A negative electrode for a lithium secondary battery and a lithium secondary battery comprising the negative electrode

Abstract

The present invention relates to the technical field of lithium secondary batteries, and specifically to a negative electrode for a lithium secondary battery and a lithium secondary battery comprising the negative electrode. The negative electrode comprises the following technical features: a composite matrix structure: the negative electrode is composed of a multilayer composite structure, including (a) a conductive support layer, (b) a porous active material layer, and (c) a surface functionalized coating. In the present invention, the high porosity structure of the three-dimensional mesh metal matrix and the vertical conductive channels of the nanowire array are used to achieve rapid lithium ion transmission, reduce interface resistance, and improve rate performance. Under 10C high rate conditions, the capacity retention rate of the negative electrode is still ≥80%. The gradient pore structure design further optimizes the lithium ion diffusion path, and combined with the optimization parameters of the Poiseuille flow equation, the diffusion rate of lithium ions is increased to, effectively reducing polarization and improving the fast charging capability of the electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium secondary batteries, and in particular to a negative electrode for a lithium secondary battery and a lithium secondary battery comprising the negative electrode. Background Art

[0002] Lithium secondary batteries have become the core energy technology for new energy vehicles, portable electronic devices and energy storage systems due to their high energy density, long cycle life and good safety. As a key component of battery performance, the negative electrode material directly affects the battery's energy density, rate performance and cycle life. Currently, commercial negative electrodes are mainly represented by graphite, whose theoretical specific capacity is only 372mAh / g, which is difficult to meet the needs of high-energy-density batteries. Based on this, silicon-based negative electrodes have attracted widespread attention due to their theoretical specific capacity of up to 4200mAh / g. However, silicon will undergo a volume expansion of up to 300% during the lithium insertion / deinsertion process, resulting in material pulverization, interface failure and cycle performance degradation, which greatly limits its practical application. Therefore, how to develop silicon-based composite negative electrode materials with high capacity, high stability and excellent rate performance has become the focus of current research.

[0003] Traditional silicon-based anodes typically utilize nano-silicon particles doped with carbon materials to mitigate silicon volume expansion and improve conductivity. Silicon-carbon composites are prepared through methods such as mechanical ball milling, chemical vapor deposition, or solution coating, and then coated onto a copper foil current collector with a binder. However, this approach presents several challenges. First, simple carbon coating cannot completely suppress silicon volume expansion, resulting in an unstable electrode structure. Second, the two-dimensional structure of traditional copper foil current collectors can easily restrict lithium ion transport during high-current charge and discharge, reducing rate performance. Furthermore, contact between silicon-carbon composites and the electrolyte easily forms an unstable solid electrolyte interface (SEI), which can induce lithium dendrite growth, severely impacting the battery's cycle life and safety. Consequently, existing silicon-based anodes still struggle to achieve stable operation in high-rate fast-charging and long-life cycling scenarios.

[0004] To this end, we propose a negative electrode for a lithium secondary battery and a lithium secondary battery including the negative electrode. Summary of the Invention

[0005] An object of the present invention is to provide a negative electrode for a lithium secondary battery and a lithium secondary battery including the negative electrode, so as to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A negative electrode for a lithium secondary battery, comprising the following technical features:

[0008] Composite matrix structure: The negative electrode is composed of a multi-layer composite structure, including (a) a conductive support layer, (b) a porous active material layer, and (c) a surface functionalized coating;

[0009] Conductive support layer: The conductive support layer is a three-dimensional mesh metal matrix, the material of which is selected from copper, nickel or titanium alloy, with a thickness of 10-50 μm, a porosity of 30% to 60%, and a pore size distribution of 0.1-5 μm. Its surface is formed by electrochemical deposition to form a nano-scale rough interface with a roughness Ra of 0.2-1.5 μm;

[0010] Porous active material layer: The porous active material layer is composed of a silicon-based composite material and a porous carbon matrix. The silicon-based composite material is a core-shell structure of nano-silicon particles (particle size 20-200nm) and a carbon coating layer (thickness 2-10nm). The porous carbon matrix is ​​a three-dimensional network formed by interweaving graphene and carbon nanotubes, with a porosity of 50% to 80% and a specific surface area of ​​500-1500m² / g.

[0011] Surface functionalized coating: The coating is a composite layer of a fluoropolymer and an inorganic lithium salt, with a thickness of 1-10 μm, wherein the fluoropolymer is polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE), and the inorganic lithium salt is LiF or Li3N, accounting for 5% to 20% by mass;

[0012] Functional synergy mechanism: The conductive support layer provides a rapid lithium ion transmission channel and inhibits volume expansion through high porosity and nano-rough interface; the porous active material layer achieves high capacity and structural stability through silicon-carbon core-shell structure and three-dimensional carbon network; the surface functionalized coating inhibits lithium dendrite growth and improves interface stability through the lithium-phobic properties of fluoropolymers and the SEI membrane regulation of inorganic lithium salts.

