Secondary battery and electric device

Abstract

Provided in the present application are a secondary battery and an electric device. The secondary battery provided in the present application comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector, a first negative electrode active material layer provided on at least one surface of the negative electrode current collector, and a second negative electrode active material layer provided on the first negative electrode active material layer. The negative electrode sheet satisfies the condition that the gas production of the first negative electrode active material layer is greater than that of the second negative electrode active material layer, which helps to reduce a difference in surface tension between the first negative electrode active material layer and the second negative electrode active material layer, thereby improving the cycle performance of the secondary battery, enhancing the interfacial bonding strength between the first negative electrode active material layer and the second negative electrode active material layer, mitigating the powder shedding of the negative electrode sheet while ensuring the fast charging performance of the secondary battery, and also improving the electrochemical performance of the secondary battery.

Description

A secondary battery and electrical device

[0001] Cross-reference to related applications

[0002] This application is based on and claims priority to Chinese Patent Application No. 202510472292.7, filed on April 15, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of secondary battery manufacturing technology, and in particular to a secondary battery and an electrical device. Background Technology

[0004] Fast-charging rechargeable batteries are rechargeable batteries with fast charging capabilities. They can restore most of their charge in a short charging time, meeting users' needs for efficient charging.

[0005] Currently, the negative electrode of fast-charging rechargeable batteries is generally a composite electrode. However, the surface tension difference of composite electrodes cannot be overcome, resulting in many stripes on the electrode surface after coating. This leads to a decrease in the cycle performance of fast-charging rechargeable batteries. Furthermore, the surface tension difference between layers also reduces the interfacial bonding strength between the upper and lower layers, causing powder shedding from the negative electrode and affecting the electrochemical performance of the battery. Summary of the Invention

[0006] The technical problem to be solved by this application is to provide a secondary battery and an electrical device to solve the problems of decreased cycle performance and powder shedding of composite negative electrode sheets in existing fast-charging secondary batteries.

[0007] To solve the above problems, this application provides the following technical solution:

[0008] This application proposes a secondary battery, including a negative electrode sheet; the negative electrode sheet includes a negative current collector, a first negative active material layer disposed on at least one surface of the negative current collector, and a second negative active material layer disposed on the first negative active material layer; the first negative active material layer includes a first binder, the second negative active material layer includes a second binder, and the functional groups contained in the first binder and the second binder are not completely the same;

[0009] The negative electrode sheet satisfies:

[0010] q1 > q2,

[0011] Wherein, q1 refers to the gas production rate of the first negative electrode active material layer; q2 refers to the gas production rate of the second negative electrode active material layer;

[0012] The gas production refers to the volume of gas produced by the test battery when the first negative electrode active material layer and the second negative electrode active material layer are used as the negative electrode active layers of the test battery, respectively, and the test battery is tested under the same conditions.

[0013] In some embodiments of this application, the ratio of q1 to q2 in the secondary battery is 1.16 to 1.71.

[0014] In some embodiments of this application, the negative electrode in the secondary battery satisfies the following conditions:

[0015] H1 > H2,

[0016] Wherein, H1 refers to the molar content of hydrogen in the gas produced by the first negative electrode active material layer; H2 refers to the molar content of hydrogen in the gas produced by the second negative electrode active material layer.

[0017] In some embodiments of this application, in the secondary battery, the first binder comprises at least a benzene ring, a carbon-carbon double bond, and an ester functional group, and the second binder comprises at least a carbonyl functional group; or

[0018] The ratio between the mass percentage of the first binder in the first negative electrode active material layer and the mass percentage of the second binder in the second negative electrode active material layer is 1.5 to 2.2.

[0019] In some embodiments of this application, in the secondary battery, the first binder comprises a styrene-acrylate copolymer; the second binder comprises a styrene-acrylate copolymer and polyacrylic acid.

[0020] In some embodiments of this application, in the secondary battery, the first negative electrode active material layer contains a first active material, and the second negative electrode active material layer contains a second active material;

[0021] The mass percentage of the first active material in the first negative electrode active material layer is less than the mass percentage of the second active material in the second negative electrode active material layer; or

[0022] The first active material in the first negative electrode active material layer accounts for 96.5% to 98% of the mass; the second active material in the second negative electrode active material layer accounts for 97.5% to 99% of the mass.

[0023] In some embodiments of this application, in the secondary battery, the difference between the dimension of the second negative electrode active material layer along the width direction of the negative electrode sheet and the dimension of the first negative electrode active material layer along the width direction of the negative electrode sheet is 2 mm to 6 mm.

[0024] In some embodiments of this application, in the secondary battery, the particle size Dv50 of the first active material or the second active material is 10 μm to 15 μm, wherein Dv50 represents the particle size corresponding to the cumulative volume distribution percentage of the first active material or the second active material being equal to 50%.

[0025] In some embodiments of this application, in the secondary battery, the thickness of the first negative electrode active material layer is less than or equal to the thickness of the second negative electrode active material layer.

[0026] In some embodiments of this application, the thickness of the first negative electrode active material layer in the secondary battery is 50 μm to 70 μm; and / or

[0027] The thickness of the second negative electrode active material layer is 52 μm to 90 μm.

[0028] In some embodiments of this application, in the secondary battery, the areal density of the first negative electrode active material layer is less than or equal to the areal density of the second negative electrode active material layer.

[0029] In some embodiments of this application, the areal density of the first negative electrode active material layer in the secondary battery is 39 g / m³. 2 ~52g / m 2 ; and / or

[0030] The areal density of the second negative electrode active material layer is 40 g / m². 2 ~58g / m 2 .

[0031] This application also proposes an electrical device, which includes the aforementioned secondary battery, serving as the power supply for the electrical device.

[0032] Compared with the prior art, this application has the following advantages:

[0033] In this application, the provided secondary battery includes a negative electrode sheet, which comprises a negative current collector, a first negative active material layer disposed on at least one surface of the negative current collector, and a second negative active material layer disposed on the first negative active material layer. The first negative active material layer contains a first binder, and the second negative active material layer contains a second binder. The functional groups contained in the first binder and the second binder are not entirely identical. This application employs a composite negative electrode sheet configuration, thereby improving the fast-charging performance of the secondary battery. In some embodiments of this application, the negative electrode sheet satisfies the condition that the gas production of the first negative electrode active material layer is greater than that of the second negative electrode active material layer. A higher gas production of the first negative electrode active material layer implies a higher degree of chemical reaction during charge-discharge cycles. This results in higher surface energy of molecules in the first negative electrode active material layer at the interface between the first and second negative electrode active material layers. Consequently, the microstructure of the first negative electrode active material layer shifts towards a more stable microstructure in the second negative electrode active material layer. This reduces the difference in surface tension between the first and second negative electrode active material layers, minimizing or eliminating the formation of vertical stripes in the electrode sheet and improving the cycle performance of the secondary battery. Furthermore, reducing the difference in surface tension between the first and second negative electrode active material layers also increases the interfacial bonding strength between them, preventing delamination at the interface and improving the interlayer powder shedding problem, thereby enhancing the electrochemical performance of the secondary battery.

