Secondary battery and electronic device
By employing a composite current collector structure with a single-sided positive electrode in the secondary battery, combined with multiple metal layers of aluminum and nickel or titanium, the problems of puncture resistance and energy density reduction caused by thinning are solved, achieving high energy density and improved safety mechanical performance.
Patent Information
- Application Number
- CN202480018867.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-03
- Publication Date
- 2025-11-07
AI Technical Summary
Existing technologies, in the process of reducing the thickness of secondary batteries to achieve thinner and lighter designs, result in a decrease in their resistance to puncture, compression, and breakage, and traditional methods can significantly reduce energy density or increase costs.
A composite current collector structure with a single-sided positive electrode is adopted, including multiple metal layers of aluminum and nickel or titanium, to ensure that the tensile strength of the current collector reaches more than 300MPa and the thickness is controlled to be less than 20μm. Combined with an optimized coating process for the active layer, current conduction and mechanical strength are improved.
It improves the energy density and safety mechanical performance of secondary batteries, reduces the risk of curling, extends cycle life and maintains high capacity, and has better resistance to deformation, drop and puncture.
Smart Images
Figure CN120917593A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of batteries, in particular to a secondary battery and an electronic device. BACKGROUND
[0002] As the power supply of electronic devices, the secondary battery is the key to ensure the normal use of electronic devices. With the wide application of laminated electrode assemblies, the requirement for the thinness of the battery is higher, and further reducing the thickness of the current collector will bring safety risks to the secondary battery, and the puncture, extrusion and crushing resistance of the secondary battery will be greatly reduced. SUMMARY
[0003] The present application inventors found that for an ultrathin laminated electrode assembly, the ways to improve the puncture, extrusion and crushing resistance include increasing the thickness of the positive and negative current collectors, using nickel foil for single-sided positive plate, using thick aluminum plastic film packaging bag, and reducing the thickness of the active material and increasing the number of layers, but all have obvious defects. Increasing the thickness of the positive and negative current collectors will greatly reduce the energy density of the secondary battery, and increase the cost of the electrode assembly. Pure nickel foil has low elongation and is difficult to process, and has high cost and corrosion risk (nickel foil oxidation potential is 3.3V, while the general voltage of lithium battery is up to 4.5V, and the oxidation nickel on the surface of the nickel foil shows electrochemical stability to protect the inner nickel foil; but the electrochemical window is insufficient at a high potential of more than 4.55V or even 4.57V, which may aggravate the corrosion of the battery). Using thick aluminum plastic film packaging bag will reduce the energy density of the secondary battery and increase the cost and manufacturing difficulty. Reducing the thickness of the active material and increasing the number of layers will greatly reduce the energy density of the secondary battery and increase the cost.
[0004] The purpose of the present application is to provide a secondary battery and an electronic device, which aims to improve the safety mechanical properties of the electrode assembly while improving the energy density of the secondary battery.
[0005] According to a first aspect of the present application, a secondary battery is provided, comprising an electrode assembly, the electrode assembly comprising positive plates, separators and negative plates stacked in sequence along a first direction. The positive plate comprises a single-sided positive plate, the outermost positive plate of the electrode assembly along the first direction is the single-sided positive plate, the single-sided positive plate comprises a first positive current collector and a first positive active layer, the surface of the first positive current collector facing the negative plate is provided with the first positive active layer, the first positive current collector comprises a first metal layer and a second metal layer stacked in contact along the first direction, the first metal layer comprises aluminum, the tensile strength of the first positive current collector is 300MPa or more, and the thickness of the first positive current collector is H1, H1≤20μm. Wherein, the tensile strength is 300MPa or more, which means that the tensile strength is ≥300MPa.
[0006] In the technical solution, the outermost electrode sheet of the electrode assembly is a single-face positive electrode sheet, and the first positive electrode current collector of the single-face positive electrode sheet is provided with a first positive electrode active layer only on the surface facing the negative electrode sheet, so that the energy density of the secondary battery can be improved. The thickness of the current collector of the outermost single-face positive electrode sheet of the electrode assembly can be increased, for example, an aluminum foil with a thickness of 20 μm can be used as the current collector to reduce the possibility of curling. However, the tensile strength of the 20 μm thick aluminum foil is about 270 MPa, which is still difficult to meet the demand for higher mechanical safety performance. In the present application, the first positive electrode current collector is provided with a composite structure of a first metal layer and a second metal layer, and the first metal layer includes aluminum. The excellent electrical conductivity of aluminum is used to ensure effective conduction of current. The tensile strength of the first positive electrode current collector is greater than 300 MPa, which can reduce the possibility of curling, improve the puncture resistance, and better resist deformation and fracture during charging and discharging cycles. The thickness of the first positive electrode current collector is less than 20 μm, which can improve the safety mechanical performance of the electrode assembly and the energy density of the secondary battery. Reducing the possibility of curling of the outermost single-face positive electrode sheet can improve the cycle life and capacity retention rate of the secondary battery.
[0007] In some preferred embodiments, the tensile strength of the first positive electrode current collector is greater than or equal to 360 MPa. The tensile strength of the first positive electrode current collector is greater than 360 MPa, which can further reduce the risk of damage to the electrode assembly under external force impact, so that the deformation resistance, drop resistance, and puncture resistance of the electrode assembly are improved, thereby further improving the safety performance of the secondary battery.
[0008] In some preferred embodiments, H1 is greater than or equal to 7 μm. The thickness of the first positive electrode current collector is not less than 7 μm, which is beneficial to obtaining better processing stability in processes such as active material coating and compaction. In addition, the first positive electrode current collector with a thickness of not less than 7 μm can have better mechanical strength, thereby obtaining better safety performance (mechanical strength includes bending strength, tensile strength, compressive strength, and impact strength. In the present application, mechanical strength is used to represent safety mechanical performance, and high mechanical strength means high safety mechanical performance).
[0009] In some preferred embodiments, the first metal layer is an aluminum foil, and the thickness of the first metal layer is 5 μm to 18 μm, so that the first metal layer can serve as the base layer of the first positive electrode current collector, and the surface of the first metal layer can better support the plating layer.
[0010] In some preferred embodiments, the first metal layer is provided with a second metal layer on one surface thereof along the first direction, and the thickness of the second metal layer is 0.5 μm to 8 μm. When the second metal layer is plated, the thickness of the second metal layer should not be less than 0.5 μm, so as to improve the uniformity and integrity of the plated layer, and reduce the possibility of affecting the product performance due to uneven coverage caused by too thin plating. When the thickness of the second metal layer exceeds 8 μm, the energy density of the secondary battery will be excessively consumed, and the material cost of the second metal layer will be increased.
[0011] In some preferred embodiments, the first metal layer is provided with a second metal layer on both opposite surfaces thereof along the first direction, and the thickness of any one of the second metal layers is 0.5 μm to 6 μm. When the first metal layer is provided with a second metal layer on both opposite surfaces thereof, and the thickness of the second metal layer exceeds 6 μm, the energy density of the secondary battery will be excessively consumed, and the material cost of the second metal layer will be increased.
[0012] In some preferred embodiments, the second metal layer comprises nickel or titanium, so as to improve the mechanical strength of the second metal layer. The second metal layer is provided on the surface of the first metal layer by electroplating, evaporation plating or vapor deposition, so that the first metal layer serves as a base layer, and the second metal layer serves as a plated layer plated on the surface of the first metal layer, thereby improving the stability between the first metal layer and the second metal layer.
