Composite current collector, preparation method thereof and battery

Abstract

The invention belongs to the technical field of composite current collectors, and particularly relates to a composite current collector, a preparation method thereof and a battery, and the preparation method comprises the following steps: preparing a polymer substrate; repeatedly coating the slurry containing the conductive carbon material on the upper surface and the lower surface of the polymer substrate, drying, and drilling to obtain a carbon film interlayer with uniformly distributed through holes; modifying the carbon film interlayer by using a silane coupling agent, and immersing the carbon film interlayer in an electrolyte solution to electroplate a metal conductive layer; and cleaning and drying to obtain the target composite current collector. The problems that the composite current collector is poor in conductivity, large in interface impedance with active substances, heavy in mass and the like can be effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of composite current collector technology, specifically relating to a composite current collector, its preparation method, and a battery. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] With the development of lithium batteries, higher demands are being placed on reducing the weight of lithium-ion batteries and increasing their energy density. Developing lightweight, high-performance composite current collectors is one solution. The requirements for composite current collectors generally include lightweight, good conductivity, low interfacial impedance with the active material, good mechanical properties, and good processing characteristics.

[0004] Composite current collectors often use polymer materials to replace part of the metal in the original metal foil, thereby reducing weight while retaining the mechanical properties of the metal foil. For example, a composite current collector with a "sandwich" structure consisting of a first metal layer, a polymer intermediate layer, and a second metal layer has poor conductivity, high interfacial impedance with the active material, and limited effect on weight reduction.

[0005] Another method involves coating both sides of a PET film with conductive layers such as graphene, carbon nanotubes, and conductive carbon black to create a composite current collector. While this type of current collector is significantly effective in reducing weight, its conductivity and mechanical properties are still considerably inferior to those of conventional metal foils, and its processing performance is also poor. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a composite current collector, its preparation method, and a battery.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a composite current collector, comprising a polymer substrate, a carbon material coating attached to the upper and lower surfaces of the polymer substrate, and a metal conductive layer attached to the surface of the carbon material coating. The polymer substrate and the carbon material coating are uniformly distributed with through holes, and a conductive metal material is deposited in the through holes to connect the conductive metal layers on both sides of the polymer substrate.

[0008] Secondly, the present invention provides a method for preparing the composite current collector, comprising the following steps: Preparation of polymer substrates; A slurry containing conductive carbon material is repeatedly applied to both the top and bottom surfaces of a polymer substrate. After drying, holes are drilled to obtain a carbon film interlayer with uniformly distributed through holes. The carbon film interlayer is modified with a silane coupling agent and then immersed in an electrolyte solution to electroplate a metal conductive layer. After cleaning and drying, the target composite current collector is obtained.

[0009] Thirdly, the present invention provides a battery in which the current collector of the electrode is the composite current collector.

[0010] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: The carbon film interlayer is composed of a flame-retardant composite polymer substrate and a conductive carbon material coating. The electroplated metal foil layer is uniformly attached to the upper and lower surfaces of the carbon film interlayer and the cylindrical wall surface inside the through hole. The two sides along the current collector winding direction form a thickened electroplated metal foil layer attached to the upper and lower surfaces of the flame-retardant composite polymer substrate.

[0011] This composite current collector is lighter and thinner than traditional metal current collectors, while also possessing flame retardancy, which it lacks, thus preventing the spread of thermal runaway. Compared to traditional "sandwich" structure composite current collectors, it has better conductivity, lower contact resistance with the active material, tighter coating with the active material, and is less prone to falling off during processing or cell cycling. At the same time, it has superior mechanical properties such as tensile strength. Batteries made using this current collector can achieve high energy density, excellent cycle performance, and strong thermal stability. Attached Figure Description

[0012] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0013] Figure 1 This is a schematic diagram of the cross-sectional structure of the composite current collector; Figure 2 This is a partial planar schematic diagram of a carbon thin film interlayer containing through holes; Figure 3 These are the 0.1C discharge curves of LFP coin cells prepared by the composite current collectors of Example 1 and Comparative Examples 1, 2, and 5; Figure 4 The figures show the 0.1C discharge curves of the LFP button cells prepared by the composite current collectors of Example 1 and Comparative Examples 3 and 4.

