A low-expansion, high-specific-capacity silicon-carbon negative electrode composite material and preparation method thereof

Abstract

The present invention relates to the technical field of lithium-ion batteries, and specifically discloses a low-expansion, high-specific-capacity silicon-carbon negative electrode composite material and a preparation method thereof. The composite material comprises a porous silicon-carbon composite substrate, to which nano-additives are attached, wherein the nano-additives include aluminum silicate. The present invention loads nano-additives such as aluminum silicate onto the porous silicon-carbon composite substrate, and utilizes the unique nano-layered structure and nano-pores of the nano-additives to construct lithium storage and superion transmission channels to accommodate volume expansion. At the same time, the unique mechanical properties and mechanical strength can stabilize the electrode structure, reduce particle pulverization, and inhibit volume expansion, thereby achieving a porous silicon-carbon composite substrate. While maintaining the high capacity of the silicon-carbon negative electrode composite material, the volume expansion rate of the silicon-carbon negative electrode composite material is significantly reduced. The expansion rate of the silicon-carbon negative electrode composite material prepared by the present invention is below 71%.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a low-expansion, high-specific-capacity silicon-carbon negative electrode composite material and a preparation method thereof. Background Art

[0002] In the field of lithium-ion batteries, silicon-carbon anode materials are considered ideal for next-generation lithium-ion batteries due to their high theoretical specific capacity (silicon's theoretical specific capacity is approximately 4200 mAh / g, far exceeding the 372 mAh / g of traditional graphite anodes). However, silicon undergoes significant volume expansion (approximately 300%) during charge and discharge, leading to structural damage, electrode pulverization, and capacity decay, severely limiting its practical application. Furthermore, silicon's low conductivity also affects its rate capability and cycling stability.

[0003] In order to meet the above challenges, that is, to meet the demand for high energy density of lithium-ion batteries and reduce the volume expansion of silicon during charging and discharging, researchers have proposed the design idea of silicon-carbon composite materials. By compounding silicon with porous carbon materials, the buffering effect and conductivity of porous carbon materials are used to improve the performance of silicon.

[0004] However, the silicon-carbon composite materials prepared by the above technology still have the following shortcomings:

[0005] (1) Limited expansion suppression effect: The expansion suppression effect of existing silicon-carbon composite materials is insufficient, and it is difficult to completely solve the volume expansion problem of silicon.

[0006] (2) Limited improvement in energy density: The silicon content in existing silicon-carbon composite materials is relatively low, resulting in limited improvement in energy density. Summary of the Invention

[0007] The purpose of the present invention is to provide a low-expansion, high-specific-capacity silicon-carbon negative electrode composite material and a preparation method thereof, which significantly reduces the volume expansion rate of the silicon-carbon negative electrode composite material while maintaining the high capacity of the silicon-carbon negative electrode composite material.

[0008] The present invention is achieved through the following technical solutions:

[0009] A low-expansion, high-specific-capacity silicon-carbon negative electrode composite material comprises a porous silicon-carbon composite substrate, the porous silicon-carbon composite substrate is attached with nano-additives, and the nano-additives comprise aluminosilicate.

[0010] The present invention aims to solve the following problems:

[0011] (1) Volume expansion problem of silicon: By designing a low-expansion silicon-carbon composite material, the volume expansion of silicon during the charging and discharging process is alleviated and the structural stability of the material is improved.

[0012] (2) Energy density improvement: By optimizing the composition and structure of silicon-carbon composite materials, their energy density can be improved to meet the needs of high energy density batteries.

[0013] The present invention adopts a porous silicon-carbon composite substrate as a substrate. The porous silicon-carbon composite substrate serves as a carrier of silicon, which can improve the conductivity of the silicon-carbon negative electrode and alleviate volume expansion.

[0014] The aluminosilicate of the present invention has the molecular formula xAl2O3·ySiO2, and its main components are SiO2 and Al2O3, naturally occurring materials. Its unique nano-layered structure and nanopores create lithium storage and superion transport channels, accommodating volume expansion. Its unique mechanical properties and strength stabilize the electrode structure, reduce particle pulverization, and inhibit volume expansion. Furthermore, the introduced nano-additives have little effect on the specific capacity of the resulting battery negative electrode.

[0015] Aluminosilicates mainly include feldspar, mica, kaolin, zeolite and garnet.

