Electrochemical device

Abstract

The electrochemical device comprises a negative pole piece, the negative pole piece comprises a negative current collector and a negative active material layer arranged on the negative current collector, and the negative current collector comprises a supporting layer and a metal conductive layer arranged on at least one of two opposite surfaces in the thickness direction of the supporting layer; wherein the density of the supporting layer is smaller than that of the metal conducting layer; the supporting layer comprises one or more of a high polymer material and a high polymer-based composite material, the elongation at break of the supporting layer is greater than or equal to the elongation at break of the metal conductive layer, and the Young modulus E of the supporting layer is greater than or equal to 1.9 GPa; the metal conducting layer is made of one or more of copper, copper alloy, nickel and nickel alloy, the density of the metal conducting layer is 8.0 g / cm < 3 >-8.96 g / cm < 3 >, and the thickness D1 of the metal conducting layer is larger than or equal to 300 nm and smaller than or equal to 2 microns. The electrochemical device provided by the invention has relatively high weight energy density and good electrochemical performance at the same time.

Description

[0001] This application is a divisional application based on the invention with application number 201910586045.4, application date July 1, 2019, applicant being Contemporary Amperex Technology Co., Ltd., and invention name being “Negative electrode current collector, negative electrode sheet and electrochemical device”. Technical Field

[0002] The present invention belongs to the technical field of electrochemical devices, and in particular relates to an electrochemical device. Background Art

[0003] Secondary batteries are widely used in electric vehicles and consumer electronics due to their advantages such as high energy density, high output power, long cycle life and low environmental pollution. As the application scope of secondary batteries continues to expand, people have also put forward higher and higher requirements for the energy density of secondary batteries. The metal current collectors used in the existing technology have a large thickness (usually 18μm to 30μm) and a high density, resulting in a low energy density of the secondary battery, which cannot meet the increasingly high requirements of the market. Therefore, how to reduce the weight of the current collector to increase the energy density of the secondary battery, while ensuring that the current collector has good conductivity and current collection performance, has become a technical problem that needs to be solved.

[0004] Based on this, this application is filed. Summary of the Invention

[0005] An embodiment of the present invention provides an electrochemical device that simultaneously achieves high gravimetric energy density and good electrochemical performance.

[0006] The electrochemical device provided by an embodiment of the present invention includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode current collector includes a support layer and a metal conductive layer provided on at least one of two surfaces opposite to each other in the thickness direction of the support layer itself; wherein the density of the support layer is less than the density of the metal conductive layer; the support layer includes one or more of a polymer material and a polymer-based composite material, the elongation at break of the support layer is greater than or equal to the elongation at break of the metal conductive layer, and the Young's modulus E of the support layer is E≥1.9GPa; the material of the metal conductive layer is one or more of copper, copper alloy, nickel, and nickel alloy, and the density of the metal conductive layer is 8.0g / cm 3 ~8.96g / cm 3 , and the thickness D1 of the metal conductive layer is 300nm≤D1≤2μm.

[0007] The negative electrode current collector has a thin metal conductive layer disposed on at least one surface of a support layer, and the density of the support layer is less than that of the metal conductive layer. Therefore, compared to conventional metal current collectors, the weight of the negative electrode current collector can be significantly reduced, thereby significantly improving the weight energy density of the electrochemical device. The support layer comprises one or more polymer materials and polymer-based composite materials. The elongation at break of the support layer is greater than or equal to the elongation at break of the metal conductive layer, thereby better preventing the negative electrode current collector from breaking. The Young's modulus E of the support layer is E ≥ 1.9 GPa. During the processing of the negative electrode current collector, the support layer does not undergo excessive extension or deformation, thereby preventing the support layer from breaking. It also helps to improve the bonding strength between the support layer and the metal conductive layer, making it less likely to separate, thus providing the negative electrode current collector with high mechanical stability and operational stability, thereby enabling the electrochemical device to have high electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0009] Figure 1 A schematic structural diagram of a negative electrode current collector provided by one embodiment of the present invention is shown.

[0010] Figure 2 A schematic structural diagram of a negative electrode current collector provided by another embodiment of the present invention is shown.

[0011] Figure 3 A schematic structural diagram of a negative electrode current collector provided by another embodiment of the present invention is shown.

[0012] Figure 4 A schematic structural diagram of a negative electrode current collector provided by another embodiment of the present invention is shown.

[0013] Figure 5 A schematic structural diagram of a negative electrode current collector provided by another embodiment of the present invention is shown.

[0014] Figure 6 A schematic structural diagram of a negative electrode current collector provided by another embodiment of the present invention is shown.

[0015] Figure 7 A schematic structural diagram of a negative electrode current collector provided by another embodiment of the present invention is shown.

[0016] Figure 8 A schematic structural diagram of a negative electrode current collector provided by another embodiment of the present invention is shown.

[0017] Figure 9 A schematic structural diagram of a negative electrode current collector provided by another embodiment of the present invention is shown.

[0018] Marking Description:

[0019] 10. Negative electrode current collector;

[0020] 101, support layer;

[0021] 101a, first surface; 101b, second surface;

[0022] 1011, first sublayer; 1012, second sublayer; 1013, third sublayer;

[0023] 102. Metal conductive layer;

[0024] 103. Protective layer. DETAILED DESCRIPTION

[0025] In order to make the invention purpose, technical scheme and beneficial technical effect of the present invention clearer, the present invention is further described in detail below with reference to the embodiments. It should be understood that the embodiments described in this specification are only for explaining the present invention and are not intended to limit the present invention.

[0026] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and similarly, any upper limit can be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, each point or individual value between the endpoints of a range is included in the range. Thus, each point or individual value can serve as its own lower limit or upper limit and be combined with any other point or individual value, or with other lower limits or upper limits, to form an unspecified range.

[0027] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number themselves, and “a variety” in “one or more” means more than two.

[0028] The above summary of the invention is not intended to describe every disclosed embodiment or every implementation of the present invention. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided through a series of examples, which can be used in various combinations. In each example, the enumeration is intended only as a representative group and should not be construed as exhaustive.

[0029] negative electrode current collector

[0030] The first aspect of the embodiment of the present invention provides a negative electrode current collector 10. Figure 1and Figure 2 The negative electrode current collector 10 includes a stacked support layer 101 and a metal conductive layer 102. The support layer 101 has a first surface 101a and a second surface 101b opposite to each other in the thickness direction. The metal conductive layer 102 is disposed on either or both of the first surface 101a and the second surface 101b of the support layer 101.

