Gradient elastic layer filled porous silicon negative electrode material and preparation method thereof, negative electrode plate and all-solid-state battery

Abstract

The invention provides a gradient elastic layer filled porous silicon negative electrode material and a preparation method thereof, a negative electrode plate and an all-solid-state battery, and relates to the field of lithium ion battery manufacturing. The negative electrode material comprises a porous silicon substrate, the interior of the porous silicon substrate comprises through pore channels; gradient elastic layers are arranged in the pore channels; the gradient elastic layer is of a three-stage gradient structure in the depth direction of the pore channel and comprises a first-stage filling layer located at the bottom of the pore channel, and the first-stage filling layer is a flexible elastic layer formed by pure polymers; the second-stage filling layer is positioned in the middle of the pore channel and is a mixed layer of a rigid carbon material and a polymer; the third-stage filling layer is positioned at an inlet of the pore channel and is a high-modulus layer formed by compounding a rigid carbon material and a polymer; wherein the elastic modulus of the third-stage filling layer is larger than that of the second-stage filling layer, and the elastic modulus of the second-stage filling layer is larger than that of the first-stage filling layer.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery manufacturing, and in particular to a gradient elastic layer filled porous silicon anode material and its preparation method, anode sheet and all-solid-state battery. Background Technology

[0002] In the development of lithium-ion battery anode materials, silicon-based materials have become a research hotspot due to their high theoretical capacity. To address the challenge of silicon's volume expansion rate exceeding 300% during charge-discharge cycles, existing technologies generally employ the construction of three-dimensional interconnected porous silicon structures with large pore sizes ranging from 50 to 500 nanometers. However, the selection of pore-filling materials faces a fundamental contradiction: rigid fillers such as silicon carbide or titanium dioxide, while providing high structural rigidity (Young's modulus higher than 50 gigapascals), have a fracture strain rate of less than 5%, making them highly susceptible to brittle fracture during the dramatic expansion of silicon; while flexible polymer materials, although possessing high elongation at break (exceeding 200%), have an excessively low elastic modulus (below 1 gigapascal), failing to effectively support the pore structure in the initial stages of charge-discharge, significantly increasing the risk of pore collapse. Simultaneously, to improve structural stability, existing methods often employ overfilling strategies, controlling the pore porosity below 30%. This not only weakens the material's buffering capacity but also severely hinders the transport efficiency of lithium ions within the pores, resulting in a decline in overall battery performance. The aforementioned defects make it difficult for a single homogeneous filling scheme to simultaneously meet the requirements of structural rigidity and elastic deformation, thus restricting the practical application of silicon-based anode materials. Summary of the Invention

[0003] The purpose of this application is to provide a gradient elastic layer filled porous silicon anode material, its preparation method, anode sheet, and all-solid-state battery to solve the above-mentioned problems.

[0004] To achieve the above objectives, this application adopts the following technical solution: This application provides a gradient elastic layer filled porous silicon anode material, including a porous silicon substrate; The porous silicon substrate includes through-holes; a gradient elastic layer is disposed within the through-holes. The gradient elastic layer has a three-level gradient structure along the depth direction of the channel, including: The first-stage filling layer is located at the bottom of the channel and is a flexible elastic layer formed of pure polymer. The second-level filling layer is located in the middle of the channel. The second-level filling layer is a mixture of rigid carbon material and polymer. A third-level filling layer located at the entrance of the channel, wherein the third-level filling layer is a high-modulus layer formed by a composite of rigid carbon material and polymer; The elastic modulus of the third-level filling layer is greater than that of the second-level filling layer, and the elastic modulus of the second-level filling layer is greater than that of the first-level filling layer.

[0005] Optionally, the overall porosity of the gradient elastic layer increases gradually from the inlet to the bottom of the channel, with a porosity of 15-25% at the inlet and 65-75% at the bottom.

[0006] Optionally, the pore size of the porous silicon substrate is 20-500 nm.

[0007] Optionally, the rigid carbon material includes at least one of graphene, carbon nanotubes, carbon fibers and their derivatives, graphene nanosheets, silicon carbide and silicon carbide whiskers, carbon black, acetylene black, graphyne, and carbon-coated metal nanowires.

