Electrode assembly

Abstract

The present application relates to the technical field of batteries. Provided are an electrode assembly and a battery. The electrode assembly comprises: a positive electrode sheet, wherein the positive electrode sheet has a first surface and a second surface which are opposite each other in the direction of thickness, the first surface having a plurality of protrusions, and the second surface having a plurality of recesses respectively corresponding to the protrusions and recessed towards the protrusions; and a separator, which is adhesively bonded to the first surface and the second surface, wherein the adhesive force between the first surface and the separator is N1, and the adhesive force between the second surface and the separator is N2, with N1 and N2 satisfying the relational expression: N1>N2. The embodiments of the present application can optimize the battery performance.

Description

An electrode assembly

[0001] This application claims priority to Chinese Patent Application No. 202411742310.0, filed on November 29, 2024, entitled “An Electrode Assembly”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and more particularly to an electrode assembly. Background Technology

[0003] Lithium-ion batteries (LIBs) currently dominate the portable electronic device battery market due to their high specific energy density, wide temperature range, and long cycle life; lithium iron phosphate and ternary materials are widely used in the market due to their respective characteristics.

[0004] However, during long-term use of the above materials, the electrochemical performance deteriorates significantly, the power performance is not satisfactory, and the capacity retention rate becomes increasingly worse. One reason is that the interlayer compression of the cell is quite severe, making it difficult for the electrolyte to enter, resulting in poor electrolyte wetting.

[0005] On the other hand, under high-temperature formation or high-temperature cycling test conditions, the battery may produce gas (such as hydrogen). If these gases cannot be discharged in time, they will cause the internal pressure of the battery to rise, which may lead to poor interface adhesion between the electrodes and the separator. Poor interface adhesion will hinder the transport of lithium ions, leading to lithium plating, which seriously affects the safety performance of the battery. Summary of the Invention

[0006] This application provides an electrode assembly that can solve the problems of poor electrolyte wetting and interface abnormalities caused by high-temperature gas generation in the electrode assembly.

[0007] This application provides an electrode assembly, including: a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode;

[0008] The positive electrode has a first surface and a second surface that are opposite each other in the thickness direction. The first surface has a plurality of protrusions, and the second surface has a plurality of recesses that correspond to each of the protrusions and are recessed toward the protrusions.

[0009] The diaphragm includes a first diaphragm and a second diaphragm; the first diaphragm is bonded to the first surface; the second diaphragm is bonded to the second surface; the first diaphragm extending beyond the beginning of the positive electrode and the second diaphragm extending beyond the beginning of the positive electrode are bonded together.

[0010] Wherein, the adhesion force between the first surface and the diaphragm is N1, and the adhesion force between the second surface and the diaphragm is N2, wherein N1 and N2 satisfy the following relationship:

[0011] N1>N2.

[0012] According to the electrode assembly described in the first aspect of this application, convex and concave portions are formed on the two surfaces of the positive electrode, resulting in an uneven surface. When the cell expands, the convex portions effectively support the separator, preventing deformation of the separator or the positive electrode due to the expansion stress of the negative electrode. Simultaneously, a space for accommodating electrolyte is formed between the convex portion of the positive electrode and the separator, thereby increasing the electrolyte storage space and improving the wetting ability of the electrolyte in this area, preventing abnormalities such as insufficient electrolyte or poor wetting between the positive electrode and the separator. Furthermore, the concave portions on the positive electrode further expand the electrolyte storage space, enhancing electrolyte wetting and improving the cycle performance and service life of the electrode assembly.

[0013] Furthermore, by setting the adhesion between the surface of the protrusion and the separator to be greater than that between the surface of the depression and the separator, a gas exhaust path is constructed. This allows the gas generated by the electrochemical reaction during high-temperature formation or high-temperature expansion to preferentially escape from areas with weaker adhesion (such as between the depressions and the separator). It is understood that the separator itself has a certain degree of permeability. By forming protrusions and depressions on the positive electrode, the distance between the positive electrode and the separator is increased. At the same time, the adhesion between the surface of the depression and the separator is smaller, which means that the adhesion area between the surface of the depression and the separator is relatively smaller. The more gaps between the surface of the depression and the separator, the more timely the internal pressure of the battery can be released. This reduces the possibility of gas bubbles forming due to gas accumulation inside the cell. Consequently, it reduces the possibility of purple spots caused by abnormal adhesion interfaces between the positive electrode and the separator or between the separator and the negative electrode due to gas generation in the central area of ​​the electrode assembly. This ensures good interfacial contact between the positive electrode and the separator. During cycling, this is conducive to a more uniform current density distribution on the positive electrode and the separator, avoiding uneven lithium metal deposition and the resulting lithium dendrite formation.

[0014] Furthermore, timely discharge of gas through areas with weaker adhesion can also play a role in heat dissipation to a certain extent, which helps maintain the temperature of the positive electrode during cycling, ensuring uniform heat distribution inside the cell. This creates a stable reaction environment inside the cell, preventing further side reactions, thereby improving the battery's cycle performance and extending its lifespan.

[0015] According to one embodiment of the present invention, N1 = (1.01~2)N2.

[0016] According to one embodiment of the present invention, the surface of the protrusion that contacts the diaphragm is an arc surface.

[0017] According to one embodiment of the present invention, the protrusion is spherical or near-spherical, the radius of the protrusion is R1, and the radius of the concave portion is R2; the R1 and the R2 satisfy the relationship: R1 / R2 = 1.01~2.

[0018] According to one embodiment of the present invention, R1 = 0.5mm to 8mm; and / or, R2 = 0.5mm to 8mm; and / or, the height of the end of the protrusion away from the second surface to the surface of the positive electrode is h1; h1 = 3μm to 40μm.

[0019] According to one embodiment of the present invention, a plurality of the protrusions are spaced apart, and the positive electrode includes a straight portion between two adjacent protrusions; the distance between the centers of two adjacent protrusions is L1, and the length of the straight portion between two adjacent protrusions is L2, wherein L1 and L2 satisfy the relationship: L1 / L2 = 1.05~10.

[0020] According to one embodiment of the present invention, L1 = 3mm to 10mm; and / or, L2 = 0.5mm to 8mm.

[0021] According to one embodiment of the present invention, the area of ​​the convex portion is Q1, the area of ​​the concave portion is Q2, and Q1 and Q2 satisfy the relationship: Q1 / Q2 = 1.02 to 1.21; and / or, the projected area of ​​the convex portion in the thickness direction of the positive electrode sheet is S1, the projected area of ​​the concave portion in the thickness direction of the positive electrode sheet is S2, and S1 and S2 satisfy the relationship: S1 / S2 = 1.02 to 1.21.

[0022] According to one embodiment of the present invention, the number of protrusions per unit area of ​​the positive electrode sheet is N, wherein N satisfies the relationship: 2≤N≤25, and / or, the total projected area of ​​each protrusion per unit area in the thickness direction of the positive electrode sheet is S3, wherein the proportion of S3 in the unit area satisfies the relationship: 0.2≤S3≤0.8.

[0023] According to one embodiment of the present invention, the area on the positive electrode sheet where the protrusions are concentrated is a protrusion area, the total area of ​​the protrusion area is S11, the total area of ​​the positive electrode sheet is S, and S11 and S satisfy the relationship: 0.02≤S11 / S≤0.85.

[0024] According to one embodiment of the present invention, the distance between the convex region and the two ends of the positive electrode in the length direction is K, where K = 10 mm to 100 mm; and / or the distance between the convex region and any end edge of the positive electrode in the width direction is M, where M = 5 mm to 30 mm.

[0025] According to one embodiment of the present invention, the positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound to form a core structure, and the electrode assembly includes a main body region and an arc region; the height of the protrusion located in the arc region is less than the height of the protrusion located in the main body region.

[0026] According to one embodiment of the present invention, the separator comprises: a base membrane, the base membrane comprising a multilayer microporous membrane; and a ceramic layer coated on the base membrane, wherein the ceramic layer and the positive electrode are disposed opposite to each other.

[0027] According to one embodiment of the present invention, the metal element content of the first surface is W1, the metal element content of the second surface is W2, and the W1 and the W2 satisfy the relationship: W1>W2; the metal element includes at least one of Al, Si, Ce, Mg, Zr or Ti.

[0028] According to one embodiment of the present invention, the metal element content of the protrusion is W11, the metal element content of the concave portion is W21, and W11 and W21 satisfy the relationship: W11>W21; and / or

[0029] The positive electrode includes a flat portion located between two adjacent protrusions; the metal element content of the protrusions is W11, and the metal element content of the flat portion is W3, wherein W11 and W3 satisfy the relationship: W11>W3; and / or

[0030] The positive electrode includes a flat portion located between two adjacent protrusions; the metal element content of the flat portion is W3, and the metal element content of the concave portion is W21, wherein W211 and W3 satisfy the following relationship:

[0031] W3>W21;

[0032] The metallic element includes at least one of Al, Si, Ce, Mg, Zr, or Ti.

