Composite current collector, preparation method thereof and electrochemical device

Abstract

The invention relates to the technical field of current collectors, in particular to a composite current collector, a preparation method thereof and an electrochemical device, the composite current collector comprises a base material and aluminum conductive layers, and the aluminum conductive layers are arranged on the two sides of the base material through bonding layers; the protective layer is arranged on one side, far away from the base material, of the conductive layer; the protective layer forms a layer with an element transition structure on the surface of the conductive layer, the protective layer comprises an aluminum element, a carbon element and an oxygen element, and the content of the aluminum element, the content of the carbon element and the content of the oxygen element in the protective layer are in gradient distribution in the direction from the protective layer to the conductive layer. According to the aluminum composite current collector, a gradient heterostructure of reduced graphene oxide (rGO) transition to aluminum oxide (AlxOy) and then transition to Al is constructed between the conductive layer and the protective layer through the in-situ reduction reaction, continuous element gradient transition from the Al metal conductive layer to the protective layer is successfully achieved, the interface bonding strength of the coating is enhanced, and the durability of the aluminum composite current collector is achieved.

Description

Technical Field

[0001] The present application relates to the technical field of current collectors, and in particular to a composite current collector and a preparation method thereof, as well as an electrochemical device. Background Art

[0002] As power batteries develop rapidly towards high energy density, aluminum-PET-aluminum composite aluminum foil has attracted much attention as a new generation of current collector technology. Although the current mainstream vacuum evaporation process can achieve the combination of polymer base film and aluminum layer, it is found in actual applications that the bonding strength between the aluminum layer and the PET / PP substrate is insufficient. During long-term electrolyte infiltration and charge-discharge cycles, the aluminum layer is prone to interfacial peeling with the base film, resulting in the failure of the conductive layer to fall off. The reason is that there is a lack of effective activation treatment when aluminum vapor is deposited on the surface of the base film during the evaporation process. It is difficult to form a stable chemical bond between metal aluminum and polymer materials, and only physical adsorption leads to weak bonding. At the same time, only a 5-15nm aluminum oxide protective layer is formed on the surface of the aluminum layer, which is difficult to resist electrochemical corrosion in the highly corrosive electrolyte environment of the battery. After long-term circulation, the corrosion depth can reach the micron level, which seriously affects the conductive stability of the current collector. In addition, the aluminum layer will also corrode during long-term storage, resulting in unusable. These problems have caused the cycle life of the composite aluminum foil to be lower than that of traditional aluminum foil, becoming a key technical bottleneck restricting its commercial application.

[0003] Conventional solutions include coating with corrosion-resistant materials or graphene coatings. There are also methods of depositing an adhesion-enhancing layer on the surface of a plastic (such as PET) layer, such as materials such as aluminum oxide and silicon dioxide, and then depositing an aluminum layer; and enhancing the bonding between aluminum and PET by increasing the energy of aluminum vapor during evaporation. However, these measures still cannot achieve good corrosion resistance and reliable conductivity of composite aluminum foil.

[0004] Although the graphene or graphite oxide (GO) coating prepared by the coating process can improve the short-term anti-corrosion performance of the substrate through physical barrier effect, due to the mechanical bonding method mainly based on physical adsorption, corrosion failure is still prone to occur at the interface during long-term service. Physical coating is difficult to achieve a uniform thickness of hundreds of nanometers, and graphite oxide has poor conductivity.

[0005] Pure carbon material is coated on the surface of the current collector. However, pure carbon material has low adhesion and is easy to fall off; it creates a gap with the foil, increasing impedance; and may also require a binder to increase resistance. Therefore, its overall performance is often poor. Summary of the invention

[0006] The technical problem to be solved by the present invention is that the corrosion resistance of the battery conductive layer is poor, which affects the conductive stability of the current collector.

[0007] To this end, the present invention provides a composite current collector and a preparation method thereof, as well as an electrochemical device.

