Silicon-based secondary particles and their preparation methods, negative electrode sheets and batteries

Abstract

This invention relates to the field of battery technology, specifically to a silicon-based secondary particle and its preparation method, a negative electrode sheet, and a battery. The silicon-based secondary particle comprises nano-silicon particles, a lithium-conducting polymer binder, and a conductive agent; the nano-silicon particles, the lithium-conducting polymer binder, and the conductive agent together form a partially densified secondary cluster structure; the lithium-conducting polymer binder has a mass content of 0.01%–5% in the silicon-based secondary particle. Batteries using the silicon-based secondary particle of this invention exhibit excellent rate performance and cycle stability.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a silicon-based secondary particle and its preparation method, a negative electrode sheet, and a battery. Background Technology

[0002] In the field of solid-state battery anode materials, silicon-based materials are commonly used as active components. However, silicon-based materials themselves have low ionic and electronic conductivity, which seriously affects the rate performance and cycle stability of silicon-based batteries. Related technologies generally focus on constructing efficient ion and electron transport networks to overcome the problem of poor conductivity of silicon materials. However, current technologies often face the problem of limited improvement in rate performance and cycle stability when enhancing the overall electrochemical performance of electrodes. Summary of the Invention

[0003] The purpose of this invention is to overcome the limitation of existing nano-silicon materials in improving the rate performance and cycle stability of batteries, and to provide silicon-based secondary particles, their preparation method, a negative electrode sheet, and a battery. Batteries using these silicon-based secondary particles exhibit excellent rate performance and cycle stability.

[0004] To achieve the objectives of this invention, a first aspect of this invention provides silicon-based secondary particles comprising nano-silicon particles, a lithium-conducting polymer binder, and a conductive agent; wherein the nano-silicon particles, the lithium-conducting polymer binder, and the conductive agent together form a partially densified secondary cluster structure; and wherein the lithium-conducting polymer binder has a mass content of 0.01%-5% in the silicon-based secondary particles.

[0005] In some embodiments, the conductive agent has a mass content of 0.01%-0.5% in the silicon-based secondary particles.

[0006] In some embodiments, the mass content of the nano-silicon particles in the silicon-based secondary particles is 94.5%-99.98%.

[0007] In some of these embodiments, the conductive agent includes at least one of zero-dimensional conductive agents, one-dimensional conductive agents, and two-dimensional conductive agents.

[0008] In some embodiments, the lithium-conducting polymeric binder includes, but is not limited to, lithium polyacrylate, lithium carboxymethyl cellulose, or modified polymers thereof.

[0009] In some of these embodiments, the nano-silicon particles include at least one of nanocrystalline silicon, nanoamorphous silicon, and nanosilicon suboxide.

[0010] In some embodiments, the conductive agent includes a zero-dimensional conductive agent, which includes conductive carbon black.

[0011] In some embodiments, the conductive agent includes a one-dimensional conductive agent, which includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and vapor-grown carbon fibers.

[0012] In some embodiments, the conductive agent includes a two-dimensional conductive agent, which includes graphene.

[0013] In some embodiments, the nano-silicon particles, the conductive agent, and the lithium-conductive polymer binder self-assemble to form the secondary cluster structure through capillary force and bridging effect of the lithium-conductive polymer binder.

[0014] In some embodiments, the silicon-based secondary particles have a three-dimensional loose porous aggregate morphology resembling a bunch of grapes, and the surface of the silicon-based secondary particles is composed of protruding nano-silicon particles and conductive agent ends, forming an uneven, rough morphology with a velvety or thorny outline.

[0015] In some of these embodiments, the Dv of the silicon-based secondary particles 50 The particle size is 0.2μm-10μm.

[0016] The second aspect of the present invention provides a method for preparing silicon-based secondary particles, comprising the following steps: mixing nano-silicon particles, a lithium-conducting polymer binder and a conductive agent in the presence of a solvent to obtain a slurry; then evaporating to remove the solvent to obtain silicon-based secondary particles; the amount of the lithium-conducting polymer binder is 0.01%-5% based on the total mass of the nano-silicon particles, the lithium-conducting polymer binder and the conductive agent.

[0017] In some embodiments, the solvent includes a polar solvent, which includes water and polar organic solvents.

[0018] In some of these embodiments, the evaporation conditions include a temperature of 60°C-80°C.

[0019] In some embodiments, the mixing method includes: first mixing the lithium-conductive polymer binder with a portion of a solvent to obtain a binder solution; second mixing the conductive agent with the remaining solvent to obtain a conductive agent dispersion; and then third mixing the binder solution, the conductive agent dispersion, and the nano-silicon particles to obtain the slurry.

[0020] In some embodiments, the preparation method further includes a step of dispersing the dried material obtained by evaporating to remove the solvent, wherein the dispersing method includes ball milling or dry mixing.

[0021] In some embodiments, the viscosity of the adhesive solution is less than 1000 mPa·s.

[0022] In some embodiments, the mass concentration of the adhesive solution is 0.01%-1%.

[0023] In some embodiments, the mass content of the conductive agent in the conductive agent dispersion is 0.1%-1%.

[0024] A third aspect of the present invention provides a negative electrode sheet comprising silicon-based secondary particles as described in the first aspect of the present invention, or silicon-based secondary particles prepared by the method for preparing silicon-based secondary particles as described in the second aspect of the present invention.

[0025] A fourth aspect of the present invention provides a battery comprising the negative electrode sheet described in the third aspect of the present invention.

[0026] In some of these embodiments, the battery is an all-solid-state battery, specifically a sulfide-based all-solid-state battery.

[0027] Through the above technical solution, the silicon-based secondary particles provided by the present invention provide high capacity through active material nano-silicon particles, while introducing a lithium-conducting polymer binder to provide lithium-ion conduction pathways between the active material nano-particles, and introducing a conductive agent to provide electron conduction pathways. This constructs secondary particles that have both ion and electron conduction networks inside, effectively improving the comprehensive ion and electron transport capabilities inside the particles, thereby overcoming the problem of insufficient ion and electron transport in silicon anodes, and significantly improving the rate performance and cycle stability of solid-state batteries. Attached Figure Description

[0028] Figure 1 The diagram shown is a schematic of the structure of an existing negative electrode mixture.

[0029] Figure 2 The diagram shown is a schematic diagram of the structure of silicon-based secondary particles according to an embodiment of the present invention.

[0030] Figure 3 The image shown is a SEM image of nanocrystalline silicon in Example 1.

[0031] Figure 4 The image shown is an SEM image of the silicon-based secondary particles in Example 1.

[0032] Figure 5 As shown Figure 4 A magnified view of a portion of the image.

