Carbon-silicon composites with customized cavities, methods for preparing same and uses thereof

Abstract

A carbon-silicon composite with customized cavities, its preparation method and use are disclosed. The carbon-silicon composite with customized cavities includes a core structure and a coating layer of third phase carbon covering the core structure, the core structure being a structure formed by removing pore-forming particles from a first intermediate product particle, and having a customized cavity formed by removing the pore-forming particles, the first intermediate product particle being a composite particle composed of silicon particles, the pore-forming particles, first phase carbon and second phase carbon, the first phase carbon being a carbon nanomaterial having a mesh structure, the second phase carbon being a carbon material derived from an organic compound, and the third phase carbon being a carbon material converted from tar and / or pitch. The carbon-silicon composite with customized cavities according to the present invention can not only mitigate the volume expansion effect of silicon particles, but also has a more stable structure, maximizing the volumetric capacity and energy density while effectively improving cycle stability.

Description

[Technical field]

[0001] The present application belongs to the technical field of negative electrode materials for lithium ion batteries, and relates to carbon-silicon composites, their preparation methods and uses, in particular to customized hollow carbon-silicon composites, their preparation methods and uses. [Background technology]

[0002] Silicon has a very high charge-discharge specific capacity and is expected to be a negative electrode active material for lithium-ion batteries that can replace graphite. However, silicon undergoes a large volume change during the charge-discharge process, which causes mechanical stress, resulting in crushing of the active material, structural collapse, and peeling between the material and the current collector, resulting in rapid capacity decay and deterioration of cycle performance. In addition, due to this volume expansion effect, it is difficult for silicon to form a stable solid electrolyte interface film in the electrolyte, which results in a decrease in charge-discharge efficiency and an accelerated decrease in cycle performance. By nanostructuring silicon materials and combining them with carbon (nano)materials to form composite materials, particularly silicon-carbon core-shell composite structures with internal cavities (e.g., the Yörg-eggshell structure (Liu, N. et al. A pomegranate-inspired nanoscale design for large-volume-change lithium battery anodes. Nature Nanotechnology 2014, 9, 187)), it is possible to simultaneously solve to some extent the problems of structural and interfacial instability caused by the volume expansion effect of silicon during the charge and discharge process, and improve the charge and discharge cycle performance. Summary of the Invention [Problem to be solved by the invention]

[0003] However, in most cases, traditional composite methods rely heavily on inert auxiliary materials with high content, which greatly reduces the relative content of silicon and the gravimetric capacity of the material. In addition, traditional composite methods often fail to achieve uniform and precise formation of cavities within particles. In normal cavity formation structures (e.g., silica layers, silica particles, etc.), the formed cavities may be too large, which impairs the volumetric capacity and volumetric energy density, or the formed cavities may be too small, which leaves behind a volume effect and leads to a decrease in cycle stability. In addition, in traditional composite structures, the formation of cavities always results in unstable "point" or inefficient "line" contact between the silicon phase and the carbon phase. In addition, the preparation of such composite materials relies on highly hazardous silicon source gases such as silane, expensive structured nanosilicon, highly corrosive chemicals such as hydrofluoric acid, and complex processes with high energy consumption. As described above, the material structure and preparation method greatly limit the performance and practical application of such materials. [Means for solving the problem]

[0004] The present invention aims to overcome the above-mentioned shortcomings in the prior art and provide a carbon-silicon composite with customized cavities, its preparation method and use. The customized cavities and the integrated three-phase carbon coating structure with different hardness gradients from "soft" to "hard" from the inside to the outside can not only mitigate the volume expansion effect of silicon particles, but also make the structure more stable, maximize the volume capacity and energy density, and effectively improve the cycle stability.

[0005] In order to achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a carbon-silicon composite with customized cavities, the carbon-silicon composite with customized cavities comprising a core structure and a coating layer of third phase carbon coating the core structure, the core structure being a structure formed by removing pore-forming agent particles from a first intermediate product particle, the core structure having customized cavities formed by removing the pore-forming agent particles, the first intermediate product particle being a composite particle made of silicon particles, the pore-forming agent particles, first phase carbon, and second phase carbon, the first phase carbon being a carbon nanomaterial having a network structure, the second phase carbon being a carbon material derived from an organic compound, and the third phase carbon being a carbon material converted from tar and / or pitch.