[0033] According to one embodiment of the present invention, the tensile strength of the positive electrode sheet is ≥100MPa, and the ratio of the depth of the recess (μm) to the tensile strength (MPa) of the positive electrode sheet is between 0.05 and 0.2.

[0034] According to one embodiment of the present invention, the diaphragm comprises: the ceramic layer being an inorganic ceramic particle coating, a coating composed of inorganic ceramic particles and PVDF, or a coating composed of inorganic ceramic particles and polymethyl methacrylate and PVDF; wherein,

[0035] The inorganic ceramic particles include one or more of α-Al2O3, γ-Al2O3, Al2O3, SiO2, CeO2, MgAl2O4, ZrO, and TiO2;

[0036] The polymethyl methacrylate has a raised structure distributed in blocks or strips.

[0037] According to one embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes a silicon-carbon composite material and / or a silicon-oxygen composite material. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 is a schematic diagram of the installation structure of an electrode assembly provided in an embodiment of this application;

[0040] Figure 2 is a partial cross-sectional view of the positive electrode in Figure 1;

[0041] Figure 3 is a partial cross-sectional view of the positive electrode in Figure 1.

[0042] Figure 4 is a schematic projection of the convex and concave parts on the positive electrode plate in Figure 1;

[0043] Figure 5 is a schematic diagram of the structure per unit area on the positive electrode sheet in Figure 1;

[0044] Figure 6 is a schematic diagram of the distribution structure of the convex region on the positive electrode in Figure 1;

[0045] Figure 7 is a partial structural schematic diagram of an electrode assembly provided in an embodiment of this application.

[0046] Reference numerals: 100-Positive electrode sheet; 110-First surface; 111-Protrusion; 120-Second surface; 121-Concave portion; 130-Straight portion; 140-Protrusion area; 150-Voiding area; 151-Head voiding area; 152-Tail voiding area; 153-Top voiding area; 154-Bottom voiding area; 155-Taper voiding area; 160-Taper; 200-Separator; 300-Main body area; 400-Circular arc area; 500-Negative electrode sheet. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0048] In related technologies, a battery includes a cell and an electrolyte that wets the cell. The cell consists of a positive electrode, a negative electrode, and several separators. The separators are bonded to the positive electrode and / or the negative electrode, and the separators separate the positive electrode and the negative electrode.

[0049] However, during long-term use of the above materials, the electrochemical performance deteriorates significantly, the power performance is not satisfactory, and the capacity retention rate becomes increasingly worse. One reason is that the interlayer compression of the cell is quite severe, making it difficult for the electrolyte to enter, resulting in poor electrolyte wetting.

[0050] On the other hand, under high-temperature formation or high-temperature cycling testing conditions, batteries may generate gases (such as hydrogen). If these gases cannot be discharged in time, they will form bubbles inside the cell. These bubbles will cause increased pressure and expansion of the cell materials, thereby increasing the stress between interfaces, especially between the electrodes and the separator. This can easily lead to poor interfacial adhesion between the electrodes and the separator. In particular, under high-temperature cycling and high-temperature formation conditions, poor interfacial adhesion can lead to an increase in local current density between the positive electrode and the separator, which can further exacerbate local thermal runaway or structural degradation of the materials, forming purple spots. These purple spots will seriously affect the appearance of the battery. Furthermore, poor interfacial adhesion can also hinder the transport of lithium ions, leading to lithium plating, which seriously affects the safety performance of the battery.

[0051] Based on this, embodiments of this application provide an electrode assembly and a battery. The electrode assembly includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The positive electrode has a first surface and a second surface opposite to each other in the thickness direction. The first surface has a plurality of protrusions, and the second surface has a plurality of recesses corresponding to each protrusion and recessed toward the protrusions. The separator includes a first separator and a second separator. The first separator is bonded to the first surface, and the second separator is bonded to the second surface. The first separator extends beyond the beginning of the positive electrode, and the second separator extends beyond the beginning of the positive electrode. The adhesion force between the first surface and the separator is N1, and the adhesion force between the second surface and the separator is N2. N1 and N2 satisfy the relationship: N1>N2.

[0052] During use, the recesses on the positive electrode plate increase the electrolyte storage space, improving the overall wetting effect of the electrolyte on the battery cell after long-term use. Furthermore, the recesses also provide deformation space for the negative electrode, reducing the adverse effects of negative electrode material expansion. Simultaneously, with a high adhesion between the protrusions and the separator, gases generated by the electrochemical reaction preferentially escape from areas of weaker adhesion, reducing the possibility of gas accumulation and bubble formation within the battery cell. This further reduces the likelihood of abnormal bonding interfaces between the first surface and the separator due to gas generation, thus optimizing battery performance.

[0053] The technical solution of the invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0054] As shown in Figures 1 and 2, this application provides an electrode assembly including: a positive electrode 100, a negative electrode 500, and a separator 200. The positive electrode 100 has a first surface 110 and a second surface 120 opposite to each other in the thickness direction. The first surface 110 has a plurality of protrusions 111, and the second surface 120 has a plurality of recesses 121 that correspond to each of the protrusions 111 and are recessed toward the protrusions 111.

[0055] The separator 200 includes a first separator and a second separator. The first separator is bonded to a first surface 110, and the second separator is bonded to a second surface 120. The first separator extends beyond the beginning of the positive electrode 100, and the second separator extends beyond the beginning of the positive electrode 100.

[0056] The adhesion force between the first surface 110 and the diaphragm 200 is N1, and the adhesion force between the second surface 120 and the diaphragm 200 is N2. N1 and N2 satisfy the relationship: N1>N2.

[0057] It should be noted that each convex part 111 corresponds to each concave part 121.

[0058] In practice, an embossing roller can be used to extrude the positive electrode sheet 100, causing deformation on the positive electrode sheet 100 and integrally forming multiple protrusions. The outer surface of the protrusions is the convex part 111, and the inner surface of the protrusions is the concave part 121. It can be understood that the convex part 111 and the concave part 121 are integrally formed.

[0059] The adhesive force between the first surface 110 and the diaphragm 200 is N1. The adhesive force between the second surface 120 and the diaphragm 200 is N2. For example, it can be a comparison of the adhesive forces between the protrusions of the first surface and the diaphragm and the adhesive forces between the concave portions of the second surface and the diaphragm; it can also be a comparison of the adhesive forces between the non-protrusions of the first surface and the diaphragm and the adhesive forces between the non-concave portions of the second surface and the diaphragm; or it can be a comparison of the adhesive forces between the entire first surface and the diaphragm and the entire second surface and the diaphragm. N1 and N2 satisfy the relationship: N1 > N2. For example, the preferred relationship between N1 and N2 is N1 = (1.01~2)N2, for example, N1 = 1.005N2, N1 = 1.01N2, N1 = 1.5N2, N1 = 2N2, or other relationships.

[0060] Therefore, according to the electrode assembly described in the first aspect of this application, by forming a protrusion 111 and a recess 121 on the two surfaces of the positive electrode 100, the surface of the positive electrode 100 becomes uneven. The protrusion 111 of the positive electrode 100 has deformation capability, so that when the cell expands, the protrusion 111 can effectively support the separator 200, preventing the separator 200 or the positive electrode 100 from deforming due to the expansion stress of the negative electrode 500. At the same time, a space for accommodating electrolyte is formed between the protrusion 111 of the positive electrode 100 and the separator 200, thereby increasing the electrolyte storage space, improving the electrolyte wetting ability in this area, and avoiding abnormal situations such as insufficient electrolyte or poor wetting between the positive electrode 100 and the separator 200. Furthermore, the formation of the recess 121 on the positive electrode 100 expands the electrolyte storage space, further enhancing the electrolyte wetting ability and improving the cycle performance and service life of the electrode assembly.

