Current collector, method for manufacturing the same, and lithium metal battery without negative electrode

Abstract

The application relates to the field of electrochemistry, and discloses a current collector, a preparation method thereof and a negative-electrode-free lithium metal battery. The current collector has a porous sponge-like structure; and in the thickness direction of the current collector, from one side of the current collector to the opposite side, the lithium affinity of the current collector gradually increases, and the pore diameter of the pores of the current collector gradually decreases. The lithium affinity gradient can make the free alkali metal ions preferentially deposit at the bottom, ensuring a bottom-up growth mode; the pore diameter gradient can realize the change of actual deposition kinetics from slow to fast in the vertical direction, causing the small pores in the interior to guide the dense deposition of lithium ions while the large pores on the surface still maintain relatively fast ion transmission. When the current collector is used as a negative-electrode-free battery, lithium ions can be provided with deposition space, the growth of dendrites can be limited, and the cycle life and safety performance can be improved during the cycle process.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, specifically to a gradient current collector, its preparation method, and a negative electrode-free lithium metal battery. Background Technology

[0002] Lithium metal batteries boast ultra-high energy density and hold promise for future applications in consumer electronics and power batteries. However, using lithium foil directly as the negative electrode in their manufacturing process leads to high costs and poses certain safety risks. Therefore, using only current collectors as the negative electrode material to create a negative electrode-free lithium metal battery not only theoretically achieves higher energy density but also significantly reduces costs.

[0003] CN107293754A discloses a method for preparing a porous copper current collector for lithium metal batteries. Using a Cu-X alloy sheet as the substrate, porous copper current collectors with different pore sizes are etched electrochemically using acids of varying concentrations as the medium. When this current collector is used in lithium batteries, due to the optimal lithium-ion concentration and electronic conductivity in the upper layer, metallic lithium preferentially deposits in the porous areas on the surface, easily clogging the pores, forming lithium dendrites, causing "dead lithium" and safety hazards.

[0004] CN110112367A discloses a three-dimensional composite lithium metal anode and its preparation method. The three-dimensional composite lithium metal anode includes a conductor with a three-dimensional porous structure and lithium metal, with the lithium metal embedded and filling the three-dimensional porous structure of the conductor. However, the reserved lithium-loving zinc element is uniformly distributed throughout the porous framework. Due to its good electronic and ionic conductivity, lithium metal will still preferentially deposit in the porous region on the surface. This not only fails to alleviate the severe volume expansion during lithium deposition but also easily leads to the formation of lithium dendrites.

[0005] CN110993954A discloses a lithium metal secondary battery negative electrode current collector and its preparation method. The current collector consists of three layers of ZnO / graphene / carbon nanotubes, with the ZnO content gradually decreasing from the bottom to the top, correspondingly weakening the lithiophilicity from the bottom to the top. The current collector's framework is a highly conductive porous sheet structure. Designing a lithiophilic gradient structure can induce lithium metal to preferentially deposit at the bottom of the porous current collector, effectively alleviating the problems of lithium metal volume expansion and uneven deposition. However, during long-term cycling, the lithium metal at the bottom is prone to disordered growth, forming dendrites and resulting in low porosity utilization.

[0006] Therefore, it is necessary to study a gradient current collector to solve the problems in the existing technology where lithium is easily deposited unevenly in the current collector, resulting in dead lithium or even lithium dendrites, which leads to low cycle life, short circuits and thermal runaway, and even safety hazards. Summary of the Invention

[0007] The purpose of this invention is to overcome the problem in the prior art where lithium is easily deposited unevenly in the current collector, resulting in dead lithium or even lithium dendrites. This invention provides a current collector with a porous sponge-like structure, lithium affinity, and a dual gradient variation in pore size along the thickness direction of the current collector.

[0008] To achieve the above objectives, a first aspect of the present invention provides a current collector comprising a lithiophilic metal element and an inert metal element; wherein the current collector has a porous sponge-like structure; and in the thickness direction of the current collector, from one side of the current collector to the opposite side, the lithiophilicity of the current collector gradually increases, and the pore size of the current collector gradually decreases.

[0009] A second aspect of the present invention provides a method for preparing a current collector, comprising the following steps:

[0010] (1) Using an etching solution, the alloy foil is etched from one side to the other along the thickness direction to obtain an etched alloy foil;

[0011] (2) The etched alloy foil is washed and dried in water to obtain the current collector;

[0012] The alloy foil contains both a lithium-loving metal element and an inert metal element.

[0013] A third aspect of the present invention provides a negative electrode-free lithium metal battery, characterized in that the negative electrode-free lithium metal battery comprises a lithium-intercalated positive electrode material, a positive electrode current collector, a separator, an electrolyte, and a current collector as described in the first aspect or prepared by the method described in the second aspect.

[0014] Compared with the prior art, the present invention has the following beneficial effects through the above technical solution:

[0015] (1) The current collector proposed in this invention exhibits a dual gradient change in lithiophilicity and pore size along its thickness direction from one side to the opposite side. Specifically, the lithiophilicity gradient of the current collector increases, while the pore size gradient decreases. The lithiophilicity gradient allows freely moving lithium ions to preferentially deposit at the bottom, ensuring a bottom-up growth pattern. The pore size gradient enables a change in actual deposition kinetics from slow to fast in the vertical direction, resulting in dense lithium ion deposition guided by small internal pores while maintaining relatively fast ion transport in the larger surface pores.

[0016] (2) The current collector proposed in this invention has a porous sponge-like structure, which on the one hand is conducive to the effective wetting of electrolyte in the whole battery, improves ionic / electronic conductivity and ensures electrochemical consistency inside the battery; on the other hand, it can significantly improve the electrochemical active specific surface area, reduce the actual current density of lithium during the deposition process, and alleviate lithium dendrite growth.

