Low-expansion and high-specific-capacity silicon-carbon negative electrode composite material and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and particularly discloses a low-expansion and high-specific-capacity silicon-carbon negative electrode composite material and a preparation method thereof.The low-expansion and high-specific-capacity silicon-carbon negative electrode composite material comprises a porous silicon-carbon composite base material, a nano additive is attached to the porous silicon-carbon composite base material, and the nano additive comprises aluminosilicate. Nano additives such as aluminosilicate and the like are loaded on the porous silicon-carbon composite base material, and a lithium storage and super-ion transmission channel can be constructed by utilizing a unique nano layered structure and nano pores of the nano additives to accommodate volume expansion; meanwhile, due to unique mechanical properties and mechanical strength, the electrode structure can be stabilized, particle pulverization is reduced, volume expansion is inhibited, the porous silicon-carbon composite base material is realized, and the volume expansion rate of the silicon-carbon negative electrode composite material is remarkably reduced while the high capacity of the silicon-carbon negative electrode composite material is maintained; the expansion rate of the silicon-carbon negative electrode composite material prepared by the invention is below 71%.

Description

Technical Field

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

[0002] In the field of lithium-ion batteries, silicon-carbon negative electrode materials are considered to be ideal negative electrode materials for next-generation lithium-ion batteries due to their high theoretical specific capacity (the theoretical specific capacity of silicon is about 4200 mAh / g, much higher than 372 mAh / g of traditional graphite negative electrodes). However, silicon will undergo a huge volume expansion (about 300%) during charge and discharge, resulting in problems such as material structure damage, electrode pulverization, and capacity attenuation, which severely limit its practical application. In addition, the low conductivity of silicon also affects its rate performance and cycle stability.

[0003] To address the above challenges, that is, to meet the requirements of high-energy-density lithium-ion batteries and reduce the volume expansion of silicon during charge and discharge, researchers have proposed the design concept of silicon-carbon composite materials. By compounding silicon with porous carbon materials, the buffer effect and conductivity of the porous carbon materials are used to improve the performance of silicon.

[0004] However, the silicon-carbon composite materials prepared by the above technologies still have the following deficiencies: (1) Limited expansion inhibition effect: The existing silicon-carbon composite materials have insufficient expansion inhibition effect and are difficult to completely solve the volume expansion problem of silicon.

[0005] (2) Limited energy density improvement: The content of silicon in the existing silicon-carbon composite materials is low, resulting in limited improvement in energy density. Summary of the Invention

[0006] The purpose of the present invention is to provide a silicon-carbon negative electrode composite material with low expansion and high specific capacity and a preparation method thereof, which can significantly reduce the volume expansion rate of the silicon-carbon negative electrode composite material while maintaining its high capacity.

[0007] The present invention is achieved by the following technical solutions: A silicon-carbon negative electrode composite material with low expansion and high specific capacity, comprising a porous silicon-carbon composite substrate, and a nano-additive is attached to the porous silicon-carbon composite substrate, and the nano-additive includes aluminosilicate.

[0008] The present invention aims to solve the following problems: (1) The volume expansion problem of silicon: By designing a silicon-carbon composite material with low expansion, the volume expansion of silicon during charge and discharge is alleviated, and the structural stability of the material is improved.

[0009] (2) The problem of energy density improvement: By optimizing the composition and structure of the silicon-carbon composite material, its energy density is increased to meet the requirements of high-energy-density batteries.

[0010] The present invention uses a porous silicon-carbon composite substrate as the base. The porous silicon-carbon composite substrate, as a carrier of silicon, can improve the conductivity of the silicon-carbon negative electrode and alleviate volume expansion.

[0011] The molecular formula of the aluminosilicate in the present invention is xAl2O3·ySiO2, and its main components are SiO2 and Al2O3, which are materials naturally existing in nature. It has a unique nano-layered structure and nano-pores, which can construct lithium storage and superionic transport channels to accommodate volume expansion; at the same time, it has unique mechanical properties and mechanical strength, which can stabilize the electrode structure, reduce particle pulverization, and inhibit volume expansion. Moreover, the introduced nano-additive has almost no influence on the specific capacity of the prepared battery negative electrode.