[0013] As a preferred technical solution, the silicon-based composite material of the porous active material layer is further defined as:

[0014] Composition of silicon-based composite materials: After the surface of nano-silicon particles is coated with a carbon layer, a secondary coating structure is formed with transition metal oxides. The thickness of the transition metal oxide layer is 5-20nm, and its mass accounts for 10% to 30% of the silicon-based composite material.

[0015] Optimization of the porous carbon matrix: The mass ratio of graphene to carbon nanotubes is 1:1 to 3:1. The carbon nanotubes are nitrogen-doped (nitrogen content 1-5 at%), and nanoscale metal particles with a particle size of 5-50 nm are embedded in the three-dimensional network, accounting for 0.5% to 5% of the carbon matrix by mass.

[0016] Directed design of pore structure: The pore size of the porous active material layer is distributed in a gradient, with the pore size close to the conductive support layer being 0.1-1 μm and the pore size close to the surface functional coating being 1-5 μm. The number of gradient layers is 3-5.

[0017] Performance improvement mechanism: The transition metal oxide layer alleviates the volume expansion of silicon through its high mechanical strength; nitrogen-doped carbon nanotubes and metal particles synergistically improve electronic conductivity; the gradient pore structure optimizes the lithium ion diffusion path and reduces concentration polarization.

[0018] As a preferred technical solution, the secondary coating structure of the silicon-based composite material is further optimized as follows: after coating the surface of the nano-silicon particles with a carbon layer, a transition metal oxide layer is deposited by a sol-gel method or a vapor deposition method, wherein the thickness of the carbon layer is 2-10 nm, the thickness of the transition metal oxide layer is 5-20 nm, the chemical composition of the transition metal oxide layer satisfies the balance between electronic conductivity and mechanical stability, and a doping strategy is adopted to optimize its electronic structure, wherein the doping element is Nb, Mo or W, and the doping concentration is 1-5 at%. The structural stability of the silicon-based composite material is described by a stress buffer model, assuming that the volume expansion rate of the nano-silicon is α and the elastic modulus of the carbon layer is , the elastic modulus of the transition metal oxide layer is , the effective elastic modulus of the entire coating structure Calculated by the equivalent series model: ,

[0019] By optimizing and The ratio of In the range of 50-150GPa, the overall structural stability is maintained during the volume expansion of silicon, and pulverization failure caused by interface stress concentration is suppressed.

[0020] As a preferred technical solution, the structural optimization of the porous carbon matrix includes a three-dimensional interwoven network of graphene and carbon nanotubes, wherein the spacing between graphene sheets is controlled to be 0.35-0.45nm to provide space for lithium ion embedding, the diameter distribution range of the carbon nanotubes is set to 5-20nm, and the carbon nanotubes are modified by nitrogen doping with a nitrogen doping concentration of 1-5at%. The surface charge density of the carbon nanotubes after doping is obtained by electronic structure calculation, and the metal particles (Ag, Cu) embedded in the carbon matrix are prepared by chemical reduction or sputtering deposition, and the particle size is controlled at 5-50nm. The binding energy between the metal particles and the carbon matrix is ​​optimized by density functional theory calculation to ensure the continuity of the electron transmission path. The electronic conductivity of the carbon matrix is ​​calculated by effective medium theory, and its equivalent conductivity is for: ,

[0021] in are the volume fractions of carbon nanotubes, graphene and metal particles, respectively, are their respective conductivity, after optimization In the range of 1000-5000S / m, to ensure the rapid transmission of lithium ions and the effective path of electrons, thereby improving the rate performance and reducing the polarization loss.

[0022] As a preferred technical solution, the gradient pore structure of the porous active material layer is constructed by a template method or a phase separation method. The pore size distribution gradually increases from 0.1-1 μm near the conductive support layer to 1-5 μm near the surface functional coating, forming a 3-5 layer gradient structure. The porosity of each layer is sequentially controlled between 50% and 80% to match the lithium ion transmission path and reaction kinetics. The design of the pore gradient is optimized according to the lithium ion diffusion equation, and its diffusion time constant τ satisfies: ,

[0023] Where L is the diffusion path length and D is the lithium ion diffusion coefficient. By controlling the gradient distribution of the pore size, L is reduced layer by layer. The mechanical stability of the gradient structure is verified by finite element simulation, which avoids pore collapse or structural damage during the cycle process, ensuring stable ion transmission performance under long cycle conditions, thereby improving the battery's rate capability and long life characteristics.

