Secondary battery and preparation method thereof, energy storage system and electrical equipment

Abstract

The embodiments of the present application relate to the field of secondary batteries and provide a secondary battery and its preparation method, an energy storage system, and an electrical device. The manufacturing method of the secondary battery includes: providing a battery cell assembly, the battery cell assembly including a positive electrode sheet, a separator, and a negative electrode sheet, wherein the steps of forming the negative electrode sheet include: providing a negative current collector; forming a negative active material layer on at least one side surface of the negative current collector; forming a support layer on the side surface of the negative active material layer facing away from the negative current collector, the negative current collector, the negative active material layer, and the support layer forming a stacked structure; rolling the stacked structure; removing the support layer to obtain the negative electrode sheet; providing a housing having a receiving cavity, placing the battery cell assembly in the receiving cavity, and injecting electrolyte into the receiving cavity. The embodiments of the present application can at least solve the problem of ultra-thin copper foil breaking during the rolling process.

Description

Technical Field

[0001] The present application relates to the field of secondary batteries, and in particular to a secondary battery and a preparation method thereof, an energy storage system and electrical equipment. Background Art

[0002] Lithium-ion batteries have the advantages of high specific energy density, high operating voltage, long storage life and low discharge rate, and are therefore widely used in various electronic information products.

[0003] The performance of lithium-ion batteries depends primarily on the electrode, electrolyte, separator, and other battery materials contained within. The electrode is particularly important. During electrode processing, the electrode is rolled to help the active material adhere to the current collector surface. The thinner the copper foil in the electrode, the less copper is used per battery. This lowers the production cost of the battery. Furthermore, thinner copper foil and reduced copper usage increase the available space within the battery cell while maintaining the same volume. This allows for more active material layers, thereby increasing the cell capacity and energy density.

[0004] Therefore, how to design a secondary battery with ultra-thin copper foil is a problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] The embodiments of the present application provide a secondary battery and a preparation method thereof, an energy storage system, and an electrical device, which are at least helpful in solving the problem of ultra-thin copper foil breaking during the rolling process.

[0006] According to some embodiments of the present application, on one hand, a method for manufacturing a secondary battery is provided, comprising:

[0007] A battery cell assembly is provided, the battery cell assembly comprising a positive electrode sheet, a separator, and a negative electrode sheet, wherein the steps of forming the negative electrode sheet include:

[0008] Providing a negative electrode current collector, wherein the thickness of the negative electrode current collector is the foil thickness h, wherein 3 μm≤h≤5 μm;

[0009] forming a negative electrode active material layer on at least one side surface of the negative electrode current collector;

[0010] forming a support layer on a surface of the negative electrode active material layer facing away from the negative electrode current collector, wherein the negative electrode current collector, the negative electrode active material layer and the support layer constitute a stacked structure;

[0011] performing a roll pressing process on the laminated structure;

[0012] Removing the support layer to obtain the negative electrode sheet;

[0013] A shell is provided, wherein the shell has a receiving cavity, the battery core assembly is placed in the receiving cavity and an electrolyte is injected into the receiving cavity.

[0014] In some embodiments, before the rolling process, the thickness of the support layer satisfies: 2 μm≤D≤5 μm, where D is the thickness of the support layer.

[0015] In some embodiments, after the stacked structure is subjected to roller pressing, the compaction density of the negative electrode active material layer satisfies: 1.4 g / cm 3 ≤ρ≤1.8g / cm 3 , ρ is the compaction density of the negative electrode active material layer.

[0016] In some embodiments, the material of the support layer includes at least one of a water-soluble material, a thermally decomposable material, or a photolytic material.

[0017] In some embodiments, the method of forming the support layer includes:

[0018] Providing a support slurry, wherein the support slurry contains a dispersant and a dispersant;

[0019] The support slurry is coated on the surface of the negative electrode active material layer on the side away from the negative electrode current collector and dried to remove the dispersant, and the dispersoid is solidified to form the support layer.

[0020] In some embodiments, the mass percentage of the dispersoid in the support slurry is 3 wt % to 10 wt %, calculated as a mass percentage.

[0021] In some embodiments, the material of the support layer is a water-soluble material; and the method for removing the support layer includes:

[0022] performing a steam dissolution treatment on the support layer to remove the support layer;

[0023] The surface of the negative electrode active material layer is cleaned.

[0024] In some embodiments, the process parameters of the steam dissolution treatment include: heating treatment in a water vapor atmosphere, 85°C≤T1≤110°C, 0.1MPa≤p1≤0.2MPa, T1 is the process temperature, and p1 is the steam pressure.

[0025] In some embodiments, the water-soluble material includes at least one of a PVA material, a PEG material, a PVP material, a CMC material, a PVC material, an ethylene-carbon monoxide copolymer, or a vinyl ketone copolymer material.

[0026] In some embodiments, during the rolling process, the support layer is further subjected to a heating process, and the heating temperature of the heating process satisfies: 40° C. ≤ T2 ≤ 50° C., where T2 is the heating temperature of the heating process.

[0027] In some embodiments, the rolling process includes: rolling the laminated structure multiple times, and the rolling pressure of a previous rolling process is less than or equal to the rolling pressure of a subsequent rolling process.

[0028] In some embodiments, the rolling process includes a first rolling process and a second rolling process performed successively, and the first rolling process and the second rolling process satisfy: 30MPa≤P1≤50MPa, 60MPa≤P2≤90MPa, wherein P1 is the rolling pressure of the first rolling process, and P2 is the rolling pressure of the second rolling process.

[0029] In some embodiments, the tensile strength of the support layer is a first tensile strength σb1, wherein 10 MPa≤σb1≤120 MPa.

