Battery monomer and preparation method thereof, battery device, power utilization device and energy storage device

Abstract

The embodiment of the invention relates to the technical field of energy storage, and provides a battery monomer and a preparation method thereof, a battery device, a power utilization device and an energy storage device. The negative electrode of the battery monomer comprises a silicon-based composite structure, the silicon-based composite structure comprises an outer-layer MOF structure, a middle-layer MOF structure and an inner-layer MOF structure, the outer-layer MOF structure is arranged on the outer wall of the middle-layer MOF structure in a surrounding manner, the middle-layer MOF structure is arranged on the outer wall of the inner-layer MOF structure in a surrounding manner, the aperture of the outer-layer MOF structure is larger than that of the middle-layer MOF structure, the aperture of the middle-layer MOF structure is larger than that of the inner-layer MOF structure, and the aperture of the inner-layer MOF structure is larger than that of the middle-layer MOF structure. The silicon content of the inner-layer MOF structure is larger than that of the middle-layer MOF structure, and the silicon content of the middle-layer MOF structure is larger than that of the outer-layer MOF structure. The battery monomer provided by the embodiment of the invention at least can improve the problems of material breakage and structure deterioration caused by stress concentration of the silicon-based negative electrode material of the battery monomer in the charging and discharging process.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a battery cell, a method for preparing the battery cell, a battery device, an electrical device, and an energy storage device. Background Technology

[0002] Silicon anode materials are considered a key component of next-generation lithium-ion batteries due to their high theoretical capacity. However, the significant volume change (up to approximately 300%) of silicon during charge and discharge leads to stress concentration, causing material breakage and structural instability, severely impacting the battery's cycle life. Currently, while silicon-carbon composites and porous silicon can alleviate these problems, it is difficult to ensure good mechanical strength and structural integrity while maintaining a high silicon content.

[0003] Metal-organic framework (MOF) materials, particularly ZIF-8, can provide a buffer space for silicon materials during charge and discharge processes due to their highly ordered porous structure and tunable pore size. However, the uniform pore size of MOF structures limits their stress buffering effect, especially in cases of high silicon content. Summary of the Invention

[0004] This application provides a battery cell, a method for preparing a battery cell, a battery device, an electrical device, and an energy storage device, which at least helps to improve the problem of stress concentration in the silicon-based anode material of the battery cell during the charging and discharging process, leading to material breakage and structural deterioration.

[0005] According to some embodiments of this application, one aspect of this application provides a battery cell, the negative electrode of which includes a silicon-based composite structure. The silicon-based composite structure includes an outer MOF structure, a middle MOF structure, and an inner MOF structure. The outer MOF structure surrounds the outer wall of the middle MOF structure, and the middle MOF structure surrounds the outer wall of the inner MOF structure. The pore size of the outer MOF structure is larger than that of the middle MOF structure, and the pore size of the middle MOF structure is larger than that of the inner MOF structure. The silicon content of the inner MOF structure is greater than that of the middle MOF structure, and the silicon content of the middle MOF structure is greater than that of the outer MOF structure.

[0006] According to some embodiments of this application, another aspect of this application provides a method for preparing a battery cell. The method is used to prepare any of the battery cells described above. The method includes: preparing an outer MOF structure, a middle MOF structure, and an inner MOF structure using a solvothermal growth method. The outer MOF structure surrounds the outer wall of the middle MOF structure, and the middle MOF structure surrounds the outer wall of the inner MOF structure. The pore size of the outer MOF structure is larger than that of the middle MOF structure, and the pore size of the middle MOF structure is larger than that of the inner MOF structure. The silicon content of the inner MOF structure is greater than that of the middle MOF structure, and the silicon content of the middle MOF structure is greater than that of the outer MOF structure.

[0007] According to some embodiments of this application, another aspect of this application provides a battery device, including: any of the battery cells described above, or including battery cells prepared using any of the battery cell preparation methods described above, the battery device including one or more of battery modules, battery packs, and energy storage batteries.

[0008] According to some embodiments of this application, another aspect of this application provides an electrical device, the electrical device including the aforementioned battery device, the battery device being used to provide electrical energy.

[0009] According to some embodiments of this application, another aspect of this application provides an energy storage device, the energy storage device including the aforementioned battery device, the battery device being used to provide electrical energy.

[0010] The technical solution provided in this application has at least the following advantages:

[0011] By designing the silicon-based composite material of the battery cell's negative electrode into three layers—an outer MOF structure, a middle MOF structure, and an inner MOF structure—with pore size decreasing from the outer layer to the inner layer and silicon content increasing from the outer layer to the inner layer, and the middle layer serving as a transition layer, the outer layer's large pore size and low silicon content provide stress buffering, the middle layer balances capacity and structure, and the inner layer's small pore size and high silicon content achieve high capacity output. This dual-gradient design for pore size and silicon content effectively disperses stress concentration in the silicon-based material during charging and discharging, preventing material fracture and improving the cycle stability and structural integrity of the battery cell. This solves the problem of stress concentration leading to material breakage and structural degradation in the silicon-based negative electrode material of existing battery cells during charging and discharging. Attached Figure Description

[0012] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the drawings in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of a silicon-based composite structure of a battery cell negative electrode provided in an embodiment of this application;

[0014] Figure 2 This is a schematic diagram of a process for preparing MOF structures of various layers using a solvothermal growth method according to an embodiment of this application.

[0015] The above figures include the following reference numerals:

[0016] 01. Silicon-based composite structure; 10. Outer MOF structure; 20. Middle MOF structure; 30. Inner MOF structure. Detailed Implementation

[0017] As is known from the background art, existing silicon anode materials are difficult to ensure good mechanical strength and structural integrity while maintaining high silicon content. In order to solve the problem of stress concentration in silicon-based anode materials of battery cells during the charging and discharging process, which leads to material breakage and structural deterioration, the embodiments of this application provide a battery cell, a method for preparing a battery cell, a battery device, an electrical device, and an energy storage device.

[0018] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0019] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0020] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0021] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0022] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0023] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0024] In the accompanying drawings corresponding to the embodiments of this application, the thickness and area of ​​the layers are enlarged for better understanding and ease of description. When describing a component (such as a layer, film, region, or substrate) on or on the surface of another component, the component may be "directly" located on the surface of the other component, or there may be a third component between the two components. Conversely, when describing a component on the surface of another component, or when another component is formed or disposed on the surface of a component, it indicates that there is no third component between the two components. Furthermore, when describing a component as being "generally" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a portion of the edge of the entire surface.

[0025] In the description of the embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and other components may be further included. Furthermore, when a component such as a layer, film, region, or plate is referred to as being "on / located" on another component, it can be "directly on" the other component (i.e., located on the surface of the other component with no other components between them), or another component may be present therein. Moreover, when a component such as a layer, film, region, or plate is "directly located" on another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it indicates that no other components are located therein.

[0026] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "part" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.

[0027] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0028] Figure 1 This is a schematic diagram of a silicon-based composite structure for a single-cell negative electrode provided in an embodiment of this application, as shown below. Figure 1 As shown, the silicon-based composite structure 01 includes an outer MOF structure 10, a middle MOF structure 20, and an inner MOF structure 30. The outer MOF structure surrounds the outer wall of the middle MOF structure, and the middle MOF structure surrounds the outer wall of the inner MOF structure. The pore size of the outer MOF structure is larger than that of the middle MOF structure, the pore size of the middle MOF structure is larger than that of the inner MOF structure, the silicon content of the inner MOF structure is greater than that of the middle MOF structure, and the silicon content of the middle MOF structure is greater than that of the outer MOF structure.

[0029] Specifically, in terms of structural design, the silicon-based composite structure exhibits a gradient distribution in both pore size and silicon content. The pore size gradually decreases from the outer layer to the inner layer, meaning the outer MOF structure has the largest pore size, while the inner MOF structure has the smallest. Simultaneously, the silicon content gradually increases from the outer layer to the inner layer, with the inner MOF structure having the highest silicon content. This design aims to utilize the porosity of MOF materials to accommodate and buffer the volume changes of silicon-based materials during charging and discharging. The large pore size in the outer layer provides sufficient expansion space, the transitional pore size in the middle layer balances capacity and structural stability, and the small pore size in the inner layer confines the silicon material to achieve high capacity output. Furthermore, the clever arrangement of the structure disperses stress, reducing material damage and structural instability. This silicon-based composite structure with gradient pore size and silicon content distribution can improve the cycle stability and energy density of individual battery cells. The large pore size in the outer layer acts as a buffer, absorbing and mitigating the stress generated during silicon expansion; the balance between pore size and silicon content in the middle layer provides sufficient capacity while maintaining structural stability; and the small pore size and high silicon content in the inner layer maximize the battery's capacity output. By controlling the pore size and silicon content of each layer, the stress generated during lithiation and delithiation can be effectively managed and dispersed, thereby avoiding structural damage to the material and extending the battery's lifespan.

[0030] By designing the silicon-based composite material of the battery cell's negative electrode into three layers—an outer MOF structure, a middle MOF structure, and an inner MOF structure—with pore size decreasing from the outer layer to the inner layer and silicon content increasing from the outer layer to the inner layer, and the middle layer serving as a transition layer, the outer layer's large pore size and low silicon content provide stress buffering, the middle layer balances capacity and structure, and the inner layer's small pore size and high silicon content achieve high capacity output. This dual-gradient design for pore size and silicon content effectively disperses stress concentration in the silicon-based material during charging and discharging, preventing material fracture and improving the cycle stability and structural integrity of the battery cell. This solves the problem of stress concentration leading to material breakage and structural degradation in the silicon-based negative electrode material of existing battery cells during charging and discharging.

[0031] In some embodiments of this application, the ligands of the silicon-based composite structure include 2-methylimidazole and benzimidazole, the ligand molar ratio of the outer MOF structure is greater than that of the middle MOF structure, the ligand molar ratio of the middle MOF structure is greater than that of the inner MOF structure, and the ligand molar ratio is the ratio of 2-methylimidazole to benzimidazole.

[0032] Specifically, to optimize the gradient distribution of mechanical properties of the MOF (metal-organic framework) framework and synergize the gradients of pore size and silicon content, this embodiment employs a hybrid ligand modulation strategy to precisely control the mechanical properties of each MOF layer. This strategy primarily relies on the mixed use of 2-methylimidazole and benzimidazole. By adjusting their molar ratio, these two ligands can modulate the gradual distribution of the MOF framework from flexible to rigid, thereby achieving effective stress management and stable structural support.

[0033] Among these, ZIF-8 is the preferred MOF framework, possessing good chemical stability, tunable pore structure, and suitable mechanical properties. ZIF-8 uses zinc ions as the metal center and imidazole ligands as organic linking units; gradient changes in pore size and mechanical properties can be achieved by controlling the type and ratio of ligands. Besides ZIF-8, other MOF materials with tunable pore size and structural stability can also be selected, such as ZIF-67, bimetallic MOFs of ZIF-8 and ZIF-67, UiO-66, MIL-101, and MIL-53. These materials share common characteristics: tunable pore structure, good chemical and thermal stability, and the ability to optimize performance through ligand or metal center control.

[0034] The outer MOF structure employs a high proportion of 2-methylimidazole, with a ligand molar ratio set between 3:1 and 2.5:1 (2-methylimidazole:benzimidazole) to ensure the MOF framework has a low Young's modulus (approximately 2 to 4 GPa). Young's modulus is a physical quantity reflecting the rigidity of a material, which gives the outer MOF structure excellent elasticity, enabling it to effectively absorb external stress and adapt to the volume expansion of silicon materials during charging and discharging, thus acting as the first line of defense to reduce stress concentration. The middle MOF structure, by adjusting the ligand molar ratio to between 2:1 and 1.5:1 (2-methylimidazole:benzimidazole), balances the rigidity and flexibility of the framework, with a Young's modulus of approximately 4 to 6 GPa. This design maintains structural stability while ensuring sufficient porosity buffering capacity, achieving a smooth transition in mechanical properties from the outer to the inner layer and avoiding stress concentration at the interface of materials with different mechanical properties. By increasing the proportion of benzimidazole in the inner MOF structure, with its ligand molar ratio set to 1:1 to 1:1.5 (2-methylimidazole:benzimidazole), the Young's modulus of the MOF framework is increased to 6 to 8 GPa, exhibiting high rigidity. The high rigidity of the inner framework not only helps maintain the integrity of the inner structure but also provides effective mechanical constraints on high-silicon content materials, limiting the excessive expansion of silicon particles during lithiation, thereby ensuring the structural stability and cycle performance of the material.

[0035] This ligand gradient, combined with the pore size and silicon content gradients, forms a multi-layered mechanical design that is "flexible on the outside and rigid on the inside." The large pore size, low silicon content, and low modulus of the outer layer provide ample elastic buffering; the transition parameters of the middle layer achieve a smooth connection of mechanical properties; and the small pore size, high silicon content, and high modulus of the inner layer ensure high capacity output while suppressing excessive silicon expansion through confinement effects and mechanical constraints. This multi-dimensional gradient synergistic design is one of the core mechanisms by which this application achieves stress dispersion and improved cycle stability.

[0036] Besides 2-methylimidazole and benzimidazole, other imidazole ligands or heterocyclic ligands can be used to achieve similar mechanical property modulation effects, such as imidazoles with different alkyl substitutions, carboxyl-containing imidazole derivatives, and pyridine ligands. The selection of ligands should meet the requirements of being able to form stable coordination with zinc ions or other metal ions, being able to regulate the pore size and mechanical properties of MOFs, and maintaining stability under subsequent process conditions.

[0037] By changing the molar ratio of 2-methylimidazole to benzimidazole in different layers of MOF structures, the balance between rigidity and flexibility of the MOF framework can be adjusted. A higher ligand molar ratio in the outer layer provides better flexibility to absorb external stress and adapt to volume changes; a moderate ligand molar ratio in the middle layer achieves a transition between rigidity and flexibility; and a lower ligand molar ratio in the inner layer helps maintain the structural integrity of the inner layer and provides mechanical constraint on the confined silicon.

[0038] In some embodiments of this application, the mass ratio or thickness ratio between the outer MOF structure, the middle MOF structure and the inner MOF structure is in the range of (1-3):(1-2):(1-2).

[0039] Specifically, the mass ratio or thickness ratio between the outer, middle, and inner MOF structures is in the range of (1-3):(1-2):(1-2). This range means that the outer MOF structure can be thicker or have a greater mass than the middle and inner layers, with a maximum ratio of 3 times and a minimum of 1. The ratio between the middle and inner layers is relatively close, differing by a maximum of 2 times, but can also be the same. The main purpose of this design is to coordinate with the gradient distribution of pore size and silicon content, ensuring that the composite structure can effectively disperse and buffer the stress generated during lithiation and delithiation, while ensuring efficient utilization of silicon materials and structural stability. In a preferred embodiment, the thickness of the three MOF structures is approximately equal, i.e., each layer is approximately 500 nm thick, in which case the mass ratio is approximately 1:1:1. In another embodiment, the outer layer thickness can be appropriately increased to provide more sufficient external buffering, in which case the thickness ratio can be 2:1:1 or 1.5:1:1. The selection of the interlayer ratio should comprehensively consider the overall silicon content, stress distribution, and the feasibility of the fabrication process.

[0040] Based on the aforementioned layered silicon content and interlayer ratio, the total silicon content (relative to the mass fraction of the entire composite particle) of the composite material ranges from 35 to 65 wt%, preferably 40 to 60 wt%, more preferably 45 to 55 wt%, and most preferably 48 to 52 wt%. The total silicon content is calculated by weighting the silicon content of each layer according to the interlayer mass ratio. For example, when the interlayer mass ratio is 1:1:1, and the silicon contents of each layer are 35 wt%, 55 wt%, and 75 wt%, respectively, the total silicon content is approximately 55 wt%. A higher total silicon content is beneficial for improving the specific capacity of the anode material.

