Secondary battery and electronic device
By using composite current collectors on the negative electrode, the problems of deformation and fracture caused by the expansion of silicon-based materials are solved, improving the energy density and safety of secondary batteries and achieving better processing stability and conductivity.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- NINGDE AMPEREX TECHNOLOGY LTD
- Filing Date
- 2025-11-28
- Publication Date
- 2026-07-23
Smart Images
Figure CN2025138588_23072026_PF_FP_ABST
Abstract
Description
Secondary batteries and electronic devices
[0001] Cross-reference to related applications
[0002] This application claims priority to Chinese Patent Application No. 202510070727.5, filed on January 16, 2025, entitled "Secondary Battery and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field
[0003] This application relates to the field of battery technology, and in particular to a secondary battery and electronic device. Background Technology
[0004] Secondary batteries, as the power source for electronic devices, are crucial for ensuring their normal operation. To improve energy density, silicon-based materials have attracted widespread attention and are widely used in battery negative electrode active materials due to their high specific capacity. However, silicon-based materials expand rapidly in volume during charge and discharge, making the negative electrode sheet prone to deformation and breakage during cycling. Summary of the Invention
[0005] The inventors of this application have discovered that silicon-based materials expand rapidly in volume during charging and discharging. Anode sheets containing silicon-based materials are prone to deformation and breakage during cycling. The current collector for these anode sheets is typically copper foil, which has good elongation but low strength. Therefore, anode sheets using copper foil as the current collector are not easily broken during the expansion of silicon-based materials, but are prone to deformation. By setting a high-strength metal plating layer on the surface of the copper foil to form a composite current collector, the requirements for strength, elongation, and conductivity of the current collector can be met. Anode sheets using this composite current collector can improve the problem of deformation caused by the expansion of silicon-based materials, and at the same time, the anode sheets are not easily broken during the expansion of silicon-based materials.
[0006] The purpose of this application is to provide a secondary battery and electronic device that aims to improve the problem of deformation and breakage of the negative electrode during cycling.
[0007] According to a first aspect of this application, a secondary battery is provided, including an electrode assembly. The electrode assembly includes a stacked positive electrode, a separator, and a negative electrode. The negative electrode includes a negative current collector and a negative active material layer. The negative active material layer includes a negative active material, which is a silicon-based material. At least one surface of the negative current collector in the thickness direction is provided with the negative active material layer. In the thickness direction of the negative current collector, the negative current collector includes a first metal layer and a second metal layer attached to the surface of the first metal layer. The first metal layer is a metal foil and includes copper. The tensile strength of the negative current collector is not less than 700 MPa, the elongation of the negative current collector is not less than 8%, and the thickness of the negative current collector is H1, where H1 ≥ 5 μm.
[0008] In the above technical solution, the negative electrode active material includes silicon-based materials. Silicon-based materials have high specific capacity, which can improve the energy density of the secondary battery. However, silicon-based materials are prone to rapid volume expansion during charging and discharging, making the negative electrode sheet susceptible to deformation and breakage. By setting the negative electrode current collector to include a first metal layer and a second metal layer attached to the surface of the first metal layer, the first metal layer is a metal foil containing copper. Copper has good elongation, which can give the negative electrode current collector good elongation, reducing the possibility of the negative electrode sheet breaking during the expansion of the silicon-based material. At the same time, the negative electrode current collector also has good conductivity. The tensile strength of the negative electrode current collector is not less than 700 MPa, which can reduce the possibility of deformation of the negative electrode sheet during the expansion of the silicon-based material. The elongation of the negative electrode current collector is not less than 8%, which can reduce the possibility of breakage of the negative electrode sheet during the expansion of the silicon-based material and reduce the possibility of short circuit in the secondary battery during blunting. The thickness of the negative electrode current collector is H1, where H1 ≥ 5 μm, which is beneficial for the negative electrode current collector to obtain better processing stability during the coating of negative electrode active materials and rolling processes.
[0009] In some preferred embodiments, H1≤11μm, which is beneficial to improving the energy density of the secondary battery.
[0010] In some preferred embodiments, H1≤8μm, which is beneficial to further improve the energy density of the secondary battery.
[0011] In some preferred embodiments, the tensile strength of the negative electrode current collector is no higher than 1200 MPa. The higher the tensile strength of the negative electrode current collector, the thicker the first and second metal layers need to be. Setting the tensile strength of the negative electrode current collector to no higher than 1200 MPa helps to reduce the thickness of the negative electrode current collector, thereby improving the energy density of the secondary battery.
[0012] In some preferred embodiments, the tensile strength of the negative electrode current collector is not higher than 1100 MPa, which is beneficial to further reduce the thickness of the negative electrode current collector, and thus to further improve the energy density of the secondary battery.
[0013] In some preferred embodiments, the elongation of the negative electrode current collector is no higher than 10%. The greater the elongation of the negative electrode current collector, the greater the thickness of the first metal layer needs to be, and the lower the energy density of the secondary battery. By setting the elongation of the negative electrode current collector to no higher than 10%, it is beneficial to reduce the thickness of the first metal layer, thereby improving the energy density of the secondary battery.
