Multilayer coated pole pieces, secondary batteries, battery modules, battery packs and electrical devices

Abstract

The present application provides a multilayer coated pole piece, a secondary battery, a battery module, a battery pack and an electric device. The present application particularly relates to an electrode pole piece, which uses conductive agents with different shapes and / or conductivity in different electrode film layers to construct a three-dimensional conductive network, improve the unevenness of the current density distribution in the cross section of the electrode film layer, reduce the pole piece resistance and heat generation rate, and enhance the thermal safety of the pole piece; by increasing the content of the binder in the electrode film layer close to the current collector side, the bonding force between the electrode film layer and the current collector is increased, and the structural stability of the pole piece is enhanced.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a multi-layer coated electrode, a secondary battery, a battery module, a battery pack and an electrical device. Background Art

[0002] Secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] The pole piece of a secondary battery mainly includes a current collector and an electrode film layer, wherein the electrode film layer generally includes an electrode active material, a conductive agent, a binder, and optionally other additives. During the charge and discharge process of a secondary battery, the current density on the current collector side of the pole piece is high, and the heat generation rate is large, which affects the thermal safety of the battery. In addition, the pole piece of a secondary battery also has the problem of low adhesion between the electrode film layer and the current collector, which needs to be solved urgently. Summary of the invention

[0004] During the charge and discharge process of a secondary battery, one of the main functions of the current collector in the pole piece is to collect the current of the electrode film layer. Therefore, the current density of the electrode film layer in the plane perpendicular to the current collector (hereinafter referred to as the cross section) shows a trend of gradually increasing from the side away from the current collector to the side close to the current collector. The current density on the current collector side of the pole piece is higher and the heat generation rate is higher. In addition, due to the floating of the binder during the drying process of the pole piece, the number of binder particles at the interface between the pole piece and the current collector is small, thereby reducing the bonding force of the pole piece.

[0005] Most of the electrode manufacturing processes in the prior art are to mix the slurry and disperse it evenly, and then coat, dry and roll it into an electrode. The slurry formula and the conductive structure of the electrode film layer are not designed according to the distribution characteristics of the current density, and therefore the above-mentioned technical problems cannot be solved.

[0006] The purpose of the present application is to provide a multi-layer coated electrode sheet with gradient distribution of conductive agent and adhesive and a preparation method thereof, so as to improve the problems of uneven current density distribution in the electrode film layer and low bonding force between the electrode film layer and the current collector.

[0007] In order to achieve the above-mentioned objectives, the present application provides an electrode plate and a preparation method thereof, a secondary battery, a battery module comprising the secondary battery, a battery pack comprising the secondary battery or battery module, and an electrical device comprising the secondary battery, battery module or battery pack.

[0008] The first aspect of the present application provides an electrode sheet, comprising a current collector, an electrode film layer L_1 and an electrode film layer L_2, wherein the current collector has two surfaces opposite to each other in its thickness direction, the electrode film layer L_1 is arranged on any one or both of the two opposite surfaces of the current collector, and the electrode film layer L_2 is arranged on the surface of the electrode film layer L_1;

[0009] The electrode film layer L_1 comprises active material AM_1, conductive agent C_1 and binder B_1, and the electrode film layer L_2 comprises active material AM_2, conductive agent C_2 and binder B_2; wherein, the conductive agent C_1 is selected from one-dimensional conductive agent and / or two-dimensional conductive agent, and the conductive agent C_2 is selected from zero-dimensional conductive agent; and, based on the mass percentage of each component in the electrode film layer where it is located, the content of conductive agent C_1 is greater than the content of conductive agent C_2, and the content of binder B_1 is greater than the content of binder B_2.

[0010] In some embodiments, based on the mass percentage of each component in the electrode film layer where it is located, the content of the active substance AM_1 is less than the content of the active substance AM_2.

[0011] In some embodiments, the conductive agent C_1 accounts for 1% to 4% of the total mass of the electrode film layer L_1, the binder B_1 accounts for 1% to 3% of the total mass of the electrode film layer L_1, and the active material AM_1 accounts for 93% to 97% of the total mass of the electrode film layer L_1.

[0012] In some embodiments, the conductive agent C_2 accounts for 0.5% to 3% of the total mass of the electrode film layer L_2, the binder B_2 accounts for 0.5% to 1.5% of the total mass of the electrode film layer L_2, and the active material AM_2 accounts for 95.5% to 98.5% of the total mass of the electrode film layer L_2.

