Composite current collector, its preparation method and secondary battery

Abstract

The present application relates to the technical field of secondary batteries, and particularly to a composite current collector, a preparation method thereof, and a secondary battery. The composite current collector includes a support layer, a safety coating, a protection coating, and a conductive layer that are stacked in sequence; the support layer includes a polymer material and a two-dimensional nanobelt material; the safety coating includes a binder and an inorganic foaming agent, and the thermal decomposition temperature of the inorganic foaming agent is 80°C to 130°C; the protection coating includes a high-entropy alloy material. The composite current collector provided by the present application has good electrical conductivity, high structural stability, and excellent safety performance, which can not only reduce the probability of thermal runaway of the battery at high temperatures, but also help improve the cycle performance of the battery under normal operating conditions.

Description

Technical Field

[0001] This application relates to the technical field of secondary batteries, and particularly to a composite current collector, a preparation method thereof, and a secondary battery. Background Art

[0002] The large-scale use of traditional fossil fuels has led to increasingly serious problems such as resource shortages and environmental pollution. It is of great significance to accelerate the transformation of the energy structure and develop clean and renewable new energy. Among them, as a secondary battery, lithium-ion batteries are widely used in the fields of 3C products, energy storage systems, and power batteries due to their high energy density, long cycle life, good rate performance, and low manufacturing cost. How to further improve the energy density, cycle life, and safety performance of lithium-ion batteries has also become a research hotspot in the field of lithium-ion batteries.

[0003] During the use of lithium-ion batteries, the irregular growth of negative lithium dendrites, the shrinkage or melting of the separator at high temperatures, and the occurrence of external mechanical abuse (such as puncture, extrusion, or impact) can easily cause short circuits inside the battery cell, generating a large amount of heat, resulting in a local temperature increase and triggering thermal runaway, seriously damaging the safety performance of the battery. Summary of the Invention

[0004] Based on this, it is necessary to provide a composite current collector, a preparation method thereof, and a secondary battery to solve the problems that the battery is prone to thermal runaway at high temperatures and has poor battery safety performance.

[0005] The above object of this application is achieved through the following technical solutions:

[0006] In the first aspect of this application, a composite current collector is provided, which includes a support layer, a safety coating, a protection coating, and a conductive layer laminated in sequence;

[0007] The support layer includes a polymer material and a two-dimensional nanoribbon material;

[0008] The safety coating includes a binder and an inorganic foaming agent, and the thermal decomposition temperature of the inorganic foaming agent is 80°C to 130°C;

[0009] The protection coating includes a high-entropy alloy material.

[0010] In some embodiments, the surface of the support layer is provided with a plurality of grooves, and the depth of the grooves is less than the thickness of the safety coating;

[0011] The safety coating is filled in the grooves;

[0012] The protection coating covers the safety coating and the support layer.

[0013] In some embodiments, the depth of the groove is 0.1 μm to 1 μm, the size of the groove is 1 μm to 2 μm, and the spacing between the grooves is 200 μm to 1000 μm.

[0014] In some embodiments, the polymer material includes one or more of polyethylene, polypropylene, polyimide, polyvinyl chloride, polystyrene, polyvinyl alcohol, polyethylene terephthalate, and polybutylene terephthalate.

[0015] In some embodiments, the two-dimensional nanobelt material includes one or more of tantalum arsenide nanobelts, niobium arsenide nanobelts, tantalum phosphide nanobelts, and niobium phosphide nanobelts.

[0016] In some embodiments, the thickness of the two-dimensional nanobelt material is 50 nm to 400 nm, the width is 100 nm to 500 nm, and the length is 0.1 mm to 1 mm.

[0017] In some embodiments, the mass ratio of the polymer material to the two-dimensional nanobelt material is 100:(1 to 30).

[0018] In some embodiments, the thickness of the support layer is 4 μm to 8 μm.

[0019] In some embodiments, the binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium alginate, polyvinyl alcohol, polymethyl methacrylate, hydrogenated nitrile rubber, and polyacrylic acid.

[0020] In some embodiments, the inorganic foaming agent includes one or more of carbonates, bicarbonates, and hydrated silicates.

[0021] In some embodiments, the mass ratio of the binder to the inorganic foaming agent is 1:(2 to 3).

[0022] In some embodiments, the thickness of the safety coating is 0.2 μm to 2 μm.

[0023] In some embodiments, the high-entropy alloy material includes at least five of iron, cobalt, nickel, chromium, manganese, aluminum, copper, titanium, yttrium, and tantalum.

[0024] In some embodiments, the thickness of the protective coating is 20 nm to 50 nm.

[0025] In some embodiments, the material of the conductive layer includes one or more of stainless steel, copper, nickel, and aluminum.

[0026] In some embodiments, the thickness of the conductive layer is 0.5 μm to 4 μm.

[0027] In a second aspect of the present application, a method for preparing the composite current collector as described above is provided, including the following steps:

[0028] The polymer material and the two-dimensional nanoribbon material are melt-blended and formed to form a support layer;

[0029] A safety coating, a protective coating, and a conductive layer are sequentially formed on the support layer.

[0030] In some embodiments, the method for preparing the safety coating includes the following steps:

[0031] A mixed slurry containing a binder and an inorganic foaming agent is covered on the support layer and dried to obtain the safety coating; or,

[0032] The surface of the support layer includes a first region and a second region disposed around the first region;

[0033] A plurality of grooves are formed in the first region, and a mask is covered on the second region;

[0034] A mixed slurry containing a binder and an inorganic foaming agent is filled in the grooves, dried, and the mask is removed to obtain the safety coating.

[0035] In a second aspect of the present application, a secondary battery is provided, including the composite current collector as described above, or including a composite current collector prepared by using the method for preparing the composite current collector as described above.

[0036] The present application has at least the following beneficial effects:

[0037] The composite current collector provided by this application includes a support layer, a safety coating, a protective coating, and a conductive layer stacked in sequence. Among them, the support layer is composed of a polymer material and a two-dimensional nanoribbon material, which can enhance the tensile strength, elongation at break, and toughness of the support layer, and improve the mechanical properties of the composite current collector. At the same time, the two-dimensional nanoribbon material has excellent electronic conduction performance, which can improve the conductivity of the support layer, thereby alleviating the overcurrent heating problem caused during high-rate operation and ensuring the stable performance of the battery's electrochemical properties. The safety coating is composed of a binder and an inorganic foaming agent. The thermal decomposition temperature of the inorganic foaming agent is 80°C to 130°C. The inorganic foaming agent absorbs heat and decomposes at high temperatures, releasing a large amount of gas, which generates a strong impact on the protective coating and the conductive layer, causing rupture and peeling of the conductive layer, thereby increasing the resistance impedance of the composite current collector, inhibiting abnormal loop current, and effectively improving the safety performance of the battery. The protective coating is made of a high-entropy alloy material and has excellent fracture resistance, tensile strength, corrosion resistance, oxidation resistance, and bonding properties. It can protect the support layer and the safety coating, stably store the inorganic foaming agent in the safety coating, and at the same time enhance the bonding force between layers, thereby improving the structural stability of the composite current collector. Therefore, the composite current collector provided by this application has good electrical conductivity, high structural stability, and excellent safety performance. It can not only reduce the probability of thermal runaway of the battery at high temperatures but also improve the cycle performance of the battery under normal operating conditions. Description of the Drawings

[0038] In order to more clearly illustrate the technical solutions in the embodiments of this application and more comprehensively understand this application and its beneficial effects, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of this application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0039] Figure 1 It is a schematic structural diagram of the composite current collector in an embodiment of this application;

[0040] Figure 2 It is a schematic structural diagram of the composite current collector in another embodiment of this application;

[0041] Figure 3 It is a schematic cross-sectional diagram of the support layer in an embodiment of this application;

[0042] Figure 4 It is a schematic flow diagram of the preparation method of the composite current collector in an embodiment of this application;

[0043] Figure 5 It is a schematic flow diagram of the preparation method of the safety coating in an embodiment of this application.

