Carbon material and preparation method thereof, silicon-carbon composite material and preparation method thereof, negative electrode and lithium ion battery

Abstract

The invention provides a carbon material and a preparation method thereof, a silicon-carbon composite material and a preparation method thereof, a negative electrode and a lithium ion battery, and relates to the technical field of silicon-carbon composite materials. At least one plane is arranged on the surface of each carbon material particle; based on the surface area of the carbon material particles, the total area of the plane accounts for 0.1%-100%. The silicon-carbon composite material is prepared from the carbon material, so that the energy density, the multiplying power and the cycling stability of the lithium ion battery can be improved. According to the invention, the technical problems that the multiplying power is reduced and the cycling stability is reduced due to debonding of the spherical negative electrode material in the cycling process are solved, and the technical effect of improving the multiplying power and the cycling stability of the silicon-carbon composite material is achieved.

Description

Technical Field

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

[0002] As porous materials, carbon materials have been widely used in catalysis, environmental protection, and new energy due to their high specific surface area, rich pore structure, and abundant surface functional groups. The appearance of carbon materials significantly affects their stacking morphology, flow pattern, surface and interfacial properties, and mechanical properties, thereby affecting their application performance.

[0003] Silicon-based materials have recently become the most promising anode materials for lithium-ion secondary batteries. With theoretical capacities far exceeding those of graphite and similarly abundant reserves, they hold the potential to replace graphite as the preferred anode material for lithium-ion batteries. However, the inherent limitations of their semiconductor nature and significant expansion upon full charge have limited the widespread application of pure silicon anodes.

[0004] The gas-phase silicon-carbon negative electrode is a silicon-carbon composite material obtained by vapor deposition of silane and other materials using porous carbon materials as the skeleton. It can effectively improve the electrical conductivity and ion conductivity of the composite material, and reduce the volume effect of the composite material during the silicon delithiation / lithiation process. It is one of the best structures for silicon-based negative electrodes.

[0005] The appearance and morphology of silicon-carbon composite materials will also greatly affect their stacking form, flow form, surface and interface properties, and mechanical properties, thereby affecting their application performance. Specifically in lithium-ion battery applications, it may manifest as an impact on the compaction density, inter-particle adhesion, and electrode adhesion strength, ultimately affecting the battery's energy density, rate, and cycle stability. For example, spherical silicon-carbon negative electrode materials will expand during the cycle due to lithium insertion, and during the de-lithiation process, due to the isotropic shrinkage of the spherical material's own structure, it is easy to separate from the binder and lose electrical contact, resulting in a decrease in rate and cycle stability.

[0006] In the existing technology, the morphologies of carbon materials and silicon-carbon composite materials mainly include spherical and quasi-spherical shapes. Such curved surfaces may cause debonding during the cycle, resulting in low rate and low cycle stability.

[0007] In view of this, the present invention is proposed. Summary of the Invention

[0008] One of the purposes of the present invention is to provide a carbon material that solves the problems of accumulation and adhesion of carbon materials in the prior art.

[0009] A second object of the present invention is to provide a method for preparing carbon materials, which has a simple process, a high success rate, and is suitable for industrial production.

[0010] The third object of the present invention is to provide a silicon-carbon composite material that solves the problems of stacking and bonding of silicon-carbon composite materials in the prior art, thereby improving the energy density, rate and cycle stability of lithium-ion batteries.

[0011] A fourth object of the present invention is to provide a method for preparing a silicon-carbon composite material, which has a simple process, a high success rate, and is suitable for industrial production.

[0012] A fifth object of the present invention is to provide a negative electrode that is beneficial to improving the energy density, rate and cycle stability of the battery.

[0013] A sixth object of the present invention is to provide a lithium ion battery with good rate capability and cycle stability.

[0014] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0015] In a first aspect, a carbon material comprises carbon material particles;

[0016] The carbon material particles have at least one plane on their surface;

[0017] Based on the surface area of ​​the carbon material particles, the total area of ​​the plane accounts for 0.1% to 100%.

[0018] Furthermore, the minimum value R of the distance from the mass center of the carbon material particle to any point on its surface is 1min With the maximum value R 1max The ratio is 0.1 to 0.99.

[0019] Furthermore, the carbon material satisfies at least one of the following characteristics:

[0020] (a) The specific surface area of ​​the carbon material is 200 m 2 / g~3000m 2 / g;

[0021] (b) The pore volume of the carbon material is 0.10 cm 3 / g~1.80cm 3 / g;

[0022] (c) The average pore size of the carbon material is 1.6 nm to 5.0 nm;

[0023] (d) The mesopore ratio of the carbon material is 5% to 100%.

[0024] In a second aspect, a method for preparing the carbon material according to any one of the above items comprises the following steps:

[0025] The carbon precursor is carbonized to obtain the carbon material.

[0026] Furthermore, the carbon precursor satisfies at least one of the following conditions:

[0027] (a) The carbon precursor is prepared from a carbon source, wherein the carbon source comprises at least one of a polymer or a monomer thereof, a biomass material or an extract thereof;

[0028] (b) the carbon precursor comprises spherical particles or spherical-like particles;

[0029] (c) the carbon precursor comprises particles having planar surfaces;

[0030] (d) the carbon precursor is prepared by including a material having a planar surface;

[0031] (e) The carbon precursor is prepared by carbon source pretreatment, wherein the pretreatment includes at least one of mixing, extrusion, curing, pre-oxidation, hardening, crushing and pulverization.

[0032] Furthermore, the carbonization further includes a post-processing step;

[0033] Preferably, the post-treatment includes at least one of crushing, grading, pore expansion, activation, shaping, defunctionalization and graphitization.

[0034] In a third aspect, a silicon-carbon composite material comprises silicon-carbon composite material particles;

[0035] The silicon-carbon composite material particles comprise carbon material and silicon nanoparticles;

[0036] The carbon material includes any one of the carbon materials described above;

[0037] The surface of the silicon-carbon composite material particle contains at least one plane, and the total area of ​​the plane accounts for 0.1% to 100% of the surface area of ​​the silicon-carbon composite material particle.

[0038] Furthermore, the minimum value R of the distance from the mass center of the silicon-carbon composite material particle to any point on its surface is 2min With the maximum value R 2max The ratio is 0.1 to 0.99.

[0039] In a fourth aspect, a method for preparing the silicon-carbon composite material according to any one of the above items comprises the following steps:

[0040] Chemical vapor deposition of a silicon-containing precursor on the carbon material to obtain the silicon-carbon composite material;

[0041] Preferably, the silicon-containing precursor comprises at least one of monosilane, disilane, trisilane, halosilane, polysilane, silole and its derivatives, silanol and its derivatives;

[0042] Preferably, a coating layer exists on the surface of the silicon-carbon composite material.

[0043] In a fifth aspect, a negative electrode is provided, wherein the negative electrode active material used in the negative electrode includes the silicon-carbon composite material described in any one of the above items.

[0044] In a sixth aspect, a lithium-ion battery, wherein the negative electrode of the lithium-ion battery comprises the silicon-carbon composite material described in any one of the above items.

[0045] Compared with the prior art, the present invention has at least the following beneficial effects:

[0046] The carbon material provided by the present invention comprises carbon material particles, the surface of which contains one or more planes, the total area of ​​which accounts for 0.1% to 100% of the surface area of ​​the carbon material particles. This solves the problems of accumulation and adhesion of carbon materials in the prior art and is conducive to improving the problem of particles of spherical materials being separated from the binder after expansion and contraction.

[0047] The method for preparing the carbon material provided by the present invention has a simple process, a high success rate, and is suitable for industrial production.

[0048] The silicon-carbon composite material provided by the present invention solves the problems of stacking and bonding of silicon-carbon composite materials in the prior art, and can improve the problem of particles of spherical materials detaching from the binder after expansion and contraction, thereby showing higher rate and cycle stability, which is beneficial to improving the energy density, rate and cycle stability of lithium-ion batteries.

[0049] The preparation method of the silicon-carbon composite material provided by the present invention has a simple process, a high success rate, and is suitable for industrial production.