[0014] Among them, 1-Cu coating; 2-carbon material coating; 3-through hole; 4-polymer substrate. Detailed Implementation

[0015] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0016] To address the problems of poor conductivity, easy peeling of active material after coating, high interfacial impedance between the composite current collector and the active material, and heavy weight in the existing composite current collector, the present invention provides a composite current collector, comprising a polymer substrate, a carbon material coating attached to the upper and lower surfaces of the polymer substrate, and a metal conductive layer attached to the surface of the carbon material coating. The polymer substrate and the carbon material coating are uniformly distributed with through holes, and a conductive metal material is deposited in the through holes to connect the conductive metal layers on both sides of the polymer substrate.

[0017] In this invention, the through holes in the carbon thin film interlayer serve to form a conductive path when the Cu coating is deposited. This conductive path is formed by the Cu coating deposited on the columnar surface inside the through holes in one step, creating a three-dimensional conductive path with the Cu coating connecting the upper and lower surfaces of the composite current collector. This effectively ensures the electronic conductivity of the upper and lower surfaces of the composite current collector along the thickness direction. Its electronic conductivity is improved by at least one order of magnitude compared to conventional "sandwich" structure current collectors. It also eliminates the need for welding the upper and lower surfaces of the electrode tabs to form a conductive path after the conventional "sandwich" structure current collector is made into an electrode sheet, simplifying the process and saving costs.

[0018] Furthermore, during electrode coating, the active material slurry is slightly embedded in the through-holes to some extent. Therefore, this porous array structure can also increase the contact area between the active material and the current collector, reducing the interfacial contact resistance between them at the electrochemical level. The resulting battery has less polarization and better capacity utilization. During battery cycling, the active material is less likely to pulverize and fall off. At the physical performance level, the stress of the active material coating is more evenly dispersed, and the peel force between it and the current collector is also improved. This makes it less likely for the active material to crack or fall off during the electrode rolling, winding, and stacking process, resulting in a wider battery processing window and reduced processing difficulty.

[0019] The presence of a carbon layer in the composite current collector improves its electronic conductivity compared to conventional "sandwich" structure current collectors, effectively reducing ohmic impedance when used in lithium batteries. Simultaneously, the rough surface structure of the carbon material, after electrochemical plating, allows fine Cu grains to anchor on the carbon layer, increasing the surface roughness of the Cu plating and creating a larger bonding area with the active material. This reduces the interfacial impedance between the current collector and the active material. The rough plating also provides better wetting conditions for the electrolyte, effectively reducing battery polarization impedance and allowing for better battery capacity utilization. Furthermore, compared to conventional "sandwich" structure current collectors, the presence of the carbon layer increases the thermal conductivity of the composite current collector, reducing the phenomenon of localized abnormal overheating during battery recycling that prevents timely heat conduction, thus suppressing thermal runaway to some extent.

[0020] The addition of triphenyl phosphate to the composite polymer interlayer can greatly improve the flame retardancy of the composite current collector. Triphenyl phosphate decomposes into phosphoric acid and pyrophosphoric acid through thermal decomposition, which can block heat transfer in the condensed phase and delay the combustion problem after battery thermal runaway to a certain extent.

[0021] In this invention, a flame-retardant composite polymer is used as the substrate for fabricating the composite current collector, which effectively reduces the mass of the current collector. The through-hole design of the carbon thin film interlayer also reduces some of the mass, which can effectively improve the energy density of the battery.

[0022] Chemical electroplating is used to create composite current collector metal coatings because it has a higher deposition rate and is less likely to cause interfacial stress accumulation, which means it will not cause the coating interface to crack.

[0023] In some embodiments, a flame-retardant material, namely triphenyl phosphate, is added to the polymer substrate.

[0024] Preferably, the thickness of the polymer substrate is 3-4 μm.

[0025] In some embodiments, the thickness of the carbon material coating is 0.3-0.8 μm.

[0026] In some embodiments, the through holes are staggered, with the center distance between two adjacent through holes being 1.5~2.5mm and the diameter of the through holes being 18~24μm.

