CN114050325A - Battery cell and electrochemical device - Google Patents
Battery cell and electrochemical device Download PDFInfo
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- CN114050325A CN114050325A CN202111326213.XA CN202111326213A CN114050325A CN 114050325 A CN114050325 A CN 114050325A CN 202111326213 A CN202111326213 A CN 202111326213A CN 114050325 A CN114050325 A CN 114050325A
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Images
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/058—Construction or manufacture
- H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Abstract
The invention provides an electric core and an electrochemical device, wherein the electric core comprises a negative plate and a positive plate, the negative plate and the positive plate are stacked and form a winding structure, the negative plate comprises a first section and a second section which are sequentially connected along a winding direction from inside to outside, and the positive plate comprises a third section and a fourth section which are sequentially connected along the winding direction from inside to outside; the third section is a part of the positive electrode sheet adjacent to the first section of the negative electrode sheet in the direction from the inner side to the outer side of the winding structure; the first surface of the negative current collector of the first section is provided with a negative active layer, and the second surface is not provided with the negative active layer; the surface density of the positive electrode active layer on the second surface of the positive electrode current collector in the third section is less than that of the positive electrode active layer on the second surface of the positive electrode current collector in the fourth section; one of the first surface and the second surface is a surface facing an inside of the roll-to-roll structure, and the other is a surface facing an outside of the roll-to-roll structure. The invention can improve the performances of the electrochemical device such as safety, cyclicity and the like.
Description
Technical Field
The invention relates to a battery cell and an electrochemical device, and belongs to the field of electrochemical energy storage devices.
Background
At present, electrochemical devices represented by lithium ion batteries are widely applied to consumer electronics, electric vehicles, energy storage and other aspects, wherein the lithium ion batteries have the advantages of high energy density, long cycle life, rapid charge and discharge, environmental friendliness and the like, and are a research hotspot at the present stage. The winding structure is a common form of the battery core and is mainly formed by winding after positive plates, diaphragms and negative plates are sequentially stacked, usually, the part of the negative plate, which is positioned at the innermost circle of the battery core, is provided with a single-side coating area, only one surface of the single-side coating area is provided with a negative active layer, and the lithium precipitation phenomenon is easily generated in the circulation process, so that the safety, the circulation performance and other performances of the electrochemical device are influenced.
Disclosure of Invention
The invention provides a battery cell and an electrochemical device, which at least solve the problems that the battery cell in the prior art is easy to generate a lithium precipitation phenomenon, and the safety and the cyclicity of the electrochemical device are poor due to the lithium precipitation phenomenon.
In one aspect of the invention, a battery cell is provided, which comprises a negative plate and a positive plate, wherein the negative plate comprises a negative current collector and a negative active layer arranged on the surface of the negative current collector, and the positive plate comprises a positive current collector and a positive active layer arranged on the surface of the positive current collector; the negative plate and the positive plate are stacked and wound to form a winding structure, the negative plate comprises a first section and a second section which are sequentially connected along the winding direction of the winding structure from inside to outside, and the positive plate comprises a third section and a fourth section which are sequentially connected along the winding direction of the winding structure from inside to outside; the third segment is a portion of the positive electrode sheet adjacent to the first segment of the negative electrode sheet in a direction from the inside of the winding structure to the outside of the winding structure; the first surface of the negative current collector of the first section is provided with the negative active layer, and the second surface of the negative current collector of the first section is not provided with the negative active layer; the surface density of the positive electrode active layer on the second surface of the positive electrode current collector of the third section is less than that of the positive electrode active layer on the second surface of the positive electrode current collector of the fourth section; wherein one of the first surface and the second surface is a surface facing an inside of the roll-up structure, and the other is a surface facing an outside of the roll-up structure.
According to an embodiment of the present invention, a thickness of the positive electrode active layer on the second surface of the positive electrode current collector of the third section is less than a thickness of the positive electrode active layer on the second surface of the positive electrode current collector of the fourth section.
According to an embodiment of the present invention, the thickness of the positive electrode active layer on the second surface of the positive electrode collector in the third section is b, the thickness of the positive electrode active layer on the second surface of the positive electrode collector in the fourth section is b + c, and the thicknesses of the positive electrode active layers on the first surfaces of the positive electrode collectors in the third and fourth sections are a, 0 < (a + b)/(a + b + c) < 1, respectively.
According to an embodiment of the present invention, the first surface and the second surface of the negative current collector of the second segment are both provided with the negative active layer.
According to an embodiment of the invention, the first surface is a surface facing the outside of the roll-up structure and the second surface is a surface facing the inside of the roll-up structure.
According to an embodiment of the present invention, one of the first segment of the negative electrode tab and the third segment of the positive electrode tab is located outside the other in a direction from inside the winding structure to outside the winding structure.
According to an embodiment of the present invention, the third segment of the positive electrode tab is located outside the first segment of the negative electrode tab in a direction from inside the winding structure to outside the winding structure.