[0031] The density of the support layer 101 is less than that of the metal conductive layer 102; the density of the metal conductive layer 102 is 8.0 g / cm 3 ~8.96g / cm 3 ; The thickness D1 of the metal conductive layer 102 is 300nm≤D1≤2μm; and when the tensile strain of the negative electrode current collector 10 is 2.5%, the sheet resistance growth rate T of the metal conductive layer 102 is T≤5%.

[0032] The negative electrode current collector 10 of the embodiment of the present invention has a metal conductive layer 102 with a smaller thickness disposed on at least one surface of the support layer 101, and the density of the support layer 101 is less than the density of the metal conductive layer 102. Therefore, compared with traditional metal current collectors (such as copper foil), the weight of the negative electrode current collector 10 can be significantly reduced, thereby significantly improving the weight energy density of the electrochemical device.

[0033] In addition, the negative electrode current collector 10 may be stretched during the processing and use of the negative electrode sheet and the electrochemical device, such as during the sheet rolling or battery expansion process. 3 ~8.96g / cm 3 , and when the tensile strain of the negative electrode current collector 10 is 2.5%, the sheet resistance growth rate T of the metal conductive layer 102 is T≤5%, which can effectively prevent the metal conductive layer 102 with a smaller thickness from rapidly increasing in resistance due to tensile deformation, thereby ensuring that the negative electrode current collector 10 has good conductivity and current collection properties, so that the electrochemical device has low impedance and small negative electrode polarization, thereby enabling the electrochemical device to have both high electrochemical performance, including high rate performance and cycle performance.

[0034] Therefore, by using the negative electrode current collector 10 according to the embodiment of the present invention, the electrochemical device can have both high gravimetric energy density and good electrochemical performance.

[0035] In some optional embodiments, the thickness D1 of the metal conductive layer 102 can be 2 μm, 1.8 μm, 1.5 μm, 1.2 μm, 1 μm, 900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 450 nm, 400 nm, 350 nm, or 300 nm. The thickness D1 of the metal conductive layer 102 can range from any two of the aforementioned values. Preferably, D1 is 500 nm ≤ D1 ≤ 1.5 μm.

[0036] The thickness of the metal conductive layer 102 is less than 2 μm, preferably less than 1.5 μm. This is significantly thinner than the thickness of conventional metal current collectors (such as copper foil). Furthermore, the density of the support layer 101 is less than that of the metal conductive layer 102, thereby significantly improving the gravimetric energy density of the electrochemical device. The thickness of the metal conductive layer 102 is greater than 300 nm, preferably greater than 500 nm, which facilitates the negative electrode current collector 10 to have excellent electrical conductivity and current collection properties. Furthermore, the negative electrode current collector 10 is less susceptible to damage during processing and use, resulting in good mechanical stability and a long service life.

[0037] In some optional embodiments, the density of the metal conductive layer 102 may be 8.0 g / cm 3 、8.1g / cm 3 、8.2g / cm 3 、8.3g / cm 3 、8.4g / cm 3 , 8.5g / cm 3 、8.6g / cm 3 , 8.7g / cm 3 , 8.8g / cm 3 、8.9g / cm 3 or 8.96g / cm 3 wait.

[0038] In some optional embodiments, when the tensile strain of the negative electrode current collector 10 is 2.5%, the sheet resistance growth rate T of the metallic conductive layer 102 may be 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1%, 0.5%, or 0. Preferably, T ≤ 2.5%. More preferably, T ≤ 1%.

[0039] In the negative electrode current collector 10 of the embodiment of the present invention, the thickness D2 of the support layer 101 is preferably 1 μm ≤ D2 ≤ 20 μm, and can be, for example, 1 μm, 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm. The thickness D2 of the support layer 101 can range from any two of the aforementioned values. Preferably, D2 is 2 μm ≤ D2 ≤ 10 μm. More preferably, D2 is 2 μm ≤ D2 ≤ 6 μm.

[0040] The thickness D2 of the support layer 101 is preferably 1 μm or greater, more preferably 2 μm or greater. This helps ensure that the support layer 101 has sufficient mechanical strength, making it less susceptible to breakage during processing and use of the negative electrode current collector 10. It also provides good support and protection for the metal conductive layer 102, ensuring good mechanical stability and a long service life for the negative electrode current collector 10. The thickness D2 of the support layer 101 is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 6 μm or less, which helps reduce the size and weight of the electrochemical device and improve the energy density of the electrochemical device.

[0041] In some embodiments, preferably, the volume resistivity of the support layer 101 is greater than or equal to 1.0×10 -5 Since the volume resistivity of the support layer 101 is relatively high, in the event of an abnormality such as nail penetration in the electrochemical device, the short-circuit resistance of the electrochemical device when an internal short circuit occurs can be increased, thereby improving the safety performance of the electrochemical device.

[0042] In some embodiments, preferably, the elongation at break of the support layer 101 is greater than or equal to the elongation at break of the metal conductive layer 102 , thereby better preventing the negative electrode current collector 10 from breaking.

[0043] Optionally, the elongation at break of the support layer 101 is greater than or equal to 5%. Preferably, the elongation at break of the support layer 101 is greater than or equal to 10%.

[0044] In some embodiments, the Young's modulus E of the support layer 101 is preferably E ≥ 1.9 GPa. The support layer 101 has appropriate rigidity to meet its supporting and protective functions for the metal conductive layer 102, thereby ensuring the overall strength of the negative electrode current collector 10. During the processing of the negative electrode current collector 100, the support layer 101 does not undergo excessive expansion or deformation, which can prevent the support layer 101 from breaking. It also helps to improve the bonding strength between the support layer 101 and the metal conductive layer 102, making it less likely to separate. This gives the negative electrode current collector 100 high mechanical stability and operational stability, thereby enabling the electrochemical device to have high electrochemical performance, such as a longer cycle life.

[0045] Furthermore, the Young's modulus E of the support layer 101 is 1.9 GPa≤E≤20 GPa, so that the support layer 101 has both rigidity and a certain ability to withstand deformation, and can be flexible for winding during the processing and use of the negative electrode current collector 10, thereby better preventing the occurrence of belt breakage.

