Electrode assembly, secondary battery, battery module, battery pack, and electric device

Abstract

The application provides an electrode assembly, a secondary battery, a battery module, a battery pack and a power utilization device. The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator film between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet satisfies CAP1=CAP2, CAP1 represents the capacity of a first positive electrode film layer in Ah, and CAP2 represents the capacity of a second positive electrode film layer in Ah. The electrode assembly satisfies |R4 / R3-R2 / R1|>0, R1 represents the resistance of the first positive electrode film layer in Ω, R2 represents the resistance of the second positive electrode film layer in Ω, R3 represents the resistance of the first negative electrode film layer in mΩ, and R4 represents the resistance of the second negative electrode film layer in mΩ. The application can greatly prolong the cycle life of the secondary battery.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to an electrode assembly, a secondary battery, a battery module, a battery pack, and an electrical device. Background Technology

[0002] In recent years, with the application and promotion of rechargeable batteries in various electronic products and new energy vehicles, their energy density has received increasing attention. During the charging and discharging process of rechargeable batteries, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrode plates. Due to changes in the structure of the active material, electrolyte decomposition, and the formation and destruction of the SEI film on the surface of the active material, active ions are inevitably consumed, resulting in a continuous decline in the capacity of the rechargeable battery and difficulty in achieving a longer cycle life. Summary of the Invention

[0003] The purpose of this application is to provide an electrode assembly, a secondary battery, a battery module, a battery pack, and an electrical device, which aim to significantly extend the cycle life of the secondary battery.

[0004] A first aspect of this application provides an electrode assembly comprising a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. The positive electrode includes a positive current collector and a first positive electrode film and a second positive electrode film on two opposing surfaces of the current collector. The negative electrode includes a negative current collector and a first negative electrode film and a second negative electrode film on two opposing surfaces of the current collector. The first positive electrode film is located on the side of the positive current collector closest to the separator, and the second negative electrode film... The layer is located on the side of the negative current collector close to the separator; wherein, the positive electrode sheet satisfies CAP1=CAP2, where CAP1 represents the capacity of the first positive electrode film layer in Ah, CAP2 represents the capacity of the second positive electrode film layer in Ah, and the electrode assembly satisfies |R4 / R3-R2 / R1|>0, where R1 represents the resistance of the first positive electrode film layer in Ω, R2 represents the resistance of the second positive electrode film layer in Ω, R3 represents the resistance of the first negative electrode film layer in mΩ, and R4 represents the resistance of the second negative electrode film layer in mΩ.

[0005] In the electrode assembly of this application, by rationally setting the relationship between the resistances of the positive electrode and the negative electrode to satisfy |R4 / R3-R2 / R1|>0, the voltage response speed of the film layer on one side of the positive electrode during charging can be improved, and this film layer can reach the cutoff voltage of the secondary battery first. Furthermore, by rationally setting the relationship between the resistances of the positive and negative electrodes, the film layer on the other side of the positive electrode can also have a sufficient amount of pre-stored active ions; as the secondary battery cycles, these pre-stored active ions can be gradually released to replenish the consumption of active ions, thereby delaying the capacity decay of the secondary battery and significantly extending its cycle life.

[0006] In any embodiment of this application, the electrode assembly satisfies 0 < |R4 / R3-R2 / R1| ≤ 20. Optionally, 0.2 ≤ |R4 / R3-R2 / R1| ≤ 10.

[0007] In any embodiment of this application, 0Ω < R1 ≤ 20Ω. Optionally, 0Ω < R1 ≤ 5Ω.

[0008] In any embodiment of this application, 0Ω < R2 ≤ 20Ω. Optionally, 0Ω < R2 ≤ 5Ω.

[0009] In any embodiment of this application, 0mΩ < R3 ≤ 200mΩ. Optionally, 0mΩ < R3 ≤ 50mΩ.

[0010] In any embodiment of this application, 0mΩ < R4 ≤ 200mΩ. Optionally, 0mΩ < R4 ≤ 50mΩ.

[0011] When the resistances of the first positive electrode layer, the second positive electrode layer, the first negative electrode layer, and the second negative electrode layer are all within appropriate ranges, the consistency between the positive and negative electrode plates is better, which is beneficial for the secondary battery to obtain a longer cycle life.

[0012] In any embodiment of this application, the negative electrode sheet satisfies R4 / R3≥1, and the electrode assembly satisfies 0<|R4 / R3-R2 / R1|≤20. Optionally, 0.2≤|R4 / R3-R2 / R1|≤10.

[0013] In any embodiment of this application, the negative electrode sheet satisfies 1≤R4 / R3≤30, and the electrode assembly satisfies 0<|R4 / R3-R2 / R1|≤20. Optionally, 0.2≤|R4 / R3-R2 / R1|≤10.

[0014] In any embodiment of this application, the negative electrode sheet satisfies R4 / R3≥1, the positive electrode sheet satisfies 0<R2 / R1≤20, and the electrode assembly satisfies 0<|R4 / R3-R2 / R1|≤20. Optionally, 0.2≤|R4 / R3-R2 / R1|≤10.

[0015] In any embodiment of this application, the negative electrode sheet satisfies 1≤R4 / R3≤30, the positive electrode sheet satisfies 0<R2 / R1≤20, and the electrode assembly satisfies 0<|R4 / R3-R2 / R1|≤20. Optionally, 0.2≤|R4 / R3-R2 / R1|≤10.

[0016] In any embodiment of this application, the negative electrode sheet satisfies 0 < R4 / R3 < 1, the positive electrode sheet satisfies 0 < R2 / R1 < 1, and the electrode assembly satisfies 0 < |R4 / R3 - R2 / R1| < 1. Optionally, 0.2 ≤ |R4 / R3 - R2 / R1| ≤ 0.9.

[0017] In any embodiment of this application, the negative electrode sheet satisfies 0.05≤R4 / R3≤0.9, the positive electrode sheet satisfies 0.05≤R2 / R1≤0.9, and the electrode assembly satisfies 0<|R4 / R3-R2 / R1|<1.

[0018] In any embodiment of this application, the negative electrode sheet satisfies 0 < R4 / R3 < 1, the positive electrode sheet satisfies R2 / R1 ≥ 1, and the electrode assembly satisfies 0 < |R4 / R3 - R2 / R1| ≤ 20. Optionally, 0.2 ≤ |R4 / R3 - R2 / R1| ≤ 10.

[0019] In any embodiment of this application, the negative electrode sheet satisfies 0 < R4 / R3 < 1, the positive electrode sheet satisfies 1 ≤ R2 / R1 ≤ 20, and the electrode assembly satisfies 0 < |R4 / R3 - R2 / R1| < 20. Optionally, 0.2 ≤ |R4 / R3 - R2 / R1| ≤ 10.

[0020] In any embodiment of this application, the negative electrode sheet satisfies 0.05≤R4 / R3≤0.9, the positive electrode sheet satisfies 1≤R2 / R1≤20, and the electrode assembly satisfies 0<|R4 / R3-R2 / R1|<20. Optionally, 0.2≤|R4 / R3-R2 / R1|≤10.

[0021] A second aspect of this application provides a secondary battery including an outer packaging, an electrolyte, and an electrode assembly according to a first aspect of this application.

[0022] In any embodiment of this application, the outer packaging includes a housing and a cover plate. The housing has a receiving cavity and an opening, the electrode assembly is received in the receiving cavity, and the cover plate is used to close the opening of the housing.

[0023] A third aspect of this application provides a battery module that includes the secondary battery of the second aspect of this application.

[0024] The fourth aspect of this application provides a battery pack, which includes one of the secondary battery of the second aspect of this application and the battery module of the third aspect.

[0025] The fifth aspect of this application provides an electrical device that includes at least one of the secondary battery of the second aspect of this application, the battery module of the third aspect, and the battery pack of the fourth aspect.

[0026] The battery module, battery pack, and power device of this application include the secondary battery provided in this application, and therefore have at least the same advantages as the secondary battery. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0029] Figure 2 This is an exploded view of one embodiment of the secondary battery of this application.

[0030] Figure 3 This is a schematic diagram of one embodiment of the electrode assembly of this application.

[0031] Figure 4 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0032] Figure 5 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0033] Figure 6 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0034] Figure 7 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0035] Figure 8 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0036] Figure 9 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0037] Figure 10 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0038] Figure 11 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0039] Figure 12 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0040] Figure 13 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0041] Figure 14 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0042] Figure 15 This is a schematic diagram of another embodiment of the electrode assembly of this application.

[0043] Figure 16 This is a schematic diagram of one embodiment of the battery module of this application.

[0044] Figure 17 This is a schematic diagram of one embodiment of the battery pack of this application.

[0045] Figure 18 yes Figure 17 An exploded view of an embodiment of the battery pack shown.

[0046] Figure 19 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application. Detailed Implementation

[0047] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the electrode assembly, secondary battery, battery module, battery pack, 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.

[0048] 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 "ab" 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.

[0049] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0050] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0051] 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 mention that the method may also include step (c) indicates 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.

[0052] 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.

[0053] 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).

[0054] Electrode assembly and secondary battery

[0055] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to activate its active materials and continue to be used. This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is a schematic diagram of a square-structured secondary battery 5 as an example.

[0056] The secondary battery 5 includes an outer packaging, an electrode assembly, and an electrolyte, wherein the outer packaging is used to encapsulate the electrode assembly and the electrolyte. In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS). In some embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. An electrode assembly 52 is encapsulated in the receiving cavity, and electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0057] The inventors have developed an electrode assembly with a significantly extended cycle life after extensive research. Figure 3 This is a schematic diagram of the structure of an embodiment of the electrode assembly according to this application. Figure 3 As shown, the electrode assembly 52 includes a positive electrode 10, a negative electrode 20, and a separator 30, wherein the separator 30 is located between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 can be formed into the electrode assembly 52 by a winding process or a stacking process.

