A negative electrode sheet and a battery

Abstract

The application provides a negative electrode sheet and a battery. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector, and the negative electrode active layer comprises silicon-based particles. The negative electrode sheet satisfies the following relationship: 1 < Ar ≤ 5, 0 < (Ar90-Ar10) / Ar50 ≤ 3; wherein Ar is the length-to-shortness ratio of the silicon-based particles, the length-to-shortness ratio of the silicon-based particles refers to the ratio of the length of the long axis to the length of the short axis of the silicon-based particles, Ar10, Ar50 and Ar90 are respectively the length-to-shortness ratios corresponding to the cumulative number distribution of 10%, 50% and 90% of the silicon-based particles arranged in the order of the length-to-shortness ratio from small to large. The application can effectively reduce or even avoid the rearrangement and rotation of the silicon-based particles in the direction perpendicular to the negative electrode current collector, ensure the stability of the lithium ion transmission path, and improve the rate performance, cycle retention rate and fast charging performance of the battery. The battery of the application comprises the above negative electrode sheet.

Description

Technical Field

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

[0002] With the increasing demands for energy density in lithium-ion batteries from consumer electronics, electric vehicles, and energy storage systems, silicon-based materials are considered ideal next-generation anode materials due to their high specific capacity. To mitigate the significant volume effect of silicon during cycling, spherical silicon-based particle structures have been extensively studied. Their regular shape helps disperse internal stress, improves the pressure resistance of silicon-based materials, reduces the breakage and pulverization of anode materials caused by the enormous stress generated by silicon expansion during processing and cycling, and ultimately improves the battery's initial efficiency and energy density.

[0003] However, the contact area between spherical silicon-based particles and conductive agents and binders in the electrode is small, and the bonding force is limited. During long-term cycling, they are prone to detachment due to volume changes, which leads to the failure of electrical contact between the active material and the current collector, resulting in rapid capacity decay. Summary of the Invention

[0004] Research has shown that ellipsoidal silicon-based particles with inconsistent major and minor axes have a larger contact area compared to spherical particles. This enhances the bonding strength between particles and between particles and the conductive network, effectively suppressing material shedding due to poor contact during cycling, thus significantly improving the cycle stability of the electrode. However, ellipsoidal silicon-based particles have unequal major and minor axes. During cycling, the expansion stress of ellipsoidal silicon-based particles is released unevenly along the major and minor axes. Therefore, ellipsoidal silicon-based particles are susceptible to compressive stress from other particles along the major axis, resulting in rotation and rearrangement. This causes the major axis of the ellipsoidal silicon-based particles to tend to be perpendicular to the negative electrode current collector. This orientation of the major axis perpendicular to the negative electrode current collector leads to a longer migration path for lithium ions within the electrode, increasing diffusion resistance and affecting the rate performance and cycle stability of the battery. Especially during high-rate charge and discharge, the hysteresis of ion transport kinetics can easily lead to increased local polarization, limited capacity utilization, and deterioration of fast-charging performance.

[0005] To overcome the problem of prolonged lithium-ion transport paths caused by changes in silicon particle orientation due to silicon particle expansion in existing technologies, this invention provides a negative electrode and a battery including the negative electrode of this invention. During battery cycling, the negative electrode of this invention allows silicon particles to form a suitable interlocking structure, effectively reducing or even avoiding silicon particle rearrangement. This effectively reduces or even avoids the problem of prolonged lithium-ion transport paths caused by silicon particle rearrangement, thereby improving the battery's rate performance and cycle retention rate.

[0006] To achieve the above objectives, a first aspect of the present invention provides 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 silicon-based particles, the negative electrode sheet satisfying the following relationship: 1 < Ar ≤ 5, 0 < (Ar90 - Ar10) / Ar50 ≤ 3; wherein, Ar is the length of the silicon-based particles, the length of the silicon-based particles refers to the ratio of the length of the major axis to the length of the minor axis of the silicon-based particles, and Ar10, Ar50 and Ar90 are the lengths of the silicon-based particles arranged in ascending order of length, with the cumulative number distribution reaching 10%, 50% and 90% respectively.

[0007] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: Controlling the length of silicon-based particles in the negative electrode sheet satisfies the relationship 1 < Ar ≤ 5. The silicon-based particles possess a suitable elongated structure, exhibiting both adhesion and more uniform stress release along both the long and short axes, reducing the probability of silicon-based particle rearrangement. This also reduces or even eliminates the risk of silicon-based particles breaking due to uneven expansion stress caused by excessively long long axes, preventing a decrease in the compaction density of the negative electrode sheet. Controlling the length distribution of silicon-based particles in the negative electrode active layer satisfies the relationship 0 < (Ar90 - Ar10) / Ar50 ≤ 3, indicating a more concentrated length distribution of silicon-based particles. This prevents uneven stress distribution in the negative electrode active layer caused by uneven particle length distribution, avoiding increased voids that could lead to silicon-based particles detaching from binders, graphite, etc., and rearranging. Furthermore, it allows for effective mechanical interlocking between the appropriately elongated silicon-based particles, creating motion resistance and inhibiting rotation and movement, further reducing or even eliminating rearrangement and rotation of silicon-based particles in the direction perpendicular to the negative electrode current collector along their long axis. Therefore, by controlling the length and distribution of silicon-based particles, this invention ensures that the negative electrode sheet satisfies the following relationship: 1 < Ar ≤ 5, 0 < (Ar90 - Ar10) / Ar50 ≤ 3. This guarantees that the active layer of the negative electrode contains silicon-based particles of diverse and suitable lengths. Smaller silicon-based particles can orderly and tightly fill the gaps formed by larger silicon-based particles, forming a stable stacking structure. This enhances the mechanical interlocking effect between silicon-based particles and transforms the expansion force generated by the silicon-based particles into internal structural force. This effectively buffers the expansion force generated along the long axis of the silicon-based particles, reducing or even avoiding the rearrangement and rotation of silicon-based particles in the direction perpendicular to the negative electrode current collector. This maintains the stability of the lithium-ion transport path, reduces or even avoids increasing the diffusion resistance of lithium ions, reduces polarization at high rates, reduces the risk of lithium metal deposition, improves the rate performance and cycle stability of the battery, and reduces or even avoids the deterioration of the battery's fast charging performance.

[0008] In addition, by controlling the length of the negative electrode sheet to satisfy 1 < Ar ≤ 5, the silicon-based particles are more likely to achieve an arrangement with their long axis approximately parallel to the negative electrode current collector under the action of fluid shear and mechanical external force during the coating and rolling process. This increases the stress that the silicon-based particles need to overcome to rotate and rearrange in the direction with their long axis perpendicular to the negative electrode current collector during the expansion process, reduces the probability of rearrangement, and further reduces or even avoids the increase in lithium-ion transport paths.

[0009] A second aspect of the present invention provides a battery comprising a positive electrode, a separator, an electrolyte, and a negative electrode provided in the first aspect of the present invention.

[0010] Other features and advantages of the present invention will be described in detail in the following detailed description section.

[0011] 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

[0012] Figure 1 The image shown is one of the cross-sectional schematic diagrams of the negative electrode.

[0013] Figure 2 The second schematic diagram shows the cross-section of the negative electrode.

[0014] Figure 3 The image shows the TGA curve of the negative electrode active layer. Detailed Implementation

[0015] 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 invention. Unless otherwise specified herein, data ranges include endpoints.

[0016] 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.

[0017] A first aspect of the present invention provides 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 silicon-based particles, the negative electrode sheet satisfying the following relationships: 1 < Ar ≤ 5 (e.g., 1.2, 1.5, 2, 2.2, 2.4, 2.5, 3, 3.2, 3.5, 3.7, 4, 4.3, 4.5, 4.8 or 5), 0 < (Ar90 - Ar10) / Ar50 ≤ 3 (e.g., 0 < (Ar90 - Ar10) / Ar50 ≤ 3). For example, 0.1, 0.2, 0.5, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8 or 3); where Ar is the length of the silicon-based particle, which refers to the ratio of the length of the major axis to the length of the minor axis of the silicon-based particle. Ar10, Ar50 and Ar90 are the lengths of the silicon-based particles arranged in ascending order of length, with the cumulative number distribution reaching 10%, 50% and 90% respectively.