[0008] Preferably, the carbon material comprises at least one of carbon nanofibers, carbon nanotubes, graphene, and carbon black.

[0009] Optionally, in the second-level filling layer, the mass ratio of the rigid carbon material is 10-29 wt%.

[0010] Optionally, in the third-level filling layer, the mass ratio of the rigid carbon material is 30-60 wt%.

[0011] Optionally, the polymer constituting the gradient elastic layer is a thermoplastic polymer or thermoplastic elastomer with an elastic modulus of 0.1-10 GPa, an elongation at break of ≥150%, and a loss factor tanδ of 0.12-0.35.

[0012] Optionally, the thermoplastic polymer and the thermoplastic elastomer each independently include at least one of polyurethane, styrene-butadiene-styrene block copolymer, polyether block amide, polyvinylidene fluoride, polycarbonate, polylactic acid and polybutylene adipate / terephthalate blend.

[0013] This application also provides a method for preparing a porous silicon anode material filled with a gradient elastic layer, including: A porous silicon substrate with through-holes was filled with a three-level gradient solution and dried to obtain a gradient elastic layer. First-stage filling: A first-stage filling solution is injected into a porous silicon substrate. The first-stage filling solution contains a high concentration of rigid carbon material and polymer, and a 10% stress is applied to the system. -3 The Pa-level vacuum causes the solution to remain mainly at the pore inlet, forming a third-level filling layer; Second-stage filling: A second filling solution is permeated into the porous silicon substrate. The second filling solution includes a low-concentration rigid carbon material and a polymer, which permeates into the middle of the pores to form a second-stage filling layer. Third-stage filling: A pure polymer solution is permeated into the porous silicon substrate under normal pressure, allowing it to penetrate to the bottom of the pores to form a first-stage filling layer.

[0014] Optionally, the viscosity of the first filling solution is 90-110 mPa·s.

[0015] Optionally, the viscosity of the second filling solution is 2-30 mPa·s.

[0016] Optionally, in the first stage of filling, the mass concentration of the polymer is 10-20 wt%.

[0017] Optionally, in the third stage of filling, the mass concentration of the polymer is 2-4 wt%.

[0018] This application also provides a negative electrode sheet, wherein the negative electrode is filled with porous silicon negative electrode material using the gradient elastic layer.

[0019] This application also provides an all-solid-state battery, including the aforementioned negative electrode sheet.

[0020] Compared with the prior art, the beneficial effects of this application include: This application provides a gradient elastic layer-filled porous silicon anode material, its preparation method, and an all-solid-state battery. By constructing a three-level gradient elastic layer with decreasing elastic modulus along the depth of the pores, the structural failure problem caused by volume expansion of silicon-based anode materials during charge-discharge cycles is solved. By setting the three-level gradient elastic layer in the through-channels within the porous silicon substrate, effective control of stress distribution during silicon volume expansion is achieved. The design of the through-channels within the porous silicon substrate provides space to accommodate silicon volume expansion, thereby reducing overall stress concentration. Furthermore, the gradient elastic layer within the pores serves as a dynamically responsive filling material, avoiding structural failure problems caused by brittle fracture of a single hard material or insufficient support of a single flexible material. Compared to existing filling methods using only hard or flexible materials, this approach can maintain sufficient porosity while simultaneously ensuring structural stability and ion transport capacity. This avoids the problems of brittle fracture of hard materials during expansion and the inability of flexible materials to suppress initial channel collapse, while also preventing over-filling that reduces lithium-ion diffusion efficiency. Detailed Implementation

[0021] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0022] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0023] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0024] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0025] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0026] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0027] To better explain the technical solution provided in this application, the technical solution provided in this application will be described in general before the specific implementation.

