Anode current collector, anode sheet, electrochemical device and apparatus

Abstract

The negative electrode current collector (10), negative electrode sheet (30), and electrochemical device and apparatus are disclosed. The negative electrode current collector (10) includes a polymer-based support layer (101) and a copper-based conductive layer (102) disposed on at least one surface of the support layer (101). The thickness D1 of the copper-based conductive layer (102), the tensile strength T of the support layer (101), and the thickness D2 of the support layer (101) satisfy the relationship 0.01≦(300×D1) / (T×D2)≦0.5. The negative electrode current collector (10) has high mechanical and electrical properties, as well as good electrical conductivity and current collection performance and low weight. This improves the manufacturing efficiency and reliability of the negative electrode current collector (10), negative electrode sheet (30), and electrochemical device, and contributes to the electrochemical device having high electrochemical performance and weight energy density.

Description

[Technical field]

[0001] This application claims priority to Chinese Patent Application No. 201910469957.3, entitled “NEGATIVE ELECTRODE CURRENT COLLECTOR, NEGATIVE ELECTRODE SHEET AND ELECTROCHEMICAL DEVICE,” filed on May 31, 2019, the entire contents of which are incorporated herein by reference.

[0002] The present application belongs to the technical field of electrochemical devices, and in particular to negative electrode current collectors, negative electrode sheets, electrochemical devices and apparatus. [Background technology]

[0003] Electrochemical devices such as lithium-ion secondary batteries have high charge and discharge performance and are environmentally friendly, and are widely used in electric vehicles and consumer electronic products. Current collectors are an important component of electrochemical devices, which not only provide support for the active material layer, but also collect and output the current generated by the active material layer to the outside. Therefore, the current collector has an important effect on the performance of the electrode sheet and the electrochemical device. Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, there remains a need for a negative electrode current collector with superior performance. [Means for solving the problem]

[0005] In a first aspect, the present application provides a negative electrode current collector, the negative electrode current collector including a polymer-based support layer and a copper-based conductive layer disposed on at least one surface of the support layer, wherein a thickness D1 of the copper-based conductive layer, a tensile strength T of the support layer, and a thickness D2 of the support layer satisfy a relationship 1, 0.01≦(300×D1) / (T×D2)≦0.5 Formula 1 In formula 1, D1 and D2 have the same unit, and T has the unit of MPa.

[0006] In a second aspect, the present application provides a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode current collector being the negative electrode current collector according to the first aspect of the present application.

[0007] In a third aspect, the present application provides an electrochemical device, the electrochemical device comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the negative electrode sheet being the negative electrode sheet according to the second aspect of the present application.

[0008] In a fourth aspect, the present application provides a device comprising an electrochemical device according to the third aspect.

[0009] The negative electrode current collector provided by the present application includes a polymer material-based support layer and a copper-based conductive layer disposed on the support layer, and the thickness D1 of the copper-based conductive layer, the tensile strength T of the support layer, and the thickness D2 of the support layer satisfy the relational expression 1. It has been found that the negative electrode current collector has suitable toughness and good conductive and current collecting performance. Suitable toughness ensures that the negative electrode current collector has high mechanical performance and mechanical performance, and enables the negative electrode current collector to be subjected to a certain deformation during the manufacturing, processing, and operation of the electrochemical device without causing fracture. This improves the processability and stability performance of the negative electrode current collector during use, thereby effectively preventing it from breaking or cracking during subsequent processing and use. This significantly improves the yield rate during the manufacturing process of the negative electrode current collector and the negative electrode sheet and electrochemical device using the same, and the reliability during use. By adopting a negative electrode current collector with high conductive current collecting performance, the electrochemical device has high electrochemical performance. In addition, the weight energy density of the electrochemical device can be further improved by using the negative electrode current collector provided by the present application.

[0010] The device of the present application includes an electrochemical device provided by the present application and therefore has at least the same advantages as said electrochemical device. [Brief description of the drawings]

[0011] In order to more clearly describe the technical solutions of the embodiments of the present application, the following briefly describes the drawings necessary for the embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without any creative efforts.

[0012] [Figure 1] FIG. 2 is a structural schematic diagram of a negative electrode current collector according to an embodiment of the present application. [Diagram 2] FIG. 2 is a structural schematic diagram of a negative electrode current collector according to another embodiment of the present application. [Diagram 3] FIG. 2 is a structural schematic diagram of a negative electrode current collector according to another embodiment of the present application. [Figure 4] FIG. 2 is a structural schematic diagram of a negative electrode current collector according to another embodiment of the present application. [Diagram 5] FIG. 2 is a structural schematic diagram of a negative electrode current collector according to another embodiment of the present application. [Figure 6] FIG. 2 is a structural schematic diagram of a negative electrode sheet according to one embodiment of the present application. [Figure 7] FIG. 1 is a schematic diagram of a battery according to an embodiment of the present application. [Figure 8] FIG. 1 is a schematic diagram of a battery module according to an embodiment of the present application. [Figure 9] FIG. 1 is a schematic diagram of a battery pack according to an embodiment of the present application. [Figure 10] FIG. 10 is an exploded view of FIG. [Figure 11] 1 is a schematic diagram of an apparatus according to an embodiment of the present application; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In order to make the inventive objectives, technical solutions and beneficial technical effects of the present application clearer, the present application will be described in more detail below with reference to examples. It should be understood that the examples described herein are only for illustrating the present application, and are not intended to limit the present application.

[0014] For the sake of brevity, this specification only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range that is not explicitly stated. Also, any lower limit can be combined with any other lower limit to form a range that is not explicitly stated, and similarly, any upper limit can be combined with any other upper limit to form a range that is not explicitly stated. Also, although not explicitly stated, each point or single value between the endpoints of a range is included within the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit, or can be combined with any other lower limit or upper limit to form a range that is not explicitly stated.

[0015] In the description of this specification, it should be explained that unless otherwise specified, "more than or equal to" and "less than or equal to" are inclusive of the target number, and "multiple types" in "one type or multiple types" means two or more.

[0016] The above summary of the invention of the present application is not intended to describe all embodiments or implementations of the present application. The present embodiments are more specifically exemplified below. In several places throughout the application, guidance is provided through a series of examples, which can be used in various combinations. Each example is listed as only a representative group and should not be construed as exhaustive.

[0017] (Negative electrode current collector) A first aspect of the present application provides a negative electrode current collector 10. Fig. 1 is a schematic diagram of an example of the negative electrode current collector 10. As shown in Fig. 1, the negative electrode current collector 10 includes a polymer material-based support layer 101 and a copper-based conductive layer 102 that are laminated together. The support layer 101 has a first surface 101a and a second surface 101b that face each other in the thickness direction, and the copper-based conductive layer 102 is disposed on the first surface 101a and the second surface 101b of the support layer 101.

[0018] It should be understood that the copper-based conductive layer 102 may further be disposed on either one of the first surface 101a and the second surface 101b of the support layer 101. For example, the copper-based conductive layer 102 is disposed on the first surface 101a of the support layer 101. It should be understood that the copper-based conductive layer 102 may also be disposed on the second surface 101b of the support layer 101.