[0030] In some embodiments, the tensile strength of the stacked structure is a second tensile strength σb2, wherein 40 MPa≤σb2≤250 MPa.

[0031] According to some embodiments of the present application, another aspect of the present application further provides a secondary battery, wherein the secondary battery is obtained by any of the above-mentioned methods for preparing a secondary battery;

[0032] The secondary battery includes:

[0033] A housing having an accommodating cavity therein;

[0034] A battery cell assembly, the battery cell assembly being installed in the accommodating cavity; the battery cell assembly comprising: a positive electrode sheet, a separator and a negative electrode sheet; the negative electrode sheet comprising: a negative electrode current collector and a negative electrode active material layer;

[0035] The thickness of the negative electrode current collector is the foil thickness h, wherein 3 μm≤h≤5 μm.

[0036] According to some embodiments of the present application, on the other hand, an energy storage system is provided. The energy storage system includes: a plurality of secondary batteries, wherein the secondary batteries are obtained by the preparation method of the secondary battery as described in any one of the above items or are the secondary batteries as described above.

[0037] According to some embodiments of the present application, on the other hand, an electrical device is provided, which includes: a plurality of secondary batteries, wherein the secondary batteries are obtained by the preparation method of the secondary battery as described in any one of the above items or are the secondary batteries as described above.

[0038] The technical solution provided in the embodiment of the present application has at least the following advantages: the embodiment of the present application improves the overall mechanical strength by forming a support layer on the surface of the negative electrode active material layer during the formation of the negative electrode plate. The support layer provides support force in the subsequent rolling process to avoid the problem of broken belts in the negative electrode current collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplified descriptions do not constitute a limitation on the embodiments. Unless otherwise stated, the pictures in the drawings do not constitute a scale limitation. In order to more clearly illustrate the embodiments of the present application or the technical solutions in the traditional technology, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 A flowchart of a method for manufacturing a secondary battery according to an embodiment of the present application;

[0041] Figure 2 A flowchart of the steps of forming a negative electrode sheet in a method for manufacturing a secondary battery provided in one embodiment of the present application;

[0042] Figure 3 A schematic cross-sectional structure diagram of a negative electrode current collector provided in a method for manufacturing a secondary battery provided in one embodiment of the present application;

[0043] Figure 4 A schematic cross-sectional view of a negative electrode material layer formed in a method for manufacturing a secondary battery provided in one embodiment of the present application;

[0044] Figure 5 This is a schematic cross-sectional structure diagram of forming a support layer in a method for manufacturing a secondary battery provided in one embodiment of the present application;

[0045] Figure 6 A schematic diagram of a roll-pressing process in a method for manufacturing a secondary battery provided in one embodiment of the present application;

[0046] Figure 7 This is a schematic cross-sectional view of the structure of a secondary battery after the first rolling process is completed in a manufacturing method of the secondary battery provided in one embodiment of the present application;

[0047] Figure 8 A schematic cross-sectional view of the second rolling process completed in a method for manufacturing a secondary battery provided in one embodiment of the present application;

[0048] Figure 9A schematic cross-sectional structure diagram of forming a negative electrode plate in a method for manufacturing a secondary battery provided in one embodiment of the present application.

[0049] Description of reference numerals:

[0050] 10. Laminated structure; 100. Negative electrode current collector; 200. Negative electrode active material layer; 300. Support layer; 1000. Rolling shaft. DETAILED DESCRIPTION

[0051] As we can see from the background, with the increasing market demand for lithium-ion batteries, there's a need to reduce battery production costs and increase battery capacity. The thinner the copper foil in a battery cell, the less copper is used per unit battery. This reduction in copper usage reduces production costs while increasing battery capacity. Therefore, the copper foil in battery cells is becoming increasingly thin. During the electrode processing process, the electrode sheet undergoes a roller-pressing process to ensure that the active material adheres more closely to the current collector surface.

[0052] However, the tensile strength and elongation of ultra-thin copper foils struggle to meet the requirements of roller-pressing processes. During roller-pressing, the foil is prone to breakage due to uneven tension and insufficient interfacial bonding. Related technologies attempt to mitigate this problem by improving the mechanical properties of the copper foil itself or by creating composite copper foil structures (such as PET copper foil, which consists of a PET film substrate covered with metallic copper on both sides). However, the former is costly and the latter is complex.

[0053] The present application provides a method for preparing a secondary battery. During the manufacturing process of a negative electrode sheet, a support layer is formed after the negative electrode active material layer of the sheet is formed. The overall structural strength of the laminated structure formed by the support layer, the negative electrode active material layer, and the negative electrode current collector is significantly increased compared to the overall structural strength of a negative electrode sheet without a support layer. This prevents the negative electrode current collector from breaking during subsequent rolling. Furthermore, a greater rolling pressure can be applied to the laminated structure, allowing the negative electrode active material layer to better adhere to the surface of the negative electrode current collector, thereby reducing the contact resistance between the negative electrode active material layer and the negative electrode current collector and improving the energy density of the secondary battery. The support layer is removed in a subsequent step without affecting the performance of the negative electrode sheet.

[0054] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly indicate the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined. Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0055] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0056] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0057] In the description of the embodiments of the present application, the technical terms "center," "longitudinal," "transverse," "length," "width," "thickness," "up," "down," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inside," "outside," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely for ease of description and simplification of the embodiments of the present application. They are not intended to indicate or imply that the devices or elements referred to must have, be constructed, or operate in a specific orientation, and are therefore not to be construed as limiting the embodiments of the present application. For example, if the device or element in the figure is inverted, then an element described as being "below," "beneath," "under," or "below" another element or feature would be oriented "above" or "on top" of the other element or feature. Therefore, the term "below" can encompass both above and below orientations, depending on the context in which the term is used, as will be apparent to one of ordinary skill in the art. Materials can be oriented in other ways (e.g., rotated 90 degrees, inverted, flipped), and the spatially relative descriptors used herein should be interpreted accordingly.

