Battery pole piece and secondary battery

Abstract

The invention discloses a battery pole piece and a secondary battery, belongs to the technical field of pole pieces, and overcomes the defect that the cycle capacity retention ratio of the battery is reduced as the mechanical property and the coating uniformity of an active layer of the battery pole piece are difficult to consider simultaneously in the prior art. The battery pole piece comprises a current collector and an active layer arranged on at least one side of the current collector, wherein the active layer comprises an active substance and a fiber material; the dyne value of the current collector is DmN / m, the length-diameter ratio of the fiber material is A, and D and A meet the relational expression 4 > = D / A > = 0.1. According to the secondary battery adopting the negative electrode plate, the mechanical property of the battery and the coating uniformity of the active layer are considered at the same time, the breakage condition and the lithium precipitation condition of the electrode plate are improved, and the cycle capacity retention rate of the battery is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of pole pieces, and in particular relates to a battery pole piece and a secondary battery. Background Art

[0002] Traditional battery pole pieces are typically made by coating a current collector with a mixture of active materials, conductive agents, and adhesives. However, existing battery pole pieces have poor tensile strength and are brittle, making them difficult to adapt to bending requirements. This can lead to pole pieces easily breaking during secondary battery cycling, causing a drop in battery capacity.

[0003] Introducing fiber materials into the active layer can improve the strength and toughness of the electrode to a certain extent, but adding fiber materials during slurry preparation will increase the slurry viscosity, causing uneven coating of the slurry on the collector surface, leading to lithium deposition during battery cycling. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect in the prior art that it is difficult to balance the mechanical properties of the battery electrode and the uniformity of the active layer coating, which leads to a decrease in the battery cycle capacity retention rate, thereby providing a battery electrode and a secondary battery. The secondary battery using the negative electrode of the present application takes into account both the mechanical properties of the battery and the uniformity of the active layer coating, improves the electrode fracture and lithium plating conditions, and significantly improves the battery cycle capacity retention rate.

[0005] To this end, the present invention provides the following technical solutions.

[0006] In a first aspect, the present application provides a battery electrode, comprising a current collector and an active layer disposed on at least one side of the current collector, wherein the active layer comprises an active substance and a fiber material;

[0007] The dyne value of the current collector is DmN / m, the aspect ratio of the fiber material is A, and D and A satisfy the relationship 4≥D / A≥0.1.

[0008] In one possible implementation, 10≤A≤500;

[0009] In one possible implementation, 30≤D≤100.

[0010] In one possible embodiment, the aspect ratio A=L / d, wherein L is the average length of the fiber material; d is the diameter of the fiber material;

[0011] 8μm≤L≤500μm;

[0012] 0.1μm≤d≤50μm.

[0013] In a possible implementation manner, the active layer further includes a binder;

[0014] Optionally, the binder includes at least one of styrene-butadiene rubber, modified styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polyvinyl alcohol, polyacrylonitrile, polyacrylamide, polyacrylic acid-acrylonitrile copolymer and its derivatives, acrylic acid-acrylamide and its derivatives, acrylic acid-acrylate copolymer, polymethacrylate, styrene-acrylic emulsion, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and potassium carboxymethyl cellulose.

[0015] In one possible embodiment, the fiber material includes one or more of first fibers and second fibers;

[0016] The first fiber includes one or more of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, viscose-based carbon fiber, graphene fiber, carbon nanofiber, and carbon nanotube;

[0017] The second fiber includes one or more of alumina fiber, silica fiber, polyacrylonitrile fiber, polyethylene fiber, aramid fiber, and polyimide fiber.

[0018] In one possible embodiment, the fiber material includes at least one of the first fibers and at least one of the second fibers.

[0019] In one possible embodiment, based on the mass of the active layer, the total mass content of the first fibers is 1% to 10%;

[0020] In one possible embodiment, based on the mass of the active layer, the total mass content of the second fibers is 0.5%-10%;

[0021] In one possible embodiment, the electrode sheet is a negative electrode sheet, the negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes a silicon-carbon composite material; the ratio of the average length of the second fiber to the volume average particle size Dv50 of the silicon-carbon composite material is less than 1.

[0022] In one possible embodiment, the fiber material is selected from one of the first fiber and the second fiber;

[0023] The length distribution curve of the fiber material is a bimodal curve, with a first peak length of L1 and a second peak length of L2;

[0024] In one possible embodiment, the thickness of the active layer is T, T≤L1≤2T, 8μm≤L2≤T;

[0025] In one possible embodiment, T is 30 to 250 μm;

[0026] In one possible implementation, L1 / L2 is 5-10.

[0027] In a possible embodiment, the battery electrode includes a straight area and an arc area;

[0028] The fiber material in the active layer of the straight region includes at least one of the first fibers;

[0029] The fiber material in the active layer of the arc area includes at least one of the polyacrylonitrile fiber, polyethylene fiber, aramid fiber, and polyimide fiber;

[0030] In a possible embodiment, the fiber material in the active layer of the straight area and / or the active layer of the arc area further includes at least one of the alumina fibers and the silica fibers.

[0031] In a second aspect, the present application provides a secondary battery comprising a battery cell formed by winding a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet and / or the negative electrode sheet is the above-mentioned battery electrode sheet.

[0032] The technical solution of the present invention has the following advantages:

[0033] 1. The present application provides a battery electrode, comprising a current collector and an active layer disposed on at least one side of the current collector, wherein the active layer comprises an active substance and a fiber material; the dyne value of the current collector is DmN / m, the aspect ratio of the fiber material is A, and D and A satisfy the relationship 4≥D / A≥0.1.