[0058] The positive electrode 10 includes a first positive electrode film 101, a second positive electrode film 102, and a positive electrode current collector 103. The first positive electrode film 101 and the second positive electrode film 102 are located on two opposite surfaces of the positive electrode current collector 103, with the first positive electrode film 101 located on the side of the positive electrode current collector 103 closest to the separator 30. The first positive electrode film 101 includes a first positive electrode active material, a first positive electrode conductive agent, and a first positive electrode binder, while the second positive electrode film 102 includes a second positive electrode active material, a second positive electrode conductive agent, and a second positive electrode binder.

[0059] The negative electrode sheet 20 includes a first negative electrode film layer 201, a second negative electrode film layer 202, and a negative electrode current collector 203. The first negative electrode film layer 201 and the second negative electrode film layer 202 are located on two opposite surfaces of the negative electrode current collector 203, and the second negative electrode film layer 202 is located on the side of the negative electrode current collector 203 closer to the separator 30. The first negative electrode film layer 201 includes a first negative electrode active material, a first negative electrode conductive agent, and a first negative electrode binder, and the second negative electrode film layer 202 includes a second negative electrode active material, a second negative electrode conductive agent, and a second negative electrode binder.

[0060] In the embodiments of the electrode assembly of this application, the positive electrode 10 satisfies CAP1 = CAP2, where CAP1 represents the capacity of the first positive electrode film 101 in Ah, and CAP2 represents the capacity of the second positive electrode film 102 in Ah. The electrode assembly 52 satisfies |R4 / R3-R2 / R1| > 0, where R1 represents the resistance of the first positive electrode film 101 in Ω, R2 represents the resistance of the second positive electrode film 102 in Ω, R3 represents the resistance of the first negative electrode film 201 in mΩ, and R4 represents the resistance of the second negative electrode film 202 in mΩ.

[0061] During the charging process of a secondary battery, active ions are released from the positive electrode. The rate and quantity of active ion release are related to the charging current and charging time. A higher charging current and longer charging time result in a greater number of active ions released, leading to a higher ratio of released capacity to stored capacity and a higher positive electrode voltage. During charging, the current is evenly distributed across the positive electrode, and both sides of the electrode simultaneously release active ions in equal quantities. Conventional double-sided coating designs for the positive electrode often fail in practical applications due to insufficient voltage response, resulting in inadequate or no pre-storage of active ions. This does not significantly improve the cycle life of the secondary battery and prevents it from achieving a longer cycle life.

[0062] In the electrode assembly of this application, by rationally setting the relationship between the resistances of the positive electrode and the negative electrode to satisfy |R4 / R3-R2 / R1|>0, the voltage response speed of the film layer on one side of the positive electrode during charging can be improved, and this film layer can reach the cutoff voltage of the secondary battery first. Furthermore, by rationally setting the relationship between the resistances of the positive and negative electrodes, the film layer on the other side of the positive electrode can also have a sufficient amount of pre-stored active ions; as the secondary battery cycles, these pre-stored active ions can be gradually released to replenish the consumption of active ions, thereby delaying the capacity decay of the secondary battery and significantly extending its cycle life.

[0063] When R4 / R3 = R2 / R1, the positive electrode cannot achieve pre-storage of active ions, which does not significantly improve the cycle life of the secondary battery and cannot give the secondary battery a longer cycle life.

[0064] In this application, the capacity of the positive electrode film has a meaning known in the art and can be measured using instruments and methods known in the art. For example, a blue electrode tester can be used for testing. As an example, the capacity of the positive electrode film can be tested by the following method: the positive electrode film on one side of a cold-pressed positive electrode sheet is wiped off to obtain a single-sided coated positive electrode sheet. The single-sided coated positive electrode sheet is punched into a small circular piece with an area of ​​S0, and then assembled into a button cell in a glove box. It is charged at a constant current of 0.1mA to the charging cutoff voltage, and discharged at a constant current of 0.1mA to the discharging cutoff voltage to obtain the discharge capacity CAP0. The capacity of the positive electrode film is obtained by the formula CAP0×S / S0, where S0 is the area of ​​the small circular piece and S is the area of ​​the positive electrode film.

[0065] Specifically, the capacity CAP1 of the first positive electrode film can be tested using the following method: After wiping off the second positive electrode film of the cold-pressed positive electrode sheet, it is punched into a small circular piece with an area of ​​S0. The small circular pieces are assembled into a button cell in a glove box. Then, it is charged at a constant current of 0.1mA to the charging cutoff voltage on a blue electric current tester, and then discharged at a constant current of 0.1mA to the discharging cutoff voltage to obtain the discharge capacity CAP0. The capacity CAP1 of the first positive electrode film is obtained by the formula CAP0×S1 / S0, where S0 is the area of ​​the small circular piece and S1 is the area of ​​the first positive electrode film. The capacity CAP2 of the second positive electrode film can be tested using the following method: After wiping off the first positive electrode film of the cold-pressed positive electrode sheet, it is punched into a small circular piece with an area of ​​S0. The small circular pieces are assembled into a button cell in a glove box. Then, it is charged at a constant current of 0.1mA to the charging cutoff voltage on a blue electric current tester, and then discharged at a constant current of 0.1mA to the discharging cutoff voltage to obtain the discharge capacity CAP0. The capacity CAP2 of the second positive electrode film is obtained by the formula CAP0×S2 / S0, where S0 is the area of ​​the small circular piece and S2 is the area of ​​the second positive electrode film.

[0066] Coin cell batteries can be assembled in the following order: negative electrode casing, lithium foil, a drop of electrolyte, separator, a drop of electrolyte, a small circular electrode with an area of ​​S0, a gasket, and a spring contact. The diameter of the coin cell battery can be 14mm. During testing, the film layer on one side of the electrode can be wiped off using water or other solvents. Testing can be performed using a punching machine from IEST of Yuaneng Technology Co., Ltd.

[0067] In this application, film resistance has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be tested using an electrode resistance meter (e.g., an IEST BER1000 electrode resistance meter from Yuaneng Technology Co., Ltd.). As an example, the film resistance can be tested using the following method: the film layer on one side of a cold-pressed electrode is wiped off to obtain a single-sided coated electrode. The single-sided coated electrode is placed parallel between the two conductive terminals of the electrode resistance meter, and a certain pressure is applied to fix it, thus obtaining the film resistance.

[0068] Specifically, the resistance R1 of the first positive electrode film can be tested using the following method: The second positive electrode film of the cold-pressed positive electrode sheet is wiped off, and then the sheet is placed parallel between the two conductive terminals of an electrode resistance meter. A certain pressure is applied to fix it, thus obtaining the resistance R1 of the first positive electrode film. The resistance R2 of the second positive electrode film can be tested using the following method: The first positive electrode film of the cold-pressed positive electrode sheet is wiped off, and then the sheet is placed parallel between the two conductive terminals of an electrode resistance meter. A certain pressure is applied to fix it, thus obtaining the resistance R2 of the second positive electrode film. The resistance R3 of the first negative electrode film can be tested using the following method: The second negative electrode film of the cold-pressed negative electrode sheet is wiped off, and then the sheet is placed parallel between the two conductive terminals of an electrode resistance meter. A certain pressure is applied to fix it, thus obtaining the resistance R3 of the first negative electrode film. The resistance R4 of the second negative electrode film can be tested by the following method: wipe off the first negative electrode film of the cold-pressed negative electrode sheet, then place it parallel between the two conductive terminals of the electrode resistance meter, apply a certain pressure to fix it, and obtain the resistance R4 of the second negative electrode film.

[0069] Optionally, the diameter of the conductive terminal can be 14 mm, the applied pressure can be 15 MPa to 27 MPa, and the sampling time range can be 10 s to 20 s. During testing, the electrode can be cut into a certain area (e.g., 10 cm × 10 cm) before testing. During testing, the film layer on one side of the electrode can be wiped off using water or other solvents.

[0070] It should be noted that during testing, the electrode sheets (e.g., positive or negative electrode sheets) can be freshly prepared and cold-pressed, or obtained from a secondary battery. An exemplary method for obtaining electrode sheets from a secondary battery is as follows: After fully discharging the secondary battery, disassemble the electrode sheets, immerse the electrode sheets in an organic solvent (e.g., dimethyl carbonate) for a period of time (e.g., 30 min), and then remove the electrode sheets and dry them at a specific temperature and time (e.g., 80°C, 6 h).

[0071] In some embodiments, the electrode assembly 52 satisfies 0 < |R4 / R3-R2 / R1| ≤ 20. When |R4 / R3-R2 / R1| > 20, the positive electrode plate will quickly reach the charging cutoff voltage during the charging of the secondary battery, resulting in a large number of active ions remaining in both the first and second positive electrode films, thus reducing the energy density of the secondary battery.

[0072] For example, |R4 / R3-R2 / R1| is a range consisting of any of the following values: 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or above. Optionally, the electrode assembly 52 satisfies 0 < |R4 / R3 - R2 / R1| ≤ 15, 0 < |R4 / R3 - R2 / R1| ≤ 10, 0 < |R4 / R3 - R2 / R1| ≤ 8, 0 < |R4 / R3 - R2 / R1| ≤ 5, 0 < |R4 / R3 - R2 / R1| ≤ 2, and 0.1 ≤ |R4 / R3 - R2 / R1| ≤ 15. 1∣≤20, 0.1≤∣R4 / R3-R2 / R1∣≤15, 0.1≤∣R4 / R3-R2 / R1∣≤10, 0.1≤∣R4 / R3- R2 / R1∣≤8, 0.1≤∣R4 / R3-R2 / R1∣≤5, 0.1≤∣R4 / R3-R2 / R1∣≤2, 0.2≤∣R4 / R3- R2 / R1∣≤20, 0.2≤∣R4 / R3-R2 / R1∣≤15, 0.2≤∣R4 / R3-R2 / R1∣≤10, 0.2≤∣R4 / R3-R2 / R1∣≤8, 0.2≤∣R4 / R3-R2 / R1∣≤5, or 0.2≤∣R4 / R3-R2 / R1∣≤2.