[0018] In this invention, the length of the silicon-based particle refers to the ratio of the length of its major axis to the length of its minor axis. The major axis of the silicon-based particle is the longest line segment intersecting the edge line of the silicon-based particle in a direction parallel to the long side of the smallest rectangle tangent to the outer side of the particle's outline. The minor axis of the silicon-based particle is the longest line segment intersecting the edge line of the silicon-based particle in a direction parallel to the short side of the smallest rectangle tangent to the outer side of the particle's outline. This length can be measured by the following method: discharging the battery to 0% SOC, disassembling the negative electrode, rinsing with DMC to remove lithium salt from the surface of the negative electrode, cutting the cross-section of the negative electrode in the thickness direction using argon ions, and scanning... A cross-sectional image of the negative electrode sheet along its thickness direction is captured using a scanning electron microscope (SEM). Combined with image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, ParticleMetric, etc.), the smallest rectangle tangent to the outline of the silicon-based particle on the outside is drawn. The length of this rectangle is denoted as the length of the major axis of the silicon-based particle, and the width is denoted as the length of the minor axis. The ratio of the length to the width of this rectangle is denoted as the length of the silicon-based particle. The arithmetic mean of the lengths of any 100 silicon-based particles is calculated to obtain the length of the silicon-based particle. If the number of silicon-based particles in a single image is less than 100, multiple images are captured until a total of 100 particles are accumulated.

[0019] In this invention, the silicon-based particles are arranged in ascending order of length, with a cumulative distribution of 10%, 50%, and 90% of the particles, respectively. The lengths corresponding to these proportions can be measured using the following method: The battery is discharged to 0% SOC, the negative electrode is disassembled, and the surface of the negative electrode is washed with DMC to remove lithium salt. An argon-ion section is cut across the thickness of the negative electrode, and a cross-sectional image of the cross-section is captured using a scanning electron microscope (SEM). The image is then analyzed using image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, ParticleMetric, etc.). Identify silicon-based particles and draw the smallest rectangle tangent to the outline of the silicon-based particle on the outside. The ratio of the length to the width of this rectangle is recorded as the length of the silicon-based particle. Count the lengths of any 100 silicon-based particles and arrange them in ascending order of length. The length corresponding to the 10th (10%) silicon-based particle is Ar10, the length corresponding to the 50th (50%) silicon-based particle is Ar50, and the length corresponding to the 90th (90%) silicon-based particle is Ar90. If the number of silicon-based particles in a single image is less than 100, take multiple images until the total number reaches 100.

[0020] In this invention, the negative electrode sheet is controlled to satisfy the following relationships: 1 < Ar ≤ 5, 0 < (Ar90 - Ar10) / Ar50 ≤ 3. The length of the silicon-based particles in the negative electrode sheet is controlled to satisfy the relationship 1 < Ar ≤ 5. The silicon-based particles have a suitable flat and elongated structure, which can improve their contact with the negative electrode conductive agent and negative electrode binder, enhance the adhesion, and ensure that the stress release in the long and short axis directions is relatively uniform. This reduces the compressive stress of other particles on the silicon-based particles in the long axis direction, reduces the probability of silicon-based particle rearrangement, and at the same time, it can reduce or even avoid the risk of silicon-based particle breakage due to uneven expansion stress caused by excessively long silicon-based particles, and prevent the negative electrode sheet from reducing compaction density. The length distribution of silicon-based particles in the negative electrode active layer is controlled to satisfy the relationship 0 < (Ar90 - Ar10) / Ar50 ≤ 3. On the one hand, this indicates that the length of the silicon-based particles is more uniform. Concentration can reduce or even avoid uneven distribution of expansion stress caused by large differences in the length distribution of silicon-based particles, prevent the increase of voids, and reduce the probability of silicon-based particles detaching from binders, graphite, etc. and rearranging. On the other hand, it also allows the orderly stacking of silicon-based particles with flat and elongated structures to form a "mortise and tenon" structure, which is conducive to the formation of mechanical interlock between silicon-based particles. When silicon-based particles expand, a certain degree of movement resistance is generated between silicon-based particles, inhibiting the rotation and movement of silicon-based particles and reducing the tendency of silicon-based particles to rearrange in the direction of the long axis perpendicular to the negative electrode current collector. When (Ar90-Ar10) / Ar50>3, the length distribution of silicon-based particles is too wide, and the long axis of some silicon-based particles is too long, which reduces the effect of the interlocking structure formed by silicon-based particles in the negative electrode active layer. The rearrangement of silicon-based particles will still affect the rate performance and cycle performance of the battery.

[0021] Therefore, by simultaneously controlling the length and distribution of silicon-based particles in the negative electrode active layer, ensuring that the negative electrode sheet satisfies the relationship: 1 < Ar ≤ 5, 0 < (Ar90 - Ar10) / Ar50 ≤ 3, it is possible to ensure that the negative electrode active layer contains silicon-based particles of diverse and suitable lengths. Smaller silicon-based particles can orderly and tightly fill the gaps formed by larger silicon-based particles, forming a stable stacking structure. This further enhances the mechanical interlocking effect between silicon-based particles, while converting the expansion force generated by the silicon-based particles into internal structural forces. This effectively buffers the expansion force generated along the long axis of the silicon-based particles, reducing or even avoiding the rearrangement and rotation of silicon-based particles in the direction perpendicular to the negative electrode current collector, thereby maintaining the stability of the lithium-ion transport path, reducing or even avoiding the increase in lithium-ion diffusion resistance, reducing polarization at high rates, lowering the risk of lithium metal deposition, and improving the rate performance, cycle stability, and fast charging performance of the battery.

[0022] Furthermore, controlling the length of the negative electrode sheet to satisfy 1 < Ar ≤ 5 ensures that the silicon-based particles have suitable length, high compressive strength, and mechanical strength. During rolling and cycling, these particles are less prone to breakage under mechanical forces or expansion stress, reducing side reactions, improving battery cycle performance, and decreasing thickness expansion. When Ar > 5, the silicon-based particles are too flat or have excessively long axes, making them more susceptible to breakage during rolling and cycling. This exposes new active interfaces, increases side reactions, and forms a thick SEI film, leading to active lithium loss, accelerated cycle life decay, and increased battery thickness expansion.

[0023] In this invention, by controlling the negative electrode to satisfy the following relationship: 1<Ar≤5,0<(Ar90-Ar10) / Ar50≤3, compared with the prior art, it is possible to reduce or even avoid the increase in ion transport paths caused by the rotation and rearrangement of silicon-based particles, thereby improving the rate performance, cycle stability and fast charging performance of the battery. In order to further improve the effect, one or more of the technical features can be further optimized.

[0024] In some embodiments, 0.1 ≤ (Ar90 - Ar10) / Ar50 ≤ 1.5.

[0025] In some embodiments, within a 50μm × 50μm area in the cross-sectional SEM of the negative electrode active layer, the average angle between the long axis of the silicon-based particles and the negative electrode current collector is less than 45°, for example, 0°, 1°, 3°, 5°, 8°, 10°, 12°, 15°, 17°, 20°, 22°, 25°, 27°, 30°, 32°, 35°, 38°, 40°, 43°, 44°.