[0014] In some preferred embodiments, the thickness of the first metal layer is 3 μm to 6 μm, which is beneficial to improving the elongation of the negative electrode current collector and also to improving the energy density of the secondary battery.
[0015] In some preferred embodiments, the thickness of the second metal layer is 0.5 μm to 3 μm, which is beneficial to improving the uniformity and integrity of the second metal layer adhering to the surface of the first metal layer, as well as to improving the tensile strength of the negative electrode current collector, and at the same time, to improving the energy density of the secondary battery.
[0016] In some preferred embodiments, a second metal layer is provided on both opposite surfaces of the first metal layer in the thickness direction of the negative electrode current collector. By providing a second metal layer on both opposite surfaces of the first metal layer, the negative electrode current collector can have better tensile strength compared to providing a second metal layer on only one surface of the first metal layer.
[0017] In some preferred embodiments, the thickness of the second metal layer on a single surface of the first metal layer is 0.5 μm to 2 μm, which is beneficial to improving the uniformity and integrity of the second metal layer adhering to the surface of the first metal layer, as well as to improving the tensile strength of the negative electrode current collector, and at the same time, to improving the energy density of the secondary battery.
[0018] In some preferred embodiments, the first metal layer is a copper foil and the second metal layer is a nickel layer, which is beneficial to improving the tensile strength and elongation of the negative electrode current collector, while also helping to reduce the cost of the negative electrode current collector.
[0019] In some preferred embodiments, the electrode assembly is a wound structure, formed by stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet. A second metal layer is disposed on the surface of the first metal layer away from the winding center. For wound electrode assemblies, the bending curvature of the inner winding layer is greater than that of the outer winding layer, making the inner winding metal layer more prone to breakage. By disposing the second metal layer on the surface of the first metal layer away from the winding center, the likelihood of breakage of the second metal layer is reduced, thereby improving the fracture resistance of the negative electrode current collector.
[0020] In some preferred embodiments, the nickel content in the second metal layer is not less than 99.5% by mass, so that the second metal layer has excellent electrical conductivity and excellent mechanical strength.
[0021] In some preferred embodiments, the second metal layer is a plating layer, which is deposited on the surface of the first metal layer by electroplating, vapor deposition or vapor deposition, which helps to improve the stability between the first metal layer and the second metal layer.
[0022] In some preferred embodiments, the silicon-based material includes at least one of elemental silicon, silicon oxide, silicon carbide, or silicon alloy, which is beneficial for improving the specific capacity of the negative electrode active material.
[0023] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.
[0024] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description
[0025] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the dimensions in the drawings do not constitute a limitation on scale.
[0026] Figure 1 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;
[0027] Figure 2 is a schematic diagram of the structure of an electrode assembly according to some embodiments of this application;
[0028] Figure 3 is a partial schematic diagram of an electrode assembly according to some embodiments of this application;
[0029] Figure 4 is a schematic diagram of the negative electrode current collector in some embodiments of this application;
[0030] Figure 5 is a schematic diagram of the negative electrode current collector in some embodiments of this application;
[0031] Figure 6 is a schematic diagram of the negative electrode current collector in some embodiments of this application.
[0032] Explanation of reference numerals in the attached figures:
[0033] 100. Secondary batteries;
[0034] 10. Shell;
[0035] 20. Electrode assembly; 21. Positive electrode sheet; 211. Positive current collector; 212. Positive active material layer; 22. Negative electrode sheet; 221. Negative current collector; 2211. First metal layer; 2212. Second metal layer; 222. Negative active material layer; 23. Separator;
[0036] X, the first direction. Embodiments of the present invention
[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.
[0038] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.
[0039] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.
[0040] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.
[0041] The term "perpendicular" is used to describe an ideal state between two components. In actual production or use, two components can exist in a state that is approximately perpendicular. For example, in numerical terms, perpendicularity can refer to the angle between two straight lines within the range of 90 ± 10°, the dihedral angle between two planes within the range of 90 ± 10°, or the angle between a straight line and a plane within the range of 90 ± 10°. The two components described as "perpendicular" do not have to be absolutely straight lines or planes; they can be approximately straight lines or planes. From a macroscopic perspective, if the overall direction of extension is straight or plane, the component can be considered a "straight line" or "plane".
[0042] The technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.
[0043] In a first aspect, embodiments of this application provide a secondary battery 100. Referring to FIG1, the secondary battery 100 includes a housing 10 and an electrode assembly 20. The housing 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure), and the electrolyte wets the electrode assembly 20 within the housing 10.
[0044] Referring to Figure 2, which shows the wound structure of the electrode assembly 20, the electrode assembly 20 includes a positive electrode 21, a separator 23, and a negative electrode 22. The positive electrode 21, separator 23, and negative electrode 22 are stacked and wound together, with a separator 23 between adjacent positive electrode 21 and negative electrode 22. In the embodiments of this application, the electrode assembly 20 is described as a wound structure. In other embodiments, the electrode assembly 20 may also be a stacked structure, for example, the positive electrode 21, separator 23, and negative electrode 22 are sequentially stacked to form a stacked electrode assembly 20.
