Negative electrode sheet, secondary battery, and electric device

Abstract

The application belongs to the technical field of batteries, and particularly relates to a negative pole piece, a secondary battery and an electric device. The negative pole piece comprises a current collector and a negative film layer, the negative film layer comprises a first negative film layer and a second negative film layer, the first negative film layer is located on at least one side surface of the current collector, the second negative film layer is located on the surface of the first negative film layer away from the current collector, the first negative film layer comprises first negative active particles, the first negative active particles are graphitized carbon, the second negative film layer comprises second negative active particles, the second negative active particles have a core-shell structure, the core of the core-shell structure is graphitized carbon, and the shell of the core-shell structure is aluminum oxide; wherein the compaction density of the first negative active particles under the same condition is greater than the compaction density of the second negative active particles. The negative pole piece designed in the application can be used to balance the direct current impedance, rate capability and energy density and other performances of the battery.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] Secondary batteries are widely used in various consumer electronics and electric vehicles due to their outstanding characteristics such as light weight, no pollution, and no memory effect. Among them, lithium-ion batteries have a very wide range of applications in portable electronic devices and electric vehicles.

[0003] As the application of rechargeable batteries becomes more and more widespread, the requirements for battery performance are also becoming higher and higher. Summary of the Invention

[0004] This application provides a negative electrode sheet, a secondary battery, and an electrical device. The negative electrode sheet designed in this application is used to balance the overall performance of the battery, such as balancing energy density and fast charging performance to a certain extent.

[0005] In a first aspect, this application provides a negative electrode sheet, comprising:

[0006] current collector;

[0007] Negative electrode film layer: comprising a first negative electrode film layer and a second negative electrode film layer, wherein the first negative electrode film layer is located on at least one side surface of the current collector; and the second negative electrode film layer is located on the surface of the first negative electrode film layer away from the current collector.

[0008] The first negative electrode film layer contains first negative electrode active particles, which are graphitized carbon.

[0009] The second negative electrode film layer contains second negative electrode active particles. The second negative electrode active particles have a core-shell structure. The core of the core-shell structure is graphitized carbon, and the shell of the core-shell structure is aluminum oxide.

[0010] Under the same conditions, the compaction density of the first negative electrode active particle is greater than that of the second negative electrode active particle.

[0011] The first and second negative electrode layers of this application use different types of active materials. Therefore, electron conduction is stronger in the first negative electrode layer than in the second, while ion diffusion is stronger in the second. This application places the first negative electrode layer closer to the current collector and the second negative electrode layer further away. The second negative electrode layer, positioned further away from the current collector, facilitates contact with the electrolyte and promotes rapid electrolyte diffusion within it. The first negative electrode layer, positioned closer to the current collector, facilitates rapid electron transfer between the current collector and the first negative electrode layer. This helps alleviate the problem of increased DC resistance (DCR) caused by the second negative electrode layer. Furthermore, it improves rate performance from the perspectives of ion diffusion and electron transfer. Simultaneously, the compaction density of the second negative electrode layer decreases due to the type of active material it uses; however, this decrease can be compensated for by the first negative electrode layer, thereby improving the energy density of the negative electrode. Therefore, the negative electrode designed in this application can be used to balance various performance aspects such as DC resistance, rate performance, and energy density.

[0012] In some embodiments of this application, the negative electrode film layer satisfies one or two of the following:

[0013] (1.1) The first negative electrode active particle has a compaction density ρ1 of 5 tons of powder, and ρ1 is 1.85 g / cm³. 3 ~2.05g / cm 3 The second negative electrode active particles have a compacted density ρ2 of 5 tons of powder, with ρ2 being 1.60 g / cm³. 3 ~1.80g / cm 3 ;

[0014] (1.2) Based on the total mass of the second negative electrode active particles, the mass percentage content of alumina is 0.5%~5%;

[0015] (1.3) Graphitized carbon includes any one of natural graphite, artificial graphite, composite graphite or mesophase carbon microspheres.

[0016] In some embodiments of this application, the mass percentage content of alumina is 1% to 2% based on the total mass of the second negative electrode active particles.

[0017] In some embodiments of this application, the negative electrode film layer satisfies one or more of the following:

[0018] (2.1) The specific capacity of the first negative electrode active particle is A1, and the specific capacity of the second negative electrode active particle is A2, satisfying A1 > A2;

[0019] (2.2) The orientation degree OI value of the first negative electrode active particle is OI1, and the orientation degree OI value of the second negative electrode active particle is OI2; satisfying OI1>OI2;

[0020] (2.3) The median particle size of the first negative electrode active particle is Dv150, and the median particle size of the second negative electrode active particle is Dv250; satisfying: Dv150>Dv250;

[0021] (2.4) The specific surface area of ​​the first negative electrode active particle is S1, and the specific surface area of ​​the second negative electrode active particle is S2; satisfying: S1 < S2;

[0022] (2.5) The tap density of the first negative electrode active particle is ρr1, and the tap density of the second negative electrode active particle is ρr2; satisfying: ρr1>ρr2.

[0023] In some embodiments of this application, the second negative electrode active particle satisfies one or more of the following:

[0024] (3.1) The specific capacity A2 of the second negative electrode active particles is 350 mAh / g ~ 358 mAh / g;

[0025] (3.2) The orientation degree OI2 of the second negative electrode active particles is 2~8;

[0026] (3.3) The median particle size Dv250 of the second negative electrode active particles is 8μm~16μm;

[0027] (3.4) The specific surface area S2 of the second negative electrode active particle is 2.0 m². 2 / g~4.0m 2 / g;

[0028] (3.5) The tap density ρr2 of the second negative electrode active particles is 0.90 g / cm³. 3 ~1.20g / cm 3 .

[0029] In some embodiments of this application, the second negative electrode active particle satisfies one or more of the following:

[0030] (4.1) The specific capacity A2 of the second negative electrode active particles is 350 mAh / g ~ 355 mAh / g;

[0031] (4.2) The orientation degree OI2 of the second negative electrode active particles is 3~6;

[0032] (4.3) The median particle size Dv250 of the second negative electrode active particles is 9 μm to 15 μm;

[0033] (4.4) The specific surface area S2 of the second negative electrode active particle is 2.5 m². 2 / g~3.5m 2 / g;

[0034] (4.5) The tap density ρr2 of the second negative electrode active particles is 0.95 g / cm³. 3 ~1.15g / cm 3 .

[0035] In some embodiments of this application, the first negative electrode active particle satisfies one or more of the following:

[0036] (5.1) The specific capacity A1 of the first negative electrode active particle is 354 mAh / g~365 mAh / g;

[0037] (5.2) The orientation degree OI1 of the first negative electrode active particle is 5~20;

[0038] (5.3) The median particle size Dv150 of the first negative electrode active particles is 12 μm ~ 20 μm;

[0039] (5.4) The specific surface area S1 of the first negative electrode active particle is 1.2 m². 2 / g~2.0m 2 / g;

[0040] (5.5) The tap density ρr1 of the first negative electrode active particle is 0.95 g / cm³. 3 ~1.30g / cm 3 .

[0041] In some embodiments of this application, the first negative electrode active particle satisfies one or more of the following:

[0042] (6.1) The specific capacity A1 of the first negative electrode active particle is 360 mAh / g~365 mAh / g;

[0043] (6.2) The orientation degree OI1 of the first negative electrode active particle is 8~15;

[0044] (6.3) The median particle size Dv150 of the first negative electrode active particles is 14 μm to 18 μm;

[0045] (6.4) The specific surface area S1 of the first negative electrode active particle is 1.4 m². 2 / g~1.8 m 2 / g;

[0046] (6.5) The tap density ρr1 of the first negative electrode active particle is 1.0 g / cm³. 3 ~1.2 g / cm 3 .

[0047] In some embodiments of this application, the thickness of the negative electrode film is H, and the thickness of the first negative electrode film is 0.4H to 0.8H;

[0048] The thickness of the second negative electrode film is 0.2H~0.6H.

[0049] In some embodiments of this application, the negative electrode film layer satisfies one or two of the following:

[0050] (7.1) The compaction density of the negative electrode film layer is ≥1.45 g / cm³. 3 ;

[0051] (7.2) The areal density of the negative electrode film is ≥6.5 mg / cm³. 2 .