[0041] The layered silicon content refers to the mass fraction relative to that layer of the composite material, determined through individual analysis of each ring or layer. The total silicon content refers to the mass fraction relative to the entire composite particle, calculated by weighting the silicon content of each layer by mass ratio or by directly measuring the entire sample.

[0042] By limiting the mass ratio or thickness ratio between the layers of the MOF structure, combined with gradient pore size and silicon content distribution, a multi-level and multi-dimensional structural control strategy is formed, which ensures the overall structural balance and optimization of the composite material. This proportional control helps maintain the gradient characteristics of the material, optimizes the function of each layer, and thus improves the overall performance of the battery cell.

[0043] In some embodiments of this application, the outer MOF structure, the middle MOF structure, and the inner MOF structure all include channels, and the negative electrode of the battery cell also includes an aluminum oxide protective layer, which is located on the inner wall of the channels.

[0044] Specifically, all three-layer MOF structures include channels. Their highly ordered pore structure can provide space for the storage and transport of lithium ions, while also supporting the embedding and confinement of silicon materials, ensuring that volume changes during charging and discharging are managed and avoiding structural damage.

[0045] An alumina protective layer is located on the inner wall of the pores, a design that enhances the chemical stability and mechanical strength of the MOF framework. The thickness of the alumina protective layer ranges from 0.5 to 5 nm, preferably 1 to 2 nm, more preferably 1.2 to 1.8 nm, and most preferably around 1.5 nm. This thickness range takes into account both the protective effect and the preservation of pore space. A protective layer that is too thin cannot completely cover the MOF surface or provide sufficient protection, while a protective layer that is too thick will significantly reduce the pore size, decrease the effective pore volume, and increase ion transport resistance. A thickness of 1 to 2 nm allows for the formation of a continuous inorganic protective layer on the MOF surface without excessively sacrificing pore space.

[0046] The alumina protective layer is located on the inner wall of the pores in each MOF structure. On the one hand, the inorganic alumina layer significantly improves the mechanical strength of the MOF framework, especially in dealing with the high-temperature challenges of subsequent chemical vapor deposition (CVD) filling of silicon materials, and in terms of structural stability during charge-discharge cycles, preventing the MOF framework from breaking and the silicon material from fracturing. On the other hand, as a barrier layer, the alumina protective layer can, to some extent, regulate the diffusion and deposition behavior of silicon precursors in different pore size regions, thereby achieving a gradient distribution of silicon content. This helps to evenly disperse stress and avoid structural damage caused by local stress concentration. Furthermore, the alumina protective layer can improve the interfacial compatibility between silicon and MOF and, to some extent, inhibit the erosion of MOF by the electrolyte. In addition, as a solid electrolyte material, alumina can provide lithium-ion transport channels, reducing electrolyte blockage of the pores, thereby optimizing lithium-ion transport efficiency and helping to improve the rate performance and extend the cycle life of the battery.

[0047] Besides alumina, other suitable atomic layer deposition materials can also be selected, such as metal oxides like titanium oxide, zirconium oxide, hafnium oxide, and zinc oxide, or materials like nitrides and carbides. The selection of materials should consider factors such as their chemical stability, mechanical properties, compatibility with MOFs and silicon, and the maturity of the atomic layer deposition process.

[0048] Furthermore, the negative electrode of the aforementioned battery cell also includes a nano-silicon layer, which is located within the aforementioned pores.

[0049] Specifically, the nano-silicon layer is located within the pores of each MOF structure. By utilizing the pore size and structural characteristics of MOF, the silicon material can be effectively confined, reducing the stress caused by its volume changes, thereby avoiding material breakage and loss of electrical contact.

[0050] The nano-silicon layer, located within the pores, allows for full utilization of the high specific surface area and ordered pore structure of the MOF material, ensuring uniform expansion and contraction of the silicon during charge and discharge. This is crucial for maintaining the structural integrity of the material and improving cycle stability. Furthermore, the synergistic effect of the alumina protective layer on the inner wall of the MOF pores and the nano-silicon layer not only enhances the mechanical strength of the MOF framework but also improves the interfacial bonding between silicon and the MOF, protecting the silicon layer from electrolyte corrosion.

[0051] In some embodiments of this application, the battery cell further includes a conductive layer located on the surface of the outer MOF structure away from the middle MOF structure.

[0052] Specifically, MOF materials themselves have low electronic conductivity. To ensure electron transport in the electrodes, conductivity enhancement treatment is required. One approach is to coat the outer surface of the composite particles (i.e., the surface of the outer MOF structure far from the middle MOF structure) with a conductive layer. This conductive layer can be a carbon coating, formed on the surface of the composite particles through methods such as chemical vapor deposition, pyrolysis of organic matter, or hydrothermal carbonization, with a thickness ranging from 3 to 15 nm, preferably 5 to 10 nm. The conductive carbon layer should be uniform and dense, providing electron transport channels without excessively increasing particle size and mass. Alternatively, conductive polymers such as polypyrrole, polyaniline, and polythiophene can be used for coating. Conductive polymers have a certain degree of flexibility, which helps to adapt to volume changes.

[0053] By adding a conductive layer to the outermost MOF structure, the problem of poor conductivity of MOF materials is not only solved, but the charge transport path of silicon-based composite structures is also optimized, avoiding the interruption of electron transport paths in high-stress regions, and further improving the electrochemical performance of the battery cells, especially the rate performance and cycle stability.

[0054] This application provides several optional conductivity enhancement schemes, which can be used individually or in combination. In addition to the above schemes, another approach is to perform localized low-temperature carbonization of the MOF, converting some organic ligands into conductive carbon while preserving the MOF's pore structure and gradient characteristics. The carbonization temperature is generally controlled between 300 and 500°C, and the time is 1 to 4 hours, carried out in an inert atmosphere. By controlling the degree of carbonization, a conductive carbon network can be formed in the MOF framework without completely destroying the MOF's crystal structure and pore characteristics, achieving a balance between conductivity and structural function.

[0055] In the electrode fabrication stage, adding conductive agents is also an effective way to improve the overall conductivity of the electrode. Conductive agents can be materials such as carbon black, carbon nanotubes, and graphene, with a dosage range of 3 to 15 wt% relative to the active material mass, preferably 5 to 10 wt%. Binders can be composite systems of polyacrylic acid, sodium carboxymethyl cellulose and styrene-butadiene rubber, polyimide, etc., with a dosage range of 5 to 15 wt%, preferably 8 to 12 wt%. Appropriate amounts of conductive agents and binders ensure electron and ion transport in the electrode without excessively reducing the proportion of active material.

[0056] In some embodiments of this application, the pore size range of the outer MOF structure is 10-30 nm, the pore size range of the middle MOF structure is 6-20 nm, and the pore size range of the inner MOF structure is 2-10 nm.

[0057] Specifically, the pore size range of the outer MOF structure is 10-30 nm, preferably 12-25 nm, more preferably 15-20 nm, and most preferably 16-18 nm. This range is chosen by comprehensively considering the volume expansion of silicon, the need for buffer space, and the structural stability of the MOF framework. The relatively large pore size of the outer layer is designed primarily to provide sufficient buffer space to accommodate the significant volume changes of silicon during charging and discharging. This large pore size design allows the expansion of silicon during initial lithiation to be alleviated within the pores of the outer MOF, avoiding structural damage caused by instantaneous stress concentration, thereby improving the cycle stability of the material and the overall structural durability.

[0058] The pore size range of the middle MOF structure is 6-20 nm, preferably 7-14 nm, more preferably 8-12 nm, and most preferably 9-11 nm. As a transition layer, the middle layer's pore size must be smaller than the outer layer to achieve a gradient, yet larger than the inner layer to maintain a certain buffering capacity. The pore size design of the middle MOF structure is a transition region, between the large pore size of the outer layer and the small pore size of the inner layer. This range aims to balance the material's capacity contribution with structural stability. The smaller pore size of the middle layer compared to the outer layer helps limit the expansion and migration range of silicon, while the relatively large pore size still provides some buffering and prevents stress concentration. The moderate pore size of the middle layer ensures that the material contributes capacity while maintaining appropriate structural elasticity and mechanical strength.

[0059] The pore size of the inner MOF structure ranges from 2-10 nm, preferably 2.5-7 nm, more preferably 3-5 nm, and most preferably 3.5-4.5 nm. The small pore size of the inner layer creates a confinement effect on the silicon material, suppressing excessive agglomeration and long-range migration of silicon particles. The pore size of the inner MOF structure is designed to be as small as possible, consistent with its functional positioning. The small pore size of the inner layer gives it a stronger confinement effect on the silicon material, effectively suppressing excessive expansion and agglomeration of silicon particles and reducing structural changes during cycling. The small pore size design of the inner layer also promotes silicon deposition in a more confined environment. This confinement effect helps improve the stability and capacity retention of the silicon material, while ensuring a high silicon content, thereby achieving the goal of high energy density.

[0060] It should be noted that the pore size in this application refers to the equivalent mesopore size of the MOF framework measured by nitrogen adsorption-desorption before silicon introduction, rather than the inherent micropore size of the MOF. The inherent micropore cage diameter of ZIF-8 is approximately 1.16 nm, but mesoporous structures can be formed within the MOF framework through ligand mixing and adjusting synthesis conditions. These mesopores are the primary spaces for silicon deposition. After silicon filling, the pore size will decrease accordingly. The residual pore size can be measured using the same method as a reference indicator for process control or performance characterization, but the determination of the dual gradient of pore size and silicon content is mainly based on the pore size before silicon filling.

[0061] By setting the pore size range of each MOF structure layer, this application aims to construct a pore size gradient that decreases step by step from the outside to the inside. This design can effectively disperse and alleviate the stress generated during charging and discharging, reduce mechanical damage to the material, and optimize silicon embedding and capacity output, thereby achieving the dual goals of high energy density and long cycle life.

[0062] In some embodiments of this application, the silicon content of the outer MOF structure is 20-45 wt%, the silicon content of the middle MOF structure is 45-65 wt%, and the silicon content of the inner MOF structure is 60-85 wt%.

[0063] Specifically, the silicon content (by mass fraction of the composite material) of the outer MOF structure ranges from 20-45 wt%, preferably 30-40 wt%, more preferably 32-38 wt%, and most preferably 34-36 wt%. The lower silicon content ensures sufficient porosity in the outer layer to accommodate the stress transmitted from the expansion of the inner silicon layer, while the silicon in the outer layer itself also contributes a certain specific capacity. The thickness of the outer layer ranges from 300-800 nm, preferably 400-700 nm, and more preferably 500 ± 50 nm. The low silicon content design of the outer MOF structure aims to ensure sufficient porosity to accommodate the stress generated during the expansion of the inner silicon layer. Lower silicon content means more space for stress buffering, reducing the risk of structural failure.

[0064] The silicon content of the middle MOF structure ranges from 45-65 wt%, preferably 50-60 wt%, more preferably 52-58 wt%, and most preferably 54-56 wt%. The silicon content of the middle MOF structure is between that of the outer and inner layers, providing a high capacity contribution while maintaining moderate structural stability. The thickness of the middle layer is the same as that of the outer layer, ranging from 300-800 nm, preferably 500 ± 50 nm. The increased silicon content of the middle MOF structure reflects the need to improve battery capacity while providing good stress buffering. This layer of MOF structure not only needs sufficient porosity to alleviate pressure from the inner layer but also needs to support more silicon material to balance the relationship between capacity contribution and structural stability. The moderate silicon content of the middle layer allows it to maintain reasonable structural rigidity while contributing to capacity, avoiding a series of problems caused by excessive volume changes.

[0065] The silicon content of the inner MOF structure ranges from 60-85 wt%, preferably 70-80 wt%, more preferably 72-78 wt%, and most preferably 74-76 wt%. The high silicon content of the inner layer is the main source of the overall specific capacity. Through gradient structure design, the stress generated by the high silicon content in the inner layer can be buffered stepwise through the middle and outer layers without directly affecting the outermost interface. The thickness of the inner layer also ranges from 300-800 nm, preferably 500 ± 50 nm. The highest silicon content in the inner MOF structure means it can store more lithium ions, thereby increasing the overall battery capacity. However, high silicon content also leads to greater volume changes. Therefore, the design of small pore size and high mechanical modulus in the inner MOF is particularly crucial. They work together to limit silicon expansion, reduce internal stress, and ensure that the structural integrity and cycle stability of the material are not affected even with high silicon content.

[0066] By setting a silicon content gradient in each MOF layer, this application aims to construct a composite structure with a flexible outer layer and a rigid inner layer to optimize the application of silicon-based anode materials in lithium-ion batteries. The outer MOF layer with a lower silicon content provides stress buffering, the middle MOF layer with a moderate silicon content balances capacity and structural stability, while the inner MOF layer with a high silicon content focuses on achieving the battery's high energy density. This gradient design not only improves the battery's initial coulombic efficiency and overall capacity but also significantly enhances the battery's cycle stability and structural safety.

[0067] To achieve quantitative determination of the gradient structure, this application employs a three-ring measurement criterion. The composite particles are divided into three equivalent rings based on radial distance (the straight-line distance from the outermost surface of the particle to its geometric center): the outer ring represents 0-30% of the radial distance, the middle ring represents 30-70% of the radial distance, and the inner ring represents 70-100% of the radial distance. The pore size and silicon content of each ring are measured separately. Pore size is determined using a 77K nitrogen adsorption-desorption isotherm, and the equivalent mesopore size distribution is obtained by inversion using NLDFT or BJH methods. The median pore size of each ring is taken as the representative pore size of that layer. Silicon content is determined by line scanning using focused ion beam scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, or by inductively coupled plasma atomic emission spectrometry (ICP-AES) after slicing the rings. The median silicon mass fraction of each ring is taken as the representative silicon content of that layer. When the outer layer pore diameter is greater than the middle layer pore diameter, the middle layer pore diameter is greater than the inner layer pore diameter, and the outer layer silicon content is less than the middle layer silicon content, and the middle layer silicon content is less than the inner layer silicon content, the composite material is determined to have the radial double gradient structure of this application.

[0068] The metal source for MOFs can be zinc salts such as zinc acetate, zinc nitrate, and zinc chloride, or other metal salts such as cobalt salts and nickel salts, selected according to the target MOF structure. The synthesis solvent is generally methanol, ethanol, dimethylformamide, water, or a mixture thereof. Synthesis conditions include solvothermal methods, room temperature stirring methods, and microwave-assisted synthesis methods, adjusted according to the MOF type and desired pore size.

[0069] Pore ​​size refers to the equivalent mesopore size obtained by measuring the nitrogen adsorption-desorption isotherm at 77 K and inverting it using NLDFT or BJH methods. Methods for determining silicon content include energy-dispersive X-ray spectroscopy, inductively coupled plasma atomic emission spectroscopy, and thermogravimetric analysis. Mechanical modulus is determined by nanoindentation or atomic force microscopy. All measurements should be performed after appropriate sample pretreatment to ensure the accuracy and comparability of the data.

[0070] This invention provides a method for preparing a battery cell. The method is used to prepare any of the aforementioned battery cells. The method includes: preparing an outer MOF structure, a middle MOF structure, and an inner MOF structure using a solvothermal growth method. The outer MOF structure surrounds the outer wall of the middle MOF structure, and the middle MOF structure surrounds the outer wall of the inner MOF structure. The pore size of the outer MOF structure is larger than that of the middle MOF structure, and the pore size of the middle MOF structure is larger than that of the inner MOF structure. The silicon content of the inner MOF structure is greater than that of the middle MOF structure, and the silicon content of the middle MOF structure is greater than that of the outer MOF structure.

