Battery pole piece, preparation method thereof and battery

Abstract

The invention discloses a battery pole piece, the pole piece comprises a current collector, at least one surface of the current collector is provided with an active material layer, the active material layer comprises active substance particles and a binder, the active material layer is provided with a groove, and the groove is formed in the surface of the current collector. The depth of the groove and the content of the binder in the active material layer of the pole piece meet the following relation: D is less than or equal to delta * B; wherein D is the depth of the groove; delta is the depth coefficient, B% is the mass percentage content of the binder in the active material layer of the pole piece, the pole piece is a negative pole piece, and delta is equal to 20; and / or the pole piece is a positive pole piece, and delta is equal to 15. The invention also provides a preparation method of the pole piece and a battery. According to the pole piece, infiltration of the electrolyte in a thin isolating membrane system is increased, the electrolyte amount in the middle of the battery cell in the circulation process is increased, and within the parameter range of the pole piece, the safety risk can be avoided, and meanwhile the wettability is improved.

Description

Technical Field

[0001] This application belongs to the technical field of batteries, and particularly relates to a battery electrode sheet, a preparation method thereof, and a battery. Background Art

[0002] Compared with traditional energy storage forms, lithium-ion batteries have higher energy density and power density, and their cycle life is also more excellent. Thanks to the above advantages, lithium-ion batteries have quickly become the preferred technology for portable electronic devices, power tools, and hybrid / full electric vehicles. However, with the development of science and technology and industrial technology, batteries have gradually become a bottleneck for electronic and electric devices, and consumers and the market have a more urgent need for lithium-ion batteries with higher energy density and longer cycle life.

[0003] In the prior art, a solution to solve the battery infiltration problem by setting laser grooves on the surface of the electrode sheet has been noticed, but in the prior art, how to make the final formed product of the electrode sheet better in the electrode sheet process has not been considered.

[0004] In the existing solution, generally grooves are engraved on the electrode sheet to form multiple groove positions to solve the problem of battery wettability. This solution designs the relationship between the binder content and the groove depth in the electrode sheet, which can solve the safety problems brought by grooving and better improve the wettability.

[0005] Since grooves are engraved on the surface of the electrode sheet, the grooving process will have a thermal effect on the area near the grooves of the electrode sheet. The thermal effect will make the bonding effect of the binder in the electrode sheet worse. The deeper the groove, the greater the thermal effect. If the amount of binder in the active material near the groove is too small, the active material particles in the thermal affected zone will be more likely to fall off, resulting in a larger amount of dust generated. The risk of dust particles piercing the separator will increase, leading to short circuit between the positive and negative electrodes and generating safety risks. At the same time, the remaining dust particles inside the grooves will also reduce the effect of electrolyte infiltration. Summary of the Invention

[0006] In order to overcome the defects of the prior art, this application provides a battery electrode sheet, a preparation method thereof, and a battery.

[0007] In the first aspect of this application, a battery electrode sheet is provided. The electrode sheet includes a current collector, and an active material layer is provided on at least one surface of the current collector. The active material layer contains active material particles and a binder. Grooves are provided on the active material layer, and the depth of the grooves and the binder content in the active material layer of the electrode sheet satisfy the following relationship:

[0008] D≤δ×B;

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

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

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

[0012] This application provides a battery electrode with grooves. By defining the relationship between the groove depth and the binder content in the active material layer, the active material layer can overcome the thermal influence brought by the grooving process, ensuring the bonding effect of the active substance particles. Meanwhile, within this range, the amount of dust will be significantly reduced, and the electrolyte transmission channels of the grooves will not be blocked, further enhancing the wettability.

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

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

[0015] By setting the mass percentage content of the binder in the active material layer of the electrode within the above range, it is beneficial to balance the battery energy density and the bonding effect, enabling the electrode to maintain a good bonding effect under the thermal influence of the grooving process, reducing the risk of the active substance particles piercing the separator after falling off, and providing a relatively high energy density.

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

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

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

[0019] For the electrode according to 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 binder is selected from one or more of the following: styrene-butadiene rubber SBR, sodium carboxymethyl cellulose Na-CMC, polyacrylic acid PAA, polyvinyl alcohol PVA, polytetrafluoroethylene PTFE.