[0045] In some embodiments, referring to FIG3, the positive electrode sheet 21 includes a positive electrode current collector 211 and a positive electrode active material layer 212, and at least one surface of the positive electrode current collector 211 is provided with the positive electrode active material layer 212. In some embodiments, the positive electrode current collector 211 may be an aluminum foil.
[0046] In some embodiments, the positive electrode active material layer 212 is immersed in the electrolyte within the housing 10 to undergo an electrochemical reaction. The positive electrode active material layer 212 includes a positive electrode active material, a conductive agent, a binder, etc., and the above materials are mixed and stirred evenly and coated onto at least one surface of the positive electrode current collector 211 to obtain the positive electrode active material layer 212. The positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium manganese iron phosphate.
[0047] In some embodiments, the negative electrode 22 includes a negative electrode current collector 221 and a negative electrode active material layer 222, wherein at least one surface of the negative electrode current collector 221 is provided with the negative electrode active material layer 222.
[0048] In some embodiments, the negative electrode active material layer 222 is immersed in the electrolyte within the housing 10 to undergo an electrochemical reaction. The negative electrode active material layer 222 includes a negative electrode active material, a conductive agent, a binder, etc., and the above materials are mixed and stirred evenly and coated onto at least one surface of the negative electrode current collector 221 to obtain the negative electrode active material layer 222. The negative electrode active material may include at least one of graphite, silicon, hard carbon, and carbon fiber.
[0049] In some embodiments, the negative electrode active material includes a silicon-based material. Silicon-based materials have a high specific capacity, which can improve the energy density of the secondary battery 100. However, silicon-based materials are prone to rapid volume expansion during charging and discharging, making the negative electrode sheet 22 susceptible to deformation and breakage. The negative electrode current collector 221 is typically copper foil. Copper foil has good elongation but low strength. Therefore, the negative electrode sheet 22 using copper foil as the negative electrode current collector 221 is less prone to breakage during the expansion of the silicon-based material, but it is easily deformed. Increasing the thickness of the negative electrode current collector 221 can reduce the possibility of deformation, but it will reduce the energy density of the secondary battery 100 and increase its weight. Using rolled copper foil as the negative electrode current collector 221 can reduce the possibility of deformation, but the processing of rolled copper foil is difficult, complex, and costly, and its elongation is poor. Reducing the thickness and cold-pressing density of the negative electrode active material layer 222 can decrease the likelihood of expansion, thereby reducing the possibility of deformation and breakage of the negative electrode sheet 22. However, both reducing the thickness and cold-pressing density will increase the thickness of the electrode assembly 20, thus reducing the energy density of the secondary battery 100. While reducing the silicon-based material content in the negative electrode active material layer 222 can also reduce the likelihood of expansion and thus the possibility of deformation and breakage of the negative electrode sheet 22, it will decrease the specific capacity of the negative electrode sheet 22, thereby reducing the energy density of the secondary battery 100.
[0050] To address the aforementioned issues, in the embodiments of this application, referring to Figures 3 and 4, the negative electrode current collector 221 includes a first metal layer 2211 and a second metal layer 2212 attached to the surface of the first metal layer 2211. The first metal layer 2211 is a metal foil comprising copper. The tensile strength of the negative electrode current collector 221 is not less than 700 MPa, the elongation of the negative electrode current collector 221 is not less than 8%, and the thickness of the negative electrode current collector 221 is H1, where H1 ≥ 5 μm. The first metal layer 2211, comprising copper, possesses good elongation, which allows the negative electrode current collector 221 to have good elongation, reducing the possibility of breakage of the negative electrode sheet 22 during the expansion of the silicon-based material. Simultaneously, the negative electrode current collector 221 also exhibits good conductivity. The tensile strength of the negative electrode current collector 221, not less than 700 MPa, can reduce the possibility of deformation of the negative electrode sheet 22 during the expansion of the silicon-based material. The elongation of the negative electrode current collector 221 is not less than 8%, which can reduce the possibility of breakage of the negative electrode sheet 22 during the expansion of the silicon-based material and reduce the possibility of short circuit in the secondary battery 100 during the blunting process. The thickness of the negative electrode current collector 221 is H1, where H1≥5μm, which helps to ensure that the negative electrode current collector 221 has good safety performance and also helps to obtain better processing stability of the negative electrode current collector 221 in processes such as coating negative electrode active material and rolling.
[0051] In some embodiments, H1≤11μm is beneficial to improving the energy density of the secondary battery 100.
[0052] In some embodiments, H1≤8μm is beneficial to balance the energy density of the secondary battery 100 while ensuring that the current collector has good safety performance, so as to obtain better overall benefits.