[0034] Introducing fiber materials into the active layer can form a skeleton and increase the strength of the pole piece. However, adding fiber materials during pulping will increase the viscosity of the slurry, resulting in uneven coating of the slurry on the surface of the current collector. The dyne value D of the current collector of this application and the aspect ratio A of the fiber material satisfy 4≥D / A≥0.1 to ensure that there is a specific range of D matching corresponding to a specific A, to ensure a good wetting effect, and there are more binding sites between the foil with a high dyne value and the slurry, the contact angle between the current collector and the slurry is reduced, and the interface defects are reduced, thereby increasing the effective bonding area. This application can increase the strength of the pole piece while improving the coating uniformity of the slurry on the current collector, improving the pole piece fracture and lithium plating conditions, and significantly improving the battery cycle capacity retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 Schematic diagram of the negative electrode structure of Example 21.

[0037] Reference numerals:

[0038] 1-first fiber; 2-second fiber. DETAILED DESCRIPTION

[0039] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0040] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0041] The present application provides a battery pole piece, comprising a current collector and an active layer disposed on at least one side of the current collector, wherein the active layer comprises an active substance and a fiber material;

[0042] The dyne value of the current collector is DmN / m, the aspect ratio of the fiber material is A, and D and A satisfy the relationship 4≥D / A≥0.1.

[0043] Introducing fiber materials into the active layer can form a skeleton and increase the strength of the pole piece. However, adding fiber materials during pulping will increase the viscosity of the slurry, especially the length and diameter of the added fibers have a greater impact on the viscosity of the slurry, resulting in uneven coating of the slurry on the surface of the current collector. The dyne value D of the current collector of this application and the aspect ratio A of the fiber material satisfy 4≥D / A≥0.1 to ensure that there is a specific range of D matching corresponding to a specific A to ensure a good wetting effect. There are more binding sites between the foil with a high dyne value and the slurry, and the contact angle between the current collector and the slurry is reduced, reducing interface defects, thereby increasing the effective bonding area. This application can increase the strength of the pole piece while improving the coating uniformity of the slurry on the current collector, improving the pole piece fracture and lithium precipitation, and significantly improving the battery cycle capacity retention rate. If D / A>4, assuming D is too high (surface energy is too large), the slurry may be excessively spread on the surface of the current collector, forming an uneven coating, or even causing local depressions or edge thickening on the coating surface; if A is too small, the fibers are similar to equiaxed particles, the "bridging" effect is lost, the tensile strength decreases, and the pole pieces are prone to brittle cracking. If D / A<0.1, assuming D is too small, the contact angle between the current collector and the slurry is large, making it difficult to apply uniformly; assuming A is too large, due to the pinning effect of the fibers on the polymer chains (binders), the viscosity increases significantly. High-viscosity slurries are often non-Newtonian fluids (such as pseudoplastic fluids), and sufficiently high shear forces are required to reduce the viscosity. If the process shear force cannot effectively trigger shear thinning, the slurry will remain in a highly viscous state, making it difficult to stretch into a uniform thin layer, which will affect the uniformity of the coating. Illustratively, D / A may be any value of 0.1, 0.2, 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 1.7, 2.0, 2.5, 3.0, 3.5, or 4.0.

[0044] When the fibrous material comprises a plurality of fibers, each fiber satisfies 4≥D / A≥0.1.

[0045] In one possible embodiment, 10≤A≤500; the fibers overlap each other to form a three-dimensional network, sharing external forces like a "skeleton" and preventing crack propagation, thereby improving the strength of the electrode; the high aspect ratio fibers can undergo elastic deformation like a "spring" when the electrode is bent, absorbing mechanical stress without breaking, ensuring that the electrode has a certain strength while having good toughness, preventing the electrode from cracking and pulverizing due to volume expansion during charging and discharging, leading to problems such as reduced cycle life. If the aspect ratio is too small, L / d<10, assuming L is small, the length of the fiber is short, the fiber cannot span the distance between adjacent active particles, the overlap between the fibers is insufficient, and it is difficult to effectively build a continuous network, thereby limiting the improvement of the electrode strength; assuming d is large, the diameter of the fiber is too large, and it is difficult to deform during rolling due to the strong rigidity of the fiber. During the rolling process, due to the large difference in modulus between the two, they cannot deform synergistically, the active material will be forcibly compressed by the nearby coarse fiber, and microcracks are easily generated at the fiber-matrix interface. If the aspect ratio is too large, L / d>500, assuming that L is large, the length of the fiber is long, and the long fibers are easy to tangle, forming "fiber clumps", resulting in poor slurry fluidity and difficulty in uniform coating; assuming that d is small, the fiber diameter is too small, the specific surface area of ​​the fiber is large, the van der Waals force is strong, and it is difficult to disperse evenly, which leads to uneven coating. There are weak strength areas in the areas with low fiber content in the pole piece. The weak areas act as stress concentration points and accelerate crack propagation, so the effect of improving the strength of the pole piece is limited. For example, A can be any value of 10, 20, 30, 50, 100, 150, 200, 250, 300, 350, 400, 450 or 500.

[0046] In one possible embodiment, 30≤D≤100. For example, D can be any value among 30, 40, 50, 60, 70, 80, 90, or 100. Adding fibers during slurrying increases the viscosity of the slurry. Fibers with an aspect ratio of 10≤A≤500, when applied with a current collector having an appropriate dyne value, can avoid uneven coating.

