Battery cell formation method

Abstract

The battery cell formation method comprises the following steps: carrying out first-stage charging and second-stage charging on a to-be-formed battery cell in sequence; the environment temperature of the first-stage charging is lower than the environment temperature of the second-stage charging. The environment temperature of the first-stage charging is lower than the environment temperature of the second-stage charging, in the first-stage charging process, the environment temperature is low, the chemical reaction rate can be slowed down, the growth speed of the SEI film can be controlled, and therefore a uniform SEI film framework is formed on the electrode surface of the to-be-formed battery cell, and the formation efficiency of the battery cell is improved. The probability of overgrowth or loose structure of the SEI film is reduced, and the uniformity of the SEI film is improved; in the second-stage charging process, the environment temperature is relatively high, so that more sufficient reaction between the electrode material and the electrolyte can be promoted, generation of an inorganic phase in an SEI film is facilitated, the SEI film structure can be further optimized, the electrode material structure densification is accelerated, the SEI film impedance is further reduced, and the cycle performance of a battery cell is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a cell formation method. Background Technology

[0002] In the manufacturing process of lithium-ion batteries, the formation process is a crucial step. The formation process primarily involves the initial charging process, which causes the electrode materials to react with the electrolyte, forming a stable solid electrolyte interphase (SEI) film on the electrode surface. The performance of the SEI film plays a decisive role in the electrochemical performance of lithium-ion batteries. It not only effectively prevents further reactions between the electrolyte and electrode materials, reducing self-discharge, but also allows lithium ions to pass freely, ensuring normal charge and discharge. Therefore, optimizing the formation process and improving the quality of the SEI film are key to enhancing the performance and lifespan of lithium-ion batteries.

[0003] The formation process in related technologies is often difficult to control precisely, resulting in high SEI film impedance and poor cycle performance. Summary of the Invention

[0004] This application provides a cell formation method that can reduce SEI film impedance and improve cell cycle performance.

[0005] This application provides a cell formation method, including: The cells to be formed are charged in the first stage and the second stage sequentially. The ambient temperature during the first stage of charging is lower than the ambient temperature during the second stage of charging.

[0006] Optionally, in some embodiments of this application, after the second stage of charging is completed, the process further includes: The cells to be formed are then subjected to a third stage of charging after the second stage of charging is completed.

[0007] Optionally, in some embodiments of this application, the ambient temperature of the third stage of charging is higher than the ambient temperature of the first stage of charging; and / or The ambient temperature during the third stage of charging is lower than that during the second stage of charging.

[0008] Optionally, in some embodiments of this application, the ambient temperature for the first stage of charging is 0°C to 10°C; and / or The ambient temperature for the second stage of charging is 40℃~55℃; and / or The ambient temperature for the third stage of charging is 25℃~35℃.

[0009] Optionally, in some embodiments of this application, the charging current in the first stage is lower than the charging current in the second stage; and / or The charging current in the third stage is higher than the charging current in the first stage, and the charging current in the third stage is less than or equal to the charging current in the second stage.

[0010] Optionally, in some embodiments of this application, the charging current in the first stage is 0.02C~0.05C; and / or The charging current in the second stage is 0.2C~0.5C; and / or The charging current in the third stage is 0.1C~0.2C.

[0011] Optionally, in some embodiments of this application, before the first stage of charging, the process further includes: performing a first stage of resting treatment on the cell to be formed; The first stage of settling is carried out at 0℃~10℃ for 1h~2h; and / or Between the first stage of charging and the second stage of charging, the process also includes: performing a second stage of resting treatment on the battery cell to be formed after the first stage of charging is completed; The second stage of settling is carried out at 40℃~55℃ for 1h~2h; and / or Between the second stage of charging and the third stage of charging, the method further includes: performing a third stage resting treatment on the cell to be formed after the completion of the second stage of charging; and / or The third stage of settling is carried out at 25℃~35℃, and the settling time is 1h~2h.

[0012] Optionally, in some embodiments of this application, the internal pressure of the cell to be formed is controlled to be negative during the first stage of charging, the second stage of charging, and the third stage of charging. Wherein, the internal pressure of the cell to be formed during the first stage of charging is higher than the internal pressure of the cell to be formed during the second stage of charging; and / or The internal pressure of the cell to be formed during the second stage of charging is higher than the internal pressure of the cell to be formed during the third stage of charging.