[0053] In some embodiments, the tensile strength of the negative electrode current collector 221 is not higher than 1200 MPa. The greater the tensile strength of the negative electrode current collector 221, the greater the thickness of the first metal layer 2211 and the second metal layer 2212 need to be. Setting the tensile strength of the negative electrode current collector 221 to be no higher than 1200 MPa is beneficial to reducing the thickness of the negative electrode current collector 221, and thus beneficial to improving the energy density of the secondary battery 100.
[0054] In some embodiments, the tensile strength of the negative electrode current collector 221 is no higher than 1100 MPa. When the tensile strength of the negative electrode current collector 221 reaches 1100 MPa, it can have a good ability to suppress expansion. Further increasing the tensile strength requires setting a thicker second metal layer 2212, which will affect the energy density and gradually reduce the cost-effectiveness. Therefore, setting the tensile strength of the negative electrode current collector 221 to no higher than 1100 MPa is beneficial to further reduce the thickness of the negative electrode current collector 221, and thus to further improve the energy density of the secondary battery 100.
[0055] In some embodiments, the elongation of the negative electrode current collector 221 is not higher than 10%. The greater the elongation of the negative electrode current collector 221, the greater the thickness of the first metal layer 2211 needs to be, and the lower the energy density of the secondary battery 100. By setting the elongation of the negative electrode current collector 221 to be no higher than 10%, it is beneficial to reduce the thickness of the first metal layer 2211, thereby improving the energy density of the secondary battery 100.
[0056] In some embodiments, the thickness of the first metal layer 2211 is 3 μm to 6 μm, which is beneficial to improving the elongation of the negative electrode current collector 221 and also beneficial to improving the energy density of the secondary battery 100.
[0057] In some embodiments, the thickness of the second metal layer 2212 is 0.5 μm to 3 μm, which is beneficial to improving the uniformity and integrity of the second metal layer 2212 attached to the surface of the first metal layer 2211, as well as to improving the tensile strength of the negative electrode current collector 221, and at the same time, to improving the energy density of the secondary battery 100.
[0058] In some embodiments, referring to FIG5, a second metal layer 2212 is provided on both opposite surfaces of the first metal layer 2211 in the thickness direction (first direction X) of the negative electrode current collector 221. By providing the second metal layer 2212 on both opposite surfaces of the first metal layer 2211, the negative electrode current collector 221 can have better tensile strength than by providing the second metal layer 2212 on only one surface of the first metal layer 2211.
[0059] In some embodiments, the thickness of the second metal layer 2212 on a single surface of the first metal layer 2211 is 0.5 μm to 2 μm, which is beneficial to improving the uniformity and integrity of the second metal layer 2212 attached to the surface of the first metal layer 2211, as well as to improving the tensile strength of the negative electrode current collector 221, and at the same time, to improving the energy density of the secondary battery 100.
[0060] In some embodiments, the first metal layer 2211 is a copper foil and the second metal layer 2212 is a nickel layer, which is beneficial to improving the tensile strength and elongation of the negative electrode current collector 221, while also helping to reduce the cost of the negative electrode current collector 221.
[0061] In some embodiments, referring to Figures 2 and 6, the electrode assembly 20 is a wound structure, formed by stacking and winding a positive electrode 21, a separator 23, and a negative electrode 22. A second metal layer 2212 is disposed on the surface of the first metal layer 2211 away from the winding center. For the wound electrode assembly 20, the bending curvature of the inner winding layer is greater than that of the outer winding layer, making the inner winding metal layer more prone to breakage. The elongation of the copper foil is greater than that of the nickel layer, thus the copper foil has greater fracture resistance than the nickel layer. By disposing the second metal layer 2212 on the surface of the first metal layer 2211 away from the winding center, compared to the second metal layer 2212 being located on the surface of the first metal layer 2211 facing the winding center, the likelihood of the second metal layer 2212 breaking is reduced, thereby improving the fracture resistance of the negative electrode current collector 221.
[0062] In some embodiments, the nickel content in the second metal layer 2212 is not less than 99.5% by mass, so that the second metal layer 2212 has excellent electrical conductivity and excellent mechanical strength.
[0063] In some embodiments, the second metal layer 2212 is a plating layer, which is deposited on the surface of the first metal layer 2211 by electroplating, vapor deposition or vapor deposition, so that the first metal layer 2211 serves as a base layer and the second metal layer 2212 serves as a plating layer deposited on the surface of the first metal layer 2211, thereby improving the stability between the first metal layer 2211 and the second metal layer 2212.
[0064] In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon oxide, silicon carbide, or silicon alloy, which is beneficial for improving the specific capacity of the negative electrode active material.
[0065] A second aspect of this application also provides an electronic device including a secondary battery 100 as described in any embodiment of the first aspect above. The electronic device in this application is not particularly limited and can be any electronic device known in the prior art. For example, electronic devices include, but are not limited to, Bluetooth headsets, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.
