Electrode sheet and battery

Abstract

An electrode sheet and a battery. The electrode sheet comprises a current collector and an electrode film arranged on at least one functional surface of the current collector, wherein the electrode film comprises fibers, and at least some of the fibers extend in a first direction of the electrode sheet. By defining the composition and structure of the electrode sheet, the breaking strength and adhesion of the electrode sheet can be significantly improved, thereby increasing the tensile strength of the electrode sheet and reducing the risk of breakage; and by applying the electrode sheet to a battery, the cycle performance and thickness expansion rate of the battery can be significantly improved.

Description

Electrode sheet and battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 21, 2023, with application number 202311773277.3 and application name “An Electrode Sheet and Battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to an electrode sheet and a battery, belonging to the technical field of lithium-ion batteries. Background Art

[0003] Lithium-ion batteries are widely used in electronics, communications, electric vehicles and other fields due to their advantages such as high energy efficiency, wide operating temperature range and environmental friendliness. As an important component of lithium-ion batteries, electrode sheets have a crucial impact on the performance of lithium-ion batteries. Currently, a wet process is often used in the preparation of electrode sheets, in which a slurry is prepared using an organic solvent for coating, and then the electrode sheets are obtained after drying and rolling. However, organic solvents are prone to pollution, and the solvents need to be dried and removed later, resulting in a huge waste of energy and increasing production costs. In addition, the electrode sheets are prone to cracking, poor toughness, delamination and other phenomena, which cannot further improve the energy density.

[0004] Currently, to increase battery energy density, reduce energy consumption during electrode preparation, and lower production costs, most electrodes are produced using a dry electrode process. Compared to wet processes, dry electrode processes place higher demands on the operating pressure, precision, and uniformity of roller pressing equipment. Furthermore, the greater compaction force can lead to issues such as breakage and powder loss during the rolling process. Therefore, increasing the breaking force of electrode sheets and reducing the risk of tape breakage during rolling remain pressing challenges.

[0005] Summary of the Invention

[0006] The electrode sheet provided by the present invention can significantly improve the breaking tensile force and adhesion of the electrode sheet by limiting the composition and structure of the electrode sheet, increase the tensile strength of the electrode sheet, and reduce the risk of band breakage. The electrode sheet can be directly applied to batteries and can significantly improve the battery's cycle performance and thickness expansion rate.

[0007] The present invention also provides a battery, which comprises the electrode sheet and has excellent performance in terms of cycle performance and thickness expansion rate.

[0008] A first aspect of the present invention provides an electrode sheet, comprising a current collector and an electrode film disposed on at least one functional surface of the current collector;

[0009] The electrode film includes fibers, and at least a portion of the fibers extend along a first direction of the electrode sheet.

[0010] In the electrode sheet as described above, the angle between the extending direction of the fibers and the first direction of the electrode sheet is 0-30°.

[0011] The electrode sheet as described above, wherein the breaking tensile force of the electrode sheet in the first direction is greater than or equal to the breaking tensile force of the electrode sheet in the second direction;

[0012] The second direction is perpendicular to the first direction.

[0013] The electrode sheet as described above, wherein the ratio of the breaking tensile force of the electrode sheet in the first direction to the breaking tensile force of the electrode sheet in the second direction is (1-2):1, preferably, (1.02-1.52):1.

[0014] The electrode sheet as described above, wherein the ratio of the breaking tensile force of the electrode sheet in the first direction to the thickness of the electrode sheet is (0.008-0.1):1;

[0015] The unit of the breaking tensile force of the electrode sheet in the first direction is kgf, and the unit of the thickness of the electrode sheet is μm.

[0016] The electrode sheet as described above, wherein the breaking tensile force of the electrode sheet in the first direction is 3 to 6 kgf; and / or,

[0017] The breaking tensile force of the electrode sheet in the second direction is 2 to 5.5 kgf; and / or,

[0018] The thickness of the electrode sheet is 65 to 350 μm.

[0019] The electrode sheet as described above, wherein the breaking tensile force of the current collector in the second direction is smaller than the breaking tensile force of the current collector in the first direction.

[0020] The electrode sheet as described above, wherein the ratio of the breaking tensile force of the current collector in the first direction to the breaking tensile force of the current collector in the second direction is (0.67-2.75):1, preferably, (0.875-1.67):1.

[0021] The electrode sheet as described above, wherein the electrode film further comprises an active material body, and the size of at least part of the fibers in the first direction is larger than the median particle size of the active material body.

[0022] The electrode sheet as described above, wherein the active material body includes LiCoO2, LiMn2O4, LiMnO2, LiNiO2, LiFePO4, LiMnPO4, LiCo x Ni 1-x O2、LiCo x Ni1-x-y Al y O2, where 0≤x≤1, 0≤y≤1, or

[0023] The active material body includes artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, Si, SiO x 、Si-C、SiO x -At least one of C.