[0044] Reference numerals: support layer 10, groove 11, safety coating 20, protective coating 30, conductive layer 40. Detailed implementation manners

[0045] To facilitate the understanding of the present application, the present application will be further described in detail below in conjunction with specific embodiments. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosed content of the present application more thorough and comprehensive.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the description of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0047] In this application, the meaning of "and / or" includes any and all combinations of one or more of the related listed items. The meaning of "at least one" is more than one, such as one, two or more. The meaning of "multiple" or "several" is at least two, such as two, three, etc., and the meaning of "multiple layers" is at least two layers, such as two layers, three layers, etc., unless otherwise specifically defined. In the description of this application, the meaning of "several" is at least one, such as one, two, etc., unless otherwise specifically defined.

[0048] When a numerical range is disclosed in this application, the above range is considered continuous and includes the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to an integer, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed in this application should be understood to include any and all sub-ranges subsumed therein.

[0049] If there is no special instruction, all steps of this application can be carried out in sequence or randomly. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or can also include steps (a), (c) and (b), or can also include steps (c), (a) and (b), etc.

[0050] In this application, both "above" and "below" include the number itself. For example, below 1 includes 1.

[0051] The temperature parameters in this application, unless otherwise specified, are allowed to be for isothermal treatment or to vary within a certain temperature range. It should be understood that the isothermal treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0052] In this application, room temperature refers to indoor temperature, normal temperature, or general temperature. Generally speaking, the range of room temperature can be any one of the following temperature ranges: 23°C ± 2°C, 25°C ± 5°C, or 20°C ± 5°C.

[0053] Current collectors can be divided into two major categories: metal current collectors and composite current collectors. Composite current collectors usually consist of a polymer layer and a metal layer covering at least one side of the polymer layer. Compared with metal current collectors such as copper foil and aluminum foil, composite current collectors are lighter in mass, thinner in thickness, and better in safety performance. However, traditional composite current collectors cannot cut off the circuit in time when a short circuit occurs inside the battery cell, which easily leads to heat accumulation and then thermal runaway, and the safety performance urgently needs to be further improved.

[0054] Based on this, in the first aspect of this application, a composite current collector is provided, aiming to reduce the probability of thermal runaway of the battery at high temperatures and improve the poor safety performance of the battery.

[0055] Please refer to Figure 1 , which is a schematic structural diagram of the composite current collector in an embodiment of this application.

[0056] As Figure 1 shown, the composite current collector includes a support layer 10, a safety coating 20, a protective coating 30, and a conductive layer 40 that are stacked in sequence;

[0057] The support layer 10 includes a polymer material and a two-dimensional nanobelt material;

[0058] The safety coating 20 includes a binder and an inorganic foaming agent, and the thermal decomposition temperature of the inorganic foaming agent is 80°C to 130°C;

[0059] The protective coating 30 includes a high-entropy alloy material.

[0060] The composite current collector provided by the present application includes a support layer 10, a safety coating 20, a protective coating 30, and a conductive layer 40 stacked in sequence. Among them, the support layer 10 is composed of a polymer material and a two-dimensional nanoribbon material, which can enhance the tensile strength, elongation at break, and toughness of the support layer 10, and improve the mechanical properties of the composite current collector. At the same time, the two-dimensional nanoribbon material has excellent electron conduction performance, which can improve the conductivity of the support layer 10, thereby improving the overcurrent heating problem caused during high-rate operation and ensuring the stable performance of the battery's electrochemical properties. The safety coating 20 is composed of a binder and an inorganic foaming agent. The thermal decomposition temperature of the inorganic foaming agent is 80°C to 130°C. The inorganic foaming agent absorbs heat and decomposes thermally at high temperatures, releasing a large amount of gas, generating a strong impact on the protective coating 30 and the conductive layer 40, causing the rupture and peeling of the conductive layer 40, thereby increasing the resistance impedance of the composite current collector, inhibiting abnormal loop current, and effectively improving the safety performance of the battery. The protective coating 30 is made of a high-entropy alloy material and has excellent fracture resistance, tensile strength, corrosion resistance, oxidation resistance, and bonding properties. It can protect the support layer 10 and the safety coating 20, enabling the stable storage of the inorganic foaming agent in the safety coating 20. At the same time, it can also enhance the bonding force between layers, thereby improving the structural stability of the composite current collector. Therefore, the composite current collector provided by the present application has good electrical conductivity, high structural stability, and excellent safety performance. It can not only reduce the probability of thermal runaway of the battery at high temperatures but also help improve the cycle performance of the battery under normal operating conditions.

[0061] Optionally, the polymer material includes one or more of polyethylene (PE), polypropylene (PP), polyimide (PI), polyvinyl chloride (PVC), polystyrene (PS), polyvinyl alcohol (PVA), polyethylene terephthalate (PET), and polybutylene terephthalate (PBT), and further optionally one or more of polypropylene (PP), polyimide (PI), and polyethylene terephthalate (PET).

[0062] Optionally, the two-dimensional nanoribbon material includes one or more of tantalum arsenide (TaAs) nanoribbons, niobium arsenide (NbAs) nanoribbons, tantalum phosphide (TaP) nanoribbons, and niobium phosphide (NbP) nanoribbons, and further optionally NbAs nanoribbons.

[0063] Two-dimensional nanoribbon materials refer to ribbon-shaped materials with a nanoscale width in a two-dimensional plane. Their length can reach the micron level or even the millimeter level, and the width and thickness are generally between a few nanometers and a few hundred nanometers, showing typical two-dimensional characteristics, which can endow the support layer with better conductivity and mechanical strength. Among them, TaAs, NbAs, TaP, and NbP belong to Weyl semimetal materials, with topologically protected conductive states on the surface, high carrier mobility, and a band structure with linear dispersion, so they exhibit excellent conductive properties.

[0064] Optionally, the thickness of the two-dimensional nanoribbon material is 50 nm to 400 nm, the width is 100 nm to 500 nm, and the length is 0.1 mm to 1 mm. As an example, the thickness of the two-dimensional nanoribbon material includes but is not limited to 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, or 400 nm; the width of the two-dimensional nanoribbon material includes but is not limited to 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, or 500 nm; the length of the two-dimensional nanoribbon material includes but is not limited to 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, or 1 mm.

[0065] Optionally, the mass ratio of the polymer material to the two-dimensional nanoribbon material is 100:(1 - 30). As an example, the mass ratio of the polymer material to the two-dimensional nanoribbon material includes but is not limited to 100:1, 100:2, 100:4, 100:6, 100:8, 100:10, 100:12, 100:14, 100:16, 100:18, 100:20, 100:22, 100:24, 100:26, 100:28, 100:30, and is further optionally 100:(5 - 15).