[0050] The negative electrode provided by the present invention is beneficial to improving the energy density, rate and cycle stability of the battery.

[0051] The lithium ion battery provided by the present invention has good rate capability and good cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0053] Figure 1This is an SEM image of the carbon material provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0054] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0055] A material's appearance significantly influences its stacking, flow, surface, and mechanical properties, thus impacting its performance. Curved surfaces in existing materials can lead to stacking and bonding issues. In lithium-ion batteries, these issues can impact compaction density, interparticle adhesion, and electrode bond strength, ultimately impacting the battery's energy density, rate capability, and cycling stability.

[0056] In order to solve the above problems, the technical solution of the present invention is proposed.

[0057] According to a first aspect of the present invention, there is provided a carbon material comprising carbon material particles;

[0058] The carbon material particles have at least one flat surface on their surface;

[0059] Based on the surface area of ​​the carbon material particles, the total area of ​​the plane accounts for 0.1% to 100%.

[0060] The carbon material of the present invention solves the problems of accumulation and adhesion of carbon materials in the prior art, and is conducive to improving the problem of particles of spherical materials being separated from the binder after expansion and contraction.

[0061] It should be noted that the surface of the carbon material particles contains one or more planes, and the other surfaces have a certain curvature, which may be spherical, cylindrical, conical, arc-shaped, curved plane or nearly flat; the planes of the carbon material particles may have common edges or may not have common edges.

[0062] In some embodiments, some of the planes of the carbon material particles have common edges, while some of the planes do not have common edges.

[0063] In some embodiments, the angles between the planes of the carbon material particles are acute, right, or obtuse.

[0064] In some embodiments, the angles between the planes of the carbon material particles are right angles or obtuse angles.

[0065] In some embodiments, the angles between the planes of the carbon material particles are obtuse.

[0066] In some embodiments, the carbon material particles include a flat surface on their surface.

[0067] In some embodiments, the surface of the carbon material particle comprises two planes.

[0068] In some embodiments, the surface of the carbon material particle comprises 2 to 5 planes.

[0069] In some embodiments, the surface of the carbon material particle comprises 2 to 10 planes.

[0070] In some embodiments, the carbon material particles comprise 10 or more planes on their surfaces.

[0071] In some embodiments, the carbon material particles comprise 20 or more planes on their surfaces.

[0072] In some embodiments, the planes on the surface of the carbon material particles are of different sizes, and the area ratio of the smallest plane to the largest plane is less than 0.8.

[0073] In some embodiments, the planes on the surface of the carbon material particles are of different sizes, and the area ratio of the smallest plane to the largest plane is less than 0.5.

[0074] In some embodiments, the planes on the surface of the carbon material particles are of different sizes, and the area ratio of the smallest plane to the largest plane is less than 0.2.

[0075] In some embodiments, the planes on the surface of the carbon material particles are of different sizes, and the area ratio of the smallest plane to the largest plane is less than 0.1.

[0076] In some embodiments, the planes on the surface of the carbon material particles are similar in size, and the area ratio of the smallest plane to the largest plane is greater than 0.8.

[0077] In some embodiments, the planes on the surface of the carbon material particles are similar in size, and the area ratio of the smallest plane to the largest plane is greater than 0.9.

[0078] In some embodiments, the planes on the surface of the carbon material particles are similar in size, and the area ratio of the smallest plane to the largest plane is greater than 0.95.

[0079] In some embodiments, the planes on the surface of the carbon material particles are similar in size, and the area ratio of the smallest plane to the largest plane is greater than 0.98.

[0080] In a preferred embodiment, the minimum value R of the distance from the mass center of the carbon material particle to any point on its surface is 1min With the maximum value R 1max The ratio, that is, R 1min / R 1max It can be 0.1~0.99, R1min / R 1max Typical but non-limiting ratios are, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.99.

[0081] It should be noted that when the minimum value R 1min With the maximum value R 1max When the ratio is less than 0.1, the material has large anisotropy, which may cause problems in fluid mechanics, stress, etc. in its application.

[0082] In some embodiments, the ratio R of the minimum to maximum distance from the center of mass of the carbon material particle to the surface point is 1min / R 1max The particle size is 0.1 to 0.3, and there is a certain degree of anisotropy in the particles, which may show a certain degree of advantage in terms of stacking, such as increasing the stacking and compaction density through the presence of graded filling.

[0083] In some embodiments, the ratio R of the minimum to maximum distance from the center of mass of the carbon material particle to the surface point is 1min / R 1max It is 0.3~0.5.

[0084] In some embodiments, the ratio R of the minimum to maximum distance from the center of mass of the carbon material particle to the surface point is 1min / R 1max It is 0.5 to 0.8.

[0085] In some embodiments, the ratio R of the minimum to maximum distance from the center of mass of the carbon material particle to the surface point is 1min / R 1max It is 0.8~0.95.

[0086] In some embodiments, the ratio R of the minimum to maximum distance from the center of mass of the carbon material particle to the surface point is 1min / R 1max When the particle size is 0.95-0.99, the particles are nearly isotropic and their appearance is closer to spherical.

[0087] In the present invention, the specific surface area of ​​the carbon material can be 200m 2 / g~3000m 2 / g, with a typical but non-limiting specific surface area of, for example, 200 m 2 / g, 400m 2 / g、600m 2 / g、800m 2 / g、1000m 2 / g、1500m 2 / g、2000m 2 / g、2500m 2 / g、3000m 2 / g; the pore volume of the carbon material can be 0.10cm 3 / g~1.80cm 3 / g, with a typical but non-limiting pore volume of 0.10 cm 3 / g, 0.50cm 3 / g, 1.00cm 3 / g, 1.10cm 3 / g, 1.20cm 3 / g, 1.30cm 3 / g, 1.40cm 3 / g, 1.50cm 3 / g, 1.60cm 3 / g, 1.70cm 3 / g, 1.80cm 3 / g; the average pore size of the carbon material can be 1.6nm~5.0nm, and its typical but non-limiting average pore size is, for example, 1.6nm, 1.8nm, 2.0nm, 2.5nm, 3.0nm, 3.5nm, 4.0nm, 4.5nm, and 5.0nm; the mesopore proportion of the carbon material can be 5%~100%, and its typical but non-limiting mesopore proportion is, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%.

[0088] In some embodiments, the carbon material has a particle size distribution, with a median particle size d V50 2μm~200μm.

[0089] Specifically, in some embodiments, the median particle size d of the carbon material is V50 It may be 2 μm to 5 μm, 5 μm to 10 μm, 10 μm to 20 μm, 20 μm to 50 μm, 50 μm to 100 μm, or 100 μm to 200 μm, but is not limited thereto.

[0090] According to a second aspect of the present invention, there is provided a method for preparing the carbon material according to any one of the above, comprising the following steps:

[0091] The carbon precursor is carbonized to obtain a carbon material.

[0092] The preparation method of the carbon material of the present invention has simple process, high success rate and is suitable for industrial production.

[0093] It should be noted that the morphology of the carbon precursor determines the final morphology of the carbon material to a large extent, especially for particles that are directly solidified and formed. If no subsequent grinding or shaping treatment is performed, the morphology of the carbon precursor can basically be maintained as the carbon material particles; the shaping treatment will adjust the morphology of a single particle, and grinding may change one particle into multiple particles. Therefore, the carbon material particles will only retain part of the morphology of the carbon precursor particles, or even not retain the morphology of the carbon precursor particles. Their outer boundary or appearance morphology is only determined by the grinding method.

[0094] In some embodiments, the carbon precursor comprises a spherical or quasi-spherical material; wherein the quasi-spherical material comprises an ellipsoidal, cylindrical, prismatic, or other material having partially or entirely curved surfaces.

[0095] In some embodiments, the carbon precursor comprises spherical and / or spheroidal materials produced by suspension polymerization.

[0096] In some embodiments, the carbon precursor includes spherical phenolic resin, quasi-spherical phenolic resin, polyhedral phenolic resin, spherical graphene prepolymer, quasi-spherical graphene prepolymer, spherical ion exchange resin, quasi-spherical ion exchange resin, spherical asphalt, and quasi-spherical asphalt prepared by suspension polymerization.

