Electrode sheet, battery and electrical device

Abstract

Provided in the present application are an electrode sheet, a battery, and an electrical device. The electrode sheet comprises a current collector and an active material layer provided on the surface of at least one side of the current collector, the active material layer comprising a first active material layer and a second active material layer provided in the same layer as the first active material layer and connected thereto. In the direction from the first active material layer to the second active material layer, the thickness of the second active material layer gradually decreases. The first active material layer comprises a first active material, and the second active material layer comprises a second active material, the mass content of the first active material in the first active material layer being less than the mass content of the second active material in the second active material layer. The electrode sheet provided in the present application is not prone to lithium plating reaction, has high volumetric energy density and mass energy density, involves low manufacturing cost, and helps to improve the capacity and service life of batteries.

Description

Electrode tab, battery and electric device

[0001] The present application claims priority to the Chinese patent application No. 202410851853.X, filed on June 27, 2024, and entitled "Electrode tab, battery and electric device", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the field of battery, in particular to the electrode tab, battery and electric device. BACKGROUND

[0003] At present, in order to improve the production capacity of the electrode tab, the electrode tab is prepared by adopting multi-width coating. The relative area capacity in the electrode tab is not matched, which leads to the decrease of the ratio of the negative electrode capacity to the positive electrode capacity, and the lithium precipitation phenomenon is easy to occur, which is not conducive to improving the cycle stability of the battery. In the related technology, the ratio of the negative electrode capacity to the positive electrode capacity is improved by increasing the area density of the electrode tab to reduce the probability of lithium precipitation phenomenon, but this method will lead to the decrease of the volume energy density and the weight energy density of the electrode tab, the increase of the preparation cost, and is not conducive to improving the wide application of the electrode tab. Therefore, an electrode tab which is not easy to occur lithium precipitation phenomenon, has high volume energy density and weight energy density, and low preparation cost is needed. SUMMARY

[0004] In view of this, the present application provides an electrode tab, battery and electric device. The electrode tab is not easy to occur lithium precipitation phenomenon, has high volume energy density and weight energy density, and low preparation cost, which is conducive to improving the electrochemical performance and industrial application of the battery.

[0005] In a first aspect, the present application provides an electrode tab, which comprises a current collector and an active material layer arranged on at least one side surface of the current collector. The active material layer comprises a first active material layer and a second active material layer arranged in the same layer and connected with the first active material layer. In the direction from the first active material layer to the second active material layer, the thickness of the second active material layer gradually decreases. The first active material layer comprises a first active material, and the second active material layer comprises a second active material. The mass content of the first active material in the first active material layer is less than the mass content of the second active material in the second active material layer.

[0006] Optionally, the second active material layer is arranged on one side of the first active material layer, or the second active material layer is arranged on opposite sides of the first active material layer.

[0007] Optionally, in the first active material layer, the mass content of the first active material is 93%-97.2%.

[0008] Optionally, in the second active material layer, the mass content of the second active material is 96.2%-98.5%.

[0009] Optionally, the primary particle size D50 of the first active material is less than the primary particle size D50 of the second active material.

[0010] Optionally, the mass content of the carbon coating layer of the first active material is greater than the mass content of the carbon coating layer of the second active material.

[0011] Optionally, the primary particle size D50 of the first active material is 0.3 μm-9 μm.

[0012] Optionally, the primary particle size D50 of the second active material is 0.7 μm-15 μm.

[0013] Optionally, the mass content of the carbon coating layer of the first active material is 0.5%-2%.

[0014] Optionally, the mass content of the carbon coating layer of the second active material is less than or equal to 0.5%.

[0015] Optionally, the first active material layer further comprises a first conductive agent and a first binder, and the second active material layer further comprises a second conductive agent and a second binder.

[0016] Optionally, the mass content of the first conductive agent in the first active material layer is greater than the mass content of the second conductive agent in the second active material layer.

[0017] Optionally, the mass content of the first binder in the first active material layer is greater than the mass content of the second binder in the second active material layer.

[0018] Optionally, in the first active material layer, the mass content of the first conductive agent is 0.5%-2%, and the mass content of the first binder is 1%-3%.

[0019] Optionally, in the second active material layer, the mass content of the second conductive agent is less than or equal to 1%, and the mass content of the second binder is 0.5%-2%.

[0020] Optionally, the thickness of the first active material layer is 92 μm-300 μm, and the maximum thickness of the second active material layer is 92 μm-300 μm.

[0021] Optionally, the size of the first active material layer in the direction from the second active material layer to the first active material layer is 80 mm-1000 mm.

[0022] Optionally, the size of the second active material layer in the direction from the first active material layer to the second active material layer is 10mm-30mm.

[0023] Optionally, the areal density of the electrode tab is 150g / m 2 -600g / m 2 .

[0024] The electrode tab provided by the application has a low probability of lithium precipitation, high volume energy density and mass energy density, improved cycle stability of the electrode tab, and improved service life of the battery.

[0025] In a second aspect, the application provides a battery, which comprises a positive electrode tab and a negative electrode tab, and a separator arranged between the positive electrode tab and the negative electrode tab, wherein the negative electrode tab comprises the electrode tab of the first aspect.

[0026] Optionally, the positive electrode tab comprises the electrode tab of the first aspect.

[0027] The battery provided by the application has excellent electrochemical performance, long service life, and strong product competitiveness.

[0028] In a third aspect, the application provides an electrical device, which comprises the battery of the second aspect.

[0029] The electrical device provided by the application has excellent comprehensive performance, high safety performance, and strong market competitiveness. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. The specific embodiments described herein are only used to explain the application and not to limit the application.

[0031] FIG. 1 is a schematic cross-sectional view of an electrode tab provided by an embodiment of the application.

[0032] FIG. 2 is a schematic cross-sectional view of an electrode tab provided by another embodiment of the application.

[0033] FIG. 3 is a schematic cross-sectional view of an electrode tab provided by still another embodiment of the application.

[0034] Legend of reference signs: 100-electrode tab; 10-current collector; 20-active material layer; 21-first active material layer; 22-second active material layer; 11-tab. DETAILED DESCRIPTION

[0035] With reference to the accompanying drawings, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0036] Please refer to FIG. 1, which is a cross-sectional schematic diagram of an electrode tab provided by an embodiment of the present application. The electrode tab 100 includes a current collector 10 and an active material layer 20 arranged on at least one side surface of the current collector 10. The active material layer 20 includes a first active material layer 21 and a second active material layer 22 arranged in the same layer as the first active material layer 21 and connected to the first active material layer 21. In the direction from the first active material layer 21 to the second active material layer 22, the thickness of the second active material layer 22 gradually decreases. The first active material layer 21 includes a first active material, and the second active material layer 22 includes a second active material. The mass content of the first active material in the first active material layer 21 is less than the mass content of the second active material in the second active material layer 22. In the electrode tab provided by the present application, by controlling the relationship between the mass content of the first active material in the first active material layer and the mass content of the second active material in the second active material layer, the number of ion intercalation sites in the second active material layer is increased, the capacity of the second active material layer is improved, and thus the capacity, volume energy density and weight energy density of the electrode tab are improved, the probability of lithium precipitation in the electrode tab during use is reduced, and the capacity, cycle stability and service life of the battery are improved.

