CN118575294A - Electrode plate and preparation method thereof, secondary battery and preparation method thereof, battery module, battery pack and electricity utilization device - Google Patents

Abstract

The present application provides an electrode plate and a preparation method thereof, a secondary battery and a preparation method thereof, a battery module, a battery pack and an electric device. The electrode plate (7) comprises a current collector (71), a first active layer (72) and a second active layer (73), wherein the first active layer (72) is located on at least one surface of the current collector (71), the second active layer (73) is located on the first active layer (72), and the electronic conductivity of the first active layer (72) is less than the electronic conductivity of the second active layer (73).

Description

Electrode sheet and preparation method thereof, secondary battery and preparation method thereof, battery module, battery pack and power-consuming device Technical Field

The present application relates to the field of secondary batteries, and specifically to an electrode plate and a preparation method thereof, a secondary battery and a preparation method thereof, a battery module, a battery pack and an electrical device.

Background Art

During the use of secondary batteries, lithium deposition on the surface of the electrode plates is inevitable. The occurrence of lithium deposition will generate lithium dendrites on the surface of the electrode plates. The growth of lithium dendrites may destroy the solid electrolyte interface (SEI) film and reduce the cycle performance of the battery. Therefore, inhibiting lithium deposition on the surface of the electrode plates is of great significance to improving the cycle performance of the battery.

Summary of the invention

Based on the above problems, the present application provides an electrode plate and a preparation method thereof, a secondary battery and a preparation method thereof, a battery module, a battery pack and an electrical device, which can effectively suppress the lithium plating problem on the surface of the electrode plate and improve the cycle performance of the secondary battery.

In order to achieve the above-mentioned objectives, the first aspect of the present application provides an electrode plate, including a current collector, a first active layer and a second active layer, wherein the first active layer is located on at least one surface of the current collector, the second active layer is located on the first active layer, and the electronic conductivity of the first active layer is less than the electronic conductivity of the second active layer.

In the electrode plate provided in the first aspect of the present application, a first active layer is formed on at least one surface of the current collector, a second active layer is formed on the surface of the first active layer, and the electronic conductivity of the first active layer is made smaller than the electronic conductivity of the second active layer, so that the transmission dynamics of electrons in the first active layer can be suppressed, the electrons are aggregated in the first active layer, and the lithium ions have a large concentration polarization on the surface of the first active layer. At this time, the lithium dendrites generated by lithium precipitation mainly grow on the surface of the first active layer, so that the growth of lithium dendrites on the surface of the electrode plate can be effectively avoided, and lithium precipitation on the surface of the electrode plate can be suppressed, thereby improving the cycle performance of the secondary battery.

In some embodiments, the first active layer includes a first active material and an electronic conductivity suppressor.

Optionally, the electronic conductivity suppressor includes at least one of styrene-butadiene rubber, barium titanate and lithium titanate.

In some embodiments, the mass percentage of the electronic conductivity inhibitor in the first active layer is 0.3% to 10%.

In some embodiments, the first active layer further includes a lithium-philic material.

Optionally, the lithium-philic material includes at least one of zinc oxide, magnesium oxide, silver and tin.

In some embodiments, the mass percentage of the lithium-philic material in the first active layer is 1% to 5%.

In some embodiments, the second active layer includes a second active material, and the second active material is the same as or different from the first active material.

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

The first active layer is formed on at least one surface of the current collector, and the second active layer is formed on the first active layer.

In some embodiments, the first active layer and the second active layer are each independently formed using a corresponding active slurry, optionally by coating.

A third aspect of the present application provides a secondary battery, comprising the electrode sheet of the first aspect or the electrode sheet prepared by the method for preparing the electrode sheet of the second aspect.

The fourth aspect of the present application provides a method for preparing the secondary battery of the third aspect, comprising the following steps:

The secondary battery pre-product equipped with the electrode plate is subjected to a formation treatment.

In some embodiments, after the chemical formation treatment, the method further comprises:

At 40°C to 50°C, the product after the formation treatment is charged from the lower limit of its voltage window to the upper limit of its voltage window, and then discharged to the lower limit of its voltage window.

In some embodiments, the lower limit of the voltage window is 2.3V to 2.7V.

In some embodiments, the upper limit of the voltage window is 4.4V to 4.6V.

In some embodiments, the charging current is 1C to 3C.