[0097] In some embodiments, the carbon precursor comprises a spherical or quasi-spherical material produced by a spraying method.

[0098] In some embodiments, the carbon precursor includes spherical phenolic resin, quasi-spherical phenolic resin, polyhedral phenolic resin, spherical graphene prepolymer, quasi-spherical graphene prepolymer, spherical ion exchange resin, quasi-spherical ion exchange resin, spherical asphalt, and quasi-spherical asphalt prepared by a spray method.

[0099] For spherical or quasi-spherical materials, a crushing process can be added before and after the subsequent carbon precursor pretreatment and carbonization process, that is, before pretreatment, before carbonization after pretreatment, and after carbonization. By controlling the shape of the crushing tool and the crushing force of the crushing equipment, the obtained carbon material particles can have planes of different sizes and contents.

[0100] In some embodiments, the flat surfaces in the carbon precursor are obtained by grinding and / or shaping.

[0101] In some embodiments, the plane in the carbon precursor is directly obtained during the curing process of the thermoplastic material. For example, during the curing process of the thermoplastic material, a carbon precursor with a plane can be obtained by using an appropriate flat plate material as an auxiliary molding substrate.

[0102] In some embodiments, the planes in the carbon precursor are formed simultaneously during the formation and curing of the high molecular weight polymer. For example, by introducing a material with a plane into a suspension polymerization method, a carbon precursor with a plane can be obtained.

[0103] In some embodiments, a planar carbon precursor can be obtained by using ions or molecules that restrict polymer polymerization or slow down its polymerization rate.

[0104] In some embodiments, the carbon precursor is prepared to include a material having a planar surface.

[0105] In some embodiments, the material having a flat surface includes one or more inorganic sheet materials such as mica sheets, graphene, boron nitride nanosheets, and talc.

[0106] In some embodiments, the material having a flat surface includes one or more organic sheet materials such as polystyrene (PS) sheets and polylactic acid (PLA) films.

[0107] In some embodiments, the material having a flat surface includes one or more of mica sheets, graphene, boron nitride nanosheets, talc, polystyrene (PS) sheets, and polylactic acid (PLA) film sheets.

[0108] For carbon precursors containing inorganic flaky materials during the preparation process, the carbon material obtained therefrom needs to be cleaned to remove the inorganic flaky materials. In some embodiments, selectively retaining some inorganic flaky materials may give the carbon material more properties, such as catalytic active sites, defect sites, loaded active sites, etc.

[0109] It should be noted that the planar carbon material particles formed in one step by the solution method are usually spherical materials. Due to the existence of the planes, a nearly spherical material containing planes is formed; when the planes are large enough and numerous enough, a polyhedron is formed; if the planes are large and relatively uniform in size, they are close to forming a regular polyhedron.

[0110] In the present invention, the carbon precursor can be prepared by pre-treating a carbon source.

[0111] In a preferred embodiment, the carbon source includes but is not limited to at least one of a high molecular weight polymer and its monomers, a biomass material and its extracts.

[0112] In a preferred embodiment, the pretreatment includes but is not limited to at least one of mixing, extruding, curing, pre-oxidation, hardening, crushing and pulverizing.

[0113] In some embodiments, the steps of mixing, extruding, curing, pre-oxidation, hardening, crushing, and pulverizing can be combined in any combination and performed in any order.

[0114] In some embodiments, the crushing comprises one or more crushing methods such as jaw crushing, roller crushing, ball mill crushing, and air flow crushing.

[0115] In some embodiments, the pulverization includes one or more of air flow pulverization, grinding pulverization, and chemical etching.

[0116] In some embodiments, the carbon source is mixed with one or more chemicals such as an acid, a base, or a salt.

[0117] In some embodiments, the carbon source is mixed with phosphoric acid.

[0118] In some embodiments, the carbon source is mixed with HNO3 and / or H2SO4.

[0119] In some embodiments, the carbon source is mixed with one or more of KOH, K2CO3, NaOH, Na2CO3, and sodium acetate.

[0120] In some embodiments, the carbon source is mixed with NaCl and / or ZnCl2.

[0121] In some embodiments, a carbon source is mixed with a template, and the template includes a soft template and / or a hard template; wherein the soft template will be volatilized and removed during the subsequent carbonization process, and the hard template needs to be etched and washed away after carbonization.

[0122] In some embodiments, extrusion comprises one or more of dough kneading, sheeting, and extrusion.

[0123] In some embodiments, curing is to achieve a higher degree of cross-linking of molecules in the carbon precursor at a certain temperature without causing deformation during a subsequent temperature increase.

[0124] In some embodiments, the monomers of the high molecular weight polymer in the liquid phase are polymerized and solidified simultaneously.

[0125] In some embodiments, the polymer forms a certain degree of cross-linking before undergoing curing.

[0126] In some embodiments, a curing agent is mixed into an already stable high molecular weight polymer and curing is achieved at a certain temperature.

[0127] In some embodiments, the material before curing comprises a thermoplastic material.

[0128] In some embodiments, the material before curing is a phenolic resin.

[0129] In some embodiments, the molecular weight of the thermoplastic novolac resin is 500 to 20,000.

[0130] In some embodiments, the molecular weight of the thermoplastic novolac resin is 500-1000.

[0131] In some embodiments, the molecular weight of the thermoplastic novolac resin is 1,000 to 5,000.

[0132] In some embodiments, the molecular weight of the thermoplastic novolac resin is 5,000 to 20,000.

[0133] In some embodiments, the carbon source is subjected to a pre-oxidation treatment and the material may undergo partial oxidation.

[0134] In some embodiments, curing and pre-oxidation occur simultaneously, ie, a higher degree of cross-linking and partial oxidation occur simultaneously.

[0135] In some embodiments, the carbon precursor is hardened before carbonization to have a certain fixed shape, which facilitates the continuous dynamic implementation of subsequent process flows.

[0136] In some embodiments, curing, pre-oxidation, and hardening may occur simultaneously.

[0137] In a preferred embodiment, the carbon material further includes a post-processing step after carbonization.

[0138] In the present invention, post-processing includes but is not limited to at least one of crushing, grading, pore expansion, activation, shaping, defunctionalization and graphitization.

[0139] In some embodiments, the steps of crushing, grading, pore expansion, activation, shaping, defunctionalization, and graphitization can be combined in any combination and performed in any order.

[0140] In some embodiments, the crushing comprises one or more crushing methods such as jaw crushing, roller crushing, ball mill crushing, and air flow crushing.

[0141] In some embodiments, classification refers to screening the crushed particles according to their particle size distribution, including one or more of classification by a classifying wheel, screening, and the like.

[0142] In some embodiments, the carbon material is subjected to pore expansion treatment after carbonization to achieve a larger pore volume and a more optimized pore distribution. The pore expansion can be performed by gas activation or chemical activation.

[0143] In some embodiments, activation of the carbon material comprises one or more of H2O activation, CO2 activation, KOH activation, H3PO4 activation, and ZnCl2 activation.

[0144] In some embodiments, the carbon material is subjected to a shaping process to remove stress points such as sharp corners.

[0145] In some embodiments, high-temperature treatment can be performed to remove functional groups from the surface of the carbon material. Typically, the oxygen content of carbon materials after carbonization and activation is above 3%, and may even reach above 5%. After defunctionalization, the oxygen content may drop below 1%. Simultaneously, the volatile matter decreases, the carbon content increases, and the resistivity increases.

[0146] In some embodiments, the carbon material is further graphitized, including high-temperature graphitization and / or catalytic graphitization, so that the carbon material obtains a certain degree of graphitized structure, with improved carbon layer stacking order and shortened carbon layer spacing.

[0147] According to a third aspect of the present invention, a silicon-carbon composite material is provided, comprising any one of the carbon materials described above and silicon nanoparticles.

[0148] The silicon-carbon composite material provided by the present invention solves the problems of stacking and bonding of silicon-carbon composite materials in the prior art, and can improve the problem of particles of spherical materials detaching from the binder after expansion and contraction, thereby showing higher rate and cycle stability, which is beneficial to improving the energy density, rate and cycle stability of lithium-ion batteries.

