Method for manufacturing secondary battery, secondary battery, energy storage system, and electric device

Abstract

This invention relates to the field of energy storage cells, and provides a method for preparing a secondary battery, a secondary battery, an energy storage system, and an electrical device. The method includes: subjecting a cell in a processing stage on a cell carrier to high-temperature static treatment for a preset time to obtain a target moisture value for the target cell; determining formation processing parameters for the cell in the processing stage on the cell carrier based on the target moisture value, the formation processing parameters including at least a formation current and a formation method, wherein the formation method is either unconstrained formation or constrained formation; and performing formation processing on the cell in the processing stage on the cell carrier using the formation processing parameters to reduce the amount of gas generated by the cell in the processing stage during the formation process, thereby reducing the brown spot coverage on the surface of the cell in the processing stage. This method reduces gas generation per unit time by decreasing the current during the formation process based on the cell moisture value, and makes it easier for the gas to escape through constrained formation, thus reducing brown spots.

Description

Technical Field

[0001] This invention relates to the field of energy storage cells, and more specifically, to a method for preparing a secondary battery, a secondary battery, an energy storage system, and an electrical device. Background Technology

[0002] With the development of science and technology, the performance requirements for batteries in existing technologies are becoming increasingly stringent. However, the brown spot problem in battery cells is a serious defect in battery performance. The formation of brown spots in battery cells can lead to further lithium plating, thereby affecting battery capacity and performance. In severe cases, it can lead to battery thermal runaway and cause battery safety accidents. Summary of the Invention

[0003] The main objective of this invention is to provide a method for preparing a secondary battery, a secondary battery, an energy storage system, and an electrical device, in order to solve the problem that existing battery preparation methods easily cause brown spots to form on the prepared battery cells, thereby leading to a decrease in battery performance.

[0004] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a secondary battery is provided, comprising: subjecting a processed battery cell on a cell carrier to high-temperature static treatment for a preset time and then obtaining a target moisture value for a target processed battery cell, wherein the target processed battery cell is a portion of the processed battery cells on the cell carrier; determining formation processing parameters for the processed battery cells on the cell carrier based at least on the target moisture value, the formation processing parameters including at least a formation current and a formation method, wherein the formation method is unconstrained formation or constrained formation; performing formation treatment on the processed battery cells on the cell carrier using the formation processing parameters to at least reduce the gas production of the processed battery cells on the cell carrier during the formation treatment process, thereby reducing the brown spot coverage rate on the surface of the processed battery cells on the cell carrier; wherein, at least based on the target moisture value of the target processed battery cell... Determining the formation processing parameters of the battery cell in the process on the battery cell carrier includes: when the target moisture value of the battery cell in the target process is less than or equal to a first moisture value, determining the formation current of the battery cell in the process on the battery cell carrier as a first current and the formation method as unconstrained formation; when the target moisture value of the battery cell in the target process is greater than the first moisture value and less than or equal to a second moisture value, determining the formation current of the battery cell in the process on the battery cell carrier as a second current and the formation method as unconstrained formation, wherein the second current is less than the first current; when the target moisture value of the battery cell in the target process is greater than the second moisture value and less than or equal to a third moisture value, determining the formation current of the battery cell in the process on the battery cell carrier as a third current and the formation method as constrained formation, wherein the third current is less than the second current.

[0005] Furthermore, the first current ranges from 0.1C to 0.3C, the second current ranges from 0.1C to 0.02C, and the third current is 0.02C, where C is the rated capacity of the battery cell in the process.

[0006] Further, the target moisture value of the battery cell in the target processing is greater than the first moisture value and less than or equal to the second moisture value. The battery cell in the processing on the battery cell carrier is processed using the formation processing parameters, including: using the second current as the initial formation current to perform a first formation processing on the battery cell in the processing on the battery cell carrier; during the first formation processing on the battery cell in the processing on the battery cell carrier, the liquid level in the formation cup of the target processed battery cell is detected in real time to obtain a first formation cup liquid level, where the formation cup is a container holding the electrolyte of the target processed battery cell during the formation processing; if the liquid level in the first formation cup is less than or equal to a first preset liquid level, the second current is continued to be used to perform the first formation processing on the battery cell in the processing on the battery cell carrier; if the liquid level in the first formation cup is greater than the first preset liquid level, the formation current is reduced until the liquid level in the first formation cup is less than or equal to the first preset liquid level or the formation current is the third current.

[0007] Further, the target moisture value of the battery cell in the target processing is greater than the second moisture value and less than or equal to the third moisture value. The battery cell in the processing on the battery cell carrier is processed using the formation processing parameters, including: performing a second formation processing on the battery cell in the processing on the battery cell carrier using the third current and a restraint formation method; during the second formation processing of the battery cell in the processing on the battery cell carrier, the liquid level of the formation cup of the target battery cell in the processing is detected in real time to obtain the second formation cup liquid level; based on the second formation cup liquid level, the pressure processing method of the battery cell in the processing on the battery cell carrier is determined, and the second formation processing is performed on the battery cell in the processing on the battery cell carrier using the pressure processing method, wherein the pressure processing method is an alternating negative pressure and normal pressure method or an alternating normal pressure and vacuum method.

[0008] Further, based on the liquid level in the second formation cup, the pressure treatment method of the processed battery cell on the battery cell carrier is determined, and the second formation treatment is performed on the processed battery cell on the battery cell carrier using the pressure treatment method, including: when the liquid level in the second formation cup is less than or equal to a second preset liquid level, determining to perform the second formation treatment on the processed battery cell on the battery cell carrier using the alternating negative pressure and normal pressure method, and determining that the single application duration of negative pressure is a first duration and the single application duration of normal pressure is a second duration; performing the second formation treatment on the processed battery cell on the battery cell carrier using the alternating negative pressure and normal pressure method, wherein the time for each application of negative pressure is the first duration and the time for each application of normal pressure is the second duration.

[0009] Further, based on the liquid level in the second formation cup, the pressure treatment method for the processed battery cell on the battery cell carrier is determined, and the second formation treatment is performed on the processed battery cell on the battery cell carrier using the pressure treatment method, including: when the liquid level in the second formation cup is greater than the second preset liquid level, determining to perform the second formation treatment on the processed battery cell on the battery cell carrier using the alternating method of atmospheric pressure and vacuum, and determining that the single application duration of atmospheric pressure is the third duration and the single application duration of vacuum is the fourth duration; performing the second formation treatment on the processed battery cell on the battery cell carrier using the alternating method of atmospheric pressure and vacuum until the liquid level in the second formation cup is less than or equal to the second preset liquid level, wherein the time for each application of atmospheric pressure is the third duration and the time for each application of vacuum is the fourth duration.

[0010] Further, the target processed battery cell is a processed battery cell that has undergone a lithium replenishment process with added lithium replenishment material. The formation processing parameters of the processed battery cell on the battery cell carrier are determined at least based on the target moisture value of the target processed battery cell, including: when the target moisture value of the target processed battery cell is less than or equal to a first moisture value and the lithium replenishment amount of the target processed battery cell is less than or equal to the first lithium replenishment amount, determining the formation current of the processed battery cell on the battery cell carrier as a fourth current and the formation method as the unconstrained formation; when the target moisture value of the target processed battery cell is greater than the first moisture value and less than or equal to a second moisture value and the target processed… When the lithium replenishment amount of the battery cell is greater than the first lithium replenishment amount and less than or equal to the second lithium replenishment amount, the formation current of the battery cell in the process on the battery cell carrier is determined to be the fifth current and the formation method is the unconstrained formation, and the fifth current is less than the fourth current; when the target moisture value of the battery cell in the target process is greater than the second moisture value and less than or equal to the third moisture value and the lithium replenishment amount of the battery cell in the target process is greater than the second lithium replenishment amount and less than or equal to the third lithium replenishment amount, the formation current of the battery cell in the process on the battery cell carrier is determined to be the sixth current and the formation method is the constrained formation, and the sixth current is less than the fifth current.

[0011] Furthermore, before determining the performance parameters of the target processing cell, the method further includes: obtaining basic parameters of each processing cell on the cell carrier, wherein the basic parameters of the processing cell include the weight and thickness of the processing cell, and the thickness of the processing cell is positively correlated with the width of the electrolyte channel of the processing cell; if the weight difference between two processing cells on the cell carrier is greater than a preset weight difference, then the processing cell with the largest weight is determined as the target processing cell; if the weight difference between any two processing cells on the cell carrier is less than or equal to the preset weight difference, then the processing cell with the smallest thickness on the cell carrier is determined as the target processing cell.