In some embodiments, the discharge current is 1C to 3C.

In some embodiments, between the charging and the discharging, the following steps are further included:

Allowing the charged product to stand still;

Optionally, the standing time is 5 min to 30 min.

A fifth aspect of the present application provides a battery module, comprising the secondary battery of the third aspect or a secondary battery prepared by the method for preparing the secondary battery of the fourth aspect.

A sixth aspect of the present application provides a battery pack, comprising the secondary battery of the third aspect, or a secondary battery prepared by the method for preparing a secondary battery of the fourth aspect, or a battery module of the fifth aspect.

The seventh aspect of the present application provides an electrical device, comprising at least one of the secondary battery of the third aspect, the secondary battery prepared by the secondary battery preparation method of the fourth aspect, the battery module of the fifth aspect, and the battery pack of the sixth aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

FIG. 1 is a schematic diagram of an electrode plate according to an embodiment of the present application.

FIG. 2 is a schematic diagram of an electrode plate according to another embodiment of the present application.

FIG. 3 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 4 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG. 3 .

FIG. 5 is a schematic diagram of a battery module according to an embodiment of the present application.

FIG. 6 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 7 is an exploded view of the battery pack shown in FIG. 6 according to an embodiment of the present application.

FIG. 8 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

Description of reference numerals:

1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module; 5. Secondary battery; 51. Shell; 52. Electrode assembly; 53. Cover plate; 6. Electrical device; 7. Electrode pole piece; 71. Current collector; 72. First active layer; 73. Second active layer.

In order to better describe and illustrate the embodiments and/or examples of the inventions disclosed herein, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed inventions, the embodiments and/or examples currently described, and any of the best modes of these inventions currently understood.

DETAILED DESCRIPTION

In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and/or" used herein includes any and all combinations of one or more related listed items.

The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 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 ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both 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.

If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

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.

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.

If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent 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.

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).

Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

The present application provides an electrode plate and a preparation method thereof, a secondary battery and a preparation method thereof, a battery module, a battery pack and an electric device. The secondary battery is suitable for various electric devices using batteries, such as mobile phones, portable devices, laptop computers, electric vehicles, electric toys, electric tools, electric vehicles, ships and spacecraft, etc. For example, spacecraft include airplanes, rockets, space shuttles and spacecrafts, etc.

In a first aspect, the present application provides an electrode plate. The electrode plate includes a current collector, a first active layer, and a second active layer. The first active layer is located on at least one surface of the current collector, the second active layer is located on the first active layer, and the electronic conductivity of the first active layer is less than the electronic conductivity of the second active layer.

In the electrode plate of the present embodiment, a first active layer is formed on at least one surface of the current collector, a second active layer is formed on the surface of the first active layer, and the electronic conductivity of the first active layer is made smaller than the electronic conductivity of the second active layer, so that the transmission dynamics of electrons in the first active layer can be suppressed, the electrons are aggregated in the first active layer, and the lithium ions have a large concentration polarization on the surface of the first active layer. At this time, the lithium dendrites generated by lithium precipitation mainly grow on the surface of the first active layer, which can effectively prevent the growth of lithium dendrites on the surface of the electrode plate, and then inhibit the lithium precipitation on the surface of the electrode plate, thereby improving the cycle performance of the secondary battery. In addition, in the electrode plate of the present embodiment, the lithium precipitation problem is effectively avoided from appearing on the surface of the electrode plate, so that the influence of the growth of lithium dendrites on the diaphragm can be effectively avoided, and the problem of thermal runaway of the battery caused by lithium dendrites piercing the diaphragm can be avoided, so the safety performance of the battery can also be effectively improved.

In one embodiment, the electronic conductivity can be tested in the following manner: the prepared electrode plate can be placed in a resistor meter, and the conductivity of the electrode plate can be obtained using the formula σ=U*A/I/(δ-Δδ), where σ is the electronic conductivity, U is the detection voltage, I is the loading current, δ is the thickness of the plate, and Δδ is the change in thickness of the plate after pressurization.

Please refer to FIG. 1 , as a specific embodiment, the electrode plate 7 includes a current collector 71, a first active layer 72, and a second active layer 73. The first active layer 72 is located on one surface of the current collector 71, and the second active layer 73 is located on the first active layer 72, and the electronic conductivity of the first active layer 72 is less than the electronic conductivity of the second active layer 73. In this embodiment, the first active layer 71 and the second active layer 72 are respectively one layer, wherein the current collector 71, the first active layer 72, and the second active layer 73 are stacked in sequence.

