Battery electrode sheet and preparation method therefor, and battery

Abstract

The present application discloses a battery electrode sheet. The electrode sheet comprises a current collector; an active material layer is provided on at least one surface of the current collector; the active material layer comprises active material particles and a binder; grooves are formed on the active material layer; the depth of the grooves and the amount of the binder in the active material layer of the electrode sheet satisfy the following relationship: D≤δ×B, wherein D is the depth of the grooves, δ is a depth coefficient, and B% is the mass percentage of the binder in the active material layer of the electrode sheet; when the electrode sheet is a negative electrode sheet, δ=20; and / or, when the electrode sheet is a positive electrode sheet, δ=15. The present application further provides a preparation method for the electrode sheet and a battery. The electrode sheet of the present application increases electrolyte infiltration in a thin separator system, increases the amount of electrolyte in the middle of a battery cell during cycling, and within the ranges of parameters of the present application, can avoid safety risks and improve infiltration performance.

Description

Battery electrodes, their preparation methods and batteries

[0001] This PCT application claims priority to Chinese invention patent application No. 202510297082.9, filed on March 13, 2025 with the China National Intellectual Property Administration, entitled "Battery Electrode, Method for Preparation Thereof and Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of battery technology, specifically relating to a battery electrode, its preparation method, and the battery. Background Technology

[0003] Compared to traditional energy storage methods, lithium-ion batteries offer higher energy and power densities, along with superior cycle life. These advantages have made them the preferred technology for portable electronic devices, power tools, and hybrid / fully electric vehicles. However, with advancements in science and industry, batteries are increasingly becoming a bottleneck for electronic and electric devices, leading to a growing demand from consumers and the market for lithium-ion batteries with higher energy density and longer cycle life.

[0004] Existing technologies have focused on solutions to battery wetting problems by setting laser grooves on the electrode surface, but they have not considered how to improve the final product quality of the electrode during the electrode manufacturing process.

[0005] In existing solutions, grooves are typically etched into the electrode to form multiple grooves, thus addressing the battery wettability issue. This solution designs the relationship between the binder content in the electrode and the groove depth, which can solve the safety issues caused by grooving and further improve wettability.

[0006] Because of the grooves etched on the electrode surface, the grooving process will have a thermal impact on the area near the grooves. The thermal impact will reduce the bonding effect of the binder in the electrode. The deeper the groove, the greater the thermal impact. If there is too little binder in the active material near the groove, the active material particles in the thermal impact zone will be more likely to fall off, resulting in a larger amount of dust. The risk of dust particles piercing the separator will increase, causing a short circuit between the positive and negative electrodes and creating a safety risk. At the same time, the dust particles remaining inside the groove will also reduce the wetting effect of the electrolyte. Summary of the Invention

[0007] In order to overcome the shortcomings of the prior art, this application provides a battery electrode, a method for preparing the electrode, and a battery.

[0008] The first aspect of this application provides a battery electrode, the electrode including a current collector, an active material layer disposed on at least one surface of the current collector, the active material layer comprising active material particles and a binder, and trenches disposed on the active material layer, the depth of the trenches and the binder content in the active material layer of the electrode satisfying the following relationship: D≤δ×B;

[0009] In the formula, D is the trench depth in μm; B% is the mass percentage of binder in the active material layer of the electrode; δ is a proportionality constant, where

[0010] The electrode is a negative electrode with δ = 20; and / or

[0011] The electrode is a positive electrode with δ = 15.

[0012] This application provides a battery electrode with trenches. By limiting the relationship between the trench depth and the binder content of the active material layer, the active material layer can overcome the thermal effects of the trenching process, ensuring the bonding effect of the active material particles. Simultaneously, within this range, the amount of dust is significantly reduced, preventing blockage of the electrolyte transport channels in the trenches and further enhancing wettability.

[0013] According to the electrode in the first aspect, the electrode is a negative electrode, 0.5 ≤ B ≤ 15; and / or

[0014] The electrode is a positive electrode, and 0.5 ≤ B ≤ 5.

[0015] By setting the mass percentage of binder in the active material layer of the electrode within the above range, it is beneficial to balance the battery energy density and bonding effect, so that the electrode can still maintain a good bonding effect under the heat effect of the grooving process, reduce the risk of active material particles puncturing the separator, and provide a higher energy density.

[0016] According to the electrode in the first aspect, the electrode is a negative electrode, 1≤B≤6; and / or

[0017] The electrode is a positive electrode, and 1 ≤ B ≤ 3.