[0047] In one possible implementation, the aspect ratio A=L / d, wherein L is the average length of the fiber material, and d is the diameter of the fiber material; 8 μm≤L≤500 μm; and 0.1 μm≤d≤50 μm.

[0048] During the pulping process, the mutual entanglement or overlap between fibers will hinder the flow of fluid, increase internal friction resistance, and thus increase the apparent viscosity. Fibers with larger diameters and longer lengths tend to form a denser physical network, increase the van der Waals force or mechanical entanglement strength between fibers, hinder the flow of slurry, and thus increase the apparent viscosity of the slurry. High-viscosity slurry is difficult to spread evenly on the current collector during the coating process. The diameter d of the fiber material is between 0.1μm and 50μm to avoid the fiber diameter being too large and the viscosity being too high, which makes it difficult to coat. It also avoids the fiber diameter being too small and making it difficult to disperse evenly. The length of the fiber material is between 8μm and 500μm to avoid the fiber length being too large, which increases the risk of puncturing the diaphragm. It also avoids the fiber length being too small, which makes it difficult to cross the average spacing between adjacent fibers (especially at low addition amounts), and it is impossible to form enough overlap points, resulting in a discontinuous network, difficulty in forming a long-range conductive network, limited conductive enhancement effect, and reduced contribution to mechanical strength. Illustratively, L can be any value among 8μm, 10μm, 20μm, 30μm, 50μm, 80μm, 100μm, 150μm, 200μm, 250μm, 300μm, 350μm, 400μm, 450μm, 500μm; d can be any value among 0.1μm, 0.5μm, 1μm, 3μm, 5μm, 10μm, 20μm, 50μm.

[0049] In a possible implementation, the active layer further includes a binder, the binder includes a polar functional group, and the polar functional group includes at least one of a carboxyl group, a cyano group, an amide group, an amino group, and a hydroxyl group.

[0050] The surface of the fiber material is smooth, and adding fiber material to the active layer may result in insufficient bonding with the active substance, which may lead to the risk of the active layer demolding. This application adds a binder containing specific groups (such as modified polyacrylic acid or polyurethane PU) to the active layer to enhance the bonding with the smooth fiber material through hydrogen bonding or van der Waals forces, thereby avoiding the above demolding problem.

[0051] In one possible embodiment, the binder includes at least one of styrene-butadiene rubber, modified styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polyvinyl alcohol, polyacrylonitrile, polyacrylamide, polyacrylic acid-acrylonitrile copolymer and its derivatives, acrylic acid-acrylamide and its derivatives, acrylic acid-acrylate copolymer, polymethacrylate, styrene-acrylic emulsion, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and potassium carboxymethyl cellulose.

[0052] In one possible embodiment, the binder includes a polar functional group, and the polar functional group includes at least one of a carboxyl group, a cyano group, an amide group, an amino group, and a hydroxyl group;

[0053] In one possible embodiment, the fiber material includes one or more of first fibers and second fibers;

[0054] The first fiber includes one or more of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, viscose-based carbon fiber, graphene fiber, carbon nanofiber, and carbon nanotube;

[0055] The second fiber includes one or more of alumina fiber, silica fiber, polyacrylonitrile fiber, polyethylene fiber, aramid fiber, and polyimide fiber.

[0056] In one possible embodiment, the fiber material includes at least one of the first fibers and at least one of the second fibers.

[0057] In the above embodiment, the first fiber and the second fiber are different types of fibers. The first fiber is a conductive fiber, and the three-dimensional conductive skeleton formed can connect the active material particles, reduce the internal resistance of the electrode, and improve the charge transfer efficiency. The second fiber is a thermally stable insulating fiber. The three-dimensional network formed around the active material can maintain structural stability at high temperatures, play a role in insulation, and help improve the thermal safety of the battery. At the same time, the second fiber has good chemical stability and does not react with the electrolyte. The three-dimensional network structure it forms can prevent the active layer from reacting with the electrolyte. The synergistic effect of the first and second fibers can simultaneously improve the thermal safety performance, cycle stability, and rate performance of the battery cell.

[0058] The first fiber may be a porous or solid structure, preferably a porous structure. When the first fiber is a porous structure, the electrolyte infiltration effect can be increased to promote lithium ion transmission.

[0059] In one possible embodiment, the mass content of the first fiber is 1% to 10% based on the mass of the active layer. This is to avoid insignificant reinforcement due to a low first fiber content, or to avoid a reduction in the active material content due to a high first fiber content. For example, the mass content of the first fiber can be any value of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0060] In one possible embodiment, the mass content of the second fiber is 0.5%-10% based on the mass of the active layer. This ensures that the second fiber can effectively form a three-dimensional network with the binder, coating the surface of the active material, hindering side reactions between the active layer and the electrolyte, and effectively providing thermal insulation, while also avoiding excessive content that would reduce the content of the active material. Exemplary values ​​include any of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0061] In one possible embodiment, the electrode is a negative electrode, which includes a negative electrode active material layer, and the negative electrode active material layer includes a silicon-carbon composite material; the ratio of the average length of the second fiber to the volume average particle size Dv50 of the silicon-carbon composite material is less than 1. The active material also includes graphite. Generally, the particle size of the silicon-carbon composite material is smaller than that of graphite. Therefore, the average length of the second fiber is smaller than the volume average particle size Dv50 of the active material, thereby ensuring that the second fiber can be well distributed on the surface of the active material. When a short circuit occurs inside the battery cell, the second fiber can slow down the diffusion rate of heat from the heat source (such as the short circuit point) to the surrounding electrolyte, thereby reducing the overall temperature rise rate. Even if the local temperature rises instantaneously, the fiber network can buffer the heat transfer, so that the actual temperature of most of the electrolyte is lower than its violent decomposition threshold, thereby improving the thermal safety performance of the battery cell.