[0028] This application provides a gradient elastic layer filled porous silicon anode material, including a porous silicon substrate; The porous silicon substrate includes through-holes; a gradient elastic layer is disposed within the through-holes. The gradient elastic layer has a three-level gradient structure along the depth direction of the channel, including: The first-stage filling layer is located at the bottom of the channel and is a flexible elastic layer formed of pure polymer. The second-level filling layer is located in the middle of the channel. The second-level filling layer is a mixture of rigid carbon material and polymer. A third-level filling layer located at the entrance of the channel, wherein the third-level filling layer is a high-modulus layer formed by a composite of rigid carbon material and polymer; The elastic modulus of the third-level filling layer is greater than that of the second-level filling layer, and the elastic modulus of the second-level filling layer is greater than that of the first-level filling layer.

[0029] In practical applications, porous silicon substrates can be understood as silicon materials with a three-dimensional interconnected pore structure, whose main function is to provide space for silicon volume expansion. Furthermore, the through-pores refer to continuous channels extending from the surface of the porous silicon substrate into its interior, whose main purpose is to provide pathways for lithium-ion transport and alleviate stress concentration caused by silicon expansion.

[0030] Specifically, the gradient elastic layer filling porous silicon anode material achieves effective control of stress distribution during silicon volume expansion by setting a three-level gradient elastic layer in the through-channels inside the porous silicon matrix. The through-channel design within the porous silicon matrix provides space to accommodate silicon volume expansion, thereby reducing overall stress concentration. Furthermore, the gradient elastic layer within the channels acts as a dynamic response filling material, avoiding structural failures caused by brittle fracture of a single rigid material or insufficient support of a single flexible material. The gradient elastic layer is designed as a three-level gradient structure along the depth of the channels, with each level of filling layer having a customized modulus distribution based on the stress state at different locations within the channels. The first-level filling layer at the bottom of the channels is a flexible elastic layer formed from pure polymer, providing high elongation at break to accommodate large deformations, effectively alleviating stress concentration caused by the high expansion rate at the bottom, and preventing cracking. The second-level filling layer in the middle of the channels uses a hybrid layer of rigid carbon material and polymer, combining the rigid support of the carbon material and the elastic buffer of the polymer to form a transition layer with a moderate modulus, maintaining structural integrity while allowing controllable deformation. The third-level filling layer located at the pore inlet is a high-modulus layer formed by a high-concentration rigid carbon material and polymer composite, enhancing the mechanical strength of the inlet region and preventing pore collapse during the initial expansion phase. Consequently, the elastic modulus of the third-level filling layer is greater than that of the second-level filling layer, and the elastic modulus of the second-level filling layer is greater than that of the first-level filling layer. This decreasing relationship ensures a smooth transition in modulus from the inlet to the bottom, allowing the expansion force to be gradually absorbed and avoiding localized failure caused by sudden stress changes. Through this three-level gradient structure design, sufficient porosity is maintained while balancing structural stability and ion transport capacity. This solves the structural failure problem caused by silicon volume expansion during charge-discharge cycles in silicon-based anode materials, while also avoiding the phenomenon of overfilling reducing lithium-ion diffusion efficiency.

[0031] The porous silicon substrate is prepared as follows: SiO2, Mg, and NaCl are mixed in a certain proportion (preferably by mass ratio 1:0.8:2), ball-milled at 300 rpm for 2 hours, and the resulting mixture is pressed into sheets with a diameter of 10 mm (pressure 10 MPa). The sample is placed in a tube furnace and heated to 650°C at 5°C / min under argon protection, and held at that temperature for 4 hours. After cooling, the sample is removed and soaked successively in 1 M HCl (to remove MgO) and HF (5 wt%, to remove unreacted SiO2) for 2 hours; washed with deionized water until neutral, and vacuum dried at 60°C for 12 hours to obtain the final product.

[0032] In one optional embodiment, the overall porosity of the gradient elastic layer increases gradually from the inlet to the bottom of the channel, with a porosity of 15-25% at the inlet and 65-75% at the bottom.

[0033] Optionally, the porosity at the inlet can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or any value between 15% and 25%; the porosity at the bottom can be 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, or any value between 65% and 75%.

[0034] In one optional embodiment, the pore size of the porous silicon substrate is 20-500 nm.

[0035] Optionally, the pore size of the porous silicon substrate can be 20 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or any value between 20 and 500 nm.