[0034] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0035] Figure 1 is a cross-sectional view of a negative electrode sheet along the thickness direction provided in this application.

[0036] Explanation of reference numerals in the attached figures: 10 - negative electrode current collector; 20 - first negative electrode active material layer; 30 - second negative electrode active material layer. Detailed Implementation

[0037] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] This application provides a secondary battery, which includes a negative electrode sheet. Referring to FIG1, the negative electrode sheet includes a negative current collector 10, a first negative active material layer 20 disposed on at least one surface of the negative current collector 10, and a second negative active material layer 30 disposed on the first negative active material layer 20. The first negative active material layer 20 includes a first binder, the second negative active material layer 30 includes a second binder, and the functional groups contained in the first binder and the second binder are not completely the same.

[0039] The negative electrode plate satisfies:

[0040] q1 > q2,

[0041] Wherein, q1 refers to the gas production of the first negative electrode active material layer 20; q2 refers to the gas production of the second negative electrode active material layer 30; the gas production refers to the volume of gas produced by the test battery when the first negative electrode active material layer 20 and the second negative electrode active material layer 30 are used as the negative electrode active layers of the test battery, respectively, and measured under the same conditions.

[0042] It should be noted that during the charge-discharge cycle of a secondary battery, the negative electrode active material layer with low gas production experiences fewer side reactions, resulting in higher stability. This higher stability provides a good diffusion channel for ions (e.g., lithium ions), improving charge transfer efficiency during charge and discharge, and allowing the negative electrode active material layer to maintain high kinetic performance. In this application, the first binder and the second binder contain different functional groups, and the gas production of the second negative electrode active material layer 30 is less than that of the first negative electrode active material layer 20. Therefore, the kinetic performance of the second negative electrode active material layer 30 is higher than that of the first negative electrode active material layer 20. Using the second negative electrode active material layer 30 with low gas production as the upper layer of the negative electrode active material layer in the negative electrode sheet can fully utilize the high kinetic performance of the second negative electrode active material layer 30, allowing lithium ions to quickly diffuse from the upper layer of the negative electrode active material layer. The insertion and extraction of material into layer 30 increases the overall charge / discharge rate of the negative electrode sheet, which is beneficial for improving the kinetic performance of the negative electrode sheet and thus enhancing the fast-charging capability of the secondary battery. Furthermore, this application uses the first negative electrode active material layer 20, which has a high gas production rate, as the lower layer of the negative electrode active material layer in the negative electrode sheet. The higher surface energy of the first negative electrode active material layer 20 during charge / discharge cycles can be utilized to increase the tightness of the bond between the first negative electrode active material layer 20 and the surface of the negative electrode current collector 10, preventing the first negative electrode active material layer 20 from detaching from the surface of the negative electrode current collector 10. In some embodiments of this application, the higher degree of chemical reaction and microstructure change of the first negative electrode active material layer 20 can be utilized to improve the interfacial bonding strength between the first negative electrode active material layer 20 and the second negative electrode active material layer 30, preventing the second negative electrode active material layer 30 from detaching during charge / discharge cycles, solving the problem of powder shedding from the negative electrode sheet, and thus improving the electrochemical performance of the secondary battery.

[0043] In this application, the negative electrode sheet satisfies q1 > q2, which makes the gas production of the first negative electrode active material layer 20 in the negative electrode sheet greater than that of the second negative electrode active material layer 30. This can reduce the difference in surface tension between the first negative electrode active material layer 20 and the second negative electrode active material layer 30, reduce or avoid the generation of vertical stripes on the electrode sheet, and improve the cycle performance of the secondary battery. In addition, it can reduce the difference in surface tension between the first negative electrode active material layer 20 and the second negative electrode active material layer 30, thereby improving the interfacial bonding strength between the first negative electrode active material layer 20 and the second negative electrode active material layer 30, avoiding the problem of delamination at the bonding interface of the first negative electrode active material layer 20 and the second negative electrode active material layer 30, and improving the interlayer powder shedding problem of the first negative electrode active material layer 20 and the second negative electrode active material layer 30 in the negative electrode sheet. Thus, this application solves the powder shedding problem of the negative electrode sheet while ensuring the fast charging performance of the secondary battery, and improves the electrochemical performance of the secondary battery.

[0044] It is understandable that in secondary batteries, the gas production in the negative electrode active material layer is mainly due to the chemical reactions of the binder in the negative electrode active material layer during charge-discharge cycles. Specifically, during battery charge-discharge, the binder in the negative electrode active material layer undergoes chemical reactions due to electrolyte erosion and the high-temperature environment inside the secondary battery. These chemical reactions lead to the decomposition of the binder, producing small molecule gases such as hydrogen and methane.

[0045] In this application, the method for controlling the gas production of the first negative electrode active material layer 20 to be greater than that of the second negative electrode active material layer 30 may include, but is not limited to: adjusting the content of the first binder in the first negative electrode active material layer 20 and the second binder in the second negative electrode active material layer 30, as well as the types of the first binder and the second binder; for example, when the mass percentage of the first binder in the first negative electrode active material layer 20 is the same as the mass percentage of the second binder in the second negative electrode active material layer 30, the first binder is selected from a polymer with lower stability, and the second binder is selected from a polymer with higher stability than the first binder; when the types of the first binder and the second binder are the same, the mass percentage of the first binder in the first negative electrode active material layer 20 is greater than the mass percentage of the second binder in the second negative electrode active material layer 30.

[0046] The gas production of the first negative electrode active material layer 20 refers to the volume of gas produced by the test battery when the first negative electrode active material layer 20 is used as the negative electrode active layer of the test battery and under preset charge-discharge cycle test conditions; correspondingly, the gas production of the second negative electrode active material layer 30 refers to the volume of gas produced by the test battery when the second negative electrode active material layer 30 is used as the negative electrode active layer of the test battery and under preset charge-discharge cycle test conditions; wherein, the preset charge-discharge cycle test conditions corresponding to the test battery prepared based on the first negative electrode active material layer 20 are the same as the preset charge-discharge cycle test conditions corresponding to the test battery prepared based on the second negative electrode active material layer 30.

