Composite current collector, preparation method and negative plate

Abstract

The invention provides a composite current collector, a preparation method and a negative plate, the composite current collector comprises a porous copper substrate layer, a composite doping layer, a conductive layer and a lithium-loving modification layer, the composite doping layer comprises a rare earth element doped copper layer, the composite doping layer is arranged on the pore surface of the porous copper substrate layer, the conductive layer is arranged on the surface of the composite doping layer, and the lithium-loving modification layer is arranged on the surface of the conductive layer. And the lithium-philic modification layer is formed on one surface, deviating from the composite doping layer, of the conductive layer. According to the composite current collector provided by the invention, the porous copper substrate layer can provide a buffer space for volume expansion of a silicon-carbon negative electrode, and a compound containing rare earth elements in the composite doping layer improves the mechanical strength and conductivity of the current collector through lattice distortion optimization, provides structural support for expansion constraint, and reduces electron transfer resistance at the same time; the composite conductive material of the conductive layer can form a high-speed conductive channel, so that the migration efficiency of electrons and lithium ions is improved; the lithium-loving modification layer guides uniform deposition of lithium ions; in conclusion, the composite current collector can effectively inhibit the expansion of the current collector and synchronously optimize the conductivity and the cycling stability.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a composite current collector, its preparation method, and a negative electrode. Background Technology

[0002] With the widespread application of lithium-ion batteries in new energy vehicles and energy storage systems, the market demand for batteries with "high energy density, fast charging performance, and long cycle life" continues to increase. To meet the combined requirements of new energy vehicles and energy storage systems for these characteristics, and especially to address the significant volume expansion challenge posed by high-capacity materials such as silicon-carbon anodes (whose specific capacity is 10 times that of graphite), existing technologies modify the copper foil used as the anode current collector. Current modification schemes for copper foil primarily focus on "inhibiting the expansion of active materials" or "enhancing the interfacial electrochemical reaction kinetics." Specifically, one approach is a composite current collector scheme, employing a composite structure of "polymer substrate + copper layer," relying on the flexibility of the lightweight polymer layer to buffer the volume expansion of the active material. Another approach is surface roughening, using mechanical polishing and electrochemical corrosion. There are several modification schemes. One is to increase the surface roughness of the copper foil, strengthen the interfacial adhesion with the active material, and reduce the contact resistance. Another is alloying modification, which involves doping copper with alloying elements such as Zn, Al, and Sn, and using smelting or electroplating processes to improve the mechanical strength and ductility of the copper foil, thereby constraining the deformation of the electrode structure. A third is carbon coating, which involves coating the surface of the copper foil with amorphous carbon or randomly distributed carbon nanotubes to improve the conductivity of the current collector. However, all of the above modification schemes have the problem of not being able to simultaneously achieve both expansion suppression and kinetic improvement, making it difficult to meet the comprehensive performance requirements of high energy density, fast charging, and long cycle life of batteries. Especially when matching high specific capacity anode materials such as silicon-carbon, the volume expansion rate of silicon-carbon anodes is much higher than that of traditional graphite anodes. Existing copper foil modification schemes cannot effectively alleviate the problems of electrode volume deformation and interfacial impedance growth, resulting in a sharp decline in battery cycle stability. Summary of the Invention

[0003] To address the problem that existing technologies cannot simultaneously suppress the volume expansion of the negative electrode current collector and improve kinetics, a composite current collector, its preparation method, and a negative electrode sheet are provided.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: On one hand, the present invention provides a composite current collector, comprising a porous copper substrate, a composite doped layer, a conductive layer, and a lithiophilic modification layer. The composite doped layer comprises a copper layer doped with rare earth elements. The composite doped layer is disposed on the pore surface of the porous copper substrate. The conductive layer is disposed on the surface of the composite doped layer. The lithiophilic modification layer is formed on the side of the conductive layer opposite to the composite doped layer.

[0005] Optionally, the porosity of the porous copper substrate layer gradually decreases from the interior of the porous copper substrate layer to the surface of the porous copper substrate layer, and the porosity of the porous copper substrate layer is 40~60%.

[0006] Optionally, the internal pore size of the porous copper substrate is 10~30μm, and the surface pore size of the porous copper substrate is 1~3μm.

[0007] Optionally, the porous copper substrate layer has a plurality of interconnected spherical pores.

[0008] Optionally, the pore wall thickness of the porous copper substrate is 1~3μm; The thickness of the porous copper substrate is 30~40μm.

[0009] Optionally, based on the total mass of the porous copper substrate and the composite doped layer as 100%, the doping amount of the rare earth element is 0.05~0.2wt%.

[0010] Optionally, the conductive layer comprises a composite of carbon nanotubes and graphene, wherein the carbon nanotubes are grown vertically on the surface of the composite doped layer, and the graphene sheets are perpendicular to the axial position of the carbon nanotubes. The vertical orientation of the carbon nanotubes in the conductive layer is ≥90%; The network density of carbon nanotubes in the conductive layer is 10. 10 ~10 12 root / cm 2 .

[0011] Optionally, the thickness of the conductive layer is 50~200nm.

[0012] Optionally, the diameter of the carbon nanotubes is 10~30nm, and the thickness of the graphene sheets is 1~3nm; The mass ratio of the carbon nanotubes to the graphene is 1:1 to 3:1.

[0013] Optionally, the lithiophilic modification layer comprises a lithiophilic material, which includes one or more substances containing silver, zinc, tin, and bismuth; and / or, Compounds containing rare earth elements include one or more of lanthanum nitrate and cerium nitrate; The porous copper substrate has a copper content of ≥99.9%.

[0014] Optionally, the total thickness of the composite current collector is 6~30μm; The thickness of the composite doped layer is 1~10μm; The thickness of the lithiophilic modification layer is 5~20nm.

[0015] Optionally, the method for preparing the composite current collector includes the following operations: Copper material is mixed with a pore-forming agent, cold-pressed and then sintered in a hydrogen atmosphere. The pore-forming agent is then removed to obtain a porous copper substrate layer. A compound containing rare earth elements is prepared into a mixed solution, and a porous copper substrate is placed in the mixed solution for electroplating to form a composite doped layer, thus obtaining the first precursor. Obtain composite conductive materials; A conductive layer is formed on the surface of a first precursor by chemical vapor deposition of a composite conductive material to obtain a second precursor. A lithiophilic substance is prepared into a solution, and then a second precursor is placed in the solution. Under thermal reaction conditions, a lithiophilic modification layer is formed on the surface of the second precursor.