[0062] In one possible embodiment, the volume average particle size Dv50 of the silicon-carbon composite material is 5 to 15 μm. For example, it can be any value among 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0063] In one possible embodiment, the fiber material is selected from one of the first fiber and the second fiber; the length distribution curve of the fiber material is a bimodal curve, with a first peak length of L1 and a second peak length of L2; that is, the fiber material includes fibers of the same type but different lengths;

[0064] In the bimodal curve, the length corresponding to the longer peak is the first peak length L1, and the length corresponding to the shorter peak is the second peak length L2.

[0065] Optionally, the thickness of the active layer is T, T≤L1≤2T, 8μm≤L2≤T;

[0066] Optionally, T is 30 to 250 μm; illustratively, T may be any value of 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 150 μm, 200 μm or 250 μm.

[0067] The length distribution curve of the fiber material is a bimodal curve, that is, the fiber material includes both fibers A with a longer length and fibers B with a relatively shorter length. The average length of fiber A and the thickness of the active layer satisfy T≤L1≤2T to ensure that fiber A builds a skeleton and plays a role in enhancing the strength of the electrode, while avoiding the risk of fiber A being too long and puncturing the diaphragm. The average length of fiber B and the thickness T of the active material layer satisfy the relationship 8μm≤L2≤T to ensure that fiber B can fill the pores between fiber A and the main material of the active layer. When the fibers are dispersed in the electrode matrix, they can absorb external forces by bending or twisting, reduce local stress concentration, increase the flexibility of the electrode, and avoid the difficulty of uniform dispersion of fibers with too low a length. By setting this form of L1 and L2, it is further ensured that fibers A and fibers B are interwoven to form a flexible network structure. When subjected to force, this network disperses stress through slippage and rearrangement between fibers, avoiding brittle fracture, and playing a role in enhancing the strength and flexibility of the electrode. At the same time, the longer fibers A form a continuous conductive skeleton inside the electrode, providing a long-range electron conduction path and reducing the overall resistance; the shorter fibers B can fill the areas not covered by the long fibers, enhance local conductivity, and reduce the contact resistance between active particles, thereby further improving the battery's cycle capacity retention rate.

[0068] In one possible embodiment, L1 / L2 is 5-10. This ensures that fiber A penetrates the electrode, forming a supporting framework and stabilizing the electrode structure. Fiber A is rod-shaped or tubular, and inevitably creates pores with the irregular active material. Fiber B can effectively fill the pores between fiber A and the active material, increasing the electrode's compaction density. For example, L1 / L2 can be any value among 5, 6, 7, 8, 9, or 10.

[0069] In a possible embodiment, the battery electrode includes a straight area and an arc area;

[0070] The fiber material in the active layer of the straight region includes at least one of the first fibers;

[0071] The fiber material in the active layer of the arc area includes at least one of the polyacrylonitrile fiber, polyethylene fiber, aramid fiber, and polyimide fiber;

[0072] Optionally, the fiber material in the active layer of the straight area and / or the active layer of the arc area further includes at least one of the alumina fibers and the silica fibers.

[0073] The arc region is subjected to repeated bending stress during battery charging and discharging, making it prone to cracking. Highly flexible, fatigue-resistant polymer fibers, such as aramid and polyimide fibers, are added to the arc region of the electrode. These fibers have high elongation at break and excellent toughness, effectively inhibiting crack propagation. High-modulus, highly conductive primary fibers are added to the straight region to minimize electrode deformation. The conductive fibers reduce internal resistance, thereby ensuring structural stability and uniform current distribution.

[0074] The difference in fiber types in the straight area and the arc area can be judged by the diaphragm resistance. The conductivity of the fibers themselves is different. The addition of the first fiber to the electrode can effectively reduce the diaphragm resistance of the electrode itself. The diaphragm resistance can be measured by a diaphragm resistance meter. A flat probe is used to apply a certain pressure to the sample to be tested, automatically read the current value flowing through, and automatically analyze the resistance of the electrode.

[0075] In one possible implementation, the mass solid content of the negative electrode slurry is 20-70%.

[0076] The present application also provides a secondary battery, comprising a battery cell formed by winding a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet and / or the negative electrode sheet is the above-mentioned battery electrode sheet.

[0077] Test method:

[0078] 1) The average length L of the fiber material can be measured and calculated using a scanning electron microscope: multiple images of the electrode are taken using a scanning electron microscope, and the fiber length is automatically measured using image analysis software (ImageJ). The average length of 10 fibers is calculated and recorded as L.

[0079] 2) The diameter d of the fiber material can be measured by ion beam cutting the pole piece using a focused ion beam (FIB-SEM) to obtain a cross-section with nanometer-level precision, and then d can be measured under SEM.

[0080] 3) The length L1 and length L2 testing method is as follows: High-resolution scanning electron microscopy (SEM) is used to image the electrode surface to obtain the microscopic distribution of the fibers. The images are then preprocessed using specialized image processing software (ImageJ), including noise reduction and skeletonization, to accurately measure the geometric length of each fiber and establish a statistical dataset. A Gaussian mixture model (GMM) is used to perform bimodal fitting analysis on the fiber length distribution curve, accurately identifying two characteristic peaks corresponding to fibers A and B. The peak values ​​of these two characteristic peaks correspond to lengths L1 and L2, respectively.