[0047] The secondary battery provided in this application improves the problem of interlayer powder shedding between the first negative electrode active material layer 20 and the second negative electrode active material layer 30, thereby improving the cycle performance and electrochemical performance of the secondary battery. Moreover, it does not require increasing the adhesive content of the first negative electrode active material layer and the second negative electrode active material layer, nor does it require surface modification treatment of the first active material in the first negative electrode active material layer 20 and the second active material in the second negative electrode active material layer 30, thus reducing the manufacturing cost of the secondary battery.

[0048] The first and second active materials can include, but are not limited to, natural graphite, artificial graphite, mixtures of silicon suboxide and graphite, and mixtures of silicon and graphite. This gives the secondary battery excellent cycle stability and high energy density.

[0049] In some embodiments, the first active material and the second active material can be the same type of material or different materials. In some embodiments, the first active material and the second active material are set to be the same type of material, which can further reduce the difference in surface tension between the first negative electrode active material layer 20 and the second negative electrode active material layer 30, and further improve the cycle performance of the secondary battery; and setting the first active material and the second active material to be the same material can also improve the interfacial bonding strength between the first negative electrode active material layer 20 and the second negative electrode active material layer 30, thereby further reducing the interlayer powder shedding problem of the first negative electrode active material layer 20 and the second negative electrode active material layer 30, and improving the electrochemical performance of the secondary battery. In some embodiments, the first negative electrode active material and the second negative electrode active material of this application are graphite materials.

[0050] When the first active material and the second active material are the same material, the gas production of the first negative electrode active material layer 20 and the gas production of the second negative electrode active material layer 30 can be adjusted by adjusting the proportion of each component in the first negative electrode active material layer 20 and the proportion of each component in the second negative electrode active material layer 30, so that the gas production of the first negative electrode active material layer 20 is greater than that of the second negative electrode active material layer 30. The kinetic performance of the negative electrode sheet can be improved by using the second negative electrode active material layer 30 with low gas production and high kinetic performance, thereby improving the fast charging performance of the secondary battery.

[0051] In some embodiments, the ratio of q1 to q2 is 1.16 to 1.71, that is, the ratio between the gas production of the first negative electrode active material layer 20 and the gas production of the second negative electrode active material layer 30 is 1.16 to 1.71. Controlling the ratio of q1 to q2 within the range of 1.16 to 1.71 in this application is beneficial because adjusting the proportional relationship between the gas production of the first negative electrode active material layer 20 and the second negative electrode active material layer 30 allows for the utilization of the higher chemical reaction degree of the first negative electrode active material layer 20 with its larger gas production during charge-discharge cycles. At the interface of the layers, the microstructure of the first negative electrode active material layer is induced to change towards the more stable microstructure in the second negative electrode active material layer; the surface tension of the first negative electrode active material layer 20 and the second negative electrode active material layer 30 is adjusted to reduce the difference in surface tension between the first negative electrode active material layer 20 and the second negative electrode active material layer 30, reduce or avoid the generation of vertical stripes on the electrode sheet, improve the cycle performance of the secondary battery, and improve the interfacial bonding strength between the first negative electrode active material layer 20 and the second negative electrode active material layer 30, solve the problem of powder shedding from the negative electrode sheet, and improve the electrochemical performance of the secondary battery.

[0052] Specifically, in some embodiments, the ratio of q1 to q2 can be a range of one or both of 1.16, 1.20, 1.25, 1.3, and 1.71.

[0053] In some embodiments, the negative electrode sheet satisfies: H1 > H2; where H1 refers to the molar content of hydrogen in the gas produced by the first negative electrode active material layer 20; and H2 refers to the molar content of hydrogen in the gas produced by the second negative electrode active material layer 30.

[0054] In the process of using the first negative electrode active material layer 20 and the second negative electrode active material layer 30 as the negative electrode active layers of the test battery, and testing the volume of gas generated by the test battery under the same conditions, during the growth of lithium dendrites on the surface of the negative electrode sheet, the lithium dendrites react with the binder in the first negative electrode active material layer 20 and / or the second negative electrode active material layer 30, causing the binder to decompose and release hydrogen gas.

[0055] This application, under the premise that the negative electrode sheet satisfies q1>q2, further controls the negative electrode sheet to satisfy H1>H2, which can further improve the cycle performance of the battery.

[0056] Specifically, when the first negative electrode active material layer 20 and the second negative electrode active material layer 30 are used as the negative electrode active layers of the test battery, and the volume of gas produced by the test battery is tested under the same conditions, the composition of the gas produced by the test battery can be analyzed at the same time to determine the molar content H1 of hydrogen in the gas produced by the first negative electrode active material layer 20 and the molar content H2 of hydrogen in the gas produced by the second negative electrode active material layer 30.

[0057] In some embodiments, the ratio of H1 to H2 is 1.15 to 1.70, that is, the ratio between the molar content of hydrogen in the gas produced by the first negative electrode active material layer 20 and the molar content of hydrogen in the gas produced by the second negative electrode active material layer 30 is 1.15 to 1.70. In some embodiments, the ratio of H1 to H2 can be a range of one or both of 1.15, 1.4, 1.6, 1.68, and 1.70.

[0058] This application controls the ratio of H1 to H2 within the range of 1.15 to 1.70, which is beneficial for adjusting the molar content of hydrogen in the gas produced by the first negative electrode active material layer 20 and the second negative electrode active material layer 30. This allows for more precise control of the degree of chemical reaction in the first negative electrode active material layer 20, which has a large gas production, during charge-discharge cycles. At the interface between the first and second negative electrode active material layers, the microstructure of the first negative electrode active material layer is encouraged to change towards a more stable microstructure in the second negative electrode active material layer. This reduces the difference in surface tension between the first and second negative electrode active material layers 20 and 30, reduces or avoids the generation of vertical stripes during electrode coating, improves the cycle performance of the secondary battery, and increases the interfacial bonding strength between the first and second negative electrode active material layers 20 and 30. This solves the problem of powder shedding from the negative electrode and improves the electrochemical performance of the secondary battery.

[0059] In some embodiments, the ratio of the mass percentage of the first binder in the first negative electrode active material layer 20 to the mass percentage of the second binder in the second negative electrode active material layer 30 is 1.5 to 2.2. In some embodiments, the ratio of the mass percentage of the first binder in the first negative electrode active material layer 20 to the mass percentage of the second binder in the second negative electrode active material layer 30 can be a value within the range of one or both of 1.5, 1.7, 1.9, 2.1, and 2.2.