[0008] The technical solution adopted by the present invention to solve its technical problem is:

[0009] A composite current collector, comprising:

[0010] substrate, and

[0011] A conductive layer, wherein the conductive layer is disposed on both sides of the substrate through an adhesive layer, and the conductive layer is aluminum;

[0012] A protective layer, the protective layer being arranged on a side of the conductive layer away from the substrate, the protective layer forming a layer having an element transition structure on the surface of the conductive layer;

[0013] The protective layer contains aluminum, carbon and oxygen. Along the direction from the protective layer to the conductive layer, the aluminum content, carbon content and oxygen content in the protective layer with an element transition structure are distributed in a gradient.

[0014] Furthermore, the oxygen and aluminum elements in the protective layer exist in the form of Al-O chemical bonds, and the carbon and oxygen elements in the continuous transition zone exist in the form of CO chemical bonds and / or C=O chemical bonds.

[0015] Furthermore, in the protective layer, the carbon element exists in the form of graphite or amorphous carbon, and the aluminum element exists in the form of aluminum oxide or Al.

[0016] Furthermore, the protective layer contains at least one of graphene oxide, multilayer graphite oxide, reduced graphite oxide, and reduced multilayer graphite oxide.

[0017] Furthermore, along the direction from the protective layer to the conductive layer, the element transition structure of the protective layer is generally: transition from reduced graphene oxide (rGO) to aluminum oxide (Al x O y ) and then transition to Al.

[0018] Furthermore, along the direction from the protective layer to the conductive layer, the element transition structure of the protective layer satisfies at least one of the following conditions: a. the aluminum content in the element transition structure increases; b. the carbon content generally shows a decreasing trend; c. the oxygen content generally shows a trend of first increasing and then decreasing.

[0019] Furthermore, the roughness of the side of the conductive layer facing the bonding layer is greater than the roughness of the side of the conductive layer facing the protective layer, and the roughness Ra2 of the side of the conductive layer facing the bonding layer is ≥20 nm.

[0020] Furthermore, the conductive layer is a layered structure formed by a plurality of aluminum metal layers, and along the thickness direction of the conductive layer, the number of gap pores between adjacent metal layers is less than 10 / 1 μm.

[0021] An electrochemical device comprises a positive electrode, a negative electrode, and a separator arranged between the positive electrode and the negative electrode, wherein at least one of the positive electrode or the negative electrode is the composite current collector as described above.

[0022] A current collector manufacturing process comprises the following steps:

[0023] S1, coating graphene oxide and / or multilayer graphite oxide material as a release agent layer on a substrate to obtain an A0 film;

[0024] S2, using a vacuum coating machine to evaporate aluminum on the side of the substrate coated with the release agent layer to obtain an A1 prefabricated conductive layer;

[0025] S3, applying glue on the aluminum surface of the A1 film, drying it to form an adhesive layer, and then hot rolling it to the two sides of the substrate to obtain a B1 semi-finished composite film. In this step, the aluminum grains at the end of aluminum growth are oriented toward the substrate and covered with the adhesive layer;

[0026] S4, placing B1 in an oven for curing and curing, so that the adhesive layer, the substrate and the Al conductive layer are fully adhered to each other, and a semi-finished composite film B2 is obtained;

[0027] S5, using a stripping and reeling device to strip the A substrates on both sides of B2, and cut them into finished products M.

[0028] The beneficial effect of the present invention is that the present invention constructs reduced graphene oxide (rGO), aluminum oxide (Al x O y )-Al gradient heterogeneous structure, successfully realizing the continuous element gradient transition from Al metal conductive layer to protective layer. This unique structural design not only significantly enhances the interfacial bonding strength of the coating, but also forms a passivation layer at the interface through chemical bonding, which significantly improves the acid resistance and electrochemical corrosion resistance of the composite coating, and realizes the durability of the aluminum composite current collector.

[0029] The present invention inverts the direction of the aluminum layer, so that one side of the aluminum grains at the end of growth faces the substrate and covers the bonding layer. This avoids corrosion damage to the aluminum grains at the end of growth, and the roughness of one side of the aluminum grains at the end of growth is high, and the adhesive solution can fully wet the grains and gaps, so that the grains and the gaps between the grains are fully filled with the bonding layer, thereby improving the stability and corrosion resistance of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0031] Figure 1 It is a schematic diagram of the structure of the composite current collector in the present invention.

