Secondary battery and use thereof

Abstract

The application discloses a secondary battery and application thereof. The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a current collector and a negative electrode active layer arranged on at least one side of the current collector, the negative electrode active layer comprises a negative electrode active material, and a conductive agent, the surface density of the conductive agent on the side close to the current collector is greater than the surface density of the conductive agent on the side away from the current collector, the aspect ratio of the conductive agent is a, and the negative electrode active material comprises graphite and SiO x , 0 < x < 2, the mass fraction of SiO x in the negative electrode active material is b%, and the mass fraction of graphite is c%, wherein a, b and c satisfy a:(c-7b) > 10. The negative electrode sheet in the secondary battery has good conductivity, and the secondary battery has good electrochemical performance.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a secondary battery and its application. Background Technology

[0002] Secondary batteries, especially lithium-ion batteries, have seen rapid development and widespread application in consumer electronics and electric vehicles due to their long cycle life, lack of memory effect, and environmental friendliness. Simultaneously, the demand for energy density in lithium-ion batteries is increasing. Currently, the focus on anode materials is on silicon-based materials with high theoretical specific capacity, exceeding that of traditional graphite anode materials by more than ten times. However, silicon-based materials have relatively poor conductivity compared to traditional graphite, hindering electron transport and lithium-ion diffusion in the silicon bulk phase. This affects the kinetic performance of the silicon anode, impacting the battery's rate performance and cycle stability. Summary of the Invention

[0003] This application aims to at least solve one of the technical problems existing in the prior art. To this end, this application proposes a secondary battery, wherein the negative electrode of the secondary battery has good conductivity and the secondary battery has good electrochemical performance.

[0004] This application also proposes an electrical device that includes the aforementioned secondary battery.

[0005] A first aspect of this application discloses a secondary battery comprising a negative electrode sheet, the negative electrode sheet comprising a current collector layer and a negative electrode active layer disposed on at least one side of the current collector layer, the negative electrode active layer comprising a negative electrode active material and a conductive agent, wherein the areal density of the conductive agent on the side closer to the current collector layer is greater than the areal density on the side farther from the current collector layer, the aspect ratio of the conductive agent is a, and the negative electrode active material comprises graphite and SiO2. x 0 < x ≤ 2, the SiO in the negative electrode active material x The mass fraction of a is b%, and the mass fraction of graphite is c%, where a, b, and c satisfy the following relationship: a:(c-7b)≥10.

[0006] Graphite is valued for its stable properties, low price, and easy availability; however, it has a low energy density. Therefore, silicon-based materials (SiO2) are often combined with graphite. x This effectively improves the energy density of the negative electrode, thus overcoming the problem of low energy density in graphite negative electrodes. However, due to the poor conductivity of silicon-based materials, the conductivity of the electrode sheet is affected, which in turn affects the electrochemical performance of the battery. Therefore, this application adds a conductive agent to the negative electrode sheet and adjusts the aspect ratio of the conductive agent particles in relation to the graphite content and silicon-based material content, i.e., a:(c-7b)≥10, where a represents the aspect ratio of the conductive agent and b represents the SiO2 content. xThe mass fraction of graphite is represented by 'c', where 'c' represents the mass fraction of graphite. The aspect ratio represents the ratio of the longest diameter passing through the interior of the particle to the longest diameter perpendicular to it. Based on these relationships, the conductive agent can be more fully wrapped around the graphite surface and SiO₂. x The surface ensures sufficient contact between the conductive agent and the negative electrode active material, constructing a stable conductive network. This optimizes the conductivity of the negative electrode, ensures electron conduction within the negative electrode active material, reduces internal resistance of the negative electrode, minimizes battery polarization, and improves the battery's rate performance and cycle performance. Based on the negative electrode configuration of this application, the energy density of the battery can be increased while ensuring the stability of the negative electrode, and the rate performance and cycle performance of the battery can also be improved.

