Negative electrode sheet and battery

Abstract

The present disclosure provides a negative electrode sheet and a battery. The negative electrode sheet comprises a negative electrode current collector and a negative electrode coating, which is located on the surface of the negative electrode current collector, wherein the negative electrode coating comprises a negative electrode active material, with the negative electrode active material comprising graphite and a silicon-based material. A concave part is provided on the surface of the negative electrode coating, the ratio of the width of the concave part to the particle diameter Dv50 of the silicon-based material is greater than or equal to 2, and the depth of the concave part is greater than or equal to the particle diameter Dv50 of the silicon-based material. The present disclosure can improve both the thermal safety and the low-temperature cycle performance of a battery.

Description

A negative electrode and a battery Technical Field

[0001] This disclosure relates to the field of electrochemical devices, specifically to a negative electrode and a battery. Background Technology

[0002] Silicon-based materials have higher capacity. To improve the energy density of batteries, silicon-doped anodes are usually used (that is, silicon-based materials are doped into the anode sheet of the battery as the anode active material). The most common silicon-doped anode sheet is the graphite silicon-doped anode.

[0003] However, existing silicon-doped anode sheets generally suffer from poor safety and low-temperature performance. Specifically, silicon-based materials undergo more side reactions after contact with the electrolyte, resulting in severe gas and heat generation in the battery, which can easily lead to safety issues such as fire. At the same time, the gas generated by the side reactions between silicon-based materials and the electrolyte increases the gap between the silicon-based materials and graphite. Furthermore, the side reactions between silicon-based materials and the electrolyte also thicken the SEI film on the surface of the silicon-based material particles, thereby increasing the impedance and affecting the charge and discharge performance of the battery in low-temperature environments. Summary of the Invention

[0004] This disclosure provides a negative electrode and a battery to at least solve the problems of poor safety and poor low-temperature performance of silicon-doped negative electrodes.

[0005] In one aspect, this disclosure provides a negative electrode sheet, including a negative electrode current collector and a negative electrode coating located on one or both surfaces of the negative electrode current collector. The negative electrode coating includes a negative electrode active material, which includes graphite and a silicon-based material. The surface of the negative electrode coating is provided with a recess, the width of which is greater than or equal to the particle size Dv50 of the silicon-based material in a ratio greater than or equal to 2, and the depth of which is greater than or equal to the particle size Dv50 of the silicon-based material.

[0006] In another aspect of this disclosure, a battery is provided, including the aforementioned negative electrode.

[0007] The negative electrode sheet and battery disclosed herein contain a negative electrode active material comprising both graphite and silicon-based materials. By doping with silicon-based materials, the energy density of the negative electrode sheet and battery can be improved. Furthermore, recesses are formed on the surface of the negative electrode coating, and the ratio of the width of the recess to the particle size Dv50 of the silicon-based material is controlled to be greater than or equal to 2, and the depth of the recess is greater than or equal to the particle size Dv50 of the silicon-based material. This facilitates the rapid discharge of gases generated around the silicon-based material particles during battery charging and discharging due to side reactions between the silicon-based material particles and the electrolyte. The gas can be discharged through the gaps between the recesses and graphite, as well as the interlayer gaps of graphite, to avoid overheating and fire hazards. At the same time, the gas around the silicon-based material particles in the negative electrode is quickly discharged, which can suppress the increase of the gap between the silicon-based material particles and graphite (i.e., ensure that the gap between the silicon-based material particles and graphite does not increase as much as possible) and suppress the thickening of the SEI film on the surface of the silicon-based material particles. This can improve the migration speed of ions (such as lithium ions) between the silicon-based material particles and graphite particles under low temperature conditions and improve the low temperature performance of the battery. Attached Figure Description

[0008] Figure 1 is a schematic diagram of the projection structure of the negative electrode coating on the negative electrode current collector according to an embodiment of the present disclosure;

[0009] Figure 2 is a schematic diagram of the projection structure of the negative electrode coating on the negative electrode current collector according to another embodiment of the present disclosure;

[0010] Figure 3 is a schematic cross-sectional view of the negative electrode sheet according to an embodiment of the present disclosure;

[0011] Figure 4 is a thermogravimetric curve of Embodiments 1 and 3 of this disclosure.

[0012] Explanation of reference numerals in the attached figures: 1: Negative electrode current collector; 2: Negative electrode coating; 21: Recess; 210: Recess group; 101: First side; 102: Second side; L: Width of the recess; △L: Spacing between two adjacent recesses; h: Depth of the recess; △L1: Distance between the outer edge of the recess closest to the outer edge of the first side of the negative electrode coating and the outer edge of the first side of the negative electrode coating; △L2: Distance between the recess closest to the outer edge of the second side of the negative electrode coating and the outer edge of the second side of the negative electrode coating; x: First direction; y: Second direction; z: Third direction. Detailed Implementation

[0013] The technical solutions of this application will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of this application, and should not be construed as limiting the scope of protection of this application. All technologies implemented based on the above content of this application are covered within the scope of protection intended by this application.

[0014] It should be noted that the numerical designations such as "first" and "second" in this disclosure are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0015] To enable those skilled in the art to better understand the solutions disclosed herein, the present disclosure will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present disclosure, and the examples are only for explaining the present disclosure and are not intended to limit its scope. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without inventive effort are within the scope of protection of the present disclosure.

[0016] This disclosure provides a negative electrode sheet, as shown in Figures 1 to 3. The negative electrode sheet includes a negative electrode current collector 1 and a negative electrode coating 2 located on one or both sides of the surface of the negative electrode current collector 1. The negative electrode coating 2 includes a negative electrode active material, which includes graphite and silicon-based materials. The surface of the negative electrode coating 2 is provided with a recess 21. The ratio of the width L of the recess 21 to the particle size Dv50 of the silicon-based material is greater than or equal to 2 (i.e., L / Dv50≥2), and the depth h of the recess 21 is greater than or equal to the particle size Dv50 of the silicon-based material (i.e., h≥Dv50).

[0017] This facilitates the rapid discharge of gases generated around silicon particles during battery charging and discharging due to side reactions between silicon particles and electrolyte (these gases can be discharged through gaps between the recesses and graphite, as well as interlayer gaps in graphite), preventing overheating and potential fires. Simultaneously, the rapid discharge of gases around the silicon particles in the negative electrode inhibits the increase in the gap between the silicon particles and graphite (ensuring the gap between them remains as small as possible) and suppresses the thickening of the SEI film on the surface of the silicon particles. This, in turn, improves the migration speed of ions (such as lithium ions) between the silicon and graphite particles at low temperatures, thus enhancing the battery's low-temperature performance.

[0018] The inventors, through research and analysis, believe that one reason why this disclosure, by controlling L / Dv50≥2 and h≥Dv50 through embodiments, can simultaneously improve the thermal safety performance and low-temperature cycle performance of the battery is that, during battery cycling, the silicon-based material undergoes volume expansion, but its maximum particle size after expansion usually does not exceed twice its particle size before expansion. In the negative electrode sheet of this disclosure, controlling the width L of the recess 21 to be no less than twice the particle size DV50 of the silicon-based material, and simultaneously controlling the depth h of the recess 21 to be greater than or equal to the particle size DV50 of the silicon-based material, helps to ensure that silicon-based material particles do not fill the recess 21 during battery cycling, thereby ensuring an exhaust channel to facilitate the extremely rapid discharge of the silicon-based material particles from the negative electrode sheet. The gas generated by the side reactions between the negative electrode material (such as silicon-based material) and the electrolyte helps prevent safety issues such as battery fires. At the same time, the gas generated in the negative electrode is discharged very quickly, which can prevent the gap between the silicon-based material and graphite from increasing. Meanwhile, the heat generated in the negative electrode due to side reactions is also carried away by the gas, which lowers the temperature of the negative electrode and can alleviate the side reactions between the negative electrode material and the electrolyte. This reduces the thickness of the SEI film formed on the surface of the silicon-based material due to the side reactions between the silicon-based material and the electrolyte. As a result, the gap between the silicon-based material and graphite and the thickness of the SEI film on the surface of the silicon-based material are suppressed, thereby reducing impedance and improving the low-temperature cycle performance of the battery.