[0019] For convenience, the brittleness parameter C of the negative electrode current collector 10 is defined as follows. C=(300×D1) / (T×D2) Equation 1

[0020] Here, 300 is a coefficient, D1 is the thickness of the copper-based conductive layer 102, T is the tensile strength of the support layer 101, D2 is the thickness of the support layer 101, D1 and D2 have the same units, and T has the unit of MPa.

[0021] The brittleness parameter C of the negative electrode current collector 10 satisfies the relationship 0.01≦C≦0.5.

[0022] Formula 1 can be applied to the negative electrode current collector 10 having a copper-based conductive layer 102 provided on at least one surface of the support layer 101, and further applies to the negative electrode current collector 10 having a copper-based conductive layer 102 provided on each of two opposing surfaces of the support layer 101, and particularly applies to the negative electrode current collector 10 having a copper-based conductive layer 102 provided on each of two opposing surfaces of the support layer 101, and the thicknesses of the copper-based conductive layers 102 on both sides are equal or approximately equal. The above-mentioned approximately equal means that the difference in thickness of the copper-based conductive layers 102 on both sides does not exceed 10%, for example, does not exceed 10%, 9%, 8%, 7%, 6%, 5%, 3%, 2%, or 1%.

[0023] In some embodiments, the “thickness D 1 of the copper-based conductive layer 102 ” refers to the thickness of the copper-based conductive layer 102 on one side of the support layer 101 .

[0024] In another embodiment, the “thickness D1 of the copper-based conductive layer 102” refers to the average thickness of the copper-based conductive layer 102 on both sides of the support layer 101, i.e., half the sum of the thicknesses of the copper-based conductive layer 102 on both sides of the support layer 101.

[0025] For example, for a negative electrode current collector 10 in which a copper-based conductive layer 102 is provided on one side of a support layer 101, the "thickness D1 of the copper-based conductive layer 102" refers to the thickness of the copper-based conductive layer 102 on one side of the support layer 101. For a negative electrode current collector 10 in which a copper-based conductive layer 102 is provided on each of two opposing surfaces of the support layer 101, and the thicknesses of the copper-based conductive layers 102 on both sides are equal or approximately equal, the "thickness D1 of the copper-based conductive layer 102" refers to the thickness of the copper-based conductive layer 102 on one side of the support layer 101 or the average thickness of the copper-based conductive layer 102 on both sides of the support layer 101. For a negative electrode current collector 10 in which a copper-based conductive layer 102 is provided on each of two opposing surfaces of the support layer 101, and the difference in thickness of the copper-based conductive layer 102 on both sides exceeds 10%, the "thickness D1 of the copper-based conductive layer 102" refers to the average thickness of the copper-based conductive layer 102 on both sides of the support layer 101. This allows formula 1 to be applied more preferably.

[0026] The tensile strength T of the support layer 101 can be measured using devices and methods known in the art, for example, using a universal tensile tester of the American INSTRON 3365 type. An exemplary measurement method is as follows: The support layer 101 is cut into strip-shaped samples, for example, samples with a width of 15 mm and a length of 150 mm. The samples are then attached to two opposing fixtures of the universal tensile tester, the initial length is set to 50 mm, and a tensile test is performed at a tensile speed of 5 mm / min, and the tension is stopped before the sample breaks. The maximum tensile force F received when the sample breaks is recorded, and the tensile strength T of the support layer 101 is calculated based on T=F / S, where S is the initial cross-sectional area of ​​the sample. S can be calculated by the product of the width and thickness of the sample, and the above-mentioned thickness of the sample is the thickness D2 of the support layer 101.

[0027] The thickness D1 of the copper-based conductive layer 102 and the thickness D2 of the support layer 101 can be measured using devices and methods known in the art, for example, using a measuring tape.

[0028] The negative electrode current collector 10 includes a polymer material-based support layer 101 and a copper-based conductive layer 102 disposed on the support layer 101, and the brittleness parameter C of the negative electrode current collector 10 satisfies 0.01≦C≦0.5. This ensures that the negative electrode current collector 10 has appropriate toughness and high mechanical and mechanical properties. The negative electrode current collector 10 is not subject to a certain deformation during the manufacturing, processing and operation of the electrochemical device, resulting in no fracture or breakage. This is helpful in improving the processability and stability of the negative electrode current collector 10 during use, which effectively prevents breakage or cracks during the manufacturing and use. Therefore, the present application can significantly improve the yield rate during the manufacturing process of the negative electrode current collector 10 and the negative electrode sheet and electrochemical device using the same, and the reliability during use.

[0029] The negative electrode current collector 10 is not easily broken or cracked during the manufacturing, processing and operation of the electrochemical device. On the one hand, it ensures that the conductive and current collecting performance of the negative electrode current collector 10 is effectively exhibited, and on the other hand, it prevents the negative electrode active material layer from breaking or cracking and maintains the continuity of its internal conductive network, which ensures that the performance of the negative electrode active material layer is effectively exhibited. The use of the negative electrode current collector 10 of the present application is helpful in improving the service life of the electrochemical device.

[0030] The brittleness parameter C of the negative electrode current collector 10 is within the above range, and at the same time ensures that the negative electrode current collector 10 has good electrical conductivity and current collecting properties, which helps the negative electrode sheet and the electrochemical device to have low impedance and reduce the polarization of the electrochemical device, so that the electrochemical device has high electrochemical performance. The electrochemical device has high multiplication and cycle performance.

[0031] In addition, since the density of the support layer 101 is smaller than that of metals, the weight of the electrochemical device can be reduced by adopting the negative electrode current collector 10 of the present application, thereby further improving the energy density of the electrochemical device.

[0032] In some embodiments, the brittleness parameter C of the negative electrode current collector 10 may be ≦0.5, ≦0.48, ≦0.45, ≦0.42, ≦0.4, ≦0.38, ≦0.36, ≦0.35, ≦0.32, ≦0.3, ≦0.28, or ≦0.25, or even ≧0.01, ≧0.05, ≧0.08, ≧0.1, ≧0.12, ≧0.15, ≧0.17, ≧0.19, ≧0.2, or ≧0.22.

[0033] The inventors of the present application have found that by setting the brittleness parameter C of the negative electrode current collector 10 within an appropriate range, it is possible to improve the energy density of the electrochemical device and at the same time ensure that the negative electrode current collector 10 and the negative electrode sheet have high overcurrent capability. An electrochemical device using this negative electrode current collector 10 has excellent overall performance. The brittleness parameter C of the negative electrode current collector 10 is preferably 0.1 to 0.3. This negative electrode current collector 10 can better exert the above-mentioned effects.

[0034] In some embodiments, the thickness D1 of the copper-based conductive layer 102 is preferably 30 nm≦D1≦3 μm. For example, the thickness D1 of the copper-based conductive layer 102 may be ≦3 μm, ≦2.5 μm, ≦2 μm, ≦1.8 μm, ≦1.5 μm, ≦1.2 μm, ≦1 μm, ≦900 nm, ≦750 nm, ≦450 nm, ≦250 nm, or ≦100 nm, or may be ≧30 nm, ≧80 nm, ≧100 nm, ≧150 nm, ≧300 nm, ≧400 nm, ≧600 nm, ≧800 nm, ≧1 μm, or ≧1.6 μm.