[0013] Optionally, in some embodiments of this application, during the first stage of charging, the internal pressure of the cell to be formed is -0.2MPa to -0.3MPa; and / or During the second stage of charging, the internal pressure of the cell to be formed is -0.4MPa to -0.5MPa; and / or During the third stage of charging, the internal pressure of the cell to be formed is -0.6MPa to -0.7MPa.

[0014] Optionally, in some embodiments of this application, the cutoff voltage for the first stage of charging is 3.6V~3.7V; and / or The cutoff voltage for the second stage of charging is 3.6V~3.7V; and / or The cutoff voltage for the third stage of charging is 3.6V~3.7V; and / or The first stage charging time is 0.5h~1h; and / or The second stage charging time is 1 hour to 1.5 hours; and / or The third stage charging time is 2 hours to 2.5 hours.

[0015] This application achieves this by keeping the ambient temperature of the first stage charging lower than that of the second stage charging. During the first stage charging, the lower ambient temperature slows down the chemical reaction rate and controls the growth rate of the SEI film, thereby forming a uniform SEI film skeleton on the electrode surface of the cell to be formed. This reduces the probability of excessive SEI film growth or a loose structure, and improves the uniformity of the SEI film. During the second stage charging, the higher ambient temperature promotes a more complete reaction between the electrode material and the electrolyte, which is conducive to the formation of the inorganic phase in the SEI film. This further optimizes the SEI film structure, accelerates the densification of the electrode material structure, and thus reduces the SEI film impedance and improves the cycle performance of the cell. Detailed Implementation

[0016] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the examples. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0017] This application provides a method for battery cell formation. Detailed descriptions are provided below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative and do not impose numerical requirements or establish an order. Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0018] This application provides a cell formation method, including: The cells to be formed are charged in the first stage and the second stage sequentially. The ambient temperature during the first stage of charging is lower than the ambient temperature during the second stage of charging.

[0019] In this application, by making the ambient temperature of the first stage charging lower than that of the second stage charging, the lower ambient temperature during the first stage charging process can slow down the chemical reaction rate and control the growth rate of the SEI film, thereby forming a uniform SEI film skeleton on the electrode surface of the cell to be formed, reducing the probability of excessive SEI film growth or loose structure, and improving the uniformity of the SEI film. During the second stage charging process, the higher ambient temperature can promote a more complete reaction between the electrode material and the electrolyte, which is conducive to the generation of inorganic phase in the SEI film, thereby further optimizing the SEI film structure, accelerating the densification of the electrode material structure, and thus reducing the SEI film impedance and improving the cycle performance of the cell.

[0020] It is understood that the first and second stages of charging are typically performed in a formation cabinet, and the ambient temperatures for the first and second stages of charging refer to the set temperatures of the formation cabinet. The cell formation method of this application can be applied to lithium iron phosphate cells. At different temperatures, the reaction rates and products between the electrode materials and the electrolyte differ; a single temperature cannot simultaneously guarantee the uniformity, density, and integrity of the SEI film.

[0021] Optionally, in some embodiments of this application, after the second stage of charging is completed, the process further includes: The cell to be formed is then subjected to a third stage of charging after the second stage of charging. Thus, by performing a third stage of charging after the second stage, defects in the SEI film formed on the electrode surface of the cell to be formed can be repaired, thereby improving the quality and stability of the SEI film.

[0022] It is understandable that the third stage of charging is usually carried out in the formation cabinet, and the ambient temperature for the third stage of charging refers to the set temperature of the formation cabinet.

[0023] Optionally, in some embodiments of this application, the ambient temperature of the third stage of charging is higher than the ambient temperature of the first stage of charging.

[0024] Optionally, in some embodiments of this application, the ambient temperature of the third stage of charging is lower than the ambient temperature of the second stage of charging.

[0025] Understandably, by setting the ambient temperature of the third stage higher than that of the first stage charging but lower than that of the second stage charging, the chemical reaction rate can be controlled, the surface state of the electrode can be finely adjusted, and the SEI film defects can be repaired, thereby improving the consistency and stability of the battery cell. At different temperatures, the reaction rate and products between the electrode material and the electrolyte differ, and a single temperature cannot simultaneously guarantee the uniformity, density, and integrity of the SEI film.

[0026] Optionally, in some embodiments of this application, the ambient temperature for the first stage of charging is 0°C to 10°C, for example, it can be 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, etc. In this way, during the first stage of charging, the SEI film framework formed on the electrode surface of the cell to be formed can be evenly distributed, thereby improving the uniformity of the SEI film.