[0019] Generally, the negative electrode coating 2 includes a negative electrode active material layer, which includes the aforementioned negative electrode active material, negative electrode conductive agent, negative electrode binder, and negative electrode thickener, etc. The negative electrode active material includes graphite and / or silicon-based materials (i.e., the negative electrode sheet in this embodiment is a silicon-doped graphite negative electrode).

[0020] Specifically, based on the total mass of the negative electrode active material layer, the mass fraction of the negative electrode active material can be 70% to 99%, for example, a range of 70%, 75%, 80%, 85%, 90%, 95%, 99%, or any two of these; the mass fraction of the negative electrode conductive agent can be 0.3% to 12%, for example, a range of 0.3%, 0.5%, 1%, 3%, 5%, 8%, 10%, 12%, or any two of these; and the mass fraction of the negative electrode binder can be 0%. The mass fraction of the negative electrode thickener can be 0.05% to 15%, for example, 0%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 7%, 9%, 10%, 12%, 15%, or any combination thereof. However, it is not limited to this range. When the mass fraction of the negative electrode binder is 0%, it indicates that there is no negative electrode binder in the negative electrode active material layer.

[0021] In some embodiments, the amount of silicon doped in the negative electrode coating 2 (the mass ratio of silicon-based material to graphite) can be 0.01 to 0.3, for example, a range of 0.01, 0.05, 0.08, 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3 or any combination thereof.

[0022] Specifically, silicon-based materials may include one or more of silicon-carbon materials, silicon-oxygen materials, silicon, and silicon alloys. In this embodiment, by providing a recess 21 on the surface of the negative electrode coating 2 and controlling L / Dv50≥2 and h≥Dv50, the safety problems such as the easy side reaction between these silicon-based materials and the electrolyte, as well as the resulting serious gas generation of the negative electrode sheet, easy fire and explosion, can be effectively solved. At the same time, the low-temperature cycling performance of the negative electrode sheet doped with these silicon-based materials is also improved.

[0023] Specifically, the ratio of the width L of the recess 21 to the particle size Dv50 of the silicon-based material is less than or equal to 20 (i.e., 2 ≤ L / Dv50 ≤ 20), where L / Dv50 is, for example, a range consisting of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 14, 16, 18, 20, or any combination thereof. This approach helps to improve both the battery's thermal safety and low-temperature cycling performance while avoiding excessive energy density loss in the negative electrode due to an excessively large width of the recess 21, thus maintaining a relatively high energy density for the battery.

[0024] In some instances, the ratio of the width L of the recess 21 to the particle size Dv50 of the silicon-based material is 2 ≤ L / Dv50 ≤ 10.

[0025] Specifically, the ratio of the depth h of the recess 21 to the particle size Dv50 of the silicon-based material is less than or equal to 3.5 (i.e., 1≤h / Dv50≤3.5). h / Dv50 is, for example, a range consisting of 1, 1.3, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, 3.4, 3.5, or any two of these ranges. This is beneficial in balancing the improvement of battery thermal safety and low-temperature cycle performance while avoiding excessive energy density loss of the negative electrode due to an excessively large width of the recess 21, thus maintaining a high energy density of the battery.

[0026] In some instances, the ratio of the depth h of the recess 21 to the particle size Dv50 of the silicon-based material is 1 ≤ h / Dv50 ≤ 3.

[0027] In some instances, the ratio of the depth h of the recess 21 to the particle size Dv50 of the silicon-based material is 2 ≤ h / Dv50 ≤ 3.

[0028] In some embodiments, the particle size Dv50 of the silicon-based material can be 5μm to 30μm, for example, a range of 5μm, 8μm, 10μm, 13μm, 15μm, 18μm, 20μm, 23μm, 25μm, 28μm, 30μm or any combination thereof.

[0029] In this embodiment of the disclosure, the particle size Dv50 of the silicon-based material represents the particle size that reaches 50% of the volume accumulation of the silicon-based material particles from the smallest particle size side in the volume-based particle size distribution. It can be measured by conventional methods in the art, such as by laser particle size analyzer.

[0030] In some embodiments, the width L of the recess 21 can be 15μm to 150μm, for example, a range of 15μm, 20μm, 250μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 120μm, 140μm, 150μm or any combination thereof, which is beneficial to further improve the thermal safety and low-temperature cycle performance of the battery.

[0031] In some embodiments, the width L of the recess 21 can be 50 μm to 150 μm.

[0032] In some embodiments, the depth h of the recess 21 can be 5μm to 30μm, for example, a range of 5μm, 8μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 22μm, 25μm, 27μm, 30μm or any combination thereof, which is beneficial for further improving the thermal safety and low-temperature cycle performance of the battery.

[0033] In some embodiments, the depth h of the recess 21 can be 10 μm to 30 μm.

[0034] In this disclosure, the width L and depth h of the recess can be obtained by the following method: After discharging the lithium-ion secondary battery to 0% SOC, the negative electrode is disassembled and removed. It is then soaked in dimethyl carbonate (DMC) solvent for 12 hours, followed by rinsing with DMC to remove lithium salts adhering to the electrode. A 3D profilometer is used for measurement. The depths of 20 non-adjacent recesses are measured along the electrode width direction. Outliers (measurements deviating from the mean by more than two standard deviations) are removed, and the average value is taken as the h value. The depths of 20 non-adjacent recesses are measured along the electrode width direction. Outliers (measurements deviating from the mean by more than two standard deviations) are removed, and the average value is taken as the L value.

[0035] Specifically, the surface of the negative electrode coating 2 may be provided with a recess 21 (i.e., the recess 21 is continuously provided on the surface of the negative electrode coating 2), or, as shown in Figures 1 to 3, the surface of the negative electrode coating 2 is provided with at least two recesses 21. These recesses 21 may be distributed along the first direction x (as shown in Figure 2), or along the second direction y, or some recesses 21 may be distributed along the first direction x and some recesses 21 may be distributed along the second direction y.

[0036] As shown in Figures 1 to 3, at least some of the recesses 21 are distributed along the first direction x. Two adjacent recesses 21 in the first direction x are separated by the negative electrode coating 2. The distance between two adjacent recesses 21 in the first direction x (i.e., the distance between two adjacent recesses 21 in the first direction x) ΔL > 0.

[0037] Specifically, the surface of the negative electrode coating 2 may include at least one set of recesses 210, each set of recesses 210 including at least two recesses 21 distributed along the first direction x. When the number of recesses 210 is at least two (i.e. the surface of the negative electrode coating includes at least two sets of recesses), these recesses are distributed along the second direction y.

[0038] For example, as shown in FIG1, the surface of the negative electrode coating 2 includes two sets of recesses 210; or, as shown in FIG2, the surface of the negative electrode coating 2 has a set of recesses 210.

[0039] In some embodiments, in two adjacent recess groups, the distance w between a recess 21 in one recess group and a recess 21 in another recess group in the second direction y is less than or equal to 1 mm (i.e., w ≤ 1 mm).