[0016] Optionally, in the "process of preparing a porous copper substrate", the cold pressing pressure is 100~200 MPa, and the cold pressing pressure gradually decreases from the surface of the porous copper substrate to the interior of the porous copper substrate. The sintering temperature is 900~1000℃, and the sintering time is 3~5h.

[0017] Optionally, the operation of "plating the mixture onto the surface of the porous copper substrate" is electroplating, in which the current density is 2~5 A / dm³. 2 Temperature 40~60℃, pH value 1~2, electroplating time 30~60min.

[0018] Optionally, the pore-forming agent includes one or more of ammonium carbonate and ammonium bicarbonate; The particle size of the pore-forming agent is 1~50μm.

[0019] Optionally, in the operation of "forming a lithiophilic modification layer", the high temperature is 30~60℃.

[0020] Optionally, the composite conductive material is prepared by the following method: Methane and ethylene are used as carbon sources and introduced into the reaction chamber, along with hydrogen gas. Under the conditions of a catalyst and high temperature, a composite conductive material is formed.

[0021] Optionally, the catalyst comprises iron-cobalt mixed metal nanoparticles with a particle size of 5-10 nm; The catalyst content is 0.1~0.3 wt%; The high-temperature conditions are described, with a processing temperature of 750~850℃ and a processing time of 1~2 hours.

[0022] On the other hand, the present invention provides a negative electrode sheet, including the composite current collector described above, or a composite current collector prepared by the method for preparing the composite current collector described above.

[0023] The beneficial effects of this application are as follows: The composite current collector provided in this application comprises a porous copper substrate, a composite doped layer, a conductive layer, and a lithiophilic modification layer. The porous copper substrate, with its porous structure, provides a buffer for the volume expansion of the silicon-carbon anode and forms a three-dimensional conductive network to ensure basic electron transport. In the composite doped layer, rare-earth element compounds are dispersed at the atomic level to form a solid solution, which improves the current collector's mechanical strength and conductivity through lattice distortion optimization, providing structural support for expansion constraint while reducing electron transport resistance. The composite conductive material in the conductive layer forms high-speed conductive channels, effectively improving electron and lithium-ion migration efficiency. The lithiophilic modification layer guides the uniform deposition of lithium ions, inhibits lithium dendrite growth, and strengthens interlayer bonding, further improving cycle stability. In summary, the composite current collector provided in this application, through buffering expansion, strengthening structure, improving kinetics, and optimizing the deposition layer structure, can effectively suppress the expansion of the current collector, promoting the simultaneous optimization of its high conductivity and long cycle stability. Detailed Implementation

[0024] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] The present invention provides a composite current collector, comprising a porous copper substrate, a composite doped layer, a conductive layer, and a lithiophilic modification layer. The composite doped layer comprises a copper layer doped with rare earth elements. The composite doped layer is disposed on the pore surface of the porous copper substrate. The conductive layer is disposed on the surface of the composite doped layer. The lithiophilic modification layer is formed on the side of the conductive layer opposite to the composite doped layer.

[0026] Specifically, the composite current collector provided in this application includes a porous copper substrate layer, a composite doped layer, a conductive layer, and a lithiophilic modification layer. The porous copper substrate layer, with its porous structure, provides a buffer space for the volume expansion of the silicon-carbon anode and forms a three-dimensional conductive network to ensure basic electron transport. In the composite doped layer, rare-earth element compounds are dispersed at the atomic level to form a solid solution, which improves the mechanical strength and conductivity of the current collector through lattice distortion optimization, providing structural support for expansion constraint while reducing electron transport resistance. The composite conductive material in the conductive layer can form high-speed conductive channels, effectively improving electron and lithium-ion migration efficiency. The lithiophilic modification layer guides the uniform deposition of lithium ions, inhibits lithium dendrite growth, and strengthens interlayer bonding, further improving cycle stability. In summary, the composite current collector provided in this application, through buffering expansion, strengthening structure, improving kinetics, and optimizing the deposition layer structure, can effectively suppress the expansion of the current collector, promoting the simultaneous optimization of its high conductivity and long cycle stability.

[0027] In some embodiments, the porosity of the porous copper substrate gradually decreases from the interior of the porous copper substrate to the surface of the porous copper substrate, and the porosity of the porous copper substrate is 40-60%.

[0028] Specifically, the porosity of the porous copper substrate gradually decreases from the interior to the surface of its spherical structure, forming a spherical structure that is loose inside and dense on the surface. The high porosity inside can effectively buffer expansion and prevent electrode cracking caused by changes in the volume of the active material, while the low porosity on the surface ensures close contact between the current collector and the conductive layer and the active material, reduces the generation of interfacial voids, lowers contact resistance, and at the same time improves the mechanical strength of the current collector to support the overall stability of the electrode structure, thereby promoting the comprehensive improvement of the battery's energy density, fast charging performance and cycle performance.

[0029] Furthermore, the porosity of the porous copper substrate layer includes, but is not limited to, 40%, 45%, 50%, 55% or 60%, and within this range, the porosity of the porous copper substrate layer must be set to gradually decrease from the interior of the porous copper substrate layer to the surface of the porous copper substrate layer.

[0030] In some embodiments, the internal pore size of the porous copper substrate is 10~30μm, and the surface pore size of the porous copper substrate is 1~3μm.

[0031] Specifically, compared to the surface pore size of the porous copper substrate, the large pore size inside the porous copper substrate provides ample space to accommodate the volume expansion of high-capacity materials such as silicon-carbon anodes, preventing the electrode structure from collapsing due to stress generated during the expansion of active materials. At the same time, the large-pore channels facilitate rapid electrolyte penetration, ensuring the continuity of ion transport. In addition, the small-pore structure on the core surface can significantly increase the surface area, strengthen the interfacial bonding strength with the composite doped layer, reduce the generation of interfacial voids, and lower the contact resistance. Meanwhile, the dense surface structure can enhance the mechanical support capacity of the current collector, preventing active material detachment or electrode structure deformation, further ensuring the structural integrity of the electrode during long-term cycling, thereby achieving a dual improvement in anode volume expansion suppression and electrochemical reaction kinetics.