Please refer to FIG. 2 , as another specific embodiment, the electrode plate 7 includes a current collector 71, a first active layer 72 and a second active layer 73. The first active layer 72 is located on both surfaces of the current collector 71, and the second active layer 73 is located on the first active layer 72, and the electronic conductivity of the first active layer 72 is less than the electronic conductivity of the second active layer 73. In this embodiment, the first active layer 71 and the second active layer 72 are two layers respectively, wherein the second active layer 73, the first active layer 72, the current collector 71, the first active layer 72 and the second active layer 73 are stacked in sequence.

In some embodiments, the first active layer includes a first active material and an electronic conductivity inhibitor. By using the electronic conductivity inhibitor, the electronic conductivity of the first active layer can be reduced, so that the electronic conductivity of the first active layer is less than the electronic conductivity of the second active layer. Optionally, the electronic conductivity inhibitor includes at least one of styrene-butadiene rubber, barium titanate and lithium titanate. Alternatively, the mass percentage of the electronic conductivity inhibitor in the first active layer is 0.3% to 10%. When the amount of the electronic conductivity inhibitor added is too small, the effect of reducing the electronic conductivity of the first active layer is limited. When the amount of the electronic conductivity inhibitor added is too large, the proportion of the first active material will be reduced accordingly, sacrificing part of the energy density of the electrode plate and being unfavorable to the improvement of the battery energy density. Specifically, the mass percentage of the electron conductivity inhibitor in the first active layer can be but is not limited to 0.3%, 0.5%, 0.7%, 1%, 1.2%, 1.5%, 1.7%, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.2%, 3.5%, 3.7%, 4%, 5%, 7%, 10%, etc.

In some embodiments, the first active layer further includes a lithium-philic material. By using the lithium-philic material, the nucleation barrier of lithium in the first active layer can be reduced, lithium precipitation on the surface of the first active layer can be promoted, and the growth of lithium dendrites on the surface of the electrode plate can be further inhibited, thereby further improving the cycle performance and safety performance of the secondary battery. As an optional example of the lithium-philic material, the lithium-philic material includes at least one of zinc oxide, magnesium oxide, silver and tin.

Optionally, when the first active layer includes a lithium-philic material, the mass percentage of the lithium-philic material in the first active layer is 1% to 5%. When the amount of lithium-philic material added is too small, the effect on reducing the lithium nucleation energy barrier is limited. When the amount of lithium-philic material added is too large, the proportion of the first active material will be reduced accordingly, sacrificing part of the energy density of the electrode plate and being unfavorable to the improvement of the battery energy density. Alternatively, as some specific examples of the mass percentage of the lithium-philic material in the first active layer, the mass percentage of the lithium-philic material in the first active layer can be but is not limited to 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4% or 4.5%, etc.

It is understood that the second active layer includes a second active material, which is the same as or different from the first active material.

It can also be understood that the first active layer may further include at least one of a binder, a conductive agent, and a thickener. The second active layer may further include at least one of a binder, a conductive agent, and a thickener. Optionally, the binder, conductive agent, and thickener of the first active layer may be the same as or different from the binder, conductive agent, and thickener of the second active layer.

In some embodiments, the electrode plate in the present application is a positive electrode plate or a negative electrode plate. Optionally, since the lithium plating problem mainly affects the negative electrode of the battery, the electrode plate in the present application is a negative electrode plate.

The second aspect of the present application provides a method for preparing the electrode sheet of the first aspect. The method for preparing the electrode sheet comprises the following steps: forming a first active layer on at least one surface of a current collector, and forming a second active layer on the surface of the first active layer.

Optionally, as an example of a method for forming the first active layer and the second active layer, the first active layer and the second active layer are each independently formed by coating using a corresponding active slurry. For example, the first active slurry is transferred to at least one surface of the current collector by coating to form the first active layer. The second active slurry is transferred to the first active layer by coating to form the second active layer.

It is understood that after the first active material is coated on at least one surface of the current collector, it is dried to form a first active layer. Then, the second active slurry is coated on the dried first active layer and dried again to form a second active layer.