[0026] In this invention, the angle between the long axis of the silicon-based particle and the negative electrode current collector refers to the angle less than or equal to 90 degrees formed by the extension of the long axis of the silicon-based particle and the extension of the horizontal direction of the negative electrode current collector (e.g., ...). Figure 1As shown in Figures A and B), the extension of the long axis refers to the extension of the length of the smallest rectangle tangent to the outer contour of the silicon-based particle in the silicon-based particle, and the horizontal direction refers to the direction perpendicular to the thickness direction of the negative electrode current collector. The average angle between the silicon-based particles and the negative electrode current collector can be measured by the following method: Discharge the battery to 0% SOC, disassemble the negative electrode sheet, rinse with DMC to remove lithium salt from the surface of the negative electrode sheet, cut the cross-section of the negative electrode sheet in the thickness direction using argon ions, and take a cross-sectional image of the negative electrode sheet in the thickness direction using a scanning electron microscope (SEM). Within any 50μm×50μm area of ​​the negative electrode active layer, identify the silicon-based particles using image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, ParticleMetric, etc.), count the angles less than or equal to 90 degrees formed by the extension of the long axis of any 50 silicon-based particles and the extension of the horizontal direction of the negative electrode current collector, and calculate the arithmetic mean, which is the average angle between the long axis of the silicon-based particles and the negative electrode current collector. If the number of silicon-based particles in a single image is less than 50, take multiple images until the total number reaches 50.

[0027] In this invention, by adjusting the rolling compaction and rolling speed during the preparation of the negative electrode sheet, the average angle between the silicon-based particles and the negative electrode current collector within the 50μm×50μm cross-sectional area of ​​the negative electrode active layer is less than 45°.

[0028] In some embodiments, within a 50μm × 50μm area in the cross-sectional SEM of the negative electrode active layer, the average angle between the long axis of the silicon-based particles and the negative electrode current collector is greater than or equal to 0° and less than 1°, for example, 0°, 0.1°, 0.2°, 0.3°, 0.4°, 0.5°, 0.6°, 0.7°, 0.8° or 0.9°.

[0029] In this invention, within a 50μm × 50μm area of ​​the cross-section SEM of the negative electrode active layer, the average angle between the long axis of the silicon-based particles and the negative electrode current collector is greater than or equal to 0° and less than 1°. The long axis of the silicon-based particles is approximately parallel to the negative electrode current collector, which further reduces the rearrangement of silicon-based particles during cycling. This results in a less tortuous Li ion migration path within the electrode, making the current distribution more uniform in the electrode thickness direction. This effectively avoids localized uneven charge states caused by ion transport obstruction, significantly reduces the diffusion resistance of ions between active particles, reduces polarization at high rates, helps suppress and reduce lithium metal deposition, and improves the rate performance and capacity retention of the battery. Furthermore, the approximately parallel alignment of the long axis of the silicon-based particles with the negative electrode current collector allows for a larger contact area and denser packing between silicon-based particles and between silicon-based particles and conductive and binder agents. This helps maintain the integrity of the conductive network during long-term cycling, improves cycle stability, and the denser packing contributes to increased battery energy density.

[0030] In some embodiments, within a 50μm × 50μm area in the cross-sectional SEM of the negative electrode active layer, the average angle between the long axis of the silicon-based particle and the negative electrode current collector is greater than or equal to 1° and less than 45°, for example, 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 12°, 14°, 16°, 18°, 20°, 22°, 24°, 26°, 28°, 30°, 35°, 40°, or 44°.

[0031] In this invention, within a 50μm × 50μm area in the cross-sectional SEM of the negative electrode active layer, the average angle between the long axis of the silicon-based particles and the negative electrode current collector is greater than or equal to 1° and less than 45°. This tilted arrangement of silicon-based particles helps optimize the pore structure, improves the wettability of the electrolyte, and thus enhances the kinetic performance of the battery, further improving its cycle performance and rate performance. Simultaneously, the stress vector of silicon-based particles satisfying the above tilt angle can be decomposed into two components during expansion: one perpendicular to the current collector direction and the other parallel to the current collector direction. This avoids concentrated stress release in a single direction, particularly avoiding concentrated stress release in the electrode thickness direction, effectively reducing the degree of battery expansion.

[0032] In some embodiments, within a 50μm × 50μm area in the cross-sectional SEM of the negative electrode active layer, the average angle between the long axis of the silicon-based particles and the negative electrode current collector is 1°-15°.

[0033] In some embodiments, the average included angle between the long axes of two adjacent silicon-based particles is less than 45°, for example, 0°, 1°, 5°, 8°, 10°, 15°, 18°, 20°, 22°, 25°, 26°, 40°, 38°, 36°, 34°, 32°, 30°, 38°, 40°, 42° or 44°.

[0034] In this invention, the included angle between the major axes of two adjacent silicon-based particles refers to the included angle formed by the extensions of the major axes of the two adjacent silicon-based particles (e.g., ...). Figure 2 As shown in C and D), it can be understood that when the extensions of the major axes of two adjacent silicon-based particles are parallel, the angle between the major axes of the two adjacent silicon-based particles is 0°. The average angle between the major axes of two adjacent silicon-based particles can be measured by the following method: Discharge the battery to 0% SOC, disassemble the negative electrode, rinse with DMC to remove lithium salt from the surface of the negative electrode, cut the cross-section of the negative electrode in the thickness direction using argon ions, and take a cross-sectional image of the negative electrode in the thickness direction using a scanning electron microscope (SEM). In the image, combine with image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, ParticleMetric, etc.) to identify silicon-based particles, count the angles formed by the extensions of the major axes of any 50 groups of adjacent silicon-based particles, and calculate the arithmetic mean, which is the average angle between the major axis of the silicon-based particles and the negative electrode current collector. If the number of silicon-based particles in a single image is less than 50, take multiple images until a total of 50 groups are accumulated.

[0035] In some embodiments, the average included angle between the major axes of two adjacent silicon-based particles is greater than or equal to 0° and less than 1°, for example, 0°, 0.1°, 0.2°, 0.3°, 0.4°, 0.5°, 0.6°, 0.7°, 0.8°, and 0.9°.

[0036] In this invention, the average included angle between the major axes of two adjacent silicon-based particles is controlled to be greater than or equal to 0° and less than 1°. At this time, the major axes of the two adjacent silicon-based particles are parallel or approximately parallel, and the orientation of the silicon-based particles is consistent. Consistent orientation helps to make the volume changes of multiple silicon-based particles more coordinated in the same direction during charging and discharging, thereby reducing the local shear stress caused by anisotropic expansion, further reducing or even avoiding the rearrangement of silicon-based particles due to mutual compression and separation, which damages the negative electrode structure, and further improving the cycle stability, rate performance and anti-expansion performance of the battery.

[0037] In some embodiments, the average included angle between the long axes of two adjacent silicon-based particles is greater than or equal to 1° and less than 45°, for example, 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 12°, 14°, 16°, 18°, 20°, 22°, 24°, 26°, 28°, 30°, 35°, 40°, and 44°.

[0038] In this invention, the average included angle between the major axes of two adjacent silicon-based particles is controlled to be greater than or equal to 1° and less than 45°. This tilted arrangement of silicon-based particles helps optimize the pore structure, improves the wettability of the electrolyte, and thus enhances the kinetic performance of the battery, further improving its cycle performance and rate performance. Simultaneously, when silicon-based particles satisfying the aforementioned tilt angle expand, their stress vector can be decomposed into two components: one perpendicular to the current collector direction and the other parallel to the current collector direction. This avoids the concentrated release of stress in a single direction, particularly avoiding the concentrated release of stress in the electrode thickness direction, effectively reducing the degree of battery expansion.

[0039] According to a specific embodiment, within a 50μm × 50μm area in the cross-sectional SEM of the negative electrode active layer, the average angle between the long axis of the silicon-based particles and the negative electrode current collector is greater than or equal to 0° and less than 1°, the average angle between the long axes of two adjacent silicon-based particles is greater than or equal to 0° and less than 1°, the long axis of the silicon-based particles is approximately parallel to the negative electrode current collector, and the silicon-based particles are oriented in the same direction. This orderly arrangement of silicon-based particles reduces structural changes such as rearrangement of silicon-based particles caused by expansion of silicon-based particles, can form a low-torsion lithium-ion transport channel, reduce ion diffusion resistance, thereby effectively suppressing local polarization and lithium metal deposition, and improving the rate performance of the battery.