[0024] In the electrode sheet as described above, the ratio of the size of a single fiber in the first direction to the median particle size of the active material body is 1:(1-4000), preferably 1:(1-400).

[0025] The electrode sheet as described above, wherein the size of a single fiber in the first direction is 250 nm to 1 mm; and / or,

[0026] The median particle size of the active material body is 250 nm to 30 μm.

[0027] The electrode sheet as described above, wherein in the thickness direction of the electrode sheet, the fibers extend along the thickness direction of the electrode sheet.

[0028] The electrode sheet as described above, wherein adjacent active material bodies are connected via the fibers along the thickness direction of the electrode sheet.

[0029] The electrode sheet as described above, wherein the electrode sheet further comprises a glue layer, and the glue layer is located between the current collector and the electrode film.

[0030] The electrode sheet as described above, wherein the adhesive layer includes an adhesive and a conductive agent; the adhesive includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, EVA hot melt adhesive, TPR hot melt adhesive, polyolefin hot melt adhesive, polyamide hot melt adhesive, polyester hot melt adhesive, polyethylene hot melt adhesive, polyesteramide hot melt adhesive, and / or

[0031] The conductive agent includes at least one of conductive carbon black, carbon nanotubes, and graphene.

[0032] The electrode sheet as described above, wherein the fibers include at least one of fibrous polytetrafluoroethylene, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, fluorinated ethylene propylene copolymer, polyvinyl pyrrolidone, polyethylene oxide, carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, hot melt adhesive, and polyethylene.

[0033] The electrode sheet as described above, wherein the electrode film further comprises a recessed portion, the recessed portion is located on a surface of the electrode film away from the current collector, and / or the recessed portion is located inside the electrode film.

[0034] In the electrode sheet as described above, the recess is filled with a lithium-containing compound, and the lithium-containing compound includes at least one of lithium oxide, lithium carbonate, and lithium fluoride.

[0035] A second aspect of the present invention provides a battery comprising the electrode sheet described in the first aspect.

[0036] The implementation of the present invention has at least the following beneficial effects:

[0037] The fibers in the electrode sheet provided by the present invention extend along the first direction of the electrode sheet, which can increase the adhesion between the electrode film and the current collector, while better transmitting stress, enhancing the breaking tension of the electrode sheet in the first direction, reducing the risk of tape breakage during rolling, and improving process efficiency, thereby ensuring the stability of the electrode sheet during long cycles.

[0038] The battery provided by the present invention, because it includes the above-mentioned electrode sheet, has excellent electrochemical properties, for example, excellent cycle performance and low thickness expansion rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG1 is a top view SEM image of an electrode sheet at a first magnification in one embodiment of the present invention;

[0040] FIG2 is a top view SEM image of an electrode sheet at a second magnification in one embodiment of the present invention;

[0041] FIG3 is a cross-sectional SEM image of an electrode sheet according to one embodiment of the present invention;

[0042] FIG4 is a schematic structural diagram of an electrode sheet in one embodiment of the present invention.

[0043] Description of reference numerals:

[0044] 1-electrode film; 2-glue layer; 3-current collector. DETAILED DESCRIPTION

[0045] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0046] In FIG. 1 to FIG. 4 , the X direction is the length direction of the electrode sheet, the Y direction is the width direction of the electrode sheet, and the Z direction is the thickness direction of the electrode sheet.

[0047] In a first aspect of the present invention, an electrode sheet is provided, comprising a current collector 3 and an electrode film 1 disposed on at least one functional surface of the current collector; the electrode film comprises fibers, at least part of which extend along a first direction of the electrode sheet.

[0048] The present invention does not limit the specific shapes of the electrode sheet and the current collector, which may be conventional rectangular parallelepiped shapes in the art.

[0049] The current collector has two largest and opposite functional surfaces, which are used to set the electrode film. The electrode film in the electrode sheet of the present invention can be set on only one functional surface of the current collector, or on both functional surfaces of the current collector.

[0050] Electrode membranes are used to generate electrochemical reactions, thereby converting chemical energy into electrical energy.

[0051] The electrode membrane components of the present invention include at least an active material body and a binder, wherein the active material body includes at least an active material and a conductive agent; the active material is used to generate an electrochemical reaction, the conductive agent is used to improve the conductivity of the electrode membrane, and the binder is used to bond the active material and the conductive agent, thereby forming a complete electrode membrane.

[0052] Wherein, fiber refers to continuous or discontinuous filaments. In some embodiments, the fiber is a filamentous structure formed by a binder through a fibrillation method or an electrostatic spraying method. The present invention does not limit the specific material of the fiber, and can specifically be a binder commonly used in the art. For example, the fiber can be at least one of fibrous polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETEF), fluorinated ethylene propylene copolymer (FEP), polyvinyl pyrrolidone (PVP), polyethylene oxide (PEO), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), hot melt adhesive, and polyethylene (PE).

[0053] The fiber and the active material body are in line-surface contact, which increases the contact area between the fiber and the active material body, enables a tighter connection between the fiber and the active material body, improves the flexibility of the electrode sheet, and prevents cracking and powdering.

