Battery cell negative pressure formation method and battery cell

Abstract

This invention belongs to the technical field of batteries, specifically relating to a method for negative pressure formation of battery cells, including: Step 1, placing the battery cell in a first negative pressure environment for a first time period; Step 2, performing a first constant current charge on the battery cell in the first negative pressure environment and during a second time period; Step 3, placing the battery cell in the first negative pressure environment for a first time period; Step 4, placing the battery cell in a second negative pressure environment for a first time period; Step 5, performing a second constant current charge on the battery cell in the second negative pressure environment and during a third time period; Step 6, placing the battery cell in the first negative pressure environment for a fourth time period. This invention can improve the problem of battery cell swelling. Furthermore, this invention also discloses a battery cell prepared by the above-described negative pressure formation method.

Description

Technical Field

[0001] This invention belongs to the technical field of batteries, specifically relating to a negative pressure formation method for battery cells and a battery cell. Background Technology

[0002] Lithium-ion batteries possess advantages such as high voltage, high specific energy, long charge-discharge life, and safety and environmental friendliness, making them widely used in various electronic products (such as mobile phones, digital cameras, laptops, and power tools), portable small appliances, electric vehicles, and energy storage systems. The manufacturing process of lithium-ion batteries is complex, including stirring, coating, drying, bare cell preparation, packaging, and formation. Among these, the formation process is an indispensable step in the lithium-ion battery manufacturing process, playing a crucial role in the battery's performance.

[0003] In the process of realizing this invention, the inventors discovered at least the following problems in the prior art: Existing formation processes can cause battery cells to swell, affecting their performance. Summary of the Invention

[0004] One of the objectives of this invention is to address the shortcomings of existing technologies by providing a negative pressure formation method for battery cells, which can improve the problem of battery cell bulging.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for negative voltage formation of a battery cell includes the following steps: Step 1, placing the battery cell in a first negative voltage environment for a first time period; Step 2, performing a first constant current charge on the battery cell in the first negative voltage environment and during a second time period; Step 3, placing the battery cell in the first negative voltage environment for a first time period; Step 4, placing the battery cell in a second negative voltage environment for a first time period; Step 5, performing a second constant current charge on the battery cell in the second negative voltage environment and during a third time period; Step 6, placing the battery cell in the first negative voltage environment for a fourth time period; wherein the current of the first constant current charge is 0.05~0.12C, the current of the second constant current charge is 0.1~0.3C, the first negative voltage is -20~-50kPa, and the second negative voltage is -60~-100kPa.

[0006] Preferably, the first time period is 5 minutes and the fourth time period is 10 minutes.

[0007] Preferably, in step two, the second time period is 7 minutes and the cutoff voltage is 3V.

[0008] Preferably, in step five, the third time period is 117 minutes and the cutoff voltage is 3.4V.

[0009] Preferably, the formation temperature is 40℃~50℃.

[0010] Preferably, the process also includes: standing before and after formation, with a standing temperature of 42℃~48℃ and a standing time of 22~26min.

[0011] The second objective of this invention is to provide a battery cell prepared by the aforementioned negative voltage formation method.

[0012] One of the above technical solutions has the following beneficial effects: This invention employs low negative pressure and low current to reduce secondary gas generation caused by SEI film rupture; in the mid-term, the negative pressure is increased and the current is increased in a stepwise manner to accelerate electrolyte wetting and gas discharge, thus improving the problem of cell swelling; in the later stage, a stable negative pressure and constant pressure heat preservation are maintained to ensure lithium dendrite suppression and interface stability, thereby improving the cycle performance of the battery. Attached Figure Description

[0013] The features, advantages and technical effects of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings.

[0014] Figure 1 The image shows the long-cycle test results of the battery prepared by the formation method in Example 1 of this invention.

[0015] Figure 2 The image shows the long-cycle test results of the battery prepared by the formation method of Comparative Example 1 in this invention. Detailed Implementation

[0016] If certain terms are used in the specification and claims to refer to specific components, those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The term "comprising" as used throughout the specification and claims is an open-ended term and should be interpreted as "comprising but not limited to." "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error.

[0017] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be interpreted as indicating or implying relative importance.