[0066] Adding an appropriate amount of two-dimensional nanoribbon material to the support layer 10 can fully exert its toughening effect, enabling it to play a role in buffering stress and maintaining structural stability during the preparation and operation of the battery cell. At the same time, it can also form a perfect conductive network within the support layer 10, improving the heat generation problem caused during the large-current transportation process, thereby providing a guarantee for the stable performance of the battery.

[0067] Optionally, the thickness of the support layer 10 is 4 μm to 8 μm. As an example, the thickness of the support layer 10 includes, but is not limited to, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, or 8 μm.

[0068] Optionally, the binder includes one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium alginate (SA), polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), hydrogenated nitrile butadiene rubber (HNBR), and polyacrylic acid (PAA), and is further optionally polyvinylidene fluoride (PVDF).

[0069] Optionally, the inorganic blowing agent includes one or more of carbonates, bicarbonates, and hydrated silicates. Further optionally, the inorganic blowing agent includes beryllium carbonate (BeCO 3 ), sodium bicarbonate (NaHCO 3 ), potassium bicarbonate (KHCO 3 ), cesium bicarbonate (CsHCO 3 ), and sodium silicate decahydrate (Na 2 SiO 3 ·10H 2 O), and is even more optionally beryllium carbonate (BeCO 3 ), or sodium silicate decahydrate (Na 2 SiO 3 ·10H 2 O).

[0070] The thermal decomposition temperature of BeCO 3 is ~100 °C, the thermal decomposition temperature of NaHCO 3 is 100 °C to 120 °C, KHCO 3 starts to decompose at around 100 °C, CsHCO 3 starts to decompose at around 100 °C, and Na 2 SiO 3 ·10H 2 O starts to lose crystal water at around 100 °C. Using the above carbonates, bicarbonates, and hydrated silicates as inorganic blowing agents, they can absorb heat and decompose to form non-combustible gases such as CO 2 , H 2 O, etc., and do not form combustion-supporting gases such as NH 4 O, etc., which can help isolate oxygen and play a role in flame retardancy and explosion prevention.

[0071] Optionally, the mass ratio of the binder to the inorganic foaming agent is 1:(2 - 3). As an example, the mass ratio of the binder to the inorganic foaming agent includes, but is not limited to, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, or 1:3.

[0072] Optionally, the thickness of the safety coating 20 is 0.2 μm - 2 μm. As an example, the thickness of the safety coating 20 includes, but is not limited to, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, or 2 μm.

[0073] Optionally, the high-entropy alloy material includes at least five of iron (Fe), cobalt (Co), nickel (Ni), chromium (Cr), manganese (Mn), aluminum (Al), copper (Cu), titanium (Ti), yttrium (Y), and tantalum (Ta), further optionally at least five of nickel (Ni), cobalt (Co), chromium (Cr), aluminum (Al), yttrium (Y), and tantalum (Ta), and still further optionally, the high-entropy alloy material is NiCoCrAlY or NiCoCrAlYTa.

[0074] High-entropy alloys (HEA) materials are alloy materials composed of at least five metals transported in equiatomic or near-equiatomic ratios. Different from traditional alloys dominated by one or two metal elements, multiple metal elements in HEA materials jointly dominate, with a relatively high mixing entropy, usually presenting simple crystal structures (such as face-centered cubic structure, body-centered cubic structure, or close-packed hexagonal structure), and having microstructural uniformity. Therefore, they exhibit excellent fracture resistance, tensile strength, corrosion resistance, and oxidation resistance, enabling the protective coating 30 to play a good protective role for the support layer 10 and the safety coating 20. Their excellent bonding properties also contribute to enhancing the bonding strength between the safety coating 20 and the conductive layer 40, preventing the safety coating 20 from peeling off, delaminating, decomposing, etc. before it functions.

[0075] Optionally, the thickness of the protective coating 30 is 20 nm - 50 nm. As an example, the thickness of the protective coating 30 includes, but is not limited to, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm.

[0076] Optionally, the material of the conductive layer 40 includes one or more of stainless steel, copper (Cu), nickel (Ni), and aluminum (Al), and further optionally copper (Cu) or aluminum (Al).

[0077] Optionally, the thickness of the conductive layer 40 is 0.5 μm to 4 μm. As an example, the thickness of the conductive layer 40 includes, but is not limited to, 0.5 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, or 4 μm.

[0078] Please refer to Figure 2 , which is a schematic structural diagram of a composite current collector in another embodiment of the present application.

[0079] As Figure 2 shown, a plurality of grooves 11 are provided on the surface of the support layer 10, and the depth of the grooves 11 is less than the thickness of the safety coating 20;

[0080] The safety coating 20 is filled in the grooves 11;

[0081] The protective coating 30 covers the safety coating 20 and the support layer 10.

[0082] In a traditional composite current collector, the surface of the polymer layer is usually roughened to increase the surface roughness in order to improve the adhesion between the polymer layer and the metal layer. In the embodiment of the present application, a plurality of grooves 11 are provided on the surface of the support layer 10, and the safety coating 20 is filled in the grooves 11. Since the depth of the grooves 11 is less than the thickness of the safety coating 20, the safety coating 20 protrudes from the surface of the support layer 10. On the one hand, the grooves increase the contact area between the safety coating 20 and the support layer 10, improving the adhesion between the two. On the other hand, the surface roughness of the combination formed by the support layer 10 and the safety coating 20 is also improved, thereby improving the adhesion between the combination and the protective coating 30 and the conductive layer 40. Therefore, the peeling strength of the entire composite current collector is high and the structural stability is good, thus improving the cycle stability of the battery. In addition, the safety coating 20 is filled in the grooves 11. When the temperature inside the battery cell rises abnormally to the thermal decomposition temperature of the inorganic foaming agent, the inorganic foaming agent can generate a stronger impact force when thermally decomposed in a limited space, so that the conductive layer 40 can be torn or peeled off more quickly, and the safety performance is further improved.

[0083] Optionally, the depth of the grooves 11 is 0.1 μm to 1 μm, the size of the grooves 11 is 1 μm to 2 μm, and the spacing of the grooves 11 is 200 μm to 1000 μm.

[0084] Understandably, the depth of the groove 11 refers to the size of the groove 11 in the thickness direction, the size of the groove 11 refers to the size of the groove 11 in the horizontal direction, and the spacing of the grooves 11 refers to the shortest distance between the edges of two adjacent grooves 11. As an example, the depth of the groove 11 includes but is not limited to 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm or 1μm; the size of the groove 11 includes but is not limited to 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm or 2μm; the spacing of the grooves 11 includes but is not limited to 200μm, 250μm, 300μm, 350μm, 400μm, 450μm, 500μm, 550μm, 600μm, 650μm, 700μm, 750μm, 800μm, 850μm, 900μm, 950μm or 1000μm.

[0085] Please refer to Figure 3 , which is a schematic cross-sectional view of the support layer 10 in an embodiment of the present application.

[0086] Optionally, the cross-sectional shape of the groove 11 in the thickness direction includes one or more of a square, a rectangle, a regular trapezoid, an inverted trapezoid, an inverted triangle, a semi-circle, and an irregular shape.

[0087] Optionally, the shape of the groove 11 in the direction perpendicular to the thickness includes one or more of a circle, a square, a rhombus, an equilateral triangle, and an irregular shape.