[0061] Furthermore, by setting the adhesion between the surface of the protrusion 111 (i.e., the first surface 110) and the separator 200 to be greater than the adhesion between the surface of the recess 121 (i.e., the second surface 120) and the separator 200, a gas discharge path is constructed. This allows the gas generated by the electrochemical reaction during high-temperature formation or high-temperature expansion to preferentially discharge from areas with weaker adhesion (such as the adhesion between the surface of the recess 121 and the separator 200, specifically between each recess 121 and the separator 200 or between adjacent recesses 121 and the separator 200). It is understood that the separator 200 itself has a certain degree of permeability, and by forming the protrusion 111 and the recess 121 on the positive electrode 100, the distance between the positive electrode 100 and the separator 200 is increased. Simultaneously, the recess... The smaller the adhesion between the surface of recess 121 and the separator 200, the smaller the bonding area between the surface of recess 121 and the separator 200. The more gaps between the surface of recess 121 and the separator 200, the more timely the internal pressure of the battery can be released, reducing the possibility of gas bubbles forming due to gas accumulation inside the cell. This reduces the possibility of purple spots caused by abnormal bonding interfaces between the positive electrode 100 and the separator 200 or between the separator 200 and the negative electrode 500 due to gas generation in the central area of ​​the electrode assembly. This ensures good interfacial contact between the positive electrode 100 and the separator 200. During cycling, this promotes a more uniform current density distribution on the positive electrode 100 and the separator 200, avoiding uneven lithium metal deposition and the resulting lithium dendrite formation.

[0062] Furthermore, timely discharge of gas through areas with weaker adhesion can also play a role in heat dissipation to a certain extent, which helps maintain the temperature of the positive electrode 100 during the cycle process, making the heat inside the cell evenly distributed, thereby creating a stable reaction environment inside the cell, preventing further side reactions, improving the cycle performance of the battery, and extending the battery's lifespan.

[0063] According to one embodiment of this application, the adhesive force between the protrusion 111 and the diaphragm 200 is greater than the adhesive force between the straight portion 130 and the diaphragm 200 between two adjacent protrusions 111, so that the gas generated by the electrochemical reaction during high-temperature formation or high-temperature expansion can also be discharged from the straight portion 130 between adjacent protrusions 111.

[0064] The positive electrode 100 includes a positive current collector and a positive active material layer on the positive current collector; the negative electrode 500 includes a negative current collector and a negative active material layer on the negative current collector.

[0065] According to one embodiment of this application, the negative electrode active material layer comprises a silicon-carbon composite material and / or a silicon-oxygen composite material. In one embodiment, the silicon-carbon composite material and / or the silicon-oxygen composite material accounts for less than or equal to 50 wt% of the mass of the second active material, for example, 1.5-40 wt%.

[0066] The silicon-carbon composite material comprises a porous carbon matrix, silicon grains located within the pores of the porous carbon matrix, and a carbon layer located on the surface of the porous carbon matrix. This invention allows silicon grains to be deposited within the pores of the porous carbon matrix. By placing the silicon grains within the pores and forming a carbon layer on the surface of the porous carbon matrix, this carbon layer can be either shaped or amorphous carbon. When the silicon grains expand, the interior of the porous carbon matrix provides sufficient expansion space, thereby preventing overall structural deformation of the silicon-carbon composite material. Furthermore, the carbon layer can constrain the outward expansion force of the porous carbon matrix during silicon expansion, ensuring the structural strength of the silicon-carbon material. This avoids problems such as cracking, pulverization, and detachment of the negative electrode active layer, improving the cycle performance and rate performance of the battery.

[0067] In one specific embodiment, the carbon layer includes openings corresponding to the pores of the porous carbon matrix. When openings are provided on the carbon layer, the wettability of the electrolyte to the negative electrode sheet can be improved, and the expansion performance of the silicon-based material can be reduced, thereby reducing the battery impedance and improving the battery's cycle performance and rate performance.

[0068] In one specific embodiment, the specific surface area of ​​the silicon-carbon composite material and / or silicon-oxygen composite material is 0.5-10 m². 2 / g, for example, 0.5m 2 / g, 1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g or 10m 2 / g etc. When the specific surface area in the silicon-carbon composite material is within the above range, the SEI film formed on the surface of the negative electrode active layer during charging and discharging is suitable, which can reduce the battery impedance and improve the battery's cycle performance and rate performance.

[0069] In one specific embodiment, the particle size Dv50 of the silicon-carbon composite material and / or silicon-oxygen composite material is 6-15 μm, for example, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm. When the particle size Dv50 of the silicon-carbon composite material and / or silicon-oxygen composite material is within the above range, the particle size Dv50 of the silicon-carbon composite material is suitable. This avoids the situation where the particle size is too small, which can easily lead to an increase in the specific surface area of ​​silicon particles and an increase in side reactions. At the same time, it avoids the situation where the particle size is too large, which can easily lead to excessive expansion of silicon particles, causing blockage of the pores of the porous carbon matrix and affecting the wetting of the electrolyte. This can improve the cycle performance and rate performance of the battery.

[0070] In one specific embodiment, the powder resistivity of the silicon-carbon composite material and / or silicon-oxygen composite material is 0.1-1000 Ω·cm, for example, 0.1 Ω·cm, 0.5 Ω·cm, 1 Ω·cm, 5 Ω·cm, 10 Ω·cm, 50 Ω·cm, 100 Ω·cm, 200 Ω·cm, 300 Ω·cm, 400 Ω·cm, 500 Ω·cm, 600 Ω·cm, 700 Ω·cm, 800 Ω·cm, 900 Ω·cm, or 1000 Ω·cm. When the powder resistivity of the silicon-carbon composite material is within the above range, the silicon-carbon composite material has high conductivity, which can improve the conductivity of the negative electrode active layer, thereby improving the cycle performance and rate performance of the battery.

[0071] In one specific embodiment, the silicon content in the silicon-carbon composite material and / or silicon-oxygen composite material is 30-75%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%. When the silicon content in the silicon-carbon composite material and / or silicon-oxygen composite material is within the above range, it can avoid excessive silicon content, which would lead to excessive expansion of the silicon-carbon composite material and / or silicon-oxygen composite material, causing deformation of the overall structure of the silicon-carbon composite material and / or silicon-oxygen composite material. This prevents cracking and pulverization of the negative electrode active layer, ensures the energy utilization of the silicon-carbon composite material and / or silicon-oxygen composite material, and improves the cycle performance and rate performance of the battery.

[0072] Furthermore, as shown in Figure 2, the surface of the protrusion 111 that contacts the separator 200 can be set as an arc surface. This avoids the possibility of the protrusion 111 piercing the separator 200 due to being too sharp during the stacking and winding of the separator 200 and the positive and negative electrode sheets, thereby preventing the problem of the protrusion of the positive electrode sheet 100 piercing the separator 200 and the negative electrode sheet 500 and causing a short circuit.

[0073] Specifically, as shown in Figure 2, the convex portion 111 is spherical or near-spherical, with a radius of R1 and a radius of R2 for the concave portion 121; the positive electrode 100 includes a flat portion 130 with a thickness of H; R1, R2, and H satisfy the following relationships: R1>R2; and / or, R1-R2≤H; and / or, R1 / R2=1.01~2.

[0074] It should be noted that the protrusion 111 is equivalent to a spherical shell, where R1 is the outer surface radius of the shell and R2 is the inner surface radius. Since the outer surface radius of the shell is greater than the inner surface radius (R1 > R2), and the difference between the outer and inner surface radii is less than the thickness of the flat portion 130 of the positive electrode 100 (i.e., R1 - R2 ≤ H), the thickness of the protrusion 111 is less than the thickness of the flat portion 130 of the positive electrode 100. This improves the deformation capability of the protrusion 111, thereby effectively alleviating the expansion stress of the negative electrode 500 during charging and discharging, and preventing the negative electrode 500 or the positive electrode 100 from cracking.

[0075] Furthermore, R1 = 0.5mm to 8mm; and / or, R2 = 0.5mm to 8mm. Preferably, R1 = 1mm to 5mm, and R2 = 1mm to 5mm.

[0076] Therefore, by limiting the inner and outer surface radii of the protrusion 111, the projected area of ​​the protrusion 111 in the thickness direction of the positive electrode 100 can be adjusted.

[0077] For example, R1 can be 0.5mm, 1mm, 3mm, 5mm, 8mm or other values, preferably R1 = 1mm to 5mm. R2 can be 0.5mm, 1mm, 3mm, 5mm, 8mm or other values, preferably R2 = 1mm to 5mm. R1 / R2 = 1.01 to 2, R1 / R2 can be 1.01, 1.05, 1.09, 1.1, 2 or other values.

[0078] Conversely, if R1 or R2 < 0.5 mm, the projected area of ​​the protrusion 111 is small, making it too sharp and prone to piercing the diaphragm 200 and contacting the opposite positive electrode 100, leading to a short circuit. In addition, the small projected area of ​​the protrusion 111 also results in poor wetting effect on the electrolyte and poor improvement effect on the expansion of the negative electrode material. If R1 or R2 > 8 mm, the projected area of ​​the protrusion 111 is large, making the positive electrode 100 susceptible to excessive deformation under the extrusion pressure of embossing and the stretching force of the electrode itself during the process of forming the protrusion 111, which can easily lead to electrode breakage.