[0046] In some optional embodiments, the Young's modulus E of the support layer 101 can be 1.9 GPa, 2.5 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. The Young's modulus E of the support layer 101 can range from any two of the aforementioned values.

[0047] In some embodiments, the support layer 101 preferably comprises one or more polymer materials and polymer-based composite materials. Since the density of polymer materials and polymer-based composite materials is significantly lower than that of metals, the weight of the negative electrode current collector 10 is significantly reduced compared to traditional metal current collectors, thereby increasing the weight energy density of the electrochemical device.

[0048] The above-mentioned polymer materials are, for example, one or more of polyamide (PA), polyimide (PI), polyesters, polyolefins, polyalkynes, siloxane polymers, polyethers, polyols, polysulfones, polysaccharide polymers, amino acid polymers, polysulfur nitrides, aromatic ring polymers, aromatic heterocyclic polymers, epoxy resins, phenolic resins, their derivatives, their cross-linked products and their copolymers.

[0049] Furthermore, polymer materials include polycaprolactam (commonly known as nylon 6), polyhexamethylene adipamide (commonly known as nylon 66), polyparaphenylene terephthalamide (PPTA), polyisophenylene terephthalamide (PMIA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polycarbonate (PC), polyethylene (PE), polypropylene (PP), polypropylene (PPE), polyvinyl alcohol (PVA), polystyrene (PS), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTEE), sodium polystyrene sulfonate (PSS), polyacetylene, polypyrrole (PPy), polyaniline (PAN), polythiophene (PT), polypyridine (PPY), silicone rubber ( rubber), polyoxymethylene (POM), polyphenylene, polyphenylene ether (PPO), polyphenylene sulfide (PPS), polyethylene glycol (PEG), acrylonitrile-butadiene-styrene copolymer (ABS), cellulose, starch, protein, derivatives thereof, cross-linked products thereof and copolymers thereof.

[0050] The polymer-based composite material may include, for example, the aforementioned polymer material and an additive. The additive can be used to adjust the volume resistivity, elongation at break, and Young's modulus of the polymer material. The additive may be one or more of a metallic material and an inorganic non-metallic material.

[0051] The metal material additive is, for example, one or more of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, iron, iron alloy, silver, and silver alloy.

[0052] Inorganic non-metallic materials, such as additives, are one or more of carbon-based materials, aluminum oxide, silicon dioxide, silicon nitride, silicon carbide, boron nitride, silicates, and titanium oxide. Further examples include one or more of glass materials, ceramic materials, and ceramic composite materials. Examples of carbon-based materials include one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0053] In some embodiments, the additive may be a carbon-based material coated with a metal material, such as one or more of nickel-coated graphite powder and nickel-coated carbon fiber.

[0054] Preferably, the support layer 101 is made of one or more insulating polymer materials and insulating polymer-based composite materials. The support layer 101 has a high volume resistivity, which can improve the safety performance of the electrochemical device.

[0055] More preferably, the support layer 101 is made of one or more of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), sodium polystyrene sulfonate (PSS) and polyimide (PI).

[0056] In the negative electrode current collector 10 of the embodiment of the present invention, the support layer 101 may be a single-layer structure, or a composite layer structure of two or more layers, such as two layers, three layers, or four layers.

[0057] As an example of the support layer 101 of the composite layer structure, please refer to Figure 3 The support layer 101 is a composite layer structure formed by stacking a first sub-layer 1011, a second sub-layer 1012, and a third sub-layer 1013. The composite layer structure of the support layer 101 has a first surface 101a and a second surface 101b opposite to each other, and the metal conductive layer 102 is stacked on the first surface 101a and the second surface 101b of the support layer 101. Of course, the metal conductive layer 102 can be disposed only on the first surface 101a of the support layer 101, or only on the second surface 101b of the support layer 101.

[0058] When the support layer 101 is a composite layer structure of two or more layers, the materials of each sub-layer may be the same or different.

[0059] In some embodiments, the material of the metal conductive layer 102 is one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, preferably one or more of copper, copper alloy, nickel, nickel alloy, titanium and silver, more preferably one or more of copper and copper alloy.

[0060] The nickel alloy is, for example, a nickel-copper alloy.

[0061] The weight percentage of copper element in the copper alloy is preferably above 90%.

[0062] In some embodiments, the volume resistivity of the metal conductive layer 102 is preferably 1.3×10 -8 Ω·m~3.3×10 -8 Ω·m, which is beneficial to improving the conductivity and current collection performance of the negative electrode current collector 10, thereby improving the performance of the electrochemical device, wherein the rate performance and cycle performance of the electrochemical device are improved. More preferably, the volume resistivity of the metal conductive layer 102 is 1.8×10 -8 Ω·m~2.3×10 -8 Ω·m.

[0063] In some embodiments, please refer to Figures 4 to 9 The negative electrode current collector 10 may also optionally include a protective layer 103. Specifically, the metal conductive layer 102 includes two opposing surfaces along its thickness direction. The protective layer 103 is laminated on either or both of the two surfaces of the metal conductive layer 102 to protect the metal conductive layer 102 from chemical corrosion or mechanical damage, thereby ensuring the operational stability and service life of the negative electrode current collector 10, thereby improving the electrochemical performance of the electrochemical device. Furthermore, the protective layer 103 can enhance the mechanical strength of the negative electrode current collector 10.

[0064] The material of the protective layer 103 can be one or more of metal, metal oxide and conductive carbon. Among them, the protective layer 103 made of metal material is a metal protective layer; the protective layer 103 made of metal oxide material is a metal oxide protective layer.

[0065] The above-mentioned metals are, for example, one or more of nickel, chromium, nickel-based alloys and copper-based alloys. The aforementioned nickel-based alloy is an alloy composed of pure nickel as a matrix and one or more other elements, preferably a nickel-chromium alloy. Nickel-chromium alloy is an alloy formed by metallic nickel and metallic chromium. Optionally, the weight ratio of nickel to chromium in the nickel-chromium alloy is 1:99 to 99:1, such as 9:1. The aforementioned copper-based alloy is an alloy composed of pure copper as a matrix and one or more other elements, preferably a nickel-copper alloy. Optionally, the weight ratio of nickel to copper in the nickel-copper alloy is 1:99 to 99:1, such as 9:1.