[0036] In one optional embodiment, the rigid carbon material includes at least one of graphene, carbon nanotubes, carbon fibers and their derivatives, graphene nanosheets, silicon carbide and silicon carbide whiskers, carbon black, acetylene black, graphylene, and carbon-coated metal nanowires. Preferably, it includes at least one of carbon nanofibers, carbon nanotubes, graphene, and carbon black.

[0037] In an optional embodiment, the rigid carbon material in the second-level filling layer has a mass ratio of 10-29 wt%.

[0038] Optionally, in the second-stage filler layer, the mass ratio of rigid carbon material can be 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, 20wt%, 22wt%, 24wt%, 26wt%, 29wt%, or any value between 12-29wt%.

[0039] In an optional embodiment, the rigid carbon material in the third-level filling layer has a mass ratio of 30-60 wt%.

[0040] Optionally, in the third-level filler layer, the mass ratio of rigid carbon material can be 30wt%, 32wt%, 34wt%, 36wt%, 38wt%, 40wt%, 42wt%, 44wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, or any value between 30wt% and 60wt%.

[0041] In an optional embodiment, the polymer constituting the gradient elastic layer is a thermoplastic polymer or thermoplastic elastomer with an elastic modulus of 0.1-10 GPa, an elongation at break of ≥150%, and a loss factor tanδ of 0.12-0.35.

[0042] Optionally, the elastic modulus of the polymer can be 0.1 GPa, 0.5 GPa, 1 GPa, 1.5 GPa, 2 GPa, 2.5 GPa, 3 GPa, 3.5 GPa, 4 GPa, 4.5 GPa, 5 GPa, 5.5 GPa, 6 GPa, 6.5 GPa, 7 GPa, 7.5 GPa, 8 GPa, 8.5 GPa, 9 GPa, 9.5 GPa, or 10 GPa, or between 0.1 and 10 GPa. The elongation at break of the polymer can be any value of 150%, 155%, 160%, 165%, 170%, 175%, 180%, 185%, 190%, 195%, 200%, or any value not less than 150%; the loss factor tanδ can be 0.12, 0.15, 0.18, 0.21, 0.24, 0.27, 0.3, 0.33, 0.35, or any value between 0.12 and 0.35.

[0043] In an optional embodiment, the thermoplastic polymer and the thermoplastic elastomer each independently include at least one of polyurethane, styrene-butadiene-styrene block copolymer, polyether block amide, polyvinylidene fluoride, polycarbonate, polylactic acid and polybutylene adipate / terephthalate blend.

[0044] Secondly, a method for preparing a porous silicon anode material filled with a gradient elastic layer is provided, comprising: A porous silicon substrate with through-holes was filled with a three-level gradient solution and dried to obtain a gradient elastic layer. First-stage filling: A first-stage filling solution is injected into a porous silicon substrate. The first-stage filling solution contains a high concentration of rigid carbon material and polymer, and a 10% stress is applied to the system. -3 The Pa-level vacuum causes the solution to remain mainly at the pore inlet, forming a third-level filling layer; Second-stage filling: A second filling solution is permeated into the porous silicon substrate. The second filling solution includes a low-concentration rigid carbon material and a polymer, which permeates into the middle of the pores to form a second-stage filling layer. Third-stage filling: A pure polymer solution is permeated into the porous silicon substrate under normal pressure, allowing it to penetrate to the bottom of the pores to form a first-stage filling layer.

[0045] In one optional embodiment, the viscosity of the first filling solution is 90-110 mPa·s.

[0046] Optionally, the viscosity of the first filling solution can be 90 mPa·s, 91 mPa·s, 92 mPa·s, 93 mPa·s, 94 mPa·s, 95 mPa·s, 96 mPa·s, 97 mPa·s, 98 mPa·s, 99 mPa·s, 100 mPa·s, 101 mPa·s, 102 mPa·s, 103 mPa·s, 104 mPa·s, 105 mPa·s, 106 mPa·s, 107 mPa·s, 108 mPa·s, 109 mPa·s, 110 mPa·s, or any value between 90 and 100 mPa·s.

[0047] In one optional embodiment, the viscosity of the second filling solution is 2-30 mPa·s.

