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

Abstract

The embodiment of the invention relates to the field of secondary batteries, and provides a secondary battery and a preparation method thereof, an energy storage system and electric equipment, the manufacturing method of the secondary battery comprises the following steps: providing a battery cell assembly, the battery cell assembly comprises a positive pole piece, a diaphragm and a negative pole piece, and the negative pole piece is formed by the following steps: providing a negative current collector; forming a negative electrode active material layer on at least one side surface of the negative electrode current collector; a supporting layer is formed on the surface of one side, deviating from the negative current collector, of the negative active material layer, and the negative current collector, the negative active material layer and the supporting layer form a laminated structure; carrying out rolling treatment on the laminated structure; removing the supporting layer to obtain a negative pole piece; a shell is provided, the shell is provided with a containing cavity, the battery cell assembly is arranged in the containing cavity, and electrolyte is injected into the containing cavity. According to the embodiment of the invention, at least the problem of strip breakage of the ultrathin copper foil in the rolling treatment process can be solved.

Description

Technical Field

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

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

[0003] The performance of lithium-ion batteries mainly depends on the electrode sheets, electrolyte, separator and other battery materials contained therein, among which the electrode sheets are particularly important. During the processing of the electrode sheets, in order to help the active material better adhere to the surface of the current collector, the electrode sheets need to be roll-pressed. The thinner and lighter the copper foil in the electrode sheet, the less the copper consumption per unit battery. On the one hand, the reduction of copper consumption reduces the production cost of the battery; on the other hand, when the copper foil becomes thinner and the copper consumption decreases, the available space inside the battery cell can be increased without changing the volume of the battery cell, and more active material layers can be provided, thereby increasing the battery cell capacity and battery energy density.

[0004] Therefore, how to design a secondary battery with an 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, a preparation method thereof, an energy storage system and an electrical device, which are at least beneficial to solving the problem of tape breakage occurring during the roll-pressing process of the ultra-thin copper foil.

[0006] According to some embodiments of the present application, on the one hand, a manufacturing method of a secondary battery is provided, including: Providing a battery cell assembly, the battery cell assembly including a positive electrode sheet, a separator and a negative electrode sheet, wherein the formation steps of the negative electrode sheet include: Providing a negative current collector, the thickness of the negative current collector being the foil thickness h, where 0 < h ≤ 5 μm; Forming a negative active material layer on at least one surface of the negative current collector; Forming a support layer on the 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 constituting a laminated structure; Performing a roll-pressing process on the laminated structure; Removing the support layer to obtain the negative electrode sheet; Providing a housing having an accommodation cavity, placing the battery cell assembly in the accommodation cavity and injecting an electrolyte into the accommodation cavity.

[0007] 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.

[0008] In some embodiments, after the rolling process on the laminated structure, the tap density of the negative electrode active material layer satisfies: 1.4 g / cm 3 ≤ ρ ≤ 1.8 g / cm 3 , where ρ is the tap density of the negative electrode active material layer.

[0009] In some embodiments, the material of the support layer includes at least one of water-soluble materials, thermally decomposable materials, or photolytic materials.

[0010] In some embodiments, the method of forming the support layer includes: Providing a support slurry, which contains a dispersoid and a dispersant; Coating the support slurry on the surface of the negative electrode active material layer facing away from the negative electrode current collector and performing a drying process to remove the dispersant, and the dispersoid solidifies to form the support layer.

[0011] In some embodiments, by mass percentage, the mass percentage of the dispersoid in the support slurry is 3 wt% to 10 wt%.

[0012] In some embodiments, the material of the support layer is a water-soluble material; the method of removing the support layer includes: Performing a steam dissolution process on the support layer to remove the support layer; Performing a cleaning process on the surface of the negative electrode active material layer.

[0013] In some embodiments, the process parameters of the steam dissolution process include: performing a heating process in a water vapor atmosphere, 85 °C ≤ T1 ≤ 110 °C, 0.1 MPa ≤ p1 ≤ 0.2 MPa, where T1 is the process temperature and p1 is the steam pressure.

[0014] In some embodiments, the water-soluble material includes at least one of PVA material, PEG material, PVP material, CMC material, PVC material, ethylene-carbon monoxide copolymer, or vinyl ketone copolymer material.

[0015] In some embodiments, in the step of performing the rolling process, the support layer is also heated, and the heating temperature of the heating process satisfies: 40 °C ≤ T2 ≤ 50 °C, where T2 is the heating temperature of the heating process.

[0016] In some embodiments, the rolling process includes: rolling the laminated structure multiple times, and the rolling pressure of the previous rolling is less than or equal to the rolling pressure of the subsequent rolling.

[0017] In some embodiments, the rolling process includes a first rolling and a second rolling performed successively. The first rolling and the second rolling satisfy: 30 MPa ≤ P1 ≤ 50 MPa, 60 MPa ≤ P2 ≤ 90 MPa, where P1 is the rolling pressure of the first rolling and P2 is the rolling pressure of the second rolling.