[0088] In the second aspect of the present application, a method for preparing the composite current collector as described above is provided.

[0089] Please refer to Figure 4 , which is a schematic process diagram of the method for preparing the composite current collector in an embodiment of the present application. As Figure 4 shown, the method for preparing the composite current collector includes the following steps:

[0090] S100: Perform melt blending treatment and shaping treatment on the polymer material and the two-dimensional nanoribbon material to form the support layer 10;

[0091] S200: Sequentially form a safety coating 20, a protective coating 30, and a conductive layer 40 on the support layer 10.

[0092] Optionally, the conditions for melt blending treatment include: temperature of 180°C to 450°C and time of 0.5 h to 8 h. Among them, the temperature for melt blending treatment includes but is not limited to 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, 420°C, 440°C or 450°C; the time for melt blending treatment can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h.

[0093] Optionally, the forming treatment method includes one or more of compression molding method, hot pressing molding method, autoclave molding method and calendering molding method.

[0094] Optionally, the preparation method of the two-dimensional nanobelt material is chemical vapor deposition (CVD) method.

[0095] Optionally, the preparation method of NbAs nanobelts includes the following steps: using NbCl 3 particles and As blocks as precursors, placing the precursors in a crucible, heating to 200°C to vaporize the NbCl 3 particles, and heating to 500°C to vaporize the As blocks; using a mixed gas of Ar and H 2 with a volume ratio of 95:5 as the carrier gas, feeding the vaporized precursors into the center of a tube furnace; using Si as the substrate, depositing a thin SiO 2 layer on the surface of the Si substrate, and pre-depositing a 15-nm-thick Au layer on the surface of the SiO 2 layer as a catalyst, placing the substrate in the tube furnace for chemical vapor deposition, and reacting on the substrate to generate NbAs nanobelts. Among them, the conditions for chemical vapor deposition are: raising the temperature of the tube furnace to 840°C to 870°C within 15 minutes, reacting for 15 minutes, cooling to 700°C within 30 minutes, and then naturally cooling to room temperature. After the chemical vapor deposition is completed, the NbAs nanobelts are peeled off from the substrate by laser etching, plasma etching, chemical etching or mechanical peeling method. For example, using NH 4 F solution to etch away the SiO 2 layer, thereby removing the Si substrate.

[0096] Optionally, the preparation method of the safety coating 20 includes the following steps:

[0097] S210: Cover the support layer 10 with a mixed slurry containing a binder and an inorganic foaming agent, and perform a drying treatment to obtain the safety coating 20.

[0098] Please refer to Figure 5 , which is a schematic flow chart of the preparation method of the safety coating 20 in an embodiment of the present application. As Figure 5As shown, the preparation method of the security coating 20 includes the following steps:

[0099] S221: The surface of the support layer 10 includes a first region and a second region disposed around the first region;

[0100] S222: Form a plurality of grooves 11 on the first region and cover a mask on the second region;

[0101] S223: Fill the mixed slurry containing a binder and an inorganic foaming agent into the grooves 11, perform a drying process, and remove the mask to obtain the security coating 20.

[0102] Optionally, the method for forming a plurality of grooves 11 on the first region includes one or more of a laser etching method and a die cutting method.

[0103] Optionally, the mask is provided with a plurality of through holes, and each through hole corresponds to the groove 11 on the support layer 10 for filling the mixed slurry into the groove.

[0104] Optionally, the mixed slurry includes an organic solvent, and the mass ratio of the binder to the organic solvent is 1:(4 - 20). As an example, the mass ratio of the binder to the organic solvent includes, but is not limited to, 1:4, 1:6, 1:8, 1:10, 1:12, 1:14, 1:16, 1:18, or 1:20.

[0105] Optionally, the organic solvent includes one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO).

[0106] Optionally, the method for covering the mixed slurry on the support layer 10 and the method for filling the mixed liquid into the groove each independently include one or more of a spraying method, a spin coating method, a brush coating method, a drop coating method, a scraping method, an impregnation method, a screen printing method, and an inkjet printing method, and further optionally the scraping method.

[0107] Optionally, the temperature of the drying process is 50°C - 80°C, and the time is 24h - 96h. As an example, the temperature of the drying process includes, but is not limited to, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C, and the time includes, but is not limited to, 24h, 36h, 48h, 60h, 72h, 84h, or 96h.

[0108] Optionally, the preparation method of the protective coating 30 includes a magnetron sputtering method.

[0109] Optionally, the conditions for preparing the protective coating 30 by magnetron sputtering method include: the sputtering atmosphere is an inert gas, the sputtering pressure is 0.1 Pa to 1 Pa, and the sputtering power is 20 W to 50 W. Among them, the sputtering atmosphere includes one or more of helium, neon, argon, krypton, and xenon; the sputtering pressure includes but is not limited to 0.1 Pa, 0.2 Pa, 0.3 Pa, 0.4 Pa, 0.5 Pa, 0.6 Pa, 0.7 Pa, 0.8 Pa, 0.9 Pa, or 1 Pa; the sputtering power includes but is not limited to 20 W, 25 W, 30 W, 35 W, 40 W, 45 W, or 50 W.

[0110] Optionally, preparing the protective coating 30 by magnetron sputtering method includes the following steps: after forming the safety coating 20, evacuate the reaction chamber to 1×10 -5 Pa to 6×10 -5 Pa, introduce argon at a flow rate of 10 sccm to 100 sccm, use the high-entropy alloy material as the sputtering target, and perform DC magnetron sputtering coating under the conditions of a sputtering pressure of 0.1 Pa to 1 Pa and a sputtering power of 20 W to 50 W to form the protective coating 30 on the safety coating 20 (or on the safety coating 20 and the support layer 10).

[0111] Optionally, the preparation method of the conductive layer 40 includes the magnetron sputtering method.

[0112] Optionally, the conditions for preparing the conductive layer 40 by magnetron sputtering method include: the sputtering atmosphere is an inert gas, the sputtering pressure is 0.5 Pa to 5 Pa, and the sputtering power is 100 W to 200 W. Among them, the sputtering atmosphere includes one or more of helium, neon, argon, krypton, and xenon; the sputtering pressure includes but is not limited to 0.5 Pa, 1 Pa, 1.5 Pa, 2 Pa, 2.5 Pa, 3 Pa, 3.5 Pa, 4 Pa, 4.5 Pa, or 5 Pa; the sputtering power includes but is not limited to 100 W, 120 W, 140 W, 160 W, 180 W, or 200 W.

[0113] Optionally, preparing the conductive layer 40 by magnetron sputtering method includes the following steps: after forming the protective coating 30, evacuate the reaction chamber to 1×10 -5 Pa to 6×10 -5 Pa, introduce argon at a flow rate of 50 sccm to 100 sccm, use the conductive metal material as the sputtering target, and perform DC magnetron sputtering coating under the conditions of a sputtering pressure of 0.5 Pa to 5 Pa and a sputtering power of 100 W to 200 W to form the conductive layer 40 on the protective coating 30.

[0114] In a third aspect of the present application, a secondary battery is provided, which includes the composite current collector as described above, or a composite current collector prepared by the preparation method of the composite current collector as described above.