[0013] In some embodiments, the ratio of the mass percentage of binder B_1 in the electrode film layer L_1 to the mass percentage of binder B_2 in the electrode film layer L_2 is 2-6.

[0014] In some embodiments, the zero-dimensional conductive agent is selected from one or more of conductive carbon black, Ketjen black, acetylene black, and ultrafine conductive graphite.

[0015] In some embodiments, the one-dimensional conductive agent is selected from one or more of carbon nanotubes and carbon fibers.

[0016] In some embodiments, the two-dimensional conductive agent is selected from one or more of lamellar conductive graphite and graphene.

[0017] The second aspect of the present application provides a method for preparing the electrode sheet of the first aspect of the present application, comprising the following steps:

[0018] (1) mixing, stirring and dispersing the active material AM_1, the conductive agent C_1 and the binder B_1 and any other optional components with a solvent in proportion to form a slurry 1;

[0019] (2) mixing, stirring and dispersing the active material AM_2, the conductive agent C_2, the binder B_2 and any other optional components with a solvent in proportion to form a slurry 2;

[0020] (3) Slurry 1 is coated on the surface of the current collector, and then slurry 2 is coated on the surface of slurry 1, and after drying and rolling, an electrode sheet is formed;

[0021] There is no particular order in which steps (1) and (2) are performed.

[0022] A third aspect of the present application provides a secondary battery, comprising the electrode plate of the first aspect of the present application.

[0023] A fourth aspect of the present application provides a battery module, comprising the electrode sheet of the first aspect of the present application or the secondary battery of the third aspect of the present application.

[0024] The fifth aspect of the present application provides a battery pack, comprising the electrode plate of the first aspect of the present application, the secondary battery of the third aspect of the present application, or the battery module of the fourth aspect of the present application.

[0025] The sixth aspect of the present application provides an electrical device, including the electrode plate of the first aspect of the present application, the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application.

[0026] The present invention constructs a three-dimensional conductive network by using conductive agents with different shapes and conductivities in different electrode film layers, thereby improving the unevenness of current density distribution in the cross section of the electrode film layer, reducing the electrode sheet resistance and heat generation rate, and enhancing the thermal safety of the electrode sheet; by increasing the content of the binder in the electrode film layer close to the current collector side, the bonding force between the electrode film layer and the current collector is increased, thereby enhancing the structural stability of the electrode sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the structure of the electrode provided in the present application, wherein L_1 and L_2 are electrode film layers and have the same thickness, AM is an active material, C_0 is a zero-dimensional conductive agent, C_1 is a one-dimensional conductive agent, C_2 is a two-dimensional conductive agent, B is a binder, and C_base is a current collector (substrate).

[0028] Figure 2 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0029] Figure 3 yes Figure 2 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0030] Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application.

[0031] Figure 5 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0032] Figure 6 yes Figure 5 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0033] Figure 2-Figure 6 Description of the reference numerals appearing in the figure: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly.

[0034] Figure 7 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source. DETAILED DESCRIPTION

[0035] Below, the electrode plate and its preparation method, as well as the implementation methods of the secondary battery, battery module, battery pack and power device of the present application are specifically disclosed with appropriate reference to the accompanying drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0036] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0038] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0039] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0040] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0041] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0042] [Electrode Plate]

[0043] In one embodiment of the present application, an electrode sheet is provided, comprising a current collector, an electrode film layer L_1 and an electrode film layer L_2, wherein the current collector has two surfaces opposite to each other in its thickness direction, the electrode film layer L_1 is arranged on any one or both of the two opposite surfaces of the current collector, and the electrode film layer L_2 is arranged on the surface of the electrode film layer L_1;

[0044] The electrode film layer L_1 comprises active material AM_1, conductive agent C_1 and binder B_1, and the electrode film layer L_2 comprises active material AM_2, conductive agent C_2 and binder B_2; wherein, the conductive agent C_1 is selected from one-dimensional conductive agent and / or two-dimensional conductive agent, and the conductive agent C_2 is selected from zero-dimensional conductive agent; and, based on the mass percentage of each component in the electrode film layer where it is located, the content of conductive agent C_1 is greater than the content of conductive agent C_2, and the content of binder B_1 is greater than the content of binder B_2.

[0045] The electrode plate of the present application includes a current collector and an electrode film layer disposed on the current collector and including an electrode active material. The electrode film layer can be disposed on one surface of the current collector or on both surfaces of the current collector.

