Three-dimensional porous lithium metal material, secondary battery, and electric device

Abstract

The present invention belongs to the technical field of secondary batteries, and disclosed herein are a three-dimensional porous lithium metal material, a secondary battery, and an electric device. The three-dimensional porous lithium metal material comprises a matrix layer and a polymer layer at least partially coated on the periphery of the matrix layer, and the matrix layer comprises a three-dimensional conductive metal and lithium metal filled in the three-dimensional conductive metal. The three-dimensional porous lithium metal material in the present application combines the characteristics of high specific surface area and high interfacial stability, which can effectively improve the energy density of the secondary battery. The polymer layer coated on the periphery exhibits good mechanical stability and good solubility for lithium salts, which can effectively enhance interfacial stability. The polymer layer can isolate the lithium metal from direct contact with an electrolyte, reducing side reactions caused by the contact with same. The matrix layer provides highly active deposition sites and sufficient deposition space for lithium ions during the charging process, thereby effectively improving the rate performance and cycling performance of the secondary battery.

Description

A three-dimensional porous lithium metal material, a secondary battery, and an electrical device. Technical Field

[0001] This invention relates to the field of battery technology, specifically to a three-dimensional porous lithium metal material, a secondary battery, and an electrical device. Background Technology

[0002] With the rapid development of technology and the widespread adoption of electronic devices and electric vehicles, the demand for high-efficiency, high-energy-density batteries is increasing daily. Traditional battery technologies can no longer meet this growing demand, thus necessitating the development of new battery technologies to satisfy the urgent market needs.

[0003] Among these new types of batteries, lithium metal batteries have attracted much attention due to their higher energy density. Lithium metal boasts a specific capacity of up to 3860 mAh / g (11 times higher than graphite), and its redox potential is as low as -3.04V compared to a standard hydrogen electrode (meaning a higher discharge voltage plateau). According to our calculations, replacing the graphite anode in a battery with lithium metal could increase the volumetric energy gain by up to 62% and the gravimetric energy gain by up to 45%. This means that, with the same volume and weight, the battery can store more energy, resulting in longer driving ranges for electric vehicles, mobile phones, and other devices.

[0004] However, lithium metal batteries face numerous challenges in practical applications, such as impractical rate performance, unsafe cycling conditions, and limited cycle life. To address these issues, researchers have undertaken extensive work, including surface modification of lithium metal and the construction of three-dimensional / composite materials. However, conventional three-dimensional material designs also have several drawbacks. For instance, while a high specific surface area facilitates rapid lithium-ion insertion and extraction, it also exacerbates side reactions between lithium metal and the electrolyte. Lithium metal and electrolyte are rapidly consumed during charge-discharge cycles, significantly shortening battery cycle life.

[0005] Therefore, this application is submitted. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a lithium metal three-dimensional porous material, a secondary battery and an electrical device, which can effectively improve the cycle stability of the secondary battery.

[0007] To achieve the above objectives, a first aspect of this application provides a three-dimensional porous lithium metal material, comprising a matrix layer and a polymer layer at least partially covering the outer periphery of the matrix layer, wherein the matrix layer comprises a three-dimensional conductive metal and lithium metal filling the pores of the three-dimensional conductive metal.

[0008] The polymer layer has an ionic conductivity of 10.-5 ~1S / cm, electronic conductivity 10 -9 ~10 -5 S / cm.

[0009] As an embodiment of this application, the ionic conductivity of the polymer layer is 5.4*10⁻⁶. -5 ~8.9*10 -4 S / cm, electronic conductivity 7.4*10 -7 ~2.1*10 -5 S / cm.

[0010] As an embodiment of this application, the three-dimensional conductive metal includes at least one of foamed copper, foamed nickel, and foamed aluminum.

[0011] As an embodiment of this application, the porosity of the matrix layer is A, where 10% ≤ A ≤ 30%.

[0012] As an embodiment of this application, the average pore size of the three-dimensional conductive metal is 20–80 μm.

[0013] As an embodiment of this application, the mass percentage of lithium metal in the substrate layer is B, which satisfies: 0.2% ≤ B ≤ 1%.

[0014] As an implementation scheme of this application, the following condition must be met: 10 ≤ A / B ≤ 125.

[0015] As an embodiment of this application, the thickness of the three-dimensional conductive metal is 2 to 350 μm.

[0016] As an embodiment of this application, the thickness of the polymer layer is 5 to 50 nm.

[0017] As an embodiment of this application, the viscosity-average molecular weight of the polymer in the polymer layer is 100,000 to 10,000,000.

[0018] A second aspect of this application provides a method for preparing a three-dimensional porous lithium metal material, comprising the following steps:

[0019] The three-dimensional conductive metal is rolled and heat-treated to obtain a pretreated three-dimensional conductive metal.