[0035] By providing a thin copper-based conductive layer 102 on the surface of the support layer 101, the weight of the negative electrode current collector 10 can be significantly reduced compared to conventional metal current collectors (e.g., copper foil), thereby reducing the weight of the electrochemical device and significantly improving the energy density of the electrochemical device.

[0036] In addition, the thickness D1 of the copper-based conductive layer 102 is suitable for the copper-based conductive layer 102 to have high conductive performance, so that the negative electrode current collector 10 has high conductive and current collecting performance, thereby improving the performance of the electrochemical device and preventing lithium deposition in the negative electrode. In addition, the copper-based conductive layer 102 is not easily broken during processing and use, so that the negative electrode current collector 10 has high fracture toughness, ensuring that the negative electrode current collector 10 has high mechanical stability and operational stability.

[0037] Preferably, 300 nm≦D1≦2 μm. More preferably, 500 nm≦D1≦1.5 μm. Particularly preferably, 800 nm≦D1≦1.2 μm.

[0038] In some embodiments, the copper-based conductive layer 102 may include one or more of copper and a copper alloy, the mass percent content of copper element in the copper alloy being preferably 80 wt% or more, more preferably 90 wt% or more.

[0039] In some embodiments, the tensile strength T of the support layer 101 is preferably 100MPa≦T≦400MPa, more preferably 150MPa≦T≦300MPa. The tensile strength of the support layer 101 is within a suitable range, which helps the negative electrode current collector 10 to have high mechanical properties, and therefore the negative electrode current collector 10 is less likely to break or crack. In addition, the support layer 101 does not undergo excessive elongation or deformation, which further prevents the copper-based conductive layer 102 from breaking or cracking, and at the same time, the support layer 101 and the copper-based conductive layer 102 have high bond fastness, and the copper-based conductive layer 102 is not easily peeled off. Therefore, the use of the negative electrode current collector 10 helps to improve the service life and cycle performance of the electrochemical device.

[0040] The appropriate tensile strength T is also suitable for the supporting layer 101 to perform a good supporting function for the copper-based conductive layer 102 .

[0041] In some embodiments, the Young's modulus E of the support layer 101 is ≧2 Gpa. The support layer 101 has a high rigidity, which provides a high support for the copper-based conductive layer 102 and ensures the overall strength of the negative current collector 10. The support layer 101 does not elongate or deform excessively during the processing of the negative current collector 10, and prevents the support layer 101 and the copper-based conductive layer 102 from breaking, while improving the bond strength between the support layer 101 and the copper-based conductive layer 102 and making them less likely to peel off. This improves the mechanical stability and operational stability of the negative current collector 10, thereby improving the performance of the electrochemical device, such as improving the cycle life.

[0042] Preferably, the Young's modulus E of the support layer 101 satisfies 2 GPa ≦ E ≦ 20 GPa. For example, E is 2 GPa, 3 GPa, 4 GPa, 5 GPa, 6 GPa, 7 GPa, 8 GPa, 9 GPa, 10 GPa, 11 GPa, 12 GPa, 13 GPa, 14 GPa, 15 GPa, 16 GPa, 17 GPa, 18 GPa, 19 GPa, or 20 GPa. This allows the support layer 101 to have both appropriate rigidity and appropriate toughness, and ensures the flexibility of the support layer 101 and the negative electrode current collector 10 using the same when wound during processing.

[0043] The Young's modulus E of the support layer 101 can be measured using known devices and methods. For example, a universal tensile tester of the US INSTRON 3365 type is used. As an example, the support layer 101 is cut into a sample of 15 mm x 200 mm, the thickness h (μm) of the sample is measured with a 100-minute scale, and a tensile test is performed using a tensile tester at room temperature and normal pressure (25°C, 0.1 MPa). The initial position is set to make the sample between the jigs 50 mm long, the tensile speed is set to 5 mm / min, and the load L (N) to tensile until breakage is recorded. When the device is displaced by y (mm), the stress ε (GPa) = L / (15 x h), the strain η = y / 50, and a stress-strain curve is created, and the initial linear region curve is taken, and the slope of the curve is the Young's modulus E.

[0044] In some embodiments, the thickness D2 of the support layer 101 satisfies 1 μm≦D2≦30 μm. The support layer 101 has a thickness D2, which provides high mechanical strength and is less likely to break during processing and use, and provides good support and protection for the copper-based conductive layer 102, thereby improving the mechanical stability and operational stability of the negative electrode current collector 10. At the same time, the thickness D2 of the support layer 101 is small, which allows the electrochemical device to have a small volume and low weight, thereby improving the volumetric energy density and gravimetric energy density of the electrochemical device.

[0045] In some preferred embodiments, the thickness D2 of the support layer 101 may be ≦30 μm, ≦25 μm, ≦20 μm, ≦18 μm, ≦15 μm, ≦12 μm, ≦10 μm, or ≦8 μm, or may be ≧1 μm, ≧1.5 μm, ≧2 μm, ≧3 μm, ≧4 μm, ≧5 μm, ≧6 μm, ≧7 μm, ≧9 μm, or ≧16 μm. Preferably, 1 nm≦D2≦20 μm. More preferably, 1 μm≦D2≦15 μm. Particularly preferably, 2 μm≦D2≦10 μm. Particularly preferably, 2 μm≦D2≦8 μm. More preferably, 2 μm≦D2≦6 μm.

[0046] The support layer 101 includes one or more polymeric materials. In some embodiments, the polymeric materials can be selected from one or more of polyamides, polyimides, polyesters, polyolefins, polyacetylene hydrocarbons, siloxane polymers, polyethers, polyalcohols, polysulfones, polysaccharide polymers, amino acid-based polymers, polysulfur nitrides, aromatic ring polymers, aromatic heterocyclic polymers, epoxy resins, phenolic resins, derivatives of the above materials, crosslinked materials of the above materials, and copolymers of the above materials.

[0047] In some preferred embodiments, the polymeric material is polycaprolactam (also known as nylon 6), polyhexamethylene adipamide (also known as nylon 66), polyparaphenylene terephthalamide (PPTA), polymetaphenylene isophthalamide (PMIA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polycarbonate (PC), polyethylene (PE), polypropylene (PP), ethylene-propylene rubber (PPE), polyvinyl alcohol (PVA), polystyrene (PS), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), poly The material may include one or more of tetrafluoroethylene (PTEE), sodium polystyrene sulfonate (PSS), polyacetylene, silicone rubber, polyoxymethylene (POM), polyphenylene ether (PPO), polyphenylene sulfide (PPS), polyethylene glycol (PEG), cellulose, starch, protein, polyphenyl, polypyrrole (PPy), polyaniline (PAN), polythiophene (PT), polypyridine (PPY), acrylonitrile-butadiene-styrene copolymer (ABS), derivatives of the above materials, crosslinked products of the above materials, and copolymers of the above materials.