[0066] The metal oxide is, for example, one or more of aluminum oxide, cobalt oxide, chromium oxide, and nickel oxide.

[0067] The conductive carbon mentioned above is, for example, one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, preferably one or more of carbon black, carbon nanotubes, acetylene black, and graphene.

[0068] For some examples, see Figure 4 and Figure 5 The negative electrode current collector 10 includes a stacked support layer 101, a metal conductive layer 102, and a protective layer 103. The support layer 101 has a first surface 101a and a second surface 101b opposite to each other in the thickness direction. The metal conductive layer 102 is stacked on at least one of the first surface 101a and the second surface 101b of the support layer 101. The protective layer 103 is stacked on the surface of the metal conductive layer 102 facing away from the support layer 101.

[0069] A protective layer 103 (referred to as an upper protective layer) is provided on the surface of the metal conductive layer 102 facing away from the support layer 101 to protect the metal conductive layer 102 from chemical corrosion and mechanical damage. It can also improve the interface between the negative electrode current collector 10 and the negative electrode active material layer, thereby increasing the bonding force between the negative electrode current collector 10 and the negative electrode active material layer.

[0070] In some embodiments, the upper protective layer of the negative electrode current collector 10 can 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 better corrosion resistance, and can better protect the metal conductive layer 102.

[0071] Furthermore, the upper protective layer of the negative electrode current collector 10 is preferably a metal protective layer, which can improve the conductivity of the negative electrode current collector 10, reduce battery polarization, reduce the risk of lithium plating on the negative electrode, and improve the cycle performance and safety performance of the electrochemical device; more preferably, it is a double-layer protective layer, that is, a composite layer formed by a metal protective layer and a metal oxide protective layer, wherein preferably, the metal protective layer is arranged on the surface of the metal conductive layer 102 facing away from the support layer 101, and the metal oxide protective layer is arranged on the surface of the metal protective layer facing away from the support layer 101, so that the conductivity and corrosion resistance of the negative electrode current collector 10, as well as the interface between the metal conductive layer 102 and the negative electrode active material layer, etc., can be improved at the same time, and a negative electrode current collector 10 with better comprehensive performance can be obtained.

[0072] For some other examples, see Figure 6 and Figure 7 The negative electrode current collector 10 includes a stacked support layer 101, a metal conductive layer 102, and a protective layer 103. The support layer 101 has a first surface 101a and a second surface 101b opposite to each other in the thickness direction. The metal conductive layer 102 is stacked on at least one of the first surface 101a and the second surface 101b of the support layer 101. The protective layer 103 is stacked on the surface of the metal conductive layer 102 facing the support layer 101.

[0073] A protective layer 103 (referred to as the lower protective layer for short) is provided on the surface of the metal conductive layer 102 facing the support layer 101. The lower protective layer not only protects the metal conductive layer 102 from chemical corrosion and mechanical damage, but also improves the bonding force between the metal conductive layer 102 and the support layer 101, prevents the metal conductive layer 102 from separating from the support layer 101, and improves the supporting and protective effect of the support layer 101 on the metal conductive layer 102.

[0074] Optionally, the lower protective layer is a metal oxide or a metal protective layer. The metal oxide protective layer has high corrosion resistance and a large specific surface area, which can further improve the interfacial bonding force between the metal conductive layer 102 and the support layer 101, so that the lower protective layer can better protect the metal conductive layer 102, improve the performance of the electrochemical device, and the metal oxide protective layer has higher hardness and better mechanical strength, which is more conducive to improving the strength of the negative electrode current collector 10. The metal protective layer can protect the metal conductive layer 102 from chemical corrosion and mechanical damage while also improving the conductivity of the negative electrode current collector 10, reducing battery polarization, reducing the risk of negative electrode lithium plating, and improving the cycle performance and safety performance of the electrochemical device. Therefore, the lower protective layer of the negative electrode current collector 10 is preferably a metal protective layer.

[0075] For further examples, see Figure 8 and Figure 9 The negative electrode current collector 10 includes a stacked support layer 101, a metal conductive layer 102, and a protective layer 103. The support layer 101 has a first surface 101a and a second surface 101b opposite to each other in the thickness direction. The metal conductive layer 102 is stacked on at least one of the first surface 101a and the second surface 101b of the support layer 101. The protective layer 103 is stacked on the surface of the metal conductive layer 102 facing away from the support layer 101 and the surface facing the support layer 101.

[0076] Protective layers 103 are provided on both surfaces of the metal conductive layer 102 , that is, an upper protective layer and a lower protective layer are provided on the metal conductive layer 102 respectively, so as to more fully protect the metal conductive layer 102 and make the negative electrode current collector 10 have higher comprehensive performance.

[0077] It is understandable that the materials of the protection layers 103 on the two surfaces of the metal conductive layer 102 can be the same or different, and the thicknesses can be the same or different.

[0078] Preferably, the thickness D3 of the protective layer 103 is 1 nm ≤ D3 ≤ 200 nm, and D3 ≤ 0.1 D1. When the thickness D3 of the protective layer 103 is within the above range, it can effectively protect the metal conductive layer 102 and enable the electrochemical device to have a higher energy density.

[0079] In some embodiments, the thickness D3 of the protective layer 103 can 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, 20 nm, 18 nm, 15 nm, 12 nm, 10 nm, 8 nm, 5 nm, 2 nm, 1 nm, etc. The thickness D3 of the protective layer 103 can range from any two of the aforementioned values. Preferably, 5 nm ≤ D3 ≤ 200 nm. More preferably, 10 nm ≤ D3 ≤ 200 nm.

[0080] Furthermore, when the protective layer 103 is provided on both surfaces of the metal conductive layer 102, that is, an upper protective layer and a lower protective layer are provided on the two surfaces of the metal conductive layer 102, respectively, the thickness D of the upper protective layer is a 1nm≤D a ≤200nm, and D a ≤0.1D1, thickness of lower protective layer D b 1nm≤D b ≤200nm, and D b ≤0.1D1. Preferably, D a >D b, which is beneficial for the protective layer 103 to play a good protective role on the metal conductive layer 102 and enables the electrochemical device to have a higher weight energy density. More preferably, 0.5D a ≤D b ≤0.8D a .