[0006] In a second aspect, the present invention provides a method for preparing the carbon-silicon composite material with customized cavities, which includes the steps of dispersing silicon particles, first-phase carbon, which is a carbon nanomaterial having a network structure, pore-forming agent particles, which are water-soluble salts, and an organic compound in a solvent to obtain a precursor solution, spray-drying the precursor solution to obtain precursor particles, which are mixture particles consisting of the silicon particles, the first-phase carbon, the pore-forming agent particles, and the organic compound, performing a first heat treatment on the precursor particles in a non-oxidizing atmosphere to convert the organic compound into a carbon substance to form second-phase carbon and obtain first intermediate product particles, and melting the first intermediate product particles. and coating the second intermediate product particles with tar and / or pitch in a state similar to that of the first intermediate product particles to obtain second intermediate product particles; subjecting the second intermediate product particles to a second heat treatment in a non-oxidizing atmosphere to convert the tar and / or pitch into a carbonaceous material and form a coating layer of third phase carbon to obtain third intermediate product particles; and removing the pore-forming agent particles from the third intermediate product particles using water to obtain the carbon-silicon composite with customized pores.

[0007] In a third aspect, the present invention provides the use of the customized void carbon-silicon composite as defined above or the customized void carbon-silicon composite prepared by the preparation method as defined above in an anode active material, an anode, an electrochemical energy storage device or an electrochemical energy storage system. Effect of the Invention

[0008] By implementing embodiments of the present invention, the following beneficial effects can be obtained.

[0009] (1) The present invention can form precisely customized cavities by using pore-forming particles. On the one hand, the cavities can provide a buffer space for the expansion of silicon particles, and avoid the problems of structural collapse and interface instability. On the other hand, the formation of custom cavities by pore-forming agents can form appropriate cavities according to the expansion volume of silicon particles, so as to avoid the cavities being too large or too small. If the cavities are too small, there is a risk of structural collapse and interface instability, and if they are too large, the volumetric capacity and volumetric energy density will be impaired.

[0010] (2) The present invention adopts continuous three-phase carbon made of different materials, and in the interior, the silicon particles are coated with a flexible carbon nanomaterial having a mesh structure, which can better absorb the expansion force of the silicon particles and maintain the stability of the structure. In the outermost layer, the coating layer produced by high-temperature carbonization of tar or pitch has excellent heat resistance, acid and alkali resistance, and impact resistance, and the structure is more stable. In the middle part, the carbon material derived from an organic compound plays the role of a bridge that bonds the first phase carbon and the third phase carbon. Therefore, the carbon structure forms a gradient-type integrated carbon structure with different hardness from "soft" to "hard" from the inside to the outside, which can provide a continuous carbonaceous electron transport channel, making the particle structure more stable, maximizing the volume capacity and energy density while effectively improving the cycle stability, and contributing to its use as a negative electrode active material in lithium-ion batteries.

[0011] The carbon-silicon composite material according to the present invention is suitable as an electrode active material for lithium-ion batteries that are restricted by volume expansion, and silicon-based batteries prepared therewith have excellent charge / discharge volumetric capacity and cycle stability.

[0012] The preparation method according to the present invention has low cost, simple process, safety, low energy consumption, is suitable for industrialized equipment, and is suitable for mass production. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a schematic structural diagram of a carbon-silicon composite material with customized cavities according to a specific embodiment of the present invention, and is a partially enlarged view of the interface structure of a single particle in the carbon-silicon composite material with customized cavities. [Diagram 2] FIG. 2 is a schematic diagram of the carbon-silicon composite material according to Comparative Example 1 or Comparative Example 2, and is a partially enlarged view of the interface configuration of a single particle in the carbon-silicon composite material. [Diagram 3] 1 is a scanning electron microscope photograph of spray-dried composite particles in a process for preparing a carbon-silicon composite material with customized cavities according to a specific embodiment of the present invention. [Figure 4] 1 is a scanning electron micrograph of a heat-treated composite particulate in the preparation process of a carbon-silicon composite material with customized cavities according to the present invention. [Diagram 5] 1 is a low magnification scanning electron micrograph of a carbon-silicon composite with customized cavities according to an illustrative embodiment of the present invention. [Figure 6] 1 is a high magnification scanning electron micrograph of a carbon-silicon composite with customized cavities according to an illustrative embodiment of the present invention. [Figure 7] 1 is a scanning electron microscope photograph of composite fine particles that were subjected to a first heat treatment in the process of preparing a carbon-silicon composite material according to Comparative Example 2. [Figure 8] 1 is a scanning electron microscope photograph of a carbon-silicon composite material according to Comparative Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] In order to more clearly describe the technical solutions of the embodiments of the present application or the prior art, the drawings necessary for describing the embodiments or the prior art are briefly described below. The drawings described only show some embodiments of the present application, and those skilled in the art can obtain other related drawings based on these drawings without using inventive abilities. Hereinafter, the technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings used in the embodiments of the present application, and it goes without saying that the described embodiments are only some of the embodiments of the present application, and do not include all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without using their inventive abilities all fall within the scope of protection of the present application. As used herein, the term "and / or" refers to a relationship between related objects and refers to a ternary relationship, for example, A and / or B refers to a ternary relationship in which only A is present, both A and B are present, or only B is present.

