Silicon-based composite negative electrode, preparation method thereof and all-solid-state battery

Abstract

The invention provides a silicon-based composite negative electrode, a preparation method thereof and an all-solid-state battery, the silicon-based composite negative electrode comprises a fluoro conductive polyoxadiazole binder and a Li-M alloy lithium supplement agent, and M is one of Al, Ag, Sn, Mg and Zn. According to the silicon-based composite negative electrode, the preparation method of the silicon-based composite negative electrode and the all-solid-state battery, a fluorinated conductive polyoxadiazole binder and metal lithium supplement agent synergistic system is constructed, comprehensive improvement of the performance of a silicon negative electrode material is realized through a molecular-level synergistic effect, and a composite electrode system with multiple functions is constructed; and obvious advantages are shown in the sulfide all-solid-state battery.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to a silicon-based composite anode and its preparation method, and an all-solid-state battery. Background Technology

[0002] With the rapid development of energy storage technology, all-solid-state lithium batteries have become a key research focus for next-generation energy storage systems due to their significant safety performance and energy density advantages. Compared to traditional liquid electrolyte systems, solid-state batteries use non-flammable inorganic solid electrolytes, fundamentally eliminating the risks of electrolyte leakage and thermal runaway. Their theoretical energy density can exceed 500Wh / kg, their operating temperature window extends to -30~100℃, and their cycle life is expected to exceed 2000 cycles. These characteristics give them enormous application potential in electric vehicles and large-scale energy storage. However, breakthroughs in anode material systems are crucial for the commercial application of solid-state batteries.

[0003] Among numerous anode material candidates, silicon-based anodes have attracted significant attention from academia and industry due to their theoretical specific capacity of up to 4200 mAh / g (approximately 11.4 times that of graphite anodes). However, in-depth research reveals that the practical application of silicon anodes still faces multiple challenges: firstly, the high volume expansion coefficient of up to 300% during lithiation leads to severe damage to the electrode structure; secondly, the intrinsic conductivity is only 10... -3 The S / cm range necessitates the introduction of substantial conductive additives; more importantly, interfacial stability with solid-state electrolytes is a significant issue, particularly in sulfide electrolyte systems. These interdependent factors severely hinder the commercialization of silicon-based anodes.

[0004] Current research mainly focuses on three directions: 1) Developing novel polymer binder systems with conductive properties; poly(3,4-ethylenedioxythiophene) (PEDOT), as a typical representative of polythiophene-based conductive binders, is characterized by its high conductivity (film conductivity 6259 S·cm). -1 Single crystal conductivity 8797 S·cm -1 PEDOT, with its low oxidation potential (only an order of magnitude lower than conductive metals like copper and silver), excellent chemical stability, and mechanical flexibility, has attracted considerable attention. PEDOT-based conductive polymers (such as PEDOT:PSS) can have their performance significantly improved through ionic and glycerol crosslinking. Glycerol-crosslinked PEDOT:PSS / Si anodes exhibit excellent cycle stability at 500 mA·g. -1 At a current density of 3335.8 mAh·g, its initial discharge specific capacity is as high as 3335.8 mAh·g. -1 After 200 cycles, it still maintains a capacity of over 1900 mAh·g. -1 The reversible capacity retention rate reaches 60%. At 8.0 A·g -1Even at high current densities, the specific capacity of this negative electrode can still reach 804 mAh·g. -1 After 200 cycles, only slight cracks appeared in the negative electrode, indicating that it has good electrode integrity during deep cycling; 2) the volume expansion effect was mitigated through nanostructure design; 3) pre-lithiation technology was used to compensate for lithium loss during the first cycle.

[0005] However, these methods all have inherent drawbacks: conductive polymers often lack sufficient mechanical properties; the preparation process of nano-silicon materials is complex and costly; and traditional lithium supplementation agents are prone to inducing side reactions. Especially in sulfide solid electrolyte systems, the interface problem of silicon anodes is even more complex, necessitating the development of novel material systems with multiple synergistic effects. This situation highlights the necessity and urgency of developing innovative silicon anode technologies that combine volume expansion suppression and improved interface stability.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a silicon-based composite anode and its preparation method, as well as an all-solid-state battery. It constructs a synergistic system of fluorinated conductive polyoxadiazole (F-POD) binder and metal lithium supplementer. Through the synergistic effect at the molecular level, it achieves a comprehensive improvement in the performance of silicon anode materials and constructs a composite electrode system with multiple functions, which shows significant advantages in sulfide all-solid-state batteries.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A silicon-based composite negative electrode comprises a fluorinated conductive polyoxadiazole binder and a Li-M alloy lithium supplementer, wherein M is one of Al, Ag, Sn, Mg, and Zn; preferably, the fluorinated conductive polyoxadiazole binder is carbonized F-POD, and M is Al or Zn.

[0009] Furthermore, the silicon-based composite anode raw material comprises the following components by weight: 50-90 parts of nano-Si particles, 1-15 parts of Li-M alloy powder, and 1-15 parts of F-POD binder.