According to an embodiment of the present invention, the length of the third section is L, where L is greater than 0 and less than or equal to 400 mm; and/or the ratio of the length of the third section to the length of the fourth section is 1: 1-1: 50.
According to one embodiment of the present invention, the negative electrode sheet has at least two first straight portions and a first bent portion connected between every two first straight portions, the positive electrode sheet has at least two second straight portions and a second bent portion connected between every two second straight portions, and the negative electrode sheet and the positive electrode sheet are bent by the first bent portion and the second bent portion to form the winding structure; calculating the sequence of first bent parts along the winding direction of the winding structure from inside to outside, wherein the first bent part positioned at the innermost side of the winding structure is taken as a first bent part, the first section comprises an nth first bent part, at least one part of a first straight part connected to one end of the nth first bent part, and at least one part of a second straight part connected to the other end of the nth first bent part, and n is 1 or n is 2; and/or calculating the sequence of second bent parts along the winding direction of the winding structure from inside to outside, taking the second bent part positioned at the innermost side of the winding structure as a first second bent part, wherein the third section comprises an mth second bent part, at least one part of a second straight part connected to one end of the mth second bent part, and at least one part of a second straight part connected to the other end of the mth second bent part, and m is 1 or m is 2.
According to an embodiment of the present invention, the negative electrode tab is provided with a negative electrode tab, and the negative electrode tab is disposed on the first straight portion.
According to an embodiment of the present invention, the positive electrode tab is provided with a positive electrode tab, and the positive electrode tab is disposed on the second straight portion.
In another aspect of the present invention, an electrochemical device is provided, which includes the battery cell.
In the invention, the first section of the negative plate is a single-sided coating area, the first surface of the negative current collector with the negative active layer of the first section faces the second surface of the positive current collector of the third section of the positive plate, and the surface density of the positive active layer of the second surface of the positive current collector of the third section is lower, so that the surface density of the positive plate part corresponding to the single-sided coating area of the negative plate is reduced, the N/P value corresponding to the single-sided coating area of the negative plate can be increased, the lithium precipitation phenomenon is inhibited, the problems of electric core deformation and the like caused by lithium precipitation are avoided, and the safety, the cyclicity, the cycle life and other performances of the electric core and the electrochemical device are improved, and the specific expression is that: the electrochemical device does not have the phenomenon of lithium precipitation after 1000 cycles, the capacity retention rate after 1000 cycles is up to more than 85%, and the expansion rate of the battery cell after 1000 cycles is lower than 9.5%.
Drawings
Fig. 1 a is a schematic structural view of a negative electrode sheet according to an embodiment of the present invention before winding, and fig. 1B is a schematic structural view of a positive electrode sheet according to an embodiment of the present invention before winding;
fig. 2 is a schematic diagram of a roll-to-roll structure according to an embodiment of the invention.
Description of reference numerals: 1: a negative plate; 2: a positive plate; 3: a diaphragm; 11: a first stage; 12: a second stage; 14: a first straight portion; 15: a first bent portion; 21: a third stage; 22: a fourth stage; 23: a fifth stage; 24: a second straight portion; 25: a second bent portion; 101: a first surface of the negative current collector of the first section; 102: a first surface of a negative current collector of the second segment; 201: a second surface of the positive current collector of the third section; 202: a second surface of the positive current collector of the fourth section; a. b, c: and (4) thickness.
Detailed Description
The present invention is described in further detail below in order to enable those skilled in the art to better understand the aspects of the present invention. The following detailed description is merely illustrative of the principles and features of the present invention, and the examples are intended to be illustrative of the invention and not limiting of the scope of the invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without any creative effort belong to the protection scope of the present invention. In the description of the present invention, the terms "first", "second", "third", "fourth", "fifth", and the like are used for descriptive purposes only, such as to distinguish the respective components for more clearly explaining/explaining the technical solution, and are not to be construed as indicating or implying any number of technical features or order of significance or the like.
The battery cell comprises a negative plate and a positive plate, wherein the negative plate comprises a negative current collector and a negative active layer arranged on the surface of the negative current collector, and the positive plate comprises a positive current collector and a positive active layer arranged on the surface of the positive current collector; the negative plate and the positive plate are stacked and wound to form a winding structure, the negative plate comprises a first section and a second section which are sequentially connected along the winding direction of the winding structure from inside to outside, and the positive plate comprises a third section and a fourth section which are sequentially connected along the winding direction of the winding structure from inside to outside; the third section is a part of the positive electrode sheet adjacent to the first section of the negative electrode sheet in the direction from the inside of the winding structure to the outside of the winding structure; a negative active layer is arranged on the first surface of the negative current collector of the first section, and a negative active layer is not arranged on the second surface of the negative current collector of the first section; the surface density of the positive electrode active layer on the second surface of the positive electrode current collector of the third section is less than the surface density of the positive electrode active layer on the second surface of the positive electrode current collector of the fourth section. Wherein one of the first surface and the second surface refers to a surface facing an inside of the roll-to-roll structure, and the other refers to a surface facing an outside of the roll-to-roll structure (i.e., a surface facing away from the inside of the roll-to-roll structure).