[0066] Test section:
[0067] 1. Tensile strength test of current collector:
[0068] Referring to the national standard GB / T 29847-2013 "Test Methods for Copper Foil for Printed Circuit Boards", the negative current collector in this embodiment was tested according to actual test conditions. A universal testing machine was used as the tensile strength testing equipment. First, a current collector without an active material coating was selected, or the active material coating on the surface of the current collector was removed (e.g., by scraping with a scraper). The sample was then cut into specimens with a length of L1 = 100 ± 0.5 mm (for specimens less than 100 mm, the original length was used) and a width of 20 ± 0.25 mm. Clamps were then installed at both ends of the specimen to ensure that it would not slip during tensile testing. Next, the specimen was fixed on the clamps of the testing machine, and a load sensor was used to record the force applied to the specimen, while a displacement sensor recorded the deformation of the specimen. A tensile speed of 50 mm / min was set, and other test parameters such as the measurement length and the distance between the clamps of the testing machine were determined according to the actual situation and in accordance with the test standards. The test is stopped when the specimen is stretched to break. The maximum tensile force F that the specimen withstands at the point of breakage is recorded. The tensile strength T of the specimen is calculated using T = F / S, where S is the initial cross-sectional area of the specimen, which is equal to the product of the specimen's width and thickness. Five parallel specimens are tested, and the average value is taken as the test result. During the test, the length direction of the specimen is parallel to the axis of the fixture, and the specimen is kept in a straight position. The experimental temperature is 20±5℃.
[0069] 2. Elongation test of current collector:
[0070] Referring to the national standard GB / T 29847-2013 "Test Methods for Copper Foil for Printed Circuit Boards", the negative current collector in this embodiment was tested according to the actual test conditions. A universal testing machine was used as the tensile strength testing equipment. First, a current collector without an active material coating was selected, or the active material layer on the surface of the current collector was removed, such as by scraping with a scraper. Then, a sample with a length of L1 = 100 ± 0.5 mm (if less than 100 mm, the original length was used) and a width of 20 ± 0.25 mm was cut. Then, clamps were installed at both ends of the sample to ensure that the sample would not slip during tensile testing. Next, the sample was fixed on the clamps of the testing machine, and the force applied to the sample was recorded using a load sensor, and the deformation of the sample was recorded using a displacement sensor. The tensile speed was set to 50 mm / min, and other test parameters such as the measurement length and the distance between the clamps of the testing machine were determined according to the actual situation and in accordance with the test standards. The test was stopped when the sample was stretched to break, and the maximum deformation L that the sample underwent when it broke was recorded. The elongation of the sample was calculated as (L - L1) / L1. Five parallel samples were tested, and the average value was taken as the test result. During the test, the length direction of the sample was parallel to the axis of the fixture, and the sample was kept in a straight line. The experimental temperature was 20±5℃.
[0071] 3. Energy density test of secondary batteries:
[0072] Place the secondary battery in a 25℃ constant temperature chamber and let it stand for 30 minutes to allow it to reach a constant temperature. Once the battery has reached a constant temperature, charge it at a constant current of 0.5C until it reaches a full charge voltage of 4.5V. Then charge it at a constant voltage of 4.5V until the current reaches 0.05C. Finally, discharge it at 0.5C until the voltage reaches 3.0V, and record the discharge energy.
[0073] Energy density = Discharge energy / (Length × Width × Thickness of secondary battery).
[0074] 4. Thrust test for secondary batteries:
[0075] The test temperature was adjusted to a constant 25℃, and the following steps were performed on the secondary battery sample:
[0076] (1) Discharge at a constant current of 0.5C to 3.0V;
[0077] (2) Let stand for 10 minutes;
[0078] (3) Charge at a constant current of 0.5C to 4.5V;
[0079] (4) Charge at a constant voltage of 4.5V to 0.05C;
[0080] (5) Let stand for 10 minutes;
[0081] (6) Place the sample on the test platform with half of it facing up. Use a blunt nail with a diameter of 6mm, apply a pressure of 1600N, and drop at a speed of 300N / min. Test from the center of the sample. Monitor the cell voltage and surface temperature rise during the test. Judgment criteria: No explosion, no fire; record the pass rate.
[0082] Finish
[0083] Blunt puncture pass rate: Record the number of times the needle did not ignite / the number of tests.
[0084] 5. Cycle test of secondary batteries:
[0085] The test temperature was adjusted to a constant 25℃, and the following steps were performed on the secondary battery sample:
[0086] (1) Charge to 4.3V using 3C constant current;
[0087] (2) Charge at a constant voltage of 4.3V to 2C;
[0088] (3) Charge at a constant current of 2C to 4.4V;
[0089] (4) Charge at a constant voltage of 4.4V to 1C;
[0090] (5) Charge at 1C constant current to 4.5V;
[0091] (6) Charge at a constant voltage of 4.5V to 0.1C;
[0092] (7) Let stand for 5 minutes;
[0093] (8) 1C constant current discharge to 3.0V
[0094] (9) Let stand for 5 minutes;
[0095] (10) Repeat steps (1) to (9) 1000 times;
[0096] Finish
[0097] Capacity retention: The ratio of discharge capacity after 1000 cycles to discharge capacity after the first cycle;
[0098] Thickness expansion rate: (Cell thickness after 1000 cycles - Initial cell thickness) / Initial cell thickness;
[0099] Corner breakage rate: Number of corner breaks per 1000 battery cells / Number of tests.