[0010] Furthermore, the silicon-based composite anode raw material comprises the following components: 70-90 wt% nano-Si particles, 5-15 wt% Li-M alloy powder, and 5-15 wt% F-POD binder.

[0011] Furthermore, the particle size of the nano-Si particles is 200~800nm.

[0012] Furthermore, the Li-M alloy is Li5Al4, Li 22 Sn5, Li 10Ag3, Li9Ag4, LiAg, LiAl, Li3Al2, Li9Al4, L 13 Sn4, Li3Sn, Li 15 Sn4, Li4Sn, Li 4.25 Sn, Li 22 At least one of Sn5, LiMg, and LiZn; preferably Li5Al4 or Li 22 Sn5.

[0013] The preparation method of the above-mentioned silicon-based composite anode includes the following steps: Step S1: Add F-POD adhesive to a solvent to prepare an adhesive solution; Step S2: Add nano-Si particles and Li-M alloy powder in sequence, mix thoroughly to obtain a mixed slurry; Step S3: Ball mill the mixed slurry to obtain a uniform dispersion system; Step S4: Apply the slurry onto the current collector and let it dry; Step S5: The electrode is carbonized at low temperature and then cooled to obtain a silicon-based composite anode product.

[0014] Further, in step S1, the solvent is one or more of xylene, toluene, ethanol, isopropanol, n-heptane, hexyl butyrate, and N-methylpyrrolidone.

[0015] Further, in step S3, zirconia grinding balls with a diameter of 1-5 mm are added to the grinding jar, and the mixture is ball-milled on a planetary ball mill at a speed of 300-500 rpm for 4-6 hours.

[0016] Furthermore, in step S4, the coating gap is 50~120μm and the coating speed is 2~30mm / s.

[0017] Furthermore, in step S4, the drying process employs a stepped heating method, first drying at a low temperature to remove most of the solvent, and then heating to completely remove the residual solvent; during the drying process, the system vacuum is maintained below -0.095 MPa, and argon gas is introduced as a protective gas.

[0018] Furthermore, in step S5, the low-temperature carbonization treatment temperature is 300~750℃, preferably 650~750℃, and the temperature is maintained for 2~4 hours.

[0019] Furthermore, in step S5, the low-temperature carbonization process employs a gradient heating carbonization process and an N2 atmosphere.

[0020] An all-solid-state battery is assembled from a positive electrode mixed powder sheet, an electrolyte layer, and the aforementioned silicon-based composite negative electrode sheet.

[0021] Furthermore, the positive electrode mixed powder includes a positive electrode active material, a conductive agent, and an electrolyte powder.

[0022] Furthermore, the positive electrode active material is one of ternary positive electrode materials, lithium cobalt oxide, and lithium iron phosphate.

[0023] Furthermore, both the electrolyte layer and the electrolyte powder are selected from sulfide electrolytes, specifically Li7P3S. 11 Li 10 GeP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 C l0.3 Li6PS5Cl, Li 5.5 PS 4.5 C l1.5 Li6PS5Br, Li6PS5I, Li 11 Si2PS 12 Li 10 SnP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, Li 6.6 Ge 0.6 P 0.4 One or more of S5I.

[0024] Furthermore, the conductive agent is one or more of conductive carbon black SP, Keqin black, vapor-grown carbon fiber VGCF, carbon nanotubes CNT, and conductive graphite.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention relates to a silicon-based composite anode and its all-solid-state battery, achieving synergistic electron / ion transport. After F-POD carbonization, a nitrogen-doped aromatic carbon framework is formed, constructing a three-dimensional conductive network for lithium-ion transport. Simultaneously, the lithium alloy provides a stable electron transport channel through a reversible phase transition. The synergistic effect of these two components reduces the interface impedance to 45Ω. This unique "electron-ion" dual-channel design achieves efficient coupling through interface Li-OC bonds, providing an innovative solution for charge transport in high-capacity silicon anodes.

[0026] 2. The silicon-based composite anode and its all-solid-state battery of this invention exhibit a remarkable synergistic effect in terms of structural stability: the flexible aromatic ether bond network of F-POD (elastic modulus > 5 GPa) and the three-dimensional metal skeleton formed by lithium alloy support each other, jointly buffering the volume change of silicon material. Experiments have confirmed that this dual protection mechanism significantly suppresses the expansion rate of the silicon anode from 300% to 120%. This dynamic volume control capability breaks through the structural stability bottleneck of high silicon content anodes (Si ≥ 84%) during long-cycle processes.

[0027] 3. The silicon-based composite anode and its all-solid-state battery of this invention have the advantage of interface stability: F-POD carbonization products and lithium alloy synergistically induce the formation of a composite interface layer rich in Li3P / LiF, reducing the interface impedance to 45Ω. The full cell prepared based on this technology achieves an initial efficiency of 85% and a capacity retention rate of 82% after 100 cycles. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0029] A silicon-based composite anode includes a fluorinated conductive polyoxadiazole (F-POD) binder and a Li-M alloy lithium supplementer, wherein M is one of Al, Ag, Sn, Mg, and Zn; forming a composite anode material with a synergistic system of F-POD binder and metal alloy.

