Preparation method of secondary battery, secondary battery, energy storage system and electric equipment

Abstract

The invention relates to the field of energy storage cells, and provides a preparation method of a secondary battery, the secondary battery, an energy storage system and electric equipment, and the method comprises the following steps: performing high-temperature standing treatment on a to-be-treated cell on a cell bearing part for a preset duration, and then obtaining a target moisture value of the to-be-treated cell; according to the target moisture value, formation processing parameters of the processed battery cell on the battery cell bearing part are determined, the formation processing parameters at least comprise formation current and a formation mode, and the formation mode is unrestrained formation or restrained formation; and performing formation treatment on the processed battery cell on the battery cell bearing part by adopting the formation treatment parameters so as to reduce the gas production rate of the processed battery cell on the battery cell bearing part in the formation treatment process and reduce the brown spot coverage rate of the surface of the processed battery cell on the battery cell bearing part. According to the method, gas production in unit time is reduced by reducing current in the formation process according to the moisture value of the battery cell, and gas is easier to discharge by restraining formation, so that brown spots are reduced.

Description

Technical Field

[0001] The present invention relates to the field of energy storage cells, and in particular to a method for preparing a secondary battery, a secondary battery, an energy storage system, and electrical equipment. Background Art

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

[0003] The main purpose of the present invention is to provide a method for preparing a secondary battery, a secondary battery, an energy storage system and an electrical device, so as to solve the problem in the prior art that the battery preparation method easily causes brown spots on the prepared battery cells, thereby leading to a decrease in battery performance.

[0004] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a method for preparing a secondary battery is provided, comprising: obtaining a target moisture value of a target processed cell after subjecting the processed cell on a cell carrier to a high-temperature standing treatment for a preset period of time, wherein the target processed cell is a portion of the processed cell on the cell carrier; determining formation treatment parameters of the processed cell on the cell carrier at least according to the target moisture value, wherein the formation treatment parameters at least include a formation current and a formation mode, wherein the formation mode is unconstrained formation or constrained formation; performing formation treatment on the processed cell on the cell carrier using the formation treatment parameters, so as to at least reduce the gas production of the processed cell on the cell carrier during the formation treatment, so as to reduce the brown spot coverage rate on the surface of the processed cell on the cell carrier; wherein, at least according to the target moisture value of the target processed cell Determining the formation processing parameters of the battery cell being processed on the battery cell carrier includes: when the target moisture value of the battery cell being processed in the target processing is less than or equal to the first moisture value, determining that the formation current of the battery cell being processed on the battery cell carrier is a first current and the formation mode is the unconstrained formation; when the target moisture value of the battery cell being processed in the target processing is greater than the first moisture value and less than or equal to the second moisture value, determining that the formation current of the battery cell being processed on the battery cell carrier is a second current and the formation mode is the unconstrained formation, and the second current is less than the first current; when the target moisture value of the battery cell being processed in the target processing is greater than the second moisture value and less than or equal to a third moisture value, determining that the formation current of the battery cell being processed on the battery cell carrier is a third current and the formation mode is the constrained formation, and the third current is less than the second current.

[0005] Furthermore, the first current has a value range of 0.1C to 0.3C, the second current has a value range of 0.1C to 0.02C, and the third current is 0.02C, wherein C is the rated capacity of the battery cell being processed.

[0006] Furthermore, the target moisture value of the target processed battery cell is greater than the first moisture value and less than or equal to the second moisture value, and the processing battery cell on the battery cell carrier is subjected to the processing processing parameter, including: using the second current as the initialization current to perform the first formation treatment on the processing battery cell on the battery cell carrier; in the process of performing the first formation treatment on the processing battery cell on the battery cell carrier, the liquid level of the formation cup of the target processed battery cell is detected in real time to obtain the first formation cup liquid level, the formation cup being a container for carrying the electrolyte of the target processed battery cell during the formation treatment; when the first formation cup liquid level is less than or equal to the first preset liquid level, continuing to use the second current to perform the first formation treatment on the processing battery cell on the battery cell carrier; when the first formation cup liquid level is greater than the first preset liquid level, reducing the formation current until the first formation cup liquid level is less than or equal to the first preset liquid level or the formation current is the third current.

[0007] Furthermore, the target moisture value of the target processed battery cell is greater than the second moisture value and less than or equal to the third moisture value, and the processed battery cell on the battery cell carrier is subjected to formation treatment using the formation treatment parameters, including: using the third current and constrained formation method to perform a second formation treatment on the processed battery cell on the battery cell carrier; in the process of performing the second formation treatment on the processed battery cell on the battery cell carrier, the liquid level of the formation cup of the target processed battery cell is detected in real time to obtain the second formation cup liquid level; according to the second formation cup liquid level, the pressure treatment method of the processed battery cell on the battery cell carrier is determined, and the pressure treatment method is used to perform the second formation treatment on the processed battery cell on the battery cell carrier, and the pressure treatment method is used to perform the second formation treatment on the processed battery cell on the battery cell carrier, and the pressure treatment method is a negative pressure and normal pressure alternating method or a normal pressure and vacuum alternating method.

[0008] Furthermore, according to the liquid level of the second formation cup, the pressure treatment method of the battery cell being processed on the battery cell carrier is determined, and the pressure treatment method is used to perform the second formation treatment on the battery cell being processed on the battery cell carrier, including: when the liquid level of the second formation cup is less than or equal to the second preset liquid level, determining to use the alternating negative pressure and normal pressure method to perform the second formation treatment on the battery cell being processed on the battery cell carrier, and determining that the single application time of negative pressure is the first time length and the single application time of normal pressure is the second time length; using the alternating negative pressure and normal pressure method to perform the second formation treatment on the battery cell being processed on the battery cell carrier, wherein the time for each application of the negative pressure is the first time length, and the time for each application of the normal pressure is the second time length.

[0009] Furthermore, according to the liquid level of the second formation cup, the pressure treatment method of the battery cell being processed on the battery cell carrier is determined, and the pressure treatment method is used to perform the second formation treatment on the battery cell being processed on the battery cell carrier, including: when the liquid level of the second formation cup is greater than the second preset liquid level, determining to use the alternating method of normal pressure and vacuum to perform the second formation treatment on the battery cell being processed on the battery cell carrier, and determining that the single application time of normal pressure is the third time length and the single application time of vacuum is the fourth time length; using the alternating method of normal pressure and vacuum to perform the second formation treatment on the battery cell being processed on the battery cell carrier until the liquid level of the second formation cup is less than or equal to the second preset liquid level, wherein the time for each application of normal pressure is the third time length, and the time for each application of vacuum is the fourth time length.

[0010] Furthermore, the target processed battery cell is a processed battery cell to which a lithium replenishing material is added by a lithium replenishing process, and the formation processing parameters of the processed battery cell on the battery cell carrier are determined at least according to 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 the 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 that the formation current of the processed battery cell on the battery cell carrier is a fourth current and the formation mode is 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 the second moisture value and the target processed battery cell When the amount of lithium replenishment in the battery cell is greater than the first lithium replenishment amount and less than or equal to the second lithium replenishment amount, it is determined that the formation current of the battery cell being processed on the battery cell carrier is 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 being processed in the target treatment is greater than the second moisture value and less than or equal to the third moisture value and the amount of lithium replenishment in the battery cell being processed in the target treatment is greater than the second lithium replenishment amount and less than or equal to the third lithium replenishment amount, it is determined that the formation current of the battery cell being processed on the battery cell carrier is 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 processed battery cell, the method also includes: obtaining basic parameters of each of the processed battery cells on the battery cell carrier, the basic parameters of the processed battery cells including the weight of the processed battery cells and the thickness of the processed battery cells, the thickness of the processed battery cells being positively correlated with the width of the electrolyte channel of the processed battery cells; if the weight difference between two of the processed battery cells among all the processed battery cells on the battery cell carrier is greater than a preset weight difference, the processed battery cell with the largest weight is determined as the target processed battery cell; if the weight difference between any two of the processed battery cells among all the processed battery cells on the battery cell carrier is less than or equal to the preset weight difference, the processed battery cell with the smallest thickness among all the processed battery cells on the battery cell carrier is determined as the target processed battery cell.