[0016] In summary, the present invention significantly reduces the volume expansion rate of the silicon-carbon negative electrode composite material while maintaining the high capacity of the silicon-carbon negative electrode composite material by loading nano-additives such as aluminosilicate on the porous silicon-carbon composite substrate.

[0017] In a preferred embodiment, during the preparation of the silicon-carbon negative electrode composite material, the nano-additive is introduced in the form of a slurry, and the slurry-state nano-additive is mixed with other raw materials for preparing the silicon-carbon negative electrode composite material.

[0018] Introducing nano-additives in the form of slurry has the following advantages:

[0019] 1) The preparation process of slurry nano-additives is simple:

[0020] The preparation of traditional nanomaterial additives requires multiple complex processes such as dispersion, coarse grinding, fine grinding, spray drying, furnace sintering, and airflow crushing; however, the slurry-state nanoadditives of the present invention do not require subsequent processes such as spray drying, furnace sintering, and airflow crushing. The slurry-state nanoadditives formed after dispersion, coarse grinding, and fine grinding can be used directly. This improvement not only greatly reduces spray drying and subsequent processes, but also significantly reduces production costs and time costs.

[0021] 2) The introduction process is simple:

[0022] The slurry-state nano-additive can be directly added to the slurry process of preparing the silicon-carbon negative electrode composite material without the need for a composite process in advance, which is beneficial to saving processes and reducing costs.

[0023] In a preferred embodiment, the expansion rate of the silicon-carbon negative electrode composite material is less than or equal to 71%.

[0024] A method for preparing a low-expansion, high-specific-capacity silicon-carbon negative electrode composite material comprises the following steps:

[0025] S1. Preparation of slurry additive: Mixing the raw materials for preparing the nano-additive (usually micron-sized additives) with water to form a suspension, and sequentially coarsely grinding and finely grinding the suspension to obtain a slurry additive;

[0026] S2. Slurry preparation: first dissolving a binder in a solvent to obtain a binder solution, dispersing a conductive agent in the solvent to form a dispersion, dissolving polyacrylic acid in the solvent to obtain a PAA solution, then mixing the binder solution and the dispersion with the porous silicon-carbon composite substrate, then adding the PAA solution and the slurry additive, and then adding the slurry additive; stirring evenly to form a slurry;

[0027] S3, coating: evenly apply the slurry on the current collector;

[0028] S4. Drying.

[0029] The slurry-state nano additive prepared by the present invention is evenly dispersed with water as a medium to form a suspension. There is no agglomeration between the nanoparticle materials and no sedimentation when left standing, thus achieving nano-level uniform dispersion.

[0030] Moreover, the method of introducing nano-additives in the present invention is more direct and does not involve complex pretreatment processes such as ball milling and sintering between the active material (porous silicon-carbon composite substrate) and the additive. Instead, the additive is directly added during the homogenization process when preparing the negative electrode sheet, thereby completing the introduction work.

[0031] In a preferred embodiment, in step S1, the nano-additive has a nano-layered structure and nano-pores.

[0032] In a preferred embodiment, in step S1, the particle size of the nano-additive is 200 nm to 500 nm.

[0033] In a preferred embodiment, in step S2, the proportion of the nano additive is 0.8-1.2 wt% based on the weight of the slurry.

[0034] In a preferred embodiment, in step S3, the coating thickness is 50-250 μm.

[0035] In a preferred embodiment, the preparation method further comprises:

[0036] S5, Roller Pressing: Compact the dried electrode by roller press;

[0037] S6. Cutting: Cut the rolled pole pieces into the required size and shape.

[0038] The silicon-carbon negative electrode composite material prepared by the above preparation method is a negative electrode plate of a lithium-ion battery.

[0039] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0040] 1. The present invention loads nano-additives such as aluminosilicate on a porous silicon-carbon composite substrate, and utilizes the unique nano-layered structure and nano-pores of the nano-additives to construct lithium storage and superion transmission channels to accommodate volume expansion; at the same time, the unique mechanical properties and mechanical strength can stabilize the electrode structure, reduce particle pulverization, and inhibit volume expansion, thereby realizing a porous silicon-carbon composite substrate. While maintaining the high capacity of the silicon-carbon negative electrode composite material, the volume expansion rate of the silicon-carbon negative electrode composite material is significantly reduced; the expansion rate of the silicon-carbon negative electrode composite material prepared by the present invention is below 71%.