[0032] Furthermore, the internal pore size of the porous copper substrate layer includes, but is not limited to, 10μm, 15μm, 20μm, 25μm or 30μm; The pore size of the porous copper substrate surface includes, but is not limited to, 1μm, 2μm, or 3μm.

[0033] In some embodiments, the porous copper substrate has a plurality of interconnected spherical pores.

[0034] Specifically, multiple interconnected spherical pore structures form continuous interconnected channels, which on the one hand facilitates rapid penetration of electrolyte and uniform wetting inside the electrode, significantly reduces ion transport resistance, and solves the problem of insufficient electrolyte wetting; on the other hand, it provides buffer space for the volume expansion of silicon-carbon anode, avoids stress concentration caused by local pore closure, and ensures the integrity of the electrode structure. In some embodiments, the wall thickness of the porous copper substrate is 1~3μm; The thickness of the porous copper substrate is 30~40μm.

[0035] The pore wall thickness is limited to 1~3μm, which ensures the supporting strength of the pore structure and prevents the pore wall from collapsing during cycling. At the same time, the 1~3μm ultra-thin pore wall can reduce the current collector mass. The thickness of the porous copper substrate is 30~40μm, which provides sufficient space for the expansion of the active material while avoiding the decrease in battery energy density caused by the porous copper substrate being too thick. In addition, the through-hole honeycomb structure of the porous copper substrate further optimizes the transport path of ions and electrons. In summary, this technology achieves the optimization of overall performance of expansion buffering, dynamic improvement and energy density through the synergistic regulation of pore connectivity, mechanical support strength and the thickness of the porous copper substrate.

[0036] Furthermore, the wall thickness of the porous copper substrate layer includes, but is not limited to, 1 μm, 2 μm, or 3 μm; The thickness of the porous copper substrate layer includes, but is not limited to, 30 μm, 35 μm, or 40 μm.

[0037] In some embodiments, the amount of rare earth element doping is 0.05~0.2wt%, based on the total mass of the porous copper substrate and the composite doped layer as 100%.

[0038] Specifically, a low content of rare earth elements (0.05~0.2wt%) can serve as heterogeneous nucleation sites to refine copper grains, improve the tensile strength and ductility of the composite doped layer, enhance the deformation resistance of the porous copper substrate, effectively constrain the electrode structure deformation caused by the expansion of the silicon-carbon anode, and avoid the problem of decreased conductivity due to excessive doping. In addition, the doping of rare earth elements can regulate the electronic state of the surface of the composite doped layer, reduce the nucleation overpotential of lithium ion deposition, and at the same time improve the interfacial bonding strength with the subsequent conductive layer, reduce interfacial impedance, and promote efficient electron and ion transport. In addition, the rare earth element doping amount is in the range of 0.05~0.2wt%, which can avoid interface defects caused by excessive agglomeration of rare earth elements and ensure the structural uniformity of the composite doped layer.

[0039] In some embodiments, the conductive layer comprises a composite of carbon nanotubes and graphene, wherein the carbon nanotubes are grown vertically on the surface of the composite doped layer, and the graphene sheets are perpendicular to the axial position of the carbon nanotubes. The vertical orientation of the carbon nanotubes in the conductive layer is ≥90%; The network density of carbon nanotubes in the conductive layer is 10. 10 ~10 12 root / cm 2 .

[0040] Specifically, the carbon nanotubes are grown vertically on the surface of the composite doped layer with an orientation degree of ≥90%, which can construct directional electron transport channels that penetrate the conductive layer. Compared with traditional randomly distributed carbon nanotubes, this is beneficial to shorten the electron transport path and improve the interfacial electron migration rate. The graphene sheets are arranged perpendicular to the carbon nanotube axis, which can form an interwoven conductive network with the carbon nanotubes, increasing the contact area between the conductive layer and the active material and reducing the interfacial contact resistance. 10 10 ~10 12 root / cm 2 The high density of carbon nanotube networks ensures both the structural support strength of the conductive layer and its excellent flexibility, allowing it to elastically deform with the volume expansion of the silicon-carbon anode, preventing the conductive layer from cracking and falling off, and ensuring the continuity of ion transport. This achieves synergistic optimization of improved electron / ion transport dynamics, volume expansion buffering, and interface structure stability.

[0041] In some embodiments, the thickness of the conductive layer is 50~200nm.

[0042] Specifically, the conductive layer thickness of 50-200 nm can shorten the transport path of lithium ions within the conductive layer and reduce ion migration resistance while ensuring the integrity of the carbon nanotube-graphene three-dimensional conductive network, and at the same time avoid the interface impedance superposition problem caused by excessively thick carbon layers. Compared with traditional micron-level carbon coating layers, the thinner conductive layer of 50-200 nm can reduce the proportion of inactive materials. Combined with the lightweight setting of the porous copper substrate, it is beneficial to further improve the energy density of the battery. In addition, the conductive layer in this thickness range has excellent flexibility and adhesion strength. It can undergo adaptive deformation within limits with the volume expansion of the silicon-carbon anode, avoiding the conductive layer from cracking and falling off due to excessive thickness. This ensures the structural stability and conductivity continuity of the electrode during long-term cycling, and achieves synergistic optimization of dynamic improvement and energy density guarantee.

[0043] Furthermore, the thickness of the conductive layer can be 50nm, 80nm, 100nm, 120nm, 150nm, 180nm or 200nm.

[0044] In some embodiments, the diameter of the carbon nanotubes is 10-30 nm, and the thickness of the graphene sheets is 1-3 nm. The mass ratio of the carbon nanotubes to the graphene is 1:1 to 3:1.

[0045] Specifically, carbon nanotubes with a diameter of 10~30nm have good axial conductivity and structural flexibility, while 1~3nm ultrathin graphene sheets can form a three-dimensional conductive network with vertically oriented carbon nanotubes, thereby improving electron transport efficiency. The mass ratio of carbon nanotubes to graphene is 1:1 to 3:1, which ensures that carbon nanotubes account for a significant proportion of the main conductive framework. Furthermore, the graphene sheets fill the gaps between the carbon nanotubes, preventing voids and defects in the conductive network and optimizing electron transport efficiency.