[0027] Optionally, in some embodiments of this application, the ambient temperature for the second stage of charging is 40°C to 55°C, for example, 40°C, 42°C, 45°C, 47°C, 50°C, 52°C, 55°C, etc. This can promote the formation of the inorganic phase in the SEI film and improve the compactness of the SEI film, thereby enhancing the performance of the SEI film.

[0028] Optionally, in some embodiments of this application, the ambient temperature for the third-stage charging is 25°C to 35°C, for example, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, etc. This effectively repairs defects in the SEI film, improving its quality and stability.

[0029] Optionally, in some embodiments of this application, the charging current in the first stage is lower than the charging current in the second stage. This allows for matching with the ambient temperatures of the first and second stages of charging, enabling the first stage to form an SEI film slowly and uniformly, while the second stage allows the electrode material to fully react with the electrolyte, promoting the densification of the SEI film.

[0030] Optionally, in some embodiments of this application, the charging current in the third stage is higher than the charging current in the first stage, and the charging current in the third stage is less than or equal to the charging current in the second stage. This allows for matching with the ambient temperature of the third stage charging, resulting in a moderate chemical reaction rate, which is beneficial for finely adjusting the surface state of the electrode and repairing SEI film defects.

[0031] Optionally, in some embodiments of this application, the charging current in the first stage is 0.02C~0.05C, for example, it can be 0.02C, 0.03C, 0.04C, 0.05C, etc.

[0032] Understandably, a smaller current, combined with the low-temperature environment of the first stage of charging, allows the SEI film to form slowly and uniformly.

[0033] Optionally, in some embodiments of this application, the charging current in the second stage is 0.2C to 0.5C, for example, it can be 0.2C, 0.25C, 0.3C, 0.35C, 0.4C, 0.45C, 0.5C, etc.

[0034] Understandably, this current can be matched with the ambient temperature of the second stage of charging. The high temperature environment of the second stage of charging will accelerate the chemical reaction rate, improve the reactivity of the electrode material and the electrolyte, and increase the current can accelerate the formation process, so that the electrode material can react more fully with the electrolyte at high temperature, and promote the densification of the SEI film.

[0035] Optionally, in some embodiments of this application, the charging current in the third stage is 0.1C to 0.2C, for example, it can be 0.1C, 0.12C, 0.14C, 0.16C, 0.18C, 0.2C, etc.

[0036] Understandably, this current can be matched with the ambient temperature of the third stage of charging. At the ambient temperature of the third stage of charging, the chemical reaction rate is relatively moderate. After the first and second stages of charging, the internal structure of the cell has been basically formed. At this time, using a smaller current for the final formation and repair can finely adjust the surface state of the electrodes and improve the consistency and stability of the cell.

[0037] Optionally, in some embodiments of this application, before the first stage of charging, the following steps are further included: The cells to be formed are subjected to a first-stage static treatment.

[0038] Optionally, in some embodiments of this application, the first stage of settling is performed at 0℃~10℃, for example, 0℃, 1℃, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, 9℃, 10℃, etc., and the settling time is 1h~2h, for example, 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, etc. This allows for a uniform temperature distribution within the battery cell, ensuring that all parts of the cell reach the set temperature state, creating stable temperature conditions for the subsequent charging and formation process.

[0039] Optionally, in some embodiments of this application, the charging process between the first stage and the second stage further includes: The cells to be formed are subjected to a second stage of resting treatment after the first stage of charging is completed.

[0040] Optionally, in some embodiments of this application, the second-stage settling process is performed at 40℃~55℃, for example, 40℃, 42℃, 45℃, 47℃, 50℃, 52℃, 55℃, etc., and the settling time is 1h~2h, for example, 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, etc. This allows the battery cell to adapt to rapid temperature changes, avoiding damage caused by sudden temperature fluctuations; on the other hand, it further homogenizes the temperature of different parts inside the battery cell, while allowing the electrolyte to better wet the electrode material at high temperatures, promoting a full reaction between the electrode material and the electrolyte, which is beneficial to the densification process of the electrode material.

[0041] Optionally, in some embodiments of this application, the second stage of charging and the third stage of charging further include: The cells to be formed are subjected to a third stage of static treatment after the second stage of charging is completed.

[0042] Optionally, in some embodiments of this application, the third-stage settling treatment is performed at 25℃~35℃, for example, 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, etc., and the settling time is 1h~2h, for example, 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, etc. This allows the battery cell to smoothly transition from a high-temperature state to a room-temperature state, while also contributing to the stability of the internal electrochemical performance of the battery cell, enabling the battery cell to undergo final formation and repair in a more stable state at the third-stage charging temperature.