[0021] For the electrode according to the first aspect, the electrode is a positive electrode, and the active material is selected from one or more of the following: lithium cobaltate, lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium manganate, nickel cobalt manganese ternary cathode material;

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

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

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

[0025] For the electrode sheet according to the first aspect, a plurality of grooves are provided on the active material layer, and the plurality of grooves are parallel to each other.

[0026] By providing a plurality of parallel grooves on the active material layer, the surface area of the active material layer is increased, the reaction active sites are increased, which is beneficial to improving the cycle performance of the battery.

[0027] For the electrode sheet according to the first aspect, the depth of the groove is 5 μm to 40 μm; and / or

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

[0029] the distance between two adjacent grooves is 100 μm to 5000 μm.

[0030] For the electrode sheet according to the first aspect, the depth of the groove is 7 μm to 25 μm; and / or

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

[0032] the distance between two adjacent grooves is 400 μm to 2500 μm.

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

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

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

[0036] In the above scheme, the cohesive force of the electrode sheet satisfies the above range. If the cohesive force is too large, the flexibility of the electrode sheet will be low and it is easy to break. If the cohesive force is too small, the risk of powder falling off during the processing will increase.

[0037] According to 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 30 N / m - 60 N / m.

[0039] In the above solution, the cohesive force of the electrode satisfies the above range, further reducing the risk of the electrode being easily broken and further reducing the risk of powder falling off during the processing.

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

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

[0042] the laser power is 10% - 90%; and / or

[0043] the laser scanning speed is 1000 mm / s - 70000 mm / s.

[0044] In the above solution, by limiting the upper limit of the laser power, the risk of overburning of the electrode or melting and perforation of the current collector is reduced. If the laser power is too low, the groove depth will be shallow, the edge will be unclear, and even a continuous channel cannot be formed.

[0045] If the laser scanning speed is too slow, the laser residence time is longer, and the energy accumulation effect is significant, resulting in too large a groove width and the thermal influence area extending to both sides of the groove, damaging the active material; if the laser scanning speed is too fast, discontinuous groove lines or shallow grooves may be formed.

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

[0047] A thinner separator can reduce the energy density, but the thinner it is, the easier it is to be punctured. By adopting the solution of the present application, the risk of being punctured can be reduced while the separator is thinned.

[0048] The electrode of the present application improves the bonding effect of the active substance by regulating the binder content, enabling it to still maintain good bonding in a thin separator system, reducing the risk of the thin separator being punctured, and thus improving the volumetric energy density of the battery.

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

[0050] The present application provides a battery electrode plate with grooves. By defining the relationship between the groove depth and the binder content in the active material layer, the active material layer can overcome the thermal influence brought by the grooving process and ensure the bonding effect of the active material particles. Meanwhile, within this range, the amount of dust will be significantly reduced, and the electrolyte transmission channels of the grooves will not be blocked, further enhancing the wettability. The electrode plate of the present application increases the wetting of the electrolyte in the thin separator system (the thickness of the separator is not more than 15 μm), increases the amount of electrolyte in the middle of the battery cell during the cycling process, and can avoid safety risks and improve the wettability within the parameter range of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 FIG. shows a cross-sectional view (double-sided electrode) of the battery electrode plate of the present application.

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

[0053] Figure 3 FIG. shows a top view of the battery electrode plate of the present application observed along the thickness direction.

[0054] DESCRIPTION OF THE REFERENCE NUMERALS:

[0055] 1. Current collector; 2. Active material layer; 3. Groove. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] The present application will be further described in detail below with reference to the drawings and embodiments. Through these descriptions, the features and advantages of the present application will become more clear and definite.

[0057] The special term "exemplary" here means "serving as an example, embodiment or illustration". Any embodiment described here as "exemplary" does not have to be construed as superior or better than other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings do not have to be drawn to scale unless otherwise specified.

[0058] In addition, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0059] The present application provides a battery electrode plate, which includes a current collector 1. An active material layer 2 is provided on at least one surface of the current collector 1. The active material layer 2 contains active material particles and a binder. A groove 3 is provided on the active material layer 2. The depth of the groove 3 and the binder content in the active material layer 2 of the electrode plate satisfy the following relationship:

[0060] D ≤ δ × B;

[0061] Wherein, D is the groove depth, with the unit of μm; B% is the mass percentage of the binder in the active material layer 2 of the electrode; δ is a proportionality constant, where

[0062] When the electrode is a negative electrode, δ = 20;

[0063] When the electrode is a positive electrode, δ = 15.