[0058] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0059] In the accompanying drawings corresponding to the embodiments of the present application, the thickness and area of ​​each layer are exaggerated for better understanding and ease of description. In addition, when a component is described as being "substantially" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a portion of the edge of the entire surface.

[0060] In the description of the embodiments of the present application, when a certain component "includes" another component, unless otherwise stated, other components are not excluded, and other components may be further included. A second component is formed or provided above or on the first component, or a second component is formed or provided on the surface of the first component, or a second component is formed or provided on one side of the first component. Embodiments in which the first component and the second component are in direct contact may be included, and embodiments in which additional components may be provided between the first component and the second component so that the first component and the second component may not be in direct contact may also be included. For the sake of simplicity and clarity, various components may be arbitrarily drawn in different proportions. In the accompanying drawings, some layers / components may be omitted for simplicity. Unless otherwise specified, a second component is formed or provided on the surface of the first component, which means that the first component is in direct contact with the second component. Among them, the above-mentioned "components" may refer to layers, films, regions, parts, structures, etc.

[0061] The terms used herein in the description of the various embodiments are intended only to describe the specific embodiments and are not intended to be limiting. As used in the description of the various embodiments and the appended claims, "the component" is intended to include the plural form unless the context clearly indicates otherwise. A component includes a layer, film, region, or plate.

[0062] The following detailed description of the various embodiments of the present application is provided in conjunction with the accompanying drawings. However, those skilled in the art will appreciate that many technical details are provided in the various embodiments of the present application to facilitate a better understanding of the present application. However, even without these technical details and the various variations and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0063] Figure 1 、 Figure 2 A flowchart of the steps of a method for manufacturing a secondary battery provided in an embodiment of the present application.

[0064] refer to Figure 1 、 Figure 2 , a method for manufacturing a secondary battery includes:

[0065] S10, providing a battery cell assembly, the battery cell assembly including a positive electrode sheet, a separator, and a negative electrode sheet, wherein the steps of forming the negative electrode sheet include:

[0066] S1, providing a negative electrode current collector 100, the thickness of the negative electrode current collector 100 is h, wherein 0<h≤5μm;

[0067] S2, forming a negative electrode active material layer 200 on at least one side of the negative electrode current collector 100;

[0068] S3, forming a support layer 300 on the surface of the negative electrode active material layer 200 facing away from the negative electrode current collector 100, the negative electrode current collector 100, the negative electrode active material layer 200 and the support layer 300 constitute a stacked structure 10;

[0069] S4, performing a roll pressing process on the stacked structure 10;

[0070] S5, removing the support layer 300 to obtain a negative electrode sheet;

[0071] S20, providing a housing, wherein the housing has a receiving cavity, placing the battery cell assembly in the receiving cavity and injecting electrolyte into the receiving cavity.

[0072] The following will be combined Figures 1 to 8 The embodiments of the present application are described in more detail.

[0073] Reference Figure 1 As shown, Figure 1 A flowchart of a method for manufacturing a secondary battery according to an embodiment of the present application is shown, including:

[0074] In step S10, a battery cell assembly is provided, which includes a positive electrode sheet, a separator, and a negative electrode sheet. The separator separates the positive electrode sheet from the negative electrode sheet. The battery cell assembly can be a wound structure, in which the positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence and wound more than two times to form the battery cell assembly. The battery cell assembly can also be a laminated structure, in which multiple positive electrode sheets and negative electrode sheets are provided, and multiple positive electrode sheets and negative electrode sheets are alternately stacked, and the separator separates adjacent positive electrode sheets and negative electrode sheets.

[0075] The negative electrode is an electrode with a low potential that contains active substances that undergo oxidation reactions during discharge.

[0076] In step S20, a housing is provided, wherein the housing has a receiving cavity, a battery cell assembly is placed in the receiving cavity, and an electrolyte is injected into the receiving cavity, thereby finally obtaining a secondary battery.

[0077] The shape of the shell can be cylindrical, square or any other shape.

[0078] The secondary battery may be a lithium-ion battery or a sodium-ion battery, or other batteries that can be recharged to activate the active material after discharge for continued use.

[0079] Reference Figure 2As shown, Figure 2 A flowchart of the steps of forming a negative electrode sheet in a method for manufacturing a secondary battery according to an embodiment of the present application is shown. The method of forming the negative electrode sheet includes:

[0080] In step S1, Figure 3 As shown, a negative electrode current collector 100 is provided. The negative electrode current collector 100 is a sheet-like structure extending along the length direction.

[0081] The negative electrode current collector 100 is made of copper foil, nickel foil, or cobalt foil. These materials are characterized by their inherent good electrical conductivity and a unique porous surface structure that allows for better integration with the active material, providing more contact points and diffusion channels, facilitating electron conduction and ion diffusion, thereby improving the charge-discharge performance and cycle stability of the secondary battery. This porous structure also provides a larger surface area and more active reaction sites, facilitating uniform distribution of the active material and more efficient electrochemical reactions.

[0082] Furthermore, the thickness of the negative electrode current collector 100 is the foil thickness h, which satisfies 0μm < h ≤ 5μm. Optionally, 3μm ≤ h ≤ 5μm, and the foil thickness h of the negative electrode current collector 100 can be 3μm, 3.5μm, 4μm, or 4.5μm. Compared to related technologies, the negative electrode current collector 100 in the secondary battery of the present embodiment is thinner, which reduces the amount of copper used in the secondary battery, but the secondary battery of the present embodiment has a higher energy density.