[0054] The distribution of fibers in an electrode sheet affects its mechanical properties. By limiting at least some fibers to extend along a first direction within the electrode sheet, the present invention significantly increases the breaking force of the electrode sheet, reduces the risk of breakage, and thus significantly improves the battery's cycling performance and reduces thickness expansion.

[0055] The first direction of the electrode sheet refers to the extension direction of the electrode sheet, for example, the length direction or width direction of the electrode sheet. In other words, the extension direction of the fiber is consistent with the extension direction of the electrode sheet.

[0056] As shown in Figure 1, when the first direction is the length direction of the electrode sheet (X direction), the extension direction of the fiber is consistent with the length direction of the electrode sheet, which ensures that the fiber and the active material body form a closer bond, increases the tensile strength of the electrode sheet in the length direction, and enables it to withstand greater tension.

[0057] The present invention does not limit the breaking force of the electrode sheet in its extension direction. In some embodiments, the breaking force of the electrode sheet in the first direction is greater than or equal to the breaking force of the electrode sheet in the second direction; the second direction is perpendicular to the first direction. The electrode sheet extends along the rolling direction during the rolling process and is wound along the winding direction during the winding process. Therefore, the electrode sheet needs to withstand a certain tensile strength in both the rolling and winding directions. When both the rolling and winding directions are consistent with the first direction, by limiting the breaking force of the electrode sheet in the first direction to be greater than or equal to the breaking force of the electrode sheet in the second direction, the electrode sheet is prevented from breaking during the rolling process and cracking due to excessive force during the winding process.

[0058] When the first direction is the length direction of the electrode sheet, the second direction refers to the width direction of the electrode sheet.

[0059] In the electrode membrane, at least 90% by mass of the fibers extend along the first direction of the electrode sheet, that is, the angle between the extension direction of at least 90% by mass of the fibers and the first direction of the electrode sheet is 0°. In some embodiments, the angle between the extension direction of the fibers and the first direction of the electrode sheet is 0 to 30°.

[0060] When the electrode sheet is applied to the battery, the battery inevitably expands and contracts during the charge and discharge process. In some embodiments, the ratio of the breaking force of the electrode sheet in the first direction to the breaking force of the electrode sheet in the second direction is (1-2):1. By limiting the ratio of the breaking force of the electrode sheet in the first direction and the second direction, the expansion of the electrode sheet in the first direction and the second direction during the charge and discharge process can be effectively alleviated, especially the expansion of the electrode sheet in the first direction. Preferably, the ratio of the breaking force of the electrode sheet in the first direction to the breaking force in the second direction is (1.02-1.52):1. This can not only reduce the resistance and interface reaction inside the electrode sheet and improve the electrochemical performance of the battery, but also improve the mechanical stability of the battery and extend the service life of the battery.

[0061] The thickness of the electrode film affects the loading of active materials, which in turn affects the energy density of the battery. In some embodiments, the ratio of the breaking force of the electrode sheet in the first direction to the thickness of the electrode sheet is (0.008-0.1):1, where the breaking force of the electrode sheet in the first direction is in kgf and the thickness of the electrode sheet is in μm. This ensures that while maintaining the mechanical strength of the electrode sheet, it can increase the loading of active materials in the battery, improve the battery's energy density (the amount of electrical energy stored per unit volume or unit weight), and ensure that the battery has a higher capacity for the same size.

[0062] The thickness of the electrode sheet is equal to the sum of the thickness of the current collector and the thickness of the electrode film.

[0063] The present invention does not limit the specific values ​​of the breaking force and thickness of the electrode sheet, which can be determined based on actual conditions. For example, in some embodiments, the breaking force of the electrode sheet in the first direction is 3 to 6 kgf, preferably 4.3 to 5 kgf; and / or the breaking force of the electrode sheet in the second direction is 2 to 5.5 kgf, preferably 3.3 to 4.2 kgf; and / or the thickness of the electrode sheet is 65 to 350 μm.

[0064] In the present invention, the breaking force of the current collector in the second direction is less than the breaking force of the current collector in the first direction. The ratio of the breaking force of the current collector in the first direction to the breaking force of the current collector in the second direction is (0.67-2.75):1, preferably (0.875-1.67):1, to ensure the strength of the electrode sheet during processing and reduce the risk of tape breakage.

[0065] Furthermore, the breaking tensile force of the current collector in the first direction is 3 to 5.5 kgf, preferably 3.5 to 5 kgf; the breaking tensile force of the current collector in the second direction is 2 to 4.5 kgf, preferably 3 to 4 kgf.

[0066] The electrode film comprises multiple fibers and multiple active material bodies, with at least some of the fibers having a size in the first direction that is larger than the median particle size of the active material bodies. The fiber size in the first direction refers to the fiber length, while the median particle size of the active material bodies refers to the particle size corresponding to a cumulative volume fraction of 50%. The fiber size in the first direction refers to the absolute size of all fibers in the first direction, i.e., the size spanned in the first direction.