[0040] In two adjacent recess groups, a recess 21 in one recess group may or may not be connected to the recess 21 in the other recess group that is closest to it. When the two recesses 21 are connected, the gap (distance in the second direction y) w between them is approximately zero. When the two recesses 21 are not connected, the distance w in the second direction y between a recess 21 in one recess group and a recess 21 in the other recess group is the shortest distance between the edge lines of any recess in one recess group and the recess in the other recess group that is closest to it.

[0041] Referring again to Figures 1 to 3, the width direction of the recesses 21 is basically parallel to the first direction x, and the length direction (extension direction) of these recesses 21 is basically perpendicular to the first direction x.

[0042] Referring again to Figures 1 to 3, the distance between two adjacent recesses 21 in the first direction x is ΔL > 0. The negative electrode coating 2 has a first side 101 and a second side 102 opposite to each other in the first direction x. The distance ΔL1 between the recess 21 closest to the outer edge of the first side 101 of the negative electrode coating 2 and the outer edge of the first side 101 of the negative electrode coating 2 is less than or equal to the distance ΔL between two adjacent recesses 21 (ΔL1 ≤ ΔL). The distance ΔL2 between the recess 21 closest to the outer edge of the second side 102 of the negative electrode coating 2 and the outer edge of the second side 102 of the negative electrode coating 2 is less than or equal to ΔL (ΔL2 ≤ ΔL). This makes the recesses 21 arranged at a distance ΔL on the entire surface of the negative electrode coating 2, which is more conducive to the rapid discharge of gas generated in the negative electrode sheet, and further improves the thermal safety and low-temperature cycle performance of the battery.

[0043] The distance ΔL between two adjacent recesses 21 in the first direction x refers to the shortest distance between the edge lines of the two adjacent recesses 21 in the first direction x, which is also the distance between two adjacent recesses 21 in each recess group.

[0044] In some embodiments, the distance ΔL between two adjacent recesses 21 in the first direction x can be 0.8mm to 5mm, for example, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.7mm, 1.9mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm or any combination thereof, which is beneficial for forming an exhaust channel on the surface of the negative electrode sheet, and further improves the thermal safety and low-temperature cycling performance of the negative electrode sheet.

[0045] In this embodiment, a laser can be used to create a recess 21 with a preset shape and parameters such as thickness, width, length and spacing on the surface of the negative electrode coating 2. Specifically, the thickness and other parameters of the formed recess 21 can be adjusted by controlling parameters such as laser intensity. These control methods are conventional operations in the field and will not be described in detail.

[0046] Specifically, the recess 21 can be a hole or a groove, etc. Preferably, the recess 21 is a linear groove 21, that is, the projection of the recess 21 on the negative electrode current collector 1 is strip-shaped (as shown in Figures 1 and 2). Specifically, it can be a rectangle (as shown in Figure 2) or other regular or irregular shapes.

[0047] Referring again to Figures 1 and 2, when the surface of the negative electrode coating 2 is provided with at least two recesses 21, each recess 21 is a linear groove, and its projection on the negative electrode current collector 1 is basically rectangular. The length direction (extension direction) of these recesses 21 is basically parallel to each other, specifically parallel to the second direction y. The width direction of these recesses 21 is basically parallel, and basically parallel to the first direction x.

[0048] As shown in Figure 2, the recess 21 can be a complete continuous groove, that is, the laser is used to continuously drill holes on the surface of the negative electrode coating 2 along the extension direction of the preset linear groove to form a continuous groove (at this time, a set of recesses is formed on the surface of the negative electrode coating 2).

[0049] Alternatively, when using a laser to drill holes on the surface of the negative electrode coating 2, the drilling is not continuous, but intermittent. For example, as shown in Figure 1, in the second direction y, the upper half of the recess 21 is drilled first (the recess 21 in one recess group), and then the lower half of the recess 21 (the recess 21 in another recess group) is drilled. These two recesses 21 can be basically connected or not connected (gap w≤1mm), which is equivalent to a total recess that runs through the entire surface of the negative electrode coating 2 in the second direction y (i.e., the total recess is formed by splicing multiple recesses 21). At this time, the surface of the negative electrode coating 2 includes at least two groups of recesses.

[0050] Generally, when forming a recess 21 by laser, due to limitations of laser equipment and laser operation process, it is usually necessary to drill multiple times in the area of ​​the preset recess 21 (each drilling forms a recess 21), so that at least two sets of recesses are formed on the surface of the negative electrode coating 2. This can improve the thermal safety and low-temperature cycling performance of the negative electrode sheet, and at the same time adapt to the laser drilling process, which is conducive to the formation of the recess 21.

[0051] Specifically, as shown in Figures 1 and 2, the second direction y, the length direction of the recess 21, the width direction of the negative electrode coating 2, the width direction of the negative electrode current collector 1, and the width direction of the negative electrode sheet are basically parallel to each other, and the first direction x, the width direction of the recess 21, the length direction of the negative electrode coating 2, the length direction of the negative electrode current collector 1, and the length direction of the negative electrode sheet are basically parallel to each other.

[0052] Furthermore, as shown in Figure 3, the recess 21 extends from the surface of the negative electrode coating 2 into the interior of the negative electrode coating 2. The depth direction of the recess 21 can be basically parallel to the third direction z. The third direction z, the thickness direction of the negative electrode coating 2, the thickness direction of the negative electrode current collector 1, and the thickness direction of the negative electrode sheet are parallel to each other.

[0053] Generally, as shown in Figure 3, the depth of the recess 21 is less than the thickness of the negative electrode coating 2, that is, the recess 21 does not penetrate the negative electrode coating 2 in the thickness direction of the negative electrode coating 2, that is, there is a negative electrode coating 2 between the recess 21 and the negative electrode current collector 1.

[0054] Further research showed that the above-mentioned negative electrode can meet the requirements. Where h is the depth of the recess 21 in mm; L is the width of the recess 21 in mm; and e is the elongation at break of the negative electrode current collector 1, that is, It helps improve the thermal safety and low-temperature cycle performance of batteries.

[0055] Research has shown that using lasers to form recesses 21 on the surface of the negative electrode coating results in a larger elongation at break (fracture elongation) of the negative electrode current collector 1, which in turn can withstand greater maximum stress and thus higher laser intensity. This leads to a larger area (h×L) of the recesses 21 formed on the surface of the negative electrode coating 2. Increasing the lateral surface area of ​​the recesses 21 (the lateral surface area inside a single recess) helps improve the contact distance between the electrolyte and the silicon-based material, enhances the fluidity of the electrolyte at high and low temperatures, accelerates ion transport, and improves the low-temperature cycle performance of the battery. However, if the lateral surface area of ​​the recesses 21 is too large, it can also lead to excessive unevenness on the surface of the negative electrode coating 2, affecting its bonding strength with the separator in the battery, resulting in a larger ion transport path, and consequently affecting the battery's low-temperature cycle performance. Therefore, considering these factors comprehensively, the elongation at break (e), the depth (h), and the width (L) of the recesses 21 are synergistically controlled to meet the following requirements. While maintaining the high strength of the negative electrode current collector 1, the area of ​​the recess 21 can be increased, thereby improving the contact distance between the electrolyte and the silicon-based material, increasing the fluidity of the electrolyte at high and low temperatures, accelerating ion transport, and improving the low-temperature cycle performance of the battery. At the same time, it can avoid the problem of uneven surface of the negative electrode coating 2 caused by the excessively large side area of ​​the recess 21, and is conducive to withstanding the unevenness caused by the recess, improving the bonding strength between the negative electrode sheet and the separator in the battery, strengthening the integration of the negative electrode current collector 1, the negative electrode coating 2 and the separator in the battery, further improving the ion transport speed, and thus further improving the low-temperature cycle performance of the battery.