[0083] In step S2, as Figure 4 As shown, the negative electrode active material layer 200 is formed on at least one side of the negative electrode current collector 100 .

[0084] The material of the negative electrode active material layer 200 includes at least one of a carbon-based compound, a silicon-based compound, or a titanium-based compound. During discharge, the negative active material in the negative electrode active material layer 200 releases stored ions and electrons, which are transported to the positive electrode through an external circuit, generating an output current. During charging, the negative active material absorbs ions migrating from the positive electrode through an intercalation reaction.

[0085] It should be noted that, in some embodiments, the negative electrode active material layer 200 is provided on both sides of the negative electrode current collector 100; in other embodiments, the negative electrode active material layer 200 is provided on only one side of the negative electrode current collector 100, which is not specifically limited here.

[0086] In step S3, Figure 5As shown, a support layer 300 is formed on the surface of the negative electrode active material layer 200 facing away from the negative electrode current collector 100. The negative electrode current collector 100, the negative electrode active material layer 200 and the support layer 300 are configured to form a stacked structure 10. The support layer 300 provides mechanical support. The tensile strength of the stacked structure 10 is greatly improved compared to the tensile strength of the transition structure formed by the negative electrode current collector 100 and the negative electrode active material layer 200 obtained in step S2. This is to avoid the occurrence of the problem of the negative electrode current collector 100 in the stacked structure 10 being broken due to uneven tension or insufficient interfacial bonding force during the rolling process of the stacked structure 10 in the subsequent step S4. In addition, the provision of the support layer 300 before the rolling process allows the thickness of the negative electrode current collector 100 to be designed to be thinner, thereby reducing the amount of copper used in the secondary battery and improving the energy density of the secondary battery.

[0087] In some embodiments, the tensile strength of the support layer 300 is a first tensile strength σb1, wherein 10 MPa≤σb1≤120 MPa. Alternatively, 20 MPa≤σb1≤100 MPa. The first tensile strength σb1 of the support layer 300 may be 50 MPa, 70 MPa, or 100 MPa.

[0088] In some embodiments, the tensile strength of the stacked structure 10 is a second tensile strength σb2, wherein 40 MPa≤σb2≤250 MPa. Alternatively, 50 MPa≤σb2≤250 MPa. The second tensile strength σb2 of the stacked structure 10 may be 100 MPa, 150 MPa, or 200 MPa.

[0089] Furthermore, the thickness of the support layer 300 is the support layer thickness D, which satisfies 2 μm<D≤15 μm. Optionally, 8 μm≤D≤15 μm. The support layer thickness D of the support layer 300 can be 8 μm, 10 μm, 12 μm or 15 μm.

[0090] Furthermore, the material of the support layer 300 includes at least one of a water-soluble material, a thermally decomposable material, or a photolytic material. The support layer 300 made of the above material facilitates removal of the support layer 300 in the subsequent step S5, thereby preventing the formation or removal of the support layer 300 from damaging the structure or chemical properties of the negative electrode sheet.

[0091] In some embodiments, when the material of the support layer 300 is a water-soluble material, the material of the support layer 300 includes any one of PVA (polyvinyl alcohol) material, PEG (PEG) material, PVP (polyvinyl pyrrolidone) material or CMC (carboxymethyl cellulose) material.

[0092] In some embodiments, when the material of the support layer 300 is a thermally decomposable material, the material of the support layer 300 includes a PVC material.

[0093] In some embodiments, when the material of the support layer 300 is a photolytic material, the material of the support layer 300 includes at least one of an ethylene-carbon monoxide copolymer material or a vinyl ketone copolymer material.

[0094] Furthermore, the method of forming the support layer 300 includes a wet forming process or a dry forming process.

[0095] In some embodiments, the support layer 300 is formed using a wet molding process. The wet molding process involves coating a negative electrode slurry containing a negative electrode active material on the surface of the negative electrode current collector 100 and then drying the negative electrode slurry to obtain a solidified negative electrode active material layer 200. In other embodiments, the support layer 300 is formed using a dry molding process. The dry molding process involves forming a negative electrode active material film with adhesion properties by combining the negative electrode active material with a binder, and then attaching the negative electrode active material film to the surface of the negative electrode current collector 100 to form the negative electrode active material layer 200. Alternatively, the negative electrode active material is mixed with a binder and then sprayed directly onto the surface of the negative electrode current collector 100 to form a solidified negative electrode active material layer 200.

[0096] The method of forming the support layer 300 includes:

[0097] In step S31, a support slurry is provided. The support slurry contains a dispersoid and a dispersant, wherein the dispersoid is uniformly dispersed in the liquid dispersant. The support slurry can be any one of a solution, a suspension, and an emulsion.

[0098] In step S32 , a support slurry is coated on the surface of the negative electrode active material layer 200 facing away from the negative electrode current collector 100 and dried. The dispersant is evaporated by heat to remove the dispersant, and the remaining dispersoid is solidified to form a support layer 300 .

[0099] Furthermore, the mass percentage of the dispersoid in the support slurry is 3 wt % to 10 wt %. Optionally, the mass percentage of the dispersoid in the support slurry is 5 wt % to 8 wt %, and the mass percentage of the dispersoid in the support slurry can be 6 wt %, 7 wt %, or 8 wt %. A support slurry having an appropriate mass percentage of dispersoids provides the support slurry with good adhesion and film-forming properties, facilitating coating on the surface of the negative electrode active material layer 200 while ensuring that the thickness of the support layer 300 formed after drying is within a reasonable range.