[0073] In some embodiments, the resistance R1 of the first positive electrode film 101 satisfies 0Ω < R1 ≤ 20Ω. Optionally, 0Ω < R1 ≤ 5Ω.

[0074] In some embodiments, the resistance R2 of the second positive electrode film 102 satisfies 0Ω < R2 ≤ 20Ω. Optionally, 0Ω < R2 ≤ 5Ω.

[0075] In some embodiments, the resistance R3 of the first negative electrode film layer 201 satisfies 0mΩ < R3 ≤ 200mΩ. Optionally, 0mΩ < R3 ≤ 50mΩ.

[0076] In some embodiments, the resistance R4 of the second negative electrode film 202 satisfies 0mΩ < R4 ≤ 200mΩ. Optionally, 0mΩ < R4 ≤ 50mΩ.

[0077] When the resistances of the first positive electrode layer, the second positive electrode layer, the first negative electrode layer, and the second negative electrode layer are all within appropriate ranges, the consistency between the positive and negative electrode plates is better, which is beneficial for the secondary battery to obtain a longer cycle life.

[0078] In some embodiments, the negative electrode 20 satisfies R4 / R3≥1, and the electrode assembly 52 satisfies 0<|R4 / R3-R2 / R1|≤20. In this case, the secondary battery has a longer cycle life and a high energy density.

[0079] For example, R4 / R3 is a range consisting of any of the following values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or above. Optionally, the negative electrode 20 satisfies 1≤R4 / R3≤30, 1≤R4 / R3≤25, 1≤R4 / R3≤20, 1≤R4 / R3≤15, 1≤R4 / R3≤10, 1≤R4 / R3≤8, 1≤R4 / R3≤5, 1≤R4 / R3≤4, 1≤R4 / R3≤3, 1≤R4 / R3≤2, 1<R4 / R3≤30, 1<R4 / R3≤25, 1<R4 / R3≤20, 1<R4 / R3≤15, 1<R4 / R3≤10, 1<R4 / R3≤8, 1<R4 / R3≤5, 1<R4 / R3≤4, 1<R4 / R3≤3, or 1<R4 / R3≤2.

[0080] For example, |R4 / R3-R2 / R1| is a range consisting of any of the following values: 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or above. Optionally, the electrode assembly 52 satisfies 0 < |R4 / R3-R2 / R1| ≤ 15, 0 < |R4 / R3-R2 / R1| ≤ 10, 0 < |R4 / R3-R2 / R1| ≤ 8, 0 < |R4 / R3-R2 / R1| ≤ 5, 0 < |R4 / R3-R2 / R1| ≤ 2, 0.1 ≤ |R4 / R3-R2 / R1| ≤ 20, 0.1 ≤ |R4 / R3-R2 / R1| ≤ 15, 0.1 ≤ |R4 / R3-R2 / R1| ≤ 10, 0.1 ≤ |R4 / R3-R2 / R1∣≤8, 0.1≤∣R4 / R3-R2 / R1∣≤5, 0.1≤∣R4 / R3-R2 / R1∣≤2, 0.2≤∣R4 / R3-R2 / R1∣≤20, 0.2≤∣R4 / R3-R2 / R 1∣≤15, 0.2≤∣R4 / R3-R2 / R1∣≤10, 0.2≤∣R4 / R3-R2 / R1∣≤8, 0.2≤∣R4 / R3-R2 / R1∣≤5, or 0.2≤∣R4 / R3-R2 / R1∣≤2.

[0081] At this point, there are no particular restrictions on the resistance ratio R2 / R1 between the first positive electrode film layer 101 and the second positive electrode film layer 102.

[0082] R2 / R1 can be greater than 1, equal to 1, or less than 1. For example, R2 / R1 is a range consisting of any of the following values: 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or more. Optionally, the positive electrode 10 satisfies 0 < R2 / R1 ≤ 20, 0 < R2 / R1 ≤ 15, 0 < R2 / R1 ≤ 10, 0 < R2 / R1 ≤ 8, 0 < R2 / R1 ≤ 5, 0 < R2 / R1 ≤ 4, 0 < R2 / R1 ≤ 3, 0 < R2 / R1 ≤ 2, or 0 < R2 / R1 ≤ 1.

[0083] For example, the negative electrode 20 satisfies R4 / R3≥1, the positive electrode 10 satisfies 0<R2 / R1≤20, and the electrode assembly 52 satisfies 0<|R4 / R3-R2 / R1|≤20.

[0084] For example, the negative electrode 20 satisfies R4 / R3≥1, the positive electrode 10 satisfies 0<R2 / R1≤20, and the electrode assembly 52 satisfies 0.2≤|R4 / R3-R2 / R1|≤10.

[0085] For example, the negative electrode 20 satisfies R4 / R3≥1, the positive electrode 10 satisfies 0<R2 / R1≤20, and the electrode assembly 52 satisfies 0.2≤|R4 / R3-R2 / R1|≤5.

[0086] For example, the negative electrode 20 satisfies 1≤R4 / R3≤30, the positive electrode 10 satisfies 0<R2 / R1≤20, and the electrode assembly 52 satisfies 0<|R4 / R3-R2 / R1|≤20.

[0087] For example, the negative electrode 20 satisfies 1≤R4 / R3≤30, the positive electrode 10 satisfies 0<R2 / R1≤20, and the electrode assembly 52 satisfies 0.2≤|R4 / R3-R2 / R1|≤10.

[0088] For example, the negative electrode 20 satisfies 1≤R4 / R3≤30, the positive electrode 10 satisfies 0<R2 / R1≤20, and the electrode assembly 52 satisfies 0.2≤|R4 / R3-R2 / R1|≤5.

[0089] In some embodiments, the negative electrode 20 satisfies 0 < R4 / R3 < 1, the positive electrode 10 satisfies 0 < R2 / R1 < 1, and the electrode assembly 52 satisfies 0 < |R4 / R3 - R2 / R1| < 1. In this case, the secondary battery has a longer cycle life and a high energy density.

[0090] For example, R4 / R3 is a range consisting of any value of 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or higher. Optionally, the negative electrode 20 satisfies 0 < R4 / R3 < 1, 0 < R4 / R3 ≤ 0.9, 0 < R4 / R3 ≤ 0.8, 0 < R4 / R3 ≤ 0.7, 0 < R4 / R3 ≤ 0.6, 0.05 ≤ R4 / R3 < 1, 0.05 ≤ R4 / R3 ≤ 0.9, 0.05 ≤ R4 / R3 ≤ 0.8, 0.05 ≤ R4 / R3 ≤ 0.7, and 0.05 ≤ R4 / R3 ≤ 0. 0.6, 0.1≤R4 / R3<1, 0.1≤R4 / R3≤0.9, 0.1≤R4 / R3≤0.8, 0.1≤R4 / R3≤0.7, 0.1≤R4 / R3≤0.6, 0.2≤R4 / R3<1, 0.2≤R4 / R3≤0.9, 0.2≤R4 / R3≤0.8, 0.2≤R4 / R3≤0.7, or 0.2≤R4 / R3≤0.6.

[0091] For example, R2 / R1 is a range consisting of any value of 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or higher. Optionally, the positive electrode 10 satisfies 0 < R2 / R1 < 1, 0 < R2 / R1 ≤ 0.9, 0 < R2 / R1 ≤ 0.8, 0 < R2 / R1 ≤ 0.7, 0 < R2 / R1 ≤ 0.6, 0.05 ≤ R2 / R1 < 1, 0.05 ≤ R2 / R1 ≤ 0.9, 0.05 ≤ R2 / R1 ≤ 0.8, 0.05 ≤ R2 / R1 ≤ 0.7, and 0.05 ≤ R2 / R1 ≤ 0. 0.6, 0.1≤R2 / R1<1, 0.1≤R2 / R1≤0.9, 0.1≤R2 / R1≤0.8, 0.1≤R2 / R1≤0.7, 0.1≤R2 / R1≤0.6, 0.2≤R2 / R1<1, 0.2≤R2 / R1≤0.9, 0.2≤R2 / R1≤0.8, 0.2≤R2 / R1≤0.7, or 0.2≤R2 / R1≤0.6.

[0092] For example, |R4 / R3-R2 / R1| is a range consisting of any of the values ​​0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or higher. Optionally, the electrode assembly 52 satisfies 0 < |R4 / R3-R2 / R1| < 1, 0 < |R4 / R3-R2 / R1| ≤ 0.9, 0 < |R4 / R3-R2 / R1| ≤ 0.8, 0 < |R4 / R3-R2 / R1| ≤ 0.7, and 0 < |R4 / R3-R2 / R1| ≤ 0.6. 0.05≤|R4 / R3-R2 / R1| .6, 0.1≤∣R4 / R3-R2 / R1∣<1, ​​0.1≤∣R4 / R3-R2 / R1∣≤0.9, 0.1≤∣R4 / R3-R2 / R1∣≤0.8, 0.1≤∣R4 / R3-R2 / R1∣≤0.7, 0.1≤∣R4 / R3-R2 / R1∣≤0.6 , 0.2≤∣R4 / R3-R2 / R1∣<1, 0.2≤∣R4 / R3-R2 / R1∣≤0.9, 0.2≤∣R4 / R3-R2 / R1∣≤0.8, 0.2≤∣R4 / R3-R2 / R1∣≤0.7, or 0.2≤∣R4 / R3-R2 / R1∣≤0.6.