[0012] The aluminosilicate mainly includes feldspar, mica, kaolin, zeolite, garnet, etc.

[0013] In summary, by loading nano-additives such as aluminosilicate on the porous silicon-carbon composite substrate, 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.

[0014] 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.

[0015] Introducing the nano-additive in the form of a slurry has the following advantages: 1) The preparation process of the slurry-state nano-additive is simple: The preparation of traditional nano-material type additives requires multiple complex processes such as dispersion, coarse grinding, fine grinding, spray drying, furnace sintering, and air flow pulverization; while the slurry-state nano-additive of the present invention does not require subsequent processes such as spray drying, furnace sintering, and air flow pulverization, and the slurry-state nano-additive formed after dispersion, coarse grinding, and fine grinding can be directly used. This improvement not only greatly reduces the spray drying and subsequent processes, but also significantly reduces the production cost and time cost.

[0016] 2) The introduction process is simple: The slurry-state nano-additive can be directly added in the slurry process for preparing the silicon-carbon negative electrode composite material without prior composite process, which is beneficial to saving processes and reducing costs.

[0017] In a preferred embodiment, the expansion rate of the silicon-carbon negative electrode composite material is less than or equal to 71%.

[0018] A method for preparing a silicon-carbon negative electrode composite material with low expansion and high specific capacity, comprising the following steps: S1. Preparation of slurry - state additive: Mix the raw materials for preparing the nano - additive (usually micron - level additives) with water to form a suspension, and successively perform coarse grinding and fine grinding on the suspension to obtain the slurry - state additive; S2. Preparation of slurry: First, dissolve the binder in a solvent to obtain a binder solution, disperse the conductive agent in a 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 and mix them again. Stir evenly to form a slurry; S3. Coating: Uniformly coat the slurry on the current collector; S4. Drying.

[0019] The slurry - state nano - additive prepared by the present invention is uniformly dispersed in water as a medium to form a suspension. There is no agglomeration among the nano - particle materials, and there is no sedimentation after standing, achieving uniform dispersion at the nano - level.

[0020] Moreover, the method for introducing the nano - additive in the present invention is more direct. 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. Instead, the additive is directly added during the homogenization process when preparing the negative electrode sheet, thus completing the introduction work.

[0021] In a preferred embodiment, in step S1, the nano - additive has a nano - layered structure and nano - pores.

[0022] In a preferred embodiment, in step S1, the particle size of the nano - additive is 200nm - 500nm.

[0023] In a preferred embodiment, in step S2, based on the weight of the slurry, the proportion of the nano - additive is 0.8 - 1.2wt%.

[0024] In a preferred embodiment, in step S3, the coating thickness is 50 - 250 μm.

[0025] In a preferred embodiment, the preparation method further includes: S5. Rolling: Compress the dried electrode sheet through a rolling machine; S6. Cutting: Cut the rolled electrode sheet into the required size and shape.

[0026] The silicon - carbon negative - electrode composite material prepared by the above - mentioned preparation method is the negative electrode sheet of a lithium - ion battery.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. By loading nano-additives such as aluminosilicate on the porous silicon-carbon composite substrate, the present invention can construct lithium storage and superionic conduction channels and accommodate volume expansion by utilizing the unique nano-layered structure and nano-pores of the nano-additives. At the same time, with the unique mechanical properties and mechanical strength, the electrode structure can be stabilized, particle pulverization can be reduced, and volume expansion can be inhibited, achieving that the porous silicon-carbon composite substrate 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. The expansion rate of the silicon-carbon negative electrode composite material prepared by the present invention is below 71%.

