Battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery. The battery comprises a negative plate, the negative plate comprises a negative current collector and a negative active layer located on at least one side surface of the negative current collector, the negative active layer comprises a negative active material, the negative active material comprises a silicon carbon material, the silicon carbon material comprises first silicon carbon, second silicon carbon and third silicon carbon, the sphericity degree of the first silicon carbon is alpha1, 0.45 < = alpha1 < 0.8, and 0.45 < = alpha2 < = 0.8. The sphericity degree of the second silicon carbon is alpha2, 0.8 < = alpha2 < = 0.95, the sphericity degree of the third silicon carbon is alpha3, and alpha3 > 0.95; the section of the first silicon carbon has a first interior angle which is smaller than 180 degrees; a second inner angle is formed in the section of the second silicon carbon and is larger than 180 degrees. The rate capability and the K-value yield of the battery can be improved on the premise of maintaining good cycling stability of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a battery. Background Technology

[0002] With the widespread application of lithium-ion batteries in consumer electronics, electric vehicles, and energy storage systems, the energy density of traditional graphite anode materials has reached its limit. Silicon-carbon materials, due to their high theoretical capacity, have become a research hotspot. Although silicon-carbon materials have shown great potential in lithium-ion batteries, they also face problems such as large volume expansion and poor cycle stability during cycling, hindering their application in battery anodes. Therefore, providing a silicon-carbon anode that maintains high energy density while improving battery expansion and cycle stability is crucial for the commercial application of silicon-carbon materials. Summary of the Invention

[0003] The purpose of this invention is to solve the above-mentioned problems existing in the prior art and to provide a battery in which the negative electrode contains silicon-carbon material. The negative electrode active material is selected from first silicon-carbon, second silicon-carbon and third silicon-carbon with different sphericity, and the interior angle of the cross section of the first silicon-carbon and second silicon-carbon is within a suitable range, so that the battery including the negative electrode sheet can improve the rate performance and K-value yield of the battery while maintaining good cycle stability.

[0004] The sphericity of silicon-carbon materials significantly affects the cycle stability, volume expansion rate, and kinetic performance of silicon-carbon anode batteries. In related technologies, silicon-carbon materials can be classified into spherical and bulk silicon-carbon materials based on their sphericity. While low-sphericity bulk silicon-carbon materials (first-order silicon-carbon) exhibit excellent kinetic performance, they have poor compressive strength. After rolling, the electrodes are prone to particle breakage, leading to a thicker SEI film that affects battery cycle performance. Furthermore, their sharp edges can puncture the separator, causing localized micro-short circuits and poor K-value in the battery. Conversely, high-sphericity spherical silicon-carbon materials (third-order silicon-carbon) have good compressive strength and can uniformly distribute expansion stress to alleviate volume expansion. However, their smooth surface results in weak adhesion between particles, poor electrode kinetics, and rapid capacity decay during battery cycle.

[0005] The inventors of this invention discovered that when first and third silicon-carbon materials are used together, the advantages of both bulk and spherical silicon-carbon materials cannot be simultaneously utilized, resulting in a battery that suffers from the problems associated with both spherical and bulk silicon-carbon materials. A near-spherical silicon-carbon material (second silicon-carbon), with a sphericity between that of spherical and bulk silicon-carbon materials, not only possesses certain advantages of both but also compensates for their disadvantages. This is because: firstly, the near-spherical silicon-carbon material also has a relatively smooth surface without sharp edges or corners, reducing the risk of puncturing the separator and avoiding the problem of decreased battery K-value yield caused by bulk silicon-carbon materials; secondly, the near-spherical silicon-carbon material has grooves on its surface, which can enhance the contact area and adhesion between particles, improving the electrode dynamics; and thirdly, the near-spherical silicon-carbon material has a regular morphology, which can evenly distribute expansion stress in all directions, avoiding stress concentration that could lead to silicon-carbon material cracking and failure, resulting in decreased battery cycle stability. The inventors of this invention further discovered that when the size of the second interior angle in the cross-section of the second silicon-carbon material is within a suitable range, it indicates that the surface of the second silicon-carbon material has a groove-like structure with a certain depth and curvature, composed of smooth curved portions and straight sections, which can further improve the performance of the negative electrode: the groove-like structure of the second silicon-carbon material has better toughness under rolling stress, its smooth curved portions can disperse rolling stress, while the straight sections provide a certain rigid support; the grooves of the second silicon-carbon material can absorb energy, reduce stress concentration, and thus reduce the risk of silicon-carbon material breakage; when the second silicon-carbon material and the first silicon-carbon material... When carbon and third silicon-carbon are used together, the second silicon-carbon can fill the gaps between spherical and bulk silicon-carbon materials, acting as a buffer to prevent the bulk silicon-carbon material from breaking under direct stress, thus avoiding membrane puncture and K-value increase. The trench structure also helps to fix other particles in the electrode, reduce voids, and form a more stable three-dimensional network. This not only improves the mechanical stability of the negative electrode, but also ensures efficient conduction of ions and electrons. Thus, it combines the high packing density of spherical silicon-carbon materials with the kinetic advantages of bulk silicon-carbon, which is conducive to improving rate performance and reducing the risk of lithium plating caused by insufficient rate performance.

[0006] Based on this, the present invention proposes the following technical solution: A battery includes a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector, the negative electrode active layer including a negative electrode active material, the negative electrode active material including a silicon-carbon material, the silicon-carbon material including a first silicon-carbon, a second silicon-carbon and a third silicon-carbon, the first silicon-carbon having a sphericity of α1, 0.45≤α1<0.8, the second silicon-carbon having a sphericity of α2, 0.8≤α2≤0.95, and the third silicon-carbon having a sphericity of α3, α3>0.95; the first silicon-carbon having a first interior angle in its cross-section, the first interior angle being less than 180°; the second silicon-carbon having a second interior angle in its cross-section, the second interior angle being greater than 180°.

[0007] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: The battery of the present invention can improve the rate performance and K-value yield of the battery while maintaining good cycle stability.

[0008] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0009] Figure 1 The image shown is a scanning electron microscope image of a second silicon carbide in one embodiment of the present invention.

[0010] Figure 2 The image shown is a scanning electron microscope image of the first silicon carbon according to an embodiment of the present invention.

[0011] Figure 3 The image shown is a cross-sectional scanning electron microscope image of the negative electrode sheet along the thickness direction in one embodiment of the present invention. The scale bar in the image is 20 μm.

[0012] The attached diagram is labeled as follows: 1 represents the first silicon-carbon, 2 represents the second silicon-carbon, 3 represents the third silicon-carbon, ∠1 represents the first interior angle, and ∠2 represents the second interior angle. Detailed Implementation

[0013] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0014] The present invention provides a battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising a silicon-carbon material, the silicon-carbon material comprising a first silicon-carbon, a second silicon-carbon, and a third silicon-carbon.

[0015] In this invention, the sphericity of the first silicon carbide is α1, 0.45≤α1<0.8 (e.g., 0.45, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.6, 0.65, 0.7, 0.75 or 0.79).

[0016] In one embodiment, 0.6 ≤ α1 ≤ 0.7.

[0017] In this invention, the sphericity of the second silicon carbide is α2, 0.8≤α2≤0.95 (e.g., 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92 or 0.95).

[0018] In one embodiment, 0.85 ≤ α2 ≤ 0.92.

[0019] In this invention, the sphericity of the third silicon carbide is α3, where α3 > 0.95 (e.g., 0.96, 0.97, 0.98, or 0.99).

[0020] In one embodiment, 0.98 ≤ α3 < 1.

[0021] In this invention, the cross-section of the first silicon carbide has a first interior angle, which is less than 180°, for example, 10°, 15°, 20°, 30°, 40°, 50°, 60°, 80°, 100°, 120°, 140°, 160° or 170°.

[0022] In one embodiment, the first interior angle is 60°-120°.

[0023] It is understood that the first interior angle refers to the angle formed by drawing two straight lines tangent to the outer contour of the first silicon carbon cross-section, starting from the vertex furthest from the center of the first silicon carbon contour.

[0024] It is understandable that the aforementioned contour center is not a strictly mathematical geometric center. During measurement, meaningful points such as the midpoint of the longest diameter of the cross-section, the center of the inscribed circle, and the center of the circumscribed circle can be selected as the contour center based on experience. Generally speaking, for the first silicon carbide particle with a convex polygonal cross-section, the interior angle with the smallest degree in its convex hull is a first interior angle. Since, under a certain SEM magnification, the corners of some silicon carbide particles are not enclosed by a straight contour but are uneven, they can still be regarded as interior angles based on the extension trend of the contour.

[0025] In this invention, the cross-section of the second silicon-carbon material has a second interior angle, which is greater than 180°, for example, 185°, 190°, 200°, 220°, 240°, 260°, 280°, 300°, 320° or 350°.

[0026] In one embodiment, the second interior angle is 200°-300°.

[0027] It is understood that the second interior angle refers to a straight line tangent to the contour of the second silicon carbon particle, drawn from a single point on the contour of the second silicon carbon particle with a vertical distance of more than 0.25 μm from its convex hull segment. In this case, there are two different tangent lines, and the angle formed by the two tangent lines on the cross section of the second silicon carbon particle is denoted as the second interior angle.