[0018] In some embodiments, the tensile strength of the support layer is a first tensile strength σb1, where 10 MPa ≤ σb1 ≤ 120 MPa.

[0019] In some embodiments, the tensile strength of the laminated structure is a second tensile strength σb2, where 40 MPa ≤ σb2 ≤ 250 MPa.

[0020] According to some embodiments of the present application, on the other hand, the present application embodiments further provide a secondary battery, which is obtained by the preparation method of the secondary battery as described in any one of the above; The secondary battery includes: A housing having an accommodation cavity inside; A battery cell assembly installed in the accommodation cavity; the battery cell assembly includes: a positive electrode plate, a separator, and a negative electrode plate; the negative electrode plate includes: a negative electrode current collector and a negative electrode active material layer; Wherein, the thickness of the negative electrode current collector is a foil thickness h, where 0 < h ≤ 5 μm.

[0021] According to some embodiments of the present application, on the other hand, the present application embodiments further provide an energy storage system, which includes: a plurality of secondary batteries, and the secondary batteries are obtained by the preparation method of the secondary battery as described in any one of the above or the secondary battery as described above.

[0022] According to some embodiments of the present application, on the other hand, the present application embodiments further provide an electrical device, which includes: a plurality of secondary batteries, and the secondary batteries are obtained by the preparation method of the secondary battery as described in any one of the above or the secondary battery as described above.

[0023] The technical solution provided by the embodiments of the present application has at least the following advantages: By forming a support layer on the surface of the negative electrode active material layer during the formation of the negative electrode plate, the overall mechanical strength is improved. The support layer provides a supporting force during the subsequent rolling process, avoiding the problem of the negative electrode current collector breaking. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the figures in the drawings do not constitute a scale limitation. To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0025] Figure 1 It is a flowchart of the steps of a manufacturing method of a secondary battery provided by an embodiment of the present application; Figure 2 It is a flowchart of the steps of forming a negative electrode plate in a manufacturing method of a secondary battery provided by an embodiment of the present application; Figure 3 It is a schematic cross-sectional structure diagram of a negative electrode current collector provided in a manufacturing method of a secondary battery provided by an embodiment of the present application; Figure 4 It is a schematic cross-sectional structure diagram of forming a negative electrode material layer in a manufacturing method of a secondary battery provided by an embodiment of the present application; Figure 5 It is a schematic cross-sectional structure diagram of forming a support layer in a manufacturing method of a secondary battery provided by an embodiment of the present application; Figure 6 It is a schematic diagram of roll pressing treatment in a manufacturing method of a secondary battery provided by an embodiment of the present application; Figure 7 It is a schematic cross-sectional structure diagram of completing the first roll pressing treatment in a manufacturing method of a secondary battery provided by an embodiment of the present application; Figure 8 It is a schematic cross-sectional structure diagram of completing the second roll pressing treatment in a manufacturing method of a secondary battery provided by an embodiment of the present application; Figure 9 It is a schematic cross-sectional structure diagram of forming a negative electrode plate in a manufacturing method of a secondary battery provided by an embodiment of the present application.

[0026] Explanation of reference numerals: 10. Laminated structure; 100. Negative electrode current collector; 200. Negative electrode active material layer; 300. Support layer; 1000. Roll pressing shaft. Detailed implementation manners

[0027] As is known from the background art, with the gradual increase in the market demand for lithium batteries, it is necessary to reduce the production cost of batteries and increase the battery capacity. The thinner and lighter the copper foil in the battery cell, the less copper is used per unit battery. The reduction in copper usage can not only reduce the production cost of the battery but also increase the battery capacity. Therefore, the copper foil in the battery cell is developing towards being extremely thin. During the processing of the electrode sheet, it is necessary to perform rolling treatment on the electrode sheet to make the active material better adhere to the surface of the current collector.

[0028] However, the tensile strength and elongation rate of ultra-thin copper foil are difficult to meet the index requirements in the rolling process. The ultra-thin copper foil is prone to tape breakage during the rolling process due to uneven tension and insufficient interfacial bonding force. In related technologies, the problem is alleviated by improving the mechanical properties of the copper foil itself or the composite copper foil structure (such as PET copper foil, which is a structure with a PET film as the base material and metal copper covered on both sides), but the former has a high cost and the latter has a complex process.

[0029] The present application provides a method for preparing a secondary battery. By forming a support layer after the formation of the negative electrode active material layer on the negative electrode sheet during the manufacturing process of the negative electrode sheet, the overall structural strength of the laminated structure composed of the support layer, the negative electrode active material layer, and the negative electrode current collector is greatly increased compared to the overall structural strength of the negative electrode sheet without the support layer. In the subsequent rolling process, the problem of tape breakage of the negative electrode current collector is avoided; and a greater rolling pressure can be applied to the laminated structure, enabling the negative electrode active material layer to better adhere to the surface of the negative electrode current collector, 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 at the same time. The support layer is removed in subsequent steps and does not affect the performance of the negative electrode sheet.