[0027] By staggering the vias, the center distance between adjacent vias can be kept the same. Ensuring a consistent center distance maximizes the electron transfer efficiency per unit area in the un-drilled area of ​​the current collector, thus guaranteeing conductivity between the two metal layers. If the via diameter is too small, the electroplated Cu layer may not be deposited onto the inner cylindrical surface of the via, or it may accumulate or clog the hole, affecting the performance of the composite current collector. If the via diameter is too large, it will directly affect the physical strength of the composite current collector and cause noticeable pits and unevenness in the coating surface when the active material is applied.

[0028] Preferably, the distance between the outermost through hole and the edge of the composite current collector is 0.5-1cm.

[0029] During the die-cutting process, a certain edge portion of the electrode sheet is retained as a tab. Before being installed into the battery casing, the tabs are uniformly welded to form the positive and negative electrodes of the finished battery cell. In order to ensure the welding strength, as much metal as possible is retained in the outermost area, so through holes are not drilled.

[0030] In some embodiments, the thickness of the metal conductive layer is 0.5-1 μm.

[0031] Preferably, the composite current collector has a thickened area of ​​metal conductive layer on both sides, the width of the thickened area of ​​metal conductive layer is 0.5-1cm, and the thickness of metal conductive layer is 0.75-1.5μm.

[0032] The thicker edge plating on both sides is to prevent burn-through during subsequent welding of the full-cell electrode tabs.

[0033] The polymer substrate is a long rectangle with the winding direction as the central axis, which is parallel to the long side. The two long sides are the "two sides", and the two long rectangular surfaces are the "top" and "bottom" surfaces.

[0034] Preferably, the material of the metal conductive layer is copper.

[0035] Secondly, the present invention provides a method for preparing the composite current collector, comprising the following steps: Preparation of polymer substrates; A slurry containing conductive carbon material is repeatedly applied to both the top and bottom surfaces of a polymer substrate. After drying, holes are drilled to obtain a carbon film interlayer with uniformly distributed through holes. The carbon film interlayer is modified with a silane coupling agent and then immersed in an electrolyte solution to electroplate a metal conductive layer. After cleaning and drying, the target composite current collector is obtained.

[0036] In some embodiments, the polymer is selected from at least one of PET, PE, PP, TPU, PEEK, PMIA, PMIA-PU, PBO, PVDF, PBI, PPS, and PI.

[0037] Preferably, triphenyl phosphate is added to the polymer substrate, and the triphenyl phosphate accounts for 8%-12% of the mass of the polymer substrate.

[0038] In some embodiments, the mass ratio of the conductive carbon material, ethanol, and surfactant in the slurry containing the conductive carbon material is 0.8-1.2:3.8-4.2:0.008-0.012.

[0039] Preferably, the conductive carbon material is selected from at least one of SP, CNT, VGCF, ECP, rGO, acetylene black, and Carbon ECP.

[0040] Preferably, the surfactant is selected from at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium stearate, Tween 60, Tween 70, Tween 80, sodium hexametaphosphate, and sodium pyrophosphate.

[0041] In some embodiments, after the slurry containing conductive carbon material is applied to the surface of the polymer substrate, it is dried by slow-flowing air at 80-100°C, and the application and drying are repeated 5-10 times.

[0042] The main reason for choosing this temperature range is cost control. The solvent for the slurry containing conductive carbon materials is ethanol, which has a high evaporation rate within this temperature range. Maintaining this drying temperature also keeps the cost relatively controllable. It is important to note that the temperature should not exceed 180℃, otherwise the high temperature will degrade the physical properties of the polymer substrate.

[0043] In some embodiments, the method for modifying the carbon film interlayer with a silane coupling agent is as follows: the carbon film interlayer with through holes is immersed in a silane coupling agent modification solution and treated at a constant temperature of 60~80°C for 8~16 minutes, and then the modified through-hole carbon film interlayer is quickly washed in DI water and transferred to a slow-flow forced-air drying zone at 45~55°C for drying.

[0044] Preferably, the silane coupling agent comprises at least one of 3-mercaptopropyltriethoxysilane, γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltriethoxysilane, or 3-chloropropyltriethoxysilane.