[0017] (3) The current collector proposed in this invention is applied to a negative electrode-free lithium metal battery. The chemical energy released by the alloying between lithium metal and the lithium-loving metal, as well as the strong capillary effect of the nanopores, promote the effective deposition of lithium ions.

[0018] (4) The current collector proposed in this invention can be applied to a cathodeless lithium metal battery. During the cycle, it can provide deposition space for lithium ions, limit dendrite growth, improve cycle life and safety performance, and promote the commercial application of cathodeless batteries.

[0019] (5) The current collector prepared by the present invention has excellent self-supporting properties and can meet the needs of large-scale production and manufacturing. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a current collector structure with surfaces a, b, and c selected at equal intervals;

[0021] Figure 2 This is a SEM image of a current collector nanoporous structure in a specific embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the current collector structure;

[0023] Figure 4 This is a schematic diagram of a negative electrode-free lithium metal battery;

[0024] Figure 5 This is a SEM image of the current collector prepared in Example 1. Detailed Implementation

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​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.

[0026] The first aspect of the present invention provides a current collector comprising a lithiophilic metal element and an inert metal element; wherein the current collector has a porous sponge-like structure; and in the thickness direction of the current collector, from one side of the current collector to the opposite side, the lithiophilicity of the current collector gradually increases, and the pore size of the current collector gradually decreases.

[0027] In this invention, to illustrate the structure of the current collector, for the phrase "from one side of the current collector to the opposite side in the thickness direction of the current collector", "one side of the current collector" is defined as side A, and "the opposite side" is side B, which is opposite to side A.

[0028] The inventors discovered in their research that the lithiophilicity of the current collector gradually increases from surface A to surface B, and the pore size of the current collector gradually decreases.

[0029] like Figure 1 As shown. The content of the lithophile element on side A is defined as x. A The aperture size is y A The content of the lithophile element on side B is x. B The aperture size is y B From surface A to surface B, take surfaces a, b, and c at equal intervals along the thickness direction of the current collector. The content of the lithiophilic element on surface a is x. a The aperture size is y a The content of the lithophile element on side b is x. b The aperture size is y b The content of the lithophile element on the c-plane is x. c The aperture size is y c Then x A x a x b x c and x B Satisfy x A <x a <x b <x c <x B ;y A y a y b y c and y B Satisfy y A >y a >y b >y c >y B .

[0030] Furthermore, the size of the A-surface ligament is defined as z. A The size of the B-side ligament is z. BFrom surface A to surface B, take surfaces a, b, and c at equal intervals along the thickness direction of the current collector, where the ligament dimension of surface a is z. a The size of the facet ligament is z. b The c-face ligament dimension is z. c z A z a z b z c and z B Satisfy z A >z a >z b >z c >z B .

[0031] In this invention, the affinity gradient allows freely moving lithium ions to preferentially deposit at the bottom, ensuring a bottom-up growth pattern; the pore size gradient enables the actual deposition kinetics to change from slow to fast in the vertical direction, causing the internal small pores to guide the dense deposition of lithium ions while the surface large pores still maintain relatively fast ion transport.

[0032] According to the present invention, the porosity of the current collector is 30%-80%, preferably 40-60 wt%. When the porosity of the current collector is less than 30%, the internal space of the current collector is too small, and the pores cannot completely accommodate the lithium extracted from the positive electrode during charging, which easily leads to the formation of dendrites and a reduction in cycle life. When the porosity of the current collector is greater than 80%, the internal space of the current collector is too large, the current collector strength is reduced, and the battery cycle life is affected.

[0033] In this invention, the porosity is tested using mercury porosimetry. A 1g sample of current collector is taken, ensuring the sample (current collector) is dry, and placed in a mercury porosimeter for testing. The pressure used is 200MPa. Each sample (current collector) is tested three times, and the average value is taken. Since mercury does not wet ordinary solids, external pressure needs to be applied to allow mercury to enter the pores. The higher the external pressure, the smaller the radius of the pore that mercury can enter. By measuring the amount of mercury entering the pores under different external pressures, the corresponding pore size and pore volume can be determined.

[0034] In this invention, under preferred conditions, the porosity of the current collector can reach 40-60 wt%. Compared to the porosity of 5%-95% for current collectors disclosed in the prior art, the porosity of the current collector of this invention, greater than 40%, can ensure complete containment of lithium extracted from the positive electrode during charging, promote rapid diffusion of the electrolyte, reduce polarization, improve rate performance, increase specific surface area, reduce actual current density, slow down lithium dendrite growth, and improve cycle life. On the other hand, the porosity of the current collector of this invention, less than 60%, can ensure good self-support after corrosion, resulting in good stability during battery manufacturing and use.

[0035] According to the present invention, the thickness of the current collector is 10-100 μm, preferably 20-50 μm. When the thickness is greater than 100 μm, it will lead to a further increase in battery size, thereby reducing the energy density of the battery; when the thickness is less than 10 μm, the internal pores of the current collector cannot completely accommodate the lithium extracted from the positive electrode during charging, resulting in a reduced cycle life. In addition, an excessively thin negative electrode current collector will affect the mechanical strength and stability of the material, which may cause the battery to deform or be damaged during operation. Moreover, an excessively thin negative electrode current collector will increase the internal resistance of the battery, leading to battery damage with a shorter service life.

[0036] In this invention, to ensure that the negative electrode can fully accommodate the lithium deposited by the positive electrode during charging, the porosity β and thickness d of the current collector must satisfy the following formulas with respect to the areal capacity C and capacity-thickness constant k of the positive electrode:

[0037]

[0038] The k = 4.84 × 10 -4 cm 3 / mAh.

[0039] Where k represents the volume occupied by dense lithium deposition per unit capacity, calculated as follows: the theoretical specific capacity m of lithium is 3860 mAh / g, and the theoretical density of lithium is 0.534 g / cm³. 3 The value of k is 1 / (m*p).