[0037] In an embodiment of the present application, in the direction from the first active material layer to the second active material layer (as shown by the arrow in FIG. 1), the thickness of the second active material layer gradually decreases. The gradual decrease can be linear decrease, or non-linear decrease, such as gradient decrease, parabolic decrease, etc. The region in the active material layer of the electrode tab where the thickness gradually decreases is defined as a thinning region, and the region where the thickness remains unchanged is defined as a non-thinning region. Therefore, the first active material layer is a non-thinning region, and the second active material layer is a thinning region. By increasing the content of the second active material in the thinning region, the capacity of the thinning region in the electrode tab is improved, the capacity of the electrode tab is improved, the lithium precipitation phenomenon is alleviated, and the energy density of the electrode tab is improved.

[0038] In the present application, the current collector converts chemical energy into electrical energy for output, and improves the conductivity of the electrode tab. The current collector is a positive current collector or a negative current collector. When the electrode tab is a positive electrode tab, the current collector is a positive current collector. When the electrode tab is a negative electrode tab, the current collector is a negative current collector. In an embodiment of the present application, the positive current collector can be, but is not limited to, at least one of copper, aluminum, nickel, and stainless steel. The negative current collector can include, but is not limited to, at least one of copper, aluminum, nickel, and stainless steel. In an embodiment of the present application, when the current collector is a positive current collector and the electrode tab is a positive electrode tab, the current collector can be an aluminum foil. In another embodiment of the present application, when the current collector is a negative current collector and the electrode tab is a negative electrode tab, the current collector can be a copper foil.

[0039] In an embodiment of the present application, the active material layer completely covers the surface of the current collector; that is, the orthographic projection of the active material layer on the surface of the current collector completely covers the surface of the current collector. Please refer to FIG. 2, which is a schematic cross-sectional view of an electrode tab provided in another embodiment of the present application. In the electrode tab 100, there is an area on the surface of the current collector 10 that is not covered by the active material layer 20. The area of the current collector 10 that is not covered by the active material layer 20 serves as a tab 11. One end of the tab 11 is connected to the second active material layer 22 (thinning area), and the other end of the tab 11 can be connected to an external device for charging and discharging cycles. In some embodiments, the second active material layer is disposed on one side of the first active material layer. Specifically, when the electrode tab has a tab, the second active material layer can be disposed between the first active material layer and the tab. In other embodiments, the second active material layer is disposed on opposite sides of the first active material layer. Specifically, when the electrode tab has a tab, the second active material layer can be disposed between the first active material layer and the tab.

[0040] In an embodiment of the present application, as shown in FIG. 1, the electrode tab 100 includes a current collector 10 and an active material layer 20 arranged on one side surface of the current collector 10, the active material layer 20 includes a first active material layer 21 and a second active material layer 22, and the first active material layer 21 and the second active material layer 22 are arranged on the same side surface of the current collector 10. Please refer to FIG. 3, which is a schematic cross-sectional view of an electrode tab provided in another embodiment of the present application, the electrode tab 100 includes a current collector 10 and an active material layer 20 arranged on opposite side surfaces of the current collector 10, which can further improve the energy density of the electrode tab and reduce the probability of occurrence of lithium precipitation phenomenon of the electrode tab. In the present application, the first active material can be a positive active material or a negative active material, the first active material is a positive active material when the electrode tab is a positive electrode tab, and the first active material is a negative active material when the electrode tab is a negative electrode tab. In an embodiment of the present application, the positive active material can include, but is not limited to, at least one of lithium cobaltate material, nickel-cobalt-manganese material, nickel-cobalt-aluminum material, nickel-cobalt-manganese-aluminum material, lithium iron phosphate material, lithium manganese phosphate material, lithium vanadium phosphate material, lithium manganate material, and lithium-rich manganese-based material; and the negative active material can include, but is not limited to, at least one of artificial graphite, natural graphite, hard carbon, soft carbon, and graphene. In an embodiment of the present application, when the first active material is a positive active material, the first active material can be a lithium iron phosphate material. In another embodiment of the present application, when the first active material is a negative active material, the first active material can be artificial graphite.

[0041] In the present application, the second active material layer includes a second active material, the second active material can be a positive active material or a negative active material, the second active material is a positive active material when the electrode tab is a positive electrode tab, and the second active material is a negative active material when the electrode tab is a negative electrode tab, which can improve the conductivity and the capacity density of the electrode tab. In an embodiment of the present application, the positive active material can include, but is not limited to, at least one of lithium cobaltate material, nickel-cobalt-manganese material, nickel-cobalt-aluminum material, nickel-cobalt-manganese-aluminum material, lithium iron phosphate material, lithium manganese phosphate material, lithium vanadium phosphate material, lithium manganate material, and lithium-rich manganese-based material; and the negative active material can include, but is not limited to, at least one of artificial graphite, natural graphite, hard carbon, soft carbon, and graphene. In an embodiment of the present application, when the second active material is a positive active material, the second active material can be a lithium iron phosphate material. In another embodiment of the present application, when the second active material is a negative active material, the second active material can be artificial graphite.

[0042] In an embodiment of the present application, the mass content of the first active material in the first active material layer is 93%-97.2%, which can improve the energy density and the conductivity of the electrode sheet. Specifically, the mass content of the first active material in the first active material layer can be, but is not limited to, 93%, 94%, 95%, 96%, 9.65%, or 97.2%, etc. In an embodiment of the present application, when the first active material is a negative electrode active material, the mass content of the first active material in the first active material layer can be 93%-97%, which can improve the energy density of the negative electrode sheet. In another embodiment of the present application, when the first active material is a positive electrode active material, the mass content of the first active material in the first active material layer can be 95%-97.2%, which can improve the energy density of the positive electrode sheet.

[0043] In an embodiment of the present application, the mass content of the second active material in the second active material layer is 96.2%-98.5%, which can improve the energy density and the conductivity of the electrode sheet. Specifically, the mass content of the second active material in the second active material layer can be, but is not limited to, 96.2%, 96.5%, 96.8%, 97%, 9.75%, or 98.5%, etc. In an embodiment of the present application, when the second active material is a negative electrode active material, the mass content of the second active material in the second active material layer can be 96.2%-98.5%, which can improve the energy density of the negative electrode sheet. In another embodiment of the present application, when the second active material is a positive electrode active material, the mass content of the second active material in the second active material layer can be 97%-98.5%, which can improve the energy density of the positive electrode sheet.

[0044] In the present application, the particle size D50 is the particle size corresponding to the cumulative volume distribution percentage of 50%. In an embodiment of the present application, the primary particle size D50 of the first active material is smaller than the primary particle size D50 of the second active material. With the same active material mass, the smaller the primary particle size D50 of the active material, the larger the specific surface area, the more ion deintercalation sites, and the shorter the lithium ion diffusion distance, which is beneficial to improve the conductivity and the specific capacity. Since the second active material layer is close to the tab area, the temperature rises during charging and discharging, and a large-particle-size active material can be used to improve the conductivity of the second active material layer by taking advantage of the improved kinetic performance of the active material at high temperature, which is beneficial to improve the high-temperature resistance and the service life of the electrode sheet, reduce the preparation cost of the electrode sheet, and avoid the lithium precipitation phenomenon during use of the electrode sheet.