[0045] 3-Mercaptopropyltriethoxysilane has a strong coordination ability with noble metals such as copper and can be directly used to induce electroless plating, especially on non-metallic surfaces such as plastics. Therefore, this type of silane coupling agent must be used as the main component. Other silane coupling agents, such as amino-based ones, can be used to improve the adhesion of coatings to resin substrates. Methacryloxy-based ones provide crosslinking degree and adhesion. Amino-based ones can improve the density and corrosion resistance of the coating. Epoxy-based ones readily react with resin substrates and enhance the corrosion resistance of the coating. Therefore, at least one other silane coupling agent is needed to work synergistically with 3-mercaptopropyltriethoxysilane to improve the coating's performance in terms of reaction compatibility, density, and corrosion resistance, thereby achieving a synergistic modification effect.

[0046] More preferably, in the silane coupling agent modified solution, 3-mercaptopropyltriethoxysilane accounts for 40-60% of the total mass fraction of the silane coupling agent.

[0047] In some embodiments, the solute in the electrolyte solution is copper sulfate, copper pyrophosphate, or copper carbonate.

[0048] Preferably, the concentration of the copper sulfate solution is 100-150 g / L. Excessive concentration will accelerate the electroplating process but result in poorer electroplating uniformity and tightness.

[0049] Preferably, when electroplating the conductive metal layer, the electroplating current density is 1~1.5A / dm³. 2 During the electroplating process, the electroplating solution is continuously stirred by an air pump to avoid unevenness of the electrolyte solution.

[0050] In some embodiments, the thickness of the metal conductive layer deposited at both edges of the composite current collector is greater than the thickness of the metal conductive layer in the composite current collector body.

[0051] The thicker edge plating on both sides is to prevent burn-through during subsequent welding of the full-cell electrode tabs.

[0052] Thirdly, the present invention provides a battery in which the current collector of the electrode is the composite current collector.

[0053] The present invention will be further described below with reference to the embodiments.

[0054] Example 1 The preparation method of the composite current collector includes the following steps: 1) Preparation of flame-retardant composite polymer substrate: PET is heated to 255°C until it is molten. Triphenyl phosphate at a mass fraction of 10% is added to the molten PET and then transferred to a melt extruder for mixing and stirring. A flame-retardant composite polymer substrate with a thickness of 3μm is then rolled out by melt co-extrusion.

[0055] 2) Preparation of carbon thin film sandwich with through holes: SP, CNT, and graphene were mixed in a mass ratio of 1:1:1 to prepare a conductive carbon material, which was then mixed with ethanol and sodium dodecylbenzenesulfonate in a mass ratio of 1:4:0.01. The mixture was stirred evenly in a high-pressure homogenizer at a pressure of 2000 psi, a flow rate of 0.75 L / min, and a temperature of 23.5 °C to obtain a uniform carbon suspension. The obtained suspension was slowly and evenly coated onto the flame-retardant composite polymer substrate in step 1) using a soft brush. After the substrate traveled through a 90°C, 1.75m long slow-flow drying zone at a speed of 6cm / s, the coating and drying steps were repeated 6 times to obtain a thin film with a uniform carbon layer covering 0.5μm. The film was then drilled using a laser to obtain a carbon film interlayer with through holes. The through holes were spaced 1.5 mm apart, with a diameter of 20 μm, and the outermost through holes were 1 cm away from both sides of the carbon film.

[0056] 3) Composite current collector preparation and electroplating process: First, the carbon film interlayer with through holes obtained in step 2) is immersed in a surface modification solution and treated at a constant temperature of 70°C for 15 minutes. The mass ratio of 3-mercaptopropyltriethoxysilane to 3-aminopropyltriethoxysilane in the surface modification solution is 1:1, and the concentration of silane coupling agent in the surface modification solution is 1%. % is a mass percentage. The modified porous carbon film interlayer is then rapidly washed in DI water and transferred to a slow-flow drying zone at 50°C and 2m in length at a travel speed of 3cm / min for drying. Subsequently, at an electroplating current density of 1.25 A / dm 2 The modified through-hole carbon film interlayer was placed in a 150 g / L copper sulfate electrolyte solution for 6 min, and a copper metal layer with a thickness of about 0.5 μm was deposited on both sides of the interlayer and the inner cylindrical surface of the through hole. Finally, the strip-shaped edge region of the thin film interlayer, 1 cm away from both sides, is placed in a copper sulfate electrolyte solution for 3 minutes to make the copper plating metal layer thickness on both sides of this region 0.75 μm. Then, the finished product is washed in DI water and ethanol in sequence, and after slow-flow drying in the same way as in this step, the target composite current collector can be obtained.