[0012] Furthermore, when the formation method is the constraint formation, during the formation process, a mechanical clamp is used to constrain the processed battery cell on the battery cell carrier to perform the constraint formation on the processed battery cell on the battery cell carrier.

[0013] According to another aspect of the present invention, a secondary battery is provided, wherein the secondary battery is prepared by any of the methods described above.

[0014] According to another aspect of the present invention, an energy storage system is provided, comprising: at least one of the aforementioned secondary batteries.

[0015] According to another aspect of the present invention, an electrical device is provided, comprising: at least one of the aforementioned secondary batteries or the aforementioned energy storage system.

[0016] The beneficial effects of this application are as follows: The above-mentioned method for preparing a secondary battery first obtains the target moisture value of the cell in the target treatment. Then, if the target moisture value of the cell in the target treatment is less than or equal to a first moisture value, the formation current of the cell in the treatment on the cell carrier is determined to be a first current and the formation method is unconstrained formation. If the target moisture value of the cell in the target treatment is greater than the first moisture value and less than or equal to a second moisture value, the formation current of the cell in the treatment on the cell carrier is determined to be a second current and the formation method is unconstrained formation. The second current is less than the first moisture value. A current is used to determine whether a cell is prone to brown spots. If the target moisture content of the cell in the target processing stage is greater than a second moisture content and less than or equal to a third moisture content, the formation current of the cell on the cell carrier is determined to be the third current, and the formation method is constraint formation. The third current is less than the second current. Finally, the formation processing parameters are used to perform formation processing on the cell on the cell carrier to at least reduce the amount of gas generated by the cell during the formation process, thereby reducing the brown spot coverage on the surface of the cell. This method determines whether a cell is prone to brown spots based on its moisture content. When the moisture content is high, the current is reduced during the formation process to decrease gas generation per unit time, and constraint formation makes it easier for the gas to escape, thus reducing brown spots. This solves the problem in existing battery manufacturing methods where brown spots easily form in the prepared cells, leading to a decrease in battery performance. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0018] Figure 1 A schematic flowchart of a method for preparing a secondary battery according to an embodiment of the present invention is shown;

[0019] Figure 2 A schematic diagram of a battery cell assembly provided according to an embodiment of this application is shown;

[0020] Figure 3 A schematic flowchart of a formation charging process according to an embodiment of this application is shown;

[0021] Figure 4A schematic diagram of a formation apparatus provided according to an embodiment of this application is shown;

[0022] Figure 5 A schematic flowchart of a method for preparing a secondary battery according to another embodiment of the present invention is shown.

[0023] The above figures include the following reference numerals:

[0024] 10. Battery cell tray; 20. Battery cell in processing; 21. Target battery cell in processing; 50. Negative pressure nozzle; 60. Buffer cup; 70. Busbar; 80. Buffer container. Detailed Implementation

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present application.

[0027] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0028] In existing technologies, the formation of brown spots in battery cells mainly refers to the chemical reaction that occurs between the battery structural layers when the internal moisture environment of the battery is high. This causes black metal oxides to form on the surface of the positive electrode material, which affects the battery capacity and performance. In severe cases, it can lead to battery thermal runaway and cause battery safety accidents.

[0029] Brown spots on the outer ring of a battery typically form during the battery formation process. Formation involves charging the cell at a specific voltage to activate its materials and structure. If gas generation is too rapid during formation, it indicates an overly vigorous electrochemical reaction inside the battery, potentially generating a large amount of gas before the SEI film (Sediment Injection Layer) is fully formed and stabilized. This results in a poor-quality SEI film, failing to effectively prevent further electrolyte decomposition and increasing the risk of lithium plating. The rapidly generated gas accumulates inside the battery, creating high internal pressure. If this pressure is not released promptly, it can cause uneven deposition of lithium ions on the electrode surface, particularly in the outer ring of the cell, potentially leading to localized lithium plating and brown spots.

[0030] Larger gaps in the outer rings of the battery cell facilitate gas flow within the battery. However, this also means that gas is more easily forced into these gaps under high pressure, leading to localized pressure and deformation of the electrode material. As the gas expands rapidly within these gaps, the outer electrode material is easily compressed, altering its original packing density and structure. This affects the uniform insertion and extraction of lithium ions, resulting in localized lithium plating and the formation of brown spots. Larger gaps may also cause uneven electrolyte distribution in the affected area, leading to inconsistent formation reactions. Some areas may experience more vigorous reactions and a higher tendency for lithium plating, ultimately resulting in brown spots.

[0031] Therefore, in order to solve the problem that the existing battery manufacturing methods easily cause brown spots to form on the prepared cells, thereby leading to a decrease in battery performance, the embodiments of this application provide a method for preparing a secondary battery, a secondary battery, an energy storage system, and an electrical device.

[0032] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0033] This embodiment provides a method for preparing a secondary battery. It should be noted that although the logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than that shown here.

[0034] Figure 1 This is a flowchart of a method for preparing a secondary battery according to an embodiment of this application. Figure 1 As shown, the method includes the following steps:

[0035] Step S101: After subjecting the battery cells in the process of processing on the battery cell carrier to a high-temperature static treatment for a preset time, the target moisture value of the target battery cells in the process of processing is obtained. The target battery cells in the process of processing are a portion of the battery cells in the process of processing on the battery cell carrier.

[0036] Before performing step S101, the process includes obtaining a processing cell, which involves winding the separator, the positive electrode sheet of the battery after the electrode baking process, and the negative electrode sheet of the battery and placing them into the casing to form an initial cell. Then, the initial cell is subjected to hot pressing and assembly to obtain a processing cell. The processing cell is first injected with electrolyte and then subjected to high-temperature static treatment.

[0037] Specifically, the battery cell carrier is generally a battery cell tray. Figure 2 This is a schematic diagram of a battery cell assembly structure, such as... Figure 2 As shown, the cell assembly consists of a cell tray 10 and multiple cells 20 under processing. The cell tray 10 holds multiple cells 20 under processing; typically, the cell tray 10 holds 24 cells 20 under processing. Electrolyte injection is the process of injecting electrolyte into the cell after electrode fabrication, cell assembly (winding or stacking), and the first baking (pre-baking). The electrolyte is the carrier for the electrochemical reactions inside the cell; it contains lithium salts, organic solvents, and possible additives, providing the necessary medium for the movement of lithium ions between the positive and negative electrodes, thereby enabling the cell's charging and discharging functions. High-temperature settling treatment involves placing the cell in a specific temperature environment above room temperature, allowing the battery to remain in a static state at that temperature for a period of time. High-temperature settling treatment involves baking the cell to initially reduce its moisture content.

[0038] like Figure 2 As shown, the target processing cell 21 is installed at the preset detection position of the above-mentioned cell carrier, and then all the processing cells 20 in the cell tray 10 are simultaneously subjected to electrolyte injection treatment and high-temperature static treatment.

[0039] The target cell is generally selected as the cell with the highest moisture content. After the target cell is determined, it is installed in the preset detection position of the cell carrier to detect the moisture value of the target cell. Then, all the cells in the cell tray are simultaneously injected with electrolyte and subjected to high-temperature static treatment.

[0040] Step S102: Determine the formation processing parameters of the battery cell in the above-mentioned process on the battery cell carrier at least according to the above-mentioned target moisture value. The formation processing parameters include at least the formation current and the formation method. The formation method is unconstrained formation or constrained formation.

[0041] Specifically, the formation current directly affects the speed and extent of the electrochemical reaction inside the battery cell. High current may lead to an overly vigorous electrochemical reaction, affecting the quality of the SEI film formation; conversely, low current can promote the reaction more gently, which is conducive to the formation of a stable and dense SEI film. Formation methods are divided into unconstrained formation and constrained formation. Unconstrained formation allows the battery cell to expand freely during the formation process, which is suitable for situations with low moisture content and low gas production; constrained formation applies a certain pressure to the battery cell through an external device to restrict its expansion, which is suitable for situations with high moisture content and high gas production. Therefore, the formation current and formation method are determined according to the target moisture content. When the moisture content is low, a simple formation process can be used to simplify the formation process and save costs; when the moisture content is high, low-current formation or constrained formation can be used to reduce the formation of brown spots in the battery cell.