[0100] 6. Negative electrode sheet specific capacity test:
[0101] First, remove the negative electrode from the fully discharged secondary battery and dry the electrolyte in the negative electrode at 60°C in an electric baking oven. After scraping off the positive electrode active material layer from the negative electrode with a knife, scrape off the negative electrode active material layer powder with a knife and weigh it by a balance, taking a weight of m1 = 100 mg. Immerse it in hydrochloric acid solution (mass fraction 10%) for 3 hours. Then, filter out the remaining solid material and bake the solid material in an electric baking oven at 60°C for 24 hours. Weigh the solid material again, taking a weight of m2. Calculate (m1-m2) / m1, which is the mass ratio x of the negative electrode active material in the original electrode formulation. The negative electrode active material powder was scraped off from the negative electrode sheet again with a knife, and its weight (m3 = 100 mg) was weighed using a balance. This powder was then mixed with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) in a mass ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 65 wt%, and the mixture was stirred evenly. The slurry was then evenly coated onto the copper foil on the negative electrode current collector. After the electrode sheet was dried, it was assembled with the lithium metal sheet, separator, and electrolyte to form a button cell. Finally, the cell was charged at a constant current rate of 0.1C to 4.5V, charged at a constant voltage rate of 4.5V to 0.02C, and then discharged at a constant current rate of 0.1C to 2.8V to obtain the effective capacity of the button cell. The effective capacity is calculated by dividing the effective active material powder weight (m4) by the specific capacity (m4 = m3 × x).
[0102] Calculation of the mass percentage of silicon-based materials: Assuming the mass percentage of silicon-based materials is X, X×1750+(1-X)×358=specific capacity of the negative electrode active material, from which the mass percentage of silicon-based materials X can be calculated.
[0103] Example 1
[0104] <Preparation of the positive electrode>:
[0105] The positive electrode active material is lithium cobalt oxide, the positive electrode conductive agent is acetylene black, and the positive electrode binder is polyvinylidene fluoride (PVDF, with a weight average molecular weight of 5×10⁻⁶). 5 Mix according to a mass ratio of 94:3:3, and add N. Methylpyrrolidone (NMP) was used as a solvent and stirred in a vacuum mixer until a positive electrode slurry with a solid content of 75 wt% and a homogeneous system was obtained.
[0106] The above-mentioned positive electrode slurry was uniformly coated on one surface of a 7 μm thick aluminum foil for positive electrode current collectors. The positive electrode slurry was then dried to obtain a positive electrode sheet with a single-sided coating of positive electrode active material layer. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode active material layer.
[0107] <Preparation of the negative electrode>:
[0108] The negative electrode active materials graphite, silicon carbide, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 87:10:1.5:1.5. Deionized water was added as a solvent, and the mixture was stirred under vacuum until a negative electrode slurry with a solid content of 70 wt% and a homogeneous system was obtained.
[0109] High-purity copper foil with a thickness of 4μm was selected as the substrate. The surface of the copper foil was cleaned with an alkaline solution to remove grease and impurities; then, an acidic solution (such as nitric acid) was used to treat the surface to remove oxides and activate the surface. A plating bath was prepared using nickel sulfate, nickel chloride, and boric acid, and the temperature was maintained between 40℃ and 60℃. The copper substrate was immersed in the plating bath, and a uniform nickel layer with a thickness of 1μm and a nickel mass percentage of 99.9% was deposited through electrolysis. After double-sided plating of the copper foil, a 6μm copper-plated nickel negative electrode current collector was obtained. The above negative electrode slurry was coated on one surface of the negative electrode current collector, leaving an empty foil section. The negative electrode slurry was dried to obtain a single-sided negative electrode sheet coated with a negative electrode active material layer on one side. Then, the above steps were repeated on the other surface of the negative electrode current collector to obtain a double-sided negative electrode sheet coated with a negative electrode active material layer on both sides. The silicon-carbon mass percentage of the negative electrode active material was 10%.
[0110] <Preparation of the diaphragm>:
[0111] A porous polyethylene (PE) membrane with a thickness of 8 μm was used as the diaphragm.
[0112] <Electrolyte Preparation>:
[0113] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate are mixed in a mass ratio of 30:50:20 to obtain an organic solution. Then, lithium hexafluorophosphate is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.
[0114] <Preparation of Secondary Batteries>:
[0115] The positive and negative electrode sheets prepared above are subjected to cold pressing and slitting processes to obtain electrode sheets of the required length and width. The sheets are cut into a fixed shape and wound together with the separator to form an electrode assembly. After encapsulation, liquid injection, and formation, the finished secondary battery is produced.
[0116] The relevant parameters in Comparative Examples 1 to 3 and Examples 1 to 11 are shown in Table 1 below.