[0045] In an embodiment of the present application, the mass content of the carbon coating layer of the first active material is greater than the mass content of the carbon coating layer of the second active material. The higher the mass content of the carbon coating layer, the thicker the coating layer, which can improve the conductivity of the active material. Since the second active material layer is close to the tab area, the temperature rises during charging and discharging. Therefore, the active material with a small mass content of the carbon coating layer can be used to maintain the high conductivity of the second active material layer, improve the volume energy density and weight energy density of the electrode tab, and further improve the thermal stability and safety performance of the battery and reduce the risk of thermal runaway of the battery.

[0046] In an embodiment of the present application, the primary particle size D50 of the first active material is 0.3-9 μm. Specifically, the primary particle size D50 of the first active material can be, but is not limited to, 0.3 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, or 9 μm, etc. In an embodiment of the present application, when the first active material is a negative electrode active material, the primary particle size D50 of the first active material can be 6-9 μm. In another embodiment of the present application, when the first active material is a positive electrode active material, the primary particle size D50 of the first active material can be 0.3-1.3 μm.

[0047] In an embodiment of the present application, the primary particle size D50 of the second active material is 0.7-15 μm. Specifically, the primary particle size D50 of the second active material can be, but is not limited to, 0.7 μm, 1 μm, 2 μm, 8 μm, 10 μm, 13 μm, or 15 μm, etc. In an embodiment of the present application, when the second active material is a negative electrode active material, the primary particle size D50 of the second active material can be 9-15 μm. In another embodiment of the present application, when the second active material is a positive electrode active material, the primary particle size of the second active material can be 0.7-2 μm.

[0048] In an embodiment of the present application, the mass content of the carbon coating layer of the first active material is 0.5-2%. The higher the mass content of the carbon coating layer, the more carbon content on the surface of the active material, and the thicker the carbon layer. An appropriate mass content of the carbon coating layer is beneficial to improve the conductivity of the active material, improve the safety performance of the battery, and reduce the risk of thermal runaway of the battery. Specifically, the mass content of the carbon coating layer of the first active material can be, but is not limited to, 0.5%, 1%, 1.2%, 1.6%, 1.8%, or 2%, etc.

[0049] In an embodiment of the present application, the mass content of the carbon coating layer of the second active material is less than or equal to 0.5%. Specifically, the mass content of the carbon coating layer of the second active material can be, but is not limited to, less than or equal to 0.5%, less than or equal to 0.4%, less than or equal to 0.3%, less than or equal to 0.2%, or less than or equal to 0.1%, etc. In an embodiment of the present application, when the electrode sheet is a negative electrode sheet, the mass content of the carbon coating layer of the second active material can be less than or equal to 0.5%.

[0050] In an embodiment of the present application, the first active material layer further comprises a first conductive agent and a first binder. The first conductive agent can improve the conductivity of the electrode sheet, and the first binder can improve the binding ability between the components of the first active material layer and between the first active material layer and the current collector, thereby improving the mechanical properties of the electrode sheet.

[0051] The first conductive agent can be a positive electrode conductive agent or a negative electrode conductive agent. When the electrode sheet is a positive electrode sheet, the first conductive agent is a positive electrode conductive agent, and when the electrode sheet is a negative electrode sheet, the first conductive agent is a negative electrode conductive agent, which can improve the conductivity of the electrode sheet. In an embodiment of the present application, the positive electrode conductive agent can include, but is not limited to, at least one of carbon nanotubes, acetylene black, graphene, conductive graphite, and carbon black; and the negative electrode conductive agent can include, but is not limited to, at least one of carbon nanotubes, acetylene black, graphene, conductive graphite, and carbon black. In an embodiment of the present application, when the first conductive agent is a positive electrode conductive agent, the first conductive agent can be carbon nanotubes. In another embodiment of the present application, when the first conductive agent is a negative electrode conductive agent, the first conductive agent can be carbon black.

[0052] In an embodiment of the present application, the mass content of the first conductive agent in the first active material layer is 0.5%-2%, which can improve the conductivity of the electrode sheet. Specifically, the mass content of the first conductive agent in the first active material layer can be, but is not limited to, 0.5%, 0.8%, 1%, 1.5%, 1.8%, or 2%, etc. In an embodiment of the present application, when the first conductive agent is a positive electrode conductive agent, the mass content of the first conductive agent in the first active material layer can be 1%-2%. In another embodiment of the present application, when the first conductive agent is a negative electrode conductive agent, the mass content of the first conductive agent in the first active material layer can be 0.5%-2%.

[0053] The first binder can be a positive electrode binder or a negative electrode binder. When the electrode tab is a positive electrode tab, the first binder is a positive electrode binder. When the electrode tab is a negative electrode tab, the first binder is a negative electrode binder. The first binder can improve the mechanical properties of the electrode tab. In an embodiment of the present application, the positive electrode binder can include, but is not limited to, at least one of polyvinylidene fluoride, polyvinylidene difluoride, polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polybutadiene, acrylic resin, epoxy resin, polyethylene oxide, sodium carboxymethyl cellulose, and styrene butadiene rubber. The negative electrode binder can include, but is not limited to, at least one of polyvinylidene fluoride, polyvinylidene difluoride, polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polybutadiene, acrylic resin, epoxy resin, polyethylene oxide, sodium carboxymethyl cellulose, and styrene butadiene rubber. In an embodiment of the present application, when the first binder is a positive electrode binder, the first binder can be polyvinylidene fluoride. In another embodiment of the present application, when the first binder is a negative electrode binder, the first binder can be styrene butadiene rubber.

[0054] In an embodiment of the present application, the mass content of the first binder in the first active material layer is 1% to 3%. The suitable first binder can improve the mechanical properties of the electrode tab. Specifically, the mass content of the first binder in the first active material layer can be, but is not limited to, 1%, 1.2%, 1.8%, 2%, 2.4%, 2.6%, 2.8%, or 3%, etc. In an embodiment of the present application, when the first binder is a positive electrode binder, the mass content of the first binder in the first active material layer can be 1.8% to 3%. In another embodiment of the present application, when the first binder is a negative electrode binder, the mass content of the first binder in the first active material layer can be 1% to 2%.

[0055] In an embodiment of the present application, the second active material layer further includes a second conductive agent and a second binder. The second conductive agent can improve the conductivity of the electrode tab. The second binder can improve the binding ability between the components of the second active material layer and between the second active material layer and the current collector, which is conducive to improving the mechanical properties of the electrode tab.