[0064] In the prior art process, since the grooving process, especially the laser grooving method, will have a thermal effect on the area near the grooves of the electrode, as the temperature rises, the thermal motion of the binder molecules in the active material layer 2 intensifies, the intermolecular interaction force weakens, and the cohesive force decreases accordingly, thus making the bonding effect of the binder in the active material layer 2 worse. When the content of the binder in the active material layer 2 is too low, the thermal effect of the grooving process will cause the active material particles near the grooves 3 to fall off, posing a risk of piercing the separator membrane. As the groove depth increases, the thermal effect of the grooving process also increases accordingly. The present application provides a battery electrode with grooves. By defining the relationship between the groove depth and the binder content of the active material layer 2, the active material layer 2 can overcome the thermal effect brought by the grooving process and ensure the bonding effect of the active material particles. Meanwhile, within this range, the amount of dust will be significantly reduced, and the electrolyte transmission channels of the grooves 3 will not be blocked, further enhancing the wettability.

[0065] The mass percentage B% of the binder in the active material layer 2 can be determined by thermogravimetric analysis. For example, it can be tested by the following method:

[0066] Scrape powder (not less than 1 g) from the active material layer of the battery electrode and place the powder in a thermogravimetric analyzer. Set the temperature range from 20 to 500 °C, the heating rate is 5 °C / min, and the gas atmosphere is air. Then run the equipment. The weight reduction that occurs between 200 and 400 °C is the mass of the binder, and the mass percentage of the weight reduction in the total weight of the powder is the mass percentage B% of the binder in the active material layer.

[0067] Since the magnitude of the thermal effect is mainly related to the groove depth, and at the same time, due to the different hardnesses of the positive and negative dusts, the main components of the positive dust include positive electrode material particles and some products obtained by high-temperature carbonization of a small amount of positive electrode binders, and the main components of the negative dust include negative electrode material particles and some products obtained by high-temperature carbonization of a small amount of negative electrode binders. The positive dust is harder, so the risks of the positive and negative dusts piercing the separator are different. Therefore, the depth coefficients δ of the positive and negative electrodes are different, and the depth coefficient δ of the positive electrode is less than that of the negative electrode. Under this condition, the dust generated by grooving will not pose a safety risk.

[0068] In one embodiment, when the electrode is a negative electrode, 0.5 ≤ B ≤ 15, preferably 1 ≤ B ≤ 6;

[0069] When the electrode is a positive electrode, 0.5 ≤ B ≤ 5, preferably 1 ≤ B ≤ 3.

[0070] If the mass percentage B% of the binder in the active material layer 2 of the electrode is too high, it will cause a decrease in the energy density of the battery, further affecting 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 binding effect is poor, and the active material particles are extremely easy to fall off under the thermal influence of the grooving process. The risk of the fallen active material particles piercing the separator increases.

[0071] 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, metal oxide negative electrode; specifically, the metal oxide negative electrode can be cobalt oxide negative electrode, titanium oxide negative electrode, etc.; and / or

[0072] The binder is selected from one or more of the following: styrene-butadiene rubber SBR, sodium carboxymethyl cellulose Na-CMC, polyacrylic acid PAA, polyvinyl alcohol PVA, polytetrafluoroethylene PTFE.

[0073] In one embodiment, when the electrode is a positive electrode, the active material is selected from one or more of the following: lithium cobaltate, lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium manganate, nickel cobalt manganese ternary cathode material;

[0074] The binder is selected from one or more of the following: polyvinylidene fluoride PVDF, polytetrafluoroethylene PTFE, polyacrylic acid PAA.

[0075] In one embodiment, the average particle size Dv50 of the active material particles is 5 μm to 20 μm.

[0076] When the average particle size of the active material particles is greater than 20 μm, the particle size is too large, which is likely to cause a long ion diffusion path, uneven reaction, and stress concentration due to volume expansion, and the electrode is prone to cracking; when the average particle size of the active material particles is less than 5 μm, the particle size is too small, the specific surface area is large, which is likely to cause an increase in side reactions, and the porosity of the electrode decreases, affecting the infiltration of the electrolyte and ion transport.