[0117] In Comparative Examples 1 and 2, the negative electrode current collectors used were both 6 μm thick electrolytic copper foils, but their lattice structures differed. The copper foil in Comparative Example 2 had a more refined lattice structure. Lattice refinement can effectively hinder dislocation movement, thereby improving strength. However, lattice refinement weakens the plastic deformation ability of the current collector, i.e., the elongation deteriorates. In terms of processing, lattice refinement can be achieved through cold rolling, heat treatment, etc. In Comparative Examples 3 and Examples 1 to 14, the negative electrode current collectors were nickel-plated copper foils. The nickel layer in Comparative Examples 3 and Examples 1 to 10 was two layers, while the nickel layer in Examples 11 to 14 was a single layer, and the nickel layer was located on the surface of the copper foil away from the winding center.
[0118] Table 1
[0119]
[0120] Note: In Table 1, "\" indicates that the parameter is not included.
[0121] According to Table 1 above, and in conjunction with Comparative Examples 1 to 3 and Examples 1 to 14, it can be seen that when electrolytic copper foil is used as the negative electrode current collector, the elongation of the negative electrode current collector is high, but the tensile strength is low. The negative electrode current collector is prone to deformation during silicon expansion, resulting in a low capacity retention rate and a high expansion rate of the battery. Using small-lattice electrolytic copper foil as the negative electrode current collector can increase the tensile strength of the negative electrode current collector, reduce the possibility of deformation during silicon expansion, reduce the battery expansion rate, and improve the battery capacity retention rate. However, the elongation of small-lattice electrolytic copper foil is poor, resulting in a low blunt puncture pass rate and a large proportion of corner breakage. By using nickel-plated copper foil as the negative electrode current collector, compared to electrolytic copper foil, the tensile strength of the negative electrode current collector can be no less than 700 MPa. This reduces the possibility of deformation of the negative electrode current collector during silicon expansion, thereby improving the battery's capacity retention rate and reducing its expansion rate. Simultaneously, the elongation of the negative electrode current collector is not too poor, with an elongation of no less than 8%, preventing the battery from exhibiting a low blunt burr pass rate and a high corner breakage rate. Furthermore, if the thickness H1 of the negative electrode current collector is less than 5 μm, the process is difficult and the safety performance is poor. When H1 ≥ 5 μm, it is beneficial for the negative electrode current collector to achieve better processing stability during processes such as coating active materials and compaction.
[0122] As can be seen from Examples 1 to 14, the thicker the negative electrode current collector, the lower the energy density of the secondary battery. When the thickness H1 of the negative electrode current collector is greater than 11 μm, it is easy to lose a lot of energy density of the secondary battery. Therefore, H1 ≤ 11 μm is preferred. Further preferred is H1 ≤ 8 μm, which is beneficial to balance the energy density of the secondary battery while ensuring that the current collector has good safety performance, so as to obtain better overall benefits.
[0123] As can be seen from Examples 1 to 14, the greater the tensile strength of the negative electrode current collector, the greater the thickness of the first and second metal layers needs to be. Therefore, it is preferable that the tensile strength of the negative electrode current collector is not higher than 1200 MPa, which is beneficial to reducing the thickness of the negative electrode current collector and thus improving the energy density of the secondary battery. Further preferably, the tensile strength of the negative electrode current collector is not higher than 1100 MPa. When the tensile strength of the negative electrode current collector reaches 1100 MPa, it can have a good ability to suppress expansion. Further increasing the tensile strength requires a thicker second metal layer, which gradually reduces the cost-effectiveness. Therefore, it is further preferable that the tensile strength of the negative electrode current collector is not higher than 1100 MPa, which is beneficial to further reducing the thickness of the negative electrode current collector and thus further improving the energy density of the secondary battery.
[0124] As can be seen from Examples 1 to 4 and Example 6, the greater the elongation of the negative electrode current collector, the greater the thickness of the first metal layer needs to be, and the lower the energy density of the secondary battery. Therefore, it is preferable that the elongation of the negative electrode current collector is not higher than 10%, which is beneficial to reducing the thickness of the first metal layer and thus improving the energy density of the secondary battery.
[0125] As can be seen from Examples 5 and 14, when the total thickness of the first metal layer (copper foil) and the total thickness of the second metal layer (nickel layer) remain unchanged, by setting the second metal layer on both opposite surfaces of the first metal layer, the negative electrode current collector has better tensile strength, the battery has higher capacity retention rate and lower expansion rate compared to setting the second metal layer on only one surface of the first metal layer. Therefore, two layers of second metal layers are more effective than a single layer of second metal layer.
[0126] Based on Examples 1 to 4 and Example 6, it can be seen that, with the second metal layer thickness remaining constant, the greater the thickness of the first metal layer, the greater the elongation of the negative electrode current collector. A first metal layer thickness ≥ 3 μm allows the negative electrode current collector to have a large elongation; furthermore, a first metal layer thickness less than 3 μm is difficult to fabricate. When the thickness of the first metal layer increases to 6 μm, further increasing the thickness of the first metal layer does not significantly increase the elongation of the negative electrode current collector, but the energy density of the secondary battery decreases. Therefore, a first metal layer thickness ≤ 6 μm is preferred.