The third aspect of the present application provides a secondary battery, which includes the electrode sheet of the first aspect or the electrode sheet prepared by the preparation method of the electrode sheet of the second aspect. During the charge and discharge process of the secondary battery, lithium dendrites preferentially grow on the surface of the first active layer of the electrode sheet, which can effectively suppress the adverse effects of lithium plating on the SEI film and the isolation film, so that the secondary battery can maintain good cycle performance and safety performance. Optionally, the electrode sheet of the first aspect or the electrode sheet prepared by the preparation method of the electrode sheet of the second aspect is used as the negative electrode sheet of the secondary battery.

The fourth aspect of the present application provides a method for preparing a secondary battery of the third aspect. The method for preparing a secondary battery comprises the following steps: performing a formation treatment on a secondary battery pre-finished product equipped with an electrode sheet of the first aspect or an electrode sheet prepared by the method for preparing an electrode sheet of the second aspect. The active material in the secondary battery pre-finished product is activated by the formation treatment so that the battery can begin to charge and discharge normally.

In some embodiments, after the formation treatment, the process further includes: charging the product after the formation treatment from the lower limit of its voltage window to the upper limit of its voltage window at 40°C to 50°C, and then discharging it to the lower limit of its voltage window. The product after the formation treatment is charged and discharged at a higher temperature of 40°C to 50°C to promote the movement of lithium ions from the second active layer of the electrode plate to the first active layer, promote the growth of lithium dendrites on the surface of the first active layer, and reduce the effect of lithium precipitation on the surface of the electrode plate. Optionally, as a temperature selection for charging and discharging at a higher temperature, the temperature can be but is not limited to 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C or 49°C, etc.

In some embodiments, the voltage of the secondary battery preformed product is brought to the lower limit of its voltage window through the formation process.

Optionally, when the product after the formation treatment is charged from the lower limit of its voltage window to the upper limit of its voltage window and then discharged to the lower limit of its voltage window, the lower limit of the voltage window is 2.3V to 2.7V. For example, the lower limit of the voltage window can be selected as 2.3V, 2.4V, 2.5V, 2.6V or 2.7V. The upper limit of the voltage window is 4.4V to 4.6V. For example, the lower limit of the voltage window can be selected as 4.4V, 4.5V or 4.6V.

Optionally, when the product after the formation treatment is charged from the lower limit of its voltage window to the upper limit of its voltage window and then discharged to the lower limit of its voltage window, the charging current is 1C to 3C. For example, the charging current can be selected as 1C, 2C or 3C. The discharging current is 1C to 3C. For example, the discharging current can be selected as 1C, 2C or 3C. Alternatively, the charging process can be performed in a segmented charging or a one-time direct charging manner.

It is understandable that the voltage window represents a voltage range, within which the material has a relatively stable structure and performance, and the voltage range can be determined according to the type of material. For example, the voltage window of the product after the formation treatment represents that within the voltage range of the voltage window, the structure and performance of the product are relatively stable. When charged to exceed the upper limit of the voltage window, or discharged to below the lower limit of the voltage window, the product may have unstable structure and performance. The upper and lower limits of the voltage window of the product after the formation treatment can be confirmed according to the material and structural properties of the product.

In some embodiments, between charging and discharging, the charged product is allowed to stand. Optionally, the standing time is 5 minutes to 30 minutes. For example, the standing time may be, but is not limited to, 5 minutes, 8 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes.

In a fifth aspect, the present application provides a battery module, which includes the secondary battery in the third aspect or the secondary battery prepared by the method for preparing the secondary battery in the fourth aspect.

In a sixth aspect, the present application provides a battery pack, which includes the secondary battery of the third aspect, or the secondary battery prepared by the method for preparing the secondary battery of the fourth aspect, or the battery module of the fifth aspect.

The seventh aspect of the present application provides an electric device, which includes at least one of the secondary battery of the third aspect, the secondary battery prepared by the method for preparing the secondary battery of the fourth aspect, the battery module of the fifth aspect, and the battery pack of the sixth aspect.

The secondary battery, battery module, battery pack, and electric device of the present application are described below with reference to the accompanying drawings as appropriate.

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.

Positive electrode

The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active layer includes a positive electrode active material.

As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode active layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

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.).

