Modified current collector for a negative electrode-free metal battery, method of making and use thereof

Abstract

This invention discloses a modified current collector for a cathode-free metal battery, its preparation method, and its application, belonging to the field of cathode-free metal battery technology. The current collector comprises a nucleating functional layer, a mixed conductive porous layer, and a low-electron-conductivity ion-conducting layer sequentially stacked along the thickness direction. The nucleating functional layer contains an alkali-philic metal nucleating material; the mixed conductive porous layer is made of at least one material selected from porous carbon materials, two-dimensional carbon-based materials, porous metal materials, porous organic polymers, aerogels, porous framework materials, and their derivatives; the low-electron-conductivity ion-conducting layer contains an ion-conducting material. This invention, by controlling the electric field and the accessibility of electrons / ions in the thickness direction, enables metal ions to preferentially deposit near the current collector during charging and grow uniformly from bottom to top along the electrode thickness direction, thereby improving deposition uniformity and cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of negative electrode-free metal battery technology, specifically relating to a modified current collector for negative electrode-free metal batteries, its preparation method, and its application. Background Technology

[0002] Metal-free batteries (such as lithium, sodium, and potassium metal batteries) do not have an active metal pre-placed on the negative electrode side in the initial state. During the charging process, alkali metal ions are directly deposited in situ on the surface of the current collector to form a metal negative electrode. As a result, they have extremely high volumetric and gravimetric energy densities, significant material cost advantages, and simplified battery manufacturing processes. They are regarded as an important development direction for the next generation of high-energy-density rechargeable batteries.

[0003] However, the commercialization of anode-free metal batteries has long been hampered by two major problems: poor metal deposition uniformity and insufficient cycle reversibility. During charging, traditional current collectors generally suffer from uneven surface energy distribution, local roughness differences, and uneven conductivity and electric field distribution. Furthermore, they lack efficient metalophilic nucleation sites, leading to preferential local nucleation of metal ions during reduction deposition. As cycling progresses, the electric field at these local protrusions intensifies, triggering a tip effect that promotes irregular metal growth towards the electrolyte, forming dendritic or moss-like deposition morphologies. This high specific surface area deposition structure not only continuously induces side reactions and consumes active metal and electrolyte, but also causes repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, resulting in electrochemically deactivated dead metal and rapid decay of coulombic efficiency. Crucially, the anode-free system lacks a pre-installed metal buffer; any irreversible deposition loss directly consumes the active lithium / sodium source on the positive electrode side, significantly amplifying the impact of uneven deposition on battery cycle life and safety.

[0004] To address the aforementioned issues, those skilled in the art have conducted extensive research on anode interface engineering. Existing technologies primarily focus on two-dimensional modification and three-dimensional framework construction of the current collector surface. For example, this involves depositing metalophilic coatings such as silver, tin, zinc, or bismuth on the current collector surface, or introducing heteroatom-doped carbon materials to reduce nucleation overpotential and increase initial nucleation density; employing three-dimensional conductive frameworks such as copper foam, porous carbon cloth, carbon nanotube networks, or graphene aerogels to increase specific surface area, reduce local current density, and provide space for deposited metals; or using electrolyte additives and artificial polymer / ceramic interface layer construction to attempt to uniform ion flux and stabilize the SEI film. These approaches have made some progress in improving initial deposition uniformity and interface stability.

[0005] However, the aforementioned existing technologies still have significant limitations in practical applications. Most surface modification techniques only focus on two-dimensional interface control, failing to effectively address the problem of uncontrolled spatial distribution of metal deposition along the electrode thickness. For three-dimensional porous framework systems, due to their high overall electronic conductivity and lack of partitioned design for ion / electron transport paths, metal ions tend to preferentially reduce and deposit near the electrolyte or pore openings after reaching the electrode. This easily leads to premature pore blockage, unused internal pore space, and insufficient deposition, making it difficult to fully utilize the volume of the three-dimensional framework. Furthermore, existing artificial interface layers or composite films often suffer from significantly increased interfacial impedance, high mechanical brittleness, and easy delamination after cycling, making it difficult to balance low impedance transport with long-term structural stability. Modification schemes that rely on noble metals or complex nanostructures face engineering bottlenecks such as cumbersome preparation processes, high costs, and difficulties in large-scale mass production.

[0006] It should be noted that this part of the present invention only provides background technology related to the present invention, and does not necessarily constitute prior art or known technology. Summary of the Invention

[0007] This invention provides a modified current collector for anode-free metal batteries, its preparation method, and its application, to at least solve the problems of uncontrolled metal deposition location, preferential growth on the surface, low utilization of internal pores, poor cycle reversibility, and insufficient coulombic efficiency in existing anode-free metal batteries.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a modified current collector for a negative electrode-free metal battery, comprising a current collector substrate and a functional layer disposed on the surface of the current collector substrate; the functional layer comprises a nucleation functional layer, a mixed conductive porous layer and a low electron conductivity ion conduction layer sequentially stacked along a direction away from the current collector substrate. The nucleation functional layer includes an alkali-loving metal nucleation material, which is selected from at least one of elemental metals, metal alloys, and metal compounds. The material for the hybrid conductive porous layer is selected from at least one of porous carbon materials, two-dimensional carbon-based materials, porous metal materials, porous organic polymers, aerogels, porous framework materials and their derivatives; The low electronic conductivity ion-conducting layer contains an ion-conducting material, which is selected from at least one of inorganic solid electrolytes, ion-conducting polymers, and composite layers of ceramic particles and polymers.

[0009] Preferably, the alkali-loving metal nucleating material is selected from at least one of Ag, Sn, Zn, Bi, Sb, Pb, Ca, Mg, Cu, Al, Si, Ge, Ga, P, In, Nb, Mo, V, Ti and their oxides, fluorides, iodides, bromides, sulfides, borides, nitrides or alloys.

[0010] Preferably, the thickness of the nucleation functional layer is ≤10μm.

[0011] Preferably, the porosity of the mixed conductive porous layer is 40% to 90%, its thickness is ≤50 μm, and its average pore size is 10 nm to 100 μm.

[0012] Preferably, the material of the mixed conductive porous layer is selected from at least one of carbon nanotube networks, graphene framework, MXene, expanded graphite, porous copper foam, porous nickel foam, porous aluminum foam, carbon aerogel, organic aerogel, MOF, ZIF, COF and their derivatives.

[0013] Preferably, the low electronic conductivity ion-conducting layer has a dense structure or a microporous structure with a thickness ≤10μm.

[0014] Preferably, the inorganic solid electrolyte is selected from NASICON-type electrolytes or sulfide electrolytes; the ion-conducting polymer is selected from polyethylene oxide, polyacrylonitrile-based, or polyurethane-based ion-conducting membranes; the composite layer of ceramic particles and polymer is selected from at least one ceramic particle selected from SiO2, Al2O3, ZrO2, and LiZrO3, and at least one polymer selected from PEO, PVDF-HFP, PMMA, PAN, PU, ​​and their copolymers.

[0015] Preferably, the current collector substrate is selected from at least one of copper foil, aluminum foil, nickel foil, stainless steel foil, carbon paper, and carbon cloth.