[0081] 4) The oven temperature pass rate test method is to place fully charged batteries in a test chamber and heat them at a rate of 5°C / min to a constant temperature of 130°C for 60 minutes. If no fire or explosion occurs, the battery is considered to have passed the oven temperature test. If fire or explosion occurs, the battery fails the oven temperature test. Ten batteries are tested, and the number of batteries that pass the oven temperature test is recorded. For example, if the number is 8 / 10, it is considered that 8 batteries passed the oven temperature test.

[0082] 5) The degree of lithium deposition is determined by disassembling the battery and directly observing the distribution and area of ​​lithium metal deposition on the negative electrode surface using SEM. A lithium deposition area of ​​0% indicates no lithium deposition, 0% < lithium deposition area ≤ 5% indicates slight lithium deposition, 5% < lithium deposition area ≤ 20% indicates moderate lithium deposition, and a lithium deposition area > 20% indicates extreme lithium deposition.

[0083] 6) Capacity retention after 500 cycles: Under standard conditions (25±2°C), the battery was fully charged and discharged (1C charging to a cutoff voltage of 4.5V, constant voltage charging to a cutoff current of 0.05C, and 1C discharge to a lower limit voltage of 3V) to determine the initial capacity (C0). After 500 cycles of charge and discharge, its capacity (C1) was measured. The capacity retention was calculated using the formula C1 / C0×100%.

[0084] 7) Expansion rate of the battery cell after 500 cycles: Under specified environmental conditions (such as constant temperature and humidity), use a laser thickness gauge to first measure the initial thickness of the battery cell and record the initial value H0; then charge the battery cell at 1C to a cutoff voltage of 4.5V, charge it at a constant voltage to a cutoff current of 0.05C, and discharge it at 1C to a lower limit voltage of 3V for cyclic charge and discharge. After 500 cycles, measure the battery cell thickness H1 again; expansion rate = (H1-H0) / H0*100%.

[0085] 8) Whether the electrode in the battery cell is broken is tested by CT (computed tomography). The specific process is as follows: Place the battery cell to be tested on the rotating table of the CT equipment, adjust the parameters of the X-ray source and detector (such as voltage, current, and resolution) to ensure that the scan can clearly present the microstructure of the electrode; then perform a 360° rotation scan, obtain multi-angle projection data by X-rays penetrating the sample, and use a three-dimensional reconstruction algorithm to generate a high-resolution tomographic image. During the analysis, focus on the continuity of the electrode coating surface and the current collector. If cracks exist, the image will show obvious fracture lines or local density anomalies (such as black gaps), and combine image processing software (such as VG Studio, Avizo) to perform three-dimensional positioning and size measurement of the cracks. Every 50 cycles, check whether the electrode inside the battery cell is broken. Stop the test after detecting a break in the electrode or after 1000 cycles.

[0086] The test results are shown in Tables 1 to 11.

[0087] Example 1

[0088] This embodiment provides a method for preparing a secondary battery, comprising:

[0089] Preparation of the positive electrode sheet: Lithium cobalt oxide and conductive carbon black binder PVDF are mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 96:2:2. The mixture is stirred continuously in a blender to form a uniform positive electrode active slurry. The positive electrode active slurry is then coated on the surface of aluminum foil, baked, rolled, and slit to produce the positive electrode sheet.

[0090] Preparation of the negative electrode sheet: Graphite, silicon-carbon composite material, fiber material, conductive carbon black, styrene-butadiene rubber, and carboxymethyl cellulose are mixed in deionized water at a weight ratio of 52:42:2:1:2:1. The mixture is continuously stirred in a blender to form a uniform, fluid negative electrode active slurry with a solids content of 40%. The negative electrode active slurry is coated onto a current collector copper foil with a dyne value (D) of 60 mN / m. The negative electrode sheet is obtained by baking, rolling, and slitting. The fiber material is pitch-based carbon fiber. Specific parameters are shown in Table 1. It should be noted that current collector copper foils with different dyne values ​​can be used in other embodiments to meet application requirements.

[0091] Preparation of electrolyte: Battery assembly:

[0092] The production and assembly process for soft-pack batteries primarily involves electrode preparation, cell assembly, packaging and activation, and testing and sorting. The active layer of the positive electrode is formulated as: LiCoO2 (96%) + conductive carbon black (2%) + PVDF binder (2%); the negative electrode is prepared using the negative electrode sheets prepared in the Example and Comparative Example, respectively; and the electrolyte is formulated as: 1M LiPF6 in EC + 2wt% VC. Cells are assembled with separators through a lamination or winding process, encapsulated with aluminum-plastic film, and then filled with electrolyte. The cells are then activated through a formation process to form a stable SEI film, followed by aging and screening. Finally, OCV testing and sorting are performed to obtain the finished batteries.

[0093] In a dry argon atmosphere glove box, a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) in a mass ratio of 1:1:1:2, and a carboxylic acid ester solvent (ethyl propionate (EP) and propyl propionate (PP) in a 1:1 ratio) was added as a non-aqueous organic solvent. 2% by mass of fluoroethylene carbonate was added, dissolved, and thoroughly stirred. Lithium hexafluorophosphate (LiPF6) was then added and mixed thoroughly to form an electrolyte. The LiPF6 concentration was 1 mol / L.