[0046] Furthermore, the diameter of the carbon nanotubes includes, but is not limited to, 10 nm and 30 nm, and the thickness of the graphene sheets is 1-3 nm. In some embodiments, the lithiophilic modification layer comprises a lithiophilic material, which includes one or more substances containing silver, zinc, tin, and bismuth; and / or, Compounds containing rare earth elements include one or more of lanthanum nitrate and cerium nitrate; The porous copper substrate has a copper content of ≥99.9%.

[0047] The lithiophilic material includes one or more of silver nitrate and bismuth nitrate; Rare earth element-doped copper layers are formed through electroplating using lithiophilic substances and rare earth element-containing compounds. Specifically, rare earth element-containing compounds such as lanthanum nitrate and cerium nitrate dissociate into La in the electroplating system. 3+ Ce 3+ These rare earth ions migrate together to the surface of the porous copper substrate under the action of an electric field. Due to the strong interfacial adsorption and lattice embedding ability between the rare earth ions and the copper atoms in the porous copper substrate, while the copper ions are being reduced and deposited, the rare earth ions will embed into the gaps in the copper lattice or replace some of the copper atoms in the form of doped atoms, thereby forming a copper layer doped with rare earth elements.

[0048] Lithophilic materials can be deposited onto the surface of conductive layers through high-temperature deposition processes. Their excellent lithiophilic properties can reduce the nucleation overpotential of lithium ion deposition and inhibit the growth of lithium dendrites. At the same time, they form a synergistic effect with copper layers doped with rare earth elements, further optimizing the interfacial compatibility between the current collector and the negative electrode active material, improving ion transport dynamics, and, together with the mechanical strengthening effect of rare earth doped copper layers, achieving expansion suppression and improved interfacial dynamics.

[0049] In some embodiments, the total thickness of the composite current collector is 6~30μm; The thickness of the composite doped layer is 1~10μm; The thickness of the lithiophilic modification layer is 5~20nm.

[0050] Specifically, the composite current collector has a total thickness of 6~30μm, which reduces the volume ratio of the current collector in the electrode, significantly reducing the electrode weight compared to traditional copper foil and improving the battery energy density. The thickness range of 1~10μm of the composite doped layer can match the pore structure of the porous copper substrate, ensuring the uniformity of rare earth element doping and mechanical strengthening effect. This provides sufficient stress buffer space for the expansion of silicon-carbon anode and avoids the extension of ion transport path due to excessive doping layer thickness. The 5-20nm ultrathin lithophile modification layer can effectively utilize the lithophile properties and reduce the lithium deposition overpotential, while avoiding the interface impedance superposition problem caused by a thicker lithophile modification layer, thus ensuring efficient cross-interface transport of electrons and ions.

[0051] Furthermore, the total thickness of the composite current collector includes, but is not limited to, 6μm, 10μm, 15μm, 18μm, 20μm, 25μm or 30μm; The thickness of the composite doped layer includes, but is not limited to, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0052] The thickness of the lithiophilic modification layer includes, but is not limited to, 5 nm, 10 nm, 15 nm, 18 nm, or 20 nm.

[0053] In some embodiments, the method for preparing the composite current collector includes the following operations: Copper material is mixed with a pore-forming agent, cold-pressed and then sintered in a hydrogen atmosphere. The pore-forming agent is then removed to obtain a porous copper substrate layer. A compound containing rare earth elements is prepared into a mixed solution, and a porous copper substrate is placed in the mixed solution for electroplating to form a composite doped layer, thus obtaining the first precursor. Obtain composite conductive materials; A conductive layer is formed on the surface of a first precursor by chemical vapor deposition of a composite conductive material to obtain a second precursor. A lithiophilic substance is prepared into a solution, and then a second precursor is placed in the solution. Under thermal reaction conditions, a lithiophilic modification layer is formed on the surface of the second precursor.

[0054] Specifically, the preparation method of the composite current collector includes the following operations: 500g of high-purity copper powder (purity ≥99.9%) with a particle size of 2μm was mixed evenly with 333g of ammonium carbonate pore-forming agent (particle size 10μm). The mixture was cold-pressed into a substrate with a thickness of 10mm under a pressure of 150MPa. The substrate was sintered at 950℃ for 4h in a hydrogen atmosphere. After natural cooling, the pore-forming agent was removed by soaking in 1.5mol / L hydrochloric acid solution for 24h, resulting in a porous copper substrate layer with a thickness of 30μm. The porous copper substrate has an internal pore size of 10 μm and a surface pore size of 1 μm.

[0055] Lanthanum nitrate and cerium nitrate, compounds containing rare earth elements, were dissolved in deionized water at a mass ratio of 4:1 to prepare a mixed solution with a total concentration of 0.2 mol / L. The pH was adjusted to 1.5. A porous copper substrate was then electroplated in this mixed solution at a current density of 3 A / dm³. 2 At a temperature of 50℃ and a time of 45 min, a composite doped layer with a thickness of 2 μm was formed on a porous copper substrate to obtain the first precursor. The rare earth element doping amount in the first precursor is 0.12wt%.

[0056] Methane and ethylene were used as carbon sources and introduced into the reaction chamber in a ratio of 1.5:1, along with hydrogen gas. The catalyst iron-cobalt mixed metal nanoparticles (0.2 g / L, particle size 5 nm) were immersed in an ethanol solution for 30 min and reacted at 800 °C for 1.5 h to form a composite conductive material. A conductive layer is formed on the surface of a first precursor by chemical vapor deposition of a composite conductive material to obtain a second precursor. A solution was prepared by mixing 0.03 mol / L silver nitrate and 0.01 mol / L bismuth nitrate, which are lithiophilic substances. Then, the second precursor was placed in the solution for 10 min and reacted at 60 °C to form a lithiophilic modification layer with a thickness of 10 nm on the surface of the second precursor.