[0020] The pretreated three-dimensional conductive metal is placed in a reaction solution and reacted to obtain the precursor.

[0021] The precursor was placed in an electrolyte for electrochemical deposition to obtain a three-dimensional porous lithium metal material.

[0022] The reaction solution includes a first lithium salt and a compound containing at least one of halogen groups, sulfonate groups, sulfate groups, and epoxy groups;

[0023] The electrolyte comprises a second lithium salt and an organic solvent.

[0024] As an embodiment of this application, the heat treatment temperature is 200-300°C, and the heat treatment time is 0.5-6 hours.

[0025] As an embodiment of this application, the heat treatment is carried out in a mixed atmosphere of argon and hydrogen, wherein the volume ratio of hydrogen to argon is (0.5-2):(18-19.5).

[0026] As an embodiment of this application, the reaction temperature is 50-100°C, and the reaction time is 10-600 min.

[0027] As an embodiment of this application, the concentration of the first lithium salt in the reaction solution is 0.05 to 0.8 mmol / L.

[0028] As an embodiment of this application, the concentration of the second lithium salt in the electrolyte is 0.5 to 2 mol / L.

[0029] As an embodiment of this application, the first lithium salt and the second lithium salt each independently include at least one of LiTFSI, LiFSI, LiPF6, and LiBF4.

[0030] As an embodiment of this application, the molecular formula of the compound containing the epoxy group is C3H5O2-(C2H4O). n -C3H5O, wherein the number-average molecular weight of the epoxy group-containing compound is 300 to 800.

[0031] A third aspect of this application provides a secondary battery including a negative electrode comprising the aforementioned lithium metal three-dimensional porous material.

[0032] A fourth aspect of this application provides an electrical device comprising the aforementioned secondary battery.

[0033] The beneficial effects of this invention are as follows: The matrix layer of the lithium metal three-dimensional porous material described in this application is a three-dimensional conductive metal with internal pores filled with lithium metal. The polymer layer at least partially covers the outer periphery of the matrix layer, presenting an overall three-dimensional porous structure. The lithium metal three-dimensional porous material combines the characteristics of high specific surface area and high interface stability, which is beneficial for the insertion and extraction of lithium ions and can effectively improve the energy density of secondary batteries. The outer polymer layer has excellent mechanical stability and is well-suited for the preparation of secondary batteries, especially lithium metal batteries. It has good solubility for lithium salts, which can effectively increase interface stability. The polymer layer can isolate the direct contact between lithium metal and electrolyte, reducing the side reactions of their contact. During the charging process, the matrix layer provides highly active deposition sites and sufficient deposition space for lithium ions, and slowly releases the compressive stress during the charging and discharging process and the rolling process, effectively improving the rate performance and cycle performance of secondary batteries. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0036] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0037] 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 at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0038] Unless otherwise specified, all components, raw materials, or instruments used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0039] This application provides a lithium metal three-dimensional porous material, including a matrix layer and a polymer layer at least partially covering the outer periphery of the matrix layer. The matrix layer includes a three-dimensional conductive metal and lithium metal filling the pores of the three-dimensional conductive metal.

[0040] The polymer layer has an ionic conductivity of 10. -5 ~1S / cm, electronic conductivity 10 -9 ~10 -5 S / cm. The matrix layer of the lithium metal three-dimensional porous material described in this application is a three-dimensional conductive metal filled with lithium metal, and the polymer layer at least partially covers the outer periphery of the matrix layer, presenting an overall three-dimensional porous structure. The ionic conductivity of the polymer layer is 10. -5 ~1S / cm, electronic conductivity 10 -3 ~10 -2 The lithium metal three-dimensional porous material, with a surface area of ​​S / cm, combines high specific surface area and high interfacial stability, which is beneficial for lithium ion insertion and extraction, effectively improving the energy density of secondary batteries. The outer polymer coating has excellent mechanical stability, making it well-suited for the preparation of secondary batteries, especially lithium metal batteries. It has good solubility for lithium salts, which can effectively increase interfacial stability. The polymer layer can isolate the direct contact between lithium metal and electrolyte, reducing side reactions between the two. The substrate layer provides highly active deposition sites and sufficient deposition space for lithium ions during the charging process, and slowly releases compressive stress during charging, discharging, and rolling processes, effectively improving the cycle performance of secondary batteries.

[0041] The ionic conductivity of the polymer layer was tested using EIS impedance testing.

[0042] Specifically, the method for testing the ionic conductivity of the polymer layer is as follows: Take an appropriate amount of oligomer reaction solution (a reaction solution containing a first lithium salt and a compound containing at least one of halogen groups, sulfonate groups, sulfate groups, and epoxy groups) onto a thin plate, initiate thermal polymerization using the same method, remove the thin plate to obtain a polymer film, and record the thickness and area of ​​the polymer film as L and S, respectively. Assemble symmetrical cladding of stainless steel with the polymer film as a separator, perform EIS analysis, and obtain R0. The formula for calculating the ionic conductivity is as follows: L / (RoS).