[0071] Specifically, a solvothermal growth method was used to prepare outer, middle, and inner MOF structures. This method achieves a radial gradient structure by sequentially growing MOF layers with different pore sizes on the same particle by changing the ligand composition and reaction conditions during the growth of each layer. The solvothermal growth method constructs the composite structure layer by layer using solvothermal synthesis technology. Initially, a large-pore outer MOF structure is formed. Subsequently, by adjusting the reaction conditions and ligand ratio, a smaller-pore middle MOF structure is grown on its surface. Finally, the inner MOF structure with the smallest pore size and the highest silicon content is formed. Each MOF structure is grown on the basis of the previous layer, ensuring seamless connection and chemical bond formation between layers, thus improving the integrity and stability of the material.

[0072] Through a solvothermal growth method, the pore size range of the outer, middle, and inner MOF structures gradually decreases, while the silicon content gradually increases. This unique gradient structure design aims to achieve effective stress dispersion and optimal utilization of silicon materials, thereby improving the capacity contribution and cycle stability of the battery cells.

[0073] The aforementioned dual-gradient design of pore size and silicon content can be achieved through either a discrete layered approach or a continuous gradient approach. The discrete layered approach refers to a relatively defined interface between layers, with pore size and silicon content changing in a stepwise manner. The layers are chemically bonded through coordination bonds, providing good controllability and facilitating structural characterization. The continuous gradient approach refers to a smooth transition in pore size and silicon content from the outside in, without defined interlayer interfaces. This is achieved by gradually changing the growth conditions, resulting in smoother stress transfer. This application prefers the discrete layered approach because the layer-by-layer solvothermal growth method allows for more precise control, the interlayer coordination bonds ensure structural stability, and it facilitates verification of the gradient structure formation using techniques such as focused ion beam scanning electron microscopy and transmission electron microscopy.

[0074] A three-layer MOF composite anode was precisely fabricated using a solvothermal growth method. The anode consists of an outer MOF layer, a middle MOF layer, and an inner MOF layer. The pore size decreases from the outer layer to the inner layer, while the silicon content increases from the outer layer to the inner layer. The middle layer serves as a transition layer. The outer layer's large pore size and low silicon content provide stress buffering, the middle layer balances capacity and structure, and the inner layer's small pore size and high silicon content achieve high capacity output. This method ensures a dual-gradient design for pore size and silicon content, effectively dispersing stress concentration in the silicon-based material during charge and discharge, preventing material fracture, and improving the cycle stability and structural integrity of the battery cell. This solves the problem of stress concentration leading to material breakage and structural degradation in silicon-based anode materials during charge and discharge in existing battery technologies.

[0075] In some embodiments of this application, an outer layer MOF structure, a middle layer MOF structure, and an inner layer MOF structure are prepared using a solvothermal growth method, such as... Figure 2 As shown, it includes the following steps:

[0076] Step S201: Under preset growth conditions, the zinc source solution and the first ligand solution are mixed to react and form a cyclic outer MOF structure. The first ligand solution is a mixed solution obtained by dissolving 2-methylimidazole and benzimidazole in a solvent after mixing them according to the first preset ligand molar ratio. The preset growth conditions include: a reaction temperature of 120 to 140°C and a reaction time of 12 to 24 hours.

[0077] Specifically, the growth of the outer MOF structure aims to form a large-pore MOF. A zinc source (such as zinc acetate) is dissolved in a synthesis solvent such as methanol to prepare a solution with a concentration of 0.1 to 0.5 mol / L, i.e., the zinc source solution. 2-Methylimidazole and benzimidazole are mixed and dissolved in a solvent according to a first predetermined ligand molar ratio of 3:1 to 2.5:1, yielding a first ligand solution with a total concentration of 0.2 to 1.0 mol / L. The zinc source solution and the first ligand solution are mixed and transferred to a reaction vessel, where they are reacted at 120 to 140°C for 12 to 24 hours. The choice of reaction temperature and time affects the crystallinity and pore size of the MOF; higher temperatures and longer reaction times favor the formation of MOFs with better crystallinity and larger pore sizes. After the reaction, the product is collected, washed several times with a solvent to remove unreacted precursors and solvent molecules, and then vacuum dried at 60 to 80°C. This process forms an outer MOF structure with a large pore size.

[0078] Step S202: The outer MOF structure is placed in the mixture of the zinc source solution and the second ligand solution to form a ring-shaped middle MOF structure on the inner wall of the outer MOF structure according to the preset growth conditions. The second ligand solution is a mixed solution obtained by dissolving 2-methylimidazole and benzimidazole in the solvent according to the second preset ligand molar ratio.

[0079] Specifically, the growth of the middle-layer MOF structure involves continuing to grow a medium-pore-size MOF layer on the surface of the outer MOF particles. The formed outer MOF structure is then re-immersed in a mixture of a zinc source solution and a second ligand solution (also a mixture of 2-methylimidazole and benzimidazole dissolved in a solvent, but with a lower molar ratio than the first preset ligand). The second preset ligand molar ratio is 2:1 to 1.5:1. Other conditions, such as zinc source concentration, total ligand concentration, reaction temperature, and time, are similar to those in the first step or adjusted appropriately according to the target pore size. The change in the ligand ratio results in a MOF layer with different pore size characteristics than the outer layer. After the reaction, the layer is washed and dried to obtain composite particles of the outer and middle layers, i.e., the middle-layer MOF structure.

[0080] Step S203: The above-mentioned intermediate MOF structure is placed in the mixture of the above-mentioned zinc source solution and the third ligand solution to form a ring-shaped inner MOF structure on the inner wall of the above-mentioned intermediate MOF structure according to the above-mentioned preset growth conditions. The above-mentioned third ligand solution is a mixed solution obtained by dissolving the above-mentioned 2-methylimidazole and the above-mentioned benzimidazole in the above-mentioned solvent after mixing them according to the third preset ligand molar ratio.

[0081] Wherein, the first preset ligand molar ratio is greater than the second preset ligand molar ratio, and the second preset ligand molar ratio is greater than the third preset ligand molar ratio.

[0082] Specifically, the growth of the inner MOF structure follows a similar process, using particles with two existing layers as cores, and reacting again under the same growth conditions in a mixture containing a zinc source and ligands in a molar ratio (a third preset ligand molar ratio, lower than the second preset ligand molar ratio, implying higher rigidity). The resulting inner layer has a relatively small pore size and a high benzimidazole ratio, corresponding to a higher mechanical modulus. After three layer-by-layer growths, a MOF framework with radially three-layered gradient pore sizes is finally obtained.

[0083] The decreasing ligand molar ratios, where the first preset ligand molar ratio is greater than the second preset ligand molar ratio, and the second preset ligand molar ratio is greater than the third preset ligand molar ratio, result in a gradient distribution of the mechanical properties of the MOF structure. The outer MOF is more flexible, while the inner MOF is more rigid, forming a structural characteristic of being flexible on the outside and rigid on the inside, providing an ideal stress dispersion and buffering system for the material.

[0084] Key control points to consider during layer-by-layer growth include: First, the growth time and temperature of each layer need precise control. Too short a time or too low a temperature will result in incomplete or uneven growth of that layer, while too long a time or too high a temperature will cause structural changes in the existing layers. Second, the coordination connections between layers need to be ensured. This requires appropriate activation treatments of existing layers before the next layer is grown, such as solvent displacement or low-temperature annealing, to maintain the activity of surface coordination sites. Third, the gradient change in ligand ratio should be gradual rather than abrupt to ensure the matching of mechanical properties and interfacial bonding strength between layers.

[0085] The resulting MOF structure exhibits a ring-like characteristic. This morphology can be either a circular ring structure or extended to non-circular geometric shapes with ring-like properties, such as square rings or other polygonal ring structures. Designing the MOF structure as ring-like, whether circular or not, aims to maximize the surface area and pore volume of the material, thereby improving the lithium-ion storage efficiency and the overall performance of the battery.

[0086] A solvothermal growth method was used to precisely control the outer, middle, and inner layers of MOF composite materials, constructing a silicon composite anode material with a ring structure and a radially gradient distribution of pore size and silicon content. By mixing 2-methylimidazole and benzimidazole in different molar ratios, MOF composite particles with a flexible outer layer and a rigid inner layer were prepared layer by layer through a solvothermal reaction under predetermined temperature and time conditions. The outer layer had large pore size and low silicon content, the middle layer had moderate pore size and relatively high silicon content, and the inner layer had small pore size and the highest silicon content. By optimizing the decreasing sequence of ligand molar ratios, the stress of the silicon-based material during charge and discharge was effectively dispersed, and the capacity contribution and cycle stability of the composite material were significantly improved.

[0087] In some embodiments of this application, after preparing the outer MOF structure, the middle MOF structure, and the inner MOF structure using a solvothermal growth method, the method further includes: depositing an alumina protective layer on the inner wall of the pores of the outer MOF structure, the middle MOF structure, and the inner MOF structure; and filling the pores of the outer MOF structure, the middle MOF structure, and the inner MOF structure with the deposited alumina protective layer into a nano-silicon layer.

[0088] Specifically, after constructing the three-layer gradient MOF framework, atomic layer deposition (ALD) is performed to form an alumina protective layer on the inner walls of the pores. ALD is performed using standard ALD equipment and processes. The MOF sample is placed in the ALD reaction chamber under vacuum or an inert atmosphere. The advantage of ALD is its ability to uniformly cover the complex pore structure of the MOF, achieving comprehensive protection of the inner walls. Because ALD is a self-limiting reaction, the film thickness can be precisely controlled by the number of cycles, resulting in a dense and uniform film. After deposition, the sample is cooled to room temperature in an inert atmosphere and then removed for use.

[0089] Following the deposition of the alumina protective layer, a nano-silicon layer was selectively filled into the inner walls of the pores of each MOF structure using chemical vapor deposition (CVD). This process requires precise control of temperature, pressure, and precursor flow rate to ensure uniform silicon deposition within the MOF pores, forming a flexible outer structure with a rigid inner structure, while simultaneously achieving a gradient distribution of silicon content. The introduction of nano-silicon not only improves the specific capacity of the composite material but also effectively manages the stress issues of silicon-based materials during charge and discharge processes through the confinement effect of the MOF pores and the stability of the alumina protective layer, thereby enhancing the overall performance and cycle life of the battery.

[0090] By depositing a nanoscale alumina protective layer on the inner walls of the pores in the outer, middle, and inner MOF structures, the mechanical strength and thermal stability of the MOF framework were significantly enhanced, ensuring structural integrity and performance consistency during subsequent high-temperature silicon filling and long-term electrochemical cycling. Furthermore, this improved the interfacial compatibility between the MOF and silicon, reduced side reactions, and lowered interfacial impedance. Subsequently, chemical vapor deposition was used to fill the nanoscale silicon layer, achieving a selective gradient distribution of silicon within the MOF pores. This design effectively managed the volumetric expansion stress of silicon during charge and discharge, preventing material pulverization and structural degradation while maintaining high capacity output.

[0091] Further, depositing an alumina protective layer on the inner walls of the pores of the outer MOF structure, the middle MOF structure, and the inner MOF structure includes: placing the outer MOF structure, the middle MOF structure, and the inner MOF structure in an atomic layer deposition reaction chamber; a first processing step, introducing trimethylaluminum into the atomic layer deposition reaction chamber to adsorb the trimethylaluminum onto the inner walls of the pores, wherein the pulse time of the first processing step is the first pulse time; a first purging step, purging the atomic layer deposition reaction chamber with nitrogen or argon to remove unreacted trimethylaluminum and byproducts, wherein the purging time of the first purging step is the first purging time; and a second processing step, introducing water vapor into the atomic layer deposition reaction chamber to react the water vapor with the trimethylaluminum adsorbed onto the inner walls of the pores to generate A. The pulse time of the second processing step is the second pulse time; the second purging step involves purging the atomic layer deposition reaction chamber with nitrogen or argon to remove unreacted water vapor and byproducts, and the purging time of the second purging step is the second purging time; the first processing step, the first purging step, the second processing step, and the second purging step are repeated a preset number of times to deposit the alumina protective layer on the inner walls of the pores of the outer MOF structure, the middle MOF structure, and the inner MOF structure, the preset number of times being determined based on the target thickness of the alumina protective layer, and the first pulse time, the second pulse time, the first purging time, and the second purging time being determined based on the reaction conditions in the atomic layer deposition reaction chamber.

[0092] The above series of steps constitutes atomic layer deposition (ALD) to form an alumina protective layer on the inner wall of the pores. ALD is performed using standard ALD equipment and processes. The MOF sample is placed in the ALD reaction chamber and the deposition is carried out under vacuum or an inert atmosphere. Alumina deposition typically uses trimethylaluminum and water as precursors, achieving layer-by-layer growth through alternating pulses and reactions. The deposition temperature is controlled between 100 and 200°C, preferably 150 ± 10°C. This temperature ensures sufficient reaction of the precursor and compactness of the alumina without causing significant thermal damage to the MOF framework. Each deposition cycle includes four steps: trimethylaluminum pulse, nitrogen or argon purging, water vapor pulse, and re-purging (i.e., first treatment step, first purging step, second treatment step, and second purging step). The first and second pulse times are typically 0.1 to 1 second, and the first and second purging times are 5 to 20 seconds to ensure sufficient reaction of the precursor and complete removal of unreacted materials. The number of deposition cycles is determined based on the target thickness. Each cycle deposits approximately 0.1 to 0.2 nm of alumina, and 50 to 100 cycles can yield a thickness of 1 to 2 nm.

[0093] Specifically, firstly, pre-constructed particles containing outer, middle, and inner MOF structures are placed into an atomic layer deposition (ALD) reaction chamber. ALD is a technique for depositing atomic layer films layer by layer on a material surface. In the first processing step, trimethylaluminum (TMA) is introduced into the reaction chamber. TMA contacts and adsorbs onto the active sites on the inner walls of the MOF channels, laying the foundation for subsequent alumina formation. The first pulse time is a key parameter controlling the TMA supply and is typically adjusted based on the deposition rate and specific conditions of the reaction chamber. In the first purging step, nitrogen or argon is used to purge the reaction chamber to remove unreacted TMA and any byproducts, such as volatile organic compounds. The first purging time ensures the cleanliness of the chamber and prevents unreacted TMA from reacting with subsequent water vapor, which could affect the quality of the alumina film. In the second processing step, water vapor is introduced into the reaction chamber. The water vapor reacts with the TMA adsorbed on the inner walls of the channels to generate alumina (Al). The second pulse time controls the water vapor supply, affecting the deposition rate and quality of alumina. In the second purging step, nitrogen or argon is used again to remove unreacted water vapor and byproducts (methane). The second purging time ensures that no residual water vapor remains in the reaction chamber, avoiding unnecessary reactions in subsequent operations.

[0094] The above steps constitute a complete ALD deposition cycle. Depending on the target thickness of the alumina protective layer, a certain number of cycles need to be repeated. Each cycle adds a layer of alumina to the inner wall of the pores. By controlling the number of cycles, the final thickness of the alumina protective layer can be precisely controlled. The specific values ​​of the first pulse time, second pulse time, first purge time, and second purge time are adjusted according to the actual reaction conditions in the ALD reaction chamber, including substrate characteristics and reaction conditions, to achieve the best deposition effect and target thickness.

[0095] This series of steps ensures that the alumina protective layer is deposited uniformly and precisely on the inner wall of the MOF channels, providing the necessary physical and chemical protection, helping to maintain the integrity and stability of the MOF structure, and providing a stable foundation for the subsequent chemical vapor deposition (CVD) silicon filling steps.