[0024] As a preferred technical solution, the surface functionalized coating is further defined as:

[0025] Layered structure of the composite coating: The coating consists of an inner layer (contacting the porous active material layer) and an outer layer. The inner layer is a composite of LiF and PVDF (LiF accounts for 20% to 50% by weight), and the outer layer is a composite of Li3N and PTFE (Li3N accounts for 10% to 30% by weight).

[0026] Interface modification process: The inner layer is formed by solution coating with a thickness of 0.5-3 μm, and the outer layer is formed by vapor deposition with a thickness of 0.5-2 μm;

[0027] Functional collaborative design: The inner layer LiF-PVDF composite reacts preferentially with the electrolyte to form a dense SEI film, and the outer layer Li3N-PTFE composite reacts preferentially with the electrolyte to form a dense SEI film. above) and lithium-phobic properties inhibit dendrite penetration;

[0028] Dynamic repair mechanism: During the cycle, the outer layer of Li3N decomposes into and , Reacts with lithium to generate Li3N, achieving self-repair of the coating.

[0029] As a preferred technical solution, the preparation method of the conductive support layer is further defined as follows:

[0030] Substrate pretreatment: A metal foil is acid-etched to form micron-sized pores, and then nanowire arrays (Cu or Ni, 1-5 μm in length, 50-200 nm in diameter) are grown within the pores by electrochemical deposition.

[0031] Interface modification: The surface of the nanowire is coated with an ultra-thin carbon layer (thickness 1-3nm) or a metal oxide layer, and the coating is achieved by atomic layer deposition (ALD) technology;

[0032] Structural advantages: Nanowire arrays provide vertical lithium ion transport channels, and carbon / oxide coatings reduce interfacial impedance and prevent electrolyte corrosion;

[0033] Optimized mechanical properties: The tensile strength of the support layer is ≥200MPa, the elastic modulus is ≥50GPa, and it can withstand 300% volume expansion of the silicon-based material.

[0034] As a preferred technical solution, the substrate pretreatment method of the conductive support layer is further optimized as follows: during the acid etching process of the metal foil, the concentration of the acid solution and the etching time are precisely controlled so that the diameter of the micron-scale pores formed is in the range of 0.5-5μm, the distribution is uniform, and the porosity reaches 30% to 60%. On the metal substrate after acid etching, a pulse electrochemical deposition method is used to grow a nanowire array, wherein the deposition current density is 5-50mA / cm² and the pulse period is controlled at 1-10ms to adjust the length and density of the nanowires so that the final nanowires are 1-5μm in length and 50-200nm in diameter, and are evenly distributed inside the pores of the metal substrate. The vertical arrangement structure of the nanowire array optimizes the transport path of lithium ions, and its ion diffusion rate It can be calculated by Poiseuille flow equation: ,

[0035] Where ε is the porosity, r is the pore radius, ΔP is the pressure difference caused by the lithium ion concentration gradient, η is the dynamic viscosity of the electrolyte, and L is the length of the nanowire. The optimized parameters are exist within the range.

[0036] As a preferred technical solution, the interface modification method of the conductive support layer is further optimized as follows: an ultra-thin carbon layer or metal oxide layer is deposited on the surface of the nanowire array by atomic layer deposition technology, and the thickness of the coating layer is precisely controlled to be 1-3nm. The carbon layer is prepared by CVD method, using methane or acetylene as a precursor, and by regulating the deposition temperature and pressure, the carbon layer forms a graphite-like structure, and the metal oxide layer is formed by or The deposition temperature is controlled at 100-300 ° C to form a dense and uniform coating layer. The interface resistance of the coating layer is calculated by the equivalent circuit model, where the interface resistance The relationship between the coating thickness d and the material conductivity σ is: ,

[0037] Where A is the unit area, optimize the matching relationship between d and σ so that Control within the range.

[0038] A lithium secondary battery adopts the negative electrode for lithium secondary battery according to any one of the above solutions.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. Through the high porosity structure of the three-dimensional mesh metal matrix and the vertical conductive channels of the nanowire array, rapid lithium ion transmission is achieved, the interface resistance is reduced, and the rate performance is improved. Under the condition of 10C high rate, the capacity retention rate of the negative electrode is still ≥80%. The gradient pore structure design further optimizes the lithium ion diffusion path, and combined with the optimization parameters of the Poiseuille flow equation, the lithium ion diffusion rate is increased to , effectively reducing polarization and improving the fast charging capability of the electrode.