[0015] In a first aspect, the present invention provides a customized cavity carbon-silicon composite, the schematic diagram of which is shown in FIG. 1, which is a partially enlarged view of the interface configuration of a single particle in the customized cavity carbon-silicon composite, in which the reference numerals 1 represent the customized cavity carbon-silicon composite, 10 represent the custom cavity, 11 represent the silicon particle, 12 represent the first phase carbon, 13 represent the second phase carbon, and 14 represent the third phase carbon. The carbon-silicon composite with customized cavities according to the present invention comprises a core structure and a coating layer of third phase carbon coating the core structure, the core structure being a structure formed by removing pore-forming agent particles from a first intermediate product particle, and having customized cavities formed by removing the pore-forming agent particles, the first intermediate product particle being a composite particle made of silicon particles, pore-forming agent particles, first phase carbon, and second phase carbon, the first phase carbon being a carbon nanomaterial having a network structure, the second phase carbon being a carbon material derived from an organic compound, and the coating layer of the third phase carbon being a coating layer made of a carbon material converted from tar and / or pitch.

[0016] In the present invention, the custom cavities can be uniformly and precisely customized by introducing pore-forming particles according to the volume expansion of the silicon particles (for example, the custom cavities in FIG. 1 can accommodate 300% volume expansion of the silicon particles).

[0017] In the above technical solution, the use of pore-forming agent particles can form a precisely customized custom cavity. On the one hand, the cavity can provide a buffer space for the expansion of silicon particles, and avoid the problems of structure collapse and interface instability. On the other hand, the formation of a custom cavity by the pore-forming agent can form a suitable cavity according to the expansion volume of silicon particles, so as to avoid the cavity being too large or too small. If the cavity is too small, there is a risk of structure collapse and interface instability, and if it is too large, the volumetric capacity and volumetric energy density will be impaired.

[0018] The present invention adopts a continuous three-phase carbon made of different materials, and the silicon particles are coated with a flexible carbon nanomaterial having a mesh structure inside, which can better absorb the expansion force of the silicon particles and maintain the stability of the structure. In the outermost layer, the coating layer produced by high-temperature carbonization of tar or pitch has excellent heat resistance, acid and alkali resistance, and impact resistance, and has a more stable structure. In the middle part, the carbon material derived from an organic compound plays the role of a bridge that bonds the first phase carbon and the third phase carbon. Therefore, the carbon structure provided by coating on the outside forms a gradient-type integrated carbon structure with different hardness from "soft" to "hard" from the inside to the outside, which can provide a continuous carbonaceous electron transport channel, making the particle structure more stable, maximizing the volume capacity and energy density, and effectively improving the cycle stability, which contributes to its use as a negative electrode active material in lithium-ion batteries. In addition, the carbon-silicon composite material according to the present invention is composed only of silicon active material and lightweight carbon material, and does not require other auxiliary materials, so that the relative silicon content and the gravimetric capacity of the material can be maximized.

[0019] The carbon-silicon composite material according to the present invention is suitable as an electrode active material for lithium-ion batteries that are restricted by volume expansion, and silicon-based batteries prepared therewith have excellent charge / discharge volumetric capacity and cycle stability.

[0020] In a specific embodiment, the mass content of the silicon particles is 50% to 99%, for example, 50%, 55%, 60%, 62.5%, 65%, 68%, 72%, 75%, 77%, 78%, 80%, 83%, 85%, 87.5%, 90%, 91%, 93%, 95%, 96.5%, 98%, 99%, etc., of the total mass of the customized cavity carbon-silicon composite material.

[0021] Taking the total mass of the cavity customized carbon-silicon composite as 100%, the mass content of the first phase carbon is 0.1%-49%, the mass content of the second phase carbon is 0.1%-49%, and the mass content of the third phase carbon is 0.1%-49%.