[0041] 2. The slurry-state additive of the present invention not only has the advantages of a simple preparation process, good dispersibility and no sedimentation, but can also be directly added to the slurry-state additive during the homogenization process when preparing the negative electrode sheet, thereby completing the introduction work. It does not involve complex pretreatment processes such as ball milling and sintering between the active material (porous silicon-carbon composite substrate) and the additive, saving the process of preparing the negative electrode sheet and helping to save cost and time. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0043] Figure 1 HRTEM image (100 nm) of the porous silicon-carbon composite substrate in an embodiment of the present invention;

[0044] Figure 2 for Figure 1 Corresponding C and Si element mapping (50nm);

[0045] Figure 3 for Figure 1 Corresponding C element mapping diagram (50nm);

[0046] Figure 4 for Figure 1 Corresponding Si element mapping (50nm);

[0047] Figure 5 This is the SEM of the slurry additive in Example 1 of the present invention. Figure 1 (200nm);

[0048] Figure 6 This is the SEM of the slurry additive in Example 1 of the present invention. Figure 2 (500nm);

[0049] Figure 7 This is the SEM of the slurry additive in Example 1 of the present invention. Figure 3 (5μm);

[0050] Figure 8 HRTEM image of the silicon-carbon negative electrode composite material of Example 1 of the present invention;

[0051] Figure 9 for Figure 8 Corresponding mapping of C, Al and Si elements (500nm);

[0052] Figure 10 for Figure 8 Corresponding Si element mapping (500nm);

[0053] Figure 11 for Figure 8 Corresponding C element mapping diagram (500nm);

[0054] Figure 12 for Figure 8 Corresponding Al element mapping diagram (500nm);

[0055] Figure 13 for Figure 8 The corresponding K element mapping diagram;

[0056] Figure 14 A GCD curve diagram showing the performance test results of the silicon-carbon negative electrode composite materials prepared in Example 1 of the present invention and Comparative Example 1;

[0057] Figure 15 This is the SEM of the dry powder additive in Comparative Example 2 of the present invention. Figure 1 (200nm);

[0058] Figure 16 This is the SEM of the dry powder additive in Comparative Example 2 of the present invention. Figure 2 (500nm);

[0059] Figure 17 This is the SEM of the dry powder additive in Comparative Example 2 of the present invention. Figure 3 (5μm);

[0060] Figure 18 This is a GCD curve chart showing the performance test results of the carbon silicon substrate of Comparative Example 2 of the present invention, the carbon silicon substrate modified with a slurry-state additive, and the carbon silicon substrate modified with a dry powder-state additive. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the examples. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention. The examples described below are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0062] In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that these specific details are not necessarily required to practice the present invention. In other examples, well-known structures, materials, or methods are not specifically described to avoid obscuring the present invention. The materials, instruments, and reagents used in the following examples, unless otherwise specified, are commercially available. The techniques used in the examples, unless otherwise specified, are conventional techniques well known to those skilled in the art.

[0063] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0064] In order to solve the problem of high expansion rate of existing lithium-ion negative electrodes, this embodiment provides a low-expansion, high-specific capacity silicon-carbon negative electrode composite material, including a porous silicon-carbon composite substrate, the porous silicon-carbon composite substrate is attached with a nano-additive, and the nano-additive includes aluminosilicate, wherein the porous silicon-carbon composite substrate is composed of porous carbon and silicon particles loaded on the porous carbon, that is, the silicon-carbon negative electrode composite material of this embodiment can be understood as silicon particles and aluminosilicate loaded on the porous carbon at the same time.

[0065] The porous silicon-carbon composite substrate of this embodiment is an active material, which can be obtained commercially, specifically purchased from Luoyang Lianchuang Lithium Energy Technology Co., Ltd., and the active material was used in the relevant experiments of Example 1. The HRTEM image of the porous silicon-carbon composite substrate is as follows Figure 1 , Figure 1 The corresponding C and / or Si element mapping diagram is as follows Figure 2-Figure 4 shown.

[0066] Depend on Figures 1-4 It can be seen that:

[0067] The silicon particles are uniform in size (approximately 20 nm) and attached to the porous carbon surface.