[0046] The current density of the electrode film layer in the cross section shows a trend of gradually increasing from the side away from the current collector to the side close to the current collector. The present application uses a one-dimensional or two-dimensional conductive agent in the electrode film layer L_1 close to the current collector, and a zero-dimensional conductive agent in the electrode film layer L_2 far from the current collector, and the content of the conductive agent C_1 is greater than the content of the conductive agent C_2, and the content of the binder B_1 is greater than the content of the binder B_2.

[0047] By adopting the technical solution of the present application, conductive agents and binders of different shapes and conductivities can be layered and distributed in gradients in the cross section, and can be used together with active materials to construct a three-dimensional mesh conductive structure, and the conductivity and bonding force of the conductive structure tend to increase in gradients from the side away from the current collector to the side close to the current collector, which matches the current density distribution trend of the electrode film layer in the cross section. The conductivity and binder content of the electrode film layer with high current density and close to the current collector are high, thereby reducing the pole piece resistance in the electrode film layer, increasing the bonding force, and reducing the heat generated by the pole piece; the electrode film layer L_1 in contact with the current collector has the highest binder content, which can enhance the bonding force between the electrode film layer and the current collector and improve the structural stability of the pole piece.

[0048] The gradient distribution of the binder and conductive agent content is one of the innovative features of the present invention. During the drying process of the pole piece, the solvent evaporation will carry a portion of the small particles of the binder and conductive agent upward (i.e., away from the current collector). The content of the binder and conductive agent is designed to be higher in the lower layer (the layer in contact with the current collector) than in the upper layer, which can offset the adverse effects of the thermal movement of the solvent evaporation.

[0049] The pole piece prepared by adopting the technical solution can improve the thermal safety and structural stability of the pole piece at the same time.

[0050] Furthermore, the ratio of each component can be adjusted to better reduce the electrode resistance while improving the structural stability of the electrode.

[0051] In some embodiments, based on the mass percentage of each component in the electrode film layer where it is located, the content of the active substance AM_1 is less than the content of the active substance AM_2.

[0052] In some embodiments, the conductive agent C_1 accounts for 1% to 4% (e.g., 1% to 1.5%, 1.5% to 2%, 2% to 2.5%, 2.5% to 3%, 3% to 3.5% or 3.5% to 4%) of the total mass of the electrode film layer L_1, the binder B_1 accounts for 1% to 3% (e.g., 1% to 1.5%, 1.5% to 2%, 2% to 2.5% or 2.5% to 3%) of the total mass of the electrode film layer L_1, and the active substance AM_1 accounts for 93% to 97% (e.g., 93%, 94%, 95%, 96% or 97%) of the total mass of the electrode film layer L_1.

[0053] In some embodiments, the conductive agent C_2 accounts for 0.5% to 3% (for example, 0.5% to 1%, 1% to 1.5%, 1.5% to 2%, 2% to 2.5% or 2.5% to 3%) of the total mass of the electrode film layer L_2, the binder B_2 accounts for 0.5% to 1.5% (for example, 0.5% to 1% or 1% to 1.5%) of the total mass of the electrode film layer L_2, and the active substance AM_2 accounts for 95.5% to 98.5% (for example, 95.5%, 96%, 96.5%, 97%, 97.5%, 98% or 98.5%) of the total mass of the electrode film layer L_2.

[0054] The above ratio can better reduce the electrode resistance and improve the structural stability of the electrode.

[0055] Binders B_1 and B_2 may be the same or different, and the types are not specifically limited and may be selected according to actual needs. As an example, the binder may include one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, etc. Different binders may be used in combination, such as a combination of sodium carboxymethyl cellulose and styrene-butadiene rubber, and the mass ratio thereof may be 1:1 or other ratios.

[0056] In some embodiments, the ratio of the mass percentage of the binder B_1 in the electrode film layer L_1 to the mass percentage of the binder B_2 in the electrode film layer L_2 is 2 to 6 (e.g., 2, 3, 4, 5, or 6). With such a ratio, it can be better ensured that a gradient gradually decreases from bottom to top is formed after the electrode film layer is dried, and a stable conductive structure is formed in the upper layer of the electrode film layer.