[0042] The process of determining the formation parameters of the battery cell on the battery cell carrier based on at least the target moisture value of the battery cell in the target treatment includes the following steps:

[0043] Step S1021: If the target moisture value of the cell in the above target processing is less than or equal to the first moisture value, determine that the formation current of the cell in the above processing on the cell carrier is the first current and the formation method is the above unrestrained formation.

[0044] Unconstrained formation refers to a process method in which no external physical constraints or pressures are applied to the battery cells during the formation process. In other words, unconstrained formation is performed without external mechanical constraints.

[0045] Constraint formation refers to applying physical restrictions or pressure to the battery cell during the formation stage to control the expansion and deformation that may occur during the formation process, ensuring the stability of the cell structure and the consistency of its dimensions. This process is usually achieved with the help of specially designed jigs, molds, or other forms of support structures.

[0046] The specific methods of achieving restraint may include, but are not limited to, the following:

[0047] 1. Using a clamp is one of the most common restraint formation methods. The cell is placed in a specially designed clamp, which continuously applies appropriate pressure during the formation process to limit the expansion of the cell.

[0048] 2. Customized molds: Special molds can be designed to wrap the battery cells. The strength and elasticity of the molds can be adjusted according to the characteristics of the battery cells and the degree of expansion during the formation process.

[0049] 3. Outer ring coating: A coating material, such as blue film or other insulating material, is used on the outer ring of a specific battery cell to increase the mechanical strength of the cell and reduce deformation during the formation process.

[0050] In this embodiment, it is preferable to use a clamp for restraint formation.

[0051] The initial moisture content typically ranges from 18 ppm to 22 ppm. For example, it can be set to 19 ppm, 20 ppm, or 21 ppm, with 20 ppm being the preferred value. During the first charge and discharge cycle, a solid electrolyte interphase (SEI) film forms on the negative electrode surface of a lithium-ion battery, playing a crucial role in the battery's cycle performance and lifespan. A moisture content exceeding 20 ppm may affect SEI film formation, leading to instability or excessive thickness, increasing internal resistance, and impacting battery performance. Setting a moisture content of 20 ppm helps optimize SEI film formation conditions, improving its quality and consistency.

[0052] Since the target cell in the processing stage is generally the cell with the highest moisture content, if the target moisture value of the target cell is less than or equal to the first moisture value, it proves that the moisture values ​​of all other cells in the processing stage are also less than the first moisture value. That is, the moisture values ​​of all cells in the processing stage are relatively low. Therefore, even if a larger formation current or an unconstrained formation method is used, the cell is less likely to develop brown spots. Thus, to simplify the formation process, a larger formation current and an unconstrained formation method can be used in this case.

[0053] Step S1022: In the case that the target moisture value of the battery cell in the above target processing is greater than the first moisture value and less than or equal to the second moisture value, it is determined that the formation current of the battery cell in the above processing on the battery cell carrier is the second current and the formation method is the above unconstrained formation, and the second current is less than the first current.

[0054] The second moisture value typically ranges from 48 ppm to 52 ppm. For example, the second moisture value can be set to 49 ppm, 50 ppm, or 51 ppm, with 50 ppm being the preferred value. The 50 ppm moisture standard, compared to lower values ​​(such as 20 ppm), relaxes the requirements for internal battery moisture to some extent. Although the 50 ppm moisture content is somewhat relaxed compared to lower levels, it is still far below the threshold that can cause severe internal reactions (such as hydrolysis producing large amounts of gas). This helps prevent excessive internal pressure from suddenly occurring during battery formation, reducing the risk of thermal runaway, explosions, and other safety accidents. Since the target cell in the processing stage is generally the cell with the highest moisture content, if the target moisture value of the target cell is less than or equal to the second moisture value, it proves that the moisture values ​​of all other cells in the processing stage are less than the second moisture value. That is, there are cells in the processing stage with moisture values ​​greater than the first moisture value. In this case, it is necessary to use a low-current formation process or a confinement formation method to reduce the probability of brown spots forming in the cell.

[0055] The above steps preferably employ a low-current formation process because, compared to constrained formation, it requires fewer additional mechanical devices. For example, it does not require specialized fixtures to limit cell expansion, thus offering a cost advantage while reducing equipment investment and maintenance costs. Low-current formation is relatively simple to implement, requiring no complex mechanical structures or additional operating steps, reducing the complexity of the production process and potential failure points. Therefore, when the target moisture content of the cell is less than or equal to the second moisture content, the low-current formation process is preferred. However, in some special cases, a constrained formation process can also be used; the choice between the two is sufficient.

[0056] Step S1023: In the case that the target moisture value of the battery cell in the above target processing is greater than the second moisture value and less than or equal to the third moisture value, it is determined that the formation current of the battery cell in the above processing on the battery cell carrier is the third current and the formation method is the above restraint formation, and the third current is less than the second current.

[0057] The third moisture value typically ranges from 96 ppm to 102 ppm. For example, it can be set to 98 ppm, 99 ppm, or 100 ppm, with 100 ppm being preferred. 100 ppm is the maximum moisture value required, a preset value obtained by comprehensively considering factors such as electrolyte formulation, membrane type, and cell structure. Since the target cell in the processing is generally the one with the highest moisture content, if the target moisture value of the target cell is less than or equal to the third moisture value, it proves that the moisture values ​​of all other cells in the processing are less than the third moisture value. That is, there are cells in the processing with moisture values ​​greater than the second moisture value. In this case, using only low-current formation or confinement formation is insufficient to reduce brown spots on the cells. Therefore, both low-current formation and confinement formation are needed simultaneously to reduce brown spots on the cells.

[0058] In some embodiments, if the target moisture value of the battery cell is greater than the third moisture value during the target processing, the battery cell is directly discarded.

[0059] Step S103: The above-mentioned formation processing parameters are used to perform formation processing on the battery cell carrier to at least reduce the amount of gas generated by the battery cell carrier during the formation process, so as to reduce the brown spot coverage rate on the surface of the battery cell carrier.

[0060] During the formation process, the electrochemical reactions inside the battery cell generate gases, primarily hydrogen and carbon dioxide. The amount of gas produced is influenced by various factors, with moisture content being a key parameter. Moisture decomposes in the electrolyte to produce gas, accelerating the formation of the SEI film and leading to localized lithium plating, resulting in visible brown spots. The formation current directly affects the cell formation rate and gas production. A smaller current slows down the electrochemical reaction, thus reducing the amount of gas produced during formation. Unconstrained and constrained formation correspond to different gas production control strategies. Unconstrained formation allows the battery cell to expand freely and is suitable for situations with low gas production; while constrained formation restricts cell expansion through mechanical pressure and is suitable for situations with high gas production, but may also introduce additional costs and complexity. By adjusting the formation process parameters and effectively controlling the gas production during formation, localized lithium plating caused by gas pressure on the cell surface can be reduced, thereby significantly reducing the coverage of brown spots on the cell surface.

[0061] The above-mentioned method for preparing secondary batteries in this application first obtains the target moisture value of the battery cell in the target treatment;

[0062] Subsequently, if the target moisture value of the battery cell in the target processing is less than or equal to the first moisture value, the formation current of the battery cell on the battery cell carrier during processing is determined to be the first current and the formation method is unconstrained formation; if the target moisture value of the battery cell in the target processing is greater than the first moisture value and less than or equal to the second moisture value, the formation current of the battery cell on the battery cell carrier during processing is determined to be the second current and the formation method is unconstrained formation, with the second current being less than the first current; if the target moisture value of the battery cell in the target processing is greater than the second moisture value and less than or equal to the third moisture value, the formation current of the battery cell on the battery cell carrier during processing is determined to be the third current and the formation method is constrained formation, with the third current being less than the second current;

[0063] Finally, the above-mentioned formation processing parameters are used to perform formation processing on the battery cell carrier to at least reduce the amount of gas generated by the battery cell carrier during the formation process, thereby reducing the brown spot coverage on the surface of the battery cell carrier.

[0064] This method determines whether a battery cell is prone to brown spots by measuring its moisture content. When the moisture content is high, the method reduces the current during the formation process to decrease gas production per unit time and uses confinement formation to facilitate gas expulsion, thereby reducing brown spots. This solves the problem that existing battery manufacturing methods easily cause brown spots in the prepared battery cells, leading to a decrease in battery performance.

