Pole piece, preparation method thereof and battery

Abstract

The embodiment of the present application relates to a kind of pole piece and its preparation method and battery, pole piece includes: current collector;First coating is arranged on at least one surface of current collector along the thickness direction, first coating includes first active material and composite temperature-sensitive polymer, composite temperature-sensitive polymer includes graphene oxide and temperature-sensitive polymer on the surface of graphene oxide, temperature-sensitive polymer has thermal expansion;Second coating is arranged on the surface of first coating away from current collector, second coating includes second active material and conductive agent, and conductive agent includes carbon nanotube and graphene;Third coating is arranged on the surface of second coating away from first coating, and third coating includes third active material, porous carbon and lyophilic polymer.Such as through the synergistic effect of first coating, second coating and third coating can effectively improve the wettability of pole piece to electrolyte, while being able to guarantee the conductivity of pole piece, so as to effectively improve the rate capability and cycle performance of battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to an electrode, its preparation method, and a battery. Background Technology

[0002] Lithium iron phosphate (LFP) is a cathode material for lithium-ion batteries, offering advantages such as high safety, long cycle life, and low cost, and is currently widely used in power batteries and energy storage. However, traditional LFP electrodes generally suffer from low electrolyte absorption and insufficient electrolyte wetting, which affects the lithium-ion transport rate and consequently reduces the battery's rate performance.

[0003] Currently, the main technical means to improve the liquid absorption performance of traditional lithium iron phosphate electrodes include the following three categories: First, the electrode adopts a single active material layer structure to reduce the total thickness of the electrode and ensure electrolyte wetting. However, this has a limited effect on improving the electrode's liquid absorption rate. Second, a hydrophilic coating is applied to the electrode surface to improve the electrode's wettability to the electrolyte. However, this method may cause some pores to be blocked, hindering the lithium-ion transport path, thereby reducing the overall conductivity of the electrode and affecting the battery's rate performance. Third, a pore-forming agent is introduced during the electrode preparation to form a porous structure in the active material layer to improve the electrode's liquid absorption rate. However, excessive pores may weaken the electrode's mechanical strength and affect its stability during long-term cycling.

[0004] Therefore, how to effectively improve the wettability of the electrode to the electrolyte and ensure the rate performance and cycle performance of the battery has become an urgent technical problem to be solved. Summary of the Invention

[0005] In view of this, the present application provides an electrode sheet, a method for preparing the same, and a battery to solve at least one problem existing in the prior art.

[0006] In a first aspect, embodiments of this application provide an electrode sheet, comprising: current collector; A first coating is disposed on at least one surface of the current collector along the thickness direction. The first coating comprises a first active material and a composite thermosensitive polymer. The composite thermosensitive polymer comprises graphene oxide and a thermosensitive polymer located on the surface of the graphene oxide. The thermosensitive polymer has thermal expansion properties. A second coating is disposed on the surface of the first coating away from the current collector. The second coating includes a second active material and a conductive agent, wherein the conductive agent includes carbon nanotubes and graphene. A third coating is disposed on the surface of the second coating away from the first coating, the third coating comprising a third active material, porous carbon, and a hydrophilic polymer.

[0007] In conjunction with the first aspect of this application, in an alternative embodiment, the electrode satisfies at least one of the following features: (1) The temperature-sensitive polymer includes poly(N-acryloylglycine); (2) The hydrophilic polymer includes at least one of polyvinylpyrrolidone, polyolefin, polydiolefin and its derivatives; (3) The first coating also includes a first dispersant and a first binder, wherein the mass ratio of the first active material, the composite temperature-sensitive polymer, the first dispersant and the first binder is (91~92):(5~6):(0.2~0.3):(1.7~3.8). (4) The second coating also includes a second dispersant and a second binder, wherein the mass ratio of the second active material, the conductive agent, the second dispersant and the second binder is (96~97):(1~1.2):(0.2~0.3):(1.5~2.8); (5) The mass ratio of the carbon nanotubes to graphene is (1~3):1; (6) The third coating also includes a third dispersant and a third binder, and the mass ratio of the third active material, the porous carbon, the hydrophilic polymer, the third dispersant and the third binder is (95~96):(0.8~1):(1.5~2):(0.2~0.3):(0.7~2.5).

[0008] In conjunction with the first aspect of this application, in an alternative embodiment, the electrode satisfies at least one of the following features: (1) The thickness ratio of the first coating, the second coating and the third coating is 1:(1~2):(1~2); (2) The thickness of the first coating is 30μm~60μm; (3) The thickness of the second coating is 30μm~60μm; (4) The thickness of the third coating is 30μm~60μm; (5) The compaction density of the electrode sheet is 2.62 g / cm³. 3 ~2.65g / cm 3 .

[0009] In conjunction with the first aspect of this application, in an optional embodiment, the porosity of the first coating is less than the porosity of the second coating and the third coating; preferably, the porosity of the second coating is less than the porosity of the third coating; more preferably, the porosity of the first coating is 20% to 30%; the porosity of the second coating is 30% to 40%; and the porosity of the third coating is 40% to 50%.

[0010] Secondly, embodiments of this application provide a method for preparing an electrode sheet, the method comprising the following steps: S1: The first active material, the composite thermosensitive polymer, the first dispersant and the first binder are added to the first solvent and mixed evenly to obtain the first slurry; the composite thermosensitive polymer includes graphene oxide and a thermosensitive polymer located on the surface of the graphene oxide, and the thermosensitive polymer has thermal expansion properties; S2: The second active material, conductive agent, second dispersant, and second binder are added to the second solvent and mixed evenly to obtain the second slurry; the conductive agent includes carbon nanotubes and graphene; S3: Add the third active material, porous carbon, lyophilic polymer, third dispersant and third binder to the third solvent, mix them evenly to obtain the third slurry; S4: The first slurry, the second slurry, and the third slurry are layered and coated on at least one side surface of the current collector in such a manner that the first slurry is closer to the current collector than the second slurry and the second slurry is closer to the current collector than the third slurry. After drying and rolling, a first coating, a second coating, and a third coating are sequentially layered on the current collector to obtain the electrode.

[0011] In conjunction with the second aspect of this application, in an alternative embodiment, the method satisfies at least one of the following features: (1) The mass ratio of the first active material, the composite thermosensitive polymer, the first dispersant and the first binder is (91~92):(5~6):(0.2~0.3):(1.7~3.8); (2) The mass ratio of the second active material, the conductive agent, the second dispersant and the second binder is (96~97):(1~1.2):(0.2~0.3):(1.5~2.8); (3) The mass ratio of the carbon nanotubes to graphene is (1~3):1; (4) The mass ratio of the third active material, the porous carbon, the hydrophilic polymer, the third dispersant, and the third binder is (95~96):(0.8~1):(1.5~2):(0.2~0.3):(0.7~2.5); (5) The hydrophilic polymer includes at least one of polyvinylpyrrolidone, polyolefin, polydiolefin and its derivatives; (6) The first dispersant, the second dispersant and the third dispersant each independently comprise at least one of sodium dodecyl sulfate and polyethylene glycol, sodium dodecyl sulfate and fatty alcohol polyoxyethylene ether, polyacrylonitrile, and polyvinylpyrrolidone; (7) The first adhesive, the second adhesive and the third adhesive each independently comprise polyacrylate and / or polyvinylidene fluoride.