[0018] By setting the mass percentage of binder in the active material layer of the electrode within the above range, it is easier to further improve the bonding effect of active material particles in the battery electrode and to obtain a higher energy density. Since the dust of the positive electrode active material and the dust of the negative electrode active material have different hardness, the risk of puncturing the separator is also different, so there are different ranges.

[0019] According to the electrode of the first aspect, the electrode is a negative electrode, and the active material is selected from one or more of the following: graphite, silicon carbide, germanium negative electrode, lithium titanate, hard carbon, metal oxide negative electrode; and / or

[0020] The adhesive is selected from one or more of the following: styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (Na-CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), and polytetrafluoroethylene (PTFE).

[0021] According to the first aspect of the electrode, the electrode is a positive electrode, and the active material is selected from one or more of the following: lithium cobalt oxide, lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium manganese oxide, and nickel-cobalt-manganese ternary positive electrode materials.

[0022] The adhesive is selected from one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA).

[0023] According to the electrode in the first aspect, the average particle size Dv50 of the active material particles is 5μm to 20μm.

[0024] When the average particle size of the active material is greater than 20 μm, the excessively large particle size can lead to a long ion diffusion path, uneven reaction, and stress concentration due to volume expansion, making the electrode prone to cracking. When the average particle size of the active material is less than 5 μm, the particle size is too small, the specific surface area is large, which can easily lead to an increase in side reactions and a decrease in electrode porosity, affecting electrolyte wetting and ion transport.

[0025] According to the electrode in the first aspect, multiple grooves are provided on the active material layer, and the multiple grooves are parallel to each other.

[0026] By setting multiple parallel trenches on the active material layer, the surface area of ​​the active material layer is increased, and the number of reactive sites is increased, which is beneficial to improving the cycle performance of the battery.

[0027] According to the electrode of the first aspect, the depth of the trench is 5 μm to 40 μm; and / or

[0028] The width of the trench is 50μm to 200μm; and / or

[0029] The spacing between two adjacent grooves is 100μm to 5000μm.

[0030] According to the electrode of the first aspect, the depth of the trench is 7 μm to 25 μm; and / or

[0031] The width of the trench is 60μm to 150μm; and / or

[0032] The spacing between two adjacent grooves is 400μm to 2500μm.

[0033] By setting the groove depth of the electrode within the above range, it is beneficial to control the thermal impact of the grooving process, so that the active material particles can still be firmly bonded and maintain good electrical connection after grooving within the range of the binder in this application.

[0034] According to the first aspect, the electrode is a negative electrode, and the cohesive force of the electrode is 5 N / m to 50 N / m; and / or

[0035] The electrode is a positive electrode, and the cohesive force of the electrode is 5 N / m to 80 N / m.

[0036] In the above scheme, the cohesive force of the electrode sheet meets the above range. Excessive cohesive force will result in low electrode sheet flexibility and easy breakage, while insufficient cohesive force will increase the risk of powder shedding during processing.

[0037] According to the electrode in the first aspect, the electrode is a negative electrode, and the cohesive force of the electrode is 8 N / m to 20 N / m; and / or

[0038] The electrode is a positive electrode, and the cohesive force of the electrode is 30N / m-60N / m.

[0039] In the above scheme, the cohesive force of the electrode meets the above range, further reducing the risk of electrode breakage and further reducing the direction of powder shedding during processing.

[0040] The second aspect of this application provides a method for preparing the battery electrode of the first aspect, including preparing trenches on the active material layer by laser processing.

[0041] According to the method in the second aspect, the process parameters for laser processing include:

[0042] Laser power is 10%–90%; and / or

[0043] The laser scanning speed is 1000mm / s to 70000mm / s.

[0044] In the above solution, by limiting the upper limit of laser power, the risk of electrode overheating or current collector melting and perforation is reduced. If the laser power is too low, it will result in shallow groove depth, unclear edges, or even failure to form continuous grooves.

[0045] If the laser scanning speed is too slow, the laser dwell time will be longer, and the energy accumulation effect will be significant, resulting in a wide groove and the heat-affected zone will extend to both sides of the groove, damaging the active material. If the laser scanning speed is too fast, it may form discontinuous groove lines or shallow grooves.

[0046] A third aspect of this application provides a battery, including the battery electrode and separator of the first aspect, wherein the thickness H of the separator satisfies 2μm≤H≤15μm.

[0047] A thinner separator can reduce energy density, but the thinner it is, the easier it is to be punctured. The solution in this application can reduce the risk of puncture while thinning the separator.