[0079] As shown in FIG. 2, in some embodiments, the height from the end point of the convex portion 111 away from the second surface 120 to the surface of the positive electrode sheet 100 is h1; h1 = 3 μm to 40 μm.

[0080] In some embodiments, the distance between the end point of the convex portion 111 away from the flat portion 130 and the surface of the flat portion 130 facing away from the convex portion 111 is less than the radius R1 of the convex portion 111, R3 < R1; preferably, R3 < 1 / 5R1.

[0081] Exemplarily, h1 can be 3 μm, 5 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm or other values. Preferably, h1 = 5 μm to 30 μm. Thus, by limiting the height of the final convex portion 111, a suitable gap can be formed between the positive electrode sheet 100 and the separator 200, so that while the battery has better effects, the possibility of increasing the overall thickness can be reduced.

[0082] As shown in FIG. 3, in some embodiments, the curve length of the concave portion 121 in the cross-section passing through the center of the convex portion 111 is C1, and C1 and R2 satisfy the relationship: C1 = πR2.

[0083] It can be understood that since R2 = 0.5 mm to 8 mm, then C1 = 0.5π mm to 8π mm. And preferably, R2 is 1 mm to 5 mm, then C1 is preferably π mm to 5π mm. By limiting the length of C1, a more appropriate projected area of the convex portion 111 in the thickness direction of the positive electrode sheet 100 can be determined. In addition, by referring to the values of C1 and R2 simultaneously, the possibility of the convex portion 111 being too large or too small can be reduced, that is, preventing the convex portion 111 from being too large and causing loss of the volumetric energy density of the battery cell; at the same time, preventing the convex portion 111 from being too small, resulting in a small deformation ability and a small deformation space of the convex portion 111 of the positive electrode sheet 100, and a poor improvement effect on the expansion of the negative electrode sheet 500, to ensure better use effects.

[0084] In other embodiments, the curve length of the convex portion 111 in the cross-section passing through the center of the convex portion 111 can also be limited.

[0085] As shown in FIG. 2, in some embodiments, a plurality of convex portions 111 are spaced apart, and the positive electrode sheet 100 includes a flat portion 130 between two adjacent convex portions 111; the distance between the centers of two adjacent convex portions 111 is L1, and the length of the flat portion 130 between two adjacent convex portions 111 is L2, and L1 and L2 satisfy the relationship: L1 / L2 = 1.05 to 10.

[0086] For example, L1 / L2 can be 1.05, 1.1, 1.5, 2, 3, 5, 8, 10, or other values. Preferably, L1 / L2 = 1.1 to 8. By limiting the value of L1 / L2, the density of the protrusions 111 can be ensured, so that the protrusions 111 can provide sufficient support and deformation space to alleviate the expansion of the negative electrode 500, while ensuring the wetting effect of the electrolyte. If the ratio is too small, that is, the distance between two adjacent protrusions 111 is too large, the protrusions 111 will hardly be able to alleviate the expansion of the negative electrode 500 and improve the wetting effect of the electrolyte; if the ratio is too large, the diameter of the protrusions 111 will be too large, resulting in a loss of volumetric energy density of the cell.

[0087] In addition, L1 and L2 can be set as follows: L1 = 2mm to 10mm, for example, L1 can be 2mm, 3mm, 5mm, 8mm, 10mm or other values, preferably L1 = 2mm to 8mm; and / or L2 = 0.5mm to 8mm, for example, L2 can be 0.5mm, 1mm, 3mm, 4mm, 8mm or other values, preferably L2 = 1mm to 4mm.

[0088] Therefore, by limiting the size of L1 or L2, a suitable distance can be provided between two adjacent protrusions 111 so as to allow for the adjustment of the appropriate volume of the protrusions 111 during the processing.

[0089] Conversely, if L1 < 2 mm, the protrusions 111 on the positive electrode 100 are densely distributed, meaning the protrusions on the roller used for embossing are also very dense. During the formation of the protrusions 111, the extension of the positive electrode 100 cannot meet the density of the protrusions on the roller, and the stress within the positive electrode 100 is prone to concentration, leading to localized fractures. Moreover, the height of the protrusions 111 is also difficult to meet, resulting in a smaller deformation space for the protrusions 111. If L1 > 8 mm, the protrusions on the embossing roller are too sparse, making the protrusions 111 on the positive electrode 100 too dispersed and lacking sufficient support surface, making it difficult to achieve a good adhesion effect between the first surface 110 and the separator 200.

[0090] In some embodiments, the area of ​​the protrusion 111 is Q1, and the area of ​​the concave portion 121 is Q2, where Q1 and Q2 satisfy the relationship: Q1 / Q2 = 1.02 to 1.21;

[0091] And / or, as shown in Figure 4, the projected area of ​​the protrusion 111 in the thickness direction of the positive electrode 100 is S1, and the projected area of ​​the concave part 121 in the thickness direction of the positive electrode 100 is S2. S1 and S2 satisfy the relationship: S1 / S2 = 1.02~1.21.

[0092] It should be noted that Q1 = 2πR1 2Q2 = 2πR2 2 Then Q1 / Q2 = R1 2 / R2 2 S1=πR1 2 S2 = πR2 2 Then S1 / S2 = R1 2 / R2 2 Here, Q1 / Q2 and S1 / S2 are both set to 1.02 to 1.21.

[0093] For example, Q1 / Q2 or S1 / S2 can be 1.02, 1.1, 1.5, 1.21 or other values.

[0094] Therefore, by controlling the ratio between Q1 and Q2, or the ratio between S1 and S2, it is possible to ensure that the protrusion 111 of the positive electrode 100 has sufficient deformation space to alleviate the expansion of the negative electrode 500, and also to ensure that the protrusion 111 of the positive electrode 100 and the separator 200 have a larger bonding area and better adhesion between the protrusion 111 and the separator 200.

[0095] As shown in Figure 5, in some embodiments, the number of protrusions 111 per unit area of ​​the positive electrode 100 is N, where N satisfies the relationship: 2≤N≤25.

[0096] For example, N can be 2, 4, 6, 8, 9, 15, 25 or other values, preferably 4≤N≤15.

[0097] The unit area is 1, 2, 3, 4, or 5 cm². 2 Therefore, by controlling the number of protrusions 111 per unit area, the density of the protrusions 111 can be reasonably set. This reduces the situation where too few protrusions 111 result in poor wetting effect on the electrolyte or inadequate improvement in reducing the expansion of the negative electrode 500; or where too many protrusions 111 cause the roller pressure to easily exceed the tensile strength of the positive electrode 100 during the embossing process, resulting in the height of the protrusions 111 failing to reach the optimal value, or even causing the positive electrode 100 to break.

[0098] In some embodiments, the total projected area of ​​each protrusion 111 in the unit area in the thickness direction of the positive electrode sheet 100 is S3, and the proportion of S3 in the unit area satisfies the relationship: 0.2≤S3≤0.8.

[0099] For example, S3 can be 0.2, 0.4, 0.5, 0.6, 0.7, 0.8 or other values, preferably 0.4≤S3≤0.6.

[0100] The unit area is 1, 2, 3, 4, or 5 cm². 2Therefore, by controlling the area of ​​the protrusions 111 per unit area, the density of the protrusions 111 can be reasonably set, thereby reducing the situation where the area of ​​the protrusions 111 is too small, resulting in poor wetting effect on the electrolyte or ineffective relief of the expansion of the negative electrode 500; or where the area of ​​the protrusions 111 is too large, causing the pressure of the rollers to easily exceed the tensile strength of the positive electrode 100 during the embossing process, which may lead to the height of the protrusions 111 not reaching the optimal value, or even causing the positive electrode 100 to break.

[0101] As shown in Figure 6, in some embodiments, the area on the positive electrode 100 where the protrusions 111 are concentrated is called the protrusion region 140, the total area of ​​the protrusion region 140 is S11, the total area of ​​the positive electrode 100 is S, and S11 and S satisfy the relationship: 0.02≤S11 / S≤0.85.

[0102] For example, S11 / S can be 0.02, 0.1, 0.3, 0.6, 0.85 or other values.

[0103] It should be noted that the area on the positive electrode 100 where the protrusions 111 are concentrated is called the protrusion region 140. The length of the protrusion region 140 refers to the distance between the first protrusion 111 and the last protrusion 111 in the protrusion region 140 along the length direction; the width of the protrusion region 140 refers to the distance between the first protrusion 111 and the last protrusion 111 in the protrusion region 140 along the width direction.