[0012] In conjunction with the second aspect of this application, in an alternative embodiment, the method satisfies at least one of the following features: (1) The coating surface density of the first slurry, the second slurry, and the third slurry is independently 0.08 g / mm². 2 ~0.2g / mm 2 ; (2) The drying temperature is 100℃~120℃; (3) The thickness ratio of the first coating, the second coating and the third coating is 1:(1~2):(1~2); (4) The thickness of the first coating is 30μm~60μm; (5) The thickness of the second coating is 30μm~60μm; (6) The thickness of the third coating is 30μm~60μm; (7) The compaction density of the electrode sheet is 2.62 g / cm³. 3 ~2.65g / cm 3 .

[0013] In conjunction with a second aspect of this application, in an optional embodiment, the porosity of the first coating is less than the porosity of the second coating and the third coating; preferably, the porosity of the second coating is less than the porosity of the third coating; more preferably, the porosity of the first coating is 20% to 30%; the porosity of the second coating is 30% to 40%; and the porosity of the third coating is 40% to 50%.

[0014] In conjunction with the second aspect of this application, in an optional embodiment, the method for preparing the composite thermosensitive polymer includes: dispersing the thermosensitive polymer monomer and graphene oxide in deionized water, heating, adding an initiator, stirring and reacting under the condition of passing an inert gas, growing the thermosensitive polymer in situ on the surface of the graphene oxide, and obtaining the composite thermosensitive polymer after filtration, washing and drying. The preparation method of the composite thermosensitive polymer satisfies at least one of the following characteristics: (1) The mass ratio of the thermosensitive polymer monomer to the graphene oxide is (2~2.5):1; (2) The heating temperature is 60℃~80℃; (3) The initiator includes ammonium persulfate; (4) The ratio of the total mass of the thermosensitive polymer monomer and the graphene oxide to the mass of the initiator is (19~21):1; (5) The reaction time is 40 min to 60 min with stirring; (6) The temperature-sensitive polymer includes poly(N-acryloylglycine).

[0015] Thirdly, embodiments of this application provide a battery comprising an electrode sheet as described in any one of the first aspects or an electrode sheet prepared by a method comprising an electrode sheet as described in any one of the second aspects.

[0016] Compared with the prior art, the embodiments of this application have the following beneficial effects: The electrode, its preparation method, and battery provided in this application embodiment include: a current collector; a first coating disposed on at least one surface of the current collector along its thickness direction, the first coating comprising a first active material and a composite thermosensitive polymer, the composite thermosensitive polymer comprising graphene oxide and a thermosensitive polymer located on the surface of the graphene oxide, the thermosensitive polymer having thermal expansion properties; a second coating disposed on the surface of the first coating away from the current collector, the second coating comprising a second active material and a conductive agent, the conductive agent comprising carbon nanotubes and graphene; and a third coating disposed on the surface of the second coating away from the first coating, the third coating comprising a third active material, porous carbon, and a hydrophilic polymer. In this embodiment, the third coating uses porous carbon to construct a high porosity, while a hydrophilic polymer is used to improve the wettability of the electrode, enabling rapid adsorption of electrolyte and transport to the inner layer. The conductive agent in the second coating is a combination of one-dimensional carbon nanotubes and two-dimensional graphene, which can construct a complete three-dimensional conductive network structure and has a high specific surface area, thereby further improving the wettability of electrolyte while ensuring the conductivity of the electrode. The first coating includes a composite thermosensitive polymer. The thermosensitive polymer has thermal expansion properties. When there is a temperature rise in the early stage of battery cycling, the thermosensitive polymer expands due to heat, which can fill the pores to better lock the electrolyte in the innermost first coating, thereby avoiding the problem of electrolyte drying in the innermost layer as cycling progresses. After the battery cools down, the thermosensitive polymer shrinks, which can restore the pores. Moreover, the thermosensitive polymer is placed on the surface of graphene oxide with excellent mechanical strength, which can significantly improve the structural stability of the thermosensitive polymer. In the embodiments of this application, the synergistic effect of the first coating, the second coating and the third coating can effectively improve the wettability of the electrode to the electrolyte, avoid the problem of local electrolyte drying on the electrode, and at the same time ensure the conductivity of the electrode, thereby effectively improving the rate performance and cycle performance of the battery.

[0017] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A schematic cross-sectional view of an electrode sheet provided in an embodiment of this application; Figure 2 This is a schematic flowchart illustrating a method for preparing an electrode sheet according to an embodiment of this application. Detailed Implementation

[0019] To make the technical solution and beneficial effects of the present invention more apparent and understandable, a detailed description is provided below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional experimental conditions. Unless otherwise specified, all reagents and raw materials used in this invention are commercially available.

[0020] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and steps described in detail.

[0021] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0022] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0023] Unless otherwise defined, the technical and scientific terms used in this application have the same meanings as those in the technical and scientific field to which this application pertains.

[0024] Unless otherwise specified, the techniques or conditions described in the following embodiments are generally performed in accordance with conventional techniques or conditions described in the literature in this field, or in accordance with the product manual and the manufacturer's recommendations. All numerical ranges in the following embodiments include endpoint values.

[0025] This application provides an electrode sheet, such as... Figure 1 As shown, the electrode includes a current collector 100; a first coating 200 disposed on at least one surface of the current collector 100 along its thickness direction, the first coating 200 comprising a first active material and a composite thermosensitive polymer, the composite thermosensitive polymer comprising graphene oxide and a thermosensitive polymer located on the surface of the graphene oxide, the thermosensitive polymer having thermal expansion properties; a second coating 300 disposed on the surface of the first coating 200 away from the current collector 100, the second coating 300 comprising a second active material and a conductive agent, the conductive agent comprising carbon nanotubes and graphene; and a third coating 400 disposed on the surface of the second coating 300 away from the first coating 200, the third coating 400 comprising a third active material, porous carbon, and a hydrophilic polymer.

[0026] In this embodiment, the third coating 400 uses porous carbon to construct a high porosity, while a hydrophilic polymer is used to improve the wettability of the electrode, enabling rapid adsorption of electrolyte and transport to the inner layer. The conductive agent in the second coating 300 is a combination of carbon nanotubes with a one-dimensional structure and graphene with a two-dimensional structure, which can construct a complete three-dimensional conductive network structure and has a high specific surface area, thereby further improving the wettability of electrolyte while ensuring the conductivity of the electrode. The first coating 200 includes a composite thermosensitive polymer. The thermosensitive polymer has thermal expansion properties. When there is a temperature rise in the early stage of battery cycling, the thermosensitive polymer expands due to heat, which can fill the pores to better lock the electrolyte in the innermost first coating 200, thereby avoiding the problem of electrolyte drying in the innermost layer as cycling progresses. After the battery cools down, the thermosensitive polymer shrinks, which can restore the pores to open up, ensuring the wettability and transport of electrolyte. Moreover, the thermosensitive polymer is placed on the surface of graphene oxide with excellent mechanical strength, which can significantly improve the structural stability of the thermosensitive polymer. In the embodiments of this application, the synergistic effect of the first coating 200, the second coating 300 and the third coating 400 can effectively improve the wettability of the electrode to the electrolyte, avoid the problem of local electrolyte drying on the electrode, and at the same time ensure the conductivity of the electrode, thereby effectively improving the rate performance and cycle performance of the battery.