[0028] 2. The slurry-state additive of the present invention not only has the advantages of simple preparation process, good dispersibility and no sedimentation, but also can be directly added to the slurry mixing process when preparing the negative electrode sheet, thus completing the introduction work, without involving 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 being beneficial to cost and time savings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings: Figure 1 is the HRTEM image (100 nm) of the porous silicon-carbon composite substrate in the embodiment of the present invention; Figure 2 is Figure 1 the corresponding Mapping images of C and Si elements (50 nm); Figure 3 is Figure 1 the corresponding Mapping image of C element (50 nm); Figure 4 is Figure 1 the corresponding Mapping image of Si element (50 nm); Figure 5 is the SEM of the slurry-state additive in Example 1 of the present invention Figure 1 (200 nm); Figure 6 is the SEM of the slurry-state additive in Example 1 of the present invention Figure 2 (500 nm); Figure 7 is the SEM of the slurry-state additive in Example 1 of the present invention Figure 3 (5 μm); Figure 8 is the HRTEM image of the silicon-carbon negative electrode composite material in Example 1 of the present invention; Figure 9 is Figure 8Mapping diagrams (500 nm) of the corresponding C, Al, and Si elements; Figure 10 is Figure 8 Mapping diagram (500 nm) of the corresponding Si element; Figure 11 is Figure 8 Mapping diagram (500 nm) of the corresponding C element; Figure 12 is Figure 8 Mapping diagram (500 nm) of the corresponding Al element; Figure 13 is Figure 8 Mapping diagram of the corresponding K element; Figure 14 Performance test result comparison - GCD curve diagram of the silicon-carbon anode composite material prepared in Example 1 and Comparative Example 1 of the present invention; Figure 15 SEM of the dry powder additive in Comparative Example 2 of the present invention Figure 1 (200 nm); Figure 16 SEM of the dry powder additive in Comparative Example 2 of the present invention Figure 2 (500 nm); Figure 17 SEM of the dry powder additive in Comparative Example 2 of the present invention Figure 3 (5 μm); Figure 18 Performance test result comparison - GCD curve diagram of the carbon-silicon substrate, the carbon-silicon substrate modified with the slurry additive, and the carbon-silicon substrate modified with the dry powder additive in Comparative Example 2 of the present invention. Detailed implementation manners

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and do not limit the present invention. The following described embodiments are some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0031] In the following description, a number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those of ordinary skill in the art that the present invention may be practiced without these specific details. In other embodiments, well-known structures, materials, or methods have not been specifically described in order to avoid obscuring the present invention. Materials, instruments, reagents, etc. used in the following examples are commercially available unless otherwise specified. The technical means used in the examples are conventional means well-known to those skilled in the art unless otherwise specified.

[0032] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, "a plurality of" means two or more unless otherwise specifically defined.

[0033] In order to solve the problem of the relatively high expansion rate of existing lithium-ion negative electrodes, the present embodiment provides a silicon-carbon negative electrode composite material with low expansion and high specific capacity, including a porous silicon-carbon composite substrate, and a nano-additive is attached to the porous silicon-carbon composite substrate. The nano-additive includes aluminosilicate. Among them, 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 the present embodiment can be understood as having both silicon particles and aluminosilicate loaded on the porous carbon.

[0034] The porous silicon-carbon composite substrate of the present embodiment is an active material, which can be obtained commercially. Specifically, it is purchased from Luoyang Lianchuang Lithium Energy Technology Co., Ltd. This active material is used in the related experiments of Example 1. The HRTEM image of the porous silicon-carbon composite substrate is as Figure 1 , Figure 1 The corresponding Mapping image of C and / or Si elements is as Figures 2 - 4 shown.

[0035] It can be seen from Figures 1 - 4 that: The silicon particles have uniform particle sizes (about 20 nm in diameter) and are attached to the surface of the porous carbon.

[0036] The substrate uses flaky porous carbon as a carrier to improve the conductivity of the silicon negative electrode and relieve volume expansion: The porous structure of the porous carbon can not only provide a buffer space for the volume expansion of silicon, but also improve the wettability of the electrolyte and the lithium-ion transmission rate, thereby enhancing the cycle stability and rate performance of the negative electrode material. In order to introduce the porous structure, a silicon source (such as silane, silicate, or nano-silicon powder) is often introduced on the surface or pores of the porous carbon by methods such as chemical vapor deposition (CVD), and the silicon source is converted into silicon through subsequent treatment (such as thermal reduction method, chemical reduction method) to form a silicon-carbon composite material.