[0040] In this invention, the positive electrode surface capacity C ranges from 1 to 5 mAh / cm². 2 Preferably 2-4mAh / cm 2 .

[0041] In this invention, if this formula is not satisfied, the lithium deposited from the positive electrode during charging will exceed the maximum lithium content that the current collector pores of the negative electrode can accommodate, causing lithium to deposit on the surface of the current collector, which easily leads to the growth of lithium dendrites and causes severe volume expansion during long-term cycling, thereby reducing the cycle life of the battery.

[0042] According to the present invention, the porous sponge-like structure includes ligaments and pores.

[0043] In this invention, the ligament is a framework formed by the enrichment of inert metal elements; the pores are formed by the dissolution or precipitation of lithium-loving metal elements in a corrosive solution.

[0044] According to the present invention, preferably, the ligaments are interconnected and the pores are interconnected to form a unique bicontinuous distribution structure, which is conducive to the effective wetting of electrolyte in the entire battery, improves ionic / electronic conductivity and ensures electrochemical consistency inside the battery.

[0045] In this invention, the ligament has tortuosity. The abundant tortuosity of the ligament can significantly increase the electrochemically active specific surface area, reduce the actual current density of lithium during the deposition process, and alleviate lithium dendrite growth.

[0046] In this invention, the pores are tortuous, which effectively increases the electrolyte capacity, facilitates electrolyte wetting throughout the battery, improves ionic and electronic conductivity, and ensures electrochemical consistency within the battery. Simultaneously, the ample internal space can accommodate lithium deposited during charging.

[0047] According to the present invention, preferably, the average size of the ligament gradually decreases from one side of the current collector to the opposite side;

[0048] According to the present invention, from one side of the current collector to the opposite side, the average size of the ligament gradually decreases from 0.1-10 μm to 10-200 nm.

[0049] In this invention, the average size gradient of the ligament decreases from one side of the current collector to the opposite side, resulting in a larger bottom surface area, reducing the actual exchange current density during charging, which is conducive to more dense lithium deposition at the bottom, thereby improving the utilization rate of internal space.

[0050] In this invention, the average size of the ligament can be obtained by combining SEM and statistical analysis using the image processing software ImageJ.

[0051] According to the present invention, the lithiophilic metal element includes one or more of lithium, sodium, magnesium, aluminum, manganese, iron, zinc, tin, antimony, and bismuth;

[0052] And / or, the inert metal element includes one or more of gold, silver, platinum, titanium, chromium, copper, nickel, and cobalt.

[0053] According to the present invention, from one side of the current collector to the opposite side, the content of the lithium-loving metal element gradually increases from 0.2-10 wt% to 20-70 wt%.

[0054] Preferably, the content of the lithium-loving metal element gradually increases from 1-8 wt% to 30-40 wt%.

[0055] In this invention, the lithiophilic gradient from one side of the current collector to the opposite side significantly reduces the kinetic barrier for electrochemical reactions of lithium ions at the bottom, allowing freely moving lithium ions to preferentially deposit at the bottom. This ensures a bottom-up growth pattern, thereby preventing dendrite formation and improving battery safety. Simultaneously, during long-term deposition / stripping, lithium nucleation can be dispersed and uniform, dense lithium deposition can be induced, slowing down lithium dead deposition and improving battery cycle life. Furthermore, the gradient content change caused by one-sided corrosion allows the bottom to maintain the high mechanical properties of the original alloy foil, improving the processability of the current collector during fabrication and assembly, as well as its stability during long-term cycling.

[0056] In this invention, the surface elemental testing method involves taking a 5mm × 5mm square sample after etching, ensuring the sample is flat and dry, and using X-ray photoelectron spectroscopy (XPS) to quantitatively analyze the elements on the surface. Each sample is tested three times, and the average value is taken. XPS obtains the required information by measuring the energy distribution of excited photoelectrons by irradiating the sample surface with X-rays. It has a high ability to identify the chemical properties of the sample surface and good sensitivity to the chemical state of elements, and can detect all elements on the periodic table except hydrogen and helium.

[0057] According to the present invention, the pore size gradually decreases from 0.1-100 μm to 1-500 nm from one side of the current collector to the opposite side;

[0058] Preferably, the pore size gradually decreases from 0.1-10 μm to 10-200 nm.

[0059] In this invention, the pore size gradient can realize the change of actual deposition kinetics from slow to fast in the vertical direction, so that the small pores inside guide the dense deposition of alkali metals while the large pores on the surface still maintain a relatively fast ion transport.

[0060] The pore size distribution of the current collector in one specific embodiment of the present invention is as follows: Figure 2 As shown.

[0061] A second aspect of the present invention provides a method for preparing a current collector, comprising the following steps:

[0062] (1) Using an etching solution, the alloy foil is etched from one side to the other along the thickness direction to obtain an etched alloy foil;

[0063] (2) The etched alloy foil is washed and dried in water to obtain the current collector;

[0064] The alloy foil contains both a lithium-loving metal element and an inert metal element.

[0065] In this invention, an alloy foil is fixedly suspended above a corrosive solution. The corrosive solution gradually corrodes and penetrates the alloy foil under capillary action. During this process, the lithiophilic metal elements are partially etched to form pores, while inert metal elements form ligaments. The pores and ligaments undergo a dynamic evolution, gradually forming a stable and uniform porous sponge-like structure with good mechanical properties. The side of the alloy foil in direct contact with the corrosive solution is surface A, and the side opposite surface A along the thickness direction of the current collector is surface B. The pores formed on surface A, which is in direct contact with the corrosive solution, are larger; the pores formed on surface B, which is not in direct contact with the corrosive solution, are smaller. Therefore, the pore size gradient decreases from surface A to surface B along the thickness direction. Simultaneously, surface A, which is in direct contact with the corrosive solution, is etched more completely, resulting in a lower content of lithiophilic metal elements; surface B, which is not in direct contact with the corrosive solution, is etched less, resulting in a higher content of lithiophilic metal elements. Therefore, the lithiophilic gradient increases from surface A to surface B along the thickness direction. A schematic diagram of the current collector structure is shown below. Figure 3 As shown.

