Lithium anode, secondary batteries containing it, and electrical devices

Abstract

This application discloses a lithium anode, a secondary battery containing the anode, and an electrical device thereof, belonging to the field of electrochemical energy storage technology. The lithium anode provided in this application sequentially introduces a first layer comprising at least one of a metal-organic framework material and alumina, a second layer with a porosity of 40%-60% containing a metal element, and a third layer with a porosity of 80%-99% containing a metal element on the surface of a lithium metal layer; this effectively improves the coulombic efficiency and cycle performance of the prepared secondary battery and reduces the volume expansion of the anode before and after cycling.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to a lithium anode, a secondary battery containing the anode, and an electrical device thereof. Background Technology

[0002] Lithium metal is considered an ideal anode material for next-generation high-energy-density batteries due to its extremely high theoretical specific capacity (3860 mAh / g) and the lowest electrochemical potential (-3.04 V vs. SHE). However, its commercial application has long been limited by two major challenges: (1) uncontrollable lithium dendrite growth, which can lead to battery short circuits and safety accidents; and (2) huge volume expansion / contraction, which can damage the integrity of the electrode structure, accelerate the rupture and regeneration of the solid electrolyte interface (SEI), and continuously consume electrolyte and active lithium.

[0003] Existing technologies for suppressing dendrites employ three-dimensional hosts (such as porous copper) or lithiophilic coatings. However, the poor lithiophilicity of the three-dimensional host surface limits its guiding effect on lithium deposition; while lithiophilic coatings often crack due to volume expansion after a small amount of lithium deposition because of insufficient porosity. In addition, existing technologies struggle to address the drastic volume changes caused by external physical constraints, and current designs generally lack built-in active lithium replenishment mechanisms, failing to compensate for continuous lithium consumption during cycling, leading to capacity decay. Summary of the Invention

[0004] The purpose of this application is to solve the above-mentioned technical problems and to propose a lithium anode with good coulombic efficiency and cycle performance when applied in secondary batteries, and low anode volume expansion rate before and after cycling, a secondary battery containing the anode, and an electrical device.

[0005] To achieve the above objectives, a first aspect of this application provides a lithium anode, the lithium anode comprising a lithium metal layer, and a first layer, a second layer and a third layer sequentially disposed on the surface of the lithium metal layer; The first layer includes at least one of a metal-organic framework material and alumina; The second layer comprises metallic elements and has pores, with a porosity of 40-60%. The third layer comprises metallic elements and has pores, with a porosity of 80-99%.

[0006] As an embodiment of this application, the metallic element of the third layer includes at least one of silver and magnesium.

[0007] As an embodiment of this application, the metallic element of the second layer includes at least one of zinc and aluminum.

[0008] As an embodiment of this application, the apparent elastic modulus of the third layer at 20°C is 0.1 MPa-2.8 MPa.

[0009] As an embodiment of this application, the apparent elastic modulus of the second layer at 20°C is 3.5 GPa-7 GPa.

[0010] As an embodiment of this application, the average pore diameter of the pores in the third layer is 1μm-3μm.

[0011] As an embodiment of this application, the average pore diameter of the pores in the second layer is 0.2μm - 0.8μm.

[0012] As an embodiment of this application, the thickness of the third layer is 8μm-15μm.

[0013] As an embodiment of this application, the thickness of the second layer is 3μm-10μm.

[0014] As an embodiment of this application, the thickness of the first layer is 1μm-3μm.

[0015] As an embodiment of this application, the thickness of the lithium metal layer is 8μm-10μm.

[0016] In a second aspect, this application provides a secondary battery including the lithium anode described in this application.

[0017] In a third aspect, this application provides an electrical device comprising the secondary battery described in this application.

[0018] Compared with the prior art, the beneficial effects of this application are: This application provides a lithium anode by sequentially introducing a first layer comprising at least one of a metal-organic framework material and alumina, a second layer containing metal elements with a porosity of 40-60%, and a third layer containing metal elements with a porosity of 80-99% on the surface of a lithium metal layer. This effectively and actively constrains the growth direction of lithium during cycling within the anode, suppressing lithium dendrite growth and anode volume expansion. Simultaneously, it effectively reduces lithium deposition nucleation and over-site growth. Therefore, it effectively improves the coulombic efficiency and cycle performance of the prepared secondary battery, while reducing volume expansion before and after cycling. Attached Figure Description

[0019] Figure 1 Here is a schematic diagram of the lithium anode prepared in Example 1: 1-Third layer, 2-Second layer, 3-First layer, 4-Lithium metal layer. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] 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.

[0023] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.

[0024] In one embodiment of this application, a lithium anode is provided, the lithium anode comprising a lithium metal layer, and a first layer, a second layer and a third layer sequentially disposed on the surface of the lithium metal layer; The first layer includes at least one of a metal-organic framework material and alumina; The second layer comprises metallic elements and has pores, with a porosity of 40%-60%. The third layer comprises metallic elements and has pores, with a porosity of 80%-99%.

[0025] This application provides a lithium anode by sequentially introducing a first layer comprising at least one of a metal-organic framework material and alumina on the surface of a lithium metal layer, a second layer containing metal elements with a porosity of 40%-60%, and a third layer containing metal elements with a porosity of 80%-99%. This effectively and actively constrains the growth direction of lithium during cycling within the anode, suppressing lithium dendrite growth and anode volume expansion. Simultaneously, it effectively reduces lithium deposition nucleation and over-site growth. Therefore, it effectively improves the coulombic efficiency and cycle performance of the prepared secondary battery, while reducing volume expansion before and after cycling.