[0037] The main components of the aluminosilicate in this embodiment are SiO2 and Al2O3. It has a unique nano-layered structure and nano-pores, which can construct lithium storage and superionic transport channels to accommodate volume expansion; at the same time, it has unique mechanical properties and mechanical strength, which can stabilize the electrode structure, reduce particle pulverization, and inhibit volume expansion. Moreover, the introduced nano-additive has almost no effect on the specific capacity of the prepared battery anode.

[0038] Aluminosilicates mainly include feldspar, mica, kaolin, zeolite, garnet, etc.

[0039] It is true that high-entropy materials with unique nano-layered structures and nano-pores may be able to inhibit the volume expansion rate, but whether this goal can be achieved still requires comprehensive consideration of some key factors, such as the role of the nano-layered structure (the interlayer binding force needs to be moderate), the contribution of the nano-pores (too high porosity or uneven pore distribution may lead to a decrease in mechanical strength or structural collapse), etc. More factors that need to be considered are: 1) Material system compatibility: Not all high-entropy materials are applicable, and it needs to be verified in combination with specific applications (such as lithium / sodium ion batteries, catalysis, etc.); 2) Structural stability: The nano-structure may agglomerate, pore collapse or layer peeling during the cycling process, and it needs to be enhanced by surface modification or composite; 3) Preparation process: The controllable synthesis of nano-layered / porous structures (such as pore size distribution, interlayer spacing regulation) directly affects the performance.

[0040] Nano-additives with unique nano-layered structures and nano-pores include, in addition to the aluminosilicate in this embodiment, graphene-coated silicon particles (Si@Graphene), carbon nanotubes (CNTs) and silicon composites, nano-TiO2-coated silicon (Si@TiO2), porous carbon-supported silicon (Si@Porous Carbon), high-entropy oxide (HEO) nanoparticles, etc. However, except for aluminosilicates, the others all have technical defects.

[0041] Among them, the agglomeration of graphene-coated silicon particles (Si@Graphene) leads to structural rupture: Case (Adv. Mater., 2015): Graphene layers (Si@Graphene) were coated on the surface of silicon nanoparticles by CVD method, but wrinkles and fractures appeared in the graphene layers after cycling.

[0042] Failure reason: Although the mechanical strength of graphene is high, local stress concentration occurs when the silicon particles expand, resulting in the rupture of the coating layer; the interfacial binding force between silicon and graphene is insufficient, and peeling occurs after expansion, losing the constraint effect.

[0043] Data: The volume expansion rate still reaches 200% after 50 cycles, which is worse than the theoretical expectation (<150%).

[0044] Among them, the conductive network of carbon nanotubes (CNTs) combined with silicon fails: Case (J. Power Sources, 2017): Mechanically mix silicon nanoparticles with CNTs (Si / CNTs composite material). The initial conductivity is improved, but the CNT network collapses after cycling.

[0045] Failure reason: There is a lack of chemical bonding between CNTs and silicon. After silicon expands, the contact points with CNTs are detached; although CNTs have good flexibility themselves, they cannot effectively limit the radial expansion of silicon particles.

[0046] Data: After 100 cycles, the electrode thickness increases by 180%, and the capacity decay rate is close to that of a pure silicon anode.

[0047] Among them, the brittle cracking of silicon coated with nano-TiO₂ (Si@TiO₂): Case (ACS Nano, 2016): Coating a nano-TiO₂ layer (thickness ~20 nm) on the surface of silicon by sol-gel method, but cracks appear in the TiO₂ layer after cycling.

[0048] Failure reason: TiO₂ has high hardness but is brittle and cannot adapt to the repeated expansion / contraction of silicon; the cracks cause the electrolyte to penetrate, accelerating the thickening of the SEI film.

[0049] Data: The volume expansion rate only drops from 300% to 220%, and the interfacial impedance increases significantly.

[0050] Among them, the pore collapse of silicon supported on porous carbon (Si@Porous Carbon): Case (Nano Energy, 2018): Embed silicon nanoparticles into commercial porous carbon (pore size ~50 nm), but the pore structure collapses after cycling.