[0012] Furthermore, when the formation method is the constrained formation, during the formation process, a mechanical clamp is used to constrain the processed battery cell on the battery cell carrier to perform the constrained 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. The secondary battery is prepared by using any one of the methods for preparing a secondary battery.

[0014] According to another aspect of the present invention, there is provided an energy storage system comprising: at least one secondary battery as described above.

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

[0016] The beneficial effects of the present application are as follows: the above-mentioned method for preparing a secondary battery first obtains the target moisture value of the target processed battery cell, and then, when the target moisture value of the target processed battery cell is less than or equal to the first moisture value, determines that the formation current of the processed battery cell on the battery cell carrier is the first current and the formation mode is 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 the second moisture value, determines that the formation current of the processed battery cell on the battery cell carrier is the second current and the formation mode is unconstrained formation, and the second current is less than the first moisture value. a current; when the target moisture value of the target treated battery cell is greater than the second moisture value and less than or equal to the third moisture value, determining that the formation current of the treated battery cell on the battery cell carrier is the third current and the formation mode is constrained formation, the third current is less than the second current, and finally using the formation treatment parameters to perform formation treatment on the treated battery cell on the battery cell carrier, so as to at least reduce the gas production of the treated battery cell on the battery cell carrier during the formation treatment, so as to reduce the brown spot coverage rate of the surface of the treated battery cell on the battery cell carrier. This method determines whether the battery cell is prone to brown spots by the moisture value of the battery cell, and when the moisture value is large, reduces the gas production per unit time by reducing the current during the formation process, and makes it easier to discharge the gas by constrained formation to reduce the brown spots, thereby solving the problem that the battery preparation method in the prior art easily causes brown spots in the prepared battery cell, thereby leading to a decrease in battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

[0021] Figure 4A schematic structural diagram of a formation device provided according to an embodiment of the present application is shown;

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

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

[0024] 10. Battery cell tray; 20. Battery cell being processed; 21. Target battery cell being processed; 50. Negative pressure nozzle; 60. Buffer cup; 70. Bus bar; 80. Buffer tank. DETAILED DESCRIPTION

[0025] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0026] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0027] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0028] In the prior art, the generation of brown spots in battery cells mainly refers to the chemical reaction between the battery structural layers when the moisture content in the internal environment of the battery is high, resulting in the generation of black metal oxides on the surface of the battery's positive electrode material, thereby affecting the battery capacity and performance. In severe cases, it can cause thermal runaway of the battery, leading to battery safety accidents.

[0029] Brown spots on the outer ring of a battery typically form during the battery formation process, which involves charging the battery cell at a certain voltage to activate its materials and structure. Excessive gas production during the formation process indicates excessive electrochemical reactions within the battery, potentially producing large amounts of gas before the SEI film is fully formed and stabilized. This results in a poor-quality SEI film, which is unable to effectively prevent further decomposition of the electrolyte, increasing the risk of lithium plating. Rapidly generated gas accumulates within the battery, generating high internal pressure. If the gas isn't discharged promptly, this high pressure can cause uneven deposition of lithium ions in the electrolyte on the electrode surface, particularly in the outer region of the cell. This can lead to localized lithium plating and produce brown spots.

[0030] Larger gaps in the outer ring of the battery cell make it easier for gas to flow within the battery, but this also means that gas is more likely to squeeze into these gaps under high pressure, causing localized compression and deformation of the electrode material. As the gas rapidly expands in these gaps, the electrode material in the outer ring is easily squeezed, changing its original packing density and structure, thereby affecting the uniform insertion and extraction of lithium ions, resulting in localized lithium deposition and the formation of brown spots. When the outer ring gaps are large, the electrolyte may be unevenly distributed in this area, resulting in inconsistent formation reactions. The reaction is more intense in some areas, and the tendency for lithium deposition is higher, which in turn forms brown spots.

[0031] Therefore, in order to solve the problem that the battery preparation method in the prior art easily causes brown spots on the prepared battery cells, thereby leading to a decrease in battery performance, the embodiments of the present application provide a secondary battery preparation method, a secondary battery, an energy storage system and an electrical device.

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

[0033] In this embodiment, a method for preparing a secondary battery is provided. It should be noted that although a logical sequence is shown in the flow chart, in some cases, the steps shown or described may be performed in a different order than here.

[0034] Figure 1 FIG. 1 is a flow chart of a method for preparing a secondary battery according to an embodiment of the present application. Figure 1 As shown, the method includes the following steps:

[0035] Step S101, performing a high-temperature static treatment on a processing cell on a cell carrier for a preset time to obtain a target moisture value of a target processing cell, wherein the target processing cell is a portion of the processing cells on the cell carrier;

[0036] Among them, before executing step S101, it also includes the step of obtaining a processed battery cell, that is, the diaphragm, the positive electrode sheet of the battery after the electrode baking process, and the negative electrode sheet of the battery are wound and placed in the shell to form an initial battery cell, and then the above-mentioned initial battery cell is subjected to hot pressing and assembly processing to obtain a processed battery cell, and the processed battery cell is first injected with electrolyte treatment, and then subjected to high-temperature static treatment.

[0037] Specifically, the battery cell carrier is generally a battery cell tray. Figure 2 It is a structural diagram of a battery cell assembly, such as Figure 2 As shown, the cell assembly tray is composed of a cell tray 10 and a plurality of cells in process 20. The cell tray 10 stores a plurality of cells in process 20. Generally, the number of cells in process 20 stored in the cell tray 10 is 24. The electrolyte injection treatment is the process of injecting electrolyte into the cell after the electrode production, cell assembly (winding or lamination) and the first baking (pre-baking) are completed. The electrolyte is the carrier of the electrochemical reaction inside the cell. It contains lithium salts, organic solvents and possible additives, which provide the necessary medium for the movement of lithium ions between the positive and negative electrodes, thereby realizing the charge and discharge function of the cell. High-temperature standing treatment is a treatment in which the cell is placed in a specific temperature environment above room temperature and the battery is kept in a standing state at this temperature for a period of time. High-temperature standing treatment is to bake the cell to reduce the moisture value of the cell for the first time.

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

[0039] The target processed battery cell is generally selected as the processed battery cell with the highest moisture content. After determining the target processed battery cell, the target processed battery cell is installed in the preset detection position of the above-mentioned battery cell carrier for subsequent detection of the moisture value of the target processed battery cell. After that, all the processed battery cells in the battery cell tray are simultaneously injected with electrolyte treatment and high-temperature static treatment.