[0043] The electronic conductivity of the polymer layer was tested using a four-probe test method.

[0044] Specifically, the method for testing the electronic conductivity of the polymer layer is as follows: take an appropriate amount of oligomer reaction liquid on a thin plate, initiate thermal polymerization using the same method, and obtain a polymer film after removing the thin plate; during the test, press four equally spaced probes on the surface of the film, two of which are used to inject current and the other two probes to measure voltage, calculate the material resistance using Ohm's law, and then calculate the electronic conductivity.

[0045] In one embodiment, the polymer layer includes at least one of PEO (polyethylene oxide), PAN (polyacrylonitrile), PVDF (polyvinylidene fluoride), PMMA (polymethyl methacrylate), and PC (polycarbonate).

[0046] The present invention uses at least one of PEO, PAN, PVDF, PMMA and PC as a polymer layer, and the polymer layer has the characteristics of good compatibility with lithium metal and high mechanical stability.

[0047] In one embodiment, the ionic conductivity of the polymer layer is 5.4 × 10⁻⁶. -5 ~8.9*10 -4 S / cm, electronic conductivity 7.4*10 -7 ~2.1*10 -5 S / cm.

[0048] In one embodiment, the polymer layer comprises PEO, and the infrared spectrum of the polymer layer is in the range of 1080-1160 cm⁻¹. -1 It has characteristic peaks.

[0049] As an embodiment of this application, the three-dimensional conductive metal includes at least one of foamed copper, foamed nickel, and foamed aluminum. This invention uses three-dimensional conductive metals such as foamed copper, foamed nickel, and foamed aluminum as framework materials, which can effectively improve the structural stability of lithium metal three-dimensional porous materials. Compared with carbon materials, lithium metal has a lower nucleation overpotential on its surface (nucleation overpotential refers to the energy barrier that needs to be overcome when lithium nucleates and deposits). This type of three-dimensional conductive metal has ductility and can maintain the continuity of its own conductive network during large volume expansion. At the same time, it can effectively suppress dendrite growth and side reactions with electrolyte to a certain extent, thereby further improving the cycle performance of secondary batteries.

[0050] In one embodiment, the porosity of the matrix layer is A, 10% ≤ A ≤ 30%, for example, it can be 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 30%, or a range of any two of these values.

[0051] In one embodiment, the average pore size of the three-dimensional conductive metal is 20 to 80 μm, for example, it can be 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm or any two of these values.

[0052] It should be noted that the porosity and average pore size of this application are obtained by conventional testing methods in the art, such as gas adsorption.

[0053] For example, the porosity and average pore size testing method of this application is as follows: the sample is placed in an adsorption device, nitrogen gas is passed through it, the change in gas volume before and after adsorption is measured, a nitrogen adsorption-desorption curve is obtained, and the porosity and average pore size are calculated and converted.

[0054] In one embodiment, the mass percentage of lithium metal in the substrate layer is B, satisfying the condition: 0.2% ≤ B ≤ 1%. For example, it can be a range of 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, or any two of these values. This application ensures that the lithium metal three-dimensional porous material has a certain porosity when the mass percentage of lithium metal in the substrate layer is within this range, promoting the insertion and extraction of lithium ions. Simultaneously, it provides highly active deposition sites and sufficient deposition space for lithium ions during charging, offsetting the consumption of lithium elements by side reactions or dead lithium formation during cycling. It should be noted that the mass percentage of lithium metal in the substrate layer in this application can be obtained by removing the lithium layer using an ethanol-water solution or other mildly reactive solutions, and the mass percentage of lithium metal in the substrate layer can be obtained by weighing and calculating the weight loss before and after removal.

[0055] In one embodiment, the following condition is satisfied: 10 ≤ A / B ≤ 125. For example, it can be a range of 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 125, or any two of these values. By controlling A / B within this range, the characteristics of high specific surface area and high interface stability can be better balanced. The lithium metal three-dimensional porous material has better structural stability and can provide more reaction sites, thereby improving the charge storage capacity of the secondary battery, reducing the impedance of the current conduction path, ensuring that the battery can maintain a stable current output during high-power discharge, maintaining structural stability during charging and discharging, effectively mitigating volume expansion and contraction during battery charging and discharging, avoiding breakage and detachment, facilitating lithium ion insertion and extraction, and further improving the cycle performance of the secondary battery.