[0030] Preferably, the fluorinated conductive polyoxadiazole (F-POD) binder is carbonized F-POD.

[0031] Preferably, M in the Li-M alloy lithium supplement is Al or Zn.

[0032] The silicon-based composite anode of the present invention has the following advantages: (1) The fluorine-containing and sulfonic acid groups (5-15wt%) of the F-POD binder form Li-F / O-Al / Sn bonds with the alloy surface, which enhances the interface stability; (2) The carbonized F-POD provides a flexible skeleton, and the three-dimensional metal skeleton formed by the lithium alloy during cycling provides rigid support for the electrode. The synergistic effect of the two significantly suppresses the expansion rate of the silicon anode from 300% to 120%; (3) A double continuous conductive network is formed, which significantly improves the electrode dynamic performance.

[0033] Preferably, the silicon-based composite anode raw material comprises the following components by weight: 50-90 parts of nano-Si particles, 1-15 parts of Li-M alloy powder, and 1-15 parts of F-POD binder.

[0034] Preferably, the silicon-based composite anode raw material comprises the following components: 70-90 wt% nano-Si particles, 5-15 wt% Li-M alloy powder, and 5-15 wt% F-POD binder.

[0035] Preferably, the fluorinated conductive polyoxadiazole (F-POD) binder is prepared by copolymerizing a fluorinated aromatic dicarboxylic acid monomer, a non-fluorinated dicarboxylic acid monomer, and a hydrazine compound.

[0036] Preferably, the particle size of the nano-Si particles is 200~800nm, including but not limited to 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, and 800nm.

[0037] Preferably, the Li-M alloy is Li5Al4 or Li 22 Sn5, Li 10 Ag3, Li9Ag4, LiAg, LiAl, Li3Al2, Li9Al4, L 13 Sn4, Li3Sn, Li 15 Sn4, Li4Sn, Li 4.25 Sn, Li 22 At least one of Sn5, LiMg, and LiZn; preferably Li5Al4 or Li 22 Sn5.

[0038] Preferably, the preparation method of the fluorinated conductive polyoxadiazole (F-POD) adhesive includes the following steps: Step A: Mix 4,4'-oxobenzoic acid, 2,3,5,6-tetrafluoroterephthalic acid and biphenyl-4,4'-dicarboxylic acid, add hydrazine sulfate and dissolve in fuming sulfuric acid; Step B: Stir the reaction under nitrogen protection; Step C: After the reaction is complete, pour the mixed solution into NaHCO3 solution to precipitate, and then wash until neutral. Step D: Drying to obtain F-POD powder.

[0039] Preferably, in step A, 4,4'-oxobenzoic acid (15 mmol), 2,3,5,6-tetrafluoroterephthalic acid (7.5 mmol) and biphenyl-4,4'-dicarboxylic acid (7.5 mmol) are mixed in a molar ratio of 2:1:1, and then dissolved in 50 mL of 20% fuming sulfuric acid after adding hydrazine sulfate (20 mmol).

[0040] Preferably, step B involves stirring the reaction at 120°C under nitrogen protection for 5 hours, and monitoring the reaction at 1720 cm⁻¹ using FTIR (Fourier Transform Infrared Spectroscopy). -1 The disappearance of the carbonyl peak indicates the end point of the reaction.

[0041] Preferably, in step C, the mixed solution is poured into an ice-water mixture containing 5% NaHCO3 to precipitate, and then washed successively with 0.1M HCl, ethanol / water (volume ratio 1:1) and ultrapure water until neutral; Preferably, step D involves vacuum drying at 60°C for 12 hours to obtain fluorinated conductive F-POD powder, which is then analyzed by FTIR at 1230 cm⁻¹. -1 The area shows a clear CF characteristic peak; A method for preparing a silicon-based composite anode includes the following steps: Step S1: Add F-POD adhesive to a solvent to prepare an adhesive solution; Step S2: Add nano-Si particles and Li-M alloy powder in sequence, mix thoroughly to obtain a mixed slurry; Step S3: Ball mill the mixed slurry to obtain a uniform dispersion system; Step S4: Apply the slurry onto the current collector and let it dry; Step S5: The electrode is carbonized at low temperature and then cooled to obtain a silicon-based composite anode product.

[0042] Preferably, in step S1, the F-POD binder is added to a pre-dried solvent to prepare a binder solution with a concentration of 10-15 wt% (including but not limited to 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%). The solution is stirred with a magnetic stirrer at 30-50°C (including but not limited to 30°C, 35°C, 40°C, 45°C, 50°C) for 2-4 hours (including but not limited to 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours) to ensure complete dissolution. Preferably, the solvent in step S1 is one or more of xylene, toluene, ethanol, isopropanol, n-heptane, hexyl butyrate, and N-methylpyrrolidone.

[0043] Preferably, in step S2, after each raw material is added, a planetary mixer is used to premix it for 10 to 30 minutes (10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm) for 100 to 300 minutes (10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes) and then dispersed at high speed at 2000 rpm for 5 minutes.