[0115] It can be understood that the secondary battery includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During the charge and discharge process of the battery, active ions (such as Li + , Na + , K + ) are intercalated and deintercalated back and forth between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly functioning to prevent short circuit between the positive and negative electrodes, and at the same time allowing active ions to pass through. The electrolyte is between the positive electrode plate and the negative electrode plate, mainly functioning to conduct active ions.

[0116] Optionally, the positive electrode plate and / or the negative electrode plate includes the composite current collector as described above.

[0117] Optionally, the positive electrode plate includes the composite current collector as described above and a positive electrode active layer covering at least one surface of the composite current collector; wherein, the material of the conductive layer 40 in the composite current collector includes aluminum.

[0118] Optionally, the positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder. Among them, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (80~95):(2.5~10):(2.5~10), and further optionally 80:10:10.

[0119] Optionally, when the secondary battery is a lithium battery, the positive electrode active material includes one or more of lithium transition metal oxides and lithium-containing phosphates with an olivine structure. Among them, the lithium transition metal oxides include, but are not limited to: lithium cobalt oxide, such as LiCoO 2 ; lithium nickel oxide, such as LiNiO 2 ; lithium manganese oxide, such as LiMnO 2 or LiMn 2 O 4 ; lithium nickel cobalt oxide; lithium manganese cobalt oxide; lithium nickel manganese oxide; lithium nickel cobalt manganese oxide, such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.1 Mn 0.3 O 2 (NCM613), LiNi 0.6 Co0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811); lithium nickel cobalt aluminum oxide, such as LiNi 0.8 Co 0.15 Al 0.05 O 2 ; and modified compounds of the above lithium transition metal oxides. Olivine-structured lithium-containing phosphates include, but are not limited to: lithium iron phosphate, such as LiFePO 4 (LFP); composites of lithium iron phosphate and carbon; lithium manganese phosphate, such as LiMnPO 4 ; composites of lithium manganese phosphate and carbon; lithium iron manganese phosphate, such as LiFe 0.5 Mn 0.5 PO 4 ; composites of lithium iron manganese phosphate and carbon; and modified compounds of the above olivine-structured lithium-containing phosphates. The modified compounds of each material can be one or more of doping modification and surface coating modification.

[0120] Optionally, when the secondary battery is a sodium battery, the positive electrode active material includes one or more of transition metal oxide materials, polyanion compound materials, Prussian blue compounds, and organic positive electrode materials. Among them, the transition metal oxides mainly include layered structures and tunnel structures, and the structural formula can be expressed as Na x TMO 2 (TM = Co, Cu, Ni, Fe, Mn, etc.), such as NaMnO 2 , NaNiO 2 , NaCrO 2 or NaCu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 O 2 ; the polyanion compound materials include Na 3 V 2 (PO 4 ) 3 (NVP), Na 3 V 2 (PO 4 ) 2 F 3 (NVPF) and Na 2 MP 2 O 7 (M = Fe, Co, Mn or Cu), etc.; the molecular general formula of Prussian blue compounds is KM II Fe III(CN) 6 (M = Mn, Fe, Co, Ni, Zn, etc.); The organic cathode materials include disodium rhodizonate (Na 2 C 6 O 6 ), perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), and perylene diimide (PTCDI). And the modified compounds of the above transition metal oxide materials, polyanion compound materials, Prussian blue compounds, and organic cathode materials. The modified compounds of each material can be one or more of doping modification and surface coating modification.

[0121] Optionally, when the secondary battery is a potassium battery, the positive electrode active material includes one or more of transition metal oxide materials, polyanion compound materials, Prussian blue compounds, and organic cathode materials. Among them, the transition metal oxides mainly include a layered structure, such as K x CrO 2 (x = 0.69, 0.8, 1), K x MnO 2 (x = 0.3, 0.5, 0.7), K x CoO 2 (x = 0.44, 0.6), K 0.48 Mn 0.4 Co 0.6 O 2 ), K x Fe0.5Mn 0.5 O 2 (x = 0.45, 0.65, 0.7), K 0.45 Mn 0.5 Co 0.5 O 2 ), K 0.5 Mn 0.8 Co 0.1 Ni 0.1 O 2 ), K 0.67 Ni 0.17 Co 0.17 Mn 0.66 O 2 ), K 1.39 Mn 3 O 6 ), K 2 V 3 O 8 ), K 0.72 Li 0.27 Ni 0.6 Co 0.2 Mn 0.2 O 2 ), K 0.7 Fe 0.05 Co 0.1 Mn0.75 Ni 0.05 V 0.05 O 2 ; The polyanion compound materials include KFeSO 4 F, KCuSO 4 F, KVPO 4 F, KVOPO 4 , K 3 V 2 (PO 4 ) 3 etc.; The molecular general formula of the Prussian blue compounds is K x M[M′(CN) 6 1-y (0 ≤ x ≤ 2, 0 ≤ y < 1,), M and M′ are transition metals such as Zn, Cu, Ni, Co, Fe, Cr, and Ti, etc.; The organic cathode materials include 1,4-benzoquinone polymers (PAQS), polytriphenylamine (PTPAn), copper tetracyano-p-benzoquinodimethane (CuTCNQ), and sodium anthraquinone-2,6-disulfonate (AQDs), etc. And the modified compounds of the above transition metal oxide materials, polyanion compound materials, Prussian blue compounds, and organic cathode materials. The modified compounds of each material can be one or more of doping modification and surface coating modification.

[0122] Optionally, the binder in the positive electrode active layer includes one or more of polyvinylidene fluoride (PVDF), sodium alginate (SA), polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), hydrogenated nitrile rubber (HNBR), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA), and further preferably polyvinylidene fluoride (PVDF).

[0123] Optionally, the conductive agent in the positive electrode active layer includes one or more of conductive carbon black, super conductive carbon black, acetylene black, Ketjen black, carbon quantum dots, carbon nanotubes, graphene, and carbon nanofibers, and further preferably conductive carbon black (Super-P, SP).

[0124] Optionally, the preparation method of the positive electrode sheet includes the following steps: dispersing the positive electrode active material, conductive agent, and binder in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; covering the positive electrode slurry on at least one surface of the composite current collector, and through drying, rolling, and cutting treatments, a positive electrode sheet is obtained.

[0125] Optionally, the negative electrode sheet includes the composite current collector as described above and a negative electrode active layer covering at least one surface of the composite current collector; wherein, the material of the conductive layer 40 in the composite current collector includes one or more of stainless steel, copper, and nickel.

[0126] ​Optionally, the negative electrode active layer includes a negative electrode active material, a conductive agent, and a binder. Among them, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (80-95):(2.5-10):(2.5-10), and further optionally 80:10:10.

[0127] Optionally, the negative electrode active material includes one or more of a carbon-based material, a silicon-based material, a tin-based material, and lithium titanate. Among them, the carbon-based material includes one or more of artificial graphite, natural graphite, graphene, soft carbon, and hard carbon; the silicon-based material includes one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys; the tin-based material includes one or more of elemental tin, tin oxide compounds, and tin alloys.

[0128] Optionally, the binder in the negative electrode active layer includes one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), sodium carboxymethyl cellulose (CMC), and carboxymethyl chitosan (CMCS).

[0129] Optionally, the conductive agent in the negative electrode active layer includes one or more of conductive carbon black, super conductive carbon black, acetylene black, Ketjen black, carbon quantum dots, carbon nanotubes, graphene, and carbon nanofibers, and further optionally conductive carbon black (Super-P, SP).