[0016] Preferably, the modified current collector satisfies at least one of the following conditions along the direction perpendicular to the current collector substrate: the cross-sectional resistivity gradually decreases from the low electron conductivity ion conduction layer to the nucleation functional layer; the ion transport capability gradually increases from the nucleation functional layer to the low electron conductivity ion conduction layer; and the pore size gradually increases from the low electron conductivity ion conduction layer to the mixed conductive porous layer or the nucleation functional layer.

[0017] Secondly, the present invention provides a method for preparing the modified current collector of the first aspect, comprising the following steps: S1. Prepare a nucleation functional layer on the surface of the current collector substrate; S2. Prepare a hybrid conductive porous layer on the surface of the nucleation functional layer; S3. Prepare a low-electron-conductivity ion-conducting layer on the surface of the hybrid conductive porous layer to obtain a modified current collector.

[0018] Preferably, the preparation method of S1 is selected from physical vapor deposition, chemical vapor deposition, atomic layer deposition, printing, coating, spraying, electroplating or electroless plating; the preparation method of S2 is selected from electrospinning, printing, coating, freeze drying, stencil method, spraying or deposition combined with etching; the preparation method of S3 is selected from electrospinning, printing, coating, spraying, physical vapor deposition, chemical vapor deposition, atomic layer deposition or spin coating.

[0019] Thirdly, the present invention provides an application of the modified current collector of the first aspect or the modified current collector prepared by the preparation method of the second aspect in negative electrode-free lithium metal batteries, negative electrode-free sodium metal batteries, negative electrode-free potassium metal batteries and other secondary metal batteries that adopt in-situ deposition of negative electrode mechanism.

[0020] The beneficial effects of this invention are as follows: This invention achieves directional guidance and spatial control of metal deposition, which helps to effectively suppress dendrite growth. By sequentially constructing a gradient functional layer structure along the electrode thickness direction—high electron conductivity at the bottom, bicontinuous transport in the middle, and low electron conductivity at the top—this invention achieves synergistic control over the electric field distribution and electron / ion accessibility. The top low electron conductivity ion-conducting layer effectively suppresses electron leakage to the electrolyte side, forcing the reduction reaction to migrate inwards towards the electrode. The bottom nucleation functional layer provides abundant metal-philic nucleation sites and forms a low-impedance contact with the current collector, promoting preferential nucleation of metal ions near the substrate. The synergistic effect of these two layers changes the random preferential growth pattern of metal on the surface in traditional anode-free systems, achieving control over the deposition initiation position and bottom-up directional growth, significantly reducing local current density peaks and dendrite nucleation probability.

[0021] This invention improves the utilization rate of internal porosity and volume buffering capacity, helping to maintain structural integrity. The intermediate hybrid conductive porous layer constructs a three-dimensional network of non-interfering but interconnected electronic and ion-conducting phases, forming a dual continuous transport network of electrons and ions. This structure homogenizes the internal charge distribution while providing continuous and accessible three-dimensional space for deposited metal. Combined with a top-to-bottom gradually increasing pore size gradient design, it effectively avoids the problems common in traditional three-dimensional frameworks, such as rapid surface deposition leading to premature pore blockage and unused internal space, allowing the metal to gradually and uniformly fill upwards along the pores. The structural flexibility of the porous layer itself can also effectively buffer the volume expansion stress during deposition / stripping, reducing local stress concentration and significantly decreasing the electrode thickness change rate and interface peeling risk during cycling.

[0022] This invention improves interfacial reaction kinetics and cycle reversibility, contributing to a significant increase in first-efficiency and lifespan. The top low-electron-conductivity ion-conducting layer not only blocks the persistent electrolyte decomposition side reactions caused by electron leakage but also promotes the formation of a uniform, dense solid electrolyte interphase (SEI) film. Combined with the synergistic current-equalizing effect of the bottom nucleation layer and the middle porous layer, the metal maintains a dense and uniform morphology during charge and discharge, significantly reducing the generation of electrochemically deactivated dead metal and the accumulation of interfacial impedance.

[0023] This invention combines excellent high-rate performance with compatibility for engineering fabrication. The gradient conductive network effectively homogenizes the charge distribution within the electrode, reducing concentration polarization and electrochemical polarization, enabling the battery to maintain stable deposition / stripping behavior even under high areal capacity and high-rate charge / discharge conditions. Simultaneously, each functional layer is independently constructed using mature processes such as magnetron sputtering, chemical vapor deposition, coating, spraying, and electrospinning, offering a wide process parameter window and strong material system compatibility. This structure can be flexibly adapted to various current collector substrates such as copper foil, aluminum foil, and carbon cloth, and is widely applicable to negative electrode-less lithium, sodium, and potassium metal batteries, as well as other rechargeable battery systems with in-situ deposition of negative electrodes, demonstrating good potential for large-scale mass production and industrial application prospects. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a microstructure diagram of the modified current collector provided in Embodiment 1 of the present invention; Figure 2 The image shows the microstructure of the modified current collector provided in Embodiment 1 of the present invention after 100 cycles. Detailed Implementation

[0026] In this invention, unless otherwise stated, directional terms such as "up," "down," "left," and "right" are generally understood in conjunction with the accompanying drawings and the directions shown in actual applications.

[0027] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0028] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0029] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "discretionary" mean that they may or may not be included (or may or may not be present).

[0030] To achieve the above objectives, in a first aspect, the present invention provides a modified current collector for a negative electrode-free metal battery, comprising a current collector substrate and a functional layer disposed on the surface of the current collector substrate; the functional layer comprises, in a direction away from the current collector substrate, a nucleation functional layer (hereinafter referred to as the bottom layer), a mixed conductive porous layer (hereinafter referred to as the middle layer), and a low electron conductivity ion conduction layer (hereinafter referred to as the top layer) stacked sequentially.

[0031] To address the technical shortcomings of the prior art in anode-free systems, such as uncontrolled metal deposition sites, preferential surface growth, and the difficulty of balancing internal space utilization and interface stability with traditional two-dimensional modifications or three-dimensional skeletons, this invention constructs a three-layer gradient functional layer structure with a specific sequence along the thickness direction to achieve synergistic control of electron transport paths, ion migration flux, and deposition reaction sites. The nucleation functional layer is directly attached to the current collector substrate, aiming to establish a fast electron channel with low interfacial impedance and provide a high density of metal-affinity nucleation sites, thereby minimizing the thermodynamic barrier of the reduction reaction and forcing metal ions to preferentially nucleate near the substrate. The hybrid conductive porous layer is placed in the middle region, and its core function is to effectively disperse local electric field concentration by constructing a three-dimensional interconnected electron and ion dual pathway, avoiding dendrite growth caused by the tip effect, while providing physical space for subsequent continuous metal deposition. The low electron conductivity ion-conducting layer is located on the outermost side, contacting the electrolyte interface. Its low electron conductivity helps to cut off continuous side reactions and random surface deposition caused by electron leakage on the electrolyte side, allowing only ions to pass smoothly and migrate downwards. The three-layer structure is stacked accordingly. Through the stepwise design of bottom-promoting deposition, middle-flow equalization and conduction, and top-limited electron-conducting ion-conducting, it changes the disordered growth mode caused by the uneven distribution of surface energy of the traditional non-anode current collector. It realizes metal deposition from bottom to top, ensuring the controllability and uniformity of the deposition process in the spatial dimension, and providing a clear structural guide for the optimization of materials and parameters of subsequent layers.