[0060] The gas production of the first negative electrode active material layer 20 and the second negative electrode active material layer 30 mostly originates from the gases released by the decomposition of the first binder and the second binder. This application controls the ratio between the mass percentage of the first binder in the first negative electrode active material layer 20 and the mass percentage of the second binder in the second negative electrode active material layer 30 within the range of 1.5 to 2.2. This allows for an increase in the gas production of the first negative electrode active material layer based on the higher mass percentage of the first binder in the first negative electrode active material layer, and a decrease in the gas production of the second negative electrode active material layer based on the lower mass percentage of the second binder in the second negative electrode active material layer. This results in a greater gas production of the first negative electrode active material layer 20 than the second negative electrode active material layer 30.

[0061] In some embodiments, the first binder comprises at least a benzene ring, a carbon-carbon double bond, and an ester functional group, and the second binder comprises at least a carbonyl functional group. In some embodiments of this application, the first binder in the first negative electrode active material layer 20 comprises a styrene-acrylate copolymer; and the second binder in the second negative electrode active material layer 30 comprises a styrene-acrylate copolymer and polyacrylic acid. The styrene-acrylate copolymer is a polymer synthesized by copolymerization of styrene (C8H8) and acrylate (CH2=CHCOOR) monomers.

[0062] In the second binder, styrene-acrylate copolymer and polyacrylic acid are compounded. The styrene-acrylate copolymer provides good mechanical support and chemical resistance, while the polyacrylic acid provides strong adhesion and adjustable physical properties. During the compounding process, synergistic effects occur between the styrene-acrylate copolymer and polyacrylic acid, such as hydrogen bonding and van der Waals forces, which enhance the stability and adhesion performance of the compounded second binder. This makes the stability and adhesion performance of the second binder superior to that of the first binder. Consequently, during the charge-discharge cycle of the secondary battery, the first binder in the first negative electrode active material layer 20 is more likely to decompose and generate gas, increasing the gas production of the first negative electrode active material layer 20. This results in the gas production of the first negative electrode active material layer 20 being greater than that of the second negative electrode active material layer 30.

[0063] In some embodiments, the first negative electrode active material layer 20 includes a first active material, and the second negative electrode active material layer 30 includes a second active material. The mass percentage of the first active material in the first negative electrode active material layer 20 is less than the mass percentage of the second active material in the second negative electrode active material layer 30. In some embodiments of this application, the mass percentage of the first active material in the first negative electrode active material layer 20 is 96.5% to 98%. Specifically, in some embodiments, the mass percentage of the first active material in the first negative electrode active material layer 20 can be a range of one or any two of 96.5%, 96.9%, 97.3%, 97.7%, and 98%. In some embodiments, the mass percentage of the second active material in the second negative electrode active material layer 30 is 97.5% to 99%. Specifically, the mass percentage of the second active material in the second negative electrode active material layer 30 can be a range of one or any two of 97.5%, 97.9%, 98.3%, 98.7%, and 99%.

[0064] The secondary battery provided in this application controls the mass percentage of the first active material in the first negative electrode active material layer 20 to be within the range of 96.5% to 98%, and controls the mass percentage of the second active material in the second negative electrode active material layer 30 to be within the range of 97.5% to 99%. This ensures that the mass percentage of the first active material in the first negative electrode active material layer 20 and the mass percentage of the second active material in the second negative electrode active material layer 30 are both maintained within a certain range, thereby improving the mass energy density and fast charging performance of the secondary battery.

[0065] In some embodiments, the difference W2-W1 between the dimension W2 of the second negative electrode active material layer 30 along the width direction of the negative electrode sheet and the dimension W1 of the first negative electrode active material layer 20 along the width direction of the negative electrode sheet is 2 mm to 6 mm. In some embodiments, the difference W2-W1 between the dimension W2 of the second negative electrode active material layer 30 along the width direction of the negative electrode sheet and the dimension W1 of the first negative electrode active material layer 20 along the width direction of the negative electrode sheet can be a value within the range of one or both of 2 mm, 3 mm, 4 mm, 5 mm, and 6 mm. This can improve the dynamic performance of the negative electrode sheet and the fast charging capability of the secondary battery.

[0066] In some embodiments, the particle size Dv50 of the first active material or the second active material is 10 μm to 15 μm; wherein, the particle size Dv50 of the first active material represents the particle size corresponding to a volumetric cumulative distribution percentage of 50% for the first active material, and the particle size Dv50 of the second active material represents the particle size corresponding to a volumetric cumulative distribution percentage of 50% for the second active material. Dv50 is obtained according to GB / T 19077-2016, using deionized water as the dispersion medium, adding an appropriate amount of surfactant, ultrasonically dispersing for 3 minutes, and then testing using a Mastersizer 3000 laser particle size analyzer (Malvern Panalytical, England).

[0067] Specifically, in some embodiments, the particle size Dv50 of the first active material can be a range of one or any two of 10 μm, 11 μm, 12 μm, 13 μm, 14 μm and 15 μm; the particle size Dv50 of the second active material can be a range of one or any two of 10 μm, 11 μm, 12 μm, 13 μm, 14 μm and 15 μm; the particle size Dv50 of the first active material and the particle size Dv50 of the second active material can be the same or different.

[0068] In this application, the particle size Dv50 of the first or second active material is controlled within the range of 10μm to 15μm. On the one hand, this helps to reduce the volume expansion and contraction of the active material during the charge-discharge cycle of the secondary battery, reduce stress concentration, reduce the pulverization and shedding of the negative electrode active material, and further reduce the amount of powder loss of the negative electrode active material. On the other hand, it helps to increase the specific surface area of ​​the active material, increase the contact area between the negative electrode active material and the electrolyte, and improve the mass energy density of the secondary battery. Furthermore, it helps to promote the formation of a porous structure of the active material in the negative electrode active material layer, which facilitates the wetting and distribution of the electrolyte and improves the structural stability of the secondary battery.

[0069] In some embodiments, the average particle size of the second active material is larger than that of the first active material. The second active material with a larger average particle size serves as the upper layer (the second negative electrode active material layer), which can increase the porosity of the upper layer of the negative electrode sheet and improve the wetting performance of the electrolyte on the negative electrode sheet. The first active material with a smaller average particle size serves as the lower layer (the first negative electrode active material layer), which may ensure that the first negative electrode active material layer can have a larger effective contact area with the current collector. This can reduce the impedance of the negative electrode sheet and has a positive effect on improving the fast charging performance of the battery.