[0007] Furthermore, in this embodiment, the areal density of the conductive agent on the side closer to the current collector layer is greater than that on the side farther from the current collector layer. That is, in the negative electrode sheet, the mass concentration of the conductive agent in the lower layer is greater than that in the upper layer. This is beneficial for increasing the rate at which electrons enter the current collector layer, thereby improving the overall conductivity of the negative electrode sheet, reducing the battery's drain-rate-compression (DCR), and improving the battery's rate performance. In some embodiments, the areal density of the conductive agent on the side closer to the current collector layer is 0.01–0.5 mg / 1540 mm². 2 The areal density of the conductive agent on the side away from the current collector is 0.01–0.35 mg / 1540 mm². 2 In some embodiments, the ratio of the areal density of the conductive agent on the side near the current collector to the areal density on the side away from the current collector is 1:(1 to 3). Within the above range, the conductivity of the negative electrode is further optimized, and the battery dynamics performance is further improved.

[0008] In some embodiments, the value of a:(c-7b) is less than 750. When the value of a:(c-7b) is less than 750, it can prevent the internal chemical reaction rate of the battery from being too fast and avoid causing the battery performance to deteriorate.

[0009] In some embodiments, the areal density of the negative electrode active material near the current collector is greater than that away from the current collector. This effectively reduces the consumption of lithium in the negative electrode and decreases the contact surface area between the negative electrode active material and the electrolyte, thereby reducing battery side reactions, reducing gas production, and improving the battery's cycle performance and rate performance. In some embodiments, the areal density of the negative electrode active material near the current collector is 50–200 mg / 1540 mm². 2 The areal density of the negative electrode active material on the side away from the current collector is 30–145 mg / 1540 mm². 2 .

[0010] In some embodiments of this application, the conductive agent includes at least one of single-walled carbon nanotubes, carbon black, and fumed carbon fibers, and the aspect ratio α of the conductive agent is (1000-10000):1. Among the above conductive agents, single-walled carbon nanotubes have excellent conductivity, flexibility, and structural stability, and when the aspect ratio α of the single-walled nanotubes is within the above range, it can be more fully wound around SiO₂. x Surface and SiO x Sufficient contact, in SiO x A stable conductive network is constructed on the surface. This greatly improves the conductivity of SiO₂. x On the one hand, the conductivity of single-walled carbon nanotubes is good; on the other hand, the flexibility of single-walled carbon nanotubes makes them suitable for silicon-based materials (SiO2). x The volume expansion during charge-discharge cycles provides a binding and buffering effect, thereby suppressing SiO2. x The volume expansion during charge-discharge cycles can cause electrode rebound, pulverization, and even delamination from the current collector. Furthermore, carbon black and fumed carbon fibers possess superior conductivity and buffering capacity, and are widely available. Within the aforementioned aspect ratio range, they exhibit similar effects to single-walled carbon nanotubes. In some embodiments, the conductive agent is a mixture of single-walled carbon nanotubes and carbon black, with a mass ratio of (0.1–0.5):1.

[0011] In some embodiments, 88 ≤ c ≤ 95, 5 ≤ b ≤ 12. That is, based on the mass of the negative electrode active material, the mass fraction of graphite is 88% to 95%, and the mass fraction of SiO is... x It accounts for 5% to 12%.

[0012] This application uses SiO x When mixed with graphite as a negative electrode active material, it can both improve energy density and reduce the volume expansion of silicon-based materials during charging and discharging. Furthermore, this application utilizes SiO₂... x The synergistic effect of graphite content (mass fraction in negative electrode active material) and the aspect ratio of conductive agent significantly improves the conductivity, stability and energy density of negative electrode sheet.

[0013] In some embodiments of this application, the graphite includes at least one of artificial graphite or natural graphite.

[0014] In some embodiments, the diameter of the single-walled carbon nanotubes is 0.5–100 nm. When the diameter of the single-walled carbon nanotubes is within the above range, the conductivity of the negative electrode can be further improved, the electron transport efficiency can be increased, and the electrochemical performance of the battery can be enhanced.

[0015] In some embodiments, the specific surface area of ​​the conductive agent is 600–1500 m². 2 / g. When the specific surface area of ​​the conductive agent is within the above range, it is beneficial to the battery performance.

[0016] Through the above embodiments, single-walled carbon nanotubes exhibit excellent conductivity, flexibility, and structural stability. This application uses single-walled carbon nanotubes with high aspect ratio and specific surface area as conductive agents, further promoting the complete entanglement of single-walled carbon nanotubes within SiO₂. x The surface is in full contact with it, in SiO x A stable conductive network is constructed on the surface, which greatly improves the conductivity of SiO₂. x The high conductivity ensures electron conduction, improves lithium-ion transport, reduces electrode internal resistance and polarization, and enhances the rate performance and cycle performance of the battery cell. The optimized aspect ratio and specific surface area further promote the dispersion of single-walled carbon nanotubes and reduce the likelihood of SiO₂ formation. x A situation where they are intertwined and clustered together.