[0052] In some embodiments of this application, the negative electrode film layer satisfies one or two of the following:

[0053] (8.1) The compaction density of the negative electrode film is 1.55 g / cm³. 3 ~1.65g / cm 3 ;

[0054] (8.2) The areal density of the negative electrode film is 8 mg / cm³. 2 ~15mg / cm 2 .

[0055] A second aspect of this application is to provide a secondary battery, including the negative electrode sheet described in the first aspect.

[0056] A third aspect of this application is to provide an electrical device, comprising the negative electrode sheet described in the first aspect or the secondary battery described in the second aspect.

[0057] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0058] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0059] Figure 1 This is a schematic diagram of the battery structure of some embodiments of this application;

[0060] Figure 2 This is an exploded structural diagram of a battery according to some embodiments of this application;

[0061] Figure 3 This is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0062] Figure 4 This is a schematic diagram of the battery pack structure of some embodiments of this application;

[0063] Figure 5A This is a schematic diagram of the structure of a negative electrode sheet according to some embodiments of this application;

[0064] Figure 5B This is a schematic diagram of the structure of another negative electrode sheet according to some embodiments of this application;

[0065] Figure 6 This is a schematic diagram of the structure of another negative electrode sheet according to some embodiments of this application;

[0066] Figure 7 Here are SEM images of the first negative electrode active particles in some embodiments of this application;

[0067] Figure 8 Here are SEM images of the second negative electrode active particles in some embodiments of this application;

[0068] Figure 9 EDS diagrams of the second negative electrode active particles in some embodiments of this application.

[0069] The reference numerals in the detailed embodiments are as follows:

[0070] 10000, vehicles;

[0071] 1000, Battery; 2000, Controller; 3000, Motor;

[0072] 100. Battery cell;

[0073] 200. Box body; 210. First part; 220. Second part;

[0074] 10. Secondary batteries;

[0075] 101. Housing; 102. Electrode assembly; 103. Cover plate;

[0076] 1. Negative electrode plate;

[0077] 11. Negative electrode current collector;

[0078] 12. Negative electrode film;

[0079] 12a. First negative electrode film layer;

[0080] 12b. Second negative electrode film layer;

[0081] The x-axis of the coordinate axis represents the length or width of the negative electrode sheet.

[0082] The z-axis of the coordinate axis represents the thickness direction of the negative electrode sheet.

[0083] H: Thickness of the negative electrode film;

[0084] H1: Thickness of the first negative electrode film;

[0085] H2: Thickness of the second negative electrode film. Detailed Implementation

[0086] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the electrode assembly, battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0087] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0088] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0089] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0090] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0091] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0092] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0093] Unless otherwise specified, in this application, the terms "first," "second," etc., are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features.

[0094] Unless otherwise specified, in this application, the term "multiple" means two or more (including two), similarly, "multiple sets" means two or more (including two sets), and "multiple pieces" means two or more (including two pieces).

[0095] Unless otherwise specified, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0096] Due to their advantages such as high energy density, long cycle life, and safety and reliability, secondary batteries have been widely used in various products. In recent years, with the significant increase in demand for secondary batteries as an energy source, higher requirements have been placed on their performance, such as kinetic performance.

[0097] Graphite is the most commonly used negative electrode active material in secondary batteries, but its kinetic properties are poor, especially during high-rate discharge, when the capacity of secondary batteries decays rapidly.

[0098] If it is possible to improve the dynamic performance of graphite while also reducing the DC resistance (DCR) of the electrode and improving the energy density of the battery, the performance of the secondary battery can be further improved.

[0099] Based on the above considerations, in order to solve the problems of increased DC resistance (DCR) and reduced energy density caused by coating graphite with alumina, a negative electrode, a secondary battery and an electrical device were obtained based on the above design concept and related experimental research.

[0100] First, this application discloses a negative electrode sheet comprising a current collector and a negative electrode film layer. The negative electrode film layer comprises a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is located on at least one side surface of the current collector; the second negative electrode film layer is located on the surface of the first negative electrode film layer away from the current collector. The first negative electrode film layer comprises a first negative electrode active particle, which is graphitized carbon. The second negative electrode film layer comprises a second negative electrode active particle, which has a core-shell structure, with the core being graphitized carbon and the shell being alumina. Under the same conditions, the compaction density of the first negative electrode active particle is greater than that of the second negative electrode active particle.

[0101] The first and second negative electrode layers of this application use different types of active materials. Therefore, electron conduction is stronger in the first negative electrode layer than in the second, while ion diffusion is stronger in the second. This application places the first negative electrode layer closer to the current collector and the second negative electrode layer further away. The second negative electrode layer, positioned further away from the current collector, facilitates contact with the electrolyte and promotes rapid electrolyte diffusion within it. The first negative electrode layer, positioned closer to the current collector, facilitates rapid electron transfer between the current collector and the first negative electrode layer. This helps alleviate the problem of increased DC resistance (DCR) caused by the second negative electrode layer. Furthermore, it improves rate performance from the perspectives of ion diffusion and electron transfer. Simultaneously, the compaction density of the second negative electrode layer decreases due to the type of active material it uses; however, this decrease can be compensated for by the first negative electrode layer, thereby improving the energy density of the negative electrode. Therefore, the negative electrode designed in this application can be used to balance various performance aspects such as DC resistance, rate performance, and energy density.

[0102] The negative electrode sheet provided in this application is used to form a battery, achieving the technical purpose of improving battery performance. For example, it improves the battery's rate capability, allowing for high-current charging and discharging, and reduces internal DC resistance, resulting in better power performance. It also improves the battery's energy density. The battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte, wherein the electrode assembly includes the aforementioned negative electrode sheet. The battery outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The battery outer packaging can also be a soft pack, such as a pouch. The soft pack material can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0103] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 10.

[0104] According to some embodiments of this application, reference is made to Figure 2 The outer packaging may include a housing 101 and a cover plate 103. The housing 101 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 101 has an opening communicating with the receiving cavity, and the cover plate 103 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 102 by a winding process or a stacking process. The electrode assembly 102 is encapsulated within the receiving cavity. The electrolyte is immersed in the electrode assembly 102. The secondary battery 10 may contain one or more electrode assemblies 102, which can be selected by those skilled in the art according to specific practical needs.

[0105] The electrode assembly provided in this application is beneficial for improving battery performance when applied in a battery. The battery can be used as a power source for an electrical device or as an energy storage unit for an electrical device. This electrical device is used in the power field, such as mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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 is not limited to the above fields.

[0106] For ease of explanation, some embodiments of this application are illustrated using a vehicle as an example of an electrical device. The negative electrode sheet provided in this application is used in a vehicle battery. Due to the battery's good power performance, the vehicle starts up quickly. On the other hand, the battery has high energy density, thus providing a longer driving range for the vehicle within a limited space.

[0107] Please refer to Figure 3 , Figure 3This is a schematic diagram of the structure of a vehicle 10000 provided in some embodiments of this application. The vehicle 10000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 1000 is disposed inside the vehicle 10000, and the battery 10000 can be located at the bottom, front, or rear of the vehicle 10000. The battery 10000 can be used to power the vehicle 10000; for example, the battery 10000 can serve as the operating power source for the vehicle 10000. The vehicle 10000 may also include a controller 2000 and a motor 3000. The controller 2000 is used to control the battery 10000 to supply power to the motor 3000, for example, to meet the power needs of the vehicle 10000 during startup, navigation, and driving.

[0108] In some embodiments of this application, the battery 1000 can not only serve as the operating power source for the vehicle 10000, but also as the driving power source for the vehicle 10000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 10000.

[0109] Please refer to Figure 4 , Figure 4 This is an exploded view of a battery 1000 provided in some embodiments of this application. The battery 1000 includes a housing 200 and a battery cell 100. A conventional battery cell includes a primary battery or a secondary battery. This application specifically protects a secondary battery. The battery cell 100 is housed within the housing 200. The housing 200 provides space for the battery cell 100, and the housing 200 can adopt various structures.