[0028] In one embodiment, the second silicon carbide has two second interior angles.

[0029] In yet another embodiment, the second silicon carbide has a second interior angle.

[0030] like Figure 1 The image shown is a scanning electron microscope image of the second silicon carbide according to an embodiment of the present invention, as follows: Figure 2 The image shown is a scanning electron microscope image of the first silicon-carbon substrate according to an embodiment of the present invention. Figure 3 The image shown is a cross-sectional scanning electron microscope image of the negative electrode sheet along the thickness direction in one embodiment of the present invention, wherein 1 is the first silicon-carbon, 2 is the second silicon-carbon, 3 is the third silicon-carbon, ∠1 is the first interior angle, and ∠2 is the second interior angle.

[0031] Adjusting α1, α2, and α3 within appropriate ranges allows for matching the sphericity of the first, second, and third silicon-carbon particles, improving the overall compressive strength and particle packing density of the negative electrode, and optimizing the battery's cycle performance and rate performance. When α1 is too small (e.g., <0.45), the surface area of ​​the first silicon-carbon is too large, making it prone to side reactions with the electrolyte, consuming more active lithium, and hindering the improvement of battery cycle capacity retention. When α1 is too large (e.g., >0.8), the surface of the first silicon-carbon is too smooth, resulting in poor interparticle adhesion, which is detrimental to improving the dynamic performance of the negative electrode. When α2 is too small (e.g., <0.8), the compressive strength of the second silicon-carbon particles is poor, and the particles are prone to cracking or breakage after the negative electrode is rolled, which is detrimental to improving battery cycle performance and K-value yield. When α2 is too large (e.g., >0.95), the surface of the second silicon-carbon particles is too smooth, and the groove depth on the particle surface is shallow, making it difficult to fill the gaps between the first and third silicon-carbon particles, thus failing to provide more buffer space for them. When α3 is small (e.g., <0.95), the third silicon-carbon layer's ability to withstand expansion stress decreases, its buffering effect weakens, and the overall rolling resistance of the negative electrode active layer decreases.

[0032] Silicon-carbon materials are inherently brittle. First-stage silicon-carbon (SPC) has low sphericity, and its surface edges and corners are weak points where stress concentrates. Under significant external pressure, it is prone to cracking or breakage, leading to the formation of more solid electrolyte interphase (SEI) film at the negative electrode. This accelerates the consumption of lithium ions and electrolyte, resulting in lower initial charge-discharge efficiency and shorter cycle life. Furthermore, the sharp parts of broken SPC can compress or even puncture the separator, causing localized micro-short circuits and resulting in poor K-value in the battery. Third-stage silicon-carbon (DSC), with its higher sphericity, can distribute stress evenly across the surface of silicon-carbon particles, avoiding localized stress concentration and breakage. This effectively improves the poor K-value problem. However, the smooth surface and insufficient contact area between particles of DSC hinder the transport of lithium ions and electrons, resulting in poor kinetics of the negative electrode. When SPC and DSC are mixed in a silicon negative electrode system battery, not only are the advantages of both materials not fully utilized, but their shortcomings are also not overcome, making it difficult to significantly improve battery performance.

[0033] The sphericity of the second silicon-carbon material falls between that of the first and third silicon-carbon materials. It not only possesses a relatively smooth surface, thus preventing poor K-value in the battery, but also exhibits a second interior angle in its cross-section, indicating the presence of a groove structure on its surface. This further enhances battery performance. The reasons are as follows: First, the groove structure increases the contact area between the second silicon-carbon material and the binder and conductive agent in the negative electrode active layer, improving particle adhesion, preventing powder shedding or particle demolding, and enhancing battery cycle stability. Second, the groove structure also serves as an expansion space, reducing cracking and pulverization of the electrode due to expansion, maintaining structural integrity, and improving battery cycle stability. Third, the groove structure distributed on the surface of the second silicon-carbon material forms microscale ion channels, shortening the migration distance of lithium ions, improving internal electrode polarization, and enhancing the battery's rate performance. Fourth, the second silicon-carbon material has moderate sphericity, a groove structure on its surface without sharp edges, and the smooth curved portions of the groove structure can disperse rolling stress, while the straight sections provide rigid support, improving the silicon-carbon material's resistance to rolling stress.

[0034] The size of the first interior angle on the first silicon-carbon cross section reflects the sharpness of the edges on the first silicon-carbon. When the first interior angle is too small, the morphology of the first silicon-carbon is more irregular, the edges are too sharp, and stress concentration and separator puncture are more likely to occur. The strength of the first silicon-carbon decreases, which is not conducive to improving battery cycle performance, safety performance and K-value yield. Adjusting the second inner angle within a suitable range can reflect the depth and curvature of the trench structure. When the second inner angle is too small, the trench structure on the second silicon-carbon surface is shallow and has a small curvature, presenting an overall gentle trend. During the rolling process of the negative electrode sheet, it is difficult to provide sufficient buffer space for the expansion stress of the first silicon-carbon, leading to the breakage of the first silicon-carbon particles, affecting the K-value yield of the battery, and also causing the bonding network to deteriorate during battery cycling, thus affecting the cycle stability of the battery. When the second inner angle is too large, the trench structure on the second silicon-carbon surface is too deep and has a curvature that is too high, making it prone to local stress concentration. This is not conducive to improving the overall strength of the silicon-carbon particles, and the tolerance of the negative electrode sheet to rolling stress and expansion stress decreases, thereby affecting the K-value yield and cycle capacity retention rate of the battery.

[0035] When the second silicon-carbon compound is used in conjunction with the first and third silicon-carbon compounds, the second silicon-carbon compound fills the gaps between the first and third silicon-carbon compounds. Through its own stress-buffering effect, it prevents the low-strength first silicon-carbon compound from cracking under external forces, thus improving the battery's K-value yield and safety performance. Simultaneously, the second silicon-carbon compound, due to its trench structure, increases the contact area with other components in the negative electrode and with the first and third silicon-carbon particles, helping to anchor other particles and form a stable three-dimensional structure in the negative electrode. This ensures efficient lithium-ion transport between silicon-carbon particles and within the negative electrode active layer, thereby improving the battery's rate performance. The first, second, and third silicon-carbon compounds work synergistically, avoiding their individual shortcomings while exhibiting high packing density and good kinetic performance, comprehensively improving the battery's cycle stability, rate performance, and K-value yield, and reducing the risk of lithium plating.

[0036] In this invention, α1, α2, and α3 can be obtained using conventional testing methods in the art, such as scanning electron microscopy. Specifically, the battery is discharged to 0% SOC, the negative electrode is disassembled and removed, or the negative electrode is directly removed. The cross-section of the negative electrode is polished using an argon ion mill, and then the obtained cross-section is imaged using backscatter imaging mode on a scanning electron microscope (SEM). Image processing software such as ImagePro is then used to obtain the image. Plus) The images of each silicon-carbon particle in the SEM image (backscattered mode) of the negative electrode active layer at a certain magnification (e.g., 2500x) are analyzed to obtain the perimeter and area of ​​each particle. The equivalent radius of perimeter r1 and the equivalent radius of area r2 of each silicon-carbon particle are calculated. Then the sphericity of each particle is S=r2 / r1. The sphericity of each particle is then weighted and averaged to obtain the average sphericity of the silicon-carbon material. Silicon-carbon particles with a sphericity less than 0.8 are classified as first silicon-carbon, silicon-carbon particles with a sphericity between 0.8 and 0.95 are classified as second silicon-carbon, and silicon-carbon particles with a sphericity greater than 0.95 are classified as third silicon-carbon.

[0037] In this invention, the second interior angle can be obtained by conventional testing methods in the art, such as by scanning electron microscopy (SEM), specifically as follows: discharge the battery to 0% SOC, disassemble and remove the negative electrode, or directly remove the negative electrode, polish its cross-section with an argon ion mill, and image the obtained cross-section using backscatter imaging mode on a scanning electron microscope (SEM) device. Determine the second silicon carbon by sphericity, find the point on the outline of the second silicon carbon particle that is more than 0.25 μm away from its convex hull line segment as the vertex, draw two tangent lines through the vertex to the cross-sectional outline of the second silicon carbon, and use image processing software to measure the angle of the two tangent lines on the cross-section. A total of 10 different second silicon carbon particles are measured, and the average value is taken as the size of the second interior angle.

[0038] In this invention, the first interior angle can be obtained by conventional testing methods in the art, such as by scanning electron microscopy (SEM), specifically as follows: discharge the battery to 0% SOC, disassemble and remove the negative electrode, or directly remove the negative electrode, polish its cross-section with an argon ion mill, and image the obtained cross-section using backscatter imaging mode on a scanning electron microscope (SEM) device, determine the first silicon carbon by sphericity, find the point farthest from the center of the interface, and use image processing software to measure the angle between the two tangent lines passing through the point and tangent to the cross-sectional contour of the first silicon carbon on the cross-section. A total of 10 different first silicon carbon particles are measured, and the average value is taken as the size of the first interior angle.