[0041] 2. A porous active material layer with a silicon-carbon core-shell structure and a secondary transition metal oxide coating utilizes the high mechanical strength of the metal oxide to suppress the volume expansion of silicon particles. Nitrogen-doped carbon nanotubes and metal particles synergistically enhance electronic conductivity, maintaining the structural integrity of the material during cycling. The negative electrode support layer has a tensile strength of ≥200MPa and an elastic modulus of ≥50GPa, capable of withstanding 300% volume expansion of the silicon-based material, thereby extending the battery's cycle life and achieving ≥2000 cycles at 5C charge and discharge conditions.

[0042] 3. Optimized interfacial stability is achieved through a composite coating design of fluoropolymers and inorganic lithium salts. The inner LiF-PVDF composite promotes the formation of a dense SEI film, while the outer Li3N-PTFE composite effectively inhibits lithium dendrite growth through its high ionic conductivity (≥10⁻³S / cm) and lithium-repellent properties. Furthermore, the outer Li3N decomposes into Li⁺ and N3⁻ in localized high-voltage regions and self-repairs during cycling, achieving long-term interfacial stability and significantly reducing the risk of negative electrode short-circuiting at high current densities.

[0043] 4. A three-dimensional network of interwoven graphene and carbon nanotubes enhances the material's electronic conductivity. Nitrogen-doped carbon nanotubes and embedded nanometal particles (Ag and Cu) further enhance overall conductivity. The optimized electronic conductivity reaches 10²-10³ S / m. Combined with a gradient pore structure to reduce concentration polarization, the battery maintains a high energy density even at high charge and discharge rates, ensuring a full-cell energy density of ≥400Wh / kg.

[0044] 5. The negative electrode material is compatible with a high-nickel ternary cathode (NCM811) and a solid-state electrolyte (such as sulfide Li6PS5Cl), achieving a capacity retention rate of ≥70% at -20°C. A pre-lithiation process pre-embeds metallic lithium (0.1% to 1% by weight) into a surface functionalized coating, or uses a chemical pre-lithiation agent (LiPAA) to treat the porous active material layer, reducing irreversible capacity loss in the first cycle and improving initial coulombic efficiency. Furthermore, the negative electrode material, combined with a thermal shutdown separator (melting point 130-150°C) and an overcharge protection additive (biphenyl), can pass the UL1642 needle penetration test, ensuring battery safety under extreme operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0046] Figure 1 Schematic diagram of the overall structure of the negative electrode of the present invention;

[0047] Figure 2 Schematic diagram of the structure of the silicon-based composite material of the present invention;

[0048] Figure 3 Schematic diagram of the gradient pore structure of the porous active material layer of the present invention;

[0049] Figure 4 Schematic diagram of the layered structure of the surface functionalized coating of the present invention. DETAILED DESCRIPTION

[0050] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0051] Example 1

[0052] According to the attached Figure 1-4 As shown, a negative electrode for a lithium secondary battery includes the following technical features:

[0053] Composite matrix structure: The negative electrode is composed of a multi-layer composite structure, including (a) a conductive support layer, (b) a porous active material layer, and (c) a surface functionalized coating;

[0054] Conductive support layer: The conductive support layer is a three-dimensional mesh metal matrix, the material of which is selected from copper, nickel or titanium alloy, with a thickness of 10-50 μm, a porosity of 30% to 60%, and a pore size distribution of 0.1-5 μm. Its surface is formed by electrochemical deposition to form a nano-scale rough interface with a roughness Ra of 0.2-1.5 μm;

[0055] Porous active material layer: The porous active material layer is composed of a silicon-based composite material and a porous carbon matrix. The silicon-based composite material is a core-shell structure of nano-silicon particles (particle size 20-200nm) and a carbon coating layer (thickness 2-10nm). The porous carbon matrix is ​​a three-dimensional network formed by interweaving graphene and carbon nanotubes, with a porosity of 50% to 80% and a specific surface area of ​​500-1500m² / g.

[0056] Surface functionalized coating: The coating is a composite layer of a fluoropolymer and an inorganic lithium salt, with a thickness of 1-10 μm, wherein the fluoropolymer is polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE), and the inorganic lithium salt is LiF or Li3N, accounting for 5% to 20% by mass;

[0057] Functional synergy mechanism: The conductive support layer provides a rapid lithium ion transmission channel and inhibits volume expansion through high porosity and nano-rough interface; the porous active material layer achieves high capacity and structural stability through silicon-carbon core-shell structure and three-dimensional carbon network; the surface functionalized coating inhibits lithium dendrite growth and improves interface stability through the lithium-phobic properties of fluoropolymers and the SEI membrane regulation of inorganic lithium salts.

[0058] Example 2

[0059] Based on the above embodiment 1, the silicon-based composite material of the porous active material layer is further defined as:

[0060] Composition of silicon-based composite materials: After the surface of nano-silicon particles is coated with a carbon layer, a secondary coating structure is formed with transition metal oxides. The thickness of the transition metal oxide layer is 5-20nm, and its mass accounts for 10% to 30% of the silicon-based composite material.

