Composite negative electrode material and preparation method and application thereof

Abstract

The present application belongs to the technical field of batteries, and particularly relates to a composite negative electrode material and a preparation method and application thereof. The composite negative electrode material comprises three-dimensional porous carbon aerogel and polymer-coated nanosilicon; the polymer-coated nanosilicon is embedded in the pore channels of the three-dimensional porous carbon aerogel. The present application solves the problems of volume expansion, poor conductivity and cycle attenuation of the silicon-based negative electrode by means of a three-in-one synergistic strategy of "straw-based three-dimensional porous carbon aerogel, in-situ coating of nanosilicon with conductive polymer and composite binder (such as PI-PU-GO)", starting from three dimensions of structural buffering, conductive enhancement and interface anchoring, so as to obviously reduce the volume expansion of the silicon-based negative electrode and improve the cycle stability, first-cycle coulombic efficiency and other electrochemical performances of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and specifically relates to a composite anode material, its preparation method, and its application. Background Technology

[0002] Silicon-based anodes are considered key materials for breaking through the current energy density bottleneck of lithium-ion batteries due to their theoretical specific capacity of up to 4200 mAh / g. However, they exhibit approximately 300% volume expansion during charge and discharge, which leads to serious structural failure problems, including active material pulverization, current collector stripping, and repeated rupture and regeneration of the solid electrolyte interphase (SEI) membrane, severely restricting their commercial application.

[0003] To alleviate the above problems, existing main technical solutions include: 1) Silicon / carbon composite structure design: embedding nano-silicon into a porous carbon matrix, utilizing the carbon framework to buffer expansion and improve conductivity. However, commercially available porous carbon (such as template carbon and activated carbon) is expensive and mostly consists of isolated channels, lacking a three-dimensional interconnected network, making it difficult to achieve efficient stress release; 2) Conductive polymer coating: using polypyrrole (PPy), polyaniline (PANI), etc., to modify the surface of silicon can improve electronic conduction. However, the coating layer is prone to detachment during cycling, and 3) Binder optimization: The traditional sodium carboxymethyl cellulose / styrene-butadiene rubber (CMC / SBR) system has insufficient binding force on high-expansion silicon; although some studies have introduced polyimide (PI) to improve the bonding strength, PI is too rigid and lacks elastic recovery ability, and is still prone to cracking under high silicon loading; 4) Exploration of biomass carbon materials: Some studies have prepared carbon materials from raw materials such as rice husks and sawdust and applied them to the negative electrode, but the preparation process mostly adopts high-temperature carbonization to directly form carbon, resulting in dense pore structure and low specific surface area. Therefore, the above technical solutions cannot effectively solve the problems of volume expansion, poor conductivity and cycle decay of silicon-based negative electrodes.

[0004] Therefore, it is of great significance to provide a composite anode material that enables silicon-based anodes to have low volume expansion, good cycle stability, and conductivity. Summary of the Invention

[0005] The present invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial alternative. Specifically, the present invention provides a composite anode material that still has a low expansion rate even with a silicon content as high as 40-50%, which can simultaneously solve the problems of volume expansion, poor conductivity and cycle degradation of silicon-based anodes.

[0006] The inventive concept of this invention: The composite negative electrode material of this invention includes three-dimensional porous carbon aerogel and polymer-coated nano-silicon; the polymer-coated nano-silicon is embedded in the pores of the three-dimensional porous carbon aerogel.

[0007] The polymer-coated nano-silicon of this invention is embedded in the pores of the three-dimensional porous carbon aerogel, achieving true "cage encapsulation" embedding rather than being attached to the aerogel surface. The structural feature of the polymer-coated nano-silicon embedded in the pores of the three-dimensional porous carbon aerogel can effectively buffer the volume change of the silicon anode during charging and discharging, thereby improving the electrochemical performance of the battery.

[0008] Therefore, a first aspect of the present invention provides a composite anode material.

[0009] Specifically, the composite negative electrode material includes three-dimensional porous carbon aerogel and polymer-coated nano-silicon; the polymer-coated nano-silicon is embedded in the pores of the three-dimensional porous carbon aerogel.

[0010] Preferably, the pore size of the three-dimensional porous carbon aerogel is 100-300 nm.

[0011] Preferably, the specific surface area of ​​the three-dimensional porous carbon aerogel is ≥1500 m². 2 / g.

[0012] Preferably, the pore volume of the three-dimensional porous carbon aerogel is ≥1.0 cm³. 3 / g.