[0048] The electrode in this application improves the bonding effect of the active material by controlling the binder content, so that it can still maintain good adhesion in the thin separator system, reducing the risk of the thin separator being punctured, thereby improving the volumetric energy density of the battery.

[0049] The battery electrode of this application has, but is not limited to, the following beneficial effects:

[0050] This application provides a trenched battery electrode. By limiting the relationship between the trench depth and the binder content of the active material layer, the active material layer can overcome the thermal effects of the grooving process, ensuring the adhesion of the active material particles. Simultaneously, within this range, the amount of dust is significantly reduced, preventing blockage of the electrolyte transport channels in the trenches and further enhancing wettability. The electrode of this application increases the electrolyte wetting in the thin separator system (separator thickness not exceeding 15 μm), increasing the amount of electrolyte in the center of the cell during cycling. Within the parameter range of this application, safety risks can be avoided while improving wettability. Attached Figure Description

[0051] Figure 1 shows a cross-sectional view of a battery electrode (double-sided electrode) according to this application.

[0052] Figure 2 shows a cross-sectional view (single-sided electrode) of the battery electrode of this application.

[0053] Figure 3 shows a top view of the battery electrode sheet of this application viewed along the thickness direction.

[0054] Explanation of reference numerals in the attached diagram: 1. Current collector; 2. Active material layer; 3. Trench. Detailed Implementation

[0055] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present application will become clearer and more apparent.

[0056] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0057] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0058] This application provides a battery electrode, which includes a current collector 1. An active material layer 2 is disposed on at least one surface of the current collector 1. The active material layer 2 contains active material particles and a binder. A trench 3 is disposed on the active material layer 2. The depth of the trench 3 and the binder content in the active material layer 2 of the electrode satisfy the following relationship: D≤δ×B.

[0059] In the formula, D is the trench depth in μm; B% is the mass percentage of the binder in the active material layer 2 of the electrode; δ is a proportionality constant, where

[0060] When the electrode is a negative electrode, δ = 20;

[0061] When the electrode is a positive electrode, δ = 15.

[0062] In existing technologies, the grooving process, especially laser grooving, has a thermal impact on the area near the electrode trenches. As the temperature rises, the thermal motion between binder molecules intensifies, the intermolecular interaction force weakens, and the cohesive force decreases, resulting in a poorer bonding effect of the binder in the active material layer 2. When the binder content in the active material layer 2 is too low, the thermal impact of the grooving process can cause active material particles near the trench 3 to detach, posing a risk of puncturing the separator. Furthermore, the thermal impact of the grooving process increases with the increase in trench depth. This application provides a battery electrode with trenches. By limiting the relationship between trench depth and binder content in the active material layer 2, the active material layer 2 can overcome the thermal impact of the grooving process, ensuring the bonding effect of the active material particles. Simultaneously, within this range, the amount of dust is significantly reduced, preventing blockage of the electrolyte transport channels in the trench 3 and further enhancing wettability.

[0063] The mass percentage B% of the binder in the active material layer 2 can be determined by thermogravimetric analysis, for example, by the following methods:

[0064] Scrape at least 1g of powder from the active material layer of the battery electrode and place the powder in a thermogravimetric analyzer. Set the temperature range to 20–500℃, the heating rate to 5℃ / min, and the gas atmosphere to air. Then run the equipment. The weight reduction that occurs between 200 and 400℃ is the mass of the binder. The mass percentage of the weight reduction to the total weight of the powder is the mass percentage of the binder in the active material layer, B.

[0065] Since the magnitude of the heat-affected zone is mainly related to the depth of the trench, and since the hardness of the positive and negative electrode dust is different (positive electrode dust mainly consists of positive electrode material particles and a small amount of positive electrode binder carbonized at high temperature, while negative electrode dust mainly consists of negative electrode material particles and a small amount of negative electrode binder carbonized at high temperature), the risk of positive and negative electrode dust puncturing the diaphragm is different. Therefore, the depth coefficient δ of the positive and negative electrode sheets is different, with the depth coefficient δ of the positive electrode sheet being smaller than that of the negative electrode sheet. Under these conditions, the dust generated by the trenching will not pose a safety risk.

[0066] In one embodiment, when the electrode is a negative electrode, 0.5≤B≤15, preferably 1≤B≤6;

[0067] When the electrode is a positive electrode, 0.5≤B≤5, preferably 1≤B≤3.