[0056] In one embodiment, the thickness of the three-dimensional conductive metal is 2 to 350 μm, for example, it can be 2 μm, 3 μm, 5 μm, 10 μm, 20 μm, 30 μm, 50 μm, 60 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 220 μm, 250 μm, 260 μm, 280 μm, 300 μm, 320 μm, 350 μm or any two of these values.

[0057] In one embodiment, the thickness of the three-dimensional conductive metal is 50–100 μm.

[0058] In one embodiment, the thickness of the polymer layer is 0.5 to 20 μm, for example, it can be 0.5 μm, 1 μm, 2 μm, 5 μm, 10 μm, 12 nm, 15 nm, 20 nm, 25 nm or any two of these values. By controlling the thickness of the polymer layer within this range, it is beneficial for the rapid conduction of ions and the chain segments are less likely to shift during large volume expansion, thereby ensuring that the polymer protection does not fail after long cycling and further improving the cycling performance.

[0059] In one embodiment, the polymer in the polymer layer has a viscosity-average molecular weight of 100,000 to 1,000,000.

[0060] In one embodiment, the polymer in the polymer layer has a viscosity-average molecular weight of 300,000 to 5,000,000. By controlling the viscosity-average molecular weight of the polymer within this range, it has better structural stability. During battery charging and discharging, it effectively alleviates volume expansion and contraction, can fully isolate the lithium battery and electrolyte, and the chain segments are less likely to shift during large volume expansion, further improving cycle performance.

[0061] One embodiment of this application provides a method for preparing a three-dimensional porous lithium metal material, comprising the following steps:

[0062] The three-dimensional conductive metal is rolled and heat-treated to obtain a pretreated three-dimensional conductive metal.

[0063] The pretreated three-dimensional conductive metal is placed in a reaction solution and reacted to obtain the precursor.

[0064] The precursor was placed in an electrolyte for electrochemical deposition to obtain a three-dimensional porous lithium metal material.

[0065] The reaction solution includes a first lithium salt and a compound containing at least one of halogen groups, sulfonate groups, sulfate groups, and epoxy groups;

[0066] The electrolyte comprises a second lithium salt and an organic solvent.

[0067] This application prepares a three-dimensional porous lithium metal material using the above-described preparation method. The matrix layer of the lithium metal three-dimensional porous material is a three-dimensional conductive metal filled with lithium metal, and a PEO (polyethylene oxide) layer is coated on the outer periphery of the matrix layer. The pore size of the matrix layer is 20-80 μm, and the porosity is 10-25%, exhibiting a three-dimensional porous structure overall.

[0068] In this process, the three-dimensional conductive metal is rolled to compress the porous space inside, achieving a predetermined thickness. Then, heat treatment effectively reduces the oxides on the surface of the three-dimensional conductive metal into the three-dimensional conductive metal itself. The metal is then placed in a reaction solution to react in situ and generate the PEO film. Finally, electrolysis is performed, allowing lithium ions to pass through the PEO film (the PEO layer has high ionic conductivity and low electronic conductivity, so during deposition, lithium ions will pass through the PEO layer to reach the interior of the three-dimensional conductive metal) and undergo an electron reduction reaction, thereby forming lithium metal inside the three-dimensional conductive metal.

[0069] In this invention, a compound containing at least one of halogen groups, sulfonate groups, sulfate groups, and epoxy groups is used for in-situ polymerization to obtain a polymer layer with the above-mentioned ionic conductivity and electronic conductivity. The resulting polymer has a high amorphous ratio (0-10%), which is beneficial for rapid ion conduction. At the same time, after in-situ polymerization, the chain segments are not easily displaced during the large volume expansion process, thereby ensuring that the polymer protection does not fail after long-term cycling.

[0070] In one embodiment, before rolling, the thickness of the three-dimensional conductive metal is 10 to 500 μm, for example, it can be 10 μm, 20 μm, 30 μm, 50 μm, 60 μm, 80 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm or any two of these values.

[0071] In one embodiment, before rolling, the porosity of the three-dimensional conductive metal is 50-99%, for example, it can be a range of 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or any two of these values.

[0072] In one embodiment, before rolling, the average pore size of the three-dimensional conductive metal is 20 to 80 μm, for example, it can be 20 to 80 μm, for example, it can be 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm or any two of these values.

[0073] In one embodiment, the pressure of the roller is 1 to 100 MPa, for example, it can be 1 MPa, 2 MPa, 5 MPa, 10 MPa, 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, 100 MPa or any two of these values.

[0074] In one embodiment, the temperature of the heat treatment is 200 to 300°C, for example, it can be 200°C, 220°C, 240°C, 250°C, 260°C, 280°C, 300°C or any two of these values.

[0075] In one embodiment, the heat treatment time is 0.5 to 6 hours, for example, it can be 0.5 hours, 0.6 hours, 0.8 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours or any two of these values.