[0040] Step S102, determining formation processing parameters of the battery cell being processed on the battery cell carrier based on at least the target moisture value, wherein the formation processing parameters include at least a formation current and a formation mode, and the formation mode is either unconstrained formation or constrained formation;

[0041] Specifically, the formation current directly affects the speed and extent of the electrochemical reaction within the battery cell. High currents may cause the electrochemical reaction to be too intense, affecting the quality of the SEI film formation; conversely, low currents can promote the reaction more gently, which is conducive to the formation of a stable and dense SEI film. The formation methods are divided into unconstrained formation and constrained formation. Unconstrained formation allows the battery cell to expand freely during the formation process and 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 limit its expansion and is suitable for situations with high moisture content and high gas production. Therefore, the formation current and formation method are determined based on the target moisture value. When the moisture content is low, a simple formation process can be used for formation, simplifying the formation process and saving costs. When the moisture content is high, low current formation or constrained formation can be used to reduce the occurrence of brown spots in the battery cell.

[0042] The step of determining the formation treatment parameters of the battery cell being processed on the battery cell carrier at least according to the target moisture value of the battery cell being processed comprises the following steps:

[0043] Step S1021, when the target moisture value of the target processed battery cell is less than or equal to the first moisture value, determining that the formation current of the processed battery cell on the battery cell carrier is the first current and the formation mode is the unconstrained formation;

[0044] Unconstrained formation refers to a process in which no external physical restrictions or pressure are imposed on the battery cells during the electroformation process. In other words, unconstrained formation is carried out without external mechanical constraints.

[0045] Constrained formation refers to applying physical restrictions or pressure to battery cells during the formation phase to control possible expansion and deformation of the cells during the formation process, ensuring structural stability and dimensional consistency. This process is usually achieved with the help of specially designed fixtures, molds, or other forms of support structures.

[0046] The specific operation methods of constraint formation may include but are not limited to the following:

[0047] 1. Use a fixture, which is one of the most common ways to constrain the battery. The battery cell is placed in a special fixture, which continuously applies appropriate pressure during the formation process to limit the expansion of the battery cell.

[0048] 2. Customized molds: Special molds can be designed to wrap the battery cells. The strength and elasticity of the mold 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: Use coating materials, such as blue film or other insulating materials, on the outer ring of specific battery cells to increase the mechanical strength of the battery cells and reduce deformation during the formation process.

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

[0051] Among them, the range of the first moisture value is generally 18ppm to 22ppm. For example, the first moisture value can be set to 19ppm, 20ppm, 21ppm, preferably 20ppm. During the first charge and discharge process of lithium-ion batteries, a solid electrolyte interface film (SEI film) will be formed on the surface of the negative electrode, which plays a key role in the cycle performance and life of the battery. When the moisture content is higher than 20ppm, it may affect the formation of the SEI film, causing the SEI film to be unstable or too thick, increasing the internal resistance of the battery and affecting the battery performance. Setting a moisture value of 20ppm helps to optimize the formation conditions of the SEI film and improve its quality and consistency.

[0052] Since the target treated cell is generally the one with the highest moisture content, if the target moisture value of the target treated cell is less than or equal to the first moisture value, it is proven that the moisture values ​​of all other treated cells are less than the first moisture value. In other words, the moisture values ​​of all treated cells are relatively low. In this case, even if a higher formation current or an unconstrained formation method is used, the cells are unlikely to develop brown spots. Therefore, in this case, a higher formation current and an unconstrained formation method can be used to simplify the formation process.

[0053] Step S1022, when the target moisture value of the target processed battery cell is greater than the first moisture value and less than or equal to the second moisture value, determining that the formation current of the processed battery cell on the battery cell carrier is a second current and the formation mode is the unconstrained formation, and the second current is less than the first current;

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

[0055] Above-mentioned steps preferably adopts low-current formation process, is because low-current formation is relative to constraint formation, and required extra mechanical device is less, such as, does not need special fixture to limit the expansion of battery core, therefore more advantageous in manufacturing cost, reduces equipment investment and operation and maintenance cost simultaneously.The implementation of low-current formation is relatively simple, does not need complicated mechanical structure and extra operating step, reduces the complexity and potential failure point of production process.Therefore, when the target moisture value of battery core is less than or equal to the second moisture value in target processing, preferably adopt low-current formation process, but in some special cases, also can adopt unconstrained formation process, the two select and get final product.

[0056] Step S1023, when the target moisture value of the battery cell in the above-mentioned target treatment is greater than the above-mentioned second moisture value and less than or equal to the third moisture value, determine that the formation current of the battery cell in the above-mentioned treatment on the above-mentioned battery cell carrier is the third current and the above-mentioned formation method is the above-mentioned constrained formation, and the above-mentioned third current is less than the above-mentioned second current.

[0057] Among them, the range of the third moisture value is generally 96ppm to 102ppm. For example: the third moisture value can be set to 98ppm, 99ppm, 100ppm, preferably 100ppm. 100ppm is the maximum moisture value setting that meets the requirements, and is a preset value obtained by comprehensively considering factors such as the electrolyte formula, diaphragm type, and battery cell structure. Since the target processed battery cell is generally the processed battery cell with the highest moisture content, therefore, when the target moisture value of the target processed battery cell is less than or equal to the third moisture value, it is proved that the moisture values ​​of all other processed battery cells are less than the third moisture value. That is, there are processed battery cells with a moisture value greater than the second moisture value, then in this case, only using a small current forming process or a constrained forming method is not enough to reduce the brown spots of the battery cell. Therefore, it is necessary to use both a small current forming process and a constrained forming method to reduce the brown spots of the battery cell.

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

[0059] Step S103, performing formation treatment on the above-mentioned battery cells on the above-mentioned battery cell carrier using the above-mentioned formation treatment parameters, so as to at least reduce the gas production of the above-mentioned battery cells on the above-mentioned battery cell carrier during the above-mentioned formation treatment, so as to reduce the brown spot coverage rate on the surface of the above-mentioned battery cells on the above-mentioned battery cell carrier.

[0060] During the formation process, electrochemical reactions within the battery cell generate gases, primarily hydrogen and carbon dioxide. The amount of gas produced is influenced by multiple factors, with moisture content being a key parameter. Water decomposes in the electrolyte to produce gases, which exacerbate the formation of the SEI film and lead to localized lithium deposition, resulting in visible brown spots. The formation current directly affects the cell's formation speed and gas production. A lower current slows the electrochemical reaction, thereby reducing the amount of gas produced during the formation process. Unconstrained and constrained formations correspond to different gas production control strategies. Unconstrained formation allows the cell to expand freely and is suitable for low gas production. Constrained formation, on the other hand, restricts cell expansion through mechanical pressure and is suitable for high gas production, but may also incur additional cost and complexity. By adjusting the formation process parameters to effectively control gas production during the formation process, localized lithium deposition caused by gas pressure on the cell surface can be reduced, significantly reducing the coverage of brown spots on the cell surface.

[0061] The method for preparing the secondary battery of the present application first obtains the target moisture value of the battery cell in the target process;

[0062] Then, when the target moisture value of the battery cell in the target treatment is less than or equal to the first moisture value, the formation current of the battery cell in the treatment on the battery cell carrier is determined to be a first current and the formation method is unconstrained formation; when 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 current of the battery cell in the treatment on the battery cell carrier is determined to be a second current and the formation method is unconstrained formation, and the second current is less than the first current; when 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 current of the battery cell in the treatment on the battery cell carrier is determined to be a third current and the formation method is constrained formation, and the third current is less than the second current;

[0063] Finally, the above-mentioned battery cells under treatment on the above-mentioned battery cell carrier are subjected to formation treatment using the above-mentioned formation treatment parameters, so as to at least reduce the gas production of the above-mentioned battery cells under treatment on the above-mentioned battery cell carrier during the above-mentioned formation treatment, so as to reduce the brown spot coverage rate on the surface of the above-mentioned battery cells under treatment on the above-mentioned battery cell carrier.