For example, the first surface is a surface facing the outside of the winding structure, the second surface is a surface facing the inside of the winding structure, the surface facing the outside of the winding structure of the negative current collector of the first section is provided with a negative active layer, the surface facing the inside of the winding structure of the negative current collector of the first section is not provided with a negative active layer, and meanwhile, the surface density of the positive active layer of the surface facing the inside of the winding structure of the positive current collector of the third section is less than the surface density of the positive active layer of the surface facing the inside of the winding structure of the positive current collector of the fourth section; or the first surface is a surface facing the inner side of the winding structure, the second surface is a surface facing the outer side of the winding structure, a negative active layer is arranged on the surface of the negative current collector facing the inner side of the winding structure at the first section, a negative active layer is not arranged on the surface of the negative current collector facing the outer side of the winding structure at the first section, and meanwhile, the surface density of the positive active layer on the surface of the positive current collector facing the outer side of the winding structure at the third section is smaller than that of the positive active layer on the surface of the positive current collector facing the outer side of the winding structure at the fourth section. It is generally preferred that the former, i.e. the first surface, is the surface facing the outside of the roll-to-roll structure and the second surface is the surface facing the inside of the roll-to-roll structure.
In some embodiments, in a direction from the inside of the winding structure to the outside of the winding structure, one of the first section of the negative electrode tab and the third section of the positive electrode tab is located on the outside of the other, the first surface of the negative electrode current collector of the first section is a surface facing the third section, the second surface of the negative electrode current collector of the first section is a surface facing away from the third section, the second surface of the positive electrode current collector of the third section is a surface facing the first section, and the first surface of the positive electrode current collector of the third section is a surface facing away from the first section. It is generally preferred that the third segment of the positive electrode tab is located outside the first segment of the negative electrode tab, i.e., the third segment of the positive electrode tab is located closer to the outside of the winding structure than the first segment of the negative electrode tab, the first segment of the negative electrode tab is located closer to the inside of the winding structure than the third segment of the positive electrode tab, and the first segment of the negative electrode tab may be specifically located in an area surrounded by the third segment of the positive electrode tab (i.e., the third segment of the positive electrode tab surrounds the outside of the first segment of the negative electrode tab), but is not limited thereto. When the third section of the positive plate is positioned on the outer side of the first section of the negative plate, the first surface is a surface facing the outer side of the winding structure, and the second surface is a surface facing the inner side of the winding structure, that is, the surface of the first section facing the third section is provided with a negative electrode active layer, the surface of the first section departing from the third section is not provided with a negative electrode active layer, and the surface density of the positive electrode active layer on the surface of the third section facing the first section is less than that of the positive electrode active layer on the same surface of the fourth section.
Generally, the negative electrode plate has at least two first straight portions and a first bending portion connected between every two first straight portions (i.e. one end of the first bending portion is connected to one first straight portion, and the other end of the first bending portion is connected to another first straight portion), the positive electrode plate has at least two second straight portions and a second bending portion connected between every two second straight portions (i.e. one end of the second bending portion is connected to one second straight portion, and the other end of the second bending portion is connected to another second straight portion), and the negative electrode plate and the positive electrode plate are respectively bent by the first bending portion and the second bending portion to form a winding structure.
Generally, the first section is a single-side coating region of the negative electrode sheet, the second section is a main body section of the negative electrode sheet, the length of the second section is not less than the length of the first section, the length of the second section is generally greater than the length of the first section, the number of the first straight portions located in the second section is greater than the number of the first straight portions located in the first section, the number of the first bending portions located in the second section is greater than the number of the first bending portions located in the first section, the number of the first straight portions located in the first section is not greater than 2, the number of the first bending portions located in the first section is not greater than 2, and the rest first straight portions and the first bending portions are located in the second section.
The third section of the positive plate corresponds to the first section of the negative plate, the fourth section corresponds to the second section of the negative plate, the fourth section is a main section of the positive plate, the length of the fourth section is not less than that of the third section, generally, the length of the fourth section is greater than that of the third section, the number of the second straight parts located in the fourth section is greater than that of the second straight parts located in the third section, the number of the second bent parts located in the fourth section is greater than that of the second bent parts located in the third section, the number of the second straight parts located in the third section is usually not greater than 2, and the number of the second bent parts located in the third section is not greater than 2.
In some embodiments, the third segment has a length L, 0 < L ≦ 400mm, L being, for example, 10mm, 30mm, 50mm, 80mm, 100mm, 120mm, 150mm, 180mm, 200mm, 250mm, 300mm, 350mm, 400mm, or a range consisting of any two thereof. The ratio of the length of the third segment to the length of the fourth segment is 1:1 to 1:50, for example, 1:1, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, or any two thereof.