[0067] In some embodiments, the ratio of the size of a single fiber in the first direction to the median particle size of the active material body is 1:(1-4000), ensuring that multiple fibers can span the active material body, bonding and fixing the active material body, thereby reducing the cyclic expansion rate.

[0068] The present invention does not limit the specific sizes of the fibers and active material bodies. In some embodiments, the size of the fibers in the first direction is 250 nm to 1 mm; and / or the median particle size of the active material bodies is 250 nm to 30 μm.

[0069] In some embodiments, in the thickness direction of the electrode sheet, the fibers extend along the thickness direction of the electrode sheet. That is, when viewed in the thickness direction of the electrode sheet, the fibers are distributed along the thickness direction of the electrode sheet.

[0070] Fibers serve as bonding components connecting multiple active material bodies. In some embodiments, adjacent active material bodies are connected by fibers along the thickness of the electrode sheet. The fibers provide a tighter connection between the active material bodies, further ensuring that the fibers bond and secure the active material bodies, thereby reducing the cyclic expansion rate.

[0071] The present invention does not limit the specific types of active materials and conductive agents in the active material body. For example, in some embodiments, the conductive agent can be at least one of conductive carbon black, carbon fiber, conductive graphite, graphene, carbon nanotubes, acetylene black, Ketjen black, copper, nickel, aluminum, silver, and gold; the active material can be a positive electrode active material or a negative electrode active material; for example, the positive electrode active material includes LiCoO2, LiMn2O4, LiMnO2, LiNiO2, LiFePO4, LiMnPO4, LiCo x Ni 1-x O2(0≤x≤1), LiCo x Ni 1-x-y Al y At least one of O2 (0≤x≤1, 0≤y≤1); the negative electrode active material includes artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, Si, SiO x 、Si-C、SiO x -C, in this case, the mass content of silicon in the electrode film is 3 to 100%.

[0072] The present invention does not limit the preparation method of the above-mentioned electrode sheet, and it can be prepared by conventional methods in the field. For example, the active material, the conductive agent and the binder are mixed, and then an external high shear force is applied to fibrillate the binder to form a fiber network, which bonds the active material and the conductive agent. After extrusion, an electrode film is formed, and finally the electrode film is compounded with the current collector to obtain an electrode sheet. Compared with the wet process, such a dry electrode process has higher requirements on the working pressure, rolling accuracy and uniformity of the rolling equipment. The present invention avoids problems such as breakage and powder loss in the electrode sheet during the rolling process by limiting at least part of the fibers to extend along the first direction of the electrode sheet.

[0073] In one embodiment, the active material layer can be produced by a dry process, in which the active material, fiber particles, and conductive agent are dry-mixed without the use of a solvent to produce a composite material having a substantially 100% solids concentration. Dry mixing refers to mixing the active material and fiber particles without the use of a solvent at a substantially 100% solids concentration. During dry mixing, a first conductive agent, etc., may be added in addition to the active material and fiber particles. Even when materials other than the active material and fiber particles are added, the solids concentration during dry mixing is substantially 100%.

[0074] The adhesive layer slurry is then applied to the current collector and dried to form a hot-melt current collector. The composite material is then rolled into a sheet to form the active material layer. The hot-melt current collector and active material layer are then stacked and hot-pressed to form the electrode sheet.

[0075] Compared with the existing wet method for preparing pole pieces, in its production process, it is necessary to mix the solvent, active material and binder to form a slurry, and then apply the slurry to the surface of the current collector, and then dry the slurry coating on the surface of the current collector to volatilize the solvent. It can be seen that the drying process of the wet method makes the production process of the battery more complicated and reduces the production efficiency. In an embodiment of the present invention, by adopting a dry method to prepare pole pieces, there is no need to use a solvent, the active material and fiber particles are mixed to form a composite material, the composite material is rolled into a sheet, and then the sheet-like active material layer is hot-pressed with the hot-melt current collector. There is no need to dry the slurry coating on the surface of the current collector to volatilize the solvent, thereby simplifying the production process of the pole piece and improving the production efficiency of the battery.

[0076] In one embodiment, the preparation process of the above-mentioned electrode sheet includes the following steps: premixing the binder, conductive agent, and active material, shearing and rolling to obtain an electrode film; and then hot-pressing the electrode film onto the current collector to obtain an electrode sheet.

[0077] In the premixing process, the rotation speed is 300 to 10,000 rpm, the temperature is 0 to 90° C., and the time is 10 to 600 min.

[0078] Specifically, during the shearing process, the molecular chains of the binder are fully expanded to form fibers, and the formed fibers can fully bond the active material body formed by the active material and the conductive agent; finally, a hot pressing process is performed to obtain an electrode film.

[0079] The present invention does not impose any specific restrictions on the premixing process, as long as the above-mentioned rotation speed, temperature and time are met. In some embodiments, the premixing process can be performed in a blender.