[0064] The method determines whether a battery cell is prone to brown spots by the moisture value of the battery cell, and reduces the gas production per unit time by reducing the current during the formation process when the moisture value is large. The method restrains the formation so that the gas is more easily discharged to reduce the brown spots, thereby solving the problem in the prior art that the battery preparation method easily causes the prepared battery cell to produce brown spots, thereby leading to a decrease in battery performance.

[0065] In some embodiments, 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 being processed. The third current is preferably 0.02C.

[0066] For example, if a battery has a rated capacity of 1000mAh (1Ah), a formation current of 0.1C is 100mA, and a formation current of 0.02C is 20mA. The specific current setting also depends on the manufacturer's process requirements, formation time, and battery performance and safety considerations. 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 a normal formation current. When the moisture value of the battery cell is small, 0.1C to 0.3C will be used as the formation current. 0.02 to 0.2C is a smaller current, that is, a small current is used to perform formation treatment on the above-mentioned battery cell. The lithium ion deposition rate is slow, which helps the lithium ions to be evenly deposited on the negative electrode surface, avoiding side reactions caused by local excessive concentration, such as the precipitation of metallic lithium, and thus reducing the generation of brown spots. In addition, the small current formation provides a relatively mild electrochemical environment, which helps to control the reaction rate inside the battery cell, reduce local overheating, avoid electrolyte decomposition and the generation of harmful substances under high temperature conditions, and effectively reduce the brown spots of the battery cell.

[0068] In some embodiments, the target moisture value of the target processed battery cell is greater than the first moisture value and less than or equal to the second moisture value, and the target processed battery cell on the battery cell carrier is subjected to a formation treatment using the formation treatment parameters, including the following steps:

[0069] Step S201, performing a first formation treatment on the battery cell being processed on the battery cell carrier using the second current as an initialization current;

[0070] Step S202, during the process of performing the first formation treatment on the battery cell on the battery cell carrier, detecting in real time the liquid level of a formation cup of the target battery cell to obtain a first formation cup liquid level, wherein the formation cup is a container for holding the electrolyte of the target battery cell during the formation treatment;

[0071] Step S203, when the liquid level in the first formation cup is less than or equal to the first preset liquid level, continuing to use the second current to perform the first formation treatment on the battery cell being processed on the battery cell carrier;

[0072] Step S204 : when the liquid level in the first formation cup is greater than the first preset liquid level, reducing 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 range of the first preset liquid level is generally 76ml~84ml. For example, the first preset liquid level can be set to 78ppm, 80ppm, 82ppm, preferably 80ml. During the formation process, the moisture in the electrolyte and the lithium supplementation reaction of the battery cell itself will produce a certain amount of gas. The first preset liquid level is 80ml, which is equivalent to setting a maximum threshold value of the gas volume in the formation cup. This helps to ensure accurate control during gas generation and discharge and prevents excessive gas accumulation. Specifically, first, a suitable formation current is set according to the target moisture value (i.e., when the target moisture value is greater than the above-mentioned 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). In the process of forming using the second current, the liquid level of the formation cup of the battery cell in the target process is detected in real time. The first preset liquid level is the upper limit set according to the battery cell design and the formation process safety standard. If the first formation cup liquid level 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, it is necessary to immediately reduce the formation current to reduce the electrochemical reaction rate and gas production.

[0074] If the liquid level in the formation cup is too high, it can not only lead to electrolyte overflow, damage to the cell structure, and safety accidents, but also cause an increase in brown spots on the outer ring of the cell. The above steps ensure that the gas production during the formation process is maintained at a safe and stable level by precisely controlling the formation current and monitoring the liquid level in the formation cup in real time. This prevents the increase in brown spots on the cell surface caused by excessive reaction speed and excessive gas accumulation.

[0075] Moreover, in the above steps, only the liquid level of the formation cup of the target processed battery cell is monitored. Therefore, the target processed battery cell has the highest moisture content among all the processed battery cells. Therefore, it can be inferred by the same logic that the target processed battery cell produces the most gas among all the processed battery cells. Therefore, it is only necessary to detect the liquid level of the formation cup of the target processed battery cell.

[0076] In some embodiments, the target moisture value of the target processed battery cell is greater than the second moisture value and less than or equal to the third moisture value, and the target processed battery cell on the battery cell carrier is subjected to a formation treatment using the formation treatment parameters, including the following steps:

[0077] Step S301, performing a second formation treatment on the battery cell being processed on the battery cell carrier using the third current and the constrained formation method;

[0078] Step S302 , during the process of performing the second formation process on the target battery cell on the battery cell carrier, detecting the liquid level of the formation cup of the target battery cell in process in real time to obtain a second formation cup liquid level;

[0079] Step S303: Determine the pressure treatment method of the battery cell being processed on the battery cell carrier according to the liquid level of the second formation cup, and perform the second formation treatment on the battery cell being processed on the battery cell carrier using the pressure treatment method. The pressure treatment method is a method of alternating between negative pressure and normal pressure or a method of alternating between normal pressure and vacuum.

[0080] Specifically, the third current is usually lower than the second current, and the purpose of selecting a lower current formation is to reduce the electrochemical reaction rate, thereby reducing the amount of gas produced during the formation of the battery cell in a high-moisture environment. Doing so can avoid a sharp increase in internal pressure due to rapid gas production, reduce instability during SEI film formation, and reduce the probability of lithium precipitation and brown spots. Constrained formation limits the expansion of the battery cell during the formation process through external mechanical pressure (such as a clamp), and is particularly suitable for high-moisture battery cells. It can help the battery cell maintain its structural integrity and stability when it is subjected to internal gas production pressure, prevent deformation of the battery cell, and reduce problems such as poor contact and internal short circuit caused by deformation. It also helps to uniformly discharge gas and avoid problems caused by local gas accumulation.

[0081] Real-time monitoring of the liquid level within the formation cup is a critical step in monitoring gas production during the battery cell formation process. A rising liquid level reflects an increase in gas production within the battery cell. Therefore, by monitoring liquid level changes, we can promptly understand gas production during the formation process. Based on the monitored liquid level in the second formation cup, the system determines one of two different pressure treatment methods: alternating negative and normal pressure or alternating normal and vacuum pressure. Both methods are designed to better control gas emissions during the battery cell formation process, ensuring that gases are effectively removed without affecting the battery cell's structure and performance.

[0082] In some embodiments, determining a pressure treatment method for the battery cell being processed on the battery cell carrier according to the liquid level of the second formation cup, and performing the second formation treatment on the battery cell being processed on the battery cell carrier using the pressure treatment method includes the following steps:

[0083] Step S30311, 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 battery cell being processed on the battery cell carrier in the alternating negative pressure and normal pressure manner, and determining that the single application time of the negative pressure is a first time length and the single application time of the normal pressure is a second time length;

[0084] Step S30312, performing the second formation treatment on the battery cell being treated on the battery cell carrier by alternating between negative pressure and normal pressure, wherein the time for applying the negative pressure each time is the first duration, and the time for applying the normal pressure each time is the second duration.