[0033] Explanation of reference numerals in the attached figures: 110. Nano-silicon particles; 111. Lithium-conducting polymer binder; 112. Conductive agent; 1ax. Silicon particles; 1ay. Polymer; 1a. Secondary particles; 1b. Sulfide solid electrolyte. Detailed Implementation

[0034] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0035] In the field of solid-state battery anode material technology, to achieve a balance between high capacity and good processability of electrode active materials, a common approach is to use nano-silicon as the active material. This is achieved by simply mixing it with conductive agents, binders, and other components through mechanical mixing to form a slurry, which is then directly coated and molded. However, this approach is not ideal when applied to sulfide-based solid-state battery systems where ion / electron conduction efficiency and interface stability are extremely demanding. The main reason is that this approach can only form macroscopic physical contacts and cannot build a continuous ion and electron dual transport network between active material particles, resulting in high charge transport impedance, severe polarization, and limited battery rate performance. Based on this, to further optimize the process, a secondary granulation scheme has been proposed. This involves introducing polymers to combine silicon particles into secondary particles and optimizing the mechanical matching between the polymer and the electrolyte to improve cycle interface stability. Figure 1 The diagram shows a schematic of the structure of an existing negative electrode mixture, which mainly contains secondary active material particles 1a and a sulfide solid electrolyte 1b. The secondary particles 1a include multiple silicon particles 1ax and a polymer 1ay. The polymer 1ay binds the silicon particles 1ax together, but its granulation process does not simultaneously build independent electron transport paths inside the particles. Moreover, the polymer content is high, and the resulting structure tends to be dense. The polymer 1ay completely covers or fills all the gaps between the silicon particles 1ax, making it difficult to effectively deform and fill the electrolyte gaps during the solid-state battery pressing process, resulting in poor interface contact and volume expansion stress concentration. In addition, some schemes that use high-temperature fusion and graphitization for secondary granulation can improve the compaction density of the material, but the high-temperature process makes the particle structure completely dense, sacrificing the ion transport pore channels and pressing deformation ability of the particles, and no special lithium-conducting polymer is set to build an ion conduction network. Therefore, in solid-state batteries, which require higher ion / electron co-transmission capabilities within the electrodes, the introduction of a single ion-conducting component cannot comprehensively improve the combined ion and electron transport performance within the secondary particles and the electrodes, thus limiting the optimization of battery rate and cycle stability.

[0036] In view of this, the present invention introduces a self-assembly method based on capillary force and binder bridging, in which nano-silicon particles, lithium-conducting polymer binders and conductive agents are pre-constructed into a non-fully densified, loose and porous secondary cluster structure during solvent evaporation. This pre-construction of ion conduction and electron conduction pathways at the microscopic level is completed before entering the electrode preparation process, fundamentally solving the processing problem of nano-silicon and better optimizing the rate and cycle stability of the battery.

[0037] Silicon-based secondary particles According to a first aspect of the invention, with reference to Figure 2 The present invention provides a silicon-based secondary particle comprising nano-silicon particles 110, a lithium-conducting polymer binder 111, and a conductive agent 112; the nano-silicon particles 110, the lithium-conducting polymer binder 111, and the conductive agent 112 together form a non-fully densified secondary cluster structure; the mass content of the lithium-conducting polymer binder 111 in the silicon-based secondary particle is 0.01%-5%, for example, it can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 3%, 3.5%, 3.8%, 4%, 4.5%, 5%, or any two of the above values.

[0038] In this invention, by forming a non-fully densified secondary cluster structure with nano-silicon particles 110, lithium-conducting polymer binder 111, and conductive agent 112, the self-assembly of each component to form a non-fully densified secondary cluster structure is mainly achieved by utilizing capillary force and the bridging effect of the binder. This solves the problem of missing mixed conductive pathways caused by the low conductivity and difficulty in dispersion of nano-silicon. Furthermore, the content of lithium-conducting polymer binder 111 in the silicon-based secondary particles is controlled within the aforementioned low range, so that the lithium-conducting polymer binder 111 does not completely cover or fill all the gaps between particles, but only exists in the contact neck between the active material nano-silicon particles 110, forming a point-like bridging structure. That is, the lithium-conducting polymer binder 111 exists in the neck region where any two of the active material nanoparticles and the conductive agent come into contact, forming a point-like bridging, rather than forming a continuous coating film or filling layer on the particle surface. This structure is similar to spot welding at the contact points between particles. A very small amount of lithium-conducting polymer binder 111 is used to aggregate and connect the nanoparticles, while simultaneously providing a pathway for lithium-ion conduction between particles. More importantly, this point-like bridging method avoids the structural densification caused by excessive filling of the interparticle gaps with binder, allowing the secondary particles to retain a large number of pores. Therefore, when silicon-based secondary particles are used in batteries, especially solid-state batteries, they can improve the reversible capacity, rate performance, and cycle stability of solid-state batteries.

[0039] In this invention, "secondary clusters" or "secondary particles" refer to a non-fully densified secondary cluster structure formed by multiple nano-silicon particles 110, a lithium-conducting polymer binder 111, and a conductive agent 112 through a self-assembly process. In this invention, the secondary cluster structure is not fully densified; the particles are held together by capillary forces but are not completely fused. That is, the nano-silicon particles 110, the conductive agent 112, and the lithium-conducting polymer binder 111 self-assemble to form the secondary cluster structure through capillary forces and the bridging effect of the lithium-conducting polymer binder.

[0040] In this invention, "capillary force" refers to the physical force generated by the surface tension of a liquid in fine channels or interparticle gaps, which can drive nanoscale particles to approach each other and aggregate. For example, it may include, but is not limited to: during solvent evaporation, as the liquid-gas interface recedes, the capillary contraction pressure generated by the liquid bridge existing between the nano-silicon particles 110, the conductive agent 112 and the lithium-conductive polymer binder 111, or the tensile force caused by the meniscus formed by the solvent in the interparticle gaps.

[0041] In this invention, "incomplete densification" refers to the fact that the nanoparticles constituting the secondary cluster structure are not tightly packed together with no obvious gaps. Instead, they retain a large number of interconnected or disconnected micron- or submicron-sized pores. In contrast, "densified structure" refers to solid particles with extremely low internal porosity, such as those obtained through conventional granulation methods (e.g., high-temperature sintering, vigorous mechanical ball milling, spray drying).

[0042] Therefore, since the lithium-conductive polymer binder 111 exists only in an ultra-low amount at the contact neck between the active material nanoparticles and the conductive agent 112, forming a point-like bridge, the silicon-based secondary particles retain a large number of micropores, forming a loose cluster structure that is not completely dense. This loose structure maintained by point-like bridges can also endow the silicon-based secondary particles with a unique microstructure. In some embodiments, the silicon-based secondary particles have a grape-like three-dimensional loose porous aggregate morphology; furthermore, the surface of the silicon-based secondary particles is composed of protruding nano-silicon particles 110 and the ends of the conductive agent 112, forming an uneven, rough morphology with a velvety or thorny outline.