[0013] In some preferred embodiments, the second metal layer is a nickel layer or a titanium layer.
[0014] In some preferred embodiments, the second metal layer is a nickel foil or a titanium foil, and the thickness of the second metal layer is 5 μm to 18 μm. By providing the second metal layer as a nickel foil or a titanium foil, the mechanical strength of the first positive current collector can be improved. By limiting the thickness of the second metal layer to 5 μm to 18 μm, the second metal layer can serve as a base layer of the first positive current collector, and the surface of the second metal layer can better support the plated layer.
[0015] In some preferred embodiments, the first metal layer is provided on one surface of the second metal layer along the first direction, and the thickness of the first metal layer is 0.5 μm to 8 μm. When the first metal layer serves as a plated layer, the thickness of the first metal layer should not be less than 0.5 μm, so as to improve the uniformity and integrity of the plated layer, and reduce the possibility of affecting the product performance due to uneven coverage caused by too thin plating. When the thickness of the first metal layer exceeds 8 μm, the energy density of the secondary battery will be excessively consumed.
[0016] In some preferred embodiments, the second metal layer is provided with a first metal layer on each of the two opposite surfaces along the first direction, and the thickness of any first metal layer is 0.5-6 μm. If the second metal layer is provided with a first metal layer on each of the two opposite surfaces, and the thickness of the first metal layer exceeds 6 μm, the energy density of the secondary battery will be excessively reduced.
[0017] In some preferred embodiments, the first metal layer is provided on the surface of the second metal layer by electroplating, evaporation or vapor deposition, so that the second metal layer serves as a base layer and the first metal layer serves as a plating layer plated on the surface of the second metal layer, thereby improving the stability between the first metal layer and the second metal layer.
[0018] In some preferred embodiments, the first metal layer is an aluminum layer.
[0019] In some preferred embodiments, the second metal layer is a nickel layer or a nickel foil, and along the first direction, the second metal layer is located between the first metal layer and the first positive active layer, so that the second metal layer is wrapped by the first metal layer and the first positive active layer for protection, thereby reducing the possibility of corrosion of the second metal layer in a high-voltage system.
[0020] In some preferred embodiments, the second metal layer includes nickel, and the mass percentage of nickel in the second metal layer is not less than 99.8%, so that the second metal layer has excellent electrical conductivity and excellent mechanical strength. Alternatively, the second metal layer includes titanium, and the mass percentage of titanium in the second metal layer is not less than 99.8%, so that the second metal layer has excellent electrical conductivity and excellent mechanical strength.
[0021] In some preferred embodiments, 10 μm≤H1≤15 μm. By limiting the thickness of the first positive current collector to not less than 10 μm, the processing precision of the first positive current collector is improved, the first positive current collector is easier to process in coating, compaction and cutting manufacturing processes, and defects such as cracks are less likely to occur, thereby improving the yield. Furthermore, the mechanical strength of the first positive current collector can be further improved. By limiting the thickness of the first positive current collector to not more than 15 μm, the electrode assembly has better safety mechanical properties, and the energy density of the secondary battery is further improved.
[0022] In some preferred embodiments, the positive electrode sheet includes a double-sided positive electrode sheet, and along the first direction, the double-sided positive electrode sheet is arranged between two adjacent negative electrode sheets. The double-sided positive electrode sheet includes a second positive current collector and a second positive active layer, and the second positive active layer is arranged on each of the two opposite surfaces of the second positive current collector, so as to improve the energy density of the secondary battery. The second positive current collector includes a third metal layer and a fourth metal layer stacked in contact along the first direction, the third metal layer includes aluminum, and the fourth metal layer includes nickel or titanium, so as to further improve the safety mechanical properties of the electrode assembly.
[0023] In a second aspect, the present application also provides an electronic device comprising the secondary battery according to any one of the above embodiments of the first aspect.
[0024] Additional aspects and advantages of the embodiments of the present application will be described in part below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS
[0025] One or more embodiments are illustrated by way of example in the accompanying drawings in which like reference numerals indicate like elements, the dimensions are not intended to scale unless specifically stated, and in which:
[0026] Figure 1 Structure diagram of a secondary battery according to some embodiments of the present application;
[0027] Figure 2 Structure diagram of an electrode assembly according to some embodiments of the present application;
[0028] Figure 3 Structure diagram of a first positive current collector according to some embodiments of the present application;
[0029] Figure 4 Structure diagram of a first positive current collector according to some embodiments of the present application;
[0030] Figure 5 Structure diagram of a first positive current collector according to some embodiments of the present application;
[0031] Figure 6 Structure diagram of a first positive current collector according to some embodiments of the present application;
[0032] Figure 7 Structure diagram of a single-sided positive electrode sheet according to some embodiments of the present application;
[0033] Figure 8 Structure diagram of a second positive current collector according to some embodiments of the present application.
[0034] BRIEF DESCRIPTION OF DRAWINGS
[0035] 100, secondary battery; 10, packaging bag; 20, electrode assembly;
[0036] 21, positive electrode sheet; 211, single-sided positive electrode sheet; 2111, first positive current collector; 2113, first metal layer; 2114, second metal layer; 2112, first positive active layer; 212, double-sided positive electrode sheet; 2121, second positive current collector; 2123, third metal layer; 2124, fourth metal layer; 2122, second positive active layer;
[0037] 22. A negative electrode sheet; 221. A first negative electrode current collector; 222. A first negative electrode active layer;
[0038] 23. A separator;
[0039] X. A first direction. DETAILED DESCRIPTION
[0040] In order to make the objects, technical solutions, and advantages of the embodiments of the present application clearer, the following will be used in conjunction with the accompanying drawings for describing the technical solutions of the embodiments of the present application in a clearer way. Obviously, the described embodiments are only some but not all of the embodiments of the present application.
[0041] In the present application, the phrase "embodiments" means that the specific features, structures, or characteristics described in conjunction with the embodiments can be included in at least one embodiment of the present application. The phrase appears in various places in the specification does not necessarily all refer to the same embodiment, nor is each embodiment mutually exclusive or alternative to the other embodiments.
[0042] In the description of the embodiments of the present application, the technical terms "first", "second", and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified.
[0043] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship between the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents a "or" relationship between the front and rear associated objects.
[0044] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict between them.
[0045] In a first aspect, embodiments of the present application provide a secondary battery 100, please refer to Figure 1 The secondary battery 100 includes a packaging bag 10 and an electrode assembly 20, the packaging bag 10 can accommodate the electrode assembly 20 and an electrolyte (not marked in the figure), and the electrolyte infiltrates the electrode assembly 20 in the packaging bag 10.
[0046] For the above-mentioned electrode assembly 20, please refer to Figure 2 , Figure 2The electrode assembly 20 is shown in a stack structure. The electrode assembly 20 includes a negative electrode sheet 22, a positive electrode sheet 21, and a separator 23. The positive electrode sheet 21 and the negative electrode sheet 22 are alternately stacked along a first direction X, and the separator 23 is arranged between adjacent positive electrode sheet 21 and negative electrode sheet 22, and the separator 23 is used to insulate and separate the positive electrode sheet 21 and the negative electrode sheet 22. In the embodiments of the present application, the electrode assembly 20 is taken as an example to illustrate the stack structure. In some other embodiments, the electrode assembly 20 can also be in a wound structure, for example, the positive electrode sheet 21, the separator 23 and the negative electrode sheet 22 are sequentially stacked and then wound to form a wound electrode assembly 20. It should be noted that the first direction X of the present application is a bidirectional direction, that is, the first direction X includes Figure 2 the direction indicated by the arrow and the opposite direction thereof.