[0056] For example, It can be a range consisting of 0.008, 0.009, 0.01, 0.015, 0.02, 0.025, 0.03, 0.032, 0.035, 0.04, 0.07, 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3, or any two of them.

[0057] In some embodiments, the elongation at break e of the negative electrode current collector 1 can be 0.5% to 5% (i.e. 0.5% ≤ e ≤ 5%), for example, a range of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any two of these.

[0058] Specifically, the negative current collector 1 may include copper foil, for example, it may also include carbon-coated copper foil and / or composite copper foil, wherein the composite copper foil may include a polymer layer and a copper metal layer present on the surface of the polymer layer, and copper metal layers are usually present on opposite sides of the polymer layer, and the copper metal layer and the polymer layer are stacked; the carbon-coated copper foil is usually a copper foil with a carbon layer intermittently coated on the surface of the copper foil, and the carbon coating can be performed on the surface of the copper foil by conventional equipment and processes in the art such as gravure rollers and skip coating equipment to form carbon-coated copper foil, and the embodiments disclosed herein do not impose any particular limitation on this.

[0059] In addition, the negative electrode can meet the requirements. Where A is the weight loss rate of the negative electrode coating 2 in the TG process within the range of 200℃ to 600℃; h is the depth of the recess 21, in μm; and f is the dyne value of the negative electrode current collector 1, in dynes, i.e. This is beneficial for further improving the structural stability and electrochemical performance of the negative electrode.

[0060] For example, It can be a range consisting of 0.1, 0.12, 0.15, 0.2, 0.3, 0.4, 0.45, 0.48, 0.5, 0.55, 0.6, 0.62, or any two of them.

[0061] Specifically, A represents the thermogravimetric parameter of the negative electrode coating 2, which is mainly related to the thermal decomposition of organic materials such as the negative electrode binder and negative electrode thickener in the negative electrode coating 2. Research and analysis show that during the thermogravimetric analysis of the negative electrode coating 2, after the temperature reaches 600℃, a portion (approximately 60% of the total mass of the organic materials) of the organic materials such as the negative electrode binder and negative electrode thickener is burned off, while the remaining portion (approximately 40% of the total mass of the organic materials) exists in the sintered negative electrode coating 2 as solid carbon residue. Therefore, A / 0.6 is essentially equal to the mass percentage of organic materials such as the binder and negative electrode thickener in the negative electrode coating 2. Correspondingly, 1-A / 0.6 is essentially equal to the sum of the mass percentages of the negative electrode active material and other materials such as the negative electrode conductive agent in the negative electrode coating 2.

[0062] Research shows that when forming the recess 21 on the surface of the negative electrode coating 2, the depth h of the recess 21 is mainly increased by increasing the laser intensity. However, when increasing the laser intensity, it is necessary to ensure strong adhesion between the negative electrode coating 2 and the negative electrode current collector 1 to avoid large gaps between them or even the negative electrode coating 2 peeling off completely from the surface of the negative electrode current collector 1. Therefore, considering these influencing factors, the depth h of the recess 21, the thermogravimetric parameter A of the negative electrode coating 2, and the dyne value f of the negative electrode current collector 1 are synergistically controlled to meet the requirements. It is beneficial to form a recess 21 on the surface of the negative electrode coating 2, which can improve the thermal safety and low-temperature cycle performance of the battery, while maintaining a large adhesion between the negative electrode coating 2 and the negative electrode current collector 1, and avoiding situations such as large gaps between the negative electrode coating 2 and the negative electrode current collector 1, or even the negative electrode coating 2 falling off the surface of the negative electrode current collector 1 in one piece.

[0063] In some embodiments, the dyne value of the negative electrode current collector 1 can be 30 to 50 dynes, for example, a range of 35, 37, 39, 40, 42, 44, 45 or any two of these, which is beneficial for further improving the thermal safety and low-temperature cycle performance of the battery.

[0064] In some embodiments, the dyne value of the negative electrode current collector 1 can be 35 (dynes) to 45 (dynes).

[0065] In addition, A is the thermogravimetric parameter of the negative electrode coating 2, which is mainly related to the type, composition and content of organic materials such as negative electrode binder and negative electrode thickener in the negative electrode coating 2. These parameters of organic materials such as negative electrode binder and negative electrode thickener will affect the adhesion between the negative electrode coating 2 and the negative electrode current collector 1, as well as the adhesion between particles in the negative electrode coating 2 (the particles in the negative electrode coating 2 are mainly negative electrode active material particles (such as silicon-based material particles and graphite) and negative electrode conductive agent particles). At the same time, the negative electrode coating 2 is formed on the surface of the negative electrode coating 2 by using a laser. The negative electrode coating 2 at the recess 21 will be removed, which will reduce the areal capacity of the negative electrode coating 2. Therefore, if the spacing ΔL between adjacent recesses 21 is too small (i.e. the recesses 21 are too dense), it will cause excessive loss of areal capacity of the negative electrode sheet and affect the energy density of the battery. In addition, if the silicon doping amount B is too small, it will also affect the energy density of the battery. Taking into account factors such as the adhesion between the negative electrode coating 2 and the negative electrode current collector, the adhesion between particles in the negative electrode coating 2, the areal capacity of the negative electrode sheet, and the energy density of the battery, the optimal negative electrode sheet can meet the requirements. Where △L is the distance between two adjacent recesses 21, specifically the distance between two adjacent recesses in the first direction x, in mm; A is the weight loss rate of the negative electrode coating 2 in the TG process within the range of 200℃ to 600℃; B is the mass ratio of silicon-based material to graphite (i.e., B is the silicon doping amount, which can be understood as the proportion of silicon content in the negative electrode active material), that is, This helps to improve the problems of severe gas generation, poor thermal safety, and poor low-temperature cycling performance caused by side reactions between silicon-based materials and electrolytes in negative electrodes, while maintaining the high capacity and structural stability of negative electrodes.

[0066] For example, It can be a range consisting of 4, 8, 10, 12, 15, 20, 50, 80, 100, 110, 120, 130, 150, 160 or any two of them.

[0067] In this embodiment of the disclosure, a conventional thermogravimetric analyzer in the art can be used to perform thermogravimetric analysis on the negative electrode coating 2. Specifically, TGA analysis can be performed to measure its weight loss rate A in the range of 200℃ to 600℃ during thermal decomposition.

[0068] In specific implementation, the negative electrode coating 2 material (powder) can be heated from room temperature to 900℃±30℃ at a heating rate of 5℃ / min±2℃ / min under an inert atmosphere (such as nitrogen). The initial weight m0 is the powder weight at 200℃ and the initial weight m1 is the powder weight at 600℃. Then, the weight loss rate of the negative electrode coating 2 in the 200℃~600℃ range during thermal decomposition (i.e., the percentage reduction in weight of the negative electrode coating 2 in the 200℃~600℃ range) A=(m1-m0) / m0.

[0069] Generally, during thermogravimetric analysis, a corresponding thermogravimetric curve can be obtained. This curve can be a curve showing the change of powder weight with temperature (with temperature on the horizontal axis and powder weight on the vertical axis). The powder weight at different temperatures can be directly obtained from the thermogravimetric curve, and then the weight loss rate A can be obtained according to A = (m1-m0) / m0. Alternatively, the thermogravimetric curve can be a curve showing the change of weight loss rate with temperature, and the weight loss rate A can be obtained from this curve.