[0093] For example, the negative electrode 20 satisfies 0 < R4 / R3 < 1, the positive electrode 10 satisfies 0 < R2 / R1 < 1, and the electrode assembly 52 satisfies 0.2 ≤ |R4 / R3 - R2 / R1| ≤ 0.9.

[0094] For example, the negative electrode 20 satisfies 0.05≤R4 / R3≤0.9, the positive electrode 10 satisfies 0.05≤R4 / R3≤0.9, and the electrode assembly 52 satisfies 0<|R4 / R3-R2 / R1|<1.

[0095] For example, the negative electrode 20 satisfies 0.05≤R4 / R3≤0.9, the positive electrode 10 satisfies 0.05≤R4 / R3≤0.9, and the electrode assembly 52 satisfies 0.2≤|R4 / R3-R2 / R1|<1.

[0096] In some embodiments, the negative electrode 20 satisfies 0 < R4 / R3 < 1, the positive electrode 10 satisfies R2 / R1 ≥ 1, and the electrode assembly 52 satisfies 0 < |R4 / R3 - R2 / R1| ≤ 20. In this case, the secondary battery has a longer cycle life and a high energy density.

[0097] For example, R4 / R3 is a range consisting of any value of 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or higher. Optionally, the negative electrode 20 satisfies 0 < R4 / R3 < 1, 0 < R4 / R3 ≤ 0.9, 0 < R4 / R3 ≤ 0.8, 0 < R4 / R3 ≤ 0.7, 0 < R4 / R3 ≤ 0.6, 0.05 ≤ R4 / R3 < 1, 0.05 ≤ R4 / R3 ≤ 0.9, 0.05 ≤ R4 / R3 ≤ 0.8, 0.05 ≤ R4 / R3 ≤ 0.7, and 0.05 ≤ R4 / R3 ≤ 0. 0.6, 0.1≤R4 / R3<1, 0.1≤R4 / R3≤0.9, 0.1≤R4 / R3≤0.8, 0.1≤R4 / R3≤0.7, 0.1≤R4 / R3≤0.6, 0.2≤R4 / R3<1, 0.2≤R4 / R3≤0.9, 0.2≤R4 / R3≤0.8, 0.2≤R4 / R3≤0.7, or 0.2≤R4 / R3≤0.6.

[0098] For example, R2 / R1 is a range consisting of any of the values ​​1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or higher. Optionally, the positive electrode 10 satisfies 1≤R2 / R1≤20, 1≤R2 / R1≤15, 1≤R2 / R1≤10, 1≤R2 / R1≤8, 1≤R2 / R1≤5, 1≤R2 / R1≤4, 1≤R2 / R1≤3, or 1≤R2 / R1≤2.

[0099] For example, |R4 / R3-R2 / R1| is a range consisting of any of the following values: 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or above. Optionally, the electrode assembly 52 satisfies 0 < |R4 / R3-R2 / R1| ≤ 15, 0 < |R4 / R3-R2 / R1| ≤ 10, 0 < |R4 / R3-R2 / R1| ≤ 8, 0 < |R4 / R3-R2 / R1| ≤ 5, 0 < |R4 / R3-R2 / R1| ≤ 2, 0.1 ≤ |R4 / R3-R2 / R1| ≤ 20, 0.1 ≤ |R4 / R3-R2 / R1| ≤ 15, 0.1 ≤ |R4 / R3-R2 / R1| ≤ 10, 0.1 ≤ |R4 / R3-R2 / R1∣≤8, 0.1≤∣R4 / R3-R2 / R1∣≤5, 0.1≤∣R4 / R3-R2 / R1∣≤2, 0.2≤∣R4 / R3-R2 / R1∣≤20, 0.2≤∣R4 / R3-R2 / R 1∣≤15, 0.2≤∣R4 / R3-R2 / R1∣≤10, 0.2≤∣R4 / R3-R2 / R1∣≤8, 0.2≤∣R4 / R3-R2 / R1∣≤5, or 0.2≤∣R4 / R3-R2 / R1∣≤2.

[0100] For example, the negative electrode 20 satisfies 0 < R4 / R3 < 1, the positive electrode 10 satisfies R2 / R1 ≥ 1, and the electrode assembly 52 satisfies 0.2 ≤ |R4 / R3 - R2 / R1| ≤ 10.

[0101] For example, the negative electrode 20 satisfies 0 < R4 / R3 < 1, the positive electrode 10 satisfies R2 / R1 ≥ 1, and the electrode assembly 52 satisfies 0.2 ≤ |R4 / R3 - R2 / R1| ≤ 5.

[0102] For example, the negative electrode 20 satisfies 0 < R4 / R3 < 1, the positive electrode 10 satisfies 1 ≤ R2 / R1 ≤ 20, and the electrode assembly 52 satisfies 0 < |R4 / R3 - R2 / R1| < 20.

[0103] For example, the negative electrode 20 satisfies 0 < R4 / R3 < 1, the positive electrode 10 satisfies 1 ≤ R2 / R1 ≤ 20, and the electrode assembly 52 satisfies 0.2 ≤ |R4 / R3 - R2 / R1| ≤ 10.

[0104] For example, the negative electrode 20 satisfies 0 < R4 / R3 < 1, the positive electrode 10 satisfies 1 ≤ R2 / R1 ≤ 20, and the electrode assembly 52 satisfies 0.2 ≤ |R4 / R3 - R2 / R1| ≤ 5.

[0105] For example, the negative electrode 20 satisfies 0.05≤R4 / R3≤0.9, the positive electrode 10 satisfies 1≤R2 / R1≤20, and the electrode assembly 52 satisfies 0<|R4 / R3-R2 / R1|<20.

[0106] For example, the negative electrode 20 satisfies 0.05≤R4 / R3≤0.9, the positive electrode 10 satisfies 1≤R2 / R1≤20, and the electrode assembly 52 satisfies 0.2≤|R4 / R3-R2 / R1|≤10.

[0107] For example, the negative electrode 20 satisfies 0.05≤R4 / R3≤0.9, the positive electrode 10 satisfies 1≤R2 / R1≤20, and the electrode assembly 52 satisfies 0.2≤|R4 / R3-R2 / R1|≤5.

[0108] It should be noted that there are several theoretically feasible ways to adjust the resistance R1 of the first positive electrode film 101, the resistance R2 of the second positive electrode film 102, the resistance R3 of the first negative electrode film 201, and the resistance R4 of the second negative electrode film 202. Some of these adjustment methods are listed in this application. It should be understood that the methods listed in this specification are only for explaining this application and are not intended to limit this application.

[0109] As an example, when the positive electrode 10 satisfies one or more of the following (1) to (7), the resistance R2 of the second positive electrode film 102 is less than the resistance R1 of the first positive electrode film 101.

[0110] (1) The surface of the second positive electrode active material has a conductive carbon layer. When the surface of the second positive electrode active material has a conductive carbon layer and the surface of the first positive electrode active material does not have a conductive carbon layer, the resistance R2 of the second positive electrode film 102 can be less than the resistance R1 of the first positive electrode film 101.

[0111] (2) The conductivity of the second positive electrode conductive agent is greater than that of the first positive electrode conductive agent. By making the second positive electrode film 102 contain a second positive electrode conductive agent with higher conductivity, the resistance R2 of the second positive electrode film 102 can be made less than the resistance R1 of the first positive electrode film 101.

[0112] (3) w1 < w2, where w1 represents the mass percentage of the first positive electrode conductive agent based on the total mass of the first positive electrode film 101, and w2 represents the mass percentage of the second positive electrode conductive agent based on the total mass of the second positive electrode film 102.

[0113] (4) w3 > w4, where w3 represents the mass percentage of the first positive electrode binder based on the total mass of the first positive electrode film layer 101, and w4 represents the mass percentage of the second positive electrode binder based on the total mass of the second positive electrode film layer 102.

[0114] (5) The compaction density of the second positive electrode film layer 102 is less than that of the first positive electrode film layer 101.

[0115] (6) Figure 4 As shown, the second positive electrode film layer 102 includes a second positive electrode host layer 1021 and a second positive electrode conductive carbon layer 1022, with the second positive electrode conductive carbon layer 1022 located on at least one of the two opposing surfaces of the second positive electrode host layer 1021.

[0116] (7) Figure 5 As shown, the first positive electrode film layer 101 includes a first positive electrode host layer 1011 and a first positive electrode ceramic layer 1013, wherein the first positive electrode ceramic layer 1013 is located on at least one of the two opposing surfaces of the first positive electrode host layer 1011. Optionally, the first positive electrode ceramic layer 1013 includes one or more of alumina ceramic, silicon nitride ceramic, silicon carbide ceramic, and boron nitride ceramic.

[0117] Understandably, despite Figure 4 The diagram shows the second positive conductive carbon layer 1022 located on two opposing surfaces of the second positive electrode body layer 1021. However, in other embodiments, the second positive conductive carbon layer 1022 may also be located on one of the two opposing surfaces of the second positive electrode body layer 1021. Although Figure 5 The diagram shows the first positive electrode ceramic layer 1013 located on two opposing surfaces of the first positive electrode body layer 1011. However, in other embodiments, the first positive electrode ceramic layer 1013 may also be located on one of the two opposing surfaces of the first positive electrode body layer 1011. For example... Figure 6 As shown, the positive electrode 10 can also simultaneously satisfy the above (6) and (7) so that the resistance R2 of the second positive electrode film 102 is less than the resistance R1 of the first positive electrode film 101.

[0118] As an example, when the positive electrode 10 satisfies one or more of the following (8) to (14), the resistance R2 of the second positive electrode film 102 is greater than the resistance R1 of the first positive electrode film 101.