[0076] In one embodiment, the heat treatment is carried out in a mixed atmosphere of argon and hydrogen, wherein the volume ratio of hydrogen to argon is (0.5-2):(18-19.5), for example, it can be 0.5:19.5, 0.8:19.2, 1:19, 1.2:18.8, 1.5:18.5, 1.8:18.2, 2:18 or any range of two of these values.

[0077] In one embodiment, the reaction temperature is 50 to 100°C, for example, it can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C or any two of these values.

[0078] In one embodiment, the reaction time is 10 to 600 min, for example, it can be 10 min, 20 min, 40 min, 50 min, 60 min, 100 min, 200 min, 300 min, 400 min, 500 min, 600 min or any two of these values.

[0079] In one embodiment, the concentration of the first lithium salt in the reaction solution is 0.05 to 0.8 mmol / L, for example, it can be 0.05 mmol / L, 0.08 mmol / L, 0.1 mmol / L, 0.2 mmol / L, 0.3 mmol / L, 0.4 mmol / L, 0.5 mmol / L, 0.6 mmol / L, 0.7 mmol / L, 0.8 mmol / L, or any two of these values.

[0080] In one embodiment, the concentration of the second lithium salt in the electrolyte is 0.5 to 2 mol / L, for example, it can be 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, or 2 mol / L.

[0081] In one embodiment, the first lithium salt and the second lithium salt each independently include at least one of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiFSI (lithium bis(fluorosulfonyl)imide), LiPF6 (lithium hexafluorophosphate), and LiBF4 (lithium tetrafluoroborate).

[0082] In one embodiment, the molecular formula of the epoxy group is C3H5O2-(C2H4O). n -C3H5O, wherein the number average molecular weight of the epoxy group-containing compound is 300 to 800, within the above range, which makes the oligomer have better fluidity under room temperature conditions, and adheres to and is retained on the foam metal surface through wetting and capillary effect, with uniform coating.

[0083] In one embodiment, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), diphenyl carbonate (DPhC), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone (γ-GBL), acetonitrile (AN), and sulfolane (TMS).

[0084] In one embodiment, the current density of the electrochemical deposition is 0.1–0.5 mA / cm². 2 For example, it could be 0.1 mA / cm 2 0.2mA / cm 2 0.3mA / cm 2 0.4mA / cm 2 0.5mA / cm 2 Or a range consisting of any two of these values.

[0085] In one embodiment, the electrochemical deposition time is 0.5 to 6 hours, for example, it can be 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours or any two of these values.

[0086] In one embodiment, during the electrochemical deposition, the precursor serves as the working electrode, the platinum plate as the counter electrode, and the calomel electrode as the reference electrode.

[0087] One embodiment of this application provides a secondary battery including a negative electrode, wherein the negative electrode comprises the lithium metal three-dimensional porous material described above.

[0088] In one embodiment, the secondary battery further includes a positive electrode.

[0089] In one embodiment, the positive electrode comprises a lithium foil.

[0090] In another embodiment, the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer comprising a positive active material.

[0091] In one embodiment, the positive electrode active material may be selected from sodium-iron composite oxides, sodium-cobalt composite oxides, sodium-manganese composite oxides, sodium-nickel composite oxides, sodium-nickel-titanium composite oxides, sodium-nickel-manganese composite oxides, sodium-iron-manganese composite oxides, sodium-nickel-cobalt-manganese composite oxides, sodium-iron phosphate compounds, sodium-manganese phosphate compounds, sodium-cobalt phosphate compounds, lithium nickel cobalt-manganese oxide, and lithium nickel cobalt-aluminum oxide, etc. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials of batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0092] In one embodiment, the type of positive electrode current collector is not particularly limited, and it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.

[0093] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.

[0094] In one embodiment, the positive electrode active material layer further includes a conductive agent and a binder.

[0095] In one embodiment, there is no limitation on the type of conductive agent mentioned in this application, and any known conductive agent may be used.

[0096] In one embodiment, the conductive agent includes at least one of carbon materials such as acetylene black, needle coke, carbon nanotubes, and graphene.

[0097] In one embodiment, there is no limitation on the type of adhesive mentioned in this application, and any known positive electrode adhesive can be used.

[0098] In one embodiment, the adhesive includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer or its hydrogenation, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene-α-olefin copolymer, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer.

[0099] In the secondary battery mentioned in this application, a separator is usually provided between the positive and negative electrodes to prevent short circuits. There are no particular restrictions on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application.

[0100] In one embodiment, the diaphragm comprises a porous sheet-like or nonwoven material with excellent liquid retention properties. Materials for resin or glass fiber diaphragms include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone.

[0101] In one embodiment, the polyolefin is polyethylene or polypropylene. The materials of the diaphragm described above can be used alone or in any combination.

[0102] In one embodiment, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte.