[0100] In step S4, Figure 6As shown, the stacked structure 10 is subjected to a roll-pressing process. The stacked structure 10 is fed to two oppositely disposed and rotating rolling shafts 1000 to roll the thickness of the negative electrode active material layer 200 to a smaller thickness. On the one hand, the roll-pressing process can make the surface of the negative electrode active material layer 200 facing away from the negative electrode current collector 100 smoother and flatter, thereby preventing burrs on the surface of the negative electrode active material layer 200 from piercing the separator and causing a short circuit; the roll-pressing process can also reduce the thickness of the negative electrode active material layer 200 and the thickness of the electrode sheet, thereby increasing the energy density of the secondary battery. On the other hand, the roll-pressing process can also increase the compaction density of the negative electrode active material layer 200, making the negative electrode active material in the negative electrode active material layer 200 more closely in contact and improving electronic conductivity; the roll-pressing process can also make the negative electrode active material layer 200 better adhere to the surface of the negative electrode current collector 100, reducing the contact resistance between the negative electrode active material layer 200 and the negative electrode current collector 100, and improving the performance of the secondary battery.

[0101] In some embodiments, after the stacked structure 10 is subjected to a roll pressing process, the compaction density of the negative electrode active material layer 200 is a compaction density ρ, which satisfies 1.4 g / cm 3 ≤ρ≤1.8g / cm 3 Optional, 1.5g / cm 3 ≤ρ≤1.7g / cm 3 The compaction density ρ of the negative electrode active material layer 200 may be 1.5 g / cm 3 , 1.6g / cm 3 or 1.7 g / cm 3 .

[0102] The method for rolling the laminated structure 10 includes a secondary rolling process, that is, the first rolling and the second rolling are performed on the laminated structure 10 in sequence. Figure 7 As shown, the laminated structure 10 after the second rolling is completed is as shown in FIG. Figure 8 As shown in the figure, the secondary rolling process first rolls the negative electrode active material layer 200 to a certain thickness after the first rolling process, and then rolls the negative electrode active material layer 200 to the designed thickness and density through a second rolling process. The secondary rolling process not only minimizes the breakage of active material particles within the active material layer, but also evenly distributes the pores within the active material layer, thereby promoting electrolyte infiltration, reducing the internal resistance of the negative electrode sheet, and thus improving the performance of the secondary battery.

[0103] Furthermore, the first rolling pressure is a first rolling pressure P1, and the second rolling pressure is a second rolling pressure P2, satisfying P1 < P2. The second rolling pressure is greater than the first rolling pressure, thus avoiding the phenomenon in the related art where the negative electrode current collector 100 in the negative electrode sheet undergoes instantaneous deformation under high pressure and then tears due to concentrated gravity when the negative electrode sheet is only rolled once.

[0104] In the secondary rolling process of the embodiment of the present application, the compaction density of the negative electrode active material layer 200 in the stacked structure 10 is first increased and the thickness is reduced through the first rolling, so that the negative electrode active material layer 200 in the stacked structure 10 has higher mechanical strength to improve the overall mechanical strength of the stacked structure 10; the thickness of the negative electrode active material layer 200 is reduced in the first rolling so that the thickness change of the negative electrode active material layer 200 in the second rolling is reduced, and the deformation amplitude of the negative electrode current collector 100 in the second rolling is reduced, thereby reducing the probability of tearing of the negative electrode current collector 100 during the rolling process, thereby improving the yield rate of the secondary battery.

[0105] In some embodiments, the first rolling pressure P1 of the first rolling process satisfies 30 MPa≤P1≤50 MPa. Alternatively, 35 MPa≤P1≤45 MPa. The first rolling pressure P1 of the first rolling process may be 35 MPa, 40 MPa, or 45 MPa.

[0106] In some embodiments, the second rolling pressure P2 of the second rolling process satisfies 60 MPa≤P2≤90 MPa. Alternatively, 70 MPa≤P2≤80 MPa. The second rolling pressure P2 of the second rolling process may be 70 MPa, 75 MPa, or 80 MPa.

[0107] It should be noted that, in some embodiments, the rolling process is a secondary rolling process; in other embodiments, the number of rolling processes may be greater than two times, and the rolling pressure gradually increases, that is, the latter rolling pressure is greater than the former rolling pressure, which is not specifically limited here.

[0108] Furthermore, the thickness of the negative electrode active material layer 200 before the roll-pressing process is a first thickness H1, the thickness of the negative electrode active material layer 200 after the first roll-pressing process is a second thickness H2, and the thickness of the negative electrode active material layer 200 after the second roll-pressing process is a third thickness H3, satisfying 0.5H1≤H2≤0.95H1, 0.6H1≤H3≤0.9H1. Optionally, 0.7H1≤H2≤0.9H1, 0.75H1≤H3≤0.8H1.

[0109] In some embodiments, the first thickness H1 of the negative electrode active material layer 200 before the roll-pressing process satisfies 165 μm ≤ H1 ≤ 200 μm. Alternatively, 175 μm ≤ H1 ≤ 195 μm. The first thickness H1 of the negative electrode active material layer 200 before the roll-pressing process may be 175 μm, 180 μm, 185 μm, or 190 μm.

[0110] In some embodiments, the second thickness H2 of the negative electrode active material layer 200 after the first rolling process satisfies 130 μm ≤ H2 ≤ 170 μm. Alternatively, 140 μm ≤ H2 ≤ 160 μm. The second thickness H2 of the negative electrode active material layer 200 after the first rolling process may be 140 μm, 145 μm, 150 μm, or 155 μm.