[0043] Optionally, in some embodiments of this application, the internal pressure of the cell to be formed is controlled to be negative during the first stage of charging, the second stage of charging, and the third stage of charging. This allows the gas generated inside the cell during the formation process to be expelled from the cell, thereby preventing the SEI film from rupturing due to high internal pressure and avoiding gas residue, thus ensuring the stability and reliability of the formation process.

[0044] It is understandable that gas will be generated during the formation process. If it cannot be discharged in time, it will cause the internal pressure of the cell to increase, affecting the formation quality of the SEI film, and may even cause safety problems such as cell bulging and leakage.

[0045] Understandably, negative pressure inside the battery cell can be achieved through a vacuuming process.

[0046] Optionally, in some embodiments of this application, the internal pressure of the cell to be formed during the first stage of charging is higher than the internal pressure of the cell to be formed during the second stage of charging.

[0047] It is understandable that the second stage of the charging process has a higher temperature and produces more gas, while the first stage of the charging process has a lower temperature and produces less gas. By making the internal pressure of the cell to be formed in the first stage of the charging process higher than that in the second stage of the charging process, it is possible to match the gas generation rate and ensure the effective and rapid discharge of gas.

[0048] Optionally, in some embodiments of this application, the internal pressure of the cell to be formed during the second stage of charging is higher than the internal pressure of the cell to be formed during the third stage of charging. This establishes a stable gas path through a higher negative pressure, ensuring efficient gas escape and avoiding gas residue, thereby improving the performance and reliability of the cell.

[0049] Optionally, in some embodiments of this application, during the first stage of charging, the internal pressure of the cell to be formed is -0.2MPa to -0.3MPa, for example, -0.2MPa, -0.22MPa, -0.24MPa, -0.26MPa, -0.28MPa, -0.3MPa, etc. This allows the generated gas to be effectively and quickly discharged.

[0050] Optionally, in some embodiments of this application, during the second stage of charging, the internal pressure of the cell to be formed is -0.4MPa to -0.5MPa, for example, -0.4MPa, -0.42MPa, -0.44MPa, -0.46MPa, -0.48MPa, -0.5MPa, etc. This allows the generated gas to be effectively and quickly discharged.

[0051] Optionally, in some embodiments of this application, during the third-stage charging process, the internal pressure of the cell to be formed is -0.6MPa to -0.7MPa, for example, -0.6MPa, -0.62MPa, -0.64MPa, -0.66MPa, -0.68MPa, -0.7MPa, etc. This allows the generated gas to be effectively and quickly discharged.

[0052] Optionally, in some embodiments of this application, the cutoff voltage for the first stage of charging is 3.6V~3.7V, such as 3.6V, 3.62V, 3.64V, 3.66V, 3.68V, 3.7V, etc. This allows for precise control of the charging level, preventing overcharging of the battery cell and ensuring it achieves better charging performance under safe conditions, thus maintaining its performance stability and safety.

[0053] Optionally, in some embodiments of this application, the cutoff voltage for the second stage of charging is 3.6V~3.7V, such as 3.6V, 3.62V, 3.64V, 3.66V, 3.68V, 3.7V, etc. This allows for precise control of the charging level, preventing overcharging of the battery cell and ensuring it achieves better charging performance under safe conditions, thus maintaining its performance stability and safety.

[0054] Optionally, in some embodiments of this application, the cutoff voltage for the third stage of charging is 3.6V~3.7V, such as 3.6V, 3.62V, 3.64V, 3.66V, 3.68V, 3.7V, etc. This allows for precise control of the charging level, preventing overcharging of the battery cell and ensuring it achieves better charging performance under safe conditions, thus maintaining its performance stability and safety.

[0055] Optionally, in some embodiments of this application, the charging time of the first stage is 0.5h to 1h, for example, it can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h, etc. This ensures that the SEI film is fully and uniformly formed during the low-temperature film formation stage.

[0056] Optionally, in some embodiments of this application, the second stage charging time is 1 hour to 1.5 hours, for example, 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, etc. Thus, by appropriately extending the charging time, the electrode material can be further reacted to form an SEI film, ensuring the stability and densification of the SEI film structure.

[0057] Optionally, in some embodiments of this application, the third-stage charging time is 2 hours to 2.5 hours, for example, 2 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, etc. This allows for the repair and adjustment of some microscopic defects that may occur in the SEI film during the first and second-stage charging processes, resulting in more stable cell performance.