[0057] It should be noted that the porosity of the spherical porous copper substrate gradually decreases from the interior to the surface. During the cold pressing stage, the cold pressing pressure gradually decreases from the core surface to the interior. The pressure transmission in the surface area is direct and uniform, causing the pore-forming agent to be squeezed and densed, and even some particles to break, significantly reducing the gaps between the pore-forming agent particles. In contrast, the pressure inside the porous copper substrate decreases significantly. As a result, the pore-forming agent that has penetrated into the porous copper substrate retains its original particle size and loosely packed state, forming an initial particle distribution difference of densely packed on the surface and loosely distributed inside. This difference causes the porosity of the spherical porous copper substrate to gradually decrease from the interior to the surface. Furthermore, during the sintering stage of preparing the porous copper substrate, the heat dissipation rate on the surface of the porous copper substrate is greater than that inside, the migration rate of copper powder atoms on the surface is higher, and the degree of sintering densification is more complete, further compressing the space occupied by the pore-forming agent particles and reducing the reserved pore volume; the heat dissipation inside is slower, the degree of copper powder sintering is lower, the shrinkage of the copper skeleton around the pore-forming agent is smaller, and the reserved pore volume is preserved; after the pore-forming agent is subsequently leached with hydrochloric acid, the surface forms small pores due to the breakage and dense accumulation of the pore-forming agent and the full sintering of the copper powder, while the interior forms large pores due to the intact and loose distribution of the pore-forming agent and the low degree of copper powder sintering, ultimately showing a decreasing trend in pore size from the interior to the surface.

[0058] In some embodiments, during the “processing of a porous copper substrate”, the cold pressing pressure is 100-200 MPa, and the cold pressing pressure gradually decreases from the surface of the porous copper substrate to the interior of the porous copper substrate. The sintering temperature is 900~1000℃, and the sintering time is 3~5h.

[0059] Specifically, during the cold pressing stage, the pressure of 100~200MPa gradually decreases from the surface of the porous copper substrate to the interior. The high pressure in the surface area allows the copper powder and pore-forming agent particles to be tightly compacted, and the pore-forming agent particles to deform or even break, laying the foundation for the subsequent formation of a surface structure with small pore size and low porosity. The low pressure inside the core, on the other hand, preserves the loosely packed state of the copper powder and pore-forming agent, ensuring the reserved space for the internal structure with large pore size and high porosity. During the hydrogen atmosphere sintering stage, the temperature range of 900~1000℃ ensures the neck growth and sintering densification of copper powder particles, improving the mechanical strength of the porous copper substrate, while avoiding abnormal growth of copper grains or premature decomposition and failure of the pore-forming agent caused by excessively high temperatures. The sintering time of 3~5h ensures the full removal of the pore-forming agent and the stable formation of the copper skeleton structure. Combined with the gradient structure formed by cold pressing, the surface copper powder is sintered more fully and the pores are finer and denser, while the internal copper powder is sintered to a moderate degree and the pores are looser and larger. Ultimately, a gradient porous structure with gradually decreasing porosity and pore size from the inside to the outside can be formed in a controllable manner, which alleviates the volume expansion of silicon-carbon anodes and improves the interfacial dynamic performance.

[0060] In some embodiments, the operation of "plating the mixture onto the surface of a porous copper substrate" is electroplating, in which the current density is 2~5A / dm³. 2 Temperature 40~60℃, pH value 1~2, electroplating time 30~60min.

[0061] Specifically, in a strongly acidic system with a pH of 1-2, rare earth ions can exist stably and are not prone to hydrolysis and precipitation, providing a stable reaction environment for the co-deposition of rare earth elements and copper ions; a temperature range of 40-60℃ can increase the migration rate of ions in the electrolyte, accelerate the electrodeposition reaction process, and avoid the problems of electrolyte volatilization and coarse coating grains caused by high temperatures; 2-5 A / dm 2 The current density can be adjusted to control the co-deposition rate of copper and rare earth ions, so that rare earth ions are uniformly embedded in the copper lattice in the form of doped atoms; the electroplating time of 30~60min ensures that the composite doped layer reaches the target thickness, while achieving uniform coverage of rare earth elements on the pore surface of the porous copper substrate, strengthening the interfacial bonding force between the composite doped layer and the core. The synergistic control of the above process parameters prepares a composite doped layer with uniform rare earth element doping and complete pore structure, improving the mechanical strength of the porous copper substrate to suppress the volume expansion of silicon-carbon anode.

[0062] In some embodiments, the pore-forming agent includes one or more of ammonium carbonate and ammonium bicarbonate; The particle size of the pore-forming agent is 1~50μm.

[0063] Specifically, the pore-forming agent with a particle size range of 1~50μm can be easily mixed with copper powder, avoiding uneven pore distribution caused by the agglomeration of the pore-forming agent, ensuring the structural stability and mechanical support performance of the porous copper substrate, providing sufficient buffer space for the volume expansion of the silicon-carbon anode, and optimizing the electrolyte penetration and ion transport channels.

[0064] In some embodiments, the thermal reaction conditions for "forming a lithiophilic modified layer" are at a temperature of 30-60°C.

[0065] Specifically, this thermal reaction temperature provides sufficient activation energy for the film formation of the lithiophilic material, enabling it to spread evenly on the surface of the conductive layer and form a dense, strongly adherent lithiophilic modification layer.

[0066] In some embodiments, the composite conductive material is prepared by the following method: Methane and ethylene are used as carbon sources and introduced into the reaction chamber, along with hydrogen gas. Under the conditions of a catalyst and high temperature, a composite conductive material is formed.

[0067] Specifically, methane, as a carbon source with high carbon conversion rate, can provide a stable carbon source supply to ensure the vertical orientation growth of carbon nanotubes and the control of aspect ratio. Ethylene contains unsaturated bonds, resulting in a faster carbon deposition rate and easy induction of graphene sheet nucleation and growth on the surface of carbon nanotubes. The synergy of the two can achieve in-situ composite of carbon nanotubes and graphene. The hydrogen atmosphere can both serve as a carrier gas to promote the uniform distribution of carbon source and inhibit the excessive deposition of amorphous carbon, ensuring the high crystallinity and excellent conductivity of the composite conductive material. The synergy of catalyst and high temperature conditions provides kinetic support for the vertical orientation growth of carbon nanotubes and the directional arrangement of graphene sheets. Ultimately, a three-dimensional ordered conductive network with vertically grown carbon nanotubes and graphene sheets perpendicular to the carbon nanotube axis can be controlled and prepared, improving the electron transport efficiency and structural flexibility of the conductive layer, adapting to the conductivity continuity requirements under the volume expansion of silicon-carbon anodes, and strengthening the electrolyte penetration channels to achieve dual optimization of electrochemical reaction kinetics and structural stability.