[0044] Preferably, in step S3, the mixed slurry is transferred to a 100 mL zirconia ball mill jar, and zirconia grinding balls with a diameter of 1-5 mm (including but not limited to 1 mm, 2 mm, 3 mm, 4 mm, 5 mm) are added. The slurry is then ball-milled on a planetary ball mill at a speed of 300-500 rpm (including but not limited to 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm) for 4-6 hours (4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours) to ensure that the slurry obtains a uniform dispersion system. The final slurry should be uniformly grayish-black in color and free from obvious particle agglomeration or sedimentation.

[0045] Preferably, in step S3, the ball milling process is paused for 5 to 10 minutes every 30 minutes to avoid overheating.

[0046] Preferably, in step S4, the ball-milled slurry is rapidly transferred to the glove box of the coating equipment, and a precision coating machine is used to coat the 10μm thick foil with a doctor blade. The coating gap is controlled to be 50~120μm (including but not limited to 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm), and the coating speed is 2~30mm / s (including but not limited to 2mm / s, 4mm / s, 6mm / s, 8mm / s, 10mm / s, 12mm / s, 14mm / s, 16mm / s, 18mm / s, 20mm / s, 22mm / s, 24mm / s, 26mm / s, 28mm / s, 30mm / s). After coating, the electrode is immediately transferred to a vacuum drying oven for drying.

[0047] Preferably, the drying in step S4 adopts a stepped heating method, first drying at a low temperature of 60°C for 2 hours to slowly remove most of the solvent, and then heating to 80°C and holding for 10 hours to ensure complete removal of residual solvent; during the drying process, the system vacuum is maintained below -0.095 MPa, and argon gas is introduced as a protective gas.

[0048] Preferably, in step S4, the dried electrode sheet is immediately lightly pressed in a glove box using a roller press with a linear pressure of 2 kN / m to enhance the contact between the active layer and the current collector, and finally punched into sheets according to a specific shape for later use.

[0049] Preferably, the low-temperature carbonization process in step S5 is as follows: the dried electrode is placed in the quartz reaction tube of a tube furnace, and high-purity nitrogen (99.999%) is first introduced at a flow rate of 5 L / min for 30 minutes to replace the air; then the temperature is programmed to rise to 300~750℃ (preferably 650~750℃) at a heating rate of 5℃ / min, and maintained at this temperature for 2~4 hours; during the heating process, the nitrogen flow rate is maintained at 1L / min to ensure the stability of the inert atmosphere; after carbonization is completed, the sample can be taken out only after the furnace temperature has naturally cooled to below 80℃.

[0050] Preferably, in step S5, the low-temperature carbonization process employs a gradient heating carbonization process and an N2 atmosphere, with the temperature being raised sequentially to 150°C, 350°C, and / or 650°C at different heating rates; more preferably, the temperature is raised sequentially at different heating rates from 150°C to 350°C to 650°C.

[0051] In the preparation process of the silicon-based composite anode of the present invention, the slurry is prepared using an anhydrous NMP / xylene solvent system, and the solid content is controlled at 25±2% and the viscosity at 2500±500cP. Uniform dispersion is achieved by ball milling with zirconia beads (350rpm×5h). The preparation of the gradient silicon-based composite anode of the present invention adopts a carbonization process (150℃→350℃→650℃, N2 atmosphere) to precisely control the degree of carbonization (ID / IG=1.2-1.3).

[0052] This invention utilizes low-temperature carbonization to partially carbonize the aromatic ring structure in the F-POD binder, forming a three-dimensional network structure with electronic conductivity while retaining sufficient polymer segments to maintain adhesion performance. The carbonized electrode surface should exhibit a uniform dark gray color, free from visible cracks or peeling. The F-POD binder is copolymerized from fluorinated aromatic dicarboxylic acid monomers (15-35 mol% of 2,3,5,6-tetrafluoroterephthalic acid), non-fluorinated dicarboxylic acid monomers (4,4'-oxobenzoic acid), and hydrazine compounds. Its molecular structure integrates rigid fluorinated aromatic rings, flexible aromatic ether bonds, and sulfonic acid groups (5-15 wt%). After carbonization at 650-750℃, a nitrogen-doped porous carbon framework containing LiF / Li3P (specific surface area ≥200 m²) is formed. 2 A conductive network ( / g) containing retained CF bonds (XPS fluorine content 3-8 at.%) and continuous ion channels (ionic conductivity ≥1×10⁻⁶). -4 The S / cm ratio together improves the thermal stability and interfacial ion transport efficiency of the material.

[0053] An all-solid-state battery is assembled from a positive electrode mixed powder sheet, an electrolyte layer, and the aforementioned silicon-based composite negative electrode sheet.

[0054] Preferably, the electrolyte layer is an electrolyte powder tablet, and the electrolyte layer forms a structure similar to a diaphragm.