[0068] If the mass percentage B% of the binder in the active material layer 2 of the electrode is too high, it will lead to a decrease in the energy density of the battery and further affect the conductivity and other properties of the electrode. If the mass percentage B% of the binder in the active material layer 2 of the electrode is too low, the bonding effect will be poor, and the active material particles will be very easy to fall off under the heat effect of the grooving process. The risk of the detached active material particles piercing the separator will increase.

[0069] In one embodiment, when the electrode is a negative electrode, the active material is selected from one or more of the following: graphite, silicon carbide, germanium negative electrode, lithium titanate, hard carbon, and metal oxide negative electrode; specifically, the metal oxide negative electrode can be a cobalt oxide negative electrode, a titanium oxide negative electrode, etc.; and / or

[0070] The adhesive is selected from one or more of the following: styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (Na-CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), and polytetrafluoroethylene (PTFE).

[0071] In one embodiment, when the electrode is a positive electrode, the active material is selected from one or more of the following: lithium cobalt oxide, lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium manganese oxide, and nickel-cobalt-manganese ternary positive electrode materials.

[0072] The adhesive is selected from one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA).

[0073] In one embodiment, the average particle size Dv50 of the active substance particles is 5 μm to 20 μm.

[0074] When the average particle size of the active material is greater than 20 μm, the excessively large particle size can lead to a long ion diffusion path, uneven reaction, and stress concentration due to volume expansion, making the electrode prone to cracking. When the average particle size of the active material is less than 5 μm, the particle size is too small, the specific surface area is large, which can easily lead to an increase in side reactions and a decrease in electrode porosity, affecting electrolyte wetting and ion transport.

[0075] In this application, the average particle size Dv50 of the active material particles refers to the diameter corresponding to when the cumulative percentage of active material particles reaches 50%.

[0076] In this application, the Dv50 particle size of the active material particles in the counter electrode can be obtained by the following method:

[0077] a) Disassemble the fully discharged battery to obtain the electrode sheet, and then cut any position in the active material area of ​​the electrode sheet to obtain a cross-sectional sample of the electrode sheet; b) Place the above cross-sectional sample of the electrode sheet in an SEM for observation. Adjust the SEM voltage and magnification according to actual needs to ensure that enough particles in the above sample can be clearly seen and photographed to obtain SEM images; c) The particle size of the particles in the obtained SEM images can be counted; d) Perform 20 experiments in total, and count no less than 500 particles in each experiment. After counting the above results, obtain the Dv50 particle size of the electrode active material particles in the electrode sheet.

[0078] In one embodiment, the active material layer 2 is provided with multiple grooves 3, which are parallel to each other.

[0079] This application provides multiple parallel grooves 3 on the surface of the active material layer 2. The shape of the grooves 3 is not particularly limited. The top view distribution shape of the grooves 3 along the thickness direction can be a straight line, a broken line, a curve, etc.

[0080] In the embodiments of this application, parallel distribution of trenches means that the axes of any two trenches 3 along their length are parallel to each other, as shown by the dashed center line of the trenches 3 in Figure 3. However, due to process errors, measurement errors, etc., a certain angle is allowed between the axes of the two trenches 3, which is ±10°. These embodiments are all included within the protection scope of the claims of this application.

[0081] In one embodiment, the depth of the trench 3 is 5 μm to 40 μm, preferably 7 μm to 25 μm;

[0082] The width of the groove 3 is 50 μm to 200 μm, preferably 60 μm to 150 μm; and / or

[0083] The spacing between two adjacent grooves 3 is 100μm to 5000μm, preferably 400μm to 2500μm.

[0084] In this application, there are no particular limitations on the measurement methods for trench depth D, trench width L, and trench spacing S; all can be measured using conventional methods, such as the following methods:

[0085] A VK-1050 laser confocal microscope was used to photograph the groove area, acquiring optical and depth information of the electrode within the microscope's field of view. The electrode surface was scanned using laser confocal mode at 20x magnification. After scanning, the acquired measurement data was processed in the instrument's associated data analysis software. The "Reference Plane Setting" function in "Image Processing" was used to set the reference plane for the measurement data. Then, the "Smoothing" function was selected, choosing a size of 5×5 and the "Simple Average" type to smooth the image. After processing, the groove parameters were measured using the "Contour Measurement" function.

[0086] Trench depth D and trench width L: As shown in Figures 1 and 2, the depth difference between the deepest point of the trench and the reference surface is the trench depth D, and the distance between the intersection points of the two sides of the trench and the reference surface is the trench width L. Measurements are taken along the same trench at 10 μm intervals, for a total of 20 measurements. The average value of the depth and width from these 20 measurements is calculated and recorded as the trench depth D and width L.