[0048] Optionally, the viscosity of the second filling solution can be 2 mPa·s, 3 mPa·s, 4 mPa·s, 6 mPa·s, 8 mPa·s, 10 mPa·s, 12 mPa·s, 14 mPa·s, 16 mPa·s, 18 mPa·s, 20 mPa·s, 22 mPa·s, 24 mPa·s, 26 mPa·s, 28 mPa·s, 30 mPa·s, or any value between 2 and 30 mPa·s.

[0049] In an optional embodiment, the polymer has a mass concentration of 10-20 wt% in the first stage of filling.

[0050] Optionally, in the first stage of filling, the mass concentration of the polymer can be 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, or any value between 10-20wt%.

[0051] In an optional embodiment, the polymer concentration in the third stage of filling is 2-4 wt%.

[0052] Optionally, in the third-quarter filler, the polymer mass concentration can be 2 wt%, 3 wt%, 4 wt%, or any value between 2 and 4 wt%.

[0053] Thirdly, this application also provides a negative electrode sheet, wherein the negative electrode is filled with porous silicon negative electrode material using the gradient elastic layer.

[0054] Fourthly, this application also provides an all-solid-state battery, including the aforementioned negative electrode sheet.

[0055] Understandably, the technical solution provided in this application constructs an elastic support system capable of dynamically adapting to silicon volume expansion by precisely defining the type and key mechanical performance parameters of the polymer in the gradient elastic layer. Thermoplastic polymers or thermoplastic elastomers are selected as the polymer matrix. These materials, due to the reversible motion characteristics of their molecular chains, can continuously provide elastic recovery force during silicon expansion, ensuring the integrity of the gradient layer during repeated deformation. The reasonable design of the elastic modulus range avoids the risk of fracture caused by excessive rigidity and prevents structural collapse caused by excessive flexibility, thereby optimizing the structural robustness and cycle reliability of the anode material. The setting of the elongation at break effectively absorbs expansion energy, reduces the generation of microcracks, and maintains the continuity and structural stability of the gradient layer. Precise control of the loss factor achieves efficient conversion of mechanical energy into thermal energy, reduces internal stress accumulation and fatigue damage, and avoids energy waste due to excessive damping effects. The selection and performance limitations of the aforementioned polymers, combined with the three-level filling structure of the porous silicon matrix and the gradient elastic layer, significantly improve the durability of the material under dynamic stress environments, solving the problems of gradient layer functional failure and shortened cycle life caused by insufficient polymer performance.

[0056] The core innovation of this application lies in combining a gradient elastic layer with a porous silicon anode material to form a structural design with decreasing elastic modulus and increasing porosity along the depth of the pores, thereby effectively addressing the challenge of volume expansion of silicon during charge-discharge cycles. Specifically, a high-modulus layer at the inlet resists initial expansion pressure and prevents pore collapse; a hybrid layer of rigid carbon material and polymer in the middle balances strength and elasticity; and a flexible elastic layer formed by pure polymer at the bottom absorbs energy from volume changes. This design avoids the defects of traditional single-filler materials that are prone to fracture at high modulus or collapse at low modulus, while maintaining unobstructed ion diffusion channels, achieving the effect of suppressing structural deformation while ensuring efficient lithium-ion migration.

[0057] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0058] Example 1 This embodiment provides a gradient elastic layer-filled porous silicon anode material: The gradient elastic layer filling porous silicon anode material includes a porous silicon matrix with through-holes inside, and a gradient elastic layer with a three-level gradient structure is set in the through-holes; the outermost layer is a high-modulus layer composed of high-concentration rigid carbon material and polymer composite, the middle layer is a flexible elastic layer composed of low-concentration rigid carbon material and polymer composite, and the inner layer is a flexible elastic layer formed by pure polymer.

[0059] The pore size of the through-hole is 200 nm. The overall porosity of the gradient elastic layer increases gradually from the pore inlet to the bottom of the pore, with a porosity of 20% at the pore inlet and 70% at the bottom.