[0055] Preferably, the positive electrode mixed powder includes a positive electrode active material, a conductive agent, and an electrolyte powder. This invention adds electrolyte powder to the positive electrode mixed powder, and then dry-mixes and presses the positive electrode active material, conductive agent, and electrolyte powder into sheets. When used as a positive electrode sheet in a molded battery, this improves the ionic conductivity of the positive electrode.

[0056] Preferably, the positive electrode active material is one of ternary positive electrode materials, lithium cobalt oxide, and lithium iron phosphate.

[0057] Preferably, the ternary cathode material is NCM. 111 NCM 424 NCM 523 NCM 622 NCM 811 NCM 90 NCM 95 One of them.

[0058] Preferably, both the electrolyte layer and the electrolyte powder are made of sulfide electrolyte, specifically Li7P3S. 11 Li 10 GeP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 C l0.3 Li6PS5Cl, Li 5.5 PS 4.5 C l1.5 Li6PS5Br, Li6PS5I, Li 11 Si2PS 12 Li 10 SnP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, Li 6.6 Ge 0.6 P 0.4 One or more of S5I.

[0059] Preferably, the conductive agent is one or more of conductive carbon black SP, Keqin black, vapor-grown carbon fiber VGCF, carbon nanotubes CNT, and conductive graphite.

[0060] In a glove box, the positive electrode active material powder, conductive agent, and electrolyte powder are uniformly mixed in a ratio of 70:10:20, and then pressed into a positive electrode mixed powder sheet under high pressure in a mold battery.

[0061] The assembly of the all-solid-state mold battery includes the following steps: 1) Cut the composite negative electrode disc into 10 mm diameter discs using a cutting machine and place them in a glove box for later use; 2) Assemble the mold battery in an argon atmosphere glove box, following the structure of positive electrode mixed powder pressing - electrolyte layer - negative electrode disc. This invention establishes a synergistic system of fluorinated aromatic rings and sulfonic acid groups: a molecular design using 2,3,5,6-tetrafluoroterephthalic acid (15-35 mol%) and sulfonic acid groups (5-15 wt%) is employed, resulting in a nitrogen-doped porous carbon framework containing LiF / Li3P (fluorine content 3-8 at.%) after carbonization. This invention suppresses volume expansion through framework synergy: the expansion rate is suppressed from 300% to 120% through the synergistic effect of the F-POD carbonized layer (elastic modulus > 5 GPa) and the rigid framework of the Li5Al4 alloy. This invention also establishes an alloyed lithium supplementation-conductive network coupling: selecting Li5Al4 / Li 22 Specific components such as Sn5 (5-15wt%) form a Li-OC / Al bonding interface with the F-POD carbon layer, constructing a "electronic (metal phase)-ion (carbon skeleton)" dual continuous network; this invention can achieve in-situ SEI regulation: F-POD carbonization products and lithium alloy synergistically induce the formation of a 20-30nm thick Li3P / LiF / Li-Al-O composite interface layer (impedance growth ≤90Ω / 100 times).

[0062] Example 1 A method for preparing a wet-process carbonized F-POD-Li-Ai composite negative electrode sheet includes the following steps: In a strictly humidity- and oxygen-controlled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), raw materials are weighed according to the following ratio: 80 wt% nano-Si particles (particle size 500 ± 50 nm), 10 wt% Li5Al4 alloy powder, and 10 wt% F-POD binder. First, the F-POD binder is added to pre-dried NMP solvent to prepare a 15 wt% solution, and magnetically stirred at 800 rpm for 3 hours at 45 ℃ until completely dissolved. Then, nano-Si particles and Li5Al4 alloy powder are added sequentially, and NMP reagent is added according to the slurry viscosity. The mixture is premixed at 400 rpm for 20 minutes using a planetary mixer, and then dispersed at high speed at 2000 rpm for 5 minutes (with intermittent cooling). The mixed slurry was transferred to a zirconia ball mill jar (ball diameter ratio 3mm:5mm=3:1, ball-to-material ratio 10:1) and ball-milled at 350 rpm for 5 hours (with a 10-minute pause every 30 minutes to control the temperature below 40℃). The uniform slurry was then coated onto a 10μm copper foil using a microgravure plate, controlling the coating speed at 30mm / s and the wet film thickness at 120μm, followed by drying. Finally, the electrode was heated to 150℃ at 3℃ / min in a tube furnace, then increased to 650℃ at 5℃ / min, held at this temperature for 4 hours in a N2 atmosphere (1.2L / min), and then cooled to 200℃ at a programmed temperature of 2℃ / min before natural cooling to obtain a composite negative electrode with a carbonization degree of 55~60% (ID / IG=1.2-1.3).

[0063] Example 2 Compared to Example 1, this example is adjusted to contain 90wt% nano-Si particles, 5wt% Li5Al4 alloy powder, and 5wt% F-POD binder.

[0064] Example 3 Compared to Example 1, this example is adjusted to contain 80wt% nano-Si particles, 15wt% Li5Al4 alloy powder, and 5wt% F-POD binder.

[0065] Example 4 Compared to Example 1, this example is adjusted to contain 80wt% nano-Si particles, 5wt% Li5Al4 alloy powder, and 15wt% F-POD binder.