[0027] It should be noted that, Figure 1In this embodiment, the sequentially stacked first coating 200, second coating 300, and third coating 400 on both surfaces of the current collector 100 along the thickness direction are merely one example. In some other embodiments of this application, the first coating 200, second coating 300, and third coating 400 may be sequentially stacked on any one surface of the current collector 100 along the thickness direction.

[0028] The electrode in this application embodiment can be either a positive electrode or a negative electrode. When the electrode is a positive electrode, the first active material, the second active material, and the third active material can be common positive electrode active materials in the art, specifically, at least one of lithium iron phosphate, ternary materials, lithium manganese iron phosphate, and lithium-rich manganese-based materials. When the electrode is a negative electrode, the first active material, the second active material, and the third active material can be common negative electrode active materials in the art, specifically, at least one of graphite, silicon-based materials, soft carbon, hard carbon, and lithium metal. Of course, the first active material, the second active material, and the third active material can be the same material, or different types of materials can be selected according to actual needs. This application does not impose any limitations.

[0029] In some embodiments, the thermosensitive polymer may include poly(N-acryloylglycine).

[0030] For example, the thermosensitive polymer can be poly(N-acryloylglycamide).

[0031] Graphene oxide (GO) possesses excellent mechanical strength. In the embodiments of this application, the composite thermosensitive polymer and graphene oxide significantly improve the mechanical strength and toughness of the composite thermosensitive polymer, thereby significantly enhancing the structural stability of the thermosensitive polymer during use and avoiding the potential structural instability that may result from repeated expansion and contraction. In the actual preparation process, the thermosensitive polymer can be grown in situ on graphene oxide, thus ensuring the stability of the bond between the thermosensitive polymer and graphene oxide.

[0032] In some embodiments, the hydrophilic polymer may include at least one of polyvinylpyrrolidone, polyolefin, polydiolefin and its derivatives.

[0033] For example, the hydrophilic polymer may be at least one of polyvinylpyrrolidone, polyolefin, polydiolefin and its derivatives.

[0034] In some embodiments, the first coating 200 may further include a first dispersant and a first binder. The mass ratio of the first active material, the composite temperature-sensitive polymer, the first dispersant, and the first binder may be (91~92):(5~6):(0.2~0.3):(1.7~3.8), for example, 91:5:0.2:1.7, 91.5:5.5:0.2:2.8, 92:5:0.2:2.8, 91:6:0.2:3, 92:6:0.3:3.8, or any other ratio within the above mass ratio range. This helps to ensure the uniformity of dispersion of the first active material and the composite temperature-sensitive polymer in the first coating 200 and the stability of the connection between the first coating 200 and the current collector 100, thereby improving the structural stability and electrochemical performance of the electrode.

[0035] In some embodiments, the second coating 300 may further include a second dispersant and a second binder. The mass ratio of the second active material, the conductive agent, the second dispersant, and the second binder may be (96~97):(1~1.2):(0.2~0.3):(1.5~2.8), for example, 96:1:0.2:1.5, 96.5:1.2:0.3:2, 97:1.2:0.2:1.6, 96:1.2:0.3:1.5, 97:1.2:0.3:2.8, or any other ratio within the above mass ratio range. This helps to ensure the uniformity of dispersion of the second active material and the conductive agent in the second coating 300 and the stability of the connection between the second coating 300 and the first coating 200 and the third coating 400, thereby improving the structural stability and electrochemical performance of the electrode.

[0036] The conductive agent in the second coating 300 can be carbon nanotubes and graphene. Carbon nanotubes have a high aspect ratio, excellent mechanical strength, and axial conductivity, enabling the construction of one-dimensional conductive circuits. Graphene has extremely high in-plane conductivity and a large specific surface area, enabling the construction of two-dimensional conductive planes. When carbon nanotubes and graphene are mixed, the one-dimensional carbon nanotubes can interpenetrate and overlap between graphene sheets, effectively preventing the graphene sheets from being tightly stacked face-to-face, maintaining high porosity and electrolyte transport channels. At the same time, the graphene sheets also prevent excessive entanglement and aggregation of carbon nanotubes. The two support each other, constructing a complete, stable, and high specific surface area three-dimensional conductive network structure, thereby ensuring the conductivity of the electrode and its wettability to the electrolyte. The carbon nanotubes can be, for example, single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0037] In some embodiments, the mass ratio of carbon nanotubes to graphene in the conductive agent can be (1~3):1, for example, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, or any value between any two of the above ranges. This is beneficial for constructing a more complete and stable three-dimensional conductive network structure, thereby further improving the conductivity of the electrode and its wettability to the electrolyte.

[0038] In some embodiments, the third coating 400 may further include a third dispersant and a third binder. The mass ratio of the third active material, porous carbon, hydrophilic polymer, third dispersant, and third binder may be (95~96):(0.8~1):(1.5~2):(0.2~0.3):(0.7~2.5), for example, 95:0.8:1.5:0.2:0.7, 95.5:0.9:1.8:0.3:1.5, 96:1:1.5:0.2:1.3, 96:0.8:2:0.2:1, 96:1:2:0.3:2.5, or any other ratio within the above mass ratio range. This helps to ensure the uniformity of dispersion of the third active material, porous carbon, and hydrophilic polymer in the third coating 400 and the stability of the connection between the third coating 400 and the second coating 300, thereby improving the structural stability and electrochemical performance of the electrode.

[0039] In some embodiments, the thickness ratio of the first coating 200, the second coating 300, and the third coating 400 can be 1:(1~2):(1~2), for example, 1:1:1, 1:1.5:1.5, 1:2:1, 1:1:2, 1:2:2, or any other ratio within the aforementioned thickness ratio range. This is beneficial for further enhancing the synergistic effect of the first coating 200, the second coating 300, and the third coating 400, thereby further improving the wettability of the electrode to the electrolyte and the conductivity of the electrode, and consequently further improving the rate performance and cycle performance of the battery.

[0040] In some embodiments, the thickness of the first coating 200 can be 30μm to 60μm, for example, it can be 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm or any value between any two of the above ranges. This is beneficial for the first coating 200 to fully exert its function and facilitates control of the total thickness of the electrode.

[0041] In some embodiments, the thickness of the second coating 300 can be 30μm to 60μm, for example, it can be 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm or any value between any two of the above ranges. This allows the second coating 300 to fully exert its function and facilitates control of the total thickness of the electrode.

[0042] In some embodiments, the thickness of the third coating 400 can be 30 μm to 60 μm, for example, it can be 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm or any value between any two of the above ranges. This allows the third coating 400 to fully exert its function and facilitates control of the total thickness of the electrode.

[0043] In some embodiments, the compaction density of the electrode can be 2.62 g / cm³. 3 ~2.65g / cm 3 For example, it can be 2.62 g / cm³. 3 2.63 g / cm 3 2.64 g / cm 3 2.65g / cm 3 Or any value between any two of the above ranges. This is beneficial for ensuring both the wettability and electrolyte retention of the electrode while also considering the energy density of the electrode.