[0032] Figure 2It is a schematic diagram of the distribution of various elements in the protective layer of Example 1 of the present invention.

[0033] Figure 3 It is a schematic diagram of the distribution of various elements in the protective layer of Example 4 of the present invention.

[0034] Figure 4 It is a schematic diagram of the protective layer and the conductive layer in the present invention.

[0035] In the figure: 01, substrate; 02, first bonding layer; 03, second bonding layer; 04, first conductive layer; 05, second conductive layer; 06, first protective layer; 07, second protective layer; 08, first passivation layer; 09, second passivation layer. DETAILED DESCRIPTION

[0036] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0037] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0038] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] An electrochemical device comprises a positive electrode, a negative electrode, and a separator arranged between the positive electrode and the negative electrode, wherein at least one of the positive electrode or the negative electrode is a composite current collector.

[0040] The composite current collector includes a substrate 01, a first bonding layer 02, a second bonding layer 03, a first conductive layer 04, a second conductive layer 05, a first protective layer 06, and a second protective layer 07. The first conductive layer 04 is disposed on one side of the substrate 01 through the first bonding layer 02, the second conductive layer 05 is disposed on the other side of the substrate 01 through the second bonding layer 03, the first protective layer 06 is disposed on a side of the first conductive layer 04 away from the first bonding layer 02, and the second protective layer 07 is disposed on a side of the second conductive layer 05 away from the second bonding layer 03.

[0041] The substrate 01 is one or more of PET, PP, PE, PI or a multilayer composite film, and has a thickness of 1 μm to 30 μm. The elastic modulus E1 of the substrate 01 is greater than 1000 MPa. Preferably, the elastic modulus E1 of the substrate 01 is greater than 3000 MPa, and has better mechanical properties.

[0042] The bonding layer is a bonding polymer material, a combination of modified polyethylene, ethylene copolymer, modified polypropylene, propylene copolymer, polyurethane and at least one of an epoxy curing agent and an isocyanate curing agent, and its thickness is 0.2μm to 2μm. The electrolyte swelling of the bonding layer is less than 20%, and the elastic modulus E2 is in the range of 10MPa to 500MPa. Preferably, E2 is in the range of 50MPa to 200MPa, which has better bonding properties.

[0043] The conductive layer is a layered structure composed of one or more aluminum metal layers. Preferably, the number of aluminum metal layers is 1 to 5, and the thickness of each conductive layer is 0.3 μm to 5 μm, preferably, the thickness is 0.5 μm to 2 μm.

[0044] When the number of conductive layers is ≥2, in the cross section, in the direction toward the substrate 01, the number of gap pores between the first layer and the second layer is less than 10 / 1μm, preferably less than 5 / 1μm (pores are defined as pores with a size greater than 10nm). When the conductive layer is a multilayer structure, pores are easily generated between aluminum layers. When the current collector is in a harsh environment, the pores are often first corroded and further expanded. When multiple pores are corroded in succession, the upper aluminum layer is easily peeled off, causing the current collector to fail. The aluminum of the present invention is evaporated on the surface of the release agent material. By changing the release agent material to graphene oxide material, when aluminum is deposited on the first aluminum surface, it can better cover the first layer and almost no pores are generated. This structure has a two-layer dense aluminum layer structure, which further enhances the corrosion resistance of the aluminum layer surface.

[0045] It should be noted that the quality of bonding, in addition to the material of each layer, is often also the key to corrosion resistance. Between the bonding layer and the conductive layer, since the aluminum metal layer is prepared by evaporating aluminum, the surface aluminum grains (B) become larger as the thickness of the aluminum layer increases during the growth of the evaporating aluminum, and the gaps between the grains produce sharper acute angles. If this structure is exposed on the surface of the current collector, it is easily corroded and damaged, and even the damage extends to the bottom of the aluminum layer, resulting in the detachment of the aluminum layer and the substrate 01, making the current collector ineffective. The present invention inverts the direction of the aluminum layer, allowing the aluminum grains (B) at the end of growth to face the substrate 01 and cover the bonding layer. Thereby avoiding the corrosion damage of the aluminum grains at the end of growth, and the roughness of the aluminum grains (B) at the end of growth is high, the adhesive solution can fully wet the grains and the gaps, so that the grains and the gaps between the grains are fully filled with the bonding layer, protecting this structure. Technical solution, the aluminum layer grown on the substrate is peeled off and pasted to the substrate 01, thereby realizing the position exchange of the starting grains and the end of growth grains.