[0039] It is understandable that the above image processing is only meaningful at a certain electron microscope magnification, such as 5000x.

[0040] In this invention, the cross-section of the third silicon carbide has no interior angles. The third silicon carbide has high sphericity, a regular appearance, and a consistent surface curvature. The outer contour of its cross-section is mainly a smooth, continuous curve, and it has no interior angles.

[0041] In this invention, the silicon-carbon material comprises a porous carbon matrix and silicon material located in the internal channels of the porous carbon matrix.

[0042] In this invention, based on the total mass of the negative electrode active material, the mass content of the first silicon carbon is c1, the mass content of the second silicon carbon is c2, and the mass content of the third silicon carbon is c3, where 0% < c1 ≤ 60% (e.g., 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, or 60%); 0% < c2 ≤ 60% (e.g., 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, or 60%); and 0% < c3 ≤ 60% (e.g., 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, or 60%).

[0043] In this invention, c1, c2 and c3 satisfy: 0.1≤(c1+c3) / c2≤5, for example, 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5.

[0044] In one embodiment, 0.5 ≤ (c1+c3) / c2 ≤ 2.

[0045] In this invention, 0.2≤c1 / c3≤4, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.5, 2, 2.5, 3, 3.5 or 4.

[0046] In one embodiment, 0.5 ≤ c1 / c3 ≤ 2.

[0047] Adjusting the mass content ratio of the first, second, and third silicon-carbon materials in the negative electrode active material to conform to the above relationship can further enhance the synergistic effect among the three silicon-carbon materials, which helps to further optimize the cycle stability, rate performance, and K-value yield of the battery. When (c1+c3) / c2 is too small (e.g., <0.5), the sum of the contents of the first and third silicon carbons is too small while the content of the second silicon carbon is too high. This results in a low proportion of the first silicon carbon, which is beneficial for improving the overall dynamics of the negative electrode, and the third silicon carbon, which enhances the compressive strength of silicon carbon particles. This is not conducive to improving the rate performance and cycle stability of the battery, and the battery capacity decays quickly. When (c1+c3) / c2 is too large (e.g., >5), the content of the second silicon carbon is too small while the sum of the contents of the first and third silicon carbons is too high. The compressive strength of the first silicon carbon is low, and the adhesion performance between the third silicon carbon and other components of the negative electrode is poor. The second silicon carbon content is insufficient. When the negative electrode is subjected to rolling stress or volume expansion during battery cycling, the stress tolerance performance decreases, the structural stability of the negative electrode decreases, and this is not conducive to further improving the battery cycle performance and K-value yield.

[0048] Furthermore, adjusting the mass content ratio of the first and third silicon carbons can further optimize the composition and coordination of silicon carbon materials based on adjusting (c1+c3) / c2. When c1 / c3 is too low (e.g., <0.2), the proportion of the first silicon carbon with a blocky morphology in the negative electrode active material is too low, while the proportion of the second and third silicon carbons with higher sphericity is too high. The adhesion performance between particles in the negative electrode active layer is poor, which is not conducive to further improvement of the dynamic performance of the negative electrode sheet and the charge-discharge performance of the battery. When c1 / c3 is too high (e.g., >4), the proportion of the first silicon carbon with a blocky morphology in the negative electrode active material is too high. The proportion of the sharp edges and corners of the silicon carbon particles in the negative electrode active material increases. The sharp edges and corners easily increase the risk of separator puncture and increase the probability of local micro-short circuits inside the battery, which is not conducive to improving the yield of the battery K-value.

[0049] In this invention, the negative electrode active material further includes graphite. Based on the total mass of the negative electrode active material, the mass content of the graphite is c4, 40%≤c4<100%, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 80%, 90% or 99%.

[0050] In this invention, the average particle size of the graphite is 5μm-18μm, for example, 5μm, 6μm, 7μm, 8μm, 10μm, 12μm, 14μm, 16μm or 18μm.

[0051] In one embodiment, the average particle size of the graphite is 8 μm-12 μm.

[0052] When the graphite content in the negative electrode active material is adjusted to a suitable range, the resulting battery exhibits high energy density, low volume expansion rate, and good cycle stability. When C4 is too low (e.g., <40%), the graphite content in the negative electrode active material is too low to effectively buffer the volume expansion stress of the silicon material during battery cycling. This leads to problems such as appearance deformation and negative electrode active layer detachment during battery cycling, resulting in battery failure and hindering further improvement in battery cycle stability. When the average particle size of graphite is too large (e.g., >18μm), the lithium-ion insertion path within the graphite is too long, increasing the risk of lithium plating on the negative electrode sheet during high-rate charging. Simultaneously, a large average particle size cannot effectively fill the trench structure on the second silicon-carbon surface, resulting in a small contact area between graphite and silicon-carbon particles, which is detrimental to improving the kinetic performance of the negative electrode sheet. When the average particle size of graphite is too small (e.g., <5μm), the specific capacity and compaction density of graphite decrease, which is detrimental to improving the battery's energy density.

[0053] In this invention, c1, c2, c3, and c4 can be obtained using conventional testing methods in the art, such as SEM measurement, specifically as follows: The battery is discharged to 0% SOC, the negative electrode is removed, and then soaked and cleaned in dimethyl carbonate (DMC) and dried. After processing with argon ion polishing technology, a cross-sectional sample of the negative electrode can be obtained. This sample is then tested using a scanning electron microscope in backscatter mode at a magnification of 1.3K. The entire image is processed using image processing software such as ImageProPlus. Silicon carbon is represented as grayish-white, and graphite as grayish-black. The first silicon carbon content is statistically analyzed and calculated. The total cross-sectional area S1 of the first silicon carbide, the total cross-sectional area S2 of the second silicon carbide, the total cross-sectional area S3 of the third silicon carbide, and the total cross-sectional area S4 of graphite (where the first silicon carbide, the second silicon carbide, and the third silicon carbide are distinguished by sphericity) were collected. A total of 10 SEM images of the cross-section of the same negative electrode at different positions were collected. c1, c2, c3, and c4 were calculated and averaged respectively. c1=S1 / (S1+S2+S3+S4), c2=S2 / (S1+S2+S3+S4), c3=S3 / (S1+S2+S3+S4), c4=S4 / (S1+S2+S3+S4).

[0054] In this invention, the average particle size of the graphite can be obtained by conventional testing methods in the art, such as by SEM measurement, as follows: the battery is discharged to 0% SOC, the negative electrode is removed, and then soaked and cleaned with dimethyl carbonate (DMC) and dried. High-resolution images are obtained by SEM, and then the particle size and distribution statistics of the graphite particles are measured by electron microscopy image analysis software such as ImageJ to obtain the average particle size. The scanning electron microscope model is HITACHI SU5000 / SU8600.

[0055] In this invention, the average particle size of the silicon-carbon material is 5μm-16μm, for example, 5μm, 6μm, 7μm, 8μm, 10μm, 12μm, 14μm, 15μm or 16μm.

[0056] In one embodiment, the average particle size of the silicon-carbon material is 7 μm-11 μm.

[0057] In this invention, the average particle size of the first silicon carbide is 4μm-16μm, for example, 4μm, 5μm, 6μm, 7μm, 8μm, 10μm, 12μm, 14μm or 16μm.

[0058] In this invention, the average particle size of the second silicon carbide is 5μm-15μm, for example, 5μm, 6μm, 7μm, 8μm, 10μm, 12μm, 14μm or 15μm.

[0059] In this invention, the average particle size of the third silicon carbide is 5μm-14μm, for example, 5μm, 6μm, 7μm, 8μm, 10μm, 12μm or 14μm.

[0060] When the average particle size of silicon-carbon material is too small (e.g., <5μm), the surface area of ​​silicon-carbon material is large, the effective contact area with electrolyte is increased, the risk of electrolyte side reactions is increased, the thickness of SEI film formed at the negative electrode is increased, resulting in increased internal resistance of the negative electrode sheet, which is not conducive to improving battery dynamic performance and cycle performance. When the average particle size of silicon-carbon material is too large (e.g., >16μm), the overall compressive strength of silicon-carbon material is poor, the risk of silicon-carbon particles breaking under external pressure is increased, the SEI film repeatedly breaks and grows on the surface of silicon-carbon material, consuming electrolyte and active lithium, which is not conducive to improving the structural stability of the negative electrode sheet and the cycle performance of the battery.

[0061] In this invention, the average particle size of the first silicon-carbon, the second silicon-carbon, and the third silicon-carbon can be obtained by conventional testing methods in the art, such as the following method: discharging the battery to 0% SOC, disassembling and removing the negative electrode sheet, or directly removing the negative electrode sheet, polishing its cross-section with an argon ion milling machine, and then imaging the obtained cross-section using a scanning electron microscope (SEM) in backscatter imaging mode; the silicon-carbon particles in the image appear grayish-white, and then the particle size is measured and the distribution is statistically analyzed using electron microscope image analysis software such as ImageJ, and the first silicon-carbon, the second silicon-carbon, and the third silicon-carbon are distinguished by the size of the sphericity, and the average particle size of the first, second, and third silicon-carbon is statistically analyzed respectively. The average particle size of all silicon-carbon material particles is obtained by statistically analyzing the particle size and taking the average value.