[0068] The substrate uses flaky porous carbon as a carrier to improve the conductivity of the silicon negative electrode and alleviate volume expansion:

[0069] The porous structure of porous carbon not only provides a buffer for silicon's volume expansion, but also improves electrolyte wettability and lithium ion transfer rate, thereby enhancing the cycle stability and rate performance of the negative electrode material. To introduce a porous structure, a silicon source (such as silane, silicate, or nano-silicon powder) is often introduced into the surface or pores of the porous carbon through methods such as chemical vapor deposition (CVD). The silicon source is then converted into silicon through subsequent treatment (such as thermal reduction or chemical reduction), thereby forming a silicon-carbon composite material.

[0070] The aluminosilicate in this example is primarily composed of SiO2 and Al2O3. Its unique nano-layered structure and nanopores create channels for lithium storage and superion transport, accommodating volume expansion. Furthermore, its unique mechanical properties and strength stabilize the electrode structure, reduce particle pulverization, and inhibit volume expansion. Furthermore, the introduced nano-additives have virtually no effect on the specific capacity of the resulting battery negative electrode.

[0071] Aluminosilicates mainly include feldspar, mica, kaolin, zeolite and garnet.

[0072] High-entropy materials with unique nanolayered structures and nanopores do have the potential to suppress volume expansion. However, achieving this goal requires comprehensive consideration of several key factors, such as the role of the nanolayered structure (ensuring moderate interlayer bonding strength) and the contribution of nanopores (excessive porosity or uneven pore distribution may lead to decreased mechanical strength or structural collapse). Furthermore, the following factors need to be considered:

[0073] 1) Material system adaptability: Not all high-entropy materials are applicable, and this needs to be verified in combination with specific applications (such as lithium / sodium-ion batteries, catalysis, etc.);

[0074] 2) Structural stability: Nanostructures may aggregate, experience pore collapse, or undergo layered exfoliation during cycling, requiring surface modification or composite reinforcement.

[0075] 3) Preparation process: The controllable synthesis of nanolayered / porous structures (such as pore size distribution and interlayer spacing control) directly affects the performance.

[0076] In addition to the aluminosilicate in this embodiment, other nano-additives with unique nano-layered structures and nano-pores include graphene-coated silicon particles (Si@Graphene), carbon nanotubes (CNTs) and silicon composites, nano-TiO2-coated silicon (Si@TiO2), porous carbon-loaded silicon (Si@Porous Carbon), high-entropy oxide (HEO) nanoparticles, etc. However, except for aluminosilicate, all others have technical defects.

[0077] Among them, the agglomeration of graphene-coated silicon particles (Si@Graphene) leads to structural rupture:

[0078] Case (Adv. Mater., 2015): A graphene layer (Si@Graphene) was coated on the surface of silicon nanoparticles by CVD method, but the graphene layer wrinkled and broke after cycling.

[0079] Cause of failure: Although graphene has high mechanical strength, local stress concentration occurs when silicon particles expand, causing the coating layer to rupture; the interface bonding between silicon and graphene is insufficient, and peeling occurs after expansion, losing its restraint effect.

[0080] Data: After 50 cycles, the volume expansion rate still reaches 200%, which is worse than the theoretical expectation (<150%).

[0081] Among them, the conductive network of carbon nanotubes (CNTs) and silicon composites fails:

[0082] Case (J. Power Sources, 2017): Mechanical mixing of silicon nanoparticles with CNTs (Si / CNTs composites) improves initial conductivity, but the CNTs network collapses after cycling.

[0083] Cause of failure: There is a lack of chemical bonding between CNTs and silicon, and the silicon separates from the contact points with CNTs after expansion; although CNTs themselves are flexible, they cannot effectively limit the radial expansion of silicon particles.

[0084] Data: After 100 cycles, the electrode thickness increased by 180%, and the capacity decay rate was close to that of pure silicon negative electrode.

[0085] Among them, the brittle cracking of nano-TiO2 coated silicon (Si@TiO2):

[0086] Case (ACS Nano, 2016): A nano-TiO2 layer (thickness ~20nm) was coated on the silicon surface by the sol-gel method, but cracks appeared in the TiO2 layer after cycling.

[0087] Cause of failure: TiO2 is hard but brittle and cannot adapt to the repeated expansion / contraction of silicon; cracks lead to the infiltration of electrolyte, which accelerates the thickening of SEI film.

[0088] Data: The volume expansion rate only dropped from 300% to 220%, and the interface impedance increased significantly.

[0089] Among them, the pores of porous carbon-supported silicon (Si@Porous Carbon) collapse:

[0090] Case (Nano Energy, 2018): Silicon nanoparticles were embedded in commercial porous carbon (pore size ~50 nm), but the pore structure collapsed after cycling.