[0081] The metal conductive layer 102 can be formed on the support layer 101 by at least one of mechanical rolling, bonding, vapor deposition, electroless plating, and electroplating, among which vapor deposition or electroplating is preferred, that is, the metal conductive layer 102 is preferably a vapor deposition layer or an electroplating layer, which can better achieve a close bond between the metal conductive layer 102 and the support layer 101, and effectively play the supporting role of the support layer 101 on the metal conductive layer 102.

[0082] Preferably, the bonding force F between the support layer 101 and the metal conductive layer 102 is ≥ 100 N / m, more preferably F ≥ 400 N / m.

[0083] For example, the metal conductive layer 102 is formed on the support layer 101 by vapor deposition. By reasonably controlling the vapor deposition process conditions, such as the deposition temperature, deposition rate, and the atmosphere conditions of the deposition chamber, the sheet resistance growth rate of the metal conductive layer 102 can meet the requirements described above when the negative electrode current collector 10 is stretched.

[0084] The vapor deposition method is preferably physical vapor deposition (PVD). The physical vapor deposition method is preferably at least one of evaporation and sputtering. The evaporation method is preferably at least one of vacuum evaporation, thermal evaporation, and electron beam evaporation. The sputtering method is preferably magnetron sputtering.

[0085] As an example, the metal conductive layer 102 is formed by vacuum evaporation, including: placing the support layer 101 that has been surface cleaned in a vacuum coating chamber, melting and evaporating the high-purity metal wire in the metal evaporation chamber at a high temperature of 1300°C to 2000°C, and the evaporated metal passing through the cooling system in the vacuum coating chamber, and finally deposited on the support layer 101 to form the metal conductive layer 102.

[0086] The process of forming the metal conductive layer 102 by mechanical rolling may include: placing the metal sheet in a mechanical roller, rolling it to a predetermined thickness by applying a pressure of 20t to 40t, then placing it on the surface of the support layer 101 that has been surface cleaned, and then placing the two in a mechanical roller and applying a pressure of 30t to 50t to tightly combine the two.

[0087] The process of forming the metal conductive layer 102 by bonding may include: placing a metal sheet in a mechanical roller and rolling it to a predetermined thickness by applying a pressure of 20t to 40t; then coating the surface of the support layer 101 after the surface cleaning treatment with a mixed solution of polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP); finally, bonding the metal conductive layer 102 of the predetermined thickness to the surface of the support layer 101 and drying it to ensure that the two are tightly bonded.

[0088] When the negative electrode current collector 10 has a protective layer 103, the protective layer 103 can be formed on the metal conductive layer 102 by at least one of vapor deposition, in-situ formation, and coating. The vapor deposition method can be the vapor deposition method described above. The in-situ formation method is preferably an in-situ passivation method, i.e., a method of forming a metal oxide passivation layer in situ on the metal surface. The coating method is preferably at least one of roll coating, extrusion coating, blade coating, and gravure coating.

[0089] Preferably, the protective layer 103 is formed on the metal conductive layer 102 by at least one of a vapor deposition method and an in-situ formation method, which is conducive to having a higher bonding force between the metal conductive layer 102 and the protective layer 103, thereby better exerting the protective effect of the protective layer 102 on the negative electrode current collector 10 and ensuring that the negative electrode current collector 10 has higher working performance.

[0090] In the embodiment of the present invention, the density of the metal conductive layer can be measured by methods known in the art. As an example, the area of ​​the metal conductive layer is 10 cm 2 The negative electrode current collector (wherein the metal conductive layer is copper) is weighed with a balance accurate to 0.0001g, recorded as m1, in g, and the thickness at 20 locations is measured with a caliper, and the average value is taken, recorded as d1, in μm. The weighed negative electrode current collector is soaked in a 1mol / L FeCl3 aqueous solution for 12 hours. After the metal conductive layer is completely dissolved, the supporting layer is removed, rinsed with deionized water 5 times, and baked at 100°C for 20 minutes. After that, its mass is weighed with the same balance, recorded as m2, in g, and the thickness at 20 locations is measured with the same caliper, and the average value is taken, recorded as d2, in μm. The density of the metal conductive layer is calculated according to the following formula, in g / cm 3 .

[0091]

[0092] Take 5 pieces of negative electrode current collectors of the same size and test the density of the metal conductive layer respectively, and take the average value of the results.

[0093] The tensile strain of the negative electrode current collector is set to ε, then ε=ΔL / L×100%, where ΔL is the elongation of the negative electrode current collector caused by stretching, and L is the original length of the negative electrode current collector, that is, the length before being stretched.

[0094] When the tensile strain ε of the negative electrode collector is 2.5%, the sheet resistance growth rate T of the metal conductive layer can be determined by methods known in the art. As an example, the negative electrode collector is cut into a sample of 20mm×200mm, and the four-probe method is used to test the sheet resistance of the central area of ​​the sample, which is recorded as R1. Then, the central area of ​​the sample is stretched using a high-speed rail tensile testing machine, the initial position is set, and the sample length between the clamps is 50mm. The sample is stretched at a speed of 50mm / min, and the stretching distance is 2.5% of the original length of the sample. After that, the stretched sample is removed, and the sheet resistance of the metal conductive layer between the clamps is tested, which is recorded as R2. According to the formula T=(R2-R1) / R1×100%, the sheet resistance growth rate T of the metal conductive layer when the tensile strain of the negative electrode collector is 2.5% is calculated.

[0095] The four-probe method for measuring the sheet resistance of the metal conductive layer is as follows: using an RTS-9 dual-electric four-probe tester, the test environment is: room temperature 23±2°C, 0.1MPa, relative humidity ≤65%. During the test, the sample surface is cleaned and placed horizontally on the test bench. The four-probe tester is lowered to ensure good contact with the metal conductive layer surface. The automatic test mode is then adjusted to calibrate the sample current range. The sheet resistance is measured at the appropriate current range, and 8 to 10 data points are collected from the same sample for data measurement accuracy and error analysis. The average value is recorded as the sheet resistance value of the metal conductive layer.

[0096] The volume resistivity of the metal conductive layer is set to ρ, then ρ=R S ×d, where ρ is in Ω·m; R S is the square resistance of the metal conductive layer, in Ω; d is the thickness of the metal conductive layer in m. The square resistance R of the metal conductive layer can be measured by referring to the four-probe method described above. S , I will not go into details here.