[0044] In some embodiments, the porosity of the first coating 200 may be less than that of the second coating 300 and the third coating 400. This creates a gradient where the inner coating near the current collector 100 has low porosity and the outer coating away from the current collector 100 has high porosity, thereby promoting electrolyte wetting in the electrode and enhancing the electrode's electrolyte retention capacity.

[0045] In some specific embodiments, the porosity of the first coating 200 is less than that of the second coating 300, and the porosity of the second coating 300 is less than that of the third coating 400.

[0046] In this embodiment, a three-layer coating composite structure with gradient porosity is constructed. Specifically, from the electrode surface to the current collector 100, a composite coating structure with progressively decreasing porosity is formed. This facilitates directional electrolyte wetting. The high porosity of the outermost third coating 400, combined with the hydrophilic polymer component, helps the electrolyte wet the inner layers. The low porosity of the innermost first coating 200 increases electrolyte retention, thereby preventing significant electrolyte loss from the lower layers of the electrode during later cycling stages. This gradient porosity structure promotes uniform electrolyte distribution along the electrode thickness, preventing localized drying and thus improving the battery's rate performance and cycle performance.

[0047] In some embodiments, the porosity of the first coating 200 can be 20% to 30%, for example, 20%, 25%, 30%, or any value between any two of the above ranges; the porosity of the second coating 300 can be 30% to 40%, for example, 30%, 35%, 40%, or any value between any two of the above ranges; and the porosity of the third coating 400 can be 40% to 50%, for example, 40%, 45%, 50%, or any value between any two of the above ranges.

[0048] By controlling the porosity of the first coating 200, the second coating 300, and the third coating 400 within the aforementioned range, a suitable porosity gradient structure can be formed, which can better promote the wetting of the electrode with electrolyte and ensure the uniform distribution of electrolyte in the electrode thickness direction, avoiding local drying, thereby better improving the rate performance and cycle performance of the battery.

[0049] This application also provides a method for preparing an electrode sheet. Please refer to... Figure 2 The electrode preparation method provided in this application includes the following steps: S1: The first active material, the composite thermosensitive polymer, the first dispersant and the first binder are added to the first solvent and mixed evenly to obtain the first slurry; the composite thermosensitive polymer includes graphene oxide and a thermosensitive polymer located on the surface of graphene oxide, and the thermosensitive polymer has thermal expansion properties; S2: The second active material, conductive agent, second dispersant, and second binder are added to the second solvent and mixed evenly to obtain the second slurry; the conductive agent includes carbon nanotubes and graphene; S3: Add the third active material, porous carbon, lyophilic polymer, third dispersant and third binder to the third solvent, mix them evenly to obtain the third slurry; S4: The first slurry, the second slurry, and the third slurry are layered and coated on at least one side surface of the current collector in such a way that the first slurry is closer to the current collector than the second slurry and the second slurry is closer to the current collector than the third slurry. After drying and rolling, a first coating, a second coating, and a third coating are formed sequentially layered on the current collector to obtain an electrode.

[0050] In this embodiment, the prepared first slurry, second slurry, and third slurry are coated onto the current collector to form a first coating, a second coating, and a third coating that are sequentially stacked on the current collector. The third coating uses porous carbon to create a high porosity, while hydrophilic polymers enhance the wettability of the electrode, enabling rapid adsorption of electrolyte and transport to the inner layer. The conductive agent in the second coating combines one-dimensional carbon nanotubes and two-dimensional graphene to construct a complete three-dimensional conductive network structure with a high specific surface area, thus ensuring the conductivity of the electrode while further improving the wettability of the electrolyte. The first coating includes a composite thermosensitive polymer. The thermosensitive polymer has thermal expansion properties. During the initial temperature rise in the battery cycle, the thermosensitive polymer expands due to heat, filling the pores to better lock the electrolyte in the innermost first coating, thus avoiding the problem of electrolyte drying in the innermost layer during the later stages of cycling. After the battery cools down, the thermosensitive polymer shrinks, restoring the pores. Moreover, the thermosensitive polymer is placed on the surface of graphene oxide, which has excellent mechanical strength, thus significantly improving the structural stability of the thermosensitive polymer during use. In the embodiments of this application, by forming a first coating, a second coating, and a third coating sequentially stacked on the current collector, the wettability of the electrode to the electrolyte can be effectively improved, avoiding the problem of local electrolyte drying on the electrode, while ensuring the conductivity of the electrode, thereby effectively improving the rate performance and cycle performance of the battery.

[0051] It should be noted that although the steps in the flowchart above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Moreover, at least some of the steps in the flowchart above may include multiple steps or stages, and these steps or stages are not necessarily completed at the same time, nor are they necessarily performed sequentially.

[0052] In step S1, the first active material, the composite temperature-sensitive polymer, the first dispersant and the first binder are added to the first solvent and mixed evenly to obtain the first slurry.

[0053] In some embodiments, the mass ratio of the first active material, the composite temperature-sensitive polymer, the first dispersant, and the first binder is (91~92):(5~6):(0.2~0.3):(1.7~3.8), for example, it can be 91:5:0.2:1.7, 91.5:5.5:0.2:2.8, 92:5:0.2:2.8, 91:6:0.2:3, 92:6:0.3:3.8, or any other ratio within the above mass ratio range. This helps to ensure the uniform dispersion of the first active material and the composite temperature-sensitive polymer in the first slurry and the stability of the connection between the subsequently formed first coating and the current collector, thereby improving the structural stability and electrochemical performance of the electrode.

[0054] For example, the first active material can be a positive electrode active material or a negative electrode active material, wherein the positive electrode active material is specifically, for example, at least one of lithium iron phosphate, ternary materials, lithium manganese iron phosphate, and lithium-rich manganese-based materials; the negative electrode active material is specifically, for example, at least one of graphite, silicon-based materials, soft carbon, hard carbon, and lithium metal.

[0055] For example, the first dispersant may include at least one of sodium dodecyl sulfonate and polyethylene glycol, sodium dodecyl sulfate and fatty alcohol polyoxyethylene ether, polyacrylonitrile, and polypropylene glycol phosphate. Specifically, the first dispersant may be at least one of sodium dodecyl sulfonate and polyethylene glycol, sodium dodecyl sulfate and fatty alcohol polyoxyethylene ether, polyacrylonitrile, and polypropylene glycol phosphate.

[0056] For example, the first adhesive may include polyacrylate and / or polyvinylidene fluoride. Specifically, the first adhesive may be polyacrylate (PAA) and / or polyvinylidene fluoride (PVDF).

[0057] In one specific example, the first binder is polyacrylate. PAA is composed of a large number of long-chain linear carboxylic acid groups. The carboxylic acid groups on the PAA molecular chain can form hydrogen bonds and have a certain degree of cross-linking. Therefore, it can improve the adhesion between the first binder and the first active material, as well as the adhesion of the first coating on the current collector. This is beneficial to better ensure the integrity of the electrode structure, thereby improving battery capacity and extending battery life.

[0058] For example, the first solvent may be water or an organic solvent (specifically, N-methylpyrrolidone).