[0043] In this invention, by giving the silicon-based secondary particles a three-dimensional, loose, porous aggregate morphology resembling a bunch of grapes, the porous structure characteristics formed by the loose stacking of nanoparticles inside are further clarified. This morphology ensures that the ionic electrolyte can fully penetrate into the cluster and effectively shorten the ion transport distance. Simultaneously, the surface, composed of protruding silicon nanoparticles 110 and the ends of conductive agent 112, forms an uneven, velvety, or thorny rough morphology. This allows the particles to generate a mechanical interlocking effect with the solid electrolyte during the solid-state battery molding process, significantly increasing the interfacial contact area and reducing the interfacial impedance. This improves the bonding strength and stability of the solid-solid interface while ensuring the internal ion / electron transport efficiency. Furthermore, this structure allows the silicon-based secondary particles to undergo controllable fragmentation or plastic deformation during the solid-state battery molding process, transforming from loose clusters into sheet-like or filled morphologies tightly bonded to the solid electrolyte. Its active deformation capability of "releasing upon compression" can adaptively fill the gaps between solid electrolyte particles, avoiding the problem of traditional rigid particles damaging the solid electrolyte or causing poor interfacial contact due to stress concentration. Thus, it actively optimizes the bonding strength and stability of the solid-solid interface during the pressing process.

[0044] In this invention, "grape bunch" refers to an internal morphological feature of a secondary cluster structure, where primary particles (including nano-silicon particles 110 and conductive agent 112) are bridged together by a very small amount of "spot welding" through narrow necks or point contacts using a lithium-conductive polymer binder 111, forming a loosely packed cluster or chain-like structure. For example, this may include, but is not limited to: the surface of the primary particles may have fine granular protrusions or be relatively smooth; the particles are locally "spot welded" together at the contact points by a very small amount of binder; and a large number of micron- or submicron-sized open pores are retained between the particles. The interior of the resulting secondary cluster is a non-fully densified three-dimensional porous network formed by nano-silicon particles 110, lithium-conductive polymer binder 111, and conductive agent. Its surface is rough and uneven, and the numerous protruding nano-silicon particles 110 and conductive agent 112 end points give it a fluffy or thorny appearance. At the same time, the internal pores have excellent connectivity and a large specific surface area.

[0045] In this invention, "fluffy or thorny rough morphology" refers to the surface micro-geometric characteristics of silicon-based secondary particles, meaning that their surface is not a smooth sphere, but rather is composed of protruding nano-silicon particles 110 and the ends of conductive agents 112, exhibiting an uneven, fluffy or thorny rough state. For example, it may include, but is not limited to: nano-silicon particles 110 locally protruding from the cluster surface, the ends of one-dimensional conductive agents (such as carbon nanotubes) protruding to form fluffy tentacles, or the edges of two-dimensional conductive agents (such as graphene) exposing to form thorny protrusions, or a combination of the above features.

[0046] According to the present invention, silicon-based secondary particles are formed by capillary-driven self-assembly of primary particles, nano-silicon particles 110, a lithium-conductive polymer binder 111, and a conductive agent. The particle size of the nano-silicon particles 110 is not particularly limited as long as the purpose of the present invention can be achieved. In some embodiments, the primary particle size Dv of the nano-silicon particles 110 is... 50 It is 20nm-200nm, for example, it can be 30nm, 50nm, 80nm, 100nm, 150nm, 200nm, or any two of the above values.

[0047] Regarding the overall physical parameters of silicon-based secondary particles, in some embodiments, the Dv of silicon-based secondary particles... 50 The particle size is 0.2μm-10μm, for example, it can be 0.2μm, 0.5μm, 0.7μm, 1μm, 1.2μm, 1.6μm, 2μm, 3μm, 3.3μm, 3.5μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any combination of two of the above values. Controlling the particle size of silicon-based secondary particles within the aforementioned range allows for a better balance between processing performance and electrochemical performance.

[0048] In this invention, Dv50 Particle size can be determined using conventional methods in the art, such as using a laser particle size analyzer to determine the Dv50 particle size of the material.

[0049] In some embodiments, the mass content of conductive agent 112 in the silicon-based secondary particles is 0.01%-0.5%, for example, it can be 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.5%, or any combination of two of the above values. Controlling the content of conductive agent 112 in the silicon-based secondary particles within the aforementioned suitable range can form efficient and continuous electron conduction paths between the nano-silicon particles 110, while avoiding the problem of clogging ion transport channels or reducing the proportion of active material due to excessive addition, thereby synergistically improving the rate performance and energy density of the electrode.

[0050] In this invention, "lithium-conducting polymeric binder 111" refers to a polymer material that simultaneously possesses adhesive properties and lithium-ion conductivity. In some embodiments, the lithium-conducting polymeric binder 111 includes, but is not limited to, lithium polyacrylate, lithium carboxymethyl cellulose, or modified polymers thereof. The aforementioned polymer molecules have sufficient segmental flexibility and polar groups to achieve capillary bridging, while their own lithium-conducting ability enables ion transport within secondary clusters to no longer rely on the penetration of solid electrolytes or liquid electrolytes, but can be accomplished by pre-constructed polymer pathways.

[0051] In some embodiments, the conductive agent 112 includes at least one of zero-dimensional conductive agents, one-dimensional conductive agents, and two-dimensional conductive agents. In this invention, a "zero-dimensional conductive agent" refers to near-spherical nanoparticles, which may include, but are not limited to, conductive carbon black (e.g., acetylene black, Ketjen black). The zero-dimensional conductive agent reliably establishes electronic pathways within the silicon-based secondary particles through point contact. A "one-dimensional conductive agent" refers to a linear conductive material with a high aspect ratio, which may include, but is not limited to, at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and vapor-grown carbon fibers. The one-dimensional conductive agent can intertwine with each other within the silicon-based secondary particles to form a three-dimensional conductive network, providing long-range electron transport pathways. A "two-dimensional conductive agent" refers to a planar conductive material with a layered structure, which may include, but is not limited to, graphene. The two-dimensional conductive agent can be stacked and distributed between the active material nanoparticles to form a surface-contact conductive structure, thereby expanding the electron transport area.

[0052] In some embodiments, the conductive agent 112 includes a one-dimensional conductive agent (especially single-walled carbon nanotubes), which has an extremely high aspect ratio and excellent conductivity. It can intertwine and overlap within the secondary particles and pierce the gaps between the nano-silicon particles 110, forming a "bird's nest"-like conductive network. This intertwined conductive network has higher conductivity and structural stability compared to the electronic pathways built solely by point contacts with zero-dimensional conductive agents. Preferably, the one-dimensional conductive agent is carbon nanotubes. Carbon nanotubes have a high aspect ratio and excellent electronic conductivity, enabling the formation of an effective long-range conductive network at very low addition levels. For example, using single-walled or multi-walled carbon nanotubes as the one-dimensional conductive agent, and more preferably single-walled carbon nanotubes, allows for the physical entangling of particles to enhance cohesion while constructing stronger electronic conduction pathways.