[0066] Example 5 Compared to Example 1, this example is adjusted to contain 70wt% nano-Si particles, 15wt% Li5Al4 alloy powder, and 15wt% F-POD binder.

[0067] Comparative Example 1 A wet-process uncarbonized F-POD-Li-Ai composite negative electrode preparation method, compared with Example 1, skips the carbonization step and only performs drying treatment on the electrode.

[0068] Comparative Example 2 A method for preparing a wet-process F-POD-Li2CO3 composite negative electrode sheet, in which the alloy powder is replaced with an equal proportion of Li2CO3 compared to Example 1.

[0069] Comparative Example 3 A method for preparing a wet PVDF-Li-Ai composite negative electrode sheet, compared with Example 1, in which the binder is replaced with an equal proportion of PVDF, there is no carbonization process, and the electrode sheet is only dried.

[0070] Comparative Example 4 A method for preparing a wet-process carbonized F-POD-Al powder composite negative electrode sheet, wherein, compared with Comparative Example 1, the alloy powder is replaced with an equal proportion of Al powder.

[0071] Comparative Example 5 A method for preparing a wet-process carbonized F-POD-Li powder negative electrode sheet, wherein, compared with Comparative Example 1, the alloy powder is replaced with an equal proportion of Li powder.

[0072] I. Experimental Example: Electrochemical testing: Ion conductivity test In a glove box, the dried negative electrode was cut into 10mm diameter discs. The sample thickness L and area A were measured and recorded. A symmetrical structure of "electron-blocking electrode - silicon negative electrode sample - electron-blocking electrode" was constructed, and the mold cell was assembled and connected to the workstation. (Setting 10...) 6 EIS testing was conducted at a frequency range of ~0.01Hz and an AC signal amplitude of 5~10mV at a constant temperature of 25℃. The ion transport impedance value Ri in the high-frequency region of the Nyquist plot was analyzed using the formula σ. i =L / (R i The ionic conductivity was calculated by multiplying the sample by 1000 × A. The results were repeated three times and the average value was taken. The test results are shown in Table 1.

[0073] Electron conductivity testing (four-probe method): Select uniformly dried electrode sheets and cut them into strips of 1cm × 4cm, using a concentration of 1.5-2.0g / cm. 3 After compaction, measure the thickness (L) and effective area (A) using a micrometer; then, adjust the four-probe tester, prepare the insulating platform and fixture, fix the dried electrode sheet, and ensure the four probes are in perpendicular and uniform contact (1-2mm spacing). Set a current of 10-100mA and record the stable voltage (U) on the inner side. Repeat 3-5 times, take the average, and change the position to verify uniformity; finally, calculate the resistance using R=U / I, and then use σ e =L / (R×A) (L is the electrode thickness, R is the calculated resistance, and A is the effective area) to derive the electronic conductivity. The test results are shown in Table 1.

[0074] Constant current charge and discharge test Galvanostatic charge-discharge (GCD) testing involves charging and discharging a battery with a constant current to study its charge-discharge performance. This includes information such as charge-discharge voltage plateau, specific capacity, charge-discharge efficiency, and cycle stability. All-solid-state batteries are assembled from a positive electrode mixture of powders, a sulfide electrolyte, and a negative electrode. Their charge-discharge cutoff voltage range is 2.5–4.2V (vs. Li). + / Li-In), the test temperature was 30℃, the constant current charge-discharge rate was 1C (1C=220mA / g), and the capacity retention rate after 100 cycles was recorded. The above data are shown in Table 2.

[0075] AC impedance testing In a strictly humidity- and oxygen-controlled glove box (H2O / O2 concentration <0.1 ppm), the assembled mold battery is connected to the workstation, and set to 10. 6The EIS test was initiated with a frequency range of ~0.01Hz and an AC signal amplitude of 5~10mV. The Nyquist plot was analyzed to obtain the solid electrolyte impedance in the high-frequency region, the interface impedance in the mid-frequency region, and the ion diffusion impedance in the low-frequency region. The total impedance was calculated, and the impact of each component on battery performance was analyzed. The data are recorded in Table 2. The entire test was conducted under a constant temperature environment of 25.0±0.5 ℃.

[0076] Table 1. Ionic and electronic conductivity of the negative electrodes of Examples 1-5 and Comparative Examples 1-5 at 30°C

[0077] Table 2. First-time efficiency, initial discharge capacity, impedance, and cycle capacity retention of all-solid-state batteries in Examples 1-5 and Comparative Examples 1-5

[0078] II. The test data analysis is as follows: 1. This invention achieves synergistic electron transport: F-POD carbide and Li5Al4 construct a highly efficient conductive network. Experimental data clearly demonstrate the synergistic effect of carbonized F-POD and Li5Al4 in electron transport. The baseline group (10% Li5Al4 + 10% F-POD) achieved an excellent 1C capacity of 2350 mAh / g, while changes in Li5Al4 content significantly affected performance: when reduced to 5% (Example 2), the capacity decreased by 17%, and even when increased to 15% (Example 3), it was still limited due to insufficient F-POD. The control group data are even more convincing: pure Al powder (Comparative Example 4) had a 19% capacity reduction due to the lack of Li active phase, while Li2CO3 (Comparative Example 2) experienced a 45% capacity drop due to its insulating properties. This proves that the synergy between 10% Li5Al4 and carbonized F-POD is crucial for constructing a stable electron network, and neither can be dispensed with.