[0030] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity, specific order, or primary-secondary relationship of the indicated technical features. In the description of the embodiments of the present application, "a plurality of" means more than two, unless otherwise clearly and specifically defined. Similarly, "multiple groups" means two or more groups (including two groups), and "multiple pieces" means two or more pieces (including two pieces).

[0031] Referring to "embodiments" herein means that the specific features, structures, or characteristics described in connection with the embodiments may be included in at least one embodiment of the present application. The phrase appears in various positions in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0032] In the description of the embodiments of the present application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: the existence of A, the simultaneous existence of A and B, and the existence of B. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0033] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the embodiments of the present application. For example, if the device or element in the drawing is inverted, then the element described as "below" or "beneath" or "under" or "at the bottom" of other elements or features will be oriented "above" or "at the top" of the said other elements or features. Therefore, the term "below" can cover both the upper and lower orientations depending on the context in which the term is used, which will be obvious to those of ordinary skill in the art. The material can be oriented in other ways (for example, rotated 90 degrees, inverted, flipped), and the spatial relative descriptive terms used herein can be interpreted accordingly.

[0034] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific situations.

[0035] In the corresponding drawings of the embodiments of the present application, for better understanding and convenience of description, the thickness and area of the layer are enlarged. In addition, when describing that a component is "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 on a partial edge of the entire surface.

[0036] In the description of the embodiments of the present application, when a certain component "comprises" another component, unless otherwise stated, other components are not excluded, and other components may further be included. Forming or disposing a second component above or on a first component, or forming or disposing a second component on the surface of the first component, or forming or disposing a second component on one side of the first component, may include embodiments where the first component and the second component are in direct contact, and may also include embodiments where additional components may be present between the first component and the second component such that the first component and the second component are not in direct contact. For simplicity and clarity, various components may be drawn at arbitrary scales. In the drawings, some layers / components may be omitted for simplicity. Unless otherwise specified, forming or disposing a second component on the surface of the first component means that the first component is in direct contact with the second component. Among them, the above-mentioned "component" may refer to a layer, a film, a region, a part, a structure, etc.

[0037] The terms used in the description of the various embodiments herein are only for the purpose of describing 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 also intended to include the plural form unless the context clearly indicates otherwise. Among them, the component includes components such as a layer, a film, a region, or a plate.

[0038] The embodiments of the present application will be described in detail below with reference to the drawings. However, those of ordinary skill in the art can understand that in the embodiments of the present application, many technical details are provided for the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0039] Figure 1 、 Figure 2 It is a flowchart of the steps of a manufacturing method of a secondary battery provided for the embodiments of the present application.

[0040] Refer to Figure 1 、 Figure 2 , the manufacturing method of the secondary battery includes: S10, providing a battery cell assembly, the battery cell assembly includes a positive electrode plate, a separator, and a negative electrode plate, wherein the forming steps of the negative electrode plate include: S1, providing a negative current collector 100, the thickness of the negative current collector 100 is h, wherein 0 < h ≤ 5 μm; S2, forming a negative active material layer 200 on at least one surface of the negative current collector 100; S3, forming a support layer 300 on the surface of the negative active material layer 200 facing away from the negative current collector 100, and the negative current collector 100, the negative active material layer 200, and the support layer 300 constitute a stacked structure 10; S4, perform a rolling process on the stacked structure 10; S5, remove the support layer 300 to obtain the negative electrode sheet; S20, provide a housing having a receiving cavity, place the battery cell assembly in the receiving cavity and inject electrolyte into the receiving cavity.

[0041] The following will combine Figures 1 to 8 to describe the embodiments of the present application in more detail.

[0042] Refer to Figure 1 as shown in Figure 1 FIG. shows a flowchart of steps of a method for manufacturing a secondary battery according to an embodiment of the present application, including: In step S10, provide a battery cell assembly, the battery cell assembly includes a positive electrode sheet, a separator, and a negative electrode sheet. The separator separates the positive electrode sheet and 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 sequentially stacked and wound more than two turns to form the battery cell assembly. The battery cell assembly can also be a stacked structure, in which a plurality of positive electrode sheets and negative electrode sheets are provided, the plurality of positive electrode sheets and negative electrode sheets are alternately stacked, and the separator separates adjacent positive electrode sheets and negative electrode sheets.

[0043] Among them, the negative electrode sheet is an electrode sheet with a low potential containing an active substance that undergoes an oxidation reaction during discharge.

[0044] In step S20, provide a housing having a receiving cavity, place the battery cell assembly in the receiving cavity and inject electrolyte into the receiving cavity. Finally, a secondary battery is obtained.