[0053] As an example, the conductive agent 112 includes at least a one-dimensional conductive agent, and may also include a two-dimensional conductive agent, a one-dimensional conductive agent, and optionally, two-dimensional conductive agents that overlap each other in a secondary cluster structure to form a conductive network.

[0054] According to the present invention, the nano-silicon particles 110 can be selected as needed, as long as the objectives of the present invention are achieved. In some embodiments, the nano-silicon particles 110 include at least one of nanocrystalline silicon, nanoamorphous silicon, and nanosilicon suboxide. For example, nanocrystalline silicon has a high theoretical specific capacity, nanoamorphous silicon exhibits a relatively uniform stress distribution during volume expansion during cycling, and nanosilicon suboxide, due to the presence of oxygen atoms, generates an inert matrix such as lithium silicate during the first charge-discharge cycle, which can effectively buffer the volume changes in subsequent cycles. Therefore, each has its advantages. Those skilled in the art can select the appropriate type of nano-silicon particles according to the specific requirements for performance indicators such as capacity, cycle life, and initial coulombic efficiency. In addition, the nano-silicon particles 110 are not limited to the above three types, but may also include mixtures thereof, or nano-silicon-based materials modified by doping with other elements (such as carbon and nitrogen), as long as their particle size is on the nanometer scale and provides electrochemical activity. Nanocrystalline silicon is used as an example to illustrate the advantages of the present invention, but this does not constitute a limitation on the present invention.

[0055] In some embodiments, the mass content of nano-silicon particles 110 in the silicon-based secondary particles is 94.5%-99.98%, for example, it can be 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 98%, 99%, 99.98%, or any range of two of the above values. When the content of nano-silicon particles 110 is within the aforementioned range, it can better achieve the effective synergy between the utilization rate of highly active materials and the efficient conductive network.

[0056] The content of each component in the silicon-based secondary particles of this invention corresponds to the amount of the corresponding raw materials used.

[0057] Preparation method of silicon-based secondary particles According to a second aspect of the present invention, the present invention provides a method for preparing silicon-based secondary particles, comprising the following steps: mixing nano-silicon particles, a lithium-conducting polymer binder, and a conductive agent in the presence of a solvent to obtain a slurry; then evaporating to remove the solvent to obtain silicon-based secondary particles; the amount of the lithium-conducting polymer binder, based on the total mass of the nano-silicon particles, the lithium-conducting polymer binder, and the conductive agent, is 0.01%-5%, for example, 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 3%, 3.5%, 3.8%, 4%, 4.5%, 5%, or any range of two of the above values.

[0058] The method for preparing silicon-based secondary particles in this invention is a nanoparticle self-assembly granulation method based on capillary force and binder bridging. Essentially, it utilizes interfacial forces and material redistribution during solvent evaporation to allow the nano-sized components to naturally form secondary structures with the assistance of a trace binder. Specifically, nano-silicon particles are uniformly mixed with a low-concentration lithium-conductive polymer binder and a conductive agent, followed by solvent evaporation. During solvent evaporation, the binder is concentrated and forms capillary forces and bridging effects, guiding the particles closer together to form stable secondary cluster structures.

[0059] Unlike traditional electrode fabrication methods where a binder is dried to form a continuous film that completely coats the particles, the "spot welding" distribution of this invention is a natural result of a low-concentration, low-viscosity binder solution followed by an evaporation self-assembly process. At the end of evaporation, the binder tends to remain preferentially at the narrow necks between particles where capillary forces are strongest, rather than spreading across the large surface area of ​​the particles. Once the solvent has completely evaporated, the binder solidifies at these necks, forming point-like bridges. The advantages of this structure are: achieving highly efficient mechanical connections with minimal binder, preserving most of the open space between particles, thus not blocking the migration paths of ions and electrons in the three-dimensional network; and ensuring maximum electron transport efficiency because the conductive network of the conductive agent (especially carbon nanotubes) is exposed. Furthermore, the original nano-silicon particles have ultra-low particle size and ultra-high specific surface area, making them incompatible with existing slurry-making processes. The specific structure of the silicon-based secondary particles prepared in this invention gives them excellent processability during solid-state battery pressing.

[0060] The preparation method in this invention utilizes capillary-driven self-assembly, rather than traditional high-temperature melting or spray drying. This method is energy-efficient, gentle, and does not damage the structure of the silicon nanoparticles or introduce impurities.

[0061] Furthermore, the present invention can further regulate the macroscopic or microscopic structure of silicon-based secondary particles, such as size and morphology, by adjusting the chemical composition, concentration, and evaporation conditions of each component.

[0062] It should be understood that all the features and advantages described above regarding "silicon-based secondary particles" also apply to the "preparation method of silicon-based secondary particles," and will not be repeated here.

[0063] Conductive agents are another key component in constructing efficient electron transport networks within secondary clusters. They are used to build electron conduction channels between silicon nanoparticles, compensating for the inherent poor conductivity of the silicon nanoparticles themselves. In some embodiments, the conductive agent can be a highly conductive material with a one-dimensional or two-dimensional structure. For example, the conductive agent can be a one-dimensional carbon nanotube or a two-dimensional graphene. One-dimensional carbon nanotubes (especially single-walled carbon nanotubes) have extremely high aspect ratios and excellent conductivity, allowing them to intertwine and overlap within secondary particles, forming a "bird's nest"-like conductive framework. This conductive framework not only provides a continuous, low-resistance transport path for electrons but also enhances the mechanical cohesion of the secondary clusters through physical entanglement, reducing the shedding of silicon nanoparticles during subsequent operations or cycling. Two-dimensional graphene, known for its high specific surface area and high conductivity, can encapsulate or connect silicon nanoparticles, forming large-area conductive contacts. In addition, the conductive agent can also be zero-dimensional conductive carbon black (e.g., acetylene black, Ketjen black), or one-dimensional multi-walled carbon nanotubes, vapor-grown carbon fibers, etc., as long as it can be dispersed in the solvent system of the present invention and participate in the self-assembly process, it can be used in the present invention. That is, in some embodiments, the conductive agent includes at least one of zero-dimensional conductive agents, one-dimensional conductive agents, and two-dimensional conductive agents. Examples of zero-dimensional conductive agents include conductive carbon black (e.g., acetylene black, Ketjen black), examples of one-dimensional conductive agents include at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and vapor-grown carbon fibers, and examples of two-dimensional conductive agents include graphene.