[0062] In this invention, based on the total mass of the silicon-carbon material, the mass content of silicon element is 35%-65%, for example, 35%, 40%, 45%, 50%, 55%, 60% or 65%.

[0063] In one embodiment, the silicon content is 45%-55% by mass, based on the total mass of the silicon-carbon material.

[0064] In this invention, the mass content of silicon element in the first silicon carbon is 30%-70%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%.

[0065] In this invention, the mass content of silicon element in the second silicon carbon is 30%-70%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%.

[0066] In this invention, the mass content of silicon element in the third silicon carbon is 30%-70%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%.

[0067] When the mass content of silicon in silicon-carbon materials is too low (e.g., <35%), the specific capacity of the silicon-carbon materials decreases, the first charge-discharge efficiency decreases, which is not conducive to improving the energy density of the battery. When the mass content of silicon in silicon-carbon materials is too high (e.g., >65%), the excessive proportion of silicon in the materials generates excessive volume expansion stress. The porous carbon matrix is ​​not effective in buffering the expansion stress, and the structure of the silicon-carbon materials collapses, leading to failure, which is not conducive to improving the cycle performance of the battery.

[0068] In this invention, the mass content of silicon in the first, second, and third silicon carbon can be obtained by conventional testing methods in the art, such as the following methods: Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) are used for analysis; the battery is discharged to empty charge at a low rate, the battery is disassembled, the negative electrode is taken out, and after processing by argon ion polishing technology, a cross-sectional sample of the negative electrode can be obtained. The obtained cross-section is then tested by the backscatter mode of the scanning electron microscope at a magnification of 10K. The middle region of a single silicon carbon particle is selected for EDS analysis, and only the content of carbon and silicon is tested. The first, second, and third silicon carbons are distinguished by the size of the sphericity and the presence of a first interior angle and a second interior angle. The silicon content in each silicon carbon material is calculated separately. Ten first, second, and third silicon carbon particles are taken for calculation, and a weighted average is taken to obtain the mass content of silicon in the first, second, and third silicon carbons. The mass content of silicon in all silicon carbon material particles is counted and the average value is taken as the mass content of silicon in the silicon carbon material.

[0069] In this invention, the specific surface area of ​​the silicon-carbon material is 0.7 m². 2 / g-2m 2 / g, for example, 0.7m 2 / g, 0.8m 2 / g, 1m 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.6m 2 / g, 1.8m 2 / g or 2m 2 / g.

[0070] In one embodiment, the specific surface area of ​​the silicon-carbon material is 0.9 m². 2 / g-1.4m 2 / g.

[0071] In this invention, the specific surface area of ​​the first silicon-carbon is 0.7 m². 2 / g-2m 2 / g, for example, 0.7m 2 / g, 0.8m 2 / g、1m 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.6m 2 / g, 1.8m 2 / g or 2m 2 / g.

[0072] In this invention, the specific surface area of ​​the second silicon-carbon is 0.7 m². 2 / g-2m 2 / g, for example, 0.7m 2 / g, 0.8m 2 / g、1m 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.6m 2 / g, 1.8m 2 / g or 2m 2 / g.

[0073] In this invention, the specific surface area of ​​the third silicon-carbon is 0.7 m². 2 / g-2m 2 / g, for example, 0.7m 2 / g, 0.8m 2 / g, 1m 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.6m 2 / g, 1.8m 2 / g or 2m 2 / g.

[0074] When the specific surface area of ​​silicon-carbon materials is too large (e.g., greater than 2m²), 2 With an increased contact area between the silicon-carbon material and the electrolyte, the formation of the SEI film consumes more active lithium, leading to a decrease in the battery's initial coulombic efficiency and exacerbating side reactions with the electrolyte. Furthermore, when the specific surface area of ​​the silicon-carbon material is too small (e.g., less than 0.7 μm²), the overall contact area between the silicon-carbon material and the electrolyte increases. 2 / g), the wetting efficiency of silicon-carbon materials and electrolyte decreases, and the contact area between particles decreases, increasing the diffusion distance of lithium ions between negative electrode active materials, thus leading to the degradation of battery rate performance.

[0075] In this invention, the specific surface areas of the first silicon carbon, the second silicon carbon, and the third silicon carbon can be determined by conventional testing methods in the art, such as the Brunauer-Emmett-Teller (BET) test method, or by using a TriStar II specific surface area analyzer, with N2 being the adsorbed gas.

[0076] In this invention, the Raman spectrum of the silicon-carbon material shows a value at 470 cm⁻¹. -1 -480cm -1 It has the first characteristic peak at 507 cm⁻¹ -1 -517cm -1 It has a second characteristic peak at 1330 cm⁻¹ -1 -1350cm -1 It has a third characteristic peak at 1590 cm⁻¹ -1 -1610cm -1 It has a fourth characteristic peak; the intensity L1 of the first characteristic peak, the intensity L2 of the second characteristic peak, the intensity L3 of the third characteristic peak, and the intensity L4 of the fourth characteristic peak satisfy 0.5≤(L1+L3) / (L2+L4)≤3, for example, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.5, or 3.

[0077] When (L1+L3) / (L2+L4) is too low (e.g., less than 0.5), the silicon in the silicon-carbon material has high crystallinity, which will lead to large cycle expansion of the battery and poor cycle capacity retention. When (L1+L3) / (L2+L4) is too high (e.g., greater than 3), there are too many surface defects in the silicon-carbon material, resulting in low initial coulombic efficiency, which is not conducive to improving the energy density of the battery.

[0078] In this invention, the Raman spectrum of the silicon-carbon material can be obtained using conventional testing methods in the art, such as a Thermo Fisher Raman spectrometer with a wavenumber range of 400 cm⁻¹.-1 -4000cm -1 .

[0079] In this invention, the porosity of the negative electrode active layer is 20%-50%, for example, 20%, 22%, 24%, 26%, 28%, 30%, 35%, 40%, 45% or 50%.

[0080] In one embodiment, the porosity of the negative electrode active layer is 30%-40%.

[0081] When the porosity of the negative electrode active layer is too low (e.g., less than 20%), there is insufficient space inside the negative electrode active layer to accommodate the electrolyte, which is not conducive to ion transport between negative electrode active materials. It also increases the risk of overvoltage of the negative electrode sheet, leading to the breakage of silicon-carbon materials. When the porosity of the negative electrode active layer is too high (e.g., greater than 50%), the contact between silicon-carbon materials is not tight enough, which is not conducive to electron transport. At the same time, the amount of residual electrolyte inside the negative electrode active layer is too high, which aggravates the side reaction between silicon-carbon materials and electrolyte, resulting in a decrease in cycle performance and gas buildup.

[0082] In this invention, the porosity of the negative electrode active layer can be obtained by conventional testing methods in the art, such as by gas displacement testing. The specific method is as follows: After discharging the battery to 0% SOC, the negative electrode sheet is disassembled and removed. It is then soaked in dimethyl carbonate (DMC) solvent for 12 hours and rinsed with DMC to remove the lithium salt adhering to the electrode sheet. After drying, the negative electrode sheet is cut into 12mm diameter discs using a slicing machine. The thickness of 20 discs is measured with a micrometer, and the volume of each disc is calculated and summed to obtain the sum of the volumes of the 20 discs, V1. Subsequently, the true volume V2 of the 20 discs is tested using a true density meter (such as the Jingwei Gaobo JW-M100A fully automatic true density meter). The test gas is helium, and the test environment temperature is 25±2℃. Then, the porosity of the negative electrode active layer = (V1-V2) / V1×100%.

[0083] In this invention, the OI value of the negative electrode active layer is 5-30, for example, 5, 6, 8, 10, 12, 14, 16, 20, 25 or 30.

[0084] In one embodiment, the OI value of the negative electrode active layer is 15-20.

[0085] When the OI value of the negative electrode active layer is too low (e.g., less than 5), it indicates that the graphite layer structure is dominated by the direction perpendicular to the current collector, which increases the chance of side reactions occurring on the graphite end face and deteriorates the cycle performance. When the OI value of the negative electrode active layer is too high (e.g., greater than 30), it indicates that the graphite layer structure is dominated by the direction parallel to the current collector, which is not conducive to the migration of lithium ions in the active layer and deteriorates the rate performance of the battery.

[0086] In this invention, the OI value of the negative electrode active layer can be obtained by conventional testing methods in the art, such as by X-ray powder diffraction. The specific method is as follows: After discharging the battery to 0% SOC, the negative electrode sheet is disassembled and taken out. After soaking in dimethyl carbonate (DMC) solvent for 12 hours, it is rinsed with DMC to remove the lithium salt attached to the negative electrode sheet. After drying, it is tested with an X-ray powder diffraction instrument (such as Shimadzu XRD-6100 X-ray diffractometer). The diffraction peak appearing at 2θ=54-55° in the obtained diffraction pattern is the (004) peak of the carbon-based material, and the intensity is recorded as I004. The diffraction peak appearing at 2θ=77-78° is the (110) peak of the carbon-based material, and the intensity is recorded as I110. The OI value of the negative electrode coating is I004 / I110.