[0085] In general, the second preset liquid level generally ranges from 96ml to 102ml. For example, the second preset liquid level can be set to 98ppm, 99ppm, 100ppm, preferably 100ml. The 100ml liquid level threshold provides a larger buffer space for gas emissions during the formation process, which is especially important for battery cells whose gas production increases due to large amounts of lithium supplementation, slightly higher water content, or other reasons. A higher liquid level preset can reduce the frequent shutdown and adjustment frequency caused by the sudden increase in battery cell gas production during the formation process, thereby avoiding the resulting decrease in production efficiency and additional production costs.

[0086] The range of the first time length and the second time length is generally 55 minutes to 65 minutes. For example, the first time length can be set to 56 minutes, 60 minutes, 63 minutes, preferably 60 minutes; the second time length can be set to 56 minutes, 60 minutes, 63 minutes, preferably 60 minutes. The magnitude of negative pressure is generally -80±10kPa, for example, the magnitude of negative pressure can be set to -90kPa, -80kPa, -70kPa. The magnitude of normal pressure is generally -0±10kPa, for example, the magnitude of normal pressure can be set to -10kPa, 0kPa, 10kPa. The formation of SEI film (Solid Electrolyte Interface film) is crucial to the initial performance and long-term stability of the battery. Setting the first and second time lengths of vacuum standing under positive and negative pressure to 1 minute can accelerate the formation and maturation of SEI film, thereby improving the cycle performance and life of the battery. This is because appropriate positive and negative pressure conversion helps promote uniform gas discharge and effective infiltration of electrolyte, creating an environment conducive to the formation of SEI film. During formation, gases generated within the battery cell must be promptly and effectively exhausted to prevent excessive internal pressure. A negative pressure setting of -80±10kPa ensures efficient gas evacuation while remaining within a safe range to prevent excessive evacuation that could cause electrolyte loss or battery damage. Restoring the pressure to a normal state of 0±10kPa at the end of the formation process helps maintain the stability and integrity of the battery cell structure, preventing deformation or internal component displacement caused by sudden pressure changes, thereby reducing fluctuations in battery performance and potential failures.

[0087] During the second formation process, the liquid level in the formation cup is continuously monitored, using the second preset liquid level 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 still within a reasonable control range. When the second preset liquid level condition is met, it is determined that gas emission control is carried out by alternating between negative pressure and normal pressure. This method periodically applies negative pressure and normal pressure, using the negative pressure to absorb the gas inside the battery cell, while the normal pressure allows the battery cell to return to its natural state, avoiding excessive compression. In actual operation, negative pressure and normal pressure are periodically applied to the battery cell according to predetermined first and second durations. Each application of negative pressure lasts for a first duration (T1), the purpose of which is to accelerate the gas emission rate and reduce the internal pressure of the battery cell. Each application of normal pressure lasts for a second duration (T2), during which the battery cell can relax and return to its original state, avoiding structural damage.

[0088] Figure 3 Schematic diagram of a formation charging process, such as Figure 3 As shown in the figure, the formation treatment steps mainly include battery cell positioning, needle bed pressing, charging start, charging termination and needle bed lifting. First, the battery cell is positioned, then the needle bed is pressed, and it is in a negative pressure environment of -80±5kpa. Then charging is started, and the negative pressure of -80±5kpa is also maintained. After charging is terminated, it returns to normal pressure 0kpa, and finally the needle bed is lifted.

[0089] Figure 4 A schematic diagram of the structure of a formation device is shown in FIG. Figure 4 As shown, under a negative pressure environment, the negative pressure nozzle 50 absorbs the electrolyte in the battery cell 20 being processed and stores the electrolyte in the buffer cup 60, so that the electrolyte can flow in the device, and at the same time, the gas in the battery cell 20 being processed can be removed. The negative pressure nozzle 50 can accurately control the flow direction of the electrolyte under negative pressure; the bus 70 collects the electrolyte in each buffer cup 60 and allows the electrolyte to flow to the buffer tank 80 through the bus 70. The buffer tank 80 is externally connected to a vacuum and stores electrolyte, which can prevent external impurities from contaminating the electrolyte, provide a buffer space, stabilize the supply of electrolyte, and ensure continuous and stable operation of the device. In some embodiments, the following can be used: Figure 3 The formation charge processing steps shown and Figure 4 The formation device shown performs formation treatment on the battery cells.

[0090] Furthermore, in the process of performing the second formation treatment on the treated battery cells on the battery cell carrier in an alternating manner of negative pressure and normal pressure, a formation current of 0.02C is used in the negative pressure process and a formation current of 0.1C is used in the normal pressure process.

[0091] In a negative pressure environment, a formation current as low as 0.02C is used to further slow down the electrochemical reaction rate, reduce the amount of gas produced by water decomposition, and ensure that the ions in the electrolyte have sufficient opportunities to participate in the reaction to form a uniform and stable SEI film. During the negative pressure process, low-current formation can help control internal gas emissions, reduce internal pressure, and reduce the risk of lithium precipitation. During the normal pressure process, the external pressure of the battery cell returns to normal. At this time, a relatively high formation current (such as 0.1C) can be used to improve the formation efficiency and shorten the formation cycle. The normal pressure state allows the internal pressure of the battery cell to adjust naturally, avoiding the impact of excessive external pressure on the battery cell structure.

[0092] By using a low current formation during the negative pressure phase, rapid gas generation is reduced, preventing localized accumulation of gas inside the cell that can form brown spots. Restoring the formation to normal current during the normal pressure phase helps improve formation efficiency. The combination of these two factors significantly reduces brown spots on the cell surface.

[0093] In some embodiments, determining a pressure treatment method for the battery cell being processed on the battery cell carrier according to the liquid level of the second formation cup, and performing the second formation treatment on the battery cell being processed on the battery cell carrier using the pressure treatment method includes the following steps:

[0094] Step S30321, 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 battery cell being processed on the battery cell carrier in the alternating manner of normal pressure and vacuum, and determining the single application time of normal pressure to be a third time length and the single application time of vacuum to be a fourth time length;

[0095] Step S30322, performing the above-mentioned second formation treatment on the above-mentioned battery cells on the above-mentioned battery cell carrier by alternating the above-mentioned normal pressure and vacuum pumping, until the liquid level in the above-mentioned second formation cup is less than or equal to the above-mentioned second preset liquid level, wherein the time for applying the above-mentioned normal pressure each time is the above-mentioned third duration, and the time for applying the above-mentioned vacuum pumping each time is the above-mentioned fourth duration.

[0096] Specifically, the range of the third and fourth durations is generally 55 minutes to 65 minutes. For example, the first duration can be set to 56 minutes, 60 minutes, 63 minutes, preferably 60 minutes; the second duration can be set to 56 minutes, 60 minutes, 63 minutes, preferably 60 minutes. The normal pressure is generally -0 ± 10 kPa, for example, the normal pressure can be set to -10 kPa, 0 kPa, 10 kPa. When the second formation cup liquid level is greater than the second preset liquid level, it indicates that the gas production of the battery cell during the formation process has exceeded the range that can be effectively controlled by conventional treatment (such as alternating between negative pressure and normal pressure), and a more powerful gas exhaust strategy is required. In this case, a normal pressure vacuum alternating method is used to handle gas exhaust. Vacuuming is to extract the gas inside the battery cell in a vacuum environment to accelerate gas exhaust, reduce the internal pressure of the battery cell and the formation cup liquid level, and increasing exhaust can also effectively reduce the output of brown spots in the battery cell. The normal pressure stage is to allow the battery cell to return to a normal external pressure environment to avoid the adverse effects of continuous vacuuming on the battery cell structure. The duration of a single application of normal pressure is determined as the third duration (T3), and the duration of a single application of vacuum is determined as the fourth duration (T4). These four durations must be determined based on the characteristics of the battery cell, the gas production rate, and the equipment capabilities, in order to control the liquid level in the formation cup in the shortest possible time while not affecting the performance and structure of the battery cell (such as the formation of brown spots or overflow of the formation cup).