[0013] Preferably, the three-dimensional porous carbon aerogel includes straw-based three-dimensional porous carbon aerogel.

[0014] Specifically, the pore size, specific surface area, and pore volume of the three-dimensional porous carbon aerogel of this invention enable it to possess excellent mechanical resilience and ion transport channels.

[0015] Preferably, the polymer-coated nanosilicon includes any one of polypyrrole, polyaniline, polythiophene (PTh), and poly(3,4-ethylenedioxythiophene) (PEDOT).

[0016] Preferably, the thickness of the coating layer in the polymer-coated nano-silicon is 5-10 nm.

[0017] Preferably, the polymer-coated nano-silicon has a particle size of 30-80 nm.

[0018] Preferably, the mass of the nano-silicon in the polymer-coated nano-silicon accounts for 30-80% of the total mass of the nano-silicon and the three-dimensional porous carbon aerogel.

[0019] A second aspect of the present invention provides a method for preparing the composite negative electrode material described in the first aspect of the present invention.

[0020] Specifically, the preparation method of the composite anode material includes the following steps: (1) Cellulose hydrogel is dried, carbonized and activated to obtain three-dimensional porous carbon aerogel; (2) Mix nano-silicon and polymer monomer solution; then add the three-dimensional porous carbon aerogel, and impregnate under vacuum to obtain a suspension; (3) The oxidant is mixed with the suspension and then subjected to in-situ polymerization to obtain the product.

[0021] Preferably, in step (1), the method for preparing the cellulose hydrogel includes the following steps: Cellulose is dispersed in a solvent and subjected to freeze-thaw cycles to obtain a cellulose solution; then, the cellulose hydrogel is prepared by physical or chemical crosslinking.

[0022] Preferably, the cellulose is derived from cellulose-containing agricultural or forestry waste.

[0023] Preferably, the cellulose-containing agricultural or forestry waste includes at least one of wheat straw, rice straw, corn straw, sugarcane bagasse, rice husk, and sawdust.

[0024] Preferably, the cellulose comprises straw cellulose.

[0025] Preferably, the straw cellulose is high-purity cellulose obtained by alkali boiling to remove lignin and hemicellulose from straw.

[0026] Preferably, the straw includes at least one of wheat straw, rice straw, and corn straw.

[0027] Preferably, the solvent includes an alkali, a stabilizer, and water.

[0028] Preferably, the alkali includes sodium hydroxide.

[0029] Preferably, the stabilizer comprises urea.

[0030] Preferably, the mass ratio of the alkali, stabilizer and water can be (6-8):(11-13):81; for example, 7:12:81, etc.

[0031] Preferably, the freezing temperature in the freeze-thaw cycle is -10 to -15°C; for example, -10°C, -11°C, -12°C, -13°C, -14°C, -15°C, etc.

[0032] Preferably, the physical cross-linking is performed by water bath heating; more preferably, the temperature of the water bath heating is 55-65°C.

[0033] Preferably, the chemical crosslinking material is obtained by adding a crosslinking agent; more preferably, the crosslinking agent includes epichlorohydrin.

[0034] Specifically, by heating in a water bath or adding a cross-linking agent, the cellulose molecular chains undergo physical or chemical cross-linking, resulting in a phase transition. After washing to remove non-cellulose components, a straw cellulose hydrogel with a three-dimensional network structure is obtained.

[0035] Preferably, in step (1), the drying includes either supercritical drying or freeze drying.

[0036] Preferably, when freeze drying is used, the freeze drying temperature is -55~-45℃ and the time is 11-13h; for example, the temperature is -55℃, -50℃, -45℃, etc., and the time is 11h, 12h, 13h, etc.

[0037] Specifically, cellulose hydrogels are freeze-dried to form a three-dimensional porous framework.

[0038] Preferably, in step (1), the carbonization temperature is 750-850℃ and the time is 1.5-2.5h; for example, the temperature is 750℃, 800℃, 850℃, etc., and the time is 1.5h, 2h, 2.5h, etc.

[0039] Preferably, in step (1), the activation temperature is 550-650℃ and the time is 0.5-1.5h; for example, the temperature is 550℃, 600℃, 650℃, etc., and the time is 0.5h, 1h, 1.5h, etc.

[0040] Preferably, in step (1), potassium hydroxide is used for activation.