[0057] Example 2 The difference from Example 1 is that the polymer masterbatch used in step 1) is replaced with PE, while everything else is the same as in Example 1.

[0058] Example 3 The difference from Example 1 is that in step 2), the conductive carbon material is made by mixing graphene and rGO in a mass ratio of 1:1. Everything else is the same as in Example 1.

[0059] Example 4 The difference from Example 1 is that the flame-retardant composite polymer substrate extruded in step 1) has a thickness of 4 μm, and the carbon suspension is repeatedly coated and dried 4 times in step 2), with a final carbon layer thickness of 0.3 μm. All other aspects are the same as in Example 1.

[0060] Example 5 The difference from Example 1 is that in step 3), the mass ratio of 3-mercaptopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in the surface modification solution is 1:1, while all other aspects are the same as in Example 1.

[0061] Example 6 The difference from Example 1 is that in step 3), the mass ratio of 3-mercaptopropyltriethoxysilane and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane in the surface modification solution is 1:1, and all other aspects are the same as in Example 1.

[0062] Comparative Example 1 The difference from Example 1 is that in step 1), a flame-retardant composite polymer substrate with a thickness of 4 μm is rolled out by melt co-extrusion. In step 3), the step of modifying with silane coupling agent is omitted, and electroplating is performed directly on the substrate. Everything else is the same as in Example 1.

[0063] Comparative Example 2 The difference from Example 1 is that in step 2), a thin film uniformly covered by a carbon layer was not drilled using a laser, and a carbon film interlayer without through holes was used for subsequent electroplating to obtain a composite current collector. Everything else is the same as in Example 1.

[0064] Comparative Example 3 The difference from Example 1 is that in step 1), triphenyl phosphate was not added to the molten PET; otherwise, it is the same as Example 1.

[0065] Comparative Example 4 Comparative Example 4 uses 6μm thick copper foil for current collectors of lithium batteries purchased through conventional market channels.

[0066] Comparative Example 5 The difference from Example 1 is that step 2 is omitted, and a flame-retardant composite polymer substrate is directly electroplated to obtain a "sandwich" structure composite current collector.

[0067] Comparative Example 6 The difference from Example 1 is that in step 3), the surface modification solution contains only 3-mercaptopropyltriethoxysilane, while everything else is the same as in Example 1.

[0068] Comparative Example 7 The difference from Example 1 is that in step 3), the surface modification solution contains only 3-aminopropyltriethoxysilane, while everything else is the same as in Example 1.

[0069] Comparative Example 8 The difference from Example 1 is that in step 3), the surface modification solution contains only N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, while everything else is the same as in Example 1.

[0070] Comparative Example 9 The difference from Example 1 is that in step 2), through holes are first drilled on the flame-retardant composite polymer substrate, and then carbon suspension is applied. Only the order is changed, and other parameters are the same as in Example 1.

[0071] Note: For the current collectors of Comparative Examples 2 and 5, copper wires must be used to connect the two metal layers to form a circuit before resistivity testing. Otherwise, the basic insulation of the material will exceed the range of the resistivity tester. For the button test, copper wires must also be used to connect the active material side of the coated disc to the metal layer on the other side before placing it in the battery case for assembly and testing.

[0072] Heat shrinkage test: Cut three 10cm×10cm samples, draw cross lines along the MD and TD directions, and mark the MD and TD directions. Place the samples between two A4 sheets of paper (one on top and one on the bottom). After heating at the set temperature for 1 hour, measure the length of the cross lines to calculate the shrinkage rate. Shrinkage rate % = (L0-L1) / L0*100% (L0: initial sample cross line length, L1: measured length of the cross line after heating). Take the average of the three points as the sample heat shrinkage. Tensile strength test: cut sample: 200mm×10mm, with no burrs or tears on the edges, the thickness value is the average of the actual test, clamp spacing: 100mm, speed: 200mm / min, the result is the average of 3 points, refer to GB / T1040.3-2006.