[0097] In some embodiments, during the vacuuming process, application of the formation current is stopped, that is, the battery cell is stopped from continuing the formation reaction and gas production, and the gas is first discharged by vacuuming.

[0098] In other embodiments, in the process of performing the above-mentioned second formation treatment on the above-mentioned processed battery cells on the above-mentioned battery cell carrier, the above-mentioned processed battery cells on the battery cell carrier are first subjected to the second formation treatment by alternating between negative pressure and normal pressure. Because the alternating between negative pressure and normal pressure is a conventional formation treatment method, the alternating between normal pressure and vacuum is a formation measure adopted to deal with excessive gas production. Usually, the problem of excessive gas production will occur during the formation treatment (that is, after a period of formation treatment). Therefore, the above-mentioned processed battery cells on the battery cell carrier are first subjected to the second formation treatment by alternating between negative pressure and normal pressure. During the second formation treatment, the liquid level of the second formation cup is detected in real time. If the liquid level of the second formation cup is greater than the second preset liquid level, the formation is started by alternating between normal pressure and vacuum.

[0099] In some embodiments, the target processed battery cell is a processed battery cell to which a lithium replenishing material is added using a lithium replenishing process, and determining the formation treatment parameters of the processed battery cell on the battery cell carrier based at least on the target moisture value of the target processed battery cell comprises the following steps:

[0100] Step S401, determining that the formation current of the battery cell in the target process on the battery cell carrier is a fourth current and the formation mode is the unconstrained formation, when the target moisture value of the battery cell in the target process is less than or equal to the first moisture value and the lithium replenishment amount of the battery cell in the target process is less than or equal to the first lithium replenishment amount;

[0101] Step S402, determining that a formation current of the battery cell in the target process on the battery cell carrier is a fifth current, the formation mode is the unconstrained formation, and the fifth current is less than the fourth current, when a target moisture value of the battery cell in the target process is greater than the first moisture value and less than or equal to the second moisture value, and a lithium replenishment amount of the battery cell in the target process is greater than the first lithium replenishment amount and less than or equal to the second lithium replenishment amount;

[0102] Step S403, when the target moisture value of the battery cell in the above-mentioned target treatment is greater than the above-mentioned second moisture value and less than or equal to the third moisture value and the lithium replenishment amount of the battery cell in the above-mentioned target treatment is greater than the above-mentioned second lithium replenishment amount and less than or equal to the third lithium replenishment amount, determine that the formation current of the battery cell in the above-mentioned treatment on the above-mentioned battery cell carrier is the sixth current and the above-mentioned formation method is the above-mentioned constrained formation, and the above-mentioned sixth current is less than the above-mentioned fifth current.

[0103] The cells being processed can be either lithium-supplemented or non-lithium-supplemented. Lithium-supplemented cells are cells that have lithium-supplementing materials added using a lithium-supplementing process, while non-lithium-supplemented cells are cells that do not have lithium-supplementing materials added. For non-lithium-supplemented cells, the gas production during the formation process can be determined solely by measuring the moisture content of the target cells being processed, thereby determining the formation process parameters. For lithium-supplemented cells, the gas production during the formation process can be determined by measuring the moisture content of the target cells being processed, or by the amount of lithium supplemented, which is determined at the very beginning of cell production. Specifically, for lithium-supplemented cells, the formation process parameters can be determined solely by the moisture content of the target cells being processed, solely by the amount of lithium supplemented, or by both the moisture content and the amount of lithium supplemented. If both the moisture content and the amount of lithium supplemented are used to determine the formation process parameters, and if the two criteria conflict, the moisture content shall prevail.

[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%, 0.55%, preferably 0.5%, and 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%, 1.1%, preferably 1%, and 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%, 2.1%, preferably 2%. Since the lithium replenishment amount is pre-set when the battery cell is manufactured, there is no situation where the lithium replenishment amount is too high. The value range of the above-mentioned fourth current is greater than or equal to 0.1C and less than 0.3C, the value range of the above-mentioned fifth current is greater than 0.02C and less than 0.1C, and the above-mentioned sixth current is 0.02C, where C is the rated capacity of the battery cell in the above-mentioned process.

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

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

[0107] Step S501, obtaining basic parameters of each of the cells being processed on the cell carrier, the basic parameters of the cells being processed including the weight and thickness of the cells being processed, and the thickness of the cells being processed being positively correlated with the width of the electrolyte channel of the cells being processed;

[0108] Step S502 , if a weight difference between two of the cells being processed on the cell carrier is greater than a preset weight difference, the cell being processed with the largest weight is determined as the target cell being processed;

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

[0110] Specifically, the target cell to be processed may be one or more cells. By detecting the weight and / or thickness of the cells, the target cell to be processed can be determined. The target cell to be processed is a cell with a large amount of water.

[0111] Since cells with higher moisture levels tend to be heavier, weight is used as a target cell selection criterion. Furthermore, a thinner cell indicates a more compact cell. A thinner cell, in other words, means the positive and negative electrodes are closer together, shortening the diffusion path for water within the cell. However, this also means that water must pass through narrower channels, known as moisture channels, to penetrate from one side of the cell to the other. As cell thickness decreases, the compression of the electrodes and separator may increase, narrowing these channels. Narrow channels increase resistance to water diffusion, resulting in uneven water distribution within the cell, with significant differences in moisture levels between the edges and center. Before entering the production process, battery cells are typically baked (i.e., subjected to high-temperature quiescent treatment) to remove moisture. While a thinner cell may appear more efficient (because heat can penetrate more easily), the narrow channels can actually make it difficult to completely remove moisture from certain areas within the cell, particularly those with denser structures or areas that are less accessible to heat. That is, a battery cell with a smaller thickness may make it more difficult to completely remove moisture from the inside of the battery cell, thereby increasing the moisture value of the battery cell. Therefore, in addition to weight, thickness can also be used as a selection condition for the target battery cell.

[0112] Therefore, by detecting the weight and / or thickness of the battery cells, the battery cells with a larger moisture value can be accurately determined, that is, the target battery cells to be processed can be accurately determined.

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

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

[0115] Specifically, the mechanical clamp effectively controls the expansion and morphological changes of the battery cell during the formation process by applying a certain amount of mechanical pressure to the outside. The application of this external pressure can help the gas inside the battery cell to diffuse and discharge more evenly, avoid lithium precipitation and uneven SEI film formation caused by local high pressure, and reduce the generation of brown spots in the battery cell. During the constrained formation process, the battery cell on the battery cell carrier is fixed by a mechanical clamp, and this process runs through the entire formation process. Constrained formation reduces the random emission of gas inside the battery cell and reduces the generation of surface defects (such as brown spots) caused by uneven gas distribution.