[0057] The present invention uses a one-dimensional or two-dimensional conductive agent in the electrode film layer L_1 close to the current collector, and uses a zero-dimensional conductive agent in the electrode film layer L_2 far from the current collector. In some embodiments, the zero-dimensional conductive agent is selected from one or more of conductive carbon black, Ketjen black, acetylene black, and ultrafine conductive graphite. In some embodiments, the median particle size D of the zero-dimensional conductive agent is 50 The powder conductivity of the zero-dimensional conductive agent is 0.01 μm to 1 μm (e.g., 0.01 μm to 0.1 μm, 0.1 μm to 0.3 μm, 0.3 μm to 0.6 μm, 0.6 μm to 0.8 μm, or 0.8 μm to 1 μm). In some embodiments, the powder conductivity of the zero-dimensional conductive agent is 1 to 10 S / cm (e.g., 1 S / cm to 3 S / cm, 3 S / cm to 5 S / cm, 5 S / cm to 8 S / cm, or 8 S / cm to 10 S / cm).

[0058] In some embodiments, the one-dimensional conductive agent is selected from one or more of carbon nanotubes and carbon fibers. In some embodiments, the diameter of the one-dimensional conductive agent is 0.7nm to 30nm (e.g., 0.7nm to 1nm, 1nm to 5nm, 5nm to 10nm, 10nm to 20nm, or 20nm to 30nm). In some embodiments, the length of the one-dimensional conductive agent is 0.1μm to 50μm (e.g., 0.1μm to 1μm, 1μm to 5μm, 5μm to 10μm, 10μm to 20μm, 20μm to 30μm, 30μm to 40μm, or 40μm to 50μm). In some embodiments, the powder conductivity of the one-dimensional conductive agent is 10 S / cm to 1000 S / cm (e.g., 10 S / cm to 50 S / cm, 50 S / cm to 100 S / cm, 100 S / cm to 500 S / cm, or 500 S / cm to 1000 S / cm).

[0059] In some embodiments, the two-dimensional conductive agent is selected from one or more of lamellar conductive graphite and graphene. In some embodiments, the diameter of the two-dimensional conductive agent is 0.01 μm to 50 μm (e.g., 0.01 μm to 0.1 μm, 0.1 μm to 0.5 μm, 0.5 μm to 1 μm, 1 μm to 5 μm, 5 μm to 10 μm, or 10 μm to 50 μm). In some embodiments, the thickness of the two-dimensional conductive agent is 0.001 μm to 1 μm (e.g., 0.001 μm to 0.01 μm, 0.01 μm to 0.1 μm, 0.1 μm to 0.5 μm, or 0.5 μm to 1 μm). In some embodiments, the powder conductivity of the two-dimensional conductive agent is 10 S / cm to 1000 S / cm (e.g., 10 S / cm to 50 S / cm, 50 S / cm to 100 S / cm, 100 S / cm to 500 S / cm, or 500 S / cm to 1000 S / cm).

[0060] A one-dimensional conductive agent and a two-dimensional conductive agent may be combined for the electrode film layer L_1, for example, a combination of carbon nanotubes and graphene. The content of carbon nanotubes and graphene may be selected according to actual conditions, for example, 1.6wt% carbon nanotubes: 1wt% graphene, 1.8wt% carbon nanotubes: 1.2wt% graphene, 1.1wt% carbon nanotubes: 0.6wt% graphene, 1.6wt% carbon nanotubes: 0.8wt% graphene.

[0061] In some embodiments, the average conductive agent content of all electrode film layers is in the range of 1% to 2%, so as to better enable the electrode plate to have sufficient conductivity while ensuring a high energy density. The average conductive agent content of all electrode film layers is the weighted average of the conductive agent content of each electrode film layer.

[0062] The active material AM_1 and the active material AM_2 may be the same or different, and the type is not specifically limited and can be selected according to actual needs. As an example, one or more materials such as lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium cobalt oxide, lithium-rich manganese base, cobalt-free high nickel, graphite, hard carbon, silicon-doped graphite, silicon, and mesophase carbon microspheres can be used.

[0063] The content of active material is passively changed according to the amount of conductive agent and binder. In some embodiments, the content of active material AM_1 and active material AM_2 is independently selected from 96% to 97% (e.g., 96.0%, 96.1%, 96.2%, 96.3%, 96.4%, 96.5%, 96.6%, 96.7%, 96.8%, 96.9% or 97%) based on the mass percentage of each component in the electrode film layer. The content of AM_1 and AM_2 is between 96% and 97%, which can better achieve better rate performance and higher energy density.

[0064] In the electrode plate of the present application, the electrode film layer L_2 can be arranged on the entire electrode film layer L_1, that is, completely covering the electrode film layer L_1, or can be arranged on a partial surface of the electrode film layer L_1.