[0046] Therefore, in the present application, the grains on the B side of the conductive layer are bonded to the bonding layer, and the roughness of the A side of the grain at the beginning of the conductive layer growth is smaller than the roughness of the B side of the grain at the end of the growth. The roughness of the conductive layer B side facing the bonding layer is Ra2≥20nm, and the roughness of the conductive layer A side facing the bonding layer outward is Ra1≤20nm.

[0047] The quality of bonding, in addition to the material of each layer, is often also affected by the interface between layers. The key to corrosion resistance. During the growth process of evaporated aluminum, as the thickness of the aluminum layer increases, the surface aluminum grains (B) also become larger, and the gaps between the grains produce sharper angles. If this structure is exposed on the surface of the current collector, it is easily corroded and damaged, and even the damage extends to the bottom of the aluminum layer, resulting in the detachment of the aluminum layer and the substrate 01, making the current collector ineffective. The present invention inverts the direction of the aluminum layer, allowing the aluminum grains (B) at the end of growth to face the bonding layer and cover the bonding layer, thereby avoiding corrosion damage to the aluminum grains at the end of growth, and the roughness of the aluminum grains (B) at the end of growth is relatively high, and the adhesive solution can fully wet the grains and the gaps, so that the grains and the gaps between the grains fully fill the bonding layer, protecting this structure, and in the battery cell, avoiding direct contact between the coarse grains and the electrolyte system, inhibiting the erosion between the grains, thereby extending the life of the aluminum layer, that is, increasing the life of the battery cell. This technical solution peels off the aluminum layer grown on the substrate and sticks it to the substrate 01, thereby achieving the position exchange of the grains at the beginning and the grains at the end of the growth.

[0048] It should be noted that the protective layer covers the surface of the conductive layer, and the thickness of the protective layer is 30nm to 300nm. Preferably, the thickness of the protective layer is 70nm to 200nm. The protective layer contains at least one of graphene oxide, multilayer graphite oxide, reduced graphite oxide, and reduced multilayer graphite oxide. The protective layer forms a layer with an element gradient transition structure on the surface of the conductive layer. Specifically, the protective layer with an element gradient transition structure contains carbon, oxygen, and aluminum elements, wherein the carbon element exists in the form of graphite or amorphous carbon, and the aluminum element exists in the form of aluminum oxide or Al. Furthermore, oxygen and aluminum elements exist in the form of Al-O chemical bonds, and carbon and oxygen elements exist in the form of CO chemical bonds and / or C=O chemical bonds.

[0049] In particular, aluminum, carbon and oxygen are distributed in a gradient between the protective layer and the conductive layer and between different thicknesses of the protective layer. The element composition of the protective layer outside the conductive layer satisfies the following distribution along the thickness direction. For details, please refer to Figure 2 , Figure 3 As shown:

[0050] a. The content of aluminum (Al) element generally increases from the surface side to the conductive layer. The content of aluminum element increases from 0 to 15 at% on the surface side to 80 at% to 100 at% on the conductive layer side;

[0051] b. The content of carbon (C) element generally decreases from the surface side to the conductive layer. The carbon content decreases from 80at% to 100at% on the surface side to 0 to 15at% on the conductive layer side;

[0052] c. The content of oxygen (O) element generally increases first and then decreases from the surface side to the conductive layer. The thickness of the layer with an oxygen content of more than 10% is greater than 10nm. Preferably, at least 2 local peaks are contained within the interval of 25% to 75% in the thickness direction, the distance between adjacent peaks is 10nm to 100nm, and the peak height difference is ≤50at%.

[0053] Preferably, the surfaces of the first protective layer 06 and the second protective layer 07 away from the substrate 01 have a sheet-like pit structure, the pit depth is 10nm to 200nm, and the sheet-like structure size is 0.5μm to 20μm. Quantity 1000 pieces / mm 2 ~10000pcs / mm 2 The depth of the surface pits is 10nm to 100nm.