[0103] In one embodiment, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0104] In one embodiment, the secondary battery includes an electrolyte, and the type of electrolyte is not specifically limited. The electrolyte comprises an electrolyte salt and an organic solvent, and the specific types of the electrolyte salt and organic solvent are not specifically limited and can be selected according to actual needs. The electrolyte may also include additives, and the type of additives is not particularly limited. These additives can be film-forming additives for the positive and / or negative electrodes, or additives that can improve certain battery performance, such as additives that improve the battery's high or low temperature performance.

[0105] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0106] One embodiment of this application provides an electrical device including the secondary battery described above, wherein the secondary battery serves as the power supply for the electrical device.

[0107] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0108] The following embodiments are provided to facilitate understanding of the invention. These embodiments are not intended to limit the scope of the claims.

[0109] Example 1

[0110] A method for preparing a three-dimensional porous lithium metal material includes the following steps:

[0111] Copper foam with a thickness of 200 μm (hereinafter referred to as initial thickness), a porosity of 80% (hereinafter referred to as initial porosity), and an average pore size of 50 μm was rolled under a pressure of 10 MPa until the thickness reached 80 μm. The rolled copper foam was then heat-treated at 250 °C for 4 h in a mixed atmosphere of argon and hydrogen (volume ratio of 19:1) to obtain pretreated copper foam.

[0112] LiFSI and PEGDE (polyethylene glycol diglycidyl ether) with Mn=500 were mixed evenly (LiFSI concentration was 0.06 mmol / ml). The pretreated copper foam was then immersed in the reaction solution. After being removed, it was placed in an oven at 85°C for 300 min for thermally initiated in-situ polymerization to form a PEO layer on the outer periphery of the copper foam, thus obtaining the precursor.

[0113] An organic solvent was prepared by mixing EC and EMC at a volume ratio of 3:7. The organic solvent and 1M lithium hexafluorophosphate were then used to prepare the electrolyte. The precursor was used as the working electrode, a platinum plate as the counter electrode, and a calomel electrode as the reference electrode. An electrode with an impedance of 0.4 mA / cm² was applied. 2 A three-dimensional porous lithium metal material was obtained by electrochemical deposition at a current density of 2.061 h.

[0114] The lithium metal three-dimensional porous material prepared in Example 1 includes a matrix layer and a PEO layer that at least partially covers the outer periphery of the matrix layer. The matrix layer includes copper foam and lithium metal filling the pores of the copper foam.

[0115] The parameters of Example 1 are shown in Table 1.

[0116] Examples 2-6

[0117] The difference between Examples 2-6 and Example 1 is that Examples 2-6 change the heating temperature and time, thereby changing the molecular weight of PEO, and thus changing the ionic conductivity and electronic conductivity.

[0118] Examples 7-10

[0119] The difference between Examples 7-10 and Example 1 is that Examples 7-10 change the initial porosity of the copper foam, thereby changing the porosity of the matrix layer.

[0120] Examples 11-16

[0121] The difference between Examples 11-16 and Example 1 is that Examples 11-16 change B by adjusting the current density and deposition time of the electrochemical deposition step.

[0122] Examples 17-20

[0123] The difference between Examples 17-20 and Example 1 is that the average pore size of the copper foam is changed in Examples 17-20.

[0124] Examples 21-24

[0125] The difference between Examples 21-24 and Example 1 is that Examples 21-24 change the lithium salt concentration and the molecular weight of PEGDE, thereby changing the thickness of the PEO layer.

[0126] Comparative Example 1

[0127] A method for preparing a three-dimensional porous lithium metal material includes the following steps:

[0128] Copper foam with a thickness of 200 μm (hereinafter referred to as initial thickness), a porosity of 80% (hereinafter referred to as initial porosity), and an average pore size of 50 μm was rolled under a pressure of 10 MPa until the thickness reached 80 μm. The rolled copper foam was then heat-treated at 250 °C for 4 h in a mixed atmosphere of argon and hydrogen (volume ratio of 19:1) to obtain pretreated copper foam.

[0129] PEO (commercially available, viscosity-average molecular weight of 50W) was mixed evenly with water. The pretreated copper foam was immersed in the reaction solution, and after being taken out, it was placed in an 85°C oven for 300 minutes to dry the moisture. A PEO layer was formed on the outer periphery of the copper foam to obtain the precursor.

[0130] An organic solvent was prepared by mixing EC and EMC at a volume ratio of 3:7. The organic solvent and 1M lithium hexafluorophosphate were then used to prepare the electrolyte. The precursor was used as the working electrode, a platinum plate as the counter electrode, and a calomel electrode as the reference electrode. An electrode with an impedance of 0.4 mA / cm² was applied. 2 A three-dimensional porous lithium metal material was obtained by electrochemical deposition at a current density of 2.061 h.