[0064] The lithium-conducting polymer binder in this invention is not merely an inert adhesive material, but actively participates in the ion conduction process of the electrode. In some embodiments, the lithium-conducting polymer binder includes, but is not limited to, lithium polyacrylate, lithium carboxymethyl cellulose, or modified polymers thereof.

[0065] In this invention, the basic building blocks of the silicon-based secondary particles are a large number of nanoscale silicon particles. These nanoscale silicon particles, as active materials in electrochemical reactions, can provide high lithium storage capacity. However, nanoscale silicon materials themselves have extremely low ionic and electronic conductivity, and their extremely high specific surface area and surface energy make them very difficult to disperse in conventional pulping processes, easily leading to severe agglomeration. In this invention, nanoscale silicon particles are pre-prepared as primary particles constituting secondary clusters, which is the foundation for constructing all subsequent structures and functions. The selection of nanoscale silicon particles can be implemented in various ways. In some embodiments, the nanoscale silicon particles may specifically include at least one of nanocrystalline silicon, nanoamorphous silicon, and nanosilicon suboxide.

[0066] In some embodiments, the amount of conductive agent used is 0.01%-0.5% based on the total mass of the nano-silicon particles, lithium-conductive polymer binder, and conductive agent. For example, it can be 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.5%, or any range of two of the above values.

[0067] In some embodiments, the amount of nano-silicon particles is 94.5%-99.98% based on the total mass of the nano-silicon particles, the lithium-conductive polymer binder, and the conductive agent. For example, it can be 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 98%, 99%, 99.98%, or any range of two of the above values.

[0068] In this invention, the solvent can influence the dispersion state of each component, the solubility of the lithium-conducting polymer binder, and the driving force of the final self-assembly process to a certain extent. As long as the purpose of this invention can be achieved, any polar solvent or mixture thereof capable of dissolving a specific lithium-conducting polymer binder, dispersing nano-silicon and conductive agents, having a moderate boiling point, and being immiscible with the subsequent pulping solvent, can be used to implement this invention. In some embodiments, the solvent includes polar solvents. In this invention, "polar solvent" refers to a liquid medium with a high dielectric constant (typically greater than 15) that can effectively dissolve or disperse polymers and particles. Specifically, polar solvents include water and polar organic solvents. The polar organic solvent includes at least one of N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and acetonitrile (ACN). Water is preferred as the solvent in this invention.

[0069] In this invention, a solution of a lithium-conducting polymer binder and a dispersion of a conductive agent can be prepared first, and then nano-silicon particles can be added to them for mixing. After that, the solvent is evaporated to remove the solvent and silicon-based secondary particles are obtained. In some embodiments, the above mixing method includes: first mixing the lithium-conducting polymer binder with a portion of the solvent to obtain a binder solution; second mixing the conductive agent with the remaining solvent to obtain a conductive agent dispersion; and then third mixing the binder solution, the conductive agent dispersion and the nano-silicon particles to obtain a slurry.

[0070] In preparing silicon-based secondary particles, the amount of solvent used in this invention is sufficient to fully disperse the various components. For example, the total amount of solvent is 50 to 500 times the total mass of the solid components, such as 50, 80, 100, 120, 150, 200, 230, 260, 280, 300, 350, 400, 450, and 500 times. Furthermore, in some embodiments, the viscosity of the binder solution is less than 1000 mPa·s, for example, 50 mPa·s, 150 mPa·s, 200 mPa·s, 260 mPa·s, 310 mPa·s, 350 mPa·s, 400 mPa·s, 500 mPa·s, 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, or 980 mPa·s. This low viscosity design is intended to allow the binder to preferentially migrate to the narrow necks between particles during subsequent evaporation to form point bridging, rather than coating the particle surface. That is, the concentration can be controlled by controlling the amount of solvent used in the first mixing with the lithium-conducting polymer type adhesive. For example, the mass concentration of the adhesive solution is 0.01%-1%, such as 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%.

[0071] In some embodiments, the mass content of the conductive agent in the conductive agent dispersion is 0.1%-1%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%. This dispersion concentration is beneficial for the conductive agent to be uniformly dispersed in the slurry and to form a pre-unentangled state, laying the foundation for the subsequent construction of a continuous three-dimensional conductive network inside the secondary particles.

[0072] According to the present invention, the methods of the first mixing, second mixing, and third mixing described above are not particularly limited, as long as they enable the components to be uniformly dispersed in the solvent. For example, one or more combinations of mechanical stirring, magnetic stirring, high-speed shearing, or ultrasonic dispersion can be used for mixing to ensure that the resulting slurry is uniform and free of visible agglomerates, providing a uniform precursor for the subsequent capillary-driven self-assembly process.

[0073] According to the present invention, the evaporation conditions are not particularly limited as long as the purpose of the invention can be achieved. Conditions that allow for slow and uniform removal of the solvent to drive capillary self-assembly can be selected. In some embodiments, evaporation is carried out under low-temperature conditions, such as 60°C-80°C. The endpoint of evaporation is generally when the product reaches constant weight. "Constant weight" refers to a stable state in which the material to be tested is repeatedly dried, evaporated, cooled, and weighed under specific evaporation conditions (such as 60°C-80°C) until the residual volatile solvent is completely removed, resulting in a mass difference between two consecutive weighings not exceeding a specified tolerance of 0.3 mg. This state indicates that the capillary-driven self-assembly process has been completed, and the product structure tends to be stable. The weight of the material at this point is the net dry weight without solvent, which can be used as a benchmark for determining the evaporation endpoint and subsequent process control. The evaporation time is generally 24-96 hours. In some embodiments, evaporation can be carried out under normal pressure or slightly negative pressure to avoid structural inhomogeneity caused by rapid boiling or excessive drying. The aforementioned mild evaporation conditions ensure that the solvent evaporates at a controllable rate, allowing the binder to fully concentrate in the narrow necks between particles and form stable point-like bridges.

[0074] After evaporation to remove the solvent, the resulting product may be loose lumps or powder. To further obtain well-dispersed silicon-based secondary particle powder, the preparation method also includes a step of dispersing the dried material obtained by evaporation to remove the solvent. This dispersing method can be conventional in the art; in some embodiments, the dispersing method includes ball milling or dry mixing. As an example, the dispersion method is ball milling. The ball milling step is not particularly limited, as long as it can disperse the dried lumps into dispersed secondary particles without destroying its internal loose porous structure. As an example, the dried material can be placed in a mixer, and an appropriate amount of milling beads (such as 4 mm diameter zirconia beads) can be added. Dry mixing can be performed at a low speed (such as 20 rpm-80 rpm) for 5 min-10 min to fully disperse the silicon-based secondary particles. This ball milling step can give the final silicon-based secondary particle powder a uniform particle size and good flowability, which is convenient for mixing and coating in the subsequent electrode preparation process.