[0077] In this application, the average particle size Dv50 of the active material particles refers to the diameter corresponding to when the cumulative number percentage of the active material particles reaches 50%.

[0078] In this application, when the Dv50 particle size of the active material particles in the electrode can be obtained by the following method:

[0079] a) Disassemble the fully discharged battery to obtain the electrode sheet, and then cut any position of the active material area of the electrode sheet to obtain an electrode sheet cross-section sample; b) Place the above electrode sheet cross-section sample in an SEM for observation, adjust the electron microscope voltage and magnification according to actual needs to ensure that enough particles in the above sample can be clearly seen and take pictures to obtain SEM photos; c) The particle sizes of the particles in the obtained SEM photos can be statistically analyzed; d) Conduct 20 experiments cumulatively. In each experiment, the number of particles statistically analyzed is not less than 500 pcs. After statistically analyzing the above results, the Dv50 particle size of the electrode active material particles in the electrode sheet is obtained.

[0080] In one embodiment, a plurality of grooves 3 are provided on the active material layer 2, and the plurality of grooves 3 are parallel to each other.

[0081] In the present application, a plurality of parallel grooves 3 are provided 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 observed in the thickness direction can be a straight line, a broken line, a curve, etc.

[0082] In the embodiment of the present application, the parallel distribution of the grooves means that the axes in the length direction of any two grooves 3 are parallel to each other, as Figure 3 shown by the central dotted line of the groove 3. However, due to the existence of process errors, measurement errors, etc., a certain angle is allowed between the axes of the two grooves 3, and the angle is ±10°. These embodiments are all included in the protection scope of the claims of the present application.

[0083] In one embodiment, the depth of the groove 3 is 5 μm to 40 μm, preferably 7 μm to 25 μm;

[0084] The width of the groove 3 is 50 μm to 200 μm, preferably 60 μm to 150 μm; and / or

[0085] The distance between two adjacent grooves 3 is 100 μm to 5000 μm, preferably 400 μm to 2500 μm.

[0086] In the present application, the measurement methods of the groove depth D, the groove width L, and the groove spacing S are not particularly limited, and all can be measured by conventional methods. For example, they can be measured by the following methods:

[0087] Use a laser confocal microscope with the model number VK-1050 to photograph the groove area and obtain the optical and depth information of the electrode within the microscope's field of view. At a magnification of 20 times, scan the surface of the electrode in laser confocal mode. After the scanning is completed, process the acquired measurement data in the data analysis software associated with the instrument. Use the "datum plane setting" function in "processing images" to set the datum plane for the measurement data. Then, select the "smoothing" function, choose a size of "5×5" and a type of "simple average" to smooth the graph. After the processing is completed, use the "profile measurement" function to measure the groove parameters.

[0088] Groove depth D and groove width L: As Figure 1 and Figure 2 shown, the depth difference between the deepest part of the groove and the datum plane is the groove depth D, and the distance between the intersection points of the two sides of the groove and the datum plane is the groove width L. Along the same groove, measure once every 10 μm, and measure 20 times in total. Calculate the average value of the depth and width measured 20 times, and record it as the groove depth D and width L.

[0089] Groove pitch S: As Figures 1 - 3 shown, for two adjacent grooves, along the length direction of the electrode, the distance between the midpoints of the widths of the two adjacent grooves is the groove pitch. Along the selected groove, measure once every 10 μm, and measure 20 times in total. Calculate the average value and record it as the groove pitch S.

[0090] In one embodiment, when the electrode is a negative electrode, the cohesive force of the electrode is 5 - 50 N / m, preferably 8 - 20 N / m;

[0091] When the electrode is a positive electrode, the cohesive force of the electrode is 5 - 80 N / m, preferably 30 - 60 N / m.

[0092] In the above solution, the cohesive force of the electrode satisfies the above range. If the cohesive force is too large, it will lead to low flexibility of the electrode and easy breakage. If the cohesive force is too small, it will increase the risk of powder falling during the processing.