[0065] The electrode sheet of the present application may also include one or more other electrode film layers in addition to the electrode film layer L_1 and the electrode film layer L_2. These other electrode film layers may also include active materials, conductive agents and binders. In some embodiments, the types and contents of the conductive agents and binders of other electrode film layers may be set according to the principle of making the binder and the conductive agents of different shapes and / or conductivity present layered and gradient distribution in the cross section.

[0066] The electrode film layers included in the electrode plate of the present application may have the same or different thicknesses. In some embodiments, the electrode film layers included in the electrode plate each independently have a thickness of 10 to 200 μm (e.g., 10 to 20 μm, 20 to 50 μm, 50 to 100 μm, 100 to 150 μm, or 150 to 200 μm).

[0067] Figure 1 This is a schematic diagram of the structure of an electrode plate provided in the present application, wherein L_1 and L_2 are electrode film layers and have the same thickness, AM is an active material, C_0 is a zero-dimensional conductive agent, C_1 is a one-dimensional conductive agent, C_2 is a two-dimensional conductive agent, B is a binder, and C_base is a current collector (substrate).

[0068] The electrode plate of the present application can be a positive electrode plate or a negative electrode plate. The two types of electrode plates are described below.

[0069] [Positive electrode]

[0070] The electrode plate of the present application may be a positive electrode plate, which may include a positive electrode collector and one or more positive electrode film layers arranged on the positive electrode collector and including a positive electrode active material. The positive electrode film layer may be arranged on one surface of the positive electrode collector or on both surfaces of the positive electrode collector.

[0071] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0072] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0073] The positive electrode material layer also includes a binder. The type and content of the binder are not specifically limited and can be selected according to actual needs. As an example, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin One or more.

[0074] The positive electrode material layer further includes a conductive agent. As an example, the conductive agent can be selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0075] In some embodiments, in the electrode plate of the present application, the active material AM_1 is lithium manganese oxide, the conductive agent C_1 is carbon nanotubes and graphene, the binder B_1 is polyvinylidene fluoride, the active material AM_2 is lithium manganese oxide, the conductive agent C_2 is conductive carbon black, and the binder B_2 is polyvinylidene fluoride.

[0076] [Negative electrode]

[0077] The negative electrode plate of the present application may include a negative electrode current collector and one or more negative electrode film layers disposed on the negative electrode current collector and including a negative electrode active material. The negative electrode film layer may be disposed on one surface of the negative electrode current collector or on both surfaces of the negative electrode current collector.

[0078] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0079] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include one or more of the following materials: graphite (e.g., artificial graphite, natural graphite), soft carbon, hard carbon, mesophase carbon microspheres, carbon fiber, carbon nanotubes, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0080] The negative electrode material layer also includes a binder. The binder can be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), and sodium carboxymethyl cellulose (CMC-Na).

[0081] The negative electrode material layer also includes a conductive agent, which can be selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0082] In some embodiments, the negative electrode material layer may optionally include other additives, such as a thickener.

[0083] In some embodiments, in the electrode plate of the present application, the active material AM_1 is graphite, the conductive agent C_1 is carbon nanotubes and graphene, the binder B_1 is sodium carboxymethyl cellulose and styrene-butadiene rubber, the active material AM_2 is graphite), the conductive agent C_2 is conductive carbon black, and the binder B_2 is sodium carboxymethyl cellulose and styrene-butadiene rubber.

[0084] [Method for preparing electrode]

[0085] The second aspect of the present application provides a method for preparing the electrode sheet of the first aspect of the present application, comprising the following steps:

[0086] (1) mixing, stirring and dispersing the active material AM_1, the conductive agent C_1 and the binder B_1 and any other optional components with a solvent in proportion to form a slurry 1;

[0087] (2) mixing, stirring and dispersing the active material AM_2, the conductive agent C_2, the binder B_2 and any other optional components with a solvent in proportion to form a slurry 2;

[0088] (3) Slurry 1 is coated on the surface of the current collector, and then slurry 2 is coated on the surface of slurry 1, and after drying and rolling, an electrode sheet is formed;

[0089] There is no particular order in which steps (1) and (2) are performed.

[0090] The present invention uses a multi-layer coating method and uses a variety of conductive agents with different shapes and conductivities and different contents of binders in different electrode film layers to construct a three-dimensional conductive network, improve the unevenness of the current density distribution of the electrode in the cross section, enhance the conductivity of the electrode, and reduce the resistance of the electrode; at the same time, it enhances the bonding force between the electrode film layer and the current collector and improves the structural stability of the electrode.