[0040] According to a specific embodiment, within a 50μm×50μm area in the cross-sectional SEM of the negative electrode active layer, the average angle between the long axis of the silicon-based particles and the negative electrode current collector is greater than or equal to 1° and less than 45°, and the average angle between the long axes of two adjacent silicon-based particles is greater than or equal to 0° and less than 1°. The tilted arrangement of silicon-based particles can optimize the pore structure of the negative electrode active layer, and the volume change of multiple silicon-based particles is more coordinated in the same direction, which can reduce the local shear stress caused by anisotropic expansion, further reduce or even avoid silicon-based particle rearrangement, improve lithium-ion transport efficiency, and improve cycle performance and rate performance.

[0041] According to a specific embodiment, in a 50μm×50μm area within the cross-sectional SEM of the negative electrode active layer, the average angle between the long axis of the silicon-based particles and the negative electrode current collector is greater than or equal to 1° and less than 45°, and the average angle between the long axes of two adjacent silicon-based particles is greater than or equal to 1° and less than 45°. This can further optimize the pore structure of the negative electrode active layer, improve the wettability of the electrolyte, further enhance the battery cycle performance and rate performance, and also reduce the concentrated release of expansion stress in the electrode thickness direction, thereby reducing battery expansion.

[0042] In some embodiments, the morphology of the silicon-based particles includes at least one of oblate spheroids and elongated spheroids.

[0043] In this invention, the term "oblate spherical" refers to the shape of an oblate spheroid obtained by rotating it about the minor semi-axis of an ellipse, and the term "oblong spherical" refers to the shape of an oblong spheroid obtained by rotating it about the major semi-axis of an ellipse. It is understood that the shape of silicon-based particles fluctuates during the fabrication process and is not perfect. In such cases, the shape can be approximately determined as oblate or oblong based on the outer contour of the silicon-based particle morphology.

[0044] In some embodiments, the cross-sectional profile of the silicon-based particles includes at least one curve. The battery is discharged to 0% SOC, the negative electrode is disassembled, and lithium salt on the surface of the negative electrode is removed by DMC rinsing. An argon-ion section is cut along the thickness direction of the negative electrode, and a cross-sectional image along the thickness direction is captured using a scanning electron microscope (SEM). Within any 50μm × 50μm area of ​​the negative electrode active layer, silicon-based particles are identified using image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, ParticleMetric, etc.). A continuous line segment of 1μm length is arbitrarily cut along the outermost contour line of the silicon-based particle, and the radius of curvature (R) of this line segment is calculated using the "circle fitting" function. The curvature of this line segment is calculated using the formula 1 / R. If the curvature 1 / R of the arbitrarily cut line segment is ≥0.02, it indicates that the cross-sectional profile of the silicon-based particle includes at least one curve.

[0045] In some embodiments, the long axis of the silicon-based particles has a size of 3μm-21μm, for example, 3μm, 5μm, 7μm, 9μm, 11μm, 13μm, 15μm, 17μm, 19μm or 21μm.

[0046] In some embodiments, the short axis of the silicon-based particles has a size of 1μm-12μm, for example, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm or 12μm.

[0047] According to a specific embodiment, the long axis of the silicon-based particle is 3μm-21μm, the short axis of the silicon-based particle is 1μm-12μm, and the negative electrode sheet satisfies the following relationship: 1<Ar≤5, 0<(Ar90-Ar10) / Ar50≤3.

[0048] In some embodiments, the particle size Dn50 of the silicon-based particles is 2μm-12μm, for example, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm or 12μm.

[0049] In this invention, the particle size Dn50 of the silicon-based particles is controlled within the aforementioned range. A moderate particle size effectively reduces specific surface area and side reaction activity, while also shortening the lithium-ion transport path, further improving the battery's rate performance. When the particle size Dn50 is less than 2 μm, the specific surface area of ​​the excessively small silicon-based particles increases dramatically. During cycling, the increased interface between the silicon-based particles and the electrolyte leads to more side reactions, accelerating the consumption of active lithium and the continuous thickening of the negative electrode solid electrolyte interphase (SEI) film. This is detrimental to further improving battery cycle stability, reducing battery cycle life, and decreasing the battery's initial efficiency. Conversely, when the particle size Dn50 is greater than 12 μm, the excessively large silicon-based particles prolong the diffusion path of lithium ions within the solid phase, further exacerbating concentration polarization and volume change stress during charging and discharging. This is detrimental to further improving the rate performance of the silicon-based particles and may cause cracking of the silicon-based particles, damaging the conductive network.

[0050] In this invention, Dn represents the particle size distribution of silicon-based particles. The particle size Dn50 refers to the particle size of silicon-based particles that, when arranged in ascending order of particle size, accumulate to 50% of the total number of particles. In this invention, the particle size distribution of silicon-based particles can be determined by selecting 50 silicon-based particles within an arbitrary 100μm × 100μm region in an SEM image of the negative electrode active layer surface, and then analyzing the image using image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, Particle). Metric (or similar instruments) draws a rectangle or square tangent to the outline of a single silicon particle on the outside. The long side of the rectangle or any side of the square is taken as the particle size of the silicon particle. The particle sizes of 100 silicon particles are counted and arranged in ascending order. The particle size of the silicon particle corresponding to the cumulative number of particles that is 50% of the total number is denoted as Dn50. In addition, the particle size Dn50 of the silicon particle can also be obtained by testing with a laser particle size analyzer. For example, before preparing the negative electrode, the silicon particles are thoroughly stirred and the particle size Dn50 of the silicon particles is measured by a laser particle size analyzer.

[0051] In some embodiments, the silicon-based particles include one or more of elemental silicon particles, silicon-oxygen particles, silicon-carbon particles, silicon-nitrogen particles, and silicon alloy particles.

[0052] In some embodiments, the silicon-based particles are silicon-carbon particles.

[0053] In some embodiments, the silicon-based particles are silicon-carbon particles having a core-shell structure, the core-shell structure including a core and a coating layer wholly or partially covering the surface of the core, the core including porous carbon and silicon particles deposited within the porous carbon, and the coating layer including amorphous carbon.

[0054] In some embodiments, the surface of the silicon-based particles includes a first carbon nanotube, which wholly or partially coats the silicon-based particles.

[0055] In this invention, because carbon nanotubes have a high aspect ratio and excellent conductivity, the surface of silicon-based particles includes a first carbon nanotube. The first carbon nanotubes completely or partially cover the silicon-based particles, which can ensure that the silicon-based particles form a three-dimensional interconnected conductive network with adjacent silicon-based particles or negative electrode conductive agents in the negative electrode active layer, thereby further improving the rate performance of the battery.

[0056] In some embodiments, the aspect ratio of the first carbon nanotube is 10-2000, for example, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800 or 2000.

[0057] In some embodiments, the surface of the silicon-based particle includes at least one pit, the width of which is smaller than the dimension of the long axis of the silicon-based particle.

[0058] In this invention, the surface of the silicon-based particles includes at least one pit, the width of which is smaller than the length of the long axis of the silicon-based particles. On the one hand, this increases the surface roughness of the particles, which is beneficial to improving the adhesion between the silicon-based particles and the negative electrode binder and the negative electrode conductive agent, as well as between silicon-based particles themselves. This further reduces the slippage and rearrangement of silicon-based particles due to volume expansion during cycling, and prevents the active material from detaching from the conductive network, thus improving cycling stability. On the other hand, these pits can serve as microscopic electrolyte and Li-ion buffer regions, which can improve the wettability of the electrolyte on the silicon-based particles, thereby improving the overall wettability of the electrolyte inside the negative electrode sheet. This further shortens the diffusion distance of lithium ions from the electrolyte to the inside of the silicon-based particles. Especially at high rates, this helps to further reduce concentration polarization inside the negative electrode sheet and improve rate performance.

[0059] In some embodiments, the width of the pit is 0.01μm-10μm, for example, 0.01μm, 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 7μm or 10μm.