[0093] In this application, the cohesive force of the electrode can be tested by the following method (the test environment temperature is room temperature):

[0094] (1) Cut a double-sided tape (width: 20 mm, length: 60 - 70 mm) and stick it on the steel plate;

[0095] (2) Cut the positive electrode to be tested and stick it on the double-sided tape surface (completely cover it);

[0096] (3) Cut a low-tack adhesive paper (such as Australia-China EAS016-101), cover it on the test surface, and roll it with a 2 kg roller to ensure that the low-tack adhesive paper fits well with the test surface;

[0097] (4) The tensile testing machine stretches the low-viscosity adhesive paper at a rate of 50 mm / min with the stretching direction being 180° to the test surface until a peeling fracture surface appears. At this time, the reading of the tensile testing machine is the cohesive force of the functional protective layer (when testing the cohesive force, the peeling fracture surface is inside the coating, which 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 from the current collector).

[0098] This application also provides a method for preparing the aforementioned battery electrode sheet, including preparing the groove 3 on the active material layer 2 by a laser processing method.

[0099] In one embodiment, the process parameters of the laser processing include:

[0100] The laser power is 10% - 90%; and / or

[0101] The laser scanning speed is 1000 - 70000 mm / s.

[0102] In a specific embodiment, the method can adopt a fiber laser and a flying processing working mode.

[0103] In the above solution, by limiting the upper limit of the laser power, the risk of overheating of the electrode sheet or melting and perforation of the current collector is reduced. If the laser power is too low, the groove depth will be shallow, the edge will be unclear, and even a continuous channel cannot be formed.

[0104] If the laser scanning speed is too slow, the laser residence time is longer, and the energy accumulation effect is significant, resulting in too large a groove width and the thermal influence area extending to both sides of the groove, damaging the active material; if the laser scanning speed is too fast, discontinuous groove lines or shallow grooves may be formed. The electrode sheet of this application can maintain a good bonding effect under the thermal influence of laser processing by regulating the binder content. The method of manufacturing a uniform pore structure on the positive and negative electrode sheets by laser processing technology in this application improves the lithium deposition situation and cycle attenuation of the battery.

[0105] This application provides a lithium-ion battery, including the aforementioned battery electrode sheet and a separator. Among them, the thickness H of the separator satisfies 2.5 μm ≤ H ≤ 15 μm.

[0106] The electrode sheet of this application is applicable to a thin separator system (the separator thickness is not greater than 15 μm). The thickness of the separator refers to the total thickness including the base film, the separator functional coating (such as a ceramic coating, etc.) and the separator bonding coating. The separator can be a single-layer film or a multi-layer composite film.

[0107] The thickness H of the separator can be any value from 2.5 μm to 15 μm, such as 2.5 μm, 3 μm, 3.5 μm, 4.5 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm.

[0108] Although the thick separator system has a low risk of being pierced by the detached active material particles, due to the large thickness of the separator, the volumetric energy density of the battery is relatively low. By adjusting the binder content of the electrode sheet in this application, the binding effect of the active material is improved, so that it can still maintain good adhesiveness in the thin separator system, reducing the risk of the thin separator being pierced, and thus improving the volumetric energy density of the battery.

[0109] This application does not have special restrictions on the sources of all raw materials. Unless otherwise specified, they are all conventional products that can be obtained through commercial purchases.

[0110] Examples and Comparative Examples

[0111] The battery systems used in the examples and comparative examples of this application include:

[0112] (1) Positive electrode sheet:

[0113] Lithium cobaltate, conductive agent superconducting carbon, and binder polyvinylidene fluoride are uniformly mixed in a mass ratio of 96:2:2 to form a lithium-ion battery positive electrode slurry with a certain viscosity; the slurry is coated on both sides of the current collector 1 aluminum foil, dried at 95 °C and then cold-pressed to form a double-sided positive electrode active material layer 2; then trimming, slicing, and slitting are carried out. After slitting, it is dried at 85 °C for 4 hours under vacuum conditions, and then the tab is welded to make 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 each side of the active material layer 2 is 50 μm.

[0114] (2) Negative electrode sheet:

[0115] Graphite, conductive agent SP, stabilizer sodium carboxymethyl cellulose (CMC), and binder are mixed evenly in a mass ratio of 96.5:1.0:1.0:1.5 to form a slurry, which is coated on both sides of the current collector 1 copper foil, dried at 85 °C and then cold-pressed to form a negative electrode active material layer 2; then trimming, slicing, and slitting are carried out. After slitting, it is dried at 110 °C for 4 hours under vacuum conditions, and then the tab is welded to make a lithium-ion battery negative electrode sheet. The lithium-ion battery negative electrode sheet is a double-sided positive electrode sheet, and the thickness of each side of the active material layer 2 is 57 μm.