[0026] Specifically, firstly, there is a porosity gradient between the third and second layers, with the third layer being farther away from the lithium metal layer (the third layer being closer to the separator side of the subsequently fabricated secondary battery is referred to as the top, and the lithium metal layer as the bottom). This decrease in porosity from the third layer to the second layer physically creates an ion transport resistance gradient. This gradient guides lithium ions to migrate and deposit towards the lower porosity and more spatially confined second layer, or even the first layer or the lithium metal layer. This actively confines lithium growth within the negative electrode, effectively suppressing the growth of top lithium dendrites facing the separator side (third layer) and overall disordered expansion. Secondly, both the third and second layers contain metallic elements. These metallic elements can, to some extent, undergo alloying reactions with lithium, thereby reducing the nucleation and growth overpotential of lithium deposition, better inducing dense and uniform lithium deposition, and improving the kinetic performance of the subsequent secondary battery. Thirdly, the first layer includes at least one of metal-organic framework materials and alumina, which can serve as a robust intermediate support to enhance the overall mechanical strength and structural stability of the lithium anode. It can also effectively promote the desolvation process of lithium ions, reduce the interfacial transport energy barrier, and improve the reaction kinetics of lithium deposition interface.

[0027] It should be noted that the testing method for the porosity of the second and third layers is as follows: A lithium anode is taken, and its cross-section is imaged using a focused ion beam scanning electron microscope (FIB-SEM). The regions of the second and third layers are binarized using ImageJ image analysis software. The percentage of pore area to the total area of ​​the corresponding layer is calculated, which is the porosity of that layer. During the test, at least five different fields of view are randomly selected for measurement, and the arithmetic mean is taken.

[0028] For example, the porosity of the second layer can be any point value or any two-point range value between 40% and 60%, such as 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, etc.

[0029] In some embodiments, the porosity of the second layer is 50%-55%. For example, it can be 50%, 51%, 52%, 53%, 54%, 55%, etc.

[0030] For example, the porosity of the third layer can be any point value or any two-point range value between 80% and 99%, such as 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 99%, etc.

[0031] In some embodiments, the porosity of the third layer is 82%-90%. For example, it can be 82%, 85%, 86%, 87%, 88%, 89%, 90%, etc.

[0032] In some embodiments, the metal element of the third layer includes at least one of silver and magnesium.

[0033] This study found that when the metal element selected in the third layer includes at least one of silver and magnesium, it has a relatively low elastic modulus, which can improve the flexibility of the coating and effectively alleviate stress concentration during cycling. On the other hand, it can also significantly reduce the nucleation overpotential of lithium deposition and induce uniform and dense initial lithium deposition. At the same time, it can also help improve the ion / electron conduction rate, thereby effectively improving the coulombic efficiency and cycle performance of the secondary battery and reducing the volume expansion of the negative electrode before and after cycling.

[0034] In some embodiments, the metallic element of the second layer includes at least one of zinc and aluminum.

[0035] This study found that when the metal element selected in the second layer includes at least one of zinc and aluminum, it has a relatively high elastic modulus, which can improve the mechanical strength of the coating and better constrain lithium expansion. On the other hand, it can also significantly reduce the nucleation overpotential of lithium deposition and induce uniform and dense initial lithium deposition. At the same time, it can also help improve the ion / electron conduction rate, thereby effectively improving the coulombic efficiency and cycle performance of the secondary battery and reducing the volume expansion of the negative electrode before and after cycling.

[0036] In some embodiments, the apparent elastic modulus of the third layer at 20°C is 0.1 MPa-2.8 MPa.

[0037] For example, the apparent elastic modulus of the third layer can be any point value or any two-point range value between 0.1 MPa and 2.8 MPa, such as 0.1 MPa, 0.3 MPa, 0.5 MPa, 0.8 MPa, 1 MPa, 1.5 MPa, 1.5 MPa, 1.8 MPa, 2 MPa, 2.2 MPa, 2.5 MPa, 2.8 MPa, etc.

[0038] This study found that further controlling the elastic modulus of the third layer at 20°C within the above-mentioned range can better buffer the volume expansion of the secondary battery before and after cycling; thereby improving the cycle performance of the secondary battery and reducing the volume expansion of the negative electrode before and after cycling.

[0039] In some embodiments, the apparent elastic modulus of the second layer at 20°C is 3.5 GPa to 7 GPa.

[0040] For example, the apparent elastic modulus of the second layer at 20°C can be any point value between 3.5 GPa and 7 GPa or a range value between any two points, such as 3.5 GPa, 4.0 GPa, 4.5 GPa, 5.0 GPa, 5.5 GPa, 6.0 GPa, 6.5 GPa, 7.0 GPa, etc.

[0041] This study found that further controlling the elastic modulus of the second layer at 20°C within the above-mentioned range can better improve the mechanical strength of the lithium anode and constrain the volume expansion of the lithium anode; thereby improving the cycle performance of the secondary battery and reducing the volume expansion of the anode before and after cycling.

[0042] It should be noted that the apparent elastic modulus of the second and third layers can be obtained through calculation and testing, and the calculation formula is as follows: E / E s =C×(1-P) n Where Es is the intrinsic elastic modulus of the corresponding metallic elements in the second and third layers; C is the structural constant, ranging from 0.1 to 0.2 (the upper limit of 0.2 is taken for continuous and uniform pore size, and the lower limit of 0.1 is taken for defective and non-uniform pore size); P is the porosity of the second and third layers; and n is the structural index, taken as 2.0.