[0041] Preferably, the mass ratio of potassium hydroxide to carbonized aerogel is (1.5-2.5):1; for example, 1.5:1, 2:1, 2.5:1, etc.

[0042] Preferably, the carbonization and activation are both carried out in a nitrogen atmosphere.

[0043] Specifically, simple freeze-drying combined with carbonization can only form a micron-sized macroporous framework (macroscopic support). The pore walls themselves are dense and smooth, but the specific surface area is insufficient to provide adequate lithium-ion transport channels and interface anchoring points. The further activation with KOH in this invention serves two purposes: 1) Pore creation and expansion: At high temperatures, KOH undergoes a chemical etching reaction with the carbon framework (6KOH + 2C → 2K + 3H₂ + 2K₂CO₃), "eroding" abundant mesopores and micropores into the originally smooth pore walls, increasing the specific surface area and accommodating more nano-silicon. 2) Increased specific surface area and wettability: Activation can increase the specific surface area of ​​the aerogel from several hundred m² after carbonization to ≥1500 m². 2 / g, which not only greatly increases the wetting area of ​​the electrolyte, but more importantly, provides sufficient space for subsequent vacuum impregnation of nano-silicon, allowing the nano-silicon to penetrate deep into the pores rather than just accumulate on the outer surface of the carbon aerogel, thus truly achieving physical buffering.

[0044] Preferably, in step (2), the concentration of the polymer monomer solution is 0.05-0.2 mol / L; for example, the concentration is 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, etc.

[0045] Preferably, the polymer monomer solution is an aqueous solution containing polymer monomers.

[0046] Preferably, in step (2), the mass ratio of the nano-silicon to the polymer monomer in the polymer monomer solution is (5-10):1; for example, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc.

[0047] Specifically, by reasonably limiting the concentration of the polymer monomer solution and the mass ratio of nano-silicon to the polymer monomer in the polymer monomer solution, the coating layer thickness is ensured to be 5-10 nm.

[0048] Preferably, in step (2), the polymer monomer in the polymer monomer solution includes any one of pyrrole monomer, aniline monomer, thiophene monomer, and 3,4-ethylenedioxythiophene monomer.

[0049] Preferably, in step (2), the mass of the nano-silicon accounts for 30-80% of the total mass of the nano-silicon and the three-dimensional porous carbon aerogel; for example, 30%, 40%, 50%, 60%, 70%, 80%, etc., that is, the mass ratio of nano-silicon to three-dimensional porous carbon aerogel is 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, etc.

[0050] Preferably, in step (2), the pressure of vacuum impregnation is -0.08 to -0.1 MPa, and the time is 1-2 hours; for example, the pressure is -0.08 MPa, -0.09 MPa, -0.1 MPa, etc., and the time is 1 hour, 1.5 hours, 2 hours, etc.

[0051] Preferably, the mixing system is maintained under a negative pressure of -0.08 to -0.1 MPa for 1-2 hours, and then slowly restored to normal pressure. This process can be repeated 2-3 times to ensure that the nano-silicon and monomers are completely incorporated into the pores of the three-dimensional porous carbon aerogel.

[0052] Preferably, in step (3), the oxidant includes at least one of FeCl3 and ammonium persulfate.

[0053] Preferably, in step (3), the mixing process of the oxidant and the suspension is specifically as follows: the oxidant solution is slowly added dropwise to the impregnated suspension under ice-water bath conditions.

[0054] Preferably, the temperature of the ice-water bath is 0-5℃.

[0055] Preferably, the dripping rate is 1-2 drops / second.

[0056] Preferably, in step (3), when the polymer monomer is a pyrrole monomer, FeCl3 is used as the oxidant, and the molar ratio of FeCl3 to the pyrrole monomer in the pyrrole monomer solution is (2-2.5):1; for example, the molar ratio is 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, etc.

[0057] Preferably, in step (3), when the polymer monomer is aniline monomer, ammonium persulfate is used as the oxidant, and the molar ratio of the ammonium persulfate to the aniline monomer in the aniline monomer solution is (1-1.2):1; for example, the molar ratio is 1:1, 1.1:1, 1.2:1, etc.

[0058] Preferably, in step (3), when the polymer monomer is aniline monomer and ammonium persulfate is used as oxidant, the in-situ polymerization reaction needs to be carried out in an acidic aqueous solution to ensure that a highly conductive intermediate (emerald green imine salt) polyaniline is generated.

[0059] Preferably, the acidic aqueous solution includes an aqueous solution of hydrochloric acid.