[0058] Understandably, when both charging time and cutoff voltage are set, the one reached first is used as the end standard. Typically, charging for 1-2 hours won't reach the cutoff voltage.

[0059] Example 1 A cell formation method, comprising: (1) Place the 396389 lithium iron phosphate cell to be formed into the formation cabinet. Set the temperature of the formation cabinet to 5℃. Let it stand for 1 hour first, and then charge the cell with a current of 0.03C for the first stage. The charging time is 0.5 hours and the cut-off voltage is 3.7V. During the first stage of charging, control the internal pressure of the cell to -0.3MPa (the charging time and cut-off voltage whichever comes first). (2) Raise the temperature of the formation cabinet to 45°C, let it stand for 1 hour, and then charge the cell in the second stage with a current of 0.3C for 1 hour. The cutoff voltage is 3.7V. During the second stage of charging, control the internal pressure of the cell to -0.5MPa (the charging time and cutoff voltage shall be the earlier one). (3) Reduce the temperature of the formation cabinet to 30°C, let it stand for 1 hour, and then charge the cell in the third stage with a current of 0.1C for 2 hours. The cutoff voltage is 3.7V. During the third stage of charging, control the internal pressure of the cell to -0.7MPa (the charging time and cutoff voltage shall be the earlier one).

[0060] Example 2 This embodiment is basically the same as embodiment 1, except that the temperature of the chemical formation cabinet in step (1) is set to 10°C, the temperature of the chemical formation cabinet in step (2) is set to 55°C, and the temperature of the chemical formation cabinet in step (3) is set to 35°C.

[0061] Example 3 This embodiment is basically the same as embodiment 1, except that in this embodiment, the temperature of the chemical formation cabinet in step (1) is set to 0°C, the temperature of the chemical formation cabinet in step (2) is set to 40°C, and the temperature of the chemical formation cabinet in step (3) is set to 25°C.

[0062] Example 4 This embodiment is basically the same as Embodiment 1, except that the charging current in the first stage of charging is 0.02C, the charging current in the second stage of charging is 0.5C, and the charging current in the third stage of charging is 0.1C.

[0063] Example 5 This embodiment is basically the same as embodiment 1, except that the charging current in the first stage of charging is 0.05C, the charging current in the second stage of charging is 0.5C, and the charging current in the third stage of charging is 0.2C.

[0064] Example 6 This embodiment is basically the same as embodiment 5, except that the internal pressure of the battery cell is -0.2MPa during the first stage of charging, -0.4MPa during the second stage of charging, and -0.6MPa during the third stage of charging. In addition, no charging time is set for the second and third stages of charging, and the charging end standard is the cutoff voltage.

[0065] Example 7 This embodiment is basically the same as embodiment 5, except that the cutoff voltage for the first stage of charging, the second stage of charging, and the third stage of charging in this embodiment is 3.6V.

[0066] Example 8 This comparative example is basically the same as Example 1, except that the internal pressure of the battery cell in steps (1), (2) and (3) of this comparative example is -0.5MPa.

[0067] Example 9 This comparative example is basically the same as Example 1, except that the charging current in the first stage of charging is 0.5C, the charging current in the second stage of charging is 0.5C, and the charging current in the third stage of charging is 0.2C.

[0068] Example 10 This comparative example is basically the same as Example 1, except that no charging time is set for the first stage of charging, the second stage of charging, and the third stage of charging in this comparative example. The cutoff voltage of 3.45V is used as the cutoff standard.

[0069] Comparative Example 1 This comparative example is basically the same as Example 1, except that the temperature of the formation cabinet in steps (1), (2) and (3) of this comparative example is set to 45°C.

[0070] Test example: Performance tests were conducted on the battery cells obtained in the embodiment and comparative example. The test results are shown in Table 1.

[0071] Cyclic testing method: Charge and discharge the cell at 1C in a 25℃ environment with a cutoff voltage of 2.5V~3.65V. During the cycle, use the single-pulse method to test the DC resistance (DCR) of the battery (60% SOC, 1C rate, 10s). Measure the DCR once every 100 cycles and calculate the capacity retention rate (battery capacity after cycle / initial battery capacity) and the DCR value ((voltage before pulse V0 - voltage after pulse V1) / pulse current I).

[0072] Table 1 Test Results

[0073] Compared with Comparative Example 1, the internal resistance growth rate of the battery cell in Examples 1-3 is faster and the capacity retention rate is lower. It can be seen that by making the ambient temperature of the three charging stages of the formation process different and controlling the ambient temperature of the three charging stages separately, this application can improve the quality of the SEI formed in the formation process, thereby reducing the internal resistance of the battery cell and improving the cycle performance of the battery cell.