[0043] It should be noted that the apparent elastic modulus of the third layer at 20℃ and the second layer at 20℃ can also be obtained through testing. The testing method is the bubbling method (thin film expansion method), specifically: take a lithium anode, scrape off the second and third layers respectively to obtain second layer samples and third layer samples, and then prepare sample films; seal the sample films without stress on a rigid substrate with standard micropores, and introduce inert gas with controllable pressure through the micropores to the back of the film to make the film bulge uniformly; use a laser interferometer / confocal microscope to collect the correspondence between bubbling height and pressure in real time, and directly fit and calculate the in-plane apparent elastic modulus and Poisson's ratio of the film based on the theoretical formula of large deformation of thin plates.

[0044] In some embodiments, the average pore size of the pores in the third layer is 1 μm - 3 μm.

[0045] For example, the average pore diameter of the pores in the third layer can be any point value or any two-point range value between 1μm and 3μm, such as 1.0μm, 1.2μm, 1.5μm, 1.8μm, 2.0μm, 2.2μm, 2.5μm, 2.8μm, 3.0μm, etc.

[0046] In some embodiments, the average pore size of the pores in the second layer is 0.2 μm - 0.8 μm.

[0047] For example, the average pore diameter of the pores in the second layer can be any point value or any two-point range value between 0.2μm and 0.8μm, such as 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, etc.

[0048] This study found that the average pore size in the third layer and the average pore size in the second layer affect the stability of the corresponding layered structure, as well as the ionic / electronic conductivity and the wetting effect of the subsequent electrolyte. When the average pore size in the third layer and the average pore size in the second layer are further selected to be within the above ranges, the overall performance of the resulting secondary battery is better.

[0049] It should be noted that the testing method for the average pore diameter in the third layer and the average pore diameter in the second layer is as follows: A lithium anode is taken, and its cross-section is imaged using a focused ion beam scanning electron microscope (FIB-SEM). The imaging resolution must ensure that the pore structure is clearly discernible. The pores in the second and third layers are identified and measured using ImageJ image analysis software. The equivalent circle diameter (i.e., the diameter of a circle with the same area as the pore) of all pores in each layer is counted, and their arithmetic mean is calculated. During testing, at least five different fields of view are randomly selected for measurement, and the number of pores included in the statistics for each layer is no less than 100. Finally, the average value of all fields of view is taken as the average pore diameter of that layer.

[0050] In some embodiments, the thickness of the third layer is 8 μm - 15 μm.

[0051] For example, the thickness of the third layer can be any point value or any two-point range value between 8μm and 15μm, such as 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, etc.

[0052] This study found that the thickness of the third layer affects the ability to mitigate volume expansion during cycling, as well as its ability to reduce the nucleation overpotential of lithium deposition and the ion / electron conduction rate. When the thickness of the third layer is further selected within the above range, the coulombic efficiency and cycle performance of the secondary battery can be improved more effectively, and the volume expansion of the negative electrode before and after cycling can be reduced.

[0053] In some embodiments, the thickness of the second layer is 3 μm - 10 μm.

[0054] For example, the thickness of the second layer can be any point value or any two-point range value between 3μm and 10μm, such as 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc.

[0055] This study found that the thickness of the second layer affects the ability to constrain volume expansion during cycling, as well as its ability to reduce the nucleation overpotential of lithium deposition and the ion / electron conduction rate. When the thickness of the second layer is further selected within the above range, the coulombic efficiency and cycle performance of the secondary battery can be improved more effectively, and the volume expansion of the negative electrode before and after cycling can be reduced.

[0056] In some embodiments, the thickness of the first layer is 1 μm - 3 μm.

[0057] For example, the thickness of the first layer can be any point value or any two-point range value between 1μm and 3μm, such as 1.0μm, 1.2μm, 1.5μm, 1.8μm, 2.0μm, 2.2μm, 2.5μm, 2.8μm, 3.0μm, etc.

[0058] This study found that the thickness of the first layer affects its ability to act as a physical and chemical barrier, thereby affecting the extent to which lithium in the lithium metal layer reacts with metal elements in the second and third layers through diffusion; in addition, it also affects the ability of lithium ions to remove the solvation sheath and thus accelerate interfacial charge transfer; when the thickness of the first layer is further selected within the above range, the coulombic efficiency and cycle performance of the secondary battery can be improved more effectively, and the volume expansion of the negative electrode before and after cycling can be reduced.

[0059] In some embodiments, the thickness of the lithium metal layer is 8 μm - 10 μm.

[0060] For example, the thickness of the lithium metal layer can be any point value or any two-point range value between 8μm and 10μm, such as 8.0μm, 8.2μm, 8.5μm, 8.8μm, 9.0μm, 9.2μm, 9.5μm, 9.8μm, 10.0μm, etc.

[0061] This study found that the thickness of the lithium metal layer affects its lithium-providing capacity, and that further selection of the lithium metal layer thickness within the above-mentioned range can better improve the cycle performance of the secondary battery.