[0060] Preferably, the in-situ polymerization reaction is carried out at a temperature of 0-5°C for 4-12 hours.

[0061] Specifically, after the addition is complete, continue stirring at 0-5℃ for 4-12 hours to complete the in-situ polymerization reaction.

[0062] Preferably, the in-situ polymerization reaction further includes a washing and drying process.

[0063] Specifically, compared to polymerization followed by impregnation, steps (2) and (3) of this invention involve vacuum impregnation followed by in-situ polymerization. The polymer (such as polypyrrole or polyaniline) not only coats the nano-silicon but also "bonds" the nano-silicon to the three-dimensional porous carbon aerogel wall. In other words, the nano-silicon is wrapped by the polymer and firmly anchored to the solid carbon skeleton, which can effectively buffer the volume change of the silicon anode during charging and discharging and prevent silicon particles from pulverizing and falling off, thus possessing both conductivity and expansion buffering capabilities.

[0064] A third aspect of the present invention provides a negative electrode.

[0065] Specifically, the negative electrode includes a current collector and an active layer disposed on the surface of the current collector; the active layer comprises the composite negative electrode material described in the first aspect of the present invention and a binder; the binder comprises binder A, an elastomer and a two-dimensional material; The adhesive A includes at least one of polyimide and polyamic acid (PAAc); The elastomer includes at least one of polyurethane, polyether thermoplastic elastomer, and polyester thermoplastic elastomer; The two-dimensional material includes at least one of graphene oxide, nitrogen-doped graphene, and MXene.

[0066] Preferably, the adhesive A comprises polyimide (PI).

[0067] Preferably, the elastomer comprises polyurethane; more preferably, the elastomer comprises elastic polyurethane (PU).

[0068] Preferably, the two-dimensional material includes graphene oxide (GO).

[0069] Specifically, the two-dimensional material is a two-dimensional reinforcing material. For the binder composed of PI, PU, ​​and GO, PI provides high-strength polar groups (-COOH, -NH2), which form strong chemical adsorption with current collectors (such as copper foil) and active substances. The PU main chain contains a large number of flexible ether bonds and urethane units, which endow the adhesive film with excellent tensile strength (>150%) and elastic recovery ability. GO nanosheets, as "molecular bridges", can achieve interfacial chemical bridging, that is, crosslinking with polymers (such as PPy) and PI / PU through π–π interactions and hydrogen bonds, which significantly improves the interfacial bonding strength and the integrity of the electronic conduction network.

[0070] Specifically, the negative electrode is a silicon-based negative electrode.

[0071] Preferably, the current collector comprises copper foil.

[0072] Preferably, the active layer further comprises a conductive agent and a solvent.

[0073] Preferably, the conductive agent comprises conductive carbon black (Super P).

[0074] Preferably, the solvent comprises N-methylpyrrolidone (NMP).

[0075] Preferably, the method for preparing the negative electrode includes the following steps: The composite negative electrode material, conductive agent, and binder are dispersed in a solvent to obtain a slurry; the slurry is coated on the surface of the current collector and rolled to obtain the final product.

[0076] Specifically, the present invention does not impose any particular limitation on the solid content of the slurry, that is, the amount of solvent used in the present invention can be adjusted in a conventional manner according to actual conditions.

[0077] A fourth aspect of the present invention provides a battery.

[0078] Specifically, the battery includes the negative electrode described in the third aspect of the present invention.

[0079] Preferably, the battery comprises a lithium-ion battery.

[0080] Specifically, this invention employs a three-pronged synergistic strategy of "straw-based three-dimensional porous carbon aerogel, polymer in-situ coating of nano-silicon, and composite binder" to simultaneously address the issues of volume expansion, poor conductivity, and cycle decay of silicon-based anodes from three dimensions: structural buffering, enhanced conductivity, and interface anchoring. This approach can significantly reduce the volume expansion of silicon-based anodes and improve the electrochemical performance of batteries, such as cycle stability and first-cycle coulombic efficiency.