[0065] In some embodiments, the first current is greater than or equal to 0.1C and less than 0.3C, the second current is greater than 0.02C and less than 0.1C, and the third current is greater than 0.018C and less than or equal to 0.02C, where C is the rated capacity of the battery cell in the above process. Preferably, the third current is 0.02C.

[0066] For example, if a battery has a rated capacity of 1000mAh (1Ah), then the formation current at 0.1C is 100mA, and the formation current at 0.02C is 20mA. The specific current setting also depends on the manufacturer's process requirements, formation time, and considerations for battery performance and safety. Typically, the formation process is divided into multiple stages, and different current and voltage settings may be used in different stages.

[0067] Specifically, 0.1C to 0.3C is generally the normal formation current, and it is used when the cell moisture content is low. 0.02C to 0.2C is a smaller current, meaning a lower current is used for the formation treatment of the cell. This results in a slower lithium-ion deposition rate, which helps to ensure uniform lithium-ion deposition on the negative electrode surface, avoiding side reactions caused by excessively high local concentrations, such as the precipitation of metallic lithium, and thus reducing the formation of brown spots. Furthermore, low-current formation provides a relatively mild electrochemical environment, helping to control the reaction rate inside the cell, reducing local overheating, and preventing electrolyte decomposition and the formation of harmful substances under high-temperature conditions, effectively reducing brown spots on the cell.

[0068] In some embodiments, the target moisture value of the battery cell in the above-mentioned target treatment is greater than the first moisture value and less than or equal to the second moisture value. The above-mentioned formation treatment parameters are used to perform formation treatment on the battery cell carrier, including the following steps:

[0069] Step S201: The second current is used as the initialization current to perform the first formation process on the battery cell in the above-mentioned process on the battery cell carrier.

[0070] Step S202: During the first formation process of the battery cell in the above-mentioned processing on the battery cell carrier, the liquid level of the formation cup of the target battery cell in the above-mentioned processing is detected in real time to obtain the liquid level of the first formation cup. The formation cup is a container that carries the electrolyte of the target battery cell in the above-mentioned processing during the above-mentioned formation process.

[0071] Step S203: When the liquid level in the first formation cup is less than or equal to the first preset liquid level, the second current is used to continue to perform the first formation process on the battery cell on the battery cell carrier.

[0072] Step S204: If the liquid level in the first formation cup is greater than the first preset liquid level, reduce the formation current until the liquid level in the first formation cup is less than or equal to the first preset liquid level or the formation current is the third current.

[0073] Generally, the first preset liquid level ranges from 76ml to 84ml. For example, the first preset liquid level can be set to 78ppm, 80ppm, or 82ppm, preferably 80ml. During the formation process, the water in the electrolyte and the lithium replenishment reaction of the battery cell itself will generate a certain amount of gas. The first preset liquid level of 80ml is equivalent to setting a maximum threshold for the gas volume in the formation cup. This helps to ensure precise control of gas generation and emission, preventing excessive gas accumulation. Specifically, a suitable formation current is first set according to the target moisture value (i.e., if the target moisture value is greater than the first moisture value and less than or equal to the second moisture value, a smaller formation current, i.e., the second current, needs to be set). During the formation process using the second current, the liquid level in the formation cup of the battery cell in the target processing is monitored in real time. The first preset liquid level is the upper limit set according to the battery cell design and the safety standards of the formation process. If the liquid level in the first formation cup is greater than the first preset liquid level, it proves that the gas production under the current formation current setting is too high. At this time, the formation current needs to be reduced immediately to reduce the electrochemical reaction rate and gas production.

[0074] If the electrolyte level in the formation cup is too high, it can lead to electrolyte overflow, damage to the cell structure, and safety accidents. It can also increase the amount of brown spots on the outer ring of the cell. The above steps, by precisely controlling the formation current and monitoring the electrolyte level in the formation cup in real time, ensure that the gas production during the formation process is maintained at a safe and stable level, avoiding an increase in the coverage of brown spots on the cell surface caused by excessively fast reaction speed and excessive gas accumulation.

[0075] Furthermore, the above steps only monitor the liquid level in the formation cup of the target cell. Therefore, the target cell has the highest moisture content among all the cells in the process. Similarly, it can be inferred that the target cell produces the most gas among all the cells in the process. Therefore, it is only necessary to detect the liquid level in the formation cup of the target cell.

[0076] In some embodiments, the target moisture value of the battery cell in the above-mentioned target treatment is greater than the second moisture value and less than or equal to the third moisture value. The above-mentioned formation treatment parameters are used to perform formation treatment on the battery cell carrier in the above-mentioned treatment, including the following steps:

[0077] Step S301: The battery cell in the above-mentioned process is subjected to a second formation process using the third current and the restraint formation method described above.

[0078] Step S302: During the second formation process of the battery cell in the above-mentioned processing on the battery cell carrier, the liquid level of the formation cup of the battery cell in the target processing is detected in real time to obtain the liquid level of the second formation cup.

[0079] Step S303: Based on the liquid level in the second formation cup, determine the pressure treatment method of the battery cell in the process on the battery cell carrier, and perform the second formation treatment on the battery cell in the process on the battery cell carrier using the pressure treatment method. The pressure treatment method is either alternating between negative pressure and normal pressure or alternating between normal pressure and vacuum.

[0080] Specifically, the third current is typically lower than the second current. Choosing a lower current for formation aims to reduce the electrochemical reaction rate, thereby decreasing gas generation during cell formation in high-moisture environments. This avoids a sharp increase in internal pressure due to rapid gas generation, reducing instability during SEI film formation and lowering the likelihood of lithium plating and brown spots. Constraint formation uses external mechanical pressure (such as clamps) to limit cell expansion during the formation process, making it particularly suitable for high-moisture cells. It helps maintain the cell's structural integrity and stability under internal gas generation pressure, preventing cell deformation and reducing problems such as poor contact and internal short circuits caused by deformation. It also facilitates uniform gas discharge, avoiding problems caused by localized gas accumulation.

[0081] Real-time monitoring of the liquid level in the formation cup is a crucial step in monitoring gas generation during the cell formation process. A rise in the liquid level reflects an increase in gas generation within the cell; therefore, monitoring changes in the liquid level allows for timely understanding of gas generation during formation. Based on the monitored liquid level in the second formation cup, the system determines one of two different pressure handling methods: alternating negative and normal pressure or alternating normal pressure and vacuum. Both methods aim to better control gas emissions during cell formation, ensuring that gas is effectively removed without affecting the cell's structure and performance.

[0082] In some embodiments, based on the liquid level in the second formation cup, the pressure treatment method of the battery cell in the process on the battery cell carrier is determined, and the second formation treatment is performed on the battery cell in the process on the battery cell carrier using the pressure treatment method, including the following steps:

[0083] Step S30311: When the liquid level in the second formation cup is less than or equal to the second preset liquid level, it is determined that the second formation process is performed on the battery cell on the battery cell carrier by alternating negative pressure and normal pressure, and the single application duration of negative pressure is determined to be the first duration and the single application duration of normal pressure is determined to be the second duration.

[0084] Step S30312: The battery cell in the above-mentioned process is subjected to the above-mentioned second formation process on the battery cell carrier by the above-mentioned alternating negative pressure and normal pressure, wherein the time for applying the above-mentioned negative pressure each time is the above-mentioned first duration, and the time for applying the above-mentioned normal pressure each time is the above-mentioned second duration.

[0085] Generally, the second preset liquid level ranges from 96 ml to 102 ml. For example, the second preset liquid level can be set to 98 ppm, 99 ppm, or 100 ppm, preferably 100 ml. A liquid level threshold of 100 ml provides a larger buffer for gas emissions during the formation process, which is especially important for cells where gas production increases due to larger lithium replenishment, slightly higher moisture content, or other reasons. A higher preset liquid level can reduce the frequency of shutdowns for adjustments caused by sudden increases in cell gas production during the formation process, avoiding the resulting decrease in production efficiency and additional production costs.