As an example, the positive electrode active material may include a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, 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. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO ₂ ), lithium nickel oxide (such as LiNiO ₂ ), lithium manganese oxide (such as LiMnO ₂ , LiMn ₂ O ₄ ), 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 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also referred to as NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also referred to as NCM ₂₁₁ ), LiNi _0.6 Co 0.2 Mn _0.2 O ₂ (also referred to as NCM ₆₂₂ ), LiNi 0.8 Co _0.1 Mn 0.1 O 2 (also referred to as NCM 811 ), and LiNi _0.8 Co _0.2 Mn _0.2 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and its modified compounds. Examples of lithium phosphates containing olivine structure may include but are not limited to lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. The weight ratio of the positive electrode active material in the positive electrode film layer is 80 to 100 weight %, based on the total weight of the positive electrode active layer.

In some embodiments, the positive electrode active layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. The weight ratio of the binder in the positive electrode active layer is 0 to 20 weight %, based on the total weight of the positive electrode active layer.

In some embodiments, the positive electrode active layer may further include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode active layer is 0 to 20 weight %, based on the total weight of the positive electrode active layer.

In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry, wherein the positive electrode slurry has a solid content of 40 to 80 wt%, and the viscosity at room temperature is adjusted to 5000 to 25000 mPa·s, the positive electrode slurry is coated on the surface of the positive electrode collector, and after drying, the positive electrode sheet is formed by cold rolling; the positive electrode powder coating unit area density is 150 to 350 mg/m ² , and the positive electrode sheet compaction density is 3.0 to 3.6 g/cm ³ , and can be 3.3 to 3.5 g/cm ^3. The calculation formula of compaction density is: compaction density = coating area density/(thickness of the sheet after extrusion-thickness of the current collector).

It is understandable that in the embodiment of the present application, the positive electrode plate may include a first active layer and a second active layer, wherein the first active layer is located on at least one surface of the positive electrode collector, the second active layer is located on the first active layer, and the electronic conductivity of the first active layer is less than the electronic conductivity of the second active layer.

Negative electrode

The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material.

As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active layer is disposed on any one or both of the two facing surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a 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.).

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 at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. The tin-based material may be selected from at least one 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. The weight ratio of the negative electrode active material in the negative electrode active layer is 70 to 100% by weight, based on the total weight of the negative electrode active layer.

In some embodiments, the negative electrode active layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS). The weight ratio of the binder in the negative electrode active layer is 0 to 30% by weight, based on the total weight of the negative electrode active layer.

In some embodiments, the negative electrode active layer may further include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The weight ratio of the conductive agent in the negative electrode active layer is 0 to 20 weight %, based on the total weight of the negative electrode active layer.

In some embodiments, the negative electrode active layer may further include other additives, such as a thickener (such as sodium carboxymethyl cellulose (CMC-Na)), etc. The weight ratio of the other additives in the negative electrode film layer is 0 to 15 weight %, based on the total weight of the negative electrode active layer.

In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30-70wt%, and the viscosity at room temperature is adjusted to 2000-10000mPa·s; the obtained negative electrode slurry is coated on the negative electrode collector, and after a drying process, cold pressing such as rolling, a negative electrode sheet is obtained. The negative electrode powder coating unit area density is 75-220mg/ ^m2 , and the negative electrode sheet compaction density is 1.2-2.0g/ ^m3 .

It is understandable that in the embodiment of the present application, the negative electrode plate may include a first active layer and a second active layer, wherein the first active layer is located on at least one surface of the negative electrode current collector, the second active layer is located on the first active layer, and the electronic conductivity of the first active layer is less than the electronic conductivity of the second active layer.

Electrolytes

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.

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

In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP). The concentration of the electrolyte salt is generally 0.5 to 5 mol/L.

In some embodiments, the solvent can be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

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.

Isolation film

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.

In some embodiments, the material of the isolation membrane can be selected from at least one 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.

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.

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

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 as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. may be listed. The present application has no particular restrictions on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG. 3 is a secondary battery 5 of a square structure as an example.

In some embodiments, referring to FIG. 4 , the outer package 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 film 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.

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.

FIG5 is a battery module 4 as an example. Referring to FIG5 , in the battery module 4, a 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.

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.

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.

FIG6 and FIG7 are battery packs 1 as an example. Referring to FIG6 and FIG7 , 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, and the upper box body 2 can be covered on the lower box body 3 to 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.