[0056] The second conductive agent can be a positive electrode conductive agent or a negative electrode conductive agent. When the electrode tab is a positive electrode tab, the second conductive agent is a positive electrode conductive agent. When the electrode tab is a negative electrode tab, the second conductive agent is a negative electrode conductive agent. The second conductive agent can improve the conductivity of the electrode tab. In an embodiment of the present application, the positive electrode conductive agent can include, but is not limited to, at least one of carbon nanotube, acetylene black, graphene, conductive graphite, and carbon black. The negative electrode conductive agent can include, but is not limited to, at least one of carbon nanotube, acetylene black, graphene, conductive graphite, and carbon black. In an embodiment of the present application, when the second conductive agent is a positive electrode conductive agent, the second conductive agent can be conductive graphite. In another embodiment of the present application, when the second conductive agent is a negative electrode conductive agent, the second conductive agent can be carbon nanotube.

[0057] In an embodiment of the present application, the mass content of the second conductive agent in the second active material layer is less than or equal to 1%, and the appropriate mass of the second conductive agent can slow down the lithium precipitation phenomenon of the electrode plate. Specifically, the mass content of the second conductive agent in the second active material layer can be, but is not limited to, less than or equal to 1%, less than or equal to 0.8%, less than or equal to 0.7%, less than or equal to 0.5%, less than or equal to 0.3%, or less than or equal to 0.1%, etc.

[0058] The second binder can be a positive electrode binder or a negative electrode binder. When the electrode plate is a positive electrode plate, the second binder is a positive electrode binder, and when the electrode plate is a negative electrode plate, the second binder is a negative electrode binder, which can improve the mechanical properties of the electrode plate. In an embodiment of the present application, the positive electrode binder can include, but is not limited to, at least one of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polybutadiene, acrylic resin, epoxy resin, polyethylene oxide, sodium carboxymethyl cellulose, and styrene butadiene rubber; and the negative electrode binder can include, but is not limited to, at least one of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polystyrene, polybutadiene, acrylic resin, epoxy resin, polyethylene oxide, sodium carboxymethyl cellulose, and styrene butadiene rubber. In an embodiment of the present application, when the second binder is a positive electrode binder, the second binder can be polyvinylidene fluoride. In another embodiment of the present application, when the second binder is a negative electrode binder, the second binder can be polytetrafluoroethylene.

[0059] In an embodiment of the present application, the mass content of the second binder in the second active material layer is 0.5%-2%. Specifically, the mass content of the second binder in the second active material layer can be, but is not limited to, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, or 2%, etc. In an embodiment of the present application, when the second binder is a positive electrode binder, the mass content of the second binder in the second active material layer can be 1.5%-2%. In another embodiment of the present application, when the second binder is a negative electrode binder, the mass content of the second binder in the second active material layer can be 0.5%-1.2%.

[0060] In an embodiment of the present application, the mass content of the first conductive agent in the first active material layer is greater than the mass content of the second conductive agent in the second active material layer. Since the second active material layer is close to the tab area, the temperature rises during the charging and discharging process, and the kinetics of the second active material is improved by the temperature rise, which can maintain the high conductivity of the second active material layer, thereby reducing the use of conductive agents and reducing the preparation cost of the electrode plate.

[0061] In an embodiment of the present application, the mass content of the first binder in the first active material is greater than the mass content of the second binder in the second active material layer. Since the content of the second conductive agent in the second active material layer is reduced, the solid content is also reduced, so that a binder with low mass content can be used, which can realize the dispersion of the second active material and the second conductive agent without affecting the mechanical properties of the electrode sheet, reduces the preparation cost of the electrode sheet, and is conducive to the industrial application of the electrode sheet.

[0062] In an embodiment of the present application, when the electrode sheet is a negative electrode sheet, the first active material layer further comprises a first thickening agent, which can promote the uniform distribution of the first active material layer. Specifically, the first thickening agent can include, but is not limited to, sodium carboxymethyl cellulose or lithium carboxymethyl cellulose, etc. In an embodiment of the present application, the first thickening agent can be sodium carboxymethyl cellulose, and the negative electrode binder can be styrene-butadiene rubber.

[0063] In an embodiment of the present application, the mass content of the first thickening agent in the first active material layer is 1.5%-3%. Specifically, the mass content of the first thickening agent in the first active material layer can be, but is not limited to, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.7%, 2.8% or 3%, etc. In an embodiment of the present application, the mass content of the first thickening agent in the first active material layer can be 1.5%-2.5%. In another embodiment of the present application, the mass content of the first thickening agent in the first active material layer can be 2%-3%.

[0064] In an embodiment of the present application, when the electrode sheet is a negative electrode sheet, the second active material layer further comprises a second thickening agent, which can promote the uniform distribution of the second active material layer. Specifically, the second thickening agent can include, but is not limited to, sodium carboxymethyl cellulose or lithium carboxymethyl cellulose, etc. In an embodiment of the present application, the second thickening agent can be sodium carboxymethyl cellulose, and the negative electrode binder can be styrene-butadiene rubber.

[0065] In an embodiment of the present application, the mass content of the second thickening agent in the second active material layer is 1%-1.5%. Specifically, the mass content of the second thickening agent in the second active material layer can be, but is not limited to, 1%, 1.2%, 1.3%, 1.4% or 1.5%, etc. In an embodiment of the present application, the mass content of the second thickening agent in the second active material layer can be 1%-1.2%. In another embodiment of the present application, the mass content of the second thickening agent in the second active material layer can be 1.2%-1.5%.

[0066] In an embodiment of the present application, the thickness of the first active material layer is 92 μm-300 μm. Specifically, the thickness of the first active material layer can be, but is not limited to, 92 μm, 100 μm, 150 μm, 200 μm, 250 μm, or 300 μm, etc. In an embodiment of the present application, when the electrode tab is a positive electrode tab, the thickness of the first active material layer can be 130 μm-300 μm. In another embodiment of the present application, when the electrode tab is a negative electrode tab, the thickness of the first active material layer can be 100 μm-180 μm.

[0067] In an embodiment of the present application, the size of the first active material layer in the direction from the second active material layer to the first active material layer is 80 mm-1000 mm. The large size of the first active material layer is beneficial to improve the energy density of the electrode tab. Specifically, the size of the first active material layer in the direction from the second active material layer to the first active material layer can be, but is not limited to, 80 mm, 100 mm, 200 mm, 400 mm, 600 mm, 800 mm, or 1000 mm, etc. In an embodiment of the present application, the size of the first active material layer in the direction from the second active material layer to the first active material layer can be 80 mm-600 mm. In another embodiment of the present application, the size of the first active material layer in the direction from the second active material layer to the first active material layer can be 500 mm-1000 mm.

[0068] In an embodiment of the present application, the maximum thickness of the second active material layer is 92 μm-300 μm. Specifically, the maximum thickness of the second active material layer can be, but is not limited to, 92 μm, 100 μm, 120 μm, 150 μm, 180 μm, 220 μm, 250 μm, or 300 μm, etc. In an embodiment of the present application, when the electrode tab is a positive electrode tab, the maximum thickness of the second active material layer is 120 μm-270 μm. In another embodiment of the present application, when the electrode tab is a negative electrode tab, the maximum thickness of the second active material layer is 92 μm-165 μm. In some embodiments, the thickness of the second active material layer gradually decreases from 92 μm-300 μm to 0 μm in the direction from the first active material layer to the second active material layer.