[0086] The first and second durations are generally in the range of 55 to 65 minutes. For example, the first duration can be set to 56, 60, or 63 minutes, preferably 60 minutes; the second duration can be set to 56, 60, or 63 minutes, preferably 60 minutes. The negative pressure is generally -80 ± 10 kPa, for example, -90 kPa, -80 kPa, or -70 kPa. The ambient pressure is generally -0 ± 10 kPa, for example, -10 kPa, 0 kPa, or 10 kPa. The formation of the SEI film (Solid Electrolyte Interface film) is crucial to the initial performance and long-term stability of the battery. Setting the first and second durations of vacuum-breaking and settling under positive and negative pressure to 1 minute can accelerate the formation and maturation of the SEI film, thereby improving the cycle performance and lifespan of the battery. This is because appropriate positive and negative pressure switching helps promote uniform gas discharge and effective electrolyte wetting, creating an environment conducive to SEI film formation. During the formation process, gases generated inside the cell need to be released promptly and effectively to avoid excessive internal pressure. A negative pressure setting of -80±10 kPa ensures efficient gas release while keeping it within a safe range, preventing electrolyte loss or battery damage due to excessive release. At the end of the formation process, restoring the pressure to a normal atmospheric pressure of 0±10 kPa helps maintain the stability and integrity of the cell structure, preventing cell deformation or internal component displacement caused by sudden pressure changes, thereby reducing battery performance fluctuations and potential failures.

[0087] During the second formation process, the liquid level in the formation cup is continuously monitored, with the second preset liquid level used as a criterion. When the liquid level in the second formation cup is less than or equal to the second preset liquid level, it indicates that the current gas production and emission rate are within a reasonable control range. When the second preset liquid level condition is met, a negative pressure and normal pressure alternating method is adopted for gas emission control. This method periodically applies negative pressure and normal pressure, using negative pressure to draw out the gas inside the cell, while normal pressure allows the cell to return to its natural state, avoiding over-compression. In actual operation, negative pressure and normal pressure are periodically applied to the cell according to a predetermined first and second duration. The duration of each negative pressure application is the first duration (T1), which aims to accelerate the gas emission rate and reduce the internal pressure of the cell. The duration of each normal pressure application is the second duration (T2), during which the cell can relax and return to its original state, avoiding structural damage.

[0088] Figure 3 This is a schematic diagram of a formation charging process, such as... Figure 3 As shown, the formation process mainly includes several steps: cell positioning, needle bed pressing, charging start, charging termination, and needle bed lifting. First, the cell is positioned, then the needle bed is pressed, which is in a negative pressure environment of -80±5kpa. Then, charging is started, and the negative pressure of -80±5kpa is maintained. After charging is terminated, it is restored to the normal pressure of 0kpa, and finally the needle bed is lifted.

[0089] Figure 4 This is a schematic diagram of the structure of a formation device, such as... Figure 4 As shown, under negative pressure, the negative pressure suction nozzle 50 draws in the electrolyte from the battery cell 20 and stores it in the buffer cup 60, allowing the electrolyte to flow within the device. Simultaneously, it removes gas from the battery cell 20. The negative pressure suction nozzle 50 can precisely control the electrolyte flow direction under negative pressure. The manifold 70 collects the electrolyte from each buffer cup 60 and directs it to the buffer tank 80. The buffer tank 80 is externally connected to a vacuum and stores the electrolyte, preventing external impurities from contaminating the electrolyte, providing a buffer space, stabilizing the electrolyte supply, and ensuring continuous and stable operation of the device. In some embodiments, methods such as... Figure 3 The formation and charging process shown and as follows Figure 4 The formation device shown performs formation processing on the battery cell.

[0090] Furthermore, during the second formation process of the battery cell on the battery cell carrier using alternating negative and normal pressure, a formation current of 0.02C is used during the negative pressure process and a formation current of 0.1C is used during the normal pressure process.

[0091] Under negative pressure, a formation current as low as 0.02C is used to further slow down the electrochemical reaction rate, reduce the amount of gas generated by water decomposition, and ensure that ions in the electrolyte have sufficient opportunity to participate in the reaction to form a uniform and stable SEI film. Low-current formation under negative pressure helps control internal gas emissions, reduces internal pressure, and decreases the risk of lithium plating. Under normal pressure, the external pressure of the cell returns to normal, at which point a relatively higher formation current (e.g., 0.1C) can be used to improve formation efficiency and shorten the formation cycle. Normal pressure allows the internal pressure of the cell to adjust naturally, avoiding the impact of excessive external pressure on the cell structure.

[0092] By employing low-current formation during the negative pressure stage, the rapid generation of gas is reduced, preventing localized gas accumulation and brown spot formation within the cell. Returning to normal current formation during the atmospheric pressure stage helps improve formation efficiency. The combination of these two methods significantly reduces brown spot coverage on the cell surface.

[0093] In some embodiments, based on the liquid level in the second formation cup, the pressure treatment method of the battery cell in the process on the battery cell carrier is determined, and the second formation treatment is performed on the battery cell in the process on the battery cell carrier using the pressure treatment method, including the following steps:

[0094] Step S30321: When the liquid level in the second formation cup is greater than the second preset liquid level, it is determined that the second formation process is performed on the battery cell on the battery cell carrier by alternating atmospheric pressure and vacuum, and the single application time of atmospheric pressure is determined to be the third time and the single application time of vacuum is determined to be the fourth time.

[0095] Step S30322: The battery cell on the battery cell carrier is subjected to the second formation process by alternating atmospheric pressure and vacuum, until the liquid level in the second formation cup is less than or equal to the second preset liquid level. The time for applying atmospheric pressure each time is the third duration, and the time for applying vacuum each time is the fourth duration.

[0096] Specifically, the third and fourth durations are generally between 55 and 65 minutes. For example, the first duration can be set to 56, 60, or 63 minutes, preferably 60 minutes; the second duration can be set to 56, 60, or 63 minutes, preferably 60 minutes. The atmospheric pressure is generally -0 ± 10 kPa, for example, -10 kPa, 0 kPa, or 10 kPa. When the liquid level in the second formation cup is greater than the second preset liquid level, it indicates that the gas production during the cell formation process has exceeded the range that can be effectively controlled by conventional treatment (such as alternating negative and atmospheric pressure), and a stronger gas emission strategy is required. In this case, alternating atmospheric pressure and vacuum is used to handle gas emission. Vacuuming involves extracting gas from inside the cell in a vacuum environment to accelerate gas emission, reduce the internal pressure of the cell and the liquid level in the formation cup, and increasing venting can also effectively reduce the production of brown spots on the cell. The atmospheric pressure stage is to allow the cell to return to a normal external pressure environment and avoid the adverse effects of continuous vacuuming on the cell structure. The duration of a single application of atmospheric pressure is determined as the third duration (T3), and the duration of a single application of vacuum is determined as the fourth duration (T4). The settings of these four durations need to be determined based on the characteristics of the battery cell, the gas generation rate, and the equipment capacity, in order to control the liquid level in the formation cup in the shortest possible time, without affecting the performance and structure of the battery cell (e.g., the formation of brown spots or the overflow of the liquid level in the formation cup).

[0097] In some embodiments, the formation current is stopped during the vacuuming process, that is, the formation reaction of the cell is stopped and gas production is stopped. The gas is first discharged through vacuuming.

[0098] In other embodiments, during the second formation process of the battery cell in the above-mentioned processing on the battery cell carrier, the second formation process of the battery cell in the above-mentioned processing on the battery cell carrier is first performed by alternating negative pressure and normal pressure. This is because alternating negative pressure and normal pressure is a conventional formation process, while alternating normal pressure and vacuum is a formation measure used to deal with excessive gas production. Usually, the problem of excessive gas production will only occur during the formation process (i.e., after a period of formation process). Therefore, the second formation process of the battery cell in the above-mentioned processing on the battery cell carrier is first performed by alternating negative pressure and normal pressure. During the second formation process, the liquid level of the second formation cup is monitored in real time. If the liquid level of the second formation cup is greater than the second preset liquid level, the formation process is started by alternating normal pressure and vacuum.

[0099] In some embodiments, the target processed cell is a processed cell in which lithium-adding material has been added using a lithium-adding process. The formation processing parameters of the processed cell on the cell carrier are determined based on at least the target moisture value of the target processed cell, including the following steps:

[0100] Step S401: When the target moisture value of the cell in the above target treatment is less than or equal to the first moisture value and the lithium replenishment amount of the cell in the above target treatment is less than or equal to the first lithium replenishment amount, it is determined that the formation current of the cell in the above treatment on the cell carrier is the fourth current and the formation method is the above unrestrained formation.

[0101] In step S402, if the target moisture value of the cell in the above target treatment is greater than the first moisture value and less than or equal to the second moisture value, and the lithium replenishment amount of the cell in the above target treatment is greater than the first lithium replenishment amount and less than or equal to the second lithium replenishment amount, then the formation current of the cell in the above treatment on the cell carrier is determined to be the fifth current and the formation method is the above unconstrained formation, and the fifth current is less than the fourth current.