[0116] Laser grooving is carried out on the positive electrode sheet and the negative electrode sheet. The laser grooving methods for the positive and negative electrodes are as follows:

[0117] The positive and negative electrodes adopt the working mode of a fiber laser and flying processing.

[0118] Laser process parameters:

[0119] Power: 10% - 90%;

[0120] Laser speed: 1000 - 70000 mm / s.

[0121] For example, in Example 2, in the groove 3 with a groove depth of 13 μm, a groove width of 90 μm, and a groove pitch of 1.3 mm on the negative electrode, the laser power is 30% and the laser speed is 20000 mm / s.

[0122] (3) Electrolyte:

[0123] LiPF 6 is formulated with a solvent (the mass ratio of ethylene carbonate: diethyl carbonate: methyl ethyl carbonate: vinylene carbonate is 8:85:5:2) at a mass ratio of 8:92 to form a solution, which is used as the electrolyte of the lithium-ion battery.

[0124] (4) Separator:

[0125] In Examples 1 - 18 and Comparative Examples 1 and 5, the base material of the separator is a 5-μm thick polypropylene separator, the ceramic coating is alumina, with single-sided coating, and the total thickness of the ceramic coating is 2 μm. The adhesive coating is polyvinylidene fluoride, with double-sided coating, and the total thickness of the adhesive coating is 2 μm. The total thickness of the separator is 9 μm.

[0126] In Comparative Examples 2 - 3, the base material of the separator is a 13-μm thick polypropylene separator, the ceramic coating is alumina, with double-sided coating, and the total thickness of the ceramic coating is 2 μm. The adhesive coating is polyvinylidene fluoride, with double-sided coating, and the total thickness of the adhesive coating is 2 μm. The total thickness of the separator is 17 μm.

[0127] Preparation of the lithium-ion battery:

[0128] The above positive electrode sheet, separator, and negative electrode sheet are wound into an electrode core, with the separator located between the positive electrode sheet and the negative electrode sheet; the positive electrode is led out by spot welding with an aluminum tab, and the negative electrode is led out by spot welding with a nickel tab; then the electrode core is placed in an aluminum-plastic packaging bag, the above electrolyte is injected, and after processes such as encapsulation, formation, and capacity measurement, a polymer lithium-ion battery is made.

[0129] The battery parameters prepared in Examples 1 - 4 and Comparative Examples 1 - 3 are shown in Table 1.

[0130] Table 1

[0131]

[0132]

[0133]

[0134] The particle size of the active substance described in Table 1 refers to the average particle size Dv50.

[0135] Performance evaluation

[0136] 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.

[0137] (1) Comparison method of lithium plating interface:

[0138] At a test ambient temperature of 25 °C, the batteries in the comparative examples and examples were both cycled for charge and discharge 10 times using the same charging process, and then the batteries were disassembled to observe the anode electrode sheet to obtain the lithium plating interface.

[0139] Charging process:

[0140] Step 1: Charge the battery at a constant current of 2C to 4.5V.

[0141] Step 2: Charge the battery at a constant voltage of 4.5V to 0.05C.

[0142] Step 3: Let the battery stand for 5 minutes.

[0143] Step 4: Discharge the battery at a constant current of 0.5C to 3.0V.

[0144] Step 5: Let the battery stand for 5 minutes.

[0145] Step 6: Repeat the above steps 1 to 5 for 10 cycles.

[0146] The battery cells that had been cycled 10 times were disassembled, and the interfaces of the anode electrode sheets were observed and compared. In order to describe the lithium plating situation of the cycling interfaces, the interface situations were classified at present. Through visual observation by the operator, if the surface of the anode electrode sheet was golden yellow and there were no abnormal phenomena, it was determined that there was no lithium plating; if there were intermittent dot-like purple spots, lithium plating, or lithium plating on the purple spots on the anode electrode sheet, it was determined that there was slight lithium plating; if there were large-area continuous purple spots, lithium plating, or lithium plating on the purple spots on the main body of the anode electrode sheet, and the proportion of the abnormal area was <50%, it was determined that there was lithium plating; if there were large-area continuous purple spots, lithium plating, or lithium plating on the purple spots on the main body of the anode electrode sheet, and the proportion of the abnormal area was ≥50%, it was determined that there was severe lithium plating. The test results are shown in Table 2.