In the present invention, unless otherwise specified, the lengths of the respective portions of the negative electrode sheet, such as the length of the first segment and the length of the second segment, are the lengths in the winding direction after the negative electrode sheet is formed into the winding structure, and are also the lengths in the direction from the first segment to the second segment before the negative electrode sheet is wound; the lengths of the respective portions of the positive electrode sheet, such as the length of the third segment and the length of the fourth segment, are the lengths in the winding direction after the positive electrode sheet is formed into the winding structure, and are also the lengths in the direction from the third segment to the fourth segment before the positive electrode sheet is wound.
In some embodiments, the positive electrode sheet may further include a fifth section, where the third section, the fourth section, and the fifth section are sequentially connected in a winding direction from inside to outside along the winding structure, one of the first surface and the second surface of the positive electrode current collector of the fifth section is provided with a positive electrode active layer, the other is not provided with a positive electrode active layer (generally, an empty foil without a coating), preferably, the second surface of the positive electrode current collector of the fifth section is provided with a positive electrode active layer, and the first surface of the positive electrode current collector of the fifth section is not provided with a positive electrode active layer. The surface density of the positive electrode active layer on the second surface of the positive electrode current collector of the fifth section is basically equal to that of the positive electrode active layer on the second surface of the positive electrode current collector of the fourth section, and the thickness of the positive electrode active layer on the second surface of the positive electrode current collector of the fifth section is basically equal to that of the positive electrode active layer on the second surface of the positive electrode current collector of the fourth section; the number of the second straight parts at the fourth section is greater than that of the second straight parts at the fifth section, the number of the second bent parts at the fourth section is greater than that of the second bent parts at the fifth section, generally, the number of the second straight parts at the fifth section is not greater than 2, and the number of the second bent parts at the fifth section is not greater than 2. The third section of the positive plate corresponds to the first section of the negative plate in position, the fourth section and the fifth section of the positive plate correspond to the second section of the negative plate in position, specifically, the second section of the negative plate comprises a first part and a second part which are sequentially connected along the winding direction from inside to outside of the winding structure, the first part corresponds to the fourth section of the positive plate in position, and the second part corresponds to the fifth section of the positive plate in position.
Alternatively, the first segment may be a first straight portion of the negative electrode tab, the third segment may be a second straight portion of the positive electrode tab, and the second straight portion (i.e., the third segment) is adjacent to the first straight portion (i.e., the first segment) and located outside the first straight portion, or the third segment includes a second bending portion, at least a portion of the second straight portion connected to one end of the second bending portion, and at least a portion of the second straight portion connected to the other end of the second bending portion, and the first segment is located in an area surrounded by the third segment through bending of the second bending portion.
In general, the single-sided coating region (i.e., the first segment) of the negative electrode sheet is close to the starting end of the negative electrode sheet located at the innermost circle of the winding structure, in some preferred embodiments, the order of the first bends is calculated along the winding direction of the winding structure from inside to outside, the first bend located at the innermost circle of the winding structure is taken as the first bend, the first segment includes the nth first bend, at least a part of the first straight portion connected to one end of the nth first bend, and at least a part of the second straight portion connected to the other end of the nth first bend, and n is 1 or 2; and calculating the sequence of the second bent parts along the winding direction from inside to outside of the winding structure, wherein the second bent part positioned at the innermost side of the winding structure is used as a first second bent part, the third section comprises an mth second bent part, a second straight part at least partially connected to one end of the mth second bent part, and a second straight part at least partially connected to the other end of the mth second bent part, and m is 1 or 2, generally m is n.
Specifically, in some embodiments, one end of the first segment is connected to the second segment, the other end of the first segment is a starting end of the negative plate inside the winding structure, for example, n is 1, the first segment is composed of a first bent portion and first straight portions connected to two ends of the first bent portion, one end of one of the first straight portions is a starting end of the negative plate inside the winding structure, and the other end of the one of the first straight portions is connected to the first bent portion. In addition, one end of the third segment is connected to the fourth segment, the other end of the third segment is the starting end of the positive plate located inside the winding structure, for example, m is 1, the third segment is composed of a first second bending portion and second straight portions connected to two ends of the first second bending portion, one end of one of the second straight portions is the starting end of the positive plate located inside the winding structure, and the other end of the second straight portion is connected to the first second bending portion.
In some embodiments, the negative electrode sheet further includes a first empty foil section, neither of the first surface and the second surface of the negative electrode current collector of the first empty foil section is provided with the negative electrode active layer, one end of the first empty foil section is a starting end of the negative electrode sheet located inside the winding structure, and the other end of the first empty foil section is connected to the second section. The positive plate further comprises a second empty foil section, the first surface and the second surface of the positive current collector of the second empty foil section are not provided with positive active layers, one end of the second empty foil section is the starting end of the positive plate located on the inner side of the winding structure, and the other end of the second empty foil section is connected with the third section.