[0102] In step S403, if the target moisture value of the cell in the above target treatment is greater than the second moisture value and less than or equal to the third moisture value, and the lithium replenishment amount of the cell in the above target treatment is greater than the second lithium replenishment amount and less than or equal to the third lithium replenishment amount, then the formation current of the cell in the above treatment on the cell carrier is determined to be the sixth current and the formation method is the above restraint formation, wherein the sixth current is less than the fifth current.

[0103] The cells being processed can be categorized into two types: lithium-added cells and non-lithium-added cells. Lithium-added cells are those that have lithium-added materials added using a lithium-added process, while non-lithium-added cells are those without such materials. For non-lithium-added cells, the amount of gas generated during the formation process can only be determined by detecting the moisture content of the target cell, thus determining the formation parameters. For lithium-added cells, the amount of gas generated during the formation process can be determined by detecting the moisture content of the target cell, or by the amount of lithium added, which is determined at the very beginning of cell manufacturing. In other words, for lithium-added cells, formation parameters can be determined solely by the moisture content of the target cell, solely by the amount of lithium added, or by a combination of both. If the formation parameters are determined by a combination of moisture content and lithium added, and the two criteria contradict each other, the moisture content criterion takes precedence.

[0104] In some embodiments, the range of the first lithium replenishment amount is generally 0.4% to 0.6%. For example, the first lithium replenishment amount can be set to 0.45%, 0.5%, or 0.55%, preferably 0.5%. The range of the second lithium replenishment amount is generally 0.8% to 1.2%. For example, the second lithium replenishment amount can be set to 0.9%, 1%, or 1.1%, preferably 1%. The range of the third lithium replenishment amount is generally 1.8% to 2.2%. For example, the third lithium replenishment amount can be set to 1.9%, 2%, or 2.1%, preferably 2%. Since the lithium replenishment amount is preset during cell manufacturing, there is no situation where the lithium replenishment amount is too high. The value range of the fourth current is greater than or equal to 0.1C and less than 0.3C, the value range of the fifth current is greater than 0.02C and less than 0.1C, and the sixth current is 0.02C, where C is the rated capacity of the cell in the above process.

[0105] Specifically, when the target moisture content of the battery cell is less than or equal to the first moisture content and the lithium replenishment amount is less than or equal to the first lithium replenishment amount, it indicates that the battery cell is in a good initial state, with low moisture content and low lithium replenishment requirements. Therefore, the fourth current is selected for the formation current. This current value is usually higher than that used under conditions of high moisture content or high lithium replenishment amount, which can complete the formation process faster and improve production efficiency. If the moisture content of the battery cell exceeds the first moisture content but does not exceed the second moisture content, and the lithium replenishment amount exceeds the first lithium replenishment amount but does not exceed the second lithium replenishment amount, it indicates that the moisture content and lithium replenishment requirements of the battery cell are moderate. In order to prevent excessive gas generation from moisture decomposition and control the formation of the SEI film, the fifth current needs to be selected for the formation current, and the fifth current should be less than the fourth current. This slows down the formation rate, reduces the gas generation rate, thereby reducing gas pressure and internal stress, and reducing the formation of brown spots in the battery cell. When the moisture content of the battery cell exceeds the second moisture content and the lithium replenishment amount exceeds the second lithium replenishment amount, the internal environment of the battery cell becomes more complex, and the amount of gas generated by moisture decomposition and the action of the lithium replenishment agent increases significantly. In this case, the formation current is selected as the sixth current, which is less than the fifth current. The purpose is to further slow down the electrochemical reaction rate, reduce gas production, avoid excessive internal pressure in the cell, and further reduce the formation of brown spots in the cell.

[0106] In some embodiments, before determining the performance parameters of the battery cell in the target processing, the above method further includes the following steps:

[0107] Step S501: Obtain the basic parameters of each of the processed cells on the cell carrier. The basic parameters of the processed cells include the weight and thickness of the processed cells. The thickness of the processed cells is positively correlated with the width of the electrolyte channel of the processed cells.

[0108] Step S502: If there are two cells in the above-mentioned process that have a weight difference greater than a preset weight difference among all the cells in the above-mentioned process on the cell carrier, then the cell in the above-mentioned process with the largest weight is determined as the target cell in the above-mentioned process.

[0109] Step S503: If the weight difference between any two cells in the above-mentioned processing on the cell carrier is less than or equal to the preset weight difference, then the cell with the smallest thickness among all the cells in the above-mentioned processing on the cell carrier is determined as the target cell in the above-mentioned processing.

[0110] Specifically, the target cell can be one or more. By detecting the weight and / or thickness of the cell, the target cell can be identified as a cell with a high moisture content.

[0111] Since cells with higher moisture content tend to be heavier, weight is used as a selection criterion for target cells. Furthermore, a thinner cell indicates a more compacted cell, meaning the distance between the positive and negative electrodes is closer, resulting in a shorter diffusion path for moisture within the cell. However, this also means that moisture must pass through narrower channels—so-called moisture channels—to permeate from one side of the cell to the other. As cell thickness decreases, the compression of the electrodes and separator may increase, leading to narrower moisture channels. Narrow channels increase resistance to moisture diffusion, resulting in uneven moisture distribution within the cell, particularly between the edges and the center. Before entering the production process, cells typically undergo baking to remove moisture (i.e., high-temperature settling). While a thinner cell may appear to offer higher baking efficiency (because heat penetrates more easily), the presence of narrow channels can actually hinder the complete removal of moisture in certain areas, especially in denser structures or areas where heat is less efficient. In other words, a thinner battery cell may make it more difficult to completely remove moisture from the inside of the cell, thus increasing the moisture content of the cell. Therefore, in addition to weight, thickness can also be used as a selection criterion for target battery cells.

[0112] Therefore, by detecting the weight and / or thickness of the battery cells, it is possible to accurately identify battery cells with higher moisture content, which means it is possible to accurately identify the battery cells to be processed.

[0113] Based on the above reasons, in addition to cell weight and thickness, the compaction pressure of the cell can also be used to screen for target cells, because the compaction pressure mainly reflects the density of the internal materials of the cell. The greater the compaction pressure, the greater the density of the internal materials of the cell, and the smaller the thickness of the cell.

[0114] In some embodiments, when the formation method is the above-mentioned restraint formation, during the formation process, a mechanical clamp is used to restrain the processed battery cell on the battery cell carrier to perform the above-mentioned restraint formation on the battery cell carrier.

[0115] Specifically, the mechanical fixture effectively controls the expansion and morphological changes of the battery cell during the formation process by applying a certain amount of mechanical pressure. This external pressure helps the gas inside the cell diffuse and escape more evenly, avoiding lithium plating and uneven SEI film formation caused by localized high pressure, and reducing the formation of brown spots on the cell. During the confinement formation process, the battery cell is fixed by the mechanical fixture on the cell carrier; this process continues throughout the entire formation process. Confinement formation reduces the random emission of gas inside the cell, reducing the formation of surface defects (such as brown spots) caused by uneven gas distribution.

[0116] To enable those skilled in the art to better understand the technical solution of this application, the implementation process of the secondary battery preparation method of this application will be described in detail below with reference to specific embodiments.

[0117] This embodiment relates to a specific method for preparing a secondary battery, such as... Figure 5 As shown, the method includes the following steps:

[0118] Step S1: First, inject electrolyte and let all the cells undergoing processing stand.

[0119] Step S2: Detect the moisture value of the battery cell with the highest moisture content in the target processing.

[0120] Step S31: When the moisture content of the battery cell is less than or equal to 20 ppm in the target treatment, a normal formation process (i.e., formation current of 0.1C to 0.3C and unconstrained formation) is adopted.

[0121] Step S32: When the moisture content of the battery cell in the target treatment is greater than 20 ppm and less than or equal to 50 ppm, a small current of 0.1C to 0.02C is used for formation, and unrestrained formation is performed. During the formation process, the liquid level in the formation cup is monitored in real time. If the liquid level in the formation cup is less than or equal to 80 ml, the small current of 0.1C to 0.02C is used for formation. If the liquid level in the formation cup is greater than 80 ml, the formation current is further reduced.