[0018] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0019] The present invention will be further described in detail below with reference to the accompanying drawings, but this is not intended to limit the scope of the invention.

[0020] The battery cell negative voltage formation method includes the following steps: Step 1, placing the battery cell in a first negative voltage environment during a first time period; Step 2, performing a first constant current charge on the battery cell during the first negative voltage environment and a second time period; Step 3, placing the battery cell in a first negative voltage environment during the first time period; Step 4, placing the battery cell in a second negative voltage environment during the first time period; Step 5, performing a second constant current charge on the battery cell during the second negative voltage environment and a third time period; Step 6, placing the battery cell in a first negative voltage environment during a fourth time period; wherein the current of the first constant current charge is 0.05~0.12C, the current of the second constant current charge is 0.1~0.3C, the first negative voltage is -20~-50kPa, and the second negative voltage is -60~-100kPa.

[0021] It should be noted that: In step two, during the initial formation stage (SEI film formation stage), a low negative pressure (e.g., -20~-50kPa) and a small current (0.05~0.12C) are used to reduce secondary gas generation caused by SEI film rupture; In step five, during the intermediate stage (capacity enhancement stage), the negative pressure is increased to -60~-100kPa and the current is increased in a stepwise manner (0.1~0.3C) to accelerate electrolyte wetting and gas discharge, thus improving the problem of cell swelling; In step six, during the later stage (i.e., curing stage), a stable negative pressure and constant pressure heat preservation are maintained to ensure lithium dendrite suppression and interface stability.

[0022] In the negative pressure formation method for the battery cell according to the present invention, the first time period is 5 minutes and the fourth time period is 10 minutes. Allowing the lithium-ion battery to stand still can ensure the stability of the lithium-ion battery performance and further improve the consistency of the lithium-ion battery performance.

[0023] In the negative voltage formation method of the battery cell according to the present invention, in step two, the second time period is 7 minutes and the cutoff voltage is 3V, that is, the battery cell needs to be charged to the cutoff voltage of 3V with constant current within 7 minutes.

[0024] In the negative voltage formation method of the battery cell according to the present invention, in step five, the third time period is 117 minutes and the cutoff voltage is 3.4V, that is, the battery cell needs to be charged to the cutoff voltage of 3.4V with constant current within 117 minutes.

[0025] In the negative voltage formation method of the battery cell according to the present invention, the formation temperature is 40°C to 50°C. That is, steps one to six need to be carried out at a temperature of 40°C to 50°C.

[0026] The negative pressure formation method for the battery cell according to the present invention further includes: pre- and post-formation resting at a temperature of 42°C to 48°C for a duration of 22 to 26 minutes, which can ensure the stability of the performance of the lithium-ion battery.

[0027] This embodiment also provides a battery cell, which is prepared by a battery cell negative pressure formation method.

[0028] Based on the above description, by selecting specific negative voltage, current ratio, preset charging time, and cutoff voltage, this invention also provides a specific implementation method for the negative voltage formation method of battery cells, namely, Example 1. For example, the battery cell in Example 1 has a capacity of 25Ah, a width of 70mm, a thickness of 27mm, and a height of 170~180mm. The specific formation steps are as follows: Step 1: Within the first time period of 5 minutes, place the battery cell in an environment with a first negative pressure of -40~-50kPa; Step 2: In an environment with a first negative pressure of -40~-50kPa and a second time period of 7 minutes, charge the battery cell with a first constant current of 2.8A and a cutoff voltage of 3V. Step 3: Within the first time period of 5 minutes, place the battery cell in an environment with a first negative pressure of -40~-50kPa; Step 4: During the first time period of 5 minutes, place the battery cell in an environment with a second negative pressure of -65~-50kPa. Step 5: In an environment with a second negative pressure of -65~-50kPa and a third time period of 117min, charge the battery cell with a second constant current of 5.6A. Step 6: During the fourth time period of 10 minutes, place the battery cell in an environment with a first negative pressure of -40~-50kPa.