[0070] The negative electrode coating 2 material (powder) can be obtained through the following process: disassemble the battery and remove the negative electrode sheet; immerse the negative electrode sheet in a solvent (such as water) for 2 hours or more (until the negative electrode coating 2 can automatically detach from the negative electrode current collector 1) so that the negative electrode coating 2 can be removed from the negative electrode current collector 1 (the negative electrode coating 2 material enters the solvent to form a mixture), then remove the negative electrode current collector 1 from the mixture, and then dry the mixture (i.e. remove the solvent), specifically by baking at 80°C for about 2 hours to obtain the negative electrode coating 2 material (powder).

[0071] In some embodiments, the weight loss rate A of the negative electrode coating 2 in the TG process in the range of 200°C to 600°C can be 0.3wt% to 3wt% (i.e., 0.5wt% ≤ A / 0.6 ≤ 5wt%), and the weight loss rate A is, for example, a range of 0.3wt%, 0.5wt%, 0.8wt%, 1wt%, 1.3wt%, 1.5wt%, 1.8wt%, 2wt%, 2.3wt%, 2.5wt%, 2.8wt%, 3wt%, or any combination thereof.

[0072] Specifically, the negative electrode binder in the negative electrode coating 2 may include one or more of polyacrylic acid (PAA), polyacrylate, styrene-butadiene rubber (SBR), and polyacrylonitrile (PAN), and the polyacrylate may include lithium polyacrylate and / or sodium polyacrylate, etc.

[0073] When the negative electrode binder in the negative electrode coating 2 includes PAA, it can maintain the high adhesion between the negative electrode coating 2 and the negative electrode current collector 1, while enhancing the adhesion between particles in the negative electrode coating 2 (the particles in the negative electrode coating 2 are generally negative electrode active material particles (such as silicon-based material particles, graphite particles, etc.) and negative electrode conductive agent particles), and suppress the expansion of silicon-based material particles.

[0074] Specifically, the negative electrode thickener in the negative electrode coating 2 may include carboxymethyl cellulose (CMC) thickeners, such as carboxymethyl cellulose salts, such as lithium carboxymethyl cellulose (CMC-Li) and / or CMC-Na.

[0075] In this embodiment of the present disclosure, a negative electrode coating 2 can be provided on one side surface of the negative electrode current collector 1, or a negative electrode coating 2 can be provided on both sides of the negative electrode current collector 1 (both sides of the negative electrode current collector 1); when a negative electrode coating 2 is provided on both sides of the negative electrode current collector 1, the above-mentioned recess 21 can be provided on the negative electrode coating 2 on both sides.

[0076] This disclosure also provides a battery including the above-described negative electrode sheet, which has advantages corresponding to the above-described negative electrode sheet, and will not be described in detail here.

[0077] Specifically, the battery includes a cell, which includes the aforementioned negative electrode, positive electrode, and a separator located between the positive and negative electrode. The separator separates the positive and negative electrode to prevent the positive and negative electrode from coming into contact and short-circuiting.

[0078] The positive electrode, separator, and negative electrode can be bonded together in sequence (i.e., the positive electrode and separator are bonded together, and the negative electrode and separator are bonded together). In practice, the positive electrode, separator, and negative electrode can be placed in sequence and then hot-pressed together to heat-press them into one piece.

[0079] Specifically, the battery cell can be a wound battery cell (wound core), meaning that both the positive and negative electrode plates have wound structures. The positive electrode plate includes multiple first straight sections and a first bent section connecting two adjacent first straight sections. The number of first bent sections is typically at least one, but can be multiple. The positive electrode plate is bent through the first bent sections to form a wound structure. The negative electrode plate includes multiple second straight sections and a second bent section connecting two adjacent second straight sections. The number of second bent sections is typically at least one, but can be multiple. The negative electrode plate is bent through the second bent sections to form a wound structure.

[0080] In practice, the positive electrode, separator, and negative electrode can be placed in sequence, and the resulting stacked structure can be wound up and then hot-pressed to integrate the positive electrode, separator, and negative electrode into a single unit, forming a wound battery cell.

[0081] According to further research by the inventors, the battery can meet the following requirements. Where s is the tensile strength of the diaphragm, expressed in kgf / cm². 2 h is the depth of the recess 21, in cm; L is the width of the recess 21, in cm. This ensures the tightness of the contact interface between the separator and the negative electrode, preventing gaps caused by the presence of the recess 21. It also ensures the separator has sufficient tensile strength to allow it to be fully embedded in the recess 21 without breakage (e.g., during the hot pressing process described above, ensuring the separator is fully embedded in the recess 21 without breakage). Furthermore, it improves the elongation of the negative electrode and the separator, preventing breakage of the separator and electrode due to stress concentration in the cell (especially the wound core). It also mitigates the expansion of the silicon-based material in the first x direction and the second y direction, preventing separator breakage and puncture due to silicon expansion, thereby further improving battery safety and other performance characteristics.

[0082] For example, It can be 0.5×10 8 1×10 8 1.2×10 8 1.5×10 8 2×10 8 2.5×10 8 3×10 8 4×10 8 5×10 8 6×10 8 6.5×10 8 7×10 8 8×10 8 9×10 8 or a range consisting of any two of them.

[0083] In some embodiments, the tensile strength s of the diaphragm can be 500 kgf / cm. 2 ~3000kgf / cm 2 For example, 500 kgf / cm 2 800kgf / cm 2 1000kgf / cm 2 1300kgf / cm 21500kgf / cm 2 1800kgf / cm 2 2000kgf / cm 2 2300kgf / cm 2 2500kgf / cm 2 2800kgf / cm 2 3000 kgf / cm 2 or a range consisting of any two of them.

[0084] Generally, a separator includes a base membrane and an adhesive layer disposed on both the front and back surfaces of the base membrane. The separator is bonded to the positive and negative electrode plates through the adhesive layer on its surface. A ceramic layer, such as an alumina layer, may also be disposed between the base membrane and the adhesive layer, but it is not limited to this.

[0085] In practice, parameters such as the tensile strength of the diaphragm can be adjusted by modifying the production process and material of the base membrane. These are all standard practices in the field and will not be elaborated further.

[0086] For example, the base membrane can be a polypropylene (PP) membrane, a polyethylene (PE) membrane, a polypropylene / polyethylene (PP / PE) bilayer composite membrane, a polyimide electrospun membrane 3 (PI), a polypropylene / polyethylene / polypropylene (PP / PE / PP) trilayer composite membrane, or a cellulose nonwoven membrane, or other conventional membrane materials in the field.

[0087] In addition, the positive electrode includes a positive current collector and a positive coating on the surface of the positive current collector. Specifically, the positive coating can be provided on both the positive and negative surfaces of the positive current collector.

[0088] Specifically, the positive electrode coating may include a positive electrode active material layer, which includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The positive electrode active material may include conventional positive electrode active materials in the art, such as lithium-containing positive electrode active materials, including at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, ternary materials, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, and lithium-rich manganese-based materials. The ternary materials may include lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide, etc.

[0089] Wherein, based on the total mass of the positive electrode active material layer, the mass fraction of the negative electrode active material can be 70% to 99% (e.g., 70%, 73%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 93%, 95%, or 99%), the mass fraction of the conductive agent can be 0.5% to 15% (e.g., 0.5%, 1%, 3%, 5%, 8%, 10%, 13%, or 15%), and the mass fraction of the binder can be 0.5% to 15% (e.g., 0.5%, 1%, 3%, 5%, 8%, 10%, 13%, or 15%), but is not limited thereto.

[0090] In some embodiments, the positive electrode coating may contain aluminum, specifically a compound containing aluminum (aluminum compound) to make the positive electrode coating contain aluminum.

[0091] Specifically, the positive electrode active material contains aluminum, which may contain aluminum compounds, thus making the positive electrode coating contain aluminum.