[0081] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows: This invention is not a simple physical assembly, but rather the construction of a cross-scale "chemical-physical" three-in-one synergistic anti-expansion network. This synergistic effect of "carbon skeleton confinement + polymer-coated conductive buffer layer + chemical anchoring with composite binders (such as PI / PU / GO)" results in extremely low volume expansion (expansion rate controlled below 60%) even with ultra-high silicon loadings of 40-50%, and excellent electrochemical performance (89% coulombic efficiency in the first cycle, and 86% capacity retention after 200 cycles at 1C rate). It effectively solves the problems of volume expansion, poor conductivity, and cycle decay in silicon-based anodes. Specific beneficial effects include: (1) Precise matching of size and pore size (physical synergy): This invention obtains carbon aerogel with a pore size of 100-300 nm through "freeze-drying, carbonization, and KOH activation". This pore size range is just enough to accommodate nano-silicon particles with a particle size of 30-80 nm and a polymer coating layer with a thickness of 5-10 nm, achieving true "cage encapsulation" embedding, rather than being attached to the surface of the aerogel. The structural feature of polymer-coated nano-silicon embedded in the pores of the three-dimensional porous carbon aerogel can effectively buffer the volume change of the silicon anode during charging and discharging.

[0082] (2) Interfacial chemical bridging (chemical synergy): This invention uses three specific binders, with a focus on using GO (graphene oxide) as a "molecular bridge". The π-electron network of GO forms a strong π–π interaction with the polymer coating layer on the surface of nano-silicon. The oxygen-containing functional groups on the surface of GO form a dense hydrogen bond cross-linking network with the binders PI and PU, forming interfacial chemical anchoring, which significantly improves the interfacial bonding strength and the integrity of the electronic conduction network, thereby reducing the volume expansion rate of the electrode and improving the overall cycle stability of the cell.

[0083] (3) In the preparation of composite anode material, the present invention first performs vacuum impregnation and then in-situ polymerization. The conductive polymer not only coats the nano-silicon, but also "bonds" the nano-silicon to the three-dimensional porous carbon aerogel wall. That is, the nano-silicon is wrapped by the polymer and firmly anchored on the solid carbon skeleton to form an integrated conductive-buffer structure, which can effectively buffer the volume change of silicon anode during charging and discharging, and prevent silicon particles from pulverizing and falling off. It has both conductivity and expansion buffering capacity.

[0084] (4) Significant cost advantages: Straw is agricultural waste, and the raw material cost is almost zero; the preparation cost of three-dimensional porous carbon aerogel is about 1 / 4 of that of commercially available porous carbon (such as CMK-3 and activated carbon); the overall cost of composite anode materials is more than 35% lower than that of commercial high-silicon products, which greatly reduces the threshold for large-scale application.

[0085] (5) Environmentally friendly and resource recycling: turning straw into treasure is in line with the "dual carbon" strategy and green manufacturing orientation. Detailed Implementation

[0086] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0087] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0088] Example 1: Standard high-silicon composite anode This embodiment provides a method for preparing a composite anode material, the specific steps of which are as follows: (1) Preparation of straw-based three-dimensional porous carbon aerogel: Wheat straw was boiled with alkali to remove lignin and hemicellulose, leaving high-purity cellulose. The high-purity cellulose was dispersed in an aqueous solution containing sodium hydroxide and urea (the mass ratio of NaOH, urea and water was 7:12:81). The solution was then subjected to a freeze-thaw cycle at -12℃ to fully dissolve the cellulose and form a cellulose solution. Subsequently, epichlorohydrin, a crosslinking agent, was added to the cellulose solution to chemically crosslink the cellulose molecular chains, thereby causing a phase transition. After washing with deionized water to remove non-cellulose components, a straw cellulose hydrogel with a three-dimensional network structure was obtained. Straw cellulose hydrogel was freeze-dried (-50℃ / 12h) to form a three-dimensional porous framework, and then carbonized at 800℃ for 2h under N2 atmosphere to obtain carbonized aerogel. Subsequently, the carbonized aerogel was activated with KOH at 600℃ for 1h under N2 atmosphere, with a KOH to carbonized aerogel mass ratio of 2:1. This yielded a straw-based three-dimensional porous carbon aerogel with three-dimensional interconnected channels, a pore size of 180nm, and a specific surface area of ​​1668m². 2 / g, pore volume 1.83cm 3 / g; (2) Vacuum impregnation: Disperse nano-silicon (50nm particle size) in an aqueous solution containing pyrrole (Py) monomer at a concentration of 0.1mol / L, with a mass ratio of nano-silicon to pyrrole monomer of 8:1. Then add the straw-based three-dimensional porous carbon aerogel obtained in step (1), with a mass ratio of nano-silicon to straw-based three-dimensional porous carbon aerogel of 4:6 to obtain a mixed system. Place the mixed system in a vacuum drying oven and maintain it under a negative pressure of -0.09MPa for 1.5h, and then slowly restore it to normal pressure. This process can be repeated 3 times to ensure that the nano-silicon and monomer completely enter the pores of the straw-based three-dimensional porous carbon aerogel to obtain a suspension. (3) In-situ polymerization: 3M FeCl3 aqueous solution of oxidant was slowly added dropwise at a rate of 1 drop / second to the impregnated suspension obtained in step (2) under ice-water bath (3℃) conditions. The molar ratio of FeCl3 to pyrrole monomer was controlled at 2.2:1. After the addition was completed, the reaction was continued to be mechanically stirred at 3℃ for 8h. After the reaction was completed, the mixture was washed alternately with deionized water and ethanol until the filtrate was colorless and then vacuum dried at 60℃ to obtain the composite negative electrode material. In this material, polypyrrole was uniformly coated on the surface of silicon particles to form an 8nm thick conductive layer, and the polypyrrole (PPy) coated nano-silicon was embedded and anchored in the pores of the three-dimensional porous carbon aerogel.