[0054] A current collector manufacturing process:

[0055] S1, coating a dispersion of graphene oxide and / or multilayer graphite oxide (hereinafter referred to as graphene oxide, GO) on a substrate and drying it, which serves as a release agent layer, to obtain an A0 film. Regulating the concentration and particle size of graphene oxide, and controlling the thickness and spreading state of graphene oxide on the substrate, preferably, the graphene oxide is spread flat on the substrate. The thickness of the release agent determines the upper limit of the reaction amount.

[0056] S2, prefabricated protective layer and conductive layer. A vacuum coating machine is used to evaporate aluminum on the side of the substrate coated with the release agent layer to obtain a prefabricated protective layer and an A1 prefabricated conductive layer.

[0057] Specifically, the termination and degree of the reaction between aluminum vapor and graphene oxide are controlled by controlling the evaporation time and temperature, that is, the thickness of the first evaporation, that is, the temperature of the vapor. Then, the conductive layer is thickened to form a complete prefabricated protective layer and an A1 prefabricated conductive layer. The thickness of the first evaporation can be selected from 0.05 μm to 1.5 μm. The evaporation temperature is controlled at 1200°C to 1500°C, and the vacuum degree is controlled at less than 1×10 -2 Pa.

[0058] At this time, the structure is: substrate-release agent layer (prefabricated protective layer)-Al prefabricated conductive layer. On the one hand, during the evaporation process, aluminum vapor is deposited on the surface of the graphene oxide layer to form aluminum grains and grow, and finally form an Al prefabricated conductive layer; on the other hand, the graphene oxide or multilayer graphite oxide material is reduced by aluminum vapor to reduced graphene oxide and / or reduced multilayer graphite oxide (hereinafter referred to as reduced graphene oxide, rGO), and the C element and O element in the release agent layer diffuse into the aluminum layer, and at the same time, the Al element diffuses into the release agent layer, and finally forms a transition from reduced graphene oxide (rGO) to aluminum oxide (Al x O y ) and then transition to the Al conductive layer to form a protective layer with an element gradient transition structure.

[0059] It should be noted that the thickness of the release agent controls the total amount of the reaction, the evaporation time controls the depth of the reaction, and the evaporation temperature controls the degree of the reaction. Controlling the above parameters makes the final conductive layer have good conductivity and corrosion resistance.

[0060] S3, glue coating and drying on the aluminum surface of the A1 film to form an adhesive layer, and then hot roller pressing and laminating with the two sides of the substrate 01. It should be noted that in this step, the aluminum grains (B) at the end of aluminum growth are oriented toward the substrate 01 and covered with the adhesive layer. Laminating pressure: 0.1MPa~1MPa, hot pressing roller temperature: 50℃~120℃, substrate 01 is a polymer film. Obtain B1 semi-finished composite film

[0061] S4, placing B1 in an oven for curing and curing, so that the adhesive layer and the substrate 01 and the Al conductive layer are fully adhered. Temperature: 50°C to 80°C, duration: 48h to 120h. Obtain B2 semi-finished composite film.

[0062] S5, using a stripping and reeling device to strip the A substrates on both sides of B2, and cut them into finished products M.

[0063] At this time, the structure of the current collector is: protective layer-Al conductive layer-adhesive layer-substrate 01-adhesive layer-Al conductive layer-protective layer; wherein the structure of the protective layer from the outside to the inside is: reduced graphene oxide (rGO) / aluminum oxide (Al x O y )-Al conductive layer structure.

[0064] Wherein, the substrate A is a plastic film or a metal foil. The release agent is graphene oxide and / or multilayer graphite oxide, with a particle size of 0.01 μm to 20 μm and a carbon content of 10% to 80%.