[0110] In some embodiments, the housing 200 may include a first portion 210 and a second portion 220, which overlap each other, and together define a receiving space for accommodating the secondary battery 10. The second portion 220 may be a hollow structure with one open end, and the first portion 210 may be a plate-like structure, with the first portion 210 covering the open side of the second portion 220 so that the first portion 210 and the second portion 220 together define the receiving space; alternatively, the first portion 210 and the second portion 220 may both be hollow structures with one open side, with the open side of the first portion 210 covering the open side of the second portion 220. Of course, the housing 200 formed by the first portion 210 and the second portion 220 may be of various shapes, such as a cylinder, a cuboid, etc.

[0111] In battery 1000, there can be multiple battery cells 100, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 100 are connected in both series and parallel configurations. Multiple battery cells 100 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 100 is housed within housing 200. Alternatively, battery 1000 can also be composed of multiple battery cells 100 first connected in series, parallel, or in a mixed manner to form battery modules, and then these modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within housing 200. Battery 1000 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 100.

[0112] Negative electrode sheet

[0113] This application discloses a negative electrode sheet in some embodiments, such as Figure 5A , Figure 5B The diagram illustrates that the negative electrode 1 includes a current collector 11 and a negative electrode film 12. The negative electrode film 12 includes a first negative electrode film 12a and a second negative electrode film 12b. The first negative electrode film 12a is located on at least one side surface of the current collector 11, and the second negative electrode film 12b is located on the surface of the first negative electrode film 12a away from the current collector 11. The first negative electrode film 12a includes a first negative electrode active particle, which is graphitized carbon. The second negative electrode film 12b includes a second negative electrode active particle, which has a core-shell structure. The core of the core-shell structure is graphitized carbon, and the shell of the core-shell structure is alumina. Under the same conditions, the compaction density of the first negative electrode active particle is greater than that of the second negative electrode active particle.

[0114] Figure 5 illustrates the positional relationship between the first negative electrode film, the second negative electrode film, and the current collector in this application. This positional arrangement is influenced by the different types of active materials in each film layer. The second negative electrode film, positioned further away from the current collector, facilitates contact with the electrolyte and promotes rapid diffusion of the electrolyte within it. Conversely, the first negative electrode film, positioned closer to the current collector, facilitates rapid electron transfer between the current collector and the first negative electrode film. This helps alleviate the problem of increased DC resistance (DCR) caused by the second negative electrode film. Furthermore, it improves rate performance from the perspectives of ion diffusion and electron transfer.

[0115] The graphitized carbon in this application is a commonly used carbon material for negative electrode sheets. This application improves this carbon material to alleviate the problem of increased DC resistance (DCR).

[0116] The second negative electrode active particle of this application has a core-shell structure, wherein alumina serves as the shell and is uniformly coated on the surface of graphitized carbon, and the uniformity of the alumina coating is affected by its content. On the one hand, the coating improves the wettability between the second negative electrode active particle and the electrolyte to improve rate performance; on the other hand, it improves cycle performance by reducing side reactions between the second negative electrode active particle and the electrolyte.

[0117] The "same conditions" in this application include measuring the compaction density of each active particle under the same test conditions. Here, compaction density includes any concept conventional in the art. Generally speaking, compaction density is considered one of the reference indicators of a material's energy density; the higher the value, the greater the energy density. Compaction density is related not only to the material's inherent properties but also to the particle size distribution. The compaction density of each material can be obtained using instruments or methods known in the art, such as limiting the cold-pressing pressure to 5 tons and calculating it according to the measurement method in GB / T 24533-2009. On the other hand, due to the inherent properties of the active particles of each negative electrode in this application, the porosity of the first negative electrode film layer and the second negative electrode film layer is different under the same compaction density. This is mainly manifested in the fact that the porosity of the second negative electrode film layer is greater than that of the first negative electrode film layer. This is because the active particles in the second negative electrode film layer are more difficult to compress than those in the first negative electrode film layer. After the electrode is cold-pressed, the second negative electrode film layer releases more stress, which is manifested as an increase in porosity. This difference in porosity further promotes the faster diffusion rate of ions in the second negative electrode film layer than in the first negative electrode film layer. At the same time, the second negative electrode film layer preferentially contacts the electrolyte, which is conducive to the embedding of lithium ions into the active material and makes it less likely for lithium to be deposited on the surface of the electrode, thereby further improving the impedance.

[0118] While the second negative electrode film in this application achieves the aforementioned technical effects of improving rate capability and cycle performance, the compressive strength of alumina can easily lead to a decrease in its compaction density. This application addresses this by adding a first negative electrode film between the current collector and the second negative electrode film. This not only alleviates the problem of increased DC resistance (DCR) caused by the second negative electrode film but also compensates for the decrease in compaction density caused by it. Ultimately, this achieves the goal of improving the energy density of the negative electrode.

[0119] In summary, the negative electrode plate designed in this application can be used to balance various properties such as DC impedance, rate capability, and energy density.

[0120] In some embodiments of this application, the negative electrode film layer satisfies one or two of the following:

[0121] (1.1) The first negative electrode active particle has a compaction density ρ1 of 5 tons of powder, and ρ1 is 1.85 g / cm³. 3 ~2.05g / cm 3The second negative electrode active particles have a compacted density ρ2 of 5 tons of powder, with ρ2 being 1.60 g / cm³. 3 ~1.80g / cm 3 ;

[0122] (1.2) Based on the total mass of the second negative electrode active particles, the mass percentage content of alumina is 0.5%~5%;

[0123] (1.3) Graphitized carbon includes any one of natural graphite, artificial graphite, composite graphite or mesophase carbon microspheres.

[0124] The compacted density of the negative electrode active particles in this application, measured over 5 tons, is determined using an electronic pressure testing instrument (e.g., UTM7305) in accordance with GB / T 24533-2009. Specifically, a specific amount M of the powder sample to be tested is placed on a special mold (bottom area S0), and different pressures are set. Each pressure is maintained for 30 seconds, then released. After 10 seconds, the thickness H0 of the powder compressed under that pressure is read on the device. The compacted density under that pressure is calculated, and the compacted density of the negative electrode material under that pressure is equal to M / (H0×S0). The first negative electrode active particle in this application has a compacted density ρ1 of 1.85 g / cm³ over 5 tons. 3 ~2.05g / cm 3 The second negative electrode active particles have a compacted density ρ2 of 1.60 g / cm³. 3 ~1.80g / cm 3 The requirement is that the compacted density of the first negative electrode active particle is greater than that of the second negative electrode active particle under the same conditions, which is beneficial for both to work synergistically to balance various performance aspects such as DC impedance, rate capability, and energy density. In these embodiments, this application discloses that the compacted density ρ1 of the first negative electrode active particle (5 tons of powder) can be 1.85 g / cm³. 3 1.90 g / cm 3 1.95g / cm 3 2.0g / cm 3 2.05g / cm 3 Any one of the above values ​​or satisfying any of the above range values. The second negative electrode active particles have a powder compaction density ρ2 of 5 tons, which can be 1.60 g / cm³. 3 1.65g / cm 3 1.70 g / cm 3 1.75g / cm 3 1.80 g / cm 3 Any one of the above values ​​or any one of the above range values.

[0125] In this application, the mass percentage content of alumina can be obtained by taking microscopic photographs of the second negative electrode active particles, such as obtaining their energy-dispersive X-ray spectra (EDS), and then statistically calculating the results. This application controls the mass percentage content of alumina to be between 0.5% and 5% to facilitate uniform coating of graphitized carbon. Uniformly coated second negative electrode active particles can improve electrolyte wettability and enhance the rate capability of fast charging. In these embodiments, this application discloses that the mass percentage content of alumina can be any one of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, or any value within the aforementioned range.

[0126] In some embodiments, this application discloses that the alumina content is 1% to 2% by mass. Alumina within this content range is easier to achieve from the perspective of formation method, and is also more conducive to the uniform coating of graphitized carbon.