[0032] The nucleating functional layer comprises an alkali-loving metal nucleating material, which is selected from at least one of elemental metals, metal alloys, and metal compounds. In a more specific embodiment, the nucleating functional layer may be a metal particle layer, a metal nanowire network layer, a metal alloy layer, or a composite material layer of the same or a polymer.

[0033] Preferably, the alkali-loving metal nucleating material is selected from at least one of Ag, Sn, Zn, Bi, Sb, Pb, Ca, Mg, Cu, Al, Si, Ge, Ga, P, In, Nb, Mo, V, Ti and their oxides, fluorides, iodides, bromides, sulfides, borides, nitrides or alloys.

[0034] Preferably, the alkali-loving metal nucleating material used in the nucleating functional layer covers a wide range of systems, from elemental metals and alloy phases to multi-component compounds. The selection logic is based on the thermodynamic tendency to form solid solutions, intermetallic compounds, or low-interfacial-energy adsorbed phases with the target deposition metal (such as lithium, sodium, and potassium). Elements listed above, such as Ag, Sn, Zn, Bi, and Sb, all possess significant characteristics of forming alloys or intermediate phases with alkali metals. They can rapidly undergo in-situ alloying reactions with the deposition metal during the initial charging stage, significantly reducing the overpotential required for homogeneous nucleation and transforming the deposition mode from three-dimensional island growth to two-dimensional layered spreading, thereby providing uniformly distributed nucleation anchors at the microscale. When metal compounds (such as fluorides, iodides, sulfides, and nitrides) are used, they undergo electrochemical reduction in situ during the first discharge, transforming into metalophilic elements or nano-alloy particles. This in-situ transformation mechanism not only preserves micropores within the nucleation layer to further release volume expansion stress but also utilizes the nanoscale metal clusters generated by the transformation reaction as ultra-high-density heterogeneous nucleation centers, significantly improving the initial nucleation density. Furthermore, introducing multi-component alloys or composite phases can further adjust the surface work function and electronic density of states of the nucleation layer, optimizing the interfacial charge transfer impedance. Those skilled in the art can freely select single components or perform multi-phase composites from the aforementioned material library based on the specific battery system's cathode matching requirements, electrolyte compatibility, and cost considerations to achieve a match between nucleation kinetics and interfacial stability.

[0035] Preferably, the thickness of the nucleation functional layer is ≤10μm, specifically it can be 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any value within this range. More preferably, the thickness of the nucleation functional layer ranges from 0.1μm to 5μm.

[0036] In this invention, the thickness of the nucleation functional layer refers to the geometric dimension of the functional layer in the direction perpendicular to the surface of the current collector substrate. Specifically, it is defined as the vertical distance between the lower interface of the nucleation functional layer in contact with the current collector substrate and the upper interface in contact with the hybrid conductive porous layer. This thickness is either a macroscopic average thickness or a process-defined thickness, and can be obtained by taking multiple measurements along the electrode cross-section using a scanning electron microscope (SEM), a profilometer, or a surface profiler, and then averaging the results.

[0037] This invention optimizes the aforementioned thickness range based on a balance between interfacial charge transport efficiency and overall battery energy density. When the thickness is too low, the nucleation layer may struggle to form a continuous, pinhole-free coverage network on the current collector substrate surface. Locally exposed substrate areas will still experience random nucleation due to surface energy differences, weakening the guiding effect of directional deposition. Simultaneously, an excessively thin coating is prone to cracking during cycling due to volumetric deformation, resulting in loss of long-term stability. When the thickness exceeds 10 μm, although the number of nucleation sites increases, it may significantly prolong the lateral diffusion path of alkali metal ions in the thickness direction, increasing interfacial ion transport impedance and exacerbating concentration polarization. Furthermore, an excessively thick inactive functional layer unnecessarily occupies limited internal battery space, increasing the proportion of inactive materials and thus lowering the battery's volumetric and gravimetric energy densities. Therefore, controlling the thickness within the aforementioned range helps ensure that the nucleation material fully covers the substrate and provides sufficient low-barrier nucleation sites, enabling rapid electron injection and uniform initial deposition. It also minimizes ion diffusion resistance and structural dead weight, allowing the current collector to maintain lightweight characteristics while achieving optimal interfacial control performance.

[0038] The material of the hybrid conductive porous layer is selected from at least one of porous carbon materials, two-dimensional carbon-based materials, porous metal materials, porous organic polymers, aerogels, porous framework materials and their derivatives.

[0039] Preferably, the material of the mixed conductive porous layer is selected from at least one of carbon nanotube networks, graphene framework, MXene, expanded graphite, porous copper foam, porous nickel foam, porous aluminum foam, carbon aerogel, organic aerogel, MOF, ZIF, COF and their derivatives.

[0040] Optionally, the hybrid conductive porous layer preferably employs the aforementioned multidimensional materials with high intrinsic electronic conductivity and tunable pore structure. The core advantage of such materials lies in their ability to spontaneously construct an interwoven conductive framework and open channels in three-dimensional space through processes such as self-assembly, template methods, or directional foaming. Carbon nanotubes and graphene, with their excellent flexibility and ultra-high conductivity, can form highly interconnected electronic highways, ensuring uniform current distribution along the thickness direction and avoiding localized hot spots. MXene materials, rich in terminal functional groups, not only possess metallic conductivity but also enhance their affinity for electrolytes through polar groups, promoting rapid ion adsorption and transport at the pore walls. Expanded graphite and porous metal foam provide macroscopic rigid support and a hierarchical pore structure, effectively resisting the volume expansion stress caused by metal deposition. Carbon aerogel, with its ultra-low density and ultra-high specific surface area, achieves extreme lightweighting and pore utilization. When the aforementioned materials are used alone or in combination with other materials, their continuous conductive phase can seamlessly connect from the bottom surface of the porous layer to the nucleation functional layer, ensuring efficient electron injection. Simultaneously, intrinsic or process-introduced through-holes connect from the top surface to the electrolyte side, forming unobstructed ion-liquid phase channels. This design, where electrons travel along the framework and ions travel along the channels, solves the transport bottleneck caused by the random interweaving of electron and ion paths in traditional homogeneous porous electrodes, achieving directional homogenization and efficient utilization of charge in three-dimensional space.

[0041] Preferably, the intermediate hybrid conductive porous layer is located between the bottom nucleation functional layer and the top low-electron-conductivity ion-conducting layer, forming a dual-continuous electron-ion transport structure with a through-hole structure. Internally, it includes a continuous electron conduction network and a continuous ion transport network, which are interconnected yet spatially separated in three-dimensional space. The electron conduction network is composed of a conductive phase and extends continuously from the bottom surface of the hybrid conductive porous layer, forming direct electrical contact with the nucleation functional layer. The ion transport network is composed of a through-hole structure or an ion-conducting phase and extends continuously from the top surface of the hybrid conductive porous layer, forming ion communication with the low-electron-conductivity ion-conducting layer. This dual-continuous topology achieves coordinated electron and ion transport and charge distribution homogenization along the electrode thickness direction, balancing internal charge transport, reducing local current density, providing three-dimensional space for deposited metal, and buffering volume changes during cycling.