[0080] The present invention does not specifically limit the shearing process. In some embodiments, the shearing process can be performed in a jet mill. In the jet mill, the premixed material is fluidized through nozzles. The accelerated material converges at the intersection of the jet streams from several nozzles, generating intense collision, friction, and shearing, thereby fiberizing the binder and producing a dough-like material. The dough-like material is then extruded through a screw pump and subjected to roller compaction. The feed rate of the jet mill is 150 to 9000 g / min.

[0081] The present invention does not specifically limit the rolling process, and can be a commonly used rolling process in the art, such as rolling in an open mill. In one possible embodiment, the rolling direction during the rolling process is consistent with the first direction, which helps to ensure that at least a portion of the fibers extend along the first direction of the electrode sheet.

[0082] The present invention does not specifically limit the hot pressing treatment, and it can be a hot pressing treatment commonly used in the art, such as a multi-stage hot pressing film forming process.

[0083] In the preparation method of the electrode membrane of the present invention, the raw material system including the conductive agent, the binder and the active material is premixed through a specific process, which can achieve sufficient mixing of the conductive agent, the binder and the active material, and facilitate the subsequent shearing treatment; then the premixed raw material system is sheared through a specific process, which can make the premixed raw material system fully fiberized, thereby obtaining the electrode membrane of the present invention.

[0084] To improve the adhesion between the electrode film and the current collector, in some embodiments, the electrode sheet further includes a glue layer 2, which is located between the current collector and the electrode film. The glue layer includes a binder and a conductive agent. The binder is used to improve the adhesion between the glue layer and the current collector, as well as the adhesion between the glue layer and the electrode film. The conductive agent is used to improve the conductivity of the glue layer. At the same time, the conductive agent can also increase the roughness of the glue layer and increase the specific surface area of ​​the glue layer, thereby further improving the adhesion and peeling force between the glue layer and the current collector, and between the glue layer and the electrode film.

[0085] The adhesive layer includes an adhesive and a conductive agent.

[0086] Among them, the binder can be polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), or hot melt adhesive, and the hot melt adhesive includes EVA hot melt adhesive, TPR hot melt adhesive, polyolefin hot melt adhesive, polyamide (PA) hot melt adhesive, polyester (PES) hot melt adhesive, polyethylene (LDPE, HDPE) hot melt adhesive and polyester amide (PEA) hot melt adhesive, etc. The conductive agent can be a conductive agent with a large specific surface area such as conductive carbon black, carbon nanotubes, graphene, etc. In some embodiments, the electrode film further includes a recess, which is located on the side surface of the electrode film away from the current collector, and / or the recess is located inside the electrode film. By forming a plurality of recesses, the infiltration channel of the electrolyte can be effectively increased, the wettability of the electrolyte can be improved, and it is helpful to increase the transmission speed of lithium ions and increase the charging rate.

[0087] The present invention does not limit the formation process of the recess. In one embodiment, the recess can be formed on the surface or inside the electrode film by a laser method. In another embodiment, the recess is formed on the surface of the electrode film by physical embossing.

[0088] During the first cycle of a lithium-ion battery, a solid electrolyte interface (SEI) forms on the surface of the electrode sheet, leading to irreversible lithium loss. A lithium replenisher is typically added to the electrode sheet to achieve this. In some embodiments, the recess is filled with a lithium-containing compound. The lithium-containing compound may be, for example, at least one of lithium oxide, lithium carbonate, and lithium fluoride. Filling the recess with a lithium-containing compound helps reduce irreversible lithium loss.

[0089] In the specific implementation process of the present invention, a lithium-containing compound, a binder, a conductive agent, and an active material are premixed, sheared, and hot-pressed to obtain an electrode film. The electrode film is prepared by adding a lithium-containing compound to the raw material system. In addition, the above-mentioned electrode sheet is applied to a battery. During the injection process, the lithium-containing compound and the electrolyte react to generate lithium ions, which compensate for the lithium ions required to form the SEI film and improve the initial efficiency of the battery.

[0090] A second aspect of the present invention provides a battery comprising the electrode sheet according to the first aspect.

[0091] Specifically, the electrode sheets include a negative electrode sheet and a positive electrode sheet. The negative electrode sheet, the positive electrode sheet, and the separator can form a battery cell, wherein at least one of the negative electrode sheet and the positive electrode sheet is the electrode sheet of the first aspect described above. By installing the battery cell and the protective circuit together within the battery housing, a battery for charge and discharge is formed. The quality of the battery cell directly determines the quality of the battery. Due to the use of the aforementioned electrode sheet, the battery of the present invention exhibits excellent cycle performance and thickness expansion ratio.

[0092] The present invention is further described below by way of specific examples and comparative examples. Unless otherwise specified, the reagents, materials, and instruments used below are all conventional reagents, materials, and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthesis methods.