In addition, the present application also provides an electrical device, which includes at least one 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.

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

FIG8 is an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

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.

Example

In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

Embodiment 1:

Preparation of the positive electrode body:

The nickel-cobalt-manganese (NCM) ternary material, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are stirred and mixed evenly in a weight ratio of 97.44:1.3:1.3 to obtain a positive electrode slurry; the positive electrode slurry is then evenly coated on the positive electrode collector, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

Preparation of negative electrode sheet:

Artificial graphite, conductive agent carbon black, binder styrene butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), and electronic conductivity inhibitor are dissolved in solvent deionized water according to a weight ratio of 93.1:0.7:2.3:1.2:2.7, and mixed evenly to prepare a first active slurry. Among them, the electronic conductivity inhibitor is styrene butadiene rubber.

Artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber, and thickener sodium hydroxymethyl cellulose were dissolved in solvent deionized water at a weight ratio of 97.3:0.7:0.8:1.2, and the mixture was evenly mixed to prepare a second active slurry.

The first active slurry is applied to the surface of the current collector copper foil and dried to form a first active layer. Then the second slurry is applied on the first active layer, dried, cold pressed, and cut to obtain a negative electrode sheet.

Preparation of electrolyte:

In an argon atmosphere glove box (H ₂ O<0.1ppm, O ₂ <0.1ppm), organic solvents ethylene carbonate (EC)/ethyl methyl carbonate (EMC) were mixed evenly in a volume ratio of 3/7, 1 mol/L LiPF6 lithium salt was added and dispersed evenly, and stirred evenly to obtain an electrolyte.

Isolation film:

Polypropylene film is used as the isolation film.

Preparation of secondary batteries:

The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then the bare cell is wound, the tabs are welded to the bare cell, and the bare cell is placed in an aluminum shell, and baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery is then subjected to static, hot and cold pressing in turn to obtain a secondary battery pre-finished product, and then the battery pre-finished product is subjected to formation treatment. After the formation treatment, the voltage of the battery product is 2.5V.

Example 2

Compared with Example 1, Example 2 is different in that artificial graphite, conductive agent carbon black, binder styrene butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), and electronic conductivity inhibitor are dissolved in solvent deionized water at a weight ratio of 96.1:0.7:1.7:1.2:0.3, and mixed evenly to prepare a first active slurry. Among them, the electronic conductivity inhibitor is styrene butadiene rubber.

Example 3

Compared with Example 1, Example 3 is different in that artificial graphite, conductive agent carbon black, binder styrene butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), and electronic conductivity inhibitor are dissolved in solvent deionized water at a weight ratio of 95.1:0.7:2.3:1.2:0.7, and mixed evenly to prepare a first active slurry. Among them, the electronic conductivity inhibitor is styrene butadiene rubber.

Example 4

Compared with Example 1, Example 4 is different in that artificial graphite, conductive agent carbon black, binder styrene butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), and electronic conductivity inhibitor are dissolved in solvent deionized water at a weight ratio of 92.1:0.7:2.3:1.2:3.7, and mixed evenly to prepare a first active slurry. Among them, the electronic conductivity inhibitor is styrene butadiene rubber.

Example 5

Compared with Example 1, Example 5 is different in that the electronic conductivity inhibitor is barium titanate.

Example 6

Compared with Example 1, Example 6 is different in that the electronic conductivity inhibitor is lithium titanate.

Example 7

Compared with Example 1, Example 7 is different in that artificial graphite, conductive agent carbon black, binder styrene butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), electronic conductivity inhibitor, and lithium-philic material are dissolved in solvent deionized water at a weight ratio of 93.1:0.7:2.3:1.2:1.7:1, and mixed evenly to prepare a first active slurry. Among them, the electronic conductivity inhibitor is styrene butadiene rubber, and the lithium-philic material is zinc oxide.

Example 8

Compared with Example 7, the difference of Example 8 is that the lithium-philic material is magnesium oxide.

Example 9

Compared with Example 7, the difference of Example 9 is that the lithium-philic material is silver.

Example 10

Compared with Example 7, the difference of Example 10 is that the lithium-philic material is tin.