[0042] Preferably, the porosity of the mixed conductive porous layer is 40% to 90%, its thickness is ≤50 μm, and its average pore size is 10 nm to 100 μm.

[0043] It is understood that the porosity of the hybrid conductive porous layer ranges from 40% to 90%, specifically 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and any value within this range. Its thickness ranges from 1μm to 50μm, specifically 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, and any value within this range; more preferably, its thickness ranges from 10μm to 25μm. Its average pore size ranges from 10nm to 100μm, specifically 10nm, 50nm, 100nm, 500nm, 1μm, 5μm, 10μm, 20μm, 50μm, 100μm, and any value within this range.

[0044] In this invention, the porosity of the hybrid conductive porous layer refers to the volume percentage of the pore volume within the layer to its total volume, used to characterize the three-dimensional spatial proportion within the material capable of electrolyte wetting, ion transport, and deposited metal filling. This porosity is the macroscopic average porosity, which can be determined by mercury intrusion porosimetry, gas adsorption methods (such as the BET method), or by area ratio conversion based on cross-sectional / surface microscopic images combined with Archimedes' displacement method.

[0045] The thickness of the hybrid conductive porous layer refers to the geometric dimension of the porous layer in the direction perpendicular to the surface of the current collector substrate, specifically defined as the vertical distance between the upper interface of the nucleation functional layer and the lower interface of the low electron conductivity ion conduction layer. This thickness is a macroscopic average thickness, which can be obtained by averaging multiple measurements along the electrode cross-section using a scanning electron microscope (SEM), a profilometer, or a laser profilometer.

[0046] The average pore size of the hybrid conductive porous layer refers to the arithmetic mean of the equivalent hydraulic diameter or equivalent spherical diameter of the interconnected channels within the layer, reflecting the spatial scale characteristics of the channel network. This parameter can be determined by mercury intrusion porosimetry, gas adsorption-desorption isotherm analysis, or statistical analysis of pore size distribution based on microscopic images.

[0047] This invention, through the synergistic control of the aforementioned three-dimensional porosity parameters, aims to construct a three-dimensional network carrier for metal deposition that combines high ion permeability, low tortuosity, and ample containment space. When the porosity is below 40%, the effective cavity inside the framework is insufficient, making rapid densification during metal deposition highly likely, leading to premature closure of the channels, idle internal space, and a significant decrease in stress buffering capacity. When the porosity is above 90%, the mechanical strength of the framework is insufficient, making it prone to structural collapse or fracture during repeated charge-discharge cycles of volume expansion and contraction, thus disrupting the integrity of the dual continuous transport network. Controlling the thickness to within 50 μm effectively suppresses ohmic polarization caused by excessively long ion migration paths in the porous medium, while avoiding the areal capacity mismatch problem caused by excessively thick coatings. Setting the average pore size between 10 nm and 100 μm ensures that the electrolyte fully wets the interior of the channels, forming continuous ion liquid phase transport channels. At the same time, this pore size is much larger than the conventional metal deposition grain size, allowing the metal to grow freely within the pores without generating excessive capillary resistance or local stress concentration. The matching of these three parameters together constructs a highly transparent, strong-capacity, and deformation-resistant intermediate transition layer, providing a physical basis for the uniform filling and stable cycling of metals.

[0048] The low electronic conductivity ion-conducting layer contains an ion-conducting material, which is selected from at least one of inorganic solid electrolytes, ion-conducting polymers, and composite layers of ceramic particles and polymers.

[0049] Preferably, the inorganic solid electrolyte is selected from NASICON-type electrolytes or sulfide electrolytes; the ion-conducting polymer is selected from polyethylene oxide, polyacrylonitrile-based, or polyurethane-based ion-conducting membranes; the composite layer of ceramic particles and polymer is selected from at least one ceramic particle selected from SiO2, Al2O3, ZrO2, and LiZrO3, and at least one polymer selected from PEO, PVDF-HFP, PMMA, PAN, PU, ​​and their copolymers.

[0050] In a more specific implementation, the ion conductor material can be selected from Na3Zr2Si2PO4. 12 (NASICON type), Na3PS4, Na 10 SnP2S 12 Polyethylene oxide (PEO)-based Na + Conductive composite electrolytes, polyacrylonitrile (PAN) based ion-conducting membranes, polyurethane (PU) based membranes, Al2O3 / PEO, SiO2 / PVDF-HFP, NASICON / polymer composite membranes, NaF / polymer composite membranes, etc.

[0051] Understandably, the material system of the low electronic conductivity ion-conducting layer is selected from solid electrolytes or ion conductors with high ionic conductivity and extremely low electronic leakage current characteristics. Inorganic solid electrolytes, such as NASICON-type or sulfide electrolytes, have one-dimensional or three-dimensional fast ion migration channels in their crystal structure, exhibiting high ionic conductivity at room temperature. Simultaneously, their wide bandgap semiconductor properties result in low electronic conductivity, meeting the top-layer functional requirements of this invention: conducting ions and blocking electrons. Ion-conducting polymers, such as polyethylene oxide, polyacrylonitrile, or polyurethane-based systems, leverage their segmental flexibility and polar functional groups to dissociate alkali metal salts through coordination and promote ion transitions. Furthermore, their high elastic modulus effectively accommodates the deformation of the underlying porous structure, preventing the rigid interface from cracking during cycling. When using a ceramic particle and polymer composite system, the inorganic filler not only acts as a physical crosslinking point to enhance the mechanical strength and thermal stability of the polymer film, but also forms a space charge layer with a high ion transference number at the ceramic / polymer interface, further accelerating ion transport. Meanwhile, the fluoride composite layer, such as NaF, can in situ generate a robust SEI film rich in metal fluorides during the first cycle, significantly improving the interface's resistance to reduction. Those skilled in the art can flexibly adjust the composition of these materials according to the compatibility of the electrolyte system and the operating temperature window to construct a top layer that combines high ion permeability, electronic insulation, and mechanical flexibility.

[0052] Preferably, the low electronic conductivity ion-conducting layer has a dense structure or a microporous structure with a thickness ≤10μm.

[0053] Understandably, the low electron conductivity ion-conducting layer can be constructed as a dense, non-porous structure or a structure with micropores, and its thickness ranges from ≤10μm, specifically 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, and any value within this range.

[0054] The thickness of the low-electron-conductivity ion-conducting layer refers to its geometric dimension in the direction perpendicular to the surface of the current collector substrate. Specifically, it is defined as the vertical distance between the upper interface of the hybrid conductive porous layer and the outer surface of the ion-conducting layer exposed to the electrolyte. This thickness is a macroscopic average thickness, which can be obtained by measuring multiple points along the electrode cross-section using a scanning electron microscope (SEM), a stylus profiler, or a laser confocal profilometer and taking the arithmetic mean. When the layer has a microporous structure with large surface undulations, the thickness value is based on the average height of the solid portion of the pore wall, excluding the depth of the depression inside the micropore.