[0119] (8) The surface of the first positive electrode active material has a conductive carbon layer. When the surface of the first positive electrode active material has a conductive carbon layer and the surface of the second positive electrode active material does not have a conductive carbon layer, the resistance R2 of the second positive electrode film 102 can be greater than the resistance R1 of the first positive electrode film 101.

[0120] (9) The conductivity of the second positive electrode conductive agent is less than that of the first positive electrode conductive agent. By making the first positive electrode film 101 contain the first positive electrode conductive agent with higher conductivity, the resistance R2 of the second positive electrode film 102 can be greater than the resistance R1 of the first positive electrode film 101.

[0121] (10) w1>w2, w1 represents the mass percentage of the first positive electrode conductive agent based on the total mass of the first positive electrode film 101, and w2 represents the mass percentage of the second positive electrode conductive agent based on the total mass of the second positive electrode film 102.

[0122] (11) w3 < w4, where w3 represents the mass percentage of the first positive electrode binder based on the total mass of the first positive electrode film layer 101, and w4 represents the mass percentage of the second positive electrode binder based on the total mass of the second positive electrode film layer 102.

[0123] (12) The compaction density of the second positive electrode film layer 102 is greater than that of the first positive electrode film layer 101.

[0124] (13) such as Figure 7 As shown, the first positive electrode film layer 101 includes a first positive electrode host layer 1011 and a first positive electrode conductive carbon layer 1012, with the first positive electrode conductive carbon layer 1012 located on at least one of the two opposing surfaces of the first positive electrode host layer 1011.

[0125] (14) such as Figure 8 As shown, the second positive electrode film layer 102 includes a second positive electrode host layer 1021 and a second positive electrode ceramic layer 1023, wherein the second positive electrode ceramic layer 1023 is located on at least one of the two opposing surfaces of the second positive electrode host layer 1021. Optionally, the second positive electrode ceramic layer 1023 includes one or more of alumina ceramic, silicon nitride ceramic, silicon carbide ceramic, and boron nitride ceramic.

[0126] Understandably, despite Figure 7 The diagram shows the first positive conductive carbon layer 1012 located on two opposing surfaces of the first positive electrode body layer 1011. However, in other embodiments, the first positive conductive carbon layer 1012 may also be located on one of the two opposing surfaces of the first positive electrode body layer 1011. Although Figure 8 The diagram shows the second positive electrode ceramic layer 1023 located on two opposing surfaces of the second positive electrode body layer 1021. However, in other embodiments, the second positive electrode ceramic layer 1023 may also be located on one of the two opposing surfaces of the second positive electrode body layer 1021. For example... Figure 9 As shown, the positive electrode 10 can also simultaneously satisfy the above (13) and (14) so ​​that the resistance R2 of the second positive electrode film 102 is greater than the resistance R1 of the first positive electrode film 101.

[0127] As an example, when the negative electrode 20 satisfies one or more of the following conditions (a) to (g), the resistance R4 of the second negative electrode film 202 is greater than the resistance R3 of the first negative electrode film 201.

[0128] (a) The surface of the first negative electrode active material has a conductive carbon layer. When the surface of the first negative electrode active material has a conductive carbon layer and the surface of the second negative electrode active material does not have a conductive carbon layer, the resistance R4 of the second negative electrode film 202 can be greater than the resistance R3 of the first negative electrode film 201.

[0129] (b) The conductivity of the first negative electrode conductive agent is greater than that of the second negative electrode conductive agent. By including the first negative electrode film 201 with the first negative electrode conductive agent with higher conductivity, the resistance R4 of the second negative electrode film 202 can be greater than the resistance R3 of the first negative electrode film 201.

[0130] (c) w5 > w6, where w5 represents the mass percentage of the first negative electrode conductive agent based on the total mass of the first negative electrode film layer 201, and w6 represents the mass percentage of the second negative electrode conductive agent based on the total mass of the second negative electrode film layer 202.

[0131] (d) w7 < w8, where w7 represents the mass percentage of the first negative electrode binder based on the total mass of the first negative electrode film layer 201, and w8 represents the mass percentage of the second negative electrode binder based on the total mass of the second negative electrode film layer 202.

[0132] (e) The compaction density of the first negative electrode film layer 201 is less than the compaction density of the second negative electrode film layer 202.

[0133] (f) such as Figure 10 As shown, the first negative electrode film layer 201 includes a first negative electrode host layer 2011 and a first negative electrode conductive carbon layer 2012, with the first negative electrode conductive carbon layer 2012 located on at least one of the two opposing surfaces of the first negative electrode host layer 2011.

[0134] (g) such as Figure 11 As shown, the second negative electrode film layer 202 includes a second negative electrode host layer 2021 and a second negative electrode ceramic layer 2023, wherein the second negative electrode ceramic layer 2023 is located on at least one of the two opposing surfaces of the second negative electrode host layer 2021. Optionally, the second negative electrode ceramic layer 2023 includes one or more of alumina ceramic, silicon nitride ceramic, silicon carbide ceramic, and boron nitride ceramic.

[0135] Understandably, despite Figure 10 The diagram shows the first negative electrode conductive carbon layer 2012 located on two opposing surfaces of the first negative electrode body layer 2011. However, in other embodiments, the first negative electrode conductive carbon layer 2012 may also be located on one of the two opposing surfaces of the first negative electrode body layer 2011. Although Figure 11The diagram shows the second negative electrode ceramic layer 2023 located on two opposing surfaces of the second negative electrode body layer 2021. However, in other embodiments, the second negative electrode ceramic layer 2023 may also be located on one of the two opposing surfaces of the second negative electrode body layer 2021. For example... Figure 12 As shown, the negative electrode 20 can also simultaneously satisfy (f) and (g) above, so that the resistance R4 of the second negative electrode film 202 is greater than the resistance R3 of the first negative electrode film 201.

[0136] As an example, when the negative electrode 20 satisfies one or more of the following (h) to (n), the resistance R4 of the second negative electrode film 202 is less than the resistance R3 of the first negative electrode film 201.

[0137] (h) The surface of the second negative electrode active material has a conductive carbon layer. When the surface of the first negative electrode active material does not have a conductive carbon layer, and the surface of the second negative electrode active material has a conductive carbon layer, the resistance R4 of the second negative electrode film 202 can be less than the resistance R3 of the first negative electrode film 201.

[0138] (i) The conductivity of the first negative electrode conductive agent is less than that of the second negative electrode conductive agent. By including the second negative electrode film 202 with a second negative electrode conductive agent that has higher conductivity, the resistance R4 of the second negative electrode film 202 can be made less than the resistance R3 of the first negative electrode film 201.

[0139] (j) w5 < w6, where w5 represents the mass percentage of the first negative electrode conductive agent based on the total mass of the first negative electrode film layer 201, and w6 represents the mass percentage of the second negative electrode conductive agent based on the total mass of the second negative electrode film layer 202.

[0140] (k)w7>w8, where w7 represents the mass percentage of the first negative electrode binder based on the total mass of the first negative electrode film layer 201, and w8 represents the mass percentage of the second negative electrode binder based on the total mass of the second negative electrode film layer 202.

[0141] (l) The compaction density of the first negative electrode film layer 201 is greater than that of the second negative electrode film layer 202.

[0142] (m) such as Figure 13 As shown, the second negative electrode film layer 202 includes a second negative electrode host layer 2021 and a second negative electrode conductive carbon layer 2022, with the second negative electrode conductive carbon layer 2022 located on at least one of the two opposing surfaces of the second negative electrode host layer 2021.

[0143] (m) such as Figure 14As shown, the first negative electrode film layer 201 includes a first negative electrode host layer 2011 and a first negative electrode ceramic layer 2013, wherein the first negative electrode ceramic layer 2013 is located on at least one of the two opposing surfaces of the first negative electrode host layer 2011. Optionally, the first negative electrode ceramic layer 2013 includes one or more of alumina ceramic, silicon nitride ceramic, silicon carbide ceramic, and boron nitride ceramic.

[0144] Understandably, despite Figure 13 The diagram shows the second negative electrode conductive carbon layer 2022 located on two opposing surfaces of the second negative electrode body layer 2021; however, in other embodiments, the second negative electrode conductive carbon layer 2022 is located on one of the two opposing surfaces of the second negative electrode body layer 2021. Although Figure 14 The diagram shows the first negative electrode ceramic layer 2013 located on two opposing surfaces of the first negative electrode body layer 2011; however, in other embodiments, the first negative electrode ceramic layer 2013 is located on one of the two opposing surfaces of the first negative electrode body layer 2011. For example... Figure 15 As shown, the negative electrode 20 can also simultaneously satisfy the above (m) and (n) so that the resistance R4 of the second negative electrode film 202 is less than the resistance R3 of the first negative electrode film 201.

[0145] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, the positive electrode current collector may be aluminum foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may be selected from one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0146] In some embodiments, the first and second positive electrode active materials may be positive electrode active materials known in the art for use in secondary batteries. As examples, the first and second positive electrode active materials each independently include one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. This application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0147] In some embodiments, the modified compounds of the above-mentioned positive electrode active materials may be those that dope the positive electrode active materials, modify their surface coating, or modify their surface coating while doping.

[0148] In some embodiments, in order to further improve the energy density of the secondary battery, the first positive electrode active material and the second positive electrode active material may also independently include one or more of the lithium transition metal oxides and their modified compounds shown in Formula 1.

[0149] Li a Ni b Co c M d O e A f Formula 1

[0150] In Formula 1, 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.

[0151] In some embodiments, as an example, the first positive electrode binder and the second positive electrode binder each independently include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0152] In some embodiments, as an example, the first positive electrode conductive agent and the second positive electrode conductive agent each independently include one or more of superconducting carbon, conductive graphite (e.g., KS-6), acetylene black, carbon black (e.g., Super P), Ketjen black, carbon dots, carbon nanotubes (CNTs), graphene, and carbon nanofibers.