[0060] In this invention, controlling the width of the pit within the aforementioned range further ensures good adhesion of the silicon-based particles and electrolyte wettability. When the pit width is less than 0.01 μm, the pit size is too small, approaching a flat surface, which is detrimental to further improving the cycle stability and rate performance of the electrode. When the pit width is greater than 10 μm, it weakens the mechanical strength of the silicon-based particles. During the rolling and cycling of the negative electrode sheet, stress concentration at the pit edges of the silicon-based particles makes them more prone to cracking, leading to the destruction of the silicon-based particle structure.

[0061] In this invention, when the shape of the pit is circular or elliptical, the width of the pit is the maximum distance between any two points on the edge line of the circle or ellipse. When the shape of the pit is irregular, the width of the pit is the length of the long side of the rectangle tangent to the outer edge of the pit. When the number of pits is less than or equal to 10, the width of the pit is the average width of all pits. When the number of pits is greater than 10, the width of the pit is the average width of any 10 pits.

[0062] In some embodiments, the pit depth is less than the length of the short axis of the silicon-based particle.

[0063] In some embodiments, the pit depth is 0.01μm-5μm, for example, 0.01μm, 0.05μm, 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 4μm or 5μm.

[0064] In this invention, the depth of the pit refers to the maximum vertical distance from any point at the bottom of the pit to the surface of the silicon-based particle. When the number of pits is less than or equal to 10, the depth of the pit is the average of the depths of all pits; when the number of pits is greater than 10, the depth of the pit is the average of the depths of any 10 pits.

[0065] In this invention, the width and depth of the pit can both be obtained by SEM testing.

[0066] In some embodiments, the negative electrode active layer includes conductive fibers, wherein the conductive fibers include at least one of second carbon nanotubes and carbon nanofibers.

[0067] In some embodiments, the first carbon nanotube and the second carbon nanotube may each independently include single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0068] In some embodiments, the average width of the conductive fiber is 1nm-200nm, for example, 1nm, 10nm, 20nm, 40nm, 60nm, 80nm, 100nm, 150nm or 200nm.

[0069] In this invention, controlling the average width of the conductive fibers within the aforementioned range allows the conductive fibers to, on the one hand, possess excellent flexibility and a high aspect ratio, enabling them to connect multiple silicon-based particles within the negative electrode active layer to form a through-and-stable three-dimensional conductive network. This ensures that the electronic pathway remains connected even when the volume of the active material repeatedly expands and contracts or the orientation of the silicon-based particles changes, further reducing the overall resistance of the negative electrode sheet and thus ensuring good rate performance of the battery. On the other hand, the uniformly dispersed conductive fibers, through their intertwined physical action, work synergistically with the negative electrode binder to enhance the bonding strength and toughness of the negative electrode sheet, suppressing structural changes caused by stress during cycling and further improving the cycle stability of the battery.

[0070] In this invention, the average width of the conductive fiber is measured by the following method: the battery is discharged to 0% SOC, the negative electrode is disassembled, and lithium salt on the surface of the negative electrode is removed by rinsing with DMC. The cross-section of the negative electrode in the thickness direction is cut with argon ions, and the cross-sectional image in the thickness direction of the negative electrode is captured by scanning electron microscopy (SEM). In the image, the conductive fiber is identified by combining image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, ParticleMetric, etc.). The outer diameter of the conductive fiber is measured as the width of the conductive fiber. The arithmetic mean of the widths of any 50 conductive fibers is calculated and recorded as the average width of the conductive fiber. If the number of conductive fibers in a single image is less than 50, multiple images are captured until the total number reaches 50.

[0071] In some embodiments, the negative electrode active layer comprises graphite particles with a sphericity of 0.6-1, for example, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 or 1.

[0072] In this invention, the sphericity of graphite particles can be measured by the following method: The battery is discharged to 0% SOC, the negative electrode is disassembled, and lithium salt on the surface of the negative electrode is removed by DMC rinsing. An argon-ion section is cut along the thickness direction of the negative electrode. A scanning electron microscope (SEM) image of the cross-section along the thickness direction is captured. Within any 50μm × 50μm area of ​​the negative electrode active layer, graphite particles are identified using image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, ParticleMetric, etc.), and the radius r of the equivalent circle representing the projected circumference of a single graphite particle is calculated. 1 The radius r of the equivalent circle of the projected area of ​​graphite particles 2 The sphericity of a single graphite particle = r 2 / r 1The sphericity of any 50 graphite particles is statistically analyzed and the arithmetic mean is calculated and recorded as the sphericity of the graphite particles. If the number of graphite particles in a single image is less than 50, multiple images are taken until the total number reaches 50.

[0073] In some embodiments, the sphericity of the graphite particles is 0.9-1.

[0074] In some embodiments, the graphite particles are spherical in shape.

[0075] In some embodiments, the particle size Dn50 of the graphite particles is 2μm-12μm, for example, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm or 12μm.

[0076] In this invention, the particle size Dn50 of the graphite particles is controlled to be 2μm-12μm. Graphite particles within this size range can effectively fill the gaps between silicon-based particles, forming a denser particle packing structure. This further reduces the tendency of silicon-based particles to rearrange, and also reduces the rearrangement of graphite particles when the orientation of silicon-based particles changes. This is beneficial for maintaining the stability of the negative electrode structure and can also enhance the compaction density of the negative electrode, accommodating more active material in the same volume and improving the energy density of the battery. On the other hand, when the particle size Dn50 of the graphite particles is less than 2μm, the particle size is too small, the specific surface area is large, which will aggravate the side reactions of the negative electrode and the electrolyte, reducing the battery's first efficiency. When the particle size Dn50 of the graphite particles is greater than 12μm, the particle size is too large, the lithium-ion diffusion path of the graphite particles themselves is long, which is not conducive to further improving the rate performance of the battery.

[0077] In this invention, Dn represents the particle size distribution of graphite particles. The particle size Dn50 refers to the graphite particle size that, when arranged in ascending order of particle size, accumulates to 50% of the total number of graphite particles in the particle size distribution. In this invention, the particle size distribution of graphite particles can be determined by selecting 50 graphite particles within an arbitrary 100μm × 100μm region in the SEM image of the negative electrode active layer surface, and then analyzing the image using image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, Participation). (eMetric, etc.) Delineates a rectangle or square tangent to the outline of a single graphite particle on the outside. The long side of the rectangle or any side of the square is taken as the particle size of the silicon-based particle. The particle sizes of the 100 graphite particles are counted and arranged in ascending order. The particle size corresponding to the 50th graphite particle, i.e., the particle size of the 50th graphite particle, is denoted as Dn50. In addition, the particle size Dn50 of the graphite particles can also be obtained by testing with a laser particle size analyzer. For example, before preparing the negative electrode sheet, the graphite particles are thoroughly stirred and the particle size Dn50 of the graphite particles is measured by a laser particle size analyzer.

[0078] In some embodiments, the negative electrode active layer comprises styrene-butadiene rubber, wherein the glass transition temperature of the styrene-butadiene rubber is less than 25°C, for example, 24°C, 22°C, 20°C, 18°C, 16°C, 15°C, 14°C, 13°C, 10°C, 5°C, 0°C, -10°C, -20°C, -30°C, -40°C, -50°C, -60°C, or -75°C.

[0079] In this invention, the glass transition temperature of styrene-butadiene rubber is controlled to be less than 25°C, which enhances the molecular elasticity and flexibility of the styrene-butadiene rubber binder. This allows it to better absorb stress and undergo plastic deformation, thereby better coating and bonding silicon-based particles and filling some of the gaps between the silicon-based particles. This helps to form a more continuous and stable three-dimensional network between the silicon-based particles, the negative electrode conductive agent, and the negative electrode current collector, enhancing the bonding force and further reducing the rearrangement and rotation of silicon-based particles in the direction perpendicular to the long axis of the negative electrode current collector. This is beneficial to further maintain the long-term stability of the negative electrode structure and improve the rate performance of the battery.