[0097] The volume resistivity of the support layer is the volume resistivity at 20°C and can be measured using methods known in the art. As an example, the test is conducted in a constant temperature, normal pressure, low humidity room (20°C, 0.1 MPa, RH ≤ 20%). A 20mm diameter disc support layer sample is prepared (the sample size can be adjusted according to the actual size of the test instrument). The test is conducted using the three-electrode surface resistivity method (GB T1410-2006) using an insulation resistance tester (accuracy 10Ω). The test method is as follows: The disc sample is placed between two electrodes and a potential difference is applied between the two electrodes. The generated current will be distributed in the body of the disc sample and measured by a picoammeter or electrometer to avoid measurement errors caused by including surface leakage current in the measurement. The reading is the volume resistivity, in Ω·m.

[0098] The elongation at break of the support layer can be measured using methods known in the art. As an example, the support layer is cut into 15 mm × 200 mm samples and subjected to a tensile test using a high-speed rail tensile tester at room temperature and pressure (25°C, 0.1 MPa). The initial position is set so that the sample length between the clamps is 50 mm. The tensile speed is 50 mm / min. The device displacement y (mm) at the time of tensile failure is recorded, and the elongation at break is calculated as (y / 50) × 100%. The elongation at break of the metal conductive layer can be conveniently measured using the same method.

[0099] The Young's modulus E of the support layer can be measured using methods known in the art. As an example, the support layer is cut into a 15 mm × 200 mm sample, and the thickness of the sample l (μm) is measured with a micrometer. A tensile test is performed using a high-speed rail tensile tester at room temperature and pressure (25°C, 0.1 MPa). The initial position is set so that the sample is 50 mm long between the clamps, and the tensile speed is 50 mm / min. The load Q (N) and the equipment displacement z (mm) are recorded until the fracture. Then, stress ξ (GPa) = Q / (15 × l), strain ξ = z / 50, and a stress-strain curve is plotted. The slope of the initial linear region curve is taken. The Young's modulus E is the slope of the curve.

[0100] The bonding force F between the support layer and the metal conductive layer can be tested by methods known in the art. For example, a negative electrode current collector with a metal conductive layer arranged on one side of the support layer is selected as the sample to be tested, and the width h is 0.02m. At room temperature and pressure (25°C, 0.1MPa), 3M double-sided tape is used to evenly stick it on a stainless steel plate. The sample to be tested is then evenly stuck on the double-sided tape. The metal conductive layer of the sample to be tested is peeled off from the support layer using a high-speed rail tensile testing machine. According to the data graph of tension and displacement, the maximum tension x (N) is read, and the bonding force F (N / m) between the metal conductive layer and the support layer is calculated according to F=x / h.

[0101] Negative electrode

[0102] A second aspect of the embodiments of the present invention provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode active material layer stacked together, wherein the negative electrode current collector is the negative electrode current collector 10 of the first aspect of the embodiments of the present invention.

[0103] The negative electrode sheet of the embodiment of the present invention has higher weight energy density and better electrochemical performance compared with traditional negative electrode sheets due to the use of the negative electrode current collector 10 of the first aspect of the embodiment of the present invention.

[0104] As an example, the negative electrode plate includes a stacked support layer 101, a metal conductive layer 102 and a negative electrode active material layer, the support layer 101 includes a first surface 101a and a second surface 101b relative to each other, the metal conductive layer 102 is stacked on the first surface 101a and / or the second surface 101b of the support layer 101, and the negative electrode active material layer is stacked on the surface of the metal conductive layer 102 facing away from the support layer 101.

[0105] The negative electrode active material layer of the negative electrode plate of the embodiment of the present invention can be made of negative electrode active materials known in the art. For example, the negative electrode active material used in lithium-ion secondary batteries can be one or more of metallic lithium, natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel lithium titanate, and Li-Al alloy.

[0106] Optionally, the negative electrode active material layer may further include a conductive agent, for example, one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0107] Optionally, the negative electrode active material layer may further include a binder. For example, the binder is one or more of 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).

[0108] The negative electrode sheet can be prepared according to conventional methods in the art. Typically, the negative electrode active material, along with an optional conductive agent and binder, are dispersed in a solvent, such as N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The slurry is then coated onto the negative electrode current collector. After drying and other steps, the negative electrode sheet is obtained.

[0109] electrochemical devices

[0110] In a third aspect of the embodiments of the present invention, an electrochemical device is provided. The electrochemical device includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The negative electrode sheet is the negative electrode sheet of the second aspect of the embodiments of the present invention.

[0111] The above-mentioned electrochemical device may be a lithium-ion secondary battery, a primary lithium battery, a sodium-ion battery, a magnesium-ion battery, etc., but is not limited thereto.

[0112] Since the electrochemical device uses the negative electrode sheet provided in the second aspect of the embodiments of the present invention, the electrochemical device of the embodiments of the present invention has a high weight energy density and good electrochemical performance.

[0113] The above-mentioned positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector.

[0114] The positive electrode current collector may be a metal foil or a porous metal foil including one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0115] The positive electrode active material layer may employ positive electrode active materials known in the art. For example, for the positive electrode active material of a lithium-ion secondary battery, it may be a lithium transition metal composite oxide, where the transition metal may be one or more of Mn, Fe, Ni, Co, Cr, Ti, Zn, V, Al, Zr, Ce, and Mg. The lithium transition metal composite oxide may also be doped with elements with high electronegativity, such as one or more of S, F, Cl, and I, which can endow the positive electrode active material with high structural stability and electrochemical performance. As an example, the lithium transition metal composite oxide is, for example, 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.

[0116] Optionally, the positive electrode active material layer may further include a conductive agent. As an example, the conductive agent is one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0117] Optionally, the positive electrode active material layer may further include a binder. For example, the binder is one or more of 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).

[0118] The positive electrode sheet can be prepared according to conventional methods in the art. Typically, the positive electrode active material, along with an optional conductive agent and binder, are dispersed in a solvent (e.g., NMP) to form a uniform positive electrode slurry. The positive electrode slurry is then coated onto the positive electrode current collector. After drying and other steps, the positive electrode sheet is obtained.