[0060] This embodiment also provides a gradient elastic layer-filled porous silicon anode material, the specific steps of which are as follows: Preparation of porous silicon matrix: Si / SiO2 composite porous material with pore size of 200 nm and porosity of 80% was synthesized by magnesium thermal reduction method (as described in the specification).

[0061] Preparation of filling solutions: The inlet solution is 10 mL of NMP solution containing 20 wt% PVDF + 8 wt% CNTs (total solid content 28%) with a viscosity of 95 mPa·s; the middle solution is 10 mL of 15 wt% PVDF + 1.5 wt% graphene with a viscosity of 12 mPa·s; the bottom solution is 10 mL of 10 wt% PVDF with a viscosity of 3 mPa·s.

[0062] 1.0 g of porous silicon substrate (pore size 200 nm) was sequentially immersed in the inlet, middle, and bottom solutions. After each immersion, the substrate was centrifuged at 1000 rpm for 30 seconds to ensure layered penetration of the solution. The material was then placed in a tube furnace with argon gas (purity ≥99.99%) at a flow rate of 2-5 L / min and a heating rate of 3-5 °C / min for pre-curing at 80 °C for 1 hour (to remove solvent), followed by annealing at 180 °C for 2 hours (to crystallize), and then allowed to cool naturally before removal.

[0063] This embodiment also provides a negative electrode sheet, the preparation method of which is as follows: The obtained material was prepared in a silicon-based anode:PAA binder ratio of 95:5. 342 mg of silicon nanosheets and 18 mg of PAA binder were added to 2 mL of DMF, and a uniformly mixed anode slurry was obtained by magnetic stirring. A clean copper foil was taken, and its surface was cleaned with anhydrous ethanol. After the surface dried, the slurry was applied to the copper foil surface using a blade coating method (silicon loading ≈ 0.20 mg / cm²). 2 Then, the copper foil coated with the above negative electrode slurry was placed in an 80 ℃ vacuum drying oven and dried for 4 h to remove DMF. After drying, the electrode sheet was removed, and then the electrode sheet was punched into a composite silicon nanosheet negative electrode with a diameter of 10 mm using a punching machine.

[0064] Example 2 The only difference between this embodiment and Embodiment 1 is that: The material of the inlet layer (i.e., the third-stage filler) was replaced with: 20wt% polyurethane (PU) + 30wt% carbon nanofibers (CNF), with a solution solid content of 20% and a viscosity of 90 mPa·s.

[0065] The material of the middle layer (i.e., the second-level filler) was replaced with 15 wt% polycarbonate (PC) + 3 wt% graphene, with a solution solid content of 20% and a viscosity of 20 mPa·s.

[0066] The material of the bottom layer (i.e., the first-level filler) was replaced with 10 wt% styrene-butadiene-styrene block copolymer (SBS), with a solution solid content of 15% and a viscosity of 4 mPa·s.

[0067] Example 3 The only difference between this embodiment and Embodiment 1 is that: The material of the inlet layer was replaced with 25 wt% PVDF + 40 wt% carbon fiber, the solution solid content was 65%, and the viscosity was 120 mPa·s.

[0068] The material of the middle layer was replaced with 18 wt% PVDF + 5 wt% graphene, the solid content of the solution was 23%, and the viscosity was 25 mPa·s.

[0069] The bottom layer material was replaced with 12 wt% PVDF + 10 wt% polyurethane, with a solution solid content of 23% and a viscosity of 8 mPa·s.

[0070] Example 4 The only difference between this embodiment and Embodiment 1 is that: The material of the inlet layer was replaced with 25 wt% PVDF + 40 wt% carbon fiber, the solution solid content was 65%, and the viscosity was 120 mPa·s.

[0071] The material of the middle layer was replaced with 18 wt% PVDF + 5 wt% graphene, the solid content of the solution was 23%, and the viscosity was 25 mPa·s.

[0072] The bottom layer material was replaced with 12 wt% PVDF + 10 wt% polyurethane, with a solution solid content of 23% and a viscosity of 8 mPa·s.