[0094] The resulting positive electrode sheet, separator (11 micron thick, made of polyethylene), and negative electrode sheet are stacked in order, with the positive tabs attached to the positive and negative tabs to the negative, respectively, with the separator positioned between the positive and negative sheets to provide isolation. The electrode assembly is then wound to form an electrode assembly. The electrode assembly is then wrapped in an outer foil aluminum-plastic film, and the electrolyte is injected. After vacuum packaging, standing, and formation, OCV testing and sorting are performed to produce a lithium-ion battery.

[0095] Examples 2 to 18, Comparative Example 1, and Comparative Example 2 each provide a method for preparing a secondary battery, which is substantially the same as Example 1, with the differences shown in Table 1. The performance of the secondary batteries of Examples 1 to 18, Comparative Example 1, and Comparative Example 2 is shown in Table 2.

[0096] Table 1 Physical parameters of fiber materials in pole pieces

[0097]

[0098]

[0099] Table 2 Secondary battery performance

[0100]

[0101] As can be seen from Table 2, the secondary battery using the negative electrode sheet of the present application has no electrode breakage after 800T cycle, the degree of lithium deposition is slight or no lithium deposition, and the capacity retention rate after 500T cycle is ≥80%. At the same time, the mechanical properties of the battery and the uniformity of the active layer coating are taken into account, the electrode breakage and lithium deposition conditions are improved, and the battery cycle capacity retention rate is significantly improved.

[0102] Example 19

[0103] This embodiment provides a method for preparing a secondary battery, wherein the negative electrode active layer includes two different types of fibers. The method for preparing the secondary battery includes:

[0104] Preparation of the positive electrode sheet: Lithium cobalt oxide and conductive carbon black binder PVDF are mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 96:2:2. The mixture is stirred continuously in a blender to form a uniform positive electrode active slurry. The positive electrode active slurry is then coated on the surface of aluminum foil, baked, rolled, and slit to produce the positive electrode sheet.

[0105] Preparation of the negative electrode sheet: Graphite, silicon-carbon composite material, first fiber (pitch-based carbon fiber), second fiber (alumina fiber), conductive carbon black, styrene-butadiene rubber, and carboxymethyl cellulose were mixed in deionized water at a weight ratio of 52:42:1:1:1:2:1. The mixture was stirred continuously in a blender to form a uniform, fluid negative electrode active slurry with a solids content of 40%. The negative electrode active slurry was coated onto a current collector copper foil with a specific dyne value. The negative electrode sheet was then baked, roll-pressed, and slit. The fiber material was pitch-based carbon fiber. Specific parameters are shown in Table 2.

[0106] Preparation of electrolyte: Battery assembly:

[0107] The production and assembly process for soft-pack batteries primarily involves electrode preparation, cell assembly, packaging and activation, and testing and sorting. The active layer of the positive electrode is formulated as: LiCoO2 (96%) + conductive carbon black (2%) + PVDF binder (2%); the negative electrode is prepared using the negative electrode sheets prepared in the Example and Comparative Example, respectively; and the electrolyte is formulated as: 1M LiPF6 in EC + 2wt% VC. Cells are assembled with separators through a lamination or winding process, encapsulated with aluminum-plastic film, and then filled with electrolyte. The cells are then activated through a formation process to form a stable SEI film, followed by aging and screening. Finally, OCV testing and sorting are performed to obtain the finished batteries.

[0108] In a dry argon atmosphere glove box, a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) in a mass ratio of 1:1:1:2, and a carboxylic acid ester solvent (ethyl propionate (EP) and propyl propionate (PP) in a 1:1 ratio) was added as a non-aqueous organic solvent. 2% by mass of fluoroethylene carbonate was added, dissolved, and thoroughly stirred. Lithium hexafluorophosphate (LiPF6) was then added and mixed thoroughly to form an electrolyte. The LiPF6 concentration was 1 mol / L.

[0109] The resulting positive electrode sheet, separator (11 micron thick, made of polyethylene), and negative electrode sheet are stacked in order, with the positive tabs attached to the positive and negative tabs to the negative, respectively, with the separator positioned between the positive and negative sheets to provide isolation. The electrode assembly is then wound to form an electrode assembly. The electrode assembly is then wrapped in an outer foil aluminum-plastic film, and the electrolyte is injected. After vacuum packaging, standing, and formation, OCV testing and sorting are performed to produce a lithium-ion battery.

[0110] Example 21 provides a method for preparing a secondary battery, which is basically the same as Example 20, except that the first fiber 1 and the second fiber 2 are different. Specific parameters are shown in Tables 3 and 4. The performance of the secondary batteries of Examples 20 and 21 is shown in Table 5.

[0111] Table 3 Physical parameters of fiber materials in pole pieces

[0112]

[0113] Table 4 Physical parameters of fiber materials in pole pieces

[0114]

[0115] Table 5 Secondary battery performance

[0116]

[0117] As can be seen from Table 5, the secondary battery using the negative electrode sheet of the present application takes into account both the mechanical properties of the battery and the uniformity of the active layer coating, improves the electrode fracture and lithium plating conditions, significantly improves the battery cycle capacity retention rate, and has good furnace temperature performance.

[0118] Example 21

[0119] This embodiment provides a method for preparing a secondary battery, wherein the negative electrode active layer includes two fibers of the same type but different shapes. The method for preparing the secondary battery includes:

[0120] Preparation of the positive electrode sheet: Lithium cobalt oxide and conductive carbon black binder PVDF are mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 96:2:2. The mixture is stirred continuously in a blender to form a uniform positive electrode active slurry. The positive electrode active slurry is then coated on the surface of aluminum foil, baked, rolled, and slit to produce the positive electrode sheet.