[0087] In this invention, the compaction density of the negative electrode sheet is 0.8 g / cm³. 3 -1.8g / cm 3 For example, 0.8 g / cm³ 3 0.9g / cm 3 1g / cm 3 1.2g / cm 3 1.4g / cm 3 1.6g / cm 3 Or 1.8g / cm 3 .

[0088] In one embodiment, the compaction density of the negative electrode sheet is 1.2 g / cm³. 3 -1.6g / cm 3 .

[0089] When the compaction density of the negative electrode is too low (e.g., <0.8 g / cm³), 3 Poor adhesion between particles in the negative electrode active layer can cause the conductive network in the negative electrode sheet to fail during battery cycling, resulting in a sharp drop in battery cycle capacity. Furthermore, excessively high compaction density of the negative electrode sheet (e.g., >1.8 g / cm³) can also lead to this problem. 3 At this point, if the compaction density of the negative electrode is too high, the probability of silicon-carbon particles breaking increases, which prevents the electrolyte from fully wetting the inside of the negative electrode, thus increasing the risk of lithium plating in the battery.

[0090] The compaction density here refers to the actual compaction density measured after the battery is disassembled and the negative electrode sheet is removed, which differs from the compaction density obtained by rolling the negative electrode sheet during battery manufacturing. This is because after the negative electrode sheet is assembled into a battery, there will be physical and chemical rebound, resulting in compaction rebound. Consequently, the actual compaction density of the negative electrode sheet measured after battery manufacturing is lower than the compaction density obtained after rolling.

[0091] In this invention, the compaction density of the negative electrode sheet can be obtained by conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled and removed. After soaking in DMC solvent for 12 hours, it is rinsed with DMC solvent to remove the lithium salt adhering to the negative electrode sheet. Then, the surface residue of the negative electrode sheet is washed off with deionized water and dried. At least 20 sites are selected on the negative electrode sheet, and the thickness of the negative electrode sheet at each site is measured using a micrometer. The average value h (in μm) is taken. The negative electrode sheet is punched into a disc with a diameter of 44.3 mm using a punching die. Ten discs are taken, and the mass of each disc is weighed. The average value m (in mg) is taken. The areal density M1 is calculated as M1 = (m - m1) × 100 / 1540.25, where m1 is the mass of the negative electrode current collector in the disc (in mg), and the areal density is in mg / cm³. 2 The compaction density is calculated using the areal density M1 and the average thickness h, as follows: Compaction density = M1 × 20 / (h - thickness of the negative electrode current collector), where the unit of the thickness of the negative electrode current collector is μm.

[0092] In this invention, the battery further includes an electrolyte comprising ethyl propionate, wherein the mass content of ethyl propionate is 1%-30% based on the total mass of the electrolyte, for example, 1%, 2%, 4%, 6%, 8%, 10%, 15%, 20%, 25% or 30%.

[0093] In one embodiment, the ethyl propionate content is 5%-20% based on the total mass of the electrolyte.

[0094] The second silicon-carbon surface has a trench structure. Compared to the SEI film on a smooth surface, the SEI film on the trench structure has more concentrated stress points. During cycling, the second silicon-carbon particles continuously expand and contract, making them prone to repeated breakage. This leads to abnormal thickening of the SEI film, accelerating electrolyte consumption and active lithium loss, ultimately causing battery failure. An appropriate amount of ethyl propionate can alter the solvation structure of lithium ions, helping to form a more stable and flexible SEI film on the silicon-carbon material surface. This not only suppresses the continuous occurrence of side reactions and reduces the volume expansion of the negative electrode during charge and discharge, but also improves battery cycle stability. When the ethyl propionate content in the electrolyte is too low (e.g., <1%), the interface film formed on the silicon-carbon material surface has low density and poor stability, making the negative electrode prone to lithium plating during cycle testing, which is detrimental to further improving battery cycle performance. When the ethyl propionate content in the electrolyte is too high (e.g., >30%), the battery is prone to bulging at high temperatures, which is detrimental to improving battery cycle stability and high-temperature safety.

[0095] In this invention, the electrolyte further includes a first compound, which comprises at least one of the following structural formulas: (Equation 1-1) (Equation 1-2) (Equation 1-3) (Equation 1-4) (Equation 1-5) (Equation 1-6) (Equation 1-7) (Equation 1-8) (Equation 1-9) (Equation 1-10) (Equation 1-11) (Equation 1-12) (Equation 1-13) (Equation 1-14) (Equation 1-15) (Equation 1-16) (Equation 1-17) (Equation 1-18) (Equation 1-19) (Equation 1-20) and (Equation 1-21).

[0096] In one embodiment, the first compound includes (Equation 1-1).

[0097] In one embodiment, the mass content of the first compound is 0.1%-15% based on the total mass of the electrolyte, for example, 0.1%, 0.2%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14% or 15%.

[0098] The aforementioned substances contain sulfonyl fluoride groups or fluoroalkyl sulfonyl groups. During the battery formation process, they can decompose at the trenches of the second silicon carbon to form a hybrid SEI layer rich in LiF and organic polymer networks. This layer can adapt to the frequently changing stress conditions at the trenches of the second silicon carbon during battery charging and discharging (the second silicon carbon is subjected to compressive stress when it expands during charging, and the compressive stress is reduced during discharging). This prevents the SEI film from repeatedly rupturing and regenerating, thus comprehensively improving the battery's rate and cycle performance.

[0099] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0100] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0101] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0102] The following examples illustrate the battery of the present invention.

[0103] The battery is prepared according to the following method: Example 1: (1) Preparation of negative electrode: First silicon carbon, second silicon carbon, third silicon carbon, and graphite were mechanically mixed at a certain mass ratio for 5 minutes. After uniform mixing, they were used as negative electrode active materials. The above negative electrode active materials, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), SuperP, and single-walled carbon nanotubes were mixed at a mass ratio of 95:2:2:0.75:0.25. An appropriate amount of water was added as a solvent, and the mixture was stirred evenly by a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on both sides of a 6μm thick high-strength carbon-coated copper foil and transferred to a vacuum drying oven at 85℃ for 12 hours. After the electrode sheet was rolled by a double roller press, it was die-cut to obtain the negative electrode sheet.

[0104] Among them, c1 is 7%, c2 is 9%, c3 is 7%, c4 is 77%, (c1+c3) / c2 is 1.556, and c1 / c3 is 1; the sphericity of the first silicon-carbon is 0.662, the sphericity of the second silicon-carbon is 0.896, and the sphericity of the third silicon-carbon is 0.987; the first interior angle is 85°, the second interior angle is 264°, and the third silicon-carbon has no interior angle; the average particle size of the first silicon-carbon is 9.43 μm, the average particle size of the second silicon-carbon is 8.84 μm, the average particle size of the third silicon-carbon is 8.95 μm, and the average particle size of the silicon-carbon material is 9.05 μm; the mass content of silicon element in the first silicon-carbon, the second silicon-carbon, and the third silicon-carbon is 47.56%, 52.42%, and 52.32%, respectively, and the mass content of silicon element in the silicon-carbon material is 50.9%; the average particle size of graphite is 10.4 μm.

[0105] (2) Preparation of the positive electrode: Lithium nickel cobalt manganese oxide (NCM955), polyvinylidene fluoride (PVDF), acetylene black, and single-walled carbon nanotubes were mixed in a mass ratio of 97:1.5:1.25:0.25. N-methylpyrrolidone (NMP) solvent was added, and a positive electrode slurry was obtained by vacuum stirring. The positive electrode slurry was uniformly coated on both sides of a 10 μm thick high-strength aluminum foil and dried in a vacuum drying oven at 95 °C for 12 h. The positive electrode sheet was then rolled by a single-roll press and die-cut to obtain the positive electrode sheet.

[0106] (3) Preparation of electrolyte: A base solvent was prepared by mixing propylene carbonate (PC), ethylene carbonate (EC), propyl propionate (PP), and diethyl carbonate (DEC) in a weight ratio of 2:1:3:3. Then, ethyl propionate (EP), fluoroethylene carbonate (FEC), the first compound shown in Formula 1-1, and LiPF6 were added to the base solvent to obtain the electrolyte. Based on the total weight of the electrolyte, the content of LiPF6 was 12%, the content of FEC was 10%, the content of EP was 15%, and the content of the first compound was 8%.

[0107] (4) Battery fabrication: Die-cut positive and negative electrode sheets are baked in a vacuum drying oven at 90°C for 12 hours. An 8μm thick polyethylene film is used as the separator. The positive electrode sheets, separator, and negative electrode sheets are stacked sequentially using a stacking machine, ensuring the separator separates the positive and negative electrode sheets, resulting in a stacked core. The stacked core is then fixed in a welding mold, and the tabs of the positive and negative electrodes are welded together. It is then secured with high-temperature tape and finally encapsulated in an aluminum-plastic film. The encapsulated dry cell is baked in an oven at 90°C for 48 hours. After passing a moisture test, electrolyte is injected, and the battery undergoes aging, formation, secondary sealing, and sorting processes to obtain its final product.