[0017] In some embodiments of this application, the negative electrode sheet further includes a binder, which comprises polyacrylic acid materials and polystyrene materials, wherein the mass content of the polyacrylic acid material in the negative electrode active layer is greater than that of the polystyrene material. On the one hand, active materials, conductive agents, and other materials need to be connected to form a whole using a binder; on the other hand, the active material and the current collector also need to be bonded together using a binder. In silicon-carbon material-based negative electrodes, because SiO₂... x The volume expansion of SiO₂ is significant, and conventional polystyrene adhesives (such as styrene-butadiene rubber) have limited bonding or binding ability, resulting in poor adhesion and poor mechanical properties of the electrode, especially when SiO₂ expands significantly. x When the content is high, the phenomenon of electrode powdering and delamination is obvious, requiring the addition of a large amount of polystyrene binder to form a bond. The addition of a large amount of polystyrene binder reduces the proportion of active material, failing to achieve the goal of increasing energy density. When polyacrylic acid materials are used as binders for silicon-carbon anode materials, although the mechanical properties of the electrode are improved, a series of processing difficulties arise, such as low slurry solid content, poor coating appearance, and low coating drying efficiency. Moreover, polyacrylic acid binders generally have a glass transition temperature higher than room temperature, and are in a brittle and hard glassy state at room temperature. This makes the use of polyacrylic acid binders brittle during electrode preparation, coating, and drying, resulting in a narrow coating parameter window and easy film cracking, seriously affecting production yield and efficiency, and failing to meet actual production requirements. Based on the above reasons, this application uses a mixture of polyacrylic acid materials and polystyrene materials as binders for the anode electrode of this application. This combines the advantages of both types of binders, reducing the overall amount of binder used, thereby improving adhesion and inhibiting SiO2 formation. xThe expansion performance is good, and the processing performance is also satisfactory. The negative electrode sheet is not prone to pulverization and delamination, and the adhesion is good. Specifically, this application, on the one hand, adds polyacrylic acid materials to give the negative electrode sheet good adhesion strength, suppresses the expansion of silicon-carbon negative electrode materials during charge and discharge, and gives it sufficient adhesion and cohesive strength. On the other hand, it adds polystyrene materials (such as SBR) to give the electrode sheet a certain degree of flexibility, improves processing performance, and gives the negative electrode sheet both high adhesion and good flexibility, resulting in a high energy density negative electrode sheet. In some embodiments, the mass content of the polyacrylic acid materials is greater than that of the polystyrene materials, which is more conducive to improving the adhesion of the negative electrode sheet and improving the cycle performance of the battery.

[0018] In some embodiments of this application, the mass ratio of the polyacrylic acid material to the polystyrene material is (1.5–3):1. When the mass ratio of the polyacrylic acid material to the polystyrene material is within the above range, the adhesion of the negative electrode sheet can be further improved, and the cycle performance of the battery can be further optimized.

[0019] In some embodiments of this application, the polyacrylic material includes at least one of polyacrylic acid, polyacrylamide, polyacrylonitrile, polyacrylate, or polyacrylate.

[0020] Because polyacrylic acid adhesives contain a large number of polar functional groups such as carboxyl groups, they react with SiO₂. x Strong hydrogen bonds can form, creating a coating, binding, and buffering effect on the surface of SiO2. x The volume expansion imparts excellent mechanical properties to the electrode, thereby improving the cycle performance of the negative electrode.

[0021] In some embodiments of this application, the polyacrylate includes at least one of lithium polyacrylate or sodium polyacrylate.

[0022] In some embodiments of this application, the polyacrylate includes at least one of polyacrylate or polymethacrylate.

[0023] In some embodiments of this application, the polystyrene material includes at least one of styrene-butadiene rubber or styrene-acrylate.

[0024] In some embodiments of this application, the mass percentage of the binder in the negative electrode active layer is 2% to 6%. Using the above composite binder can reduce the binder content in the negative electrode sheet while ensuring high bonding performance, which is beneficial for improving battery energy density.