[0047] For the above-mentioned positive electrode sheet 21, the positive electrode sheet 21 includes a single-sided positive electrode sheet 211, and the outermost electrode sheet of the electrode assembly 20 along the first direction X is the single-sided positive electrode sheet 211. The single-sided positive electrode sheet 211 includes a first positive electrode current collector 2111 and a first positive electrode active layer 2112, and the surface of the first positive electrode current collector 2111 facing the negative electrode sheet 22 is provided with the first positive electrode active layer 2112. By providing the first positive electrode active layer 2112 on the surface of the first positive electrode current collector 2111 of the single-sided positive electrode sheet 211 facing the negative electrode sheet 22, the utilization rate of the positive electrode active material of the single-sided positive electrode sheet 211 can be improved, and thus the energy density of the secondary battery 100 can be improved.
[0048] For the above-mentioned first positive electrode active layer 2112, the first positive electrode active layer 2112 is soaked in the above-mentioned electrolyte in the packaging bag 10 to generate an electrochemical reaction. The first positive electrode active layer 2112 includes a first positive electrode active material, a conductive agent, an adhesive, etc. The above-mentioned materials are uniformly mixed and stirred and coated on the surface of the first positive electrode current collector 2111 facing the negative electrode sheet 22, thereby obtaining the first positive electrode active layer 2112. The first positive electrode active material can include at least one of lithium nickel cobalt manganese oxide, lithium cobaltate, lithium iron phosphate, lithium nickel cobalt aluminate, lithium manganate, and lithium iron manganate.
[0049] For the above-mentioned negative electrode sheet 22, the negative electrode sheet 22 includes a first negative electrode current collector 221 and a first negative electrode active layer 222, and the first negative electrode active layer 222 is arranged on at least one surface of the first negative electrode current collector 221 along the first direction X.
[0050] For the first negative active layer 222, the first negative active layer 222 is soaked by the electrolyte in the packaging bag 10 to generate an electrochemical reaction. The first negative active layer 222 includes a first negative active material, a conductive agent, a binder, etc., which are uniformly mixed and coated on at least one surface of the first negative current collector 221 along the first direction X, thereby obtaining the first negative active layer 222. The first negative active material can include at least one of graphite, silicon, hard carbon, and carbon fiber.
[0051] For the first negative current collector 221, the first negative current collector 221 can be a composite current collector (a composite structure of metal-polymer-metal), for example, the first negative current collector 221 includes a polymer layer and a metal layer arranged on opposite surfaces of the polymer layer, the polymer layer serves as the main mechanical support layer of the first negative current collector 221, and can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE), and the metal layer can include at least one of copper, nickel, and titanium. By taking the polymer layer as the main mechanical support layer, the first negative current collector 221 can thin the metal layer, thereby reducing the metal burrs caused by mechanical damage of the secondary battery 100, and reducing the mass of the first negative current collector 221, thereby improving the mass energy density of the secondary battery 100. In other embodiments, the first negative current collector 221 can be a single-layer metal foil, which can include at least one of copper, nickel, and titanium.
[0052] In some embodiments, reducing the thickness of the current collector to reduce the thickness of the secondary battery 100 increases the safety risk, and the puncture, extrusion, and crushing resistance of the secondary battery 100 is greatly reduced. Ways to improve the puncture, extrusion, and crushing resistance include increasing the thickness of the positive and negative current collectors, using a nickel foil for the single-sided positive electrode sheet 211, using a thick aluminum plastic film packaging bag 10, and reducing the thickness of the active material and increasing the number of layers, but all have obvious defects. Increasing the thickness of the positive and negative current collectors greatly reduces the energy density of the secondary battery 100, and increases the cost of the electrode assembly 20; pure nickel foil has low elongation and is difficult to process, and has high cost and corrosion risk (nickel foil oxidation potential 3.3V, while the general voltage of lithium battery is up to 4.5V, the oxidation nickel on the surface of the nickel foil shows electrochemical stability to protect the inner nickel foil; but the electrochemical window is insufficient at a high potential of more than 4.55V or even 4.57V, which may exacerbate corrosion of the battery); using a thick aluminum plastic film packaging bag 10 reduces the energy density of the secondary battery 100 and increases the cost and manufacturing difficulty; reducing the thickness of the active material and increasing the number of layers greatly reduces the energy density of the secondary battery 100 and increases the cost.
[0053] To improve the above problems, in the embodiments of the present application, please refer to Figure 2 andFigure 3 The first positive current collector 2111 of the single-sided positive tab 211 of the outermost layer of the electrode assembly 20 includes a first metal layer 2113 and a second metal layer 2114 stacked together, the first metal layer 2113 includes aluminum, the tensile strength of the first positive current collector 2111 is greater than or equal to 300 MPa, and the thickness of the first positive current collector 2111 is H1, H1≤20 μm. By setting the outermost layer of the electrode assembly 20 as the single-sided positive tab 211, and the first positive current collector 2111 of the single-sided positive tab 211 is provided with the first positive active layer 2112 only on the surface facing the negative tab 22, the energy density of the secondary battery 100 can be improved. The thickness of the current collector of the outermost layer of the single-sided positive tab 211 of the electrode assembly 20 can be increased, for example, an aluminum foil with a thickness of 20 μm can be used as the current collector to reduce the possibility of curling, but the tensile strength of the aluminum foil with a thickness of 20 μm is about 270 MPa, which is still difficult to meet the demand for higher mechanical safety performance. The first positive current collector 2111 is provided with a composite structure of the first metal layer 2113 and the second metal layer 2114, and the first metal layer 2113 includes aluminum, which can ensure effective conduction of current by virtue of the excellent electrical conductivity of aluminum. At the same time, the tensile strength of the first positive current collector 2111 is greater than or equal to 300 MPa, which can reduce the possibility of curling and better resist deformation and breakage during charge and discharge cycles. The thickness of the first positive current collector 2111 is less than or equal to 20 μm, which can improve the safety mechanical performance of the electrode assembly 20 and the energy density of the secondary battery 100. Reducing the possibility of curling of the outermost layer of the single-sided positive tab 211 can improve the cycle life and capacity retention rate of the secondary battery 100.
[0054] In some embodiments, the tensile strength of the first positive current collector 2111 is greater than or equal to 360 MPa. The tensile strength of the first positive current collector 2111 is greater than or equal to 360 MPa, which can further reduce the risk of damage to the electrode assembly 20 under external force impact, so that the deformation resistance, drop resistance and puncture resistance of the electrode assembly 20 are improved, thereby further improving the safety performance of the secondary battery 100.
[0055] In some embodiments, H1≥7 μm. The thickness of the first positive current collector 2111 is not less than 7 μm, so as to obtain better processing stability in processes such as active material coating and compaction. In addition, the thickness of the first positive current collector 2111 not less than 7 μm can have better mechanical strength, thereby obtaining better safety performance (mechanical strength includes bending strength, tensile strength, compressive strength, impact strength, and the mechanical strength in the present application is used to represent safety mechanical performance, and the higher the mechanical strength, the higher the safety mechanical performance).