[0108] Example 2: (1) Preparation of negative electrode: First silicon carbon, second silicon carbon, third silicon carbon, and graphite were mechanically mixed at a certain mass ratio for 5 minutes. After uniform mixing, they were used as negative electrode active materials. The above negative electrode active materials, CMC-Na, styrene-butadiene rubber (SBR), SuperP, and single-walled carbon nanotubes were mixed at a mass ratio of 95:2:2:0.75:0.25. An appropriate amount of water was added as a solvent, and the mixture was stirred evenly by a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on both sides of a 6μm thick high-strength carbon-coated copper foil and transferred to a vacuum drying oven at 85℃ for 12 hours. After the electrode sheet was rolled by a double-roll press, it was die-cut to obtain the negative electrode sheet.

[0109] Among them, c1 is 22%, c2 is 17%, c3 is 12%, c4 is 49%, (c1+c3) / c2 is 2, and c1 / c3 is 1.833; the sphericity of the first silicon-carbon is 0.613, the sphericity of the second silicon-carbon is 0.851, and the sphericity of the third silicon-carbon is 0.983; the first interior angle is 62°, the second interior angle is 297°, and the third silicon-carbon has no interior angle; the average particle size of the first silicon-carbon is 7.1μm, the average particle size of the second silicon-carbon is 7.5μm, the average particle size of the third silicon-carbon is 7.2μm, and the average particle size of the silicon-carbon material is 7.26μm; the mass content of silicon element in the first silicon-carbon, the second silicon-carbon, and the third silicon-carbon is 43.12%, 48.53%, and 47.29% respectively, and the mass content of silicon element in the silicon-carbon material is 45.9%; the average particle size of graphite is 8.2μm.

[0110] (2) Preparation of the positive electrode: NCM955, PVDF, acetylene black, and single-walled carbon nanotubes were mixed in a mass ratio of 97:1.5:1.25:0.25. NMP solvent was added, and a positive electrode slurry was obtained by vacuum stirring. The positive electrode slurry was uniformly coated on both sides of a 10 μm thick high-strength aluminum foil and dried in a vacuum drying oven at 95 °C for 12 h. The positive electrode sheet was then rolled by a single-roll press and die-cut to obtain the positive electrode sheet.

[0111] (3) Preparation of electrolyte: PC, EC, PP, and DEC were mixed in a weight ratio of 2:1:3:3 to obtain a base solvent; then EP, FEC, the first compound shown in Formula 1-2, and LiPF6 were added to the base solvent to obtain the electrolyte. Based on the total weight of the electrolyte, the content of LiPF6 was 12%, the content of FEC was 10%, the content of EP was 5%, and the content of the first compound was 8%.

[0112] (4) Battery fabrication: Die-cut positive and negative electrode sheets are baked in a vacuum drying oven at 90°C for 12 hours. An 8μm thick polyethylene film is used as the separator. The positive electrode sheets, separator, and negative electrode sheets are stacked sequentially using a stacking machine, ensuring the separator separates the positive and negative electrode sheets, resulting in a stacked core. The stacked core is then fixed in a welding mold, and the tabs of the positive and negative electrodes are welded together. It is then secured with high-temperature tape and finally encapsulated in an aluminum-plastic film. The encapsulated dry cell is baked in an oven at 90°C for 48 hours. After passing a moisture test, electrolyte is injected, and the battery undergoes aging, formation, secondary sealing, and sorting processes to obtain its final product.

[0113] Example 3: (1) Preparation of negative electrode: First silicon carbon, second silicon carbon, third silicon carbon, and graphite were mechanically mixed at a certain mass ratio for 5 minutes. After uniform mixing, they were used as negative electrode active materials. The above negative electrode active materials, CMC-Na, styrene-butadiene rubber (SBR), SuperP, and single-walled carbon nanotubes were mixed at a mass ratio of 95:2:2:0.75:0.25. An appropriate amount of water was added as a solvent, and the mixture was stirred evenly by a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on both sides of a 6μm thick high-strength carbon-coated copper foil and transferred to a vacuum drying oven at 85℃ for 12 hours. After the electrode sheet was rolled by a double-roll press, it was die-cut to obtain the negative electrode sheet.

[0114] Among them, c1 is 1%, c2 is 5%, c3 is 2%, c4 is 49%, (c1+c3) / c2 is 0.6, and c1 / c3 is 0.5; the sphericity of the first silicon-carbon is 0.697, the sphericity of the second silicon-carbon is 0.917, and the sphericity of the third silicon-carbon is 0.992; the first interior angle is 117°, the second interior angle is 201°, and the third silicon-carbon has no interior angle; the average particle size of the first silicon-carbon is 10.23 μm, the average particle size of the second silicon-carbon is 10.65 μm, the average particle size of the third silicon-carbon is 10.72 μm, and the average particle size of the silicon-carbon material is 10.62 μm; the mass content of silicon element in the first silicon-carbon, the second silicon-carbon, and the third silicon-carbon is 52.27%, 58.9%, and 60.44%, respectively, and the mass content of silicon element in the silicon-carbon material is 58.5%; the average particle size of graphite is 11.9 μm.

[0115] (2) Preparation of the positive electrode: NCM955, PVDF, acetylene black, and single-walled carbon nanotubes were mixed in a mass ratio of 97:1.5:1.25:0.25. NMP solvent was added, and a positive electrode slurry was obtained by vacuum stirring. The positive electrode slurry was uniformly coated on both sides of a 10 μm thick high-strength aluminum foil and dried in a vacuum drying oven at 95 °C for 12 h. The positive electrode sheet was then rolled by a single-roll press and die-cut to obtain the positive electrode sheet.

[0116] (3) Preparation of electrolyte: PC, EC, PP, and DEC were mixed in a weight ratio of 2:1:3:3 to obtain a base solvent; then EP, FEC, the first compound shown in Formula 1-3, and LiPF6 were added to the base solvent to obtain the electrolyte. Based on the total weight of the electrolyte, the content of LiPF6 was 12%, the content of FEC was 10%, the content of EP was 20%, and the content of the first compound was 8%.

[0117] (4) Battery fabrication: Die-cut positive and negative electrode sheets are baked in a vacuum drying oven at 90°C for 12 hours. An 8μm thick polyethylene film is used as the separator. The positive electrode sheets, separator, and negative electrode sheets are stacked sequentially using a stacking machine, ensuring the separator separates the positive and negative electrode sheets, resulting in a stacked core. The stacked core is then fixed in a welding mold, and the tabs of the positive and negative electrodes are welded together. It is then secured with high-temperature tape and finally encapsulated in an aluminum-plastic film. The encapsulated dry cell is baked in an oven at 90°C for 48 hours. After passing a moisture test, electrolyte is injected, and the battery undergoes aging, formation, secondary sealing, and sorting processes to obtain its final product.

[0118] Example 4 group: This set of examples is used to verify the impact of changes in the sphericity of the first silicon-carbon alloy, as detailed below: Example 4a is based on Example 1, except that the sphericity of the first silicon carbon is 0.514, the first interior angle is 48°, the average particle size of the first silicon carbon is 9.64 μm, the average particle size of the silicon carbon material is 9.12 μm, the mass content of silicon in the first silicon carbon is 47.82%, and the mass content of silicon in the silicon carbon material is 51%. Example 4b is based on Example 1, except that the sphericity of the first silicon carbon is 0.776, the first interior angle is 168°, the average particle size of the first silicon carbon is 9.7 μm, the average particle size of the silicon carbon material is 9.14 μm, the mass content of silicon element in the first silicon carbon is 47.44%, and the mass content of silicon element in the silicon carbon material is 50.9%.

[0119] Example 5 group: This set of examples is used to verify the impact of changes in the sphericity of the second silicon-carbon alloy, as detailed below: Example 5a is based on Example 1, except that the sphericity of the second silicon carbide is 0.814, the second interior angle is 338°, the average particle size of the second silicon carbide is 8.46 μm, the average particle size of the silicon carbide material is 8.9 μm, the mass content of silicon in the second silicon carbide is 51.96%, and the mass content of silicon in the silicon carbide material is 50.7%. Example 5b is based on Example 1, except that the sphericity of the second silicon carbide is 0.945, the second interior angle is 196°, the average particle size of the second silicon carbide is 8.29 μm, the average particle size of the silicon carbide material is 8.84 μm, the mass content of silicon in the second silicon carbide is 52.11%, and the mass content of silicon in the silicon carbide material is 50.8%.

[0120] Example 6 group: This set of examples is used to verify the impact of changes in the sphericity of the third silicon-carbon alloy, as detailed below: Example 6a, based on Example 1, except that the sphericity of the third silicon carbon is 0.952, the average particle size of the third silicon carbon is 9.27 μm, the average particle size of the silicon carbon material is 9.15 μm, the mass content of silicon element in the third silicon carbon is 52.96%, and the mass content of silicon element in the silicon carbon material is 51%. Example 6b is based on Example 1, except that the sphericity of the third silicon carbon is 0.998, the average particle size of the third silicon carbon is 8.71 μm, the average particle size of the silicon carbon material is 8.98 μm, the mass content of silicon element in the third silicon carbon is 51.87%, and the mass content of silicon element in the silicon carbon material is 50.8%.