[0149] In the present invention, the silicon-carbon composite material comprises silicon-carbon composite material particles, which comprise carbon material and silicon nanoparticles. The surface of the silicon-carbon composite material particles comprises one or more planes, and the total area of ​​the planes accounts for 0.1% to 100% of the surface area of ​​the silicon-carbon composite material particles.

[0150] It should be noted that the carbon material includes carbon material particles with a plane. If the silicon-carbon composite material obtained from the carbon material does not undergo additional physical morphological treatments such as crushing, grading and shaping, it will basically continue the appearance of the carbon material, that is, obtain silicon-carbon composite material particles with a plane.

[0151] When spherical silicon-carbon composite materials are used in lithium-ion batteries, there are problems such as low stacking density, low compaction density and poor adhesion. The presence of an appropriate amount of planes can improve the stacking density, compaction density and adhesion of the composite materials, thereby improving the volume energy density and rate performance.

[0152] In some embodiments, the surface of the silicon-carbon composite material particle includes one or more planes, and the other surfaces have a certain curvature, which may be spherical, cylindrical, conical, arc-shaped, curved, flat, or nearly flat.

[0153] In some embodiments, the planar surfaces of the silicon-carbon composite particles have common edges therebetween.

[0154] In some embodiments, the planar surfaces of the silicon-carbon composite particles do not have common edges.

[0155] In some embodiments, some planes of the silicon-carbon composite material particles have common edges, and some planes do not have common edges.

[0156] In some embodiments, the angles between the planes of the silicon-carbon composite material particles are acute angles, right angles, or obtuse angles.

[0157] In some embodiments, the angles between the planes of the silicon-carbon composite material particles are right angles or obtuse angles.

[0158] In some embodiments, the angles between the planes of the silicon-carbon composite material particles are obtuse angles.

[0159] In some embodiments, the surface of the silicon-carbon composite particle comprises a flat surface.

[0160] In some embodiments, the surface of the silicon-carbon composite particle comprises two planes.

[0161] In some embodiments, the surface of the silicon-carbon composite material particle comprises 2 to 5 planes.

[0162] In some embodiments, the surface of the silicon-carbon composite material particle comprises 2 to 10 planes.

[0163] In some embodiments, the surface of the silicon-carbon composite material particle comprises 10 or more planes.

[0164] In some embodiments, the surface of the silicon-carbon composite material particle comprises 20 or more planes.

[0165] In some embodiments, the planes on the surface of the silicon-carbon composite material particles are of different sizes, and the area ratio of the smallest plane to the largest plane is less than 0.8.

[0166] In some embodiments, the planes on the surface of the silicon-carbon composite material particles are of different sizes, and the area ratio of the smallest plane to the largest plane is less than 0.5.

[0167] In some embodiments, the planes on the surface of the silicon-carbon composite material particles are of different sizes, and the area ratio of the smallest plane to the largest plane is less than 0.2.

[0168] In some embodiments, the planes on the surface of the silicon-carbon composite material particles are of different sizes, and the area ratio of the smallest plane to the largest plane is less than 0.1.

[0169] In some embodiments, the planes on the surface of the silicon-carbon composite material particles are similar in size, and the area ratio of the smallest plane to the largest plane is greater than 0.8.

[0170] In some embodiments, the planes on the surface of the silicon-carbon composite material particles are similar in size, and the area ratio of the smallest plane to the largest plane is greater than 0.9.

[0171] In some embodiments, the planes on the surface of the silicon-carbon composite material particles are similar in size, and the area ratio of the smallest plane to the largest plane is greater than 0.95.

[0172] In some embodiments, the planes on the surface of the silicon-carbon composite material particles are similar in size, and the area ratio of the smallest plane to the largest plane is greater than 0.98.

[0173] In some embodiments, the minimum distance R from the mass center to any point on the surface of the silicon-carbon composite material particle in the silicon-carbon composite material is 2min With the maximum value R 2max The ratio is 0.1 to 0.99.

[0174] It should be noted that when the minimum value R 2min With the maximum value R 2max When the ratio is less than 0.1, the material has large anisotropy, which may cause problems in fluid mechanics, stress, etc. in its application.

[0175] In some embodiments, the ratio R of the minimum to maximum distances from the center of mass of the silicon-carbon composite material particle to the surface point is 2min / R 2max The particle size is 0.1 to 0.3, and there is a certain degree of anisotropy in the particles, which may show a certain degree of advantage in terms of stacking, such as increasing the stacking and compaction density through the presence of graded filling.

[0176] In some embodiments, the ratio R of the minimum to maximum distances from the center of mass of the silicon-carbon composite material particle to the surface point is 2min / R 2max It is 0.3~0.5.

[0177] In some embodiments, the ratio R of the minimum to maximum distances from the center of mass of the silicon-carbon composite material particle to the surface point is 2min / R 2max It is 0.5 to 0.8.

[0178] In some embodiments, the ratio R of the minimum to maximum distances from the center of mass of the silicon-carbon composite material particle to the surface point is 2min / R 2max It is 0.8~0.95.

[0179] In some embodiments, the ratio R of the minimum to maximum distances from the center of mass of the silicon-carbon composite material particle to the surface point is 2min / R 2max When the particle size is 0.95-0.99, the particles are nearly isotropic and their appearance is closer to spherical.

[0180] In some embodiments, the silicon-carbon composite material comprises a vapor-deposited silicon-carbon composite material.

[0181] In some embodiments, a coating layer exists on the surface of the silicon-carbon composite material.

[0182] In some embodiments, the material of the coating layer is selected from at least one of a solid electrolyte, a conductive polymer, a carbonaceous material, a metal, an alloy, a metal oxide, a metal hydroxide, a halogen-containing compound, a nitrogen-containing compound, a phosphorus-containing compound, a boron-containing compound, and a sulfur-containing compound.

[0183] In some embodiments, the material of the coating layer is a carbonaceous material.

[0184] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 0.1 m 2 / g~10m 2 / g.

[0185] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 0.1 m 2 / g~5m 2 / g.

[0186] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 0.1 m 2 / g~2m 2 / g.

[0187] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 0.1 m 2 / g~1m 2 / g.

[0188] In some embodiments, the silicon content of the silicon-carbon composite material is 20% to 80%.

[0189] In some embodiments, the silicon content of the silicon-carbon composite material is 30% to 70%.

[0190] In some embodiments, the silicon content of the silicon-carbon composite material is 40% to 60%.

[0191] In some embodiments, the silicon content of the silicon-carbon composite material is 45% to 65%.

[0192] In some embodiments, the silicon content of the silicon-carbon composite material is 45% to 55%.

[0193] In some embodiments, the silicon content of the silicon-carbon composite material is 55% to 60%.

[0194] In some embodiments, the silicon content of the silicon-carbon composite material is 60% to 65%.

[0195] In some embodiments, the silicon content of the silicon-carbon composite material is 65% to 70%.

[0196] In some embodiments, the silicon-carbon composite material has a particle size distribution, with a median particle size d V50 2μm~200μm.

[0197] Specifically, in some embodiments, the median particle size d of the carbon material is V50 It may be 2 μm to 5 μm, 5 μm to 10 μm, 10 μm to 20 μm, 20 μm to 50 μm, 50 μm to 100 μm, or 100 μm to 200 μm, but is not limited thereto.

[0198] According to a fourth aspect of the present invention, there is provided a method for preparing the above-mentioned silicon-carbon composite material, comprising the following steps:

[0199] A silicon-containing precursor is chemically vapor deposited on a carbon material to obtain a silicon-carbon composite material.

[0200] The preparation method of the silicon-carbon composite material provided by the present invention has a simple process, a high success rate, and is suitable for industrial production.

[0201] In some embodiments, the silicon-containing precursor is selected from one or more of monosilane, disilane, trisilane, halosilane, polysilane, silole and its derivatives, silfluorene and its derivatives.