Typically, the negative electrode tab is provided with one or more negative electrode tabs, and the negative electrode tabs are disposed on the first straight portion, for example, welded to the second surface of the negative electrode current collector of the first segment (i.e., the surface not provided with the negative electrode active layer) and/or the surface of the negative electrode current collector of the first empty foil segment. In addition, the positive plate is provided with one or more positive lugs, and the positive lugs are arranged on the second straight part, for example, welded on the surface of the positive current collector of the second hollow foil section, but not limited to.
Specifically, the positive active layer includes a positive active material, a conductive agent and a binder, the negative active layer includes a negative active material, a conductive agent, a binder and a dispersant, wherein the positive active material may include a lithium-containing positive active material, such as at least one of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganese, lithium nickel cobalt aluminate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate and lithium vanadyl phosphate, the negative active material may include at least one of graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon material, silicon carbon material and silicon lithium titanate, the conductive agent may include at least one of conductive carbon black, carbon nanotubes, conductive graphite and graphene, and the binder may include polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, silicone oxide, silicon nitride, silicon oxide, silicon nitride, silicon oxide, silicon nitride, silicon oxide, silicon nitride, silicon oxide, silicon dioxide, silicon, At least one of polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and Styrene Butadiene Rubber (SBR), and the dispersant may include sodium carboxymethyl cellulose (CMC) or the like.
In the above-mentioned battery cell, the first section of the negative plate is a single-sided coating region, the third section of the positive plate corresponds to the first section of the negative plate, the first surface of the negative current collector of the first section faces the third section, the second surface of the positive current collector of the third section faces the first section, the surface density of the positive active layer of the second surface of the positive current collector of the third section is controlled to be smaller than the surface density of the positive active layer of the second surface of the positive current collector of the fourth section, so as to improve the N/P value corresponding to the single-sided coating region of the negative plate, where N represents the gram volume of the negative active material in the negative active layer of the first surface of the negative current collector of the first section, x the surface density, x the content of the positive active material, P represents the gram volume of the positive active material in the positive active layer of the second surface of the positive current collector of the third section, x the surface density, x the content of the positive active material, and the gram volume and the content of the positive active materials in the positive active layers of the third and fourth sections are generally The same is true.
In some embodiments, the thickness of the positive electrode active layer of the second surface of the positive electrode current collector of the third section may be controlled to be smaller than that of the positive electrode active layer of the second surface of the positive electrode current collector of the fourth section, so that the areal density of the positive electrode active layer of the third section is smaller than that of the fourth section. In specific implementation, the raw material of the positive electrode active layer can be placed in a solvent to prepare positive electrode slurry, the positive electrode slurry is coated in a preset area of the positive electrode current collector, a positive electrode active layer is formed after drying and rolling, the coating thickness of the positive electrode slurry on the second surface of the third section of the positive electrode current collector is controlled to be smaller than that of the positive electrode slurry on the second surface of the fourth section of the positive electrode current collector, so that the thickness of the positive electrode active layer on the second surface of the third section of the positive electrode current collector is controlled to be smaller than that of the positive electrode active layer on the second surface of the fourth section of the positive electrode current collector, then slitting is performed according to parameters such as preset shape and size of a positive electrode piece, a scraper is used for cleaning off the coating of a preset positive electrode lug welding area, and a positive electrode lug is welded in the welding area to prepare the positive electrode piece. Alternatively, the solid content of the cathode slurry may be 70% to 75%.
The first surface and the second surface of the positive current collector of the third section and the first surface and the second surface of the positive current collector of the fourth section are both provided with positive active layers (namely a, b and c are not 0), in some preferred embodiments, the thickness of the positive active layer on the second surface of the positive current collector of the third section is b, the thickness of the positive active layer on the second surface of the positive current collector of the fourth section is b + c, the thicknesses of the positive active layers on the first surfaces of the positive current collectors of the third section and the fourth section are respectively a, and 0 < (a + b)/(a + b + c) < 1, so that the battery cell can be further improved in consideration of the performances of safety, energy density, cyclicity and the like. Typically, b + c has a value substantially equal to a, but is not limited thereto.
In addition, the first surface and the second surface of the negative current collector of the second section are both provided with a negative active layer, that is, the positive and negative surfaces of the negative current collector of the second section are both provided with a negative active layer, and the thicknesses of the negative active layers on the two surfaces can be the same or different, and are generally basically the same. During specific implementation, the raw material of the negative electrode active layer can be placed in a solvent to prepare negative electrode slurry, then the negative electrode slurry is coated in a preset area of a negative electrode current collector, the negative electrode active layer is formed after drying and rolling, then cutting is carried out according to parameters such as preset shape and size of a negative electrode piece, the coating of a preset negative electrode tab welding area (namely, a tab groove) is washed by laser, and a negative electrode tab is welded at the welding area to prepare the negative electrode piece. Alternatively, the solid content of the anode slurry may be 40% to 50%.