[0065] Transition of reduced graphene oxide (rGO) to alumina (Al2O3) via in situ reduction reaction x O y ) transitions to Al to form an outer protective layer of the conductive layer of the element gradient heterostructure, successfully realizing the continuous element gradient transition from the Al metal conductive layer to the surface coating. Figure 2 , 3 , Figure 2 The distribution of elements in the protective layer of Example 1 using graphene oxide release agent for aluminum plating is shown in FIG. Figure 3 The distribution of elements in the protective layer of Example 4 using PET aluminum plating is shown in FIG. Figure 2 The a-picture in the figure shows the distribution of the C element in the protective layer from the outermost layer (depth 0) to the conductive layer in Example 1, the b-picture shows the distribution of the O element, and the c-picture shows the distribution of the Al element; Figure 3 The a-figure in the figure shows the distribution of the C element in the protective layer from the outermost layer (depth 0) to the conductive layer in Example 4, the b-figure shows the distribution of the O element, and the c-figure shows the distribution of the Al element. The aluminum layer is more compact by using a graphene oxide release agent, and thus has a higher conductivity and a lower resistivity at the same thickness, and the longitudinal growth of aluminum is inhibited to a certain extent (specifically, there is no obvious void at the interface between the first evaporation and the second evaporation, and the interface is smooth).

[0066] In other embodiments, a first passivation layer 08 is provided between the first bonding layer 02 and the first conductive layer 04, and a second passivation layer 09 is provided between the second bonding layer 03 and the second conductive layer 05. The provision of the passivation layer further improves the corrosion resistance of the inner layer of the aluminum conductive layer and enhances the bonding force between the conductive layer and the bonding layer.

[0067] When preparing the current collector, before step S3, a passivation solution is coated on the aluminum surface of A1, and then dried and cured at high temperature. The passivation solution is a resin containing trivalent chromium, which forms a passivation layer at the interface through chemical bonding, so that the acid resistance and electrochemical corrosion resistance of the composite coating are significantly improved, and the durability of the aluminum composite current collector is achieved.

[0068] Table 1 Current collector parameters of Examples 1 to 6 and Comparative Examples 1 to 4

[0069]

[0070]

[0071]

[0072] Table 1 (continued)

[0073]

[0074]

[0075]

[0076] Table 2 Performance parameters of electrochemical devices made using current collectors of Examples 1 to 6 and Comparative Examples 1 to 4

[0077]

[0078]

[0079] In the preparation of the current collector in Examples 1 to 6, a release agent containing graphene oxide is used for evaporation transfer, thereby forming a rGO-Al film on the surface of the conductive layer (aluminum layer). x O y The protective layer of the gradient structure has good corrosion resistance, wherein the element contents in the element transition structure of the protective layer in the current collectors of Example 1 and Example 4 are respectively as follows: Figure 2 and Figure 3 shown.

[0080] From the acid corrosion test results, Examples 1 to 6 have good corrosion resistance, the surface aluminum is not easily corroded, and the aluminum layer does not fall off from the bonding layer.

[0081] In contrast, in comparison examples 1 to 2, no release agent was used, and the aluminum on the current collector surface was easily corroded by acid, and the aluminum layer also easily fell off. In comparison example 3, no release agent was used for direct evaporation, and graphene and alumina were coated on the outer surface of the conductive layer for protection. Although this method has good corrosion resistance on the surface of the conductive layer, its aluminum layer easily fell off, and the corrosion resistance was increased by alumina and graphite coating, resulting in poor conductivity of the aluminum layer, which affected its use. x O y The gradient structure, whose surface is susceptible to acid corrosion. The corrosion potential and corrosion potential deviation further prove that the invented current collector has good corrosion resistance.

[0082] The samples of Example 1 and Comparative Example 1 were placed at room temperature. The current collector in Example 1 remained normal after 24 months at room temperature, while the current collector in Comparative Example 1 began to corrode the conductive layer after 12 months at room temperature. Therefore, the storage conditions of current collector X1 are lower than those of current collector Y1, while the storage of current collector Y1 requires strict control of temperature and humidity, which increases the cost. The performance of current collector X1 is well maintained after long-term storage.

[0083] The battery cell containing the current collector of the present invention was cycled for 500 cycles, and a positive electrode coating roller pressing experiment was performed. The current collector was removed to observe the state of the current collector. The current collector and the active material in the electrochemical devices of Examples 7 to 12 have good adhesion. After being soaked in the electrolyte, the active material still does not fall off. However, after the pole piece in the comparative example is rolled, its aluminum layer easily falls off from the substrate, and the active material easily falls off from the aluminum layer. After the battery cell is cycled, the current collector of the present invention still has good performance, while the aluminum layer of the comparative example falls off or is severely corroded.