[0127] As can be seen from Examples 1, 8 to 10, and Examples 11 to 13, when the thickness of the first metal layer remains constant, the greater the thickness of the second metal layer, the greater the tensile strength of the negative electrode current collector. When the second metal layer is used as a coating, its thickness should not be less than 0.5 μm, which is beneficial to improving the uniformity and integrity of the coating and reducing the possibility of uneven coverage due to an excessively thin coating, thereby affecting product performance.
[0128] Since the second metal layer serves as a plating layer and the first metal layer as a base layer, in actual production, the base layer acts as a support layer. It is necessary to ensure that the plating thickness on a single surface of the base layer is ≤ 75% of the base layer thickness. Otherwise, excessive plating thickness makes uniformity difficult to control, increases processing difficulty, and raises costs. Referring to Examples 13 and 14, when the second metal layer is a single layer, if its thickness exceeds 3 μm, the thickness of the first metal layer also needs to exceed 4 μm. In this case, the thickness of the negative electrode current collector easily exceeds 8 μm, which significantly reduces the energy density of the secondary battery. Referring to Examples 9 and 10, when the second metal layer is a double layer, if its thickness on a single surface of the first metal layer exceeds 2 μm, the thickness of the first metal layer also needs to exceed 3 μm. In this case, the thickness of the negative electrode current collector easily exceeds 8 μm, which further reduces the energy density of the secondary battery.
[0129] The relevant parameters in Examples 15 and 16 are shown in Table 2 below.
[0130] The mass percentage of nickel in the second metal layer differs in Examples 1, 15, and 16.
[0131] Table 2
[0132]
[0133] According to Table 2 above, and in conjunction with Examples 1, 15, and 16, when the negative electrode current collector is nickel-plated copper foil, the higher the mass percentage of nickel in the second metal layer (nickel layer), the greater the tensile strength of the negative electrode current collector, the higher the battery capacity retention rate, and the lower the expansion rate. When the mass percentage of nickel in the second metal layer is not less than 99.5%, the negative electrode current collector has good tensile strength, and the battery has a high capacity retention rate and a low expansion rate.
[0134] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.
Claims
1. A secondary battery, comprising an electrode assembly, the electrode assembly comprising a stacked positive electrode sheet, a separator and a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising a silicon-based material, and the negative electrode active material layer being disposed on at least one surface in the thickness direction of the negative electrode current collector. Its features are, In the thickness direction of the negative electrode current collector, the negative electrode current collector includes a first metal layer and a second metal layer attached to the surface of the first metal layer; the first metal layer is a metal foil, the first metal layer includes copper, the tensile strength of the negative electrode current collector is not less than 700 MPa, the elongation of the negative electrode current collector is not less than 8%, and the thickness of the negative electrode current collector is H1, where H1 ≥ 5 μm.
2. The secondary battery according to claim 1, characterized in that, H1≤11μm.
3. The secondary battery according to claim 2, characterized in that, H1≤8μm.
4. The secondary battery according to any one of claims 1 to 3, characterized in that, The tensile strength of the negative electrode current collector is not higher than 1200 MPa.
5. The secondary battery according to claim 4, characterized in that, The tensile strength of the negative electrode current collector is not higher than 1100 MPa.
6. The secondary battery according to any one of claims 1 to 5, characterized in that, The elongation of the negative electrode current collector is no higher than 10%.
7. The secondary battery according to any one of claims 1 to 6, characterized in that, The thickness of the first metal layer is 3 μm to 6 μm.
8. The secondary battery according to claim 7, characterized in that, The thickness of the second metal layer is 0.5 μm to 3 μm.
9. The secondary battery according to claim 7, characterized in that, In the thickness direction of the negative electrode current collector, the second metal layer is provided on both opposite surfaces of the first metal layer.
10. The secondary battery according to claim 9, characterized in that, The thickness of the second metal layer on a single surface of the first metal layer is 0.5 μm to 2 μm.
11. The secondary battery according to any one of claims 1 to 10, characterized in that, The first metal layer is a copper foil, and the second metal layer is a nickel layer.
12. The secondary battery according to claim 11, characterized in that, The electrode assembly has a wound structure, and the second metal layer is disposed on the surface of the first metal layer away from the winding center.
13. The secondary battery according to claim 11 or 12, characterized in that, The nickel content in the second metal layer is not less than 99.5% by mass.
14. The secondary battery according to any one of claims 11 to 13, characterized in that, The second metal layer is a plating layer, which is deposited on the surface of the first metal layer by electroplating, vapor deposition or vapor deposition.
15. The secondary battery according to any one of claims 1 to 14, characterized in that, The silicon-based material includes at least one of elemental silicon, silicon oxide, silicon carbide, or silicon alloy.
16. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 15.