[0091] The solvent that can be used to form the positive electrode slurry can be an organic solvent, such as N-methylpyrrolidone. The solvent that can be used to form the negative electrode slurry can be water.

[0092] The coating of the slurry can be achieved by extrusion, transfer, spraying, printing, 3D printing, etc.

[0093] In some embodiments, the method comprises the following steps:

[0094] (1) dry-mixing the active material AM_1, the conductive agent C_1 and the binder B_1 in order according to the proportion, and then adding a solvent to stir and disperse them to form a slurry 1;

[0095] (2) dry-mixing the active material AM_2, the conductive agent C_2 and the binder B_2 according to the proportion, and then adding a solvent to stir and disperse them to form a slurry 2;

[0096] (3) coating slurry 1 on the surface of the current collector, optionally drying it, and then coating slurry 2 on the surface of slurry 1, drying it, and rolling it to form an electrode sheet;

[0097] There is no particular order in which steps (1) and (2) are performed.

[0098] In addition, the secondary battery, battery module, battery pack, and electric device of the present application will be described below with reference to the drawings as appropriate.

[0099] [Secondary battery]

[0100] In one embodiment of the present application, a secondary battery is provided.

[0101] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0102] [Electrolytes]

[0103] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0104] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0105] In some embodiments, the electrolyte salt can be selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0106] In some embodiments, the solvent can be selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0107] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0108] [Isolation film]

[0109] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0110] In some embodiments, the material of the isolation membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0111] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0112] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0113] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0114] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 2 The secondary battery 5 is a square structure as an example.

[0115] In some embodiments, reference Figure 3 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0116] In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0117] Figure 4 4 is an example of a battery module. Figure 4 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0118] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0119] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0120] Figure 5 and Figure 6 1 is a battery pack 1 as an example. Figure 5 and Figure 6 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0121] In addition, the present application also provides an electrical device, which includes one or more of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0122] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0123] Figure 7 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0124] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0125] Example

[0126] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0127] The structural and performance parameters of the carbon nanotubes used in the following examples and comparative examples are: median particle size 7.2 nm, length 0.1 μm to 50 μm, powder conductivity 783 S / cm.

[0128] The structural and performance parameters of the graphene used in the following examples and comparative examples are: median diameter 0.83 μm, median thickness 19.2 nm, length 0.1 μm to 50 μm, powder conductivity 827 S / cm.

[0129] The structure and performance parameters of the conductive carbon black used in the following examples and comparative examples are: median particle size 45.2 nm, powder conductivity 2.4 S / cm.

[0130] Example 1 Preparation of positive electrode sheet

[0131] The powders of active material AM_1 (95.2wt% lithium manganese oxide), conductive agent C_1 (1.6wt% carbon nanotubes and 1wt% graphene), and binder B_1 (2.2wt% polyvinylidene fluoride) were added in sequence for dry mixing, stirred for 15 minutes, and then solvent N-methylpyrrolidone was added and stirred for 150 minutes to prepare electrode film layer L_1 slurry. The powders of active material AM_2 (96.9wt% lithium manganese oxide), conductive agent C_2 (1.5wt% conductive carbon black), and binder B_2 (1.6wt% polyvinylidene fluoride) were added in sequence for dry mixing, stirred for 15 minutes, and then solvent N-methylpyrrolidone was added and stirred for 150 minutes to prepare electrode film layer L_2 slurry.

[0132] In an environment of 22±2℃ and humidity ≤2%, the electrode film layer L_1 slurry is first coated on the surface of double-sided aluminum foil by extrusion coating equipment. After oven drying, the electrode film layer L_2 slurry is coated on the double-sided surface of the electrode film layer L_1 in a mass ratio of 1:1, and then dried and rolled to form the positive electrode sheet.

[0133] Example 2 Preparation of positive electrode sheet

[0134] The difference between Example 2 and Example 1 is that the proportions of the components of the electrode film layer L_1 are active material AM_1 (94.3wt% lithium manganese oxide), conductive agent C_1 (1.8wt% carbon nanotubes and 1.2wt% graphene), and binder B_1 (2.7wt% polyvinylidene fluoride); the proportions of the components of the electrode film layer L_2 are active material AM_2 (97.9wt% lithium manganese oxide), conductive agent C_2 (1wt% conductive carbon black), and binder B_2 (1.1wt% polyvinylidene fluoride).