[0089] This embodiment also provides a negative electrode sheet, the preparation process of which is as follows: The aforementioned composite negative electrode material, conductive carbon black, and binder were dispersed in NMP solvent at a mass ratio of 85:5:10. The binder contained PI, PU, ​​and GO in a mass ratio of 6:4:0.5, yielding a slurry. This slurry was then coated onto copper foil, vacuum dried at 120°C, and rolled to a compaction density of 1.25 g / cm³. 3 This yields the negative electrode sheet; Example 2: Ultra-high silicon loading (silicon / carbon mass ratio = 5:5) The only difference between Example 2 and Example 1 is that in Example 2, the mass ratio of nano-silicon to straw-based three-dimensional porous carbon aerogel is 5:5, and the proportion of PU in the binder is increased, that is, the mass ratio of PI, PU and GO is 5.5:4.5:0.5. Everything else is the same as in Example 1.

[0090] Example 3 The only difference between Example 3 and Example 1 is that in Example 3, polyaniline (PANI) is used instead of PPy for in-situ coating, that is, aniline monomer is used instead of pyrrole monomer, and 0.6M ammonium persulfate aqueous solution (APS) is used as oxidant to prepare the polyaniline coating layer. The reaction needs to be carried out in 1 mol / L hydrochloric acid aqueous solution to ensure the formation of polyaniline in the form of a highly conductive intermediate (emerald green imine salt). The hydrochloric acid aqueous solution and APS are added together to the impregnated suspension. The molar ratio of APS to aniline monomer is controlled at 1.1:1. Everything else is the same as in Example 1.

[0091] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the binder in Comparative Example 1 is replaced with conventional CMC and SBR (the mass ratio of the two is 1:1, and everything else is the same as in Example 1).

[0092] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses PU to replace PI in equal amounts, that is, Comparative Example 2 does not add PI and only uses PU and GO as adhesives, otherwise it is the same as Example 1.

[0093] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that Comparative Example 3 uses PI to replace PU in equal amounts, that is, Comparative Example 3 does not add PU and only uses PI and GO as binders, otherwise it is the same as Example 1.

[0094] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that Comparative Example 4 uses only PI and PU as binders without adding GO, and the mass ratio of PI to PU is 6:4. Everything else is the same as Example 1.

[0095] Comparative Example 5 The only difference between Comparative Example 5 and Example 1 is that in Comparative Example 5, step (1) directly carbonizes the straw cellulose hydrogel. The carbonization process is the same as in Example 1, but freeze-drying and KOH activation are not performed. Everything else is the same as in Example 1.

[0096] Comparative Example 6 The only difference between Comparative Example 6 and Example 1 is that Comparative Example 6 did not use vacuum impregnation and in-situ polymerization, but instead used a physical mixing method, that is, directly grinding and mixing nano-silicon, straw-based three-dimensional porous carbon aerogel, and polypyrrole (PPy) powder, instead of in-situ polymerization coating. Otherwise, it is the same as Example 1.

[0097] Comparative Example 7 Comparative Example 7 uses commercially available silicon-carbon (40% Si content, no three-dimensional channels) as the negative electrode material, and CMC and SBR (mass ratio of 1:1) as the binder. The other preparation process of the negative electrode sheet is the same as in Example 1.