[0062] It should be noted that the testing methods for the thicknesses of the third layer, the second layer, the first layer, and the lithium metal layer are as follows: A lithium anode is taken, and its cross-section is imaged using a focused ion beam scanning electron microscope (FIB-SEM). First, a flat cross-sectional sample is prepared using low-temperature ion beam polishing technology to eliminate the influence of mechanical scratches on the layer thickness measurement. Then, in the SEM image, the layer interfaces are determined based on the obvious material contrast or morphological differences between the layers: the boundaries of the third layer (relatively high porosity layer), the second layer (relatively medium porosity layer), the first layer (relatively dense layer), and the lithium metal layer. On the image, at least 10 different locations are randomly selected along the direction perpendicular to the layer interfaces, and the vertical distances from the bottom of the lithium metal layer to the bottom of the first layer (i.e., the lithium metal layer thickness), from the first layer to the bottom of the second layer (i.e., the first layer thickness), from the second layer to the bottom of the third layer (i.e., the second layer thickness), and from the top of the third layer to the bottom of the third layer (i.e., the third layer thickness) are measured. All measurements were categorized by layer, and the arithmetic mean of each layer was calculated as the thickness value of each layer, with the result accurate to the nanometer level.

[0063] In some embodiments, the metal-organic framework material includes at least one of ZIF-8, MIL-53 (Al, Fe, Cr), MIL-100, MIL-101, UiO-66, and UiO-67.

[0064] In some embodiments, the method for preparing the lithium anode includes the following steps: (1) Introduce a first layer on top of the lithium metal layer; (2) Introduce a second layer on top of the first layer; (3) A third layer is introduced on the second layer to obtain a lithium anode.

[0065] In some embodiments, the method introduced in step (1) is a transfer method, which involves coating at least one of a metal-organic framework material and alumina onto a release film. Specifically, the method involves: first, pre-mixing the metal-organic framework material and / or alumina with N,N-dimethylformamide (DMF) solvent, and ultrasonically dispersing for 10-30 minutes; then sequentially adding a binder (polyvinylidene fluoride PVDF) and a dispersant (polyvinylpyrrolidone PVP), and continuing to stir until uniform, ensuring uniform dispersion of the metal-organic framework material without significant agglomeration; after uniform mixing, filtering through a 200-400 mesh sieve or centrifuging to remove large agglomerates to obtain a slurry; removing air bubbles from the slurry using vacuum degassing or static degassing; coating the release film at a certain speed; and drying at 120°C in an inert atmosphere. Subsequently, the slurry is rolled onto the surface of a lithium metal layer.

[0066] It is understandable that the thickness of the first layer can be adjusted by controlling the solid content of the slurry in step (1).

[0067] In some embodiments, the method introduced in steps (2) and (3) is template-assisted magnetron sputtering, which involves coating a template on the surface of the first / second layer, then sputtering and depositing metal elements, and then removing the template.

[0068] In some embodiments, the template comprises monodisperse polystyrene microspheres / polystyrene microspheres, specifically prepared as follows: 1) Take a certain amount of monodisperse polystyrene microsphere powder / polystyrene microsphere powder; 2) Add the microspheres to the ethanol; 3) Add 0.1 wt% of surfactant PVP to prevent microspheres from clumping together; 4) By ultrasonic oscillation or mechanical stirring, the microspheres are completely and uniformly dispersed in the solvent to form a stable milky white suspension, thus obtaining the template slurry; 5) Apply the prepared template slurry to the surface of the first / second layer. After drying, the solvent evaporates, and the polystyrene microspheres will automatically arrange themselves into a layer of colloidal crystals used as a template.

[0069] In some embodiments, the template removal is performed by dissolving the template in toluene.

[0070] It is understandable that the thickness of the second and third layers can be controlled by adjusting the sputtering deposition time in steps (2) and (3).

[0071] It is understandable that by controlling the size of the monodisperse polystyrene microspheres and the particle size of the polystyrene microspheres in steps (2) and (3), the average pore size of the pores in the second and third layers can be adjusted.

[0072] It is understandable that by controlling the solid content of the template slurry in steps (2) and (3), the porosity of the second and third layers can be adjusted.

[0073] It is understandable that by adjusting the porosity of the second and third layers respectively, the apparent elastic modulus of the second and third layers at 20°C can be controlled.

[0074] In a second aspect, this application provides a secondary battery including the lithium anode described in this application.

[0075] In some embodiments, the secondary battery further includes a positive electrode.

[0076] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least a portion of the surface of the positive current collector, the positive active material layer including a positive active material, a positive binder, and a positive conductive agent.

[0077] This application does not have any special requirements for the selection of the positive electrode active material; conventionally available positive electrode active materials in the art can be used. For example, the positive electrode active material may be selected from LiCoO2, LiNiO2, or LiNi. x Mn y O2, Li 1+z Ni x Mn y Co 1-x- y O2, LiNi x Co y Al z The group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, LiMnPO4, and combinations thereof, wherein each x is independently 0.2 to 0.9; each y is independently 0.1 to 0.45; and each z is independently 0 to 0.2. The positive electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode active materials.

[0078] Alternatively, the positive electrode active material can be selected from LiCoO2, LiNiO2, or LiNi. x Mn y O2, Li 1+z NixMnyCo 1-x-y O2, LiNi x Co y Al z The group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, LiFeO2, LiFePO4 and combinations thereof, wherein each x is independently 0.4 to 0.6; each y is independently 0.2 to 0.4; and each z is independently 0 to 0.1.

[0079] Or the positive electrode active material is Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2; where -0.2≤x≤0.2, 0≤a<1, 0≤b<1, 0≤c<1 and a+b+c≤1.