[0073] Comparative Example 1 The only difference between this comparative example and Example 1 is that: 1.0 g of porous silicon substrate (same as in Example 1) was immersed in 10 mL of phenolic resin / ethanol solution (30 wt%) with a viscosity of 50 mPa·s. After sintering in nitrogen at 800 °C for 2 hours, a hard carbon filling layer was formed, yielding the negative electrode material.

[0074] Comparative Example 2 The only difference between this comparative example and Example 1 is that: 1.0g of porous silicon matrix, small tar molecules, and pitch were ball-milled and mixed at a mass ratio of 1:0.3:0.5. After drying at 180℃, the mixture was sintered at 800℃ for 4 hours in an argon atmosphere to obtain the anode material.

[0075] Comparative Example 3 The only difference between this comparative example and Example 1 is that: Instead of filling the porous silicon material with a gradient elastic layer, 1.0 g of porous silicon substrate was immersed in 10 mL of a homogeneous solution of 15 wt% PVDF + 5 wt% CNTs to impregnate the porous silicon substrate.

[0076] Comparative Example 4 The only difference between this comparative example and Example 1 is that: The material of the outer layer (i.e., the second-level filler in Example 1) is 10 mL of 15 wt% PVDF + 1.5 wt% graphene with a viscosity of 12 mPa·s.

[0077] The bottom layer (i.e., the first-stage filler in Example 1) is made of 10 mL of 10 wt% PVDF with a viscosity of 3 mPa·s.

[0078] Comparative Example 5 The only difference between this comparative example and Example 1 is that: The material of the outer layer (i.e., the third-level filler in Example 1) is an NMP solution with an inlet solution of 10 mL of 20 wt% PVDF + 8 wt% CNTs (total solid content 28%) and a viscosity of 95 mPa·s.

[0079] The bottom layer (i.e., the first-quarter filler in Example 1) contains 10 mL of 10 wt% PVDF with a viscosity of 3 mPa·s.

[0080] The electrical properties of the negative electrode sheets prepared in the examples and comparative examples are shown in Table 1. Test method: In an argon glove box, 100 mg of Li6PS5Cl sulfide solid electrolyte powder was weighed and placed in an insulating outer cylinder. It was then pressurized to 300 MPa. Simultaneously, all-solid-state mold batteries were assembled using the silicon-based negative electrode and Li / In alloy counter electrode of Examples 1-4 and Comparative Examples 1-5, respectively. Charge-discharge tests were conducted at 0.1C and 0.5C rates. The ratio of the 0.5C discharge specific capacity to the 0.1C discharge specific capacity was used as the capacity retention rate under the rate test. Charge-discharge cycle performance tests were conducted at 1C rate. The ratio of the capacity after 200 cycles to the initial capacity was used as the capacity retention rate after cycling.

[0081] Table 1 Electrical properties of the electrode sheets

[0082] As shown in Table 1, Examples 1-3 comprehensively outperformed all comparative examples in terms of capacity, cycle life, and expansion control, verifying the necessity of the synergistic design of gradient modulus, porosity, and filler distribution. The combination of open pore structure and gradient filling design not only maintained high porosity and improved the utilization rate of active silicon but also reduced side reactions between the electrolyte and silicon. Compared with Comparative Examples 1-4, it significantly improved the battery's first-cycle efficiency while also significantly increasing capacity. In Example 1, the overfilling of the rigid filling layer reduced porosity, hindering lithium-ion transport and further affecting the first-cycle discharge capacity and first-cycle efficiency. In Comparative Example 2, the use of a dense carbon layer to obstruct lithium-ion insertion into a single electron transport pathway still failed to effectively improve lithium-ion transport, resulting in minimal capacity improvement. In Comparative Example 3, the single-modulus filling layer caused stress concentration, resulting in a smaller decrease in capacity compared to the first-cycle discharge, but a significant decrease in capacity retention after 200 cycles. Comparative Examples 4-5 demonstrated that simply increasing the number of filling layer levels without achieving a gradient transition was insufficient to effectively suppress stress concentration. In Comparative Example 4, the lack of a rigid layer in the inlet region led to silicon particle breakage and capacity loss, resulting in capacity loss in the first cycle of the battery. The lack of a transition layer in the middle caused stress abrupt changes, leading to crack propagation and reduced battery capacity retention. In Comparative Example 5, the rigid layer was located at the bottom and could not effectively suppress inlet particle breakage, which also resulted in capacity loss in the first cycle of the battery.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0084] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A gradient elastic layer-filled porous silicon anode material, characterized in that, Including porous silicon substrates; The porous silicon substrate includes through-holes; a gradient elastic layer is disposed within the through-holes. The gradient elastic layer has a three-level gradient structure along the depth direction of the channel, including: The first-stage filling layer is located at the bottom of the channel and is a flexible elastic layer formed of pure polymer. The second-level filling layer is located in the middle of the channel. The second-level filling layer is a mixture of rigid carbon material and polymer. A third-level filling layer located at the entrance of the channel, wherein the third-level filling layer is a high-modulus layer formed by a composite of rigid carbon material and polymer; The elastic modulus of the third-level filling layer is greater than that of the second-level filling layer, and the elastic modulus of the second-level filling layer is greater than that of the first-level filling layer.