The battery cell of the invention also comprises a diaphragm positioned between the positive plate and the negative plate, wherein the diaphragm is used for separating the positive plate from the negative plate and preventing the positive plate from being in contact with the negative plate to cause short circuit. The positive electrode current collector includes, for example, an aluminum foil, and the negative electrode current collector includes, for example, a copper foil.
The battery cell is a winding battery cell with the winding structure, and can be prepared by the conventional method in the field, for example, a positive plate, a diaphragm and a negative plate are sequentially stacked and wound to form a winding core, the winding core is packaged by packaging materials such as an aluminum plastic film and the like, electrolyte is injected into the winding core after moisture is removed by baking, and the battery cell is prepared by adopting a hot pressing formation process.
The electrochemical device of the present invention includes the above-described battery cell, and the electrochemical device is, for example, a battery, specifically, a lithium ion battery, and the form thereof is, for example, a pouch battery.
To make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
In this embodiment, the electrochemical device is a lithium ion battery, which includes a winding type battery cell, where the winding type battery cell includes a positive plate 2, a negative plate 1, and a diaphragm 3 located between the positive plate 2 and the negative plate 1, the positive plate 2, and the diaphragm 3 are sequentially stacked and wound to form a winding type structure, where a in fig. 1 is a schematic structural diagram before the negative plate 1 is wound, B in fig. 1 is a schematic structural diagram before the positive plate 2 is wound, and fig. 2 is a schematic structural diagram of the winding type structure;
the negative plate 1 comprises a first section 11 and a second section 12 which are sequentially connected along the winding direction of the winding structure from inside to outside, the surface (namely a first surface 101) of the negative current collector of the first section 11 facing the outside of the winding structure is provided with a negative active layer, and the surface (namely a second surface) of the negative current collector of the first section 11 facing the inside of the winding structure is not provided with the negative active layer; the surface of the negative current collector of the second segment 12 facing the inside of the current collector and the surface facing the outside of the current collector (i.e., the first surface 102) are both provided with a negative active layer;
the positive plate 2 comprises a third section 21, a fourth section 22 and a fifth section 23 which are sequentially connected from inside to outside along a winding structure, wherein the thickness of a positive active layer on the second surface 201 of the positive current collector of the third section 21 is 70 μm, the thickness of a positive active layer on the second surface 202 of the positive current collector of the fourth section 22 and the thickness of a positive active layer on the second surface of the positive current collector of the fifth section 23 are respectively b + c and c are 10 μm, the thicknesses of positive active layers on the first surfaces of the positive current collectors of the third section 21 and the fourth section 22 are respectively a-80 μm, and 0 < (a + b)/(a + b + c) < 1; wherein the first surface is a surface facing the outside of the roll-to-roll structure and the second surface is a surface facing the inside of the roll-to-roll structure; in the direction from the inside of the winding structure to the outside of the winding structure, the third segment 21 is the portion of the positive electrode sheet 2 adjacent to the first segment 11 of the negative electrode sheet 1, i.e., the third segment 21 corresponds to the first segment 11 of the negative electrode sheet 1, and the fourth segment 22 and the fifth segment 23 correspond to the second segment 12 of the negative electrode sheet 1; the length L of the third section 21 is 120mm, and the ratio of the lengths of the third section 21 to the fourth section 22 is 1: 7;
specifically, the negative electrode plate 1 comprises a plurality of first straight portions 14 and a first bent portion 15 connected between every two first straight portions 14, the positive electrode plate 2 comprises a plurality of second straight portions 24 and a second bent portion 25 connected between every two second straight portions 24, and the negative electrode plate 1 and the positive electrode plate 2 are bent to form a winding structure through the first bent portion 15 and the second bent portion 25 respectively;
calculating the sequence of the first bending parts 15 along the winding direction from inside to outside of the winding structure, taking the first bending part 15 located at the innermost side of the winding structure as the first bending part 15, wherein the first section 11 comprises the first bending part 15 and first straight parts 14 connected to two ends of the first bending part 15 (i.e. the first section 11 comprises one first bending part 15 and two first straight parts 14);
calculating the sequence of the second bending parts 25 along the winding direction from inside to outside of the winding structure, taking the second bending part 25 located at the innermost side of the winding structure as the first second bending part 25, and the third section 21 comprises the first second bending part 25 and the second straight parts 24 connected to two ends of the first second bending part 25 (i.e. the first section 11 comprises one second bending part 25 and two second straight parts 24);
in the direction from the inside of the winding structure to the outside of the winding structure, the third section 21 of the positive electrode sheet 2 is located outside the first section 11 of the negative electrode sheet 1, i.e. the first section 11 of the negative electrode sheet 1 is located in the area surrounded by the third section 21 of the positive electrode sheet 2;
the negative plate 1 is provided with negative tabs disposed on the first straight portion 14 (not shown), and the positive plate 2 is provided with positive tabs disposed on the second straight portion 24 (not shown).