[0080] In some embodiments, the negative electrode active layer includes a negative electrode binder, which, in addition to styrene-butadiene rubber, also includes one or more of polyvinylidene fluoride (PVDF), polyurethane, polyacrylonitrile, acrylate adhesives, polytetrafluoroethylene (PTFE), lithium polyacrylate (PAALi), polyacrylic acid (PAA), sodium polymethyl cellulose (CMC-Na), and lithium polymethyl cellulose (CMC-Li).

[0081] In some embodiments, the TGA curve of the negative electrode active layer under N2 atmosphere shows a weight loss decrease step at 350℃-500℃ (e.g., 350℃, 370℃, 390℃, 410℃, 430℃, 450℃, 470℃, 490℃ or 500℃), and the weight loss rate tends to stabilize at 400℃-550℃ (e.g., 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃ or 550℃).

[0082] In this invention, the TGA curve of the negative electrode active layer under N2 atmosphere can be obtained by the following method: using a ceramic scraper to scrape the powder on the surface of the negative electrode active layer in the negative electrode sheet, placing the powder in a thermogravimetric analyzer, and raising the temperature to 900°C at a heating rate of 10°C / min under N2 atmosphere, thereby obtaining the TGA curve of the negative electrode active layer under N2 atmosphere.

[0083] In some embodiments, the negative electrode sheet is subjected to hot rolling treatment at 35°C-150°C (e.g., 35°C, 50°C, 65°C, 80°C, 95°C, 110°C, 125°C, 140°C or 150°C).

[0084] In this invention, the negative electrode sheet is subjected to hot rolling treatment at 35℃-150℃, which can avoid excessive softening of styrene-butadiene rubber due to excessive rolling temperature, prevent the styrene-butadiene rubber bonding strength from decreasing, avoid damage to the pore structure of the negative electrode sheet, further improve the electrolyte wetting and lithium-ion transport performance of the negative electrode sheet, and improve the rate performance and cycle stability of the battery.

[0085] In some embodiments, the negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer, wherein the first negative electrode active layer is located between the negative electrode current collector and the second negative electrode active layer, and the second negative electrode active layer includes the silicon-based particles.

[0086] In some embodiments, the distance between the silicon-based particles and the negative electrode current collector is greater than or equal to 1 μm, for example, 1 μm, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm.

[0087] In this invention, the distance between the silicon-based particle and the negative electrode current collector being greater than or equal to 1 μm means that the distance between the silicon-based particle closest to the negative electrode current collector needs to be greater than or equal to 1 μm. In this invention, the distance between the silicon-based particle and the negative electrode current collector being greater than or equal to 1 μm can be obtained through SEM testing. Specifically, the negative electrode sheet is disassembled from the battery or a freshly prepared negative electrode sheet is used. An SEM image of the cross-section along the thickness direction of the negative electrode sheet is taken. The silicon-based particle closest to the negative electrode current collector is selected, and the minimum vertical distance between the outer contour edge of this silicon-based particle and the negative electrode current collector is measured to be greater than or equal to 1 μm.

[0088] In this invention, controlling the distance between the silicon-based particles and the negative electrode current collector within the aforementioned range can guide the expansion space of the silicon-based particles away from the negative electrode current collector, thereby reducing the risk of the negative electrode active layer peeling off from the negative electrode current collector and preventing the silicon-based particles from contacting the current collector during rearrangement. This avoids mechanical stress caused by expansion that could scratch or crack the negative electrode current collector, thus further improving the structural stability of the negative electrode sheet and enhancing the cycle stability of the battery.

[0089] A second aspect of the present invention provides a battery comprising a positive electrode, a separator, an electrolyte, and a negative electrode provided in the first aspect of the present invention.

[0090] In some embodiments, the bonding force between the negative electrode sheet and the separator is 3N / m-20N / m, for example, 3N / m, 5N / m, 8N / m, 10N / m, 15N / m, 20N / m.

[0091] In this invention, the bonding force between the negative electrode and the separator is controlled to be 3N / m-20N / m, which can further reduce the rearrangement and rotation of silicon-based particles on the surface of the negative electrode, reduce the risk of silicon-based particles puncturing the separator, improve the rate performance of the battery, and ensure the safety performance of the battery.

[0092] In this invention, the adhesion force between the negative electrode sheet and the separator can be measured using a tensile tester. Specifically, after the batteries are sorted and removed from the sorting platform, they are placed in an environment of (25±2)℃ and left to stand for 2-3 hours. The batteries are then charged at a constant current of 0.7C with a cutoff current of 0.05C. When the battery terminal voltage reaches the charging limit voltage, constant voltage charging is switched until the charging current is ≤ the cutoff current. Charging is then stopped and the batteries are left to rest for 5 minutes. The fully charged batteries are then dissected using the national standard GB / T2790-1995, i.e., a 180° peel test. To test the adhesion between the separator and the negative electrode sheet, the separator and negative electrode sheet were cut into composite strips of 15mm × 54.2mm. The adhesion between the separator and the negative electrode sheet was tested according to the 180° peel test standard. The cut composite strips were fixed to a steel plate with double-sided tape, ensuring the separator was facing the steel plate. A 2kg roller was used for one pass. A universal tensile testing machine was used, with the upper clamp holding the negative electrode sheet and the lower clamp holding the steel plate, to perform a 180° peel test at a speed of 100mm / min and a displacement distance of 100mm. The average peel force (in N) was obtained by testing any three points during the test. The adhesion force is the average adhesion force (in N / m), calculated as: average adhesion force = average peel force / composite strip width.

[0093] In some embodiments, the adhesion force between the negative electrode and the separator is 5 N / m-15 N / m.

[0094] In some embodiments, the diaphragm includes a substrate layer and a coating layer located on at least one side of the substrate layer, wherein the coating surface and the other side of the substrate layer include an adhesive layer.

[0095] In some embodiments, the coating comprises heat-resistant particles, the heat-resistant particles being composed of at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, cerium oxide, aluminum nitride, boron nitride, zirconium titanate, barium titanate, and magnesium fluoride.

[0096] In some embodiments, the adhesive layer comprises polymer particles, the polymer particles comprising at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyacrylic acid, and polyvinyl alcohol.

[0097] In some embodiments, the thickness of the diaphragm is 6.5 μm-9.5 μm, for example, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm or 9.5 μm.

[0098] In this invention, the positive electrode and electrolyte are conventional positive electrode, separator and electrolyte in the art, and can all be obtained by conventional preparation methods in the art.

[0099] In some instances, the battery is a lithium-ion rechargeable battery.

[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] Example 1 (1) Preparation of positive electrode The positive electrode active material (lithium cobalt oxide), positive electrode binder (polyvinylidene fluoride PVDF500), and positive electrode conductive agent (conductive carbon black: carbon nanotubes (mass ratio) = 1:1) were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 96:2:2 and continuously stirred under the action of a stirrer to form a homogeneous and fluid positive electrode slurry. Subsequently, the positive electrode slurry was coated on both sides of the positive electrode current collector (aluminum foil) and dried in a vacuum oven at 120°C for 6 hours. Then, it was rolled and slit to obtain the desired positive electrode sheet.

[0102] (2) Preparation of silicon-based particles and negative electrode sheets Ammonia solution and anhydrous ethanol were mixed in a volume ratio of 2:1. Then, formaldehyde and phenol were added to the mixed solvent in a molar ratio of 3:1. The mixture was stirred and polymerized at 80°C for 24 hours. After the reaction was completed, the mixture was washed with deionized water and dried at 80°C for 12 hours to obtain phenolic resin. Phenolic resin and potassium hydroxide were uniformly mixed at a mass ratio of 1:1 and transferred to a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 200°C at a rate of 5°C / min and held for 2 hours. After the holding period, pre-carbonized phenolic resin powder was obtained. The pre-carbonized phenolic resin powder was added to a ball mill and ball-milled at 500 rpm for 10 hours to obtain flattened spherical phenolic resin powder. The oblate spheroid phenolic resin powder was transferred to a tube furnace and heated to 750°C at a rate of 10°C / min under N2 atmosphere protection and held for 3 hours. After the holding period, oblate spheroid porous carbon was obtained. Flattened spherical porous carbon was transferred to a fluidized bed reactor. Nitrogen gas was introduced and the temperature was raised to 1000°C and held for 2 hours to create surface pits. The temperature was then lowered to 500°C and silane gas (SiH4) and N2 were introduced and held for 5 hours to allow the silane to pyrolyze and generate nano-silicon particles, which were uniformly embedded in the pores of the porous phenolic resin carbon microspheres. After the process was completed, the silane was stopped and the temperature was raised to 550°C and acetylene gas was introduced. The acetylene decomposition time was controlled to be 2 hours to obtain flattened spherical silicon-carbon particles. The flattened spherical silicon-carbon particles were added to the first carbon nanotube dispersion and stirred at room temperature for 2 hours to obtain silicon-carbon particles with the surface partially coated with the first carbon nanotubes.