[0092] In some embodiments, the positive electrode active material includes lithium cobalt oxide containing aluminum (i.e., lithium cobalt oxide doped with aluminum).

[0093] Research shows that the recessed portion 21 on the surface of the negative electrode coating 2 reduces the polarization of the negative electrode surface and interior, increasing the negative electrode potential. Under a constant voltage, the positive electrode potential also increases. This means that under the same voltage system, the positive electrode requires a material with higher voltage stability. Furthermore, the negative electrode is a silicon-doped negative electrode, which suffers from severe side reactions between silicon-based materials and electrolyte components, leading to gas and heat generation problems. This exacerbates the damage to the entire cell system, specifically causing structural changes in positive electrode active materials such as lithium cobalt oxide, resulting in irreversible damage and affecting battery performance. Considering all these factors, the optimal control for the battery is to satisfy the following relationship: Where r is the aluminum doping content of the positive electrode coating, which is the concentration of aluminum in the standard solution measured according to the test method in GB / T 30902-2014, in ppm; B is the mass ratio of silicon-based material to graphite; h is the depth of recess 21, in μm, that is, By synergistically controlling the aluminum content r in the positive electrode coating, the silicon doping amount B in the negative electrode coating 2, and the depth h of the recess 21 on the surface of the negative electrode coating 2 to satisfy the above-mentioned relationship range, it is beneficial for ions to shuttle between the positive and negative electrodes, improve the low-temperature performance of the battery, and at the same time, it is beneficial to remove the gas generated in the negative electrode sheet due to the side reaction between silicon-based materials and electrolyte, solve the gas generation and heat generation problems caused by these factors, avoid damage to the entire cell system, and suppress the structural changes of positive electrode active materials such as lithium cobalt oxide and the irreversible damage caused therefrom.

[0094] For example, It can be 1000, 2000, 2600, 3000, 3250, 5000, 6500, 10000, or 1.3 × 10⁻⁶. 4 1.6×10 4 1×10 5 1.6×10 5 1.9×10 5 1.95×10 5 2×10 5 .

[0095] In some specific embodiments, the battery satisfies the following relationship: This approach helps to improve the battery's low-temperature performance and safety while also increasing its energy density and other performance characteristics.

[0096] In some specific embodiments, the battery satisfies the following relationship:

[0097] In some specific embodiments, the aluminum doping level r of the positive electrode coating can be 3000ppm to 10000ppm.

[0098] In some specific embodiments, the aluminum doping amount r of the positive electrode coating can be 5000ppm to 10000ppm (i.e., 5000ppm≤r≤10000ppm), for example, a range of 5000ppm, 5500ppm, 5800ppm, 6000ppm, 6300ppm, 6500ppm, 6800ppm, 7000ppm, 8000ppm, 9000ppm, 10000ppm or any two of these.

[0099] In this embodiment, the aluminum doping amount r of the positive electrode coating is the concentration of aluminum in a standard solution measured according to the test method in GBT 30902-2014. Specifically, the battery can be disassembled, the positive electrode sheet can be removed, and the positive electrode coating (powder) can be removed from the positive electrode sheet. Then, the positive electrode coating (powder) sample can be prepared into a standard solution according to GBT 30902-2014 according to the method in GBT 30902-2014. The concentration of the standard solution can then be tested according to the test method in GBT 30902-2014. The concentration of the standard solution obtained is the aluminum doping amount r of the positive electrode coating.

[0100] In this embodiment of the disclosure, the battery also includes a package for encapsulating the battery cell. The package may include a flexible packaging film (i.e., the battery is a flexible packaged battery), which can be a flexible packaging film formed from conventional flexible packaging materials in the art. For example, the package may include an aluminum-plastic film, but is not limited thereto.

[0101] In this embodiment of the disclosure, the battery further includes an electrolyte, which is injected into the package to wet the battery cell.

[0102] The embodiments disclosed herein may employ conventional electrolytes in the art. For example, the electrolyte includes a solvent, a solute, and additives. Specifically, the electrolyte may be a non-aqueous electrolyte. The solvent may include organic solvents, specifically carbonate solvents, such as one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC), and propyl propionate (PP). The additives may include one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and 1,3-propanesulfonyl lactone (PS). The solute may include lithium salts, such as lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0103] In this embodiment of the disclosure, the positive electrode binder in the positive electrode coating can be a conventional bonding material in the art, such as one or more of polyvinylidene fluoride (PVDF), a copolymer of PVDF and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose (CMC), polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and styrene-butadiene rubber (SBR).

[0104] In this embodiment of the disclosure, the positive electrode conductive agent in the positive electrode coating and the negative electrode coating 2 can be a conventional conductive material in the art, such as one or more of carbon nanotubes (carbon tubes), carbon black (SP), acetylene black, and graphene.

[0105] In this embodiment of the disclosure, the positive electrode sheet can be prepared by conventional methods in the art, such as coating. For example, the preparation process of the positive electrode sheet may include: placing materials such as positive electrode active material, positive electrode conductive agent and positive electrode binder in a solvent to prepare a positive electrode slurry, the solvent of which includes, for example, N-methylpyrrolidone (NMP), then coating the positive electrode slurry onto the surface of the positive electrode current collector, and after drying, rolling and other processes, forming a positive electrode active material layer on the surface of the positive electrode current collector to obtain the positive electrode sheet.

[0106] In this embodiment, a negative electrode coating 2 can be formed on the surface of the negative electrode current collector 1 using conventional methods in the art, such as coating. Then, a laser is used to drill holes in the surface of the negative electrode coating 2 to obtain a negative electrode sheet. For example, the process of obtaining a negative electrode sheet may include: preparing a negative electrode slurry by placing materials such as a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder in a solvent, such as water; applying the negative electrode slurry to the surface of the negative electrode current collector 1; and after drying, rolling, and other processes, forming a negative electrode active material layer on the surface of the negative electrode current collector 1; then, forming a recess 21 in a predetermined area on the surface of the negative electrode active material layer by laser drilling to obtain a negative electrode sheet. In this embodiment, a conventional laser drilling machine in the art is used for laser drilling.

[0107] In this embodiment of the present disclosure, the battery can be manufactured according to conventional methods in the art. For example, the positive electrode 22, the separator 23, and the negative electrode 21 are stacked in sequence and hot-pressed together, then wound to form a core, and then packaged with a package body. After liquid injection (injecting electrolyte into the package body), formation, capacity testing, OCV (testing open circuit voltage), and other processes, the battery is obtained. These steps / processes are all conventional operations in the art, and the present disclosure does not impose any special restrictions on them, and will not be described in detail.

[0108] In some embodiments, the battery is a lithium-ion secondary battery.

[0109] The present disclosure will be further described below through specific embodiments. In the following embodiments, the aluminum doping amount r of the positive electrode active material layer is the concentration of aluminum element in the standard solution measured according to the test method in GBT 30902-2014; the copper foil used is carbon-coated copper foil.

[0110] Example 1

[0111] 1. Preparation of positive electrode sheet

[0112] Lithium cobalt oxide, SP, and PVDF were mixed in a mass ratio of 97.6:1.3:1.1, and NMP was added. The mixture was stirred until homogeneous to prepare a positive electrode slurry.

[0113] The positive electrode slurry is coated on both sides of the aluminum foil. After baking and rolling, a positive electrode active material layer is formed on both sides of the aluminum foil, thus obtaining the positive electrode sheet.

[0114] 2. Preparation of negative electrode sheet

[0115] The negative electrode active material, SP, CMC-Li, and PAA were mixed in a mass ratio of 97:0.1:0.4:2.5, and deionized water was added to prepare a negative electrode slurry. The negative electrode active material included graphite and silicon carbide, and the mass ratio of silicon carbide to graphite (silicon doping) was 10%.