[0096] Further, filling the pores of the outer MOF structure, the middle MOF structure, and the inner MOF structure with the aforementioned alumina protective layer into a nano-silicon layer includes: placing the outer MOF structure, the middle MOF structure, and the inner MOF structure with the aforementioned alumina protective layer in a chemical vapor deposition reaction tube, evacuating the tube, and then introducing an inert carrier gas; introducing silane gas into the chemical vapor deposition reaction tube at a preset flow rate, the preset flow rate being in the range of 10 to 50 standard cubic centimeters per minute; controlling the temperature of the chemical vapor deposition reaction tube to a target deposition temperature, and at the target deposition temperature, depositing the nano-silicon layer on the inner walls of the pores of the outer MOF structure, the middle MOF structure, and the inner MOF structure to obtain the silicon-based composite structure of the battery cell, wherein the deposition time of the nano-silicon is determined according to the target silicon content.

[0097] Specifically, silicon filling is achieved using chemical vapor deposition (CVD) with silane as a precursor. The MOF sample treated with ALD (atomic layer deposition) (i.e., the outer, middle, and inner MOF structures with deposited alumina protective layers) is placed in a CVD reaction tube. After evacuation, an inert carrier gas, such as argon or nitrogen, is introduced. Silane gas is then introduced into the reaction tube at a preset flow rate, ranging from 10 to 50 standard cubic centimeters per minute. The reaction tube temperature is controlled to reach the target deposition temperature, ranging from 450 to 550°C, with the heating rate controlled below 5°C / min to avoid thermal shock to the MOF due to rapid heating.

[0098] Silicon deposition is carried out at the target deposition temperature for a certain period of time, which is determined according to the target silicon content and is generally 30 minutes to 1 hour. Silane undergoes pyrolysis at high temperature to produce elemental silicon, which is deposited on the inner walls and pores of the MOF channels. An appropriate vacuum or low-pressure environment is maintained during the reaction, with a pressure range of 0.1 to 10 Torr. Low pressure is beneficial for the diffusion and uniform deposition of the gas precursor. After deposition, the silane supply is stopped, and the temperature is slowly lowered to room temperature under carrier gas protection, with the cooling rate also controlled below 5°C / min, ultimately yielding the silicon-based composite structure of the battery cell.

[0099] The process control strategies for achieving silicon gradient distribution include the following aspects. First, by controlling deposition time and precursor concentration, the difference in diffusion resistance across different pore sizes allows the gaseous precursor to remain longer and deposit more silicon in the inner, smaller pore areas. Second, multi-step deposition can be employed. The first step uses a lower silane flow rate and shorter time to preferentially deposit silicon in the inner, high-surface-area regions. The second step increases the flow rate and extends the time to supplement silicon deposition in the middle and outer layers, achieving gradient control through the differentiation of these two steps. Third, temperature or concentration gradients can be used to create different deposition conditions at different locations in the reactor tube, enabling more precise gradient control.

[0100] The following is an example of a multi-step deposition process; here it is a two-step deposition process. Step 1 (Inner layer preferential deposition): Si The flow rate is set to a low value (e.g., 10-20 sccm), the deposition temperature is 450-500°C, and the deposition time is short (e.g., 15-30 minutes). The aim is to utilize the low concentration of precursor to preferentially deposit in the inner layer's small-pore region where diffusion resistance is high. The second step (outer layer supplementary deposition): Si Increase the flow rate (e.g., 30-50 sccm), set the deposition temperature to 500-550°C, and extend the deposition time (e.g., 30-60 minutes). The aim is to supplement silicon deposition in the large-pore regions of the middle and outer layers. Adjust parameters between the two steps under carrier gas protection. Maintain the heating / cooling rate below 5°C / min throughout the process, and limit the total high-temperature residence time to within 2 hours to ensure the stability of the MOF framework structure. This two-step strategy can be further extended to three or more steps depending on the target gradient.

[0101] To ensure the structural stability of the MOF framework under the high-temperature conditions of CVD, in addition to the role of the ALD protective layer mentioned above, it is also necessary to strictly control the temperature, heating and cooling rates, and atmospheric conditions. An inert atmosphere prevents oxidation of the MOF and silicon, slow heating and cooling reduce thermal stress, and an appropriate upper temperature limit (not exceeding 550°C) and a short high-temperature residence time (controlled within 2 hours) reduce the risk of thermal degradation. The CVD-processed samples can be characterized using X-ray diffraction, nitrogen adsorption-desorption, and transmission electron microscopy to verify the preservation of the MOF's crystal structure and the integrity of its pore structure.

[0102] By controlling the conditions of chemical vapor deposition, such as the flow rate of silane gas and the deposition temperature, nano-silicon was precisely filled into the pores of a MOF structure with an alumina protective layer. This process ensured a gradient distribution of silicon content, enhanced the thermal stability and mechanical strength of the material, and reduced side reactions between silicon and the electrolyte, thereby significantly improving the electrochemical performance and cycle stability of the composite structure.

[0103] Furthermore, after obtaining the silicon-based composite structure of the aforementioned battery cell, the method further includes: coating a conductive layer onto the first surface of the aforementioned silicon-based composite structure, wherein the first surface of the aforementioned silicon-based composite structure is the surface of the outer MOF structure that is far from the middle MOF structure.

[0104] Specifically, depending on the requirements, the conductivity of silicon-based composite structures after silicon filling can be enhanced. One method is an outer surface carbon coating. The composite particles are impregnated in a solution containing carbon precursors such as glucose, sucrose, or pitch, and then carbonized at 500 to 700°C in an inert atmosphere to form a carbon coating layer of 3 to 15 nm. This carbon coating not only provides conductive pathways but also further stabilizes the outer surface structure. Another method is localized low-temperature carbonization. The silicon-based composite structure after silicon filling is treated at 300 to 500°C in an inert atmosphere for 1 to 4 hours, causing some MOF ligands to convert into conductive carbon while preserving as much of the MOF's pore structure and gradient characteristics as possible. The degree of carbonization needs to be precisely controlled; excessive carbonization will destroy the MOF structure and pore size gradient, while insufficient carbonization will result in limited improvement in conductivity.

[0105] The addition of a conductive layer not only establishes an effective electron transport channel but also provides additional protection, preventing electrode material peeling or pulverization during battery operation and further enhancing the structural stability of the electrode. This step broadens the performance of the composite material, ensuring its superior performance in lithium-ion battery applications, especially in scenarios requiring high energy density and long-term stable cycling. By coating the surface of the outer MOF structure with a conductive layer, stress relief, structural stability, and enhanced conductivity are effectively integrated.

[0106] The prepared gradient pore size MOF-silicon composite material is used as the active material and mixed with a conductive agent and a binder in a certain proportion to form an electrode slurry. The mass fraction of the active material is 70-90%, preferably 80-85%; the mass fraction of the conductive agent, such as carbon black or carbon nanotubes, is 3-15%, preferably 5-10%; and the mass fraction of the binder, such as a composite system of polyacrylic acid or sodium carboxymethyl cellulose and styrene-butadiene rubber, is 5-15%, preferably 8-12%. The components are thoroughly mixed and dispersed in an appropriate amount of solvent, such as deionized water, to form a uniform slurry. The slurry is coated onto a current collector, such as copper foil, with the coating thickness determined according to the surface loading, generally 1-5 mg / cm². After coating, the electrode is dried at 60-80°C to remove the solvent, and then rolled to improve the compaction density of the electrode and the bonding force between the active material and the current collector. The rolled electrode is further dried in a vacuum oven at 80-120°C to ensure that the moisture content is below 200 ppm. The electrode sheets are cut to the required size and assembled into a battery with a separator, electrolyte and counter electrode. It can be in the form of a button cell, pouch cell or cylindrical cell, and is used as the negative electrode of a lithium-ion battery.

[0107] In some embodiments of this application, to enhance the dynamic adaptability of the composite material, the ligands of the MOF framework are designed to be responsive to lithium-ion concentration, enabling the pore size to automatically adjust with the battery's state of charge. During charging, the ligand molecules expand the pore size through conformational changes, providing additional space for silicon expansion; during discharging, they return to their original size, reducing electrolyte penetration and thus minimizing side reactions. This intelligent responsive design further enhances the material's cycle stability and safety. This is achieved by introducing specific ligand molecules that undergo conformational changes in the presence of lithium ions, thereby altering the pore size. For example, compounds containing reversible coordinating groups can be used as ligands. These groups can loosely or loosely bind to the metal center during lithium-ion insertion and extraction, achieving dynamic pore size adjustment. Specifically, sulfur- or phosphorus-containing ligands can be introduced during synthesis; their interaction strength with lithium ions varies with lithium-ion concentration, thus affecting the pore size of the MOF. This design enables composite materials to adapt more intelligently to the battery's operating state, effectively manage volume changes and stress issues during the lithiation process, reduce side reactions during charging / discharging, significantly extend battery cycle life, and improve safety.

[0108] In some embodiments of this application, a MOF framework containing multiple metal centers, such as a mixed metal MOF containing zinc, nickel, and cobalt, can be constructed. The synergistic effect of different metals within the framework enhances the overall performance of the composite material. MOFs with different metal centers exhibit varying stability, conductivity, and lithium-ion adsorption capacity. By precisely controlling their proportions and distribution, the overall performance of the composite material can be further optimized. This is achieved by simultaneously using two or more metal salts, such as zinc acetate, nickel nitrate, and cobalt nitrate, during the synthesis of the MOF structure. By adjusting the proportions of the metal salts and the reaction conditions, a multi-metal center structure can be formed within the MOF framework. For example, the outer layer can be enriched with zinc centers to improve flexibility and conductivity, the middle layer can incorporate nickel centers to enhance lithium-ion adsorption, and the inner layer can be rich in cobalt centers to improve mechanical strength. This multi-metal MOF can be prepared via solvothermal synthesis or microwave-assisted synthesis. By precisely controlling the order of metal source addition and the reaction environment, a hierarchical distribution of the multi-metal centers can be achieved. The synergistic effect of the multi-element MOF framework can improve the performance of silicon-based composite anodes from multiple perspectives, including enhancing mechanical strength, improving conductivity, and optimizing the lithium-ion transport process. This design can more comprehensively address various challenges in battery operation, contributing to the development of higher-performance, more reliable, and safer lithium-ion battery anode materials.

[0109] The preparation process described in this application has the following advantages: Solvent-thermal growth allows for precise design of pore size and structure through parameter control. Atomic layer deposition (ALD) technology enables precise control of nanoscale thickness and uniform coverage of complex structures. Chemical vapor deposition (CVD) has good process maturity. Each step in the entire preparation process is relatively independent, facilitating quality control and process optimization. From a large-scale production perspective, solvothermal synthesis can be scaled up by increasing the reactor capacity or using a continuous flow reactor. ALD and CVD equipment can be designed for batch processing, handling multiple samples at once to improve efficiency. Regarding material costs, the synthesis cost of MOFs is gradually decreasing with in-depth research and increased scale; silicon material costs are relatively low; and the unit product operating costs of ALD and CVD processes are controllable. Considering the value brought by performance improvements, the composite material described in this application has economic feasibility for industrial application.

[0110] Existing silicon-based anode technologies mainly employ two design approaches to address the volume expansion problem of silicon. The first approach is nano-sizing and porosification. The limitation of this method is that nano-silicon has a large specific surface area, leading to increased side reactions with the electrolyte and significant initial irreversible capacity loss; the porous structure is also prone to collapse and pulverization during cycling. The second approach is silicon-carbon composite strategy. However, traditional silicon-carbon composites are mostly uniform mixing or simple coating, lacking a system design for stress control. When the silicon content is high, stress issues remain prominent.

[0111] Existing research on MOF-based silicon anodes mainly includes methods such as physical mixing of MOF and silicon, growing MOF layers on silicon surfaces, or filling MOF channels with silicon. Physical mixing may lead to poor contact between MOF and silicon, failing to fully utilize the channel structure and confinement effect of MOF. Growing MOF layers on silicon surfaces, where the pore size of the MOF layer is usually uniform, makes it difficult to effectively disperse stress. Filling silicon into MOFs with uniform pore size, when all channel sizes are the same, stress may concentrate at certain locations, leading to structural degradation.

[0112] This application breaks through the traditional uniform structure design thinking and proposes a technical route for a three-layer gradient pore size MOF-silicon composite structure based on the concept of stress graded buffering. First, it introduces the concept of radial dual gradients, namely the synergistic design of pore size gradient and silicon content gradient. The outer layer has large pore size and low silicon content, providing ample buffer space and primary stress absorption; the middle layer has transitional pore size and moderate silicon content, achieving a balance between mechanical performance and capacity contribution; the inner layer has small pore size and high silicon content, achieving high capacity output through confinement effect while suppressing excessive silicon expansion. This gradient design, progressing step-by-step from the outside in, allows the stress generated by lithiation to be buffered layer by layer, preventing sudden concentration at any point, thus effectively avoiding material breakage and structural collapse. Second, this application not only introduces gradients in pore size and silicon content but also in mechanical modulus. Through gradient changes in ligand ratios, a continuous transition from the flexibility of the outer layer to the rigidity of the inner layer is achieved in the MOF framework, forming a multi-layered mechanical structure that is flexible on the outside and rigid on the inside. The flexibility of the outer layer is beneficial for absorbing and adapting to stress, while the rigidity of the inner layer is beneficial for maintaining structural stability and providing mechanical constraints on silicon. This synergistic design of three-dimensional gradients (pore size + silicon content + mechanical modulus) surpasses single-gradient or dual-gradient designs, representing a paradigm shift in material design from single-parameter optimization to multi-parameter synergistic optimization. Furthermore, this application emphasizes the importance of interfacial stability by forming a nanometer-thick alumina protective layer on the inner wall of the MOF pores through atomic layer deposition. This protective layer enhances the mechanical strength and thermal stability of the MOF framework, enabling it to withstand the high temperatures of subsequent CVD processes and maintain structural integrity during cycling. It may also improve the interfacial compatibility between the MOF and silicon and, to some extent, regulate silicon deposition behavior. Compared to direct filling or unprotected filling, this inner wall protection strategy offers significant advantages in interfacial stability and process controllability. Finally, this application employs a layer-by-layer construction and overall functionalization preparation strategy. Through solvothermal layer-by-layer growth, the pore size and mechanical properties of each layer are precisely controlled, and uniform coverage of the protective layer and gradient distribution of silicon are achieved through overall ALD and CVD processes. Compared to one-step synthesis or physical mixing, this preparation strategy enables precise control over structure and composition.

[0113] The core technological advantages of this application are as follows. First, the volume expansion of a silicon anode during lithiation during charging can reach approximately 300%. If the stress generated by this huge volume change cannot be effectively dispersed, it will lead to material breakage, loss of electrical contact, and rapid degradation of battery performance. The three-layer gradient pore structure of this application can achieve graded stress buffering. The large pore size and low silicon content of the outer layer mean that there is sufficient void space. When the silicon in the inner and middle layers expands, the stress is first transmitted to the outer layer. The voids in the outer layer can accommodate part of the expansion volume and absorb part of the stress. The middle layer, as a transition layer, bears the stress transmitted from the inner layer and to the outer layer. Its moderate pore size and silicon content give it both a certain buffering capacity and prevent it from becoming a weak point of stress. Although the inner layer has a high silicon content and a large expansion, its small pore size creates a confinement effect on the silicon, inhibiting long-range movement and aggregation of silicon, while its high mechanical modulus provides mechanical constraints. The advantage of this graded buffering is that the stress gradually decreases rather than suddenly concentrates. In a uniform pore structure, stress distribution is relatively uniform throughout the material. However, when the total stress exceeds the material's strength limit, it will concentrate at a certain defect, leading to cracking. The gradient structure of this application allows stress to be gradually transferred and released from the high-stress area (inner layer) to the low-stress area (outer layer). Each layer shares a portion of the stress, reducing the peak stress overall, thereby delaying or preventing material failure. This "divide and conquer" stress management strategy is the core mechanism by which this application achieves long-cycle stability.