2. The gradient elastic layer-filled porous silicon anode material according to claim 1, characterized in that, The overall porosity of the gradient elastic layer increases gradually from the inlet to the bottom of the channel, with a porosity of 15-25% at the inlet and 65-75% at the bottom.

3. The gradient elastic layer-filled porous silicon anode material according to claim 1, characterized in that, The porous silicon substrate has a pore size of 20-500 nm.

4. The gradient elastic layer filled porous silicon anode material according to claim 1, characterized in that, At least one of the following conditions must be met: a. The rigid carbon material includes at least one of graphene, carbon nanotubes, carbon fibers and their derivatives, graphene nanosheets, silicon carbide and silicon carbide whiskers, carbon black, acetylene black, graphyne, and carbon-coated metal nanowires. b. In the second-level filling layer, the mass ratio of the rigid carbon material is 10-29 wt%; c. In the third-level filling layer, the mass ratio of the rigid carbon material is 30-60 wt%.

5. The gradient elastic layer-filled porous silicon anode material according to claim 1, characterized in that, The polymer constituting the gradient elastic layer is a thermoplastic polymer or thermoplastic elastomer with an elastic modulus of 0.1-10 GPa, an elongation at break of ≥150%, and a loss factor tanδ of 0.12-0.

35.

6. The gradient elastic layer-filled porous silicon anode material according to claim 5, characterized in that, The thermoplastic polymer and the thermoplastic elastomer each independently include at least one of polyurethane, styrene-butadiene-styrene block copolymer, polyether block amide, polyvinylidene fluoride, polycarbonate, polylactic acid and polybutylene adipate / terephthalate blend.

7. A method for preparing a porous silicon anode material filled with a gradient elastic layer according to any one of claims 1-6, characterized in that, include: A porous silicon substrate with through-holes was filled with a three-level gradient solution and dried to obtain a gradient elastic layer. First-stage filling: A first-stage filling solution is injected into a porous silicon substrate. The first-stage filling solution contains a high concentration of rigid carbon material and polymer, and a 10% stress is applied to the system. -3 The vacuum on the order of Pa causes the solution to remain mainly at the pore inlet, forming a third-level filling layer. Second-stage filling: A second filling solution is permeated into the porous silicon substrate. The second filling solution includes a low-concentration rigid carbon material and a polymer, which permeates into the middle of the pores to form a second-stage filling layer. Third-stage filling: A pure polymer solution is permeated into the porous silicon substrate under normal pressure, allowing it to penetrate to the bottom of the pores to form a first-stage filling layer.

8. The preparation method according to claim 7, characterized in that, At least one of the following conditions must be met: A. The viscosity of the first filling solution is 90-110 mPa·s; B. The viscosity of the second filling solution is 2-30 mPa·s. C. In the first stage of filling, the polymer concentration is 10-20 wt%; D. In the third stage of filling, the polymer concentration is 2-4 wt%.

9. A negative electrode sheet, characterized in that, Its negative electrode is a porous silicon negative electrode material filled with a gradient elastic layer as described in any one of claims 1-6.

10. An all-solid-state battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

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