[0130] Optionally, the method for preparing the negative electrode pole piece includes the following steps: dispersing the negative electrode active material, the conductive agent, and the binder in a solvent (such as deionized water) to form a negative electrode slurry; covering the negative electrode slurry on at least one surface of the composite current collector, and obtaining the negative electrode pole piece after drying, rolling, and cutting treatments.

[0131] Understandably, the electrolyte in the secondary battery can be liquid, gel or all-solid state. Optionally, the electrolyte adopts an electrolytic solution, which includes an alkali metal salt and an organic solvent. Among them, the alkali metal salts include lithium salts, sodium salts and potassium salts; the lithium salts include one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro(bis(oxalato))phosphate and lithium tetrafluoro(oxalato)phosphate; the sodium salts include sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide; the potassium salts include potassium hexafluorophosphate, potassium bis(fluorosulfonyl)imide, potassium bis(trifluoromethanesulfonyl)imide; the organic solvents include one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, trimethyl phosphate, triethyl phosphate, sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone and diethylene glycol dimethyl ether.

[0132] Understandably, the separator in the secondary battery can be a porous separator with good chemical stability and mechanical stability; at the same time, 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, without special limitation. Optionally, the material of the separator includes one or more of glass fiber, non-woven fabric, polyethylene (PE) and polypropylene (PP).

[0133] Optionally, the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly by a winding process or a stacking process, and then an electrolytic solution is injected to make a battery.

[0134] Optionally, the secondary battery can include an outer package for encapsulating the above-mentioned electrode assembly and electrolyte. The outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch soft package, and the material of the soft package can be an aluminum-plastic film, etc.

[0135] Understandably, the present application has no special limitation on the shape of the secondary battery, and it can be cylindrical, square or any other shape.

[0136] The following will be further described in conjunction with specific examples and comparative examples. The raw materials involved in the following specific examples and comparative examples, unless otherwise specified, can all be obtained commercially. The instruments used, unless otherwise specified, can all be obtained commercially. The processes involved, unless otherwise specified, are all conventional selections of those skilled in the art.

[0137] Example 1

[0138] Please refer to Tables 1 to 2. The preparation method of the secondary battery provided in this embodiment is as follows:

[0139] (1) Preparation of the positive electrode sheet:

[0140] (1.1) Preparation of the support layer 10:

[0141] The polymer material and the two-dimensional nanobelt material are melt-blended at 300 °C, uniformly dispersed at a rotation speed of 1000 rpm for 4 h, and the support layer 10 is formed by calendering.

[0142] Among them, the polymer material is polyethylene terephthalate (PET);

[0143] The two-dimensional nanobelt material is NbAs, with a thickness of 250 nm, a width of 400 nm, and a length of 0.5 mm;

[0144] The mass ratio of the polymer material to the two-dimensional nanobelt material is 100:12;

[0145] The thickness of the support layer 10 is 6 μm.

[0146] (1.2) Preparation of the safety coating 20:

[0147] The surface of the support layer 10 is divided into a first region and a second region surrounding the first region. A plurality of grooves 11 are formed on the first region by laser etching, and a mask 14 is covered on the second region, and the mask 14 is provided with a plurality of through holes corresponding to the grooves 11. The binder and the inorganic foaming agent are dissolved in an organic solvent to obtain a mixed solution. The mixed solution is filled into the grooves 11 by a doctor blade method, dried at 60 °C for 48 h, and the mask 14 is removed to obtain the safety coating 20.

[0148] Among them, the cross-sectional shape of the groove 11 in the thickness direction is an inverted trapezoid, with a depth of 0.5 µm, the short side dimension of the inverted trapezoid is 1 µm, the long side dimension of the inverted trapezoid is 2 µm, and the spacing is 800 µm;

[0149] The binder is polyvinylidene fluoride (PVDF), the inorganic foaming agent is sodium silicate decahydrate (Na 2 SiO 3 ·10H 2 O), the organic solvent is N-methylpyrrolidone (NMP), and the mass ratio is 1:3:6;

[0150] The thickness of the safety coating 20 is 1.5 µm, that is, the thickness of the safety coating 20 filled in the groove 11 is 0.5 µm, and the thickness of the safety coating 20 protruding from the support layer 10 is 1 µm.

[0151] (1.3)Preparation of the protective coating 30:

[0152] The reaction chamber is evacuated to below 5×10 -5 Pa, argon is introduced at a flow rate of 20 sccm, a high-entropy alloy material is used as the sputtering target, and DC magnetron sputtering coating is carried out under the conditions of a sputtering pressure of 0.1 Pa and a sputtering power of 40 W to form a protective coating 30 on the support layer 10 and the safety coating 20.

[0153] Among them, the high-entropy alloy material is NiCoCrAlY, and the thickness of the protective coating 30 is 30 nm.

[0154] (1.4)Preparation of the conductive layer 40:

[0155] The reaction chamber is evacuated to below 5×10 -5 Pa, argon is introduced at a flow rate of 80 sccm, a conductive metal material is used as the sputtering target, and DC magnetron sputtering coating is carried out under the conditions of a sputtering pressure of 2 Pa and a sputtering power of 150 W to form a conductive layer 40 on the protective coating 30.

[0156] Among them, the conductive metal material is Al, and the thickness of the conductive layer 40 is 1 µm.

[0157] (1.5)Preparation of the positive electrode plate:

[0158] The positive electrode active material NCM811, the binder PVDF, and the conductive agent SP are dispersed in the solvent NMP according to a mass ratio of 80:10:10, and after homogenization, a positive electrode slurry is obtained; the positive electrode slurry is coated on the conductive layer 40 of the composite current collector P1, and after drying, rolling, and cutting treatments, a positive electrode plate is obtained.

[0159] (2)Preparation of the negative electrode plate:

[0160] (2.1)Preparation of the support layer 10:

[0161] The polymer material and the two-dimensional nanoribbon material are melt-blended at 220 °C, uniformly dispersed at a rotation speed of 1000 rpm for 4 h, and made into the support layer 10 by calendering.

[0162] Among them, the polymer material is polypropylene (PP);

[0163] The two-dimensional nanoribbon material is NbAs, with a thickness of 250 nm, a width of 400 nm, and a length of 0.5 mm;

[0164] The mass ratio of the polymer material to the two-dimensional nanoribbon material is 100:12;

[0165] The thickness of the support layer 10 is 4.5 µm.

[0166] (2.2) Preparation of the safety coating 20: The same as in step (1.2).

[0167] (2.3) Preparation of the protective coating 30: The same as in step (1.3).

[0168] (2.4) Preparation of the conductive layer 40:

[0169] Pump the reaction chamber to a vacuum below 5×10 -5 Pa, introduce argon at a flow rate of 60 sccm, use a conductive metal material as the sputtering target, and perform DC magnetron sputtering coating under the conditions of a sputtering pressure of 1.5 Pa and a sputtering power of 180 W to form a conductive layer 40 on the protective coating 30.

[0170] Among them, the conductive metal material is Cu, and the thickness of the conductive layer 40 is 1 µm.

