current ranges from 0.25C to 0.5C, and the size of the third interval current ranges from 0.02C to 0.3C. 3.The formation method for the lithium supplementing positive electrode battery cell according to claim 1, characterized in that, The application comprises: first applying a first current to the battery cell after injecting electrolyte at the first temperature and the first negative pressure to perform constant current charging, and then applying a second current to perform constant current charging after standing; wherein the first current and the second current are within the value range of the first interval current, and the first current is less than the second current. 4.The formation method for the lithium supplementing positive electrode battery cell according to claim 3, characterized in that, The size of the first current ranges from 0.01C to 0.03C, and the size of the second current ranges from 0.03C to 0.05C; the application time of the first current and the second current is 110min to 130min respectively. 5.The formation method for the lithium supplementing positive electrode battery cell according to claim 1, characterized in that, The application comprises: applying a third current, a fourth current and a fifth current to the battery cell after the first stage formation at the second temperature and the second negative pressure to perform constant current charging in turn; wherein the third current, the fourth current and the fifth current are within the value range of the second interval current, and the third current and the fifth current are less than the fourth current respectively.

6. The formation method for the lithium supplementing positive electrode cell according to claim 5, characterized in that, The size of the third current and the fifth current ranges from 0.25C to 0.4C, and the size of the fourth current ranges from 0.4C to 0.5C; and / or, the application time of the third current is 50 to 70min, and the application time of the fourth current is 10 to 20min.

7. The formation method for the lithium supplementing positive electrode cell according to claim 1, characterized in that, The application comprises: The second stage of the battery after the formation is applied with a sixth current for constant current charging at the third temperature and the third negative pressure until the voltage of the battery reaches an intermediate set voltage, and then a seventh current is applied for constant current charging; wherein the sixth current and the seventh current are located in the value range of the third interval current, and the sixth current is greater than the seventh current. 8.The formation method for the lithium supplementing positive electrode battery cell according to claim 7, characterized in that, The sixth current ranges from 0.1C to 0.3C, and the seventh current ranges from 0.02C to 0.1C. 9.The formation method for the lithium supplementing positive electrode battery cell according to claim 7, characterized in that, The first set voltage ranges from 3.6V to 3.7V, the intermediate set voltage ranges from 3.7V to 3.8V, and the second set voltage ranges from 4.0V to 4.2V. 10.The formation method for the positive lithium supplementing battery cell according to claim 1, characterized in that, The third stage of the battery after the formation is applied with a third interval current for constant current charging at the third temperature and the third negative pressure until the voltage of the battery reaches an intermediate set voltage, and then a seventh current is applied for constant current charging; wherein the sixth current and the seventh current are located in the value range of the third interval current, and the sixth current is greater than the seventh current. After the third stage of the battery after the formation is exhausted, the battery is discharged at a constant current until the voltage of the battery reaches 50% SOC.

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