[0055] The core purpose of densifying or microporous designing the top layer structure is to block the transboundary migration of electrons to the electrolyte side from both physical and electrochemical perspectives. When a dense structure is used, the intrinsic wide bandgap or ion-selective lattice channels of the material can isolate the tunneling effect of free electrons, forcing the reduction reaction to occur only in regions within the electrode where electron supply is available. When a microporous structure is used, the pore size is strictly limited to below the ion desolvation scale, allowing only bare or solvated ions to pass through, while large electron clouds or conductive byproducts are effectively blocked. This invention sets the upper limit of thickness to 10 μm based on ion migration impedance and interfacial mechanical stability. If the thickness is too large, the diffusion resistance of ions through the top layer will increase exponentially, leading to a sharp increase in battery polarization voltage and a severe decrease in rate performance. Simultaneously, excessively thick brittle inorganic layers or polymer films are prone to macroscopic cracks during repeated volumetric deformation of the electrode. By controlling the thickness within the range of ≤10μm, the integrity and density of the top layer structure can be guaranteed, effectively suppressing electrolyte decomposition and surface parasitic deposition, while minimizing the ion transport pressure drop, ensuring rapid charge and discharge capability under high areal capacity conditions, and achieving a balance between interface stability and kinetics.

[0056] Preferably, the current collector substrate is selected from at least one of copper foil, aluminum foil, nickel foil, stainless steel foil, carbon paper, and carbon cloth.

[0057] Preferably, the current collector substrate can be selected from conventional conductive substrates such as copper foil, aluminum foil, nickel foil, stainless steel foil, carbon paper, or carbon cloth, or a composite conductive structure of the above materials. The selection of substrate material mainly depends on the electrochemical window, cost constraints, and mechanical support requirements of the target metal battery system. For electrodeless lithium metal batteries, copper foil is the most widely used substrate because its operating potential is lower than the lithium plating potential and it has excellent conductivity and ductility. For electrodeless sodium / potassium metal batteries, aluminum foil is a better choice because it can form a stable passivation film on its surface under the corresponding operating voltage and is not prone to alloying corrosion, while also having the advantages of lightweight and low cost. Nickel foil and stainless steel foil are suitable for long-cycle testing under high stress or harsh electrolyte environments due to their extremely high mechanical strength and corrosion resistance. Three-dimensional flexible carbon-based substrates such as carbon paper and carbon cloth further reduce the weight of the current collector through their inherent porous network and lightweight characteristics, and provide a better anchoring interface for the adhesion of subsequent functional layers. Regardless of the substrate chosen, the core requirements are high in-plane electronic conductivity, low surface roughness, and good chemical inertness to ensure the interfacial bonding force after the functional layer is coated and the structural integrity of the overall current collector, providing a stable and reliable physical support platform for the subsequent construction of the three-layer gradient structure.

[0058] Preferably, the modified current collector satisfies at least one of the following conditions along the direction perpendicular to the current collector substrate: the cross-sectional resistivity gradually decreases from the low electron conductivity ion conduction layer to the nucleation functional layer; the ion transport capability gradually increases from the nucleation functional layer to the low electron conductivity ion conduction layer; and the pore size gradually increases from the low electron conductivity ion conduction layer to the mixed conductive porous layer or the nucleation functional layer.

[0059] Preferably, the modified current collector is designed in the thickness direction to satisfy the gradient distribution characteristics of cross-sectional resistivity, ionic conductivity, and pore size. This invention achieves the construction of this gradient through material component ratio control and parameter optimization. The cross-sectional resistivity gradually decreases from top to bottom, meaning that the electron injection capability reaches its peak near the substrate side and is actively suppressed near the electrolyte side. This electron distribution gradient directly determines the thermodynamic priority region of the reduction reaction, forcing metal ions to preferentially nucleate in the region with the lowest potential barrier to gain electrons. The ionic conductivity gradually increases from bottom to top, ensuring that metal ions in the electrolyte can penetrate the top layer and migrate smoothly to the depth of the electrode, avoiding ion accumulation on the surface that leads to excessively high local concentrations and dendrite initiation. The structural gradient of gradually increasing pore size from top to bottom further optimizes the deposition behavior from the perspective of fluid dynamics and spatial confinement. The smaller pore size at the top restricts the lateral expansion of the surface metal and guides ions to penetrate downwards; the larger pore size in the middle and lower parts provides sufficient growth chambers for the nucleated metal, achieving layer-by-layer filling from bottom to top. The gradient synergy of the three layers creates a directional deposition microenvironment inside the electrode, characterized by downward focusing of the electric field, vertical penetration of ion flux, and upward narrowing of the space. This eliminates the randomness of deposition location caused by parameter homogenization in traditional electrodes, ensuring that metal deposition follows a preset spatial trajectory and achieving a highly controllable bottom-up growth mode.

[0060] It should be noted that the above gradient characteristics are the result of the synergy between the intrinsic properties of the material and the spatial topology. In a complete battery wetted with a liquid electrolyte, the ion transport channels are jointly formed by the electrolyte and the pores of the functional layers; therefore, the intrinsic ionic conductivity of each layer is usually not tested separately. The "gradually increasing ion transport capacity" and "gradually increasing pore size" described in this invention belong to the structural and material design gradient. The dense / microporous structure and high ion conductor content of the top layer ensure excellent directional ion conductivity; the interconnected porous network of the middle layer provides space for ion penetration and metal deposition; the continuous thin film of the bottom layer focuses on electron injection. This gradient does not rely on mercury intrusion porosimetry or independent ionic conductivity test data, and has been verified by cross-sectional SEM images (…). Figure 1 The morphology comparison, the process parameters described in the following examples, and the low polarization, high rate, and long cycle data shown in Table 1 were verified.

[0061] Secondly, the present invention provides a method for preparing the modified current collector of the first aspect, comprising the following steps: S1. Prepare a nucleation functional layer on the surface of the current collector substrate; S2. Prepare a hybrid conductive porous layer on the surface of the nucleation functional layer; S3. Prepare a low-electron-conductivity ion-conducting layer on the surface of the hybrid conductive porous layer to obtain a modified current collector.

[0062] Preferably, the preparation method of S1 is selected from physical vapor deposition, chemical vapor deposition, atomic layer deposition, printing, coating, spraying, electroplating or electroless plating; the preparation method of S2 is selected from electrospinning, printing, coating, freeze drying, stencil method, spraying or deposition combined with etching; the preparation method of S3 is selected from electrospinning, printing, coating, spraying, physical vapor deposition, chemical vapor deposition, atomic layer deposition or spin coating.