[0022] In a specific embodiment, the silicon particles include one or more of micron-sized silicon particles, nano-sized silicon particles, silicon nanowires, and silicon nanotubes. The micron-sized silicon particles can be specifically micron-sized silicon particles of 1 micron to 20 microns. The nano-sized silicon particles can be nano-sized silicon particles of 1 nanometer to 1000 nanometers. The silicon nanowires can have a diameter of 1 nanometer to 1000 nanometers and a length of 10 nanometers to 10 microns. The silicon nanotubes can have a diameter of 1 nanometer to 1000 nanometers and a length of 10 nanometers to 10 microns. The silicon particles can be silicon particles of different sizes. The silicon particles are not limited to the above-exemplified silicon particles, and other silicon particles commonly used in the field can also be used in the present invention.

[0023] In a specific embodiment, the carbon nanomaterials include one or more of carbon nanotubes, graphene, graphene oxide, reduced graphene oxide, carbon nanofibers, bacterial cellulose-derived carbon fibers, and bacterial cellulose-derived carbon pili.

[0024] The organic compound includes one or more of ascorbic acid, citric acid, glucose, sucrose, fructose, maltose, chitosan, urea, starch, and protein. When it includes a mixture of two or more, the mixture includes, but is not limited to, typical examples such as a mixture of ascorbic acid and sucrose, a mixture of ascorbic acid and glucose, a mixture of sucrose and citric acid, a mixture of fructose, chitosan, and urea, a mixture of ascorbic acid, maltose, and starch, and a mixture of ascorbic acid, sucrose, citric acid, and protein.

[0025] The tar includes coal tar and / or petroleum tar, and the pitch includes coal pitch and / or petroleum pitch. When a mixture of two or more types is used, the combination includes, but is not limited to, typical examples such as a combination of petroleum pitch and petroleum tar, and a combination of coal tar and petroleum pitch.

[0026] In a second aspect, the present invention further provides a method for preparing the above-mentioned customized cavity carbon-silicon composite, the method comprising the steps of:

[0027] (1) A precursor solution is obtained by dispersing silicon particles, first-phase carbon, which is a carbon nanomaterial having a network structure, pore-forming agent particles, which are water-soluble salts, and an organic compound in a solvent.

[0028] In this step, the first phase carbon is a carbon nanomaterial having a mesh structure and has a strong adsorption power, so that it easily bonds with the silicon particles and the pore-forming agent particles in the solution. In the present invention, the above-exemplified organic compounds are also used as dispersants to sufficiently and uniformly disperse the silicon particles, the first phase carbon, and the pore-forming agent particles in the solvent.

[0029] In one particular embodiment, the solvent is water.

[0030] In a specific embodiment, the mass content of the solvent in the precursor solution is 2% to 99.9%.

[0031] In a specific embodiment, the pore-forming agent particles are water-soluble salts having a melting point of 710° C. to 1000° C. Specifically, the salts include one or more of sodium chloride (801° C.), potassium chloride (770° C.), calcium chloride (772° C.), magnesium chloride (714° C.), sodium carbonate (851° C.), potassium carbonate (891° C.), sodium sulfate (884° C.), etc., but are not limited to the above exemplified salts. In a specific embodiment, the volume ratio of silicon particles to pore-forming agent particles is 1:0.1-9, preferably 1:1-4.

[0032] (2) The precursor solution is spray-dried to obtain precursor particles, which are mixture particles consisting of silicon particles, first phase carbon, pore-forming agent particles, and an organic compound.

[0033] In this step, the spray drying is carried out by turning the precursor solution into droplets using any one of a pressure atomizer, a gas flow atomizer, a rotary atomizer, an ultrasonic atomizer, etc., and then drying to obtain precursor particles.

[0034] In a specific embodiment, the material supply speed is 0.5mL / min-100mL / min, such as 0.5mL / min, 1mL / min, 5mL / min, 10mL / min, 20mL / min, 30mL / min, 35mL / min, 40mL / min, 47.5mL / min, 50mL / min, 60mL / min, 70mL / min, 77mL / min, 80mL / min, 90mL / min, 100mL / min, etc. The gas inflow temperature is 100-300°C, such as 100°C, 150°C, 180°C, 210°C, 250°C, 275°C, 300°C, etc. The gas outflow temperature is automatically adjusted by the device. The carrier gas is air. (3) The precursor particles are subjected to a first heat treatment in a non-oxidizing atmosphere to convert the organic compounds into carbonaceous materials to form second-phase carbon, thereby obtaining first intermediate product particles.