[0127] The natural graphite, artificial graphite, composite graphite, or mesophase carbon microspheres in this application encompass any conventional preparation method in the art. In some embodiments, this application discloses graphitized carbon comprising artificial graphite, the preparation method of which includes: providing raw materials, crushing and shaping → granulation → graphitization treatment → surface roughening treatment to obtain artificial graphite material. The raw materials in these embodiments of this application can be one or more of raw coke and calcined coke; preferably, the raw materials include one or more of needle-shaped raw petroleum coke, non-needle-shaped raw petroleum coke, needle-shaped coal-based raw coke, non-needle-shaped coal-based raw coke, calcined needle-shaped coke, and calcined petroleum coke. The crushing in this application can be performed using equipment and methods known in the art, such as air jet mills, mechanical mills, or roller mills. During the crushing process, a large number of excessively small particles are usually generated, and sometimes excessively large particles are also produced. Therefore, after crushing, the particles can be classified as needed to remove excessively small and excessively large particles from the crushed powder. Classification yields granular products with a better particle size distribution, which is beneficial for subsequent molding and / or granulation processes. Grading can be performed using apparatus and methods known in the art, such as grading sieves, gravity classifiers, or centrifugal classifiers. Shaping in this application can be performed using equipment (e.g., molding machines or other molding equipment) and methods known in the art. For example, the edges of the resulting granular product can be polished to facilitate subsequent operations and improve the stability of the resulting product. Granulation in this application involves granulation using apparatus known in the art, such as a granulator. A granulator typically includes a stirred reactor and a reactor temperature control module. Furthermore, the median particle size of the resulting product can be controlled by adjusting process conditions during granulation, such as stirring speed, heating rate, granulation temperature, and cooling rate. Graphitization treatment in this application includes high-temperature graphitization treatment and low-temperature graphitization treatment. In some embodiments, any one or both of high-temperature and low-temperature graphitization treatments can be appropriately selected for treatment according to specific needs. Alternatively, high-temperature and / or low-temperature graphitization treatments can be repeated. High-temperature graphitization treatment can yield graphite with an appropriate degree of graphitization and interlayer spacing. Graphite prepared at appropriate graphitization temperatures can achieve suitable graphitization degrees and interlayer spacing, thereby enabling composite artificial graphite to obtain high structural stability and specific capacity. The surface roughening treatment in this application includes methods conventional in the art, such as physical methods.

[0128] This application discloses, in some embodiments, methods for preparing second negative electrode active particles, including sol-gel methods and heterogeneous nucleation methods.

[0129] The difference between the artificial graphite in the first negative electrode active particles and the second negative electrode active particles is mainly represented by the following orientation degree OI value.

[0130] In some embodiments, this application discloses that the negative electrode film layer satisfies one or more of the following:

[0131] (2.1) The specific capacity of the first negative electrode active particle is A1, and the specific capacity of the second negative electrode active particle is A2, satisfying A1 > A2;

[0132] (2.2) The orientation degree OI value of the first negative electrode active particle is OI1, and the orientation degree OI value of the second negative electrode active particle is OI2; satisfying OI1>OI2;

[0133] (2.3) The median particle size of the first negative electrode active particle is Dv150, and the median particle size of the second negative electrode active particle is Dv250; satisfying: Dv150>Dv250;

[0134] (2.4) The specific surface area of ​​the first negative electrode active particle is S1, and the specific surface area of ​​the second negative electrode active particle is S2; satisfying: S1 < S2;

[0135] (2.5) The tap density of the first negative electrode active particle is ρr1, and the tap density of the second negative electrode active particle is ρr2; satisfying: ρr1>ρr2.

[0136] The specific capacity mentioned in this application refers to the actual specific capacity, which is another reference indicator for the energy density of materials. However, the specific capacity of materials is usually mainly affected by their own properties. It involves fabricating each negative electrode active particle into a positive electrode sheet, using a lithium metal sheet as the negative electrode sheet of a coin cell, charging and discharging the coin cell, and recording the actual discharge capacity of the coin cell. Therefore, the specific capacity of each negative electrode active particle = the actual charge / discharge capacity of the coin cell / the actual mass of each negative electrode active particle. In this application, the specific capacity of each negative electrode active particle is affected by the type of material; the specific capacity of the first negative electrode active particle is greater than that of the second negative electrode active particle. Specifically, in these embodiments, this application discloses: mixing the prepared negative electrode active particles, conductive agent Super P, thickener (CMC-Na), and binder (SBR) in a mass ratio of 94.5:1.5:1.5:2.5 in deionized water to obtain a slurry. The prepared slurry is coated onto a copper foil current collector and dried in an oven for later use. A lithium metal plate is used as the counter electrode, and a polyethylene (PE) film is used as the separator. Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. LiPF6 was then uniformly dissolved in this solution to obtain an electrolyte with a LiPF6 concentration of 1 mol / L. All components were assembled into a CR2430 coin cell in an argon-protected glove box. After standing for 12 hours, the coin cell was discharged at a constant current of 0.05C to 0.005V, and then discharged again at a constant current of 10μA to 0.005V. After standing for 5 minutes, the coin cell was charged at a constant current of 0.1C to 2V, and then stood for 5 minutes. The charging capacity was recorded.

[0137] The orientation degree in this application includes graphite orientation degree, which is the ratio of the peak integral area of ​​the 004 / 110 crystal plane peaks, and can be used to characterize the overall isotropy of graphite. Generally speaking, graphite orientation degree is affected by the structural characteristics of the material itself, and the smaller the graphite orientation degree value, the more favorable it is for ion diffusion inside. In this application, the graphite orientation degree of the first negative electrode active particle is greater than that of the second negative electrode active particle, satisfying the requirement that the ion diffusion ability in the second negative electrode film layer is stronger than that in the first negative electrode film layer.

[0138] The median particle size Dv50 in this application includes particles with a diameter greater than 50% of the total volume and particles smaller than 50% of the total volume. Also known as the median diameter, it is commonly used to represent the average particle size. Dv50 can be measured using conventional methods in the art, such as using a particle size analyzer to determine the particle size distribution and then statistically analyzing it. In these embodiments, this application selects laser diffraction particle size analysis as the reference method, specifically referring to standard GB / T19077-2016 to obtain the particle size distribution map, and then calculating it. The median particle size Dv50 in this application affects compacted density, specific surface area, and tapped density. Generally speaking, under the same conditions, the larger the median particle size Dv50, the greater the compacted density and tapped density, and the smaller the specific surface area.

[0139] The specific surface area in this application includes any concept conventional in the art, which can be obtained by testing with instruments or methods known in the art, such as using the gas adsorption method to test the specific surface area, specifically according to the standard GB / T19587-2017.

[0140] The tap density in this application includes any concept conventional in the art, which can be obtained by testing with instruments or methods known in the art, such as by testing with reference to standard GB / T5162-2006.

[0141] In some embodiments, this application discloses that the second negative electrode active particle satisfies one or more of the following:

[0142] (3.1) The specific capacity A2 of the second negative electrode active particles is 350 mAh / g ~ 358 mAh / g;

[0143] (3.2) The orientation degree OI2 of the second negative electrode active particles is 2~8;

[0144] (3.3) The median particle size Dv250 of the second negative electrode active particles is 8μm~16μm;

[0145] (3.4) The specific surface area S2 of the second negative electrode active particle is 2.0 m². 2 / g~4.0m 2 / g;

[0146] (3.5) The tap density ρr2 of the second negative electrode active particles is 0.90 g / cm³. 3 ~1.20g / cm 3 .

[0147] In these embodiments, this application discloses that the specific capacity A2 of the second negative electrode active particle is any one of 350 mAh / g, 355 mAh / g, 358 mAh / g, or any one of the above range values.

[0148] In these embodiments, this application discloses that the orientation degree OI2 of the second negative electrode active particle is any one of 2, 3, 4, 5, 6, 7, 8 or any one of the above range values.

[0149] In these embodiments, this application discloses that the median particle size Dv250 of the second negative electrode active particles is any one of 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm or any one of the above range values.

[0150] In these embodiments, this application discloses that the specific surface area S2 of the second negative electrode active particle is 2.0 m². 2 / g, 3.0m 2 / g, 4.0 m 2 Any one of / g or any one of the above range values.