[0103] Subsequently, graphite particles, flattened spherical silicon carbon particles (silicon-based particles), styrene-butadiene rubber, second carbon nanotubes (conductive fibers), and conductive carbon black were mixed in an aqueous solvent at a weight ratio of 77:15:6:1:1. The mixture was continuously stirred under the action of a stirrer to form a uniform and flowing negative electrode slurry. Then, the first negative electrode slurry was coated on both sides of the copper foil and dried in a vacuum oven at 120°C for 6 hours to obtain the first negative electrode active layer. Graphite particles, styrene-butadiene rubber, second carbon nanotubes (conductive fibers), and conductive carbon black were mixed in an aqueous solvent at a weight ratio of 92:6:1:1. The mixture was continuously stirred under the action of a stirrer to form a homogeneous, flowing negative electrode slurry. Subsequently, the second negative electrode slurry was coated onto the surface of the first negative electrode active layer and dried in a vacuum oven at 120°C for 6 hours to obtain the second negative electrode active layer. Then, the layer was rolled and slit to obtain the negative electrode sheet. The rolling temperature of the negative electrode sheet was 120°C. The length of the major axis of the silicon-based particles was 12.3 μm, the length of the minor axis of the silicon-based particles was 6.2 μm, the Ar value of the silicon-based particles was 2, the Ar90 value was 2.8, the Ar10 value was 1.2, and the Ar50 value was 2. The ratio of (Ar90-Ar10) / Ar50 was... =(2.8-1.2) / 2=0.8, the particle size Dn50 of the silicon-based particles is 8.7μm, in the cross-sectional SEM of the negative electrode active layer, within a 50μm×50μm area, the average angle between the long axis of the silicon-based particles and the negative electrode current collector is 2°, the average angle between the long axes of two adjacent silicon-based particles is 1°, the morphology of the silicon-based particles is oblate, the surface of the silicon-based particles includes at least one pit, the width of the pit is less than the length of the long axis of the silicon-based particles, the width of the pit is 1.5μm, the depth of the pit is 1μm, the depth of the pit is less than the length of the short axis of the silicon-based particles, the average width of the conductive fiber is 95.6nm, the sphericity of the graphite particles is 0.92, the particle size Dn50 of the graphite particles is 8.5μm, and the distance between the silicon-based particles and the negative electrode current collector is 20μm.

[0104] (3) Electrolyte preparation In an argon-filled glove box (moisture content <1 ppm, oxygen content <1 ppm), the following non-fluorinated solvents, propyl propionate, ethyl propionate, propylene carbonate, and ethylene carbonate, were mixed in a volume ratio of 3:4:2:1 to form a homogeneous solvent. Then, 21.2% of fluoroethylene carbonate, 16% of LiPF6, and 2.1% of 1,3,6-hexanetrionitrile based on the total weight of the electrolyte were slowly added and stirred until homogeneous to obtain the desired lithium-ion battery electrolyte.

[0105] (4) Preparation of the diaphragm Heat-resistant granules (boehmite) and binder (polyacrylic acid) are added to deionized water at a weight ratio of 95:5. After thorough stirring, a first slurry with a solid content of 25% is obtained. The first slurry is coated onto one side of the substrate layer (polyethylene) using a gravure roller and then dried in a multi-section oven at 60°C to form a coating. Polyvinylidene fluoride (polymer particles) is added to deionized water and mixed thoroughly until the polyvinylidene fluoride is dissolved, resulting in a second slurry with a solid content of 8%. The second slurry is then coated onto the surface of the coating layer and the other side of the substrate layer using a gravure roller, and then dried in a multi-section oven at 60°C to form a coating layer.

[0106] The diaphragm is thus prepared.

[0107] (5) Preparation of lithium-ion batteries The positive electrode, negative electrode, and separator prepared above are sequentially subjected to processes such as stacking and winding, electrolyte injection, vacuum sealing, room temperature standing, and high temperature formation to obtain the desired lithium-ion battery. The adhesion force between the negative electrode and the separator is 15 N / m.

[0108] Example 2 group This set of examples illustrates the effects of changes in the length (Ar) of silicon-based particles.

[0109] This embodiment group is based on Embodiment 1, except that the length Ar of the silicon-based particles is changed, as detailed in Table 1.

[0110] Table 1 Example 3 Group This set of examples illustrates the effects of changes in (Ar90-Ar10) / Ar50.

[0111] This embodiment group is based on Embodiment 1, except that (Ar90-Ar10) / Ar50 is changed, as detailed in Table 2.

[0112] Table 2 Example 4 group This set of examples illustrates the effects of changes in the average angle between the long axis of the silicon-based particles and the negative electrode current collector and / or the average angle between the long axes of two adjacent silicon-based particles within a 50μm×50μm area in a cross-sectional SEM of the negative electrode active layer.

[0113] This embodiment group is based on Embodiment 1, except that the average angle between the long axis of the silicon-based particles and the negative electrode current collector and / or the average angle between the long axes of two adjacent silicon-based particles is changed within a 50μm×50μm area in the cross-sectional SEM of the negative electrode active layer, as detailed in Table 3.

[0114] Table 3 Example 5 group This set of examples illustrates the effects of changes in the carbon nanotubes coating the surface of silicon-based particles.

[0115] Example 5-1 This embodiment is based on Embodiment 1, except that the surface of the silicon-based particles includes a first carbon nanotube, and the first carbon nanotube completely covers the silicon-based particles.

[0116] Example 5-2 This embodiment is based on Embodiment 1, except that the surface of the silicon-based particles does not include the first carbon nanotubes.

[0117] Example 6 group This set of examples illustrates the effects of changes in the width and / or depth of pits on the surface of silicon-based particles.

[0118] This embodiment group is based on Embodiment 1, except that the width and / or depth of the pits on the surface of the silicon-based particles are changed, as detailed in Table 4.

[0119] Table 4 Example 7 group This set of examples illustrates the effects of changes in the average width of conductive fibers.

[0120] Example 7-1 This embodiment is based on Embodiment 1, except that the average width of the conductive fiber is 20 nm.

[0121] Example 7-2 This embodiment is based on Embodiment 1, except that the average width of the conductive fiber is 150 nm.

[0122] Example 7-3 This embodiment is based on Embodiment 1, except that the average width of the conductive fiber is 1 nm.

[0123] Example 7-4 This embodiment is based on Embodiment 1, except that the average width of the conductive fiber is 200 nm.

[0124] Example 8 group This set of examples illustrates the effects of changes in the adhesive force between the negative electrode and the separator.

[0125] Example 8-1 This embodiment is based on Embodiment 1, except that the adhesion force between the negative electrode and the separator is 5 N / m.

[0126] Example 8-2 This embodiment is based on Embodiment 1, except that the adhesion force between the negative electrode and the separator is 15 N / m.

[0127] Example 8-3 This embodiment is based on Embodiment 1, except that the adhesion force between the negative electrode and the separator is 3 N / m.

[0128] Example 8-4 This embodiment is based on Embodiment 1, except that the adhesion force between the negative electrode and the separator is 20 N / m.

[0129] Example 8-5 This embodiment is based on Embodiment 1, except that the adhesion force between the negative electrode and the separator is 1 N / m.