[0070] In this application, the average particle size refers to the volume median particle size, i.e., Dv50. It is determined according to GB / T 19077-2016, using deionized water as the dispersion medium, adding an appropriate amount of surfactant, ultrasonically dispersing for 3 minutes, and then testing using a Mastersizer 3000 laser particle size analyzer (Malvern Panalytical, England). The Dv50 value is recorded as the average particle size. In other words, the average particle size and Dv50 are interchangeable in this application.

[0071] In some embodiments, the thickness of the first negative electrode active material layer 20 is less than or equal to the thickness of the second negative electrode active material layer 30. It is understood that because the gas production of the first negative electrode active material layer 20 is greater than that of the second negative electrode active material layer 30, the kinetic performance of the second negative electrode active material layer 30 is higher than that of the first negative electrode active material layer 20. By controlling the thickness of the first negative electrode active material layer 20 to be less than or equal to the thickness of the second negative electrode active material layer 30, the proportion of the high-kinetic-performance second negative electrode active material layer 30 in the negative electrode sheet can be increased, thereby improving the kinetic performance of the negative electrode sheet and the fast-charging performance of the secondary battery.

[0072] In some embodiments, the thickness of the first negative electrode active material layer 20 is 50 μm to 70 μm; and / or, the thickness of the second negative electrode active material layer 30 is 52 μm to 90 μm.

[0073] In some embodiments, the thickness of the first negative electrode active material layer 20 can be a value within the range of one or any two of 50 μm, 54 μm, 58 μm, 62 μm, 66 μm, and 70 μm. In some embodiments, the thickness of the second negative electrode active material layer 30 can be a value within the range of one or any two of 52 μm, 58 μm, 66 μm, 72 μm, 80 μm, 84 μm, and 90 μm.

[0074] The secondary battery provided in this application controls the thickness of the first negative electrode active material layer 20 within the range of 50μm to 70μm and the thickness of the second negative electrode active material layer 30 within the range of 52μm to 90μm. The first negative electrode active material layer 20 establishes good contact between the second negative electrode active material layer 30 and the negative electrode current collector 10, preventing the second negative electrode active material layer 30 from detaching during charge-discharge cycles, thus improving the cycle performance of the secondary battery and solving the problem of powder shedding from the negative electrode sheet. In some embodiments of this application, where the thickness of the first negative electrode active material layer 20 is less than or equal to the thickness of the second negative electrode active material layer 30, increasing the upper limit of the thickness range of the second negative electrode active material layer 30 can increase the proportion of the high-dynamic-performance second negative electrode active material layer 30 in the negative electrode sheet, thereby improving the dynamic performance of the negative electrode sheet and the fast-charging performance of the secondary battery.

[0075] In some embodiments, the areal density of the first negative electrode active material layer 20 is less than or equal to the areal density of the second negative electrode active material layer 30. It is understood that because the gas production of the first negative electrode active material layer 20 is greater than that of the second negative electrode active material layer 30, the kinetic performance of the second negative electrode active material layer 30 is higher than that of the first negative electrode active material layer 20. By controlling the areal density of the first negative electrode active material layer 20 to be less than or equal to the areal density of the second negative electrode active material layer 30, the coating amount of the high-kinetic-performance second negative electrode active material layer 30 in the negative electrode sheet can be increased, thereby improving the kinetic performance of the negative electrode sheet and the fast-charging performance of the secondary battery.

[0076] In some embodiments, the areal density of the first negative electrode active material layer 20 is 39 g / m². 2 ~52g / m 2 ; and / or, the areal density of the second negative electrode active material layer 30 is 40 g / m². 2 ~58g / m 2 The areal density is measured using the following method: 1. Sampling: A sample of a specific area (usually circular or square, with a known area, such as 100 cm²) is punched out from the electrode using a punching machine (e.g., a circular punch). 2. Weighing: The mass of the sample is weighed using a high-precision analytical balance (with an accuracy typically of 0.1 mg). 3. Calculation: Areal density = Sample mass (g) / Sample area (m²).

[0077] In some embodiments, the areal density of the first negative electrode active material layer 20 is 39 g / m². 2 42g / m 2 44g / m 2 48g / m 2 50g / m 2 and 52g / m 2 The range of one or both of these values. In some embodiments, the areal density of the second negative electrode active material layer 30 is 40 g / m². 2 44g / m 2 48g / m 2 50g / m 2 54g / m 2 and 58g / m 2 The range of one or any two of them.

[0078] The secondary battery provided in this application controls the areal density of the first negative electrode active material layer 20 to 39 g / m². 2 ~52g / m 2 Within the specified range, the areal density of the second negative electrode active material layer 30 is controlled at 40 g / m². 2 ~58g / m 2 Within the specified range, the first negative electrode active material layer 20 establishes good contact between the second negative electrode active material layer 30 and the negative electrode current collector 10, preventing the second negative electrode active material layer 30 from falling off during charge-discharge cycles, improving the cycle performance of the secondary battery and solving the problem of powder shedding from the negative electrode sheet. In some embodiments of this application, under the premise that the areal density of the first negative electrode active material layer 20 is less than or equal to the areal density of the second negative electrode active material layer 30, by increasing the upper limit of the areal density range of the second negative electrode active material layer 30, the coating amount of the second negative electrode active material layer 30 with high dynamic performance in the negative electrode sheet can be increased, thereby improving the dynamic performance of the negative electrode sheet and the fast charging performance of the secondary battery.

[0079] In the secondary battery provided in this application, the negative electrode sheet further includes a conductive agent. In some embodiments, the conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0080] The secondary battery provided in this application also includes a positive electrode, a separator, and an electrolyte.

[0081] The positive electrode includes a positive current collector and a positive electrode film layer disposed on the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a lithium-ion transition metal oxide. The lithium-ion transition metal oxide includes at least one of lithium cobalt oxide, lithium manganese oxide, and lithium nickel cobalt manganese oxide.

[0082] In some embodiments, the molar ratio of Ni in the lithium transition metal oxide relative to the total amount of metal elements other than Li is 75% to 95%. A molar ratio of Ni within this range can improve the energy density of the battery and enhance its range.

[0083] In some embodiments, the molar ratio of Ni in the lithium transition metal oxide relative to the total amount of metal elements other than Li is 80% to 92%. In some embodiments, the molar ratio of Ni in the lithium transition metal oxide relative to the total amount of metal elements other than Li is 88% to 91%.

[0084] In some embodiments, the average particle size of the lithium transition metal oxide is 5–15 μm, for example, 5 μm, 8 μm, 10 μm, 12 μm, or 15 μm. An average particle size within this range is beneficial for increasing the compaction density of the positive electrode sheet, while also ensuring that the positive electrode sheet has suitable porosity, thereby improving the electrochemical performance of the battery.