[0080] Or the positive electrode active material is Li 1+x Ni a Mn b Co c Al (1-a-b-c)O2, where 0.33≤a≤0.92, 0.33≤a≤0.9, 0.33≤a≤0.8, 0.5≤a≤0.92, 0.5≤a≤0.9, 0.5≤a≤0.8, 0.6≤a≤0.92 or 0.6≤a≤0.9; 0≤b≤0.5, 0≤b≤0.3, 0.1≤b≤0.5, 0.1≤b≤0.4, 0.1≤b≤0.3, 0.1≤b≤0.2 or 0.2≤b≤0.5; 0≤c≤0.5, 0≤c≤0.3, 0.1≤c≤0.5, 0.1≤c≤0.4, 0.1≤c≤0.3, 0.1≤c≤0.2 or 0.2≤c≤0.5.

[0081] In some embodiments, the positive electrode active material is doped with a dopant selected from the group consisting of Fe, Ni, Mn, Al, Mg, Zn, Ti, La, Ce, Sn, Zr, Ru, Si, Ge, and combinations thereof. In some embodiments, the dopant is not Fe, Ni, Mn, Mg, Zn, Ti, La, Ce, Ru, Si, or Ge. In some embodiments, the dopant is not Al, Sn, or Zr.

[0082] In some embodiments, the positive electrode active material may include LiNi. 0.33 Mn 0.33 Co 0.33 O2, LiNiO2, LiNi 0.4 Mn 0.4 Co 0.2 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.7 Mn 0.15 Co 0.15 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2, LiNi 0.92 Mn 0.04 Co 0.04 O2, LiNi 0.8 Co 0.15 Al 0.05 At least one of O2.

[0083] This application does not have specific requirements for the selection of the positive electrode binder; conventionally available positive electrode binders in the art can be used. Exemplarily, the positive electrode binder may be at least one of the following: polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder in this application is not limited to the above materials and also includes other materials that can be used as battery positive electrode binders.

[0084] This application does not have any special requirements for the selection of the positive electrode conductive agent; conventionally available positive electrode conductive agents in the art can be used. For example, the positive electrode conductive agent may be at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, carbon nanotubes, activated carbon, and mesoporous carbon. The positive electrode conductive agent in this application is not limited to the above materials and also includes other materials that can be used as positive electrode conductive agents in batteries.

[0085] In some embodiments, the secondary battery further includes an electrolyte.

[0086] Electrolytes include liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, etc., which can be used in the production of secondary batteries, but are not limited to these.

[0087] Liquid electrolytes (electrolytes) can include organic solvents and lithium salts. The use of organic solvents is unrestricted, as long as they serve as a medium for the movement of ions participating in the battery's electrochemical reactions. Specifically, organic solvents can be ester-based solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc.; ether-based solvents, such as dibutyl ether, tetrahydrofuran, etc.; ketone-based solvents, such as cyclohexanone; aromatic hydrocarbon-based solvents, such as benzene, fluorobenzene, etc.; carbonate-based solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), etc.; alcohol-based solvents, such as ethanol, isopropanol, etc.; nitriles, such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C20 hydrocarbon group, and may include double-bonded aromatic rings or ether bonds); amide solvents, such as dimethylformamide; dioxolane solvents, such as 1,3-dioxolane; or sulfolane solvents, etc. Preferably, carbonate solvents are used, and more preferably, cyclic carbonates with high ionic conductivity and high dielectric constant, such as ethylene carbonate or propylene carbonate, which can improve the charge and discharge performance of the battery, are used in mixtures with low-viscosity linear carbonate compounds (such as ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.). In this case, when cyclic carbonates and chain carbonates are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.

[0088] The lithium salt can be any compound that can provide lithium ions for lithium secondary batteries, without any particular limitation. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent electrolyte performance, and lithium ions can move effectively.

[0089] In addition to the electrolyte components mentioned above, additives can be added to the electrolyte, such as halogenated alkylene carbonates like ethylene difluorocarbonate; or pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexaphosphotriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc., to improve battery life characteristics, inhibit battery capacity decline, and increase battery discharge capacity. The content of the additives can be 0.1 to 5% by weight of the total electrolyte.

[0090] In some embodiments, the electrochemical device further includes a diaphragm.

[0091] The separator separates the negative and positive electrodes and provides a pathway for lithium-ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in electrochemical devices. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.) or laminated structures with two or more layers. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used as single-layer or multi-layer structures.

[0092] In a third aspect, this application provides an electrical device comprising the secondary battery described in this application.