[0147] (2) Cycle performance test of lithium-ion batteries:

[0148] The calculation method of the capacity retention rate includes:

[0149] When the test environment temperature is 25°C, the batteries of the comparative examples and the examples are both cycled for charge and discharge 500 times using the same charging process, and then the discharge capacity of the battery after 500 cycles of charge and discharge is divided by its discharge capacity at the first cycle to obtain the capacity retention rate.

[0150] Charging process:

[0151] Step 1: Charge the battery at a constant current of 2C to 4.5V;

[0152] Step 2: Charge the battery at a constant voltage of 4.5V to 0.05C;

[0153] Step 3: Let the battery stand for 5 minutes;

[0154] Step 4: Discharge the battery at a constant current of 0.5C to 3.0V;

[0155] Step 5: Let the battery stand for 5 minutes;

[0156] Step 6: Repeat the above steps 1 to 5 for 500 cycles.

[0157] The test results are shown in Table 2.

[0158] (3) Self-discharge test:

[0159] The self-discharge rate test is a characterization method that can characterize the internal short-circuit situation of the battery cell. When dust particles pierce the separator, it will cause an internal short-circuit of the battery cell and the self-discharge rate will increase.

[0160] Test process:

[0161] Charge the battery cell at a rate of 0.2C to 3.9V, and after standing for 2 hours, measure its initial voltage V 0 , let the battery cell stand at 25°C for 72 hours, and measure the voltage V 1 , then:

[0162] Self-discharge rate = (V 1 - V 0 ) / 72 mV / h;

[0163] When the self-discharge rate ≤ 0.04 mV / h, it means passing the test.

[0164] For each example and comparative example of this application, 1000 battery cells are prepared for the self-discharge test respectively, and the test passing rate results are shown in Table 2.

[0165] (4) Test method for volume energy density:

[0166] Capacity test of battery monomer:

[0167] Let the battery cell stand still at 25°C for 2 h to ensure that the temperature of the battery cell is 25°C, and then discharge the battery at a constant current of 1 / 3C until 3.0V; after standing still for 5 min, charge the battery cell at a constant current of 1 / 3C to 4.48V, and continue to charge at a constant voltage of 4.5V until the current is 0.05C. Then stand still for 5 min and discharge the battery cell at a constant current of 1 / 3 until 3.0V, and record the total discharge capacity C of the battery cell. 0 , and the total discharge energy is E. 0 , and the unit of the total discharge energy is Wh.

[0168] Measurement of the battery cell volume:

[0169] Use a caliper to measure the length, width, and height of the outer surface of the battery, and calculate the volume V of the single battery cell. 0 , with the unit of L.

[0170] Calculation of the volume energy density:

[0171] The discharge energy E of the battery cell 0 / the battery volume V 0 is the volume energy density of the battery cell, with the unit of Wh / L. The test results are shown in Table 2.

[0172] Table 2

[0173]

[0174]

[0175] As can be seen from the results in Table 2, for the electrode of Comparative Example 1 in a thin separator system (separator thickness of 10 μm), the electrode without surface grooves had poor wettability, serious lithium plating occurred, and the capacity retention rate decreased significantly; Comparative Examples 2 and 3 used a 17-μm thick separator. Although the self-discharge test passing rate was high and a relatively high capacity retention rate and wetting effect could be maintained, since the thickness of its separator increased by 70% compared with that of the separator in the examples, the overall thickness of the battery cell increased, resulting in a significant decrease in the overall volume energy density of the battery cell; in Comparative Examples 4 and 5, due to the excessive depth of the groove 3 and the too low content of the electrode binder, the active material layer 2 was greatly affected by the heat of the grooving process, so that the risk of the positive active material particles falling off near the groove 3 due to heat influence and piercing the separator increased, and the self-discharge test passing rate was low; in Examples 15 and 17, due to the too low content of the electrode binder B, the internal cohesion of the electrode was low, and under the heat influence of the grooving process, the risk of the active material particles falling off near the groove 3 due to heat influence and piercing the separator increased, and the self-discharge test passing rate was low; in Example 16, due to the too high content of the positive electrode binder B, the volume energy density of the electrode decreased significantly; in Example 18, due to the too high content of the electrode binder B, the kinetic performance of the electrode decreased, resulting in poor electrolyte wetting and lithium plating during the cycle.