[0035] The temperature of the first heat treatment is set lower than the melting point of the pore-forming agent particles so as to avoid loss due to melting of the pore-forming agent particles at high temperatures and failure to customize the cavities. During the heating process, the organic compound melts and, driven by the thermal expansion of the air inside the particles, moves along the gap between the silicon particles and the pore-forming agent particles to the particle surface so as to fill the gap. When the heat treatment temperature is reached, the organic compound is modified, crosslinked and / or carbonized and formed on the particle surface. In the method of the present invention, the second phase carbon and the first phase carbon are bonded by a covalent bond.

[0036] In a specific embodiment, the temperature of the first heat treatment is 300° C. to 700° C., such as 300° C., 350° C., 400° C., 425° C., 500° C., 575° C., 650° C., 700° C., etc. The time of the first heat treatment is 1 h (hour) to 24 h (hour), such as 1 h, 2 h, 3 h, 5 h, 7 h, 10 h, 12 h, 13 h, 15 h, 16 h, 18 h, 20 h, 21 h, 22 h, 23 h, 24 h, etc.

[0037] (4) Coating the first intermediate product particles with molten tar and / or pitch to obtain second intermediate product particles.

[0038] In this step, a carbon layer derived from an organic compound is formed on the surface of the first intermediate product particles, and since the pore-forming agent particles are not removed, the molten tar and / or pitch do not penetrate into the inside of the particles, thereby realizing a gradient structure with different hardness from "soft" to "hard" from the inside to the outside, in which the second phase carbon is bonded to the first phase carbon and the third phase carbon is bonded to the second phase carbon. Preferably, the coating is carried out in a non-oxidizing atmosphere to prevent the introduction of impurities.

[0039] In this step, specifically, the first intermediate product particles are dispersed in molten tar and / or pitch, and stirred and mixed in a non-oxidizing atmosphere. The stirring and mixing time is 1h to 24h, for example, 1h, 2h, 3h, 5h, 7h, 10h, 12h, 13h, 15h, 16h, 18h, 20h, 21h, 22h, 23h, 24h, etc.

[0040] (5) subjecting the second intermediate product particles to a second heat treatment in a non-oxidizing atmosphere to convert the tar and / or pitch into a carbon coating layer, forming a coating layer of third phase carbon, and obtaining third intermediate product particles.

[0041] In this step, the temperature of the second heat treatment is 600°C to 1400°C, such as 600°C, 650°C, 700°C, 725°C, 750°C, 760°C, 780°C, 800°C, 850°C, 880°C, 900°C, 925°C, 950°C, 975°C, 1050°C, 1150°C, 1200°C, 1250°C, 1300°C, 1400°C, etc. The time of the second heat treatment is 1h to 24h, such as 1h, 2h, 3h, 5h, 7h, 10h, 12h, 13h, 15h, 16h, 18h, 20h, 21h, 22h, 23h, 24h, etc.

[0042] (6) The pore-forming agent particles are removed from the third intermediate product particles using water to obtain a carbon-silicon composite with customized cavities. In this step, the third intermediate product particles are washed with water and dried to obtain a carbon-silicon composite with customized cavities.

[0043] The non-oxidizing atmosphere in the above step includes one or more of a nitrogen gas atmosphere, an argon gas atmosphere, a hydrogen gas atmosphere, and a helium gas atmosphere. When used in combination, typical examples of the combination include an argon gas / hydrogen gas mixed atmosphere and a helium gas / hydrogen gas mixed atmosphere, but are not limited to these. The preparation method according to the present invention has low cost, simple process, safety, low energy consumption, is suitable for industrialized equipment, and is suitable for mass production.

[0044] In a third aspect, the present invention further provides a use of the customized cavity carbon-silicon composite as defined above or the customized cavity carbon-silicon composite prepared by the preparation method as defined above in an anode active material, an anode, an electrochemical energy storage device or an electrochemical energy storage system.

[0045] When the carbon-silicon composite with customized cavities is used as the negative electrode active material, the carbon-silicon composite with customized cavities may be used alone as the negative electrode active material or may be used in combination with other negative electrode active materials. When used in combination with other negative electrode active materials, the amount of the carbon-silicon composite with customized cavities used is 1% or more of the total mass of the negative electrode active material.

[0046] Examples of the "other negative electrode active material" include artificial graphite, natural graphite, single-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, reduced graphene oxide, hard carbon materials, metals capable of alloying with lithium and their precursors (tin, germanium, aluminum, cobalt, etc.), transition metal compounds capable of conversion reaction with lithium (iron oxide, etc.), and lithium-inserted transition metal oxides (lithium titanate, etc.). The negative electrode active material can be a lithium ion battery negative electrode active material.