[0051] Failure reason: The mechanical strength of the porous carbon is insufficient. After silicon expands, it squeezes the pore walls, resulting in structural damage; the pore distribution is uneven, and local silicon particle agglomeration intensifies the volume effect.

[0052] Data: The rate of change of the electrode thickness is still as high as 160% after 100 cycles.

[0053] Among them, the interfacial incompatibility caused by the addition of high-entropy oxide (HEO) nanoparticles: Case (Chem. Eng. J., 2022): In the anode composed of the composite of high-entropy oxide ((MgCoNiCuZn)O) nanoparticles and silicon, the effect of suppressing expansion is weak.

[0054] Reasons for failure: The interfacial 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.

[0055] Data: The volume expansion rate only decreases by 10% (from 300% to 270%), and the specific capacity decreases by 30%.

[0056] In summary, on the one hand, the present invention utilizes the porous structure of porous carbon to provide a buffering space for the volume expansion of silicon, realizing the suppression of the volume expansion rate of the silicon-carbon anode composite material. On the other hand, by simultaneously loading silicon particles and nano-additives with a unique nano-layered structure and nano-pores on the porous carbon, the nano-additives are used to accommodate the volume expansion of the carbon anode composite material and suppress the volume expansion. Finally, while maintaining the high capacity of the silicon-carbon anode composite material, the volume expansion rate of the silicon-carbon anode composite material is significantly reduced; the expansion rate of the silicon-carbon anode composite material prepared by the present invention is below 71%.

[0057] Preferably, in the process of preparing the silicon-carbon anode composite material, the nano-additive is introduced in a slurry state, and the nano-additive in the slurry state is mixed with other raw materials for preparing the silicon-carbon anode composite material.

[0058] The preparation method of the above-mentioned silicon-carbon anode composite material with low expansion and high specific capacity includes the following steps: S1. Preparation of slurry-state additive: Mix the micron-sized aluminosilicate material with water (weight ratio of material: water = 1:4), and perform coarse grinding for 20 min and fine grinding for 40 min in sequence. The nano-additive is completed, and a suspension of the slurry-state additive is formed by mixing with water, which is the slurry-state additive. There is no agglomeration between the nano-particle materials in the slurry-state additive, and there is no sedimentation after standing, realizing uniform dispersion at the nano-level. If the slurry-state additive is left standing for a long time, it is best to perform ultrasonic treatment (time is 10 - 30 min) when taking the amount for use. Among them, coarse grinding and fine grinding are conventional ball milling operations. Among them, the nano-additive has a nano-layered structure and nano-pores, and can specifically be aluminosilicate. The particle size of the nano-additive is 200 nm - 500 nm.

[0059] S2. Slurry Preparation: First, dissolve the binder in a solvent to obtain a binder solution, disperse the conductive agent in a 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 and mix. Based on the weight of the slurry, the proportion of the nano-additive is 0.8 - 1.2 wt%. 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 generating bubbles in the slurry. The viscosity of the slurry needs to be moderate for subsequent coating. Among them, deionized water is used as the solvent for the binder solution, the dispersion, and the PAA solution, and magnetic stirring is carried out until completely dissolved or evenly dispersed.

[0060] Among them, the binder includes carboxymethyl cellulose (CMC), styrene-butadiene copolymer (SBR), or polyvinylidene fluoride (PVDF). The corresponding solvent for polyvinylidene fluoride (PVDF) is N-methylpyrrolidone (NMP); the corresponding solvents for carboxymethyl cellulose (CMC) and styrene-butadiene copolymer (SBR) are water.

[0061] Among them, the conductive agent can specifically be any commonly used conductive agent in the art, including carbon nanotubes (CNT), etc.

[0062] S3. Coating: Use a doctor blade to evenly coat the slurry on the current collector (usually a 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 surface of the copper foil and avoid inconsistent thickness.

[0063] S4. Drying: Dry the coated electrode sheet to remove the solvent. According to the solvent selection, carry out atmospheric or vacuum drying at 80 - 120 °C to avoid solvent residue.

