Silicon-graphene-graphite composite

Abstract

The present invention is a method for producing a silicon-graphene-graphite composite for silicon-based anodes of lithium-ion batteries, wherein the particle size distribution D is greater than 100 nm. 10 Silicon particles and a peelable graphene-based material are combined in a first organic solvent, the weight ratio of silicon to the peelable graphene-based material being between 1.5 and 9, the silicon particles are pulverized into nanoparticles, at least a portion of the peelable graphene-based material is peeled off into graphene, and the mixture is mixed at at least 500 rpm for at least 20 minutes to form a silicon-graphene composite, the silicon-graphene composite and graphite are combined, the weight ratio of carbon to silicon being between 1.5 and 19, and the viscosity is 1 s -1 The present invention relates to a method for mixing silicon-graphene-graphite composites for at least two minutes, with a shear rate between 0.025 and 160 Pa·s.

Description

Technical Field

[0001] The present invention relates to a silicon-graphene-graphite composite for a silicon-based anode of a lithium-ion battery. The present invention also relates to a method for manufacturing the silicon-graphene-graphite composite and an active material thereof.

Background Art

[0002] A typical lithium-ion cell includes a carbon-based anode (e.g., graphite), a lithium metal oxide-based cathode (e.g., LiCoO2), and a carbonate-based organic electrolyte (e.g., ethylene carbonate (EC), dimethyl carbonate (DMC)) having a lithium salt (e.g., LiPF6). Energy is stored in the electrodes as a Li intercalation compound (LIC). Li + ions intercalate and de-intercalate between graphite (anode) and LiCoO2 (cathode) through the electrolyte during discharge and charge, respectively.

[0003] Carbon / graphite is the active material selected for the anode. It has the ability to intercalate lithium into its structure with a small amount of expansion. Nevertheless, graphite-based anodes provide a limited specific capacity (372 mA h g -1 ) along with several significant problems including Li plating that leads to dendrite formation.

[0004] As a promising anode material for lithium-ion batteries, silicon has many advantages over graphite, such as a very high capacity, wide availability, good stability, and environmental friendliness. In particular, this has the highest weight capacity (4200 mA h g -1 , Li 22 uptake to Li22Si5 stoichiometry) and a volume capacity (9786 mA h cm -3 , based on the initial volume of Si) superior to that of lithium metal.

[0005] However, several obstacles, namely, large volume expansion, low electrical conductivity, poor cycle performance, and low Faradaic efficiency in the first cycle, impede the use of silicon. In particular, the volume expansion during Li alloying (Li 22 with respect to Si5 is approximately 360%) generates huge mechanical stress in repeated charge and discharge processes, leading to a series of serious destructive consequences. The gradual increase in pulverization during repeated lithiation / delithiation cycles deteriorates the electrode structure, the interfacial stress cuts off the electrical connection between the active material and the current collector, and the continuous formation-breakage-reformation of the solid electrolyte interface (SEI) film continuously consumes the electrolyte and lithium ions.

[0006] One strategy to overcome the above limitations of Si anode materials involves constructing an efficient conductive network and an external buffer for the volume variation of Si by combining Si with a second phase, such as carbonaceous compounds like carbon, metal, ceramic, and graphene and its derivatives.

[0007] Blending nanosized Si particles with graphene sheets prepared by high-temperature (1050 °C) thermal expansion of graphite is particularly known from H. Xiang, K. Zhang, G. Ji, J.Y. Lee, C. Zou, X. Chen, J. Wu, Graphene / nanosized silicon composites for lithium battery anodes with improved cycling stability, Carbon 49(2011) 1787-1796.

[0008] The incorporation of another carbon phase such as graphite or amorphous carbon has been demonstrated to be superior to the simple fabrication of binary Si / graphene hybrids and is another effective method to enhance the cycle stability of Si-based anodes.

[0009] Si / few-layered graphene / C composites (Si / FLG / C) can be prepared by a) sonicating a mixture of Si powder, few-layered graphite, and pitch (as a carbon precursor) in acetone until the solvent evaporates, b) drying in an oven at 80°C for 1 hour to remove residual solvent, and c) calcining at 1000°C for 2 hours under argon flow at a rate of 5°C / min, as is known particularly from CCHsieh, W. Liu, Carbon-coated Si particles binding with few-layered graphene via a liquid exfoliation process as potential anode materials for lithium-ion batteries, Surf.Coating.Technol.387(2020)125553.

[0010] Nevertheless, the production of Si-based anodes with high mass load and high area capacity using simple, scalable, and environmentally friendly technologies remains an unresolved concern. [Prior art documents] [Non-patent literature]

[0011] [Non-Patent Document 1] H.Xiang, K.Zhang, G.Ji,JYLee, C.Zou, X.Chen, J.Wu, Graphene / nanosized silicon composites for lithium battery anodes with improved cycling stability, Carbon 49(2011) 1787-1796 [Non-Patent Document 2] CCHsieh, W. Liu, Carbon-coated Si particles binding with few-layered graphene via a liquid exfoliation process as potential anode materials for lithium-ion batteries, Surf.Coating.Technol.387(2020)125553 [Overview of the project] [Problems that the invention aims to solve]

[0012] Therefore, an object of the present invention is to improve upon the shortcomings of the prior art by providing an efficient method for producing silicon-graphene composites. [Means for solving the problem]

[0013] For this purpose, the first object of the present invention is a method for producing a silicon-graphene-graphite composite for a silicon-based anode of a lithium-ion battery, comprising the following steps -(i) Particle size distribution D exceeding 100 nm 10 A peelable graphene-based material containing silicon particles and at least 85% by weight of carbon is supplied. -(ii) The silicon particles and the peelable graphene-based material are combined in a first organic solvent, wherein the weight ratio of silicon to the peelable graphene-based material is between 1.5 and 9. -(iii) Mix the composition of step (ii) at at least 500 rpm for at least 20 minutes to pulverize the silicon particles into nanoparticles, exfoliate at least a portion of the exfoliable graphene-based material into graphene, and form a silicon-graphene composite. -(iv) A silicon-graphene composite and graphite are combined, where the weight ratio of carbon from both graphene and graphite to silicon is between 1.5 and 19, and the viscosity is 1 s -1 The shear rate is between 0.025 and 160 Pa·s. -(v) Mixing the composition of step (iv) for at least 2 minutes to form a silicon-graphene-graphite composite comprising a method.

[0014] The method according to the present invention may also have any of the following optional features, considered individually or in combination. - The exfoliable graphene-based material is selected from graphite, intercalated graphite, expanded graphite, graphite oxide, reduced graphite oxide, graphene oxide, reduced graphene oxide, and mixtures thereof - The first organic solvent is selected from isopropanol, ethanol, and mixtures thereof - The weight ratio of silicon to the first organic solvent is less than 0.66 - Steps ii) and iii) are carried out simultaneously - At the end of step iii), the Si particles have a particle size distribution D up to 70 nm 50 having - The graphite in step iv) has a particle size distribution D less than 20 μm 90 and a particle size distribution D less than 10 μm 50 [ having - The graphite in step iv) is battery-grade graphite - Adding a second solvent in step iv) - In steps iv) and v), the solid content is maintained above 11% - In step v), the graphite is not exfoliated - In step v), the mixing continues for less than 20 minutes - The method further includes a step (vi) of evaporating the solvent from the silicon-graphene-graphite composite to dry the silicon-graphene-graphite composite - The method further includes a step (vii) of heat-treating the silicon-graphene-graphite composite under an inert atmosphere.