[0111] In some embodiments, the third thickness H3 of the negative electrode active material layer 200 after the second rolling process satisfies 125 μm ≤ H3 ≤ 150 μm. Alternatively, 130 μm ≤ H3 ≤ 140 μm. The third thickness H3 of the negative electrode active material layer 200 after the second rolling process may be 130 μm, 135 μm, 138 μm, or 140 μm.

[0112] In order to better illustrate the beneficial effects brought about by the embodiments of the present application, the following corresponding embodiments and comparative examples are provided for illustration, and the specific reference is made to the table below:

[0113] Table 1:

[0114]

[0115] It can be seen from Examples 1 to 8, Comparative Example 1 and Comparative Example 2 in Table 1 that the tape breakage rate of the stacked structure 10 formed after the support layer 300 is set and the roll pressing process is much lower than the tape breakage rate of the electrode piece without the support layer 300 being directly rolled. The support layer 300 provides mechanical support during the rolling process, improves the tensile strength of the stacked structure 10, and thereby reduces the tape breakage rate of the negative electrode current collector 100 during the rolling process.

[0116] As can be seen from Examples 1 to 4, Comparative Examples 3, and 4 in Table 1, when the material of the support layer 300, the process, and parameters of the roll-pressing treatment are the same, the thicker the support layer 300, the lower the tape breakage rate of the negative electrode current collector 100 during the roll-pressing treatment. However, when the thickness of the support layer 300 is less than 3 μm, the tape breakage rate of the negative electrode current collector 100 is still too high, and the support layer 300 is unable to play a protective role during the roll-pressing treatment. When the thickness of the support layer 300 is greater than 12 μm, although the tape breakage rate of the negative electrode current collector 100 decreases, the decrease is small, and the excessive thickness of the support layer 300 leads to excessively high costs for the subsequent process of removing the support layer 300.

[0117] It can be seen from Example 2, Example 5, Example 6, Comparative Example 5 and Comparative Example 6 in Table 1 that, when the material and thickness of the support layer 300 are the same, the tape breakage rate of the embodiment using the secondary rolling process is lower than the tape breakage rate of the comparative example using the single rolling process. The secondary rolling process used in the embodiment of the present application reduces the probability of the negative electrode current collector 100 being broken during the rolling process, thereby improving the yield rate of the secondary battery.

[0118] It can be seen from Example 2, Example 5, Example 6, Comparative Example 7 and Comparative Example 8 in Table 1 that in the embodiments using the secondary rolling process, when the material and thickness of the support layer 300 are the same, the broken belt rate of the embodiments in which the rolling pressure of the second rolling is greater than the rolling pressure of the first rolling is lower than that of the embodiments in which the rolling pressures of the two rollings are equal or the rolling pressure of the first rolling is greater than the rolling pressure of the second rolling. The rolling treatment of the embodiments of the present application adopts the technical solution that the rolling pressure of the latter rolling is greater than the rolling pressure of the previous rolling, which further reduces the probability of the negative electrode current collector 100 being broken during the rolling process and improves the yield rate of the secondary battery.

[0119] Furthermore, during the roll-pressing step of the stacked structure 10, the support layer 300 is also heated. Heating the support layer 300 to a certain temperature increases the tensile strength of the support layer 300, thereby increasing the tensile strength of the stacked structure 10, further preventing the negative electrode current collector 100 from tearing during the roll-pressing process.

[0120] Furthermore, the heat treatment method includes heating the rolling shaft 1000 used in the rolling process, so that heat is conducted between the rolling shaft 1000 and the support layer 300 in the laminated structure 10 in contact therewith, thereby increasing the temperature of the support layer 300 and thereby improving the tensile strength of the support layer 300. In some embodiments, a heating resistor is disposed within the rolling shaft 1000, and when the heating resistor is energized, the rolling shaft 1000 is heated.

[0121] In some embodiments, the heating temperature T2 of the heat treatment satisfies 40°C ≤ T2 ≤ 50°C. Alternatively, 42°C ≤ T2 ≤ 48°C. The heating temperature T2 of the heat treatment may be 42°C, 44°C, 46°C, or 48°C.

[0122] It should be noted that, since the support layer 300 has a high tensile strength, the thickness of the support layer 300 hardly changes after the rolling process, so that the negative electrode active material layer 200 can reach the target thickness.

[0123] It should also be noted that, in some embodiments, Figure 6 As shown, the thickness of the negative active material layer 200 on both sides of the negative current collector 100 is equal, and the thickness of the support layer 300 on both sides of the negative current collector 100 is also equal. During the roll pressing process of the stacked structure 10, the negative active material layers 200 on both sides of the negative current collector 100 are subjected to the same rolling pressure, and the thickness of the negative active materials on both sides after rolling is also the same, and the negative current collector 100 will not undergo sudden deformation during the rolling process.

[0124] In other embodiments, the thickness of the negative active material layer 200 on both sides of the negative current collector 100 is different, and the thickness of the support layer 300 on both sides of the negative current collector 100 is also different. The negative active material layer 200 and the support layer 300 on one side of the negative current collector 100 are constructed into a combined structure. The thickness of the negative electrode active material layer 200 in the combined structure on one side of the negative electrode current collector 100 is greater than the thickness of the other negative electrode active material layer 200, but the thickness of the support layer 300 in the combined structure of the negative electrode active material layer 200 with a larger thickness is greater than the thickness of the other support layer 300, that is, the negative electrode active material layer 200 with a larger thickness is matched with the support layer 300 with a smaller thickness, and the negative electrode active material layer 200 with a smaller thickness is matched with the support layer 300 with a larger thickness, so that the tensile strength of the combined structure on both sides of the negative electrode current collector 100 is consistent, avoiding the problem of sudden deformation or even belt breakage of the negative electrode current collector 100 during rolling due to inconsistent tensile strength of the combined structure on both sides of the negative electrode current collector 100, thereby further improving the yield rate of the secondary battery.