[0064] S5. Rolling: Compact the dried electrode sheet through a rolling press to improve the density and conductivity of the electrode sheet.

[0065] S6. Cutting: Cut the rolled electrode sheet into the required size and shape, and conduct quality inspection on the cut electrode sheet to ensure that its performance meets the requirements. Store the qualified electrode sheets for subsequent battery assembly use.

[0066] The silicon-carbon negative electrode composite material prepared by the above preparation method is the negative electrode sheet of a lithium-ion battery.

[0067] Simply put, the method of introducing the nano-additive in the present invention is more direct. It 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, but directly adds the additive in the homogenization process when preparing the negative electrode sheet, thus completing the introduction work.

[0068] The silicon-carbon anode composite material prepared in this embodiment has the following advantages: 1) Nano-layered structure: The nano-additive has a nano-layered structure and nano-pores, which can construct efficient lithium storage and superionic transport channels. At the same time, its nano-scale voids can effectively accommodate volume expansion and inhibit the destruction of the electrode structure.

[0069] 2) Uniform dispersion: The energy spectrum results show that the nano-additive is uniformly dispersed in the silicon-carbon substrate, and has stronger interfacial compatibility with silicon than the carbon matrix. This characteristic forms a strong coating layer on the surface of silicon while protecting the original carbon coating layer.

[0070] 3) Mechanical properties and mechanical strength: The unique mechanical properties and mechanical strength of the nano-additive help to stabilize the electrode structure, reduce particle pulverization, and further inhibit volume expansion, thereby improving the cycle stability and service life of the battery.

[0071] To better illustrate the technical effects of this embodiment, it is described through the following specific cases. Since the effects of feldspar, mica, kaolin, zeolite, and garnet are not very different, the following case is described with feldspar.

[0072] Example 1: A silicon-carbon anode composite material with low expansion and high specific capacity, including a porous silicon-carbon composite substrate, and a nano-additive is attached to the porous silicon-carbon composite substrate, and the nano-additive is feldspar.

[0073] The preparation method of the silicon-carbon anode composite material in this embodiment includes the following steps: S1. Preparation of slurry-state additive: Mix micron-sized feldspar with water (weight ratio of feldspar: water = 1:4), and perform rough grinding for 20 min and fine grinding for 40 min in sequence to obtain a slurry-state additive. The above slurry-state additive is directly used after wet ball milling. The nano-particles exist in the water solvent, and the inter-particle force is small, so they are not easy to agglomerate. Therefore, the dispersion is strong and the particle size is uniform. As Figures 5 - 7 shown.

[0074] S2. Preparation of slurry: Dissolve carboxymethyl cellulose (CMC), carbon nanotubes (CNT), and polyacrylic acid (PAA) in water in advance according to the solid content of CMC being 1.25%, the solid content of CNT being 0.8%, and the solid content of PAA being 5% to obtain a CMC solution, a CNT dispersion, and a PAA solution. Then, mix the CMC solution and the CNT dispersion with the porous silicon-carbon composite substrate, and then add the slurry-state additive and the PAA solution and mix them. Based on the weight of the slurry, the proportion of the nano-additive is 1.0 wt%; then use a high-speed stirrer to stir the mixture evenly to form a slurry.

[0075] The specific steps of step S2 are as follows: S21. Solution pretreatment stage: Prepare the following three kinds of pre-dissolved solutions respectively: ① Sodium carboxymethyl cellulose (CMC) solution: solid content 1.25%; ② Carbon nanotube (CNT) dispersion: solid content 0.8%; ③ Polyacrylic acid (PAA) solution: solid content 5%; (Note: All solutions use deionized water as the solvent and are magnetically stirred until completely dissolved).

[0076] S22. Primary homogenization process: Add the porous silicon-carbon substrate to the homogenization tank; sequentially add the pre-prepared CMC solution and CNT dispersion; start the homogenization program (button-type half-cell small batch preparation: rotation speed 1500 rpm, rotation time 5 min).

[0077] S23. Secondary homogenization stage: Add the slurry-state 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); continue the homogenization treatment (button-type half-cell small batch preparation: rotation speed 1500 rpm, rotation time 15 min).