Embodiment 11

Compared with Example 5, Example 11 is different in that artificial graphite, conductive agent carbon black, binder styrene butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), electronic conductivity inhibitor, and lithium-philic material are dissolved in solvent deionized water at a weight ratio of 93.1:0.7:2.3:1.2:1.7:1, and mixed evenly to prepare a first active slurry. Among them, the electronic conductivity inhibitor is barium titanate, and the lithium-philic material is zinc oxide.

Example 12

Compared with Example 11, the difference of Example 12 is that the lithium-philic material is magnesium oxide.

Example 13

Compared with Example 11, Example 13 is different in that the lithium-philic material is silver.

Embodiment 14

Compared with Example 11, the difference of Example 14 is that the lithium-philic material is tin.

Embodiment 15

Compared with Example 6, Example 15 is different in that the first active material artificial graphite, the conductive agent carbon black, the first binder styrene butadiene rubber (SBR), the thickener sodium hydroxymethyl cellulose (CMC), the electronic conductivity inhibitor, and the lithium-philic material are dissolved in the solvent deionized water at a weight ratio of 93.1:0.7:2.3:1.2:1.7:1, and mixed evenly to prepare the first active slurry. Among them, the electronic conductivity inhibitor is lithium titanate, and the lithium-philic material is zinc oxide.

Example 16

Compared with Example 15, the difference of Example 16 is that the lithium-philic material is magnesium oxide.

Embodiment 17

Compared with Example 15, the difference of Example 17 is that the lithium-philic material is silver.

Embodiment 18

Compared with Example 15, the difference of Example 18 is that the lithium-philic material is tin.

Embodiment 19

Compared with Example 9, the difference of this example is that artificial graphite, conductive agent carbon black, binder styrene butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), electronic conductivity inhibitor, and lithium-philic material are dissolved in solvent deionized water at a weight ratio of 94.5:0.7:2.3:1.2:0.3:1, and mixed evenly to prepare a first active slurry. Among them, the electronic conductivity inhibitor is styrene butadiene rubber, and the lithium-philic material is silver.

Embodiment 20

Compared with Example 19, the difference of this embodiment is that artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), electronic conductivity inhibitor, and lithium-philic material are dissolved in solvent deionized water in a weight ratio of 92.1:0.7:2.3:1.2:2.7:1, and the first active slurry is prepared after uniform mixing.

Embodiment 21

Compared with Example 19, the difference of this embodiment is that artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), electronic conductivity inhibitor, and lithium-philic material are dissolved in solvent deionized water in a weight ratio of 84.8:0.7:2.3:1.2:10:1, and the first active slurry is prepared after uniform mixing.

Embodiment 22

Compared with Example 19, the difference of this embodiment is that artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), electronic conductivity inhibitor, and lithium-philic material are dissolved in solvent deionized water in a weight ratio of 83.8:0.7:2.3:1.2:10:2, and the first active slurry is prepared after uniform mixing.

Embodiment 23

Compared with Example 19, the difference of this embodiment is that artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), electronic conductivity inhibitor, and lithium-philic material are dissolved in solvent deionized water in a weight ratio of 80.8:0.7:2.3:1.2:10:5, mixed evenly and prepared into a first active slurry.

Comparative Example 1

Compared with Example 1, the difference of Comparative Example 1 is:

Artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium hydroxymethyl cellulose (CMC) were dissolved in solvent deionized water at a weight ratio of 95.8:0.7:2.3:1.2, and mixed evenly to prepare a first active slurry.

Artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium hydroxymethyl cellulose (CMC) were dissolved in solvent deionized water at a weight ratio of 97.3:0.7:0.8:1.2, and mixed evenly to prepare a second active slurry.

Comparative Example 2

Compared with Example 1, Comparative Example 2 is different in that the electronic conductive agent is replaced by zinc oxide.

Comparative Example 3

Compared with Example 9, the difference of this comparative example is that artificial graphite, conductive agent carbon black, binder styrene butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), electronic conductivity inhibitor, and lithium-philic material are dissolved in solvent deionized water according to a weight ratio of 95.2:0.7:2.3:1.2:0.1:0.5, and mixed evenly to prepare a first active slurry. Among them, the electronic conductivity inhibitor is styrene butadiene rubber, and the lithium-philic material is silver.

Comparative Example 4

Compared with Example 9, the difference of this comparative example is that artificial graphite, conductive agent carbon black, binder styrene butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), electronic conductivity inhibitor, and lithium-philic material are dissolved in solvent deionized water according to a weight ratio of 74.8:0.7:2.3:1.2:15:6, and mixed evenly to prepare a first active slurry. Among them, the electronic conductivity inhibitor is styrene butadiene rubber, and the lithium-philic material is silver.