[0025] In some embodiments of this application, the compaction density of the negative electrode active layer is 1.5 g / cm³. 3~1.8g / cm 3 The preferred value is 1.6 / cm. 3 ~1.8g / cm 3 When the compaction density of the negative electrode active layer is within the above range, the energy density of the battery can be effectively improved, while also enhancing the battery's cycle performance and rate performance.

[0026] In some embodiments, the peeling force of the negative electrode sheet is 26-36 N / m. The peeling force of the negative electrode sheet is the force required to peel the negative electrode active material layer from the current collector layer. Under the action of the binder, the peeling force of the negative electrode sheet can be improved, effectively improving the stability of the negative electrode sheet and improving the cycle performance of the battery.

[0027] A second aspect of this application provides a method for preparing the aforementioned secondary battery, comprising the following steps: winding a negative electrode sheet, a diaphragm, and a positive electrode sheet and assembling them into a casing, injecting an electrolyte to obtain a secondary battery, wherein the negative electrode sheet comprises a negative electrode active material and a conductive agent, the aspect ratio of the conductive agent is a, and the negative electrode active material comprises graphite and SiO₂. x 0 < x ≤ 2, the SiO in the negative electrode active material x The mass fraction of a is b%, and the mass fraction of graphite is c%, where a, b, and c satisfy the following condition: a:(c-7b)≥10.

[0028] In some embodiments of this application, the negative electrode sheet includes a current collector layer and a negative electrode active layer disposed on at least one side of the current collector layer. The negative electrode active layer includes the negative electrode active material and a conductive agent. The areal density of the conductive agent on the side closer to the current collector layer is greater than the areal density on the side farther from the current collector layer.

[0029] In some embodiments of this application, the secondary battery includes at least one of a lithium-ion battery or a sodium-ion battery.

[0030] A third aspect of this application provides an electrical device comprising the aforementioned secondary battery, the secondary battery serving as a power source for the electrical device. Detailed Implementation

[0031] The following will clearly and completely describe the concept and technical effects of this application in conjunction with embodiments, so as to fully understand the purpose, features and effects of this application. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the scope of protection of this application. In the description of this application, greater than, less than, and exceeding are understood to exclude the stated number, while above, below, and within are understood to include the stated number.

[0032] Unless otherwise specified, the experimental methods described in the following examples are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used are all commercially available from the conventional market unless otherwise specified.

[0033] Example 1

[0034] A process for preparing a secondary battery is provided, comprising the following steps:

[0035] (I) Preparation of negative electrode sheet:

[0036] The negative electrode active material (with a mass ratio of 95.5:1.1:2:1:0.4, wherein the mass fractions of graphite and SiO in the negative electrode active material are 90% and 10%, respectively), and single-walled carbon nanotubes (with an aspect ratio of 1000 and a specific surface area of ​​600 m²) are used. 2 (g), polyacrylic acid, SBR, and sodium carboxymethyl cellulose are added to deionized water and stirred until homogeneous to obtain a negative electrode slurry. The prepared negative electrode slurry is then coated onto copper foil using a double-layer coating machine (the lower layer is defined as the layer closest to the copper foil, and the upper layer is the layer furthest from the copper foil). The flow rate parameters of the feed pump of the extrusion die of the double-layer coating machine are adjusted to obtain upper and lower slurry layers with different coating surface densities. After baking, drying, rolling, slitting, and cutting, a negative electrode sheet is obtained. In the negative electrode sheet, the surface density of the single-walled nanotubes on the side closest to the copper foil is 0.4 mg / 1540 mm². 2 The areal density of the single-walled nanotube on the side away from the copper foil is 0.3 mg / 1540 mm². 2 The areal density of the negative electrode active material on the side closest to the copper foil is 180 mg / 1540 mm². 2 The areal density of the negative electrode active material on the side furthest from the current collector is 135 mg / 1540 mm². 2 .

[0037] (II) Preparation of the positive electrode: LiNi alloy with a mass ratio of 97:1.5:1:0.5 0.8 Co 0.1 Mn 0.1 O2, PVDF5130, carbon black, and carbon nanotubes are mixed evenly in N-methylpyrrolidone to obtain a positive electrode slurry. The positive electrode slurry is coated onto both sides of an aluminum foil, and then baked, dried, rolled, slit, and cut into sheets to obtain the positive electrode sheet.