[0085] In some embodiments, the positive electrode sheet is prepared as follows: the components used to prepare the positive electrode sheet, such as the positive active material, binder and any other components, are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on both sides of a positive current collector such as an aluminum foil; after baking, rolling, cutting and slitting, the positive electrode sheet can be obtained.

[0086] The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte can be liquid, gel-like, or entirely solid. In some embodiments, the electrolyte is a liquid electrolyte comprising an electrolyte salt and a solvent. The electrolyte salt is a lithium salt, and the solvent includes cyclic ester solvents and chain ester solvents. In some embodiments, the cyclic ester solvent includes at least one of ethylene carbonate, propylene carbonate, butenyl carbonate, fluoroethylene carbonate, and γ-butyrolactone; the chain ester solvent includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and diphenyl carbonate. In some embodiments, the organic solvent includes ethylene carbonate, propylene carbonate, and methyl ethyl carbonate.

[0087] In practical applications, the negative electrode sheet, separator and positive electrode sheet are stacked in sequence and wound to obtain a core. The core is then packaged to obtain a bare cell. After baking, the bare cell is injected with electrolyte, formed, repackaged and sorted to obtain the above-mentioned secondary battery.

[0088] This application also proposes an electrical device, which includes the aforementioned secondary battery, serving as the power supply for the electrical device.

[0089] The above-described electrical equipment embodiment includes the aforementioned secondary battery and achieves the same technical effect. To avoid repetition, it will not be described again here. For relevant details, please refer to the description of the secondary battery embodiment.

[0090] To make the inventive objectives, technical solutions, and beneficial effects of this application clearer, the application is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application.

[0091] The present application will be described in detail below through embodiments.

[0092] Example 1

[0093] (1) Preparation of negative electrode slurry

[0094] Artificial graphite (first active material with a particle size Dv50 of 13 μm), conductive agent SP (Super P), styrene-acrylate copolymer (first binder), and butanediol (dispersant) were added to water at a mass ratio of 97:0.3:1.9:0.8 and stirred to obtain a first negative electrode slurry with a solid content of 50%. Artificial graphite (second active material, the same as the first active material), conductive agent SP, styrene-acrylate copolymer (second binder), polyacrylic acid (mass ratio 1:1), and polyvinylpyrrolidone (dispersant) were added to water at a mass ratio of 98:0.3:0.9:0.8 and stirred to obtain a second negative electrode slurry with a solid content of 52%.

[0095] (2) Preparation of negative electrode sheet

[0096] The first negative electrode slurry prepared in step (1) is uniformly coated on the upper and lower surfaces of the negative electrode current collector copper foil using a coating machine to obtain the first coating layer; the second negative electrode slurry prepared in step (1) is uniformly coated on the surface of the first coating layer using a coating machine to obtain the second coating layer; after baking, rolling, cutting and other processes, the negative electrode sheet can be obtained, which includes a first negative electrode active material layer formed by the first coating layer and a second negative electrode active material layer formed by the second coating layer;

[0097] The second negative electrode active material layer has a width of 101 mm along the width direction of the negative electrode sheet, and the first negative electrode active material layer has a width of 97 mm along the width direction of the negative electrode sheet; the thickness of the first negative electrode active material layer is 60 μm; the thickness of the second negative electrode active material layer is 70 μm; and the areal density of the first negative electrode active material layer is 50 g / m³. 2 The areal density of the second negative electrode active material layer is 58 g / m². 2 .

[0098] (3) Preparation of positive electrode slurry

[0099] LiNi, the positive electrode active material 0.8 Mn 0.1 Co 0.1 O2, conductive agent acetylene black, binder polyvinylidene fluoride and dispersant polyvinylpyrrolidone (PVP) are mixed evenly in a mass ratio of 97.5:0.5:1.8:0.2 and then evenly dispersed in 1-methyl-2-pyrrolidone to form a uniform positive electrode slurry.

[0100] (4) Preparation of positive electrode sheet

[0101] The positive electrode slurry prepared in step (3) is uniformly coated on the upper and lower surfaces of the positive electrode current collector aluminum foil using a coating machine; after baking, rolling, cutting and other processes, the positive electrode sheet can be obtained.

[0102] (5) Preparation of secondary batteries

[0103] The negative electrode sheet prepared in step (2), the positive electrode sheet prepared in step (4), and the separator (PP separator) are wound in a predetermined order to prepare a bare cell. The bare cell is placed in an outer packaging aluminum-plastic film, baked to remove moisture, and then injected with electrolyte (the solvent is a 1:1 mass ratio of ethylene carbonate and dimethyl carbonate, and the lithium salt is 1 mol / L lithium hexafluorophosphate). The cell is then vacuum-sealed, formed, and capacity-tested to prepare a secondary battery.

[0104] Examples 2-3

[0105] The difference between Examples 2 and 3 and Example 1 is that in step (1):

[0106] The particle sizes Dv50 of the first active material are 10 μm and 15 μm, respectively, and the particle size Dv50 of the second active material is the same as that of the first active material.

[0107] Examples 4-5

[0108] The difference between Examples 4 and 5 and Example 1 is that in step (1):

[0109] In the first negative electrode slurry, the mass ratios of the first active material artificial graphite, the conductive agent SP, the first binder styrene-acrylate copolymer, and the dispersant butanediol are 96.5:0.4:2.3:0.8 and 98:0.3:1.0:0.7, respectively.

[0110] In the second negative electrode slurry, the mass ratios of the second active material artificial graphite, the conductive agent SP, the second binder styrene-acrylate copolymer and polyacrylic acid, and the dispersant polyvinylpyrrolidone are 97.5:0.4:1.1:1.0 and 99:0.23:0.47:0.3, respectively.

[0111] Example 6

[0112] The difference between Example 6 and Example 1 is that in step (1):

[0113] In the first negative electrode slurry, the mass ratio of the first active material artificial graphite, the conductive agent SP, the first binder ethylene-acrylate copolymer, and the dispersant butanediol is 98:0.3:1.4:0.3.

[0114] In the second negative electrode slurry, the mass ratios of the second active material artificial graphite, the conductive agent SP, the second binder styrene-acrylate copolymer and polyacrylic acid, and the dispersant polyvinylpyrrolidone are 97.5:0.33:0.67:1.5, respectively.

[0115] Examples 7-9

[0116] The difference between Examples 7-9 and Example 1 is that in step (1):

[0117] In the second negative electrode slurry, the mass ratios of the second active material artificial graphite, the conductive agent SP, the second binder styrene-acrylate copolymer and polyacrylic acid, and the dispersant polyvinylpyrrolidone are 97.43:0.3:1.27:0.8, 97.84:0.3:1.06:0.8, and 98.04:0.3:0.86:0.8, respectively.