[0131] Comparative Example 2

[0132] A method for preparing a three-dimensional porous lithium metal material includes the following steps:

[0133] Copper foam with a thickness of 200 μm (hereinafter referred to as initial thickness), a porosity of 80% (hereinafter referred to as initial porosity), and an average pore size of 50 μm was rolled under a pressure of 10 MPa until the thickness reached 80 μm. The rolled copper foam was then heat-treated at 250 °C for 4 h in a mixed atmosphere of argon and hydrogen (volume ratio of 19:1) to obtain pretreated copper foam.

[0134] LiFSI and N-doped polypyrrole with Mn=500 were mixed evenly (LiFSI concentration was 0.06 mmol / ml). Pretreated copper foam was then immersed in the reaction solution. After being removed, it was placed in an oven at 85°C for 300 min for thermally initiated in-situ polymerization to form a PEO layer on the outer periphery of the copper foam, thus obtaining the precursor.

[0135] An organic solvent was prepared by mixing EC and EMC at a volume ratio of 3:7. The organic solvent and 1M lithium hexafluorophosphate were then used to prepare the electrolyte. The precursor was used as the working electrode, a platinum plate as the counter electrode, and a calomel electrode as the reference electrode. An electrode with an impedance of 0.4 mA / cm² was applied. 2 A three-dimensional porous lithium metal material was obtained by electrochemical deposition at a current density of 2.061 h.

[0136] Comparative Example 3

[0137] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 is not immersed in the reaction solution, and therefore does not contain a PEO layer.

[0138] Comparative Example 4

[0139] The difference between Comparative Example 4 and Example 1 is that Comparative Example 4 does not undergo electrochemical deposition, and therefore the copper foam is not filled with lithium metal.

[0140] Table 1

[0141] Performance testing

[0142] Test method for the cycle capacity retention rate of secondary batteries: The sheets obtained in the comparative examples and embodiments were cut into 19mm small round pieces as negative electrodes. Ternary material NCM811, polyvinylidene fluoride (PVDF), and carbon black were mixed in a ratio of 8:1:1, and then NMP was added for dispersion. The mixture was then uniformly coated onto an aluminum foil current collector using a scraper and dried at 100°C to obtain the positive electrode sheet. The positive electrode sheet was cut into 16mm small round pieces as positive electrodes, and 2430 coin cells were assembled. The electrolyte formulation of the secondary battery was a 1M LiPF6 EC / EMC electrolyte, with EC:EMC = 3:7, and a 14μm thick PE separator was used. The coin cells were cycled at a rate of 0.5C charge 1C discharge. The cycle count was recorded when the capacity retention rate was below 80%.

[0143] Thickness change rate: The sheets obtained in the comparative and examples were cut into 19mm small circular pieces and assembled with 16mm commercial lithium foil to form 2430 coin cell half-cells. The electrolyte formulation was a 1M LiPF6 EC / EMC electrolyte with EC:EMC = 3:7, and the separator was a 14μm thick PE membrane. After depositing a capacity of 1mAh / cm2 on the negative electrode side at a current of 1mA / cm2, the coin cell was disassembled, the negative electrode was removed, and the thickness of the electrode sheet was measured to obtain the thickness change rate before and after deposition.

[0144] Table 2

[0145] As can be seen from Table 2, the matrix layer of the lithium metal three-dimensional porous material described in this application is a three-dimensional conductive metal filled with lithium metal, and the PEO (polyethylene oxide) layer at least partially covers the outer periphery of the matrix layer. The ionic conductivity of the polymer layer is 10. -5 ~1S / cm, electronic conductivity 10 -9 ~10 -5The lithium metal three-dimensional porous material exhibits a three-dimensional porous structure with a surface area of ​​S / cm. It combines high specific surface area and high interfacial stability, which can effectively increase interfacial stability. The polymer layer can isolate the lithium metal from direct contact with the electrolyte, reducing side reactions between the two. The matrix layer provides highly active deposition sites and sufficient deposition space for lithium ions during the charging process, and slowly releases the compressive stress during the charging and discharging process and the rolling process, effectively improving the cycle performance of the secondary battery.

[0146] Comparing Examples 1-7-10, it can be seen that the optimal porosity of the substrate layer is in the range of 10%-30%. If the porosity is too low, there is not enough space to accommodate lithium metal during battery charging and discharging, resulting in large volume expansion. At the same time, lithium metal exceeding the substrate layer will deposit on the surface, easily forming dendrites and shortening cycle life. If the porosity is too high, the lithium ion transport path becomes longer, and lithium ions tend to deposit on and near the surface. The utilization rate of the substrate layer is insufficient, and lithium metal cannot be densely deposited, which also leads to dendrite growth.