[0038] (III) A core is formed by winding the positive electrode, negative electrode, and separator, and then encapsulated with an aluminum-plastic film. After baking under vacuum for 48 hours to remove moisture, electrolyte is injected, and after formation and capacity testing, a soft-pack secondary battery is manufactured. The prepared secondary battery has the parameter characteristics shown in Table 1.

[0039] The diaphragm is made of PP membrane;

[0040] The electrolyte is prepared as follows: take ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) and mix them in a mass ratio of EC:PC:DEC = 2.5:3:5. Then slowly add LiPF6 until the concentration of LiPF6 is 1 mol / L. Finally, add 5% fluoroethylene carbonate (FEC) and 0.5% vinylene carbonate (VC) by weight of the total electrolyte.

[0041] Example 2

[0042] This embodiment prepares a secondary battery, which differs from Example 1 only in that: in step one, a single-walled carbon nanotube with an aspect ratio of 1500 is selected.

[0043] Example 3

[0044] This embodiment prepares a secondary battery, which differs from Example 1 only in that: in step one, a single-walled carbon nanotube with an aspect ratio of 3000 is selected.

[0045] Example 4

[0046] This embodiment prepares a secondary battery, which differs from Example 1 only in that: in step one, a single-walled carbon nanotube with an aspect ratio of 5000 is selected.

[0047] Example 5

[0048] This embodiment prepares a secondary battery, which differs from Example 1 only in that: in step one, a single-walled carbon nanotube with an aspect ratio of 10000 is selected.

[0049] Example 6

[0050] This embodiment prepares a secondary battery, which differs from Example 1 only in that: in step one, the mass fraction b% of SiO in the negative electrode active material is 5%, the mass fraction c% of graphite is 95%, and the compaction density of the active material layer is 1.6 g / cm³. 3 .

[0051] Example 7

[0052] This embodiment prepares a secondary battery, which differs from Example 3 only in that: in step one, the mass fraction b% of SiO in the negative electrode active material is 12%, the mass fraction c% of graphite is 88%, and the compaction density of the active material layer is 1.8 g / cm³. 3 .

[0053] Example 8

[0054] This embodiment prepares a secondary battery, which differs from Example 4 only in that: in step one, the specific surface area of ​​the single-walled carbon nanotubes is 900 m². 2 / g.

[0055] Example 9

[0056] This embodiment prepares a secondary battery, which differs from Embodiment 4 only in that: in step one, the specific surface area of ​​the single-walled carbon nanotubes is 1100 m². 2 / g.

[0057] Example 10

[0058] This embodiment prepares a secondary battery, which differs from Example 4 only in that: in step one, the content of polyacrylic acid is adjusted to 1.7%, and the specific surface area of ​​single-walled carbon nanotubes is 1200 m². 2 / g.

[0059] Example 11

[0060] This embodiment prepares a secondary battery, which differs from Example 4 only in that: in step one, the content of polyacrylic acid is adjusted to 2.8%, and the specific surface area of ​​single-walled carbon nanotubes is 1300 m². 2 / g.

[0061] Example 12

[0062] This embodiment prepared a secondary battery, which differs from Example 4 only in that: polyacrylic acid is replaced with polymethacrylate at a content of 3.0%, and the specific surface area of ​​the single-walled carbon nanotubes is 1450 m². 2 / g.

[0063] Example 13

[0064] This embodiment prepares a secondary battery, which differs from Example 4 only in that: in step one, the mass fraction b% of SiO in the negative electrode active material is 5%, the mass fraction c% of graphite is 95%, SBR is replaced with styrene-acrylic acid, and the content of polyacrylic acid is adjusted to 1.5%.

[0065] Examples 14-17

[0066] Examples 14-17 respectively prepared a secondary battery, which differed from Example 1 only in that the content of single-walled carbon nanotubes was adjusted to obtain negative electrode sheets with different conductive agent contents.

[0067] Comparative Example 1

[0068] This comparative example prepared a negative electrode secondary battery, which differs from Example 1 only in that: in step one, the mass fraction b% of SiO in the negative electrode active material is 3%, the mass fraction c% of graphite is 97%, and the aspect ratio of the single-walled carbon nanotubes is 700.

[0069] Comparative Example 2

[0070] This comparative example prepared a negative electrode secondary battery, which differs from Example 1 only in that the negative electrode slurry is coated on only one side with a single layer.