[0079] 2. This invention achieves structural stability and synergy: a dual protection mechanism inhibits electrode degradation. Carbonized F-POD and Li5Al4 exhibit perfect complementarity in terms of structural stability. The baseline group's 82% cycle retention and 82Ω final-state impedance demonstrate the dual protective effect of the carbonized F-POD flexible carbon layer and Li5Al4 (Al phase buffer + Li phase lithium supplementation). Proportioning experiments show that increasing F-POD to 15% (Example 4) achieves an 80% retention rate, while decreasing it to 5% (Example 3) reduces it to 75%, proving the crucial importance of carbon layer integrity. The dismal performance of the uncarbonized control group (Comparative Example 1, retention rate 45%) and the PVDF group (Comparative Example 3, retention rate 38%) conversely validates the irreplaceable role of carbonized F-POD in maintaining the electrode structure.

[0080] 3. This invention achieves stable interface coordination: dynamically controlling the SEI evolution process. In terms of interface stability, the synergistic effect of carbonized F-POD and Li5Al4 is particularly remarkable. The baseline group's 85% first-time efficiency and only 82% impedance increase are attributed to the combined effect of the 25nm thin SEI guided by carbonized F-POD and the Li-Al-O passivation layer formed by Li5Al4. Changes in the ratio immediately affect interface stability: insufficient F-POD (Example 3) caused an impedance increase of up to 118%, while insufficient Li5Al4 (Example 2) led to accelerated capacity decay. In the control group, Li2CO3 (Comparative Example 2) and pure Li (Comparative Example 5) caused impedance increases of over 220% due to insulation and volume effects, respectively, fully demonstrating that only the synergy of the two can achieve interface stability. This dual mechanism of "SEI regulation + dynamic lithium replenishment" is the key to obtaining long-term cycling performance.

[0081] III. The synergistic mechanism between the conductive polyoxadiazole (F-POD) binder and the Li-M metal lithium supplementer of this invention is shown in Table 3. Table 3. Coordination Mechanism Table

[0082] IV. This invention addresses key technical bottlenecks faced by silicon-based anode materials in industrial applications, including poor conductivity, severe volume expansion, and insufficient interface stability. It innovatively proposes a novel material system based on the synergistic effect of fluorinated conductive polyoxadiaazole (F-POD) binder and lithium metal supplementers (Li-Al / Li-Sn). This system achieves a comprehensive improvement in the performance of silicon anode materials through molecular-level synergistic effects. Specifically, by precisely controlling the interaction between the sulfonic acid groups (-SO3H) in the F-POD molecular structure and lithium alloys (such as Li-Al and Li-Sn), a multifunctional composite electrode system is constructed. This system achieves a triple breakthrough in electron / ion synergistic transport, enhanced structural stability, and interface optimization through precise molecular-level design and advanced interface engineering and structural control strategies. Specifically, by systematically optimizing the distribution density and spatial configuration of the sulfonic acid groups (-SO3H) in the F-POD molecular structure, a stable chemical bond is formed between them and the lithium alloy surface, thereby constructing a multifunctional composite electrode system.

[0083] Regarding charge transport mechanisms, this invention constructs an innovative "electron-ion" synergistic transport system, effectively solving the core problem of poor conductivity in silicon-based anode materials. Through systematic thermogravimetric-differential scanning calorimetry (TG-DSC) analysis and in-situ X-ray diffraction (XRD) characterization, the optimal carbonization conditions for the F-POD binder were determined to be 650-750℃ for 2-4 hours. Under these conditions, F-POD can be transformed into a nitrogen-doped carbon network with a hierarchical porous structure, achieving an electronic conductivity of (1.2±0.2)×10⁻⁶. -2 S / cm, compared to traditional PVDF adhesives (~10 -5 The S / cm ratio was improved by three orders of magnitude. Electrochemical impedance spectroscopy (EIS) analysis showed that the Li-Al / Li-Sn alloy underwent reversible alloying / dealloying reactions during charge and discharge, forming a continuous ion transport pathway. Particularly noteworthy is the formation of stable Li-OC interfacial bonds between the oxygen-containing functional groups in the F-POD carbide products and the lithium alloy surface. This chemical bonding enables molecular-level coupling of the electron and ion transport networks, reducing the electrode / electrolyte interfacial impedance to 45 Ω. This synergistic transport mechanism provides important scientific evidence and technical support for the practical application of high-capacity silicon anodes.