[0091] Failure reasons: The mechanical strength of porous carbon is insufficient, and silicon expands and squeezes the pore wall, causing structural damage; the pore distribution is uneven, and local silicon particles agglomerate, exacerbating the volume effect.

[0092] Data: The electrode thickness change rate is still as high as 160% after 100 cycles.

[0093] Among them, the interface added by high entropy oxide (HEO) nanoparticles is incompatible:

[0094] Case (Chem. Eng. J., 2022): In the negative electrode composed of high-entropy oxide ((MgCoNiCuZn)O) nanoparticles and silicon, the expansion suppression effect is weak.

[0095] Cause of failure: The interface compatibility between HEO and silicon is poor, and the expansion stress cannot be effectively transmitted; HEO itself is inert to lithium and cannot participate in the buffering mechanism.

[0096] Data: The volume expansion rate is reduced by only 10% (from 300% to 270%), and the specific capacity is reduced by 30%.

[0097] In summary, the present invention, on the one hand, utilizes the porous structure of porous carbon to provide a buffer space for the volume expansion of silicon, thereby suppressing the volume expansion rate of the silicon-carbon negative electrode composite material. On the other hand, by simultaneously loading silicon particles and nano-additives with unique nano-layered structure and nano-pores on the porous carbon, the nano-additives are utilized to accommodate the volume expansion of the carbon negative electrode composite material and suppress the volume expansion, thereby ultimately achieving the goal of significantly reducing the volume expansion rate of the silicon-carbon negative electrode composite material while maintaining the high capacity of the silicon-carbon negative electrode composite material. The expansion rate of the silicon-carbon negative electrode composite material prepared by the present invention is below 71%.

[0098] Preferably, during the preparation of the silicon-carbon negative electrode composite material, the nano-additive is introduced in the form of a slurry, and the slurry-state nano-additive is mixed with other raw materials for preparing the silicon-carbon negative electrode composite material.

[0099] The method for preparing the above-mentioned low expansion, high specific capacity silicon-carbon negative electrode composite material comprises the following steps:

[0100] S1. Preparation of Slurry Additive: Mix a micron-sized aluminosilicate material with water (weight ratio of material:water = 1:4), coarsely grind for 20 minutes, and finely grind for 40 minutes. This completes nanocrystallization of the additive and forms a suspension of the slurry additive with water. The nanoparticles in the slurry additive exhibit no agglomeration and no sedimentation upon standing, achieving uniform nanoscale dispersion. If the slurry additive is allowed to stand for extended periods, ultrasonic treatment (for 10-30 minutes) is recommended before dispensing. The coarse and fine grinding procedures are conventional ball milling.

[0101] The nano additive has a nano-layered structure and nano-pores, and can be specifically aluminosilicate. The particle size of the nano additive is 200nm to 500nm.

[0102] S2. Slurry preparation: First, dissolve the binder in a solvent to obtain a binder solution, disperse the conductive agent in the solvent to form a dispersion, dissolve polyacrylic acid in a solvent to obtain a PAA solution, then mix the binder solution and the dispersion with the porous silicon-carbon composite substrate, and then add the PAA solution and the slurry-state additive to mix. The nano additive accounts for 0.8~1.2wt% based on the weight of the slurry; then use a high-speed mixer or a planetary mixer to stir the mixture evenly to form a slurry. The stirring speed and time need to be controlled to avoid bubbles in the slurry. The viscosity of the slurry needs to be moderate to facilitate subsequent coating. Among them, the binder solution, dispersion and PAA solution use deionized water as the solvent and are magnetically stirred until they are completely dissolved or evenly dispersed.

[0103] The binder includes carboxymethyl cellulose (CMC), styrene-butadiene copolymer (SBR), or polyvinylidene fluoride (PVDF). The solvent for polyvinylidene fluoride (PVDF) is N-methylpyrrolidone (NMP); the solvent for carboxymethyl cellulose (CMC) and styrene-butadiene copolymer (SBR) is water.

[0104] The conductive agent may be any commonly used conductive agent in the art, including carbon nanotubes (CNTs) and the like.

[0105] S3. Coating: Use a scraper to evenly apply the slurry on the current collector (usually copper foil). The coating thickness is usually 50-250 μm (wet film thickness). The coating speed is adjusted according to the slurry viscosity and equipment performance to ensure that the slurry is evenly distributed on the copper foil surface to avoid inconsistent thickness.