[0048] In some embodiments, the support layer 101 further preferably includes an additive. The additive may include one or more of a metallic material and an inorganic non-metallic material. The metallic material additive may include one or more of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, iron, iron alloy, silver, and silver alloy. The inorganic non-metallic material additive may include one or more of a carbon-based material, aluminum oxide, silicon dioxide, silicon nitride, silicon carbide, boron nitride, silicate, and titanium oxide, and further includes one or more of a glass material, a ceramic material, and a ceramic composite material, for example. The carbon-based material additive may be one or more of graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, for example.

[0049] The additive may further include a carbon-based material coated with a metallic material, such as one or more of nickel-coated graphite powder and nickel-coated carbon fiber.

[0050] In some preferred embodiments, the support layer 101 adopts one or more of insulating polymer materials and insulating polymer composite materials. The insulating polymer composite material can include one or more of the above polymer materials and one or more of the above additives, and has electrical insulation properties. The support layer 101 has a high volume resistivity, which is helpful in improving the safety performance of the electrochemical device.

[0051] Preferably, the support layer 101 may include one or more of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), sodium polystyrene sulfonate (PSS), and polyimide (PI).

[0052] In some embodiments, the support layer 101 may be a single layer structure or a composite layer structure having two or more layers, such as two layers, three layers, four layers, etc.

[0053] 2 is a structural schematic diagram of another negative electrode current collector 10 according to the present application. As shown in FIG. 2, the support layer 101 has a composite layer structure formed by stacking a first sublayer 1011, a second sublayer 1012, and a third sublayer 1013. The support layer 101 of the composite layer structure has a first surface 101a and a second surface 101b facing each other, and the copper-based conductive layer 102 is stacked on the first surface 101a and the second surface 101b of the support layer 101. It should be understood that the copper-based conductive layer 102 may be stacked only on the first surface 101a of the support layer 101, or may be stacked only on the second surface 101b of the support layer 101.

[0054] When the support layer 101 has a composite layer structure of two or more layers, the materials of each sub-layer may be the same or different.

[0055] The inventors have found through extensive research that the brittleness parameter of the negative electrode current collector 10 is a more important parameter for the dynamic and mechanical performance of the negative electrode current collector 10, particularly when the thickness of the support layer 101 is 10 μm or less, and more particularly when the thickness is 8 μm or less, and that this parameter has a significant effect on the processability, manufacturing efficiency, and usage reliability of the negative electrode current collector 10.

[0056] In some embodiments, the negative electrode current collector 10 further preferably includes a protective layer 103. As shown in Fig. 3 to Fig. 5, the protective layer 103 can be provided between the copper-based conductive layer 102 and the support layer 101. Alternatively, the protective layer 103 may be provided on a surface of the copper-based conductive layer 102 that is remote from the support layer 101. Alternatively, the protective layer 103 may be provided both between the copper-based conductive layer 102 and the support layer 101 and on a surface of the copper-based conductive layer 102 that is remote from the support layer 101.

[0057] The protective layer 103 protects the copper-based conductive layer 102 and prevents the copper-based conductive layer 102 from being damaged, such as chemical corrosion or mechanical destruction, and can ensure the operational stability and service life of the negative electrode current collector 10. This helps the electrochemical device to have high safety performance and electrochemical performance. In addition, the protective layer 103 can further improve the strength of the negative electrode current collector 10.

[0058] 3 to 5 show that the support layer 101 has a copper-based conductive layer 102 on one side thereof. The copper-based conductive layer 102 itself has a protective layer 103 on one or both of two surfaces that face each other in the thickness direction. In other embodiments, the support layer 101 may further have a copper-based conductive layer 102 on each of two facing surfaces, any one of the copper-based conductive layers 102 may have a protective layer 103 on one or both of two surfaces that face each other in the thickness direction, or two copper-based conductive layers 102 may have a protective layer 103 on one or both of two surfaces that face each other in the thickness direction.

[0059] In some embodiments, protective layer 103 may include one or more of a metal, a metal oxide, and a conductive carbon.

[0060] The metal may include one or more of nickel, chromium, a nickel-based alloy, and a copper-based alloy. The nickel-based alloy is an alloy formed by adding one or more other elements to a pure nickel base, and is preferably a nickel-chromium alloy. The nickel-chromium alloy is an alloy formed of metallic nickel and metallic chromium, and preferably, the weight ratio of nickel to chromium in the nickel-chromium alloy is 1:99 to 99:1, for example, 9:1. The copper-based alloy is an alloy formed by adding one or more other elements to a pure copper base, and is preferably a nickel-copper alloy. Preferably, the weight ratio of nickel to copper in the nickel-copper alloy is 1:99 to 99:1, for example, 9:1.

[0061] The metal oxide may include one or more of aluminum oxide, cobalt oxide, chromium oxide, and nickel oxide.

[0062] The conductive carbon may include one or more of graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and further may be one or more of carbon black, carbon nanotubes, acetylene black, and graphene.

[0063] In some embodiments, the protective layer 103 can include one or more of nickel, chromium, nickel-based alloys, copper-based alloys, aluminum oxide, cobalt oxide, chromium oxide, nickel oxide, graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0064] 3, the negative electrode current collector 10 includes a support layer 101, a copper-based conductive layer 102, and a protective layer 103, which are stacked together. Here, the support layer 101 has a first surface 101a and a second surface 101b facing each other in the thickness direction of the support layer 101, the copper-based conductive layer 102 is stacked on at least one of the first surface 101a and the second surface 101b of the support layer 101, and the protective layer 103 is stacked on the surface of the copper-based conductive layer 102 facing away from the support layer 101.

[0065] The protective layer 103 (abbreviated as upper protective layer) disposed on the surface of the copper-based conductive layer 102 facing the support layer 101 serves to protect the copper-based conductive layer 102 from chemical corrosion and mechanical damage. In particular, the upper protective layer can further improve the interface between the negative electrode current collector 10 and the negative electrode active material layer 20, and can increase the bonding strength between the negative electrode current collector 10 and the negative electrode active material layer 20.

[0066] In some embodiments, the upper protective layer of the negative electrode current collector 10 may be a metal oxide protective layer, such as aluminum oxide, cobalt oxide, nickel oxide, chromium oxide, etc. The metal oxide protective layer has high hardness and mechanical strength, a larger specific surface area, and higher corrosion resistance, and can better protect the copper-based conductive layer 102.

[0067] Preferably, the upper protective layer of the negative electrode current collector 10 is a metal protective layer. The metal protective layer can improve the conductive performance of the negative electrode current collector 10, thereby reducing the polarization of the electrochemical device, and reducing the risk of lithium precipitation of the negative electrode, thereby improving the cycle performance and safety performance of the electrochemical device. More preferably, the upper protective layer of the negative electrode current collector 10 is a two-layer protective layer, that is, a composite layer formed of one metal protective layer and one metal oxide protective layer. Preferably, the metal protective layer is disposed on the surface of the copper-based conductive layer 102 facing the support layer 101, and the metal oxide protective layer is disposed on the surface of the metal protective layer facing the support layer 101. In this way, the conductive performance, corrosion resistance, and interface between the copper-based conductive layer 102 and the negative electrode active material layer 20 of the negative electrode current collector 10 can be improved simultaneously, thereby obtaining a negative electrode current collector with higher overall performance.