[0066] In this invention, preferably, the alloy foil is brass foil.

[0067] In this invention, a cleaning step of the alloy foil is included before step (1). The cleaning method is selected from any one of solvent ultrasonic cleaning, airflow cleaning, laser cleaning, ultra-high pressure water cleaning, sandblasting cleaning, and nano aerosol cleaning, with solvent ultrasonic cleaning being preferred.

[0068] Among them, airflow cleaning uses airflow to flush the surface and remove surface dust and impurities; laser cleaning uses a laser beam to remove surface dirt and impurities; ultra-high pressure water cleaning uses ultra-high pressure water to clean the surface and remove dirt and impurities attached to the surface; sandblasting cleaning uses high pressure gas to spray sand particles onto the surface to flush it and remove surface dirt and oxide layers; and nano aerosol cleaning uses nano aerosol spray to clean and disinfect the surface, which can remove tiny dust, bacteria and other pollutants.

[0069] In this invention, the solvent for ultrasonic cleaning is selected from at least one of ethanol, methanol, acetone, and deionized water, preferably ethanol. The ultrasonic cleaning conditions include a temperature of 10-60°C and a time of 5-30 minutes. After ultrasonic cleaning, the sample is dried for later use. The purpose of ultrasonic cleaning is to remove oxides and impurities from the surface of the alloy foil.

[0070] According to the present invention, the alloy foil comprises a lithiophilic metal element and an inert metal element, wherein the electrode potential difference between the lithiophilic metal element and the inert metal element is >0.5V.

[0071] In this invention, when the electrode potential difference between the lithiophilic metal element and the inert metal element is >0.5V, the electrochemically active metal element in the alloy foil can be selectively dissolved into the corrosion solution under the action of the corrosion solution, leaving the inert metal element behind. The remaining components then form a porous sponge-like structure.

[0072] In this invention, the lithiophilic metal element is selected from at least one of lithium, sodium, magnesium, aluminum, manganese, iron, zinc, tin, antimony, and bismuth; the inert metal element is selected from at least one of gold, silver, platinum, titanium, chromium, copper, nickel, and cobalt.

[0073] According to the present invention, the content of the lithium-loving metal element in the alloy foil is 20-80 wt%, preferably 40-60 wt%.

[0074] In this invention, the lithiophilic metal element is partially etched to form pores. The pores formed on surface A, which is in direct contact with the corrosive solution, are larger, while those on surface B, which is not in direct contact with the corrosive solution, are smaller. Therefore, the pore size gradient decreases from surface A to surface B along the thickness direction. Simultaneously, surface A, which is in direct contact with the corrosive solution, is etched more completely, resulting in a lower content of the lithiophilic metal element; surface B, which is not in direct contact with the corrosive solution, is etched less, resulting in a higher content of the lithiophilic metal element. Therefore, the lithiophilic gradient increases from surface A to surface B along the thickness direction. On the other hand, the inert metal element is not etched by the corrosive solution and mainly serves to form an interconnected three-dimensional framework, acting as an electron conduction and support carrier.

[0075] According to the present invention, the permeation method in step (1) is selected from at least one of chemical dealloying, electrochemical dealloying, liquid metal dealloying, vapor phase evaporation dealloying, and radio frequency plasma-assisted dealloying.

[0076] According to the present invention, preferably, the permeation method is a chemical dealloying method.

[0077] According to the present invention, preferably, the chemical dealloying method is a single-sided etching method.

[0078] In this invention, a single-sided etching method is used, where only one side of the alloy foil is in contact with the surface of the etching solution. Movement of the alloy foil should be avoided to prevent it from sinking into the etching solution. During the etching process, due to the differences in electrochemical behavior among the different components of the alloy foil, the lithium-loving metal elements in the alloy foil can be selectively dissolved by the etching solution, forming pores. The undissolved alloy elements will reorganize into a bicontinuous structure different from the initial alloy composition, forming ligaments.

[0079] According to the present invention, the reaction conditions of the single-sided etching method include: etching temperature of 50-200℃ and etching time of 8-120h;

[0080] Preferably, the etching temperature is 80-120℃ and the etching time is 24-48h.

[0081] In this invention, if the etching reaction temperature is too low, the etching time will be too long, which will affect the manufacturing efficiency; if the etching reaction temperature is too high, the energy consumption will increase, and the etching reaction speed will also be too fast, which will make the A-face hole structure easy to collapse, resulting in poor mechanical strength of the current collector.

[0082] In this invention, if the etching reaction time is too short, the holes on surface A will be few and small, while the unetched dense layer on surface B will be thicker, resulting in a lower overall porosity. This is not conducive to accommodating lithium deposition and alleviating severe volume expansion during cycling. If the etching reaction time is too long, energy consumption will increase, surface A will be larger, and surface B will be easily corroded through, resulting in poor overall mechanical strength of the current collector and easy breakage.

[0083] According to the present invention, the corrosive solution comprises ammonium chloride and an acid solution, wherein the acid solution is selected from one or more of perchloric acid, sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, phosphoric acid, formic acid, and acetic acid;

[0084] Preferably, the corrosive solution is a mixture of hydrochloric acid and ammonium chloride;

[0085] Preferably, the molar ratio of hydrochloric acid to ammonium chloride is 1:(3-6).

[0086] A third aspect of this invention provides a negative electrode-free lithium metal battery, wherein the negative electrode-free lithium metal battery comprises a lithium-intercalated positive electrode material, a positive electrode current collector, a separator, an electrolyte, and a current collector as described in the first aspect or prepared by the method described in the second aspect. A schematic diagram of a negative electrode-free lithium metal battery is shown below. Figure 4 As shown, the A side of the current collector is disposed close to the diaphragm, and the B side is disposed away from the diaphragm.