[0147] Comparing Examples 1 and 11-16, it can be seen that the proportion of lithium metal plays an important role in improving cycle life. This is because lithium metal is inevitably consumed during the cycle process, and the amount of lithium metal in stock will offset the consumption caused by side reactions or the formation of dead lithium.

[0148] Comparing Examples 1 and 17-20, it can be seen that the average pore size of the copper foam also affects the cycle life. This is because the pore size can regulate the deposition behavior of lithium ions. Pores that are too small or too large are not conducive to the rapid transport of lithium ions.

[0149] Comparing Examples 1 and 21-24, it can be seen that the thickness of the PEO layer affects the cycle life. This is because the thickness of PEO can affect its mechanical modulus. During the charging and discharging process, in addition to isolating the lithium metal from direct contact with the electrolyte, the PEO layer also needs to induce local lithium dendrites to undergo plastic deformation. Therefore, the PEO layer needs to have a certain thickness to effectively reduce the risk of dendrite puncture. However, when the PEO layer is too thick, the transport difficulty of lithium ions increases, the path becomes longer, and it is not conducive to the uniform deposition of lithium metal, thus leading to a decrease in cycle life.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A lithium metal three-dimensional porous material, characterized in that, It includes a substrate layer and a polymer layer that at least partially covers the periphery of the substrate layer, wherein the substrate layer includes a three-dimensional conductive metal and lithium metal filling the pores of the three-dimensional conductive metal; The polymer layer has an ionic conductivity of 10. -5 ~1S / cm, electronic conductivity 10 -9 ~10 -5 S / cm.

2. The lithium metal three-dimensional porous material of claim 1, wherein, The polymer layer has an ionic conductivity of 5.4 × 10⁻⁶. -5 ~8.9*10 -4 S / cm, electronic conductivity 7.4*10 -7 ~2.1*10 -5 S / cm.

3. The lithium metal three-dimensional porous material according to claim 1, characterized in that, The porosity of the matrix layer is A, where 10% ≤ A ≤ 30%.

4. The lithium metal three-dimensional porous material according to claim 1, characterized in that, The three-dimensional conductive metal includes at least one of foamed copper, foamed nickel, and foamed aluminum; and / or The average pore size of the three-dimensional conductive metal is 20–80 μm.

5. The lithium metal three-dimensional porous material according to claim 1, characterized in that, The lithium metal content in the matrix layer is B, which satisfies the following condition: 0.2% ≤ B ≤ 1%.

6. The lithium metal three-dimensional porous material according to any one of claims 4 to 5, characterized in that, It satisfies: 10≤A / B≤125.

7. The lithium metal three-dimensional porous material according to claim 1, characterized in that, The thickness of the three-dimensional conductive material is 2–350 μm; and / or The thickness of the polymer layer is 0.5–20 μm.

8. The lithium metal three-dimensional porous material according to claim 1, characterized in that, The polymer in the polymer layer has a viscosity-average molecular weight of 100,000 to 1,000,000.

9. A method for preparing a three-dimensional porous lithium metal material, characterized in that, Includes the following steps: The three-dimensional conductive metal is rolled and heat-treated to obtain a pretreated three-dimensional conductive metal. The pretreated three-dimensional conductive metal is placed in a reaction solution and reacted to obtain the precursor. The precursor was placed in an electrolyte for electrochemical deposition to obtain a three-dimensional porous lithium metal material. The reaction solution includes a first lithium salt and a compound containing at least one of halogen groups, sulfonate groups, sulfate groups, and epoxy groups; The electrolyte comprises a second lithium salt and an organic solvent.

10. The method for preparing a three-dimensional porous lithium metal material according to claim 9, characterized in that, Satisfy at least one of (a) to (h): (a) The heat treatment temperature is 200–300°C, and the heat treatment time is 0.5–6 h; (b) The heat treatment is carried out in a mixed atmosphere of argon and hydrogen, wherein the volume ratio of hydrogen to argon is (0.5–2):(18–19.5); (c) The reaction temperature is 50–100°C, and the reaction time is 10–600 min; (d) The concentration of the first lithium salt in the reaction solution is 0.05–0.8 mmol / L; (e) The concentration of the second lithium salt in the electrolyte is 0.5–2 mol / L; (f) The first lithium salt and the second lithium salt each independently include at least one of LiTFSI, LiFSI, LiPF6, and LiBF4; (g) the molecular formula of the compound containing an epoxy group is C3H5O2-(C2H4O) n -C3H5O; (h) The number average molecular weight of the compound containing at least one of halogen groups, sulfonate groups, sulfate groups, and epoxy groups is 300 to 800.

11. A secondary battery, characterized in that, Includes a negative electrode, wherein the negative electrode comprises the lithium metal three-dimensional porous material according to any one of claims 1 to 8.

12. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 11.

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