[0063] To construct the aforementioned three-layer gradient structure, this invention employs a step-by-step sequential deposition process. This process sequence corresponds to the structural logic, aiming to ensure clear boundaries and performance independence of each functional layer at the interface, avoiding component cross-contamination and loss of gradient characteristics caused by mixing multiple slurries. In stage S1, dry processes such as physical vapor deposition or chemical vapor deposition, or high-precision coating and spraying techniques, are preferentially used to form a dense, uniform, and thickness-controllable nucleation functional layer on the substrate surface. Dry processes effectively avoid solvent residue contamination of subsequent interfaces and achieve nanoscale thickness control. In stage S2, for the construction of the three-dimensional network of the mixed conductive porous layer, processes such as electrospinning, freeze-drying, or template etching are introduced. By controlling the fiber cross-linking density or solvent evaporation kinetics, a pervasive porous structure and a bicontinuous phase are spontaneously formed. Coating and printing techniques are suitable for the rapid prototyping of slurry systems, facilitating industrial scale-up. In the S3 stage, techniques such as spin coating, spraying, or vapor deposition under mild conditions are used to construct a dense or microporous ion-conducting layer in situ on top of the porous layer, avoiding damage to the underlying porous framework caused by high temperatures or strong solvents. This process combination fully considers the physicochemical properties and film formation mechanisms of each layer, and also achieves robust bonding between layers using interface engineering, ensuring no interlayer delamination occurs during battery assembly and cycling. This stepwise preparation route has a wide process window and strong compatibility, enabling a smooth transition from laboratory preparation to roll-to-roll manufacturing on production lines without complex equipment, demonstrating significant engineering application value.

[0064] Thirdly, the present invention provides an application of the modified current collector of the first aspect or the modified current collector prepared by the preparation method of the second aspect in negative electrode-free lithium metal batteries, negative electrode-free sodium metal batteries, negative electrode-free potassium metal batteries and other secondary metal batteries that adopt in-situ deposition of negative electrode mechanism.

[0065] Based on the significant advantages of the modified current collector in regulating deposition kinetics and interfacial stability, this invention can be widely applied to electrodeless lithium, sodium, and potassium metal batteries, as well as other secondary energy storage systems that rely on in-situ deposition mechanisms. The core bottleneck of electrodeless batteries lies in the lack of initial active metal, which makes the deposition process highly sensitive to the characteristics of the current collector interface. Small nucleation inhomogeneities or interfacial side reactions can be exponentially amplified with cycle accumulation. The gradient three-layer structure proposed in this invention, through the design principles of low-resistivity nucleation at the bottom, uniform mass transfer in the middle, and electron-blocking ion conduction at the top, matches the common physicochemical requirements of alkali metal ions in the reduction deposition process. This structure does not depend on a solvation shell of specific metal ions or a specific electrolyte formulation, providing a universal interface for various in-situ deposition systems from the perspective of the intrinsic charge transport path and spatial confinement of the electrode. In electrodeless lithium systems, it can effectively suppress lithium dendrite penetration and dead lithium formation; in electrodeless sodium / potassium systems, it can alleviate the polarization and volume expansion problems caused by the slow migration of large-radius ions; and in novel systems such as potassium metal batteries, it can also play a role in directional guidance and stress buffering. Therefore, this modified current collector is not only suitable for current mainstream high-energy-density liquid and semi-solid batteries, but also has broad application prospects for all-solid metal batteries, flexible wearable energy storage devices and next-generation high-safety energy storage systems, providing a key solution for the commercialization of anode-free technology.

[0066] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0067] Unless otherwise specified, the raw materials and reagents used in the embodiments of this application are all commercially available products or can be prepared by conventional methods; the equipment used are all conventional equipment in the art; and the test methods used are all conventional test methods in the art.

[0068] Example 1 This embodiment provides a modified current collector for use in negative electrode-free metal batteries, and its preparation method includes the following steps: (1) Preparation of nucleation functional layer: A BiF3 thin film with a thickness of 1 μm was deposited on the surface of an aluminum foil substrate with a thickness of 15 μm by magnetron sputtering. The deposition power was 80 W, the argon flow rate was 30 sccm, and the deposition time was 15 min, thus obtaining a substrate with a nucleation functional layer. (2) Preparation of a mixed conductive porous layer: Carbon nanotubes are dispersed in deionized water, and an appropriate amount of binder lithium polyacrylate (PAALi) is added. The mixture is ultrasonically dispersed for 30 min to form a uniform slurry. The slurry is coated on the surface of the nucleation functional layer of the substrate obtained in step (1) and dried at 80°C for 2 h to form a carbon nanotube porous layer with a thickness of 20 μm. The porosity of the porous layer is 75% and the average pore size is 5 μm. (3) Preparation of low electronic conductivity ion conduction layer: SiO2 nanoparticles and PVDF-HFP polymer are dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 3:1 and stirred to form a uniform slurry. The slurry is sprayed onto the surface of the porous layer obtained in step (2) using a spraying process and dried at 60°C for 1 h to form a dense composite layer with a thickness of 2 μm, thus obtaining the modified current collector.

[0069] Example 2 The only difference between this embodiment and embodiment 1 is that in step (1), a MgF2 thin film with a thickness of 1 μm is deposited on the surface of the aluminum foil substrate using magnetron sputtering as a nucleation functional layer. The other preparation conditions and parameters are the same as in embodiment 1.

[0070] Example 3 The only difference between this embodiment and Example 1 is that in step (1), a ZnI2 film with a thickness of 5 μm is formed on the surface of the aluminum foil substrate as a nucleation functional layer using a solution coating process. The coating slurry concentration is 0.5 mol / L, the coating speed is 50 mm / s, and the drying temperature is 80 °C. The other preparation conditions and parameters are the same as in Example 1.

[0071] Example 4 The only difference between this embodiment and Example 1 is that in step (1), a TiB2 film with a thickness of 5 μm is formed on the surface of the aluminum foil substrate as a nucleation functional layer using a solution coating process, and the coating slurry concentration is 0.3 mol / L. The other preparation conditions and parameters are the same as in Example 1.

[0072] Example 5 The only difference between this embodiment and Example 1 is that in step (1), a Sn-Zn alloy film with a thickness of 1 μm is deposited on the surface of an aluminum foil substrate using magnetron sputtering as a nucleation functional layer. The atomic ratio of Sn to Zn is 1:1, and the deposition power is 100W. The other preparation conditions and parameters are the same as in Example 1.

[0073] Example 6 The only difference between this embodiment and embodiment 5 is that in step (2), expanded graphite is used instead of carbon nanotubes as the main material of the mixed conductive porous layer. The expanded graphite is dispersed in deionized water to form a slurry, which is then coated and dried to form a porous layer with a thickness of 20 μm and a porosity of 80%. The other preparation conditions and parameters are the same as in embodiment 5.

[0074] Example 7 The only difference between this embodiment and embodiment 5 is that in step (2), carbon aerogel is used instead of carbon nanotubes as the main material of the mixed conductive porous layer. The carbon aerogel precursor is freeze-dried and carbonized to form a porous layer with a thickness of 20 μm and a porosity of 85%. The other preparation conditions and parameters are the same as those in embodiment 5.

[0075] Example 8 The only difference between this embodiment and embodiment 5 is that in step (2), a composite of carbon nanotubes and graphene (mass ratio 1:1) is used instead of a single carbon nanotube as the main material of the mixed conductive porous layer. The other preparation conditions and parameters are the same as in embodiment 5.

[0076] Example 9 The only difference between this embodiment and embodiment 5 is that: in step (2), a porous copper framework is used instead of carbon nanotubes as the main material of the mixed conductive porous layer. The specific preparation method is as follows: first, a copper layer with a thickness of 20 μm is vacuum-deposited on the surface of the nucleation functional layer, and then a chemical etching method (the etching solution is 0.1 mol / L ammonium persulfate solution) is used to remove part of the copper to form a through-hole structure, and a porous copper framework with a porosity of 70% and an average pore size of 10 μm is obtained. The other preparation conditions and parameters are the same as those in embodiment 5.