[0015] A second object of the present invention is a silicon-graphene-graphite composite for a silicon-based anode of a lithium-ion battery, - A particle size distribution up to 70 nm encased in a graphene layer D 50 Silicon particles having - Graphite particles in which the weight ratio of carbon to silicon is between 1.5 and 19. - First organic solvent The viscosity of the silicon-graphene-graphite composite is 1 s -1 It consists of complexes that fall within the shear rate range of 0.025 to 160 Pa·s.

[0016] A third object of the present invention is an active material for a silicon-based anode of a lithium-ion battery, comprising a silicon-graphene-graphite composite, - A particle size distribution up to 70 nm encased in a graphene layer D 50 Silicon particles having - Graphite particles in which the weight ratio of carbon to silicon is between 1.5 and 19. It consists of an active material containing [specific components].

[0017] A fourth object of the present invention is a silicon-based anode for a lithium-ion battery containing the active material according to the present invention.

[0018] A fifth object of the present invention is a lithium-ion battery comprising a silicon-based anode according to the present invention.

[0019] As is evident, the present invention is based, on the one hand, on the pulverization of Si particles into nanoparticles, exfoliation of at least a portion of the exfoliable graphene-based material into graphene, and encapsulation of the Si particles in a graphene layer to form a composite, and on the other hand, on the careful control of viscosity during a second mixing step in which graphite is further introduced into the composite.

[0020] Other features and advantages of the present invention will be described in more detail in the following description.

[0021] This invention is provided purely for illustrative purposes and will be better understood by reading the following description, which is not restrictive. [Brief explanation of the drawing]

[0022] [Figure 1] Figure 1 is an SEM image of a two-phase mixture of silicon particles and a detachable graphene-based material mixed at 3350 rpm for 15 minutes. [Figure 2] Figure 2 is an SEM image of the silicon-graphene composite according to the present invention. [Figure 3] Figure 3 is an SEM image of the silicon-graphene composite according to the present invention. [Figure 4] Figure 4 shows the EDX analysis of a two-phase mixture of silicon particles and a peelable graphene-based material mixed at less than 500 rpm for 30 minutes. [Figure 5] Figure 5 shows the EDX analysis of the silicon-graphene composite according to the present invention. [Modes for carrying out the invention]

[0023] Nanoparticles have a particle size distribution of less than 100 nm. 50 It is defined as a particle that holds together

[0024] In the first step (step i), the particle size distribution D is greater than 100 nm. 10 A peelable graphene-based material containing silicon particles and at least 85% by weight of carbon is supplied.

[0025] Si particles have a particle size distribution D greater than 100 nm. 10 It has the properties of nanoparticles, i.e., it is not nanoparticles. By avoiding nanoparticles as a raw material, the handling of the raw material becomes safer. Grinding Si particles during mixing with a detachable graphene-based material is more energy-efficient than grinding Si particles before mixing.

[0026] The Si particles preferably have a size within the submicron range. More preferably, the particle size distribution D90 It is less than 1 μm. More preferably, D 90 The particle size is less than 300 nm. This particle size distribution improves the mixing yield, meaning that the Si particles are efficiently pulverized while being mixed with the exfoliable graphene-based material without requiring excessive energy for mixing.

[0027] The shape of the Si particles is not limited. They can be spherical or irregular.

[0028] The Si particles preferably have a purity of at least 98% by weight, and preferably at least 99.9% by weight. High purity of Si particles improves the performance of electrodes and, therefore, lithium-ion batteries. Si may contain impurities such as Al, Ca, Fe, Ti, P, Cu, Cr, K, V, Ni, SiO2, and Na.

[0029] Si particles are preferably crystalline. This improves the performance of the electrodes and, therefore, the lithium-ion battery.

[0030] Si particles can be supplied in an organic solvent. This prevents the silicon particles from oxidizing during transport and storage. Any organic solvent offers this advantage and can be used for this purpose. Alcohols are preferred because they have a low boiling point and further improve the dispersibility of the Si particles. More preferably, the organic solvent is selected from isopropanol, ethanol, and mixtures thereof.

[0031] A peelable graphene-based material means that the material is based on a graphene layer, i.e., a monolayer of carbon atoms arranged in a two-dimensional honeycomb lattice nanostructure that can be peeled or further peeled. There are no restrictions on how the graphene layers of a peelable graphene-based material are stacked. It may be ABA stacking or ABC stacking. The graphene layers can be intercalated, expanded, or partially peeled into monolayers, bilayers, and / or fewer layers.

[0032] Examples of possible peelable graphene-based materials include graphite, intercalated graphite, expanded graphite, graphite oxide, reduced graphite oxide, graphene oxide, and reduced graphene oxide.

[0033] The peelable graphene-based material is preferably in the form of graphite. The graphite may be natural or synthetic. It may also be quiche graphite.

[0034] The peelable graphene-based material contains at least 85% by weight, preferably at least 97% by weight, and more preferably at least 99% by weight of carbon. It improves the performance of electrodes and, therefore, lithium-ion batteries.

[0035] The particle size distribution of the peelable graphene-based material is not limited. When the same material is used in steps iii) and iv), the particle size distribution D is up to 20 μm. 90 It is preferable to use particles having the following characteristics. Otherwise, a high size distribution D of 250 μm or 500 μm is preferable. 90 Particles having the following properties can be used.

[0036] The peelable graphene-based material is preferably in the form of a nanoplatelet, i.e., a nano-object having one external dimension at the nanoscale, while the other two external dimensions are significantly larger and not necessarily at the nanoscale. This is advantageous for peeling the peelable graphene-based material and thus for wrapping Si particles.

[0037] The peelable graphene-based material is preferably not partially peeled, and more preferably not peeled at all. This makes the manufacturing process more energy-efficient because the peelable graphene-based material is peeled only during the process according to the present invention and does not need to be peeled before this process.

[0038] In the second step (step ii), the silicon particles and the exfoliable graphene-based material are combined in the first organic solvent.

[0039] The organic solvent prevents oxidation of silicon particles, prevents weak aggregation of silicon particles, and prevents the graphene layer from being re-laid when the peelable graphene-based material is peeled or further peeled. Therefore, the organic solvent helps to obtain a homogeneous mixture.

[0040] Any organic solvent can provide these advantages and be used for this purpose. Alcohols are preferred because they have a low boiling point and further improve the dispersibility of Si particles. More preferably, the organic solvent is selected from isopropanol, ethanol, and mixtures thereof. For clarity, water is not considered an organic solvent.