[0114] Secondly, the mechanical properties of a material significantly influence its behavior under cyclic stress. Overly rigid materials are prone to brittle fracture under stress, while overly flexible materials, although adaptable to deformation, may not provide sufficient structural support. This application achieves a continuous transition from an outer flexible layer to an inner rigid layer through a gradient design of ligand ratios, enabling different mechanical functions at different locations. The higher flexibility of the outer layer allows it to undergo elastic or plastic deformation under stress, absorbing energy through deformation and avoiding direct stress transmission and accumulation. This is similar to flexible foam in cushioning materials, absorbing impact through its own deformation. The transition modulus of the middle layer achieves a match between flexibility and rigidity, avoiding stress concentration at the interface of materials with different mechanical properties. The higher rigidity of the inner layer provides mechanical constraints on the high-silicon content regions, limiting excessive silicon expansion while maintaining the integrity of the inner structure. This design concept of outer flexibility and inner rigidity draws inspiration from many high-performance structures in nature, such as the gradient porosity structure of bamboo, which provides both toughness and strength. In the composite material of this application, the gradient configuration of mechanical modulus achieves an optimal match between mechanical properties and functional requirements at different locations, representing a significant improvement over traditional homogeneous material design.

[0115] Thirdly, the atomic layer-deposited alumina protective layer plays multiple roles. First, the inorganic alumina layer significantly enhances the mechanical strength of the MOF organic framework. While pure MOF materials possess a regular pore structure, their organic ligand-based framework is relatively weak in mechanical strength and prone to fracture under stress. Alumina, as an inorganic material, has high Young's modulus and hardness. The nanoscale alumina layer coating the inner walls of the MOF pores enhances the overall mechanical properties of the framework and improves its fracture resistance. Second, the alumina layer improves the thermal stability of the MOF framework, enabling it to withstand the high temperatures of subsequent CVD processes. Pure MOFs may experience ligand removal or structural collapse at high temperatures. The protection of the alumina layer can delay or inhibit this thermal degradation process, ensuring that the pore structure of the MOF is largely maintained under CVD conditions. Third, the alumina layer acts as a barrier layer, regulating the diffusion and deposition behavior of silicon precursors. The coverage of the alumina layer in different pore size regions may exhibit subtle differences, or the barrier effect of the alumina layer on silicon precursor diffusion may be related to the pore size. These factors contribute to achieving a gradient distribution of silicon. Furthermore, the alumina layer can improve the interfacial compatibility between MOF and silicon, reducing defects and stress concentration at the interface. As a solid electrolyte material, alumina, at a thickness of nanometers, can provide certain transport channels for lithium ions.

[0116] Fourthly, this application achieves a gradient distribution of silicon through precise control of CVD process parameters. This gradient distribution improves structural stability while maintaining a high overall silicon content. The high silicon content in the inner layer is the main source of the overall specific capacity. Through the confinement of small pores and the constraint of high modulus, the expansion of silicon in the inner layer is suppressed to a certain extent. The moderate silicon content in the middle layer contributes to the capacity while retaining sufficient pore space as a buffer. Although the low silicon content in the outer layer contributes relatively little to the capacity, its ample pore space and flexible framework can effectively absorb stress from the inner layer. The advantage of this gradient distribution compared to a uniform distribution is that it achieves functional zoning, with different regions undertaking different main functions. The inner layer focuses on high capacity output, the outer layer focuses on stress buffering, and the middle layer achieves transition and balance. Through this zoning and synergy, the overall material can find a better balance between high silicon content (and therefore high specific capacity) and good structural stability (and therefore long cycle life), which is difficult to achieve with a single uniform structure.

[0117] Based on the aforementioned core technological advantages, this application achieves significant improvements in overall performance. Regarding cycle stability, the synergistic effect of multiple mechanisms—graded buffering, modulus gradient, and interface protection—effectively suppresses material breakage and pulverization, reduces electrical contact loss, and lowers the rate of interface impedance growth, thereby significantly extending cycle life. Compared to existing uniform-pore MOF-silicon composites or simple silicon-carbon composites, the gradient structure design of this application fundamentally improves stress distribution, achieving longer cycle life under the same or higher silicon content conditions. Regarding initial coulombic efficiency, the confinement effect of MOF channels and the interface stabilization effect of the alumina protective layer reduce side reactions between the silicon surface and the electrolyte, lowering irreversible capacity loss and improving initial coulombic efficiency. Higher initial coulombic efficiency means less active lithium is consumed, positively impacting the energy density and cost of actual batteries. Regarding rate performance, although the MOF itself has low electronic conductivity, an effective electron transport network can be established through the combination of an outer surface carbon coating, localized carbonization, or electrode-level conductive agents. The ordered pore structure of the MOF and the lithium-ion transport pathways provided by the alumina layer facilitate ion transport and improve rate performance. The gradient pore size structure allows the electrolyte to effectively wet regions of different pore sizes, ensuring sufficient ion contact. In terms of safety, the structural support and interfacial stability provided by the MOF framework and alumina layer help suppress silicon particle dispersion and electrode pulverization, reducing the risk of internal short circuits. A gradient distribution of silicon content, compared to a high-content uniform distribution, reduces the risk of localized overheating and stress abrupt changes, improving battery safety. Regarding energy density, by achieving a high overall silicon content (45-55 wt% or higher) and good cycle stability, this application can significantly improve the specific capacity of the anode material while maintaining a long lifespan, thereby increasing the overall battery energy density. This is of great significance for applications such as electric vehicles and portable electronic devices.

[0118] Silicon-based anodes are considered important candidate materials for next-generation lithium-ion battery anodes due to their ultra-high theoretical specific capacity (approximately 4200 mAh / g, far exceeding graphite's 372 mAh / g). However, the significant volume expansion of silicon has been a major bottleneck restricting its practical application. Although researchers have proposed various strategies such as nanostructuring, porosimetry, and carbon coating, achieving long cycle life while maintaining high silicon content remains a technical challenge. This application systematically addresses this issue from a stress management perspective through gradient structure design, providing a new technical approach for the practical application of silicon-based anodes. Furthermore, metal-organic frameworks (MOFs) possess high specific surface area, tunable pore size, and structural diversity; however, their application in energy storage is still in the exploratory stage. This application demonstrates the application potential of MOFs in lithium-ion battery anode materials by combining MOFs with silicon, introducing gradient structure design, and employing an ALD protective layer.

[0119] Based on this application, in terms of materials, other types of MOFs, different ligand combinations, and composite MOFs with multiple metal centers can be explored to achieve better pore size gradients and mechanical properties. Regarding protective layers, other ALD materials such as titanium dioxide and zirconium oxide, or multilayer composite protective layers, can be tried to further improve stability. In terms of silicon filling, CVD process parameters can be optimized, and other silicon introduction methods such as plasma-enhanced CVD and liquid-phase chemical deposition can be explored to improve the accuracy of gradient control and silicon dispersion. Regarding conductivity, more efficient methods for constructing conductive networks can be studied, such as in-situ growth of carbon nanotubes and doping with conductive polymers. In terms of applications, the gradient structure design concept of this application may also be extended to other high-capacity anode materials such as tin-based and germanium-based materials, or applied to new systems such as sodium-ion batteries. These continuous optimization and expansion possibilities give the technology of this application a long life cycle and sustained development potential.

[0120] To verify the impact of the proposed silicon-based composite structure on battery performance, a series of embodiments and comparative examples were designed to systematically explore the mechanisms by which core technical features such as gradient pore size distribution, silicon content gradient, ligand ratio gradient, ALD protective layer, and CVD gradient filling method affect the cycle stability, initial coulombic efficiency, volume expansion control, and rate performance of the anode material. The experimental design followed a three-tiered progressive logic of core innovation verification, parameter window optimization, and material process expansion. Through a combination of single-variable comparison and multi-parameter collaborative optimization, the technical advantages and practical value of the gradient structure design were comprehensively evaluated.

[0121] The core innovation verification group includes Example E1 as the baseline example of the complete technical solution, and comparative examples CE1 to CE7, which respectively verify the necessity of a uniform structure baseline, physical mixing method, single gradient element, and the rationality of gradient direction. The parameter window optimization group systematically examined the impact of outer layer aperture boundary, inner layer aperture optimization, total silicon content range, ALD thickness window, layer thickness ratio, and continuous gradient implementation method on performance through Examples E2 to E9. The materials and process expansion group verified the substitutability of MOF materials, ALD material selection, and the feasibility and performance improvement potential of multi-parameter synergistic optimization through Examples E10 to E12.

[0122] Example E1

[0123] Example E1 is designed to provide a complete technical solution benchmark. The MOF structure is a three-layer ZIF-8; the pore size distribution is 17 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient is 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) is 1:1:1; and an alumina protective layer (A... The thickness is 1.5 nm, the deposition temperature is 150°C, and the number of cycles is 75. The CVD silicon filling is a two-step gradient method. The silicon content of each layer is 35 wt% for the outer layer, 55 wt% for the middle layer, and 75 wt% for the inner layer. The total silicon content is 55 wt%.

[0124] Example E1, as a baseline embodiment of the complete technical solution, integrates a three-layer gradient aperture structure (outer layer 17nm, middle layer 10nm, inner layer 4nm), a radial gradient distribution of silicon content (outer layer 35wt%, middle layer 55wt%, inner layer 75wt%), and a ligand ratio gradient of outer layer 3:1, middle layer 2:1, inner layer 1:1, and A A protective layer (1.5 nm) and a two-step CVD gradient silicon filling process are expected to achieve excellent overall electrochemical performance. Example E1 achieves an initial coulombic efficiency of 87%, a reversible specific capacity of 1850 mAh / g, a capacity retention of 88% after 200 cycles, an average coulombic efficiency of 99.6% from 50 to 200 cycles, an initial lithium-charge expansion rate of only 105%, and a cumulative expansion rate controlled at 115% after 100 cycles. These performance indicators demonstrate that the gradient structure design effectively solves the problems of rapid capacity decay and severe volume expansion in silicon anodes while achieving high capacity.

[0125] Comparative Example CE1

[0126] The comparative example CE1 was designed to verify the overall value of the gradient structure. The MOF structure was a monolayer uniform ZIF-8; the pore size distribution was uniform at 10 nm; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was a single 2:1; and an alumina protective layer (A... The thickness was 1.5 nm, the deposition temperature was 150°C, and the number of cycles was 75; the CVD silicon filling was uniform; the silicon content was uniform at 50 wt%; and the total silicon content was 50 wt%.

[0127] Comparative Example CE1 employs a traditional single-structure design with uniform aperture (10 nm) and uniform silicon content (50 wt%). Although it also undergoes ALD protection layer treatment, its cycling performance is significantly inferior to E1. Comparative Example CE1's capacity retention after 200 cycles is only 68%, a decrease of 20 percentage points compared to Example E1. Its initial expansion rate reaches 165%, and its cumulative expansion rate after 100 cycles is as high as 195%, which are 57% and 70% higher than Example E1, respectively. This comparison demonstrates the fundamental advantage of gradient structures over uniform structures. In uniform aperture structures, the volume expansion of silicon during lithium intercalation lacks a graded buffering mechanism. The uniform distribution of stress throughout the structure leads to localized stress concentration, ultimately causing mechanical damage and loss of electrical contacts in the MOF framework. In contrast, the gradient aperture design employs a three-tiered strategy: large outer apertures provide primary buffer space, middle transition apertures coordinate stress transfer, and small inner apertures achieve confinement effects. This strategy enables orderly stress dispersion and gradual release, fundamentally suppressing the structural degradation process.

[0128] Comparative Example CE2

[0129] The design purpose of the comparative example CE2 was to verify the necessity of in-situ recombination. The MOF structure was a three-layer ZIF-8; the pore size distribution was 17 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) was 1:1:1; and an alumina protective layer (A...) was used. The thickness was 1.5 nm, the deposition temperature was 150°C, and the number of cycles was 75; the CVD silicon filler was commercial nano-silicon (D50~100nm) ball-milled and mixed; the total silicon content was 50 wt%.

[0130] Comparative Example CE2, prepared using a simple physical mixing method of commercially available nano-silicon and a gradient-pore MOF framework, exhibited further performance degradation. Its capacity retention after 200 cycles dropped to 58%, and after 100 cycles, the expansion rate reached a staggering 220%, with the average coulombic efficiency also decreasing to 98.8%. The physical mixing method fails to achieve in-situ filling and confinement of silicon within the MOF channels; the silicon particles and MOF framework only have weak physical contact, lacking robust chemical bonding. During cycling, the volume changes of silicon particles cannot be effectively constrained by the MOF framework, leading to particle agglomeration, loss of electrical contact, and continuous SEI film rupture-repair cycles, consuming significant amounts of lithium and accelerating capacity decay. Example E1, compared to Comparative Example CE2, demonstrated a 52% improvement in capacity retention after 200 cycles and a 43% reduction in the initial expansion rate, fully validating the necessity of CVD in-situ gradient filling technology. The in-situ filling method ensures uniform dispersion of silicon within the MOF channels and forms a tight interface with the framework. The gradient filling strategy further ensures a synergistic match between silicon content distribution and pore size distribution, achieving optimal stress buffering effects.

[0131] Comparative Example CE3

[0132] The design purpose of the comparative example CE3 was to verify the necessity of the pore size gradient. The MOF structure was a three-layer ZIF-8; the pore size distribution was 10 nm for all three layers; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) was 1:1:1; and an alumina protective layer (A... The thickness is 1.5 nm, the deposition temperature is 150°C, and the number of cycles is 75. The CVD silicon filling is a two-step gradient method. The silicon content of each layer is 35 wt% for the outer layer, 55 wt% for the middle layer, and 75 wt% for the inner layer. The total silicon content is 55 wt%.

[0133] Comparative Example CE3 retained both silicon content and ligand gradients, but with a uniform pore size of 10 nm. Its capacity retention after 200 cycles was 78%, falling between Comparative Example CE1 (68%) and Example E1 (88%). The performance improvement of Comparative Example CE3 compared to Comparative Example CE1 demonstrates that silicon content and ligand gradients can optimize stress distribution to some extent. However, due to the lack of physical buffer space provided by the pore size gradient, expansion stress is still difficult to fully release, resulting in limited improvement in cycling performance. The difference between Comparative Example CE3 and Example E1 clearly indicates that the pore size gradient is an indispensable element in constructing a complete stress dispersion system; composition and modulus gradients alone cannot replace the hierarchical buffering effect of physical space.

[0134] Comparative Example CE4

[0135] The design purpose of the comparative example CE4 was to verify the necessity of a silicon content gradient. The MOF structure was a three-layer ZIF-8; the pore size distribution was 17 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) was 1:1:1; and an alumina protective layer (A... The thickness was 1.5 nm, the deposition temperature was 150°C, and the number of cycles was 75; the CVD silicon filling was uniform; the silicon content was uniform at 55 wt%; and the total silicon content was 55 wt%.

[0136] Comparative Example CE4 retained both the pore size gradient and the ligand gradient, but employed a uniform silicon content distribution (approximately 55 wt%). Its 200-cycle capacity retention was 75%, significantly lower than Example E1. While the gradient pore size provides a tiered buffer for silicon volume expansion, the uniform silicon content distribution results in similar absolute expansion amounts in the outer, middle, and inner layers during lithium intercalation, leading to an expansion mismatch between layers. The large pores in the outer layer can accommodate expansion, but the insufficient silicon content to fill the space causes capacity loss, while the small pores in the inner layer face severe localized stress concentration due to excessive silicon content. This mismatch disrupts the stress-gradient release mechanism originally designed for the gradient pore size. Example E1, through a gradient configuration of low silicon in the outer layer, medium silicon in the middle layer, and high silicon in the inner layer, matches the absolute expansion amount of each layer with its corresponding pore size buffering capacity, achieving an ideal state where each layer approaches but does not exceed its stress-bearing limit, thereby maximizing the overall cycle life.