[0075] Negative electrode plate According to a third aspect of the present invention, the present invention provides a negative electrode sheet comprising silicon-based secondary particles as described in the first aspect of the present invention, or silicon-based secondary particles prepared by the method for preparing silicon-based secondary particles as described in the second aspect of the present invention.

[0076] It should be understood that all the features and advantages described above regarding "silicon-based secondary particles and methods for preparing silicon-based secondary particles" also apply to this "negative electrode sheet", and will not be repeated here.

[0077] The materials in the negative electrode sheet other than silicon-based secondary particles (such as solid electrolyte, auxiliary conductive agent, binder, current collector, etc.) and their proportions and preparation methods can all be carried out in accordance with conventional methods in the field, as long as the purpose of this invention can be achieved.

[0078] There are no particular restrictions on the type of solid electrolyte; various solid electrolyte materials known in the art can be used. For example, sulfide solid electrolytes (such as Li6PS5Cl, Li6PS5Br, Li3PS4, etc.) and oxide solid electrolytes (such as Li7La3Zr2O) can be used. 12 Li 1.3 Al 0.3 Ti 1.7 (PO4)3, etc.) or polymer solid electrolytes (such as polyethylene oxide electrolytes, polyvinylidene fluoride electrolytes, etc.), and composites of the above materials. Preferably, the solid electrolyte is a sulfide solid electrolyte.

[0079] For auxiliary conductive agents, in addition to the conductive agents already contained within the secondary particles, at least one commonly used conductive agent in the art, such as conductive carbon black, carbon nanotubes, and graphene, can be added during the preparation of the negative electrode slurry to further optimize the overall electronic conductivity network of the electrode. The amount of the auxiliary conductive agent can be adjusted according to the electrode formulation, for example, accounting for 0.5%-10% of the total mass of the negative electrode active material layer.

[0080] For the binder, in addition to the lithium-conducting polymer binder already contained within the silicon-based secondary particles, conventional electrode binders in the art can be added during the preparation of the negative electrode slurry, such as at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and polyisobutylene (PIB).

[0081] For the current collector, commonly used negative electrode current collector materials in this field can be used, such as copper foil, nickel foil, stainless steel foil, perforated steel strip, or metal foil with roughened surface treatment.

[0082] The fabrication process of the negative electrode sheet can be implemented by referring to conventional wet or dry electrode fabrication techniques in this field. As an example, the aforementioned silicon-based secondary particles, solid electrolyte, auxiliary conductive agent, and binder are dispersed in an organic solvent (such as anhydrous xylene, toluene, butyl butyrate, etc.) in a predetermined ratio, and mixed by high-speed stirring or grinding to form a uniform negative electrode slurry. This slurry is then uniformly coated onto the surface of the current collector (using methods such as blade coating, slot coating, or screen printing). After drying to remove the solvent, it is pressed into shape (using roller pressing or flat pressing, with a pressure generally between 100 MPa and 500 MPa) to obtain a dense negative electrode sheet with good interfacial bonding. This negative electrode sheet can be directly used in subsequent battery assembly processes.

[0083] The negative electrode sheet containing any of the above-mentioned silicon-based secondary particles has the advantages of dense structure, good interfacial bonding and excellent electrochemical performance. In some embodiments, the porosity of the negative electrode sheet is 15%-40%, for example, 15%, 19%, 20%, 21%, 22%, 25%, 28%, 30%, 31%, 34%, 35%, 39%, 40%, or any two of the above values.

[0084]

Battery

[0085] It should be understood that all the features and advantages described above regarding "silicon-based secondary particles, the preparation method of silicon-based secondary particles, and the negative electrode sheet" also apply to this "battery," and will not be repeated here.

[0086] The materials used in the battery, except for the negative electrode, can all be manufactured in accordance with the methods described in this field, and all can achieve excellent rate performance and long cycle life.

[0087] In some embodiments, the battery is an all-solid-state battery, preferably a sulfide-based all-solid-state battery.

[0088] When a sulfide solid electrolyte is used, it can form a tight mechanically interlocked interface with the rough morphology of the silicon-based secondary particles of the present invention, which consists of protruding nano-silicon particles and conductive agent ends, during the pressing process. This significantly reduces interface impedance and improves cycle stability. The positive electrode of the battery can be a high-voltage positive electrode material known in the art, such as lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, or lithium-rich manganese-based materials. The battery can be assembled using conventional stacking, winding, or integrated pressing processes, as long as tight contact between the layers can be achieved. By integrating the silicon-based secondary particles of the present invention into the battery, while maintaining high specific capacity, it is possible to effectively utilize their ion / electron dual transport network and deformable mechanical interlocking characteristics, enabling the battery to achieve excellent rate performance and long cycle life.

[0089] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0090] In the following examples, unless otherwise specified, the specific techniques or conditions are as described in the literature in this field or in accordance with the product instructions; and the materials or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0091] Example 1 Step 1: Weigh 0.5g of nanocrystalline silicon, 5g of low-concentration (0.2% by mass) lithium polyacrylate binder aqueous solution (viscosity 150mPa·s), and 0.1g of single-walled carbon nanotube (diameter range 1nm-2nm, aspect ratio >3000) aqueous dispersion (0.4% by mass). Mix the above components evenly to obtain a slurry.

[0092] Step 2: Dry the slurry obtained in Step 1 at a low temperature (60℃) to constant weight to obtain secondary particles.

[0093] Step 3: Place the dried secondary particles in a mixer, add 8 grinding balls with a diameter of 4mm, set the speed to low (35rpm) and dry mix for 10 minutes. After mixing, stop the machine and unload the material. Use a sieve with a pore size slightly larger than 4mm to separate the grinding balls and obtain powdered silicon-based secondary particles.

[0094] Step 4: In a dry environment with a dew point below -50°C, the silicon-based secondary particles obtained in Step 3 are mixed with a sulfide solid electrolyte (Li6PS5Cl), conductive carbon black, and a 6% (w / w) polyisobutylene (PIB) binder solution at a mass ratio of 70:15:10:5. The mixture is thoroughly stirred to obtain a uniform negative electrode slurry. This negative electrode slurry is then coated onto the negative electrode current collector using a scraper. After drying and pressing, a negative electrode sheet for solid-state batteries is obtained.

[0095] Step 5: Solid-state battery assembly: Using the negative electrode sheet prepared in Step 4 as the working electrode, lithium indium as the counter electrode, and Li6PS5Cl as the solid electrolyte layer, a solid-state half-cell is assembled in the mold battery.

[0096] The SEM image of the nanocrystalline silicon in this embodiment is as follows: Figure 3 As shown.