[0121] Example 7 group: This set of examples is used to verify the impact of changes in the "first interior angle", as detailed below: Example 7a is based on Example 1, except that the first interior angle is 34°. In this case, the sphericity of the first silicon carbon is 0.459, the average particle size of the first silicon carbon is 9.2 μm, the average particle size of the silicon carbon material is 8.98 μm, the mass content of silicon in the first silicon carbon is 47.28%, and the mass content of silicon in the silicon carbon material is 50.8%. Example 7b is based on Example 1, except that the first interior angle is 175°. In this case, the sphericity of the first silicon carbon is 0.785, the average particle size of the first silicon carbon is 9.58 μm, the average particle size of the silicon carbon material is 9.1 μm, the mass content of silicon element in the first silicon carbon is 48.12%, and the mass content of silicon element in the silicon carbon material is 51.1%.

[0122] Example 8 group: This set of examples is used to verify the impact of changes in the "second interior angle", as detailed below: Example 8a, based on Example 1, except that the second interior angle is 188°. In this case, the sphericity of the second silicon carbide is 0.937, the average particle size of the second silicon carbide is 9.05 μm, the average particle size of the silicon carbide material is 9.14 μm, the mass content of silicon in the second silicon carbide is 52.11%, and the mass content of silicon in the silicon carbide material is 50.8%. Example 8b is based on Example 1, except that the second interior angle is 325°. In this case, the sphericity of the second silicon carbide is 0.802, the average particle size of the second silicon carbide is 8.62 μm, the average particle size of the silicon carbide material is 8.97 μm, the mass content of silicon in the second silicon carbide is 52.69%, and the mass content of silicon in the silicon carbide material is 51%.

[0123] Example 9 group: This set of examples is used to verify the impact of changes in "(c1+c3) / c2" and "c1 / c3", as follows: Example 9a is based on Example 1, except that c1 is 0.5%, c2 is 20%, c3 is 2.5%, (c1+c3) / c2 is 0.15, c1 / c3 is 0.2, and the mass content of silicon in the silicon-carbon material is 52.3%. Example 9b is based on Example 1, except that c1 is 15%, c2 is 4%, c3 is 4%, (c1+c3) / c2 is 4.75, c1 / c3 is 3.75, and the mass content of silicon in the silicon-carbon material is 49.2%. Example 9c is based on Example 1, except that c1 is 0.2%, c2 is 21%, c3 is 1.8%, (c1+c3) / c2 is 0.095, c1 / c3 is 0.11, and the mass content of silicon in the silicon-carbon material is 52.4%. Example 9d is based on Example 1, except that c1 is 17%, c2 is 3%, c3 is 3%, (c1+c3) / c2 is 6.667, c1 / c3 is 5.67, and the mass content of silicon in the silicon-carbon material is 48.8%.

[0124] Example 10 group: This set of examples is used to verify the impact of changes in the average particle size of silicon carbide materials and graphite: Example 10a is based on Example 1, except that the average particle size of the first silicon carbon is 4.3 μm, the average particle size of the second silicon carbon is 5.3 μm, the average particle size of the third silicon carbon is 5.5 μm, the average particle size of the silicon carbon material is 5.06 μm, and the average particle size of the graphite is 5.3 μm. Example 10b is based on Example 1, except that the average particle size of the first silicon carbon is 15.8 μm, the average particle size of the second silicon carbon is 15.6 μm, the average particle size of the third silicon carbon is 15.5 μm, the average particle size of the silicon carbon material is 15.63 μm, and the average particle size of the graphite is 17.8 μm.

[0125] Example 11 group: This set of examples is used to verify the impact of changes in the "mass content of silicon in silicon-carbon materials", as detailed below: Example 11a, based on Example 1, except that the mass content of silicon in the first silicon-carbon, second silicon-carbon, and third silicon-carbon is 34.7%, 38.5%, and 37.6%, respectively, and the mass content of silicon in the silicon-carbon material is 37.1%. In this case, the sphericity of the first silicon-carbon is 0.625, the sphericity of the second silicon-carbon is 0.916, and the sphericity of the third silicon-carbon is 0.958; the first interior angle is 83°, the second interior angle is 251°, the average particle size of the first silicon-carbon is 9.7 μm, the average particle size of the second silicon-carbon is 8.47 μm, the average particle size of the third silicon-carbon is 8.39 μm, and the average particle size of the silicon-carbon material is 8.82 μm. Example 11b is based on Example 1, except that the mass content of silicon in the first silicon-carbon, the second silicon-carbon, and the third silicon-carbon is 60.7%, 63.8%, and 64.4%, respectively, and the mass content of silicon in the silicon-carbon material is 63%; the sphericity of the first silicon-carbon is 0.671, the sphericity of the second silicon-carbon is 0.882, and the sphericity of the third silicon-carbon is 0.963; the first interior angle is 81°, the second interior angle is 269°, the average particle size of the first silicon-carbon is 10.19 μm, the average particle size of the second silicon-carbon is 8.73 μm, the average particle size of the third silicon-carbon is 8.24 μm, and the average particle size of the silicon-carbon material is 9.03 μm.

[0126] Example 12 group: This set of examples is used to verify the impact of changes in the "ethyl propionate content in the electrolyte", as detailed below: Example 12a is based on Example 1, except that the mass content of ethyl propionate is 1.3% based on the total mass of the electrolyte; Example 12b is based on Example 1, except that the mass content of ethyl propionate is 28% based on the total mass of the electrolyte.

[0127] Example 13 group: This set of examples is used to verify the impact of changes in the "content of the first compound in the electrolyte", as detailed below: Example 13a is based on Example 1, except that the mass content of the first compound is 0.2% based on the total mass of the electrolyte; Example 13b is based on Example 1, except that the mass content of the first compound is 14.7% based on the total mass of the electrolyte; Example 13c is based on Example 1, except that the mass content of the first compound is 0% based on the total mass of the electrolyte.

[0128] In Examples 1-13, the following conditions are met: The specific surface area of ​​silicon-carbon materials is all around 0.7 m². 2 / g-2m 2 Within the range of / g, the specific surface area of ​​the first silicon-carbon is consistently around 0.7m². 2 / g-2m 2 Within the range of / g, the specific surface area of ​​the second silicon-carbon is consistently around 0.7m². 2 / g-2m 2 Within the range of / g, the specific surface area of ​​the third silicon-carbon is consistently around 0.7m². 2 / g-2m 2 Within the range of / g; it has the first characteristic peak (470cm) in the Raman spectrum of silicon-carbon materials. -1 -480cm -1 ), second characteristic peak (507cm) -1 -517cm -1 The third characteristic peak (1330cm) -1 -1350cm -1 ) and the fourth characteristic peak (1590cm) -1 -1610cm -1 The strengths are L1, L2, L3, and L4, respectively, satisfying 0.5 ≤ (L1 + L3) / (L2 + L4) ≤ 3; the porosity of the negative electrode active layer is in the range of 20%-50%; the OI value of the negative electrode active layer is in the range of 5-30; and the compaction density of the negative electrode sheet is in the range of 0.8 g / cm³. 3 -1.8g / cm 3 Within the range.

[0129] Comparative Example 1: This set of comparative examples is used to verify the impact of changes in the sphericity of the first silicon-carbon alloy, as detailed below: Comparative Example 1a, based on Example 1, differs in that the sphericity of the first silicon carbon is 0.423, the first interior angle is 31°, the average particle size of the first silicon carbon is 8.59 μm, the average particle size of the silicon carbon material is 8.8 μm, the mass content of silicon in the first silicon carbon is 47.71%, and the mass content of silicon in the silicon carbon material is 51%. Comparative Example 1b is based on Example 1, except that the sphericity of the first silicon carbon is 0.837, the first interior angle is 174°, the average particle size of the first silicon carbon is 8.9 μm, the average particle size of the silicon carbon material is 8.89 μm, the mass content of silicon in the first silicon carbon is 47.18%, and the mass content of silicon in the silicon carbon material is 50.8%.

[0130] Comparative Example 2: This set of comparative examples is used to verify the impact of changes in the sphericity of the second silicon-carbon alloy, as detailed below: Comparative Example 2a, based on Example 1, differs in that the sphericity of the second silicon carbon is 0.753, the second interior angle is 352°, the average particle size of the second silicon carbon is 8.27 μm, the average particle size of the silicon carbon material is 8.83 μm, the mass content of silicon in the second silicon carbon is 51.75%, and the mass content of silicon in the silicon carbon material is 50.6%. Comparative Example 2b is based on Example 1, except that the sphericity of the second silicon carbide is 0.964, the second interior angle is 188°, the average particle size of the second silicon carbide is 9.36 μm, the average particle size of the silicon carbide material is 9.26 μm, the mass content of silicon in the second silicon carbide is 52.05%, and the mass content of silicon in the silicon carbide material is 50.8%.

[0131] Comparative Example 3: Based on Example 1, the difference is that the sphericity of the third silicon carbon is 0.926, the average particle size of the third silicon carbon is 8.35 μm, the average particle size of the silicon carbon material is 8.87 μm, the mass content of silicon element in the third silicon carbon is 52.75%, and the mass content of silicon element in the silicon carbon material is 51%.