[0087] Trench spacing S: As shown in Figure 1-3, for two adjacent trenches, the distance between the midpoints of the widths of the two adjacent trenches along the length of the electrode is the trench spacing. Measurements are taken every 10 μm along the selected trench, for a total of 20 measurements. The average value is calculated and recorded as the trench spacing S.

[0088] In one embodiment, when the electrode is a negative electrode, the cohesive force of the electrode is 5 to 50 N / m, preferably 8 to 20 N / m;

[0089] When the electrode is a positive electrode, the cohesive force of the electrode is 5 to 80 N / m, preferably 30 to 60 N / m.

[0090] In the above scheme, the cohesive force of the electrode sheet meets the above range. Excessive cohesive force will result in low electrode sheet flexibility and easy breakage, while insufficient cohesive force will increase the risk of powder shedding during processing.

[0091] In this application, the cohesive force of the electrode can be tested by the following method (test environment temperature is room temperature):

[0092] (1) Cut a piece of double-sided tape (width: 20mm, length: 60-70mm) and stick it on the steel plate;

[0093] (2) Cut a piece of the positive electrode to be tested and attach it to the double-sided adhesive (completely cover it);

[0094] (3) Cut a piece of low-tack paper (such as Australia-China EAS016-101), cover it on the test surface, and use a 2kg pressure roller to ensure that the low-tack paper adheres to the test surface;

[0095] (4) The tensile tester stretches the low-adhesion paper at 50 mm / min and with the stretching direction at 180° to the test surface until a peeling fracture surface appears. The reading of the tensile tester at this time is the cohesion of the functional protective layer (when testing the cohesion, the peeling fracture surface is inside the coating. It can be determined by observing the appearance on both sides of the fracture surface, and can also be confirmed by the height of the fracture surface and the current collector).

[0096] This application also provides a method for preparing the aforementioned battery electrode, including preparing trenches 3 on the active material layer 2 by laser processing.

[0097] In one embodiment, the process parameters for laser processing include:

[0098] Laser power is 10%–90%; and / or

[0099] The laser scanning speed is 1000–70000 mm / s.

[0100] In one specific implementation, the method may employ a fiber laser and a flight processing approach.

[0101] In the above solution, by limiting the upper limit of laser power, the risk of electrode overheating or current collector melting and perforation is reduced. If the laser power is too low, it will result in shallow groove depth, unclear edges, or even failure to form continuous grooves.

[0102] If the laser scanning speed is too slow, the laser dwell time will be longer, resulting in a significant energy accumulation effect, leading to excessively wide grooves and the heat-affected zone extending to both sides of the groove, damaging the active material. Conversely, if the laser scanning speed is too fast, it may create discontinuous groove lines or shallow grooves. The electrode in this application maintains good adhesion even under the heat-affected zone of laser processing by controlling the binder content. This application also improves lithium plating and cycle degradation of the battery by using laser processing technology to create a uniform channel structure in the positive and negative electrode sheets.

[0103] This application provides a lithium-ion battery, including the aforementioned battery electrode and separator, wherein the thickness H of the separator satisfies 2.5μm≤H≤15μm.

[0104] The electrode in this application is applicable to thin separator membrane systems (separator membrane thickness not greater than 15 μm). The thickness of the separator membrane refers to the total thickness including the base membrane, the functional coating of the separator membrane (such as ceramic coating), and the adhesive coating of the separator membrane. The separator membrane can be a single-layer membrane or a multi-layer composite membrane.

[0105] The thickness H of the separator can be any value from 2.5μm to 15μm, such as 2.5μm, 3μm, 3.5μm, 4.5μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, and 15μm.

[0106] While thick separator systems have a low risk of being punctured by detached active material particles, their greater thickness results in a lower volumetric energy density. The electrode in this application improves the adhesion of the active material by controlling the binder content, allowing it to maintain good adhesion even in a thin separator system. This reduces the risk of the thin separator being punctured, thereby increasing the volumetric energy density of the battery.

[0107] This application does not impose any special restrictions on the source of any raw materials. Unless otherwise specified, all raw materials are conventional products that can be obtained through commercial purchase.