[0125] In step S5, Figure 9 As shown, the support layer 300 is removed to obtain a negative electrode sheet consisting of the negative electrode current collector 100 and the negative electrode active material layer 200. The removal of the support layer 300 does not affect the physical and chemical characteristics of the negative electrode sheet and the battery cell assembly formed by subsequent assembly.

[0126] In the case where the material of the support layer 300 is a water-soluble material, the method of removing the support layer 300 includes:

[0127] In step S51, the support layer 300 is subjected to a steam dissolution treatment to remove the support layer 300. The support layer 300 is heated in a water vapor atmosphere, causing the water-soluble material in the support layer 300 to dissolve into the water vapor, thereby achieving preliminary removal of the support layer 300. The high-temperature water vapor atmosphere accelerates the dissolution rate of the negative electrode active material layer 200, thereby reducing the amount of support layer 300 remaining on the surface of the negative electrode active material layer 200 after the steam dissolution treatment. The low-pressure water vapor atmosphere prevents the negative electrode active material layer 200 from being damaged by the high-pressure steam flow, thereby improving the yield rate of the secondary battery.

[0128] In step S52, the surface of the negative electrode active material layer 200 is cleaned. An aqueous solution is used to clean the surface of the negative electrode active material layer 200 at low pressure. The remaining support layer 300 dissolves in the aqueous solution, thereby removing the remaining support layer 300 from the surface of the negative electrode active material layer 200. Low-pressure cleaning of the negative electrode active material layer 200 prevents damage to the negative electrode active material layer 200 by high-pressure water flow, thereby improving the yield rate of the secondary battery.

[0129] Furthermore, the process parameters of the steam dissolution treatment include: a process temperature T1 of the water vapor atmosphere, which satisfies 85°C ≤ T1 ≤ 110°C. Optionally, 90°C ≤ T1 ≤ 105°C. The process temperature T1 of the water vapor atmosphere may be 90°C, 95°C, 100°C, or 105°C.

[0130] Furthermore, the process parameters of the steam dissolution treatment also include: a vapor pressure p1 of the water vapor atmosphere, which satisfies 0.2 MPa ≤ p1 ≤ 0.1 MPa. Optionally, 0.12 MPa ≤ p1 ≤ 0.18 MPa. The vapor pressure p1 of the water vapor atmosphere can be 0.12 MPa, 1.14 MPa, 0.16 MPa, or 0.18 MPa.

[0131] Furthermore, the water flow pressure p2 for low-pressure cleaning of the negative electrode active material layer 200 satisfies 0.1 MPa ≤ p2 ≤ 0.5 MPa. Optionally, 0.3 MPa ≤ p2 ≤ 0.4 MPa. The water flow pressure p2 of the water vapor atmosphere can be 0.3 MPa, 0.34 MPa, 0.38 MPa, or 0.4 MPa. Low-pressure cleaning of the negative electrode active material layer 200 prevents damage to the negative electrode active material layer 200 by high-pressure water flow, thereby improving the yield rate of the secondary battery.

[0132] In the case where the material of the support layer 300 is a thermally decomposable material, the method for removing the support layer 300 includes:

[0133] In step S53 , the support layer 300 is subjected to a heat treatment to thermally decompose the support layer 300 . The support layer 300 is thermally decomposed into gas and a small amount of small molecular particles remain.

[0134] Step S54: Removing small molecule particles remaining on the surface of the negative electrode active layer. In some embodiments, a soot blowing process is used to remove small molecule particles remaining on the surface of the negative electrode active layer. This process involves using a high-pressure airflow to remove small molecule particles, thereby cleaning the surface of the negative electrode active layer without affecting the physical and chemical properties of the negative electrode sheet. In other embodiments, low-pressure cleaning is used to remove small molecule particles remaining on the surface of the negative electrode active layer.

[0135] In the case where the material of the support layer 300 is a photolytic material, the method for removing the support layer 300 includes:

[0136] In step S55 , the support layer 300 is subjected to light irradiation treatment to cause photolysis of the support layer 300 . The support layer 300 is decomposed into gas and a small amount of residual small molecular particles under the light irradiation.

[0137] Step S56: Removing small molecule particles remaining on the surface of the negative electrode active layer. In some embodiments, a soot blowing process is used to remove small molecule particles remaining on the surface of the negative electrode active layer. This process involves using a high-pressure airflow to remove small molecule particles, thereby cleaning the surface of the negative electrode active layer without affecting the physical and chemical properties of the negative electrode sheet. In other embodiments, low-pressure cleaning is used to remove small molecule particles remaining on the surface of the negative electrode active layer.

[0138] Accordingly, another embodiment of the present application further provides a secondary battery, which can be obtained by the above-mentioned secondary battery manufacturing method. The secondary battery includes:

[0139] A housing having an accommodating cavity therein;

[0140] The battery cell assembly is installed in the accommodating cavity; the battery cell assembly includes: a positive electrode sheet, a separator and a negative electrode sheet; the negative electrode sheet includes: a negative electrode current collector 100 and a negative electrode active material layer 200;

[0141] The thickness of the negative electrode current collector 100 is the foil thickness h, where 0<h≤5 μm.

[0142] Correspondingly, another embodiment of the present application further provides an energy storage system, which includes a plurality of secondary batteries. The secondary batteries can be obtained by the above-mentioned secondary battery manufacturing method or are the above-mentioned secondary batteries.