[0041] The first organic solvent may be an organic solvent in which silicon particles can be dispersed when supplied in step (i).

[0042] The weight ratio of silicon to exfoliable graphene-based material falls between 1.5 (corresponding to 60% silicon by weight and a 60:40 ratio) and 9 (corresponding to 90% silicon by weight and a 90:10 ratio). This range is crucial for achieving the ideal performance of electrodes and, therefore, lithium-ion batteries. Below 1.5, an excess amount of exfoliable graphene-based material is exfoliated during the process, affecting the battery's performance, particularly its Coulombic efficiency (imper). Above 9, there is insufficient graphene to encase the silicon particles. As a result, the volume expansion of silicon during Li alloying is not adequately buffered by the graphene, and the active material does not benefit from graphene's high electrical conductivity.

[0043] The weight ratio of silicon to the peelable graphene-based material is preferably between 3 and 6, which further improves performance.

[0044] The weight ratio of silicon to the organic solvent is preferably less than 0.66 (which corresponds to 40% by weight silicon and a 40:60 ratio) to further prevent oxidation of Si particles and facilitate mixing. The weight ratio of silicon to the organic solvent is preferably at least 0.05 (which corresponds to 5% by weight silicon and a 5:95 ratio) to facilitate the encapsulation of Si particles in graphene and accelerate the evaporation of the organic solvent at the end of the process. Limiting the amount of organic solvent also prevents the Si particles and the exfoliable graphene-based material (or graphene obtained from this material) from settling in the solvent. More preferably, the weight ratio of silicon to the organic solvent is 0.11 (which corresponds to 10% by weight silicon and a 10:90 ratio) to 0.43 (which corresponds to 30% by weight silicon and a 30:70 ratio), which further facilitates the process.

[0045] The solids content is preferably at least 6%, more preferably at least 20%, and even more preferably between 20% and 30%. This prevents the Si particles and the exfoliable graphene-based material (or graphene obtained from this material) from settling in the solvent. Furthermore, it facilitates the next step.

[0046] Preferably, in step (ii), no elements other than silicon particles, exfoliable graphene-based material, and organic solvent are combined. No additional elements are necessary to achieve the desired performance of the electrodes and, therefore, the lithium-ion battery.

[0047] In the third step (iii), silicon particles, a detachable graphene-based material, and the first organic solvent are mixed to form a silicon-graphene composite in the first organic solvent. This composite corresponds to Si nanoparticles encased in a graphene layer.

[0048] Mixing should be done at least 500 rpm, and simultaneously -Si particles are crushed into nanoparticles, - At least a portion of the peelable graphene-based material is peeled off into graphene, - Enclosing Si particles within a graphene layer Generates high shear.

[0049] In particular, the Si particles are intercalated between the graphene layers, which is advantageous for the delamination of the detachable graphene-based material. Furthermore, the encapsulation of Si particles within the graphene layer prevents weak aggregation of Si particles or re-lamination of graphene.

[0050] Below 500 rpm, the shearing of the mixture is insufficient to achieve proper pulverization, exfoliation, and encapsulation. As a result, two phases remain, and the mixture is not a composite. At 500 rpm, a silicon-graphene composite is formed. The faster the mixing speed, the more exfoliable graphene-based material can be exfoliated. This further buffers the volume expansion of silicon during Li alloying, and thus further improves the battery life.

[0051] Preferably, the mixing speed is between 1000 and 8000 rpm, more preferably between 2500 and 6000 rpm.

[0052] The mixing should be carried out for at least 20 minutes. A shorter duration would not give enough time for the Si particles to be pulverized and incorporated into the graphene obtained from the exfoliable graphene-based material.

[0053] With longer mixing durations, the exfoliable graphene-based material can be further exfoliated. This further buffers the volume expansion of silicon during Li alloying, and thus further improves battery life.

[0054] Preferably, the mixing duration is between 25 minutes and 1 hour.

[0055] Mixing is preferably carried out in a high-shear mixer. Mixing is preferably carried out in a rotor-stator mixer, also known as an impeller mixer. This mixer may be a blade mixer, a sawtooth blade mixer, or a paddle mixer.

[0056] Steps ii) and iii) can be performed simultaneously. In other words, mixing can be started before all the raw materials have been added to the mixture. For example, silicon particles and organic solvents can be combined first, and mixing can be started. Then, the exfoliable graphene-based material can be added in stages.

[0057] Step iii) may include one single mixing step or multiple consecutive mixing steps. In the latter case, the peelable graphene-based material can be peeled more effectively.

[0058] At the end of this process, the Si nanoparticles preferably have a size distribution D up to 70 nm. 50 It has the following properties: This buffers the volume expansion of silicon during the Li alloying process, and thus further improves the performance of the battery.

[0059] Graphene obtained by exfoliating a detachable graphene-based material is not limited to a single layer of carbon atoms. It includes single-layer graphene, double-layer graphene, and thin-layer graphene. It can also be partially oxidized.

[0060] At the end of this process, a silicon-graphene composite is obtained. Since some of the exfoliable graphene-based material may not be exfoliated from the graphene, or may not be completely exfoliated, the silicon-graphene composite may contain some of the exfoliable graphene-based material. In this specification, the term “silicon-graphene composite” means a composite comprising silicon, graphene as defined above, and optionally an exfoliable graphene-based material.

[0061] The silicon-graphene composite contains silicon particles having a particle size distribution D50 up to 70 nm, encased in a graphene layer. Specifically, the silicon-graphene composite contains silicon particles having a particle size distribution D50 up to 70 nm, encased in a graphene layer from a graphene-based material. The weight ratio of silicon to graphene-based material is between 1.5 and 9. More specifically, the silicon-graphene composite contains silicon particles having a particle size distribution D50 up to 70 nm, encased in a graphene layer exfoliated from a peelable graphene-based material. The weight ratio of silicon to peelable graphene-based material is between 1.5 and 9.

[0062] In the fourth step (step iv), the silicon-graphene composite obtained earlier in the first organic solvent is combined with graphite.

[0063] Adding graphite to a silicon-graphene composite improves the electrical conductivity of the active material, thereby enhancing battery performance.

[0064] Graphite preferably contains more than 99% Cg to further improve battery performance. Cg refers to carbon in graphite form, as opposed to carbon atoms bonded to the molecular structure of other minerals. Graphite is in the form of particles. It can be in the form of nanoplatelets or spheres. Graphite particles preferably have a particle size distribution of less than 20 μm. 90 and particle size distribution D of less than 10 μm 50 It holds.

[0065] Typical graphites for lithium-ion cells include (1) natural graphite, (2) graphitized mesocarbon or microbeads formed by graphitizing mesophase pitch materials, (3) hard carbon formed by thermal decomposition of polymer materials, and (4) natural or artificial graphite materials coated with a hard or soft carbon surface layer, in some cases. It may also be quiche graphite in particular.