[0084] Furthermore, Figure 4 The small figure a in the figure is a cross section of the prefabricated conductive layer A1 in Example 5. After the conductive layer in Example 5 is processed, the surface of the third layer is bonded with the adhesive layer, which is the innermost layer of the conductive layer. The number of bubbles in the first and second conductive layers of Example 5 is 0 / mm; Figure 4 The small picture b in the figure is the cross section of the conductive layer of the current collector of comparative example 2. The third layer of the conductive layer is the innermost layer. The number of bubbles in the third and second conductive layers of the current collector of comparative example 2 is 50 / mm, and a large number of pores are easily corroded. In addition, the surface roughness Ra of the first layer (the outermost layer close to the protective layer) of Example 5 is 10.2nm, while the surface roughness Ra of the first layer of comparative example 2 is 46.2nm. A higher roughness is also easily corroded, forming a weak point.

[0085] The following are the specific operating steps of the acid resistance test, electrochemical corrosion potential, self-corrosion potential offset test and electrolyte immersion test in the examples and comparative examples of the present application:

[0086] 1. Acid resistance test

[0087] 1. Sample Preparation

[0088] Cut the aluminum foil into fixed sizes (such as 2×2cm 2 ), record the area (A).

[0089] After drying, weigh the initial mass (W0, accuracy 0.1 mg).

[0090] 2. Corrosion conditions:

[0091] Corrosive liquid: 10% H2SO4 (mass fraction), temperature controlled at 25±1°C (constant temperature in water bath).

[0092] Soaking time: Select according to preliminary experiments (such as 10 to 60 minutes) to avoid complete dissolution of the aluminum foil.

[0093] Post-processing: After taking out the sample, rinse it with deionized water, dehydrate it with alcohol, dry it and weigh it (W1).

[0094] Calculate weight loss: ΔW = W0-W1.

[0095] 3. Corrosion rate calculation

[0096] Mass loss rate V: V = ΔW / (A×t) (ΔW: mass loss, A: surface area, t: time)

[0097] 2. Test of electrochemical corrosion potential and self-corrosion potential offset of current collector

[0098] 2.1 Sample preparation

[0099] Material processing: Cut the current collector into suitable sizes (such as 1×1cm 2 ), use ethanol or acetone ultrasonic cleaning to remove surface grease and pollutants, and then dry for use.

[0100] Electrolyte selection: Select according to the actual application scenario (e.g. 1M LiPF6 in EC / DMC electrolyte is commonly used in lithium-ion batteries).

[0101] Environmental control: It is recommended to operate in an inert atmosphere (such as an argon glove box) to avoid interference from oxygen and moisture.

[0102] 2.2 Electrochemical test system

[0103] Three-electrode system:

[0104] Working electrode (WE): Aluminum foil sample (ensuring consistent effective exposure area).

[0105] Reference electrode (RE): Ag / AgCl (applicable to organic electrolyte) or saturated calomel electrode (SCE, aqueous solution system).

[0106] Counter electrode (CE): platinum sheet or graphite rod.

[0107] Equipment: Electrochemical workstation (such as Gamry, BioLogic, etc.).

[0108] 2.3 Testing Process

[0109] Open Circuit Potential (OCP) Test:

[0110] Immerse the aluminum foil in the electrolyte and record the potential change over time until it stabilizes (usually 30 to 60 minutes). The stable value is the self-corrosion potential (E_corr).

[0111] Potentiodynamic polarization curve (Tafel curve) test: scanning range: E_corr±250mV; scanning rate: 0.1~1mV / s.

[0112] The corrosion current density (I_corr) and corrosion potential (E_corr) were calculated by Tafel extrapolation method.

[0113] Self-corrosion potential offset (ΔE_corr):

[0114] Repeat the OCP test before and after 100 cycles and calculate the potential change:

[0115] ΔE_corr=E_(corr,after)-E_(corr,before)

[0116] Explanation: Negative shifts indicate increased corrosion tendency, positive shifts indicate passivation or improved corrosion resistance.