[0068] 4 , the negative electrode current collector 10 includes a support layer 101, a copper-based conductive layer 102, and a protective layer 103, which are laminated together. Here, the support layer 101 has a first surface 101a and a second surface 101b facing each other in the thickness direction of the support layer 101, the copper-based conductive layer 102 is laminated on at least one of the first surface 101a and the second surface 101b of the support layer 101, and the protective layer 103 is laminated between the copper-based conductive layer 102 and the support layer 101.

[0069] The protective layer 103 (abbreviated as lower protective layer) disposed between the copper-based conductive layer 102 and the support layer 101 serves to protect the copper-based conductive layer 102 from chemical corrosion and mechanical damage. At the same time, the lower protective layer further improves the bonding strength between the copper-based conductive layer 102 and the support layer 101, and can prevent the copper-based conductive layer 102 and the support layer 101 from being separated, thereby improving the supporting and protecting effect on the copper-based conductive layer 102.

[0070] Preferably, the lower protective layer is a metal oxide or a metal protective layer. The corrosion resistance of the metal oxide protective layer is high, and the specific surface area is large, so that the interfacial bonding force between the copper-based conductive layer 102 and the support layer 101 can be improved. As a result, the lower protective layer can better protect the copper-based conductive layer 102, and improve the performance of the electrochemical device. In addition, the hardness of the metal oxide protective layer is higher, and the mechanical strength is higher, which helps to improve the strength of the negative electrode current collector 10. The metal protective layer can protect the copper-based conductive layer 102 from chemical corrosion and mechanical damage, and can improve the conductive performance of the negative electrode current collector 10 at the same time. Therefore, the polarization of the electrochemical device is reduced, and the risk of lithium precipitation of the negative electrode is reduced. As a result, the cycle performance and safety performance of the electrochemical device can be improved. Therefore, preferably, the lower protective layer of the negative electrode current collector 10 is a metal protective layer.

[0071] 5, the negative electrode current collector 10 includes a support layer 101, a copper-based conductive layer 102, and a protective layer 103, which are stacked together. Here, the support layer 101 has a first surface 101a and a second surface 101b facing each other in the thickness direction of the support layer 101, the copper-based conductive layer 102 is stacked on at least one of the first surface 101a and the second surface 101b of the support layer 101, and protective layers 103 are provided between the copper-based conductive layer 102 and the support layer 101, and on the surface of the copper-based conductive layer 102 away from the support layer 101.

[0072] The protective layer 103 is provided on both sides of the copper-based conductive layer 102, which can more fully protect the copper-based conductive layer 102, thereby providing the negative electrode current collector 10 with high overall performance.

[0073] Naturally, the protective layers 103 on the two surface sides of the copper-based conductive layer 102 may be made of the same or different materials and may have the same or different thicknesses.

[0074] In some embodiments, the thickness D3 of the protective layer 103 satisfies 1 nm≦D3≦200 nm and D3≦0.1D1, so as to protect the copper-based conductive layer 102 and at the same time provide the electrochemical device with a high energy density.

[0075] For example, the thickness D3 of the protective layer 103 may be ≦200 nm, ≦180 nm, ≦150 nm, ≦120 nm, ≦100 nm, ≦80 nm, ≦60 nm, ≦55 nm, ≦50 nm, ≦45 nm, ≦40 nm, ≦30 nm, or ≦20 nm, or may be ≧1 nm, ≧2 nm, ≧5 nm, ≧8 nm, ≧10 nm, ≧12 nm, ≧15 nm, or ≧18 nm. Preferably, 5 nm≦D3≦200 nm. More preferably, 10 nm≦D3≦200 nm.

[0076] The "thickness D3 of the protective layer 103" means the thickness of the protective layer 103 located on one side of the copper-based conductive layer 102. That is, when the negative electrode current collector 10 includes an upper protective layer, the thickness D a D is 1 nm or less a ≦200 nm and D a ≦0.1D1. Furthermore, 5nm≦D a ≦200 nm. Furthermore, 10 nm ≦ D a When the negative electrode current collector 10 includes a lower protective layer, the thickness D of the lower protective layer is b D is 1 nm or less b ≦200 nm and D b ≦0.1D1. Furthermore, 5nm≦D b ≦200 nm. Furthermore, 10 nm ≦ D b ≦200 nm.

[0077] D a and D. b The protective layer 103 effectively protects the copper-based conductive layer 102 and ensures that the electrochemical device has a high energy density.

[0078] When the protective layer 103 is provided on both surfaces of the copper-based conductive layer 102, that is, when the negative electrode current collector 10 includes an upper protective layer and a lower protective layer, it is preferable to use a protective layer of a >D b In this way, the upper protective layer and the lower protective layer cooperate to provide good protection against chemical corrosion and mechanical damage to the copper-based conductive layer 102, and at the same time, the electrochemical device has a high energy density. More preferably, the upper protective layer and the lower protective layer are 0.5D a ≦D b ≦0.8D a This allows the upper protective layer and the lower protective layer to exhibit a synergistic protective effect more satisfactorily.

[0079] Naturally, the effect of the presence or absence of protective layer 103 on the brittleness parameter C of negative electrode current collector 10 can be ignored.

[0080] The copper-based conductive layer 102 can be formed on the support layer 101 by at least one of mechanical rolling, adhesion, vapor deposition, electroless plating, and electroplating. Here, vapor deposition and electroplating are preferred, that is, the copper-based conductive layer 102 is a vapor deposition layer and an electroplating layer, respectively. By forming the copper-based conductive layer 102 on the support layer 101 by vapor deposition or electroplating, a high bonding strength is obtained between the copper-based conductive layer 102 and the support layer 101, thereby improving the performance of the negative electrode current collector 10.

[0081] The vapor deposition method is preferably a physical vapor deposition method, which is preferably at least one of an evaporation method and a sputtering method, where the evaporation method is preferably at least one of a vacuum deposition method, a thermal evaporation method and an electron beam evaporation method, and the sputtering method is preferably a magnetron sputtering method.

[0082] As an example, the copper-based conductive layer 102 can be formed by a vacuum deposition method, which can include the following: The support layer 101 that has been subjected to a surface cleaning treatment is placed in a vacuum plating chamber, and the metal wire in the metal evaporation chamber is melted and evaporated at a high temperature of 1300°C to 2000°C, and the evaporated metal passes through a cooling system in the vacuum plating chamber and is finally deposited on the support layer 101 to form the copper-based conductive layer 102.

[0083] If the protective layer 103 is provided, it may be formed on the copper-based conductive layer 102 by at least one of a vapor deposition method, an in-situ formation method, and a coating method. The vapor deposition method may be the vapor deposition method described above. Preferably, the in-situ formation method is an in-situ passivation method, i.e., a method of in-situ formation of a metal oxide passivation layer on a metal surface. Preferably, the coating method is at least one of roll coating, extrusion coating, knife coating, and gravure coating.

[0084] Preferably, the protective layer 103 is formed on the copper-based conductive layer 102 by at least one of a vapor deposition method and an in-situ formation method, so that there is a high bonding strength between the copper-based conductive layer 102 and the protective layer 103. This allows the protective layer 103 to better protect the negative electrode current collector 10 and ensures good operating performance of the negative electrode current collector 10.