[0104] Therefore, the proportion of the total area of ​​the convex region 140 to the total area of ​​the positive electrode 100 is set so as to reasonably control the size of the distribution area of ​​the convex region 111 on the positive electrode 100, thereby ensuring that the positive electrode 100 has a better performance.

[0105] Conversely, if S11 / S is too large (i.e., greater than 0.85), the area of ​​the protrusion region 140 is too large. During the process of forming the protrusion 111 by embossing, the pressure of the roller is likely to exceed the tensile strength of the positive electrode 100, which will result in the height of the protrusion 111 not reaching the preferred value, or even cause the positive electrode 100 to break. If S11 / S is too small (i.e., less than 0.02), the protrusion 111 will not be effective in wetting the electrolyte or in improving the expansion of the negative electrode 500.

[0106] Furthermore, the distance between the two ends of the convex region 140 and the positive electrode 100 in the length direction is K, where K = 10 mm to 100 mm; and / or, the distance between the convex region 140 and the positive electrode 100 in the width direction is M, where M = 5 mm to 30 mm.

[0107] In this embodiment of the application, the area on the positive electrode 100 where the protrusion 111 is not provided is the clearance area 150. The positive electrode 100 extends horizontally, and the clearance area 150 may include a head clearance area 151, a tail clearance area 152, a top clearance area 153 and / or a bottom clearance area 154.

[0108] Among them, the head clearance area 151 is the area between the convex area 140 and the head of the positive electrode 100, and the distance between the convex area 140 and the head of the positive electrode 100 is K1, K1 = K = 10mm ~ 100mm.

[0109] The tail clearance area 152 is located between the convex region 140 and the tail of the positive electrode 100. The distance between the convex region 140 and the tail of the positive electrode 100 is K2, where K2 = K = 10mm to 100mm. In practice, the tail clearance area 152 can also be the area between the convex region 140 and the junction of the single-sided and double-sided areas of the tail of the positive electrode 100.

[0110] For example, K1 or K2 can be 10mm, 30mm, 60mm, 80mm, 100mm or other values.

[0111] The bottom clearance area 154 is located between the convex region 140 and the bottom edge of the positive electrode 100. The distance between the convex region 140 and the bottom edge of the positive electrode 100 is M1, where M1 = M = 5mm to 30mm.

[0112] The top clearance area 153 is the area between the convex region 140 and the top edge of the positive electrode 100. The distance between the convex region 140 and the top edge of the positive electrode 100 is M2, where M2 = M = 5mm to 30mm.

[0113] For example, M1 or M2 can be 5mm, 10mm, 15mm, 20mm, 30mm or other values. Preferably, M1 or M2 = 5mm to 20mm.

[0114] Therefore, by setting a suitable clearance area 150 at the edge of the positive electrode 100, the optimal performance of the positive electrode 100 itself can be ensured. The top clearance area 153 and the bottom clearance area 154 can reduce the possibility of edge curling and poor interface uniformity caused by rolling stress in the edge area of ​​the positive electrode 100, and can also prevent the problem of powder falling off the edge of the positive electrode 100 during the embossing process; the head clearance area 151 can improve the stability of the head of the positive electrode 100, and can prevent the head from folding and the problem of unstable feeding during winding, which leads to structural instability; in practice, foil is usually set at the tail of the positive electrode 100, and the tail clearance area 152 can reduce the possibility of foil breakage.

[0115] Conversely, if K1 or K2 is less than 10mm and M1 or M2 is less than 5mm, the convex region 140 will be too wide, making the positive electrode 100 prone to cracking, deformation, or wrinkling at the beginning and end during subsequent processing, thus making it difficult to wind. If K1 or K2 is greater than 100mm and M1 or M2 is greater than 30mm, the convex region 140 will be narrow, and the number of convex parts 111 will be less, resulting in poor wetting effect of the convex parts 111 on the electrolyte or poor effect on alleviating the expansion of the negative electrode 500.

[0116] As shown in Figure 6, in some embodiments, a tab 160 is provided on the positive electrode 100, and the distance between the protruding region 140 and the tab 160 is J, where J = 5mm to 30mm.

[0117] For example, J can be 5mm, 10mm, 25mm, 30mm or other values.

[0118] In practice, to facilitate the connection of the positive electrode 100 with other components, tabs 160 are often provided on the positive electrode 100 to provide connection points. In this embodiment, the tabs 160 are provided on the top edge of the positive electrode 100 by welding, bonding or other means, and the clearance area 150 also includes a tab clearance area 155.

[0119] The convex region 140 includes at least two spaced-apart unit regions, with the tab 160 located between two adjacent unit regions. Furthermore, the tab clearance area 155 is the region between the tab 160 and the adjacent unit regions, with the distances between the tab 160 and the adjacent unit regions on both sides being J1 and J2, respectively, where J1 = J = 5mm to 30mm and J2 = J = 5mm to 30mm.

[0120] Therefore, the tab clearance zone 155 can ensure the stability of the tab 160 and prevent the tab 160 from being crushed by the current collector below during the rolling process of the tab 160 after the embossing process, which would affect the welding effect of the tab 160.

[0121] As shown in Figure 1, in some embodiments, the positive electrode 100, the separator 200 and the negative electrode 500 are stacked and wound to form a core structure, and the electrode assembly includes a main body region 300 and an arc region 400; the height of the protrusion 111 located in the arc region 400 is less than the height of the protrusion 111 located in the main body region 300.

[0122] In practice, the battery is internally configured with a wound core structure, which requires the positive electrode sheet 100 to be wound. At this time, setting the height of the protrusion 111 in the arc region 400 to be smaller than the height of the protrusion 111 in the main body region 300 can ensure that the arc region 400 of the positive electrode sheet 100 is not prone to breakage during the winding process. It can also prevent the protrusion 111 in the arc region 400 from being too large, which would affect the overall width of the cell and thus the energy density of the cell.

[0123] For example, the ratio of the height of the protrusion 111 in the main body area 300 to the height of the protrusion 111 in the arc area 400 can be 1.05, 1.1, 1.5, 1.8, 2, or 3. Preferably, the ratio of the height of the protrusion 111 in the main body area 300 to the height of the protrusion 111 in the arc area 400 can be set to 1.1 to 2.

[0124] In some embodiments, the separator 200 includes: a base membrane comprising multiple layers of microporous membranes, including several layers of PE (polyethylene) microporous membranes, PP (polypropylene) microporous membranes, and PP and PE composite microporous membranes; and a ceramic layer coated on the base membrane, the ceramic layer being disposed opposite to the positive electrode 100, that is, the ceramic layer being disposed opposite to the protrusion 111 of the positive electrode 100. Considering that the top of the protrusion 111 is too sharp and could puncture the separator 200, the ceramic layer inside the separator 200 will cover the top of the protrusion 111, so that even if the protrusion 111 of the positive electrode 100 and the negative electrode 500 come into contact, the ceramic layer can isolate the positive electrode 100 and the negative electrode 500, improving the safety performance of the battery cell.

[0125] In some examples, the diaphragm 200 includes: a ceramic layer that is an inorganic ceramic particle coating, a coating composed of inorganic ceramic particles and PVDF, or a coating composed of inorganic ceramic particles and polymethyl methacrylate and PVDF; wherein the inorganic ceramic particles include one or more of α-Al2O3, γ-Al2O3, Al2O3, SiO2, CeO2, MgAl2O4, ZrO, and TiO2; and the polymethyl methacrylate is in the form of a blocky or strip-shaped protruding structure.

[0126] In practice, the inorganic ceramic particles in the separator 200 can mitigate the potential hazards caused by burrs from the die-cutting of the positive electrode 100. Furthermore, the inorganic ceramic particles can neutralize the decomposed HF in the electrolyte, improving the electrolyte retention capacity of the positive electrode 100 and thus enhancing battery cycle performance. Additionally, it can reduce the likelihood of the protrusion 111 puncturing the separator 200 and causing a short circuit, thereby improving battery safety.

[0127] In some embodiments, the metal element content of the first surface 110 is W1, and the metal element content of the second surface 120 is W2, wherein W1 and W2 satisfy the relationship: W1>W2; the metal element includes at least one of Al, Si, Ce, Mg, Zr or Ti.