[0068] In some embodiments, the catalyst comprises iron-cobalt mixed metal nanoparticles, wherein the iron-cobalt mixed metal nanoparticles have a particle size of 5-10 nm; The catalyst content is 0.1~0.3 wt%; The high-temperature conditions are described, with a processing temperature of 750~850℃ and a processing time of 1~2 hours.

[0069] Specifically, the synergistic catalytic effect of the iron-cobalt bimetallic catalyst significantly enhances the cracking and deposition activity of the carbon source compared to a single metal catalyst. The small particle size of 5-10 nm serves as a uniform heterogeneous nucleation site, enabling more precise induction of vertical orientation growth of carbon nanotubes while simultaneously promoting the directional nucleation of graphene sheets on the carbon nanotube surface. A catalyst content of 0.1-0.3 wt% ensures sufficient catalytic activity for efficient carbon material growth while avoiding conductive network defects and electrochemical side reactions caused by excessive catalyst agglomeration. A treatment temperature of 750-850℃ and a treatment time of 1-2 hours allow for the control of the carbon material growth rate while maintaining high crystallinity of both carbon nanotubes and graphene, preventing excessive growth, agglomeration, or graphene sheet stacking due to excessively high temperatures or long treatment times. Ultimately, this results in carbon nanotubes with a vertical orientation degree ≥90% and a network density of 102. 10 ~10 12 root / cm 2 The conductive network enhances the electron transport efficiency and structural flexibility of the conductive layer.

[0070] Another embodiment of the present invention provides a negative electrode sheet, including the composite current collector described above, or a composite current collector prepared by the method for preparing the composite current collector described above.

[0071] Specifically, the negative electrode includes the composite current collector provided in this application. The porous copper substrate layer of the composite current collector, with its porous structure, can provide buffer space for the volume expansion of the silicon-carbon negative electrode and form a three-dimensional conductive network to ensure basic electron transport. The rare earth element compound in the composite doped layer is dispersed at the atomic level to form a solid solution. Through lattice distortion optimization, the mechanical strength and conductivity of the current collector are improved, providing structural support for expansion constraint and reducing electron transport resistance. The composite conductive material of the conductive layer can form a high-speed conductive channel, effectively improving the electron and lithium-ion migration efficiency. The lithiophilic modification layer guides the uniform deposition of lithium ions, inhibits lithium dendrite growth and strengthens interlayer bonding, further improving cycle stability. In summary, the composite current collector provided in this application can effectively suppress the expansion of the current collector by buffering expansion, strengthening the structure, improving kinetics and optimizing the deposition of each layer, thus promoting the simultaneous optimization of its high conductivity and long cycle stability.

[0072] The present invention will be further illustrated by the following examples.

[0073] Table 1 Table 2 Example 1 This embodiment illustrates the composite current collector, preparation method, and negative electrode sheet disclosed in this invention, including the following operational steps: 500g of high-purity copper powder (purity ≥99.9%) with a particle size of 2μm was mixed evenly with 333g of ammonium carbonate pore-forming agent (particle size 10μm). The mixture was cold-pressed into a substrate with a thickness of 10mm under a pressure of 150MPa. The substrate was sintered at 950℃ for 4h in a hydrogen atmosphere. After natural cooling, the pore-forming agent was removed by soaking in 1.5mol / L hydrochloric acid solution for 24h, resulting in a porous copper substrate layer with a thickness of 30μm. The porous copper substrate has an internal pore size of 10 μm and a surface pore size of 1 μm.

[0074] Lanthanum nitrate and cerium nitrate, compounds containing rare earth elements, were dissolved in deionized water at a mass ratio of 4:1 to prepare a mixed solution with a total concentration of 0.2 mol / L. The pH was adjusted to 1.5. A porous copper substrate was then electroplated in this mixed solution at a current density of 3 A / dm³. 2 At a temperature of 50℃ and a time of 45 min, a composite doped layer with a thickness of 2 μm was formed on a porous copper substrate to obtain the first precursor. The rare earth element doping amount in the first precursor is 0.12wt%.

[0075] Methane and ethylene were used as carbon sources and introduced into the reaction chamber in a ratio of 1.5:1, along with hydrogen gas. The catalyst iron-cobalt mixed metal nanoparticles (0.2 g / L, particle size 5 nm) were immersed in an ethanol solution for 30 min and reacted at 800 °C for 1.5 h to form a composite conductive material. A 50 nm thick conductive layer of composite conductive material is formed on the surface of the first precursor by chemical vapor deposition to obtain the second precursor. In the conductive layer, the vertical orientation of carbon nanotubes is 90%, and the network density of carbon nanotubes is 10. 10 root / cm 2 .

[0076] A solution was prepared by mixing 0.03 mol / L silver nitrate and 0.01 mol / L bismuth nitrate, which are lithiophilic substances. Then, the second precursor was placed in the solution for 10 min and reacted at 60 °C to form a lithiophilic modification layer with a thickness of 10 nm on the surface of the second precursor.

[0077] Examples 2-10 Examples 2-10 illustrate the composite current collector, preparation method, and negative electrode sheet disclosed in this invention, and include most of the operations in Example 1, except that: Vertical orientation degree of carbon nanotubes in Examples 2-10 / %, network density of carbon nanotubes / roots / cm 2 The diameter of carbon nanotubes (nm), the thickness of graphene sheets (nm), the mass ratio of carbon nanotubes to graphene, the internal pore size of the porous copper substrate, the surface pore size of the porous copper substrate, the thickness of the porous copper substrate, the thickness of the composite doped layer, the doping amount of rare earth elements, the thickness of the lithiophilic modification layer, and the thickness of the conductive layer are all recorded in Tables 1 and 2.