[0202] In some embodiments, a heteroatom-containing precursor is introduced during the chemical vapor deposition process of a silicon-containing precursor, wherein the heteroatom-containing precursor includes at least one of an oxygen-containing precursor, a carbon-containing precursor, a nitrogen-containing precursor, a phosphorus-containing precursor, a sulfur-containing precursor, or a boron-containing precursor.

[0203] The silicon-containing precursor and the heteroatom-containing precursor are contacted with the carbon material in a manner as desired. For example, in some embodiments, the silicon-containing precursor and the heteroatom-containing precursor are contacted with the carbon material alternately.

[0204] In some embodiments, the silicon-containing precursor and the heteroatom-containing precursor are contacted with the carbon material simultaneously.

[0205] In some embodiments, the silicon-containing precursor and the mixed gas containing the silicon-containing precursor and the heteroatom-containing precursor are contacted with the carbon material alternately.

[0206] In some embodiments, the silicon-containing precursor is continuously in contact with the carbon material, and the heteroatom-containing precursor is intermittently introduced during this process.

[0207] According to a fifth aspect of the present invention, a negative electrode is provided, wherein the negative electrode active material used in the negative electrode includes the silicon-carbon composite material described above.

[0208] The negative electrode provided by the present invention is beneficial to improving the energy density, rate and cycle stability of the battery.

[0209] In the present invention, the obtained silicon-carbon composite material is used as the negative electrode active material, stirred and evenly mixed with the conductive agent Super P, the binder and the solvent deionized water in a certain mass ratio, and then evenly coated on the negative electrode current collector and dried to obtain the negative electrode.

[0210] According to a sixth aspect of the present invention, a lithium-ion battery is provided, wherein the negative electrode of the lithium-ion battery comprises the silicon-carbon composite material described above.

[0211] The lithium ion battery provided by the present invention has good rate capability and good cycle stability.

[0212] In some embodiments, the positive electrode and the negative electrode are separated by an isolation membrane to form a battery core, which is then encapsulated in an aluminum-plastic bag or aluminum-plastic shell. An electrolyte with a corresponding capacity is injected into the aluminum-plastic bag or aluminum-plastic shell, and the battery is obtained after vacuum sealing.

[0213] In some embodiments, the positive electrode may be selected from one of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and a ternary material, and the isolation membrane may be selected from one of polyethylene and polypropylene.

[0214] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples were prepared according to existing methods or directly purchased from the market.

[0215] Example 1

[0216] This embodiment provides a carbon material, and the preparation method thereof is as follows:

[0217] Step S1: using formaldehyde and phenol as raw materials, preparing a linear phenolic resin prepolymer under the catalysis of hydrochloric acid;

[0218] Step S2: adding the linear phenolic resin prepolymer obtained in step S1 to an aqueous solution of polyvinyl alcohol and polylactic acid flakes, and stirring at high speed to form a suspension of tiny droplets;

[0219] The mass ratio of the polylactic acid sheet to the linear phenolic resin prepolymer is 0.1 / 100;

[0220] Step S3: adding hexamethylenetetramine to the suspension obtained in step S2, heating to 95° C., and stirring until a spherical solidified particle slurry is formed;

[0221] The mass ratio of hexamethylenetetramine to linear phenolic resin prepolymer is 10 / 100;

[0222] Step S4: The slurry obtained in step S4 is filtered, washed, dried, and classified to obtain d V50 Spherical resin particles with a diameter of 8.5 μm and containing 0.1 to 0.5% flat surface;

[0223] Step S5: carbonizing the resin particles obtained in step S5 at 800° C. to obtain spherical resin carbon material particles containing 0.1% to 0.5% of flat surfaces;

[0224] Step S6: activating the spherical resin carbon material particles obtained in step S5 at 900° C. in an N 2 -50% H 2 O atmosphere for 1 h to obtain a carbon material.

[0225] The obtained carbon material contains carbon material particles, and the carbon material particles contain one or more planes, the area of ​​which accounts for 0.1% to 0.5% of the surface area of ​​the carbon material particles; the minimum value R of the distance from the mass center of the carbon material particle to any point on its surface 1min With the maximum value R 1max The ratio is 0.99.

[0226] The pore volume of the obtained carbon material is 0.79 cm 3 / g, specific surface area 1718m 2 / g, and the mesopore ratio is 10.7%.

[0227] Example 2

[0228] This embodiment provides a carbon material, and its preparation method is different from that of Example 1 in that:

[0229] In step S2: the mass ratio of the polylactic acid sheet to the linear phenolic resin prepolymer is 5 / 100;

[0230] In step S4: after classification, d V50 Spherical resin particles with a diameter of 8.2 μm and containing 10% to 15% flat surfaces;

[0231] After the same carbonization and activation as in Example 1, a carbon material was obtained.

[0232] The obtained carbon material contains carbon material particles, and the carbon material particles contain one or more planes, the area of ​​which accounts for 10% to 15% of the surface area of ​​the carbon material particles; the minimum value R of the distance from the mass center of the carbon material particle to any point on its surface 1min With the maximum value R 1max The ratio is 0.8~0.99.

[0233] The pore volume of the obtained carbon material is 0.82 cm 3 / g, specific surface area 1779m 2 / g, and the mesopore ratio is 10.2%.

[0234] Example 3

[0235] This embodiment provides a carbon material, and its preparation method is different from that of Example 1 in that:

[0236] In step S2: the mass ratio of the polylactic acid sheet to the linear phenolic resin prepolymer is 10 / 100;

[0237] In step S4: after classification, d V50 Spherical resin particles with a diameter of 8.5 μm and containing 20% ​​to 50% flat surfaces;

[0238] After the carbonization step S5 is performed in the same manner as in Example 1, a carbon material is obtained.

[0239] The obtained carbon material contains carbon material particles, and the carbon material particles contain one or more planes, and the area of ​​the plane accounts for 20% to 50% of the surface area of ​​the carbon material particles; the minimum value R of the distance from the mass center of the carbon material particle to any point on its surface 1min With the maximum value R 1max The ratio is 0.8~0.99.

[0240] The pore volume of the obtained carbon material is 0.18 cm 3 / g, specific surface area 427m 2 / g, and the mesopore ratio is 8.2%.

[0241] Example 4

[0242] This embodiment provides a carbon material, and its preparation method is different from that of Example 1 in that:

[0243] In step S2: the mass ratio of the single-layer graphene oxide sheet to the linear phenolic resin prepolymer is 20 / 100;

[0244] In step S4: after classification, d V50 Spherical resin particles with a diameter of 8.7 μm and containing 50% to 80% flat surfaces;

[0245] After the same carbonization and activation as in Example 1, a carbon material was obtained.

[0246] The obtained carbon material contains carbon material particles, and the carbon material particles contain one or more planes, the area of ​​which accounts for 50% to 80% of the surface area of ​​the carbon material particles; the minimum value R of the distance from the mass center of the carbon material particle to any point on its surface 1min With the maximum value R 1max The ratio is 0.6~0.99.

[0247] Figure 1 This is the SEM image of the carbon material of Example 4.

[0248] The pore volume of the obtained carbon material is 0.85 cm 3 / g, specific surface area 1878m 2 / g, and the mesopore ratio is 9.5%.

[0249] Example 5

[0250] This embodiment provides a carbon material, and its preparation method is different from that of Example 2 in that:

[0251] In step S6: the activation time is extended to 3 hours to obtain a carbon material.

[0252] The obtained carbon material contains carbon material particles, and the carbon material particles contain one or more planes, the area of ​​which accounts for 10% to 15% of the surface area of ​​the carbon material particles; the minimum value R of the distance from the mass center of the carbon material particle to any point on its surface 1min With the maximum value R 1max The ratio is 0.8~0.99.

[0253] The pore volume of the obtained carbon material is 1.25 cm 3 / g, specific surface area 2289m 2 / g, and the mesopore ratio is 20.1%.

[0254] Example 6

[0255] This embodiment provides a carbon material, and the preparation method thereof is as follows:

[0256] Step S1: Add linear phenolic resin particles of a certain size into an aqueous solution of polyvinyl alcohol and urotropine, solidify at 95°C, separate the solid and liquid, and dry to obtain particles with a diameter of d V50 The phenolic resin balls are 100 μm and 1.5 mm in diameter.