[0071] The parameters of the secondary battery negative electrode sheet in the above embodiments and comparative examples are shown in Table 1. In the above embodiments, the aspect ratio of the conductive agent in the negative electrode sheet can be controlled by mechanical grinding, chemical etching, photolithography, or by controlling the reaction time to control the length of the single-walled carbon nanotubes to achieve the aspect ratio control, and the aspect ratio can be obtained by observation using transmission electron microscopy; the specific surface area can be controlled by adjusting different catalyst types, and the specific surface area value can be obtained by testing with a specific surface area meter.

[0072]

[0073]

[0074] Table 2

[0075] Experimental Example Peel strength of negative electrode sheet (N / m) Cyclic performance (cycles) DCR (Ω) at room temperature Example 1 27.6 855 36.4 Example 2 29.8 980 30.2 Example 3 30.5 1100 28.5 Example 4 35.6 1300 24.8 Example 5 28.5 1000 29.6 Example 6 26.3 977 25.5 Example 7 31.5 985 33.5 Example 8 34.2 1205 25.6 Example 9 32.9 1156 27.1 Example 10 32.1 1162 25.8 Example 11 37.8 1198 27.8 Example 12 33.3 930 35.7 Example 13 31.0 1010 27.5 Example 14 14.3 750 36.5 Example 15 20.2 850 30.5 Example 16 21.5 870 32.5 Example 17 21.2 780 31.5 Comparative Example 1 33.5 560 52.7 Comparative Example 2 28 655 45

[0076] Based on the data from the above examples and comparative examples, it can be seen that if the aspect ratio of the conductive agent particles, the graphite content, and the silicon-based material content satisfy the relationship that a:(c-7b)≥10, the secondary battery exhibits excellent cycle performance and can reduce the DC resistance of the secondary battery, which is beneficial to the battery's rate performance. Furthermore, a comparison of the data from Example 1 and Comparative Examples 1-2 shows that if the areal density of the conductive agent on the side closer to the current collector is greater than that on the side farther from the current collector, it can reduce the battery's DCR, which is beneficial to the battery's kinetic performance.

[0077] The embodiments of this application have been described in detail above. However, this application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this application. Furthermore, unless otherwise specified, the embodiments and features described in the embodiments of this application can be combined with each other.

Claims

1. A secondary battery, characterized in that, The negative electrode includes a current collector layer and a negative electrode active layer disposed on at least one side of the current collector layer. The negative electrode active layer includes a negative electrode active material and a conductive agent. The areal density of the conductive agent on the side closer to the current collector layer is greater than the areal density on the side farther from the current collector layer. The aspect ratio of the conductive agent is 'a'. The negative electrode active material includes graphite and SiO2. x 0 < x ≤ 2, the SiO in the negative electrode active material x The mass fraction of a is b%, and the mass fraction of graphite is c%, where a, b, and c satisfy the following: 750 ≥ a: (c-7b) ≥ 10, 88 ≤ c ≤ 95, and 5 ≤ b ≤ 12. The conductive agent includes at least one of single-walled carbon nanotubes, carbon black, and fumed carbon fibers, and the aspect ratio a of the conductive agent is (1000~10000):

1. The surface density of the negative electrode active material on the side closer to the current collector is greater than the surface density on the side farther from the current collector.

2. The secondary battery according to claim 1, characterized in that, The specific surface area of ​​the conductive agent is 600~1500 m². 2 / g.

3. The secondary battery according to claim 1, characterized in that, The negative electrode sheet also includes a binder, which includes polyacrylic acid materials and polystyrene materials. In the negative electrode active layer, the mass content of the polyacrylic acid materials is greater than that of the polystyrene materials.

4. The secondary battery according to claim 3, characterized in that, The mass ratio of the polyacrylic acid material to the polystyrene material is (1.5~3):

1.

5. The secondary battery according to claim 1, characterized in that, The compaction density of the negative electrode active material layer is 1.5 g / cm³. 3 ~1.8g / cm 3 .

6. The secondary battery according to claim 3, characterized in that, Based on the mass of the negative electrode active layer, the mass percentage of the binder is 2% to 6%.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The peeling force of the negative electrode sheet is 26~36 N / m.

8. An electrical device, characterized in that, The electrical device includes a secondary battery as described in any one of claims 1 to 7, wherein the secondary battery serves as the power source for the electrical device.

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