[0074] Compared with Example 9, Example 9 shows that the internal resistance growth rate of the cell is faster and the capacity retention rate is lower. It can be seen that by controlling the charging current of the three charging stages, this application can improve the quality of the SEI formed in the formation process, thereby reducing the internal resistance of the cell and improving the cycle performance of the cell.

[0075] Compared with Example 10, Example 5 and Example 6 show that the internal resistance growth rate of the battery cell in Example 10 is faster and the capacity retention rate is lower. It can be seen that by controlling the charging time during the formation process, this application can control the charging amount of the battery cell, thereby improving the quality of the SEI formed during the formation process, and thus reducing the internal resistance of the battery cell and improving the cycle performance of the battery cell.

[0076] Compared with Example 8, Example 1 shows that the internal resistance growth rate of the cell in Example 8 is faster and the capacity retention rate is lower. It can be seen that by controlling the internal pressure of the cell in the three charging stages, this application can improve the quality of the SEI formed in the formation process, thereby reducing the internal resistance of the cell and improving the cycle performance of the cell.

[0077] The cell formation method provided in the embodiments of this application has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method of forming an electrical cell, comprising: include: The cells to be formed are charged in the first stage and the second stage sequentially. The ambient temperature during the first stage of charging is lower than the ambient temperature during the second stage of charging.

2. The cell formation method of claim 1, wherein, After the second stage of charging is completed, it also includes: The cells to be formed are then subjected to a third stage of charging after the second stage of charging is completed.

3. The cell formation method of claim 2, wherein, The ambient temperature during the third stage of charging is higher than the ambient temperature during the first stage of charging; and / or The ambient temperature during the third stage of charging is lower than that during the second stage of charging.

4. The cell formation method of claim 3, wherein, The ambient temperature for the first stage of charging is 0℃~10℃; and / or The ambient temperature for the second stage of charging is 40℃~55℃; and / or The ambient temperature for the third stage of charging is 25℃~35℃.

5. The cell formation method according to claim 2, characterized in that, The charging current in the first stage is lower than the charging current in the second stage; and / or The charging current in the third stage is higher than the charging current in the first stage, and the charging current in the third stage is less than or equal to the charging current in the second stage.

6. The cell formation method according to claim 5, characterized in that, The charging current in the first stage is 0.02C~0.05C; and / or The charging current in the second stage is 0.2C~0.5C; and / or The charging current in the third stage is 0.1C~0.2C.

7. The cell formation method according to claim 2, characterized in that, Before the first stage of charging, the process also includes: performing a first stage of resting treatment on the battery cell to be formed; The first stage of settling is carried out at 0℃~10℃ for 1h~2h; and / or Between the first stage of charging and the second stage of charging, the process also includes: performing a second stage of resting treatment on the battery cell to be formed after the first stage of charging is completed; The second stage of settling is carried out at 40℃~55℃ for 1h~2h; and / or Between the second stage of charging and the third stage of charging, the method further includes: performing a third stage resting treatment on the cell to be formed after the completion of the second stage of charging; and / or The third stage of settling is carried out at 25℃~35℃, and the settling time is 1h~2h.

8. The cell formation method according to claim 2, characterized in that, It also includes controlling the internal pressure of the cell to be formed to be negative during the first stage of charging, the second stage of charging, and the third stage of charging. Wherein, the internal pressure of the cell to be formed during the first stage of charging is higher than the internal pressure of the cell to be formed during the second stage of charging; and / or The internal pressure of the cell to be formed during the second stage of charging is higher than the internal pressure of the cell to be formed during the third stage of charging.

9. The cell formation method according to claim 8, characterized in that, During the first stage of charging, the internal pressure of the cell to be formed is -0.2MPa to -0.3MPa; and / or During the second stage of charging, the internal pressure of the cell to be formed is -0.4MPa to -0.5MPa; and / or During the third stage of charging, the internal pressure of the cell to be formed is -0.6MPa to -0.7MPa.

10. The cell formation method according to claim 2, characterized in that, The cutoff voltage for the first stage of charging is 3.6V~3.7V; and / or The cutoff voltage for the second stage of charging is 3.6V~3.7V; and / or The cutoff voltage for the third stage of charging is 3.6V~3.7V; and / or The first stage charging time is 0.5h~1h; and / or The second stage charging time is 1 hour to 1.5 hours; and / or The third stage charging time is 2 hours to 2.5 hours.

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