[0045] Among them, the shape of the housing can be cylindrical, square, or any other shape.

[0046] The secondary battery can be a lithium-ion battery or a sodium-ion battery, or can also be other batteries that can activate the active substance through charging after discharge and continue to be used.

[0047] Refer to Figure 2 as shown in Figure 2 FIG. shows a flowchart of steps of forming a negative electrode sheet in a method for manufacturing a secondary battery according to an embodiment of the present application. The method for forming the negative electrode sheet includes: In step S1, as Figure 3 shown, provide a negative current collector 100, the negative current collector 100 is a sheet-like structure extending along the length direction.

[0048] The material of the negative electrode current collector 100 is any one of copper foil, nickel foil, or cobalt foil. The characteristics of these materials are that they have good electrical conductivity, and the unique porous structure on the surface can better fuse with the active material, providing more contact points and diffusion channels, which is beneficial to electron conduction and ion diffusion, thereby improving the charge and discharge performance and cycle stability of the secondary battery. This porous structure can also provide a larger surface area and richer active reaction sites, which is beneficial to the uniform distribution of the active material and more efficient electrochemical reactions.

[0049] Furthermore, the thickness of the negative electrode current collector 100 is the foil thickness h, satisfying 0 μm < h ≤ 5 μm. Optionally, 3 μm ≤ h ≤ 5 μm, and the foil thickness h of the negative electrode current collector 100 can be 3 μm, 3.5 μm, 4 μm, or 4.5 μm. Compared with the related art, the thickness of the negative electrode current collector 100 in the secondary battery of the embodiment of the present application is thinner, resulting in less copper consumption in the secondary battery, but the energy density of the secondary battery of the embodiment of the present application is higher.

[0050] In step S2, as Figure 4 shown, a negative electrode active material layer 200 is formed on at least one surface of the negative electrode current collector 100.

[0051] The material of the negative electrode active material layer 200 includes at least one of carbon-based compounds, silicon-based compounds, or titanium-based compounds. During discharge, the negative electrode active substances in the negative electrode active material layer 200 release the stored ions and electrons, which are transmitted to the positive electrode through the external circuit to form a current output; during charging, they absorb the ions migrated from the positive electrode through an insertion reaction.

[0052] It should be noted that in some embodiments, the negative electrode active material layer 200 is provided on both surfaces of the negative electrode current collector 100; in other embodiments, the negative electrode active material layer 200 is only provided on one surface of the negative electrode current collector 100, and no specific limitation is made here.

[0053] In step S3, as 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 into a laminated structure 10. The support layer 300 provides mechanical support, and the tensile strength of the laminated 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, so as to avoid the occurrence of the problem of tape breakage of the negative electrode current collector 100 in the laminated structure 10 due to uneven tension or insufficient interfacial bonding force during the rolling process of the laminated structure 10 in the subsequent step S4. And the setting of the support layer 300 before the rolling process enables the thickness of the negative electrode current collector 100 to be designed thinner, thereby reducing the amount of copper used in the secondary battery and improving the energy density of the secondary battery.

[0054] In some embodiments, the tensile strength of the support layer 300 is the first tensile strength σb1, where 10 MPa ≤ σb1 ≤ 120 MPa. Optionally, 20 MPa ≤ σb1 ≤ 100 MPa, and the first tensile strength σb1 of the support layer 300 can be 50 MPa, 70 MPa, or 100 MPa.

[0055] In some embodiments, the tensile strength of the laminated structure 10 is the second tensile strength σb2, where 40 MPa ≤ σb2 ≤ 250 MPa. Optionally, 50 MPa ≤ σb2 ≤ 250 MPa, and the second tensile strength σb2 of the laminated structure 10 can be 100 MPa, 150 MPa, or 200 MPa.

[0056] Further, the thickness of the support layer 300 is the support layer thickness D, satisfying 2 μm < D ≤ 15 μm. Optionally, 8 μm ≤ D ≤ 15 μm, and the support layer thickness D of the support layer 300 can be 8 μm, 10 μm, 12 μm, or 15 μm.

[0057] Further, the material of the support layer 300 includes at least one of a water-soluble material, a thermal decomposition material, or a photolysis material. The support layer 300 made of the above materials is convenient for removing the support layer 300 during the removal process of the support layer 300 in the subsequent step S5, and avoids the formation or removal of the support layer 300 from damaging the structure or chemical properties of the negative electrode sheet.

[0058] 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 (polyvinylpyrrolidone) material, or CMC (carboxymethyl cellulose) material.

[0059] In some embodiments, when the material of the support layer 300 is a thermal decomposition material, the material of the support layer 300 includes PVC material.

[0060] In some embodiments, when the material of the support layer 300 is a photo-degradable material, the material of the support layer 300 includes at least one of ethylene-carbon monoxide copolymer material or vinyl ketone copolymer material.

[0061] Furthermore, the method for forming the support layer 300 includes a wet forming process or a dry forming process.