[0066] Graphite, more preferably, is battery-grade graphite, also known as spherical graphite (SpG). This can be produced from flake graphite concentrates manufactured by graphite mines. In the first step, the process involves micronizing, rolling, and purifying the flake graphite to produce uncoated SpG (uSpG). Micronization involves reducing the flake size to about 10-15 microns. The rolling or spheroidizing process reduces the surface area, making more graphite into a smaller volume. This creates a smaller, denser, and more efficient anode product for batteries. It also increases the rate at which the cell can be charged and discharged. The micronized and rounded material is then purified to about 99.95% Cg using hydrofluoric acid and sulfuric acid. In the second step, the spheres can be coated with a thin layer of pitch or asphalt and fired at over 1200°C. This involves covering the uSpG with a rigid carbon shell that protects the sphere from delamination and degradation during expansion and contraction associated with charging and discharging. It also inhibits the ongoing reaction between the electrolyte and the active graphite inside the sphere itself.

[0067] The weight ratio of graphite to silicon-graphene composite is adjusted so that the weight ratio of carbon to silicon falls within the range detailed below.

[0068] The weight ratio of carbon to silicon is between 1.5 (corresponding to 40% silicon and a 60:40 ratio) and 19 (corresponding to 5% silicon and a 95:5 ratio). The term "weight of carbon" refers to the weight of carbon from all carbon sources excluding the solvent. The carbon sources are the graphene obtained in the third step, the graphite added in this step, and, in some cases, parts of the detachable graphene-based material that are not detached from the graphene or are not completely detached. Considering the purity of the detachable graphene-based material, the weight of carbon can be considered to be the sum of the weight of the detachable graphene-based material added in the second step and the weight of the graphite added in this step.

[0069] Below 1.5, there is not enough carbon to buffer the volume expansion of silicon during Li alloying. Above 19, the addition of a small amount of silicon does not provide a sufficient capacity improvement to the battery. More preferably, the carbon-to-silicon ratio is between 1.86 (corresponding to 35% silicon and a ratio of 65:35) and 9 (corresponding to 10% silicon and a ratio of 90:10). This further improves the performance of the battery.

[0070] The viscosity of the silicon-graphene / graphite / solvent mixture is 1 s -1 The shear rate is between 0.025 and 160 Pa·s. This viscosity allows for the acquisition of a silicon-graphene-graphite composite in a single, unique phase. It also prevents oxidation of the Si particles. The viscosity of the mixture is preferably 1 s. -1 Shear rate between 0.4 and 50 Pa·s, more preferably 1 s -1 The shear rate is between 1 and 10 Pa·s. This is further advantageous for the suspension of graphite particles in the mixture and for the homogeneity of the mixture.

[0071] The viscosity can be easily adjusted by adding a second solvent. For this purpose, water or any organic solvent can be used. Alcohols are preferred because they have a low boiling point and further improve the dispersibility of Si particles. More preferably, the second solvent is an organic solvent selected from isopropanol, ethanol, and mixtures thereof. The organic solvent may be the same as the first organic solvent in step (ii). This facilitates waste management in particular. Alternatively, the second solvent is a co-solvent of the first organic solvent that facilitates the evaporation of the solvent in a later step. In this step, water is optional. The duration of mixing is limited, and the silicon particles encapsulated in graphene do not oxidize. Furthermore, since water is used in the electrode manufacturing process, there is no need to evaporate water from the silicon-graphene-graphite composite before starting the electrode manufacturing process.

[0072] Generally, the minimum viscosity corresponds to a solid content of more or less 11%. Therefore, the solid content is preferably maintained at more than 11%. More preferably, the solid content is between 11% and 40%.

[0073] In the fifth step (step v), the silicon-graphene composite, graphite, and the first organic solvent are mixed to form a silicon-graphene-graphite composite.

[0074] The type of mixing is not limited. It may be planetary mixing or mechanical mixing. Preferably, the mixing is carried out in such a way that there is no opportunity for the graphite to delaminate (which would degrade the performance of the active material). Therefore, it is preferable that the mixer does not have impellers such as blades or paddles.

[0075] Mix the materials for at least 2 minutes to obtain a homogeneous mixture. Preferably, the materials are mixed for less than 20 minutes.

[0076] At the end of this process, a silicon-graphene-graphite composite is obtained. As described in relation to the third step (step iii), some of the detachable graphene-based material may not be detached from the graphene during the third step, or may not be completely detached, and the silicon-graphene composite may contain some of the detachable graphene-based material. Thus, the silicon-graphene-graphite composite may also contain some of the detachable graphene-based material. In this specification, the term “silicon-graphene-graphite composite” refers to a composite comprising silicon, graphene as defined above, graphite, and optionally other detachable graphene-based material.

[0077] The silicon-graphene-graphite composite comprises the silicon-graphene composite obtained at the end of the third step, graphite particles, and the first organic solvent, wherein the weight ratio of carbon to silicon is between 1.5 and 19, and the viscosity of the silicon-graphene-graphite composite is 1 s -1The shear rate falls between 0.025 and 160 Pa·s.

[0078] According to one variant of the present invention, in the sixth step (step vi), the solvent is evaporated from the silicon-graphene-graphite composite to dry the composite and obtain an active material.

[0079] Solvent evaporation is merely optional in industrial processing, as it may be necessary to disperse the active material in a solvent to prepare ink for electrode manufacturing.

[0080] Drying can be carried out by spray drying, freeze-drying, or rotary evaporation, in particular.

[0081] The dehydration of the active material can be assessed, particularly by thermogravimetric analysis (TGA). In such cases, no weight loss is observed at temperatures below 120°C.

[0082] If the same organic solvent is used in steps (ii) and (iv), the organic solvent can be reused at the end of the evaporation step to produce more active material. This limits waste.

[0083] According to one variant of the present invention, the active material is further heat-treated in an inert atmosphere. This removes any possible slight oxidation of the Si particles and further enhances the graphite and graphene qualities. In particular, if the peelable graphene-based material is in an oxidized form (especially graphene oxide or reduced graphene oxide), the heat treatment in an inert atmosphere reduces or further reduces the material. The inert gas is preferably selected from hydrogen, argon, nitrogen, and mixtures thereof. The temperature is preferably between 700 and 1500°C, more preferably between 900 and 1100°C. The minimum duration is preferably 30 minutes. The pressure can be atmospheric pressure or vacuum.

[0084] Once silicon-graphene-graphite composites are obtained, they can be used as active materials for manufacturing silicon-based anodes for lithium-ion batteries. These anodes are composite electrodes. In addition to the active material, they contain the following inert materials, namely a binder to hold the electrode particles together, and an electronic conductor (i.e., carbon black) to enhance electronic conductivity. These are usually all mixed together to form an ink or slurry to form a relatively homogeneous and stable coating on the current collector. The inert materials do not directly participate in the electrochemical redox reaction, but are nevertheless important for the overall electrode functionality.

[0085] The binder is preferably a polymer binder. Commonly used polymer binders include polyvinylidene fluoride (PVDF), sodium carboxymethylcellulose / styrene-butadiene rubber (CMC / SBR), polyacrylate (PAA), lithium polyacrylate (LiPAA), polyvinyl alcohol (PVA), sulfonated tetrafluoroethylene-based fluoropolymer copolymers (such as Nafion®), sodium alginate (SA), chitosan (CS), and guar gum (GG).