[0097] The SEM image of the silicon-based secondary particles prepared in this embodiment is shown below. Figure 4 As shown, Figure 5 for Figure 4 A magnified view of a portion of the image.

[0098] Depend on Figure 4-5 It can be seen that the silicon-based secondary particles have a three-dimensional loose porous aggregate morphology resembling grape bunches, and the surface of the silicon-based secondary particles is uneven and has a thorny outline. Further analysis revealed that the surface of the silicon-based secondary particles is composed of a large number of protruding nano-silicon and conductive agent ends, exhibiting a fluffy or thorny outline rather than a smooth spherical surface.

[0099] Example 2 The method is the same as in Example 1, except that the amount of the low-concentration (0.2% by mass) aqueous solution of lithium polyacrylate binder is 10g.

[0100] The rest is the same as in Example 1, and the silicon-based secondary particles, the corresponding negative electrode sheet, and the corresponding solid half-cell are finally prepared.

[0101] Example 3 The method is the same as in Example 1, except that the mass concentration of the binder lithium polyacrylate aqueous solution is 0.4% and the viscosity is 310 mPa·s.

[0102] The rest is the same as in Example 1, and the silicon-based secondary particles, the corresponding negative electrode sheet, and the corresponding solid half-cell are finally prepared.

[0103] Example 4 The method is the same as in Example 1, except that the mass concentration of the binder lithium polyacrylate aqueous solution is 0.4% and the amount of single-walled carbon nanotube aqueous dispersion is 0.2g.

[0104] The rest is the same as in Example 1, and the silicon-based secondary particles, the corresponding negative electrode sheet, and the corresponding solid half-cell are finally prepared.

[0105] Example 5 The method is the same as in Example 1, except that 0.1g of single-walled carbon nanotube aqueous dispersion is replaced with 0.1g of multi-walled carbon nanotube (inner diameter range 3-5nm, outer diameter range 8-15nm, aspect ratio range 1000-1500) aqueous dispersion (mass concentration 0.4%).

[0106] The rest is the same as in Example 1, and the silicon-based secondary particles, the corresponding negative electrode sheet, and the corresponding solid half-cell are finally prepared.

[0107] Example 6 The method of Example 1 is followed, except that 0.1g of single-walled carbon nanotube aqueous dispersion is replaced with 0.1g of graphene (layer number range 1-2, sheet diameter range 0.2-10μm, thickness range approximately 2nm) aqueous dispersion (mass concentration 0.4%).

[0108] The rest is the same as in Example 1, and the silicon-based secondary particles, the corresponding negative electrode sheet, and the corresponding solid half-cell are finally prepared.

[0109] Example 7 The method is the same as in Example 1, except that 0.1g of single-walled carbon nanotube aqueous dispersion is replaced with 0.1g of Ketjenblack (average particle size 60nm) aqueous dispersion (mass concentration 0.4%).

[0110] The rest is the same as in Example 1, and the silicon-based secondary particles, the corresponding negative electrode sheet, and the corresponding solid half-cell are finally prepared.

[0111] Example 8 The method of Example 1 is followed, except that 0.1g of single-walled carbon nanotube aqueous dispersion is replaced with 0.1g of vapor-grown carbon fiber VGCF (diameter range 100-150nm, aspect ratio range approximately 50) aqueous dispersion (mass concentration 0.4%).

[0112] The rest is the same as in Example 1, and the silicon-based secondary particles, the corresponding negative electrode sheet, and the corresponding solid half-cell are finally prepared.

[0113] Comparative Example 1 The method is the same as in Example 1, except that nanocrystalline silicon is used directly to prepare the negative electrode and the corresponding solid-state half-cell.

[0114] Comparative Example 2 The method is the same as in Example 1, except that 5g of low-concentration lithium polyacrylate adhesive aqueous solution is replaced with 5g of low-concentration (0.2% by mass) PVDF-HFP adhesive solution (viscosity 76mPa·s, N-methylpyrrolidone as solvent).

[0115] The rest is the same as in Example 1, and the silicon-based secondary particles, the corresponding negative electrode sheet, and the corresponding solid half-cell are finally prepared.

[0116] Comparative Example 3 The method is the same as in Example 1, except that single-walled carbon nanotubes are not added, that is, 0.1g of single-walled carbon nanotube aqueous dispersion is replaced with 0.1g of water.

[0117] The rest is the same as in Example 1, and the silicon-based secondary particles, the corresponding negative electrode sheet, and the corresponding solid half-cell are finally prepared.

[0118] Comparative Example 4 The method is the same as in Example 1, except that 5g of low-concentration lithium polyacrylate adhesive aqueous solution is replaced with 10g of low-concentration (0.4% by mass) lithium polyacrylate adhesive aqueous solution (viscosity 310mPa·s).

[0119] The rest is the same as in Example 1, and the silicon-based secondary particles, the corresponding negative electrode sheet, and the corresponding solid half-cell are finally prepared.

[0120] Performance testing Cluster Dv 50 Particle size testing: The particle size distribution of silicon-based secondary particles was observed using laser particle size analysis.

[0121] Porosity test of nano-silicon secondary particle-based electrode sheet: Referring to step four of Example 1, a negative electrode sheet for solid-state battery was obtained. After being subjected to 200MPa isostatic pressing, an electrode sheet of the same size was taken and its true density porosity was measured using a true density meter.

[0122] Peel force test of negative electrode sheet: The prepared negative electrode sheet is cut into strips with a width of 20 mm and a length of 100 mm. The active material layer side is attached to a stainless steel test plate with double-sided tape and rolled back and forth 3 times with a 2 kg pressure roller. Peel off one end of the negative electrode sheet and clamp it on the test machine fixture. Perform a 180° peel test at a constant speed of 100 mm / min. Record the stable peel force during the peeling process and take the average peel force of the plateau part of the force-displacement curve as the result.

[0123] Solid-state half-cell 0.05C charge specific capacity and first-charge efficiency test: The assembled solid-state half-cell was placed in a 55℃ constant temperature chamber for 6 hours and then subjected to discharge-charge cycle testing; the charge / discharge rate was 0.05C, and the voltage range was 0.01V-2.0V. The first discharge capacity and first charge capacity of this process were recorded. 0.05C specific capacity (mAh / g) = first charge capacity / mass of active material. 0.05C first-charge efficiency (%) = first charge capacity / first discharge capacity × 100%.

[0124] Rate performance testing of solid-state half-cells: The assembled solid-state half-cells were cycled 3 times at a current density of 0.05C to complete formation (discharge cutoff voltage 0.01V, charging cutoff voltage 2.0V). Then, charge and discharge tests were performed sequentially at current densities of 0.05C, 0.1C, 0.2C, 0.5C, and 1C, with 5 cycles at each rate. The percentage of the specific capacity at 1C rate relative to the specific capacity at 0.05C rate was calculated (i.e., 1C capacity retention rate, %).