[0085] When the protective layer 103 (i.e., the lower protective layer) is provided between the copper-based conductive layer 102 and the support layer 101, the lower protective layer may be first formed on the support layer 101, and then the copper-based conductive layer 102 may be formed on the lower protective layer. The lower protective layer may be formed on the support layer 101 by at least one of a vapor deposition method and a coating method, with the vapor deposition method being preferred. The copper-based conductive layer 102 may be formed on the lower protective layer by at least one of a mechanical roll-forming method, an adhesive method, a vapor deposition method, and a chemical plating method, with the vapor deposition method being preferred.

[0086] (Negative electrode sheet) A second aspect of the present application provides a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer stacked together, where the negative electrode current collector is any of the negative electrode current collectors 10 of the first aspect of the present application.

[0087] Since the negative electrode sheet of the present application employs the negative electrode current collector 10 of the first embodiment of the present application, it has high mechanical properties, high manufacturing efficiency, and high usage safety and reliability, while simultaneously combining low weight and high electrochemical performance.

[0088] An example of a negative electrode sheet 30 is shown in Fig. 6. As shown in Fig. 6, the negative electrode sheet 30 includes a negative electrode current collector 10 and a negative electrode active material layer 20 which are stacked together, the negative electrode current collector 10 has two surfaces facing each other in its thickness direction, and the negative electrode active material layer 20 is stacked on the two surfaces of the negative electrode current collector 10. Of course, the negative electrode active material layer 20 may be further stacked on any one of the two surfaces of the negative electrode current collector 10.

[0089] The negative electrode active material layer 20 can be made of a negative electrode active material capable of reversibly inserting / desorbing active ions known in the art. The present application is not limited thereto. Examples of negative electrode active materials used in lithium ion secondary batteries include metallic lithium, natural graphite, artificial graphite, mesophase microcarbon balls (abbreviated as MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, lithium titanate with a spinel structure, and Li-Al alloys.

[0090] In some embodiments, the negative electrode active material layer 20 may further include a conductive agent. The present application does not limit the type of the conductive agent. For example, the conductive agent may be selected from one or more of graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0091] In some embodiments, the negative electrode active material layer 20 may further include an adhesive. The present application does not limit the type of adhesive. For example, the binder may be one or more selected from styrene butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0092] The negative electrode sheet 30 can be manufactured based on a conventional method in the art, such as a coating method. For example, the negative electrode active material and optional conductive agent and adhesive are dispersed in a solvent, which may be NMP or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is applied to the negative electrode current collector 10, and after a process such as drying, the negative electrode sheet 30 is obtained.

[0093] (Electrochemical Equipment) A third aspect of the present application provides an electrochemical device comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet is any one of the negative electrode sheets of the second aspect of the present application.

[0094] An example of the electrochemical device may be a battery, a battery module including the battery, or a battery pack including the battery. An example of the battery may be a primary battery or a secondary battery. Specific examples include, but are not limited to, a lithium ion secondary battery, a lithium primary battery, a sodium ion battery, and a magnesium ion battery.

[0095] The electrochemical device of the present application employs the negative electrode sheet provided according to the second aspect of the present application, and thus has high overall electrochemical performance, including high energy density, multiplication performance, cycle performance and safety performance.

[0096] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. For example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is laminated and disposed on one or both of the two surfaces.

[0097] The positive electrode active material layer can employ a positive electrode active material capable of reversible insertion / desorption of active ions known in the art, and the present application is not limited thereto. For example, the positive electrode active material used in a lithium-ion secondary battery can include one or more of lithium transition metal composite oxides, composite oxides obtained by adding other transition metals, non-transition metals, or non-metals to lithium transition metal composite oxides. Here, the transition metal may be one or more of Mn, Fe, Ni, Co, Cr, Ti, Zn, V, Al, Zr, Ce, and Mg.

[0098] As an example, the positive electrode active material can be selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and olivine structure lithium-containing phosphates. For example, the positive electrode active material is LiMn2O4, LiNiO2, LiCoO2, LiNi 1-y Co y O2(0 < y < 1), LiNi a Co b Al 1-a-b O2(0 < a < 1, 0 < b < 1, 0 < a + b < 1), LiMn 1-m-n Ni m Co n O2(0 < m < 1, 0 < n < 1, 0 < m + n < 1), LiMPO4 (M may be one or more of Fe, Mn, Co), and Li3V2(PO4)3.

[0099] In some embodiments, the positive electrode active material layer may further include an adhesive. The present application does not limit the type of adhesive. For example, the adhesive may be one or more selected from styrene butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0100] In some embodiments, the positive electrode active material layer may further include a conductive agent. The present application does not limit the type of the conductive agent. For example, the conductive agent may be selected from one or more of graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0101] The positive electrode sheet can be manufactured according to a general method in the art, such as a coating method. For example, the positive electrode active material and optional conductive agent and adhesive are dispersed in a solvent, which may be N-methylpyrrolidone (NMP), to form a uniform positive electrode slurry. The positive electrode slurry is applied to a positive electrode current collector, and after a process such as drying, a positive electrode sheet is obtained.

[0102] The positive electrode current collector may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium and silver, such as one or more of aluminum and aluminum alloy. The mass percent content of aluminum element in the aluminum alloy is preferably 80wt% or more, more preferably 90wt% or more.

[0103] In some embodiments, the electrolyte may be a solid electrolyte or a non-aqueous electrolyte. The non-aqueous electrolyte may be obtained by dispersing an electrolyte salt in an organic solvent. In the electrolyte, the organic solvent may be any organic solvent in the art as a medium for transporting ions in an electrochemical reaction. The electrolyte salt may be any electrolyte salt in the art as a source of ions.

[0104] Examples of organic solvents used in lithium ion secondary batteries include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl phosphatase (PHOS), methyl phosphatase (MPH ... The fatty acids and fatty acids include one or more of the following: methyl stearate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0105] For example, the electrolyte salt used in the lithium ion secondary battery may include one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium difluorosulfonylimide), LiTFSI (lithium difluorotrifluoromethanesulfonylimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate).

[0106] The electrolyte further selectively contains an additive, and the type of additive is not specifically limited and can be selected as necessary. For example, the additive may include a negative electrode film-forming additive, a positive electrode film-forming additive, and may further include an additive that can improve certain performance of the electrochemical device, such as an additive that improves the overcharge performance of the electrochemical device, an additive that improves the high temperature performance of the electrochemical device, an additive that improves the low temperature performance of the electrochemical device, etc.

[0107] By way of example, the additive may include one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), succinonitrile (SN), adiponitrile (ADN), 1,3-propene sultone (PST), tris(trimethylsilane) phosphate (TMSP), and tris(trimethylsilane) borate (TMSB).

[0108] When the electrochemical device adopts an electrolyte, a separator is installed between the positive electrode sheet and the negative electrode sheet to play the role of isolation. The type of the separator is not particularly limited, and any known porous structure separator with good chemical stability and mechanical stability can be selected, such as one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0109] In some embodiments, the electrochemical device may be a battery. The battery includes a positive electrode sheet, a negative electrode sheet, and an outer casing for sealing the electrolyte. For example, the positive electrode sheet, the negative electrode sheet, and the separator may be stacked or rolled to form a stacked electrode assembly or a rolled electrode assembly, and the electrode assembly is enclosed in the outer casing. The electrolyte may be an electrolytic solution, and the electrolytic solution permeates the electrode assembly. The number of electrode assemblies in the battery may be one or more, and may be adjusted as needed.