[0117] 3. Positive electrode coating roller pressing experiment: observe the roller pressing condition after the composite current collector is coated with the positive electrode material and the electrode is immersed in the electrolyte.

[0118] method:

[0119] 1. Ingredients, double-sided coating of positive electrode (lithium cobalt oxide: SP: PVDF = 96: 1: 3);

[0120] 2. Cut into strips with a length of 100 mm and a width of 25 mm and roll them four times, with a compaction density of 4.1 g / cm3;

[0121] 3. Soak in an oven at 85°C for 24 hours in electrolyte solution: EC:DEC:DMC=1:1:1, 1 mol / L lithium hexafluorophosphate, containing 1000 ppm water.

[0122] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A composite current collector, characterized in that: include, a substrate (01), and A conductive layer, the conductive layer is arranged on both sides of the substrate (01) through an adhesive layer, and the conductive layer is aluminum; A protective layer, the protective layer being arranged on a side of the conductive layer away from the substrate, the protective layer forming a layer having an element transition structure on the surface of the conductive layer; The protective layer contains aluminum, carbon and oxygen. Along the direction from the protective layer to the conductive layer, the aluminum content, carbon content and oxygen content in the protective layer with an element transition structure are distributed in a gradient.

2. The composite current collector according to claim 1, characterized in that: The oxygen and aluminum elements in the protective layer exist in the form of Al-O chemical bonds, and the carbon and oxygen elements in the continuous transition zone exist in the form of CO chemical bonds and / or C=O chemical bonds.

3. The composite current collector according to claim 1, characterized in that: In the protective layer, the carbon element exists in the form of graphite or amorphous carbon, and the aluminum element exists in the form of aluminum oxide or Al.

4. The composite current collector according to claim 1, characterized in that: The protective layer comprises at least one of graphene oxide, multilayer graphite oxide, reduced graphite oxide, and reduced multilayer graphite oxide.

5. The composite current collector according to claim 1, characterized in that: Along the direction from the protective layer to the conductive layer, the element transition structure of the protective layer is generally: transition from reduced graphene oxide (rGO) to aluminum oxide (Al x O y ) and then transition to Al.

6. The composite current collector according to claim 1, characterized in that: Along the direction from the protective layer to the conductive layer, the element transition structure of the protective layer satisfies at least one of the following conditions: a. The aluminum content in the element transition structure generally shows an increasing trend; b. The carbon content generally shows a decreasing trend; c. The oxygen content generally shows a trend of first increasing and then decreasing.

7. The composite current collector according to claim 1, characterized in that: The roughness of the side of the conductive layer facing the bonding layer is greater than the roughness of the side of the conductive layer facing the protective layer, and the roughness Ra2 of the side of the conductive layer facing the bonding layer is ≥20 nm.

8. The composite current collector according to claim 1, characterized in that: The conductive layer is a layered structure formed by a plurality of aluminum metal layers. Along the thickness direction of the conductive layer, the number of gap pores between adjacent metal layers is less than 10 / 1 μm.

9. An electrochemical device, characterized in that: The invention comprises a positive electrode, a negative electrode, and a separator arranged between the positive electrode and the negative electrode, wherein at least one of the positive electrode or the negative electrode is a composite current collector as claimed in any one of claims 1 to 8.

10. A current collector manufacturing process, characterized in that: The following steps are involved: S1, coating graphene oxide and / or multilayer graphene oxide material on a substrate as a protective layer to obtain an A0 film; S2, using a vacuum coating machine to evaporate aluminum on the side of the substrate coated with the release agent layer to obtain an A1 prefabricated conductive layer; S3, applying glue on the aluminum surface of the A1 film, drying it to form an adhesive layer, and then hot rolling it to the two sides of the substrate to obtain a B1 semi-finished composite film. In this step, the aluminum grains at the end of aluminum growth are oriented toward the substrate and covered with the adhesive layer; S4, placing B1 in an oven for curing and curing, so that the adhesive layer, the substrate and the Al conductive layer are fully adhered to each other, and a semi-finished composite film B2 is obtained; S5, using a stripping and reeling device to strip the A substrates on both sides of B2, and cut them into finished products M.

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