[0116] The negative electrode slurry is coated on both sides of the carbon-coated copper foil. After baking and rolling, a negative electrode active material layer is formed on both sides of the carbon-coated copper foil (the thickness of the negative electrode active material layer on each side is about 45μm).

[0117] A linear recess (not penetrating the negative electrode active material layer) is created on the surface of the negative electrode active material layer on each side using a laser to produce a negative electrode sheet.

[0118] 3. Battery assembly

[0119] The positive and negative electrode sheets are cut according to a preset shape and size. Then, the positive electrode sheet, separator and negative electrode sheet are stacked in sequence and wound into a core and hot-pressed together. Then, the core is sealed with aluminum-plastic film. After baking, electrolyte injection, formation, secondary sealing, sorting and OCV processes, a lithium-ion battery is obtained. The lithium salt in the electrolyte is LiFP6.

[0120] As shown in Figures 1 and 3, multiple recesses 21 are formed on the surface of the negative electrode active material layer. These recesses 21 form two sets of recess groups 210. These two sets of recess groups 210 are distributed along the width direction of the negative electrode active material layer, and the recesses 21 in each set of recesses 210 are arranged along the length direction of the negative electrode active material layer. The recesses 21 in each set of recesses 210 are arranged at a spacing ΔL on the entire surface of the negative electrode active material layer. These recesses 21 are all linear recesses, and the length direction of each recess 21 is basically parallel to the width direction of the negative electrode active material layer. In the two sets of recesses 210, the distance w between the recesses 21 in one set of recesses and the recesses 21 in the other set of recesses in the width direction of the negative electrode active material layer is ≤1mm (the length of any recess 21 in one set of recesses 210 and the length of any recess 21 in the other set of recesses 210 are basically equal to the width of the negative electrode active material layer). The width direction of each recess 21 is basically parallel to the length direction of the negative electrode active material layer.

[0121] Examples 2 to 37: The differences from Example 1 are shown in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, all other conditions are the same.

[0122] Comparative Example 1: The difference from Example 1 is that no recesses are formed on the surface of the negative electrode active material layer (i.e., during the preparation of the negative electrode sheet, the negative electrode slurry is coated on both the front and back surfaces of the carbon-coated copper foil, and after baking and rolling, a negative electrode active material layer is formed on both the front and back surfaces of the carbon-coated copper foil, thus obtaining the negative electrode sheet).

[0123] Comparative Example 2: The difference from Example 1 is that the ratio of the width L of the recess to the particle size Dv50 of the silicon-based material is less than 2 (i.e., L / Dv50 < 2), as shown in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the other conditions are the same.

[0124] Comparative Example 3: The difference from Example 1 is that the depth L of the recess is less than the particle size Dv50 of the silicon-based material particles (i.e., L < Dv50), as shown in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the other conditions are the same.

[0125] The negative electrode sheets and batteries of each embodiment and comparative example were tested using the following methods:

[0126] 1. Test of weight loss rate A of negative electrode coating in the TG process within the temperature range of 200℃~600℃.

[0127] (1) Sampling: Disassemble the battery and remove the negative electrode sheet; immerse the negative electrode sheet in water to allow the negative electrode active material layer to fall off the carbon-coated copper foil to obtain a mixed solution; bake the mixed solution at 80°C for 2 hours to remove the solvent and obtain the negative electrode powder.

[0128] (2) TGA test: The negative electrode powder was subjected to a TGA test under a nitrogen atmosphere. During the test, the negative electrode powder was gradually heated from room temperature to 900℃ at a heating rate of 5℃ / min to obtain the thermogravimetric curve. The powder weight at 200℃ was taken as the initial weight m0 and the powder weight at 600℃ was taken as m1. A was calculated according to A=(m1-m0) / m0. The thermogravimetric curves (TGA curves) of Examples 1 and 3 are shown in Figure 4.

[0129] 2. The dyne value f of the negative electrode current collector was tested using a dyne pen.

[0130] 3. Test of elongation at break e of negative electrode current collector: Use a knife to cut the negative electrode current collector into test samples with a width of 15mm and a length of more than 50mm; use a WD-D3 electronic universal testing machine (accuracy grade 0.5, accuracy of ±1% of the indicated value), set the gauge length to 50mm, the speed to 50mm / min, and perform a tensile test on the test samples to measure the elongation at break e of the negative electrode current collector.

[0131] 4. Test of diaphragm tensile strength s: Use a knife to cut the diaphragm into test samples with a width of 15mm and a length of more than 50mm; use a WD-D3 electronic universal testing machine (accuracy grade 0.5, accuracy of ±1% of the indicated value), set the gauge length to 50mm, and the speed to 100mm / min to perform a tensile test on the test samples and measure the tensile strength s of the diaphragm.

[0132] 5. Battery thermal safety test: At room temperature, the battery is charged at a constant current and constant voltage rate of 0.5C to the upper limit voltage (4.48V), and then charged at 0.05C to full charge (100% SOC). The fully charged battery is placed in a high temperature chamber and heated to 130℃ at a heating rate of 5℃ / min. The temperature is then maintained for 1 hour. If the battery cell does not catch fire or explode, it is considered to have passed; otherwise, it is considered to have failed. The pass rate of the 130℃ thermal safety test is recorded. The test results of each embodiment and comparative example are shown in Table 3.

[0133] 6. Low-temperature cycle performance test of the battery (after cycling the battery 50T, discharge it at 0℃ with a low temperature of 0.2C): At room temperature, charge the battery at a constant current and constant voltage rate of 0.5C to the upper limit voltage (4.48V), cut off at 0.05C, let it stand for 5 minutes, discharge it at 0.5C to 3.0V, and cycle it 50T (50 cycles); then charge it at room temperature at a constant current and constant voltage rate of 0.2C to the upper limit voltage (4.48V), cut off at 0.02C, let it stand for 5 minutes, and then discharge it to 3.0V. Discharge the battery at 2C to 3.0V and record the discharge capacity C1. Then charge it at room temperature at 0.2C constant current and constant voltage to the upper limit voltage (4.48V), and then charge it at 0.02C to fully charge (100% SOC). Place the fully charged battery in a 0℃ constant temperature room or constant temperature chamber and let it stand for 2 hours. Then discharge it at 0.2C to 3.0V and record the discharge capacity C2. Calculate the low temperature cycle capacity retention rate according to the low temperature cycle capacity retention rate = C2 / C1. The test results of each embodiment and comparative example are shown in Table 3.

[0134] In each embodiment and comparative example, the width L of the recess, the depth h of the recess, the distance ΔL between two adjacent recesses, the particle size Dv50 of the silicon-based material, the elongation at break of the negative electrode current collector, the ratio of the weight loss A of the negative electrode active material layer in the TG process in the range of 200℃ to 600℃ to 0.6 (A / 0.6), the silicon doping amount B, the dyne value f of the negative electrode current collector, the tensile strength s of the separator, and the aluminum doping amount r are summarized in Tables 1 and 2.

[0135] Table 1 In Table 1, "E+" represents 10 to the power of x. For example, "1.25E+08" means 1.25 × 10⁻⁸. 8 。 / indicates that it does not exist.

[0136] Table 2 / indicates that it does not exist.

[0137] Table 3

[0138] As can be seen from Table 3, compared with Comparative Examples 1 to 3, Examples 1 to 37 have linear grooves (recesses) punched on the surface of the negative electrode active material layer, and the width L, depth h, and silicon-carbon particle size Dv50 of the recesses are controlled to satisfy L / Dv50≥2 and h≥Dv50. This can ensure the battery has a high energy density while also improving the battery's thermal safety and low-temperature cycle performance.