[0098] Performance testing Using the negative electrode sheets from Examples 1-3 and Comparative Examples 1-7 as the negative electrode and NCM811 as the positive electrode, commercial lithium-ion battery electrolyte (1M LiPF6 concentration, solvent consisting of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) in a volume ratio of 1:1:1:1:1) and a polyethylene (PE) ceramic-coated separator, soft-pack batteries were assembled and then their performance was tested. The test items and methods are as follows: Volume expansion rate: The initial thickness of the fresh battery is measured, and the cell thickness after 1C cycling is measured; Expansion rate = (thickness after cycling / initial thickness - 1) × 100%; Capacity retention rate after n cycles at 1C: Based on the discharge capacity of the first 1C cycle (C1), record the percentage of discharge capacity (Cn) in each cycle relative to the capacity of the first cycle. The retention rate after n cycles = Cn / C1 × 100%; First-cycle coulombic efficiency: First-cycle discharge capacity / First-cycle charge capacity × 100%.

[0099] The performance test results of the batteries prepared by the composite anode materials of Examples 1-3 and Comparative Examples 1-7 are shown in Table 1.

[0100] Table 1: Performance test results of batteries prepared with composite anode materials in Examples 1-3 and Comparative Examples 1-7

[0101] As can be seen from Table 1, the electrode of the present invention has an extremely low volume expansion rate, with a compaction density of 1.25 g / cm³. 3With a silicon content of 40wt%, the volume expansion rate of the electrode after 200 cycles is only 55%, far lower than the 200% of traditional silicon-carbon anodes, and the electrode shows no obvious bulging or delamination. Meanwhile, the coulombic efficiency of the battery in Example 1 is as high as 89% in the first cycle (due to PPy coating inhibiting excessive SEI growth and carbon aerogel reducing side reactions). After 200 cycles at 1C, the capacity retention rate reaches 86% (reversible specific capacity remains at 1800mAh / g), and tests show that the capacity still reaches 1200mAh / g at a high 5C rate, demonstrating excellent electrochemical performance.

[0102] Comparative Example 1 used a conventional binder, resulting in a significantly higher expansion rate of the electrode compared to Example 1, and a significantly lower capacity retention rate after 200 cycles. This demonstrates that even with a good negative electrode material, the use of a conventional binder can still lead to electrode expansion and cracking due to the extremely high silicon loading.

[0103] Comparative Example 2, which did not contain PI, exhibited a significantly higher expansion rate than Example 1, and its capacity retention after 200 cycles was significantly worse than that of Example 1. This is because the lack of polar groups in PI prevents the formation of strong chemical bonds with the copper foil, making the electrode prone to detachment.

[0104] Comparative Example 3, without the addition of PU, exhibited a significantly higher expansion rate than Example 1, and its capacity retention after 200 cycles was significantly worse than that of Example 1. This is because the rigidity of PI is too high, and without the elastic ether bond buffering of PU, the electrode will expand significantly during repeated charge and discharge cycles, and may even develop microcracks.

[0105] Comparative Example 4, which did not contain GO, exhibited a higher expansion rate than Example 1, and a lower capacity retention rate after 200 cycles. This is because the lack of GO's π-π interactions and hydrogen bonding resulted in a loose binder network and increased susceptibility to damage to the conductive network.

[0106] As can be seen from Comparative Examples 1-4, the present invention uses a combination of PI, PU and GO as binders, none of which can be omitted. The three work together to enable the electrode to have both extremely low volume expansion rate and good electrochemical performance.

[0107] Comparative Example 5 directly carbonized the straw cellulose hydrogel without freeze-drying and KOH activation. This resulted in a significantly higher expansion rate of the electrode in Comparative Example 5 compared to Example 1, and a significantly lower capacity retention rate after 200 cycles. This is because Comparative Example 5 could not form a porous aerogel with three-dimensional interconnected channels. Its dense carbon lacked a "cage-like" effect, failing to provide physical buffering and absorb the volume expansion stress of silicon. This also illustrates the important role of three-dimensional porous carbon aerogels.

[0108] Comparative Example 6, which directly employed a physical mixing method, resulted in a significantly higher expansion rate than Example 1, and its capacity retention after 200 cycles was significantly worse than that of Example 1. This is because physical mixing cannot form a chemically anchored interface, preventing PPy from acting as a link between the conductive buffer layer and the carbon skeleton, making the structure highly susceptible to failure. This demonstrates that the vacuum impregnation and in-situ polymerization method used in this invention plays a crucial role in reducing volume expansion and improving electrochemical performance of the composite anode material.