[0108] Examples and Comparative Examples

[0109] The battery systems used in the embodiments and comparative examples of this application include:

[0110] (1) Positive electrode plate:

[0111] Lithium cobalt oxide, superconducting carbon as a conductive agent, and polyvinylidene fluoride as a binder are uniformly mixed at a mass ratio of 96:2:2 to prepare a lithium-ion battery positive electrode slurry with a certain viscosity. The slurry is coated on both sides of the aluminum foil current collector 1, dried at 95°C, and then cold-pressed to form a double-sided positive electrode active material layer 2. Then, the edges are cut, sliced, and slit. After slitting, the slits are dried at 85°C under vacuum for 4 hours. Then, the tabs are welded to produce a lithium-ion battery positive electrode sheet. The lithium-ion battery positive electrode sheet is a double-sided positive electrode sheet, and the thickness of the active material layer 2 on each side is 50μm.

[0112] (2) Negative electrode plate:

[0113] Graphite, conductive agent SP, stabilizer sodium carboxymethyl cellulose (CMC), and binder are mixed evenly at a mass ratio of 96.5:1.0:1.0:1.5 to form a slurry. This slurry is then coated on both sides of the copper foil of current collector 1 and dried at 85°C before cold pressing to form the negative electrode active material layer 2. The slurry is then trimmed, cut into sheets, and slit. After slitting, the sheets are dried at 110°C under vacuum for 4 hours and then the tabs are welded to form the negative electrode sheet of the lithium-ion battery. The negative electrode sheet of the lithium-ion battery is a double-sided positive electrode sheet, and the thickness of the active material layer 2 on each side is 57μm.

[0114] Laser grooving is performed on the positive and negative electrode sheets. The laser grooving methods for the positive and negative electrodes are as follows:

[0115] The positive and negative electrodes utilize fiber lasers and a flight processing method.

[0116] Laser process parameters:

[0117] Power: 10%–90%;

[0118] Laser speed: 1000~70000mm / s.

[0119] In Example 2, the laser power was 30% and the laser speed was 20000mm / s in the groove 3 with a negative electrode groove depth of 13μm, a groove width of 90μm, and a groove spacing of 1.3mm.

[0120] (3) Electrolyte:

[0121] A solution was prepared by mixing LiPF6 with a solvent (ethylene carbonate: diethyl carbonate: methyl ethyl carbonate: vinyl carbonate in a mass ratio of 8:85:5:2) at a mass ratio of 8:92, and used as the electrolyte for lithium-ion batteries.

[0122] (4) Separating membrane:

[0123] In Examples 1-18 and Comparative Examples 1 and 5, the substrate of the separator is a 5μm thick polypropylene separator, the ceramic coating is alumina, a single-sided coating with a total thickness of 2μm, the adhesive coating is polyvinylidene fluoride, a double-sided coating with a total thickness of 2μm, and the total thickness of the separator is 9μm.

[0124] In Comparative Examples 2-3, the substrate of the separator was a 13μm thick polypropylene separator, the ceramic coating was alumina, and a double-sided coating was used, with a total thickness of 2μm for the ceramic coating. The adhesive coating was polyvinylidene fluoride, and a double-sided coating was used, with a total thickness of 2μm for the adhesive coating. The total thickness of the separator was 17μm.

[0125] Preparation of lithium-ion batteries:

[0126] The above-mentioned positive electrode, separator, and negative electrode are wound into a battery cell, with the separator positioned between the positive and negative electrode. The positive electrode is led out by spot welding with aluminum tabs, and the negative electrode is led out by spot welding with nickel tabs. The battery cell is then placed in an aluminum-plastic packaging bag, injected with the above-mentioned electrolyte, and processed through processes such as encapsulation, formation, and capacity testing to produce a polymer lithium-ion battery.

[0127] The battery parameters prepared in Examples 1-4 and Comparative Examples 1-3 are shown in Table 1.

[0128] Table 1

[0129] *The particle size of the active material mentioned in Table 1 refers to the average particle size Dv50.

[0130] Performance Evaluation

[0131] The lithium plating interface, cycle performance and self-discharge performance of the batteries prepared in Examples 1-3 and Comparative Examples 1-4 were evaluated.

[0132] (1) Comparison method for lithium plating interfaces:

[0133] At a test ambient temperature of 25°C, the batteries of the comparative example and the embodiment were charged and discharged 10 times using the same charging process. The batteries were then disassembled and the lithium plating interface of the anode electrode was observed for comparison.

[0134] Charging process:

[0135] Step 1: Charge the battery to 4.5V using a constant current of 2C;

[0136] Step 2: Charge the battery to 0.05C using a constant voltage of 4.5V;

[0137] Step 3: Let the battery sit for 5 minutes;

[0138] Step 4: Discharge the battery to 3.0V using a constant current of 0.5C;

[0139] Step 5: Let the battery sit for 5 minutes;

[0140] Step Six: Repeat steps one through five 10 times.