[0062] In some embodiments, the support layer 300 is formed by a wet forming process. The wet forming process is to coat a negative electrode slurry containing a negative electrode active material on the surface of the negative electrode current collector 100 and then dry the negative electrode slurry to obtain a solidified negative electrode active material layer 200. In some other embodiments, the support layer 300 is formed by a dry forming process. The dry forming process is to form a negative electrode active material film with adhesive properties by mixing a negative electrode active material and an adhesive, and paste the negative electrode active material film onto the surface of the negative electrode current collector 100 to form a negative electrode active material layer 200; or, after mixing the negative electrode active material and the adhesive, directly form a solidified negative electrode active material layer 200 on the surface of the negative electrode current collector 100 by spraying.

[0063] The method for forming the support layer 300 includes: Step S31: Provide a support slurry. The support slurry contains a dispersoid and a dispersant, and the dispersoid is uniformly diffused in the liquid dispersant. The support slurry can be any one of a solution, a suspension, and an emulsion.

[0064] Step S32: Coat the support slurry on the surface of the negative electrode active material layer 200 facing away from the negative electrode current collector 100 and perform a drying process. The dispersant volatilizes due to heat to remove the dispersant, and the remaining dispersoid solidifies to form the support layer 300.

[0065] Furthermore, by mass percentage, the mass percentage of the dispersoid in the support slurry is 3wt% - 10wt%. Optionally, the mass percentage of the dispersoid in the support slurry is 5wt% - 8wt%, and the mass percentage of the dispersoid in the support slurry can be 6wt%, 7wt%, or 8wt%. The support slurry with a suitable mass percentage of the dispersoid has good adhesiveness and film-forming properties, which is convenient for coating on the surface of the negative electrode active material layer 200 and makes the thickness of the support layer 300 formed after drying within a reasonable range.

[0066] In step S4, as Figure 6As shown, a rolling process is performed on the stacked structure 10. The stacked structure 10 is fed to two relatively arranged and rotating roller shafts 1000 to roll the thickness of the negative electrode active material layer 200 to a smaller size. On the one hand, the rolling 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 rolling process can also reduce the thickness of the negative electrode active material layer 200 and the thickness of the electrode sheet, and thus improve the energy density of the secondary battery. On the other hand, the rolling process can also increase the compaction density of the negative electrode active material layer 200, make the negative electrode active substances in the negative electrode active material layer 200 contact more closely, and improve the electron conductivity; the rolling process can also make the negative electrode active material layer 200 better adhere to the surface of the negative electrode current collector 100, reduce the contact resistance between the negative electrode active material layer 200 and the negative electrode current collector 100, and improve the performance of the secondary battery.

[0067] In some embodiments, after the rolling process is performed on the stacked structure 10, the compaction density of the negative electrode active material layer 200 is the compaction density ρ, satisfying 1.4 g / cm 3 ≤ ρ ≤ 1.8 g / cm 3 . Optionally, 1.5 g / cm 3 ≤ ρ ≤ 1.7 g / cm 3 , and the compaction density ρ of the negative electrode active material layer 200 can be 1.5 g / cm 3 , 1.6 g / cm 3 or 1.7 g / cm 3 .

[0068] The method for performing the rolling process on the stacked structure 10 includes a two-stage rolling process, that is, the first rolling and the second rolling performed on the stacked structure 10 successively. The stacked structure 10 after the first rolling is as shown in Figure 7 , and the stacked structure 10 after the second rolling is as shown in Figure 8 . The two-stage rolling process first rolls the negative electrode active material layer 200 to a certain thickness after the first rolling, and then rolls the negative electrode active material layer 200 to reach the designed thickness and density through the second rolling. The two-stage rolling process can not only reduce the breakage of the active substance particles in the active material layer as much as possible, but also make the pore distribution in the active material layer uniform, thereby promoting the infiltration of the electrolyte, reducing the internal resistance of the negative electrode sheet, and improving the performance of the secondary battery.

[0069] Further, the rolling pressure of the first rolling is the first rolling pressure P1, and the rolling pressure of the second rolling is the second rolling pressure P2, satisfying P1 < P2. The rolling pressure of the second rolling is greater than that of the first rolling, avoiding the phenomenon that in the related art, when the negative electrode sheet is only subjected to a single rolling treatment, the negative electrode current collector 100 in the negative electrode sheet undergoes an instantaneous deformation under high pressure and is then torn due to the concentration of gravity.

[0070] In the secondary rolling process of the embodiment of the present application, first, the compaction density of the negative electrode active material layer 200 in the laminated structure 10 during the first rolling becomes larger and the thickness decreases, so that the negative electrode active material layer 200 in the laminated structure 10 has higher mechanical strength to improve the overall mechanical strength of the laminated structure 10; the thickness of the negative electrode active material layer 200 decreases during the first rolling, so that the thickness change range of the negative electrode active material layer 200 during the second rolling decreases, the deformation range of the negative electrode current collector 100 during the second rolling decreases, and further the probability of the negative electrode current collector 100 being torn during the rolling treatment decreases, thereby improving the yield rate of the secondary battery.