[0069] In an embodiment of the present application, the size of the second active material layer in the direction from the first active material layer to the second active material layer is 10 mm-30 mm. The small size of the second active material layer is conducive to reducing the lithium precipitation phenomenon of the electrode tab. Specifically, the size of the second active material layer in the direction from the first active material layer to the second active material layer can be, but is not limited to, 10 mm, 15 mm, 20 mm, 25 mm, or 30 mm, etc. In an embodiment of the present application, the size of the second active material layer in the direction from the first active material layer to the second active material layer is 10 mm-20 mm. In another embodiment of the present application, the size of the second active material layer in the direction from the first active material layer to the second active material layer is 15 mm-30 mm.

[0070] In an embodiment of the present application, the area density of the electrode tab is 150 g / m 2 -600 g / m 2 The appropriate area density of the electrode tab can improve the energy density of the electrode tab, thereby improving the capacity of the battery and reducing the internal resistance of the battery. In the existing preparation process, the negative electrode tab has a thinned area, and the corresponding positive electrode tab is a normally coated area, which reduces the capacity ratio of the thinned negative electrode to the positive electrode, and causes serious lithium precipitation phenomenon, resulting in a shortened battery life. In the related art, the capacity of the negative electrode tab is improved by increasing the overall area density of the negative electrode tab, but this increases the preparation cost of the negative electrode tab and reduces the volume energy density and mass energy density of the negative electrode tab. The electrode tab provided in the present application has an area density similar to that of the electrode tab in the related art. Without changing the area density of the electrode tab, the capacity of the second active material layer (thinned area) is improved by controlling the relationship between the first active material in the first active material layer and the second active material in the second active material layer, thereby improving the capacity of the electrode tab, improving the lithium precipitation phenomenon, maintaining a high volume energy density and mass energy density of the electrode tab, and reducing the preparation cost of the electrode tab. Specifically, the area density of the electrode tab can be, but is not limited to, 150 g / m 2 , 200 g / m 2 , 250 g / m 2 , 300 g / m 2 , 350 g / m 2 , 400 g / m 2 , 450 g / m 2 , 500 g / m 2 , 550 g / m 2 , or 600 g / m 2 , etc. In an embodiment of the present application, when the electrode tab is a positive electrode tab, the area density of the positive electrode tab can be 300 g / m 2 -600 g / m 2 , and the area density of the first active material layer can be 300 g / m2 -600g / m 2 The areal density of the second active material layer is 276g / m 2 -599g / m 2 The areal density of the second active material layer gradually decreases in the direction from the first active material layer to the second active material layer. In another embodiment of the present application, when the electrode tab is a negative electrode tab, the areal density of the negative electrode tab can be 150g / m 2 -300g / m 2 The areal density of the first active material layer can be 150g / m 2 -300g / m 2 The areal density of the second active material layer is 142g / m 2 -299g / m 2 The areal density of the second active material layer gradually decreases in the direction from the first active material layer to the second active material layer.

[0071] An embodiment of the present application provides a preparation method of an electrode tab, comprising:

[0072] The first slurry and the second slurry are coated on the surface of the current collector, the first slurry comprising a first active material and the second slurry comprising a second active material; and after drying, an electrode tab is obtained. The preparation method provided by the present application is novel, simple in preparation process and low in preparation cost, and can prepare an electrode tab with high volume energy density and weight energy density and less prone to lithium precipitation. The electrode tab provided by any one of the above embodiments can be prepared by the preparation method.

[0073] In an embodiment of the present application, the first slurry further comprises a first conductive agent and a first binder, and the mass ratio of the first active material, the first conductive agent and the first binder is (93-97.2):(0.5-2):(1-3). The appropriate ratio of the first slurry can alleviate the lithium precipitation phenomenon of the electrode tab and improve the energy density of the electrode tab. Specifically, the mass ratio of the first active material, the first conductive agent and the first binder can be, but is not limited to, 93:0.5:1, 93.5:0.8:1.5, 94:1:1.8, 94.5:1.2:1.8, 95:1.5:2, 96:1.8:2.2, 96.5:1.8:2.5, 97:2:2.8 or 97.2:2:3, etc. In an embodiment of the present application, the mass ratio of the first active material, the first conductive agent and the first binder can be (93-96):(0.5-1.5):(1-2.2). In another embodiment of the present application, the mass ratio of the first active material, the first conductive agent and the first binder can be (95-97.2):(1-2):(2-3).

[0074] In an embodiment of the present application, when the electrode tab is a negative electrode tab, the first slurry further comprises a thickening agent, and the mass ratio of the first active material, the first conductive agent, the first binder and the first thickening agent is (93-97.2):(0.5-2):(1-3):(1.5-3), which can improve the viscosity of the first slurry and promote the coating ability of the first slurry. Specifically, the mass ratio of the first active material, the first conductive agent, the first binder and the first thickening agent can be, but is not limited to, 93:0.5:1:1.5, 93.5:0.8:1.5:1.8, 94:1:1.8:1.9, 94.5:1.2:1.8:2, 95:1.5:2:2.2, 96:1.8:2.2:2.5, 96.5:1.8:2.5:2.8, 97:2:2.8:2.9 or 97.2:2:3:3, etc. In an embodiment of the present application, the mass ratio of the first active material, the first conductive agent, the first binder and the first thickening agent can be (93-96):(0.5-1):(1-1.8):(1.5-2.5). In another embodiment of the present application, the mass ratio of the first active material, the first conductive agent, the first binder and the first thickening agent can be (95-97.2):(1-2):(1.5-3):(2-3).

[0075] In an embodiment of the present application, the first slurry further comprises a first solvent, and the mass content of the first solvent in the first slurry is 20%-50%, which can improve the coating ability of the first slurry and promote the uniform distribution of the first active material in the first active material layer. Specifically, the first solvent can be, but is not limited to, N-methyl pyrrolidone, etc., and the mass content of the first solvent can be, but is not limited to, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc. In an embodiment of the present application, the first solvent can be N-methyl pyrrolidone, and the mass content of the first solvent in the first slurry can be 20%-35%.

[0076] In an embodiment of the present application, the second slurry further comprises a second conductive agent and a second binder, and the mass ratio of the second active material, the second conductive agent and the second binder is (96.2-98.5):(0-1):(0.5-2), which can reduce the probability of lithium precipitation of the electrode plate and improve the energy density of the electrode plate. Specifically, the mass ratio of the second active material, the second conductive agent and the second binder can be, but is not limited to, 96.2:0:0.5, 96.5:0.1:0.7, 96.8:0.3:0.8, 97:0.5:1, 97.5:0.7:1, 97.8:0.8:1.5, 98:0.8:1.8 or 98.5:1:2, etc. In an embodiment of the present application, the mass ratio of the second active material, the second conductive agent and the second binder can be (96.2-97.5):(0-0.6):(0.5-1.5). In another embodiment of the present application, the mass ratio of the second active material, the second conductive agent and the second binder can be (97-98.5):(0.4-1):(1-2).