[0137] Comparative Example CE5

[0138] The comparative example CE5 was designed to verify the necessity of ligand gradient. The MOF structure was a three-layer ZIF-8; the pore size distribution was 17 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was a single 2:1; the layer thickness ratio (outer:middle:inner) was 1:1:1; and an alumina protective layer (A... The thickness is 1.5 nm, the deposition temperature is 150°C, and the number of cycles is 75. The CVD silicon filling is a two-step gradient method. The silicon content of each layer is 35 wt% for the outer layer, 55 wt% for the middle layer, and 75 wt% for the inner layer. The total silicon content is 55 wt%.

[0139] Comparative Example CE5 retained both the pore size gradient and the silicon content gradient, but its ligand ratio was fixed at 2:1 (no modulus gradient with an outer flexible and inner rigid structure). Its capacity retention after 200 cycles was 80%, and its expansion rate control was better than Comparative Examples CE3 and CE4, but still significantly worse than Example E1. The gradient change in ligand ratio not only affects pore size but, more importantly, modulates the mechanical modulus of the MOF framework. The high proportion of 2-methylimidazole in the outer layer provides good flexibility, allowing it to adapt to silicon volume changes without brittle fracture; the high proportion of benzimidazole in the inner layer provides high rigidity, effectively confining silicon expansion and maintaining structural integrity. Comparative Example CE5, lacking this mechanical modulus gradient, although possessing physical space and compositional gradients, suffers from insufficient uniform modulus in the framework to provide adequate flexibility in the outer layer or sufficient rigid constraint in the inner layer, leading to poor stress transfer and localized stress concentration. Example E1 achieves an externally flexible and internally rigid modulus distribution through ligand gradients, forming a three-dimensional synergy with pore size and silicon gradients, ensuring smooth stress transmission and effective dispersion throughout the structure. Comparative Examples CE3, CE4, and CE5 show performance differences of approximately 10%, 13%, and 8% compared to Example E1, respectively. These data quantitatively reveal the indispensable synergistic relationship of the three technical features; only when all three exist simultaneously and work synergistically can the stress dispersion effect be maximized.

[0140] Comparative Example CE6

[0141] The comparative example CE6 was designed to verify the necessity of an ALD protective layer. The MOF structure was a three-layer ZIF-8; the pore size distribution was 17 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) was 1:1:1; there was no alumina protective layer; the CVD silicon filling was a two-step gradient method; the silicon content of each layer was 35 wt% for the outer layer, 55 wt% for the middle layer, and 75 wt% for the inner layer; the total silicon content was 55 wt%.

[0142] Comparative Example CE6 omitted the ALD protective layer deposition step, and its other structural parameters were identical to Example E1, but its electrochemical performance showed significant degradation in several aspects. The initial coulombic efficiency of Comparative Example CE6 dropped to 79%, a decrease of 8 percentage points compared to 87% in Example E1; the capacity retention after 200 cycles was 72%, a decrease of 16 percentage points compared to Example E1; the electrochemical impedance refractory rate increased by a high 135%, three times that of Example E1 (45%); and the high-temperature cycling performance was particularly poor, with a capacity retention of only 65% ​​after 200 cycles at 45°C, far lower than the 85% of Example E1. These data comprehensively demonstrate the indispensability of the ALD protective layer in this technology system. The primary function of the ALD protective layer is to protect the structure of the MOF framework during the high-temperature CVD deposition process. The thermal stability of MOF materials such as ZIF-8 is typically below 300-350°C, while CVD silicon deposition requires a high-temperature environment of 450-550°C. In Comparative Example CE6, the MOF framework underwent partial thermal decomposition and structural collapse during CVD, resulting in the destruction of the carefully designed gradient pore structure. Pore blockage and framework damage prevented uniform silicon filling, ultimately leading to a composite structure with dense internal defects. This is evidenced by the lower first-cycle coulombic efficiency of Comparative Example CE6: structural defects and exposed MOF surfaces react violently with the electrolyte, consuming a large amount of lithium to form an unstable SEI film, leading to a significant increase in irreversible capacity loss in the first cycle. In contrast, the 1.5 nm A in Example E1... The protective layer acts as a thermal barrier, effectively isolating the MOF framework from the direct impact of CVD high temperatures, thus maintaining the integrity and precision of the gradient aperture structure.

[0143] The second important function of the ALD protective layer is its passivation protection of the MOF-electrolyte interface during cycling. Organic ligands and metal central nodes in the MOF framework can chemically react with carbonate electrolytes, especially during repeated lithiation / delithiation processes, where drastic fluctuations in electrode potential accelerate these side reactions. The average coulombic efficiency of Comparative Example CE6 (99.0%) was significantly lower than that of Example E1 (99.6%), indicating that continuous side reactions occurred in each cycle, consuming active lithium and accumulating non-conductive reaction products on the MOF surface, gradually increasing the interfacial impedance. This was quantitatively verified by EIS test results: the impedance growth rate of Comparative Example CE6 was as high as 135%, indicating that its interfacial impedance increased rapidly with cycling. In Example E1, ALD... The protective layer, as a dense ceramic coating, exhibits extremely high chemical inertness, effectively blocking direct contact between the electrolyte and the MOF framework, maintaining long-term interfacial stability, and keeping the impedance growth rate at a low level of 45%. In high-temperature cycling tests, the performance gap between Comparative Example CE6 and Example E1 widened further. At 45°C, the side reaction rate accelerated significantly; in Comparative Example CE6 without the protective layer, the MOF framework deteriorated rapidly, and electrolyte decomposition intensified, leading to a dramatic drop in capacity retention to 65% after 200 cycles. In contrast, Example E1, benefiting from the dual protection of the ALD protective layer (structural stability plus interfacial passivation), maintained a high capacity retention of 85% even under accelerated high-temperature aging conditions.

[0144] It is noteworthy that the expansion rate control of Comparative Example CE6 (118% initially, 148% after 100 cycles) is actually superior to some other comparisons, such as Comparative Example CE4. This phenomenon actually reflects another mode of structural failure. While the localized collapse of the MOF framework in Comparative Example CE6 deteriorates electrochemical performance, it also provides additional disordered space to accommodate silicon expansion to some extent. This is a passive buffer at the cost of active material utilization and cycle stability, fundamentally different from the active ordered buffer achieved through precise design in Example E1. This comparison further highlights the importance of structural integrity for achieving truly effective stress dispersion.

[0145] Comparative Example CE7

[0146] The purpose of designing the comparative example CE7 is to verify the rationality of the gradient direction. The MOF structure is a three-layer (reverse) ZIF-8; the pore size distribution is 4 nm for the outer layer, 10 nm for the middle layer, and 17 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient (reverse) is 1:1 for the outer layer, 2:1 for the middle layer, and 3:1 for the inner layer; the layer thickness ratio (outer:middle:inner) is 1:1:1; and the alumina protective layer (A... The thickness is 1.5 nm, the deposition temperature is 150°C, and the number of cycles is 75. The CVD silicon filling is a two-step gradient method (reverse). The silicon content of each layer is 75 wt% for the outer layer, 55 wt% for the middle layer, and 35 wt% for the inner layer. The total silicon content is 55 wt%.

[0147] Comparative Example CE7 employs a reverse gradient design (small pores / high silicon content in the outer layer, large pores / low silicon content in the inner layer), and its performance is even worse than that of Comparative Example CE1 with a uniform structure. Its capacity retention after 200 cycles is only 63%, and its expansion rate after cycling reaches as high as 210%. This reverse gradient design violates the fundamental principle of stress dispersion: the small pore size and high silicon content in the outer layer cause stress to concentrate in the external region, lacking sufficient buffer space to release expansion stress; while the inner layer, although having large pores, has a low silicon content, failing to fully utilize the confinement effect. This incorrect gradient direction disrupts the stress transmission path, accelerating structural failure. The performance improvement of Example E1 compared to Comparative Example CE7 directly proves the rationality and importance of the gradient direction design, emphasizing that the gradual change from "large pores - low silicon - flexible" to "small pores - high silicon - rigid" from the outside to the inside is key to achieving orderly stress dispersion.

[0148] The comparison results between Example E1 and Comparative Examples CE1-CE7 are shown in Table 1:

[0149] Table 1

[0150]

[0151] Example E2

[0152] Example E2 was designed to explore the lower limit of the outer pore size. The MOF structure was a three-layer ZIF-8; the pore size distribution was 12 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) was 1:1:1; and an alumina protective layer (A... The thickness is 1.5 nm, the deposition temperature is 150°C, and the number of cycles is 75. The CVD silicon filling is a two-step gradient method. The silicon content of each layer is 35 wt% for the outer layer, 55 wt% for the middle layer, and 75 wt% for the inner layer. The total silicon content is 55 wt%.

[0153] Example E2 explored the lower limit of the outer layer aperture. Example E2 reduced the outer layer aperture to 12 nm, with a 200-cycle capacity retention of 85%, slightly lower than E1's 88%. This indicates that the excessively small outer layer aperture restricts the primary buffer space, resulting in insufficient buffering capacity when silicon expansion is large. This leads to excessive stress transfer to the middle and inner layers, accelerating structural degradation in these regions.

[0154] Example E3

[0155] Example E3 was designed to explore the upper limit of the outer layer pore size. The MOF structure was a three-layer ZIF-8; the pore size distribution was 25 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) was 1:1:1; and an alumina protective layer (A... The thickness is 1.5 nm, the deposition temperature is 150°C, and the number of cycles is 75. The CVD silicon filling is a two-step gradient method. The silicon content of each layer is 35 wt% for the outer layer, 55 wt% for the middle layer, and 75 wt% for the inner layer. The total silicon content is 55 wt%.

[0156] Example E3 explored the upper limit of the outer pore size. In Example E3, the outer pore size was increased to 25 nm, resulting in a 90% capacity retention after 200 cycles, and the lowest initial expansion rate and post-cycle expansion rate among all samples (98% and 108%, respectively). However, the reversible specific capacity decreased to 1820 mAh / g. This result reveals the dilemma of outer pore size optimization: larger pore sizes provide more buffer space, thus improving cycling stability and expansion control, but simultaneously reduce the amount of active material loaded per unit volume, leading to a decrease in capacity density. The 17 nm outer pore size chosen in Example E1 achieved a better balance between capacity and stability.

[0157] Example E4

[0158] Example E4 was designed to optimize the inner layer pore size. The MOF structure was a three-layer ZIF-8; the pore size distribution was 17 nm for the outer layer, 10 nm for the middle layer, and 3 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) was 1:1:1; and an alumina protective layer (A... The thickness is 1.5 nm, the deposition temperature is 150°C, and the number of cycles is 75. The CVD silicon filling is a two-step gradient method. The silicon content of each layer is 35 wt% for the outer layer, 55 wt% for the middle layer, and 75 wt% for the inner layer. The total silicon content is 55 wt%.

[0159] Example E4 further optimized the inner layer pore size to 3 nm, achieving optimal cycling stability with a capacity retention of 92% after 200 cycles, and better expansion rate control than E1. The smaller inner layer pore size enhances the nanoconfinement effect on silicon, confining the silicon particle size to a smaller range. At the same time, the smaller pore size means a thicker MOF framework wall, providing stronger mechanical confinement.

[0160] Example E5

[0161] Example E5 was designed to explore the lower limit of total silicon content. The MOF structure was a three-layer ZIF-8; the pore size distribution was 17 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) was 1:1:1; and an alumina protective layer (A... The thickness is 1.5 nm, the deposition temperature is 150°C, and the number of cycles is 75. The CVD silicon filling is a two-step gradient method. The silicon content of each layer is 25 wt% for the outer layer, 45 wt% for the middle layer, and 65 wt% for the inner layer. The total silicon content is 45 wt%.

[0162] Example E5 represents the lower end of the total silicon content range. Example E5 employs a silicon gradient distribution of 25 wt% in the outer layer, 45 wt% in the middle layer, and 65 wt% in the inner layer, reducing the total silicon content to 45%. Its reversible specific capacity is 1600 mAh / g, lower than Example E1, but it achieves 92% capacity retention after 200 cycles and exhibits excellent expansion rate control (88% initially, 95% after 100 cycles). The low silicon content design sacrifices some capacity but significantly improves structural stability.

[0163] Example E6

[0164] Example E6 was designed to explore the upper limit of total silicon content. The MOF structure was a three-layer ZIF-8; the pore size distribution was 17 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) was 1:1:1; and an alumina protective layer (A... The thickness is 1.5 nm, the deposition temperature is 150°C, and the number of cycles is 75. The CVD silicon filling is a two-step gradient method. The silicon content of each layer is 45 wt% for the outer layer, 65 wt% for the middle layer, and 85 wt% for the inner layer. The total silicon content is 65 wt%.

[0165] Example E6 represents the high-end edge of total silicon content. Example E6 employs a high silicon gradient of 45 wt% in the outer layer, 65 wt% in the middle layer, and 85 wt% in the inner layer, increasing the total silicon content to 65%. It achieves a reversible specific capacity of 2100 mAh / g, demonstrating excellent capacity potential. However, the capacity retention after 200 cycles drops to 82%, and the expansion rate also increases significantly (135% initially, 158% after 100 cycles). This result again demonstrates the inherent contradiction between silicon content and cycle stability; while higher silicon content brings capacity improvement, it also increases absolute expansion. Even with the protection of the gradient structure, excessive local stress can still accelerate structural degradation. The 55% total silicon content chosen in Example E1 represents the optimal balance point after comprehensively considering capacity requirements (greater than 1800 mAh / g) and cycle life requirements (greater than 85% after 200 cycles).

[0166] Example E7

[0167] Example E7 was designed for ALD thickness window verification. The MOF structure was a three-layer ZIF-8; the pore size distribution was 17 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) was 1:1:1; and an alumina protective layer (A... The thickness is 1.0 nm, the deposition temperature is 120°C, and the number of cycles is 50. The CVD silicon filling is a two-step gradient method. The silicon content of each layer is 35 wt% for the outer layer, 55 wt% for the middle layer, and 75 wt% for the inner layer. The total silicon content is 55 wt%.

[0168] Example E7 will A When the protective layer thickness was reduced to 1.0 nm and the number of cycles was decreased to 50, the initial coulombic efficiency dropped to 83%, and the capacity retention after 200 cycles was 84%, both inferior to Example E1. The excessively thin protective layer could not provide sufficient thermal barrier and interface passivation, resulting in some damage to the MOF framework during both the CVD process and cycling. Experiments also showed that when the ALD thickness exceeded 2.5 nm, although the protective effect was further enhanced, the excessively thick ALD... The layer significantly reduces the lithium-ion transport rate, degrades rate performance, and occupies too much pore space, reducing silicon loading. The 1.5 nm thickness chosen in Example E1 achieves the optimal balance between protection and ion transport performance.

[0169] Example E8

[0170] Example E8 was designed to optimize the layer thickness ratio. The MOF structure is a three-layer ZIF-8; the pore size distribution is 17 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient is 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) is 2:1:1; and the alumina protective layer (A... The thickness is 1.5 nm, the deposition temperature is 150°C, and the number of cycles is 75. The CVD silicon filling is a two-step gradient method. The silicon content of each layer is 40 wt% for the outer layer, 60 wt% for the middle layer, and 80 wt% for the inner layer. The total silicon content is 55 wt%.

[0171] Example E8 employs a 2:1:1 layer thickness ratio, increasing the relative thickness of the outer layer. The silicon content of each layer is adjusted to 40 wt% for the outer layer, 60 wt% for the middle layer, and 80 wt% for the inner layer, maintaining a total silicon content of 55%. Example E8 exhibits significantly improved rate performance, achieving capacity retention of 85% and 72% at 1C and 2C, respectively, superior to Example E1's 82% and 68%. The thickened outer layer design increases the proportion of large-aperture regions, providing more rapid transport channels for lithium ions and reducing concentration polarization, thereby improving capacity performance at high rates. Simultaneously, Example E8 also shows a slight improvement in cycling performance (91% after 200 cycles), indicating that the thicker outer buffer layer can more effectively absorb and disperse external stress.