[0110] In some embodiments, the exterior of the battery may be a soft pack, such as a bag-type soft pack. The material of the soft pack may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc. The exterior of the battery may be a hard case, such as an aluminum case.

[0111] The present application does not particularly limit the shape of the battery, which may be cylindrical, rectangular, or any other shape. Figure 7 shows a battery 5 with a rectangular structure as an example.

[0112] In some embodiments, the batteries can be assembled into a battery module, and the number of batteries included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0113] Fig. 8 shows an example of a battery module 4. As shown in Fig. 8, in the battery module 4, the batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4. Of course, the batteries may be arranged in any other manner. Furthermore, the batteries 5 may be fixed by fasteners.

[0114] The battery module 4 optionally further includes a case having an accommodating space, and the plurality of batteries 5 are accommodated in the accommodating space.

[0115] In some embodiments, the battery modules can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0116] 9 and 10 show an example of a battery pack 1. As shown in Fig. 9 and 10, the battery pack 1 may include a battery case and a plurality of battery modules 4 installed in the battery case. The battery case includes an upper case body 2 and a lower case body 3, and the upper case body 2 may be covered by the lower case body 3 and form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery case in any manner.

[0117] (Device) A fourth aspect of the present application provides an apparatus, the apparatus includes the electrochemical apparatus of the third aspect of the present application, the electrochemical apparatus may be used as a power source for the apparatus, or may be used as an energy storage unit for the apparatus. The apparatus may be, but is not limited to, a portable device (e.g., a mobile phone, a laptop, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc. The apparatus may select different electrochemical devices, such as a battery, a battery module, or a battery pack, according to its usage needs.

[0118] An example device is shown in Figure 11. The device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. The device may employ a battery pack or a battery module to meet the requirements for high power and high energy density of electrochemical devices.

[0119] Other example devices may be mobile phones, tablet computers, notebook computers, etc. Such devices generally require thinness and may employ secondary batteries as a power source. EXAMPLES

[0120] The following examples are merely intended to more specifically and descriptively illustrate the contents disclosed in this application. It will be obvious to those skilled in the art that various modifications and changes can be made within the scope of the contents disclosed in this application. Unless otherwise specified, all parts, percentages, and ratios reported in the following examples are calculated by weight, and all reagents used in the examples are commercially available or obtained by synthesis according to conventional methods and can be used directly without the need for further treatment, and the devices used in the examples are commercially available.

[0121] [Manufacturing method] (Manufacturing of negative electrode current collectors) A polymeric material-based support layer of a predetermined thickness is selected and subjected to a surface cleaning treatment. The surface-cleaned support layer is then placed in a vacuum plating chamber, and high-purity copper wire in the metal evaporation chamber is melted and evaporated at a high temperature of 1300°C to 2000°C. The evaporated metal passes through the cooling system in the vacuum plating chamber and is finally deposited on the two surfaces of the support layer to form a copper-based conductive layer.

[0122] (Manufacturing of normal negative electrode current collectors) A copper foil with a thickness of 8 μm is used.

[0123] (Manufacturing of negative electrode sheets) The negative electrode active material graphite, conductive carbon black, thickener sodium carboxymethylcellulose, and adhesive styrene butadiene rubber latex are mixed with an appropriate amount of deionized water in a weight ratio of 96.5:1.0:1.0:1.5, and then formed into a uniform negative electrode slurry. The negative electrode slurry is applied to a negative electrode current collector, and after drying and other processes, a negative electrode sheet is obtained.

[0124] (Manufacturing of normal positive electrode current collectors) An aluminum foil having a thickness of 12 μm is used.

[0125] (Normal manufacturing of positive electrode sheets) Cathode active material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2, conductive carbon black, and polyvinylidene fluoride (PVDF) adhesive are mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent in a weight ratio of 93:2:5 with sufficient stirring to form a uniform positive electrode slurry. The positive electrode slurry is applied to a positive electrode current collector, and after processes such as drying, a positive electrode sheet is obtained.

[0126] (Preparation of electrolyte) Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with a volume ratio of 3:7 were mixed uniformly to obtain an organic solvent, which was then mixed with 1 mol / L of LiP F6 is dissolved homogeneously in the organic solvent.

[0127] (manufacturing lithium-ion secondary batteries) The positive electrode sheet, separator, and negative electrode sheet are stacked in order, and the separator is a PP / PE / PP composite film.Then, the core is wound up and placed in a packaging case, and the above electrolyte is injected into the electric core and sealed to obtain a lithium-ion secondary battery.

[0128] (Measurement part) 1. Measurement of negative electrode current collector 1) Measurement of the brittleness parameter C of the negative electrode current collector

[0129] The support layer is punched out into a sample with a width of 15 mm and a length of 150 mm, and then the sample is attached to the upper and lower jigs of the American INSTRON 3365 universal tensile tester, the initial length is set to 50 mm, and the tensile test is performed at a tensile speed of 5 mm / min. The tensile test is stopped until the sample breaks, and the maximum tensile force F received when the sample breaks is recorded, and the tensile strength T of the support layer is calculated based on 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 (i.e., the thickness D2 of the support layer).

[0130] The thickness D1 of the copper-based conductive layer and the thickness D2 of the support layer are measured in 10,000 mm units.

[0131] The brittleness parameter C of the negative electrode current collector is expressed as (300×thickness D1 of the copper-based conductive layer) / (tensile strength T of the support layer×thickness D2 of the support layer).

[0132] 2) Measurement of breaking elongation of negative electrode current collector A sample was cut into 15 mm x 200 mm from the negative electrode current collector, and a tensile test was performed using an American INSTRON 3365 universal tensile tester at room temperature and pressure (25°C, 0.1 MPa). The length of the sample between the fixtures was set to 50 mm by setting the initial position, the tensile speed was 5 mm / min, and the device displacement y (mm) at tensile break was recorded. Finally, the breaking elongation was calculated to be (y / 50) x 100%.

[0133] 2. Battery performance measurement (1) (Cycle characteristic measurement) At 45°C, the lithium ion secondary battery is charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 0.05C, and then discharged at a constant current of 1C to 2.8V, which is a charge-discharge cycle, and the discharge capacity this time is the discharge capacity of the first cycle. The lithium ion secondary battery is charged and discharged 1000 times according to the above method, the discharge capacity of the 1000th cycle is recorded, and the capacity retention rate of the lithium ion secondary battery after 1000 cycles at 1C / 1C is calculated.

[0134] Capacity retention rate (%) after 1000 cycles of lithium-ion secondary battery at 45℃ and 1C / 1C = Discharge capacity at 1000th cycle / Discharge capacity at 1st cycle x 100%

[0135] (2)(Magnification performance measurement) At 25°C, the lithium-ion secondary battery is charged at a constant current of 1C up to 4.2V, then charged at a constant voltage until the current falls to 0.05C or less, and then discharged at a constant current of 1C down to 3.0V. Testing is then performed to obtain the 1C discharge capacity of the lithium-ion secondary battery.