[0153] In some embodiments, the first and second positive electrode films are typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing positive electrode active material, positive electrode conductive agent, positive electrode binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0154] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may be selected from one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0155] In some embodiments, the first and second negative electrode active materials may be negative electrode active materials known in the art for use in secondary batteries. As an example, the first and second negative electrode active materials each independently include one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0156] In some embodiments, as an example, the first negative electrode binder and the second negative electrode binder each independently include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0157] In some embodiments, as an example, the first negative electrode conductive agent and the second negative electrode conductive agent each independently include one or more of superconducting carbon, conductive graphite (e.g., KS-6), acetylene black, carbon black (e.g., Super P), Ketjen black, carbon dots, carbon nanotubes (CNTs), graphene, and carbon nanofibers.

[0158] In some embodiments, the first negative electrode film layer and the second negative electrode film layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose CMC-Na).

[0159] In some embodiments, the first and second negative electrode films are typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing negative electrode active materials, negative electrode conductive agents, negative electrode binders, and any other components in a solvent and stirring until homogeneous. The solvent can be deionized water, but is not limited to this.

[0160] [Electrolytes]

[0161] The electrolyte acts as a conductor of active ions between the positive and negative electrodes. The secondary battery of this application does not have specific limitations on the type of electrolyte and can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0162] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0163] In some embodiments, the type of electrolyte salt is not specifically limited and can be selected according to actual needs. For example, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0164] In some embodiments, the type of solvent is not specifically limited and can be selected according to actual needs. As an example, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl 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).

[0165] In some embodiments, the solvent is a non-aqueous solvent.

[0166] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature performance, etc.

[0167] [Isolation membrane]

[0168] Secondary batteries using electrolytes, as well as some secondary batteries using solid electrolytes, also include a separator. The separator is positioned between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0169] In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0170] [Electrode Assembly Fabrication Method]

[0171] This application also provides a method for preparing an electrode assembly, the method comprising the following steps:

[0172] S10, the first positive electrode active material, the first positive electrode conductive agent, and the first positive electrode binder are dispersed in a solvent and stirred evenly to form a first positive electrode slurry. The second positive electrode active material, the second positive electrode conductive agent, and the second positive electrode binder are dispersed in a solvent and stirred evenly to form a second positive electrode slurry. The first positive electrode slurry and the second positive electrode slurry are respectively coated on two opposite surfaces of the positive electrode current collector. After drying and cold pressing, a positive electrode sheet is obtained. The first positive electrode slurry and the second positive electrode slurry respectively form a first positive electrode film layer and a second positive electrode film layer.

[0173] S20, the first negative electrode active material, the first negative electrode conductive agent, and the first negative electrode binder are dispersed in a solvent and stirred evenly to form a first negative electrode slurry. The second negative electrode active material, the second negative electrode conductive agent, and the second negative electrode binder are dispersed in a solvent and stirred evenly to form a second negative electrode slurry. The first negative electrode slurry and the second negative electrode slurry are respectively coated on two opposite surfaces of the negative electrode current collector. After drying and cold pressing, a negative electrode sheet is obtained, wherein the first negative electrode slurry and the second negative electrode slurry respectively form a first negative electrode film layer and a second negative electrode film layer.

[0174] S30, assemble the positive electrode, the separator, and the negative electrode into an electrode assembly, wherein the first positive electrode film layer is located on the side of the positive current collector close to the separator and the second negative electrode film layer is located on the side of the negative current collector close to the separator.

[0175] S40, the electrode assembly is tested, and the electrode assembly that simultaneously satisfies CAP1=CAP2 and |R4 / R3-R2 / R1|>0 is selected, where CAP1 represents the capacity of the first positive electrode film in Ah, CAP2 represents the capacity of the second positive electrode film in Ah, R1 represents the resistance of the first positive electrode film in Ω, R2 represents the resistance of the second positive electrode film in Ω, R3 represents the resistance of the first negative electrode film in mΩ, and R4 represents the resistance of the second negative electrode film in mΩ.

[0176] The electrode components obtained by the method of this application can significantly extend the cycle life of secondary batteries.

[0177] In some embodiments, as an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process or a stacking process.

[0178] In some embodiments, in step S40, optionally, electrode assemblies with 0 < |R4 / R3-R2 / R1| ≤ 20 are selected.

[0179] In some embodiments, in step S40, optionally, electrode assemblies with a 0.2 ≤ |R4 / R3-R2 / R1| ≤ 10 are selected.

[0180] In some embodiments, in step S40, optionally, electrode assemblies with a 0.2 ≤ |R4 / R3-R2 / R1| ≤ 5 are selected.

[0181] In some embodiments, the method further includes the following step: S50, selecting electrode assemblies that simultaneously satisfy 1≤R4 / R3≤30 and 0<R2 / R1≤20.

[0182] In some embodiments, the method further includes the following step: S50, selecting electrode assemblies that further simultaneously satisfy 0 < R4 / R3 ≤ 1 and 0 < R2 / R1 ≤ 1.

[0183] In some embodiments, the method further includes the following step: S50, selecting electrode assemblies that further simultaneously satisfy 0 < R4 / R3 ≤ 1 and 1 ≤ R2 / R1 ≤ 20.

[0184] Battery modules and battery packs

[0185] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0186] Figure 16 This is a schematic diagram of battery module 4 as an example. Figure 16 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0187] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0188] In some embodiments of this application, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0189] Figure 17 and Figure 18 This is a schematic diagram of battery pack 1 as an example. Figure 17 and Figure 18 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0190] Electrical appliances

[0191] This application also provides an electrical device, which includes at least one of the secondary battery, battery module, and battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, 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.

[0192] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0193] Figure 19 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0194] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0195] Example

[0196] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0197] Comparative Example 1

[0198] The structure of a secondary battery is as follows Figure 3 As shown.

[0199] Preparation of positive electrode sheet

[0200] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.1:2.7 to obtain the first positive electrode slurry. The first positive electrode slurry is then coated on the side of the positive electrode current collector aluminum foil near the separator.

[0201] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.1:2.7 to obtain a second positive electrode slurry. The second positive electrode slurry is then coated on the side of the positive electrode current collector aluminum foil away from the separator.

[0202] The coating weights of the first positive electrode slurry and the second positive electrode slurry are the same. The first positive electrode slurry is dried and cold-pressed to form the first positive electrode film layer, and the second positive electrode slurry is dried and cold-pressed to form the second positive electrode film layer.

[0203] Preparation of negative electrode sheet

[0204] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in a weight ratio of 97:1:0.5:1.5 in an appropriate amount of deionized water to obtain the first negative electrode slurry. The first negative electrode slurry is then coated on the side of the negative electrode current collector copper foil away from the separator.

[0205] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in a weight ratio of 97:1:0.5:1.5 in an appropriate amount of deionized water to obtain a second negative electrode slurry. The second negative electrode slurry is then coated on the side of the negative electrode current collector copper foil near the separator.

[0206] The first negative electrode slurry and the second negative electrode slurry have the same coating weight. The first negative electrode slurry is dried and cold-pressed to form the first negative electrode film layer, and the second negative electrode slurry is dried and cold-pressed to form the second negative electrode film layer.

[0207] Separating membrane

[0208] Porous polyethylene film is used as the separator.

[0209] Preparation of electrolyte

[0210] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent; LiPF6 was uniformly dissolved in the above organic solvent to obtain an electrolyte, wherein the concentration of LiPF6 was 1 mol / L.

[0211] Preparation of secondary batteries

[0212] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked and wound sequentially to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, the electrolyte is added, and after encapsulation, settling, formation, and capacity testing, a secondary battery is obtained. The formation process is as follows: the secondary battery is charged at a constant current of 0.1C to 3.0V, and then charged at a constant current of 0.2C to 3.75V. The capacity testing process is as follows: the secondary battery is charged at a constant current of 0.33C to 4.4V, and then charged at a constant voltage to 0.05C; the secondary battery is discharged at a constant current of 0.33C to 2.5V, then charged at a constant current of 0.33C to 3.65V, and then charged at a constant voltage to 0.05C.

[0213] Comparative Example 2

[0214] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive and negative electrode plates are adjusted.

[0215] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, conductive agent Super P, and conductive agent CNT are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.1:2.4:0.3 to obtain the first positive electrode slurry.

[0216] The side of the negative electrode current collector away from the separator is also coated with a conductive carbon layer with a thickness of 1μm.

[0217] Comparative Example 3

[0218] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive and negative electrode plates are adjusted.

[0219] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, conductive agent Super P, and conductive agent CNT are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.25:2.25:0.3 to obtain the first positive electrode slurry.

[0220] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR were mixed in a weight ratio of 97.2:0.8:0.5:1.5 in an appropriate amount of deionized water to obtain the first negative electrode slurry.

[0221] Example 1

[0222] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0223] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR were mixed in a weight ratio of 97.05:0.95:0.5:1.5 in an appropriate amount of deionized water to obtain the second negative electrode slurry.

[0224] Example 2

[0225] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0226] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR were mixed in a weight ratio of 97.1:0.9:0.5:1.5 in an appropriate amount of deionized water to obtain the second negative electrode slurry.

[0227] Example 3

[0228] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0229] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR were mixed in a weight ratio of 97.2:0.8:0.5:1.5 in an appropriate amount of deionized water to obtain the second negative electrode slurry.

[0230] Example 4

[0231] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0232] The negative electrode active material graphite, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 97:1:0.5:1.5 to obtain the second negative electrode slurry.

[0233] Example 5

[0234] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0235] The negative electrode active material graphite, conductive agent Super P, thickener CMC-Na, and binder SBR were mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 97.1:0.9:0.5:1.5 to obtain the second negative electrode slurry.