[0059] The preparation method of the composite thermosensitive polymer in step S1 may include: dispersing the thermosensitive polymer monomer and graphene oxide in deionized water, heating, adding an initiator, stirring and reacting under the condition of passing an inert gas, growing the thermosensitive polymer in situ on the surface of graphene oxide, and obtaining the composite thermosensitive polymer after filtration, washing and drying.

[0060] In some embodiments, the mass ratio of the thermosensitive polymer monomer to graphene oxide can be (2~2.5):1, for example, it can be 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1 or any value between any two of the above ranges.

[0061] In some embodiments, the ratio of the total mass of the thermosensitive polymer monomer and graphene oxide to the mass of the initiator can be (19~21):1, for example, it can be 19:1, 20:1, 21:1 or any value between any two of the above ranges.

[0062] In some embodiments, the heating temperature can be 60°C to 80°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C or any value between any two of the above ranges.

[0063] In some embodiments, the reaction time for stirring can be 40 min to 60 min, for example, 40 min, 45 min, 50 min, 55 min, 60 min or any value between any two of the above ranges.

[0064] For example, the initiator may include ammonium persulfate. Specifically, the initiator may be ammonium persulfate. The inert gas may be at least one of nitrogen, argon, and helium.

[0065] For example, the thermosensitive polymer monomer can be N-acryloylglycine. The thermosensitive polymer in the prepared composite thermosensitive polymer can be poly(N-acryloylglycine).

[0066] In step S2, the second active material, conductive agent, second dispersant, and second binder are added to the second solvent and mixed evenly to obtain the second slurry; the conductive agent includes carbon nanotubes and graphene.

[0067] In some embodiments, the mass ratio of the second active material, the conductive agent, the second dispersant, and the second binder can be (96~97):(1~1.2):(0.2~0.3):(1.5~2.8), for example, 96:1:0.2:1.5, 96.5:1.2:0.3:2, 97:1.2:0.2:1.6, 96:1.2:0.3:1.5, 97:1.2:0.3:2.8, or any other ratio within the above mass ratio range. This helps to ensure the uniform dispersion of the second active material and the conductive agent in the second slurry and the stability of the subsequent connection between the second coating and the first and third coatings, thereby improving the structural stability and electrochemical performance of the electrode.

[0068] In some embodiments, the mass ratio of carbon nanotubes to graphene can be (1~3):1, for example, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, or any value between any two of the above ranges. This is beneficial for constructing a more complete and stable three-dimensional conductive network structure, thereby further improving the conductivity of the electrode and its wettability to the electrolyte.

[0069] The types of the second active material, the second dispersant, the second binder, and the second solvent in step S2 can be selected with reference to the types of the first active material, the first dispersant, the first binder, and the first solvent in step S1 above, and will not be repeated here.

[0070] In step S3, the third active material, porous carbon, lyophilic polymer, third dispersant and third binder are added to the third solvent and mixed evenly to obtain the third slurry.

[0071] In some embodiments, the mass ratio of the third active material, porous carbon, hydrophilic polymer, third dispersant, and third binder can be (95~96):(0.8~1):(1.5~2):(0.2~0.3):(0.7~2.5), for example, 95:0.8:1.5:0.2:0.7, 95.5:0.9:1.8:0.3:1.5, 96:1:1.5:0.2:1.3, 96:0.8:2:0.2:1, 96:1:2:0.3:2.5, or any other ratio within the above mass ratio range. This helps to ensure the uniform dispersion of the third active material, porous carbon, and hydrophilic polymer in the third slurry and the stability of the subsequent connection between the third coating and the second coating, thereby improving the structural stability and electrochemical performance of the electrode.

[0072] In some embodiments, the hydrophilic polymer may include at least one of polyvinylpyrrolidone, polyolefin, polydiolefin and its derivatives.

[0073] For example, the hydrophilic polymer may be at least one of polyvinylpyrrolidone, polyolefin, polydiolefin and its derivatives.

[0074] The types of the third active material, the third dispersant, the third binder, and the third solvent in step S3 can be selected by referring to the types of the first active material, the first dispersant, the first binder, and the first solvent in step S1 above, and will not be repeated here.

[0075] In step S4, the first slurry, the second slurry, and the third slurry are layered and coated on at least one side surface of the current collector in such a way that the first slurry is closer to the current collector than the second slurry and the second slurry is closer to the current collector than the third slurry. After drying and rolling, a first coating, a second coating, and a third coating are formed sequentially layered on the current collector to obtain an electrode.

[0076] In actual manufacturing processes, a single-head coating machine can be used to sequentially coat the first, second, and third slurries onto one or both surfaces of the current collector along its thickness direction. After each coating, the slurry is allowed to dry before the next layer is applied. Alternatively, a multi-head slit coater can be used to simultaneously coat the first, second, and third slurries, followed by drying. The drying temperature can be, for example, 100℃~120℃, 100℃, 110℃, 120℃, or any value within any two of these ranges.

[0077] In some embodiments, the coating surface density of the first slurry, the second slurry, and the third slurry can each be independently 0.08 g / mm². 2 ~0.20g / mm 2 For example, it can be 0.08 g / mm 2 0.10g / mm 2 0.15g / mm 2 0.18g / mm 2 0.20g / mm 2 Or any value between any two of the above ranges.

[0078] In some embodiments, the thickness ratio of the first coating, the second coating, and the third coating in the electrode obtained in step S4 can be 1:(1~2):(1~2), for example, 1:1:1, 1:1.5:1.5, 1:2:1, 1:1:2, 1:2:2, or any other ratio within the above-mentioned thickness ratio range. This is beneficial for further enhancing the synergistic effect of the first coating, the second coating, and the third coating, thereby further improving the wettability of the electrode to the electrolyte and the conductivity of the electrode, and thus further improving the rate performance and cycle performance of the battery.

[0079] In some embodiments, the thickness of the first coating can be 30μm to 60μm, for example, it can be 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm or any value between any two of the above ranges.

[0080] In some embodiments, the thickness of the second coating can be 30μm to 60μm, for example, it can be 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm or any value between any two of the above ranges.

[0081] In some embodiments, the thickness of the third coating can be 30μm to 60μm, for example, it can be 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm or any value between any two of the above ranges.

[0082] Controlling the thickness of at least one of the first, second, and third coatings within the aforementioned range is beneficial for the first, second, and third coatings to fully exert their functions and facilitates control of the total electrode thickness.

[0083] In some embodiments, the compaction density of the electrode can be 2.62 g / cm³. 3 ~2.65g / cm 3 For example, it can be 2.62 g / cm³. 3 2.63 g / cm 3 2.64 g / cm3 2.65g / cm 3 Or any value between any two of the above ranges. This is beneficial for ensuring both the wettability and electrolyte retention of the electrode while also considering the energy density of the electrode.

[0084] In some embodiments, the porosity of the first coating may be less than that of the second and third coatings. This creates a gradient where the inner coating near the current collector has low porosity and the outer coating far from the current collector has high porosity, thereby promoting electrolyte wetting in the electrode and enhancing the electrode's electrolyte retention capacity.

[0085] In some specific embodiments, the porosity of the first coating is less than that of the second coating, and the porosity of the second coating is less than that of the third coating.

[0086] The aforementioned porosity gradient structure facilitates the uniform distribution of electrolyte along the electrode thickness direction, preventing localized drying and thus improving the battery's rate performance and cycle performance.