[0093] Example 1 This application provides a lithium anode and a secondary battery. The preparation method of the lithium anode and the secondary battery includes the following steps: (1) Preparation of lithium anode In a drying room (dew point < -40°C), prepare a lithium anode according to the following steps: S1, Lithium metal layer: using lithium metal foil with a thickness of 10μm; S2, First layer: The metal-organic framework material layer (the metal-organic framework material is UiO-66-NH2, which is added to DMF to form a first layer slurry with a solid content of 10wt%, the wet film thickness is 20μm, and after drying, a first layer with a thickness of 2μm) coated on the release film is rolled onto the surface of the lithium metal layer to form the first layer; S3, Second Layer: Prepared using template-assisted magnetron sputtering. A template slurry was spin-coated onto the surface of the first layer (the template slurry was prepared by adding monodisperse polystyrene microspheres with an average diameter of 0.5 μm to ethanol, followed by adding 0.01 wt% of surfactant PVP (polyvinylpyrrolidone), and ultrasonically dispersing to form a template slurry with a solid content of 1.2 wt%). The spin-coating speed was 1500 rpm and the spin-coating time was 60 s. Then, aluminum (Al) was sputtered and deposited at a sputtering power of 300 W, a working pressure of 0.5 Pa, and a sputtering time of 30 min. The thickness of the deposited aluminum layer was approximately 6 μm. Subsequently, the template was removed by dissolving it with toluene to form a second layer with a porous structure. S4, Third Layer: Prepared using template-assisted magnetron sputtering. A template slurry was spin-coated onto the surface of the second layer (the template slurry was prepared by adding polystyrene microspheres with an average diameter of 2 μm to ethanol, followed by adding 0.1 wt% of surfactant PVP (polyvinylpyrrolidone), and ultrasonically dispersing to form a template slurry with a solid content of 0.8 wt%). The spin-coating speed was 2000 rpm and the spin-coating time was 60 s. Then, magnesium (Mg) was sputtered and deposited at a sputtering power of 250 W, a working pressure of 0.5 Pa, and a sputtering time of 45 min. The thickness of the deposited magnesium layer was approximately 12 μm. Subsequently, the template was removed by dissolving it with toluene, forming a third layer with a porous structure. The negative electrode is die-cut to obtain a negative electrode sheet, and a schematic diagram of the negative electrode sheet structure is shown below. Figure 1 As shown; (2) Preparation of positive electrode sheet The positive electrode active material (NCM811), positive electrode conductive agent (acetylene black), positive electrode conductive agent (carbon nanotube), and positive electrode binder (polyvinylidene fluoride, PVDF) were fully dispersed and uniformly coated onto an aluminum current collector with a thickness of 9 μm in an N-methylpyrrolidone solvent system at a weight ratio of 98.2:0.5:0.3:1.0. Then, the positive electrode sheet was dried, cold-pressed, and die-cut. (3) Preparation of electrolyte In an argon-atmosphere glove box (water and oxygen content <0.1ppm), lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in a mixed solvent of ethylene glycol dimethyl ether (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 1:1, and magnetically stirred until completely dissolved to prepare an electrolyte with a concentration of 2.4mol / L. (5) Preparation of secondary batteries The prepared positive electrode, negative electrode, separator (polypropylene separator) and other battery components are assembled and then subjected to processes such as shaping, baking, packaging, liquid injection, formation and capacity testing to obtain a secondary battery.

[0094] Examples 2-4 This application provides a lithium anode and a secondary battery. The difference between the lithium anode and the secondary battery in this application and those in Example 1 is that the porosity of the third layer is changed (achieved by adjusting the solid content of the template slurry in step S4). The difference between Example 2 and Example 1 is that the solid content of the template slurry in step S4 is 0.5 wt%, while the other conditions remain unchanged, and the porosity P3 of the resulting third layer is 82%. The difference between Example 3 and Example 1 is that the solid content of the template slurry in step S4 is 3.5 wt%, while the other conditions remain unchanged, and the porosity P3 of the resulting third layer is 98%. The difference between Example 4 and Example 1 is that the solid content of the template slurry in step S4 is 1.0 wt%, and the other conditions remain unchanged, resulting in a third layer porosity P3 of 93%.

[0095] Examples 5-6 This application provides a lithium anode and a secondary battery. The difference between the lithium anode and the secondary battery in this application and that in Example 1 is that the average pore size of the third layer is changed (achieved by adjusting the average diameter of the polystyrene microspheres and the solid content of the template slurry in step S4). The difference between Example 5 and Example 1 is that polystyrene microspheres with an average diameter of 1.2 μm are used in step S4, the solid content of the template slurry is 1.2 wt%, and the other conditions remain unchanged. The average pore diameter R3 of the resulting third layer is 1.2 μm. The difference between Example 6 and Example 1 is that, in step S4, polystyrene microspheres with an average diameter of 2.8 μm are used, the solid content of the template slurry is 0.7 wt%, and the other conditions remain unchanged. The average pore diameter R3 of the resulting third layer is 2.8 μm.

[0096] Examples 7-8 This application provides a lithium anode and a secondary battery. The difference between the lithium anode and the secondary battery in this application and those in Example 1 is that the thickness of the third layer is changed (achieved by adjusting the sputtering deposition time in step S4). The difference between Example 7 and Example 1 is that the sputtering deposition time in step S4 is adjusted to 120 min, the thickness of the deposited magnesium layer is about 9 μm, and the thickness of the resulting third layer H3 is 9 μm. The difference between Example 8 and Example 1 is that the sputtering deposition time in step S4 is adjusted to 180 min, the thickness of the deposited magnesium layer is about 14 μm, and the thickness of the resulting third layer H3 is 14 μm.

[0097] Examples 9-11 This application provides a lithium anode and a secondary battery. The difference between the lithium anode and the secondary battery in this application and those in Example 1 is that the porosity of the second layer is changed (achieved by adjusting the solid content of the template slurry in step S3). The difference between Example 9 and Example 1 is that the solid content of the template slurry in step S3 is 1.5 wt%, while the other conditions remain unchanged, and the porosity P2 of the resulting second layer is 55%. The difference between Example 10 and Example 1 is that the solid content of the template slurry in step S3 is 0.8 wt%, while the other conditions remain unchanged, and the porosity P2 of the resulting second layer is 42%. The difference between Example 11 and Example 1 is that the solid content of the template slurry in step S3 is 2.8 wt%, and the other conditions remain unchanged, resulting in a second layer porosity P2 of 58%.