[0128] At this time, the metal content of the first surface 110 is greater than the metal content of the second surface 120, and the metal element includes at least one of Al, Si, Ce, Mg, Zr or Ti. Understandably, the ceramic layer and the positive electrode 100 are arranged opposite each other, that is, the ceramic layer and the protrusion 111 of the positive electrode 100 are arranged opposite each other. The content of inorganic ceramics can be mainly characterized by the content of Al, Si, Ce, Mg, Zr and Ti. Understandably, by limiting these elements, the content of inorganic ceramics on the first surface 110 and the content of inorganic ceramics on the second surface 120 are characterized. That is, the content of inorganic ceramics on the first surface 110 is greater than the content of inorganic ceramics on the second surface 120. Since the protrusion 111 area of ​​the positive electrode 100 is subjected to greater force, the inorganic ceramic material usually increases the mechanical strength of the surface where the protrusion 111 of the positive electrode 100 is located, improves the structural stability of the surface, and prevents the protrusion 111 of the positive electrode 100 from being easily deformed by the expanded negative electrode 500 when the negative electrode 500 expands. Furthermore, the higher content of inorganic ceramics on the first surface 110 compared to the second surface 120 can improve the adhesion between the first surface 110 and the diaphragm 200, resulting in relatively high stability when the first surface 110 and the diaphragm 200 are bonded together. For example, W1 can be set to 1.02W2, 1.05W2, 1.2W2, 1.4W2, 1.5W2, 2W2, or other values. Preferably, W1 = (1.05~1.5)W2.

[0129] Furthermore, the metal element content of the protrusion 111 is W11, and the metal element content of the concave portion 121 is W21, with W11 and W21 satisfying the relationship: W11>W21; and / or, the positive electrode 100 includes a flat portion 130 located between two adjacent protrusions 111; the metal element content of the protrusion 111 is W11, and the metal element content of the flat portion 130 is W3, with W11 and W3 satisfying the relationship: W11>W3; and / or, the positive electrode 100 includes a flat portion 130 located between two adjacent protrusions 111; the metal element content of the flat portion 130 is W3, and the metal element content of the concave portion is W21, with W21 and W3 satisfying the relationship: W3>W21; the metal element includes at least one of Al, Si, Ce, Mg, Zr, or Ti.

[0130] Understandably, the ceramic layer and the positive electrode 100 are arranged opposite each other, that is, the protrusions of the ceramic layer and the positive electrode 100 are arranged opposite each other. The inorganic ceramic content can be mainly characterized by the content of Al, Si, Ce, Mg, Zr, and Ti. Understandably, by limiting these elements, the inorganic ceramic content of the protrusion 111, the concave portion 121, and the straight portion 130 are characterized. That is, the inorganic ceramic content of the protrusion 111 is greater than that of the straight portion 130, which is greater than that of the concave portion 121, ensuring the adhesion between the concave portion 121, the straight portion 130, and the concave portion 121 and the separator 200. In addition, since the protrusion region 140 of the positive electrode 100 is subjected to greater force, the inorganic ceramic material usually increases the mechanical strength of the surface where the protrusion 111 of the positive electrode 100 is located, improves the structural stability of the surface, and prevents the protrusion 111 of the positive electrode 100 from being easily deformed by the expanding negative electrode 500 when the negative electrode 500 expands. Finally, it also ensures the construction of gas discharge paths, so that during high-temperature formation or high-temperature expansion, the gas generated by the electrochemical reaction preferentially exits from areas with weaker adhesion (such as the adhesion between the surface of the recess 121 and the separator 200, specifically between each recess 121 and the separator 200, or between the straight portion 130 and the separator 200). It is understood that the separator 200 itself has a certain degree of permeability, and the formation of protrusions 111 and recesses 121 on the positive electrode 100 further expands the permeability between the positive electrode 100 and the separator 200. The spacing between the recesses is smaller, and the adhesion between the surface of the recess 121 and the separator 200 is also smaller. This means that the bonding area between the surface of the recess 121 and the separator 200 is relatively small. The more gaps between the surface of the recess 121 and the separator 200, the more timely the internal pressure of the battery can be released, reducing the possibility of gas bubbles forming due to gas accumulation inside the cell. This, in turn, reduces the possibility of purple spots caused by abnormal bonding interfaces between the positive electrode 100 and the separator 200 or between the separator 200 and the negative electrode 500 due to gas generation in the central area of ​​the electrode assembly.

[0131] For example, W11 can be set to 1.02W21, 1.05W21, 1.2W21, 1.4W21, 1.5W21, 2W21 or other values; W11 can be set to 1.03W3, 1.05W3, 1.3W3, 1.4W3, 2W3 or other values. Preferably, W11 = (1.05~1.4)W3 = (1.05~1.5)W21.

[0132] In some embodiments, the tensile strength of the positive electrode 100 is ≥100MPa, and the ratio of the depth (μm) of the recess 121 to the tensile strength (MPa) of the positive electrode 100 is between 0.05 and 0.2.

[0133] Specifically, the tensile strength of the positive electrode 100 in both the transverse (TD) and longitudinal (MD) directions is set to 100 MPa or higher. For example, the tensile strength of the positive electrode 100 can be 100 MPa, 110 MPa, 1500 MPa, or other values. This ensures the strength of the positive electrode 100 itself, reducing the possibility of cracking during subsequent rolling of the protrusion 111 or winding. Furthermore, the ratio of the depth (μm) of the recess 121 to the tensile strength (MPa) of the positive electrode 100 is set within a preferred range, which can be between 0.05 and 0.2, where 0.05, 0.1, 0.15, 0.2, or other values ​​are possible. Alternatively, the ratio of the depth (μm) of the recess 121 to the tensile strength (MPa) of the current collector can also be set between 0.05 and 0.2.

[0134] It is understandable that if the depth of the recess 121 is greater, the compressive stress applied to the positive electrode 100 will be greater, and thus the tensile strength of the positive electrode 100 should be greater in order to reduce the possibility of cracking of the positive electrode 100.

[0135] Conversely, if the ratio of the depth (μm) of the recess 121 to the tensile strength (MPa) of the positive electrode 100 is less than 0.05, the required tensile strength of the positive electrode 100 is relatively high, which can easily lead to material waste and high costs. If the ratio of the depth (μm) of the recess 121 to the tensile strength (MPa) of the positive electrode 100 is greater than 0.2, the positive electrode 100 may not meet the required tensile strength during the rolling process of the protrusion 111, which can easily cause the positive electrode 100 to crack.

[0136] In summary, the electrode assembly provided in this application increases the electrolyte storage space through the recess 121 on the positive electrode 100 during use, thereby improving the overall wetting effect of the electrolyte on the battery cell after long-term use. Furthermore, the recess 121 also provides deformation space for the negative electrode 500, reducing the adverse effects caused by the expansion of the negative electrode material. Simultaneously, based on the high adhesion between the protrusion 111 and the separator 200, the gas generated by the electrochemical reaction preferentially exits from areas with weaker adhesion (such as the adhesion between the surface of the recess 121 and the separator 200, specifically between each recess 121 and the separator 200, or between the straight portion 130 and the separator 200), reducing the possibility of gas accumulation and bubble formation inside the battery cell. This further reduces the possibility of abnormal bonding interfaces between the first surface 110 and the separator 200 due to gas generation, thus optimizing battery performance.

[0137] As shown in Figure 7, this application embodiment also provides a battery, including the electrode assembly in any of the above embodiments, wherein the separator 200 in the electrode assembly is sandwiched between the negative electrode 500 and the positive electrode 100.

[0138] It should be noted that the battery also includes a casing and an electrolyte. The electrode assembly and electrolyte are all housed inside the casing, as shown in the attached diagram.

[0139] The electrode assembly has a wound structure, with the negative electrode 500 and the positive electrode 100 respectively bonded to both sides of the separator 200, such that the separator 200 separates the negative electrode 500 from the positive electrode 100. The specific structure of the positive electrode 100 has been described in detail in the above embodiments and will not be repeated here.

[0140] In practical use, the recess 121 on the positive electrode 100 increases the electrolyte storage space; furthermore, the recess 121 also provides deformation space for the negative electrode 500. Simultaneously, the gas generated by the electrochemical reaction preferentially escapes from the gaps between the protrusions 111, reducing the possibility of gas accumulation and bubble formation inside the cell. This, in turn, reduces the likelihood of abnormal adhesion between the first surface 110 and the separator 200 due to gas generation, thus optimizing battery performance.

[0141] In practice, the positive electrode 100 containing the protrusion 111 structure, the negative electrode 500, and the battery are respectively manufactured according to the following methods:

[0142] Preparation method of positive electrode 100:

[0143] For example, lithium cobalt oxide, a conductive agent (a mixture of conductive carbon black and carbon nanotubes), and PVDF (polyvinylidene fluoride) were placed in NMP (methylpyrrolidone) at a mass ratio of 97.60:1.35:1.05 and stirred until homogeneous to obtain a positive electrode slurry. This positive electrode slurry was uniformly coated on both sides of an aluminum foil, with a coating density of 0.01704 g / cm². After drying and rolling, a positive electrode sheet 100 with a double-sided thickness of 90 μm was obtained. The slit positive electrode sheet 100 was then embossed using an embossing roller containing protrusions 111.