[0073] Button cell manufacturing: Conductive carbon black was added to a polyvinylidene fluoride (PVDF) NMP solution, followed by lithium iron phosphate powder. The ratio of lithium iron phosphate to conductive carbon black to PVDF was 90:5:5 (by mass). The mixture was stirred until homogeneous, and then the slurry was evenly coated onto aluminum foil on a coating machine to form an electrode sheet. The coating thickness was 200 μm.

[0074] The coated electrode sheets are placed in a vacuum drying oven at 120℃ and dried for 6 hours. The electrode sheets are then removed and rolled on a roller press for later use.

[0075] The button cell assembly was carried out in a glove box under an argon atmosphere. The electrolyte was 1M LiPF6+EC:DEC:DMC = 1:1:1 (volume ratio). The lithium metal sheet was used as the counter electrode, and the separator was the separator prepared in the embodiments or comparative examples of this invention.

[0076] Capacity testing was conducted on an Arbin BT2000 battery tester in the United States, with a charge / discharge voltage range of 2 to 3.75V and charge / discharge rates of 0.1C and 1C, respectively.

[0077] Table 1 Comparison of current collector properties in the examples and comparative examples

[0078] As shown in Table 1, the thickness of the current collectors prepared in the examples all met expectations and had a significant advantage compared with the conventional 6μm copper foil on the market, and had a significant effect on reducing the weight of the current collector. The composite current collectors of Comparative Example 1, Comparative Example 3, Comparative Example 4 and the examples adopted the through-hole copper plating method, which formed a three-dimensional channel on the upper and lower surfaces of the current collector, so that the resistivity of the composite current collector was at a comparable level to that of conventional copper foil.

[0079] Comparative Examples 2 and 5 show that since there is no conductive path between the upper and lower surfaces of the composite current collector and it is basically insulated in the thickness direction, the resistivity measured by conventional methods exceeds the range. By using copper wire to form a path to simulate the effect of forming a path by welding the tabs in the battery, the measured resistivity is significantly lower than that of conventional copper foil.

[0080] The resistivity of Comparative Example 1 is significantly higher than that of the Example 2, because the presence of the carbon layer can also improve the conductivity of the composite current collector to some extent.

[0081] The thermal shrinkage rate of the composite current collector in the embodiment is basically at the same level as that of the conventional copper foil in Comparative Example 4, while the tensile strength is higher than that of the conventional copper foil. This is because the presence of the composite polymer interlayer greatly improves the flexibility of the composite current collector, which to some extent improves the mechanical properties of the copper foil. The thermal shrinkage rate of the embodiment is not much different from that of Comparative Example 4, and is at the same level.

[0082] Table 2 Electrical properties of LFP coin cells prepared with composite current collectors in the examples and comparative examples

[0083] As shown in Table 2, the capacity performance of the coin cell made with the composite current collector in Example 1 is comparable to that of Comparative Examples 3 and 4. Therefore, replacing the conventional current collector with the composite current collector in the example in a lithium battery does not result in a significant loss in electrical performance. Figure 4 As shown.

[0084] Compared to Comparative Examples 2 and 5, Example 1, due to its three-dimensional conductive via design, exhibits higher electron collection and extraction efficiency during battery charging and discharging. This is macroscopically manifested as higher electronic conductivity and lower ohmic impedance. Furthermore, the presence of pores ensures tighter contact between the active material and the current collector, reducing interfacial contact impedance and enhancing adhesion of the current collector to the active material during cycling. Overall, this results in higher 0.1C discharge specific capacity and initial efficiency. Under high-rate discharge and cycling conditions, the current collector conductivity is required to a greater extent, significantly amplifying polarization differences. Example 1's 1C initial charge specific capacity is at least 5 mAh / g higher than Comparative Examples 1, 2, and 5, and its capacity retention after 50 cycles is also significantly higher, demonstrating superior cycle performance. Figure 3 As shown.