[0098] Examples 12-13 This application provides a lithium anode and a secondary battery. The difference between the lithium anode and the secondary battery in this application and that in Example 1 is that the average pore size of the pores in the second layer is changed (achieved by adjusting the average diameter of the monodisperse polystyrene microspheres and the solid content of the template slurry in step S3). The difference between Example 12 and Example 1 is that in step S3, monodisperse polystyrene microspheres with an average diameter of 0.3 μm are used as templates, the solid content of the template slurry is 2.0 wt%, and the other conditions remain unchanged. The average pore size R2 of the resulting second layer is 0.3 μm. The difference between Example 13 and Example 1 is that in step S3, monodisperse polystyrene microspheres with an average diameter of 0.7 μm are used as templates, the solid content of the template slurry is 1.3 wt%, and the other conditions remain unchanged. The average pore size R2 of the resulting second layer is 0.7 μm.

[0099] Examples 14-15 This application provides a lithium anode and a secondary battery. The difference between the lithium anode and the secondary battery in this application and those in Example 1 is that the thickness of the second layer is changed (achieved by adjusting the sputtering deposition time in step S3). The difference between Example 14 and Example 1 is that the sputtering deposition time of aluminum in step S3 is adjusted to 80 min, the deposition thickness is about 4 μm, and the thickness of the second layer H2 is 4 μm. The difference between Example 15 and Example 1 is that the sputtering deposition time of aluminum in step S3 is adjusted to 160 min, the deposition thickness is about 8 μm, and the thickness of the second layer H2 is 8 μm.

[0100] Examples 16-17 This application provides a lithium anode and a secondary battery. The difference between the lithium anode and the secondary battery in this application and that in Example 1 is that the thickness of the first layer is changed (achieved by adjusting the thickness of the wet film coated in step S2). The difference between Example 16 and Example 1 is that the thickness of the wet film in step S2 is adjusted to 12 μm, and the thickness H1 of the first layer after drying is 1.2 μm. The difference between Example 17 and Example 1 is that the thickness of the wet film in step S2 is adjusted to 28 μm, and the thickness of the first layer H1 after drying is 2.8 μm.

[0101] Example 18 This application provides a lithium anode and a secondary battery. The difference between the lithium anode and the secondary battery in this application and those in Example 1 is that the silver sputtering deposition in step S4 is adjusted.

[0102] Example 19 This application provides a lithium anode and a secondary battery. The difference between the lithium anode and the secondary battery in this application and those in Example 1 is that the zinc sputtering deposition in step S3 is adjusted.

[0103] Example 20 This application provides a lithium anode and a secondary battery. The difference between the lithium anode and the secondary battery in this application and those in Example 1 is that the metal-organic framework material layer is replaced with an alumina layer in step S2.

[0104] Comparative Example 1 This application provides a lithium anode and a secondary battery in a comparative example. The difference between the lithium anode and the secondary battery in Example 1 is that a third layer is not introduced, that is, step S4 is not included.

[0105] Comparative Example 2 This application provides a lithium anode and a secondary battery in a comparative example. The difference between the lithium anode and the secondary battery in Example 1 is that a second layer is not introduced, that is, step S3 is not included.

[0106] Comparative Example 3 This application provides a lithium anode and a secondary battery in a comparative example. The difference between the lithium anode and the secondary battery in Example 1 is that the first layer is not introduced, that is, step S2 is not included.

[0107] Comparative Example 4 This application provides a lithium anode and a secondary battery in a comparative example. The difference between the lithium anode and the secondary battery in Example 1 is that the second and third layers are not introduced, that is, steps S3 and S4 are not included.

[0108] Comparative Example 5 This application provides a lithium anode and a secondary battery in comparative example. The difference between the lithium anode and the secondary battery and Example 1 is that the solid content of the template in step S4 is adjusted to 0.3wt%, while the other conditions remain unchanged, and the porosity P3 of the resulting third layer is 75%.

[0109] Comparative Example 6 This application provides a lithium anode and a secondary battery in comparative example. The difference between the lithium anode and the secondary battery and Example 1 is that the solid content of the template in step S3 is adjusted to 0.6wt%, while the other conditions remain unchanged, and the porosity P2 of the resulting second layer is 35%.

[0110] Comparative Example 7 This application provides a lithium anode and a secondary battery in comparative example. The difference between the lithium anode and the secondary battery and Example 1 is that the solid content of the template in step S3 is adjusted to 3.2 wt%, while the other conditions remain unchanged, and the porosity P2 of the resulting second layer is 65%.

[0111] Comparative Example 8 This application provides a lithium anode and a secondary battery in comparative example. The difference between the lithium anode and the secondary battery in Example 1 is that the third layer of the lithium anode is stacked on the second layer in step S4, and the above-mentioned anode is die-cut to obtain the anode sheet.

[0112] Comparative Example 9 This application provides a lithium anode and a secondary battery in a comparative example. The difference between the lithium anode and the secondary battery in Example 1 is that the second layer of the lithium anode is stacked directly on the second layer in step S3, and the above-mentioned anode is die-cut to obtain the anode sheet.

[0113] Comparative Example 10 This application provides a lithium anode and a secondary battery as comparative examples. The difference between the lithium anode and the secondary battery in Example 1 is that the lithium anode is prepared as follows: In a drying room (dew point < -40°C), prepare a lithium anode according to the following steps: S1, Lithium metal layer: using lithium metal foil with a thickness of 10μm; S2. Mix magnesium and aluminum, and hot-press them with lithium foil at 160°C to form a Mg-Al-Li alloy layer. The negative electrode is obtained by die-cutting the above negative electrode.