[0119] There is no particular limitation on the above-mentioned isolation membrane. Any known porous structure isolation membrane with electrochemical stability and chemical stability can be selected, for example, it can be a single-layer or multi-layer film of one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0120] The electrolyte solution includes an organic solvent and an electrolyte salt. The organic solvent, serving as a medium for transporting ions during the electrochemical reaction, can be any organic solvent known in the art for use in electrochemical device electrolytes. The electrolyte salt, serving as a source of ions, can be any electrolyte salt known in the art for use in electrochemical device electrolytes.

[0121] For example, the organic solvent used in lithium-ion secondary batteries can be one or more of 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 formate (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), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0122] For example, the electrolyte salt used in lithium-ion secondary batteries can be one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatophosphate) and LiTFOP (lithium tetrafluorooxalatophosphate).

[0123] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, to obtain a battery cell, or the battery cell can be obtained by winding; the battery cell is placed in a packaging shell, injected with electrolyte and sealed to prepare an electrochemical device.

[0124] Example

[0125] The following examples more particularly describe the present disclosure, and these examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0126] Preparation method

[0127] Preparation of negative electrode current collector

[0128] A support layer of predetermined thickness is selected and surface cleaned. The cleaned support layer is placed in a vacuum plating chamber. The 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 both surfaces of the support layer to form a conductive layer.

[0129] The negative electrode current collector can have different T values ​​by adjusting the material, thickness, density, preparation process conditions (such as vacuum degree, atmosphere, humidity, temperature, etc.) of the metal conductive layer, and adjusting the material and thickness of the support layer.

[0130] Preparation of negative electrode sheet

[0131] The negative electrode active material graphite, conductive carbon black, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber latex (SBR) are fully stirred and mixed in an appropriate amount of deionized water at a weight ratio of 96.5:1.0:1.0:1.5 to form a uniform negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying and other processes, a negative electrode sheet is obtained.

[0132] Conventional negative electrode current collector

[0133] Copper foil with a thickness of 8μm.

[0134] Preparation of conventional negative electrode sheets

[0135] Different from the negative electrode plate of the embodiment of the present invention, a conventional negative electrode current collector is used.

[0136] positive electrode current collector

[0137] Aluminum foil with a thickness of 12 μm.

[0138] Preparation of positive electrode

[0139] The positive electrode active material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), conductive carbon black, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent in a weight ratio of 93:2:5 to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying and other processes, the positive electrode sheet is obtained.

[0140] Preparation of electrolyte

[0141] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 were mixed uniformly to obtain an organic solvent, and then 1 mol / L LiPF6 was uniformly dissolved in the above organic solvent.

[0142] Preparation of lithium-ion secondary batteries

[0143] The positive electrode sheet, separator (PP / PE / PP composite film), and negative electrode sheet are stacked in sequence, then wound into a battery cell and placed in a packaging shell. The above-mentioned electrolyte is injected into the battery cell, and then it goes through sealing, standing, hot and cold pressing, and formation processes to obtain a lithium-ion secondary battery.

[0144] Test section

[0145] 1. Test the negative electrode current collector according to the test method described above.

[0146] 2. Battery performance test

[0147] (1) Cyclic performance test

[0148] At 45°C, charge the lithium-ion secondary battery at a constant current rate of 1C to 4.2V, then charge it at a constant voltage until the current is less than or equal to 0.05C, and then discharge it at a constant current rate of 1C to 2.8V. This is considered one charge-discharge cycle. The discharge capacity at this time is the discharge capacity of the first cycle. Perform the battery 1000 charge-discharge cycles according to the above method, and record the discharge capacity of the 1000th cycle.

[0149] Capacity retention of lithium-ion secondary battery after 1000 cycles at 45°C and 1C / 1C (%) = discharge capacity at 1000th cycle / discharge capacity at 1st cycle × 100%

[0150] (2) Rate performance test

[0151] At 25°C, the lithium-ion secondary battery was charged at a constant current rate of 1C to 4.2V, then charged at a constant voltage to a current less than or equal to 0.05C, and then discharged at a constant current rate of 1C to 3.0V. The 1C rate discharge capacity of the lithium-ion secondary battery was obtained by testing.

[0152] At 25°C, the lithium-ion secondary battery was charged at a constant current rate of 1C to 4.2V, then charged at a constant voltage to a current less than or equal to 0.05C, and then discharged at a constant current rate of 4C to 3.0V. The 4C rate discharge capacity of the lithium-ion secondary battery was obtained by testing.

[0153] Lithium-ion secondary battery 4C rate capacity retention rate (%) = 4C rate discharge capacity / 1C rate discharge capacity × 100%

[0154] Test results

[0155] 1. The role of the negative electrode current collector in improving the gravimetric energy density of electrochemical devices

[0156] Table 1

[0157]

[0158] In Table 1, the negative electrode current collector weight percentage is the percentage of the negative electrode current collector weight per unit area divided by the conventional negative electrode current collector weight per unit area.

[0159] Compared with the traditional copper foil negative electrode current collector, the weight of the negative electrode current collector of the present application is reduced to varying degrees, thereby improving the weight energy density of the battery.

[0160] 2. Electrical properties of the negative electrode current collector of this application

[0161] Table 2

[0162]

[0163]

[0164] In Table 2: The composition of the copper alloy is: copper 95wt%, nickel 5wt%;

[0165] The volume resistivity of the support layer is 2.1×10 14 Ω·m, and the thickness D2 of the support layer is 8 μm.

[0166] When the material, thickness, etc. of the metal conductive layer and the support layer are the same, negative electrode current collectors with different T values ​​can be obtained by adjusting the preparation conditions of the metal conductive layer.

[0167] The negative electrode current collectors listed in Table 2 were subjected to an overcurrent test. The overcurrent test method included cutting the negative electrode current collector into 100mm wide strips, applying an 80mm wide layer of negative electrode active material in the center of the strip, and rolling the strips to form negative electrode sheets. The rolled strips were then cut along the strips into 100mm x 30mm strips, with ten strips of each type being cut. During the test, the uncoated conductive areas on either side of the electrode sheet sample were connected to the positive and negative terminals of a charger / discharger. The charger / discharger was then set up to pass a 5A current through the electrode sheet. A pass was considered if the electrode sheet did not fuse after one hour, otherwise it was considered a failure. Ten samples were tested for each group, and the test results are shown in Table 3.