[0029] Furthermore, the present invention also provides a specific implementation method for the negative voltage formation method of battery cells, namely Example 2. For example, the battery cell in Example 2 has a capacity of 32Ah, a width of 70mm, a thickness of 27mm, and a height of 170~180mm. The specific formation steps are as follows: Step 1: Within the first time period of 5 minutes, place the battery cell in an environment with a first negative pressure of -40~-50kPa; Step 2: In an environment with a first negative pressure of -40~-50kPa and a second time period of 7 minutes, charge the battery cell with a first constant current of 3.2A and a cutoff voltage of 3V. Step 3: Within the first time period of 5 minutes, place the battery cell in an environment with a first negative pressure of -40~-50kPa; Step 4: During the first time period of 5 minutes, place the battery cell in an environment with a second negative pressure of -65~-50kPa. Step 5: In an environment with a second negative pressure of -65~-50kPa and a third time period of 117min, charge the battery cell with a second constant current of 6.4A. Step 6: During the fourth time period of 10 minutes, place the battery cell in an environment with a first negative pressure of -40~-50kPa.

[0030] Furthermore, this embodiment also provides a formation method for a battery cell without negative voltage, namely Comparative Example 1, to form a comparative analysis with the above-described Example 1. The specific formation steps of Comparative Example 1 are as follows: Step 1: During the first 5-minute period, allow the battery cells to stand still. Step 2: During the second time period of 7 minutes, the battery cell is charged with a constant current of 2.8A, and the cutoff voltage is 3V. Step 3: During the first 5-minute period, allow the battery cells to stand still. Step 4: During the first 5-minute period, allow the battery cells to stand still. Step 5: During the third time period of 117 minutes, the battery cell is charged with a second constant current of 5.6A. Step 6: During the fourth time period of 10 minutes, let the battery cells stand still.

[0031] It should be noted that all steps in Comparative Example 1 were performed under normal atmospheric pressure conditions; that is, Comparative Example 1 maintained a normal atmospheric pressure environment throughout.

[0032] The batteries obtained by the formation methods of Example 1 and Comparative Example 1 are further processed to obtain finished secondary batteries and subjected to long-cycle testing, as shown in Table 1 below.

[0033] Table 1. Long-cycle test results of the battery in Example 1 and the comparative example battery. from Figure 1 , Figure 2As can be seen from Table 1, the battery prepared in Example 1 has a better cycle capacity retention rate than that of Comparative Example 1. This indicates that the formation method of the present invention uses low negative pressure and low current to reduce secondary gas generation caused by SEI film rupture; in the middle stage, the negative pressure is increased and the current is increased in a stepwise manner to accelerate electrolyte wetting and gas discharge, thereby improving the problem of cell swelling; in the later stage, maintaining stable negative pressure and constant pressure heat preservation ensures lithium dendrite suppression and interface stability, thereby improving the cycle performance of the battery.

[0034] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A method for negative voltage formation of battery cells, characterized in that, Includes the following steps: Step 1: During the first time period, place the battery cell in the first negative pressure environment; Step 2: In the first negative pressure environment and during the second time period, perform the first constant current charging on the battery cell; Step 3: During the first time period, place the battery cell in the first negative pressure environment; Step 4: During the first time period, place the battery cell in a second negative pressure environment. Step 5: In the second negative pressure environment and during the third time period, perform a second constant current charge on the battery cell; Step Six: During the fourth time period, place the battery cell in the first negative pressure environment; Wherein, the current of the first constant current charging is 0.05~0.12C, the current of the second constant current charging is 0.1~0.3C, the first negative voltage is -20~-50kPa, and the second negative voltage is -60~-100kPa.

2. The cell negative voltage formation method as described in claim 1, characterized in that: The first time period is 5 minutes, and the fourth time period is 10 minutes.

3. The cell negative voltage formation method as described in claim 1, characterized in that: In step two, the second time period is 7 minutes and the cutoff voltage is 3V.

4. The cell negative voltage formation method as described in claim 1, characterized in that: In step five, the third time period is 117 minutes, and the cutoff voltage is 3.4V.

5. The cell negative voltage formation method as described in claim 1, characterized in that: The formation temperature is 40℃~50℃.

6. The cell negative voltage formation method as described in claim 1, characterized in that, Also includes: Before and after the formation process, the sample was allowed to stand at a temperature of 42℃~48℃ for 22~26 minutes.

7. A battery cell, characterized in that: It is prepared by the cell negative voltage formation method according to any one of claims 1-6.

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