[0077] Example 10 The only difference between this embodiment and embodiment 5 is that the inorganic solid electrolyte Na3Zr2Si2PO is used in step (3). 12 (NASICON type) replaces SiO2 / PVDF-HFP composite layer as low electronic conductivity ion conduction layer. NASICON powder is dispersed in deionized water to form a slurry, then coated and dried to form a dense layer with a thickness of 5μm. The remaining preparation conditions and parameters are the same as in Example 5.

[0078] Example 11 The only difference between this embodiment and embodiment 5 is that in step (3), a composite layer of NASICON and PVDF-HFP is used instead of a single SiO2 / PVDF-HFP composite layer. NASICON powder and PVDF-HFP are dispersed in NMP solvent at a mass ratio of 2:1 to form a slurry, which is then sprayed and dried to form a microporous composite layer with a thickness of 2μm. The other preparation conditions and parameters are the same as in embodiment 5.

[0079] Comparative Example 1 This comparative example uses unmodified aluminum foil as the current collector, with a thickness of 15μm, which is directly used for battery assembly.

[0080] Comparative Example 2 This comparative example only sets up a nucleation functional layer. The specific preparation method is as follows: a Sn-Zn alloy film with a thickness of 1 μm (Sn to Zn atomic ratio 1:1) is deposited on the surface of an aluminum foil substrate using a magnetron sputtering process. The mixed conductive porous layer and the low electron conductivity ion conduction layer are not set up. The other preparation conditions are the same as in Example 5.

[0081] Comparative Example 3 This comparative example only sets up a mixed conductive porous layer. The specific preparation method is as follows: carbon nanotube slurry is directly coated on the surface of aluminum foil substrate to form a porous layer with a thickness of 20 μm and a porosity of 75%. No nucleation functional layer and low electron conductivity ion conduction layer are set up. The other preparation conditions are the same as those in Example 1.

[0082] Comparative Example 4 This comparative example only sets up a low electron conductivity ion conduction layer. The specific preparation method is as follows: SiO2 / PVDF-HFP slurry is directly sprayed onto the surface of the aluminum foil substrate to form a dense composite layer with a thickness of 2μm. No nucleation functional layer and mixed conductive porous layer are set up. The other preparation conditions are the same as those in Example 1.

[0083] Comparative Example 5 This comparative example sets up a nucleation functional layer and a mixed conductive porous layer, but does not set a low electron conductivity ion conduction layer. The specific preparation method is as follows: a Sn-Zn alloy nucleation layer with a thickness of 1 μm (magnetron sputtering) and a carbon nanotube porous layer with a thickness of 20 μm (coating) are prepared sequentially on the surface of an aluminum foil substrate. The other preparation conditions are the same as in Example 5.

[0084] Comparative Example 6 This comparative example sets up a nucleation functional layer and a low electron conductivity ion conduction layer, but does not set up a mixed conductive porous layer. The specific preparation method is as follows: a Sn-Zn alloy nucleation layer with a thickness of 1 μm (magnetron sputtering) and a SiO2 / PVDF-HFP dense composite layer with a thickness of 2 μm (spraying) are prepared sequentially on the surface of the aluminum foil substrate. No porous layer is set in the middle. The other preparation conditions are the same as in Example 1.

[0085] Test case To verify the technical effect of the modified current collector of this invention, a sodium metal battery without a negative electrode was assembled and its performance was tested using the following method: (1) Battery assembly: Na3Fe2(PO4)2F3 (NFPP) was used as the positive electrode active material. It was mixed with conductive carbon black and binder at a mass ratio of 8:1:1 to prepare a positive electrode slurry. The slurry was coated on aluminum foil, dried, and rolled to obtain an areal capacity of 2.5 mAh / cm³. 2 The positive electrode is prepared using the modified current collector prepared in Examples 1-11 or Comparative Examples 1-6 as the negative electrode; the electrolyte is 1M NaPF6 dissolved in diethylene glycol dimethyl ether (G2); the separator is PE or PP; and a 0.5Ah soft-pack battery is assembled in a drying room (dew point ≤ -40℃) using a stacking method.

[0086] (2) First Coulombic Efficiency Test: At 25°C, the assembled battery was subjected to the first charge and discharge test at a rate of 0.5C within a voltage range of 2.0-3.4V. The first discharge capacity and the first charge capacity were recorded, and the first coulombic efficiency (%) was calculated as (first discharge capacity / first charge capacity) × 100%.

[0087] (3) Thickness change rate test: A high-precision laser thickness gauge was used to measure the overall thickness of the battery in the fully charged state and the fully discharged state respectively, and the thickness change rate (%) was calculated as (fully charged thickness - fully discharged thickness) / fully discharged thickness × 100%.

[0088] (4) Cycle life test: At 25°C, the battery is charged and discharged at a constant current rate of 0.5C / 1C within a voltage range of 2.0-3.4V, and the number of cycles when the capacity retention rate drops to 80% of the initial capacity is recorded.

[0089] (5) Rate performance test: Under 25℃, the battery was charged and discharged sequentially at 0.5C, 1C, 2C, 5C and 10C rates, with each rate cycled 3 times. The ratio of the discharge capacity at 10C rate to the discharge capacity at 0.5C rate was recorded, and the rate retention rate (%) was calculated as (10C discharge capacity / 0.5C discharge capacity) × 100%.

[0090] (6) Thickness gradient parameter test: The cross-sectional resistivity was tested using the two-electrode method. Each functional layer material was uniformly coated onto the surface of a current collector of the same size, and after drying or curing, it was cut into 1cm×1cm samples. Metal terminals were placed at both ends of the sample, and a constant contact pressure was applied. The current at both ends of the sample was collected by inputting an AC voltage signal, thereby obtaining the sample resistance. The sample resistivity was then obtained by combining the coating thickness and area through a conversion relationship, and finally converted into cross-sectional resistivity (Ω·cm) by combining the coating thickness and area.

[0091] Test Results and Analysis The performance test results of the modified current collectors assembled in each embodiment and comparative example with a negative electrode-free sodium metal battery are shown in Table 1.

[0092] Table 1

[0093] As can be seen from the data in Table 1: The three-layer gradient structure modified current collectors prepared in Examples 1-11 exhibited stable initial coulombic efficiencies between 86.8% and 90.7%, thickness change rates controlled between 1.6% and 2.1%, cycle lives generally exceeding 2000 cycles, and rate retention rates reaching 87.7% to 91.3%. Their overall electrochemical performance was significantly superior to the comparative examples. This demonstrates that the gradient synergistic design of bottom nucleation guidance, middle bicontinuous transport, and top electron-blocking ion conduction can effectively regulate metal deposition behavior, achieving bottom-up directional growth, thereby suppressing dendrite formation, reducing dead metal generation, and improving interface stability.