Test Example 1

The secondary batteries in the examples and comparative examples were charged to 4.4 V at 3 C at 45° C., left to stand for 10 min, and then discharged to 2.5 V at 1 C. The batteries were cycled 1000 times under this condition, and the capacity retention rate after 1000 cycles was measured.

Test Example 2

The secondary batteries in the examples and comparative examples were charged to 4.4 V at 1 C at 25° C., left to stand for 10 min, and then discharged to 2.5 V at 1 C. The batteries were cycled 1000 times under this condition, and the capacity retention rate after 1000 cycles was measured.

The test results of the embodiments and comparative examples are shown in Table 1.

Table 1

It can be seen from Table 1 that in the examples, by introducing a suitable amount of electronic conductivity inhibitor and/or lithium-philic material, the battery has a better cycle performance.

The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims (16)

An electrode plate, characterized in that it includes a current collector, a first active layer and a second active layer, the first active layer is located on at least one surface of the current collector, the second active layer is located on the first active layer, and the electronic conductivity of the first active layer is less than the electronic conductivity of the second active layer. The electrode plate according to claim 1, characterized in that the first active layer comprises a first active material and an electronic conductivity inhibitor; Optionally, the electronic conductivity suppressor includes at least one of styrene-butadiene rubber, barium titanate and lithium titanate. The electrode plate according to claim 2 is characterized in that the mass percentage of the electronic conductivity inhibitor in the first active layer is 0.3% to 10%. The electrode plate according to any one of claims 2 to 3, characterized in that the first active layer further comprises a lithium-philic material; Optionally, the lithium-philic material includes at least one of zinc oxide, magnesium oxide, silver and tin. The electrode plate according to claim 4, characterized in that the mass percentage of the lithium-philic material in the first active layer is 1% to 5%. The electrode plate according to any one of claims 2 to 5, characterized in that the second active layer comprises a second active material, and the second active material is the same as or different from the first active material. The method for preparing an electrode sheet according to any one of claims 1 to 6, characterized in that it comprises the following steps: The first active layer is formed on at least one surface of the current collector, and the second active layer is formed on the first active layer. The method for preparing an electrode plate according to claim 7 is characterized in that the first active layer and the second active layer are each independently formed using a corresponding active slurry, optionally by coating. A secondary battery, characterized by comprising the electrode sheet according to any one of claims 1 to 6 or the electrode sheet prepared by the method for preparing the electrode sheet according to any one of claims 7 to 8. The method for preparing a secondary battery according to claim 9, characterized in that it comprises the following steps: The secondary battery pre-product equipped with the electrode plate is subjected to a formation treatment. The method for preparing a secondary battery according to claim 10, characterized in that after the formation treatment, it further comprises: At 40°C to 50°C, the product after the formation treatment is charged from the lower limit of its voltage window to the upper limit of its voltage window, and then discharged to the lower limit of its voltage window. The method for preparing a secondary battery according to claim 11, characterized in that the product after the formation treatment is charged from the lower limit of its voltage window to the upper limit of its voltage window, and then discharged to the lower limit of its voltage window to meet at least one of the following characteristics: (1) The lower limit of the voltage window is 2.3V to 2.7V; (2) The upper limit of the voltage window is 4.4V to 4.6V; (3) The charging current is 1C to 3C; (4) The discharge current is 1C to 3C. The method for preparing a secondary battery according to any one of claims 11 to 12, characterized in that, between the charging and the discharging, the method further comprises: Allowing the charged product to stand still; Optionally, the standing time is 5 min to 30 min. A battery module, characterized by comprising the secondary battery according to claim 9 or a secondary battery prepared by the method for preparing a secondary battery according to any one of claims 10 to 13. A battery pack, characterized in that it comprises the secondary battery according to claim 9, or a secondary battery prepared by the method for preparing a secondary battery according to any one of claims 10 to 13, or a battery module according to claim 14. An electrical device, characterized in that it comprises at least one of the secondary battery according to claim 9, the secondary battery prepared by the method for preparing a secondary battery according to any one of claims 10 to 13, the battery module according to claim 14, and the battery pack according to claim 15.