[0061] Optimization of the porous carbon matrix: The mass ratio of graphene to carbon nanotubes is 1:1 to 3:1. The carbon nanotubes are nitrogen-doped (nitrogen content 1-5 at%), and nanoscale metal particles with a particle size of 5-50 nm are embedded in the three-dimensional network, accounting for 0.5% to 5% of the carbon matrix by mass.

[0062] Directed design of pore structure: The pore size of the porous active material layer is distributed in a gradient, with the pore size close to the conductive support layer being 0.1-1 μm and the pore size close to the surface functional coating being 1-5 μm. The number of gradient layers is 3-5.

[0063] Performance improvement mechanism: The transition metal oxide layer alleviates the volume expansion of silicon through its high mechanical strength; nitrogen-doped carbon nanotubes and metal particles synergistically improve electronic conductivity; the gradient pore structure optimizes the lithium ion diffusion path and reduces concentration polarization.

[0064] The secondary coating structure of the silicon-based composite material is further optimized as follows: after coating the surface of the nano-silicon particles with a carbon layer, a transition metal oxide layer is deposited by a sol-gel method or a vapor deposition method, wherein the thickness of the carbon layer is 2-10 nm, the thickness of the transition metal oxide layer is 5-20 nm, the chemical composition of the transition metal oxide layer satisfies the balance between electronic conductivity and mechanical stability, and a doping strategy is adopted to optimize its electronic structure, wherein the doping element is Nb, Mo or W, and the doping concentration is 1-5 at%. The structural stability of the silicon-based composite material is described by a stress buffer model, assuming that the volume expansion rate of the nano-silicon is α and the elastic modulus of the carbon layer is , the elastic modulus of the transition metal oxide layer is , the effective elastic modulus of the entire coating structure Calculated by the equivalent series model: ,

[0065] By optimizing and The ratio of In the range of 50-150GPa, the overall structural stability is maintained during the volume expansion of silicon, and pulverization failure caused by interface stress concentration is suppressed.

[0066] The structural optimization of the porous carbon matrix includes a three-dimensional interwoven network of graphene and carbon nanotubes, wherein the spacing between graphene sheets is controlled to be 0.35-0.45nm to provide space for lithium ion embedding, the diameter distribution range of the carbon nanotubes is set to 5-20nm, and the carbon nanotubes are modified by nitrogen doping with a nitrogen doping concentration of 1-5at%. The surface charge density of the carbon nanotubes after doping is obtained by electronic structure calculation, and the metal particles (Ag, Cu) embedded in the carbon matrix are prepared by chemical reduction or sputtering deposition, and the particle size is controlled to be 5-50nm. The binding energy between the metal particles and the carbon matrix is ​​optimized by density functional theory calculation to ensure the continuity of the electron transmission path. The electronic conductivity of the carbon matrix is ​​calculated by effective medium theory, and its equivalent conductivity is for: ,

[0067] in are the volume fractions of carbon nanotubes, graphene and metal particles, respectively, are their respective conductivity, after optimization In the range of 1000-5000S / m, to ensure the rapid transmission of lithium ions and the effective path of electrons, thereby improving the rate performance and reducing the polarization loss.

[0068] The gradient pore structure of the porous active material layer is constructed by a template method or a phase separation method. The pore size distribution gradually increases from 0.1-1 μm near the conductive support layer to 1-5 μm near the surface functional coating, forming a 3-5 layer gradient structure. The porosity of each layer is sequentially controlled between 50% and 80% to match the lithium ion transmission path and reaction kinetics. The design of the pore gradient is optimized based on the lithium ion diffusion equation, and its diffusion time constant τ satisfies: ,

[0069] Where L is the diffusion path length and D is the lithium ion diffusion coefficient. By controlling the gradient distribution of the pore size, L is reduced layer by layer. The mechanical stability of the gradient structure is verified by finite element simulation, which avoids pore collapse or structural damage during the cycle process, ensuring stable ion transmission performance under long cycle conditions, thereby improving the battery's rate capability and long life characteristics.

[0070] Example 3

[0071] Based on the above embodiment 1, the surface functionalized coating is further defined as:

[0072] Layered structure of the composite coating: The coating consists of an inner layer (contacting the porous active material layer) and an outer layer. The inner layer is a composite of LiF and PVDF (LiF accounts for 20% to 50% by weight), and the outer layer is a composite of Li3N and PTFE (Li3N accounts for 10% to 30% by weight).