[0086] Once silicon-based anodes are manufactured, they can be used in the production of lithium-ion batteries.

[0087] When the anode is first charged, it slowly approaches the lithium potential and begins to react with the electrolyte, forming a film on the electrode surface. This film is composed of products resulting from the reduction reaction between the anode and the electrolyte. This film is called the solid electrolyte interface (SEI) layer. Proper formation of the SEI layer is essential for good performance. Since the lithium in the cell originates from the lithium in the active cathode material, any loss due to the formation of the SEI layer reduces the cell capacity. At the same time, the SEI layer is Li + It provides pathways for the electrolyte to enter and exit the anode structure while protecting the graphite surface from reaction with the electrolyte.

[0088] Lithium-ion batteries based on an active material containing 16 wt% silicon are considered sufficiently efficient if they exhibit an initial Coulomb efficiency (FCE) of over 75%, an electrode charge capacity (measured after 10 cycles) of over 700 mAh / g, and a cycleability of over 500 cycles at 80% of their initial capacity.

[0089] Lithium-ion batteries based on an active material containing 32% by weight of silicon are considered sufficiently efficient if they exhibit an initial Coulomb efficiency (FCE) of over 65%, an electrode charge capacity (measured after 10 cycles) of over 1200 mAh / g, and a cycleability of over 250 cycles at 80% of the initial capacity retention rate. [Examples]

[0090] [Example 1] The following raw materials were supplied. - Dispersed in isopropanol at a concentration of 0.21 g / mL (corresponding to a silicon-to-organic solvent weight ratio of 21:79), with a purity of over 99% and particle size distribution D 90 12g of silicon particles less than 291nm, - 3 g of quiche graphite that has been washed in the previous step and has reached a purity of 99.9 wt% C. The quiche graphite has a particle size distribution of 20 μm. D90 He possessed it.

[0091] Silicon particles and quiche graphite were combined in isopropanol at a silicon / graphite weight ratio of 4 (80:20). This was done without adding any further isopropanol. As a result, the weight ratio of the exfoliable graphene-based material to the solvent was 5:95, and the solids content was 26%.

[0092] The composition was mixed under high shear in a Dispermat LC-30 at 3350 rpm for 30 minutes. A silicon-graphene composite was obtained in 44.24 g of isopropanol at a rate of 15 g. The Si nanoparticles of the composite had a size distribution of 70 nm. 50 He possessed it.

[0093] Next, 60 g of quiche graphite was added to 15 g of silicon-graphene composite dispersed in 44.24 g of isopropanol, with a graphite / composite weight ratio of 4 (80:20) corresponding to a carbon / silicon ratio of 5.25 (84:16). 120 mL of isopropanol was added, and 1 second of the mixture was added. -1 The viscosity was increased to 152.16 Pa·s at a shear rate. As a result, the solid content was 37%. The quiche graphite was pre-washed to achieve a purity of 99.9 wt% C and had a particle size distribution of 20 μm D 90 , 10 μm particle size distribution D 50 It also had a nanoplatelet shape.

[0094] The mixture was mixed in a Kakuhunter SK-350TII mixer for 5 minutes, and then dried in a rotary evaporator at 60°C under vacuum for 1 hour to obtain a 16 wt% silicon-4 wt% graphene-80 wt% graphite composite.

[0095] To investigate the performance of this active material, it was mixed with lithium polyacrylate (LiPAA) and carbon black C45 in a ratio of 80:10:10 in water in a Dispermat LC-30 at 5000 rpm for 1 hour. The resulting ink was then applied to copper foil using a doctor blade to form a 100 μm thick wet coating. This was dried in a vacuum oven at 80°C for 12 hours. The dried coating was 70 μm thick.

[0096] Electrodes made from coated copper foil were tested as half-cells for lithium in a coin cell under the following conditions. -Electrolyte: 1 mol / L lithium hexafluorophosphate (LiPF6) and 2 wt% vinylene carbonate (VC) in a solvent containing fluoroethylene carbonate (FEC) to ethyl methyl carbonate (EMC) in a volume ratio of 3:7. - Cycling protocol: • To form the SEI layer, 0.01~1.0V vs Li / Li + In the voltage window, one cycle is performed with a constant current at rate C / 20, followed by five cycles with a constant current at rate C / 10. • One cycle at a constant voltage with a maximum current rate of C / 40, followed by one cycle at a constant voltage with a maximum current rate of C / 20. 0.01~1.0V vs Li / Li + 24 cycles at a constant current rate of C / 2 in the voltage window, followed by 0.01~1.0V vs Li / Li + A cycle consisting of one cycle at a constant current rate of C / 10 within a voltage window, and one cycle at a constant voltage with a maximum current rate of C / 10.

[0097] Here, C is the battery capacity, i.e., the maximum amount of energy that can be extracted from the battery, expressed in ampere-hours (Ah).

[0098] Table 1 summarizes the results obtained.

[0099] [Table 1]

[0100] As is evident, thanks to the composite prepared by the method according to the present invention, the electrode exhibits very good performance, including an FCE of 84%, an active material capacity of 824 mAh / g, and a cycleability of 600 cycles.

[0101] [Example 2] Example 2 uses a peelable graphene-based material instead of quiche graphite, with a purity exceeding 97% by weight and a particle size distribution D90 This method differs from Example 1 in that it uses 10 μm platelet-shaped reduced graphene oxide (rGO). Furthermore, graphite was mixed with the silicon-graphene composite instead of quiche graphite.

[0102] Silicon particles and rGO were combined in isopropanol at a silicon / rGO weight ratio of 4 (80:20). This was done without adding any further isopropanol. As a result, the weight ratio of the exfoliable graphene-based material to the solvent was 5:95, and the solids content was 26%.

[0103] The composition was mixed under high shear in a Dispermat LC-30 at 3350 rpm for 30 minutes. A silicon-graphene composite of 4 g in 20 g of isopropanol was obtained. The Si nanoparticles of the composite had a size distribution D50 of 70 nm.

[0104] Next, 4 g of silicon-graphene composite dispersed in 20 g of isopropanol was mixed with 16.3 g of graphite (purity 99.9 wt% C, 20 μm D). 90 , 10 μm D 50 Nanoplatelets (supplied by Imerys) were combined with a graphite / composite weight ratio of 4 (80:20), corresponding to a carbon / silicon ratio of 5.25 (84:16). 40 mL of isopropanol was added. As a result, the solid content was 28%.

[0105] The mixture was mixed in a Kakuhunter SK-350TII mixer for 5 minutes, and then dried in a rotary evaporator at 60°C under vacuum for 1 hour to obtain a 16 wt% silicon-4 wt% graphene-80 wt% graphite composite.

[0106] The resulting 16 wt% silicon-4 wt% graphene-80 wt% graphite composite was tested under the same conditions as in Example 1.