[0071] In some embodiments, the first rolling pressure P1 of the first rolling satisfies 30 MPa ≤ P1 ≤ 50 MPa. Optionally, 35 MPa ≤ P1 ≤ 45 MPa, and the first rolling pressure P1 of the first rolling can be 35 MPa, 40 MPa, or 45 MPa.

[0072] In some embodiments, the second rolling pressure P2 of the second rolling satisfies 60 MPa ≤ P2 ≤ 90 MPa. Optionally, 70 MPa ≤ P2 ≤ 80 MPa, and the second rolling pressure P2 of the second rolling can be 70 MPa, 75 MPa, or 80 MPa.

[0073] It should be noted that, in some embodiments, the rolling treatment process is a secondary rolling process; in other embodiments, the number of rolling times of the rolling treatment can be greater than two, and the rolling pressure gradually increases, that is, the rolling pressure of the latter time is greater than that of the previous time, which is not specifically limited herein.

[0074] Further, the thickness of the negative electrode active material layer 200 before the rolling treatment is the first thickness H1, the thickness of the negative electrode active material layer 200 after the first rolling is the second thickness H2, and the thickness of the negative electrode active material layer 200 after the second rolling is the 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.

[0075] In some embodiments, the first thickness H1 of the negative electrode active material layer 200 before the rolling process satisfies 165 μm ≤ H1 ≤ 200 μm. Optionally, 175 μm ≤ H1 ≤ 195 μm, and the first thickness H1 of the negative electrode active material layer 200 before the rolling process can be 175 μm, 180 μm, 185 μm, or 190 μm.

[0076] 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. Optionally, 140 μm ≤ H2 ≤ 160 μm, and the second thickness H2 of the negative electrode active material layer 200 after the first rolling process can be 140 μm, 145 μm, 150 μm, or 155 μm.

[0077] 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. Optionally, 130 μm ≤ H3 ≤ 140 μm, and the third thickness H3 of the negative electrode active material layer 200 after the second rolling process can be 130 μm, 135 μm, 138 μm, or 140 μm.

[0078] To better illustrate the beneficial effects brought by the embodiments of the present application, the corresponding examples and comparative examples are provided below for description. Specifically, refer to the following table: Table 1:

[0079] It can be seen from Examples 1 to 8, Comparative Example 1, and Comparative Example 2 in Table 1 that the tape break rate of the laminated structure 10 formed after rolling with the support layer 300 is much lower than that of directly rolling the electrode sheet without the support layer 300. The support layer 300 provides mechanical support during the rolling process, improves the tensile strength of the laminated structure 10, and thus reduces the tape break rate of the negative electrode current collector 100 during the rolling process.

[0080] It can be seen from Examples 1 to 4, Comparative Example 3, and Comparative Example 4 in Table 1 that, under the same conditions of the material of the support layer 300, the rolling process, and the parameters, the thicker the support layer 300, the smaller the tape break rate of the negative electrode current collector 100 during the rolling process. However, when the thickness of the negative electrode current collector 100 is less than 3 μm, the tape break rate of the negative electrode current collector 100 is still too high, and it is difficult for the support layer 300 to play a protective role during the rolling process. When the thickness of the support layer 300 is greater than 12 μm, although the tape break rate of the negative electrode current collector 100 decreases, the decrease amplitude is small, and an overly thick support layer 300 will result in too high a process cost for subsequent removal of the support layer 300.

[0081] As can be seen from Examples 2, 5, and 6 and Comparative Examples 5 and 6 in Table 1, when the material and thickness of the support layer 300 are the same, the tape break rate of the examples with the double roller pressing process is less than that of the comparative examples with the single roller pressing process. The double roller pressing process adopted in the examples of the present application reduces the probability of tape breakage of the negative electrode current collector 100 during the roller pressing process and improves the yield rate of the secondary battery.

[0082] As can be seen from Examples 2, 5, and 6 and Comparative Examples 7 and 8 in Table 1, in the examples with the double roller pressing process, when the material and thickness of the support layer 300 are the same, the tape break rate of the examples with the roller pressing pressure of the second roller pressing being greater than that of the first roller pressing is less than that of the examples with the roller pressing pressures of the two roller pressings being equal or the roller pressing pressure of the first roller pressing being greater than that of the second roller pressing. The technical solution of the roller pressing process in the examples of the present application with the roller pressing pressure of the latter roller pressing being greater than that of the previous roller pressing further reduces the probability of tape breakage of the negative electrode current collector 100 during the roller pressing process and improves the yield rate of the secondary battery.