[0087] Using the current collector provided by this invention as a negative electrode-free battery can provide deposition space for lithium ions and limit dendrite growth during cycling, thereby improving cycle life and safety performance and promoting the commercial application of negative electrode-free batteries.

[0088] In this invention, the lithium-intercalated cathode material is selected from LiAl. 0.05 Co 0.15 Ni 0.80 O2, LiNi 0.80 Co 0.10 Mn 0.10 O2, LiNi 0.90 Co 0.05 Mn 0.05 O2, LiNi 0.60 Co 0.20 Mn 0.20O2, LiCoO2, LiMn2O4, LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, LiNi 0.5 Mn 1.5 At least one of O4, Li3V3(PO4)3, lithium sulfide, lithium-intercalated V2O5, lithium-intercalated MnO2, lithium-intercalated TiS2 and lithium-intercalated FeS2.

[0089] In this invention, the electrolyte comprises a lithium salt and a solvent. The lithium salt is selected from one or more of LiPF6, LiFB4, LiTFSI, LiDFOB, LiBOB, LiFSI, LiClO4, and LiAsF6. The solvent is at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), ethylene glycol dimethyl ether (DME), 1,3-dioxopentane (DOL), and triacetaldehyde (TTE).

[0090] In this invention, the material of the positive current collector is not particularly limited.

[0091] In this invention, the material of the diaphragm is not particularly limited.

[0092] The present invention will be described in detail below through embodiments. In the following embodiments,

[0093] (1) Average size of holes and ligaments: Statistically measured by SEM combined with ImageJ graphics processing software.

[0094] (2) Content of lithiophilic and inert metal elements: Quantitative analysis was performed by X-ray photoelectron spectroscopy (XPS). The specific method was as follows: a square sample with a side length of 5mm × 5mm was taken, and the elements on the surface were quantitatively analyzed by X-ray photoelectron spectroscopy (XPS). Each sample was tested three times, and the average value was taken.

[0095] (3) Porosity: Measured by mercury porosimetry. The specific method is as follows: Take a 1g sample and put it into the mercury porosimeter for testing. The test pressure is 200MPa. Each sample is tested three times and the average value is taken.

[0096] Example 1

[0097] (1) Select brass foil with a Zn content of 38wt% and a thickness of 30μm. Clean the brass foil with ethanol and deionized water by continuous ultrasonic cleaning to remove impurities on its surface. Then, vacuum dry it for later use.

[0098] (2) The obtained clean brass foil is suspended in a mixed solution of ammonium chloride and hydrochloric acid at 80°C, with a concentration ratio of 5:1, to allow the brass foil to undergo slow, continuous one-sided dealloying. Movement should be avoided as much as possible throughout the corrosion process to prevent the alloy foil from sinking into the corrosion solution. The electrode is removed after 24 hours.

[0099] (3) The etched alloy foil was washed multiple times in deionized water and dried under vacuum to obtain a lithium-affinity / porosity dual gradient nanoporous brass foil NPCuZn-1 with a porosity of 50%.

[0100] The surface that is in direct contact with the corrosive liquid is designated as surface A, and the surface that is not in direct contact with the corrosive liquid is designated as surface B. For example... Figure 5 As shown, the surface is the aforementioned surface A, and the bottom is the aforementioned surface B. (a) is a SEM image of surface A; (b) is a magnified view of a portion of (a); (c) is a SEM image of surface B; and (d) is a magnified view of a portion of (c). The Zn content of surface A, as measured by XPS, is 6.8 wt%. Using SEM with ImageJ software, the pore size is 2.0 μm, the average ligament size is 1.5 μm, and the optical image shows a distinct pure copper color. In contrast, surface B has a Zn content of 34 wt%, a pore size of 50 nm, an average ligament size of 50 nm, and the optical image shows a distinct brass color.

[0101] Example 2

[0102] (1) Select brass foil with a Zn content of 38wt% and a thickness of 20μm. Clean the brass foil with ethanol and deionized water by continuous ultrasonic cleaning to remove impurities on its surface. Then, vacuum dry it for later use.

[0103] (2) The obtained clean brass foil was suspended in a mixed solution of ammonium chloride and hydrochloric acid at 80°C, with a concentration ratio of 5:1, to allow the brass foil to undergo slow, one-sided dealloying. Movement should be avoided as much as possible throughout the corrosion process to prevent the alloy foil from sinking into the corrosion solution. The electrode was removed after 16 hours.

[0104] (3) The etched alloy foil was washed multiple times in deionized water and dried under vacuum to obtain a lithium-affinity / porosity dual gradient nanoporous brass foil NPCuZn-2 with a porosity of 45%.

[0105] The surface in direct contact with the etchant is designated as surface A, and the surface not in direct contact with the etchant is designated as surface B. Surface A has a Zn content of 8.1 wt% as determined by XPS, and its pore size is 1.1 μm, with an average ligament size of 1.2 μm as determined by SEM using ImageJ software. In contrast, surface B has a Zn content of 36 wt%, a pore size of 10 nm, and an average ligament size of 10 nm.

[0106] Example 3

[0107] (1) Select brass foil with a Zn content of 38wt% and a thickness of 50μm. Clean the brass foil with ethanol and deionized water by continuous ultrasonic cleaning to remove impurities on its surface. Then, vacuum dry it for later use.

[0108] (2) The obtained clean brass foil was suspended in a mixed solution of ammonium chloride and hydrochloric acid at 80°C, with a concentration ratio of 5:1, to allow the brass foil to undergo slow, one-sided dealloying. Movement should be avoided as much as possible throughout the corrosion process to prevent the alloy foil from sinking into the corrosion solution. The electrode was removed after 48 hours.

[0109] (3) The etched alloy foil was washed multiple times in deionized water and dried under vacuum to obtain a lithium-affinity / porosity dual gradient nanoporous brass foil NPCuZn-3 with a porosity of 60%.