[0106] S4. Drying: Dry the coated electrode to remove the solvent. Depending on the solvent selected, dry at 80-120°C under normal pressure or vacuum to avoid solvent residue.

[0107] S5. Rolling: The dried electrode is compacted by a roller press to improve the density and conductivity of the electrode.

[0108] S6. Cutting: The rolled pole pieces are cut into the required size and shape, and the cut pole pieces are quality inspected to ensure that their performance meets the requirements. The pole pieces that pass the inspection are stored for subsequent battery assembly.

[0109] The silicon-carbon negative electrode composite material prepared by the above preparation method is a negative electrode plate of a lithium-ion battery.

[0110] Simply put, the method of introducing nano-additives in the present invention is more direct and does not involve complex pretreatment processes such as ball milling and sintering between the active material (silicon-carbon negative electrode composite material) and the additive. Instead, the additive is directly added during the slurry process when preparing the negative electrode sheet to complete the introduction.

[0111] The silicon-carbon negative electrode composite material prepared in this embodiment has the following advantages:

[0112] 1) Nanolayered structure: Nanoadditives have nanolayered structures and nanopores, which can construct efficient lithium storage and superion transport channels. At the same time, their nanoscale gaps can effectively accommodate volume expansion and inhibit electrode structure damage.

[0113] 2) Uniform Dispersion: Energy spectrum results show that the nano-additive is evenly dispersed in the silicon-carbon matrix, and has a stronger interfacial compatibility with silicon than with the carbon matrix. This property not only protects the original carbon coating but also forms a strong coating on the silicon surface.

[0114] 3) Mechanical properties and mechanical strength: The unique mechanical properties and mechanical strength of nano-additives help stabilize the electrode structure, reduce particle pulverization, and further inhibit volume expansion, thereby improving the cycle stability and service life of the battery.

[0115] To better illustrate the technical effects of this embodiment, the following specific examples are used for illustration. Since the effects of feldspar, mica, kaolin, zeolite, and garnet are not much different, the following examples are illustrated using feldspar.

[0116] Example 1:

[0117] A low-expansion, high-specific-capacity silicon-carbon negative electrode composite material comprises a porous silicon-carbon composite substrate to which a nano-additive is attached, and the nano-additive is feldspar.

[0118] The preparation method of the silicon-carbon negative electrode composite material of this embodiment includes the following steps:

[0119] S1. Preparation of slurry additive: Mix micron-sized feldspar with water (weight ratio of feldspar:water = 1:4), perform coarse grinding for 20 minutes and fine grinding for 40 minutes in sequence to obtain a slurry additive.

[0120] The slurry additives are used directly after wet ball milling. The nanoparticles exist in water solvents, and the interaction between particles is small, and it is not easy to agglomerate. Therefore, the dispersion is strong and the particle size is uniform. Figure 5-Figure 7 shown.

[0121] S2. Slurry preparation: Carboxymethyl cellulose (CMC), carbon nanotubes (CNTs), and polyacrylic acid (PAA) are pre-dissolved in water at a CMC solid content of 1.25%, a CNT solid content of 0.8%, and a PAA solid content of 5% to obtain CMC solution, CNT dispersion, and PAA solution. The CMC solution and CNT dispersion are then mixed with a porous silicon-carbon composite substrate, and then a slurry additive and PAA solution are added and mixed. The nano additive accounts for 1.0 wt% based on the weight of the slurry. The mixture is then stirred evenly using a high-speed stirrer to form a slurry.

[0122] The specific steps of step S2 are as follows:

[0123] S21, solution pretreatment stage:

[0124] Prepare the following three pre-dissolved solutions respectively:

[0125] ①Sodium carboxymethyl cellulose (CMC) solution: solid content 1.25%;

[0126] ② Carbon nanotube (CNT) dispersion: solid content 0.8%;

[0127] ③ Polyacrylic acid (PAA) solution: solid content 5%;

[0128] (Note: All solutions used deionized water as solvent and were magnetically stirred until completely dissolved).

[0129] S22, primary homogenization process:

[0130] Add the porous silicon carbon substrate to the homogenization tank; add the pre-prepared CMC solution and CNT dispersion in sequence; start the homogenization program (button-type semi-electric small batch preparation: rotation speed 1500 rpm, rotation time 5 minutes).