[0125] Cycle stability test of solid-state full cells: Solid-state full cells were assembled using negative electrode sheets. The assembled solid-state full cells (octa-series positive electrode - silicon-based negative electrode, N / P=1.5) were subjected to one charge-discharge cycle at a current density of 0.05C to complete formation (charge cut-off voltage 4.3V, discharge cut-off voltage 1.8V). After formation, constant current charge-discharge was performed at a constant current of 0.5C (charge cut-off voltage 4.2V, discharge cut-off voltage 2.0V) for 300 repeated charge-discharge cycles. The discharge specific capacity of the 5th cycle was recorded (as the initial capacity reference), and the discharge specific capacity of the 300th cycle was recorded. Then, the capacity retention rate (%) after 300 cycles was calculated as (discharge specific capacity of the 300th cycle / discharge specific capacity of the 5th cycle) × 100%.

[0126] The test results are shown in Table 1.

[0127] Table 1 Performance Test Results The test results above show that the silicon-based secondary particles used in Examples 1-8 of this invention generally outperform the comparative examples in terms of overall performance. For example, Example 1 achieved a 0.05C charging specific capacity of 3600 mAh / g and an initial efficiency of 91.1%, while the directly physically mixed Comparative Example 1 only achieved a specific capacity of 3140 mAh / g and an initial efficiency of 82.6%. This indicates that the porous secondary particle structure formed through self-assembly, with internal ion and electron dual continuous transport channels, is crucial for improving the utilization rate of active materials and the initial coulombic efficiency of silicon-based anodes.

[0128] The specific capacity of Comparative Example 2 at 0.05C charge was only 3040 mAh / g, with an initial coulombic efficiency of 80.9%, significantly lower than that of Example 1. Its peel strength (7 N / m) was also lower than that of Example 1 (10 N / m), demonstrating the necessity of lithium-conducting polymer binders in the system of this invention. Although PVDF-HFP is an excellent non-lithium-conducting binder capable of bonding nanoparticles together, it lacks lithium-ion conductivity. This results in a lack of effective lithium-ion transport pathways within the constructed secondary particles, hindering ion transport and making it difficult for lithium ions to effectively insert into / extract from the active material, thus causing a significant decrease in capacity and efficiency.

[0129] In Comparative Example 3, without the addition of conductive carbon material, its 0.05C charging specific capacity dropped sharply to 2200mAh / g, with an initial efficiency of only 75.4%. This directly proves the necessity of constructing an electronic conduction path inside the secondary particles in this invention.

[0130] In Comparative Example 4, the binder content was too high (approximately 7.4%), resulting in a severe deterioration in its specific capacity (2300 mAh / g) and first-efficiency (76.6%). The analysis suggests that the excessive binder may have partially filled the internal pores of the particles and encapsulated the active material, hindering ion and electron transport. This further illustrates the rationale for controlling the binder content within a low range of 0.01%-5% in this invention, to ensure the formation of effective point-like bridging rather than dense filling.

[0131] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A silicon-based secondary particle, characterized in that, It comprises nano-silicon particles, a lithium-conducting polymer binder, and a conductive agent; the nano-silicon particles, the lithium-conducting polymer binder, and the conductive agent together form a non-fully densified secondary cluster structure; the lithium-conducting polymer binder has a mass content of 0.01%-5% in the silicon-based secondary particles.

2. The silicon-based secondary particles according to claim 1, characterized in that, The conductive agent has a mass content of 0.01%-0.5% in the silicon-based secondary particles; And / or, the mass content of the nano-silicon particles in the silicon-based secondary particles is 94.5%-99.98%; And / or, the conductive agent includes at least one of zero-dimensional conductive agents, one-dimensional conductive agents, and two-dimensional conductive agents; And / or, the lithium-conducting polymeric binder includes lithium polyacrylate, lithium carboxymethyl cellulose, or a modified polymer thereof; And / or, the nano-silicon particles include at least one of nanocrystalline silicon, nanoamorphous silicon, and nanosilicon suboxide.

3. The silicon-based secondary particles according to claim 2, characterized in that, The conductive agent includes a zero-dimensional conductive agent, which includes conductive carbon black; And / or, the conductive agent includes a one-dimensional conductive agent, which includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and vapor-grown carbon fibers. And / or, the conductive agent includes a two-dimensional conductive agent, which includes graphene.

4. The silicon-based secondary particles according to any one of claims 1-3, characterized in that, The nano-silicon particles, the conductive agent, and the lithium-conducting polymer binder self-assemble to form the secondary cluster structure through capillary force and bridging effect of the lithium-conducting polymer binder. And / or, the silicon-based secondary particles have a three-dimensional loose porous aggregate morphology in the form of grape bunches, and the surface of the silicon-based secondary particles is composed of protruding nano-silicon particles and conductive agent ends, forming an uneven, rough morphology with a velvety or thorny outline. And / or, the Dv of the silicon-based secondary particles 50 The particle size is 0.2μm-10μm.

5. A method for preparing silicon-based secondary particles, characterized in that, Includes the following steps: In the presence of a solvent, nano-silicon particles, a lithium-conducting polymer binder, and a conductive agent are mixed to obtain a slurry; then the solvent is evaporated to remove the slurry, resulting in silicon-based secondary particles; the amount of the lithium-conducting polymer binder is 0.01%-5% based on the total mass of the nano-silicon particles, the lithium-conducting polymer binder, and the conductive agent.

6. The preparation method according to claim 5, characterized in that, The solvent includes polar solvents, which include water and polar organic solvents; And / or, the evaporation conditions include: a temperature of 60°C-80°C; And / or, the mixing method includes: first mixing the lithium-conductive polymer binder with a portion of the solvent to obtain a binder solution; second mixing the conductive agent with the remaining solvent to obtain a conductive agent dispersion; and then third mixing the binder solution, the conductive agent dispersion, and the nano-silicon particles to obtain the slurry; And / or, the preparation method further includes: a step of dispersing the dried material obtained by evaporating to remove the solvent, wherein the dispersing method includes ball milling or dry mixing.

7. The preparation method according to claim 6, characterized in that, The viscosity of the adhesive solution is less than 1000 mPa·s; And / or, the mass concentration of the adhesive solution is 0.01%-1%; And / or, the mass content of the conductive agent in the conductive agent dispersion is 0.1%-1%.

8. A negative electrode sheet, characterized in that, The silicon-based secondary particles include those described in any one of claims 1-4, or those prepared by the method described in any one of claims 5-7.

9. A battery, characterized in that, Includes the negative electrode sheet as described in claim 8.

10. The battery according to claim 9, characterized in that, The battery is an all-solid-state battery, and the all-solid-state battery is a sulfide-based all-solid-state battery.

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