[0077] In an embodiment of the present application, when the electrode plate is a negative electrode plate, the second slurry further comprises a thickening agent, and the mass ratio of the second active material, the second conductive agent, the second binder and the second thickening agent is (96.2-98.5):(0-1):(0.5-2):(1-1.5), which can improve the viscosity of the second slurry and promote the coating ability of the second slurry. Specifically, the mass ratio of the second active material, the second conductive agent, the second binder and the second thickening agent can be, but is not limited to, 96.2:0:0.5:1, 96.5:0.1:0.7:1.1, 96.8:0.3:0.8:1.2, 97:0.5:1:1.3, 97.5:0.7:1:1.3, 97.8:0.8:1.5:1.4, 98:0.8:1.8:1.4 or 98.5:1:2:1.5, etc. In an embodiment of the present application, the mass ratio of the second active material, the second conductive agent, the second binder and the second thickening agent can be (96.2-97.5):(0-0.6):(0.5-1.5):(1-1.3). In another embodiment of the present application, the mass ratio of the second active material, the second conductive agent, the second binder and the second thickening agent can be (97-98.5):(0.5-1):(1-2):(1.2-1.5).

[0078] In an embodiment of the present application, the second slurry further comprises a second solvent, and the mass content of the second solvent in the second slurry is 20%-50%. The second solvent can improve the coating capacity of the second slurry and promote the uniform distribution of the second active material in the second active material layer. Specifically, the second solvent can be, but is not limited to, N-methyl pyrrolidone, etc.; and the mass content of the second solvent in the second slurry can be, but is not limited to, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc. In an embodiment of the present application, the second solvent can be N-methyl pyrrolidone, and the mass content of the second solvent in the second slurry can be 20%-35%.

[0079] The present application also provides a battery comprising a positive electrode sheet and a negative electrode sheet, and a separator arranged between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet comprises the electrode sheet of any one of the above embodiments or the electrode sheet prepared by the preparation method of any one of the above embodiments. The negative electrode sheet provided by the present application improves the capacity of the thinned area of the negative electrode sheet, improves the capacity ratio of the negative electrode sheet to the positive electrode sheet in the battery, reduces the risk of lithium precipitation of the electrode sheet, is conducive to improving the electrochemical performance and service life of the electrode sheet, and is conducive to the industrial application of the battery.

[0080] In an embodiment of the present application, the positive electrode sheet comprises the electrode sheet of any one of the above embodiments or the electrode sheet prepared by the preparation method of any one of the above embodiments. That is, both the positive electrode sheet and the negative electrode sheet are the electrode sheet provided by the present application. The negative electrode sheet comprises a negative current collector and a negative active material layer arranged on the surface of the negative current collector, the negative active material layer comprises a first negative active material layer and a second negative active material layer, the thickness of the second negative active material layer gradually decreases in the direction from the first negative active material layer to the second negative active material layer, and the mass content of the first negative active material in the first negative active material layer is less than that of the second negative active material in the second negative active material layer. The positive electrode sheet comprises a positive current collector and a positive active material layer arranged on the surface of the positive current collector, the positive active material layer comprises a first positive active material layer and a second positive active material layer, the thickness of the second positive active material layer gradually decreases in the direction from the first positive active material layer to the second positive active material layer, and the mass content of the first positive active material in the first positive active material layer is less than that of the second positive active material in the second positive active material layer. The positive electrode sheet and the negative electrode sheet are arranged oppositely, wherein the first positive active material layer of the positive electrode sheet is arranged oppositely to the second negative active material layer of the negative electrode sheet, and the second positive active material layer of the positive electrode sheet is arranged oppositely to the first negative active material layer of the negative electrode sheet, which is conducive to further relieving the lithium precipitation of the battery and improving the capacity and cycle stability of the battery.

[0081] In an embodiment of the present application, the diaphragm can be ion exchanged to form a complete ion conduction path. Specifically, the diaphragm can be, but is not limited to, a woven membrane, a non-woven fabric, a microporous membrane, a composite membrane, a calendered membrane, or a diaphragm paper, etc. In an embodiment of the present application, the battery further comprises an electrolyte. At least part of the positive electrode sheet and at least part of the negative electrode sheet are soaked in the electrolyte. The electrolyte of the present application is not particularly limited and can be, but is not limited to, a substance capable of being used as a battery electrolyte in the art.

[0082] The present application also provides a power-consuming device comprising the battery of any one of the above embodiments. The power-consuming device provided by the present application has high energy density and high safety performance, and has strong market competitiveness. The power-consuming device includes a mobile phone, a tablet, a watch, a VR glasses, a vehicle, etc. In an embodiment of the present application, the battery can be used in a vehicle, which can improve the safety and charging rate of the vehicle, improve the wide application of new energy vehicles, and is conducive to the construction of a green and environmentally friendly environment. In another embodiment of the present application, the battery can also be applied to a mobile phone, which can reduce the preparation cost of the battery and improve the service life and safety of the battery. The power-consuming device of the present application can be a vehicle, an electronic device, an energy storage system, etc., and the above-mentioned battery can be arranged in the power-consuming device in the form of a single battery, a battery module, a battery pack, a capacitor, etc.

[0083] The effects of the technical solutions of the present application are further described below through specific examples.

[0084] Embodiment 1

[0085] (1) Preparation of the positive electrode sheet: the first positive electrode active material (lithium iron phosphate, primary particle size D50 of 0.4 μm), the first positive electrode conductive agent (carbon black), and the first positive electrode binder (polyvinylidene fluoride) are mixed with the first solvent (N-methyl pyrrolidone) to obtain a first positive electrode slurry. The mass content of the first positive electrode active material in the solid components of the first positive electrode slurry is 96.5%, the mass content of the first positive electrode conductive agent is 1%, and the mass content of the first positive electrode binder is 2.5%;

[0086] The second positive electrode active material (lithium iron phosphate, primary particle size D50 of 0.8 μm), the second positive electrode conductive agent (carbon black), and the second positive electrode binder (polyvinylidene fluoride) are mixed with the second solvent (N-methyl pyrrolidone) to obtain a second positive electrode slurry. The mass content of the second positive electrode active material in the solid components of the second positive electrode slurry is 97.7%, the mass content of the second positive electrode conductive agent is 0.5%, and the mass content of the second positive electrode binder is 1.8%;

[0087] The first positive electrode slurry and the second positive electrode slurry are coated on the positive electrode current collector respectively, and after drying, a positive electrode tab is obtained; the first positive electrode slurry forms a first positive electrode active material layer (non-thinning area), the thickness of the first positive electrode active material layer is 250 μm, and the area density of the first positive electrode active material layer is 450 g / m 2 , the second positive electrode slurry forms a second positive electrode active material layer (thinning area), along the direction from the first positive electrode active material layer to the second positive electrode active material layer, the thickness of the second positive electrode active material layer gradually decreases, the thickness of the second positive electrode active material layer gradually decreases from 250 μm to 230 μm, and the area density of the second positive electrode active material layer is 420 g / m 2 .