[0110] The surface in direct contact with the etchant is designated as surface A, and the surface not in direct contact with the etchant is designated as surface B. Surface A has a Zn content of 1.2 wt% as determined by XPS, and its pore size is 8 μm, with an average ligament size of 8.9 μm as determined by SEM using ImageJ software. In contrast, surface B has a Zn content of 29 wt%, a pore size of 160 nm, and an average ligament size of 189 nm.

[0111] Example 4

[0112] (1) Select brass foil with a Zn content of 38wt% and a thickness of 30μm. Clean the brass foil with ethanol and deionized water by continuous ultrasonic cleaning to remove impurities on its surface. Then, vacuum dry it for later use.

[0113] (2) The obtained clean brass foil is suspended in a mixed solution of ammonium chloride and hydrochloric acid at 80°C, with a concentration ratio of 5:1, to allow the brass foil to undergo slow, continuous one-sided dealloying. Movement should be avoided as much as possible throughout the corrosion process to prevent the alloy foil from sinking into the corrosion solution. The electrode is removed after 28 hours.

[0114] (3) The etched alloy foil was washed multiple times in deionized water and dried under vacuum to obtain a lithium-affinity / porosity dual gradient nanoporous brass foil NPCuZn-4 with a porosity of 55%.

[0115] The surface in direct contact with the etchant is designated as surface A, and the surface not in direct contact with the etchant is designated as surface B. Surface A has a Zn content of 2 wt% as determined by XPS, and its pore size is 1.8 μm with an average ligament size of 1.9 μm as determined by SEM using ImageJ software. In contrast, surface B has a Zn content of 32 wt%, a pore size of 70 nm, and an average ligament size of 80 nm.

[0116] Example 5

[0117] (1) Select brass foil with a Zn content of 38wt% and a thickness of 30μm. Clean the brass foil with ethanol and deionized water by continuous ultrasonic cleaning to remove impurities on its surface. Then, vacuum dry it for later use.

[0118] (2) The obtained clean brass foil is suspended in a mixed solution of ammonium chloride and hydrochloric acid at 80°C, with a concentration ratio of 5:1, to allow the brass foil to undergo slow, continuous one-sided dealloying. Movement should be avoided as much as possible throughout the corrosion process to prevent the alloy foil from sinking into the corrosion solution. The electrode is removed after 20 hours.

[0119] (3) The etched alloy foil was washed multiple times in deionized water and dried under vacuum to obtain a lithium-affinity / porosity dual gradient nanoporous brass foil NPCuZn-5 with a porosity of 45%.

[0120] The surface in direct contact with the etchant is designated as surface A, and the surface not in direct contact with the etchant is designated as surface B. Surface A has a Zn content of 10 wt% as determined by XPS, and its pore size is 1.2 μm, with an average ligament size of 1.4 μm as determined by SEM using ImageJ software. In contrast, surface B has a Zn content of 36 wt%, a pore size of 30 nm, and an average ligament size of 37 nm.

[0121] Example 6

[0122] (1) Select brass foil with a Zn content of 38wt% and a thickness of 30μm. Clean the brass foil with ethanol and deionized water by continuous ultrasonic cleaning to remove impurities on its surface. Then, vacuum dry it for later use.

[0123] (2) The obtained clean brass foil was suspended in a mixed solution of ammonium chloride and hydrochloric acid at 80°C, with a concentration ratio of 5:1, to allow the brass foil to undergo slow, one-sided dealloying. Movement should be avoided as much as possible throughout the corrosion process to prevent the alloy foil from sinking into the corrosion solution. The electrode was removed after 16 hours.

[0124] (3) The etched alloy foil was washed multiple times in deionized water and dried under vacuum to obtain NPCuZn-6 nanoporous brass foil with a dual gradient of lithiophilicity and pore size, and its porosity was 40%.

[0125] The surface in direct contact with the etchant is designated as surface A, and the surface not in direct contact with the etchant is designated as surface B. Surface A has a Zn content of 13 wt% as determined by XPS, and its pore size is 0.8 μm, with an average ligament size of 0.85 μm as determined by SEM using ImageJ software. In contrast, surface B has a Zn content of 38 wt%, a pore size of 10 nm, and an average ligament size of 11 nm.

[0126] Example 7

[0127] (1) Select brass foil with a Zn content of 60wt% and a thickness of 50μm. Clean the brass foil with ethanol and deionized water by continuous ultrasonic cleaning to remove impurities on its surface. Then, vacuum dry it for later use.

[0128] (2) The obtained clean brass foil was suspended in a mixed solution of ammonium chloride and hydrochloric acid at 100°C, with a concentration ratio of 5:1, to allow the brass foil to undergo slow, one-sided dealloying. Movement should be avoided as much as possible throughout the corrosion process to prevent the alloy foil from sinking into the corrosion solution. The electrode was removed after 52 hours.

[0129] (3) The etched alloy foil was washed multiple times in deionized water and dried under vacuum to obtain NPCuZn-7 nanoporous brass foil with a dual gradient of lithiophilicity and pore size, and its porosity was 75%.

[0130] The surface in direct contact with the etchant is designated as surface A, and the surface not in direct contact with the etchant is designated as surface B. Surface A has a Zn content of 0.5 wt% as determined by XPS, and its pore size is 21 μm, with an average ligament size of 18 μm as determined by SEM using ImageJ software. In contrast, surface B has a Zn content of 23 wt%, a pore size of 300 nm, and an average ligament size of 240 nm.

[0131] Comparative Example 1

[0132] Commercially available pure copper foil with a thickness of 10μm was selected. The copper foil was continuously ultrasonically cleaned with ethanol and deionized water to remove impurities on its surface. Then it was vacuum dried for later use.

[0133] Comparative Example 2

[0134] (1) Select brass foil with a Zn content of 38wt% and a thickness of 30μm. Clean the brass foil with ethanol and deionized water by continuous ultrasonic cleaning to remove impurities on its surface. Then, vacuum dry it for later use.