[0122] Step S33: When the moisture content of the battery cell in the target processing is greater than 50 ppm and less than or equal to 100 ppm, the cell is formed by confinement and small current of 0.02C. The liquid level of the forming cup is monitored in real time during the forming process. If the liquid level of the forming cup is less than or equal to 100 ml, the forming process continues. If the liquid level of the forming cup is greater than 100 ml, the gas in the battery cell is extracted by alternating atmospheric pressure vacuuming until the liquid level of the forming cup is less than or equal to 100 ml and the forming process ends.

[0123] Step S34: If the moisture content of the battery cell is greater than 100 ppm in the target treatment, the battery cell shall be discarded.

[0124] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0125] Comparative Example 1

[0126] A secondary battery was prepared using a cell that underwent a first-target treatment. This cell was a lithium-added cell, and the lithium-added agent used was metallic lithium, with a lithium-added amount of 1%. The target moisture content of the cell was 50 ppm. The cell underwent liquid injection treatment, high-temperature standing treatment, and normal current formation treatment in sequence to prepare the secondary battery. The formation current used in the normal current formation treatment was 0.2C and it was unconstrained formation. The secondary battery finally prepared had circular brown spots with a diameter of 3 mm.

[0127] Example 1

[0128] A secondary battery was prepared using a cell that underwent a first-target treatment. This cell was a lithium-added cell, and the lithium-adding agent used was metallic lithium, with a lithium-adding amount of 1%. The target moisture content of the cell was 50 ppm. The cell underwent sequential liquid injection treatment, high-temperature settling treatment, and low-current formation treatment to prepare the secondary battery. The formation current used in the above-mentioned normal current formation treatment was 0.05C and it was unconstrained formation. The final secondary battery prepared had no brown spots. The difference between Example 1 and Comparative Example 1 is that the latter used a low-current formation treatment.

[0129] Comparative Example 2

[0130] A secondary battery was prepared using a cell that underwent a first target treatment. This cell was a lithium-added cell, and the lithium-added agent used was metallic lithium with a lithium-added amount of 2%. The target moisture content of the cell was 100 ppm. The cell underwent liquid injection treatment, high-temperature static treatment, and normal current formation treatment in sequence to prepare the secondary battery. The normal current formation treatment used a formation current of 0.2C and was unconstrained formation. The final secondary battery had circular brown spots with a diameter of 4 mm.

[0131] Example 2

[0132] A secondary battery was prepared using a cell that underwent a first-target treatment. This cell was a lithium-added cell, and the lithium-adding agent used was metallic lithium, with a lithium-adding amount of 2%. The target moisture content of the cell was 100 ppm. The cell underwent sequential liquid injection treatment, high-temperature settling treatment, and low-current formation treatment to prepare the secondary battery. The formation current used in the above-mentioned normal current formation treatment was 0.02C and it was a constrained formation process. The final secondary battery prepared had no brown spots. The difference between Example 2 and Comparative Example 2 is that the latter used a low-current formation treatment and a constrained formation treatment.

[0133] Comparative Example 3

[0134] A secondary battery was prepared using a cell in the second target treatment process. The cell in the second target treatment process was a non-lithium-added cell with a target moisture content of 50 ppm. The cell in the second target treatment process was subjected to liquid injection treatment, high-temperature static treatment, and normal current formation treatment in sequence to prepare the secondary battery. The formation current used in the above-mentioned normal current formation treatment was 0.2C and it was unconstrained formation. The secondary battery finally prepared had circular brown spots with a diameter of 3 mm.

[0135] Example 3

[0136] A secondary battery was prepared using a cell from the second target treatment process. This second target treatment cell was a non-lithium-added cell with a target moisture content of 50 ppm. The cell underwent sequential electrolyte injection, high-temperature settling, and low-current formation treatment to obtain the secondary battery. The low-current formation treatment used a formation current of 0.05C and employed unconstrained formation. The final secondary battery showed no brown spots. The difference between Example 3 and Comparative Example 3 is the use of a low-current formation treatment.

[0137] Comparative Example 4

[0138] A secondary battery was prepared using a cell in the second target treatment process. The cell in the second target treatment process was a non-lithium-added cell with a target moisture content of 100 ppm. The cell in the second target treatment process was subjected to electrolyte injection treatment, high-temperature static treatment, and normal current formation treatment in sequence to prepare the secondary battery. The formation current used in the above-mentioned normal current formation treatment was 0.2C and it was unconstrained formation. The secondary battery finally prepared had circular brown spots with a diameter of 6 mm.

[0139] Example 4

[0140] A secondary battery was prepared using a cell from the second target treatment process. This second target treatment cell was a non-lithium-added cell with a target moisture content of 100 ppm. The cell was subjected to sequential electrolyte injection, high-temperature settling, and low-current formation treatment to obtain the secondary battery. The low-current formation treatment used a formation current of 0.02C and employed restraint formation. The final secondary battery was free of brown spots. The difference between Example 4 and Comparative Example 4 lies in the use of low-current formation treatment and restraint formation treatment.

[0141] The comparison results between the final embodiment and the comparative example are shown in Table 1:

[0142] Table 1. Comparison Results of Examples and Comparative Examples

[0143]

[0144]

[0145] As shown in Table 1, when the moisture content or lithium replenishment content of the battery cell in the target processing is large, the use of low current formation process and confinement formation process can effectively reduce the generation of brown spots in the battery cell.

[0146] This application also provides a secondary battery, which is prepared using any of the above-described methods for preparing a secondary battery.

[0147] The aforementioned secondary battery is prepared using any of the above-mentioned secondary battery preparation methods. Since the above-mentioned preparation method determines whether the cell is prone to brown spots by the cell moisture value, and reduces the gas production per unit time during the formation process by reducing the current when the moisture value is high, and makes the gas easier to expel by confining the formation process, the brown spots are reduced. This solves the problem that the existing battery preparation methods easily cause brown spots in the prepared cells, which leads to a decrease in battery performance. Therefore, the secondary battery prepared by the above-mentioned preparation method has fewer brown spots.

[0148] This application also provides an energy storage system, including at least one of the above-described secondary batteries.

[0149] In energy storage systems, battery consistency is crucial to system performance. Reducing the number of brown spots helps minimize variations in battery performance, improves the overall consistency of the battery pack, and ensures stability and smoothness during charging and discharging. The aforementioned energy storage system utilizes rechargeable batteries with fewer brown spots. Batteries with fewer brown spots have longer lifespans and higher efficiency. This not only reduces the replacement cost of the batteries themselves but also reduces the system adjustment and optimization costs caused by battery performance fluctuations, thereby lowering the overall operating cost of the energy storage system.

[0150] In summary, fewer brown spots in secondary batteries mean longer lifespan, higher energy efficiency, more stable operation, lower safety risks, better charge / discharge performance, better battery pack consistency, and more economical system costs for energy storage systems. These factors work together to significantly improve the reliability and economic benefits of energy storage systems.

[0151] This application also provides an electrical device, including: at least one of the above-described secondary batteries or the above-described energy storage system.

[0152] Battery reliability directly impacts the overall reliability of electronic devices. Fewer brown spots mean the battery performs more stably under various environmental conditions, reducing the failure rate of electronic devices due to battery malfunctions and improving device durability and reliability. Using rechargeable batteries with fewer brown spots in electronic devices can significantly improve device performance, safety, and reliability, extend device lifespan, reduce maintenance costs, and is also more environmentally friendly, aligning with the concepts of green manufacturing and sustainable development.

[0153] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0154] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0155] The method for preparing the secondary battery described in this application first obtains the target moisture value of the cell in the target treatment. Then, if the target moisture value of the cell in the target treatment is less than or equal to a first moisture value, the formation current of the cell in the treatment on the cell carrier is determined to be a first current and the formation method is unconstrained formation. If the target moisture value of the cell in the target treatment is greater than the first moisture value and less than or equal to a second moisture value, the formation current of the cell in the treatment on the cell carrier is determined to be a second current and the formation method is unconstrained formation, with the second current being less than the first current. If the target moisture value of the cell in the target treatment is greater than the second moisture value and less than or equal to a third moisture value, the formation current of the cell in the treatment on the cell carrier is determined to be a third current and the formation method is constrained formation, with the third current being less than the second current. Finally, the aforementioned formation treatment parameters are used to perform formation treatment on the cell in the treatment on the cell carrier to at least reduce the amount of gas generated by the cell in the treatment on the cell carrier during the formation treatment process, thereby reducing the brown spot coverage rate on the surface of the cell in the treatment on the cell carrier. This method determines whether a battery cell is prone to brown spots by measuring its moisture content. When the moisture content is high, the method reduces the current during the formation process to decrease gas production per unit time and uses confinement formation to facilitate gas expulsion, thereby reducing brown spots. This solves the problem that existing battery manufacturing methods easily cause brown spots in the prepared battery cells, leading to a decrease in battery performance.