[0171] (2.5) Preparation of the negative electrode sheet:

[0172] Disperse the negative electrode active material graphite (Gr), binder CMC and SBR, and conductive agent SP in deionized water as the solvent according to a mass ratio of 80:4:6:10, and obtain a negative electrode slurry after homogenization; coat the negative electrode slurry on the conductive layer 40 of the composite current collector N1, and obtain a negative electrode sheet after drying, rolling and cutting.

[0173] (3) Assembly of the secondary battery:

[0174] In a glove box (Ar atmosphere, water, O 2 content <0.1 ppm), encapsulate the positive electrode sheet, glass fiber separator and negative electrode sheet with an aluminum-plastic film, and inject the electrolyte to make a laminated soft-pack battery cell; among them, the electrolyte includes 1 mol / L of LiPF 6 and an organic solvent (EC and EMC with a volume ratio of 1:1).

[0175] Examples 2 - 8

[0176] Examples 2 to 8 are basically the same as Example 1, and the differences are as follows:

[0177] Example 2: The mass ratio of the polymer material to the two-dimensional nanoribbon material is 100:5;

[0178] Example 3: The mass ratio of the polymer material to the two-dimensional nanoribbon material is 100:20;

[0179] Example 4: The two-dimensional nanoribbon material is replaced with TaAs of equal mass, with a thickness of 280 nm, a width of 350 nm, and a length of 0.5 mm;

[0180] Example 5: The two-dimensional nanoribbon material is replaced with an equal mass of NbP, with a thickness of 260 nm, a width of 380 nm, and a length of 0.5 mm;

[0181] Example 6: The mass ratio of the binder to the inorganic foaming agent is 1:2;

[0182] Example 7: The inorganic foaming agent is replaced with an equal mass of beryllium carbonate (BeCO 3 ).

[0183] Example 8: No groove 11 is formed on the surface of the support layer 10, and a safety coating 20 with a thickness of 1 µm is formed on the surface of the support layer 10 by the doctor blade method.

[0184] Comparative Examples 1 - 8

[0185] Comparative Examples 1-8 are basically the same as Example 8, and the differences are as follows:

[0186] Comparative Example 1: No two-dimensional nanomaterial is added to the support layer, and no safety coating and protective coating are provided;

[0187] Comparative Example 2: No two-dimensional nanomaterial is added to the support layer;

[0188] Comparative Example 3: The two-dimensional nanomaterial is replaced with silica with a particle size of 300 nm;

[0189] Comparative Example 4: No safety coating and protective coating are provided;

[0190] Comparative Example 5: No safety coating is provided;

[0191] Comparative Example 6: The inorganic foaming agent in the safety coating is replaced with basic copper carbonate, and the thermal decomposition temperature is about 200 °C;

[0192] Comparative Example 7: No protective coating is provided;

[0193] Comparative Example 8: The material of the positive electrode protective coating is replaced with Al, and the material of the negative electrode protective coating is replaced with Ni.

[0194] Test Example

[0195] The following tests are carried out on each example and each comparative example:

[0196] (1) Mechanical strength of the composite current collector: Cut three sample strips with a length and width of 150 mm × 15 mm, ensure that the samples are vertically placed on the test clips of the tensile testing machine, set the test parameters and start the detection, and record the tensile strength.

[0197] (2)Peeling strength of the composite current collector: The tape was flatly attached to the steel plate, the sample was fixed to the tape, an auxiliary tape was attached to the surface of the sample, and the steel plate and the auxiliary tape were fixed to a constant-speed tensile testing machine to start the test, and the peeling strength of each sample was recorded.

[0198] (3)Lift-to-drag ratio of the battery: After the battery was fully charged, its internal resistances R1 and R2 at 25 °C and 130 °C were measured respectively, and the lift-to-drag ratio of the battery was calculated according to R2 / R1.

[0199] (4)Room temperature cycle test: The battery was subjected to a room temperature cycle test at 2C / 2C, and the initial discharge specific capacity of the battery at 2C and the number of cycles when the capacity decayed to 80% were recorded.

[0200] The above test results are shown in Table 3.

[0201] As can be seen from Table 3: For Examples 1-8, the tensile strength of the composite current collector P in the positive electrode tab is 188 MPa - 196 MPa, and the peeling strength is 4.4 N / 25 mm - 4.8 N / 25 mm. The tensile strength of the composite current collector N in the negative electrode tab is 202 MPa - 210 MPa, and the peeling strength is 5.2 N / 25 mm - 5.5 N / 25 mm, having the advantages of high tensile strength and high peeling strength. After assembling into a battery, the lift-to-drag ratio from 25 °C to 130 °C is 14.3 - 26.5, proving that its internal resistance of the battery cell increases significantly at high temperature, which can inhibit abnormal loop current and effectively reduce the probability of thermal runaway of the battery at high temperature. The initial discharge specific capacity of the battery at 2C is 184.2 mAh / g - 185.3 mAh / g, and the number of cycles when the capacity decays to 80% is 743 - 863 times, having the advantages of high specific capacity and good cycle performance.

[0202] Compared with Example 1, Example 2 reduces the amount of two-dimensional nanoribbon material, and Example 3 increases the amount of two-dimensional nanoribbon material, resulting in a slightly worse mechanical property of the composite current collector, and a decrease in the lift-drag ratio of the battery, a smaller initial discharge specific capacity at 2C, and a slightly lower number of cycles. This proves that an appropriate addition amount of two-dimensional nanoribbon material has a certain improvement effect on the mechanical property of the composite current collector, as well as the capacity, cycle performance, and safety performance of the battery. Example 4 uses TaAs nanoribbons, and Example 5 uses NbP nanoribbons, resulting in a significant decrease in the number of cycles of the battery because the electron-conducting ability of TaAs and NbP two-dimensional nanoribbons is inferior to that of NbAs, thus leading to an increase in the resistance of the composite current collector and obvious heat generation during the cycling process at a 2C rate, resulting in the deterioration of the cycle performance. The amount of inorganic foaming agent in Example 6 is less, resulting in a significant decrease in the lift-drag ratio of the battery, proving that an increase in the amount of inorganic foaming agent is beneficial to reducing the probability of thermal runaway at high temperatures, thereby improving the safety performance of the battery. Example 7 uses beryllium carbonate as the inorganic foaming agent, and the lift-drag ratio decreases, proving that better safety performance can be obtained by using sodium silicate decahydrate as the inorganic foaming agent.

[0203] Neither the composite current collector P nor the composite current collector N in Example 8 is provided with a groove, the peel strength of the current collector becomes lower, and the lift-drag ratio of the battery cell under high-temperature conditions becomes smaller, thereby affecting the cycle performance and safety performance of the battery cell. This proves that the design of the groove structure helps to increase the contact area, improve the surface roughness, and enhance the bonding force between layers, thereby improving the cycle stability of the battery cell; when the foaming material layer is coated in the groove structure, after the battery cell abnormally heats up to the thermal decomposition temperature, the inorganic foaming agent will form a greater impact force in the limited groove space, which can damage the conductive layer and the electrode material layer on its surface, increase the impedance of the battery cell (increase in the lift-drag ratio value of the battery cell), and limit the abnormal current.