[0130] Examples 8-6 This embodiment is based on Embodiment 1, except that the adhesion force between the negative electrode and the separator is 16 N / m.

[0131] Example 9 group This set of examples illustrates the effects of changes in the distance between silicon-based particles and the negative electrode current collector.

[0132] Example 9-1 This embodiment is based on Embodiment 1, except that the distance between the silicon-based particles and the negative electrode current collector is 1 μm.

[0133] Example 9-2 This embodiment is based on Embodiment 1, except that the distance between the silicon-based particles and the negative electrode current collector is 0.2 μm.

[0134] Comparative Example 1 This comparative example is based on Example 1, except that the silicon-based particles are spherical and the length of the silicon-based particles is 1 (Ar is 1).

[0135] Comparative Example 2 This comparative example is based on Example 1, except that the length of the major axis of the silicon-based particles is 20.4 μm, the length of the minor axis of the silicon-based particles is 3.7 μm, the length Ar of the silicon-based particles is 5.5, and the particle size Dn50 of the silicon-based particles is 10.8 μm.

[0136] Comparative Example 3 This comparative example is based on Example 1, except that the Ar90 of the silicon-based particles is 24, the Ar10 of the silicon-based particles is 2, the Ar50 of the silicon-based particles is 7, (Ar90-Ar10) / Ar50=(24-2) / 7=3.14, the length of the major axis of the silicon-based particles is 13.8μm, the length of the minor axis of the silicon-based particles is 7.5μm, the length-to-shortness Ar of the silicon-based particles is 1.8, and the particle size Dn50 of the silicon-based particles is 8.8μm.

[0137] Test case The batteries prepared in the examples and comparative examples were subjected to the following performance tests, and the test results are shown in Table 5: (1) Capacity retention rate during 25℃ cycling: At 25℃±2℃, the battery was charged at a constant current and constant voltage of 0.7C to the upper limit voltage of 4.53V, then cut off at 0.05C, and then discharged at a constant current of 0.2C to the lower limit voltage of 3V. The initial discharge capacity is denoted as C. 1 After 10 minutes of rest, the cycle is as follows: 3C constant current / constant voltage charging to 4.25V, cut off at 2C, then 2C constant current / constant voltage charging to 4.48V, cut off at 1.5C, then 1.5C constant current / constant voltage charging to the upper limit voltage of 4.53V, cut off at 0.18C, rest for 5 minutes, and then discharge at 0.7C to the lower limit voltage of 3V. After 500 cycles, 0.7C constant current / constant voltage charging is performed to the upper limit voltage of 4.53V, cut off at 0.05C, and then 0.2C constant current discharge is performed to the lower limit voltage of 3V. The final discharge capacity is recorded as C. 2 Capacity retention rate = (C 2 / C 1 )×100%.

[0138] (2) Ratio performance: The battery was left to stand at 25±2℃ for 60 minutes, then charged at a constant current and constant voltage of 0.2C to 4.53V, with a cutoff current of 0.02C. After standing for 10 minutes, it was discharged at 0.2C to 3V. After standing for 10 minutes, the discharge capacity at this point was recorded as Q. 1 Then, it is charged at a constant current and constant voltage of 0.2C to 4.53V, with a cutoff current of 0.02C. After resting for 10 minutes, it is discharged at 1C to 3V; after resting for 5 minutes, the discharge capacity is recorded as Q. 2 Rate discharge performance = (Q 2 / Q 1 )×100%.

[0139] Table 5 As can be seen from Table 5, by comparing the comparative example and the embodiment, the room temperature cycling capacity retention rate and rate performance of the embodiment are improved. This indicates that by controlling the negative electrode to satisfy the following relationship: 1<Ar≤5,0<(Ar90-Ar10) / Ar50≤3, the increase in ion transport paths caused by the rotation and rearrangement of silicon-based particles can be reduced or even avoided, thereby improving the rate performance and cycle performance of the battery.

[0140] 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 negative electrode sheet, characterized in that, The negative electrode sheet includes a negative current collector and a negative active layer located on at least one side of the surface of the negative current collector. The negative active layer includes silicon-based particles. The negative electrode sheet satisfies the following relationship: 1 < Ar ≤ 5, 0 < (Ar90 - Ar10) / Ar50 ≤ 3; where Ar is the length of the silicon-based particles, and the length of the silicon-based particles refers to the ratio of the length of the major axis to the length of the minor axis of the silicon-based particles. Ar10, Ar50 and Ar90 are the lengths of the silicon-based particles arranged in ascending order of length, with the cumulative number distribution reaching 10%, 50% and 90% respectively.

2. The negative electrode sheet according to claim 1, wherein, 0.1≤(Ar90-Ar10) / Ar50≤1.5; And / or, in a 50μm×50μm area in the cross-sectional SEM of the negative electrode active layer, the average angle between the long axis of the silicon-based particle and the negative electrode current collector is less than 45°, preferably 1°-15°. The angle between the long axis of the silicon-based particle and the negative electrode current collector refers to the angle less than or equal to 90 degrees formed by the extension of the long axis of the silicon-based particle and the extension of the horizontal direction of the negative electrode current collector. And / or, the average included angle between the major axes of two adjacent silicon-based particles is less than 45°; And / or, the morphology of the silicon-based particles includes at least one of oblate and elongated spherical shapes.

3. The negative electrode sheet according to claim 1, wherein, The length of the major axis of the silicon-based particles is 3μm-21μm; And / or, the length of the short axis of the silicon-based particles is 1 μm-12 μm; And / or, the particle size Dn50 of the silicon-based particles is 2μm-12μm; And / or, the silicon-based particles include one or more of elemental silicon particles, silicon-oxygen particles, silicon-carbon particles, silicon-nitrogen particles, and silicon alloy particles; preferably, the silicon-based particles are silicon-carbon particles.

4. The negative electrode sheet according to claim 1, wherein, The silicon-based particles are silicon-carbon particles, which have a core-shell structure. The core-shell structure includes a core and a coating layer that covers all or part of the surface of the core. The core includes porous carbon and silicon particles deposited within the porous carbon. The coating layer includes amorphous carbon. And / or, the surface of the silicon-based particles includes a first carbon nanotube, which wholly or partially coats the silicon-based particles.

5. The negative electrode sheet according to claim 1, wherein, The surface of the silicon-based particle includes at least one pit, the width of which is less than the length of the long axis of the silicon-based particle. Preferably, the width of the pit is 0.01μm-10μm; Preferably, the depth of the pit is less than the length of the minor axis of the silicon-based particle; More preferably, the depth of the pit is 0.01μm-5μm.

6. The negative electrode according to claim 1, wherein, The negative electrode active layer includes conductive fibers, which include at least one of second carbon nanotubes and carbon nanofibers; preferably, the average width of the conductive fibers is 1 nm-200 nm. And / or, the negative electrode active layer comprises graphite particles, the sphericity of the graphite particles being 0.6-1, preferably 0.9-1; preferably, the particle size Dn50 of the graphite particles is 2μm-12μm.

7. The negative electrode sheet according to any one of claims 1-6, wherein, The negative electrode active layer includes styrene-butadiene rubber, and the glass transition temperature of the styrene-butadiene rubber is less than 25°C. And / or, the TGA curve of the negative electrode active layer under N2 atmosphere shows a weight loss step at 350℃-500℃, and the weight loss rate tends to stabilize at 400℃-550℃. And / or, the negative electrode sheet is subjected to hot rolling treatment at 35℃-150℃.

8. The negative electrode according to claim 1, wherein, The negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer. The first negative electrode active layer is located between the negative electrode current collector and the second negative electrode active layer. The second negative electrode active layer includes the silicon-based particles. Preferably, the distance between the silicon-based particles and the negative electrode current collector is greater than or equal to 1 μm.

9. A battery, characterized in that, The battery includes a positive electrode, a separator, an electrolyte, and a negative electrode as described in claims 1-8.

10. The battery according to claim 9, wherein, The adhesion between the negative electrode and the separator is 3N / m-20N / m.

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