[0135] Example 3 Preparation of negative electrode sheet

[0136] Active material AM_1 (96.1wt% graphite), conductive agent C_1 (1.1wt% carbon nanotubes and 0.6wt% graphene), binder B_1 (2.2wt% sodium carboxymethyl cellulose and styrene-butadiene rubber, mass ratio 1:1) powders were added in sequence for dry mixing and stirred for 15 minutes. Then, solvent N-methyl pyrrolidone was added and stirred for 150 minutes to prepare electrode film L_1 slurry. Active material AM_2 (97.1wt% graphite), conductive agent C_1 (1.1wt% carbon nanotubes and 0.6wt% graphene) and binder B_1 (2.2wt% sodium carboxymethyl cellulose and styrene-butadiene rubber, mass ratio 1:1) powders were added in sequence for dry mixing and stirred for 15 minutes. Then, solvent N-methyl pyrrolidone was added and stirred for 150 minutes to prepare electrode film L_1 slurry. The powders of the electrolyte C_2 (1.4wt% conductive carbon black) and the binder B_2 (1.5wt% sodium carboxymethyl cellulose and styrene-butadiene rubber, mass ratio of 1:1) were dry-mixed and stirred for 15 minutes, and then the solvent N-methylpyrrolidone was added and stirred for 150 minutes to prepare the electrode film layer L_2 slurry; then the electrode film layer L_1 and the electrode film layer L_2 were coated on the aluminum foil in a mass ratio of 1:1 (double-sided coating) through a double-layer coating device, and the positive electrode sheet was made after drying and rolling.

[0137] Example 4 Preparation of negative electrode sheet

[0138] The difference between Example 4 and Example 3 is that the proportions of the components of the electrode film layer L_1 are active substance AM_1 (94.8wt% graphite), conductive agent C_1 (1.6wt% carbon nanotubes and 0.8wt% graphene), and binder B_1 (2.8wt% sodium carboxymethyl cellulose and styrene-butadiene rubber, mass ratio of 1:1); the proportions of the components of the electrode film layer L_2 are active substance AM_2 (98.2wt% graphite), conductive agent C_2 (0.8wt% conductive carbon black), and binder B_2 (1wt% sodium carboxymethyl cellulose and styrene-butadiene rubber, mass ratio of 1:1).

[0139] Comparative Example 1 Preparation of positive electrode sheet

[0140] Electrode film slurry formula: active material AM_1 (96.1wt% lithium manganese oxide), conductive agent C_1 (2wt% conductive carbon black), binder B_1 (1.9wt% polyvinylidene fluoride), the electrode preparation method is the same as Examples 1 and 2.

[0141] Comparative Example 2 Preparation of negative electrode sheet

[0142] Electrode film slurry formula: active material AM_1 (96.6wt% graphite), conductive agent C_1 (1.6wt% conductive carbon black), binder B_1 (1.8wt% sodium carboxymethyl cellulose and styrene-butadiene rubber, mass ratio 1:1), the electrode preparation method is the same as Examples 3 and 4.

[0143] Diaphragm resistance test method:

[0144] (1) Sampling: Use a punching machine to punch out several pieces with an area of ​​1540.25 mm 2 small discs;

[0145] (2) Test: Place the small discs in the resistance tester one by one, measure the film resistance, and finally take the average value.

[0146] Pole piece adhesion test method:

[0147] (1) Take the electrode to be tested, cut a sample with a length of 100mm-160mm and a width of 30mm with a blade, stick a special double-sided tape on the steel plate, the tape length is 90mm-150mm, and the width is 20mm. Insert a paper tape with a length greater than the sample length of 80mm-200mm and a width equal to the electrode under the electrode and fix it with wrinkle glue;

[0148] (2) Turn on the power of the tensile testing machine, the indicator light will light up, adjust the limit block to the appropriate position, fix the end of the steel plate without the electrode with the lower clamp, fold the paper tape upwards, fix it with the upper clamp, and use the "up" and "down" buttons on the manual controller attached to the tensile testing machine to adjust the position of the upper clamp;

[0149] (3) Confirm that the force sensor parameter is "500N" and click "Confirm". Select the "Adhesion Test" test scheme in the test project column; click the reset icon of the "Force" parameter at the top of the interface. After the parameter is reset to zero, click "Start" at the bottom right of the interface;

[0150] (4) When the curve in the figure is flat and the displacement is greater than 70mm, click "Stop", the machine stops rising, the displacement automatically returns to zero, and the average value of the flat part of the curve in the figure is read and recorded.