[0056] In some embodiments, 10 pm≤H1≤15 pm. By limiting the thickness of the first positive current collector 2111 to be no less than 10 pm, the processing precision of the first positive current collector 2111 is improved, the first positive current collector 2111 is easier to process in manufacturing processes such as coating, compaction, and cutting, and defects such as cracks are less likely to occur, thereby improving the yield. In addition, the mechanical strength of the first positive current collector 2111 can be further improved. By limiting the thickness of the first positive current collector 2111 to be no more than 15 pm, the secondary battery 100 has better safety mechanical properties while further improving the energy density.
[0057] In some embodiments, the first metal layer 2113 is an aluminum foil, and the thickness of the first metal layer 2113 is 5 pm to 18 pm. In this way, the first metal layer 2113 can serve as a base layer of the first positive current collector 2111, and the surface of the first metal layer 2113 can better support the plating layer. In some embodiments, the thickness of the first metal layer 2113 is 7 pm to 10 pm. In this way, the first metal layer 2113 can better support the plating layer while the secondary battery 100 has better energy density.
[0058] In some embodiments, the first metal layer 2113 is provided with a second metal layer 2114 on one surface along the first direction X, and the thickness of the second metal layer 2114 is 0.5 pm to 8 pm. The second metal layer 2114 serves as a plating layer, and the thickness of the second metal layer 2114 needs to be no less than 0.5 pm to improve the uniformity and integrity of the plating layer and reduce the possibility of affecting product performance due to uneven coverage of the plating layer. When the thickness of the second metal layer 2114 exceeds 8 pm, the energy density of the secondary battery 100 is excessively wasted, and the material cost of the second metal layer 2114 is increased.
[0059] In some embodiments, please refer to Figure 4 , the first metal layer 2113 is provided with a second metal layer 2114 on opposite surfaces along the first direction X, and the thickness of any second metal layer 2114 is 0.5 pm to 6 pm. If the second metal layer 2114 is provided on the opposite surfaces of the first metal layer 2113, the thickness of the second metal layer 2114 exceeds 6 pm, the energy density of the secondary battery 100 is excessively wasted, and the material cost of the second metal layer 2114 is increased.
[0060] In some embodiments, the second metal layer 2114 includes nickel or titanium to improve the mechanical strength of the second metal layer 2114. The second metal layer 2114 is disposed on the surface of the first metal layer 2113 by electroplating, evaporation or vapor deposition, such that the first metal layer 2113 serves as a base layer and the second metal layer 2114 serves as a plating layer plated on the surface of the first metal layer 2113, thereby improving the stability between the first metal layer 2113 and the second metal layer 2114.
[0061] In some embodiments, the second metal layer 2114 is a nickel layer or a titanium layer.
[0062] In some embodiments, referring to Figure 5 , the second metal layer 2114 is a nickel foil or a titanium foil, and the thickness of the second metal layer 2114 is 5 μm to 18 μm. By setting the second metal layer 2114 as a nickel foil or a titanium foil, the mechanical strength of the first positive current collector 2111 can be improved. By limiting the thickness of the second metal layer 2114 to 5 μm to 18 μm, the second metal layer 2114 can serve as a base layer for the first positive current collector 2111, and the surface of the second metal layer 2114 can better support the plating layer. In some embodiments, the thickness of the second metal layer 2114 is 7 μm to 10 μm, so that the second metal layer 2114 can better support the plating layer while the secondary battery 100 has a better energy density.
[0063] In some embodiments, the second metal layer 2114 is provided with the first metal layer 2113 on one surface along the first direction X, and the thickness of the first metal layer 2113 is 0.5 μm to 8 μm. The first metal layer serves as a plating layer, and the thickness of the first metal layer 2113 should not be less than 0.5 μm to improve the uniformity and integrity of the plating layer and reduce the possibility of uneven coverage affecting product performance due to the plating layer being too thin. When the thickness of the first metal layer 2113 exceeds 8 μm, the energy density of the secondary battery 100 will be excessively wasted.
[0064] In some embodiments, referring to Figure 6 , the second metal layer 2114 is provided with the first metal layer 2113 on opposite surfaces along the first direction X, and the thickness of any first metal layer 2113 is 0.5 μm to 6 μm. If the first metal layer 2113 is provided on the opposite surfaces of the second metal layer 2114, the thickness of the first metal layer 2113 exceeding 6 μm will excessively waste the energy density of the secondary battery 100.
[0065] In some embodiments, the second metal layer 2114 is a nickel foil, and the first metal layer 2113 is an aluminum plating layer. Since the first positive current collector 2111 (single-sided positive current collector) is a pure nickel foil, there is a risk of corrosion in a high-voltage system. By plating aluminum on nickel, the nickel foil can be wrapped to protect the inner layer, and the oxide layer of aluminum is more dense, which can well protect the inner layer of nickel foil and reduce the possibility of corrosion of the inner layer of nickel foil.
[0066] In some embodiments, the first metal layer 2113 is disposed on the surface of the second metal layer 2114 by electroplating, evaporation or vapor deposition, so that the second metal layer 2114 serves as a base layer, and the first metal layer 2113 serves as a plating layer plated on the surface of the second metal layer 2114, thereby improving the stability between the first metal layer 2113 and the second metal layer 2114.
[0067] In some embodiments, the first metal layer 2113 is an aluminum layer.
[0068] In some embodiments, please refer to Figure 7 The second metal layer 2114 includes nickel, and the second metal layer 2114 is located between the first metal layer 2113 and the first positive active layer 2112 along the first direction X, so that the second metal layer is wrapped and protected by the first metal layer and the first positive active layer, thereby reducing the possibility of corrosion of the second metal layer in a high-voltage system.
[0069] In some embodiments, the second metal layer 2114 includes nickel, and the mass percentage of nickel in the second metal layer 2114 is not less than 99.8%, so that the second metal layer 2114 has excellent electrical conductivity and excellent mechanical strength. In some embodiments, the mass percentage of nickel in the second metal layer 2114 is 99.9% to 99.95%, so that the second metal layer 2114 has excellent electrical conductivity, and the preparation process of the second metal layer 2114 is not too complex, thereby facilitating mass production.
[0070] In some embodiments, the second metal layer 2114 includes titanium, and the mass percentage of titanium in the second metal layer 2114 is not less than 99.8%, so that the second metal layer 2114 has excellent electrical conductivity and excellent mechanical strength. In some embodiments, the mass percentage of titanium in the second metal layer 2114 is 99.9% to 99.95%, so that the second metal layer 2114 has excellent electrical conductivity, and the preparation process of the second metal layer 2114 is not too complex, thereby facilitating mass production.
[0071] In some embodiments, please refer to Figure 2 and Figure 8The positive electrode sheet 21 includes a double-sided positive electrode sheet 212, which is arranged between two adjacent negative electrode sheets 22 along the first direction X. The double-sided positive electrode sheet 212 includes a second positive electrode current collector 2121 and a second positive electrode active layer 2122. The second positive electrode active layer 2122 is arranged on both surfaces of the second positive electrode current collector 2121, so as to improve the energy density of the secondary battery 100. The second positive electrode current collector 2121 includes a third metal layer 2123 and a fourth metal layer 2124 which are stacked in contact along the first direction. The third metal layer 2123 includes aluminum, and the fourth metal layer 2124 includes nickel or titanium, so as to further improve the safety mechanical properties of the electrode assembly 20.
[0072] In some embodiments, the second positive electrode current collector 2121 can include one third metal layer 2123 and one fourth metal layer 2124, or two third metal layers 2123 sandwiching one fourth metal layer 2124, or two fourth metal layers 2124 sandwiching one third metal layer 2123.