[0073] Interface modification process: The inner layer is formed by solution coating with a thickness of 0.5-3 μm, and the outer layer is formed by vapor deposition with a thickness of 0.5-2 μm;

[0074] Functional collaborative design: The inner layer LiF-PVDF composite reacts preferentially with the electrolyte to form a dense SEI film, and the outer layer Li3N-PTFE composite reacts preferentially with the electrolyte to form a dense SEI film. above) and lithium-phobic properties inhibit dendrite penetration;

[0075] Dynamic repair mechanism: During the cycle, the outer layer of Li3N decomposes into and , Reacts with lithium to generate Li3N, achieving self-repair of the coating.

[0076] Example 4

[0077] Based on the above embodiment 1, the preparation method of the conductive support layer is further defined as follows:

[0078] Substrate pretreatment: A metal foil is acid-etched to form micron-sized pores, and then nanowire arrays (Cu or Ni, 1-5 μm in length, 50-200 nm in diameter) are grown within the pores by electrochemical deposition.

[0079] Interface modification: The surface of the nanowire is coated with an ultra-thin carbon layer (thickness 1-3nm) or a metal oxide layer, and the coating is achieved by atomic layer deposition (ALD) technology;

[0080] Structural advantages: Nanowire arrays provide vertical lithium ion transport channels, and carbon / oxide coatings reduce interfacial impedance and prevent electrolyte corrosion;

[0081] Optimized mechanical properties: The tensile strength of the support layer is ≥200MPa, the elastic modulus is ≥50GPa, and it can withstand 300% volume expansion of the silicon-based material.

[0082] The substrate pretreatment method of the conductive support layer is further optimized as follows: during the acid etching process of the metal foil, the concentration of the acid solution and the etching time are precisely controlled so that the diameter of the micron-scale pores formed is in the range of 0.5-5μm, the distribution is uniform, and the porosity reaches 30% to 60%. On the metal substrate after acid etching, a nanowire array is grown by pulse electrochemical deposition, wherein the deposition current density is 5-50mA / cm² and the pulse period is controlled at 1-10ms to adjust the length and density of the nanowires so that the final nanowires are 1-5μm in length and 50-200nm in diameter, and are evenly distributed inside the pores of the metal substrate. The vertical arrangement structure of the nanowire array optimizes the transport path of lithium ions and its ion diffusion rate It can be calculated by Poiseuille flow equation: ,

[0083] Where ε is the porosity, r is the pore radius, ΔP is the pressure difference caused by the lithium ion concentration gradient, η is the dynamic viscosity of the electrolyte, and L is the length of the nanowire. The optimized parameters are exist within the range.

[0084] The interface modification method of the conductive support layer is further optimized as follows: an ultra-thin carbon layer or a metal oxide layer is deposited on the surface of the nanowire array by atomic layer deposition technology, and the thickness of the coating layer is precisely controlled to be 1-3nm. The carbon layer is prepared by CVD method, using methane or acetylene as a precursor, and by regulating the deposition temperature and pressure, the carbon layer forms a graphite-like structure, and the metal oxide layer is formed by or The deposition temperature is controlled at 100-300 ° C to form a dense and uniform coating layer. The interface resistance of the coating layer is calculated by the equivalent circuit model, where the interface resistance The relationship between the coating thickness d and the material conductivity σ is: ,

[0085] Where A is the unit area, optimize the matching relationship between d and σ so that Control within the range.

[0086] A lithium secondary battery adopts the negative electrode for lithium secondary battery according to any one of the above embodiments.

[0087] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and improvements fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A negative electrode for a lithium secondary battery, characterized in that The negative electrode includes the following technical features: Composite matrix structure: The negative electrode is composed of a multi-layer composite structure, including a conductive support layer, a porous active material layer and a surface functionalized coating; Conductive support layer: The conductive support layer is a three-dimensional mesh metal matrix, the material of which is selected from copper, nickel or titanium alloy, with a thickness of 10-50 μm, a porosity of 30% to 60%, and a pore size distribution of 0.1-5 μm. Its surface is formed by electrochemical deposition to form a nano-scale rough interface with a roughness Ra of 0.2-1.5 μm; Porous active material layer: The porous active material layer is composed of a silicon-based composite material and a porous carbon matrix, wherein the silicon-based composite material is a core-shell structure of nano-silicon particles and a carbon coating layer, the particle size of the nano-silicon particles is 20-200nm, the thickness of the carbon coating layer is 2-10nm, and the porous carbon matrix is ​​a three-dimensional network formed by the interweaving of graphene and carbon nanotubes, with a porosity of 50% to 80% and a specific surface area of ​​500-1500m 2 / g; Surface functionalized coating: The coating is a composite layer of a fluoropolymer and an inorganic lithium salt, with a thickness of 1-10 μm, wherein the fluoropolymer is PVDF or PTFE, and the inorganic lithium salt is LiF or Li3N, accounting for 5% to 20% by mass; Functional synergy mechanism: The conductive support layer provides a fast lithium ion transmission channel and suppresses volume expansion through high porosity and nano-rough interface; the porous active material layer achieves high capacity and structural stability through a silicon-carbon core-shell structure and a three-dimensional carbon network; The surface functional coating inhibits lithium dendrite growth and improves interface stability through the lithium-repellent properties of the fluoropolymer and the SEI film regulation of the inorganic lithium salt; The silicon-based composite material of the porous active material layer is defined as: Composition of silicon-based composite materials: After the surface of nano-silicon particles is coated with a carbon layer, a secondary coating structure is formed with transition metal oxides. The thickness of the transition metal oxide layer is 5-20nm, and the mass ratio is 10% to 30% of the silicon-based composite material. Optimization of the porous carbon matrix: The mass ratio of graphene to carbon nanotubes is 1:1 to 3:

1. The carbon nanotubes are nitrogen-doped to a nitrogen content of 1-5 at%, and nano-scale metal particles with a particle size of 5-50 nm are embedded within the three-dimensional network, accounting for 0.5% to 5% of the carbon matrix by mass. Directed design of pore structure: The pore size of the porous active material layer is distributed in a gradient, with the pore size close to the conductive support layer being 0.1-1 μm and the pore size close to the surface functional coating being 1-5 μm. The number of gradient layers is 3-5. Performance improvement mechanism: The transition metal oxide layer mitigates silicon volume expansion through its high mechanical strength; nitrogen-doped carbon nanotubes and metal particles synergistically enhance electronic conductivity; the gradient pore structure optimizes the lithium ion diffusion path and reduces concentration polarization; The gradient pore structure of the porous active material layer is constructed by a template method or a phase separation method. The pore size distribution gradually increases from 0.1-1 μm near the conductive support layer to 1-5 μm near the surface functional coating, forming a 3-5 layer gradient structure. The porosity of each layer is sequentially controlled between 50% and 80% to match the lithium ion transmission path and reaction kinetics. The design of the pore gradient is optimized based on the lithium ion diffusion equation, and its diffusion time constant τ satisfies: Where L is the diffusion path length and D is the lithium ion diffusion coefficient. By controlling the gradient distribution of the pore size, L is reduced layer by layer. The mechanical stability of the gradient structure is verified by finite element simulation, which avoids pore collapse or structural damage during the cycle process, ensuring stable ion transmission performance under long cycle conditions, thereby improving the battery's rate capability and long life characteristics.

2. A negative electrode for a lithium secondary battery according to claim 1, characterized in that: The secondary coating structure of the silicon-based composite material is optimized as follows: after coating the surface of the nano-silicon particles with a carbon layer, a transition metal oxide layer is deposited by a sol-gel method or a vapor deposition method, wherein the thickness of the carbon layer is 2-10 nm, the thickness of the transition metal oxide layer is 5-20 nm, the chemical composition of the transition metal oxide layer satisfies the balance between electronic conductivity and mechanical stability, and a doping strategy is adopted to optimize its electronic structure, wherein the doping element is Nb, Mo or W, and the doping concentration is 1-5 at%. The structural stability of the silicon-based composite material is described by a stress buffer model, assuming that the volume expansion rate of the nano-silicon is α and the elastic modulus of the carbon layer is E c , the elastic modulus of the transition metal oxide layer is E ox , the effective elastic modulus E of the entire coating structure eff Calculated by the equivalent series model: By optimizing E c With E ox The ratio of E eff In the range of 50-150GPa, the overall structural stability is maintained during the volume expansion of silicon, and pulverization failure caused by interface stress concentration is suppressed.

3. The negative electrode for a lithium secondary battery according to claim 1, wherein: The structural optimization of the porous carbon matrix includes a three-dimensional interwoven network of graphene and carbon nanotubes, wherein the graphene interlayer spacing is controlled to 0.35-0.45nm to provide space for lithium ion embedding, the carbon nanotubes are set to have a diameter distribution range of 5-20nm, and are modified by nitrogen doping with a nitrogen doping concentration of 1-5at%. The surface charge density of the carbon nanotubes after doping is calculated by electronic structure calculations, and the metal particles embedded in the carbon matrix are prepared by chemical reduction or sputtering deposition. The metal particles are Ag or Cu, and the particle size is controlled to be 5-50nm. The binding energy between the metal particles and the carbon matrix is ​​optimized by density functional theory calculations to ensure the continuity of the electron transmission path. The electronic conductivity of the carbon matrix is ​​calculated by effective medium theory, and its equivalent conductivity σeff is: s eff =f CNT ·s CNT +f Gr ·s Gr +f M ·s M where f CNT ,f Gr ,f M are the volume fractions of carbon nanotubes, graphene and metal particles, σ CNT ,σ Gr ,σ M are their respective conductivity, and after optimization, σ eff In the range of 1000-5000S / m, to ensure the rapid transport of lithium ions and the effective pathway of electrons, thereby improving the rate performance and reducing the polarization loss.