[0144] Preparation method of negative electrode 500:

[0145] For example, silicon-containing artificial graphite, conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose are placed in deionized water at a mass ratio of 97.2:0.5:1.3:1, wherein the silicon content in the silicon-containing artificial graphite is 5%; the above slurry is stirred evenly to obtain a negative electrode slurry; the negative electrode slurry is uniformly coated on a negative electrode current collector, and then dried, rolled, slit, cleaned, and sheeted to obtain a negative electrode sheet 500.

[0146] Battery manufacturing methods:

[0147] In this embodiment, the separator 200 is 9 μm thick. The electrolyte includes lithium salt LiPF6 and a solvent, which includes ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC), wherein the molar ratio of the three is DEC:EC:EMC = 1:1:1. The pre-cut positive electrode 100, separator 200, and negative electrode 500 are then sequentially stacked and wound into a wound-type battery cell. After encapsulation, electrolyte injection, formation, and secondary sealing, the battery is obtained.

[0148] Battery performance testing methods:

[0149] Liquid retention test: Each battery is injected with a certain amount of electrolyte, for example, the amount of electrolyte injected into each battery n1 is 8.5g ± 0.1g. After injection, the battery is aged. After aging, the battery is sorted and then sealed twice. The second sealing is to remove the excess electrolyte. The amount of electrolyte remaining is the liquid retention n2. Then n2 = (weight after second sealing m2 - weight before injection m1).

[0150] Appearance test of positive electrode 100 after processing of convex part 111: Use a 3D microscope to observe the positive electrode after processing of convex part 111, and observe whether there is any damage and the size of the damaged area.

[0151] Test of adhesion between positive electrode 100 and separator 200: According to the experimental method, positive electrode 100, negative electrode 500 and separator 200 are assembled together by winding process to form a battery cell. The assembled battery cell is subjected to hot pressing treatment. The hot pressing temperature is 70℃, the hot pressing pressure is 1.5Mpa and the hot pressing time is 15S. Take the bare battery cell after hot pressing. Along the MD (longitudinal) direction of separator 200, use a cutter to cut separator 200 and positive electrode 100 into a matrix size with a width of 5cm and a length of 5cm. Use a tensile tester to test the peel force between the coating of separator 200 and the first surface 110 and the second surface 120 respectively.

[0152] Content testing of inorganic ceramic particles on positive electrode 100: The content of inorganic ceramics can be mainly characterized by the content of Al, Si, Ce, Mg, Zr or Ti, and can be tested by referring to the EDS in existing SEM (i.e., energy dispersive X-ray spectroscopy (EDS) in scanning electron microscopy (SEM)).

[0153] Cycle retention and expansion rate tests: The battery was subjected to electrical cycle tests on the Blue Battery test cabinet under the following conditions: 25℃±2℃, 3.2C charging to 4.37V, 2.8C charging to 4.37V, 2C charging to 4.53V, 1.5C charging to 4.58V, cutoff at 0.05C; 0.7C discharging to 3V. The specific charging regime was as follows: at 25℃±2℃, the battery was allowed to stand for 5 minutes, then discharged at 0.2C to the lower limit voltage; allowed to stand for 5 minutes, then charged at 0.7C to the upper limit voltage, cutoff at 0.025C, allowed to stand for 5 minutes, then discharged at 0.2C to the lower limit voltage. Initial capacity tests were performed: the battery was allowed to stand for 5 minutes, then charged at 3.2C to 4.37V, 2.8C to 4.37V, 2C to 4.53V, 1.5C to 4.58V, cutoff at 0.05C. The data, including voltage and thickness, were measured and recorded under fully charged conditions. The battery was left to stand for 5 minutes at 25℃±2℃, then discharged at 0.7C to 3V, left to stand for 5 minutes, charged at 3.2C to 4.37V, charged at 2.8C to 4.37V, charged at 2C to 4.53V, charged at 1.5C to 4.58V, cut off at 0.05C, left to stand for 5 minutes, discharged at 0.7C to 3V, left to stand for 5 minutes, and so on. This process was repeated 8-9 times, up to 1200 cycles. Capacity testing was performed every 100 cycles at 25℃, repeating steps 3-4. For the first 200T: the fully charged cell voltage and thickness were measured every 50T. After 200T: the fully charged cell voltage and thickness were measured every 100T. Then, the cycle retention rate and expansion rate were tested at 200T and 400T. The battery expansion rate = (full-charge thickness after N cycles - battery sample thickness) / battery sample thickness * 100%), where the battery sample thickness is the initial thickness before the start of cycling.

[0154] Cycle retention rate refers to the ratio of the battery's remaining capacity to its initial capacity after a certain number of charge-discharge cycles, usually expressed as a percentage; expansion rate refers to the change in battery thickness caused during charge-discharge processes, usually expressed as a percentage.

[0155] The present invention will be described in detail through embodiments, including but not limited to the following embodiments. The following embodiments and comparative examples all use a positive electrode 100 thickness of 90 μm, a separator 200 thickness of 9 μm, and a silicon content of 20% in the negative electrode 500 as examples. Simultaneously, the radius R1 of the protrusion 111 is 0.5 mm to 8 mm, the radius R2 of the concave portion 121 is 0.5 mm to 8 mm, the height h1 of the protrusion 111 is 3 μm to 40 μm, and the ratio S11 / S of the total area of ​​the protrusion region 140 to the total area of ​​the positive electrode 100 is 0.02 to 0.85. The impact of different protrusion 111 sizes (e.g., R1, R2, h1) and the ratio S11 / S of the total area of ​​the protrusion region 140 to the total area of ​​the positive electrode 100 on battery performance is compared.

[0156] Example 1:

[0157] In this embodiment, the radius of the recess 121 is R2 = 0.5 mm, R1 / R2 = 1.01~1.1, and here R1 / R2 = 1.05 is taken. The radius of the protrusion 111 is R1 = 0.52 mm, the height of the protrusion 111 is h1 = 20 μm, and the proportion of the total area of ​​the protrusion region 140 in the total area of ​​the positive electrode 100 is S11 / S = 0.7.

[0158] Example 2:

[0159] In this embodiment, R2 = 1 mm, R1 = 1.05 mm, and other conditions remain unchanged from those in Embodiment 1.

[0160] Example 3:

[0161] In this embodiment, R2 = 3mm, R1 = 3.15mm, and other conditions remain unchanged from those in Embodiment 1.

[0162] Example 4:

[0163] In this embodiment, R2 = 4 mm, R1 = 4.2 mm, and other conditions remain unchanged from those in Embodiment 1.

[0164] Example 5:

[0165] In this embodiment, R2 = 7 mm, R1 = 7.35 mm, and other conditions remain unchanged from those in Embodiment 1.

[0166] Comparative Example 1:

[0167] In this embodiment, R2 = 0.2 mm, R1 = 0.21 mm, h1 = 1 μm, S11 / S = 1.01, and other conditions remain unchanged from those in Example 1.

[0168] Comparative Example 2:

[0169] In this embodiment, R2 = 0.2 mm, R1 = 0.21 mm, h1 = 50 μm, S11 / S = 0.9, and other conditions remain unchanged from those in Example 1.

[0170] Comparative Example 3:

[0171] In this embodiment, R2 = 9 mm, R1 = 9.45 mm, h1 = 1 μm, S11 / S = 0.01, and other conditions remain unchanged from those in Example 1.

[0172] Comparative Example 4:

[0173] In this embodiment, R2 = 9 mm, R1 = 9.45 mm, h1 = 50 μm, S11 / S = 0.9, and other conditions remain unchanged from those in Example 1.

[0174] Comparative Example 5:

[0175] In this embodiment, R2 = 0 mm, R1 = 0 mm, h1 = 0 μm, S11 / S = 0, and other conditions remain unchanged from those in Example 1.

[0176] Comparative Example 6:

[0177] In this embodiment, the silicon content in the negative electrode 500 is set to 70%, and other conditions remain unchanged from those in Example 5.

[0178] The positive electrode 100, separator 200, negative electrode 500, and electrolyte provided in the above embodiments and comparative examples are used to form a battery as a whole. Then, the electrolyte retention, cycle retention rate, and expansion change rate of the battery are tested using the above test method. The results are shown in Table 1.