[0168] Table 3

[0169]

[0170]

[0171] As shown in Tables 2 and 3, when the tensile strain of the negative electrode current collector is 2.5%, the sheet resistance growth rate T of the metal conductive layer is no greater than 5%. At this point, the negative electrode current collector has good electrical performance, and the negative electrode sheet using this negative electrode current collector has good current flow performance after roll pressing. Otherwise, the negative electrode current collector has poor conductivity and is of little practical value in battery products. Preferably, when the tensile strain of the negative electrode current collector is 2.5%, the sheet resistance growth rate T of the metal conductive layer satisfies T≤2.5%. More preferably, T≤1%.

[0172] 3. Effect of protective layer on electrochemical performance of electrochemical devices

[0173] Table 4

[0174]

[0175] In Table 4: the negative electrode current collector is provided with a protective layer on the basis of the negative electrode current collector 6 in Table 1;

[0176] Nickel-based alloy contains: nickel, 90wt%; chromium, 10wt%;

[0177] The double protective layer includes a nickel protective layer with a thickness of 25 nm disposed on the surface of the metal conductive layer facing away from the support layer, and a nickel oxide protective layer with a thickness of 25 nm disposed on the surface of the nickel protective layer facing away from the support layer.

[0178] Table 5

[0179]

[0180] As shown in Table 5, the battery using the negative electrode current collector of the embodiment of the present application has good cycle life and rate performance, comparable to the cycle performance and rate performance of batteries using conventional negative electrode current collectors. This shows that the use of the negative electrode current collector of the embodiment of the present application does not have a significant adverse effect on the electrochemical performance of the negative electrode sheet and battery. In particular, the battery using the negative electrode current collector with a protective layer has further improved capacity retention after 1000 cycles at 45°C and 1C / 1C, as well as 4C rate capacity retention, indicating better battery reliability.

[0181] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. An electrochemical device, characterized in that The electrochemical device includes a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode current collector includes a support layer and a metal conductive layer disposed on at least one of two opposite surfaces of the support layer in a thickness direction; wherein, The density of the support layer is less than the density of the metal conductive layer; The support layer comprises one or more of a polymer material and a polymer-based composite material, the elongation at break of the support layer is greater than or equal to the elongation at break of the metal conductive layer, and the Young's modulus E of the support layer is E≥1.9 GPa; The material of the metal conductive layer is one or more of copper, copper alloy, nickel, and nickel alloy, and the density of the metal conductive layer is 8.0 g / cm 3 ~8.96g / cm 3 , and the thickness D1 of the metal conductive layer is 300nm≤D1≤2μm.

2. The electrochemical device according to claim 1, wherein The elongation at break of the support layer is greater than or equal to 5%. Preferably, the elongation at break of the support layer is greater than or equal to 10%.

3. The electrochemical device according to claim 1 or 2, characterized in that 1.9GPa≤E≤20GPa.

4. The electrochemical device according to any one of claims 1 to 3, characterized in that The material of the metal conductive layer is copper or a copper alloy, and the weight percentage of the copper element in the copper alloy is preferably above 90%.

5. The electrochemical device according to any one of claims 1 to 4, characterized in that The density of the metal conductive layer is 8.3 g / cm 3 ~8.96g / cm 3 , preferably 8.52 g / cm 3 ~8.96g / cm 3 and / or, The thickness D1 of the metal conductive layer is 500 nm ≤ D1 ≤ 1.5 μm.

6. The electrochemical device according to any one of claims 1 to 5, characterized in that When the tensile strain of the negative electrode current collector is 2.5%, the sheet resistance growth rate T of the metal conductive layer is T≤5%, preferably T≤2.5%, and more preferably T≤1%.

7. The electrochemical device according to any one of claims 1 to 6, characterized in that The volume resistivity of the metal conductive layer is 1.3×10 -8 Ω·m~3.3×10 -8 Ω·m, preferably 1.76×10 -8 Ω·m~2.77×10 -8 Ω·m, more preferably 1.76×10 -8 Ω·m~2.34×10 -8 Ω·m.

8. The electrochemical device according to any one of claims 1 to 7, characterized in that The bonding force F between the support layer and the metal conductive layer is ≥100 N / m, preferably F ≥400 N / m.

9. The electrochemical device according to any one of claims 1 to 8, characterized in that The metal conductive layer further comprises a protective layer disposed on at least one of two surfaces opposite to each other in a thickness direction of the metal conductive layer; The protective layer comprises one or more of metal, metal oxide and conductive carbon, preferably one or more of nickel, chromium, nickel-based alloy, 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; Preferably, the thickness D3 of the protective layer is 1 nm≤D3≤200 nm, and D3≤0.1D1.

10. The electrochemical device according to claim 9, characterized in that The protective layer comprises an upper protective layer provided on a surface of the metal conductive layer facing away from the support layer, and a lower protective layer provided on a surface of the metal conductive layer facing the support layer; The thickness D of the upper protective layer a 1nm≤D a ≤200nm, and D a ≤0.1D1, the thickness of the lower protective layer D b 1nm≤D b ≤200nm, and D b ≤0.1D1, the D a With D b Between satisfying D a >D b , preferably, 0.5D a ≤D b ≤0.8D a ; Preferably, the upper protective layer is a metal protective layer; Preferably, the lower protective layer is a metal protective layer; More preferably, the upper protective layer is a double-layer protective layer, comprising a metal protective layer disposed on the surface of the metal conductive layer facing away from the support layer, and a metal oxide protective layer disposed on the surface of the metal protective layer facing away from the support layer.

11. The electrochemical device according to any one of claims 1 to 10, characterized in that The thickness D2 of the support layer is 1 μm≤D2≤20 μm, preferably 2 μm≤D2≤10 μm, and more preferably 2 μm≤D2≤6 μm.

12. The electrochemical device according to any one of claims 1 to 11, characterized in that The polymer material is one or more of polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polypropylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, sodium polystyrene sulfonate, polyacetylene, silicone rubber, polyformaldehyde, polyphenylene oxide, polyphenylene sulfide, polyethylene glycol, polysulfur nitride polymer materials, polyphenylene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, derivatives thereof, crosslinked products thereof and copolymers thereof; and / or, The polymer-based composite material includes the polymer material and additives, and the additives include one or more of metal materials and inorganic non-metallic materials.

13. The electrochemical device according to any one of claims 1 to 12, characterized in that The metal conductive layer is a vapor deposition layer or an electroplating layer.

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