[0136] At 25°C, the lithium-ion secondary battery is charged at a constant current of 1C up to 4.2V, then charged at a constant voltage until the current falls to 0.05C or less, and then discharged at a constant current of 4C down to 3.0V. Testing is then performed to obtain the 4C discharge capacity of the lithium-ion secondary battery.

[0137] Secondary battery 4C magnification capacity retention rate (%) = 4C magnification discharge capacity / 1C magnification discharge capacity x 100%

[0138] (Measurement results) 1. The role of negative electrode current collectors in improving the gravimetric energy density of electrochemical devices

[0139] [Table 1]

[0140] In Table 1, the weight percentage of the negative electrode current collector is the weight of the negative electrode current collector per unit area divided by the weight of a conventional negative electrode current collector per unit area. Compared with the conventional copper foil negative electrode current collector, the weight of the negative electrode current collectors adopted in the present application is reduced to different degrees, thereby improving the gravimetric energy density of the electrochemical device.

[0141] 2. Effect of the protective layer on the electrochemical performance of the negative electrode current collector and the electrochemical device

[0142] [Table 2-1]

[0143] The negative electrode current collector in Table 2-1 is a negative electrode current collector 7 in Table 1 to which a protective layer is provided. The nickel-based alloy in Table 2-1 contains 90 wt % of nickel and 10 wt % of chromium.

[0144] The bilayer protective layer in Table 2-1 includes a nickel protective layer having a thickness of 25 nm and disposed on the surface of the copper-based conductive layer facing away from the support layer, and a nickel oxide protective layer having a thickness of 25 nm and disposed on the surface of the nickel protective layer facing away from the support layer.

[0145] [Table 2-2]

[0146] All of the batteries in Table 2-2 use a normal positive electrode sheet.

[0147] As can be seen from Table 2-2, the electrochemical device using the negative electrode current collector of the present application has good cycle life and multiplication performance, which is equivalent to the cycle performance and multiplication performance of an electrochemical device using a conventional negative electrode current collector. This shows that the use of the composite negative electrode current collector of the present application does not have a significant adverse effect on the electrochemical performance of the electrochemical device. In particular, the electrochemical device manufactured using the composite negative electrode current collector provided with a protective layer has a further improved capacity retention after 1000 cycles at 45°C and 1C / 1C and a capacity retention at 4C multiplication, showing that the reliability of the electrochemical device is higher.

[0148] 3. Brittleness parameters of negative electrode current collectors and their influence on the mechanical properties of negative electrode current collectors

[0149] [Table 3]

[0150] In Table 3, the copper alloy is a CuNi alloy, which is composed of 95 wt% Cu and 5 wt% Ni.

[0151] As can be seen from the results in Table 3, the brittleness parameter C of the negative electrode current collector is set to 0.01-0.5, and the breaking elongation rate of the negative electrode current collector is improved, and the breaking elongation rate of the negative electrode current collector is 3% or more. This ensures that the negative electrode current collector has high dynamic and mechanical properties, and does not cause fracture due to a certain deformation during the manufacturing, processing and operation of the electrochemical device. This improves the processability and stability during use of the negative electrode current collector, which can effectively prevent the occurrence of fracture or crack during manufacturing and use, thereby significantly improving the non-defective rate during manufacturing and the reliability during use of the negative electrode current collector and the negative electrode sheet and electrochemical device using the same.

[0152] As mentioned above, the present application is merely a specific embodiment, and the scope of protection of the present application is not limited thereto, and those skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and all of these modifications or replacements should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A negative electrode current collector comprising a polymeric material-based support layer, a copper-based conductive layer provided on at least one surface of the support layer, and a protective layer, the protective layer includes an upper protective layer and a lower protective layer, the upper protective layer is provided on a surface of the copper-based conductive layer facing away from the support layer, and the lower protective layer is provided between the copper-based conductive layer and the support layer; The thickness D of the copper-based conductive layer １ , the tensile strength T of the support layer and the thickness D of the support layer ２ 0.1≦(300×D １ ) / (T x D ２ )≦0.48, and in the above-mentioned formula 1, D １ and D. ２ The units of are the same, and the unit of T is MPa, The thickness D of the copper-based conductive layer １ 30 nm≦D １ ≦3 μm, the tensile strength T of the support layer satisfies 200 MPa ≦ T ≦ 300 MPa, and the thickness D of the support layer ２ 2 μm≦D ２ ≦10 μm.

2. The thickness D of the copper-based conductive layer １ , the tensile strength T of the support layer and the thickness D of the support layer ２ 0.1≦(300×D １ ) / (T x D ２ 2. The negative electrode current collector according to claim 1, which satisfies the relationship 1.1 of 0.3 or less.

3. 3. The negative electrode current collector according to claim 1, wherein the support layer has a Young's modulus E of 2 GPa or more.

4. 4. The negative electrode current collector according to claim 3, wherein the support layer has a Young's modulus E that satisfies 2 GPa≦E≦20 GPa.

5. The thickness D of the copper-based conductive layer １ 800 nm≦D １ ≦1.2 μm, and / or The thickness D of the support layer ２ 2 μm≦D ２ The negative electrode current collector according to claim 1 , wherein the average particle size satisfies ≦6 μm.

6. 6. The negative electrode current collector according to claim 1, wherein the copper-based conductive layer contains one or more of copper and a copper alloy, and the mass percent content of copper in the copper alloy is 80 wt% or more.

7. 7. The negative electrode current collector according to claim 6, wherein the copper alloy has a copper element content of 90 wt% or more by mass percent.

8. The negative electrode current collector according to claim 1 , wherein the copper-based conductive layer is a vapor-deposited layer or an electroplated layer.

9. the support layer comprises one or more polymeric materials; The negative electrode current collector according to any one of claims 1 to 8, wherein the polymer material is one or more selected from polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, ethylene-propylene rubber, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, sodium polystyrene sulfonate, polyacetylene, silicone rubber, polyoxymethylene, polyphenylene ether, polyphenylene sulfide, polyethylene glycol, polysulfur nitride, polyphenyl, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, derivatives of the above materials, crosslinked products of the above materials, and copolymers of the above materials.

10. The negative electrode current collector according to claim 1 , wherein the support layer further comprises an additive, the additive comprising one or more of a metallic material and an inorganic non-metallic material.

11. The negative electrode current collector according to claim 1 , wherein the protective layer contains one or more of a metal, a metal oxide, and conductive carbon.

12. 12. The negative electrode current collector according to claim 11, wherein the protective layer contains one or more of nickel, chromium, a nickel-based alloy, a copper-based alloy, aluminum oxide, cobalt oxide, chromium oxide, nickel oxide, graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

13. The thickness D of the protective layer ３ 1 nm≦D ３ ≦200 nm, and D ３ ≦0.1D １ The negative electrode current collector according to claim 1 , which satisfies the above condition.

14. 14. A negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode current collector being the negative electrode current collector according to claim 1.

15. 15. An electrochemical device comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the negative electrode sheet is the negative electrode sheet according to claim 14.

16. An apparatus comprising the electrochemical device of claim 15.

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