[0107] Table 2 summarizes the results obtained.

[0108] [Table 2]

[0109] As is evident, thanks to the composite prepared by the method according to the present invention, the electrode exhibits very good performance, such as an FCE of 80% and an active material capacity of 723 mAh / g.

[0110] [Example 3] Example 3 uses a different material instead of quiche graphite, with a purity of 99% by weight and particle size distribution D 90 This differs from Example 1 in that it uses 3g of 20μm expanded graphite (EG). The mixing conditions were also different.

[0111] Silicon particles and expanded graphite were combined in isopropanol at a silicon / graphite weight ratio of 4 (80:20). This was done by adding 77 g of isopropanol. As a result, the weight ratio of silicon to organic solvent was 7:93, the weight ratio of exfoliable graphene-based material to solvent was 2:98, and the solids content was 8%.

[0112] The composition was mixed under high shear in a Silverson L5 mixer at 3000 rpm for 30 minutes. A silicon-graphene composite of 15 g in 132.43 g of isopropanol was obtained. The Si nanoparticles in the composite had a size distribution D50 of 70 nm.

[0113] Next, 60 g of quiche graphite was added to 15 g of silicon-graphene composite dispersed in 132.43 g of isopropanol, with a graphite / composite weight ratio of 4 (80:20) corresponding to a carbon / silicon ratio of 5.25 (84:16). No isopropanol was added. As a result, the solid content was 36%. The quiche graphite had been washed in a previous step to achieve a purity of 99.9 wt% C, and had a particle size distribution of 20 μm D 90 , 10 μm particle size distribution D 50 It also had a nanoplatelet shape.

[0114] The mixture was mixed in a Kakuhunter SK-350TII mixer for 5 minutes, and then dried in a rotary evaporator at 60°C under vacuum for 1 hour to obtain a 16 wt% silicon-4 wt% graphene-80 wt% graphite composite.

[0115] The resulting 16 wt% silicon-4 wt% graphene-80 wt% graphite composite was tested under the same conditions as in Example 1.

[0116] Table 3 summarizes the results obtained.

[0117] [Table 3]

[0118] As is evident, thanks to the composite prepared by the method according to the present invention, the electrode exhibits very good performance, such as an FCE of 84% and an active material capacity of 714 mAh / g.

[0119] [Example 4] Example 4 uses a peelable graphene-based material instead of quiche graphite, with a purity of 99.9% by weight C and particle size distribution D. 90 This method differs from Example 1 in that it uses 3 g of 20 μm graphite (supplied by Imerys). Also, instead of quiche graphite, graphite was mixed with the silicon-graphene composite.

[0120] Silicon particles and graphite were combined in isopropanol at a silicon / graphite weight ratio of 4 (80:20). This was done without adding any further isopropanol. As a result, the weight ratio of the exfoliable graphene-based material to the solvent was 5:95, and the solids content was 26%.

[0121] The composition was mixed under high shear in a Dispermat LC-30 at 3350 rpm for 30 minutes. A silicon-graphene composite was obtained in 44.24 g of isopropanol at a rate of 15 g. The Si nanoparticles of the composite had a size distribution of 70 nm. 50 He possessed it.

[0122] Next, 15 g of silicon-graphene composite dispersed in 44.24 g of isopropanol was mixed with 60 g of graphite (purity 99.9 wt% C, 20 μm D 90 , 10 μm D 50 Nanoplatelets (supplied by Imerys) were combined in a weight ratio of 4 (80:20) of graphite / composite, corresponding to a carbon / silicon ratio of 5.25 (84:16). 120 mL of isopropanol was added, and 1 second of the mixture was added. -1 The viscosity was increased to 152.16 Pa·s at a shear rate. As a result, the solid content was 29.4%.

[0123] The mixture was mixed in a Kakuhunter SK-350TII mixer for 5 minutes, and then dried in a rotary evaporator at 60°C under vacuum for 1 hour to obtain a 16 wt% silicon-4 wt% graphene-80 wt% graphite composite.

[0124] The resulting 16 wt% silicon-4 wt% graphene-80 wt% graphite composite was tested under the same conditions as in Example 1.

[0125] Table 4 summarizes the results obtained.

[0126] [Table 4]

[0127] As is evident, thanks to the composite prepared by the method according to the present invention, the electrode exhibits very good performance, such as an FCE of 83% and an active material capacity of 790 mAh / g.

[0128] [Example 5] Example 5 differs from Example 1 in that the weight ratio of silicon to organic solvent in the second step is different. The mixing conditions were also different.

[0129] 12 g of silicon particles and 3 g of quiche graphite were combined in isopropanol at a silicon / graphite weight ratio of 4 (80:20). 172 g of isopropanol was added. As a result, the weight ratio of silicon to organic solvent was 5:95, the weight ratio of exfoliable graphene-based material to solvent was 1:99, and the solids content was 6.9%.

[0130] The composition was mixed under high shear in a Silverson L5 mixer at 3000 rpm for 30 minutes. A silicon-graphene composite was obtained in 217.4 g of isopropanol at a density of 15 g. The Si nanoparticles of the composite had a size distribution of 70 nm. 50 He possessed it.

[0131] Next, 60 g of quiche graphite was added to 15 g of silicon-graphene composite dispersed in isopropanol, with a graphite / composite weight ratio of 4 (80:20) corresponding to a carbon / silicon ratio of 5.25 (84:16). No isopropanol was added. As a result, the solid content was 25.8%. The quiche graphite had been washed in a previous step to achieve a purity of 99.9 wt% C, and had a particle size distribution of 20 μm D 90 , 10 μm particle size distribution D 50 It also had a nanoplatelet shape.

[0132] The mixture was mixed in a Kakuhunter SK-350TII mixer for 5 minutes, and then dried in a rotary evaporator at 60°C under vacuum for 1 hour to obtain a 16 wt% silicon-4 wt% graphene-80 wt% graphite composite.

[0133] The resulting 16 wt% silicon-4 wt% graphene-80 wt% graphite composite was tested under the same conditions as in Example 1.

[0134] Table 5 summarizes the results obtained.

[0135] [Table 5]

[0136] As is evident, thanks to the composite prepared by the method according to the present invention, the electrode exhibits very good performance, such as an FCE of 83% and an active material capacity of 803 mAh / g.

[0137] [Example 6] Example 6 differs from Example 4 in that the obtained 16 wt% silicon-4 wt% graphene-80 wt% graphite composite was further heat-treated at 850°C under argon for 3 hours.

[0138] The heat-treated composite was tested under the same conditions as in Example 1.

[0139] Table 6 summarizes the results obtained.

[0140] [Table 6]

[0141] Additional heat treatment reduces silicon oxidation and homogenizes the composite distribution. Additional heat treatment improves the conductivity and stability of the anode.

[0142] [Comparative Example 1] The following raw materials were supplied. - 99% purity, particle size distribution D 50 810g of 200μm silicon particles - Purity 99% by weight C, particle size distribution D 90 This is 270g of expanded graphite (EG) with a thickness of 20μm.