[0141] The battery cells that had undergone 10 cycles were disassembled, and the interface of the anode electrode was observed for comparison. To describe the lithium plating at the interface, the interface conditions were graded. By visual inspection, if the anode electrode surface was golden yellow and showed no abnormalities, it was determined to be non-lithium plating; if the anode electrode showed intermittent punctate purple spots, lithium plating, or lithium plating on purple spots, it was determined to be slight lithium plating; if the main body of the anode electrode showed large areas of continuous purple spots, lithium plating, or lithium plating on purple spots, and the abnormal area percentage was <50%, it was determined to be lithium plating; if the main body of the anode electrode showed large areas of continuous purple spots, lithium plating, or lithium plating on purple spots, and the abnormal area percentage was ≥50%, it was determined to be severe lithium plating. The test results are shown in Table 2.

[0142] (2) Cycle performance test of lithium-ion batteries:

[0143] Methods for calculating capacity retention include:

[0144] At a test ambient temperature of 25°C, the batteries of the comparative example and the embodiment were charged and discharged 500 times using the same charging process. The discharge capacity after 500 charge and discharge cycles was then divided by the discharge capacity at the first cycle to obtain the capacity retention rate.

[0145] Charging process:

[0146] Step 1: Charge the battery to 4.5V using a constant current of 2C;

[0147] Step 2: Charge the battery to 0.05C using a constant voltage of 4.5V;

[0148] Step 3: Let the battery sit for 5 minutes;

[0149] Step 4: Discharge the battery to 3.0V using a constant current of 0.5C;

[0150] Step 5: Let the battery sit for 5 minutes;

[0151] Step Six: Repeat steps one through five 500 times.

[0152] The test results are shown in Table 2.

[0153] (3) Self-discharge test:

[0154] Self-discharge rate testing is a characterization method that can characterize the internal short circuit of a battery cell. When dust particles puncture the separator, it will cause an internal short circuit in the battery cell, and the self-discharge rate will increase.

[0155] Test process:

[0156] The battery cell is charged to 3.9V at a rate of 0.2C. After standing for 2 hours, its initial voltage V0 is measured. The battery cell is then left to stand at 25℃ for 72 hours, and the voltage V1 after standing is measured. Then: Self-discharge rate = (V1-V0) / 72mV / h;

[0157] A self-discharge rate ≤ 0.04mV / h indicates that the test has been passed.

[0158] In this application, 1000 battery cells were prepared for each embodiment and comparative example and self-discharge tests were conducted. The test pass rate results are shown in Table 2.

[0159] (4) Methods for testing volumetric energy density:

[0160] Battery cell capacity testing:

[0161] The battery cells were left to stand at 25°C for 2 hours to ensure the temperature of the battery cells remained at 25°C. Then, the batteries were discharged at a constant current of 1 / 3C to 3.0V. After standing for 5 minutes, the battery cells were charged at a constant current of 1 / 3C to 4.48V. Then, they were charged at a constant voltage of 4.5V until the current was 0.05C. After standing for 5 minutes, the battery cells were discharged at a constant current of 1 / 3C to 3.0V. The total discharge capacity C0 and the total discharge energy E0 of the battery cells were recorded. The unit of total discharge energy is Wh.

[0162] Battery cell volume measurement:

[0163] Use calipers to measure the length, width, and height of the battery's outer surface, and calculate the volume V0 of a single battery cell (in liters).

[0164] Volumetric energy density calculation:

[0165] The volumetric energy density of a battery cell is calculated as E0 / V0, where E0 is the discharge energy of the individual cell and V0 is the battery volumetric energy density, expressed in Wh / L. The test results are shown in Table 2.