[0073] The second aspect of the present application also provides an electronic device including the secondary battery 100 according to any one of the embodiments of the first aspect. The electronic device according to the embodiments of the present application is not particularly limited and can be any electronic device known in the art. For example, the electronic device includes but is not limited to a Bluetooth headset, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric vehicle, an electric car, a ship, a spacecraft, and the like. The electric toy can include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, an electric plane toy, and the like. The spacecraft can include an airplane, a rocket, a space shuttle, a spacecraft, and the like.
[0074] Test section:
[0075] 1. Energy density test of lithium ion battery:
[0076] The lithium ion battery is placed in a 25℃ constant temperature box and left for 30 minutes to make the lithium ion battery reach a constant temperature. The lithium ion battery reaching the constant temperature is charged at 0.5C constant current to 4.5V full charge voltage, and then charged at 4.5V constant voltage to 0.05C current, and discharged at 0.5C to 3.0V voltage, and the discharge energy is recorded.
[0077] Energy density = discharge energy / (length x width x thickness of lithium ion battery).
[0078] 2. Pin test of lithium ion battery:
[0079] The test temperature is adjusted to 25℃ constant temperature, and the following steps are performed on the lithium ion battery sample:
[0080] (1) 0.5C constant current discharge to 3.0V;
[0081] (2) Rest for 10 min;
[0082] (3) 0.5C constant current charge to 4.5V;
[0083] (4) 4.5V constant voltage charge to 0.05C;
[0084] (5) Rest for 10 min;
[0085] (6) Place the sample on the test bed, with the positive and negative half facing upwards, use blunt nail diameter 6mm, extrusion force 1600N, falling speed 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.
[0086] End
[0087] Blunt stab pass rate: record the number of non-fire / test number.
[0088] 3. Needle stab test of lithium ion battery:
[0089] Adjust the test temperature to 25°C constant temperature, and perform the following steps on the lithium ion battery sample:
[0090] (1) 0.5C constant current discharge to 3.0V;
[0091] (2) Rest for 10 min;
[0092] (3) 0.5C constant current charge to 4.5V;
[0093] (4) 4.5V constant voltage charge to 0.05C;
[0094] (5) Rest for 10 min;
[0095] (6) Place the sample on the test bed, with the positive and negative half facing upwards, use steel nail diameter 3mm at a speed of 150mm / s from the center of the sample, the sample is completely pierced, monitor the cell voltage and surface temperature rise during the test. Judgment criteria: no explosion, no fire; record the pass rate.
[0096] End
[0097] Needle stab pass rate: record the number of non-fire / test number.
[0098] 4. Round bar extrusion test of lithium ion battery:
[0099] Adjust the test temperature to 25°C constant temperature, and perform the following steps on the lithium ion battery sample:
[0100] (1) 0.5C constant current discharge to 3.0V;
[0101] (2) Rest for 10 min;
[0102] (3) 0.5C constant current charge to 4.5V;
[0103] (4) 4.5V constant voltage charge to 0.05C;
[0104] (5) Rest for 10 min;
[0105] (6) Place the sample on the test bed, with one half of the positive and negative facing upwards, use a 25mm round bar to place in the center of the sample, with a pressing force of 13KN and a pressing speed of 0.1mm / s, monitor the cell voltage and surface temperature rise during the test. The judging standard: no explosion, no fire, no smoke; record the pass rate.
[0106] End
[0107] Round bar pressing pass rate: record the number of non-fire / test number
[0108] 5. Cycle test of lithium ion battery:
[0109] Adjust the test temperature to 25°C constant temperature, and perform the following steps on the lithium ion battery sample:
[0110] (1) 3C constant current charge to 4.3V;
[0111] (2) 2C constant current charge to 4.4V;
[0112] (3) 1C constant current charge to 4.5V;
[0113] (4) 4.5V constant voltage charge to 0.1C;
[0114] (5) Rest for 5 min;
[0115] (6) 1C constant current discharge to 3.0V
[0116] (7) Rest for 5 min;
[0117] (8) Cycle steps (1) to (7) for 1000 times;
[0118] End
[0119] Capacity retention rate: the ratio of the discharge capacity after 1000 cycles to the discharge capacity of the first cycle;
[0120] Thickness expansion rate: (the thickness of the cell after 1000 cycles - the initial thickness of the cell) / the initial thickness of the cell.
[0121] 6. Tensile strength test of current collector:
[0122] According to the national standard GB / T 29847-2013 "Test methods of copper foil for printed circuit board", the single-sided positive current collector in the embodiment of the present scheme is tested according to the actual test situation. A universal material testing machine is used as the tensile strength testing equipment. First, the active material layer on the surface of the current collector is removed, such as using a scraper to scrape off, and then cut into a sample with a length of 100±0.5mm (less than 100mm, take the original length) and a width of 20±0.25mm. Then, clamps are installed on both ends of the sample to ensure that the sample will not slip during stretching. Next, the sample is fixed on the clamps of the testing machine, and the force applied to the sample is recorded using a load sensor, and the deformation of the sample is recorded by a displacement sensor. The tensile speed is set to 50mm / min, and other test parameters such as the distance between the test machine clamps are determined according to the test standard and the actual situation. The test is stopped when the sample is stretched to break, and the maximum tensile force F when the sample is broken is recorded. The tensile strength T of the sample is calculated according to T=F / S, where S is the initial cross-sectional area of the sample, which is equal to the product of the width of the sample and the thickness of the sample. Five parallel samples are tested, and the average value is taken as the test result. The length direction of the sample is parallel to the axis of the clamp during testing, and the sample remains straight. The experimental temperature is 20±5℃.
[0123] Example 1
[0124] Preparation of positive electrode tab:
[0125] The positive electrode active material lithium cobaltate, the positive electrode conductive agent acetylene black, and the positive electrode binder polyvinylidene fluoride (PVDF, weight average molecular weight 5×10 5 ) are mixed in a mass ratio of 94:3:3, N-methyl pyrrolidone (NMP) is added as a solvent, and the positive electrode slurry is stirred in a vacuum stirrer until the solid content is 75wt% and the system is uniform.
[0126] A 10μm high-purity aluminum foil is selected as the substrate, and an alkaline solution is used to clean the surface of the aluminum foil to remove grease and impurities; then an acidic solution (such as nitric acid) is used to treat the surface of the aluminum foil to remove the oxide layer. The aluminum foil is immersed in a nickel plating solution at room temperature, the current density is adjusted to 2-4A / dm 2 , and maintained for 5-10 minutes to make the nickel layer uniformly cover the surface of the aluminum foil. The thickness of the nickel layer is 2.5 microns, the mass percentage of nickel in the nickel layer is 99.9%, and the aluminum foil with a nickel layer on both sides is obtained as a 15μm aluminum-nickel first positive electrode current collector. The positive electrode slurry is coated on one surface of the first positive electrode current collector and a positive electrode blank section is reserved, and the positive electrode slurry is dried to obtain a single-sided positive electrode tab with a positive electrode active material layer coated on one side.
[0127] The positive electrode slurry was uniformly coated on one surface of a second positive electrode current collector aluminum foil having a thickness of 10 μm, and the positive electrode slurry was dried to obtain a positive electrode tab having a single-coated positive electrode active material layer. Thereafter, the above steps were repeated on the other surface of the aluminum foil to obtain a double-coated positive electrode tab having a double-coated positive electrode active material layer.