[0139] Furthermore, in Examples 1 to 4, 7, 8, 12, 15, 16, 17, and 20 to 37, the following conditions are met: The weight loss rate A is 0.3wt% to 3wt%, which can further improve the battery's thermal safety and low-temperature cycle performance (thermal safety at 130℃ reaches more than 65%, while the low-temperature cycle capacity retention rate reaches more than 65%), while maintaining the battery's high energy density.

[0140] Among them, in relative terms, in Example 18 In Example 20, h / Dv50 > 3 and L / Dv50 > 10. In Examples 2, 8, 11, 16, 17, 20, 21, and 33-37, L / Dv50 > 10, the energy density loss of the battery is relatively large. Compared with these examples, Examples 1, 3, 4, 7, 12, 15, and 22-32 satisfy 1 ≤ h / Dv50 ≤ 3 and 2 ≤ L / Dv50 ≤ 10, and also have the advantage of high battery energy density.

[0141] Furthermore, it can be seen from the combination of Examples 19 and 23 that, At that time, the battery's thermal safety and low-temperature cycle performance showed a downward trend, and at the same time, in Example 19 Its silicon doping content is low, and the energy density of the battery is lower than that of Example 1. Therefore, considering the battery's energy density, thermal safety, and low-temperature performance, the preferred option is...

[0142] Furthermore, based on Examples 1, 14, 15, 16, and 17, it is evident that if the ratio of silicon doping B to recess depth h in the negative electrode is too small, it will negatively impact the battery's low-temperature cycle performance and, to some extent, its thermal safety performance. (The reason is that a smaller aluminum doping in the positive electrode results in a poor match between the silicon doping B and recess depth h in the negative electrode, leading to lower battery stability and consequently affecting thermal safety.) Conversely, excessive aluminum doping has little effect on improving battery performance and wastes aluminum material. For example, compared to Example 16, the aluminum doping in Example 17... Reaching 2×10 5 It offers virtually no further improvement to the battery's thermal safety and low-temperature cycle performance. Therefore, it is preferable to...

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure, and are not intended to limit them. Although this disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this disclosure.

[0144] The embodiments of this application have been described above. However, this application is not limited to the embodiments described above. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A negative electrode sheet, characterized in that, The device includes a negative electrode current collector and a negative electrode coating on the surface of the negative electrode current collector. The negative electrode coating includes a negative electrode active material, which includes graphite and silicon-based materials. The surface of the negative electrode coating has a recess, the width of which is greater than or equal to the particle size Dv50 of the silicon-based material in a ratio greater than or equal to 2, and the depth of which is greater than or equal to the particle size Dv50 of the silicon-based material.

2. The negative electrode sheet according to claim 1, characterized in that, The negative electrode plate satisfies the following relationship: Where h is the depth of the recess, in mm; L is the width of the recess, in mm; e is the elongation at break of the negative electrode current collector.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, The surface of the negative electrode coating includes at least one set of recesses, and each set of recesses includes at least two recesses distributed along a first direction; Preferably, the surface of the negative electrode coating includes at least two sets of recesses, the at least two sets of recesses being distributed along a second direction, the second direction intersecting the first direction; Preferably, in two adjacent groups of recesses, the distance between a recess in one group and a recess in the other group in the second direction is less than or equal to 1 mm; Preferably, the first direction is parallel to the length direction of the negative electrode coating; Preferably, the second direction is parallel to the width direction of the negative electrode coating.

4. The negative electrode sheet according to any one of claims 1-3, characterized in that, The negative electrode plate satisfies the following relationship: Wherein, △L is the distance between two adjacent recesses, in mm; A is the weight loss rate of the negative electrode coating in the TG process between 200℃ and 600℃; and B is the mass ratio of the silicon-based material to the graphite.

5. The negative electrode sheet according to any one of claims 1-4, characterized in that, The negative electrode sheet satisfies Wherein, A is the weight loss rate of the negative electrode coating in the range of 200℃ to 600℃ during the TG process; h is the depth of the recess in μm; and f is the dyne value of the negative electrode current collector in dynes.

6. The negative electrode sheet according to any one of claims 1-5, characterized in that, The weight loss rate of the negative electrode coating during the TG process in the range of 200℃ to 600℃ is 0.3wt% to 3wt%. And / or, the negative electrode coating includes a negative electrode binder, which includes one or more of polyacrylic acid, polyacrylate, styrene-butadiene rubber, and polyacrylonitrile; And / or, the negative electrode coating includes a negative electrode thickener, which includes a carboxymethyl cellulose thickener; And / or, the mass ratio of the silicon-based material to the graphite is 0.01 to 0.3; And / or, the silicon-based material includes one or more of silicon-carbon materials, silicon-oxygen materials, silicon, and silicon alloys; And / or, the ratio of the width of the recess to the particle size Dv50 of the silicon-based material is 2≤L / Dv50≤20, preferably 2≤L / Dv50≤10; And / or, the ratio of the depth of the recess to the particle size Dv50 of the silicon-based material is 1≤h / Dv50≤3.5, preferably 1≤h / Dv50≤3; And / or, the particle size Dv50 of the silicon-based material is 5 to 30 μm.

7. The negative electrode sheet according to any one of claims 1-6, characterized in that, The width of the recess is 15μm to 150μm, preferably 50μm to 150μm; And / or, the depth of the recess is 5μm to 30μm, preferably 10μm to 30μm. And / or, the depth of the recess is less than the thickness of the negative electrode coating; And / or, the surface of the negative electrode coating is provided with at least two of the recesses, and the distance between two adjacent recesses is 0.8 mm to 5 mm; And / or, the recess includes a hole and / or a groove; And / or, the recess includes a linear groove, preferably, the length direction of the linear groove is parallel to the width direction of the negative electrode coating, and the width direction of the linear groove is parallel to the length direction of the negative electrode coating.

8. The negative electrode sheet according to any one of claims 1-7, characterized in that, The elongation at break of the negative electrode current collector is 0.5% to 5%; And / or, the dyne value of the negative electrode current collector is 30 to 50, preferably 35 to 45; And / or, the negative current collector comprises copper foil.

9. A battery, characterized in that, The negative electrode sheet includes any one of claims 1-8.

10. The battery according to claim 9, characterized in that, The battery also includes a positive electrode and a separator located between the positive electrode and the negative electrode; Preferably, the tensile strength of the diaphragm is 500 kgf / cm. 2 ~3000kgf / cm 2 .

11. The battery according to claim 10, characterized in that, The battery satisfies Where s is the tensile strength of the diaphragm, expressed in kgf / cm². 2 h is the depth of the recess in cm; L is the width of the recess in cm.

12. The battery according to any one of claims 9-11, characterized in that, The battery also includes a positive electrode sheet, the positive electrode sheet includes a positive electrode coating, the positive electrode coating includes a positive electrode active material, and the positive electrode coating contains aluminum. The battery satisfies Where r is the amount of aluminum doping in the positive electrode coating, expressed in ppm; B is the mass ratio of the silicon-based material to the graphite; and h is the depth of the recess, expressed in μm.

13. The battery according to claim 12, characterized in that, The aluminum doping content of the positive electrode coating is 3000ppm≤r≤10000ppm; Preferably, the positive electrode coating comprises a positive electrode active material; Preferably, the positive electrode active material contains the aluminum element; Preferably, the positive electrode active material includes lithium cobalt oxide containing the aluminum element.

14. The battery according to any one of claims 9-13, characterized in that, The battery is a lithium-ion rechargeable battery.

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