[0166] Table 2

[0167] As can be seen from the results in Table 2, in Comparative Example 1, the electrode without grooves showed poor wettability under the thin separator system (10 μm separator thickness), resulting in severe lithium plating and a significant decrease in capacity retention. Comparative Examples 2 and 3 used a 17 μm thick separator, which achieved high self-discharge test pass rate and maintained high capacity retention and wettability. However, because the separator thickness was increased by 70% compared to the example, the overall cell thickness increased, leading to a significant decrease in the overall volumetric energy density of the cell. In Comparative Examples 4 and 5, the excessive depth of the trenches 3 and the low content of the electrode binder resulted in the active material layer 2 being subjected to heat from the grooving process. The impact is significant, increasing the risk of positive electrode active material particles detaching from the trench near trench 3 due to heat puncturing the separator, resulting in a low self-discharge test pass rate. In Examples 15 and 17, the low content of electrode binder B leads to low electrode cohesion, increasing the risk of active material particles detaching from the trench near trench 3 due to heat puncturing under the influence of the grooving process, resulting in a low self-discharge test pass rate. In Example 16, the high content of positive electrode binder B leads to a significant decrease in electrode volumetric energy density. In Example 18, the high content of electrode binder B leads to a decrease in electrode kinetic performance, resulting in poor electrolyte wetting and lithium plating during cycling.

[0168] In the embodiment, the electrode sheet, under the thin separator system, by limiting the relationship between the trench depth and the binder content of the active material layer 2, enables the active material layer 2 to overcome the thermal effects caused by the grooving process, ensuring the bonding effect of the active material particles, and obtaining an electrode sheet with good wetting effect, high capacity retention and high volumetric energy density, which is suitable for high energy density batteries.

[0169] The present application has been described above with reference to preferred embodiments; however, these embodiments are merely exemplary and illustrative. Various substitutions and modifications can be made to the present application based on these embodiments, all of which fall within the protection scope of the present application.

Claims

A battery electrode, characterized in that, The electrode includes a current collector, and an active material layer is disposed on at least one surface of the current collector. The active material layer comprises active material particles and a binder, and grooves are disposed on the active material layer. The depth of the grooves and the binder content in the active material layer of the electrode satisfy the following relationship: D≤δ×B; In the formula, D is the trench depth in μm; B% is the mass percentage of binder in the active material layer of the electrode; δ is a proportionality constant, where The electrode is a negative electrode with δ = 20; and / or The electrode is a positive electrode with δ = 15. The battery electrode according to claim 1 is characterized in that, The electrode is a negative electrode, with a value of 0.5 ≤ B ≤ 15; and / or The electrode is a positive electrode, with 0.5 ≤ B ≤ 5. The battery electrode according to claim 2 is characterized in that, The electrode is a negative electrode, 1≤B≤6; and / or The electrode is a positive electrode, where 1 ≤ B ≤ 3. The battery electrode according to claim 1 is characterized in that, The electrode is a negative electrode, and the active material is selected from one or more of the following: graphite, silicon carbide, germanium negative electrode, lithium titanate, hard carbon, metal oxide negative electrode; and / or The adhesive is selected from one or more of the following: styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (Na-CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), and polytetrafluoroethylene (PTFE). The battery electrode according to claim 1 is characterized in that, The electrode is a positive electrode, and the active material is selected from one or more of the following: lithium cobalt oxide, lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium manganese oxide, and nickel-cobalt-manganese ternary positive electrode materials. The adhesive is selected from one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA). The battery electrode according to claim 1 is characterized in that, The average particle size Dv50 of the active substance particles is 5μm to 20μm. The battery electrode according to claim 1 is characterized in that, The active material layer has multiple grooves, which are parallel to each other. The battery electrode according to claim 7 is characterized in that, The depth of the trench is 5μm to 40μm; and / or The width of the trench is 50μm to 200μm; and / or The distance between two adjacent grooves is 100μm to 5000μm. The battery electrode according to claim 8 is characterized in that, The depth of the trench is 7μm to 25μm; and / or The width of the trench is 60μm to 150μm; and / or The distance between two adjacent grooves is 400μm to 2500μm. The battery electrode according to claim 1 is characterized in that, The electrode is a negative electrode, and the cohesive force of the electrode is 5 N / m to 50 N / m; and / or The electrode is a positive electrode, and the cohesive force of the electrode is 5 N / m to 80 N / m. The battery electrode according to claim 10 is characterized in that, The electrode is a negative electrode, and the cohesive force of the electrode is 8 N / m to 20 N / m; and / or The electrode is a positive electrode, and the cohesive force of the electrode is 30 N / m-60 N / m. The method for preparing the battery electrode sheet according to any one of claims 1 to 11 includes preparing trenches on the active material layer by laser processing. The method according to claim 12, characterized in that, The laser processing parameters include: Laser power is 10%–90%; and / or The laser scanning speed is 1000mm / s to 70000mm / s. A battery comprising the battery electrode and separator as described in any one of claims 1 to 11, wherein, The thickness H of the isolation membrane satisfies the condition that 2μm≤H≤15μm.

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