[0143] The expanded graphite was first exfoliated by passing it through a three-roll mill (Buehler Trias-300) seven times in gap mode with isopropanol to achieve an initial solid content of 17%. The silicon particles were pre-milled at 1,450 kWh / t in a bead mill (Buehler PML2 Centex S2 SiC), and then finely milled at 30,000 kWh / t in a bead mill (Buehler MicroMedia MMX1) to obtain a particle size distribution of 150 nm. 90 and 85nm D 50 Next, in a Buehler PML2 Centex S2 SiC mill, 4.66 kg of isopropanol (corresponding to 20.7% solids), a weight ratio of Si to exfoliable graphene material of 75:25, a weight ratio of silicon to organic solvent of 16:84, and a weight ratio of exfoliable graphene material to solvent of 5:95 were used to add exfoliated expanded graphite to silicon particles. The silicon particles in the exfoliated expanded graphite and isopropanol were mixed in a bead mill at a tip speed of 11.1 m / sec for 1.25 hours, and then dried in a rotary evaporator at 60°C under vacuum for 1 hour to obtain a 75 wt% silicon-25 wt% graphene composite.

[0144] To investigate the performance of this active material, it was mixed with lithium polyacrylate (LiPAA) and carbon black C45 in an 80:10:10 ratio in water at 5000 rpm for 1 hour in a Dispermat LC-30 disperser. The resulting ink was then applied to copper foil using a doctor blade to form a 100 μm thick wet coating. This was dried in a vacuum oven at 80°C for 12 hours. The dried coating was 70 μm thick.

[0145] Electrodes made from coated copper foil were tested as half-cells for lithium in a coin cell under the following conditions. -Electrolyte: 1 mol / L lithium hexafluorophosphate (LiPF6) and 2 wt% vinylene carbonate (VC) in a solvent containing fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7. - Cycling protocol: 0.05~0.9V vs Li / Li + A cycle of constant current at the rate of C / 5 within the voltage window, followed by a cycle of constant voltage at the maximum current rate of C / 10.

[0146] Table 7 summarizes the results obtained.

[0147] [Table 7]

[0148] As is clear, if silicon particles and graphene are prepared separately and not mixed with graphite, good performance cannot be achieved. In addition, this method is expensive, energetically inefficient, time-consuming, and the silicon particles are not well incorporated into the carbon matrix.

[0149] [Comparative Example 2] The following raw materials were supplied. - Dispersed in isopropanol at a concentration of 0.21 g / mL (corresponding to a weight ratio of silicon to organic solvent of 21:79), with a purity exceeding 99% and a particle size distribution of less than 291 nm. 90 4g of silicon particles having -Purity 99.9% by weight C, particle size distribution D 90 This includes 4g of 20μm graphite (supplied by Imerys).

[0150] Silicon particles and graphite were combined in isopropanol at a silicon / graphite weight ratio of 1 (50:50). This was done without adding any further isopropanol. As a result, the weight ratio of the exfoliable graphene-based material to the solvent was 21:79, and the solids content was 37%.

[0151] The composition was mixed under high shear in a Dispermat LC-30 at 3350 rpm for 30 minutes. 8 g of silicon-graphene composite was obtained in 13.5 g of isopropanol. The Si nanoparticles of the composite had a size distribution of 70 nm. 50 He possessed it.

[0152] Next, 8 g of silicon-graphene composite dispersed in 13.5 g of isopropanol was mixed with 17 g of graphite (purity 99.9 wt% C, 20 μm D). 90 , 10 μm D 50 Nanoplatelets (supplied by Imerys) were combined at a graphite / composite weight ratio of 2.12 (68:32) (equivalent to a carbon / silicon ratio of 5.25 (84:16)). 57 mL of isopropanol was added.

[0153] The mixture was mixed in a Kakuhunter SK-350TII mixer for 5 minutes, and then dried in a rotary evaporator at 60°C under vacuum for 1 hour to obtain a 16 wt% silicon-16 wt% graphene-68 wt% graphite composite.

[0154] The resulting 16 wt% silicon-16 wt% graphene-68 wt% graphite composite was tested under the same conditions as in Example 1.

[0155] Table 8 summarizes the results obtained.

[0156] [Table 8]

[0157] As is clear, when the weight ratio of silicon / exfoliated graphene-based material is less than 1.5 (60:40), the electrode performance is unsatisfactory. In particular, the cycle life of 80% of the initial capacity retention is limited to 30 cycles.

[0158] [Comparative Example 3] The following raw materials were supplied. - Dispersed in isopropanol at a concentration of 0.21 g / mL (corresponding to a weight ratio of silicon to organic solvent of 21:79), with a purity exceeding 99% and a particle size distribution of less than 291 nm. 90 4g of silicon particles having -Purity 99.9% by weight C, particle size distribution D 90 This is 0.21g of 20μm graphite (supplied by Imerys).

[0159] Silicon particles and graphite were combined in isopropanol at a silicon / graphite weight ratio of 19 (95:5). This was done without adding any further isopropanol. As a result, the weight ratio of the exfoliable graphene-based material to the solvent was 2:98, and the solids content was 24%.

[0160] The composition was mixed under high shear in a Dispermat LC-30 at 3350 rpm for 30 minutes. 4.21 g of silicon-graphene composite was obtained in 13.5 g of isopropanol. The Si nanoparticles of the composite had a size distribution of 70 nm. 50 He possessed it.

[0161] Next, 4.21 g of silicon-graphene composite dispersed in 13.5 g of isopropanol was mixed with 20.79 g of graphite (purity 99.9 wt% C, 20 μm D 90 , 10 μm D 50 Nanoplatelets (supplied by Imerys) were combined at a graphite / composite weight ratio of 2.12 (68:32) (equivalent to a carbon / silicon ratio of 5.25 (84:16)). 62 mL of isopropanol was added.

[0162] The mixture was mixed in a Kakuhunter SK-350TII mixer for 5 minutes, and then dried in a rotary evaporator at 60°C under vacuum for 1 hour to obtain a 16 wt% silicon-0.842 wt% graphene-83.158 wt% graphite composite.

[0163] The resulting 16 wt% silicon-0.842 wt% graphene-83.158 wt% graphite composite was tested under the same conditions as in Example 1.

[0164] Table 9 summarizes the results obtained.

[0165] [Table 9]

[0166] As is clear, when the weight ratio of silicon / exfoliated graphene-based materials exceeds 9 (90:10), the electrode performance is unsatisfactory. In particular, the cycle life of 80% of the initial capacity retention is limited to less than 80 cycles.

[0167] <Effect of mixing duration on the acquisition of silicon-graphene composites> The following raw materials were supplied. - Dispersed in isopropanol at a concentration of 0.21 g / mL (corresponding to a silicon-to-organic solvent weight ratio of 21:79), with a purity exceeding 99% and a particle size distribution of less than 291 nm. 90 4g of silicon particles having - 1 g of quiche graphite that has been washed in the previous step to achieve a purity of 99.9% by weight C. The quiche graphite has a particle size distribution of 20 μm D 90 He possessed it.