[0135] (2) The obtained clean brass foil is completely immersed in a mixed solution of ammonium chloride and hydrochloric acid at 120°C, with a concentration ratio of 5:1, so that the brass foil undergoes continuous and slow one-sided dealloying. Movement should be avoided as much as possible throughout the corrosion process to prevent the alloy foil from sinking into the corrosion solution. The electrode is removed after 48 hours.

[0136] (3) The etched alloy foil was washed multiple times in deionized water and dried under vacuum to obtain the current collector Cu-2 with a porosity of 60%.

[0137] The surface in direct contact with the corrosive solution is designated as surface A, and the surface not in direct contact with the corrosive solution is designated as surface B. Surface A has a Zn content of 0 wt% as determined by XPS, and a pore size of 2.5 μm and an average ligament size of 2.8 μm as determined by SEM using ImageJ software. In contrast, surface B has a Zn content of 0 wt%, a pore size of 2.5 μm, and an average ligament size of 3.5 μm.

[0138] Comparative Example 3

[0139] (1) Select brass foil with a Zn content of 38wt% and a thickness of 30μm. Clean the brass foil with ethanol and deionized water by continuous ultrasonic cleaning to remove impurities on its surface. Then, vacuum dry it for later use.

[0140] (2) The obtained clean brass foil is suspended in a mixed solution of ammonium chloride and hydrochloric acid at 80°C, with a concentration ratio of 5:1, to allow the brass foil to undergo slow, continuous one-sided dealloying. Movement should be avoided as much as possible throughout the corrosion process to prevent the alloy foil from sinking into the corrosion solution. The electrode is removed after 24 hours.

[0141] (3) The etched alloy foil was washed multiple times in deionized water and dried under vacuum to obtain a lithium-affinity / porosity dual gradient nanoporous brass foil NPCuZn-F with a porosity of 50%.

[0142] The surface in direct contact with the corrosive solution is designated as surface B, and the surface not in direct contact is designated as surface A. Surface A has a Zn content of 34 wt% as determined by XPS, and its pore size is 50 nm, with an average ligament size of 50 nm, as measured by SEM using ImageJ software. In contrast, surface B has a Zn content of 6.8 wt%, a pore size of 1.5 μm, and an average ligament size of 1.5 μm. The pore size gradient increases from surface A to surface B, while the affinity gradient decreases.

[0143] Test Example 1

[0144] The current collectors prepared in Examples 1-6 and Comparative Examples 1-3 were assembled into electrodeless lithium metal batteries according to the following steps to test the electrochemical performance of the current collectors.

[0145] Step 1: Preparation of the positive electrode

[0146] With ternary LiNi 0.80 Co 0.10 Mn 0.10O2 was used as the positive electrode active material. The active material, carbon black, and PVDF binder were uniformly mixed in NMP at a ratio of 8:1:1 using a vacuum mixer to form a homogeneous slurry. The mixing speed was 1000 rpm for 12 hours. The resulting slurry was then coated onto an aluminum current collector sheet, dried at 80°C to remove the NMP solvent, and pressed into a sheet using a roller press to obtain the positive electrode sheet. The areal capacity C of the positive electrode is 3 mAh / cm². 2 Then cut it into 15mm diameter pieces to assemble button batteries.

[0147] Step 2: Assembly of a negative electrode-free lithium metal battery

[0148] The current collectors NPCuZn 1-7 or NPCu1-3 obtained in the above embodiments and comparative examples are directly used as negative electrodes and assembled in coin cells. From top to bottom, they are positive electrode, electrolyte, separator, electrolyte and negative electrode, with the A side of the current collector facing the positive electrode. The electrolyte is 4M LiFSI ethylene glycol dimethyl ether (DME). After being fully wetted, they are encapsulated to obtain batteries S1-S7 and DS1-DS3, respectively.

[0149] Step 3: Electrochemical Cyclic Test

[0150] Three batteries each of S1-S6 and DS1-DS3 were used. On a secondary battery performance testing device, they were charged at a constant current and constant voltage of 0.2C to 4.3V, with a cutoff current of 0.05C. After resting for 5 minutes, they were discharged at 0.5C to 3V, constituting one cycle. This process was repeated. During the cycle, the cycle was terminated when the battery's specific capacity fell below 80% of its initial capacity. The number of cycles is the battery's cycle life. The average value of each group was taken. This parameter, along with the data on the average initial discharge capacity of the batteries and the rate of change of the negative electrode thickness before and after battery cycling, are shown in Table 1 (Data on the average initial discharge capacity of batteries and the rate of change of the negative electrode thickness before and after battery cycling).

[0151] Table 1

[0152]

[0153]

[0154] Test Example 2

[0155] The first lithium deposition was performed on batteries S1-S7 and DS1-DS3, and the experiment was repeated twice. The batteries were charged to 4.3V at a current density of 0.2C.

[0156] The specific steps for sample preparation and observation are as follows:

[0157] (1) The button cell after the first charge was disassembled in a glove box filled with argon (water oxygen value < 0.1 ppm);

[0158] (2) Remove the negative electrode sheet, wash it repeatedly three times with DME (ethylene glycol dimethyl ether) solution, let it stand for 8 hours and then let it air dry naturally;

[0159] (3) Cut a square electrode sheet with a side length of 2mm×2mm using ceramic scissors and place it on the sample stage whose surface has been covered with conductive adhesive.

[0160] (4) Place the sample stage into the vacuum transfer box and remove the glove box. Observe the deposition location and morphology of lithium using SEM. The experimental results are shown in Table 2.