[0093] Example 1

[0094] The negative electrode sheet preparation process of this embodiment includes the following steps:

[0095] Artificial graphite, polytetrafluoroethylene, and conductive carbon were added to a dispersion device and thoroughly dry-mixed to obtain a uniformly dispersed mixture. The mixture was added to a jet mill and dispersed for 25 minutes at a feed rate of 150 g / min to achieve fiberization of the polytetrafluoroethylene and obtain a dough-like negative electrode material. The mass ratio of artificial graphite, polytetrafluoroethylene, and conductive carbon was 97:2:1.

[0096] The negative electrode material is extruded and drawn by a screw pump, and then rolled by a hot roller press to obtain a negative electrode film, wherein the extrusion and drawing temperature is 100° C., the rolling pressure is 20t, the rolling speed is 5m / min, and the rolling direction is controlled so that the fibers extend along the first direction;

[0097] The negative electrode film was laminated to both surfaces of a 10 μm thick copper foil through multi-stage hot pressing to obtain a 50 μm thick negative electrode sheet F1. The ratio of the fiber size in the first direction to the median particle size of the active material body was 1:1000.

[0098] Example 2

[0099] The preparation process is basically the same as that of Example 1, except that:

[0100] The parameters of the hot roller press were adjusted to obtain a negative electrode sheet F2 with a thickness of 65 μm. The ratio of the fiber size in the first direction to the median particle size of the active material body was 1:400.

[0101] Example 3

[0102] The preparation process is basically the same as that of Example 1, except that:

[0103] The parameters of the hot roller press were adjusted to obtain a negative electrode sheet F3 with a thickness of 100 μm. The ratio of the fiber size in the first direction to the median particle size of the active material body was 1:200.

[0104] Example 4

[0105] The preparation process is basically the same as that of Example 1, except that:

[0106] The parameters of the hot roller press were adjusted to obtain a negative electrode sheet F4 with a thickness of 350 μm. The ratio of the fiber size in the first direction to the median particle size of the active material body was 1:100.

[0107] Example 5

[0108] The positive electrode sheet preparation process of this embodiment includes the following steps:

[0109] Lithium cobalt oxide, polytetrafluoroethylene, and conductive carbon were added to a dispersion device and fully dry-mixed to obtain a uniformly dispersed mixture; the mixture was added to a jet mill and dispersed for 25 minutes at a feed rate of 150 g / min. After sufficient dispersion and fiberization of the polytetrafluoroethylene, a dough-like positive electrode material was obtained; wherein the mass ratio of lithium cobalt oxide, polytetrafluoroethylene, and conductive carbon was 97:2:1;

[0110] The positive electrode material is extruded and rolled through a screw pump to obtain a positive electrode film;

[0111] The positive electrode film is composited onto the current collector through multi-stage hot calendering to obtain a positive electrode sheet Z1. The thickness of the positive electrode sheet Z1 is 50 μm, and the ratio of the size of the fiber in the first direction to the median particle size of the active material body is 1:1000.

[0112] Example 6

[0113] The preparation process is basically the same as that of Example 5, except that:

[0114] The parameters of the hot roller press were adjusted to obtain a positive electrode sheet Z2 with a thickness of 65 μm. The ratio of the size of the fibers in the first direction to the median particle size of the active material body was 1:400.

[0115] Experimental Example 7

[0116] The preparation process is basically the same as that of Example 5, except that:

[0117] The parameters of the hot roller press were adjusted to obtain a positive electrode sheet Z3 with a thickness of 100 μm. The ratio of the size of the fibers in the first direction to the median particle size of the active material body was 1:200.

[0118] Experimental Example 8

[0119] The preparation process is basically the same as that of Example 5, except that:

[0120] The parameters of the hot roller press were adjusted to obtain a positive electrode sheet Z4 with a thickness of 350 μm. The ratio of the size of the fibers in the first direction to the median particle size of the active material body was 1:100.

[0121] Comparative Example 1

[0122] 1. Preparation of negative electrode sheet

[0123] A negative electrode sheet F11 was produced in the same manner as in Example 1 except that the parameters of the hot roller press were adjusted so that the fiber filaments did not extend in the first direction.

[0124] 2. Preparation of positive electrode

[0125] A positive electrode sheet Z11 was produced in the same manner as in Example 5 except that the parameters of the hot roller press were adjusted so that the fiber filaments did not extend in the first direction.

[0126] Comparative Example 2

[0127] The preparation process is basically the same as that of Example 1, except that:

[0128] The parameters of the hot roller press were adjusted so that the breaking force of the negative electrode sheet in the first direction was smaller than the breaking force of the negative electrode sheet in the second direction, and the ratio of the fiber size in the first direction to the median particle size of the active material body was 1:500, thereby obtaining the negative electrode sheet F12 of this comparative example.

[0129] Comparative Example 3

[0130] The preparation process is basically the same as that of Comparative Example 2, except that:

[0131] The parameters of the hot roller press were adjusted so that the ratio of the size of the fibers in the first direction to the median particle size of the active material body was 1:5000, thereby obtaining the negative electrode sheet F13 of this comparative example.