[0179] Table 1

[0180] As shown in Table 1, compared with a battery made using a positive electrode 100 without protrusions 111, a battery made using a positive electrode 100 with protrusions 111 has increased electrolyte storage space and relatively increased electrolyte retention, thus improving the overall wetting effect of the electrolyte on the cell after long-term use. Meanwhile, the electrolyte retention, cycle retention rate, and expansion rate vary depending on the size of the protrusions 111. Compared with Comparative Example 5, when R1 or R2 is less than 0.5 mm, h1 is less than 3 μm, and S11 / S is less than 0.02, the changes in electrolyte retention, cycle retention rate, and expansion rate are not significant, indicating poor improvement in battery performance. When R1 or R2 is greater than 8 mm, h1 is greater than 40 μm, and S11 / S is greater than 0.85, the liquid retention increases, the cycle retention rate increases, and the expansion rate decreases, but this easily leads to an increase in battery thickness. When R1 or R2 is greater than 8 mm and h1 is less than 3 μm, the thickness at the protrusion 111 is difficult to meet the requirements, and collapse is likely to occur. When R1 = 0.5 mm to 8 mm, R2 = 0.5 mm to 8 mm, h1 = 3 μm to 40 μm, and S11 / S = 0.02 to 0.85, the liquid retention increases, the cycle retention rate increases, and the expansion rate decreases, significantly improving battery performance. Furthermore, at this point, the protrusion 111 itself has a better thickness, reducing the possibility of collapse.

[0181] Furthermore, the test results in each embodiment show that the battery expansion rate is relatively low, indicating that the positive electrode 100 with protrusion 111 provides sufficient space for the expansion of the negative electrode 500. Meanwhile, comparing the parameters in Example 5 and Comparative Example 6, it can be seen that a higher silicon content has a greater impact on the battery expansion rate.

[0182] Therefore, by increasing the electrolyte storage space through the recess 121 on the positive electrode 100, the wetting effect of the electrolyte on the entire cell can be improved after long-term use; in addition, the recess 121 can also provide deformation space for the negative electrode 500, reduce the adverse effects caused by the expansion of the negative electrode 500 material, and optimize battery performance.

[0183] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0184] In the description of this application, it should be understood that the terms "comprising" and "having" and any variations thereof used in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0185] Unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the connection within two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0186] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 application.

Claims

1. An electrode assembly, characterized in that, include: A positive electrode (100), a negative electrode (500), and a separator (200) located between the positive electrode (100) and the negative electrode (500); The positive electrode (100) has a first surface (110) and a second surface (120) opposite to each other in the thickness direction. The first surface (110) has a plurality of protrusions (111), and the second surface (120) has a plurality of recesses (121) that correspond to each of the protrusions (111) and are recessed toward the protrusions (111). The diaphragm (200) includes a first diaphragm and a second diaphragm; the first diaphragm is bonded to the first surface (110), and the second diaphragm is bonded to the second surface (120); the first diaphragm extending beyond the head end of the positive electrode (100) and the second diaphragm extending beyond the head end of the positive electrode (100) are bonded together; Wherein, the adhesive force between the first surface (110) and the diaphragm (200) is N1, and the adhesive force between the second surface (120) and the diaphragm (200) is N2, wherein N1 and N2 satisfy the following relationship: N1>N2.

2. The electrode assembly according to claim 1, characterized in that, The N1 = (1.01~2)N2.

3. The electrode assembly according to claim 1, characterized in that, The surface of the protrusion (111) that contacts the diaphragm (200) is an arc surface.

4. The electrode assembly according to claim 1, characterized in that, The protrusion (111) is spherical or near-spherical, the radius of the protrusion (111) is R1, and the radius of the concave part (121) is R2. R1 and R2 satisfy the following relationship: R1 / R2 = 1.01~2.

5. The electrode assembly according to claim 4, characterized in that, The R1 = 0.5mm to 8mm; And / or, R2 = 0.5 mm to 8 mm; and / or, the height of the end of the protrusion (111) away from the second surface (120) to the surface of the positive electrode (100) is h1; h1 = 3 μm to 40 μm.

6. The electrode assembly according to claim 1, characterized in that, The plurality of protrusions (111) are spaced apart, and the positive electrode (100) includes a straight portion (130) between two adjacent protrusions (111); The distance between the centers of two adjacent protrusions (111) is L1, and the length of the straight portion (130) between two adjacent protrusions (111) is L2. L1 and L2 satisfy the following relationship: L1 / L2 = 1.05~10.

7. The electrode assembly according to claim 6, characterized in that, The L1 = 3mm to 10mm; And / or, the L2 = 0.5mm to 8mm.

8. The electrode assembly according to claim 1, characterized in that, The area of ​​the convex part (111) is Q1, and the area of ​​the concave part (121) is Q2. Q1 and Q2 satisfy the relationship: Q1 / Q2 = 1.02~1.21; And / or, the projected area of ​​the protrusion (111) in the thickness direction of the positive electrode (100) is S1, and the projected area of ​​the concave portion (121) in the thickness direction of the positive electrode (100) is S2, wherein S1 and S2 satisfy the following relationship: S1 / S2 = 1.02 to 1.

21.

9. The electrode assembly according to claim 1, characterized in that, The number of protrusions (111) per unit area of ​​the positive electrode (100) is N, and N satisfies the relationship: 2≤N≤25, and / or, the total projected area of ​​each protrusion (111) in the unit area in the thickness direction of the positive electrode (100) is S3, and the proportion of S3 in the unit area satisfies the relationship: 0.2≤S3≤0.

8.

10. The electrode assembly according to any one of claims 1-9, characterized in that, The area on the positive electrode (100) where the protrusions (111) are concentrated is called the protrusion area (140), the total area of ​​the protrusion area (140) is S11, the total area of ​​the positive electrode (100) is S, and S11 and S satisfy the relationship: 0.02≤S11 / S≤0.

85.

11. The electrode assembly according to claim 10, characterized in that, The distance between the two ends of the convex region (140) and the positive electrode plate (100) in the longitudinal direction is K, where K = 10mm to 100mm; and / or The distance between the convex region (140) and the positive electrode plate (100) at either end edge in the width direction is M, where M = 5mm to 30mm.

12. The electrode assembly according to any one of claims 1-9, characterized in that, The positive electrode (100), the separator (200) and the negative electrode (500) are stacked and wound to form a core structure. The electrode assembly includes a main body region (300) and an arc region (400). The height of the protrusion (111) located in the arc region (400) is less than the height of the protrusion (111) located in the main body region (300).

13. The electrode assembly according to any one of claims 1-9, characterized in that, The diaphragm (200) comprises: The base membrane comprises a multilayer microporous membrane; A ceramic layer is coated on the base film, and the ceramic layer and the positive electrode (100) are disposed opposite each other.

14. The electrode assembly according to claim 13, characterized in that, The metal element content of the first surface (110) is W1, and the metal element content of the second surface (120) is W2. The W1 and W2 satisfy the following relationship: W1>W2; The metallic element includes at least one of Al, Si, Ce, Mg, Zr, or Ti.

15. The electrode assembly according to claim 13, characterized in that, The metal element content of the protrusion (111) is W11, and the metal element content of the concave part (121) is W21. The W11 and the W21 satisfy the following relationship: W11>W21; and / or The positive electrode (100) includes a straight portion (130) located between two adjacent protrusions (111); The metal element content of the protrusion (111) is W11, and the metal element content of the straight part (130) is W3. The W11 and the W3 satisfy the following relationship: W11>W3; and / or The positive electrode (100) includes a straight portion (130) located between two adjacent protrusions (111); The straight portion (130) has a metal element content of W3, and the concave portion (121) has a metal element content of W21. The W21 and W3 satisfy the following relationship: W3>W21; The metallic element includes at least one of Al, Si, Ce, Mg, Zr, or Ti.

16. The electrode assembly according to any one of claims 1-9, characterized in that, The tensile strength of the positive electrode (100) is ≥100MPa, and the ratio of the depth of the recess (121) to the tensile strength (MPa) of the positive electrode (100) is between 0.05 and 0.

2.

17. The electrode assembly according to claim 13, characterized in that, The ceramic layer is an inorganic ceramic particle coating, a coating composed of inorganic ceramic particles and PVDF, or a coating composed of inorganic ceramic particles, polymethyl methacrylate, and PVDF; wherein, The inorganic ceramic particles include one or more of α-Al2O3, γ-Al2O3, Al2O3, SiO2, CeO2, MgAl2O4, ZrO, and TiO2; The polymethyl methacrylate has a raised structure distributed in blocks or strips.

18. The electrode assembly according to claim 1, characterized in that, The negative electrode sheet (500) includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes silicon-carbon composite material and / or silicon-oxygen composite material.

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