[0172] Example E9

[0173] Example E9 was designed to verify the feasibility of a continuous gradient relative to a discrete three-layer gradient. The MOF structure is a ZIF-8 continuous gradient; the pore size (outer layer to inner layer) gradually changes from 17 nm to 4 nm; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient (outer layer to inner layer) gradually changes from 3:1 to 1:1; the layer thickness ratio (outer:middle:inner layer) gradually changes; and an alumina protective layer (A... The thickness is 1.5 nm, the deposition temperature is 150°C, and the number of cycles is 75. The CVD silicon filling is a multi-step gradient method. The silicon content of each layer (from the outer layer to the inner layer) is continuously gradient from 35 wt% to 75 wt%. The total silicon content is 55 wt%.

[0174] Example E9 employed a concentration gradient growth method to achieve a continuous gradient in pore size from 17 nm to 4 nm, with corresponding continuous changes in ligand ratio and silicon content. The performance of Example E9 was essentially equivalent to that of Example E1 (88% after 200 cycles), demonstrating that the core value of gradient structures lies in establishing a gradual trend in pore size, composition, and modulus from the outside in, while the specific implementation method (discrete layering or continuous gradient) has a relatively small impact on performance. The expansion rate control of Example E9 was even slightly better than that of Example E1 (102% initially, 112% after 100 cycles), attributed to the continuous gradient eliminating interlayer interfaces and smoothing stress transmission. However, the fabrication process complexity and reproducibility control difficulty of continuous gradients are significantly higher than those of discrete three-layer structures, potentially posing more challenges in large-scale production. Therefore, the discrete three-layer gradient design represented by Example E1 achieves a better balance between performance and manufacturability.

[0175] The performance test results of Examples E2-E9 are shown in Table 2:

[0176] Table 2

[0177]

[0178] Example E10

[0179] Example E10 was designed to verify the substitutability of MOF materials. The MOF structure was a three-layer ZIF-67; the pore size distribution was 17 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand ratio was adjusted by controlling the synthesis conditions; the layer thickness ratio (outer:middle:inner) was 1:1:1; and an alumina protective layer (A... The thickness is 1.0 nm, the deposition temperature is 120°C, and the number of cycles is 50. The CVD silicon filling is a two-step gradient method. The silicon content of each layer is 35 wt% for the outer layer, 55 wt% for the middle layer, and 75 wt% for the inner layer. The total silicon content is 55 wt%.

[0180] Example E10 uses ZIF-67 instead of ZIF-8 as the MOF framework material, and its performance is close to that of Example E1 (86% after 200 cycles), demonstrating that the gradient structure design concept of this application is not limited to a specific MOF material system. ZIF-67 has a zeolite imidazole ester framework structure similar to ZIF-8, and the pore size and ligand ratio can also be controlled by adjusting the synthesis conditions. This result broadens the range of material choices and provides the possibility of optimizing the chemical composition, conductivity, and ion transport performance of the MOF framework for different application requirements.

[0181] Example E11

[0182] Example E11 was designed to verify the substitutability of ALD materials. The MOF structure was a three-layer ZIF-8; the pore size distribution was 17 nm for the outer layer, 10 nm for the middle layer, and 4 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient was 3:1 for the outer layer, 2:1 for the middle layer, and 1:1 for the inner layer; the layer thickness ratio (outer:middle:inner) was 1:1:1; the protective layer (Ti) The thickness is 1.5 nm, the deposition temperature is 150°C, and the number of cycles is 80. The CVD silicon filling method is a two-step gradient method. The silicon content of each layer is 40 wt% for the outer layer, 60 wt% for the middle layer, and 80 wt% for the inner layer. The total silicon content is 55 wt%.

[0183] Example E11 uses Ti Replace A As an ALD protective layer material, its performance is similar to that of Example E1 (87% after 200 cycles), verifying that the role of the ALD protective layer mainly depends on its density, chemical inertness, and thermal stability, rather than a specific material composition. Ti and A Both are commonly used ALD materials and can form a dense ceramic coating at low temperatures, effectively isolating the MOF from the external environment. This substitutability is of great significance for optimizing costs, improving process compatibility, and adapting to different electrolyte systems.

[0184] Example E12

[0185] The design objective of Example E12 is multi-parameter synergistic optimization. The MOF structure is a three-layer ZIF-8; the pore size distribution is 20 nm for the outer layer, 9 nm for the middle layer, and 3.5 nm for the inner layer; the ligand molar ratio (2-methylimidazole:benzimidazole) gradient is 2.5:1 for the outer layer, 1.5:1 for the middle layer, and 1:1.2 for the inner layer; the layer thickness ratio (outer:middle:inner) is 1.5:1:1; and an alumina protective layer (A... The thickness is 1.8 nm, the deposition temperature is 160°C, and the number of cycles is 85. The CVD silicon filling method is a three-step fine gradient method. The silicon content of each layer is 40 wt% for the outer layer, 60 wt% for the middle layer, and 80 wt% for the inner layer. The total silicon content is 57 wt%.

[0186] Example E12 represents the best implementation of multi-parameter synergistic optimization. Based on Example E1, Example E12 fine-tunes several key parameters: the outer layer pore size is increased to 20 nm and the inner layer pore size is decreased to 3.5 nm to enhance the buffering and confinement effects at both ends; the ligand ratio gradient is adjusted to 2.5:1 for the outer layer, 1.5:1 for the middle layer, and 1:1.2 for the inner layer to further optimize the mechanical modulus distribution; the ALD thickness is increased to 1.8 nm to find a new balance between protection and ion transport; a three-step CVD fine gradient filling is used to achieve a smoother transition of silicon content (40 wt% for the outer layer, 60 wt% for the middle layer, and 80 wt% for the inner layer); and the layer thickness ratio is adjusted to 1.5:1:1 to moderately increase the thickness of the outer and middle layers. The synergistic optimization of these parameters enabled Example E12 to achieve optimal overall performance: an initial coulombic efficiency of 88%, a reversible specific capacity of 1950 mAh / g, a capacity retention of 90% after 200 cycles and 85% after 500 cycles, an average coulombic efficiency of 99.7%, excellent expansion rate control (100% initially, 108% after 100 cycles), outstanding rate performance (86% at 1C, 74% at 2C), an EIS impedance growth rate of only 40%, and a high-temperature cycle retention of 87% after 200 cycles. The performance improvement of Example E12 compared to Example E1 lies in its comprehensive breakthrough: it achieves or approaches its optimal values ​​in all key indicators such as capacity, cycle life, expansion control, rate performance, and high-temperature stability, eliminating performance shortcomings and demonstrating extremely high overall balance. More importantly, Example E12 achieves an ultra-long cycle life of 85% after 500 cycles, demonstrating the enormous potential of finely optimized gradient structure design in practical applications.

[0187] The performance test results of Examples E10-E12 are shown in Table 3:

[0188] Table 3

[0189]

[0190] The materials prepared for the above embodiments and comparative examples are as follows:

[0191] The precursors of metal-organic framework compounds were prepared by a rapid precipitation method at room temperature to synthesize ZIF-8 or ZIF-67. Taking ZIF-8 as an example, 2-methylimidazole and benzimidazole were dissolved in methanol at a designed molar ratio to prepare a ligand mixture solution with a total concentration of 0.8 M; zinc nitrate hexahydrate was dissolved in methanol to prepare a 0.2 M metal salt solution. The ligand solution was rapidly poured into the metal salt solution, and the reaction was stirred at room temperature for 2 hours. The white precipitate was collected by centrifugation, washed three times with methanol, and then dried under vacuum at 60 °C for 12 hours to obtain ZIF-8 powders with different ligand ratios. For the three-layer gradient structure example, three ZIF-8 precursors with different ligand ratios were prepared for the outer, middle, and inner layers, with ligand ratios of 2-methylimidazole to benzimidazole molar ratios of 3:1, 2:1, and 1:1, respectively.

[0192] It should be noted that the pore size in this application refers to the mesoporous pores formed in the MOF framework through the control of mixed ligand ratios and structural defect engineering, rather than the inherent micropore size of ZIF-8 (approximately 1.16 nm). These mesoporous pores can be precisely controlled by adjusting the synthesis conditions of ZIF-8 with different ligand ratios, the subsequent thermal activation temperature, and the stacking pattern between the framework elements. The pore size distribution can be quantitatively described by the median value of the mesoporous distribution obtained through nitrogen adsorption-desorption testing combined with BJH or NLDFT methods.

[0193] The gradient-pore size MOF framework was constructed using a layer-by-layer growth method on the particle surface to achieve a radial gradient structure. First, a ZIF-8 precursor with an inner ligand ratio was used as the nucleus in solution. By controlling the growth time and concentration, a ZIF-8 shell with a middle ligand ratio was grown in situ on the particle surface. Subsequently, an outer ZIF-8 shell with a different ligand ratio was grown on the middle shell surface, ultimately forming a core-shell-shell three-layer concentric structure of gradient-pore size MOF particles. By controlling the synthesis conditions of ZIF-8 with different ligand ratios and the subsequent thermal activation temperature (150-250℃, vacuum or inert atmosphere), a radial gradient pore size distribution of 15-25 nm for the outer layer, 8-12 nm for the middle layer, and 3-5 nm for the inner layer can be achieved. For Example E9, which features a continuous gradient structure, a ligand concentration gradient growth method was used to gradually change the ligand ratio in the solution during the growth process, achieving a gradually increasing pore size structure from the inside to the outside.

[0194] The preparation of the protective layer by atomic layer deposition involved placing the gradient-pore size MOF particles prepared above in an atomic layer deposition apparatus, using trimethylaluminum and water vapor as precursors, and performing A1 deposition at 120-160°C. Thin film deposition. Each ALD cycle consists of a trimethylaluminum pulse (0.02 s), nitrogen purging (10 s), a water vapor pulse (0.015 s), and nitrogen purging (10 s). Thin film thicknesses of 1.0–1.8 nm are achieved by controlling the number of cycles (50–85). A protective layer is uniformly coated on the surface of MOF particles and the inner walls of their pores. For the use of Ti... Example E11 of the protective layer uses titanium tetrachloride and water vapor as precursors, with a deposition temperature of 150°C and 80 cycles. The function of the ALD protective layer is to enhance the structural stability of the MOF framework during subsequent high-temperature CVD processes and to passivate the interfacial reaction between the MOF and the electrolyte during cycling.

[0195] Gradient silicon filling via chemical vapor deposition (CVD) employs low-pressure CVD to permeate and fill the pores of a gradient-pore MOF framework with silicon precursors. In a two-step gradient filling example, the first step involves deposition for 30 minutes at a lower temperature (450°C) and lower flow rate (10 sccm silane, 50 sccm hydrogen carrier gas), allowing silicon to preferentially nucleate and grow in the inner, smaller-pore region. The second step increases the temperature to 520°C and the flow rate (30 sccm silane) for another 60 minutes, promoting silicon filling in the middle and outer layers, thus forming a radial gradient distribution with decreasing silicon content from the inside out. In a three-step fine gradient example (E12), a transition step with an intermediate temperature (480°C) and flow rate (20 sccm silane) is added to the two-step method, with a deposition time of 45 minutes, to achieve a smoother silicon content gradient transition. After CVD deposition, the material is slowly cooled to room temperature under argon protection. By adjusting the temperature, flow rate, and time parameters, a radial gradient distribution of silicon content can be achieved, with the outer layer at 30-45 wt%, the middle layer at 50-65 wt%, and the inner layer at 65-85 wt%, while the overall silicon content is controlled within the range of 45-65 wt%.

[0196] For the preparation of the physical mixing comparative sample, CE2, commercially available nano-silicon powder (median particle size D50 approximately 100 nm, purity 99.5%) was mixed with the aforementioned gradient pore size MOF framework powder in a planetary ball mill at a mass ratio corresponding to the target total silicon content (50 wt%). The ball milling conditions were 300 rpm for 4 hours, a ball-to-powder ratio of 10:1, and anhydrous ethanol as the dispersion medium. The milled mixture was then vacuum-dried at 60°C for 12 hours to remove the solvent. This comparative example was used to verify the advantages of in-situ CVD filling over simple physical mixing in terms of interfacial bonding and stress buffering.

[0197] For the preparation of the uniform structure comparative sample, comparative example CE1 was prepared using ZIF-8 with a single ligand ratio (2:1 molar ratio of 2-methylimidazole to benzimidazole). By adjusting the synthesis conditions, the mesoporous pores were uniformly distributed at around 10 nm. After ALD protective layer deposition, uniform CVD silicon filling was performed (single-step method, 500℃, silane flow rate 25 sccm, deposition time 90 minutes), resulting in a comparative sample with uniform pore size and uniform silicon content distribution (approximately 50 wt%). For the comparative example CE7 with the reverse gradient, the ligand ratio order was reversed during preparation (inner layer 3:1, middle layer 2:1, outer layer 1:1), and the CVD parameters were adjusted accordingly to create an incorrect gradient distribution of silicon content, with lower content in the inner layer and higher content in the outer layer.

[0198] The electrode fabrication and battery assembly process is as follows:

[0199] The prepared gradient pore size MOF-silicon composite powder was mixed with a conductive agent (Super P) and a binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:1) at a mass ratio of 80:10:10. An appropriate amount of deionized water was added, and the mixture was stirred in a planetary mixer at 800 rpm for 2 hours to form a homogeneous slurry. The slurry was then coated onto an electrolytic copper foil with a thickness of 10 micrometers, and the coating density was controlled at 1.5-2.0 mg / cm³. 2 The electrode was vacuum dried at 60℃ for 12 hours, and then rolled under 8MPa pressure to improve its density. The final electrode compaction density was controlled at 1.2-1.4 g / cm³. 3 The electrode was punched into a circular piece with a diameter of 14 mm, and then dried under vacuum at 120°C for 6 hours to remove residual moisture. It was then transferred to a glove box filled with high-purity argon (H2O less than 0.1 ppm, O2 less than 0.1 ppm) for later use.

[0200] CR2032 coin cell half-cells were assembled in a glove box. A gradient-pore size MOF-silicon composite electrode was used as the working electrode, a lithium metal sheet (0.6 mm thick, 99.9% purity) as the counter electrode and reference electrode, a polypropylene porous membrane (Celgard 2400, 25 μm thick) as the separator, and 1 M LiPF6 ethylene carbonate / diethyl carbonate (volume ratio 1:1) with 10 wt% fluoroethylene carbonate as the electrolyte. The electrolyte volume for each cell was controlled at 80 μL. After assembly, the cells were allowed to stand at room temperature for 12 hours to allow the electrolyte to fully wet the electrodes and separator before electrochemical performance testing. All performance test data were based on the arithmetic mean of at least three parallel samples, with a standard deviation controlled within 5% to ensure data reliability.

[0201] Electrochemical performance testing methods:

[0202] The initial coulombic efficiency and reversible specific capacity were tested using the Blue Battery testing system under constant temperature conditions of 25±1℃. For the half-cell system, the lithium insertion process was performed by constant current discharge from open circuit voltage to cutoff voltage of 0.01V (vs Li / Li+), followed by constant voltage charging until the current decayed to 0.01C. The capacity of this process was recorded as the initial charge capacity. The lithium removal process was performed by constant current charging from 0.01V to cutoff voltage of 1.5V. The capacity of this process was recorded as the initial discharge capacity. The initial coulombic efficiency was calculated by dividing the initial discharge capacity by the initial charge capacity and multiplying by 100%. The initial charge-discharge test used a small current of 0.01C to fully activate the material and form a stable solid electrolyte interface layer. Subsequently, four charge-discharge cycles were performed at a rate of 0.1C to stabilize the electrode structure. The discharge capacity of the fifth cycle was taken as the reversible specific capacity of the material. All specific capacity values ​​were calculated based on the total mass of the negative electrode composite material (including MOF framework, silicon, and ALD protective layer), and the unit was mAh / g.