[0118] Examples 10-11

[0119] The difference between Examples 10 and 11 and Example 1 is that in step (2):

[0120] The dimensions of the second negative electrode active material layer along the width direction of the negative electrode sheet are 100 mm and 99 mm, respectively, and the dimensions of the first negative electrode active material layer along the width direction of the negative electrode sheet are 98 mm and 93 mm, respectively.

[0121] Examples 12-13

[0122] The difference between Examples 12 and 13 and Example 1 is that, in step (2), the thickness of the second negative electrode active material layer is 60 μm and 90 μm, respectively.

[0123] Examples 14-15

[0124] The difference between Examples 14 and 15 and Example 1 is that, in step (2), the thickness of the first negative electrode active material layer is 50 μm and 70 μm, respectively.

[0125] Example 16

[0126] The difference between Example 16 and Example 1 is that in step (2), the thickness of the first negative electrode active material layer is the same as the thickness of the second negative electrode active material layer, and the thickness of the first negative electrode active material layer and the thickness of the second negative electrode active material layer are 50 μm.

[0127] Example 17

[0128] The difference between Example 17 and Example 1 is that, in step (2), the areal density of the second negative electrode active material layer is 50 g / m². 2 .

[0129] Examples 18-19

[0130] The difference between Examples 18 and 19 and Example 1 is that, in step (2), the areal density of the first negative electrode active material layer is 39 g / m³. 2 and 52g / m 2 .

[0131] Example 20

[0132] The difference between Example 20 and Example 1 is that, in step (2), the areal density of the first negative electrode active material layer is 39 g / m². 2 Furthermore, the areal density of the second negative electrode active material layer is 39 g / m². 2 .

[0133] Example 21

[0134] The difference between Example 21 and Example 1 is that, in step (1), the mass ratio of the first active material artificial graphite, the conductive agent SP, the first binder styrene-acrylate copolymer, and the dispersant butanediol in the first negative electrode slurry is 96.8:0.3:2.1:0.8; and the particle size Dv50 of both the first active material and the second active material is 12 μm.

[0135] Comparative Example 1

[0136] The difference between Comparative Example 1 and Example 1 is that in step (2), the second negative electrode slurry prepared in step (1) is uniformly coated on the upper and lower surfaces of the negative electrode current collector copper foil by a coating machine to obtain the first coating layer; the first negative electrode slurry prepared in step (1) is uniformly coated on the surface of the first coating layer by a coating machine to obtain the second coating layer.

[0137] The thickness of the first negative electrode active material layer is 70 μm, and the thickness of the second negative electrode active material layer is 60 μm; the areal density of the first negative electrode active material layer is 58 g / m³. 2 The areal density of the second negative electrode active material layer is 50 g / m². 2 .

[0138] The components and parameters of the secondary batteries prepared in each embodiment and comparative example are shown in Table 1.

[0139] Table 1

[0140] Test method:

[0141] (1) Gas production test of negative electrode active material layer: The porosity of the negative electrode sheet is observed by ion polishing cross-sectional morphology method. When there is obvious fluctuation in porosity, it indicates that this is the boundary between the first negative electrode active material layer and the second negative electrode active material layer. Thus, the first negative electrode active material layer and the second negative electrode active material layer can be determined. In the first negative electrode active material layer, a sample with a thickness of 2 / 3 is taken from the side relatively far from the second negative electrode active material layer as the first negative electrode active material layer sample; in the second negative electrode active material layer, a sample with a thickness of 2 / 3 is taken from the side relatively far from the first negative electrode active material layer as the second negative electrode active material layer sample. The first negative electrode active material layer sample is mixed with deionized water (the mass ratio of sample to deionized water is 9:1) to obtain the first negative electrode active material layer sample slurry. The second negative electrode active material layer sample is mixed with deionized water (the mass ratio of sample to deionized water is 9:1) to obtain the second negative electrode active material layer sample slurry. The first negative electrode active material layer sample slurry and the second negative electrode active material layer sample slurry are used as the negative electrode active layers of the test battery (the positive electrode sheet, separator, and electrolyte of the test battery are the same as those of the secondary battery in Example 1). The test battery is subjected to charge-discharge cycle test under the same charge-discharge cycle test conditions, and the gas production volume and gas composition of the test battery are determined by a high-precision in-situ gas production test system.

[0142] The charge-discharge cycle test conditions were as follows: (1) Adjust the temperature to 25℃ and let it stand for 30 min; (2) Discharge at 1C constant current to 2.5V; (3) Let it stand for 30 min; (4) Charge at 2.15C constant current for 8.37 min (30% SOC); Charge at 1.87C constant current for 6.42 min (50% SOC); Charge at 1.41C constant current for 4.25 min (60% SOC); Charge at 1.026C constant current for 5.85 min (70% SOC); Charge at 0.76C constant current for 7.89 min (80% SOC); Charge at 0.495C constant current for 12.1 min (90% SOC); Charge at 0.33C constant current for 14.4 min (98% SOC). SOC (when the voltage reaches 3.6V, skip to the next step); 0.1C to 3.65V, constant voltage charging to 0.05C (100%); (5) let stand for 30min; (6) 1C constant current discharge to 2.5V; (7) let stand for 30min; (8) repeat steps (4) to (7) until decay to 80%, and record the number of cycles.

[0143] The gas production test method is as follows: the in-situ gas production volume of the secondary battery is obtained by water displacement test, which is used as the gas production volume of the negative electrode active material layer; the gas composition is obtained by gas chromatography.

[0144] (2) Test of negative electrode powder shedding: The secondary battery was subjected to vibration test according to the standard GBT 31467.3-2015. The secondary battery was disassembled, the electrolyte in the secondary battery was filtered, the residue obtained after filtration was dried and weighed to obtain the amount of negative electrode powder shedding.

[0145] (3) Test of the peel force between the first negative electrode material layer and the second negative electrode active material layer in the negative electrode sheet: (1) Take a roll-pressed negative electrode sheet with a width of 35-40mm and a length of 300mm; (2) Paste a 3M double-sided tape with a width of 25mm in the middle of a steel plate with a width of 50mm and a length of 150mm, starting from the top of one side of the steel plate, with a tape length of 120-150mm; (3) Paste the cut negative electrode sheet into the area of ​​the steel plate with tape; (4) Use the peel force test software of the electronic universal testing machine, use the lower clamp of the equipment to directly clamp the lower end of the steel plate, the steel plate and the lower clamp are the same width and not exposed, the upper clamp clamps the negative electrode sheet, the negative electrode sheet is kept 1-2cm away from the steel plate, start the software, record the relationship between the 180° peel force and the peel displacement of the negative electrode sheet, and record the average value of the peel force as the peel force between the first negative electrode material layer and the second negative electrode active material layer in the negative electrode sheet.