[0121] Preparation of the negative electrode sheet: Graphite, silicon-carbon composite material, first fiber, second fiber, conductive carbon black, styrene-butadiene rubber, and carboxymethyl cellulose are mixed in deionized water at a weight ratio of 52:42:1:1:1:2:1. The mixture is stirred continuously in a blender to form a uniform, fluid negative electrode active slurry with a solids content of 40%. The negative electrode active slurry is then coated onto a current collector copper foil with a certain dyne value. The negative electrode sheet is then baked, rolled, and slit.

[0122] Preparation of electrolyte: Battery assembly:

[0123] The production and assembly process for soft-pack batteries primarily involves electrode preparation, cell assembly, packaging and activation, and testing and sorting. The active layer of the positive electrode is formulated as: LiCoO2 (96%) + conductive carbon black (2%) + PVDF binder (2%); the negative electrode is prepared using the negative electrode sheets prepared in the Example and Comparative Example, respectively; and the electrolyte is formulated as: 1M LiPF6 in EC + 2wt% VC. Cells are assembled with separators through a lamination or winding process, encapsulated with aluminum-plastic film, and then filled with electrolyte. The cells are then activated through a formation process to form a stable SEI film, followed by aging and screening. Finally, OCV testing and sorting are performed to obtain the finished batteries.

[0124] In a dry argon atmosphere glove box, a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) in a mass ratio of 1:1:1:2, and a carboxylic acid ester solvent (ethyl propionate (EP) and propyl propionate (PP) in a 1:1 ratio) was added as a non-aqueous organic solvent. 2% by mass of fluoroethylene carbonate was added, dissolved, and thoroughly stirred. Lithium hexafluorophosphate (LiPF6) was then added and mixed thoroughly to form an electrolyte. The LiPF6 concentration was 1 mol / L.

[0125] The resulting positive electrode sheet, separator (11 micron thick, made of polyethylene), and negative electrode sheet are stacked in order, with the positive tabs attached to the positive and negative tabs to the negative, respectively, with the separator positioned between the positive and negative sheets to provide isolation. The electrode assembly is then wound to form an electrode assembly. The electrode assembly is then wrapped in an outer foil aluminum-plastic film, and the electrolyte is injected. After vacuum packaging, standing, and formation, OCV testing and sorting are performed to produce a lithium-ion battery.

[0126] Examples 22 to 26 each provide a method for preparing a secondary battery, which is substantially the same as that of Example 21, with the differences being shown in Tables 6 and 7. The secondary battery performance of Examples 22 to 26 is shown in Table 8.

[0127] Table 6 Physical parameters of fiber materials in pole pieces

[0128]

[0129] Table 7 Physical parameters of fiber materials in pole pieces

[0130]

[0131]

[0132] Table 8 Secondary battery performance

[0133] Breakage of the electrode in the battery cell 500T capacity retention rate 800T lithium plating situation Example 21 1000T without breakage 95％ No lithium plating Example 22 1000T without breakage 94％ No lithium plating Example 23 1000T without breakage 94％ No lithium plating Example 24 1000T without breakage 92％ Slight lithium deposition Example 25 1000T without breakage 93％ Slight lithium deposition Example 26 1000T without breakage 94％ No lithium plating

[0134] As can be seen from Table 8, the secondary battery using the negative electrode sheet of the present application takes into account both the mechanical properties of the battery and the uniformity of the active layer coating, improves the electrode fracture and lithium plating conditions, and significantly improves the battery cycle capacity retention rate.

[0135] Example 27

[0136] This embodiment provides a method for preparing a secondary battery, wherein the straight region and the arc region of the negative electrode sheet contain different types of fibers. The method for preparing the secondary battery includes:

[0137] Preparation of the positive electrode sheet: Lithium cobalt oxide and conductive carbon black binder PVDF are mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 96:2:2. The mixture is stirred continuously in a blender to form a uniform positive electrode active slurry. The positive electrode active slurry is then coated on the surface of aluminum foil, baked, rolled, and slit to produce the positive electrode sheet.

[0138] Preparation of negative electrode sheet: Graphite, silicon-carbon composite material, first fiber (asphalt-based carbon fiber), silica fiber, conductive carbon black, styrene-butadiene rubber, and carboxymethyl cellulose are mixed in deionized water in a weight ratio of 52:42:1:1:1:2:1, and continuously stirred under the action of a stirrer to form a uniform, flowing first negative electrode active slurry, wherein the mass solid content of the first negative electrode active slurry is 40%, and then the first negative electrode slurry is coated on the flat area of ​​the negative electrode current collector.

[0139] Graphite, silicon-carbon composite material, fiber M (aramid fiber), silica fiber, conductive carbon black, styrene-butadiene rubber, and carboxymethyl cellulose are mixed in deionized water in a weight ratio of 52:42:1:1:1:2:1, and continuously stirred in a stirrer to form a uniform, flowing first negative electrode active slurry, wherein the mass solid content of the first negative electrode active slurry is 40%. The first negative electrode slurry is then coated on the arc area of ​​the negative electrode current collector, and then baked, rolled, and cut to prepare a negative electrode sheet.

[0140] Preparation of electrolyte: Battery assembly:

[0141] The production and assembly process for soft-pack batteries primarily involves electrode preparation, cell assembly, packaging and activation, and testing and sorting. The active layer of the positive electrode is formulated as: LiCoO2 (96%) + conductive carbon black (2%) + PVDF binder (2%); the negative electrode is prepared using the negative electrode sheets prepared in the Example and Comparative Example, respectively; and the electrolyte is formulated as: 1M LiPF6 in EC + 2wt% VC. Cells are assembled with separators through a lamination or winding process, encapsulated with aluminum-plastic film, and then filled with electrolyte. The cells are then activated through a formation process to form a stable SEI film, followed by aging and screening. Finally, OCV testing and sorting are performed to obtain the finished batteries.