[0203] Cyclic stability and capacity retention tests were conducted after the initial charge-discharge cycle and capacity stabilization. Long-term cycling tests were performed at a charge-discharge rate of 0.5C / 0.5C (1C is defined as 1850 mA / g) within a voltage window of 0.01-1.5V, recording the discharge capacity at the 5th, 100th, and 200th cycles. The capacity retention rate was calculated as the discharge capacity at the nth cycle divided by the discharge capacity at the 5th cycle multiplied by 100%, where n is either 100 or 200. For the multi-parameter co-optimized sample of Example E12, the cycling test was extended to 500 cycles to evaluate its long-term stability. A complete charge-discharge curve was recorded every 20 cycles during the cycling test to analyze voltage plateaus and polarization changes.

[0204] The average coulombic efficiency is calculated based on cycle stability test data. The single-cycle coulombic efficiency (equal to the discharge capacity of the cycle divided by the charge capacity of the cycle multiplied by 100%) is statistically analyzed for each cycle from 50 to 200, and its arithmetic mean is used as the average coulombic efficiency. This indicator reflects the degree of side reactions and interfacial stability of the material during long-term cycling. The closer the average coulombic efficiency is to 100%, the fewer the side reactions and the more stable the SEI film.

[0205] Electrode thickness expansion rate testing employed a digital micrometer (accuracy ±1 μm) to measure the thickness change of the electrode sheet under different conditions to assess the degree of volume expansion. The measurement consisted of two phases: For the initial expansion rate test, after the battery was initially charged to 0.01V, it was disassembled in a glove box. The negative electrode sheet was carefully removed, and residual electrolyte was gently absorbed with filter paper. The thickness was measured at five different locations, and the average value was recorded as d1. For the cyclic expansion rate test, after 100 cycles, the battery was disassembled in a fully charged state, and the thickness was measured using the same method. The initial thickness d0 was the thickness measured after electrode preparation but before battery assembly. The expansion rate was calculated as the difference between d1 and d0, divided by d0, multiplied by 100%. To ensure measurement accuracy, each sample was measured at five evenly distributed locations, and the average value was taken as the final result. The measurement pressure was kept constant (approximately 0.5 N) during the measurement.

[0206] Rate performance testing was conducted using independently fabricated parallel cells to reflect the intrinsic kinetic characteristics of the material. After completing the initial stable cycling (the first 5 cycles), the battery was charged at a fixed rate of 0.5C, and then discharged at rates of 0.2C, 0.5C, 1C, and 2C, respectively, for 5 cycles at each rate. The average discharge capacity of the last 3 cycles was taken as the capacity value at that rate. After the rate test, the battery was cycled 5 more times at 0.5C to assess the rate recoverability of the material. The rate capacity retention rate was calculated by dividing the high-rate discharge capacity by the 0.2C discharge capacity and multiplying by 100%. This test was used to evaluate the impact of the gradient pore size structure on lithium-ion transport kinetics.

[0207] Electrochemical impedance spectroscopy (EIS) was performed on the battery after the 5th and 100th cycles using an electrochemical workstation. Before testing, the battery was charged to 50% state of charge and allowed to stand for 2 hours to allow the voltage to stabilize. Test parameters were: frequency range 100 kHz to 0.01 Hz, AC amplitude 10 mV, and temperature 25 ± 1 °C. The high-frequency intercept was read from the Nyquist plot as the solution resistance, and the semicircle diameter was approximated as the total interfacial impedance (including SEI impedance and charge transfer impedance). The impedance growth rate was calculated as the difference between the total impedance at cycle 100 and cycle 5, divided by the total impedance at cycle 5, multiplied by 100%. This test employed a simplified readout-based analysis method, avoiding complex equivalent circuit fitting to ensure data processing simplicity and repeatability.

[0208] High-temperature cycling performance testing involved placing key samples (E1, CE1, CE6, and E12) in a 45±1℃ constant temperature chamber for accelerated aging cycling to evaluate the structural and interfacial stability of the materials under high-temperature conditions. The test conditions were the same as the room temperature cycling test (0.5C / 0.5C, 0.01-1.5V), cycling for 200 cycles, and recording the capacity retention at the 100th and 200th cycles. High-temperature cycling testing accelerates side reactions and structural degradation processes, providing a more rigorous test of the material's long-term stability.

[0209] Based on the above experimental results and comparative analysis, the superior performance of the silicon-based composite structure proposed in this application stems from a three-tiered synergistic mechanism. The first tier is a hierarchical buffering mechanism at the structural level. The outer layer's large pores provide ample primary buffer space, absorbing the main stress impacts from silicon expansion. The middle layer's transitional pores act as a bridge for stress transfer and redistribution, preventing abrupt stress changes at the outer-inner layer interface. The inner layer's small pores, through a nano-confining effect, confine the silicon particle size within the stress tolerance range while providing rigid constraints to maintain structural integrity. This three-tiered buffering system achieves orderly stress dispersion and gradual release, avoiding catastrophic failure caused by localized stress concentration. The second tier is a gradient matching at the compositional level. The decreasing silicon content gradient from the inside to the outside ensures that the absolute expansion of each layer matches the corresponding pore size's buffering capacity. The outer layer's low silicon content results in a smaller absolute expansion, which matches the buffer space of the large pores, avoiding space waste and capacity loss. Although the inner layer's high silicon content results in a larger absolute expansion, the strong confinement effect provided by the small pores and the mechanical support of the thick walls effectively constrain it, preventing uncontrolled expansion. This precise capacity-space matching design maximizes capacity density while ensuring each layer operates within its safe stress-bearing capacity. The third level involves modulus control at the mechanical level. The transition from flexible to rigid mechanical modulus, achieved through ligand ratio gradients, provides the optimal mechanical path for stress transfer. The outer, highly flexible framework adapts to silicon volume changes without brittle fracture, absorbing and buffering stress through elastic deformation. The middle layer's transition modulus ensures smooth stress transfer from the flexible to the rigid region, preventing interface delamination caused by abrupt modulus changes. The inner, highly rigid framework provides strong constraints, limiting excessive silicon expansion and maintaining structural integrity. This outer-flexible, inner-rigid modulus distribution aligns closely with the buffer-support composite design concept in macroscopic engineering structures, forming a crucial mechanical basis for achieving long-term cycling stability. The ALD protective layer plays a dual role in the entire technology system: protecting the MOF framework from CVD high-temperature damage during material preparation, ensuring the accuracy of the gradient pore size structure; and passivating the MOF-electrolyte interface during cyclic use, suppressing side reactions and maintaining interface stability. The CVD gradient filling process achieves precise positioning and filling of silicon in the gradient aperture framework through stepwise control of temperature and flow rate, ensuring perfect synergy between compositional gradient and structural gradient.

[0210] This invention provides a battery device, characterized in that it includes: any of the above-mentioned battery cells, or includes battery cells prepared using any of the above-mentioned battery cell preparation methods, and the battery device includes one or more of battery modules, battery packs, and energy storage batteries.

[0211] This invention provides an electrical device, characterized in that the electrical device includes a battery device as described above, the battery device being used to provide electrical energy.

[0212] This invention provides an energy storage device, characterized in that the energy storage device includes a battery device as described above, the battery device being used to provide electrical energy.

[0213] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A battery cell, characterized by, The negative electrode of the battery cell comprises a silicon-based composite structure, the silicon-based composite structure comprises an outer layer MOF structure, a middle layer MOF structure and an inner layer MOF structure, the outer layer MOF structure is arranged on the outer wall of the middle layer MOF structure, the middle layer MOF structure is arranged on the outer wall of the inner layer MOF structure, the pore size of the outer layer MOF structure is greater than that of the middle layer MOF structure, the pore size of the middle layer MOF structure is greater than that of the inner layer MOF structure, the silicon content of the inner layer MOF structure is greater than that of the middle layer MOF structure, and the silicon content of the middle layer MOF structure is greater than that of the outer layer MOF structure.

2. The battery cell of claim 1, wherein, The ligand of the silicon-based composite structure comprises 2-methylimidazole and benzimidazole, the ligand molar ratio of the outer layer MOF structure is greater than that of the middle layer MOF structure, the ligand molar ratio of the middle layer MOF structure is greater than that of the inner layer MOF structure, and the ligand molar ratio is the ratio of the 2-methylimidazole to the benzimidazole.

3. The battery cell of claim 1, wherein, The mass ratio or thickness ratio between the outer layer MOF structure, the middle layer MOF structure and the inner layer MOF structure ranges from (1-3):(1-2):(1-2).

4. The battery cell of claim 1, wherein, The outer layer MOF structure, the middle layer MOF structure and the inner layer MOF structure all comprise channels, and the negative electrode of the battery cell further comprises an aluminum oxide protective layer arranged on the inner wall of the channels.

5. The battery cell of claim 4, wherein, The negative electrode of the battery cell further comprises a nano-silicon layer arranged in the channels.

6. The battery cell of claim 1, wherein, The battery cell further comprises a conductive layer arranged on the surface of the outer layer MOF structure away from the middle layer MOF structure.

7. The battery cell of claim 1, wherein, The pore size of the outer layer MOF structure ranges from 10-30 nm, the pore size of the middle layer MOF structure ranges from 6-20 nm, and the pore size of the inner layer MOF structure ranges from 2-10 nm.

8. The battery cell of claim 1, wherein, The silicon content of the outer layer MOF structure is 20-45 wt%, the silicon content of the middle layer MOF structure is 45-65 wt%, and the silicon content of the inner layer MOF structure is 60-85 wt%.

9. A method of producing a battery cell, characterized by, The method is used for preparing the battery cell of any one of claims 1-8, and the method comprises: The outer layer MOF structure, the middle layer MOF structure and the inner layer MOF structure are prepared by a solvothermal growth method, wherein the outer layer MOF structure is arranged on the outer wall of the middle layer MOF structure, the middle layer MOF structure is arranged on the outer wall of the inner layer MOF structure, the pore size of the outer layer MOF structure is greater than that of the middle layer MOF structure, the pore size of the middle layer MOF structure is greater than that of the inner layer MOF structure, the silicon content of the inner layer MOF structure is greater than that of the middle layer MOF structure, and the silicon content of the middle layer MOF structure is greater than that of the outer layer MOF structure.

10. The method of claim 9, wherein, The outer layer MOF structure, the middle layer MOF structure and the inner layer MOF structure are prepared by a solvothermal growth method, comprising: The zinc source solution and the first ligand solution are mixed and reacted under preset growth conditions to form the outer-layer MOF structure in a ring shape, the first ligand solution being a mixed solution obtained by mixing 2-methylimidazole and benzimidazole in a first preset ligand molar ratio and then dissolving the mixture in a solvent, and the preset growth conditions including a reaction temperature of 120-140°C and a reaction time of 12-24 hours; The outer-layer MOF structure is placed in a mixture of the zinc source solution and a second ligand solution to form the middle-layer MOF structure in a ring shape on the inner wall of the outer-layer MOF structure under the preset growth conditions, the second ligand solution being a mixed solution obtained by mixing the 2-methylimidazole and the benzimidazole in a second preset ligand molar ratio and then dissolving the mixture in the solvent; The outer-layer MOF structure and the middle-layer MOF structure are placed in a mixture of the zinc source solution and a third ligand solution to form the inner-layer MOF structure in a ring shape on the inner wall of the middle-layer MOF structure under the preset growth conditions, the third ligand solution being a mixed solution obtained by mixing the 2-methylimidazole and the benzimidazole in a third preset ligand molar ratio and then dissolving the mixture in the solvent; The first preset ligand molar ratio is greater than the second preset ligand molar ratio, and the second preset ligand molar ratio is greater than the third preset ligand molar ratio.

11. The method of claim 9, wherein, After the outer-layer MOF structure, the middle-layer MOF structure and the inner-layer MOF structure are prepared by using the solvothermal growth method, the method further comprises: depositing an aluminum oxide protective layer on the inner wall of the pores of the outer-layer MOF structure, the middle-layer MOF structure and the inner-layer MOF structure; filling a nanosilicon layer in the pores of the outer-layer MOF structure, the middle-layer MOF structure and the inner-layer MOF structure after the aluminum oxide protective layer is deposited.

12. The method of claim 11, wherein, The method of depositing an aluminum oxide protective layer on the inner wall of the pores of the outer-layer MOF structure, the middle-layer MOF structure and the inner-layer MOF structure comprises: placing the outer-layer MOF structure, the middle-layer MOF structure and the inner-layer MOF structure in an atomic layer deposition reaction chamber; a first treatment step of introducing trimethylaluminum into the atomic layer deposition reaction chamber so that the trimethylaluminum is adsorbed on the inner wall of the pores, the pulse time of the first treatment step being a first pulse time; a first purging step of purging the atomic layer deposition reaction chamber with nitrogen or argon to remove unreacted trimethylaluminum and byproducts, the purging time of the first purging step being a first purging time; a second processing step of introducing water vapor into the atomic layer deposition reaction chamber, so that the water vapor reacts with the trimethylaluminum adsorbed on the inner wall of the pore to generate A , a pulse time of the second processing step is a second pulse time; a second purging step of purging the atomic layer deposition reaction chamber with nitrogen or argon to remove unreacted water vapor and byproducts, the purging time of the second purging step being a second purging time; The first processing step, the first purging step, the second processing step and the second purging step are repeatedly performed for a preset number of times to deposit the aluminum oxide protective layer on the pore inner wall of the outer layer MOF structure, the middle layer MOF structure and the inner layer MOF structure, the preset number of times being determined according to a target thickness of the aluminum oxide protective layer, and the first pulse time, the second pulse time, the first purging time and the second purging time being determined based on a reaction condition in the atomic layer deposition reaction chamber.

13. The method of claim 11, wherein, After the aluminum oxide protective layer is deposited, a nanosilicon layer is filled in the pores of the outer layer MOF structure, the middle layer MOF structure and the inner layer MOF structure, comprising: The outer layer MOF structure, the middle layer MOF structure and the inner layer MOF structure on which the aluminum oxide protective layer is deposited are placed in a chemical vapor deposition reaction tube, and after vacuumizing, an inert carrier gas is introduced; Silane gas is introduced into the chemical vapor deposition reaction tube at a preset flow rate, and the preset flow rate ranges from 10 to 50 standard cubic centimeters per minute; The chemical vapor deposition reaction tube is controlled to be heated to a target deposition temperature, and at the target deposition temperature, deposition of the nanosilicon layer is performed on the pore inner wall of the outer layer MOF structure, the middle layer MOF structure and the inner layer MOF structure, to obtain a silicon-based composite structure of the battery monomer, and the deposition time of the nanosilicon is determined according to a target silicon content.

14. The method of claim 13, wherein, After the silicon-based composite structure of the battery monomer is obtained, the method further comprises: A conductive layer is coated on a first surface of the silicon-based composite structure, the first surface of the silicon-based composite structure being a surface of the outer layer MOF structure away from the middle layer MOF structure.

15. A battery device characterized by comprising: Comprising: The battery monomer of any one of claims 1 to 8, or the battery monomer prepared using the preparation method of any one of claims 9 to 14, the battery device comprising one or more of a battery module, a battery pack, an energy storage battery.

16. An electrical device, comprising: The electrical device comprises the battery device of claim 15, and the battery device is used to provide electrical energy.

17. An energy storage device, characterized by The energy storage device comprises the battery device of claim 15, and the battery device is used to provide electrical energy. The energy storage device comprises the battery device of claim 15, and the battery device is used to provide electrical energy.

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