[0236] Example 6

[0237] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0238] The negative electrode active material graphite, conductive agent Super P, thickener CMC-Na, and binder SBR were mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 97.2:0.8:0.5:1.5 to obtain the second negative electrode slurry.

[0239] Example 7

[0240] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0241] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in a weight ratio of 97:1:0.5:1.5 in an appropriate amount of deionized water to obtain a first negative electrode slurry. The first negative electrode slurry is coated on the side of the negative electrode current collector copper foil away from the separator, and the side of the negative electrode current collector away from the separator is also coated with a conductive carbon layer with a thickness of 1 μm.

[0242] The negative electrode active material graphite, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in an appropriate amount of deionized water at a weight ratio of 97:1:0.5:1.5 to obtain a second negative electrode slurry. The second negative electrode slurry is then coated on the side of the negative electrode current collector copper foil near the separator.

[0243] Example 8

[0244] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0245] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in a weight ratio of 97:1:0.5:1.5 in an appropriate amount of deionized water to obtain a first negative electrode slurry. The first negative electrode slurry is coated on the side of the negative electrode current collector copper foil away from the separator, and the side of the negative electrode current collector away from the separator is also coated with a conductive carbon layer with a thickness of 1 μm.

[0246] The negative electrode active material graphite, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in an appropriate amount of deionized water at a weight ratio of 97.1:0.9:0.5:1.5 to obtain a second negative electrode slurry. The second negative electrode slurry is then coated on the side of the negative electrode current collector copper foil near the separator.

[0247] Example 9

[0248] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0249] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in a weight ratio of 97:1:0.5:1.5 in an appropriate amount of deionized water to obtain a first negative electrode slurry. The first negative electrode slurry is coated on the side of the negative electrode current collector copper foil away from the separator, and the side of the negative electrode current collector away from the separator is also coated with a conductive carbon layer with a thickness of 1 μm.

[0250] The negative electrode active material graphite, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in an appropriate amount of deionized water at a weight ratio of 97.2:0.8:0.5:1.5 to obtain a second negative electrode slurry. The second negative electrode slurry is then coated on the side of the negative electrode current collector copper foil near the separator.

[0251] Example 10

[0252] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0253] The negative electrode current collector is also coated with a silicon carbide ceramic layer with a thickness of 1μm on the side close to the separator.

[0254] Example 11

[0255] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0256] The negative electrode current collector is also coated with a silicon carbide ceramic layer with a thickness of 2μm on the side close to the separator.

[0257] Example 12

[0258] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0259] The negative electrode current collector is also coated with a silicon carbide ceramic layer with a thickness of 2.5 μm on the side close to the separator.

[0260] Example 13

[0261] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive electrode sheet are adjusted.

[0262] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.0:2.8 to obtain the second positive electrode slurry.

[0263] Example 14

[0264] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive and negative electrode plates are adjusted.

[0265] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.4:2.4 to obtain the first positive electrode slurry.

[0266] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, conductive agent Super P, and conductive agent CNT are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.1:2.4:0.3 to obtain the second positive electrode slurry.

[0267] The negative electrode active material graphite, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in an appropriate amount of deionized water at a weight ratio of 97.1:0.9:0.5:1.5 to obtain the first negative electrode slurry. The first negative electrode slurry is then coated on the side of the negative electrode current collector copper foil away from the separator.

[0268] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR were mixed in a weight ratio of 97:1:0.5:1.5 in an appropriate amount of deionized water to obtain a second negative electrode slurry. The second negative electrode slurry was coated on the side of the negative electrode current collector copper foil near the separator, and the side of the negative electrode current collector near the separator was also coated with a conductive carbon layer with a thickness of 1 μm.

[0269] Example 15

[0270] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive and negative electrode plates are adjusted.

[0271] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.1:2.7 to obtain the first positive electrode slurry.

[0272] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, conductive agent Super P, and conductive agent CNT are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.1:2.4:0.3 to obtain the second positive electrode slurry.

[0273] The negative electrode active material graphite, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in an appropriate amount of deionized water at a weight ratio of 96.8:1.2:0.5:1.5 to obtain the first negative electrode slurry. The first negative electrode slurry is then coated on the side of the negative electrode current collector copper foil away from the separator.

[0274] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR were mixed in a weight ratio of 97:1:0.5:1.5 in an appropriate amount of deionized water to obtain a second negative electrode slurry. The second negative electrode slurry was coated on the side of the negative electrode current collector copper foil near the separator, and the side of the negative electrode current collector near the separator was also coated with a conductive carbon layer with a thickness of 1 μm.

[0275] Example 16

[0276] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive and negative electrode plates are adjusted.

[0277] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.2:2.6 to obtain the first positive electrode slurry.

[0278] The negative electrode active material graphite, conductive agent Super P, thickener CMC-Na, and binder SBR were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 96.8:1.2:0.5:1.5 to obtain the first negative electrode slurry.

[0279] Example 17

[0280] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive and negative electrode plates are adjusted.

[0281] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.4:2.4 to obtain the first positive electrode slurry.

[0282] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, conductive agent Super P, and conductive agent CNT are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.1:2.4:0.3 to obtain the second positive electrode slurry.

[0283] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR were mixed in a weight ratio of 97.2:0.8:0.5:1.5 in an appropriate amount of deionized water to obtain the first negative electrode slurry.

[0284] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in a weight ratio of 97:1:0.5:1.5 in an appropriate amount of deionized water to obtain the second negative electrode slurry.

[0285] Example 18

[0286] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive and negative electrode plates are adjusted.

[0287] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.7:2.1 to obtain the first positive electrode slurry.

[0288] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, conductive agent Super P, and conductive agent CNT are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.1:2.4:0.3 to obtain the second positive electrode slurry.

[0289] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR were mixed in a weight ratio of 97.1:0.9:0.5:1.5 in an appropriate amount of deionized water to obtain the first negative electrode slurry.

[0290] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in a weight ratio of 97:1:0.5:1.5 in an appropriate amount of deionized water to obtain the second negative electrode slurry.

[0291] Example 19

[0292] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive electrode sheet are adjusted.

[0293] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.4:2.4 to obtain a first positive electrode slurry. The first positive electrode slurry is coated on the side of the positive electrode current collector aluminum foil near the separator, and the side of the positive electrode current collector near the separator is also coated with an alumina ceramic layer with a thickness of 1μm.

[0294] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, conductive agent Super P, and conductive agent CNT are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.1:2.4:0.3 to obtain a second positive electrode slurry. The second positive electrode slurry is then coated on the side of the positive electrode current collector aluminum foil away from the separator.

[0295] Example 20

[0296] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0297] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR were mixed in a weight ratio of 97.1:0.9:0.5:1.5 in an appropriate amount of deionized water to obtain the first negative electrode slurry.

[0298] Example 21

[0299] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0300] The negative electrode active material graphite, conductive agent Super P, thickener CMC-Na, and binder SBR were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 97:1:0.5:1.5 to obtain the first negative electrode slurry.

[0301] Example 22

[0302] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the negative electrode sheet are adjusted.

[0303] The negative electrode active material graphite, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in an appropriate amount of deionized water at a weight ratio of 97:1:0.5:1.5 to obtain the first negative electrode slurry. The first negative electrode slurry is coated on the side of the negative electrode current collector copper foil away from the separator, and a silicon carbide ceramic layer with a thickness of 1μm is also coated on the side of the negative electrode current collector away from the separator.

[0304] The negative electrode active material, graphite with a conductive carbon layer, conductive agent Super P, thickener CMC-Na, and binder SBR are mixed in a weight ratio of 97.05:0.95:0.5:1.5 in an appropriate amount of deionized water to obtain a second negative electrode slurry. The second negative electrode slurry is then coated on the side of the negative electrode current collector copper foil near the separator.

[0305] Example 23

[0306] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive and negative electrode plates are adjusted.

[0307] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, conductive agent Super P, and conductive agent CNT are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.1:2.4:0.3 to obtain the first positive electrode slurry.

[0308] The negative electrode active material graphite, conductive agent Super P, thickener CMC-Na, and binder SBR were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 97:1:0.5:1.5 to obtain the first negative electrode slurry.

[0309] Example 24

[0310] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive electrode sheet are adjusted.

[0311] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.4:2.4 to obtain the first positive electrode slurry. The first positive electrode slurry is then coated on the side of the positive electrode current collector aluminum foil near the separator.

[0312] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.4:2.4 to obtain a second positive electrode slurry. The second positive electrode slurry is coated on the side of the positive electrode current collector aluminum foil away from the separator, and an alumina ceramic layer with a thickness of 1μm is also coated on the side of the positive electrode current collector away from the separator.

[0313] Example 25

[0314] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive electrode sheet are adjusted.

[0315] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, conductive agent Super P, and conductive agent CNT are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.1:2.4:0.3 to obtain a second positive electrode slurry. The second positive electrode slurry is coated on the side of the positive electrode current collector aluminum foil away from the separator, and the side of the positive electrode current collector away from the separator is also coated with an alumina ceramic layer with a thickness of 1μm.

[0316] Example 26

[0317] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive electrode sheet are adjusted.

[0318] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.4:2.4 to obtain a second positive electrode slurry. The second positive electrode slurry is coated on the side of the positive electrode current collector aluminum foil away from the separator, and an alumina ceramic layer with a thickness of 1μm is also coated on the side of the positive electrode current collector away from the separator.

[0319] Example 27

[0320] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive electrode sheet are adjusted.

[0321] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.4:2.4 to obtain a second positive electrode slurry. The second positive electrode slurry is coated on the side of the positive electrode current collector aluminum foil away from the separator, and an alumina ceramic layer with a thickness of 1.5μm is also coated on the side of the positive electrode current collector away from the separator.

[0322] Example 28

[0323] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive electrode sheet are adjusted.