[0257] Step S2: crush and classify the phenolic resin balls obtained in step S1 to obtain d V50 Spherical resin particles with a diameter of 9.1 μm and containing 50% to 100% flat surfaces;

[0258] Step S3: carbonizing the resin particles obtained in step S2 at 800° C. to obtain spherical resin carbon material particles containing 50% to 100% flat surfaces;

[0259] Step S4: activating the spherical resin carbon material particles obtained in step S3 at 900° C. in an N 2 -50% H 2 O atmosphere for 1 h to obtain a carbon material.

[0260] The obtained carbon material contains carbon material particles, and the carbon material particles contain multiple planes, the area of ​​the planes accounts for 50% to 100% of the surface area of ​​the carbon material particles; the minimum value R of the distance from the mass center of the carbon material particle to any point on its surface 1min With the maximum value R 1max The ratio is 0.1 to 0.99.

[0261] The pore volume of the obtained carbon material is 0.85 cm 3 / g, specific surface area 1859m2 / g, and the mesopore ratio is 11.5%.

[0262] Example 7

[0263] This embodiment provides a carbon material, and its preparation method is different from that of Example 2 in that:

[0264] In step S2: replacing the polylactic acid sheet with a graphene submicron sheet;

[0265] In step S4: after classification, d V50 Spherical resin particles with a diameter of 8.5 μm and containing 10% to 20% flat surfaces;

[0266] After the same carbonization and activation as in Example 1, a carbon material was obtained.

[0267] The obtained carbon material contains carbon material particles, and the carbon material particles contain one or more planes, the area of ​​the plane accounts for 10% to 20% of the surface area of ​​the carbon material particles, and the minimum value R of the distance from the mass center of the carbon material particle to any point on its surface is 1min With the maximum value R 1max The ratio is 0.8~0.99.

[0268] The pore volume of the obtained carbon material is 0.83 cm 3 / g, specific surface area 1815m 2 / g, and the mesopore ratio is 9.8%.

[0269] Example 8

[0270] This embodiment provides a carbon material, and the preparation method thereof is as follows:

[0271] Step S1: mixing sucrose and spherical SBA-15 and carbonizing them at 800°C to obtain a carbon-SiO2 composite material;

[0272] Step S2: The carbon-SiO2 composite material obtained in step S1 is washed with HF to remove SiO2, and the filter cake is compacted with a filter press during the solid-liquid separation process, and then crushed and graded after drying to obtain a carbon material.

[0273] The obtained carbon material contains carbon material particles, and the carbon material particles contain one or more planes, the area of ​​the plane accounts for 40% to 70% of the surface area of ​​the carbon material particles, and the minimum value R of the distance from the mass center of the carbon material particle to any point on its surface is 1min With the maximum value R 1max The ratio is 0.2 to 0.99.

[0274] The pore volume of the obtained carbon material is 0.89 cm 3 / g, specific surface area 952m 2 / g, and mesopores account for 98.2%.

[0275] Example 9

[0276] This embodiment provides a carbon material, and the preparation method thereof is as follows:

[0277] Step S1: dissolving a thermoplastic resin in ethanol and mixing it with an aqueous solution of polyvinyl alcohol, poloxamer and hexamethylenetetramine, adding polystyrene flakes, and reacting at 95° C. for 4 hours to obtain a slurry containing resin particles;

[0278] The mass ratio of polyvinyl alcohol, poloxamer, hexamethylenetetramine, polystyrene flakes and resin is 10:50:10:5:100;

[0279] Step S2: The slurry obtained in step S1 is subjected to solvent evaporation, washing, drying, and classification to obtain d V50 Spherical resin particles with a diameter of 8.5 μm and containing 10% to 20% flat surfaces;

[0280] Step S3: carbonizing the spherical resin particles obtained in step S2 at 800° C. to obtain a carbon material.

[0281] The obtained carbon material contains carbon material particles, and the carbon material particles contain one or more planes, the area of ​​the plane accounts for 10% to 20% of the surface area of ​​the carbon material particles, and the minimum value R of the distance from the mass center of the carbon material particle to any point on its surface is 1min With the maximum value R 1max The ratio is 0.8~0.99.

[0282] The pore volume of the obtained carbon material is 0.97 cm 3 / g, specific surface area 1533m 2 / g, and mesopores account for 61.5%.

[0283] Example 10

[0284] This embodiment provides a carbon material, and its preparation method is different from that of Example 9 in that:

[0285] The carbon material obtained in step S3 of Example 9 was post-treated:

[0286] Step S4: The carbon material obtained in step S3 was mixed with KOH at a mass ratio of 1:1, and treated at 900°C in N2 for 2h to remove excess K. + , to obtain carbon materials.

[0287] The obtained carbon material contains carbon material particles, and the carbon material particles contain one or more planes, the area of ​​the plane accounts for 10% to 20% of the surface area of ​​the carbon material particles, and the minimum value R of the distance from the mass center of the carbon material particle to any point on its surface is1min With the maximum value R 1max The ratio is 0.8~0.99.

[0288] The pore volume of the obtained carbon material is 1.80 cm 3 / g, specific surface area 1533m 2 / g, and mesopores account for 61.5%.

[0289] Comparative Example 1

[0290] This comparative example provides a carbon material, and its preparation method is as follows:

[0291] Step S1: using formaldehyde and phenol as raw materials, preparing a linear phenolic resin prepolymer under the catalysis of hydrochloric acid;

[0292] Step S2: adding the linear phenolic resin prepolymer obtained in step S1 to an aqueous solution of polyvinyl alcohol and hexamethylenetetramine, stirring at high speed to form a suspension of tiny droplets, heating to 95° C., and stirring until a slurry of spherical solidified particles is formed;

[0293] The mass ratio of hexamethylenetetramine to linear phenolic resin prepolymer is 10 / 100;

[0294] Step S3: filtering, washing, and drying the slurry obtained in step S2 to obtain spherical resin particles;

[0295] Step S4: carbonizing the resin particles obtained in step S3 at 800° C. to obtain spherical resin carbon material particles;

[0296] Step S5: Activate the spherical resin carbon material particles obtained in step S4 at 900° C. in an N 2 -50% H 2 O atmosphere for 1 hour to obtain a carbon material.

[0297] The obtained carbon material contains carbon material particles, and the carbon material particles are spherical carbon material particles without flat surfaces.

[0298] The pore volume of the obtained carbon material is 0.81 cm 3 / g, specific surface area 1738m 2 / g, and the mesopore ratio is 10.5%.

[0299] Example 11

[0300] This embodiment provides a silicon-carbon composite material, and the preparation method thereof is as follows:

[0301] Step S1: using the carbon material provided in Example 1 as the carbon material of the silicon-carbon composite material;

[0302] Step S2: Place the carbon material of step S1 in an atmosphere furnace, heat it from room temperature to 600°C at 2°C / min in a N2 atmosphere, maintain it at 600°C for 10 hours in a 20% SiH4-N2 atmosphere to deposit silicon, and then cool it naturally under N2 protection to obtain a silicon-carbon composite material.

[0303] The obtained silicon-carbon composite material comprises silicon-carbon composite material particles, the silicon-carbon composite material particles comprise one or more planes, the area of ​​the planes accounts for 0.1% to 0.5% of the surface area of ​​the silicon-carbon composite material particles, and the ratio R of the minimum value to the maximum value of the distance from the mass center of the silicon-carbon composite material particles to the surface point is 2min / R 2max It is 0.8~0.99.

[0304] Example 12

[0305] This embodiment provides a silicon-carbon composite material, and the preparation method thereof is as follows:

[0306] Step S1: using the carbon material provided in Example 2 as the carbon material of the silicon-carbon composite material;

[0307] Step S2: Same as step S2 in Example 11.

[0308] Example 13

[0309] This embodiment provides a silicon-carbon composite material, and the preparation method thereof is as follows:

[0310] Step S1: The carbon material provided in Example 3 is used as the carbon material of the silicon-carbon composite material; Step S2: The difference from Step S2 in Example 11 is that the deposition time is changed to 3 hours.