[0168] Silicon particles and quiche graphite were combined in isopropanol at a silicon / graphite weight ratio of 4 (80:20). This was done without adding any further isopropanol. As a result, the weight ratio of the exfoliable graphene-based material to the solvent was 5:95, and the solids content was 26%.

[0169] The compositions were mixed under high shear conditions at 3350 rpm for different durations in a Dispermat LC-30 disperser. The homogeneity of the mixtures was then observed by SEM.

[0170] Table 10 summarizes the results obtained.

[0171] [Table 10]

[0172] <Effect of mixing rate on the acquisition of silicon-graphene composites> The following raw materials were supplied. - Dispersed in isopropanol at a concentration of 0.21 g / mL (corresponding to a weight ratio of silicon to organic solvent of 21:79), with a purity exceeding 99% and a particle size distribution of less than 291 nm. 90 4g of silicon particles having - 1 g of quiche graphite that has been washed in the previous step to achieve a purity of 99.9% by weight C. The quiche graphite has a particle size distribution of 20 μm D 90 He possessed it.

[0173] Silicon particles and quiche graphite were combined in isopropanol at a silicon / graphite weight ratio of 4 (80:20). This was done without adding any further isopropanol. As a result, the weight ratio of the exfoliable graphene-based material to the solvent was 5:95, and the solids content was 26%.

[0174] The compositions were mixed under high shear at different rates in a Dispermat LC-30 disperser for 30 minutes. The homogeneity of the mixtures was then observed by SEM and EDX.

[0175] Table 11 summarizes the results obtained.

[0176] [Table 11]

[0177] <Effect of viscosity on the mixing of graphite and silicon-graphene composites> The following raw materials were supplied. - Dispersed in isopropanol at a concentration of 0.21 g / mL (corresponding to a weight ratio of silicon to organic solvent of 21:79), with a purity exceeding 99% and a particle size distribution of less than 291 nm. 90 4g of silicon particles having - 1 g of quiche graphite that has been washed in the previous step to achieve a purity of 99.9% by weight C. The quiche graphite has a particle size distribution of 20 μm D 90 He possessed it.

[0178] Silicon particles and quiche graphite were combined in isopropanol at a silicon / graphite weight ratio of 4 (80:20). This was done without adding any further isopropanol. As a result, the weight ratio of the exfoliable graphene-based material to the solvent was 5:95, and the solids content was 26%.

[0179] The composition was mixed under high shear in a Dispermat LC-30 at 3350 rpm for 30 minutes. A silicon-graphene composite of 5 g in 14.7 g of isopropanol was obtained. The Si nanoparticles in the composite had a size distribution D50 of 70 nm.

[0180] Next, 5 g of silicon-graphene composite dispersed in 20.2 g of isopropanol was combined with 20 g of quiche graphite at a graphite / composite weight ratio of 4 (80:20), corresponding to a carbon / silicon ratio of 5.25 (84:16). The quiche graphite had been washed in a previous step to achieve a purity of 99.9 wt% C and had a particle size distribution of 20 μm (D90), a particle size distribution of 10 μm (D50), and a nanoplatelet shape. Various amounts of isopropanol were added to achieve various viscosities.

[0181] The mixture was mixed in a Kakuhunter SK-350TII mixer for 5 minutes. Once the distinctive phase was obtained, the viscosity was measured at room temperature using an IKA Rotavisc hi-vi I viscometer. The homogeneity of the mixture was observed visually and / or by SEM.

[0182] Table 12 summarizes the results obtained.

[0183] [Table 12]

[0184] As the results clearly show, controlling the viscosity of the silicon-graphene composite and graphite mixture is crucial for obtaining a homogeneous mixture. Insufficient and excessive dilution hinder the homogenization of the mixture.

Claims

1. A method for producing a silicon-graphene-graphite composite for a silicon-based anode of a lithium-ion battery, comprising the following steps: - (i) Particle size distribution D greater than 100 nm １０ A peelable graphene-based material containing silicon particles having at least 85% by weight of carbon is supplied. - (ii) The silicon particles and the peelable graphene-based material are combined in a first organic solvent, wherein the weight ratio of silicon to the peelable graphene-based material is between 1.5 and 9. - (iii) Mix the composition of step (ii) at at least 500 rpm for at least 20 minutes to pulverize the silicon particles into nanoparticles, exfoliate at least a portion of the exfoliable graphene-based material into graphene, and form a silicon-graphene composite. - (iv) A silicon-graphene composite and graphite are combined, where the weight ratio of carbon to silicon is between 1.5 and 19, and the viscosity is 1 s. －１ The shear rate is between 0.025 and 160 Pa·s. - (v) Mix the composition from step (iv) for at least two minutes to form a silicon-graphene-graphite composite. Methods that include...

2. The method according to claim 1, wherein the peelable graphene-based material is selected from graphite, intercalated graphite, expanded graphite, graphite oxide, reduced graphite oxide, graphene oxide, reduced graphene oxide, and mixtures thereof.

3. The method according to claim 1 or 2, wherein the first organic solvent is selected from isopropanol, ethanol, and mixtures thereof.

4. The method according to any one of claims 1 to 3, wherein the weight ratio of silicon to the first organic solvent is less than 0.

66.

5. The method according to any one of claims 1 to 4, wherein steps ii) and iii) are performed simultaneously.

6. At the end of step iii), the Si particles have a particle size distribution D up to 70 nm. ５０ The method according to any one of claims 1 to 5, comprising:

7. The graphite in step iv) has a particle size distribution of less than 20 μm. ９０ and particle size distribution D of less than 10 μm ５０ The method according to any one of claims 1 to 6, comprising:

8. The method according to any one of claims 1 to 7, wherein the graphite in step iv) is battery-grade graphite.

9. The method according to any one of claims 1 to 8, wherein a second solvent is added in step iv).

10. The method according to any one of claims 1 to 9, wherein the solid content is maintained at more than 11% in steps iv) and v).

11. The method according to any one of claims 1 to 10, wherein in step v), the mixing continues for less than 20 minutes.

12. A silicon-graphene-graphite composite for a silicon-based anode of a lithium-ion battery, - Particle size distribution up to 70 nm encased in a graphene layer D ５０ Silicon particles having - Graphite particles in which the weight ratio of carbon to silicon is between 1.5 and 19. - First organic solvent The viscosity of the silicon-graphene-graphite composite, which includes [a specific component], is 1 s. －１ A composite material that falls within the shear rate range of 0.025 to 160 Pa·s.

13. An active material for a silicon-based anode of a lithium-ion battery, comprising a silicon-graphene-graphite composite, - Particle size distribution up to 70 nm encased in a graphene layer D ５０ Silicon particles having - Graphite particles in which the weight ratio of carbon to silicon is between 1.5 and 19. An active material containing the active material.

14. A silicon-based anode for a lithium-ion battery containing the active material described in claim 13.

15. A lithium-ion battery comprising a silicon-based anode as described in claim 14.

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