[0078] S24. Slurry post-treatment: Filter with a 200-mesh standard sieve and collect the filtered slurry; quality inspection: viscosity test, fineness test.

[0079] The classic formula of the slurry is: 94.7% of porous silicon-carbon composite substrate, 0.3% of carbon nanotubes, 2% of carboxymethyl cellulose, and 3% of polyacrylic acid. Among them, the overall water volume is not fixed and is adjusted according to the actual situation. The water in the slurry is determined in the following way: 80% of the water in the slurry-state additive, and the binder dispersant is pre-dissolved in water according to the CMC solid content of 1.25%, the CNT solid content of 0.8%, and the PAA solid content of 5%.

[0080] Among them, for sodium carboxymethyl cellulose (CMC): the manufacturer / agent is Daicel of Japan, model CMC2200, and the molecular formula is C6H7O2(OH)3-x(OCH2COONa)x.

[0081] Among them, for carbon nanotubes (CNT): the manufacturer / agent is Jiangsu Tiannai Technology Co., Ltd., and the molecular formula is C, with a molecular weight of 12.01.

[0082] Among them, for polyacrylic acid (PAA): the manufacturer / agent is Chengdu Yindi Le Technology Co., Ltd., chemical formula: [C3H4O2]n, molecular weight: 72.06n.

[0083] S3. Coating: Use a doctor blade to evenly coat the slurry on the current collector (usually copper foil), and the coating thickness is usually 200 μm (wet film thickness).

[0084] S4. Drying: Dry the coated electrode sheet at 100 °C under normal pressure to remove the solvent.

[0085] S5. Rolling: Compact the dried electrode sheet through a rolling press to improve the density and conductivity of the electrode sheet.

[0086] S6. Cutting.

[0087] The HRTEM image of the silicon-carbon negative electrode composite material prepared in this example is as Figure 8 shown, Figure 8 and the Mapping of different elements corresponding to it is as Figures 9 - 13 shown: Dark feldspar and light silicon particles are attached to the porous carbon network. According to the Mapping diagram of elements, the irregular contour of feldspar can be clearly observed, and its main elements are Si, K, and Al, and they are evenly distributed in the porous carbon.

[0088] Comparative Example 1: This comparative example is based on Example 1, and the difference from Example 1 is that: The silicon-carbon negative electrode composite material does not add feldspar.

[0089] The silicon-carbon negative electrode composite materials prepared in Example 1 and Example 2 were made into button cells for electrical performance testing, and the results are shown in Table 1 and Figure 14 shown: While maintaining a high capacity, the composite material significantly reduces the swelling rate of the silicon-carbon negative electrode.

[0090] Table 1 From Table 1 and Figure 14 it can be seen that: The discharge specific capacity value of the original silicon-carbon negative electrode (Comparative Example 1) is 1886.97 mAh / g, the initial efficiency is 91.97%, and the electrode sheet swelling rate is 130.89%. The discharge specific capacity value of the modified silicon-carbon negative electrode (Example 1) is 1878.78 mAh / g, which is 0.43% lower than that of the original silicon-carbon, and the loss amount is extremely small; the electrode sheet swelling rate is 70.90%, which is 45.83% lower than that of the original silicon-carbon, and the swelling inhibition effect is greatly improved. The above results show that the prepared silicon-carbon composite material has the characteristics of high energy density and low swelling.

[0091] That is, due to the introduction of feldspar in the silicon-carbon anode composite material of this embodiment, feldspar has a unique nanostructure and high interfacial compatibility with silicon, which can enhance the coating effect while supporting the electrode structure and reducing swelling, limit the volume change caused by swelling to a certain extent, and isolate the direct erosion of the electrolyte on silicon, effectively inhibiting the volume expansion of nanosilicon and the interfacial side reaction problem.