[0114] The porosity P3, metal element type, apparent elastic modulus G3, average pore diameter R3, and thickness H3 of the third layer of the lithium anode in Examples and Comparative Examples 1-9 are shown in Table 1. Table 1 The performance tests of the products prepared in the examples and comparative examples include the following aspects: (1) Button CE test The current will be applied at 0.5 mA / cm. 2 Discharged at a current density of 1 mAh / cm³, with a capacity of 1 mAh / cm³. 2 The charging cutoff voltage is 1V. After 100 cycles, calculate the average value for CE.

[0115] (2) Sedimentary morphology 1. Loop condition The prepared coin cells were subjected to charge-discharge cycle tests using the Blue Battery Testing System at a constant temperature of 25°C. The test procedure is as follows: Formation stage: First, charge at a constant current rate of 0.1C to 4.3V, then charge at a constant voltage rate until the current drops to 0.05C; then discharge at a constant current rate of 0.1C to 2.8V. Repeat the formation cycle 3 times.

[0116] Cycling phase: Constant current charging and discharging at a rate of 0.5C, with a charging and discharging voltage range of 2.8-4.3V, for 50 cycles.

[0117] 2. Expansion Rate Calculation Formula After 50 twisting cycles, the negative electrode was removed for thickness testing, and the expansion rate was calculated.

[0118] Expansion rate = ((Anode thickness after 50 cycles - Anode thickness before cycling) / Anode thickness before cycling) × 100% (3) Cyclic performance test Five 2Ah batteries were prepared and repeatedly charged and discharged using the following steps to calculate the cycle capacity retention rate of the lithium-ion secondary batteries: First, the first charge and discharge cycle was performed at 25°C. Constant current and constant voltage charging was performed at a charging current of 0.1C (the current value required to completely discharge the theoretical capacity within 10 hours) until the upper limit voltage reached 4.25V. Then, constant current discharging was performed at a discharging current of 1C until the final voltage reached 3V. The discharge capacity of the first cycle was recorded. Then, 100 charge and discharge cycles were performed, and the discharge capacity of the 100th cycle was recorded. Cycle capacity retention rate = (discharge capacity of the 100th cycle / discharge capacity of the first cycle) × 100%; The results are shown in Table 2. Table 2 As can be seen from Table 2, when the technical solution provided in this application is adopted, the obtained secondary battery has excellent coulombic efficiency, cycle performance and low negative electrode expansion rate after cycle; specifically, the average coulombic efficiency of the obtained secondary battery is above 98.2%, the negative electrode expansion rate after cycle is below 28.5%, and the capacity retention rate after 200 cycles is above 89.5%. A comparison of Examples 1-20 with Comparative Examples 1-4 and 8-9 shows that when the three-layer structure of this application is not used (either one or more layers of the first, second, or third layer are missing, or a dense alloy layer is used to replace the porous layer), the overall performance of the secondary battery is significantly reduced. Its coulombic efficiency is generally lower than 96.5%, the negative electrode expansion rate after cycling is as high as 40% or more, and the capacity retention rate after 200 cycles is lower than 83.5%, which is significantly worse than the examples of this application. As can be seen from the comparison between Examples 1-20 and Comparative Examples 5-7, when the porosity parameters of the layered structure are not within the range defined by the claims of this application (such as the porosity of the third layer being less than 80% or the porosity of the second layer being less than 40% or more than 60%), even if the three-layer structure is maintained, it is impossible to achieve excellent overall results. Its coulombic efficiency, cycle retention rate and volume expansion rate are significantly worse than those of the examples with parameters within the range. As can be seen from Examples 1-20 and Comparative Example 10, the effects of the present invention cannot be achieved when the structure is not the layered structure of the present invention.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application 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 this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A lithium anode, characterized in that, The lithium anode includes a lithium metal layer, and a first layer, a second layer and a third layer sequentially disposed on the surface of the lithium metal layer; The first layer includes at least one of a metal-organic framework material and alumina; The second layer comprises metallic elements and has pores, with a porosity of 40%-60%. The third layer comprises metallic elements and has pores, with a porosity of 80%-99%.

2. The lithium anode according to claim 1, characterized in that, The metallic element in the third layer includes at least one of silver and magnesium.

3. The lithium anode according to claim 1, characterized in that, The second layer contains at least one of zinc and aluminum.

4. The lithium anode according to claim 1, characterized in that, The apparent elastic modulus of the third layer at 20°C is 0.1 MPa-2.8 MPa.

5. The lithium anode according to claim 1, characterized in that, The apparent elastic modulus of the second layer at 20°C is 3.5 GPa-7 GPa.

6. The lithium anode according to claim 1, characterized in that, The average pore size of the pores in the third layer is 1-3 μm.

7. The lithium anode according to claim 1, characterized in that, The average pore size in the second layer is 0.2-0.8 μm.

8. The lithium anode according to claim 1, characterized in that, The thickness of the third layer is 8μm-15μm; And / or, the thickness of the second layer is 3μm-10μm; And / or, the thickness of the first layer is 1 μm - 3 μm; And / or, the thickness of the lithium metal layer is 8 μm - 10 μm.

9. A secondary battery, characterized in that, Including the lithium anode as described in any one of claims 1-8.

10. An electrical device, characterized in that, The electrical device includes the secondary battery as described in claim 9.

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