[0132] Test example

[0133] 1. Preparation of lithium-ion batteries

[0134] The positive electrode sheet, separator (purchased from Asahi Kasei ND522), and negative electrode sheet are welded to the positive and negative electrode tabs and then wound to obtain a battery cell. The battery cell is placed in an aluminum-plastic film packaging shell and sealed, and then the electrolyte is injected. After formation and sorting, a lithium-ion battery is obtained;

[0135] The electrolyte includes a solvent, a lithium salt and an additive. The solvent is a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a mass ratio of 3:4:3. The lithium salt is lithium hexafluorophosphate. The concentration of the lithium salt in the electrolyte is 1.2 mol / L. The additives include fluoroethylene carbonate and vinylene carbonate. The mass content of fluoroethylene carbonate in the electrolyte is 3wt%, and the mass content of vinylene carbonate in the electrolyte is 1wt%.

[0136] Specifically, in the above preparation process, the positive electrode sheet Z1 is matched with the negative electrode sheet F1, the positive electrode sheet Z1 is matched with the negative electrode sheet F2, the positive electrode sheet Z1 is matched with the negative electrode sheet F3, the positive electrode sheet Z1 is matched with the negative electrode sheet F4, the positive electrode sheet Z2 is matched with the negative electrode sheet F1, the positive electrode sheet Z3 is matched with the negative electrode sheet F1, the positive electrode sheet Z4 is matched with the negative electrode sheet F1, the positive electrode sheet Z11 is matched with the negative electrode sheet F11, the positive electrode sheet Z11 is matched with the negative electrode sheet F12, and the positive electrode sheet Z11 is matched with the negative electrode sheet F13. The obtained lithium-ion batteries are respectively recorded as D1, D2, D3, D4, D5, D6, D7, D8, D9, and D10.

[0137] 2. Performance test of electrode sheet

[0138] The above-mentioned positive electrode sheet, negative electrode sheet, and current collector were cut into test samples with a width of 15±0.25 mm and a length of 75±0.5 mm, respectively. Using a universal tensile testing machine with a gauge length of 50±0.5 mm and a stretching speed of 200 mm / min, the positive electrode sheet, negative electrode sheet, and current collector were stretched along the first direction and the second direction, respectively, to test the maximum tensile force required for fracture.

[0139] 2) Use a scanning electron microscope to test the morphology of the positive and negative electrodes at different magnifications; cut the electrode cross section using argon ion gas and use a scanning electron microscope to test the cross-sectional morphology of the electrode;

[0140] 3) Number of belt breaks during 500m pole piece rolling: Count the number of belt breaks during 500m pole piece rolling.

[0141] 3. Battery performance test

[0142] 1) Capacity retention test

[0143] At 25°C, the battery was charged at a constant current of 1C to 4.45V, then charged at a constant voltage to a cutoff current of 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1C to 3.0V. This was the first cycle, and the above process was repeated 300 times. The capacity retention rate was calculated as follows: Capacity retention rate after 300 cycles (%) = discharge capacity after 300 cycles / discharge capacity after the first cycle × 100%.

[0144] 2) Thickness expansion rate test

[0145] The initial PPG thickness of the battery at 50% SOC before the test cycle is recorded as P1. After 300 cycles, the PPG thickness of the test battery at 100% SOC is recorded as P2. The thickness expansion rate % = (P2-P1) / P1×100%.

[0146] The test results are shown in Tables 1 and 2.

[0147] Table 1

[0148] Table 2

[0149] According to Table 1, at least part of the fibers in the electrode sheets of Examples 1-8 extend along the first direction of the electrode sheets, while the fibers in the electrode sheet of Comparative Example 1 do not extend along the first direction of the electrode sheets. The breaking tensile forces of the electrode sheets in Examples 1-8 in the first direction are all higher than that of Comparative Example 1, indicating that the electrode sheets of the embodiments can withstand a significantly higher tensile force range than the comparative example. It also indicates that extending at least part of the fibers along the first direction of the electrode sheet can help increase the breaking tensile force of the electrode sheet in the first direction.

[0150] By comparing Examples 1-8 and Comparative Example 2, it can be seen that by limiting the breaking force of the electrode sheet in the first direction to be greater than or equal to the breaking force of the electrode sheet in the second direction, the risk of belt breakage can be further reduced.

[0151] Comparison of Examples 1-8 and Comparative Example 3 shows that limiting the ratio of the size of a single fiber in the first direction to the median particle size of the active material body helps to further reduce the risk of tape breakage.

[0152] Comparing Examples 1-8, it can be seen that controlling the thickness of the electrode sheet can help further reduce the frequency of roller breakage.

[0153] As shown in Table 2, at the same electrode sheet thickness, the battery prepared using the electrode sheet of the embodiment has better cycle performance and thickness expansion rate, indicating that the fibers in the embodiment better wrap the active material, which helps to alleviate the cyclic expansion caused by the deintercalation and extraction of lithium ions from the active material.