[0131] S23, secondary homogenization stage:

[0132] Add the slurry additive and the pre-prepared PAA solution to the slurry prepared in step S22; add an appropriate amount of deionized water (to adjust the viscosity); and continue homogenization (short-circuit breaker for small-batch preparation: 1500 rpm, 15 min).

[0133] S24, slurry post-treatment:

[0134] Use 200 mesh standard sieve for filtration and collect the filtered slurry; quality inspection: viscosity test, fineness test.

[0135] The classic slurry formula is:

[0136] The porous silicon-carbon composite substrate is 94.7%, carbon nanotubes are 0.3%, carboxymethyl cellulose is 2%, and polyacrylic acid is 3%. The total water content is variable and adjusted based on actual conditions. The water content in the slurry is determined as follows: water accounts for 80% of the slurry additives, while the binder dispersant is pre-dissolved in water at a solid content of 1.25% CMC, 0.8% CNT, and 5% PAA.

[0137] Among them, carboxymethyl cellulose (CMC): the manufacturer / agent is Japan Daicel / DAICEL, model CMC2200, and the molecular formula is C6H7O2(OH)3-x(OCH2COONa)x.

[0138] Among them, carbon nanotubes (CNT): the manufacturer / agent is Jiangsu Tiannai Technology Co., Ltd., the molecular formula is C, and the molecular weight is 12.01.

[0139] Among them, polyacrylic acid (PAA): the manufacturer / agent is Chengdu Yindile Technology Co., Ltd., chemical formula: [C3H4O2]n, molecular weight: 72.06n.

[0140] S3. Coating: Use a scraper to evenly apply the slurry on the current collector (usually copper foil). The coating thickness is usually 200μm (wet film thickness).

[0141] S4. Drying: Dry the coated electrode at 100°C under normal pressure to remove the solvent.

[0142] S5. Rolling: The dried electrode is compacted by a roller press to improve the density and conductivity of the electrode.

[0143] S6. Cutting.

[0144] The HRTEM image of the silicon-carbon negative electrode composite material prepared in this embodiment is as follows: Figure 8 As shown, Figure 8 The corresponding mappings for different elements are as follows Figures 9-13 As shown:

[0145] Dark feldspar and light silicon particles are attached to the porous carbon network. According to the element mapping, the irregular outline of feldspar can be clearly observed. Its main elements are Si, K, and Al, which are evenly distributed in the porous carbon.

[0146] Comparative Example 1:

[0147] This comparative example is based on Example 1, and differs from Example 1 in that:

[0148] The silicon-carbon negative electrode composite material does not contain feldspar.

[0149] The silicon-carbon negative electrode composite materials prepared in Example 1 and Example 2 were made into buckle batteries for electrical performance testing. The results are shown in Table 1 and Figure 14 As shown: The composite material significantly reduces the expansion rate of the silicon-carbon negative electrode while maintaining high capacity.

[0150] Table 1

[0151]

[0152] From Table 1 and Figure 14 It can be seen that:

[0153] The original silicon-carbon anode (Comparative Example 1) had a specific discharge capacity of 1886.97 mAh / g, an initial efficiency of 91.97%, and a plate expansion rate of 130.89%. The modified silicon-carbon anode (Example 1) had a specific discharge capacity of 1878.78 mAh / g, a 0.43% decrease compared to the original silicon-carbon, with minimal loss. The plate expansion rate was 70.90%, a 45.83% decrease compared to the original silicon-carbon, significantly improving expansion suppression. These results demonstrate that the prepared silicon-carbon composite material exhibits high energy density and low expansion.

[0154] That is, the silicon-carbon negative electrode composite material of this embodiment introduces feldspar, which has a unique nanostructure and high interfacial compatibility with silicon. It can support the electrode structure, slow down the expansion, and improve the coating effect. To a certain extent, it limits the volume change caused by expansion, and at the same time isolates the direct erosion of silicon by the electrolyte, effectively suppressing the volume expansion and interfacial side reaction problems of nano-silicon.

[0155] Comparative Example 2:

[0156] In order to verify the effect of different addition forms of aluminosilicate (feldspar) on the performance of the prepared negative electrode, the method of Example 1 was used to prepare a slurry additive; the slurry additive was then subjected to spray drying and other processes to prepare a dry powder additive; the morphology of the dry powder additive is as follows Figure 15-17 As shown:

[0157] Due to the effects of electrostatic forces, van der Waals forces or chemical bonds, high specific surface energy and other factors, nanoparticles agglomerate to form micron-sized spherical or ring-shaped particles, and the particle size after agglomeration is uneven.