[0146] (4) Secondary battery mass energy density test:

[0147] The 1 / 3C energy density test is calculated as follows: 1 / 3C battery energy density = (1 / 3C discharge energy) / (battery mass). The specific test steps include: (1) placing the battery in a 25°C incubator for 30 minutes; (2) discharging at 1C constant current to 2.0V; (3) letting it stand for 60 minutes; (4) charging at 0.33C constant current to 3.65V, and charging at constant voltage to 0.05C; (5) letting it stand for 60 minutes; (6) discharging at 1 / 3C constant current to 2.0V (obtaining the discharge energy at 25°C, with a discharge capacity of C).

[0148] (5) Secondary battery charging capacity (average rate) test from 10% SOC to 80% SOC: A soft-pack three-electrode secondary battery was prepared. With the reference electrode at 0V as the cutoff condition, the charging current and charging time of the secondary battery were recorded to obtain the relationship between the SOC and charging time of the secondary battery. The charging capacity (average rate) = (80% - 10%) * 60 * C / t; where C is the 1 / 3C discharge capacity of the secondary battery, and t is the charging time from 10% SOC to 80% SOC.

[0149] The secondary batteries prepared in each embodiment and comparative example were subjected to the above tests, and the test data are shown in Table 2.

[0150] Table 2

[0151] According to the test data above, the secondary battery provided in this application, while ensuring fast charging performance and mass energy density, also improves the interfacial bonding strength between the first negative electrode active material layer and the second negative electrode active material layer in the negative electrode sheet, reduces the amount of powder shedding from the negative electrode sheet, and improves the cycle performance and charging capability of the secondary battery.

[0152] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of this application.

[0153] The above provides a detailed description of a secondary battery and electrical device provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A secondary battery, comprising a negative electrode sheet; the negative electrode sheet comprising a negative current collector, a first negative active material layer disposed on at least one surface of the negative current collector, and a second negative active material layer disposed on the first negative active material layer; the first negative active material layer comprising a first binder, the second negative active material layer comprising a second binder, and the functional groups contained in the first binder and the second binder are not completely identical; The negative electrode sheet satisfies: q1 > q2, in, q1 refers to the gas production rate of the first negative electrode active material layer; q2 refers to the gas production rate of the second negative electrode active material layer. The gas production refers to the volume of gas produced by the test battery when the first negative electrode active material layer and the second negative electrode active material layer are used as the negative electrode active layers of the test battery, respectively, and the test battery is tested under the same conditions.

2. The secondary battery according to claim 1, wherein, The ratio of q1 to q2 is 1.16 to 1.

71.

3. The secondary battery according to claim 1 or 2, wherein, The negative electrode plate satisfies: H1 > H2. Wherein, H1 refers to the molar content of hydrogen in the gas produced by the first negative electrode active material layer; H2 refers to the molar content of hydrogen in the gas produced by the second negative electrode active material layer.

4. The secondary battery according to any one of claims 1-3, wherein, The first binder contains at least a benzene ring, a carbon-carbon double bond, and an ester functional group, and the second binder contains at least a carbonyl functional group; or The ratio between the mass percentage of the first binder in the first negative electrode active material layer and the mass percentage of the second binder in the second negative electrode active material layer is 1.5 to 2.

2.

5. The secondary battery according to any one of claims 1-4, wherein, The first adhesive comprises a styrene-acrylate copolymer; the second adhesive comprises a styrene-acrylate copolymer and polyacrylic acid.

6. The secondary battery according to any one of claims 1-5, wherein, The first negative electrode active material layer contains a first active material, and the second negative electrode active material layer contains a second active material; The mass percentage of the first active material in the first negative electrode active material layer is less than the mass percentage of the second active material in the second negative electrode active material layer; or The first active material in the first negative electrode active material layer accounts for 96.5% to 98% of the mass; the second active material in the second negative electrode active material layer accounts for 97.5% to 99% of the mass.

7. The secondary battery according to any one of claims 1-6, wherein, The difference between the dimension of the second negative electrode active material layer along the width direction of the negative electrode sheet and the dimension of the first negative electrode active material layer along the width direction of the negative electrode sheet is 2mm to 6mm.

8. The secondary battery according to claim 6, wherein, The particle size Dv50 of the first active material or the second active material is 10 μm to 15 μm, wherein Dv50 represents the particle size corresponding to the cumulative volume distribution percentage of the first active material or the second active material being equal to 50%.

9. The secondary battery according to any one of claims 1-8, wherein, The thickness of the first negative electrode active material layer is less than or equal to the thickness of the second negative electrode active material layer.

10. The secondary battery according to any one of claims 1-9, wherein, The thickness of the first negative electrode active material layer is 50 μm to 70 μm; and / or The thickness of the second negative electrode active material layer is 52 μm to 90 μm.

11. The secondary battery according to any one of claims 1-10, wherein, The areal density of the first negative electrode active material layer is less than or equal to the areal density of the second negative electrode active material layer.

12. The secondary battery according to any one of claims 1-11, wherein, The areal density of the first negative electrode active material layer is 39 g / m³. 2 ~52g / m 2 ; and / or The areal density of the second negative electrode active material layer is 40 g / m². 2 ~58g / m 2 .

13. The secondary battery according to claim 3, wherein, The ratio of H1 to H2 is 1.15 to 1.

70.

14. The secondary battery according to any one of claims 6-8, wherein, The first active material and the second active material include natural graphite, artificial graphite, a mixture of silicon suboxide and graphite, and a mixture of silicon and graphite.

15. The secondary battery according to any one of claims 6-8, wherein, The average particle size of the second active material is greater than that of the first active material.

16. The secondary battery according to any one of claims 1-15, wherein, The negative electrode sheet also includes a conductive agent; the conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

17. The secondary battery according to any one of claims 1-16 further includes a positive electrode, a separator, and an electrolyte.

18. The secondary battery according to claim 17, wherein, The positive electrode includes a positive current collector and a positive electrode film layer disposed on the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a lithium transition metal oxide.

19. The secondary battery according to claim 18, wherein, The molar ratio of Ni in the lithium transition metal oxide to the total amount of metal elements other than Li is 75% to 95%.

20. An electrical device comprising a secondary battery as described in any one of claims 1-19, wherein the secondary battery serves as a power supply for the electrical device.

Images