[0204] Compared with Example 8, in Comparative Example 1, no two-dimensional nanometer filler is added to the support layer, and no safety coating and protective coating are provided, resulting in a significant decrease in the tensile strength, peel strength of the composite current collector, as well as the lift-drag ratio and cycle performance of the battery. In Comparative Example 2, no two-dimensional nanometer filler is added to the support layer, but a safety coating and a protective coating are provided. Although the lift-drag ratio of the battery is significantly increased, the tensile strength, peel strength of the composite current collector, and the cycle performance of the battery are still relatively poor. In Comparative Example 3, SiO is added to the support layer 2The tensile strength, peel strength of the composite current collector, and the cycle performance of the battery are improved compared with Comparative Example 2, but there is still an obvious gap compared with Example 1. This proves that the two-dimensional nanobelt material helps to improve the mechanical properties of the support layer, enhance the tensile strength and peel strength of the composite current collector, and the improvement effect of the two-dimensional nanobelt material is more significant than that of the nanoparticles; in addition, the excellent conductivity of the two-dimensional nanobelt material can reduce the resistance of the composite current collector itself, avoid overcurrent heating during the high-current charge and discharge process of the battery, and thus improve the electrochemical stability of the battery.

[0205] Compared with Example 8, Comparative Example 4 does not have a safety coating and a protective coating, its peel strength decreases, and the lift-to-drag ratio and cycle performance of the battery are significantly worse. Comparative Example 5 does not have a safety coating, its peel strength and cycle performance are improved compared with Comparative Example 4, but the lift-to-drag ratio is still very poor. Comparative Example 6 uses basic copper carbonate as the inorganic foaming agent, and its thermal decomposition temperature is about 200 °C, resulting in a lift-to-drag ratio of only 1.32 when the battery is heated from 25 °C to 130 °C. This proves that selecting a suitable inorganic foaming agent can ensure a lower probability of thermal runaway at high temperatures.

[0206] Compared with Example 8, Comparative Example 7 does not have a protective coating, and Comparative Example 8 uses a single metal to make the protective coating, and the cycle performance of the battery becomes worse, proving that using a high-entropy alloy material as the protective coating can not only protect the foaming material but also increase the adhesion of the conductive layer, thereby improving the cycle performance of the battery.

[0207] In summary, the composite current collector designed in this application integrates excellent mechanical properties and conductivity, which helps to ensure the cycle stability of the battery core under the charge and discharge conditions of 2C rate. When the temperature inside the battery core abnormally rises to 80 °C - 130 °C, the inorganic foaming material will undergo an endothermic decomposition reaction, releasing a large amount of non-combustible and non-flammable gases such as CO 2 、H 2 O, etc., and destroying the conductive layer on the surface, improving the safety performance of the battery core from multiple dimensions.

[0208] Table 1. Composite current collector P in the positive electrode sheet

[0209]

[0210] Note 1: Mass ratio A refers to the mass ratio of the polymer material and the two-dimensional nanobelt material, mass ratio B refers to the mass ratio of the binder and the inorganic foaming agent, the thickness of the support layer is 6 μm, the thickness of the safety coating is 1.5 µm, the thickness of the protective coating is 30 nm, and the thickness of the conductive layer is 1 µm.

[0211] Table 2. Composite current collector N in the negative electrode sheet

[0212]

[0213] Note 2: The mass ratio A refers to the mass ratio of the polymer material to the two-dimensional nanoribbon material, the mass ratio B refers to the mass ratio of the binder to the inorganic foaming agent, the thickness of the support layer is 4.5 μm, the thickness of the safety coating is 1.5 µm, the thickness of the protective coating is 30 nm, and the thickness of the conductive layer is 1 µm.

[0214] Table 3. Performance of the composite current collector and the battery

[0215]

[0216] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0217] The above-described embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the protection scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A composite current collector, characterized in that: It includes a supporting layer, a safety coating, a protective coating and a conductive layer stacked in sequence; The support layer comprises a polymer material and a two-dimensional nanobelt material, wherein the polymer material comprises one or more of polyethylene, polypropylene, polyimide, polyvinyl chloride, polystyrene, polyethylene terephthalate and polybutylene terephthalate, and the mass ratio of the polymer material to the two-dimensional nanobelt material is 100:(1-30); The safety coating comprises a binder and an inorganic foaming agent, and the thermal decomposition temperature of the inorganic foaming agent is 80° C. to 130° C.; The protective coating comprises a high entropy alloy material; The surface of the support layer is provided with a plurality of grooves, and the depth of the grooves is less than the thickness of the safety coating; The safety coating is filled in the groove; The protective coating covers the safety coating and the supporting layer.

2. The composite current collector according to claim 1, characterized in that: The depth of the groove is 0.1 μm to 1 μm, the size of the groove is 1 μm to 2 μm, and the spacing between the grooves is 200 μm to 1000 μm.

3. The composite current collector according to claim 2, characterized in that: The cross-sectional shape of the groove in the thickness direction includes one or more of a square, a rectangle, a regular trapezoid, an inverted trapezoid, an inverted triangle, a semicircle and an irregular shape.

4. The composite current collector according to any one of claims 1 to 3, characterized in that: One or more of the following conditions are met: (1) The two-dimensional nanoribbon material comprises one or more of tantalum arsenide nanoribbon, niobium arsenide nanoribbon, tantalum phosphide nanoribbon and niobium phosphide nanoribbon; (2) The two-dimensional nanobelt material has a thickness of 50 nm to 400 nm, a width of 100 nm to 500 nm, and a length of 0.1 mm to 1 mm; (3) The thickness of the support layer is 4 μm to 8 μm.

5. The composite current collector according to any one of claims 1 to 3, characterized in that: One or more of the following conditions are met: (1) The binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium alginate, polyvinyl alcohol, polymethyl methacrylate, hydrogenated nitrile rubber and polyacrylic acid; (2) The inorganic foaming agent includes one or more of carbonates, bicarbonates and hydrated silicates; (3) The mass ratio of the binder to the inorganic foaming agent is 1:(2-3); (4) The thickness of the safety coating is 0.2 μm to 2 μm.

6. The composite current collector according to any one of claims 1 to 3, characterized in that: One or more of the following conditions are met: (1) The high entropy alloy material includes at least five of iron, cobalt, nickel, chromium, manganese, aluminum, copper, titanium, yttrium and tantalum; (2) The thickness of the protective coating is 20nm~50nm.

7. The composite current collector according to any one of claims 1 to 3, characterized in that: One or more of the following conditions are met: (1) The material of the conductive layer includes one or more of stainless steel, copper, nickel and aluminum; (2) The thickness of the conductive layer is 0.5 μm to 4 μm.

8. A method for preparing a composite current collector according to any one of claims 1 to 7, characterized in that: The following steps are involved: The polymer material and the two-dimensional nanobelt material are melt-blended and molded to form a support layer; A safety coating layer, a protective coating layer and a conductive layer are sequentially formed on the support layer.

9. The method for preparing a composite current collector according to claim 8, characterized in that: The preparation method of the safety coating comprises the following steps: Covering the support layer with a mixed slurry containing a binder and an inorganic foaming agent, and drying the mixed slurry to obtain the safety coating; or, The surface of the support layer includes a first area and a second area arranged around the first area; forming a plurality of grooves on the first region and covering the second region with a mask; The groove is filled with a mixed slurry containing a binder and an inorganic foaming agent, and then dried, and the mask is removed to obtain the safety coating.

10. A secondary battery, characterized in that: The composite current collector comprises the composite current collector as claimed in any one of claims 1 to 7, or comprises the composite current collector prepared by the method for preparing the composite current collector as claimed in claim 8 or 9.

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