[0158] In this comparative example, another silicon-carbon negative electrode substrate (provided by Sichuan Angaote Electric Technology Co., Ltd.) was modified with two forms of additives (slurry additives and dry powder additives) to modify the silicon-carbon negative electrode substrate. The control group of the silicon-carbon negative electrode substrate was named silicon-carbon substrate, wherein the modification process of the slurry additive referred to Example 1, and the modified silicon-carbon negative electrode substrate was named modified carbon silicon 1; wherein the modification process of the dry powder additive (refer to Example 1, the timing of adding the dry powder additive was consistent with that of the slurry additive), and the modified silicon-carbon negative electrode substrate was named modified carbon silicon 2.

[0159] Silicon carbon substrate, modified carbon silicon 1 and modified carbon silicon 2 were made into buckle batteries for electrical performance testing. The results are shown in Table 2 and Figure 18 As shown: The composite material significantly reduces the expansion rate of the silicon-carbon negative electrode while maintaining high capacity.

[0160] Table 2

[0161]

[0162] From Table 2 and Figure 18 It can be seen that:

[0163] The discharge specific capacity of the original silicon carbon was 2155.59 mAh / g, and the electrode expansion rate was 121.57%. The discharge specific capacity of modified silicon carbon 1 was 2199.08 mAh / g, a 2.02% increase compared to the original silicon carbon; the electrode expansion rate was 96.08%, a 20.97% decrease compared to the original silicon carbon. The discharge specific capacity of modified silicon carbon 2 was 2148.15 mAh / g, a 0.30% decrease compared to the original silicon carbon; the electrode expansion rate was 113.89%, a 6.30% decrease compared to the original silicon carbon. These results show that both types of additives effectively inhibit electrode expansion while maintaining capacity, with modified silicon carbon 1 exhibiting far superior electrode expansion suppression than modified silicon carbon 2.

[0164] It can be seen from this that in the modification of silicon-carbon negative electrodes, slurry-state additives are not only prepared with lower production costs and energy consumption and higher production efficiency, but also can minimize the agglomeration of nanoparticles, achieve high dispersion and uniform particles, and exhibit better performance when used in the modification of silicon-carbon negative electrode materials.

[0165] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a low-expansion, high-specific-capacity silicon-carbon negative electrode composite material, characterized in that: The following steps are involved: S1. Preparation of a slurry additive: mixing raw materials for preparing a nano-additive with water to form a suspension, and sequentially subjecting the suspension to coarse grinding and fine grinding to obtain a slurry additive; the nano-additive comprises aluminosilicate; the nano-additive has a nano-layered structure and nano-pores; the aluminosilicate comprises feldspar, mica, kaolin, zeolite, or garnet; S2. Slurry preparation: first dissolving a binder in a solvent to obtain a binder solution, dispersing a conductive agent in the solvent to form a dispersion, dissolving polyacrylic acid in the solvent to obtain a PAA solution, then mixing the binder solution and the dispersion with the porous silicon-carbon composite substrate, and then adding the PAA solution and the slurry additive; stirring uniformly to form a slurry; S3, coating: evenly coating the slurry on the current collector; S4. Drying.

2. The preparation method according to claim 1, characterized in that In step S1, the particle size of the nano-additive is 200 nm to 500 nm.

3. The preparation method according to claim 1, characterized in that In step S2, the nano additive accounts for 0.8-1.2 wt% based on the weight of the slurry.

4. The preparation method according to claim 1, characterized in that In step S3, the coating thickness is 50-250 μm.

5. The preparation method according to any one of claims 1 to 4, characterized in that Also includes: S5, Roller Pressing: Compact the dried electrode by roller press; S6. Cutting: Cut the rolled pole pieces into the required size and shape.

6. A silicon-carbon negative electrode composite material prepared by the preparation method according to any one of claims 1 to 5.

7. The silicon-carbon negative electrode composite material according to claim 6, characterized in that The silicon-carbon negative electrode composite material is the negative electrode plate of a lithium-ion battery.

8. The silicon-carbon negative electrode composite material according to claim 6, characterized in that The expansion rate of the silicon-carbon negative electrode composite material is less than or equal to 71%.

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