[0078] Comparative Example 1 This comparative example is used to illustrate the composite current collector, preparation method, and negative electrode sheet disclosed in this invention, and includes the following operations: Take 500g of high-purity copper powder (purity ≥99.9%) with a particle size of 2μm, cold press it into a substrate with a thickness of 10mm under a pressure of 150MPa, and let it cool naturally to obtain a copper core with a thickness of 30μm; that is, the core of the composite current collector is not porous. Lanthanum nitrate and cerium nitrate, compounds containing rare earth elements, were dissolved in deionized water at a mass ratio of 4:1 to prepare a mixed solution with a total concentration of 0.2 mol / L. The pH was adjusted to 1.5. A copper core was then placed in this mixed solution for electroplating at a current density of 3 A / dm³. 2 At a temperature of 50℃ and a time of 45 min, a composite doped layer with a thickness of 2 μm was formed on the copper core to obtain the first precursor. The rare earth element doping amount in the first precursor is 0.12wt%.

[0079] Methane and ethylene were used as carbon sources and introduced into the reaction chamber in a ratio of 1.5:1, along with hydrogen gas. The catalyst iron-cobalt mixed metal nanoparticles (0.2 g / L, particle size 5 nm) were immersed in an ethanol solution for 30 min and reacted at 800 °C for 1.5 h to form a composite conductive material. A 50 nm thick conductive layer of composite conductive material is formed on the surface of the first precursor by chemical vapor deposition to obtain the second precursor. In the conductive layer, the vertical orientation of carbon nanotubes is 90%, and the network density of carbon nanotubes is 10. 10 root / cm 2 .

[0080] Comparative Example 2 This comparative example is used to illustrate the composite current collector, preparation method, and negative electrode sheet disclosed in this invention, and includes the following operations: 500g of high-purity copper powder (purity ≥99.9%) with a particle size of 2μm was mixed evenly with 333g of ammonium carbonate pore-forming agent (particle size 10μm). The mixture was cold-pressed into a substrate with a thickness of 10mm under a pressure of 150MPa. The substrate was sintered at 950℃ for 4h in a hydrogen atmosphere. After natural cooling, the pore-forming agent was removed by soaking in 1.5mol / L hydrochloric acid solution for 24h, resulting in a porous copper substrate layer with a thickness of 30μm. Methane and ethylene were used as carbon sources and introduced into the reaction chamber in a ratio of 1.5:1, along with hydrogen gas. The catalyst iron-cobalt mixed metal nanoparticles (0.2 g / L, particle size 5 nm) were immersed in an ethanol solution for 30 min and reacted at 800 °C for 1.5 h to form a composite conductive material. The composite conductive material was deposited onto the surface of a porous copper substrate by chemical vapor deposition to form a conductive layer with a thickness of 50 nm, thus obtaining the first precursor. In the conductive layer, the vertical orientation of carbon nanotubes is 90%, and the network density of carbon nanotubes is 10. 10 root / cm 2 .

[0081] A solution was prepared by mixing 0.03 mol / L silver nitrate and 0.01 mol / L bismuth nitrate, which are lithiophilic substances. Then, the first precursor was placed in the solution for 10 min and reacted at 60 °C. A lithiophilic modification layer with a thickness of 10 nm was formed on the surface of the second precursor. That is, the composite current collector has no composite doping layer.

[0082] Comparative Example 3 This comparative example is used to illustrate the composite current collector, preparation method, and negative electrode sheet disclosed in this invention, and includes the following operations: This comparative example is used to illustrate the composite current collector, preparation method, and negative electrode sheet disclosed in this invention, and includes the following operations: 500g of high-purity copper powder (purity ≥99.9%) with a particle size of 2μm was mixed evenly with 333g of ammonium carbonate pore-forming agent (particle size 10μm). The mixture was cold-pressed into a substrate with a thickness of 10mm under a pressure of 150MPa. The substrate was sintered at 950℃ for 4h in a hydrogen atmosphere. After natural cooling, the pore-forming agent was removed by soaking in 1.5mol / L hydrochloric acid solution for 24h, resulting in a porous copper substrate layer with a thickness of 30μm. Methane and ethylene were used as carbon sources and introduced into the reaction chamber in a ratio of 1.5:1, along with hydrogen gas. The catalyst iron-cobalt mixed metal nanoparticles (0.2 g / L, particle size 5 nm) were immersed in an ethanol solution for 30 min and reacted at 800 °C for 1.5 h to form a composite conductive material. A 50 nm thick conductive layer was formed on the surface of a porous copper substrate using chemical vapor deposition (deposition conditions) to obtain the first precursor. In the conductive layer, the vertical orientation of carbon nanotubes is 90%, and the network density of carbon nanotubes is 10. 10 root / cm 2 Thus, a composite current collector is obtained; that is, the composite current collector has no lithium-philic modification layer.

[0083] Performance testing The following performance tests were performed on Examples 1-10 and Comparative Examples 1-3 prepared above: After the electrode sheets are assembled into a battery, liquid is injected, formation is performed, and capacity is determined. After capacity determination, the battery capacity is adjusted to 50% SOC, and then the thickness is tested and recorded as H0. After the battery is cycled 500 times, the battery thickness H1 is recorded again. The battery expansion percentage = (H1-H0) / H0×100%.

[0084] Cyclic performance testing was conducted by placing the aforementioned lithium-ion batteries in a 25°C environment for 8 hours, charging at 1C, discharging at 1.5C, and using a voltage of 3.0~4.2V. After 500 cycles, the capacity retention rate was recorded.

[0085] The test results are entered into Table 3.

[0086] Table 3 As can be seen from the test results in Table 3, after the composite current collectors prepared in Examples 1 to 10 were applied to the negative electrode, the capacity retention rate of the battery was between 86% and 93%, and the cell expansion rate was only 8.5% to 9.7%, showing excellent cycle stability and expansion suppression effect. In contrast, the capacity retention rates of Comparative Example 1 (without porous copper substrate), Comparative Example 2 (without composite doped layer), and Comparative Example 3 (without lithium-affinity modification layer) were only 63% to 68%, while the cell expansion rate was as high as 18.5% to 20%, and the overall performance was significantly worse than that of the examples. The data from the comparative examples and comparative embodiments demonstrate the importance of the synergistic effect among the porous copper substrate, composite doped layer, conductive layer, and lithiophilic modification layer of the composite current collector. The absence of any one of these structures will lead to a significant decrease in battery cycle stability and exacerbate the expansion problem.