[0151] In these embodiments, this application discloses that the tap density ρr2 of the second negative electrode active particle is 0.90 g / cm³. 3 1.0 g / cm 3 1.10 g / cm 3 1.20 g / cm 3 Any one of the above values ​​or any one of the above range values.

[0152] In some embodiments, this application discloses that the first negative electrode active particle satisfies one or more of the following:

[0153] (5.1) The specific capacity A1 of the first negative electrode active particle is 354 mAh / g~365 mAh / g;

[0154] (5.2) The orientation degree OI1 of the first negative electrode active particle is 5~20;

[0155] (5.3) The median particle size Dv150 of the first negative electrode active particle is 12 μm ~ 20 μm;

[0156] (5.4) The specific surface area S1 of the first negative electrode active particle is 1.2 m². 2 / g~2.0m 2 / g;

[0157] (5.5) The tap density ρr1 of the first negative electrode active particle is 0.95 g / cm³. 3 ~1.30g / cm 3 .

[0158] In these embodiments, this application discloses that the specific capacity A1 of the first negative electrode active particle is any one of 354 mAh / g, 360 mAh / g, 365 mAh / g, or any one of the above range values.

[0159] In these embodiments, this application discloses that the orientation degree OI1 of the first negative electrode active particle is any one of 5, 10, 15, 20 or any one of the above range values.

[0160] In these embodiments, this application discloses that the median particle size Dv150 of the first negative electrode active particle is any one of 12 μm, 15 μm, 18 μm, 20 μm or any one of the above range values.

[0161] In these embodiments, this application discloses that the specific surface area S1 of the first negative electrode active particle is 1.2 m². 2 / g, 1.5m 2 / g, 1.8 m 2 / g, 2.0 m 2 Any one of / g or any one of the above range values.

[0162] In these embodiments, this application discloses that the tap density ρr1 of the first negative electrode active particle is 0.95 g / cm³. 3 1.0g / cm 3 1.10 g / cm 3 1.20 g / cm 3 1.30 g / cm 3 Any one of the above values ​​or any one of the above range values.

[0163] In some embodiments, this application discloses that the specific capacity A1 of the first negative electrode active particle is 354 mAh / g to 365 mAh / g; and the specific capacity A2 of the second negative electrode active particle is 350 mAh / g to 358 mAh / g.

[0164] In these embodiments, the present application selects the specific capacity of the first negative electrode active particle to be greater than that of the second negative electrode active particle in order to compensate for the defect of reduced energy density of the second negative electrode film.

[0165] In some embodiments, this application also discloses that the specific capacity A1 of the first negative electrode active particle is 360 mAh / g to 365 mAh / g; and the specific capacity A2 of the second negative electrode active particle is 350 mAh / g to 355 mAh / g. In these embodiments, the first negative electrode film layer and the second negative electrode film layer are matched, which can better compensate for the defect of reduced energy density of the second negative electrode film layer.

[0166] In some embodiments, this application discloses that the orientation degree OI1 of the first negative electrode active particle is 5 to 20; and the orientation degree OI2 of the second negative electrode active particle is 2 to 8.

[0167] In these embodiments, the orientation degree of the first negative electrode active particle is greater than that of the second negative electrode active particle to meet the requirement that the diffusion ability of ions in the second negative electrode film is stronger than that in the first negative electrode film.

[0168] In these embodiments, this application also discloses that the orientation degree OI1 of the first negative electrode active particle is 8-15, and the orientation degree OI2 of the second negative electrode active particle is 3-6. In these embodiments, the first negative electrode film layer and the second negative electrode film layer are matched to better meet the requirements that the diffusion ability of ions in the second negative electrode film layer is stronger than that in the first negative electrode film layer, and the conduction ability of electrons in the first negative electrode film layer is faster than that in the second negative electrode film layer.

[0169] In some embodiments, this application discloses that the median particle size Dv150 of the first negative electrode active particle is 12 μm to 20 μm; and the median particle size Dv250 of the second negative electrode active particle is 8 μm to 16 μm.

[0170] In these embodiments, the median particle size of the first negative electrode active particle is selected to be larger than the median particle size of the second negative electrode active particle to satisfy the condition that the compaction density of the first negative electrode active particle is greater than the compaction density of the second negative electrode active particle.

[0171] In these embodiments, this application also discloses that the median particle size Dv150 of the first negative electrode active particles is 14 μm to 18 μm; and the median particle size Dv250 of the second negative electrode active particles is 9 μm to 15 μm. In these embodiments, the first negative electrode film layer and the second negative electrode film layer are matched to better meet the requirement that the energy density of the first negative electrode film layer is greater than that of the second negative electrode film layer.

[0172] In some embodiments, this application discloses that the specific surface area S1 of the first negative electrode active particle is 1.2 m². 2 / g~2.0m 2 / g; the specific surface area S2 of the second negative electrode active particles is 2.0 m². 2 / g~4.0m 2 / g.

[0173] In these embodiments, the specific surface area of ​​the first negative electrode active particle is smaller than that of the second negative electrode active particle, mainly due to the influence of the median particle size of each particle.

[0174] In these embodiments, this application also discloses that the specific surface area S1 of the first negative electrode active particle is 1.4 m². 2 / g~1.8m 2 / g; the specific surface area S2 of the second negative electrode active particles is 2.5 m². 2 / g~3.5m 2 / g.

[0175] In some embodiments, this application discloses that the tap density ρr1 of the first negative electrode active particle is 0.95 g / cm³. 3 ~1.30g / cm 3 The tap density ρr2 of the second negative electrode active particles is 0.90 g / cm³. 3 ~1.20g / cm 3 .

[0176] In these embodiments, the tap density of the first negative electrode active particle is selected to be greater than that of the second negative electrode active particle, mainly due to the influence of the median particle size and the particle's own structure and properties.

[0177] In these embodiments, this application also discloses that the tap density ρr1 of the first negative electrode active particle is 1.0 g / cm³. 3 ~1.20g / cm 3 The tap density ρr2 of the second negative electrode active particles is 0.95 g / cm³. 3 ~1.15g / cm 3 .

[0178] The active material in the negative electrode film layer of this application meets the above-mentioned characteristics and requirements of each characteristic parameter. In addition to the active material, the negative electrode film layer of this application also includes conductive agents, thickeners, binders, etc. The conductive agents include, but are not limited to, one or a combination of two of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the thickeners include cellulose and its sodium salt, and cellulose includes methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, etc.; the binders include, but are not limited to, polyvinyl alcohol, polyethylene glycol, sodium carboxymethylcellulose, polyethylene oxide, polyacrylic acid, polyacrylamide, sodium alginate, styrene-butadiene rubber (SBR), etc.

[0179] In some embodiments, this application discloses a mass ratio of negative electrode active particles, conductive agent, thickener and binder in the first negative electrode film layer and / or the second negative electrode film layer as (90~97):(0.5~3):(0.5~3):(0.5~3).

[0180] This application discloses, in some embodiments, a negative electrode current collector comprising, but not limited to, a metal foil or a composite current collector. The metal foil may be a copper foil, and the composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector can be formed by forming a metal material, such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy, on a polymer substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE).

[0181] The method for preparing the negative electrode film layer in these embodiments of this application includes mixing each raw material with a solvent in a certain mass ratio to form a first slurry and a second slurry; after defoaming the first slurry and the second slurry, uniformly coating the first slurry onto the surface of the negative electrode current collector and uniformly coating the second slurry onto the surface of the first slurry; drying; and compacting to a certain compaction density using a cold press to obtain a negative electrode sheet containing the first negative electrode film layer and the second negative electrode film layer.

[0182] In some embodiments, this application discloses that the porosity of the first negative electrode film is q1 and the porosity of the second negative electrode film is q2, satisfying that q1 < q2.

[0183] The porosity of the first and second negative electrode films in this application includes any meaning conventional in the art and can be roughly determined using known qualitative methods. For example, microscopic photographs can be taken of the cross-section of each film along its thickness direction to observe the porosity.

[0184] In these embodiments, this application discloses that the porosity of the first negative electrode film is lower than that of the second negative electrode film, mainly due to the influence of the median particle size of each negative electrode active particle and the inherent properties of the material. A negative electrode film satisfying this characteristic facilitates a greater diffusion rate of ions in the second negative electrode film compared to the first negative electrode film.