[0151] The resistance and bonding strength test data of the embodiment electrode and the comparative example electrode are shown in Table 1.

[0152] Table 1 Electrode resistance and bonding test data

[0153]

[0154]

[0155] As can be seen from Table 1, compared with Comparative Example 1, the positive electrode sheets prepared in Examples 1 and 2 have significantly lower film resistance and significantly higher bonding force; compared with Comparative Example 2, the negative electrode sheets prepared in Examples 3 and 4 have significantly lower film resistance and significantly higher bonding force. The results show that the electrode sheets prepared in Examples 1-4 have higher conductivity and better electrode sheet structure stability.

[0156] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An electrode sheet, comprising a current collector, an electrode film layer L_1 and an electrode film layer L_2, wherein the current collector has two surfaces opposite to each other in its thickness direction, the electrode film layer L_1 is arranged on any one or both of the two opposite surfaces of the current collector, and the electrode film layer L_2 is arranged on the surface of the electrode film layer L_1; The electrode film layer L_1 comprises active material AM_1, conductive agent C_1 and binder B_1, and the electrode film layer L_2 comprises active material AM_2, conductive agent C_2 and binder B_2; wherein, The conductive agent C_1 is selected from one-dimensional conductive agents and / or two-dimensional conductive agents, and the conductive agent C_2 is selected from zero-dimensional conductive agents; and, based on the mass percentage of each component in the electrode film layer where it is located, the content of the conductive agent C_1 is greater than the content of the conductive agent C_2, and the content of the binder B_1 is greater than the content of the binder B_2.

2. According to the electrode plate according to claim 1, based on the mass percentage of each component in the electrode film layer where it is located, the content of active material AM_1 is less than the content of active material AM_2.

3. According to the electrode plate according to claim 1, the conductive agent C_1 accounts for 1% to 4% of the total mass of the electrode film layer L_1, the binder B_1 accounts for 1% to 3% of the total mass of the electrode film layer L_1, and the active material AM_1 accounts for 93% to 97% of the total mass of the electrode film layer L_1.

4. According to the electrode plate according to claim 1, the conductive agent C_2 accounts for 0.5% to 3% of the total mass of the electrode film layer L_2, the binder B_2 accounts for 0.5% to 1.5% of the total mass of the electrode film layer L_2, and the active material AM_2 accounts for 95.5% to 98.5% of the total mass of the electrode film layer L_2. 5 . The electrode plate according to claim 1 , wherein the ratio of the mass percentage of the binder B_1 in the electrode film layer L_1 to the mass percentage of the binder B_2 in the electrode film layer L_2 is 2 to 6.

6. The electrode plate according to claim 1, wherein the zero-dimensional conductive agent is selected from one or more of conductive carbon black, Ketjen black, acetylene black, and ultrafine conductive graphite. 7 . The electrode plate according to claim 1 , wherein the one-dimensional conductive agent is selected from one or more of carbon nanotubes and carbon fibers.

8. The electrode plate according to claim 1, wherein the two-dimensional conductive agent is selected from one or more of lamellar conductive graphite and graphene.

9. A method for preparing an electrode sheet according to any one of claims 1 to 8, comprising the following steps: (1) mixing, stirring and dispersing the active material AM_1, the conductive agent C_1 and the binder B_1 and any other optional components with a solvent in proportion to form a slurry 1; (2) mixing, stirring and dispersing the active material AM_2, the conductive agent C_2, the binder B_2 and any other optional components with a solvent in proportion to form a slurry 2; (3) Slurry 1 is coated on the surface of the current collector, and then slurry 2 is coated on the surface of slurry 1, and after drying and rolling, an electrode sheet is formed; There is no particular order in which steps (1) and (2) are performed.

10. A secondary battery comprising the electrode sheet according to any one of claims 1 to 8. 11 . A battery module, comprising the electrode sheet according to any one of claims 1 to 8 or the secondary battery according to claim 10 .

12. A battery pack, comprising at least one of the electrode sheet according to any one of claims 1 to 8, the secondary battery according to claim 10, or the battery module according to claim 11.

13. An electrical device, comprising at least one of the electrode sheet according to any one of claims 1 to 8, the secondary battery according to claim 10, the battery module according to claim 11, or the battery pack according to claim 12.

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