[0161] Table 2. Battery Lithium Deposition Locations

[0162] Serial Number Battery Appearance Example 1 S1 No obvious lithium deposition on the surface Example 2 S2 No obvious lithium deposition on the surface Example 3 S3 No obvious lithium deposition on the surface Example 4 S4 No obvious lithium deposition on the surface Example 5 S5 No obvious lithium deposition on the surface Example 6 S6 No obvious lithium deposition on the surface Example 6 S7 No obvious lithium deposition on the surface Comparative Example 1 DS1 The surface has a large amount of lithium deposited, and dendritic lithium is present. Comparative Example 2 DS2 A small amount of loose lithium deposits are present on the surface. Comparative Example 3 DS3 The surface has a large amount of lithium deposited, and dendritic lithium is present.

[0163] As can be seen from Tables 1 and 2, although the comparative examples initially had a capacity roughly equivalent to that of the embodiments, in Comparative Examples 1-3, lithium metal could only be deposited on the surface of the current collector or loosely deposited in the internal pores, resulting in rapid capacity decay and significant expansion of the negative electrode thickness at the end of the cycle. The batteries provided in Embodiments 1-7 of this application incorporate the current collector provided in this application, giving the batteries advantages such as high charge / discharge capacity, low susceptibility to lithium dendrite formation, high safety performance, and long cycle life.

[0164] 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 current collector characterized by comprising: The current collector comprises a lithiumophilic metal element and an inert metal element; wherein the current collector has a porous sponge-like structure; and from one side of the current collector to the opposite side, the content of the lithiumophilic metal element in the current collector gradually increases, and the pore size of the pores in the current collector gradually decreases. The porous sponge-like structure comprises ligaments and pores. The ligaments are connected to each other, and the pores are connected to each other. The ligaments are reorganized from undissolved alloy elements in the alloy foil to have a double-continuous structure different from the initial alloy composition. The pores are formed by the dissolution of the lithiumophilic metal element in the alloy foil by the corrosion solution. The alloy foil comprises a lithiumophilic metal element and an inert metal element. The lithiumophilic metal element comprises one or more of sodium, magnesium, aluminum, manganese, iron, zinc, tin, antimony, and bismuth. The inert metal element comprises one or more of gold, silver, platinum, titanium, chromium, copper, nickel, and cobalt.

2. The current collector as claimed in claim 1, wherein The porosity of the current collector is 30%-80%.

3. The current collector of claim 2, wherein The porosity of the current collector is 40-60%.

4. The current collector according to any one of claims 1 to 3, wherein The thickness of the current collector is 10-100 μm.

5. The current collector of claim 4, wherein The thickness of the current collector is 20-50 μm.

6. The current collector of any one of claims 1 or 5, wherein From one side of the current collector to the opposite side, the average size of the ligaments gradually decreases.

7. The current collector of claim 6, wherein From one side of the current collector to the opposite side, the average size of the ligaments gradually decreases from 0.1-10 μm to 10-200 nm.

8. The current collector of any one of claims 1-3, wherein From one side of the current collector to the opposite side, the content of the lithiumophilic metal element gradually increases from 0.2-10 wt% to 20-70 wt%.

9. The current collector of claim 8, wherein The content of the lithiumophilic metal element gradually increases from 1-8 wt% to 30-40 wt%.

10. The current collector of any one of claims 1-3, wherein From one side of the current collector to the opposite side, the pore size gradually decreases from 0.1-100 μm to 1-500 nm.

11. The current collector of claim 10, wherein The pore size gradually decreases from 0.1-10 μm to 10-200 nm.

12. A method of making the current collector of any one of claims 1-11, wherein, The method comprises the following steps: (1) using a corrosion solution to corrode along the thickness direction of the alloy foil from one side to the other side to obtain a corroded alloy foil; (2) placing the corroded alloy foil in water to clean and dry to obtain the current collector. The alloy foil comprises a lithiumophilic metal element and an inert metal element.

13. The method of claim 12, wherein, The electrode potential difference between the lithiumophilic metal element and the inert metal element is >0.5 V.

14. The method according to claim 12 or 13, characterized in that, The lithiumophilic metal element comprises one or more of sodium, magnesium, aluminum, manganese, iron, zinc, tin, antimony, and bismuth.

15. The method of claim 14, wherein, The inert metal element comprises one or more of gold, silver, platinum, titanium, chromium, copper, nickel, and cobalt.

16. The method according to any one of claims 12-13 and 15, characterized in that, The content of the lithiumophilic metal element in the alloy foil is 20-80 wt%.

17. The method of claim 16, wherein, The content of the lithiumophilic metal element in the alloy foil is 40-60 wt%.

18. The method according to any one of claims 12-13, 15 and 17, characterized by, The penetration mode in step (1) is a chemical dealloying method and / or an electrochemical dealloying method.

19. The method of claim 18, wherein, The penetration mode in step (1) is a chemical dealloying method.

20. The method of claim 19, wherein, The chemical dealloying method is a single-sided etching method.

21. The method of claim 20, wherein, The reaction conditions of the single-sided etching method include an etching temperature of 50-200 °C and an etching time of 8-120 h.

22. The method of claim 21, wherein, The reaction conditions of the single-sided etching method include: etching temperature is 80-120 DEG C; etching time is 24-48h.

23. The method of any one of claims 12-13, 15, 17, and 19-22, wherein, The etching solution comprises ammonium chloride and an acid solution selected from one or more of the group consisting of perchloric acid, sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, phosphoric acid, formic acid, and acetic acid.

24. The method of claim 23, wherein, The etching solution is a mixture of hydrochloric acid and ammonium chloride.

25. The method of claim 24, wherein, The molar ratio of the hydrochloric acid to the ammonium chloride is 1: (3-6).

26. A negative electrode-free lithium metal battery, characterized by, The negative electrode-free lithium metal battery comprises a lithium intercalation state positive electrode material, a positive electrode current collector, a separator, an electrolyte, and the current collector prepared by the method of any one of claims 1-11 or any one of claims 12-25. The side of the current collector with less lithiumophilic metal element content is in contact with the separator.

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