[0185] In some embodiments, this application discloses that the thickness of the negative electrode film is H, the thickness of the first negative electrode film is 0.4H~0.8H, and the thickness of the second negative electrode film is 0.2H~0.6H.

[0186] like Figure 6In this application, the X-axis represents the length or width of the negative electrode film, and the Z-axis represents the stacking direction of the negative electrode film, or it can be the thickness direction. The thickness H of the negative electrode film includes the distance along the Z-axis between the end face closest to the current collector and the end face furthest from the current collector. The thickness H1 of the first negative electrode film includes the distance between the end face closest to the current collector and the end face furthest from the current collector. The thickness H2 of the second negative electrode film includes the distance between the end face closest to the first negative electrode film and the end face furthest from the current collector. The thickness of the negative electrode film in this application refers to the thickness of the negative electrode film in the negative electrode sheet used for battery assembly after cold pressing and compaction. Furthermore, the thickness of each negative electrode film layer can be detected using equipment and methods known in the art. Relevant detection methods can refer to domestic and international testing standards and enterprise standards. Those skilled in the art can also adapt certain detection steps / instrument parameters to obtain more accurate results from the perspective of detection accuracy. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination. For example, it can be obtained according to GB / T 17359-2012 "Quantitative Analysis by Microbeam Analysis Energy Dispersive Spectroscopy," or by taking the average value after multiple measurements using a measuring instrument such as a micrometer.

[0187] In these embodiments, this application discloses that the thickness H of the negative electrode film is the sum of the thickness H1 of the first negative electrode film and the thickness H2 of the second negative electrode film. When the thickness of the first negative electrode film is 0.4H~0.8H and the thickness of the second negative electrode film is 0.2H~0.6H, the first and second negative electrode films are matched. For example, the first negative electrode film can compensate for the energy density defects of the second negative electrode film and improve the DC resistance problem. Furthermore, it can synergistically improve the rate performance of the battery through both ion diffusion and electron conduction. Ultimately, this is used to balance the various performance characteristics of the battery, such as DC resistance, rate performance, and energy density.

[0188] In some embodiments, this application discloses that the negative electrode film layer satisfies one or two of the following:

[0189] (7.1) The compaction density of the negative electrode film layer is ≥1.45 g / cm³. 3 ;

[0190] (7.2) The areal density of the negative electrode film is ≥6.5 mg / cm³. 2 .

[0191] The compaction density of the negative electrode film layer in this application has the same meaning as the compaction density of the aforementioned negative electrode active particles; both can be used to characterize the energy density of the material. However, the compaction density of the negative electrode film layer is used to evaluate the overall compaction density of the negative electrode sheet. The compaction density of the negative electrode film layer = areal density of the negative electrode film layer / thickness of the negative electrode film layer. The thickness of the negative electrode film layer is as described above. The areal density of the negative electrode film layer = weight of a single-sided negative electrode film layer / area of ​​a single-sided negative electrode film layer. The weight of a single-sided negative electrode film layer can be obtained by weighing, and the area of ​​a single-sided negative electrode film layer can be obtained using the area calculation formula based on the film layer shape.

[0192] The final calculated compaction density of the negative electrode film in this application is ≥1.45 g / cm³. 3 The areal density of the negative electrode film is ≥6.5 mg / cm³. 2 This can effectively improve the energy density of batteries.

[0193] In some embodiments, this application discloses that the negative electrode film layer satisfies one or two of the following:

[0194] (8.1) The compaction density of the negative electrode film is 1.55 g / cm³. 3 ~1.65g / cm 3 ;

[0195] (8.2) The areal density of the negative electrode film is 8 mg / cm³. 2 ~15mg / cm 2 .

[0196] This application controls the compaction density and areal density of the negative electrode film to meet the above-mentioned specific numerical range. Under the premise of satisfying the characteristics of each active particle and the positional relationship of each negative electrode film, it is more convenient and more conducive to improving the energy density of the battery.

[0197] In these embodiments, this application discloses that the compaction density of the negative electrode film can be 1.55 g / cm³. 3 1.60 g / cm 3 1.65g / cm 3 Any one of the above-mentioned values ​​or satisfying any one of the above-mentioned range values. This application also discloses in these embodiments that the areal density of the negative electrode film is 8 mg / cm³. 2 9 mg / cm 2 12 mg / cm 2 13 mg / cm 2 15mg / cm 2 Any one of the above values ​​or any one of the above range values.

[0198] Positive electrode sheet

[0199] Some embodiments of this application disclose a positive electrode sheet, which includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector. The positive electrode film layer in this application includes positive electrode active particles, a positive electrode conductive agent, a positive electrode binder, etc. This application does not specifically limit the specific types of positive electrode active particles. For example, when the positive electrode sheet is used in a lithium-ion battery, the positive electrode active particles include, but are not limited to, LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNiO2. 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM111), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 CO 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 CO 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 CO 0.15 Al 0.05 One or more of O2, LiFePO4 (LFP) and LiMnPO4.

[0200] For example, when the positive electrode is used in a sodium-ion battery, the positive electrode active particles include, but are not limited to, at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. Among these, the transition metal in the sodium transition metal oxide can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide may be Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≤ 1. Polyanionic compounds include sodium vanadium trifluorophosphate (Na3V2(PO4)2F3), sodium vanadium fluorophosphate (NaVPO4F), sodium vanadium phosphate (Na3V2(PO4)3), Na4Fe3(PO4)2P2O7, NaFePO4, and one or more of these. Prussian blue compounds are Na... x M1M2(CN)6, wherein M1 and M2 are one or more of Fe, Mn, Co, Ni, Cu, Zn, Cr, Ti, V, Zr, and Ce, and 0 < x ≤ 2.

[0201] The positive electrode conductive agent includes, but is not limited to, one or more combinations of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The positive electrode binder includes, but is not limited to, one or more combinations of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc.

[0202] The positive current collector in this application can be a metal foil or a composite current collector. The metal foil can be an aluminum foil, and the composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material, such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, on a polymer material substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0203] electrolytes

[0204] Some embodiments of this application disclose an electrolyte comprising a sodium or lithium salt and an organic solvent, which may be an organic solvent commonly used in the art for electrolytes. As an example, the organic solvent may be selected from at least one or a combination of two of the following: 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), butyl carbonate (BC), fluoroethylene carbonate (FEC), 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), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). The sodium or lithium salt can be a sodium or lithium salt commonly used in the field for electrolytes, such as sodium hexafluorophosphate or lithium hexafluorophosphate.

[0205] In some embodiments, this application discloses that the concentration of electrolyte salt in the electrolyte is 0.1 mol / L to 4 mol / L.

[0206] Separating membrane

[0207] According to some embodiments of this application, the battery includes not only a negative electrode, a positive electrode, and an electrolyte, but also a separator membrane stacked together. The stacking method includes, but is not limited to, winding or lamination conventional in the art. The material and size of the separator membrane include, but are not limited to, any conventional form in the art. Similarly, the material and size of the positive electrode membrane include, but are not limited to, any conventional form in the art. For example, the separator membrane is disposed between the positive and negative electrode membranes to provide isolation. The separator membrane includes a substrate and a functional coating disposed on at least one surface of the substrate. The functional coating can be used to improve the heat resistance, mechanical strength, etc., of the separator membrane. For example, the functional coating may also include other functional materials (e.g., ceramic particles, other polymers, etc.). The ceramic particles include, but are not limited to, boehmite, alumina, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hydropyrite, zirconium titanate, barium titanate, etc. This application does not impose any particular limitation on the type of separator substrate; any known substrate suitable for secondary battery separators can be selected. In some embodiments, the separator substrate includes, but is not limited to, a single-layer film or a multi-layer composite film of one or more of glass fiber, nonwoven fabric, polyethylene, and polypropylene.