4. The negative electrode for a lithium secondary battery according to claim 1, wherein: The surface functionalized coating is defined as: Layered structure of the composite coating: The coating consists of an inner layer and an outer layer, wherein the inner layer is a contact porous active material layer, the inner layer is a composite of LiF and PVDF, wherein LiF accounts for 20% to 50% by weight, and the outer layer is a composite of Li3N and PTFE, wherein Li3N accounts for 10% to 30% by weight; Interface modification process: The inner layer is formed by solution coating with a thickness of 0.5-3 μm, and the outer layer is formed by vapor deposition with a thickness of 0.5-2 μm; Functional collaborative design: The inner layer LiF-PVDF composite reacts preferentially with the electrolyte to form a dense SEI film, while the outer layer Li3N-PTFE composite inhibits dendrite penetration through its high ionic conductivity and lithium-phobic properties. The high ionic conductivity is 10 -4 S / cm or above; Dynamic repair mechanism: During the cycle, the outer layer of Li3N decomposes into Li + and N 3- , N 3- Reacts with lithium to generate Li3N, achieving self-repair of the coating.

5. The negative electrode for a lithium secondary battery according to claim 1, wherein: The preparation method of the conductive support layer is defined as follows: Substrate pretreatment: A metal foil is acid-etched to form micron-sized pores, and then a nanowire array is grown within the pores by electrochemical deposition; the nanowire array has a length of 1-5 μm, a diameter of 50-200 nm, and is made of Cu or Ni. Interface modification: The surface of the nanowire is coated with an ultra-thin carbon layer or metal oxide layer. The thickness of the ultra-thin carbon layer is 1-3 nm, and the coating layer is achieved by atomic layer deposition (ALD) technology; Structural advantages: Nanowire arrays provide vertical lithium ion transport channels, and carbon / oxide coatings reduce interfacial impedance and prevent electrolyte corrosion; Optimized mechanical properties: The tensile strength of the support layer is ≥200MPa, the elastic modulus is ≥50GPa, and it can withstand 300% volume expansion of the silicon-based material.

6. The negative electrode for a lithium secondary battery according to claim 5, characterized in that: The substrate pretreatment method of the conductive support layer is optimized as follows: during the acid etching process of the metal foil, the concentration of the acid solution and the etching time are precisely controlled so that the diameter of the formed micron-sized pores is within the range of 0.5-5 μm, the distribution is uniform, and the porosity reaches 30% to 60%. On the acid-etched metal substrate, a nanowire array is grown by pulse electrochemical deposition, wherein the deposition current density is 5-50 mA / cm 2 The pulse period is controlled at 1-10ms to adjust the length and density of the nanowires, so that the final nanowires are 1-5μm in length and 50-200nm in diameter, and are evenly distributed inside the pores of the metal matrix. The vertical arrangement structure of the nanowire array optimizes the transport path of lithium ions, and its ion diffusion rate v i It can be calculated by Poiseuille flow equation: Where ε is the porosity, r is the pore radius, ΔP is the pressure difference caused by the lithium ion concentration gradient, η is the dynamic viscosity of the electrolyte, L is the length of the nanowire, and the optimized parameters make v i In 10 -4 -10 -3 cm 2 / s range.

7. The negative electrode for a lithium secondary battery according to claim 5, characterized in that: The interface modification method of the conductive support layer is optimized as follows: an ultra-thin carbon layer or a metal oxide layer is deposited on the surface of the nanowire array by atomic layer deposition technology, and the thickness of the coating layer is precisely controlled to be 1-3 nm. The carbon layer is prepared by CVD method, using methane or acetylene as a precursor, and the carbon layer is formed into a graphite-like structure by regulating the deposition temperature and pressure. The metal oxide layer uses Al2O3 or TiO2, and the deposition temperature is controlled at 100-300°C to form a dense and uniform coating layer. The interface resistance of the coating layer is calculated by an equivalent circuit model, where the interface resistance R i The relationship between the coating thickness d and the material conductivity σ is: Where A is the unit area, optimize the matching relationship between d and σ so that R i Controlled within 10-100Ω·cm 2 within the range.

8. A lithium secondary battery, characterized in that: A negative electrode for a lithium secondary battery according to any one of claims 1 to 7 is used.

Images