[0176] Under the thin separator system, by defining the relationship between the depth of the groove and the content of the binder in the active material layer 2, the active material layer 2 of the electrode in the example can overcome the heat influence brought by the grooving process, ensure the bonding effect of the active substance particles, and obtain an electrode with good wetting effect, high capacity retention rate and high volume energy density, which is applicable to high-energy density batteries.

[0177] The present application has been described in conjunction with preferred embodiments above. However, these embodiments are merely exemplary and only serve an illustrative purpose. On this basis, various substitutions and improvements can be made to the present application, and all of these fall within the protection scope of the present application.

Claims

1. A battery pole piece, characterized in that: The pole piece includes a current collector, an active material layer is disposed on at least one surface of the current collector, the active material layer contains active material particles and a binder, a groove is disposed on the active material layer, and the depth of the groove and the binder content in the active material layer of the pole piece satisfy the following relationship: D≤δ×B; Where D is the groove depth in μm; B% is the mass percentage of the binder in the active material layer of the electrode; δ is the proportional constant, where The electrode is a negative electrode, δ=20; and / or The pole piece is a positive pole piece, and δ=15.

2. The battery electrode according to claim 1, characterized in that: The electrode is a negative electrode, 0.5≤B≤15; and / or The pole piece is a positive pole piece, 0.5≤B≤5.

3. The battery pole piece according to claim 2, characterized in that: The electrode is a negative electrode, 1≤B≤6; and / or The pole piece is a positive pole piece, 1≤B≤3.

4. The battery pole piece according to claim 1, characterized in that: The electrode is a negative electrode, and the active material is selected from one or more of the following: graphite, silicon carbon, germanium negative electrode, lithium titanate, hard carbon, metal oxide negative electrode; and / or The binder is selected from one or more of the following: styrene-butadiene rubber SBR, sodium carboxymethyl cellulose Na-CMC, polyacrylic acid PAA, polyvinyl alcohol PVA, polytetrafluoroethylene PTFE.

5. The battery pole piece according to claim 1, characterized in that: The pole piece is a positive pole piece, 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 material; The binder is selected from one or more of the following: polyvinylidene fluoride PVDF, polytetrafluoroethylene PTFE, and polyacrylic acid PAA.

6. The battery pole piece according to claim 1, characterized in that: The average particle size Dv50 of the active material particles is 5 μm to 20 μm.

7. The battery pole piece according to claim 1, characterized in that: The active material layer is provided with a plurality of grooves, and the plurality of grooves are parallel to each other.

8. The battery pole piece according to claim 7, characterized in that: The depth of the groove is 5 μm to 40 μm; and / or The width of the groove is 50 μm to 200 μm; and / or The distance between two adjacent grooves is 100 μm to 5000 μm.

9. The battery pole piece according to claim 8, characterized in that: The depth of the groove is 7 μm to 25 μm; and / or The width of the groove is 60 μm to 150 μm; and / or The distance between two adjacent grooves is 400 μm to 2500 μm.

10. The battery pole piece according to claim 1, characterized in that: The electrode is a negative electrode, and the cohesive force of the electrode is 5N / m to 50N / m; and / or The pole piece is a positive pole piece, and the cohesive force of the pole piece is 5N / m to 80N / m.

11. The battery pole piece according to claim 10, characterized in that: The electrode is a negative electrode, and the cohesive force of the electrode is 8N / m to 20N / m; and / or The pole piece is a positive pole piece, and the cohesive force of the pole piece is 30N / m-60N / m.

12. The method for preparing a battery pole piece according to any one of claims 1 to 11, comprising preparing grooves on the active material layer by laser processing.

13. The method according to claim 12, characterized in that The process parameters of the laser processing include: The laser power is 10% to 90%; and / or The laser scanning speed is 1000mm / s~70000mm / s.

14. A battery comprising the battery pole piece and the separator according to any one of claims 1 to 11, wherein: The thickness H of the isolation film satisfies 2 μm≤H≤15 μm.

Images