[0208] Example 1

[0209] A negative electrode sheet is provided, and the method for preparing the negative electrode sheet is as follows:

[0210] S100, provides copper foil for negative electrode current collector;

[0211] S200, Preparation of the first slurry: The first negative electrode active particles (graphite), conductive agent conductive carbon, stabilizer sodium carboxymethyl cellulose, and binder SBR are dispersed in deionized water at a mass ratio of 94.5:1.5:1.5:2.5 to form the first slurry; wherein, Figure 7 The schematic diagram of the microstructure of the second negative electrode active particle is shown.

[0212] S300, Preparation of the second slurry: The second negative electrode active particles (alumina-coated graphite core-shell structure) are dispersed in deionized water at a mass ratio of 94.5:1.5:1.5:2.5 with conductive carbon as a conductive agent, sodium carboxymethyl cellulose as a stabilizer, and SBR as a binder to form the second slurry; wherein, Figure 8 and Figure 9 These are microstructure diagrams of the first negative electrode active particles, combined with... Figure 9It can be seen that alumina is uniformly coated on the graphite surface. Statistical analysis shows that the mass percentage of alumina in the second negative electrode active particles is 0.5%~5%, and in this embodiment, the percentage is selected as 2%. Furthermore, combined with... Figure 7 , Figure 8 , Figure 9 It can be seen that the particle size of the first negative electrode active particle is significantly larger than that of the second negative electrode active particle.

[0213] S400, Forming the first and second negative electrode films: The first slurry is uniformly coated onto both sides of the copper foil of the negative electrode current collector. Then, the second slurry is uniformly coated onto the surface of the first slurry. The film is dried using a nine-section oven with temperatures set sequentially at 100℃ / 100℃ / 95℃ / 85℃ / 85℃ / 80℃ / 80℃ / 80℃ / 60℃. Finally, it is compacted using a cold press to achieve a compaction density of ≥1.45 g / cm³ for the negative electrode film. 3 .

[0214] This application forms the negative electrode sheets of Examples 2 to 4 by selecting negative electrode active particles with different characteristic parameters. At the same time, the mass percentage content of alumina in the second negative electrode active particles in Examples 2 to 4 is lower than that in Example 1. The characteristic parameters of the first and second negative electrode active particles in Examples 1 to 4 are shown in Table 1.

[0215] Table 1. Parameter list of negative electrode active particles

[0216]

[0217] [Performance Testing of Negative Electrode Film]

[0218] ①Thickness test:

[0219] It can be measured using a Mitutoyo293-100 micrometer with an accuracy of 0.1 μm.

[0220] ②Test areal density;

[0221] Each negative electrode film layer is punched into a small circular piece with a certain area, and its mass is obtained by weighing. Then the surface density = mass / area.

[0222] ③ Test compaction density;

[0223] Based on the above areal density, compaction density = areal density / thickness of small disc.

[0224] The performance parameters of the first negative electrode film and the second negative electrode film in Examples 1 to 4 are shown in Table 2.

[0225] This application also provides Examples 5, 6, 7, and 8, wherein the characteristic parameters of the negative electrode active particles in Examples 5 and 6 are the same as those in Example 1, and the characteristic parameters of the negative electrode active particles in Examples 7 and 8 are the same as those in Example 2. The difference lies in the thickness of the first negative electrode film layer and the second negative electrode film layer, as well as the compaction density and areal density of each film layer. The performance parameters of Examples 5 to 8 are illustrated in Table 2.

[0226] Furthermore, although Table 2 does not directly show the porosity relationship of each negative electrode film layer, but mainly shows the relationship between the thickness, compaction density, and areal density of each film layer, it is indeed true that the porosity of the second negative electrode film layer is greater than that of the first negative electrode film layer.

[0227] Table 2 Parameter list of negative electrode film

[0228]

[0229] In Table 1, Ha, Hb, and Hc refer to the thickness of the negative electrode film, and their meanings are the same as those of H in the attached figure. Specifically, Ha is approximately 63 μm, Hb is approximately 60 μm, and Hc is approximately 89 μm.

[0230] Preparation of positive electrode sheet

[0231] LiNi, the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, conductive agent Super-P, and binder polyvinylidene fluoride are stirred and dispersed in N-methylpyrrolidone at a mass ratio of 96:2:2 to form a positive electrode slurry. This slurry is then coated onto the positive electrode current collector aluminum foil and compacted using a cold press to obtain the positive electrode sheet.

[0232] Preparation of electrolyte

[0233] Lithium salt LiPF6 was added to a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 35:65 and mixed thoroughly to obtain an electrolyte, wherein the molar concentration of LiPF6 in the electrolyte was 1 mol / L.

[0234] Choose a release liner

[0235] A 12μm thick polyethylene porous membrane was selected.

[0236] Preparation of lithium-ion batteries

[0237] According to some embodiments of this application, the prepared negative electrode sheet, separator, and positive electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets to provide isolation. The cells are then wound to obtain a bare cell, which is then inserted into the battery casing. After baking, liquid injection, settling, encapsulation, formation, and capacity testing, a soft-pack lithium-ion battery is obtained.

[0238] Comparative Example 1

[0239] The difference from Example 1 is that the active material of the negative electrode film is artificial graphite manufactured by Barrett, and the compacted density of 5 tons of this artificial graphite powder is 2.1 g / cm³. 3 The Dv50 is 20.5μm.

[0240] Furthermore, the negative electrode film was formed by single-sided coating to investigate the effect of the negative electrode active material containing only artificial graphite on battery performance.

[0241] Comparative Example 2

[0242] The difference from Example 1 is that the active material of the negative electrode film is a second negative electrode active particle with a core-shell structure, and the physicochemical properties of this second negative electrode active particle are as shown in Table 1 of Example 1. Furthermore, the negative electrode film is formed by single-sided coating to investigate the effect of the negative electrode active material containing only the second negative electrode active particle on battery performance.

[0243] Comparative Example 3

[0244] The difference from Comparative Example 1 is that the negative electrode film layer is coated on both sides.

[0245] [Battery Performance Testing]

[0246] ④ Testing the initial capacity C0:

[0247] The prepared lithium-ion battery was placed at room temperature of 25°C and charged to 4.25V at a constant current rate of 0.33C. Then it was charged at a constant voltage rate to a current of 0.05C, left to stand for 5 minutes, and then discharged to 2.5V at a constant current rate of 0.33C. The constant current discharge capacity was recorded as the initial capacity C0.

[0248] ⑤ Test of fast charging capability at 25℃:

[0249] The prepared lithium-ion battery was placed at room temperature (25℃) and charged to 4.25V using a constant current rate of 0.33C. Then, it was charged to 0.05C using a constant voltage rate, allowed to rest for 5 minutes, and then discharged to 2.5V using a constant current rate of 0.33C. The constant current discharge capacity was recorded as the initial capacity C0. The battery was then sequentially charged to 4.25V (full cell potential) or 0mV (negative electrode cutoff potential) using constant current rates of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, and 3.5C0 (either condition indicates completion of charging). After each charge, it was discharged to 2.5V using a constant current rate of 0.33C0. At 10% SOC intervals, the corresponding negative electrode potential at different charging rates was recorded. Rate-negative electrode potential curves were plotted for different SOCs. Linear fitting was used to obtain the charging rate corresponding to a negative electrode potential of 0mV at different SOCs, denoted as Cx (x = 2~8). The charging time T (min) for a secondary battery to charge from 10% SOC to 80% SOC is calculated using the formula (1 / C2 + 1 / C3 + 1 / C4 + 1 / C5 + 1 / C6 + 1 / C7 + 1 / C8) × 0.1 * 60. A shorter charging time indicates better fast-charging performance.

[0250] ⑥ DC resistance (DCR) at 25℃:

[0251] The prepared lithium-ion battery was placed at room temperature (25°C) and charged to 4.25V using a constant current rate of 0.33C. Then, it was charged to 0.05C using a constant voltage rate and allowed to rest for 5 minutes. Next, it was discharged to 2.5V using a constant current rate of 0.33C, and the constant current discharge capacity was recorded as the initial capacity C0. The battery was then allowed to rest for 5 minutes, charged to 4.25V using a constant current rate of 0.33C0, charged to 0.05C using a constant voltage rate, allowed to rest for 5 minutes, discharged at a constant current rate of 0.33C0 for 1.5 hours, allowed to rest for 30 minutes, discharged at a constant current rate of 3C0 for 30 seconds, and allowed to rest for 5 minutes. The voltage values ​​before and after the 1.5C0 constant current discharge were recorded as U1 and U2, respectively. Based on the formula DCR = (U1 - U2) / 1.5C0, the DCR (Ω) of the secondary battery at 50% SOC was calculated. A smaller DCR indicates lower power loss when the lithium-ion battery is used in a vehicle, resulting in faster vehicle starting speed.