[0092] Comparative Example 2: To verify the influence of different addition forms of aluminosilicate (feldspar) on the performance of the prepared anode, a slurry additive was prepared by the method of Example 1; then the slurry additive was processed through spray drying and other processes to form a dry powder additive; the morphology of the dry powder additive is as Figures 15 - 17 shown: Due to the action of electrostatic force, van der Waals force or chemical bond force, high specific surface energy and other factors among nanoparticles, they agglomerate with each other to form micron-sized spherical or ring-shaped particles, and the particle size is uneven after agglomeration.

[0093] In this comparative example, another silicon-carbon anode substrate (provided by Sichuan Angaote Electric Technology Co., Ltd.) was modified with two forms of additives (slurry additive and dry powder additive) respectively. The control group of the silicon-carbon anode substrate was named silicon-carbon substrate. Among them, the modification process of the slurry additive refers to Example 1, and the modified silicon-carbon anode substrate was named modified carbon-silicon 1; among them, the modification process of the dry powder additive (refer to Example 1, and the addition time of the dry powder additive is the same as that of the slurry additive), and the modified silicon-carbon anode substrate was named modified carbon-silicon 2.

[0094] The silicon-carbon substrate, modified carbon-silicon 1 and modified carbon-silicon 2 were made into button cells for electrical performance testing, and the results are shown in Table 2 and Figure 18 shown: While maintaining a high capacity, the composite material significantly reduced the swelling rate of the silicon-carbon anode.

[0095] Table 2 From Table 2 and Figure 18 it can be seen that: The discharge specific capacity value of the original silicon-carbon was 2155.59 mAh / g, and the pole piece swelling rate was 121.57%. The discharge specific capacity value of the modified carbon-silicon 1 was 2199.08 mAh / g, a 2.02% increase compared with the original silicon-carbon; the pole piece swelling rate was 96.08%, a 20.97% decrease compared with the original silicon-carbon. The discharge specific capacity value of the modified carbon-silicon 2 was 2148.15 mAh / g, a 0.30% decrease compared with the original silicon-carbon; the pole piece swelling rate was 113.89%, a 6.30% decrease compared with the original silicon-carbon. The above results show that both types of additives can effectively inhibit the pole piece swelling while maintaining the capacity, and the pole piece swelling inhibition effect of the modified carbon-silicon 1 is much better than that of the modified carbon-silicon 2.

[0096] It can be seen from this that in the modification of the silicon-carbon negative electrode, the slurry-state additive can not only be prepared with lower production costs and energy consumption and higher production efficiency, but also minimize the agglomeration of nanoparticles to achieve high dispersion and uniform particles, showing more excellent performance when applied to the modification of silicon-carbon negative electrode materials.

[0097] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a silicon-carbon anode composite material with low expansion and high specific capacity, characterized in that, It includes the following steps: S1. Preparation of slurry - state additive: Mix the raw materials for preparing the nano - additive with water to form a suspension, and successively perform coarse grinding and fine grinding on the suspension to obtain a slurry - state additive; the nano - additive includes aluminosilicate. S2. Preparation of slurry: First, dissolve the binder in a solvent to obtain a binder solution, disperse the conductive agent in a 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 a porous silicon - carbon composite substrate, add the PAA solution and the slurry - state additive, and then add the slurry - state additive again; stir evenly to form a slurry. S3. Coating: Uniformly coat the slurry on the current collector. S4. Drying.

2. The preparation method according to claim 1, wherein In step S1, the nano - additive has a nano - layered structure and nano - pores.

3. 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.

4. The preparation method according to claim 1, characterized in that, In step S1, the aluminosilicate includes feldspar, mica, kaolin, zeolite or garnet.

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

6. The preparation method according to claim 1, wherein In step S3, the coating thickness is 50 - 250 μm.

7. The preparation method according to any one of claims 1-6, characterized in that, It also includes: S5. Rolling: Compact the dried electrode sheet through a rolling machine. S6. Cutting: Cut the rolled electrode sheet into the required size and shape.

8. A silicon - carbon negative electrode composite material prepared by the preparation method according to any one of claims 1 - 7.

9. The silicon-carbon anode composite material according to claim 8, characterized in that The silicon - carbon negative electrode composite material is the negative electrode sheet of a lithium - ion battery.

10. The silicon-carbon anode composite material according to claim 8, 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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