[0109] Comparative Example 7 uses a traditional binder, which causes the electrode to swell severely and shed powder after 50 cycles, with an expansion rate of >200%. After 100 cycles at 1C, the capacity decays to 52%, and it almost fails after 200 cycles. Its performance is significantly worse than that of Examples 1-3 of the present invention.

[0110] In summary, this invention employs a three-pronged synergistic strategy of "straw-based three-dimensional porous carbon aerogel, conductive polymer in-situ coating of nano-silicon, and composite binder" to simultaneously address the issues of volume expansion, poor conductivity, and cycle degradation of silicon-based anodes from three dimensions: structural buffering, conductivity enhancement, and interface anchoring. This approach can significantly reduce the volume expansion of silicon-based anodes and improve the battery's cycle stability, first-cycle coulombic efficiency, and other electrochemical performance.

[0111] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A composite negative electrode material, characterized by, The composite anode material comprises three-dimensional porous carbon aerogel and polymer-coated nano-silicon; the polymer-coated nano-silicon is embedded in the pores of the three-dimensional porous carbon aerogel.

2. The composite negative material of claim 1, wherein, The pore size of the three-dimensional porous carbon aerogel is 100-300 nm; and / or the three-dimensional porous carbon aerogel has a specific surface area of ≥ 1500 m 2 / g; and / or the three-dimensional porous carbon aerogel has a pore volume of > 1.0 cm3 / g 3 / g.

3. The composite negative electrode material according to claim 1, characterized in that, The polymer-coated nano-silicon includes any one of polypyrrole, polyaniline, polythiophene, and poly3,4-ethylenedioxythiophene. And / or, in the polymer-coated nano-silicon, the thickness of the coating layer is 5-10 nm; And / or, in the polymer-coated nano-silicon, the nano-silicon particle size is 30-80 nm.

4. The method for preparing the composite negative electrode material according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: (1) Cellulose hydrogel is dried, carbonized and activated to obtain three-dimensional porous carbon aerogel; (2) Mix nano-silicon and polymer monomer solution; then add the three-dimensional porous carbon aerogel, and impregnate under vacuum to obtain a suspension; (3) The oxidant and the suspension are mixed and then subjected to in-situ polymerization to obtain the product.

5. The preparation method according to claim 4, characterized in that, In step (1), the method for preparing the cellulose hydrogel includes the following steps: Cellulose is dispersed in a solvent and subjected to freeze-thaw cycles to obtain a cellulose solution; then, the cellulose hydrogel is prepared by physical or chemical crosslinking. And / or, in step (1), the drying includes either supercritical drying or freeze drying.

6. The preparation method according to claim 4, characterized in that, In step (1), the carbonization temperature is 750-850℃ and the time is 1.5-2.5h; And / or, the activation temperature is 550-650℃, and the time is 0.5-1.5h; And / or, activation is performed using potassium hydroxide.

7. The preparation method according to claim 4, characterized in that, In step (2), the concentration of the polymer monomer solution is 0.05-0.2 mol / L; And / or, the mass ratio of the nano-silicon to the polymer monomer in the polymer monomer solution is (5-10):1; And / or, the polymer monomers in the polymer monomer solution include any one of pyrrole monomers, aniline monomers, thiophene monomers, and 3,4-ethylenedioxythiophene monomers; And / or, the mass of the nano-silicon accounts for 30-80% of the total mass of the nano-silicon and the three-dimensional porous carbon aerogel; And / or, the vacuum impregnation pressure is -0.08 to -0.1 MPa, and the time is 1-2 hours.

8. The preparation method according to claim 4, characterized in that, In step (3), the oxidant includes at least one of FeCl3 and ammonium persulfate; And / or, the in-situ polymerization reaction is carried out at a temperature of 0-5°C for a time of 4-12 hours.

9. A negative electrode, characterized in that, The negative electrode includes a current collector and an active layer disposed on the surface of the current collector; the active layer comprises the composite negative electrode material according to any one of claims 1-3 and a binder; the binder comprises binder A, an elastomer and a two-dimensional material; The adhesive A includes at least one of polyimide and polyamic acid; The elastomer includes at least one of polyurethane, polyether thermoplastic elastomer, and polyester thermoplastic elastomer; The two-dimensional material includes at least one of graphene oxide, nitrogen-doped graphene, and MXene.

10. A battery, characterized in that, The battery includes the negative electrode as described in claim 9.

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