[0116] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the implementation process of the secondary battery preparation method of the present 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, all the cells being processed are injected with liquid and left to stand;

[0119] Step S2, detecting the moisture value of the target processed battery cell with the highest moisture content;

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

[0121] Step S32: When the moisture value of the battery cell in the target process is greater than 20ppm and less than or equal to 50ppm, a low current of 0.1C to 0.02C is used for forming, and unconstrained forming is performed. During the forming process, the liquid level of the forming cup is detected in real time. When the liquid level of the forming cup is less than or equal to 80ml, the low current of 0.1C to 0.02C is continued to be used. When the liquid level of the forming cup is greater than 80ml, the forming current is further reduced.

[0122] Step S33: If the moisture content of the battery cell in the target process is greater than 50 ppm and less than or equal to 100 ppm, constrained forming and 0.02C low current forming are used, and the liquid level in the forming cup is monitored in real time during the forming process. If the liquid level in the forming cup is less than or equal to 100 ml, forming is continued. If the liquid level in the forming cup is greater than 100 ml, gas in the battery cell is extracted by alternating atmospheric pressure and vacuum pumping until the liquid level in the forming cup is less than or equal to 100 ml and forming is completed.

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

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

[0125] Comparative Example 1

[0126] A secondary battery was prepared using the battery cell in the first target treatment. The battery cell in the first target treatment was a lithium-supplemented battery cell. The lithium supplement agent used was metallic lithium, and the lithium supplement amount was 1%. The target moisture content of the battery cell in the first target treatment was 50 ppm. The battery cell in the first target treatment was sequentially subjected to liquid injection treatment, high-temperature static treatment, and normal current formation treatment to prepare a secondary battery. The formation current used in the above-mentioned normal current formation treatment was 0.2C and was unrestrained 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 from the first target treatment. The cell from the first target treatment was a lithium-supplemented cell, the lithium supplement agent used was metallic lithium, the lithium supplement amount was 1%, and the target moisture content of the cell from the first target treatment was 50 ppm. The cell from the first target treatment was sequentially subjected to a liquid injection treatment, a high-temperature static treatment, and a low-current formation treatment to prepare the secondary battery. The normal current formation treatment employed a formation current of 0.05 C and was unconstrained formation. The resulting secondary battery had no brown spots. The difference between Example 1 and Comparative Example 1 is that the low-current formation treatment was employed.

[0129] Comparative Example 2

[0130] A secondary battery is prepared using the battery cell in the first target treatment. The battery cell in the first target treatment is a lithium-supplemented battery cell. The lithium supplement agent used is metallic lithium, and the lithium supplement amount is 2%. The target moisture content of the battery cell in the first target treatment is 100 ppm. The battery cell in the first target treatment is sequentially subjected to liquid injection treatment, high-temperature static treatment, and normal current formation treatment to prepare a secondary battery. The formation current used in the above-mentioned normal current formation treatment is 0.2C and is unrestrained formation. The secondary battery finally prepared has circular brown spots with a diameter of 4 mm.

[0131] Example 2

[0132] A secondary battery was prepared using a cell from the first target treatment. The cell was a lithium-supplemented cell, the lithium supplement agent used was metallic lithium, the lithium supplement amount was 2%, and the target moisture content of the cell was 100 ppm. The cell from the first target treatment was sequentially subjected to a liquid injection treatment, a high-temperature static treatment, and a low-current formation treatment to prepare the secondary battery. The normal current formation treatment employed a formation current of 0.02C and was constrained formation. The resulting secondary battery had no brown spots. The difference between Example 2 and Comparative Example 2 lies in the use of the low-current formation treatment and the constrained formation treatment.

[0133] Comparative Example 3

[0134] A secondary battery was prepared using the battery cells treated in the second target process. The battery cells treated in the second target process were non-lithium-supplemented battery cells. The target moisture content of the battery cells treated in the second target process was 50 ppm. The battery cells treated in the second target process were sequentially subjected to liquid injection treatment, high-temperature static treatment, and normal current formation treatment to prepare a secondary battery. The formation current used in the above-mentioned normal current formation treatment was 0.2C and was unrestrained 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, wherein the cell from the second target treatment was a non-lithium-supplemented cell and had a target moisture content of 50 ppm. The cell from the second target treatment was sequentially subjected to a liquid injection treatment, a high-temperature static treatment, and a low-current formation treatment to prepare a secondary battery. The low-current formation treatment employed a formation current of 0.05C and was unconstrained formation. The resulting secondary battery had no brown spots. Example 3 differs from Comparative Example 3 in that the low-current formation treatment was employed.

[0137] Comparative Example 4

[0138] A secondary battery was prepared using the battery cells treated in the second target process. The battery cells treated in the second target process were non-lithium-supplemented battery cells. The target moisture content of the battery cells treated in the second target process was 100 ppm. The battery cells treated in the second target process were sequentially subjected to liquid injection treatment, high-temperature static treatment, and normal current formation treatment to prepare a secondary battery. The formation current used in the above-mentioned normal current formation treatment was 0.2C and was unrestrained 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 cells from the second target treatment, wherein the cells were non-lithium-supplemented cells and had a target moisture content of 100 ppm. The cells from the second target treatment were sequentially subjected to a liquid injection treatment, a high-temperature static treatment, and a low-current formation treatment to prepare the secondary battery. The low-current formation treatment employed a formation current of 0.02C and was constrained. The resulting secondary battery had no brown spots. Example 4 differs from Comparative Example 4 in that the low-current formation treatment and the constrained formation treatment were employed.

[0141] The comparison results of 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] It can be seen from Table 1 that when the moisture content or lithium supplement content of the battery cell in the target treatment is large, the use of low current formation process and constrained formation process can effectively reduce the generation of brown spots in the battery cell.

[0146] An embodiment of the present application further provides a secondary battery, which is prepared by using any of the above-mentioned methods for preparing a secondary battery.

[0147] The above-mentioned secondary battery is prepared by adopting any one of the above-mentioned secondary battery preparation methods. Since the above-mentioned preparation method judges whether the battery cell is prone to brown spots by the moisture value of the battery cell, and reduces the gas production per unit time by reducing the current during the formation process when the moisture value is large, and restrains the formation to make the gas easier to discharge, thereby reducing brown spots, it solves the problem in the prior art that the battery preparation method easily causes the prepared battery cell to produce brown spots, thereby leading to a decrease in battery performance. Therefore, the secondary battery prepared by the above-mentioned preparation method has fewer brown spots.

[0148] An embodiment of the present application further provides an energy storage system, comprising: at least one of the above-mentioned 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 overall battery pack consistency, and ensures stable and smooth system charging and discharging. The aforementioned energy storage system utilizes secondary batteries with fewer brown spots. Batteries with fewer brown spots have a longer lifespan and higher efficiency. This not only reduces battery replacement costs, but also reduces 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 lifespans, higher energy efficiency, more stable operation, lower safety risks, better charge and 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] An embodiment of the present application further provides an electrical device, comprising: at least one of the above-mentioned secondary batteries or the above-mentioned energy storage system.

[0152] Battery reliability directly impacts the overall reliability of electronic devices. Fewer brown spots mean more stable battery performance across a wide range of environmental conditions, reducing the risk of electronic device failures due to battery malfunction and improving device durability and reliability. Using secondary batteries with fewer brown spots in electronic devices can significantly improve performance, safety, and reliability, extend device lifespan, reduce maintenance costs, and be more environmentally friendly, in line with the principles of green manufacturing and sustainable development.