[0094] Comparing Example 5 with Comparative Examples 2, 3, 4, 5, and 6, it is evident that the current collectors with only a single functional layer or a combination of two layers have significantly lower cycle lives than the complete three-layer structure (Comparative Examples 2-6 have cycle lives of 435-891 cycles, while Example 5 has 2638 cycles), and their thickness variation rates are generally higher (8.7%-9.1% for Comparative Examples 2, 4, and 6). This fully demonstrates that the three-layer structure is not simply a superposition, but rather achieves a synergistic effect through electron transport gradients, ion migration gradients, and pore size gradients. The absence of any one layer will lead to uncontrolled deposition locations, pore blockage, or exacerbated interfacial side reactions.

[0095] Comparing Examples 1-4, it can be seen that different metalophilic nucleating materials (BiF3, MgF2, ZnI2, TiB2) can effectively improve the initial coulombic efficiency, improve cycle stability, and increase the initial nucleation density, verifying the broad applicability of the material selection; comparing Examples 5-9, it can be seen that different porous framework materials (carbon nanotubes, expanded graphite, carbon aerogel, carbon nanotube-graphene composite, porous copper) can all construct a dual continuous transport network, providing a three-dimensional accommodation space for metal deposition; comparing Examples 5, 10, and 11, it can be seen that different ion conduction layer materials (organic composite layer, inorganic solid electrolyte, organic-inorganic composite layer) can all effectively suppress electron leakage and guide ion directional migration.

[0096] To further demonstrate the technical effectiveness of the present invention, the following analysis will be conducted in conjunction with specific experimental test results and images.

[0097] Figure 1 This is a schematic diagram of the cross-sectional microstructure of the modified current collector provided in Embodiment 1 of the present invention. Figure 1As shown, the modified current collector, along the direction perpendicular to the substrate, sequentially comprises a current collector substrate (aluminum foil substrate), a nucleating functional layer, a mixed conductive porous layer, and a low-electron-conductivity ion-conducting layer. The nucleating functional layer is tightly bonded to the substrate interface without obvious delamination; the mixed conductive porous layer exhibits a three-dimensional interconnected pore structure, with the electronically and ionicly conductive phases spatially separated but each continuous; the low-electron-conductivity ion-conducting layer has a dense structure, effectively blocking electron migration to the electrolyte side. This microstructure confirms the practical fabrication feasibility and interface integrity of the three-layer gradient structure of this invention.

[0098] Figure 2 This is a schematic diagram of the cross-sectional microstructure of the modified current collector prepared in Example 1 after 100 cycles in a sodium-ion battery without a negative electrode. Figure 2 As shown, after long-term cycling, the functional layers still maintain clear interfaces, without obvious cracks, pulverization, or interlayer delamination. The metal deposition is mainly distributed in the interface region between the nucleating functional layer and the mixed conductive porous layer, and uniformly fills the pores upwards. No dendritic morphology was observed on the surface. This result directly verifies the effectiveness of the bottom-up directional deposition mechanism of this invention, as well as the structural stability of the three-layer synergistic structure during long-term cycling.

[0099] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modified current collector for use in a negative electrode-less metal battery, characterized in that, It includes a current collector substrate and a functional layer disposed on the surface of the current collector substrate; the functional layer is provided with a nucleation functional layer, a mixed conductive porous layer and a low electron conductivity ion conduction layer stacked sequentially in a direction away from the current collector substrate; The nucleation functional layer includes an alkali-loving metal nucleation material, which is selected from at least one of elemental metals, metal alloys, and metal compounds. The material of the hybrid conductive porous layer is selected from at least one of porous carbon materials, two-dimensional carbon-based materials, porous metal materials, porous organic polymers, aerogels, porous framework materials and their derivatives; The low electronic conductivity ion-conducting layer comprises an ion-conducting material selected from at least one of inorganic solid electrolytes, ion-conducting polymers, and composite layers of ceramic particles and polymers.

2. The modified current collector according to claim 1, characterized in that, The alkali-loving metal nucleating material is selected from at least one of Ag, Sn, Zn, Bi, Sb, Pb, Ca, Mg, Cu, Al, Si, Ge, Ga, P, In, Nb, Mo, V, Ti and their oxides, fluorides, iodides, bromides, sulfides, borides, nitrides or alloys; The thickness of the nucleating functional layer is ≤10μm.

3. The modified current collector according to claim 1, characterized in that, The porosity of the hybrid conductive porous layer is 40% to 90%, its thickness is ≤50 μm, and its average pore size is 10 nm to 100 μm.

4. The modified current collector according to claim 1, characterized in that, The material of the hybrid conductive porous layer is selected from at least one of carbon nanotube networks, graphene framework, MXene, expanded graphite, porous copper foam, porous nickel foam, porous aluminum foam, carbon aerogel, organic aerogel, MOF, ZIF, COF and their derivatives.

5. The modified current collector according to claim 1, characterized in that, The inorganic solid electrolyte is selected from NASICON-type electrolytes or sulfide electrolytes; the ion-conducting polymer is selected from polyethylene oxide, polyacrylonitrile-based, or polyurethane-based ion-conducting membranes; the composite layer of ceramic particles and polymer is selected from at least one ceramic particle selected from SiO2, Al2O3, ZrO2, and LiZrO3, and at least one polymer selected from PEO, PVDF-HFP, PMMA, PAN, PU, ​​and their copolymers. The low electron conductivity ion-conducting layer has a dense structure or a microporous structure with a thickness ≤10μm.

6. The modified current collector according to claim 1, characterized in that, The current collector substrate is selected from at least one of copper foil, aluminum foil, nickel foil, stainless steel foil, carbon paper, and carbon cloth.

7. The modified current collector according to any one of claims 1 to 6, characterized in that, The modified current collector satisfies at least one of the following conditions along a direction perpendicular to the current collector substrate: The cross-sectional resistivity gradually decreases from the low electronic conductivity ion-conducting layer to the nucleation functional layer; The ion transport capability gradually increases from the nucleation functional layer to the low electron conductivity ion conduction layer; The pore size gradually increases from the low electron conductivity ion conduction layer to the mixed conductive porous layer or the nucleation functional layer.

8. A method for preparing a modified current collector as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Prepare a nucleation functional layer on the surface of the current collector substrate; S2. Prepare a hybrid conductive porous layer on the surface of the nucleation functional layer; S3. Prepare a low-electron-conductivity ion-conducting layer on the surface of the hybrid conductive porous layer to obtain the modified current collector.

9. The preparation method according to claim 8, characterized in that, The preparation method of S1 is selected from physical vapor deposition, chemical vapor deposition, atomic layer deposition, printing, coating, spraying, electroplating or electroless plating; The preparation method of S2 is selected from electrospinning, printing, coating, freeze drying, stencil method, spraying or deposition combined with etching; The preparation method of S3 is selected from electrospinning, printing, coating, spraying, physical vapor deposition, chemical vapor deposition, atomic layer deposition or spin coating.

10. The application of a modified current collector as described in any one of claims 1 to 7 or a modified current collector prepared by the preparation method described in any one of claims 8 or 9 in a negative electrode-free lithium metal battery, a negative electrode-free sodium metal battery, a negative electrode-free potassium metal battery, and other secondary metal batteries employing an in-situ deposition negative electrode mechanism.

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