The preparation processes of the positive plate, the negative plate, the battery core and the lithium ion battery in the embodiment are as follows:
1. preparation of positive plate
Mixing lithium cobaltate, conductive carbon black and polyvinylidene fluoride according to a mass ratio of 97.6: 1.1: 1.3, adding the mixture into a stirring tank, adding N-methyl pyrrolidone (NMP) into the stirring tank, and uniformly stirring to obtain anode slurry with the solid content of 70-75%;
coating the positive electrode slurry on two surfaces of an aluminum foil by a coating machine in a double-layer coating or single-layer coating mode, drying for 8 hours at 120 ℃, then performing rolling treatment, forming a positive electrode active layer on the surface of the aluminum foil, then cutting according to parameters such as the preset shape, the preset size and the like of a positive electrode plate, cleaning off the coating of a preset positive electrode tab welding area by a scraper, and welding a positive electrode tab (aluminum tab) on the welding area to obtain the positive electrode plate; controlling the coating thickness of the anode slurry on the second surface of the anode current collector at the third section to be smaller than that of the anode slurry on the second surface of the anode current collector at the fourth section, so that the thickness of the anode active layer on the second surface of the anode current collector at the third section is smaller than that of the anode active layer on the second surface of the anode current collector at the fourth section;
2. preparation of negative plate
Graphite, conductive carbon black, styrene butadiene rubber and sodium carboxymethylcellulose are mixed according to the mass ratio of 97.3: 0.5: 1.3: 0.9, adding the mixture into a stirring tank, adding deionized water into the stirring tank, and uniformly stirring to obtain negative electrode slurry with the solid content of 40-45%; coating the negative electrode slurry on preset areas on two surfaces of a copper foil by using a coating machine, drying at 100 ℃, rolling, cutting according to parameters such as preset shape, size and the like of a negative electrode sheet, cleaning a polar lug groove by using laser, and welding a negative electrode lug (nickel lug) in the polar lug groove to obtain a negative electrode sheet;
3. preparation of battery cell and lithium ion battery
The positive plate, the diaphragm and the negative plate are sequentially stacked and wound to form a winding core, the winding core is packaged by an aluminum plastic film, electrolyte is injected into the winding core after moisture is removed by baking, a hot pressing forming process is adopted to form a battery cell, and the battery cell is assembled into a lithium ion battery (a soft package battery).
Example 2
Example 2 differs from example 1 in that b is 60 μm and c is 20 μm, and the remaining conditions are the same as in example 1.
Comparative example 1
Comparative example 1 differs from example 1 in that: the conditions were the same as in example 1 except that b was 80 μm and c was 0 (the thickness of the positive electrode active layer on the second surface of the positive electrode collector in the third stage was 80 μm, which was the same as the thickness of the positive electrode active layer on the second surface of the positive electrode collector in the fourth stage).
The following performance tests were performed on the batteries of the respective examples and comparative examples: (1) carrying out 0.2C multiplying power charge-discharge test on the battery cell at 25 ℃, measuring the battery cell capacity E, and recording the voltage V in the charge-discharge process; the thickness s, width w and height h of the cell (cell volume V ═ sxw × h) were measured, and the energy density EDV of the cell was calculated from EDV ═ E/(sxw × h), and the results are shown in table 1; (2) measuring the 3C/1C cycle performance of the battery at 25 ℃, disassembling the battery under different cycle times to judge the lithium precipitation condition and the cell expansion rate of the single-side coating area (first section) of the negative plate, and the result is shown in Table 1; wherein, the expansion ratio is (V1-V0)/V0, V1 is the volume of the cell after circulation, and V0 is the volume of the cell before circulation.
TABLE 1
Note: "20T" indicates a cycle number of 20, "300T" indicates a cycle number of 300, "500T" indicates a cycle number of 500, and "1000T" indicates a cycle number of 1000.
As can be seen from table 1, compared to comparative example 1, the structural design of examples 1 and 2 significantly suppresses the cell lithium deposition phenomenon and the resulting cell deformation and expansion, and improves the capacity retention rate and cycle life of the cell.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The battery cell is characterized by comprising a negative plate and a positive plate, wherein the negative plate comprises a negative current collector and a negative active layer arranged on the surface of the negative current collector, and the positive plate comprises a positive current collector and a positive active layer arranged on the surface of the positive current collector;
the negative plate and the positive plate are stacked and wound to form a winding structure, the negative plate comprises a first section and a second section which are sequentially connected along the winding direction of the winding structure from inside to outside, and the positive plate comprises a third section and a fourth section which are sequentially connected along the winding direction of the winding structure from inside to outside; the third segment is a portion of the positive electrode sheet adjacent to the first segment of the negative electrode sheet in a direction from the inside of the winding structure to the outside of the winding structure;
the first surface of the negative current collector of the first section is provided with the negative active layer, and the second surface of the negative current collector of the first section is not provided with the negative active layer;
the surface density of the positive electrode active layer on the second surface of the positive electrode current collector of the third section is less than that of the positive electrode active layer on the second surface of the positive electrode current collector of the fourth section;
wherein one of the first surface and the second surface is a surface facing an inside of the roll-up structure, and the other is a surface facing an outside of the roll-up structure.