[0087] In summary, the composite current collector provided in this application comprises a porous copper substrate, a composite doped layer, a conductive layer, and a lithiophilic modification layer. The porous copper substrate, with its porous structure, provides a buffer for the volume expansion of the silicon-carbon anode and forms a three-dimensional conductive network to ensure basic electron transport. The rare-earth element compounds in the composite doped layer are dispersed at the atomic level to form a solid solution, which optimizes the mechanical strength and conductivity of the current collector through lattice distortion optimization, providing structural support for expansion constraint while reducing electron transport resistance. The composite conductive material in the conductive layer forms a high-speed conductive channel, effectively improving electron and lithium-ion migration efficiency. The lithiophilic modification layer guides the uniform deposition of lithium ions, inhibits lithium dendrite growth, and strengthens interlayer bonding, further improving cycle stability. In conclusion, the composite current collector provided in this application, through buffering expansion, strengthening the structure, improving kinetics, and optimizing the deposition layer structure, can effectively suppress the expansion of the current collector, promoting the simultaneous optimization of its high conductivity and long cycle stability.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite current collector, characterized in that, The material includes a porous copper substrate, a composite doped layer, a conductive layer, and a lithiophilic modification layer. The composite doped layer includes a copper layer doped with rare earth elements. The composite doped layer is disposed on the pore surface of the porous copper substrate. The conductive layer is disposed on the surface of the composite doped layer. The lithiophilic modification layer is formed on the side of the conductive layer opposite to the composite doped layer.

2. The composite current collector according to claim 1, characterized in that, The porosity of the porous copper substrate layer gradually decreases from the interior to the surface of the porous copper substrate layer, and the porosity of the porous copper substrate layer is 40~60%.

3. The composite current collector according to claim 2, characterized in that, The porous copper substrate has an internal pore size of 10~30μm and a surface pore size of 1~3μm.

4. The composite current collector according to claim 1, characterized in that, The porous copper substrate has multiple interconnected spherical pores.

5. The composite current collector according to claim 1, characterized in that, The pore wall thickness of the porous copper substrate is 1~3μm; The thickness of the porous copper substrate is 30~40μm.

6. The composite current collector according to claim 1, characterized in that, Based on the total mass of the porous copper substrate and the composite doped layer being 100%, the doping amount of the rare earth element is 0.05~0.2wt%.

7. The composite current collector according to claim 1, characterized in that, The conductive layer comprises a composite of carbon nanotubes and graphene, wherein the carbon nanotubes are grown vertically on the surface of the composite doped layer, and the graphene sheets are perpendicular to the axial position of the carbon nanotubes. The vertical orientation of the carbon nanotubes in the conductive layer is ≥90%; The network density of carbon nanotubes in the conductive layer is 10. 10 ~10 12 root / cm 2 .

8. The composite current collector according to claim 1, characterized in that, The thickness of the conductive layer is 50~200nm.

9. The composite current collector according to claim 7, characterized in that, The diameter of the carbon nanotubes is 10~30nm, and the thickness of the graphene sheets is 1~3nm; The mass ratio of the carbon nanotubes to the graphene is 1:1 to 3:

1.

10. The composite current collector according to claim 1, characterized in that, The lithiophilic modification layer includes a lithiophilic material, which includes one or more substances containing silver, zinc, tin, and bismuth; and / or, Compounds containing rare earth elements include one or more of lanthanum nitrate and cerium nitrate; The porous copper substrate has a copper content of ≥99.9%.

11. The composite current collector according to claim 1, characterized in that, The total thickness of the composite current collector is 6~30μm; The thickness of the composite doped layer is 1~10μm; the thickness of the lithiophilic modified layer is 5~20nm.

12. The method for preparing the composite current collector according to any one of claims 1 to 11, characterized in that, Includes the following operations: Copper material is mixed with a pore-forming agent, cold-pressed and then sintered in a hydrogen atmosphere. The pore-forming agent is then removed to obtain a porous copper substrate layer. A compound containing rare earth elements is prepared into a mixed solution, and a porous copper substrate is placed in the mixed solution for electroplating to form a composite doped layer, thus obtaining the first precursor. Obtain composite conductive materials; A conductive layer is formed on the surface of a first precursor by chemical vapor deposition of a composite conductive material to obtain a second precursor. A lithiophilic substance is prepared into a solution, and then a second precursor is placed in the solution. Under thermal reaction conditions, a lithiophilic modification layer is formed on the surface of the second precursor.

13. The method for preparing the composite current collector according to claim 12, characterized in that, In the process of preparing a porous copper substrate, the cold pressing pressure is 100~200 MPa, and the cold pressing pressure gradually decreases from the surface of the porous copper substrate to the interior of the porous copper substrate. The sintering temperature is 900~1000℃, and the sintering time is 3~5h.

14. The method for preparing the composite current collector according to claim 12, characterized in that, The process of depositing the mixture onto the surface of a porous copper substrate is called electroplating. During electroplating, the current density is 2~5A / dm³. 2 Temperature 40~60℃, pH value 1~2, electroplating time 30~60min.

15. The method for preparing the composite current collector according to claim 12, characterized in that, The pore-forming agent includes one or more of ammonium carbonate and ammonium bicarbonate; The particle size of the pore-forming agent is 1~50μm.

16. The method for preparing the composite current collector according to claim 12, characterized in that, In the process of "forming a lithiophilic modification layer", the high temperature is 30~60℃.

17. The method for preparing the composite current collector according to claim 12, characterized in that, The composite conductive material is prepared by the following method: Methane and ethylene are used as carbon sources and introduced into the reaction chamber, along with hydrogen gas. Under the conditions of a catalyst and high temperature, a composite conductive material is formed.

18. The method for preparing the composite current collector according to claim 17, characterized in that, The catalyst comprises iron-cobalt mixed metal nanoparticles, wherein the iron-cobalt mixed metal nanoparticles have a particle size of 5-10 nm. The catalyst content is 0.1~0.3 wt%; The high-temperature conditions are described, with a processing temperature of 750~850℃ and a processing time of 1~2 hours.

19. A negative electrode sheet, characterized in that, The composite current collector includes the composite current collector as described in any one of claims 1 to 11, or the composite current collector prepared by the method described in any one of claims 12 to 18.

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