[0087] In some embodiments, the porosity of the first coating can be 20% to 30%, for example, 20%, 25%, 30% or any value between any two of the above ranges; the porosity of the second coating can be 30% to 40%, for example, 30%, 35%, 40% or any value between any two of the above ranges; and the porosity of the third coating can be 40% to 50%, for example, 40%, 45%, 50% or any value between any two of the above ranges.

[0088] By controlling the porosity of the first, second, and third coatings within the aforementioned range, a suitable porosity gradient structure can be formed, which can better promote the wetting of the electrode with electrolyte and ensure that the electrolyte is more uniformly distributed in the thickness direction of the electrode, avoiding local drying, thereby better improving the rate performance and cycle performance of the battery.

[0089] This application also provides a battery comprising the electrode sheet described in any of the foregoing embodiments or an electrode sheet prepared by a method comprising the electrode sheet described in any of the foregoing embodiments.

[0090] It is understood that the beneficial effects of the electrode sheet described in any of the foregoing embodiments or the electrode sheet prepared by the method described in any of the foregoing embodiments are applicable to this battery. The battery in the embodiments of this application has high rate performance and high cycle performance.

[0091] In some embodiments, the battery includes a positive electrode and a negative electrode, wherein the negative electrode and / or the positive electrode may include the electrode as described in any of the foregoing embodiments or the electrode prepared by the method described in any of the foregoing embodiments.

[0092] The technical solution of this application will be further described below with reference to several embodiments and comparative examples.

[0093] Example 1

[0094] The preparation of the electrode in this embodiment includes the following steps: Step S1: Lithium iron phosphate (first active material), composite thermosensitive polymer, polypropylene glycol phosphate (first dispersant), and PAA (first binder) are added to deionized water at a mass ratio of 92:5:0.2:2.8 and mixed evenly to obtain the first slurry. The composite thermosensitive polymer is prepared as follows: N-acryloylglycine (thermosensitive polymer monomer) and GO are dispersed in deionized water at a mass ratio of 2:1. The temperature is raised to 70°C, and ammonium persulfate (initiator) is added. The mass ratio of ammonium persulfate to the total mass of N-acryloylglycine and GO is 1:20. Under Ar purging, the mixture is stirred for 60 min. After filtering the product, it is washed with deionized water and dried to obtain GO-hybridized N-acryloylglycine (composite thermosensitive polymer). Step S2: Lithium iron phosphate (second active material), conductive agent (single-walled carbon nanotubes and graphene in a mass ratio of 1:1), polypropylene glycol phosphate (second dispersant) and PVDF (second binder) are added to N-methylpyrrolidone (NMP) in a mass ratio of 97:1.2:0.2:1.6 and mixed evenly to obtain the second slurry; Step S3: Lithium iron phosphate (third active material), porous carbon, polyvinylpyrrolidone (hydrophilic polymer), polypropylene glycol phosphate (third dispersant) and PVDF (third binder) are added to NMP in a mass ratio of 96:1:1.5:0.2:1.3 and mixed evenly to obtain the third slurry; Step S4: Using a multi-head slot coater, the first slurry, the second slurry, and the third slurry are layered and coated onto the surface of the current collector along its thickness direction, with the first slurry being closer to the current collector than the second slurry, and the second slurry being closer to the current collector than the third slurry. After drying in an oven at 100°C, the coating is rolled to form the first, second, and third coatings sequentially layered on the current collector, thus obtaining the electrode sheet; wherein the coating surface density of the first, second, and third slurries is 0.12 g / mm². 2 The thickness of the first, second, and third coatings in the prepared negative electrode sheet is 50 μm, and the porosities are 29%, 38%, and 50%, respectively.

[0095] Example 2

[0096] The preparation method of the electrode sheet in this embodiment is basically the same as that in Example 1, except that: In step S4, the surface density of the first slurry coating is 0.09 g / mm². 2 The surface density of the second slurry coating is 0.09 g / mm². 2 The surface density of the third slurry coating is 0.18 g / mm². 2 Correspondingly, the thicknesses of the first, second, and third coatings in the prepared negative electrode sheet are 46 μm, 46 μm, and 58 μm, respectively, and the porosities are 25%, 35%, and 44%, respectively.

[0097] Example 3

[0098] The preparation method of the electrode sheet in this embodiment is basically the same as that in Example 1, except that: In step S4, the surface density of the first slurry coating is 0.09 g / mm². 2 The surface density of the second slurry coating is 0.18 g / mm². 2 The surface density of the third slurry coating is 0.09 g / mm². 2 Correspondingly, the thicknesses of the first coating, the second coating, and the third coating in the prepared negative electrode sheet are 46 μm, 58 μm, and 46 μm, respectively, and the porosities are 21%, 32%, and 42%, respectively.

[0099] Example 4

[0100] The preparation method of the electrode sheet in this embodiment is basically the same as that in Example 1, except that: In step S4, the areal density of the first slurry coating is 0.18 g / mm². 2 The areal density of the second slurry coating is 0.09 g / mm². 2 The surface density of the third slurry coating is 0.09 g / mm². 2 Correspondingly, the thicknesses of the first, second, and third coatings in the prepared negative electrode sheet are 58 μm, 46 μm, and 46 μm, respectively, and the porosities are 22%, 35%, and 47%, respectively.

[0101] Comparative Example 1

[0102] The preparation of the electrode in this comparative example includes the following steps: Lithium iron phosphate, dispersant, PVDF, and conductive agent SP were added to NMP at a mass ratio of 96:0.2:1.8:2 and mixed evenly to obtain a slurry. The slurry was then evenly coated onto aluminum foil using a coating machine and dried in an oven at 100°C to obtain an electrode sheet. The electrode sheet prepared in this comparative example is a traditional lithium iron phosphate single-layer positive electrode sheet. The coating thickness of the prepared electrode sheet is 132 μm, and the porosity is 30%.

[0103] Comparative Example 2

[0104] The preparation of the electrode in this comparative example includes the following steps: Lithium iron phosphate, porous carbon, polyvinylpyrrolidone, dispersant, and PVDF were added to NMP at a mass ratio of 96:1:1.5:0.2:1.3 and mixed evenly to obtain a slurry. The slurry was then evenly coated onto aluminum foil using a coating machine and dried in an oven at 100°C to obtain an electrode sheet. That is, the coating in the electrode sheet prepared in this comparative example has the same composition as the third coating in the electrode sheet prepared in Example 1. The coating thickness of the electrode sheet prepared is 132 μm, and the porosity is 30%.

[0105] Comparative Example 3

[0106] The preparation method of the electrode sheet in this comparative example is basically the same as that in Example 1, except that: Step S1 is omitted. Accordingly, in step S4, the second slurry is layered and coated on the surface of the current collector in a manner that brings it closer to the current collector than the third slurry. The areal density of both the second and third slurries is 0.18 g / mm². 2 After drying and rolling, a second coating and a third coating are formed sequentially stacked on the current collector to obtain an electrode sheet; that is, the first coating is omitted in this comparative example compared with Example 1; wherein, the thickness of the second coating and the third coating is 50 μm, and the porosity is 38% and 50%, respectively.