[0252] Table 3 Battery Performance List

[0253]

[0254] As can be seen from the list analysis, under the premise that the areal density and thickness of each negative electrode film layer are kept the same or similar, negative electrode active particles with different compaction densities are selected to form negative electrode sheets according to the negative electrode film layer design of this application, and then further formed into wound batteries. When the compaction density of the first negative electrode active particle is greater than that of the second negative electrode active particle, it is convenient to simultaneously consider the energy density and fast charging performance of the battery. Specifically, the energy density is comparable to that of commercial products, and the rate performance is better than that of commercial products (as shown in Examples 1 to 4 compared with Comparative Example 3). Further combining the DCR of Examples 1 to 4 (which belongs to real-time detection data) and comparing it with Comparative Example 3, it can be seen that since the second negative electrode active particle in this application contains aluminum oxide, which is non-conductive, the impedance is increased. However, in conjunction with the excellent conductivity of the first negative electrode active particle, the DCR is not increased too much, so it can alleviate the problem of increased DC impedance (DCR) caused by the second negative electrode active particle to a certain extent.

[0255] Meanwhile, as can be seen from the above, the aluminum oxide in the second negative electrode active particles has poor conductivity. Increasing the thickness of the second negative electrode film layer is beneficial to reducing the charging time, but it reduces the energy density to a certain extent while increasing the impedance (as in Examples 5 and 6, Examples 7 and 8). Therefore, it can be flexibly adjusted according to actual performance requirements.

[0256] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A negative electrode sheet, characterized in that: include: current collector; Negative electrode film layer: comprising a first negative electrode film layer and a second negative electrode film layer, wherein the first negative electrode film layer is located on at least one side surface of the current collector; and the second negative electrode film layer is located on the surface of the first negative electrode film layer away from the current collector. The first negative electrode film layer contains first negative electrode active particles, which are graphitized carbon. The second negative electrode film layer includes second negative electrode active particles, which have a core-shell structure. The core of the core-shell structure is graphitized carbon, and the shell of the core-shell structure is aluminum oxide. Among them, the compaction density of the first negative electrode active particle is greater than that of the second negative electrode active particle under the same conditions. The negative electrode film layer satisfies: (1.1) The first negative electrode active particle has a powder compaction density ρ1 of 5 tons, wherein ρ1 is 1.85 g / cm³. 3 ~2.05g / cm 3 The second negative electrode active particle has a powder compaction density ρ2 of 5 tons, where ρ2 is 1.60 g / cm³. 3 ~1.80g / cm 3 ; (1.2) Based on the total mass of the second negative electrode active particles, the mass percentage content of the alumina is 0.5% to 5%.

2. The negative electrode sheet according to claim 1, characterized in that: The negative electrode film layer also satisfies: (1.3) The graphitized carbon includes any one of natural graphite, artificial graphite, composite graphite or mesophase carbon microspheres.

3. The negative electrode sheet according to any one of claims 1 to 2, characterized in that: Based on the total mass of the second negative electrode active particles, the mass percentage content of the alumina is 1% to 2%.

4. The negative electrode sheet according to claim 1, characterized in that: The negative electrode film layer satisfies one or more of the following: (2.1) The specific capacity of the first negative electrode active particle is A1, and the specific capacity of the second negative electrode active particle is A2, satisfying A1 > A2; (2.2) The orientation degree OI value of the first negative electrode active particle is OI1, and the orientation degree OI value of the second negative electrode active particle is OI2; satisfying OI1>OI2; (2.3) The median particle size of the first negative electrode active particle is Dv150, and the median particle size of the second negative electrode active particle is Dv250; satisfying: Dv150>Dv250; (2.4) The specific surface area of ​​the first negative electrode active particle is S1, and the specific surface area of ​​the second negative electrode active particle is S2; satisfying: S1 < S2; (2.5) The tap density of the first negative electrode active particle is ρr1, and the tap density of the second negative electrode active particle is ρr2; satisfying: ρr1>ρr2.

5. The negative electrode sheet according to claim 1, characterized in that: The second negative electrode active particle satisfies one or more of the following: (3.1) The specific capacity A2 of the second negative electrode active particle is 350 mAh / g ~ 358 mAh / g; (3.2) The orientation degree OI2 of the second negative electrode active particle is 2~8; (3.3) The median particle size Dv250 of the second negative electrode active particles is 8 μm to 16 μm; (3.4) The specific surface area S2 of the second negative electrode active particle is 2.0 m². 2 / g~4.0m 2 / g; (3.5) The tap density ρr2 of the second negative electrode active particle is 0.90 g / cm³. 3 ~1.20g / cm 3 .

6. The negative electrode sheet according to claim 1, characterized in that: The second negative electrode active particle satisfies one or more of the following: (4.1) The specific capacity A2 of the second negative electrode active particle is 350 mAh / g ~ 355 mAh / g; (4.2) The orientation degree OI2 of the second negative electrode active particle is 3~6; (4.3) The median particle size Dv250 of the second negative electrode active particles is 9 μm to 15 μm; (4.4) The specific surface area S2 of the second negative electrode active particle is 2.5 m². 2 / g~3.5m 2 / g; (4.5) The tap density ρr2 of the second negative electrode active particle is 0.95 g / cm³. 3 ~1.15g / cm 3 .

7. The negative electrode sheet according to claim 1, characterized in that: The first negative electrode active particle satisfies one or more of the following: (5.1) The specific capacity A1 of the first negative electrode active particle is 354 mAh / g~365 mAh / g; (5.2) The orientation degree OI1 of the first negative electrode active particle is 5~20; (5.3) The median particle size Dv150 of the first negative electrode active particle is 12 μm ~ 20 μm; (5.4) The specific surface area S1 of the first negative electrode active particle is 1.2 m². 2 / g~2.0m 2 / g; (5.5) The tap density ρr1 of the first negative electrode active particle is 0.95 g / cm³. 3 ~1.30g / cm 3 .

8. The negative electrode sheet according to claim 1, characterized in that: The first negative electrode active particle satisfies one or more of the following: (6.1) The specific capacity A1 of the first negative electrode active particle is 360 mAh / g to 365 mAh / g; (6.2) The orientation degree OI1 of the first negative electrode active particle is 8~15; (6.3) The median particle size Dv150 of the first negative electrode active particle is 14μm~18μm; (6.4) The specific surface area S1 of the first negative electrode active particle is 1.4 m². 2 / g~1.8 m 2 / g; (6.5) The tap density ρr1 of the first negative electrode active particle is 1.0 g / cm³. 3 ~1.2 g / cm 3 .

9. The negative electrode sheet according to claim 1, characterized in that: The thickness of the negative electrode film is H, and the thickness of the first negative electrode film is 0.4H~0.8H; The thickness of the second negative electrode film is 0.2H~0.6H.

10. The negative electrode sheet according to claim 1, characterized in that: The negative electrode film layer satisfies one or two of the following: (7.1) The compaction density of the negative electrode film is ≥1.45 g / cm³. 3 ; (7.2) The areal density of the negative electrode film is ≥6.5 mg / cm³. 2 .

11. The negative electrode sheet according to claim 1, characterized in that: The negative electrode film layer satisfies one or two of the following: (8.1) The compaction density of the negative electrode film is 1.55 g / cm³. 3 ~1.65g / cm 3 ; (8.2) The areal density of the negative electrode film is 8 mg / cm³. 2 ~15mg / cm 2 .

12. A secondary battery, characterized in that: Includes the negative electrode sheet according to any one of claims 1 to 11.

13. An electrical device, characterized in that: It includes the negative electrode sheet according to any one of claims 1 to 11 or the secondary battery according to claim 12.

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