[0142] In a dry argon atmosphere glove box, a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) in a mass ratio of 1:1:1:2, and a carboxylic acid ester solvent (ethyl propionate (EP) and propyl propionate (PP) in a 1:1 ratio) was added as a non-aqueous organic solvent. 2% by mass of fluoroethylene carbonate was added, dissolved, and thoroughly stirred. Lithium hexafluorophosphate (LiPF6) was then added and mixed thoroughly to form an electrolyte. The LiPF6 concentration was 1 mol / L.

[0143] The resulting positive electrode sheet, separator (11 micron thick, made of polyethylene), and negative electrode sheet are stacked in order, with the positive tabs attached to the positive and negative tabs to the negative, respectively, with the separator positioned between the positive and negative sheets to provide isolation. The electrode assembly is then wound to form an electrode assembly. The electrode assembly is then wrapped in an outer foil aluminum-plastic film, and the electrolyte is injected. After vacuum packaging, standing, and formation, OCV testing and sorting are performed to produce a lithium-ion battery.

[0144] Example 28 provides a method for preparing a secondary battery, substantially the same as Example 27, wherein the silica fibers in Examples 27 and 28 have an average length of 200 μm and a diameter of 10 μm. The differences between the first and second fibers are shown in Tables 9 and 10. The secondary battery performance of Examples 27 and 28 is shown in Table 11.

[0145] Table 9 Physical parameters of fiber materials in pole pieces

[0146]

[0147] Table 10 Physical parameters of fiber materials in pole pieces

[0148]

[0149] Table 11 Secondary battery performance

[0150]

[0151] As can be seen from Table 11, the secondary battery using the negative electrode sheet of the present application takes into account both the mechanical properties of the battery and the uniformity of the active layer coating, improves the electrode fracture and lithium plating conditions, significantly improves the battery cycle capacity retention rate, and has good furnace temperature performance.

[0152] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A battery electrode, comprising a current collector and an active layer disposed on at least one side of the current collector, characterized in that: The active layer includes active substances and fiber materials; The dyne value of the current collector is DmN / m, the aspect ratio of the fiber material is A, and D and A satisfy the relationship 4≥D / A≥0.

1.

2. The battery electrode according to claim 1, characterized in that: 10≤A≤500； and / or 30≤D≤100。 3. The battery electrode according to claim 2, characterized in that: Aspect ratio A=L / d, where L is the average length of the fiber material; d is the diameter of the fiber material; 8μm≤L≤500μm; 0.1μm≤d≤50μm.

4. The battery electrode according to any one of claims 1 to 3, characterized in that: The active layer further includes a binder; Optionally, the binder includes at least one of styrene-butadiene rubber, modified styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polyvinyl alcohol, polyacrylonitrile, polyacrylamide, polyacrylic acid-acrylonitrile copolymer and its derivatives, acrylic acid-acrylamide and its derivatives, acrylic acid-acrylate copolymer, polymethacrylate, styrene-acrylic emulsion, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and potassium carboxymethyl cellulose.

5. The battery electrode according to any one of claims 1 to 3, characterized in that: The fiber material includes one or more of first fibers and second fibers; The first fiber includes one or more of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, viscose-based carbon fiber, graphene fiber, carbon nanofiber, and carbon nanotube; The second fiber includes one or more of alumina fiber, silica fiber, polyacrylonitrile fiber, polyethylene fiber, aramid fiber, and polyimide fiber.

6. The battery electrode according to claim 5, characterized in that: The fiber material includes at least one of the first fibers and at least one of the second fibers.

7. The battery electrode according to claim 6, characterized in that: At least one of the following conditions is met: (1) Based on the mass of the active layer, the total mass content of the first fiber is 1% to 10%; (2) Based on the mass of the active layer, the total mass content of the second fiber is 0.5%-10%; (3) The electrode is a negative electrode, which includes a negative electrode active material layer, which includes a silicon-carbon composite material; and the ratio of the average length of the second fibers to the volume average particle size Dv50 of the silicon-carbon composite material is less than 1.

8. The battery pole piece according to claim 5, characterized in that: The fiber material is selected from one of the first fiber or the second fiber; The length distribution curve of the fiber material is a bimodal curve, with a first peak length of L1 and a second peak length of L2; Optionally, the thickness of the active layer is T, T≤L1≤2T, 8μm≤L2≤T; Optionally, T is 30 to 250 μm; Optionally, L1 / L2 is 5 to 10.

9. The battery electrode according to claim 5, characterized in that: The battery electrode comprises a straight area and an arc area; The fiber material in the active layer of the straight region includes at least one of the first fibers; The fiber material in the active layer of the arc area includes at least one of the polyacrylonitrile fiber, polyethylene fiber, aramid fiber, and polyimide fiber; Optionally, the fiber material in the active layer of the straight area and / or the active layer of the arc area further includes at least one of the alumina fibers and the silica fibers.

10. A secondary battery, characterized in that: A battery cell comprising a positive electrode sheet, a separator and a negative electrode sheet stacked and wound in sequence, wherein the positive electrode sheet and / or the negative electrode sheet is the battery electrode sheet according to any one of claims 1 to 9.

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