2. The electrical core of claim 1, wherein the thickness of the positive electrode active layer of the second surface of the positive electrode current collector of the third section is less than the thickness of the positive electrode active layer of the second surface of the positive electrode current collector of the fourth section.
3. The battery cell of claim 1 or 2, wherein the thickness of the positive electrode active layer on the second surface of the positive electrode current collector in the third section is b, the thickness of the positive electrode active layer on the second surface of the positive electrode current collector in the fourth section is b + c, and the thicknesses of the positive electrode active layers on the first surfaces of the positive electrode current collectors in the third and fourth sections are a, 0 < (a + b)/(a + b + c) < 1, respectively.
4. The electrical core of claim 1, wherein both the first surface and the second surface of the negative current collector of the second segment are provided with the negative active layer.
5. The cell of claim 1, wherein,
the first surface is a surface facing the outside of the roll-to-roll structure, and the second surface is a surface facing the inside of the roll-to-roll structure; and/or the presence of a gas in the gas,
one of the first segment of the negative electrode tab and the third segment of the positive electrode tab is located outside the other in a direction from inside the winding structure to outside the winding structure.
6. The electrical core of claim 5, wherein the third segment of the positive electrode tab is located outside the first segment of the negative electrode tab in a direction from inside the wound structure to outside the wound structure.
7. The cell of claim 1, wherein,
the length of the third section is L, and L is more than 0 and less than or equal to 400 mm; and/or the presence of a gas in the gas,
the ratio of the length of the third section to the length of the fourth section is 1: 1-1: 50.
8. The battery cell according to claim 1 or 7, wherein the negative electrode tab has at least two first straight portions and a first bent portion connected between every two first straight portions, the positive electrode tab has at least two second straight portions and a second bent portion connected between every two second straight portions, and the negative electrode tab and the positive electrode tab are bent by the first bent portion and the second bent portion respectively to form the winding structure; wherein the content of the first and second substances,
calculating the sequence of first bending parts along the winding direction from inside to outside of the winding structure, wherein the first bending part positioned at the innermost side of the winding structure is taken as a first bending part, the first section comprises an nth first bending part, at least one part of a first straight part connected to one end of the nth first bending part, and at least one part of a second straight part connected to the other end of the nth first bending part, and n is 1 or 2; and/or the presence of a gas in the gas,
and calculating the sequence of second bent parts along the winding direction from inside to outside of the winding structure, wherein the second bent part positioned at the innermost side of the winding structure is used as a first second bent part, the third section comprises an mth second bent part, at least one part of a second straight part connected to one end of the mth second bent part, and at least one part of a second straight part connected to the other end of the mth second bent part, and m is 1 or m is 2.
9. The cell of claim 7, wherein,
the negative pole piece is provided with a negative pole lug, and the negative pole lug is arranged on the first straight part; and/or the presence of a gas in the gas,
the positive plate is provided with a positive lug, and the positive lug is arranged on the second straight part.
10. An electrochemical device comprising a cell according to any of claims 1 to 9.
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| CN111916844A (en) * | 2020-08-13 | 2020-11-10 | 东莞新能安科技有限公司 | Electrochemical device and electronic device |
| CN111916845A (en) * | 2020-08-13 | 2020-11-10 | 东莞新能安科技有限公司 | Electrochemical device and electronic device |
| CN112713258A (en) * | 2020-12-29 | 2021-04-27 | 珠海冠宇电池股份有限公司 | Lithium ion battery |
| CN112750975A (en) * | 2020-12-29 | 2021-05-04 | 珠海冠宇电池股份有限公司 | Lithium battery positive plate, winding type battery cell and lithium ion battery |
| CN214203736U (en) * | 2021-02-08 | 2021-09-14 | 宁德新能源科技有限公司 | Battery with a battery cell |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114613935A (en) * | 2022-03-31 | 2022-06-10 | 珠海冠宇电池股份有限公司 | Lithium ion battery |
| CN116666775A (en) * | 2023-07-27 | 2023-08-29 | 宁德新能源科技有限公司 | Lithium ion battery, electrochemical device, and electronic apparatus |
| CN116666775B (en) * | 2023-07-27 | 2023-11-14 | 宁德新能源科技有限公司 | Lithium ion battery, electrochemical device, and electronic apparatus |
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