[0324] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, conductive agent Super P, and conductive agent CNT are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.1:2.4:0.3 to obtain the first positive electrode slurry. The first positive electrode slurry is then coated on the side of the positive electrode current collector aluminum foil near the separator.

[0325] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.3:2.5 to obtain a second positive electrode slurry. The second positive electrode slurry is coated on the side of the positive electrode current collector aluminum foil away from the separator, and an alumina ceramic layer with a thickness of 1.5μm is also coated on the side of the positive electrode current collector away from the separator.

[0326] Example 29

[0327] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive electrode sheet are adjusted.

[0328] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.4:2.4 to obtain a second positive electrode slurry. The second positive electrode slurry is coated on the side of the positive electrode current collector aluminum foil away from the separator, and an alumina ceramic layer with a thickness of 3μm is also coated on the side of the positive electrode current collector away from the separator.

[0329] Example 30

[0330] The preparation method of the secondary battery is similar to that of Comparative Example 1, except that the relevant parameters in the preparation of the positive electrode sheet are adjusted.

[0331] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, binder PVDF, and conductive agent Super P are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 96.2:1.4:2.4 to obtain a second positive electrode slurry. The second positive electrode slurry is coated on the side of the positive electrode current collector aluminum foil away from the separator, and an alumina ceramic layer with a thickness of 4μm is also coated on the side of the positive electrode current collector away from the separator.

[0332] Performance testing section

[0333] (1) Capacity test of positive electrode film

[0334] After the second positive electrode film layer of the cold-pressed positive electrode sheet is wiped off, it is punched into small circular pieces with a diameter of 14mm. The small circular pieces are assembled into button cells in a glove box. Then, the cells are charged at a constant current of 0.1mA to the charging cutoff voltage using a blue electric current tester, and then discharged at a constant current of 0.1mA to the discharging cutoff voltage to obtain the discharge capacity CAP0. The capacity CAP1 of the first positive electrode film layer is obtained by the formula CAP0×S1 / S0, where S0 is the area of ​​the small circular piece and S1 is the area of ​​the first positive electrode film layer.

[0335] After the first positive electrode film layer of the cold-pressed positive electrode sheet is wiped off, it is punched into small circular pieces with a diameter of 14mm. The small circular pieces are assembled into button cells in a glove box. Then, the cells are charged at a constant current of 0.1mA to the charging cutoff voltage using a blue electrode tester, and then discharged at a constant current of 0.1mA to the discharging cutoff voltage to obtain the discharge capacity CAP0. The capacity CAP2 of the second positive electrode film layer is obtained by the formula CAP0×S2 / S0, where S0 is the area of ​​the small circular piece and S2 is the area of ​​the second positive electrode film layer.

[0336] (2) Resistance test of each film layer

[0337] The second positive electrode film layer of the cold-pressed positive electrode is wiped off, and then placed parallel between the two conductive terminals of the electrode resistance meter. A certain pressure is applied to fix it, resulting in the resistance R1 of the first positive electrode film layer. The first positive electrode film layer of the cold-pressed positive electrode is wiped off, and then placed parallel between the two conductive terminals of the electrode resistance meter. A certain pressure is applied to fix it, resulting in the resistance R2 of the second positive electrode film layer. The second negative electrode film layer of the cold-pressed negative electrode is wiped off, and then placed parallel between the two conductive terminals of the electrode resistance meter. A certain pressure is applied to fix it, resulting in the resistance R3 of the first negative electrode film layer. The first negative electrode film layer of the cold-pressed negative electrode is wiped off, and then placed parallel between the two conductive terminals of the electrode resistance meter. A certain pressure is applied to fix it, resulting in the resistance R4 of the second negative electrode film layer.

[0338] The electrode resistance meter is model IEST BER1000 (from Yuaneng Technology Co., Ltd.), with a conductive terminal diameter of 14mm, an applied pressure of 15Mpa~27Mpa, and a sampling time range of 10s~20s.

[0339] (3) Mass energy density test

[0340] At 25°C, the secondary battery was charged at a constant current of 0.33C to 4.4V, and then charged at a constant voltage until the current was 0.05C. After the secondary battery was left to stand for 5 minutes, it was discharged at a constant current of 0.33C to 2.5V, and the discharge energy Q was obtained.

[0341] The mass energy density of a secondary battery (Wh / Kg) = discharge energy Q / mass m of the secondary battery.

[0342] (4) Cyclic performance test

[0343] At 25℃, the secondary battery was charged at a constant current of 0.5C to 4.4V, and then charged at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged, and the charging capacity was recorded, which is the first charge capacity. After the secondary battery was left to stand for 5 minutes, it was discharged at a constant current of 0.5C to 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity was recorded, which is the first discharge capacity. The secondary battery was subjected to cyclic charge-discharge tests using the above method, and the discharge capacity after each cycle was recorded until the discharge capacity of the secondary battery decreased to 80% of the first discharge capacity. The number of cycles at this point is used to characterize the cycle performance of the secondary battery under 0.5C rate conditions. The higher the number of cycles, the better the cycle performance.

[0344] Tables 1 and 2 present the performance test results of Comparative Examples 1-3 and Examples 1-30.

[0345] Table 1

[0346]

[0347]

[0348] Table 2

[0349]

[0350]

[0351] As shown in Table 2, by appropriately setting the relationship between the resistances of the positive and negative electrodes, ensuring that |R4 / R3-R2 / R1| > 0, the capacity decay of the secondary battery can be slowed down and its cycle life significantly extended. Furthermore, when the secondary battery satisfies 0 < |R4 / R3-R2 / R1| ≤ 20, it can simultaneously possess both a significantly extended cycle life and high energy density.

[0352] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An electrode assembly, comprising: The positive electrode includes a positive current collector and a first positive electrode film and a second positive electrode film located on two opposing surfaces of the positive current collector; The negative electrode sheet includes a negative current collector and a first negative electrode film layer and a second negative electrode film layer located on two opposite surfaces of the negative current collector. A separator is located between the positive electrode and the negative electrode, wherein the first positive electrode film layer is located on the side of the positive current collector closer to the separator, and the second negative electrode film layer is located on the side of the negative current collector closer to the separator. in, The positive electrode sheet satisfies CAP1=CAP2, where CAP1 represents the capacity of the first positive electrode film layer in Ah, and CAP2 represents the capacity of the second positive electrode film layer in Ah. The electrode assembly satisfies 0 < |R4 / R3-R2 / R1| ≤ 20, where R1 represents the resistance of the first positive electrode film in Ω, R2 represents the resistance of the second positive electrode film in Ω, R3 represents the resistance of the first negative electrode film in mΩ, and R4 represents the resistance of the second negative electrode film in mΩ. The negative electrode plate satisfies R4 / R3≥1, or 0<R4 / R3<1.

2. The electrode assembly according to claim 1, wherein, The electrode assembly satisfies 0.2≤∣R4 / R3-R2 / R1∣≤10.

3. The electrode assembly according to claim 1 or 2, wherein, 0Ω<R1≤20Ω, and / or, 0Ω<R2≤20Ω, and / or, 0mΩ<R3≤200mΩ, and / or, 0mΩ<R4≤200mΩ.

4. The electrode assembly according to claim 3, wherein, 0Ω<R1≤5Ω.

5. The electrode assembly according to claim 3, wherein, 0Ω<R2≤5Ω.

6. The electrode assembly according to claim 3, wherein, 0mΩ<R3≤50mΩ.

7. The electrode assembly according to claim 3, wherein, 0mΩ<R4≤50mΩ.

8. The electrode assembly according to claim 1, wherein, The negative electrode sheet satisfies 1≤R4 / R3≤30.

9. The electrode assembly according to claim 1, wherein, The positive electrode plate satisfies 0 < R2 / R1 ≤ 20.

10. The electrode assembly according to claim 1, wherein, The negative electrode plate satisfies 1≤R4 / R3≤30, and The positive electrode plate satisfies 0 < R2 / R1 ≤ 20.

11. The electrode assembly according to claim 1 or 2, wherein, The positive electrode plate satisfies 0 < R2 / R1 < 1, and The electrode assembly satisfies 0 < |R4 / R3-R2 / R1| < 1.

12. The electrode assembly according to claim 11, wherein, 0.2≤∣R4 / R3-R2 / R1∣≤0.

9.

13. The electrode assembly according to claim 1 or 11, wherein, The negative electrode sheet satisfies 0.05≤R4 / R3≤0.9, and The positive electrode sheet satisfies 0.05≤R2 / R1≤0.

9.

14. The electrode assembly according to claim 1 or 2, wherein, The positive electrode plate satisfies R2 / R1≥1, and The electrode assembly satisfies 0 < |R4 / R3-R2 / R1| ≤ 20.

15. The electrode assembly of claim 14, wherein, 0.2≤∣R4 / R3-R2 / R1∣≤10.

16. The electrode assembly of claim 14, wherein, The positive electrode sheet satisfies 1≤R2 / R1≤20.

17. The electrode assembly of claim 14, wherein, The negative electrode sheet satisfies 0.05≤R4 / R3≤0.9, and The positive electrode sheet satisfies 1≤R2 / R1≤20.

18. A secondary battery comprising an outer packaging, an electrolyte, and an electrode assembly according to any one of claims 1-17.

19. The secondary battery according to claim 18, wherein, The outer packaging includes a housing and a cover plate. The housing has a receiving cavity and an opening, the electrode assembly is received in the receiving cavity, and the cover plate is used to close the opening of the housing.

20. A battery module comprising a secondary battery according to claim 18 or 19.

21. A battery pack comprising a secondary battery according to claim 18 or 19, or a battery module according to claim 20.

22. An electrical device comprising at least one of the following: a secondary battery according to claim 18 or 19, a battery module according to claim 20, and a battery pack according to claim 21.

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