[0156] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing a secondary battery, characterized by, include: After subjecting the battery cells on the battery cell carrier to high-temperature static treatment for a preset time, the target moisture value of the target battery cells is obtained. The target battery cells are a portion of the battery cells on the battery cell carrier. The formation processing parameters of the battery cell in the process are determined at least based on the target moisture value. The formation processing parameters include at least the formation current and the formation method, wherein the formation method is either unconstrained formation or constrained formation. The formation processing parameters are used to perform formation processing on the cells in the process of processing on the cell carrier, so as to at least reduce the amount of gas generated by the cells in the process of processing on the cell carrier, and reduce the brown spot coverage on the surface of the cells in the process of processing on the cell carrier. Specifically, the formation processing parameters of the battery cell on the battery cell carrier are determined based on at least the target moisture value of the battery cell in the target processing, including: If the target moisture value of the battery cell is less than or equal to the first moisture value during the target treatment, the formation current of the battery cell in the treatment on the battery cell carrier is determined to be the first current and the formation method is the unconstrained formation. In the target processing, if the target moisture value of the battery cell is greater than the first moisture value and less than or equal to the second moisture value, the formation current of the battery cell in the processing on the battery cell carrier is determined to be the second current and the formation method is the unconstrained formation, wherein the second current is less than the first current. In the target processing, if the target moisture value of the battery cell is greater than the second moisture value and less than or equal to the third moisture value, the formation current of the battery cell in the processing on the battery cell carrier is determined to be the third current and the formation method is the restraint formation, wherein the third current is less than the second current. The first current has a value range of greater than or equal to 0.1C and less than 0.3C, the second current has a value range of greater than 0.02C and less than 0.1C, and the third current has a value range of greater than 0.018C and less than or equal to 0.02C, where C is the rated capacity of the battery cell in the process. The first moisture value ranges from 18 ppm to 22 ppm, the second moisture value ranges from 48 ppm to 52 ppm, and the third moisture value ranges from 96 ppm to 102 ppm.

2. The method for preparing a secondary battery according to claim 1, characterized in that, The target moisture value of the battery cell in the target treatment is greater than the first moisture value and less than or equal to the second moisture value. The formation treatment parameters are used to perform formation treatment on the battery cell carrier, including: The second current is used as the initialization current to perform the first formation process on the battery cell on the battery cell carrier. During the first formation process of the battery cell in the processing of the battery cell carrier, the liquid level of the formation cup of the target battery cell in the processing is detected in real time to obtain the liquid level of the first formation cup. The formation cup is a container that carries the electrolyte of the target battery cell in the processing during the formation process. If the liquid level in the first formation cup is less than or equal to the first preset liquid level, the second current continues to be used to perform the first formation process on the battery cell on the battery cell carrier. If the liquid level in the first formation cup is greater than the first preset liquid level, the formation current is reduced until the liquid level in the first formation cup is less than or equal to the first preset liquid level or the formation current is the third current.

3. The method for preparing a secondary battery according to claim 1, characterized in that, The target moisture value of the battery cell in the target treatment is greater than the second moisture value and less than or equal to the third moisture value. The formation treatment parameters are used to perform formation treatment on the battery cell carrier, including: The second formation process is performed on the battery cell on the battery cell carrier using the third current and the constraint formation method. During the second formation process of the battery cell in the processing of the battery cell carrier, the liquid level of the formation cup of the battery cell in the target processing is detected in real time to obtain the liquid level of the second formation cup; Based on the liquid level in the second formation cup, the pressure treatment method of the battery cell in the process on the battery cell carrier is determined, and the second formation treatment is performed on the battery cell in the process on the battery cell carrier using the pressure treatment method, which is either an alternating negative pressure and normal pressure method or an alternating normal pressure and vacuum method.

4. The method for preparing a secondary battery according to claim 3, characterized in that, Based on the liquid level in the second formation cup, the pressure treatment method for the processed battery cell on the battery cell carrier is determined, and the second formation treatment is performed on the processed battery cell on the battery cell carrier using the pressure treatment method, including: When the liquid level in the second formation cup is less than or equal to the second preset liquid level, it is determined that the second formation process is performed on the battery cell on the battery cell carrier by alternating negative pressure and normal pressure, and the single application duration of negative pressure is determined to be the first duration and the single application duration of normal pressure is determined to be the second duration. The second formation process is performed on the battery cell on the battery cell carrier by alternating negative and normal pressure, wherein the duration of each negative pressure application is the first duration, and the duration of each normal pressure application is the second duration.

5. The method for preparing a secondary battery according to claim 3, characterized in that, Based on the liquid level in the second formation cup, the pressure treatment method for the processed battery cell on the battery cell carrier is determined, and the second formation treatment is performed on the processed battery cell on the battery cell carrier using the pressure treatment method, including: When the liquid level in the second formation cup is greater than the second preset liquid level, it is determined that the second formation process is performed on the battery cell on the battery cell carrier by alternating atmospheric pressure and vacuum, and the single application time of atmospheric pressure is determined to be the third time and the single application time of vacuum is determined to be the fourth time. The battery cell on the battery cell carrier is subjected to the second formation process by alternating atmospheric pressure and vacuum, until the liquid level in the second formation cup is less than or equal to the second preset liquid level. The time for each application of atmospheric pressure is the third duration, and the time for each application of vacuum is the fourth duration.

6. The method for preparing a secondary battery according to claim 1, characterized in that, The target processed battery cell is a processed battery cell that has undergone a lithium replenishment process with added lithium replenishment material. The formation processing parameters of the processed battery cell on the battery cell carrier are determined at least based on the target moisture value of the target processed battery cell, including: If the target moisture value of the cell in the target treatment is less than or equal to the first moisture value and the lithium replenishment amount of the cell in the target treatment is less than or equal to the first lithium replenishment amount, then the formation current of the cell in the treatment on the cell carrier is determined to be the fourth current and the formation method is the unconstrained formation. In the case where the target moisture value of the battery cell in the target treatment is greater than the first moisture value and less than or equal to the second moisture value, and the lithium replenishment amount of the battery cell in the target treatment is greater than the first lithium replenishment amount and less than or equal to the second lithium replenishment amount, the formation current of the battery cell in the treatment on the battery cell carrier is determined to be the fifth current and the formation method is the unconstrained formation, wherein the fifth current is less than the fourth current. If, in the target processing, the target moisture value of the cell is greater than the second moisture value and less than or equal to the third moisture value, and the lithium replenishment amount of the cell in the target processing is greater than the second lithium replenishment amount and less than or equal to the third lithium replenishment amount, then the formation current of the cell in the processing on the cell carrier is determined to be the sixth current and the formation method is the restraint formation, wherein the sixth current is less than the fifth current.

7. The method for preparing a secondary battery according to claim 1, characterized in that, Before determining the performance parameters of the battery cells in the target process, the method further includes: Obtain the basic parameters of each of the processed cells on the cell carrier, wherein the basic parameters of the processed cell include the weight of the processed cell and the thickness of the processed cell, and the thickness of the processed cell is positively correlated with the width of the electrolyte channel of the processed cell; If there are two cells in the process of being processed on the cell carrier whose weight difference is greater than a preset weight difference, then the cell in the process of being processed with the largest weight is determined as the target cell in the process of being processed. If the weight difference between any two cells in the process of processing on the cell carrier is less than or equal to the preset weight difference, then the cell with the smallest thickness among all the cells in the process of processing on the cell carrier is determined as the target cell in the process of processing.

8. The method for preparing a secondary battery according to any one of claims 1 to 7, characterized in that, When the formation method is the constraint formation, during the formation process, a mechanical clamp is used to constrain the processed battery cell on the battery cell carrier to perform the constraint formation on the battery cell carrier.

9. A secondary battery, characterized in that, The secondary battery is prepared by the method for preparing a secondary battery according to any one of claims 1 to 8.

10. An energy storage system, characterized in that, include: At least one secondary battery as described in claim 9.

11. An electrical appliance, characterized in that, include: At least one secondary battery as described in claim 9 or an energy storage system as described in claim 10.

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