[0084] To address the global challenge of 300% volume expansion of silicon materials during charge and discharge, this invention develops a dual protection mechanism based on a flexible F-POD network and a metal framework, achieving a significant breakthrough in structural stability. The invention reveals that the flexible aromatic ether bond network in the F-POD molecule possesses excellent mechanical properties (elastic modulus > 5 GPa, elongation at break > 150%), effectively buffering the volume changes of silicon particles. Simultaneously, the three-dimensional metal framework formed by the lithium alloy during cycling provides rigid support for the electrode. The synergistic effect of these two mechanisms significantly suppresses the expansion rate of the silicon anode from 300% to 120%.

[0085] In terms of interface engineering, this system exhibits significant advantages in sulfide all-solid-state batteries. The invention reveals that the synergistic effect of F-POD carbide products and lithium alloys can induce the formation of a Li3P / LiF-rich composite interface layer, which possesses excellent ionic conductivity and chemical stability. Particularly noteworthy is that by optimizing the molecular structure of F-POD and the composition ratio of the lithium alloy, the interface impedance can be reduced to 45Ω, a reduction of over 70% compared to traditional interfaces.

Claims

1. A silicon-based composite anode, characterized by, The fluorinated conductive polyoxadiazole binder and Li-M alloy lithium supplementing agent, wherein M is one of Al, Ag, Sn, Mg, and Zn; preferably, the fluorinated conductive polyoxadiazole binder is F-POD, and M is Al or Zn.

2. The silicon-based composite anode according to claim 1, wherein The silicon-based composite negative electrode raw material comprises the following components by weight: 50-90 parts of nano-Si particles, 1-15 parts of Li-M alloy powder, and 1-15 parts of F-POD binder.

3. The silicon-based composite anode according to claim 2, wherein The silicon-based composite negative electrode raw material comprises the following components: 70-90 wt% of nano-Si particles, 5-15 wt% of Li-M alloy powder, and 5-15 wt% of F-POD binder.

4. The silicon-based composite anode according to claim 2 or 3, characterized in that, The nano-Si particles have a particle size of 200-800 nm.

5. The silicon-based composite anode according to claim 1, wherein Li5Al4, Li 22 Sn5, Li 10 Ag3, Li9Ag4, LiAg, LiAl, Li3Al2, Li9Al4, Li 13 Sn4, Li3Sn, Li 15 Sn4, Li4Sn, Li 4.25 Sn, Li 22 Sn5, LiMg, LiZn; preferably Li5Al4or Li 22 Sn5.

6. The method for preparing the silicon-based composite anode according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: Step S1: adding the F-POD binder to a solvent to prepare a binder solution; Step S2: sequentially adding the nano-Si particles and the Li-M alloy powder, and thoroughly mixing to obtain a mixed slurry; Step S3: ball-milling the mixed slurry to obtain a uniform dispersion system; Step S4: coating the slurry on a current collector and drying; Step S5: low-temperature carbonizing the electrode sheet, and obtaining a silicon-based composite negative electrode product after cooling.

7. The method for preparing a silicon-based composite negative electrode according to claim 6, characterized in that, At least one of the following technical features is included: (1) The solvent in step S1 is one or more of xylene, toluene, ethanol, isopropanol, n-heptane, hexyl butyrate, and N-methyl pyrrolidone; (2) In step S3, zirconium oxide grinding balls with a diameter of 1-5 mm are added to the ball mill tank, and the planetary ball mill is operated at a speed of 300-500 rpm for 4-6 hours; (3) In step S4, the coating gap is 50-120 μm, and the coating speed is 2-30 mm / s; (4) In step S4, the drying is performed in a stepwise manner, i.e., low-temperature drying is performed first to remove most of the solvent, and then the temperature is increased to completely remove the residual solvent; during the drying process, the system vacuum degree is maintained below -0.095 MPa, and argon gas is introduced as a protective gas; (5) In step S5, the low-temperature carbonization treatment temperature is 300-750 °C, preferably 650-750 °C, and the holding time is 2-4 hours; (6) In step S5, the low-temperature carbonization treatment is performed using a gradient temperature carbonization process and a N2 atmosphere.

8. An all-solid battery, characterized by, The silicon-based composite negative electrode product is assembled from a positive electrode mixed powder, an electrolyte layer, and the silicon-based composite negative electrode sheet as claimed in any one of claims 1-5.

9. The all-solid battery according to claim 8, characterized by, The positive electrode mixed powder comprises a positive electrode active material, a conductive agent, and an electrolyte powder.

10. The all-solid battery according to claim 9, characterized by, At least one of the following technical features is included: (1) The positive electrode active material is one of a ternary positive electrode material, lithium cobaltate, and lithium iron phosphate; (2) the electrolyte layer, the electrolyte powder are all selected from sulfide electrolyte, the sulfide electrolyte is one or more of Li7P3S 11 , Li 10 GeP2S 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 C l0.3 , Li6PS5Cl, Li 5.5 PS 4.5 C l1.5 , Li6PS5Br, Li6PS5I, Li 11 Si2PS 12 , Li 10 SnP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, Li 6.6 Ge 0.6 P 0.4 S5I; (3) The conductive agent is one or more of conductive carbon black SP, Ketjen black, vapor-grown carbon fiber VGCF, carbon nanotube CNT, and conductive graphite.

Images