[0088] (2) Preparation of the negative electrode tab:

[0089] The first negative electrode active material (artificial graphite, primary particle size D50 is 8 μm), the first negative electrode conductive agent (carbon black), the first negative electrode binder (styrene-butadiene rubber), and the first thickening agent (sodium carboxymethyl cellulose) are mixed with the first solvent (N-methyl pyrrolidone) to obtain a first negative electrode slurry, the mass content of the first negative electrode active material in the solid components of the first negative electrode slurry is 96.1%, the mass content of the first negative electrode conductive agent is 1%, the mass content of the first negative electrode binder is 1.3%, and the mass content of the first thickening agent is 1.6%;

[0090] The second negative electrode active material (artificial graphite, primary particle size D50 is 13 μm), the second negative electrode binder (styrene-butadiene rubber), and the second thickening agent (sodium carboxymethyl cellulose) are mixed with the second solvent (N-methyl pyrrolidone) to obtain a second negative electrode slurry, the mass content of the second negative electrode active material in the solid components of the second negative electrode slurry is 97.6%, the mass content of the second negative electrode binder is 1.1%, and the mass content of the second thickening agent is 1.3%;

[0091] The first negative electrode slurry and the second negative electrode slurry are coated on the negative electrode current collector respectively, and after drying, a negative electrode tab is obtained; the first negative electrode slurry forms a first negative electrode active material layer (non-thinning area), the thickness of the first negative electrode active material layer is 135 μm, and the area density of the first negative electrode active material layer is 204 g / m 2 , the second negative electrode slurry forms a second negative electrode active material layer (thinning area), along the direction from the first negative electrode active material layer to the second negative electrode active material layer, the thickness of the second negative electrode active material layer gradually decreases, the thickness of the second negative electrode active material layer gradually decreases from 135 μm to 125 μm, and the area density of the second negative electrode active material layer is 190 g / m 2 .

[0092] Example 2

[0093] Different from example 1, the first negative electrode slurry comprises a first negative electrode active material (artificial graphite), a first negative electrode conductive agent (carbon black), a first negative electrode binder (styrene butadiene rubber), and a first thickening agent (sodium carboxymethyl cellulose), the mass content of the first negative electrode active material in the solid components of the first negative electrode slurry is 93%, the mass content of the first negative electrode conductive agent is 2%, the mass content of the first negative electrode binder is 2%, and the mass content of the first thickening agent is 3%.

[0094] The second negative electrode slurry comprises a second negative electrode active material (artificial graphite), a second negative electrode conductive agent (carbon black), a second negative electrode binder (styrene butadiene rubber), and a second thickening agent (sodium carboxymethyl cellulose), the mass content of the second negative electrode active material in the solid components of the second negative electrode slurry is 98.5%, the mass content of the second negative electrode conductive agent is 0.1%, the mass content of the second negative electrode binder is 0.4%, and the mass content of the second thickening agent is 1%.

[0095] Example 3

[0096] Different from example 1, the first positive electrode slurry comprises a first positive electrode active material (lithium iron phosphate), a first positive electrode conductive agent (carbon black), and a first positive electrode binder (polyvinylidene fluoride), the mass content of the first positive electrode active material in the solid components of the first positive electrode slurry is 92%, the mass content of the first positive electrode conductive agent is 4%, and the mass content of the first positive electrode binder is 4%.

[0097] The second positive electrode slurry comprises a second positive electrode active material (lithium iron phosphate), a second positive electrode conductive agent (carbon black), and a second positive electrode binder (polyvinylidene fluoride), the mass content of the second positive electrode active material in the solid components of the second positive electrode slurry is 99%, the mass content of the second positive electrode conductive agent is 0.5%, and the mass content of the second positive electrode binder is 0.5%.

[0098] Example 4

[0099] Different from example 1, in the negative electrode sheet, the first negative electrode active material is natural graphite.

[0100] Example 5

[0101] Different from example 1, the mass content of the first negative electrode active material in the solid components of the first negative electrode slurry is 96%, the mass content of the first negative electrode conductive agent is 0.6%, the mass content of the first negative electrode binder is 1.8%, and the mass content of the first thickening agent is 1.6%; the mass content of the second negative electrode active material in the solid components of the second negative electrode slurry is 96.8%, the mass content of the second negative electrode conductive agent is 0.8%, the mass content of the second negative electrode binder is 1.1%, and the mass content of the second thickening agent is 1.3%.

[0102] Example 6

[0103] The difference from Example 1 is that the mass content of the first negative electrode active material in the solid components of the first negative electrode slurry is 96.2%, the mass content of the first negative electrode conductive agent is 1%, the mass content of the first negative electrode binder is 1.2%, and the mass content of the first thickening agent is 1.6%; the mass content of the second negative electrode active material in the solid components of the second negative electrode slurry is 96.3%, the mass content of the second negative electrode conductive agent is 1%, the mass content of the second negative electrode binder is 1.4%, and the mass content of the second thickening agent is 1.3%.

[0104] Example 7

[0105] The difference from Example 1 is that the mass content of the first negative electrode active material in the solid components of the first negative electrode slurry is 94%, the mass content of the first negative electrode conductive agent is 3%, the mass content of the first negative electrode binder is 1.3%, and the mass content of the first thickening agent is 1.6%; the mass content of the second negative electrode active material in the solid components of the second negative electrode slurry is 96.1%, the mass content of the second negative electrode conductive agent is 1.5%, the mass content of the second negative electrode binder is 1.1%, and the mass content of the second thickening agent is 1.3%.

[0106] Example 8

[0107] The difference from Example 1 is that the mass content of the first negative electrode active material in the solid components of the first negative electrode slurry is 93.4%, the mass content of the first negative electrode conductive agent is 1%, the mass content of the first negative electrode binder is 4%, and the mass content of the first thickening agent is 1.6%; the mass content of the second negative electrode active material in the solid components of the second negative electrode slurry is 94.7%, the mass content of the second negative electrode conductive agent is 1%, the mass content of the second negative electrode binder is 3%, and the mass content of the second thickening agent is 1.3%.

[0108] Example 9

[0109] The difference from Example 1 is that the positive electrode sheet is prepared by coating the second positive electrode slurry on the positive electrode current collector, the thickness of the non-thinned area of the positive electrode sheet is 250 μm, and the thickness of the thinned area of the positive electrode sheet gradually decreases from 250 μm to 230 μm.

[0110] Example 10

[0111] The difference from Example 1 is that the negative electrode sheet is prepared by coating the second negative electrode slurry on the negative electrode current collector, the thickness of the non-thinned area of the negative electrode sheet is 135 μm, and the thickness of the thinned area of the negative electrode sheet gradually decreases from 135 μm to 125 μm.

[0112] Comparative Example 1

[0113] Different from example 9, the negative electrode sheet was prepared by coating the second negative electrode slurry on the negative electrode current collector, the thickness of the non-thinned region of the negative electrode sheet was 135 μm, and the thickness of the thinned region of the negative electrode sheet gradually decreased from 135 μm to 125 μm.

[0114] Comparative example 2

[0115] Different from example 9, the negative electrode sheet was prepared by coating the second negative electrode slurry on the negative electrode current collector, the thickness of the non-thinned region of the negative electrode sheet was 135 μm, and the thickness of the thinned region of the negative electrode sheet gradually decreased from 135 μm to 125 μm; the positive electrode sheet was prepared by coating the first positive electrode slurry on the positive electrode current collector, the thickness of the non-thinned region of the positive electrode sheet was 250 μm, and the thickness of the thinned region of the positive electrode sheet gradually decreased from 250 μm to 230 μm.