[0143] Correspondingly, another embodiment of the present application further provides an electrical device, which includes a plurality of secondary batteries. The secondary batteries can be obtained by the above-mentioned secondary battery manufacturing method or are the above-mentioned secondary batteries.

[0144] Those skilled in the art will appreciate that the above-described embodiments are specific examples for implementing the present application, and that in actual applications, various changes in form and detail may be made thereto without departing from the spirit and scope of the present application. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined in the claims.

Claims

1. A method for preparing a secondary battery, characterized in that: include: A battery cell assembly is provided, the battery cell assembly comprising a positive electrode sheet, a separator, and a negative electrode sheet, wherein the steps of forming the negative electrode sheet include: Providing a negative electrode current collector, wherein the thickness of the negative electrode current collector is the foil thickness h, wherein 3 μm≤h≤5 μm; forming a negative electrode active material layer on at least one side surface of the negative electrode current collector; forming a support layer on a surface of the negative electrode active material layer facing away from the negative electrode current collector, wherein the negative electrode current collector, the negative electrode active material layer and the support layer constitute a stacked structure; performing a roll pressing process on the laminated structure; Removing the support layer to obtain the negative electrode sheet; A shell is provided, wherein the shell has a receiving cavity, the battery core assembly is placed in the receiving cavity and an electrolyte is injected into the receiving cavity.

2. The method for preparing a secondary battery according to claim 1, wherein: Before the rolling process, the thickness of the support layer satisfies: 2 μm≤D≤15 μm, where D is the thickness of the support layer.

3. The method for preparing a secondary battery according to claim 1, wherein: After the stacked structure is subjected to the roll pressing process, the compaction density of the negative electrode active material layer satisfies: 1.4 g / cm 3 ≤ρ≤1.8g / cm 3 , ρ is the compaction density of the negative electrode active material layer.

4. The method for preparing a secondary battery according to claim 1, wherein: The material of the support layer includes at least one of a water-soluble material, a thermally decomposable material, or a photolytic material.

5. The method for preparing a secondary battery according to claim 1 or 4, wherein: The method of forming the support layer includes: Providing a support slurry, wherein the support slurry contains a dispersant and a dispersant; The support slurry is coated on the surface of the negative electrode active material layer on the side away from the negative electrode current collector and dried to remove the dispersant, and the dispersoid is solidified to form the support layer.

6. The method for preparing a secondary battery according to claim 5, wherein: In terms of mass percentage, the mass percentage of the dispersoid in the support slurry is 3 wt % to 10 wt %.

7. The method for preparing a secondary battery according to claim 4, wherein: The material of the support layer is a water-soluble material; The method for removing the support layer comprises: performing a steam dissolution treatment on the support layer to remove the support layer; The surface of the negative electrode active material layer is cleaned.

8. The method for preparing a secondary battery according to claim 7, wherein: The process parameters of the steam dissolution treatment include: heating treatment in a water vapor atmosphere, 85° C.≤T1≤110° C., 0.1 MPa≤p1≤0.2 MPa, T1 is the process temperature, and p1 is the steam pressure.

9. The method for preparing a secondary battery according to claim 4, wherein: The water-soluble material includes at least one of a PVA material, a PEG material, a PVP material, a CMC material, a PVC material, an ethylene-carbon monoxide copolymer or a vinyl ketone copolymer material.

10. The method for preparing a secondary battery according to claim 1, wherein: During the step of performing the rolling treatment, the support layer is also subjected to a heating treatment, and the heating temperature of the heating treatment satisfies: 40° C. ≤ T2 ≤ 50° C., where T2 is the heating temperature of the heating treatment.

11. The method for preparing a secondary battery according to claim 1, wherein: The rolling process includes: rolling the stacked structure multiple times, and the rolling pressure of the previous rolling process is less than or equal to the rolling pressure of the next rolling process.

12. The method for preparing a secondary battery according to claim 11, wherein: The rolling process includes a first rolling process and a second rolling process performed successively, and the first rolling process and the second rolling process satisfy: 30MPa≤P1≤50MPa, 60MPa≤P2≤90MPa, wherein P1 is the rolling pressure of the first rolling process, and P2 is the rolling pressure of the second rolling process.

13. The method for preparing a secondary battery according to claim 1, wherein: The tensile strength of the support layer is a first tensile strength σb1, wherein 10 MPa≤σb1≤120 MPa.

14. The method for preparing a secondary battery according to claim 1, wherein: The tensile strength of the stacked structure is a second tensile strength σb2, wherein 40 MPa≤σb2≤250 MPa.

15. A secondary battery, characterized in that: The secondary battery is obtained by the preparation method of the secondary battery according to any one of claims 1 to 14; The secondary battery includes: A housing, wherein the housing has an accommodating cavity therein; A battery cell assembly, the battery cell assembly being installed in the accommodating cavity; the battery cell assembly comprising: a positive electrode sheet, a separator and a negative electrode sheet; the negative electrode sheet comprising: a negative electrode current collector and a negative electrode active material layer; The thickness of the negative electrode current collector is the foil thickness h, wherein 3 μm≤h≤5 μm.

16. An energy storage system, characterized in that: include: Several secondary batteries are provided, wherein the secondary batteries are obtained by the method for preparing a secondary battery according to any one of claims 1 to 14 or the secondary battery according to claim 15.

17. An electrical device, characterized in that: include: Several secondary batteries are provided, wherein the secondary batteries are obtained by the method for preparing a secondary battery according to any one of claims 1 to 14 or the secondary battery according to claim 15.

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