[0311] Example 14

[0312] This embodiment provides a silicon-carbon composite material, and the preparation method thereof is as follows:

[0313] Step S1: The carbon material provided in Example 4 is used as the carbon material of the silicon-carbon composite material; Step S2: The difference from Step S2 in Example 11 is that the deposition time is changed to 3 hours.

[0314] Example 15

[0315] This embodiment provides a silicon-carbon composite material, and the preparation method thereof is as follows:

[0316] Step S1: The carbon material provided in Example 5 is used as the carbon material of the silicon-carbon composite material; Step S2: The difference from Step S2 in Example 11 is that the deposition time is changed to 11 hours.

[0317] Example 16

[0318] This embodiment provides a silicon-carbon composite material, and the preparation method thereof is as follows:

[0319] In step S1, the carbon material provided in Example 6 is used as the carbon material of the silicon-carbon composite material; in step S2, the difference from step S2 in Example 11 is that the deposition time is changed to 20 hours.

[0320] Example 17

[0321] This embodiment provides a silicon-carbon composite material, and the preparation method thereof is as follows:

[0322] Step S1: using the carbon material provided in Example 7 as the carbon material of the silicon-carbon composite material; Step S2: the same as Step S2 in Example 14.

[0323] Example 18

[0324] This embodiment provides a silicon-carbon composite material, and the preparation method thereof is as follows:

[0325] Step S1: using the carbon material provided in Example 8 as the carbon material of the silicon-carbon composite material; Step S2: the same as Step S2 in Example 11.

[0326] Example 19

[0327] This embodiment provides a silicon-carbon composite material, and the preparation method thereof is as follows:

[0328] Step S1: using the carbon material provided in Example 9 as the carbon material of the silicon-carbon composite material;

[0329] Step S2: Place the carbon material of step S1 in an atmosphere furnace, heat it from room temperature to 600°C at a rate of 2°C / min in an N2 atmosphere, maintain it at 600°C for 5 hours in a 20% SiH4-N2 atmosphere to carry out silicon deposition, then stop introducing SiH4 and only introduce N2. After cooling to 200°C, change it to 0.01% O2-N2 and maintain it at 200°C for 0.2 hours to carry out oxygen atom deposition. Silicon deposition and oxygen atom deposition are carried out on the carbon material in turn, and the cycle is repeated 3 times. The silicon-carbon composite material is obtained by naturally cooling under the protection of N2.

[0330] Example 20

[0331] This embodiment provides a silicon-carbon composite material, and the preparation method thereof is as follows:

[0332] Step S1: using the carbon material provided in Example 10 as the carbon material of the silicon-carbon composite material;

[0333] Step S2: The difference from step S2 of Example 19 is that silicon deposition and oxygen atom deposition are sequentially performed on the carbon material, and the cycle is repeated 6 times.

[0334] Comparative Example 2

[0335] This comparative example provides a silicon-carbon composite material, the preparation method of which is as follows:

[0336] Step S1: using the carbon material provided in Comparative Example 1 as the carbon material of the silicon-carbon composite material;

[0337] Step S2: the same as step S2 in Example 11.

[0338] Test Example 1

[0339] N2 static adsorption: N2 static adsorption test was performed on the carbon materials obtained in Examples 1-10 and Comparative Example 1, and the silicon-carbon composite materials obtained in Examples 11-20 and Comparative Example 2, and the specific surface area was calculated based on multi-point BET; the pore volume was calculated based on the adsorption amount at the maximum partial pressure (p / p0>0.99); the DFT method was used to fit the N2 adsorption-desorption isotherm, and the pore distribution of the first, second, and third channels of the porous matrix was analyzed, and the content information of the pore size at each level was obtained. The results have been presented in each embodiment.

[0340] Test Example 2

[0341] Plane ratio: Observe the material using SEM, select 50 particles, measure the particle diameter, the number of planes on the particles, and the plane diameter or side length. For each particle, calculate its plane ratio X:

[0342]

[0343] Where n is the total number of planes on the particle;

[0344] A i is the area of ​​the i-th plane on the particle, which can be calculated by the plane diameter or side length;

[0345] A is the total surface area of ​​the particle, which can be calculated from the particle diameter;

[0346] Considering that the electron microscope can only observe the upper half of the particle, the plane ratio on the particle is multiplied by a factor of 2.

[0347] Test Example 3

[0348] The minimum distance R from the mass center of a carbon material particle to any point on its surface 1min With the maximum value R 1max The ratio R 1min / R 1max : Observe the material by SEM, select 50 particles, measure the particle diameter, the number of planes on the particles and the plane diameter or side length, and calculate the R 1min / R 1max ;

[0349] We can use a sphere as a model and take a circular cross section containing a certain plane diameter as the chord of the circle. Based on the chord and diameter, we can calculate the distance range between the center of the circle and each point on the chord. The minimum value is the distance from the center of the circle to the chord, and the maximum value is the diameter of the circle. We can do this analysis on all planes on the particle and find the minimum value, which is R. 1min ; R 1max is the particle diameter.

[0350] The minimum distance R from the mass center of the silicon-carbon composite particle to any point on its surface in the silicon-carbon composite material 2min With the maximum value R 2max The ratio R 2min / R 2max The acquisition and R 1min / R 1max same.

[0351] Test Example 4

[0352] Silicon content test: The silicon content is determined using the loss on ignition method. Place mass m1 of silicon-carbon composite material in a muffle furnace, heat it to 1200°C in static air, and maintain it for 2 hours to obtain mass m2. Silicon content (Si%) = m2 / m1 * 100%.

[0353] Test Example 5

[0354] Electrode, half-cell preparation and electrochemical performance testing:

[0355] The silicon-carbon composite materials provided in the above examples and comparative examples were used as negative electrode active materials to prepare negative electrode sheets. The negative electrode sheets were prepared using conventional methods to prepare CR2032 button batteries, and the batteries were tested for electrical properties. The results are shown in Table 1.

[0356] The specific test method is:

[0357] Half-cell assembly: CR2032 button cells were assembled in a glove box with a lithium metal sheet as the counter electrode, a polypropylene microporous membrane as the separator, and an electrolyte consisting of LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC = 1:1), with a LiPF6 concentration of 1 mol / L.

[0358] Use the LAND battery testing system to perform charge and discharge tests on the battery;

[0359] Cyclic gram capacity and first efficiency test: After the CR2032 battery is left uncharged for 6 hours, it is discharged at 0.05C to 0.005V, and then discharged at 0.01C to 0.005V; after standing for 5 minutes, it is charged to 1.5V at a constant current of 0.05C; the 0.8V first delithiation gram capacity is the 0.8V gram capacity (or mass specific capacity) of the electrode material, and the ratio of the 0.8V first delithiation capacity to the first lithium insertion capacity is the 0.8V first coulombic efficiency of the battery.

[0360] Rate test method:

[0361] After the button cell cycle capacity and initial efficiency test, the battery was subjected to the following rate charge and discharge cycles: (1) 0.1C discharge to 0.005V, then 0.1C charge to 1.5V, three cycles, recording the discharge capacity and charge capacity each time; (2) 0.5C discharge to 0.005V, then 0.5C charge to 1.5V, three cycles, recording the discharge capacity and charge capacity each time; (3) 1C discharge to 0.005V, then 1C charge to 1.5V, three cycles, recording the discharge capacity and charge capacity each time. The 1C / 0.1C rate is calculated by dividing the third 1C, 1.5V charge capacity by the third 0.1C, 1.5V charge capacity.

[0362] Test Example 6

[0363] Full battery preparation and electrochemical performance testing:

[0364] Using the silicon-carbon composite materials provided in the above examples and comparative examples as the negative electrode active material, the pole pieces containing the negative electrode active material were prepared using conventional methods for soft-pack batteries and subjected to electrical performance testing. The soft-pack batteries were prepared in a dehumidified room with a dew point of -45°C. The batteries were subjected to charge and discharge cycle testing using a LANBTS battery testing system. The results are shown in Table 1. The specific testing method is as follows:

[0365] (1) Preparation of positive electrode sheet: The positive electrode active material LiCoO2, the conductive agent SuperP, the binder PVDF and the solvent NMP were stirred and mixed in a mass ratio of 92:3:5:150, and then evenly coated on the positive electrode current collector, and then dried at 80°C to obtain the positive electrode sheet.