[0116] Comparative example 3

[0117] Different from example 9, in the negative electrode sheet, the first negative electrode slurry formed the second negative active material layer, and the second negative electrode slurry formed the first negative active material layer.

[0118] Performance detection

[0119] The negative electrode sheet, the positive electrode sheet and the separator prepared in the above examples 1-10 and comparative examples 1-3 were stacked, and after being assembled with an aluminum shell, the processes of cover plate welding, shell welding, baking, liquid injection, aging, formation and the like were carried out to obtain a battery.

[0120] The batteries prepared in the above examples 1-10 and comparative examples 1-3 were tested for mass energy density. The test process was as follows: under the condition of room temperature 25℃, the battery was charged at 1C constant current to 3.8V, and then charged at constant voltage to the cutoff current 0.05C. After the battery was fully charged, the battery was discharged at 1 / 3C discharge rate, the energy of the battery at 1 / 3C discharge rate was calculated, recorded as the battery energy, and marked as W. At the same time, the weight of the battery was measured and recorded, and marked as M. The mass energy density (Wh / kg) = W / M. The test results are shown in Table 1.

[0121] The batteries prepared in the above examples 1-10 and comparative examples 1-3 were tested for volume energy density. The test process was as follows: under the condition of room temperature 25℃, the battery was charged at 1C constant current to 3.8V, and then charged at constant voltage to the cutoff current 0.05C. After the battery was fully charged, the battery was discharged at 1 / 3C discharge rate, the energy of the battery at 1 / 3C discharge rate was calculated, recorded as the battery energy, and marked as W. At the same time, the volume of the battery was measured and recorded, and marked as V. The volume energy density (Wh / L) = W / V. The test results are shown in Table 1.

[0122] The batteries prepared in the above Examples 1-10 and Comparative Examples 1-3 were subjected to cycle tests, and after 100 cycles, the samples after 100 cycles were disassembled and photographed to observe and record the negative electrode plate interface. The test results are shown in Table 1.

[0123] The batteries prepared in the above Examples 1-10 and Comparative Examples 1-3 were subjected to fast charging cycle tests, and the test process was as follows: under the condition of normal temperature 25℃, 30min of standing, 2.65C constant current charging to 30% SOC, 2C constant current charging to 40% SOC, 1.7C constant current charging to 65% SOC, 1.4C constant current charging to 70% SOC, 1.1C constant current charging to 75% SOC, 0.8C constant current charging to 90% SOC, 0.65C charging to 95% SOC, 0.3C constant current charging to 100% SOC, 30min of standing, discharging at 1C discharge rate, repeating the above steps until the battery state of health (SOH) was 80%, and recording the number of fast charging cycles. The results are shown in Table 1.

[0124] Table 1 Performance test results

[0125] As can be seen from Examples 1-10 and Comparative Examples 1-3, the electrode plate provided by the present application controls the mass content of the first active material in the first active material layer and the mass content of the second active material layer in the second active material layer, which reduces the probability of lithium precipitation of the electrode plate during use without reducing the volume energy density and weight energy density of the electrode plate, and is beneficial to improving the electrochemical performance of the battery. As can be seen from Examples 1 and 2-8, suitable contents of active materials, binders and conductive agents can further improve the energy density of the electrode plate and reduce the probability of lithium precipitation of the electrode plate. As can be seen from Examples 1 and Comparative Examples 1-3, the electrode plate provided by the present application improves the mass relationship between the first active material and the second active material, improves the lithium precipitation of the electrode plate, and the electrode plate has good energy density, which is beneficial to improving the comprehensive performance of the battery.

[0126] The above is a preferred embodiment of the present application, but it cannot be interpreted as limiting the scope of the present application. It should be noted that for ordinary skilled persons in the technical field, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements are also considered to be within the protection scope of the present application.

Claims

1. An electrode sheet, characterized in that, The electrode sheet includes a current collector and an active material layer disposed on at least one side surface of the current collector. The active material layer includes a first active material layer and a second active material layer disposed in the same layer as and connected to the first active material layer. The thickness of the second active material layer gradually decreases along the direction from the first active material layer to the second active material layer. The first active material layer includes a first active material, and the second active material layer includes a second active material. The mass content of the first active material in the first active material layer is less than the mass content of the second active material in the second active material layer.

2. The electrode sheet as described in claim 1, characterized in that, The second active material layer is disposed on one side of the first active material layer, or the second active material layer is disposed on opposite sides of the first active material layer.

3. The electrode sheet as described in claim 1, characterized in that, In the first active material layer, the mass content of the first active material is 93%-97.2%; In the second active material layer, the mass content of the second active material is 96.2%-98.5%.

4. The electrode sheet as described in claim 1, characterized in that, The primary particle size D50 of the first active material is smaller than the primary particle size D50 of the second active material; And / or the mass content of the carbon coating layer of the first active material is greater than the mass content of the carbon coating layer of the second active material.

5. The electrode sheet as described in claim 4, characterized in that, The primary particle size D50 of the first active material is 0.3 μm-9 μm, and the primary particle size D50 of the second active material is 0.7 μm-15 μm. And / or, the carbon coating layer of the first active material has a mass content of 0.5%-2%, and the carbon coating layer of the second active material has a mass content of less than or equal to 0.5%.

6. The electrode sheet as described in claim 1, characterized in that, The first active material layer further includes a first conductive agent and a first binder, and the second active material layer further includes a second conductive agent and a second binder; The mass content of the first conductive agent in the first active material layer is greater than the mass content of the second conductive agent in the second active material layer, and / or the mass content of the first binder in the first active material layer is greater than the mass content of the second binder in the second active material layer.

7. The electrode sheet as described in claim 6, characterized in that, In the first active material layer, the mass content of the first conductive agent is 0.5%-2%, and the mass content of the first binder is 1%-3%. In the second active material layer, the mass content of the second conductive agent is less than or equal to 1%, and the mass content of the second binder is 0.5%-2%.

8. The electrode sheet as described in claim 1, characterized in that, The thickness of the first active material layer is 92μm-300μm, and the maximum thickness of the second active material layer is 92μm-300μm.

9. The electrode sheet as described in claim 1, characterized in that, Along the direction from the second active material layer to the first active material layer, the size of the first active material layer is 80mm-1000mm; Along the direction from the first active material layer to the second active material layer, the size of the second active material layer is 10mm-30mm.

10. The electrode sheet as described in claim 1, characterized in that, The areal density of the electrode sheet is 150 g / m³. 2 -600g / m 2 .

11. A battery, characterized in that, The battery includes a positive electrode and a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode includes the electrode as described in any one of claims 1-10.

12. The battery as claimed in claim 11, characterized in that, The positive electrode includes the electrode as described in any one of claims 1-10.

13. An electrical appliance, characterized in that, The electrical equipment includes the battery as described in any one of claims 11-12.

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