[0128] <Manufacture of a negative electrode tab>:
[0129] A negative electrode active material graphite, a binder styrene butadiene rubber (SBR), and a thickening agent sodium carboxymethyl cellulose (CMC) were mixed at a weight ratio of 96:2:2, deionized water was added as a solvent, and the mixture was stirred in a vacuum stirrer until a negative electrode slurry having a solid content of 70 wt% and a uniform system was obtained.
[0130] The negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil having a thickness of 8 μm, and the negative electrode slurry was dried to obtain a negative electrode tab having a single-coated negative electrode active material layer. Thereafter, the above steps were repeated on the other surface of the copper foil to obtain a double-coated negative electrode tab having a double-coated negative electrode active material layer.
[0131] <Manufacture of a separator>:
[0132] A polyethylene (PE) porous film having a thickness of 8 μm was used as a separator.
[0133] <Manufacture of an electrolyte>:
[0134] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed at a mass ratio of 30:50:20 to obtain an organic solution, and then lithium salt lithium hexafluorophosphate was dissolved and uniformly mixed in the organic solvent to obtain an electrolyte having a lithium salt concentration of 1.15 mol / L.
[0135] <Manufacture of a lithium ion battery>:
[0136] The positive electrode tab, the separator, and the negative electrode tab prepared above were sequentially stacked to form an electrode assembly having 21 layers (the electrode assembly having 21 layers means 20 layers of a double-coated positive electrode tab + 2 layers of a single-coated positive electrode tab), and the electrode assembly was heat-pressed. The electrode assembly was placed in a packaging bag aluminum plastic film having a thickness of 110 μm, electrolyte was injected and packaged to obtain a lithium ion battery.
[0137] The related parameters in Comparative Examples 1 to 4 and Examples 1 to 11 are shown in Table 1 below.
[0138] The single-coated positive electrode current collector in Comparative Examples 1 to 4 was an aluminum foil, wherein the thickness of the aluminum plastic film in Comparative Example 2 was 130 μm, the number of layers of the electrode assembly in Comparative Example 3 was 23 layers (the number of layers was increased by reducing the thickness of the active material layer of the tab), and the thickness of the single-coated positive electrode current collector aluminum foil in Comparative Example 4 was 35 μm.
[0139] The single-sided positive electrode current collector in Examples 1 to 6 is an aluminum foil plated with a nickel layer on both surfaces.
[0140] The single-sided positive electrode current collector in Examples 7 to 9 is an aluminum foil plated with a nickel layer on one surface.
[0141] The single-sided positive electrode current collector in Example 10 is an aluminum foil plated with a titanium layer on both surfaces. The titanium plating process is chemical vapor deposition, in which titanium is deposited onto the surface of the aluminum foil substrate through a chemical reaction.
[0142] The single-sided positive electrode current collector in Example 11 is an aluminum foil plated with a titanium layer on one surface.
[0143] Table 1
[0144]
[0145]
[0146] Note: In Table 1, “\” indicates that the parameter is not included.
[0147] According to Table 1 above, in combination with Comparative Examples 1 to 4 and Examples 1 to 11, it can be seen that by increasing the thickness of the aluminum plastic film, increasing the thickness of the positive electrode current collector, and reducing the thickness of the active material layer of the electrode piece to increase the number of electrode piece layers, the blunt piercing, needle piercing, and round rod extrusion passing rates can be improved, but the energy density of the secondary battery will be reduced. The single-sided positive electrode current collector is set to a nickel-plated aluminum foil or a titanium-plated aluminum foil with a thickness of not more than 20 μm, and the tensile strength of the single-sided positive electrode current collector can be improved to more than 300 MPa. By setting the single-sided positive electrode current collector on the outermost layer of the electrode assembly to a nickel-plated aluminum foil or a titanium-plated aluminum foil with a thickness of not more than 20 μm, the energy density can be improved while improving the blunt piercing, needle piercing, and round rod extrusion passing rates. The tensile strength of the single-sided positive electrode current collector is more than 360 MPa, which can further improve the blunt piercing, needle piercing, and round rod extrusion passing rates of the secondary battery.
[0148] The single-sided positive electrode current collector uses a nickel-plated aluminum foil. It should be noted that the tensile strength of the nickel-plated aluminum foil is not only related to the thickness of the current collector, but the mass percentage of nickel in the plating layer also has an impact on the tensile strength of the nickel-plated aluminum foil to some extent. The single-sided positive electrode current collector uses a titanium-plated aluminum foil. Similarly, it should be noted that the tensile strength of the titanium-plated aluminum foil is not only related to the thickness of the current collector, but the mass percentage of titanium in the plating layer also has an impact on the tensile strength of the titanium-plated aluminum foil to some extent.
[0149] It can be seen from Comparative Example 1 and Comparative Example 2 that increasing the thickness of the aluminum plastic film can improve the pass rate of blunt thorn, needle thorn and round bar extrusion, that is, the safety performance can be improved, but the energy density will be reduced. It can be seen from Comparative Example 1 and Comparative Example 3 that reducing the thickness of the active material layer of the pole piece to increase the number of pole pieces can improve the safety performance. It can be seen from Comparative Example 1 and Comparative Example 4 that when the thickness of the single-sided positive current collector of the outermost layer of the electrode assembly is increased to 35 μm, the tensile strength of the single-sided positive current collector can reach 300 MPa, which will reduce the energy density of the secondary battery.
[0150] The single-sided positive current collector of the outermost layer of the commonly used electrode assembly is an aluminum foil with a thickness of 20 μm. It can be seen from Comparative Example 1, Example 1, Example 8, Example 10 and Example 11 that by setting the single-sided positive current collector of the outermost layer of the electrode assembly to an aluminum-nickel-plated foil or an aluminum-titanium-plated foil with a thickness of not more than 20 μm, the energy density, the capacity retention rate and the thickness expansion rate can be improved while the safety performance is improved. In addition, by plating a nickel layer or a titanium layer on the surface of the aluminum foil, the tensile strength can be enhanced.
[0151] It can be seen from Examples 1 to 4 that the thickness of the single-sided positive current collector in the range of 7 μm to 20 μm can make the secondary battery have good safety performance. The thickness of the single-sided positive current collector is not less than 7 μm, so as to obtain better processing stability in the processes such as coating active material and compaction. When the thickness of the single-sided positive current collector is greater than 20 μm, the energy density of the secondary battery will be reduced. In addition, when the thickness of the nickel-plated layer is unchanged and the thickness of the base layer aluminum foil is reduced, the tensile strength decreases slightly, but the energy density increases greatly, so the aluminum-nickel-plated layer can improve the energy density by reducing the thickness of the base layer aluminum foil. In actual application, since the nickel layer is plated as a layer and the aluminum foil is used as a base layer, in actual production, the base layer needs to have a certain thickness as a supporting layer. When the thickness of the base layer aluminum foil is less than 5 μm, the supporting effect is poor, and it is difficult to form a nickel-plated layer on the surface of the base layer aluminum foil. When the thickness of the base layer aluminum foil is greater than 18 μm, the energy density of the secondary battery will be reduced.