[0107] Comparative Example 4

[0108] The preparation method of the electrode sheet in this comparative example is basically the same as that in Example 1, except that: Step S2 is omitted. Accordingly, in step S4, the first slurry is layered and coated on the surface of the current collector in a manner that brings the third slurry closer to the current collector than the first slurry. The areal density of both the first and third slurries is 0.18 g / mm². 2 After drying and rolling, a first coating and a third coating are formed sequentially stacked on the current collector to obtain an electrode sheet; that is, the second coating is omitted in this comparative example compared with Example 1; wherein, the thickness of the first coating and the third coating is 50 μm, and the porosity is 29% and 50%, respectively.

[0109] Comparative Example 5

[0110] The preparation method of the electrode sheet in this comparative example is basically the same as that in Example 1, except that: Step S3 is omitted. Accordingly, in step S4, the first slurry is layered and coated on the surface of the current collector in a manner that brings the second slurry closer to the current collector than the first slurry. The areal density of both the first and second slurries is 0.18 g / mm². 2After drying and rolling, a first coating and a second coating are formed sequentially stacked on the current collector to obtain an electrode sheet; that is, the third coating is omitted in this comparative example compared with Example 1; wherein, the thickness of the first coating and the second coating is 50 μm, and the porosity is 29% and 38%, respectively.

[0111] The liquid absorption rate of the electrodes prepared in the above embodiments and comparative examples was tested using the following steps: Electrolyte is drawn into a capillary tube, and while the capillary tube is pressed vertically onto the electrode, the change in the liquid level in the capillary tube is monitored using a CCD camera. The test lasts for 100 seconds. The height difference between the initial liquid level of the electrolyte at the start of the test and the final liquid level at the end of the test is recorded as the liquid level change value over 100 seconds, which is used to evaluate the liquid absorption rate of the electrode. The electrolyte used is 1M LiPF6 dissolved in a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC and DMC volume ratio 1:1).

[0112] The electrodes prepared in the above embodiments and comparative examples were used to prepare batteries, and the electrochemical performance of the batteries was tested.

[0113] The battery preparation steps are as follows: First, graphite, CMC, SBR, and conductive carbon black are added to deionized water at a mass ratio of 96:1.4:1.6:1. After mixing evenly, a negative electrode slurry is obtained. The negative electrode slurry is coated onto copper foil using a coating machine and dried in an oven at 100°C. The dried electrode is then rolled to obtain a negative electrode sheet. Next, the electrode sheets prepared in the above embodiments and comparative examples are used as positive electrode sheets and assembled with the prepared negative electrode sheet, separator, and electrolyte to form a battery. The electrolyte used is the same as the electrolyte used to test the liquid absorption rate of the electrode sheets. The test results are shown in Table 1.

[0114] The performance of the prepared battery was tested as follows: (1) 3C discharge capacity retention rate: The battery was left to stand at 25℃ for 1 hour, then discharged at a constant current of 0.33C to 2.5V, left to stand for 30 minutes, then charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage of 3.65V until the current was less than or equal to 0.05C, left to stand for 30 minutes, then discharged at a constant current of 0.33C to 2.5V, then discharged at a constant voltage of 2.5V until the current was 0.05C. The discharge capacity at this point was recorded as C0. After standing for 30 minutes, the battery was charged at a constant current of 0.33C0 to 3.65V, then charged at a constant voltage of 3.65V until the current was less than or equal to 0.05C, then discharged at a constant current of 3C to 2.5V, then discharged at a constant voltage of 2.5V until the current was 0.05C. The discharge capacity at this point was recorded as C1. The 3C discharge capacity retention rate = (C1 / C0) × 100%. (2) Capacity retention rate after 1000 cycles: The battery was left to stand at 25°C for 1 hour, then discharged at a constant current of 0.33C to 2.5V, left to stand for 30 minutes, then charged at a constant current of 0.5C to 3.65V, then charged at a constant voltage of 3.65V until the current was less than or equal to 0.05C, left to stand for 30 minutes, then discharged at a constant current of 0.5C to 2.5V, and then discharged at a constant voltage of 2.5V until the current was 0.05C. The discharge capacity at this point was recorded as the discharge capacity of the first cycle. After standing for 30 minutes, the capacity of the lithium-ion battery at the 1000th cycle was recorded as the discharge capacity of the 1000th cycle. The capacity retention rate after 1000 cycles = (discharge capacity of the 1000th cycle / discharge capacity of the 1st cycle) × 100%.

[0115] The test results are shown in Table 1.

[0116] Table 1

[0117] As can be seen from the data in Table 1, the electrode prepared in Comparative Example 1 is a traditional single-layer lithium iron phosphate positive electrode. In the electrolyte absorption rate test, the change in liquid level height over 100 seconds is significantly lower, indicating poor wettability of the electrode to the electrolyte. Consequently, the 3C discharge capacity retention rate and the capacity retention rate after 1000 cycles are both significantly lower, indicating poor rate performance and cycle performance. Compared to Comparative Example 1, Comparative Example 2 added porous carbon and the hydrophilic polymer polyvinylpyrrolidone to the electrode coating. Although this significantly improved the electrolyte absorption rate, the single-coated electrode has limited liquid retention capacity. Especially in the later stages of battery cycling, the electrolyte may experience localized drying. Therefore, the 3C discharge capacity retention rate and the capacity retention rate after 1000 cycles for the corresponding battery remain at a low level.

[0118] In Examples 1 to 4, the combination of the first, second, and third coatings improves the electrolyte absorption rate of the electrode, resulting in higher 3C discharge capacity retention and 1000-cycle capacity retention for the corresponding battery. In Comparative Examples 3 to 5, the first, second, and third coatings are omitted compared to Example 1, leading to lower 3C discharge capacity retention and 1000-cycle capacity retention for the corresponding batteries, which does not meet practical requirements. Therefore, in this application, the synergistic effect of the first, second, and third coatings effectively improves the wettability of the electrode to the electrolyte, preventing localized electrolyte drying and ensuring the electrode's conductivity, thereby effectively improving the battery's rate performance and cycle performance. The absence of any one of the three coating layers makes it difficult to achieve the desired effect.

[0119] As can be seen from the data in Table 1, in Example 2, the third coating has a higher thickness proportion in the three-layer coating, resulting in better liquid absorption of the electrode and better promotion of active ion transport, thereby improving the cycle stability of the battery. Therefore, the electrode prepared in Example 2 has the best overall performance, with a high liquid absorption rate while maintaining cycle stability. In Example 3, the second coating has a higher thickness proportion in the three-layer coating, resulting in better liquid absorption performance of the electrode, and the battery's rate performance and cycle performance are both at a good level. In Example 4, the first coating has a higher thickness proportion in the three-layer coating, with a higher content of temperature-sensitive polymer. After multiple expansions and contractions during multiple cycles, the first coating may have poor contact with the current collector, resulting in a relatively low capacity retention rate of the battery corresponding to Example 4 after 1000 cycles. Therefore, in this application, it is a preferred technical solution for the thickness of the second and third coatings to be greater than or equal to the thickness of the first coating. Specifically, the preferred thickness ratio of the first, second, and third coatings is 1:(1~2):(1~2).