[0366] (2) Preparation of negative electrode sheet: The negative electrode active material, conductive agent SuperP, binder polyacrylic acid and solvent deionized water were stirred and mixed in a mass ratio of 95:1:4:120, and then evenly coated on the negative electrode current collector, and then dried at 100°C to obtain the negative electrode sheet.

[0367] (3) The positive and negative electrodes are stacked in a square shape and separated by a polypropylene separator to form a battery core. The core is then encapsulated in an aluminum-plastic bag. An electrolyte of the corresponding capacity is injected into the bag and vacuum-sealed to obtain a soft-pack battery. The electrolyte is a mixture of LiPF6, EC, and DEC, where the LiPF6 concentration is 1 mol / L and the volume ratio of EC to DEC is 1:1.

[0368] (4) Formation: After filling and sealing, the battery begins to form. It is placed in a 25°C constant temperature box for 12 hours, then charged to 3.3V at 0.02C constant current, allowed to stand for 30 minutes, charged to 3.8V at 0.025C constant current, allowed to stand for 10 minutes, and charged to 4.2V at 0.33C constant current. The formed battery is vacuumed and the air bag is sheared, and then the capacity is divided. It is charged to 4.45V at 0.33C constant current, allowed to stand for 10 minutes, discharged to 3V at 1C constant current, allowed to stand for 10 minutes, and discharged to 3V at 0.33C constant current. The capacity division is completed. The ratio of the discharge capacity divided by the charge capacity in the soft pack battery formation is the battery's initial efficiency.

[0369] (5) 25℃ cycle test: Place the battery in a 25℃ constant temperature box, charge it to 4.45V at a constant current of 1C, and then charge it to 0.1C at a constant voltage of 4.45V; after standing for 10 minutes, discharge it to 3.0V at a constant current of 1C, and stand it for 10 minutes. Repeat the above charging and discharging steps until the discharge capacity is lower than 80% of the discharge capacity of the first cycle. The number of cycles obtained at this time is the cycle life of the soft-pack battery; record the capacity retention rate after 100 cycles.

[0370] The test results of the silicon-carbon composite materials of Examples 11-20 and the silicon-carbon composite material of Comparative Example 2 are shown in Table 1.

[0371] Table 1 Physicochemical properties and electrochemical performance of silicon-carbon composites

[0372]

[0373] It can be seen that when a material with a plane is introduced during the preparation of the carbon material, the resulting carbon material contains one or more carbon material particles with the total area of ​​the planes accounting for 0.1% to 100% of the surface area of ​​the carbon material particles. When a flat material such as polylactic acid flakes is introduced during the preparation of spherical resin particles, the proportion of the planes in the particles increases with the increase in the amount of polylactic acid flakes used. When no material with a plane is introduced during the preparation process, the resulting carbon material is spherical and does not contain planes. Different carbonization and activation methods of carbon materials can produce different pore volumes and pore distributions.

[0374] Examples 11-20 utilize the carbon materials provided in Examples 1-10 for silicon deposition to obtain a silicon-carbon composite material. The resulting silicon-carbon composite material retains the appearance and morphology of the carbon material and has one or more flat surfaces, the total area of ​​which accounts for 0.1% to 100% of the surface area of ​​the material particles. Adjusting the silicon deposition time according to the pore volume of the carbon material to avoid local or surface silicon enrichment can regulate the silicon content of the silicon-carbon composite material, thereby achieving adjustable specific capacity of the negative electrode material within a specific range.

[0375] Due to the presence of planes in the silicon-carbon composite materials in Examples 11 to 20, when used in lithium-ion batteries, there will be no obvious debonding after lithium insertion expansion and delithiation shrinkage, so the rate and cycle stability are significantly improved compared with Comparative Example 2.

[0376] The 1C / 0.1C ratio of the silicon-carbon composite material in Comparative Example 2 is only 35.4%, while Example 12 contains a 10% to 15% planar silicon-carbon composite material, and its ratio reaches 45.9%. Example 14 contains a 50% to 80% planar silicon-carbon composite material, and its ratio reaches 60.1%.

[0377] The capacity retention rate of the silicon-carbon composite material at 25°C and 100 cycles in Comparative Example 2 is only 96.4%. In Examples 11 to 20, the capacity retention rate is increased to over 97% due to the presence of the plane.

[0378] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A carbon material, characterized in that including carbon material particles; The carbon material particles have at least one plane on their surface; Based on the surface area of ​​the carbon material particles, the total area of ​​the plane accounts for 0.1% to 100%.

2. The carbon material according to claim 1, characterized in that The minimum value R of the distance from the mass center of the carbon material particle to any point on its surface 1min With the maximum value R 1max The ratio is 0.1 to 0.

99.

3. The carbon material according to claim 1, characterized in that The carbon material satisfies at least one of the following characteristics: (a) The specific surface area of ​​the carbon material is 200 m 2 / g~3000m 2 / g; (b) The pore volume of the carbon material is 0.10 cm 3 / g~1.80cm 3 / g; (c) The average pore size of the carbon material is 1.6 nm to 5.0 nm; (d) The mesopore ratio of the carbon material is 5% to 100%.

4. A method for preparing the carbon material according to any one of claims 1 to 3, characterized in that: The following steps are involved: The carbon precursor is carbonized to obtain the carbon material.

5. The preparation method according to claim 4, characterized in that The carbon precursor satisfies at least one of the following conditions: (a) The carbon precursor is prepared from a carbon source, wherein the carbon source comprises at least one of a polymer or a monomer thereof, a biomass material or an extract thereof; (b) the carbon precursor comprises spherical particles or spherical-like particles; (c) the carbon precursor comprises particles having planar surfaces; (d) the carbon precursor is prepared by including a material having a planar surface; (e) The carbon precursor is prepared by carbon source pretreatment, wherein the pretreatment includes at least one of mixing, extrusion, curing, pre-oxidation, hardening, crushing and pulverization.

6. The preparation method according to claim 4, characterized in that The carbonization step also includes a post-processing step; Preferably, the post-treatment includes at least one of crushing, grading, pore expansion, activation, shaping, defunctionalization and graphitization.

7. A silicon-carbon composite material, characterized in that: The silicon-carbon composite material comprises silicon-carbon composite material particles; The silicon-carbon composite material particles comprise carbon material and silicon nanoparticles; The carbon material includes the carbon material according to any one of claims 1 to 3 and the carbon material obtained by the preparation method according to any one of claims 4 to 6; The surface of the silicon-carbon composite material particle contains at least one plane, and the total area of ​​the plane accounts for 0.1% to 100% of the surface area of ​​the silicon-carbon composite material particle.

8. The silicon-carbon composite material according to claim 7, characterized in that: The minimum value R of the distance from the mass center of the silicon-carbon composite material particle to any point on its surface 2min With the maximum value R 2max The ratio is 0.1 to 0.

99.

9. A method for preparing the silicon-carbon composite material according to claim 7 or 8, characterized in that: The following steps are involved: Chemical vapor deposition of a silicon-containing precursor on the carbon material to obtain the silicon-carbon composite material; Preferably, the silicon-containing precursor comprises at least one of monosilane, disilane, trisilane, halosilane, polysilane, silole and its derivatives, silanol and its derivatives; Preferably, a coating layer exists on the surface of the silicon-carbon composite material.

10. A negative electrode, characterized in that: The negative electrode active material used in the negative electrode includes the silicon-carbon composite material according to claim 7 or 8 and the silicon-carbon composite material obtained by the preparation method according to claim 9.

11. A lithium-ion battery, characterized in that: The negative electrode of the lithium-ion battery comprises the silicon-carbon composite material according to claim 7 or 8 and the silicon-carbon composite material obtained by the preparation method according to claim 9.

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