[0153] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0154] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0155] The preparation method of the above-mentioned secondary battery of the present application first obtains the target moisture value of the target processed battery cell, and then, when the target moisture value of the target processed battery cell is less than or equal to the first moisture value, determines that the formation current of the processed battery cell on the battery cell carrier is a first current and the formation mode is 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 the second moisture value, determines that the formation current of the processed battery cell on the battery cell carrier is a second current and the formation mode is unconstrained formation, and the second current is less than the first current; when the target moisture value of the target processed battery cell is greater than the second moisture value and less than or equal to the third moisture value, determines that the formation current of the processed battery cell on the battery cell carrier is a third current and the formation mode is constrained formation, and the third current is less than the second current; finally, the above-mentioned formation treatment parameters are used to perform formation treatment on the above-mentioned processed battery cell on the above-mentioned battery cell carrier, so as to at least reduce the gas production of the above-mentioned processed battery cell on the above-mentioned battery cell carrier during the above-mentioned formation treatment, so as to reduce the brown spot coverage rate on the surface of the above-mentioned processed battery cell on the above-mentioned battery cell carrier. The method determines whether a battery cell is prone to brown spots by the moisture value of the battery cell, and reduces the gas production per unit time by reducing the current during the formation process when the moisture value is large. The method restrains the formation so that the gas is more easily discharged to reduce the brown spots, thereby solving the problem in the prior art that the battery preparation method easily causes the prepared battery cell to produce brown spots, thereby leading to a decrease in battery performance.

[0156] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a secondary battery, characterized in that: include: Obtaining target moisture values ​​of target processed cells after subjecting the processed cells on the cell carrier to a high-temperature static treatment for a preset period of time, wherein the target processed cells are some of the processed cells on the cell carrier; determining formation processing parameters of the battery cell being processed on the battery cell carrier at least according to the target moisture value, the formation processing parameters including at least a formation current and a formation mode, the formation mode being unconstrained formation or constrained formation; Performing a formation treatment on the battery cell under treatment on the battery cell carrier using the formation treatment parameters to at least reduce the amount of gas generated by the battery cell under treatment on the battery cell carrier during the formation treatment, thereby reducing the brown spot coverage rate on the surface of the battery cell under treatment on the battery cell carrier; The step of determining the formation treatment parameters of the battery cell being processed on the battery cell carrier according to at least the target moisture value of the battery cell being processed comprises: When the target moisture value of the target processed battery cell is less than or equal to the first moisture value, determining that the formation current of the processed battery cell on the battery cell carrier is the first current and the formation mode is the unconstrained formation; When a 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, determining that a formation current of the processed battery cell on the battery cell carrier is a second current and the formation mode is the unconstrained formation, and the second current is less than the first current; When 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 current of the battery cell in the treatment on the battery cell carrier is determined to be the third current and the formation method is the constrained formation, and the third current is less than the second current.

2. The method for preparing a secondary battery according to claim 1, wherein: The value range of the first current is greater than or equal to 0.1C and less than 0.3C, the value range of 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 being processed.

3. The method for preparing a secondary battery according to claim 1, wherein: The target moisture value of the target battery cell being processed is greater than the first moisture value and less than or equal to the second moisture value, and the battery cell being processed on the battery cell carrier is subjected to a formation treatment using the formation treatment parameters, comprising: performing a first formation treatment on the battery cell being processed on the battery cell carrier by using the second current as an initialization current; During the first formation treatment of the battery cell being processed on the battery cell carrier, detecting in real time the liquid level of a formation cup of the target battery cell being processed to obtain a first formation cup liquid level, wherein the formation cup is a container for holding the electrolyte of the target battery cell during the formation treatment; When the liquid level in the first formation cup is less than or equal to a first preset liquid level, continuing to use the second current to perform the first formation treatment on the battery cell being processed on the battery cell carrier; When 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.

4. The method for preparing a secondary battery according to claim 1, wherein: The target moisture value of the target battery cell being processed is greater than the second moisture value and less than or equal to a third moisture value, and the battery cell being processed on the battery cell carrier is subjected to a formation treatment using the formation treatment parameters, comprising: performing a second formation treatment on the battery cell being processed on the battery cell carrier using the third current and the constrained formation method; During the process of performing the second formation treatment on the target battery cell on the battery cell carrier, detecting the liquid level of the formation cup of the target battery cell in process in real time to obtain the second formation cup liquid level; According to the liquid level of the second formation cup, the pressure treatment method of the battery cell being processed on the battery cell carrier is determined, and the second formation treatment is performed on the battery cell being processed on the battery cell carrier using the pressure treatment method. The pressure treatment method is a method of alternating between negative pressure and normal pressure or a method of alternating between normal pressure and vacuum.

5. The method for preparing a secondary battery according to claim 4, wherein: Determining a pressure treatment method for the battery cell being processed on the battery cell carrier according to the liquid level of the second formation cup, and performing the second formation treatment on the battery cell being processed on the battery cell carrier using the pressure treatment method, comprising: When the liquid level in the second forming cup is less than or equal to a second preset liquid level, determining to perform the second forming treatment on the battery cell being processed on the battery cell carrier in the alternating negative pressure and normal pressure manner, and determining that the single application time of the negative pressure is a first time length and the single application time of the normal pressure is a second time length; The second formation treatment is performed on the battery cell being processed on the battery cell carrier in the alternating negative pressure and normal pressure manner, wherein the time for applying the negative pressure each time is the first duration, and the time for applying the normal pressure each time is the second duration.

6. The method for preparing a secondary battery according to claim 4, wherein: Determining a pressure treatment method for the battery cell being processed on the battery cell carrier according to the liquid level of the second formation cup, and performing the second formation treatment on the battery cell being processed on the battery cell carrier using the pressure treatment method, comprising: When the liquid level in the second forming cup is greater than a second preset liquid level, determining to perform the second forming treatment on the battery cell being processed on the battery cell carrier in the alternating manner of normal pressure and vacuuming, and determining that the single application time of normal pressure is a third time length and the single application time of vacuuming is a fourth time length; The second formation treatment is performed on the battery cell being processed on the battery cell carrier in an alternating manner of normal 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 applying the normal pressure each time is the third duration, and the time for applying the vacuum each time is the fourth duration.

7. The method for preparing a secondary battery according to claim 1, wherein: The target processed battery cell is a processed battery cell to which a lithium replenishing material is added using a lithium replenishing process, and the formation treatment parameters of the processed battery cell on the battery cell carrier are determined based at least on a target moisture value of the target processed battery cell, including: When a target moisture value of the target processed battery cell is less than or equal to a first moisture value and a lithium replenishment amount of the target processed battery cell is less than or equal to the first lithium replenishment amount, determining that a formation current of the processed battery cell on the battery cell carrier is a fourth current and the formation mode is the unconstrained formation; When a target moisture value of the target processed battery cell is greater than the first moisture value and less than or equal to the second moisture value and a lithium replenishment amount of the target processed battery cell is greater than the first lithium replenishment amount and less than or equal to the second lithium replenishment amount, determining that a formation current of the processed battery cell on the battery cell carrier is a fifth current and the formation mode 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 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 battery cell in the target treatment is greater than the second lithium replenishment amount and less than or equal to the third lithium replenishment amount, it is determined that the formation current of the battery cell in the treatment on the battery cell carrier is the sixth current and the formation method is the constrained formation, and the sixth current is less than the fifth current.

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

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

10. 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 9.

11. An energy storage system, characterized in that: include: At least one secondary battery according to claim 10.

12. An electrical device, characterized in that: include: At least one secondary battery according to claim 10 or the energy storage system according to claim 11.

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