[0132] Comparative Example 4: This set of comparative examples is used to verify the impact of the "composition of silicon-carbon materials", as detailed below: Comparative Example 4a, based on Example 1, except that the silicon-carbon material is composed of first silicon-carbon and third silicon-carbon, with c1 being 11.5%, c3 being 11.5%, c1 / c3 being 1, the average particle size of the silicon-carbon material being 9.19 μm, and the mass content of silicon in the silicon-carbon material being 49.9%; Comparative Example 4b is based on Example 1, except that the silicon-carbon material is a first silicon-carbon material, c1 is 23.5%, the average particle size of the silicon-carbon material is 9.43 μm, and the mass content of silicon element in the silicon-carbon material is 47.6%. Comparative Example 4c is based on Example 1, except that the silicon-carbon material is a second silicon-carbon material, c2 is 23%, the average particle size of the silicon-carbon material is 8.84 μm, and the mass content of silicon element in the silicon-carbon material is 52.4%. Comparative Example 4d is based on Example 1, except that the silicon-carbon material is third silicon-carbon, the c3 content is 23%, the average particle size of the silicon-carbon material is 8.95 μm, and the mass content of silicon element in the silicon-carbon material is 52.3%.

[0133] Test example: (1) Cyclic capacity retention: The batteries prepared in the embodiments and comparative examples of this invention were placed in a constant temperature chamber at 25±1℃ and left to stand for 30 minutes. They were then charged at a constant rate of 1.8C (5760mA) to 4.3V, and then charged at a constant voltage of 4.3V until the charging current was less than 0.05C (160mA). After standing for 10 minutes, the thickness of the battery was measured using a thickness gauge and recorded as Qx (X = number of cycles). The batteries were then discharged at a constant current of 4C (12800mA) to 2.5V and left to stand for 10 minutes. This test constitutes one complete cycle, and the discharge capacity (mAh) is recorded as Rx (X = number of cycles). The capacity retention rate Ux = Rx / R1 × 100%. When the capacity retention rate was less than 80%, the test was stopped, and the number of cycles was recorded. The test results are recorded in Table 1.

[0134] (2) Expansion rate test: The batteries prepared in the embodiments and comparative examples of this invention were charged at a constant rate of 1.8C (5760mA) to 4.3V, and then charged at a constant voltage of 4.3V until the charging current was less than 0.05C (160mA). After standing for 10 minutes, the batteries were at 50% SOC. The thickness of the batteries was measured using a thickness gauge and was Q0mm. When the capacity retention rate was less than 80%, the test was stopped, and the battery thickness measured at this time was Qx. The cycle expansion rate of the batteries was Lx = Qx / Q0 × 100%. The test results are recorded in Table 1.

[0135] (3) K-value yield: The batteries prepared in the embodiments and comparative examples of this invention were charged to 4.3V at a constant current and constant voltage of 1C at 25℃±2℃, cut off at 0.02C, and left to stand for 5 minutes. The open-circuit voltage OCV1 (unit: volts V) of the batteries was then tested. The batteries were then left to stand open-circuit for 24 hours at (25±2)℃, and the voltage OCV2 after the standby was tested. The self-discharge coefficient K value of the batteries was calculated as: K = (OCV1 - OCV2) / 24. The normal range for the self-discharge coefficient K value is -0.02 to 0.08 (mV / h). Batteries exceeding this range are considered to have a poor K value. The total number of battery samples tested was 200. The test results are recorded in Table 1.

[0136] (4) Lithium plating test: The batteries obtained in the examples and comparative examples were charged in an environment of 25°C with the charging time controlled as follows: 11 min for 10%-80% SOC (SOC is the state of charge of the battery, 100% SOC for a fully charged state and 0% SOC for an empty state), 5 min for 0-10% SOC, 20 min for 80-100% SOC, and 60 min for discharge. The batteries were then subjected to charge-discharge cycle tests using this charge-discharge regime. One charge and one discharge were defined as one cycle. After being fully charged, the batteries were allowed to stand for 30 min before being discharged. This fast-charging regime was used to perform charge-discharge cycle tests until 50 charge-discharge cycles were completed. On the 51st cycle, the batteries were fully charged using the fast-charging regime (100% SOC). The batteries were then removed and disassembled to observe the lithium plating state on the surface of the negative electrode. The criteria for judging lithium plating on the negative electrode are as follows: 1) No lithium plating; 2) When the area of ​​lithium plating accounts for 3%-5% of the total area of ​​the negative electrode, it is recorded as "slight lithium plating"; 3) When the area of ​​lithium plating accounts for more than 5% but less than or equal to 10% of the total area of ​​the negative electrode, it is recorded as "moderate lithium plating"; 4) When the area of ​​lithium plating accounts for more than 15% of the total area of ​​the negative electrode, it is recorded as "severe lithium plating". The test results are recorded in Table 1.

[0137] Table 1: As can be seen from Table 1, the battery prepared by the present invention has better cycle performance and rate performance compared with the comparative example, effectively improving the battery K-value problem and reducing the risk of lithium plating.

[0138] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A battery, characterized in that, The battery includes a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector, the negative electrode active layer includes a negative electrode active material, the negative electrode active material includes a silicon-carbon material, the silicon-carbon material includes a first silicon-carbon, a second silicon-carbon and a third silicon-carbon, the sphericity of the first silicon-carbon is α1, 0.45≤α1<0.8, the sphericity of the second silicon-carbon is α2, 0.8≤α2≤0.95, and the sphericity of the third silicon-carbon is α3, α3>0.95; The cross-section of the first silicon-carbon material has a first interior angle, which is less than 180°. The cross-section of the second silicon-carbon material has a second interior angle, which is greater than 180°.

2. The battery according to claim 1, wherein, The first interior angle is 60°-120°; And / or, the second interior angle is 200°-300°; And / or, 0.6≤α1≤0.7; And / or, 0.85≤α2≤0.92; And / or, 0.98 ≤ α3 < 1; Preferably, the cross-section of the third silicon-carbon material has no interior angles.

3. The battery according to claim 1 or 2, wherein, Based on the total mass of the negative electrode active material, the mass content of the first silicon carbon is c1, the mass content of the second silicon carbon is c2, and the mass content of the third silicon carbon is c3, where 0% < c1 ≤ 60%; And / or, 0% < c2 ≤ 60%; And / or, 0% < c3 ≤ 60%.

4. The battery according to claim 3, wherein, c1, c2, and c3 satisfy: 0.1 ≤ (c1 + c3) / c2 ≤ 5; And / or, 0.2≤c1 / c3≤4; Preferably, 0.5 ≤ (c1 + c3) / c2 ≤ 2; Preferably, 0.5 ≤ c1 / c3 ≤ 2.

5. The battery according to claim 1, wherein, The negative electrode active material also includes graphite, and based on the total mass of the negative electrode active material, the mass content of the graphite is c4, where 40% ≤ c4 < 100%. And / or, the average particle size of the graphite is 5μm-18μm; preferably 8μm-12μm.

6. The battery according to claim 1, wherein, The average particle size of the silicon-carbon material is 5μm-16μm; preferably 7μm-11μm. And / or, the average particle size of the first silicon carbide is 4 μm-16 μm; And / or, the average particle size of the second silicon carbide is 5 μm-15 μm; And / or, the average particle size of the third silicon carbide is 5 μm-14 μm.

7. The battery according to claim 1, wherein, Based on the total mass of the silicon-carbon material, the mass content of silicon element is 35%-65%; preferably 45%-55%. And / or, the mass content of silicon in the first silicon-carbon is 30%-70%; And / or, the silicon content in the second silicon-carbon is 30%-70% by mass; And / or, the silicon content in the third silicon-carbon is 30%-70% by mass.

8. The battery according to claim 1, wherein, In the Raman spectrum of the silicon-carbon material, at 470 cm⁻¹ -1 -480cm -1 It has the first characteristic peak at 507 cm⁻¹ -1 -517cm -1 It has a second characteristic peak at 1330 cm⁻¹ -1 -1350cm -1 It has a third characteristic peak at 1590 cm⁻¹ -1 -1610cm -1 It has a fourth characteristic peak; the intensity L1 of the first characteristic peak, the intensity L2 of the second characteristic peak, the intensity L3 of the third characteristic peak, and the intensity L4 of the fourth characteristic peak satisfy 0.5≤(L1+L3) / (L2+L4)≤3; Preferably, the porosity of the negative electrode active layer is 20%-50%; more preferably, it is 30%-40%. Preferably, the OI value of the negative electrode active layer is 5-30; more preferably, it is 15-20. Preferably, the compaction density of the negative electrode sheet is 0.8 g / cm³. 3 -1.8g / cm 3 More preferably, it is 1.2 g / cm³. 3 -1.6g / cm 3 .

9. The battery according to claim 1, wherein, The battery also includes an electrolyte, which includes ethyl propionate; Preferably, the ethyl propionate content is 1%-30% based on the total mass of the electrolyte.

10. The battery according to claim 9, wherein, The electrolyte further includes a first compound, which comprises at least one of the following structural formulas: , , , , , , , , , , , , , , , , , , , and ; And / or, based on the total mass of the electrolyte, the mass content of the first compound is 0.1%-15%; Preferably, the first compound includes .

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