[0085] Compared with Comparative Example 1, Example 1 shows that due to the presence of the carbon layer, a rougher copper plating layer can adhere to it, resulting in closer contact between the current collector and the active material and a smaller interfacial contact resistance. Therefore, the discharge capacity at 0.1C and 1C and the first efficiency are significantly improved. There is also a certain difference in the capacity retention rate at 1C and 50Cycles, i.e., the cycle performance. The comparison between Comparative Example 2 and Comparative Example 5 can also corroborate the effect of the carbon layer.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite current collector, characterized in that: It includes a polymer substrate, a carbon material coating attached to the top and bottom surfaces of the polymer substrate, and a metal conductive layer attached to the surface of the carbon material coating. The polymer substrate and the carbon material coating are uniformly distributed with through holes, and a conductive metal material is deposited in the through holes to connect the conductive metal layers on both sides of the polymer substrate.

2. The composite current collector according to claim 1, characterized in that: The polymer substrate contains a flame-retardant material, namely triphenyl phosphate. Preferably, the thickness of the polymer substrate is 3-4 μm; Preferably, the thickness of the carbon material coating is 0.3-0.8 μm.

3. The composite current collector according to claim 1, characterized in that: The through holes are staggered, with a center distance of 1.5-2.5 mm between adjacent through holes and a diameter of 18-24 μm. Preferably, the distance between the outermost through hole and the edge of the composite current collector is 0.5-1cm.

4. The composite current collector according to claim 1, characterized in that: The thickness of the metallic conductive layer is 0.5-1 μm; Preferably, the composite current collector has thickened areas of metal conductive layer on both sides, the width of which is 0.5-1cm and the thickness of which is 0.75-1.5μm. Preferably, the material of the metal conductive layer is copper.

5. The method for preparing the composite current collector according to any one of claims 1-4, characterized in that: Includes the following steps: Preparation of polymer substrates; A slurry containing conductive carbon material is repeatedly applied to both the top and bottom surfaces of a polymer substrate. After drying, holes are drilled to obtain a carbon film interlayer with uniformly distributed through holes. The carbon film interlayer is modified with a silane coupling agent and then immersed in an electrolyte solution to electroplate a metal conductive layer. After cleaning and drying, the target composite current collector is obtained.

6. The method for preparing the composite current collector according to claim 5, characterized in that: The polymer is selected from at least one of PET, PE, PP, TPU, PEEK, PMIA, PMIA-PU, PBO, PVDF, PBI, PPS, and PI; Preferably, triphenyl phosphate is added to the polymer substrate, and the triphenyl phosphate accounts for 8%-12% of the mass of the polymer substrate.

7. The method for preparing the composite current collector according to claim 5, characterized in that: In the slurry containing conductive carbon material, the mass ratio of conductive carbon material, ethanol, and surfactant is 0.8-1.2:3.8-4.2:0.008-0.

012. Preferably, the conductive carbon material is selected from at least one of SP, CNT, VGCF, ECP, rGO, acetylene black, and Carbon ECP; Preferably, the surfactant is selected from at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium stearate, Tween 60, Tween 70, Tween 80, sodium hexametaphosphate, and sodium pyrophosphate.

8. The method for preparing the composite current collector according to claim 5, characterized in that: The method for modifying the carbon film interlayer with silane coupling agent is as follows: the carbon film interlayer with through holes is immersed in the silane coupling agent modification solution and treated at a constant temperature of 60-80℃ for 8-16 minutes. Then, the modified through-hole carbon film interlayer is quickly washed in DI water and transferred to a slow-flow forced-air drying zone at 45-55℃ for drying. Preferably, the silane coupling agent comprises at least one of 3-mercaptopropyltriethoxysilane, γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltriethoxysilane, or 3-chloropropyltriethoxysilane. Preferably, in the silane coupling agent modified solution, the mass fraction of 3-mercaptopropyltriethoxysilane in the total silane coupling agent is 40-60%.

9. The method for preparing the composite current collector according to claim 5, characterized in that: The solute in the electrolyte solution is copper sulfate, copper pyrophosphate, or copper carbonate. Preferably, the concentration of the copper sulfate solution is 100-150 g / L; Preferably, the electroplating current density during the electroplating of the conductive metal layer is 1-1.5 A / dm². 2 During the electroplating process, the electroplating solution is continuously stirred by an air pump; Preferably, the thickness of the metal conductive layer deposited on both sides of the composite current collector is greater than the thickness of the metal conductive layer of the composite current collector body.

10. A battery, characterized in that: The current collector of its electrode is the composite current collector as described in any one of claims 1-4.

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