[0083] Furthermore, in the step of roller pressing the laminated structure 10, the support layer 300 is also heat-treated. The support layer 300 is heated to a certain temperature to improve the tensile strength of the support layer 300, thereby improving the tensile strength of the laminated structure 10 and further avoiding the problem of tearing of the negative electrode current collector 100 during the roller pressing process.

[0084] Furthermore, the heat treatment method includes: heating the roller shaft 1000 used in the roller pressing process, and heat conduction occurs between the roller shaft 1000 and the support layer 300 in the laminated structure 10 in contact therewith, so that the temperature of the support layer 300 rises, thereby improving the tensile strength of the support layer 300. In some embodiments, a heating resistance wire is provided inside the roller shaft 1000, and the roller shaft 1000 is heated after the heating resistance wire is energized.

[0085] In some embodiments, the heating temperature T2 of the heat treatment satisfies 40°C ≤ T2 ≤ 50°C. Optionally, 42°C ≤ T2 ≤ 48°C, and the heating temperature T2 of the heat treatment can be 42°C, 44°C, 46°C, or 48°C.

[0086] It should be noted that due to its high tensile strength, the thickness of the support layer 300 hardly changes after the roller pressing process, so that the negative electrode active material layer 200 can reach the target thickness.

[0087] It should also be noted that in some embodiments, such as Figure 6As shown, the thicknesses of the negative electrode active material layers 200 on both side surfaces of the negative electrode current collector 100 are equal, and the thicknesses of the support layers 300 on both sides of the negative electrode current collector 100 are also equal. During the rolling process of the stacked structure 10, the rolling pressures applied to the negative electrode active material layers 200 on both sides of the negative electrode current collector 100 are the same, so the thicknesses of the negative electrode active material layers on both sides after being rolled are also the same, and the negative electrode current collector 100 will not undergo sudden deformation during the rolling process.

[0088] In some other embodiments, the thicknesses of the negative electrode active material layers 200 on both side surfaces of the negative electrode current collector 100 are not equal, and the thicknesses of the support layers 300 on both sides of the negative electrode current collector 100 are also not equal. The negative electrode active material layer 200 and the support layer 300 on one side surface of the negative electrode 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 surface of the negative electrode current collector 100 is greater than that of the other negative electrode active material layer 200, but the thickness of the support layer 300 in the combined structure with the negative electrode active material layer 200 having a larger thickness is greater than that 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 strengths of the combined structures on both side surfaces of the negative electrode current collector 100 are consistent, avoiding the problem that the negative electrode current collector 100 undergoes sudden deformation or even breaks during the rolling process due to the inconsistent tensile strengths of the combined structures on both sides of the negative electrode current collector 100, and further improving the yield rate of the secondary battery.

[0089] In step S5, as Figure 9 shown, the support layer 300 is removed to obtain a negative electrode tab composed 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 properties of the negative electrode tab and the cell assembly formed by subsequent assembly.

[0090] In the case where the material of the support layer 300 is a water-soluble material, the method for removing the support layer 300 includes: Step S51, performing steam dissolution treatment on the support layer 300 to remove the support layer 300. The support layer 300 is heated in a water vapor atmosphere, and the water-soluble material of the support layer 300 is dissolved into the water vapor to achieve the preliminary removal of the support layer 300. In the high-temperature water vapor atmosphere, the dissolution rate of the negative electrode active material layer 200 can be accelerated, thereby reducing the residual amount of the support layer 300 on the surface of the negative electrode active material layer 200 after the steam dissolution treatment. In the low-pressure water vapor atmosphere, the negative electrode active material layer 200 is protected from being damaged by the high-pressure steam flow, thereby improving the yield rate of the secondary battery.

[0091] Step S52: Clean the surface of the negative electrode active material layer 200. The surface of the negative electrode active material layer 200 is cleaned under low pressure with an aqueous solution, and the residual support layer 300 is dissolved in the aqueous solution to remove the residual support layer 300 on the surface of the negative electrode active material layer 200. The negative electrode active material layer 200 is cleaned under low pressure to avoid damage to the negative electrode active material layer 200 caused by high-pressure water flow, thereby improving the yield rate of the secondary battery.

[0092] Furthermore, the process parameters of the steam dissolution treatment include: the process temperature T1 of the water vapor atmosphere, satisfying 85°C ≤ T1 ≤ 110°C. Optionally, 90°C ≤ T1 ≤ 105°C, and the process temperature T1 of the water vapor atmosphere can be 90°C, 95°C, 100°C, or 105°C.

[0093] Furthermore, the process parameters of the steam dissolution treatment also include: the steam pressure p1 of the water vapor atmosphere, satisfying 0.2MPa ≤ p1 ≤ 0.1MPa. Optionally, 0.12MPa ≤ p1 ≤ 0.18MPa, and the steam pressure p1 of the water vapor atmosphere can be 0.12MPa, 1.14MPa, 0.16MPa, or 0.18MPa.