[0154] The above describes in detail the preferred embodiments of the present invention and their experimental verification. It should be understood that a person skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solution that can be derived by a person skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art shall be within the scope of protection of the present invention.

Claims

1. An electrode sheet, characterized in that: The electrode sheet includes a current collector and an electrode film disposed on at least one functional surface of the current collector; The electrode film includes fibers, and at least a portion of the fibers extend along a first direction of the electrode sheet.

2. The electrode sheet according to claim 1, characterized in that: The included angle between the extending direction of the fiber and the first direction of the electrode sheet is 0-30°.

3. The electrode sheet according to claim 1, characterized in that: The breaking tensile force of the electrode sheet in the first direction is greater than or equal to the breaking tensile force of the electrode sheet in the second direction; The second direction is perpendicular to the first direction.

4. The electrode sheet according to claim 1, characterized in that: The ratio of the breaking tensile force of the electrode sheet in the first direction to the breaking tensile force of the electrode sheet in the second direction is (1-2):1, preferably, (1.02-1.52):

1.

5. The electrode sheet according to claim 1, characterized in that: The ratio of the breaking tensile force of the electrode sheet in the first direction to the thickness of the electrode sheet is (0.008-0.1):1; The unit of the breaking tensile force of the electrode sheet in the first direction is kgf, and the unit of the thickness of the electrode sheet is μm.

6. The electrode sheet according to any one of claims 1 to 5, characterized in that: The breaking tensile force of the electrode sheet in the first direction is 3-6 kgf; and / or, The breaking tensile force of the electrode sheet in the second direction is 2 to 5.5 kgf; and / or, The thickness of the electrode sheet is 65-350 μm.

7. The electrode sheet according to any one of claims 1 to 5, characterized in that: The breaking tensile force of the current collector in the second direction is smaller than the breaking tensile force of the current collector in the first direction.

8. The electrode sheet according to claim 7, characterized in that: The ratio of the breaking tensile force of the current collector in the first direction to the breaking tensile force of the current collector in the second direction is (0.67-2.75):1, preferably, (0.875-1.67):

1.

9. The electrode sheet according to any one of claims 1 to 5, characterized in that: The electrode film further comprises an active material body, and the size of at least part of the fibers in the first direction is larger than the median particle size of the active material body.

10. The electrode sheet according to claim 9, characterized in that: The active material body includes LiCoO2, LiMn2O4, LiMnO2, LiNiO2, LiFePO4, LiMnPO4, LiCo x Ni 1-x O2、LiCo x Ni 1-x-y Al y O2, where 0≤x≤1, 0≤y≤1, or The active material body includes artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, Si, SiO x 、Si-C、SiO x -At least one of C.

11. The electrode sheet according to claim 9, characterized in that: The ratio of the size of a single fiber in the first direction to the median particle size of the active material body is 1:(1-4000), preferably 1:(1-400).

12. The electrode sheet according to claim 11, characterized in that: The size of a single fiber in the first direction is 250 nm to 1 mm; and / or, The median particle size of the active material body is 250 nm to 30 μm.

13. The electrode sheet according to any one of claims 1 to 5, characterized in that: In the thickness direction of the electrode sheet, the fibers extend along the thickness direction of the electrode sheet.

14. The electrode sheet according to claim 1, characterized in that: Along the thickness direction of the electrode sheet, adjacent active material bodies are connected by the fibers.

15. The electrode sheet according to claim 1, characterized in that: The electrode sheet further includes a glue layer, and the glue layer is located between the current collector and the electrode film.

16. The electrode sheet according to claim 15, characterized in that: The adhesive layer includes a binder and a conductive agent; The adhesive includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, EVA hot melt adhesive, TPR hot melt adhesive, polyolefin hot melt adhesive, polyamide hot melt adhesive, polyester hot melt adhesive, polyethylene hot melt adhesive, polyester amide hot melt adhesive, and / or, The conductive agent includes at least one of conductive carbon black, carbon nanotubes and graphene.

17. The electrode sheet according to claim 1, characterized in that: The fiber comprises at least one of fibrous polytetrafluoroethylene, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, fluorinated ethylene propylene copolymer, polyvinyl pyrrolidone, polyethylene oxide, carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, hot melt adhesive and polyethylene.

18. The electrode sheet according to any one of claims 1 to 4, characterized in that: The electrode film further comprises a recessed portion, wherein the recessed portion is located on a surface of the electrode film that is away from the current collector, and / or the recessed portion is located inside the electrode film.

19. The electrode sheet according to claim 18, characterized in that: The recess is filled with a lithium-containing compound; Wherein, the lithium-containing compound includes at least one of lithium oxide, lithium carbonate and lithium fluoride.

20. A battery, characterized in that: The electrode sheet comprises the electrode sheet according to any one of claims 1 to 19.

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