[0120] It should be noted that the electrode examples, electrode preparation method examples, and battery examples provided in this application belong to the same concept; the technical features in the technical solutions described in each example can be arbitrarily combined without conflict.

[0121] It should be understood that the above embodiments are exemplary and not intended to encompass all possible implementations of this application. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of the present invention and do not limit the scope of protection of this patent.

Claims

1. An electrode sheet, characterized in that, include: current collector; A first coating is disposed on at least one surface of the current collector along the thickness direction. The first coating comprises a first active material and a composite thermosensitive polymer. The composite thermosensitive polymer comprises graphene oxide and a thermosensitive polymer located on the surface of the graphene oxide. The thermosensitive polymer has thermal expansion properties. A second coating is disposed on the surface of the first coating away from the current collector. The second coating includes a second active material and a conductive agent, wherein the conductive agent includes carbon nanotubes and graphene. A third coating is disposed on the surface of the second coating away from the first coating, the third coating comprising a third active material, porous carbon, and a hydrophilic polymer.

2. The electrode sheet according to claim 1, characterized in that, The electrode satisfies at least one of the following characteristics: (1) The temperature-sensitive polymer includes poly(N-acryloylglycine); (2) The hydrophilic polymer includes at least one of polyvinylpyrrolidone, polyolefin, polydiolefin and its derivatives; (3) The first coating also includes a first dispersant and a first binder, wherein the mass ratio of the first active material, the composite temperature-sensitive polymer, the first dispersant and the first binder is (91~92):(5~6):(0.2~0.3):(1.7~3.8). (4) The second coating also includes a second dispersant and a second binder, wherein the mass ratio of the second active material, the conductive agent, the second dispersant and the second binder is (96~97):(1~1.2):(0.2~0.3):(1.5~2.8); (5) The mass ratio of the carbon nanotubes to graphene is (1~3):1; (6) The third coating also includes a third dispersant and a third binder, and the mass ratio of the third active material, the porous carbon, the hydrophilic polymer, the third dispersant and the third binder is (95~96):(0.8~1):(1.5~2):(0.2~0.3):(0.7~2.5).

3. The electrode sheet according to claim 1, characterized in that, The electrode satisfies at least one of the following characteristics: (1) The thickness ratio of the first coating, the second coating and the third coating is 1:(1~2):(1~2); (2) The thickness of the first coating is 30μm~60μm; (3) The thickness of the second coating is 30μm~60μm; (4) The thickness of the third coating is 30μm~60μm; (5) The compaction density of the electrode sheet is 2.62 g / cm³. 3 ~2.65g / cm 3 .

4. The electrode sheet according to claim 1, characterized in that, The porosity of the first coating is less than that of the second coating and the third coating; preferably, the porosity of the second coating is less than that of the third coating; more preferably, the porosity of the first coating is 20% to 30%; the porosity of the second coating is 30% to 40%; and the porosity of the third coating is 40% to 50%.

5. A method for preparing an electrode sheet, characterized in that, The method includes the following steps: S1: The first active material, the composite thermosensitive polymer, the first dispersant and the first binder are added to the first solvent and mixed evenly to obtain the first slurry; the composite thermosensitive polymer includes graphene oxide and a thermosensitive polymer located on the surface of the graphene oxide, and the thermosensitive polymer has thermal expansion properties; S2: The second active material, conductive agent, second dispersant, and second binder are added to the second solvent and mixed evenly to obtain the second slurry; the conductive agent includes carbon nanotubes and graphene; S3: Add the third active material, porous carbon, lyophilic polymer, third dispersant and third binder to the third solvent, mix them evenly to obtain the third slurry; S4: The first slurry, the second slurry, and the third slurry are layered and coated on at least one side surface of the current collector in such a manner that the first slurry is closer to the current collector than the second slurry and the second slurry is closer to the current collector than the third slurry. After drying and rolling, a first coating, a second coating, and a third coating are sequentially layered on the current collector to obtain the electrode.

6. The method for preparing the electrode according to claim 5, characterized in that, The method satisfies at least one of the following characteristics: (1) The mass ratio of the first active material, the composite thermosensitive polymer, the first dispersant and the first binder is (91~92):(5~6):(0.2~0.3):(1.7~3.8); (2) The mass ratio of the second active material, the conductive agent, the second dispersant and the second binder is (96~97):(1~1.2):(0.2~0.3):(1.5~2.8); (3) The mass ratio of the carbon nanotubes to graphene is (1~3):1; (4) The mass ratio of the third active material, the porous carbon, the hydrophilic polymer, the third dispersant, and the third binder is (95~96):(0.8~1):(1.5~2):(0.2~0.3):(0.7~2.5); (5) The hydrophilic polymer includes at least one of polyvinylpyrrolidone, polyolefin, polydiolefin and its derivatives; (6) The first dispersant, the second dispersant and the third dispersant each independently comprise at least one of sodium dodecyl sulfate and polyethylene glycol, sodium dodecyl sulfate and fatty alcohol polyoxyethylene ether, polyacrylonitrile, and polyvinylpyrrolidone; (7) The first adhesive, the second adhesive and the third adhesive each independently comprise polyacrylate and / or polyvinylidene fluoride.

7. The method for preparing the electrode according to claim 5, characterized in that, The method satisfies at least one of the following characteristics: (1) The coating surface density of the first slurry, the second slurry, and the third slurry is independently 0.08 g / mm². 2 ~0.2g / mm 2 ; (2) The drying temperature is 100℃~120℃; (3) The thickness ratio of the first coating, the second coating and the third coating is 1:(1~2):(1~2); (4) The thickness of the first coating is 30μm~60μm; (5) The thickness of the second coating is 30μm~60μm; (6) The thickness of the third coating is 30μm~60μm; (7) The compaction density of the electrode sheet is 2.62 g / cm³. 3 ~2.65g / cm 3 .

8. The method for preparing the electrode according to claim 5, characterized in that, The porosity of the first coating is less than that of the second coating and the third coating; preferably, the porosity of the second coating is less than that of the third coating; more preferably, the porosity of the first coating is 20% to 30%; the porosity of the second coating is 30% to 40%; and the porosity of the third coating is 40% to 50%.

9. The method for preparing the electrode according to claim 5, characterized in that, The preparation method of the composite thermosensitive polymer includes: dispersing thermosensitive polymer monomers and graphene oxide in deionized water, heating, adding an initiator, stirring and reacting under the condition of passing in an inert gas, growing the thermosensitive polymer in situ on the surface of the graphene oxide, and obtaining the composite thermosensitive polymer after filtration, washing and drying. The preparation method of the composite thermosensitive polymer satisfies at least one of the following characteristics: (1) The mass ratio of the thermosensitive polymer monomer to the graphene oxide is (2~2.5):1; (2) The heating temperature is 60℃~80℃; (3) The initiator includes ammonium persulfate; (4) The ratio of the total mass of the thermosensitive polymer monomer and the graphene oxide to the mass of the initiator is (19~21):1; (5) The reaction time is 40 min to 60 min with stirring; (6) The temperature-sensitive polymer includes poly(N-acryloylglycine).

10. A battery, characterized in that, The electrode includes the electrode as described in any one of claims 1 to 4, or the electrode as described in any one of claims 5 to 9, prepared by a method thereof.

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