[0094] Furthermore, the water flow pressure p2 for cleaning the negative electrode active material layer 200 under low pressure satisfies 0.1MPa ≤ p2 ≤ 0.5MPa. Optionally, 0.3MPa ≤ p2 ≤ 0.4MPa, and the water flow pressure p2 of the water vapor atmosphere can be 0.3MPa, 0.34MPa, 0.38MPa, or 0.4MPa. The negative electrode active material layer 200 is cleaned under low pressure to avoid damage to the negative electrode active material layer 200 caused by high-pressure water flow, thereby improving the yield rate of the secondary battery.

[0095] 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: Step S53: Heat-treat the support layer 300 to cause thermal decomposition of the support layer 300. The support layer 300 is thermally decomposed into gas and a small amount of residual small-molecule particles.

[0096] Step S54: Remove the residual small-molecule particles on the surface of the negative electrode active layer. In some embodiments, the residual small-molecule particles on the surface of the negative electrode active layer are blown off by a soot-blowing process, that is, the small-molecule particles are blown off by a high-pressure air flow to make the surface of the negative electrode active layer clean and not affect the physical and chemical properties of the negative electrode plate. In other embodiments, the residual small-molecule particles on the surface of the negative electrode active layer are removed by a low-pressure cleaning method.

[0097] In the case where the material of the support layer 300 is a photocleavable material, the method for removing the support layer 300 includes: Step S55: Perform a light treatment on the support layer 300 to cause photolysis of the support layer 300. The support layer 300 is decomposed by light into gas and a small amount of residual small molecule particles.

[0098] Step S56: Remove the residual small molecule particles on the surface of the negative electrode active layer. In some embodiments, a soot blowing process is used to blow away the residual small molecule particles on the surface of the negative electrode active layer, that is, high-pressure air flow is used to blow away the small molecule particles to make the surface of the negative electrode active layer clean and not affect the physical and chemical properties of the negative electrode plate. In other embodiments, a low-pressure cleaning method is used to remove the residual small molecule particles on the surface of the negative electrode active layer.

[0099] Correspondingly, another embodiment of the present application further provides a secondary battery, which can be obtained by the manufacturing method of the above secondary battery. The secondary battery includes: A housing having an accommodation cavity inside; A battery cell assembly installed in the accommodation cavity; the battery cell assembly includes: a positive electrode plate, a separator, and a negative electrode plate; the negative electrode plate includes: a negative electrode current collector 100 and a negative electrode active material layer 200; Wherein, the thickness of the negative electrode current collector 100 is the foil thickness h, where 0 < h ≤ 5 μm.

[0100] Correspondingly, another embodiment of the present application further provides an energy storage system, which includes a plurality of secondary batteries, and the secondary battery can be obtained by the manufacturing method of the above secondary battery or is the secondary battery as described above.

[0101] Correspondingly, another embodiment of the present application further provides an electrical device, which includes a plurality of secondary batteries, and the secondary battery can be obtained by the manufacturing method of the above secondary battery or is the secondary battery as described above.

[0102] Those of ordinary skill in the art can understand that the above embodiments are specific embodiments for implementing the present application. In actual applications, various changes can be made in form and details without departing from the spirit and scope of the present application. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the protection scope of the present application should be subject to the scope defined by 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 0<h≤5μm; 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 on a side 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 plate; A shell is provided, wherein the shell has a containing cavity, the battery core assembly is placed in the containing cavity and an electrolyte is injected into the containing cavity.

2. The method for preparing a secondary battery according to claim 1, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: The method of forming the support layer comprises: Providing a support slurry, wherein the support slurry contains a dispersoid and a dispersant; The support slurry is coated on the surface of the negative electrode active material layer on one 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, characterized in that: In terms of mass percentage, the mass percentage of the dispersoid in the support slurry is 3wt%~10wt%.

7. The method for preparing a secondary battery according to claim 4, characterized in that: 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, characterized in that: 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.

9. The method for preparing a secondary battery according to claim 4, characterized in that: 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, characterized in that: In 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, characterized in that: The rolling process includes: rolling the stacked structure for multiple times, wherein the rolling pressure of a previous rolling process is less than or equal to the rolling pressure of a subsequent rolling process.

12. The method for preparing a secondary battery according to claim 11, characterized in that: 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, characterized in that: 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, characterized in that: The tensile strength of the stacked structure is a second tensile strength σb2, wherein 40MPa≤σb2≤250MPa.

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 comprises: A housing, wherein the housing has a receiving cavity therein; A battery cell assembly, the battery cell assembly is installed in the accommodating cavity; the battery cell assembly comprises: a positive electrode sheet, a separator and a negative electrode sheet; the negative electrode sheet comprises: a negative electrode current collector and a negative electrode active material layer; Wherein, the thickness of the negative electrode current collector is the foil thickness h, wherein 0<h≤5μm.

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

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

Images