[0152] It can be seen from Examples 3, 5 and 6 that when the single-sided positive electrode current collector is an aluminum-nickel-plated foil and both surfaces of the aluminum foil are plated with a nickel layer, the thickness of any one of the nickel layers in the range of 0.5 μm to 6 μm can make the secondary battery have good safety performance. If the thickness of the nickel layer is reduced, the safety performance of the secondary battery will be reduced. In actual application, since the nickel layer is a plating layer and the aluminum foil is a base layer, in actual production, the base layer serves as a support layer. Therefore, the thickness of any one of the nickel layers should be ≤ 75% of the thickness of the base layer. Otherwise, the plating layer is too thick, the uniformity is difficult to control, the processing difficulty is large, and the cost is increased. Therefore, when the thickness of any one of the nickel layers exceeds 6 μm, the thickness of the aluminum foil also needs to be correspondingly increased to more than 8 μm. At this time, the thickness of the single-sided positive electrode current collector will exceed 20 μm, which will reduce the energy density of the secondary battery and increase the cost. In addition, the thickness of the nickel layer should not be less than 0.5 μm to improve the uniformity and integrity of the plating layer and reduce the possibility of affecting the performance of the product due to uneven coverage caused by the plating layer being too thin.
[0153] It can be seen from Examples 7 to 9 that when the single-sided positive electrode current collector is an aluminum-nickel-plated foil and only one surface of the aluminum foil is plated with a nickel layer, the thickness of the nickel layer in the range of 0.5 μm to 8 μm can make the secondary battery have good safety performance. When the thickness of the nickel layer exceeds 8 μm, the thickness of the aluminum layer as the base layer also needs to be correspondingly increased. At this time, the thickness of the single-sided positive electrode current collector is easy to exceed 20 μm, which will reduce the energy density of the secondary battery and increase the cost. In addition, the thickness of the nickel layer should not be less than 0.5 μm to improve the uniformity and integrity of the plating layer and reduce the possibility of affecting the performance of the product due to uneven coverage caused by the plating layer being too thin.
[0154] Since titanium and nickel have similar properties, titanium-plated aluminum foil has similar properties to nickel-plated aluminum foil. The above descriptions of the properties of nickel-plated aluminum foil are applicable to titanium-plated aluminum foil.
[0155] It should be noted that if the single-sided positive electrode current collector uses pure nickel foil, the elongation of the pure nickel foil is low, the processing difficulty is large, and the cost is high due to the high price of nickel metal. In addition, pure nickel foil has a risk of corrosion. The specific reason is that the oxidation potential of nickel foil is 3.3 V, while the voltage of a lithium battery is generally up to 4.5 V. The surface of the nickel foil is protected by the electrochemical stability of the nickel oxide. However, the electrochemical window is insufficient at a high potential of more than 4.55 V or even 4.57 V, which may form a primary battery and accelerate corrosion.
[0156] The related parameters in Examples 12 to 22 are shown in Table 2.
[0157] In Examples 12 to 17, the single-sided positive electrode current collector is a nickel foil with aluminum layers plated on both surfaces.
[0158] In Examples 18 to 20, the single-sided positive electrode current collector is a nickel foil with an aluminum layer plated on one surface.
[0159] The single-sided positive electrode current collector in Example 21 is an aluminum-plated layer on one surface of a titanium foil.
[0160] The single-sided positive electrode current collector in Example 22 is an aluminum-plated layer on one surface of a titanium foil.
[0161] Table 2
[0162]
[0163] Note: “\” in Table 2 means that the parameter is not included.
[0164] According to Table 2 above, in combination with Comparative Examples 1 to 4 and Examples 12 to 22, it can be seen that by increasing the thickness of the aluminum plastic film, increasing the thickness of the positive electrode current collector, and reducing the thickness of the active material layer of the electrode piece to increase the number of layers of the electrode piece, the blunt piercing, needle piercing, and round bar extrusion passing rates can be improved, but the energy density of the secondary battery is reduced. The single-sided positive electrode current collector is set to an aluminum-plated nickel foil or an aluminum-plated titanium foil with a thickness of not more than 20 μm, and the tensile strength of the single-sided positive electrode current collector can be improved to more than 300 MPa. By setting the single-sided positive electrode current collector on the outermost layer of the electrode assembly to an aluminum-plated nickel foil or an aluminum-plated titanium foil with a thickness of not more than 20 μm, the energy density can be improved while improving the blunt piercing, needle piercing, and round bar extrusion passing rates. The tensile strength of the single-sided positive electrode current collector is more than 360 MPa, which can further improve the blunt piercing, needle piercing, and round bar extrusion passing rates of the secondary battery.
[0165] The single-sided positive electrode current collector uses an aluminum-plated nickel foil. It should be noted that the tensile strength of the aluminum-plated nickel foil is not only related to the thickness of the current collector, but also the mass percentage of nickel in the nickel foil, which will affect the tensile strength of the aluminum-plated nickel foil to some extent. The single-sided positive electrode current collector uses an aluminum-plated titanium foil. It should also be noted that the tensile strength of the aluminum-plated titanium foil is not only related to the thickness of the current collector, but also the mass percentage of titanium in the titanium foil, which will affect the tensile strength of the aluminum-plated titanium foil to some extent.
[0166] In combination with Comparative Example 1 and Comparative Example 2, it can be seen that by increasing the thickness of the aluminum plastic film, the blunt piercing, needle piercing, and round bar extrusion passing rates can be improved, i.e., the safety performance can be improved, but the energy density is reduced. In combination with Comparative Example 1 and Comparative Example 3, it can be seen that by reducing the thickness of the active material layer of the electrode piece to increase the number of layers of the electrode piece, the safety performance can be improved.
[0167] The single-sided positive current collector of the outermost layer of the electrode assembly in the commonly used electrode assembly is a 20-μm-thick aluminum foil. As can be seen from Comparative Example 1, Example 12, Example 19, Example 21, and Example 22, by setting the single-sided positive current collector of the outermost layer of the electrode assembly to be an aluminum-plated nickel foil or an aluminum-plated titanium foil with a thickness of not more than 20 μm, the energy density, the capacity retention rate, and the thickness expansion rate can be improved while the safety performance is improved. In addition, the tensile strength of the aluminum-plated nickel foil or the aluminum-plated titanium foil is greater than that of the pure aluminum foil. In addition, since the single-sided positive current collector adopts a pure nickel foil, there is a risk of corrosion in a high-voltage system. By plating aluminum on the nickel, the nickel foil can be wrapped and protected, and the oxide layer of aluminum is more dense, which can well protect the inner nickel foil.
[0168] As can be seen from Examples 12 to 15, the thickness of the single-sided positive current collector in the range of 7 μm to 20 μm can make the secondary battery have good safety performance. The thickness of the single-sided positive current collector is not less than 7 μm, so as to obtain better processing stability in the processes such as coating of active material and compaction. When the thickness of the single-sided positive current collector is greater than 20 μm, the energy density of the secondary battery is reduced. In actual application, since the aluminum layer is a plating layer and the nickel foil is a base layer, in actual production, the base layer serves as a support layer and needs to have a certain thickness. When the thickness of the base layer nickel foil is less than 5 μm, the support effect is poor, and it is difficult to form an aluminum plating layer on the surface of the base layer nickel foil. When the thickness of the base layer nickel foil is greater than 18 μm, the energy density of the secondary battery is reduced, and the cost is increased.
[0169] As can be seen from Examples 14, 16, and 17, when the single-sided positive current collector is a nickel-plated aluminum foil and the nickel foil is plated with aluminum layers on opposite two sides, the thickness of any one of the aluminum layers in the range of 0.5 μm to 6 μm can make the secondary battery have good safety performance. When the thickness of the aluminum layer is reduced, the safety performance of the secondary battery will be reduced. In actual application, since the aluminum layer is a plating layer and the nickel foil is a base layer, in actual production, the base layer serves as a support layer and needs to be designed to have a thickness of any one of the plating layers ≤ the thickness of the base layer × 75%. Otherwise, the uniformity of the plating layer is difficult to control, the processing difficulty is great, and the cost is increased. Therefore, when the thickness of any one of the aluminum layers exceeds 6 μm, the thickness of the nickel foil also needs to correspondingly exceed 8 μm. At this time, the thickness of the single-sided positive current collector will exceed 20 μm, which will reduce the energy density of the secondary battery and increase the cost. In addition, the thickness of the plating layer needs to be not less than 0.5 μm, so as to improve the uniformity and integrity of the plating layer and reduce the possibility that the product performance is affected due to uneven coverage caused by the plating layer being too thin.
[0170] As can be seen from Examples 18 to 20, when the single-sided positive current collector is an aluminum-plated nickel foil and the nickel foil is plated with an aluminum layer on only one side, the thickness of the aluminum layer in the range of 0.5 μm to 8 μm can make the secondary battery have good safety performance. When the thickness of the aluminum layer exceeds 8 μm, the thickness of the aluminum layer as the base layer also needs to be increased accordingly. In this case, the thickness of the single-sided positive current collector is likely to exceed 20 μm, which in turn can reduce the energy density of the secondary battery and increase the cost. In addition, the thickness of the plated layer needs to be no less than 0.5 μm to improve the uniformity and integrity of the plated layer and reduce the possibility of uneven coverage due to the too thin plated layer, which can affect the performance of the product.
[0171] It should be noted that when the single-sided positive current collector is an aluminum-plated nickel foil, the double-sided positive nickel foil, the negative copper foil and / or the aluminum-plastic film of the electrode assembly can also be thinned to improve the energy density while having good safety performance.
[0172] Since titanium and nickel have similar properties, the aluminum-plated titanium foil has similar properties to the aluminum-plated nickel foil, and the above description of the properties of the aluminum-plated nickel foil is also applicable to the aluminum-plated titanium foil.
[0173] The relevant parameters in Examples 23 and 24 are shown in Table 3. In Example 23, the mass percentage of nickel in the nickel layer of the single-sided positive current collector is 99.8%, and in Example 24, the mass percentage of nickel in the nickel layer of the single-sided positive current collector is 95%.
[0174] Table 3
[0175]
[0176] According to Table 3 above, in combination with Examples 1, 23 and 24, when the single-sided positive current collector on the outermost layer of the electrode assembly is an aluminum-plated nickel foil, if the mass percentage of nickel in the nickel layer is no less than 99.8%, the secondary battery has good safety performance and the single-sided positive current collector has good tensile strength. If the mass percentage of nickel in the nickel layer is less than 99.8%, the safety performance of the secondary battery decreases and the tensile strength of the single-sided positive current collector decreases. In addition, for the aluminum-plated nickel foil, in order to make the secondary battery have good safety performance and the single-sided positive current collector have good tensile strength, the mass percentage of nickel in the nickel layer is also preferably no less than 99.8%.
[0177] It should be noted that since titanium and nickel have similar properties, the aluminum-plated titanium foil has similar properties to the aluminum-plated nickel foil, and the aluminum-plated titanium foil has similar properties to the aluminum-plated nickel foil. Therefore, when the single-sided positive current collector on the outermost layer of the electrode assembly is an aluminum-plated titanium foil or an aluminum-plated titanium foil, the mass percentage of titanium in the titanium layer is also preferably no less than 99.8%.
[0178] The above merely describes the embodiments of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation, or direct or indirect application in other related technical fields, which is made by using the content of the present application specification and drawings, is also included in the patent protection scope of the present application.
Claims
1. A secondary battery comprising an electrode assembly including a positive electrode sheet, a separator, and a negative electrode sheet which are sequentially stacked in a first direction; characterized in that, The positive electrode sheet includes a single-sided positive electrode sheet, and an outermost electrode sheet of the electrode assembly in the first direction is the single-sided positive electrode sheet, the single-sided positive electrode sheet includes a first positive current collector and a first positive active layer, the first positive current collector is provided with the first positive active layer on a surface facing the negative electrode sheet, the first positive current collector includes a first metal layer and a second metal layer stacked in contact in the first direction, the first metal layer includes aluminum, the tensile strength of the first positive current collector is 300 MPa or more, and the thickness of the first positive current collector is H1, H1≤20 μm.
2. The secondary battery according to claim 1, characterized by The tensile strength of the first positive current collector is ≥360 MPa.
3. The secondary battery according to claim 1 or 2, characterized by H1≥7 μm.
4. The secondary battery according to claim 3, characterized by 10 μm≤H1≤15 μm.
5. The secondary battery according to any one of claims 1 to 4, characterized by, The first metal layer is an aluminum foil, and the thickness of the first metal layer is 5 μm to 18 μm.
6. The secondary battery according to claim 5, characterized by The thickness of the second metal layer is 0.5 μm to 8 μm.
7. The secondary battery according to claim 6, characterized by The first metal layer is provided with the second metal layer on both surfaces in the first direction, and the thickness of the second metal layer is 0.5 μm to 6 μm.
8. The secondary battery according to any one of claims 5 to 7, characterized by, The second metal layer includes nickel or titanium, and the second metal layer is provided on the surface of the first metal layer by electroplating, evaporation or vapor deposition.
9. The secondary battery according to claim 8, characterized by The second metal layer is a nickel layer or a titanium layer.
10. The secondary battery according to any one of claims 1 to 4, characterized by The second metal layer is a nickel foil or a titanium foil, and the thickness of the second metal layer is 5 μm to 18 μm.
11. The secondary battery according to claim 10, characterized by The thickness of the first metal layer is 0.5 μm to 8 μm.
12. The secondary battery according to claim 11, characterized by The second metal layer is provided with the first metal layer on both surfaces in the first direction, and the thickness of the first metal layer is 0.5 μm to 6 μm.
13. The secondary battery according to any one of claims 10 to 12, characterized by The first metal layer is provided on the surface of the second metal layer by electroplating, evaporation or vapor deposition.
14. The secondary battery according to claim 13, characterized by The first metal layer is an aluminum layer.
15. The secondary battery according to any one of claims 1 to 14, characterized by The second metal layer includes nickel, and the mass percentage of nickel in the second metal layer is not less than 99.8%; Alternatively, the second metal layer includes titanium, and the mass percentage of titanium in the second metal layer is not less than 99.8%.
16. The secondary battery according to any one of claims 1 to 15, characterized by The second metal layer is a nickel layer or a nickel foil, and the second metal layer is located between the first metal layer and the first positive active layer in the first direction.
17. The secondary battery according to any one of claims 1 to 16, characterized by The positive electrode sheet further includes a double-sided positive electrode sheet, and the double-sided positive electrode sheet is provided between two adjacent negative electrode sheets in the first direction, the double-sided positive electrode sheet includes a second positive current collector and a second positive active layer, the second positive current collector is provided with the second positive active layer on both surfaces, the second positive current collector includes a third metal layer and a fourth metal layer stacked in contact in the first direction, the third metal layer includes aluminum, and the fourth metal layer includes nickel or titanium.
18. An electronic device, comprising: The secondary battery includes any one of the secondary batteries according to claims 1 to 17.