[0047] When the customized hollow carbon-silicon composite is used in a negative electrode, the negative electrode includes the customized hollow carbon-silicon composite as a negative electrode active material, and the negative electrode can be, for example, a lithium ion battery negative electrode.

[0048] When the customized cavity carbon-silicon composite is used in an electrochemical energy storage device or system, the electrochemical energy storage device or system comprises the customized cavity carbon-silicon composite. An "electrochemical energy storage device or electrochemical energy storage system" according to the present invention may be, for example, a lithium ion battery or a capacitor.

[0049] The following is a specific example. Example 1 Preparation of carbon-silicon composites with customized cavities:

[0050] Silicon particles of 1 to 3 microns, an aqueous solution of sodium chloride of appropriate concentration, carbon nanotubes, and ascorbic acid were mixed by stirring (mass ratio 1:3:0.05:0.3) to prepare a precursor solution to be spray-dried. The precursor solution had a solute concentration of 15 wt%. During spray-drying, the material supply rate was 20 mL / min, the gas inlet temperature was 220°C, the gas outlet temperature was 110°C, and the carrier gas was air. The obtained powder (Figure 3) was heat-treated at 550°C for 2 h under a nitrogen gas atmosphere to prepare carbon-silicon composite microparticles (Figure 4) on whose surface second-phase carbon converted from ascorbic acid was formed. The fine particles were dispersed in molten petroleum pitch (mass ratio 1:0.1), stirred in a nitrogen gas atmosphere for 6 hours in a modifying mixer, and then heated to 250°C, 550°C, and 850°C in turn in a nitrogen gas atmosphere, and kept at each temperature for 2 hours, then cooled to room temperature, washed with deionized water, and dried to obtain a carbon-silicon composite with customized cavities. The particle size of the obtained carbon-silicon composite with customized cavities was about 5 μm, and the results are shown in Figures 5 and 6. Based on the total mass of the carbon-silicon composite with customized cavities, the mass content of silicon particles was 99%.

[0051] Preparation of the negative electrode: The carbon-silicon composite with customized cavities according to this embodiment was used as the negative electrode active material, and the negative electrode active material, polyvinylidene fluoride (PVDF) as an adhesive, and acetylene black as a conductive agent were uniformly mixed in N-methylpyrrolidone (NMP) to prepare a slurry. The slurry was applied to a copper foil current collector, vacuum dried at 120°C for 12 hours, and then rolled to prepare a negative electrode sheet.

[0052] Battery Preparation: The negative sheet was used as the test electrode and lithium metal foil was used as the counter electrode. The electrolyte was 1M LiPF6 / EC:DEC (1:1, v / v) with added FEC, i.e., lithium hexafluorophosphate dissolved in a mixture of ethylene carbonate and diethyl carbonate, and the separator was Celgard 2400. The coin-type lithium-ion battery was assembled in a glove box with oxygen and water contents both less than 1 ppm.

[0053] Battery performance test results: At a current density of 0.5C, the coin-type lithium-ion battery has a capacity of 2150mAh / cm 3 It had a specific capacity of 1.0 and could be stably cycled for 550 cycles.

[0054] Example 2 Preparation of carbon-silicon composites with customized cavities:

[0055] Silicon particles of 3 to 5 microns, an aqueous solution of sodium sulfate of appropriate concentration, graphene oxide, and glucose were stirred and mixed (mass ratio 1:0.15:0.001:0.5) to prepare a precursor solution to be spray-dried. The precursor solution had a solute concentration of 85 wt%. During spray-drying, the material supply rate was 0.5 mL / min, the gas inlet temperature was 100°C, the gas outlet temperature was 80°C, and the carrier gas was air. The obtained powder was heat-treated at 300°C for 24 hours in a hydrogen gas atmosphere to prepare carbon-silicon composite microparticles on whose surface second-phase carbon converted from glucose was formed. The fine particles were dispersed in a mixture of molten coal pitch and petroleum pitch (mass ratio 1:0.1:0.2), stirred in a nitrogen gas atmosphere for 24 hours in a reforming mixer, and then heated to 250°C, 550°C, and 600°C in a hydrogen gas atmosphere, respectively, and then cooled to room temperature, washed with deionized water, and dried to obtain a carbon-silicon composite with customized cavities. The particle size of the obtained customized carbon-silicon composite was about 8 μm. The mass content of silicon particles was 87% based on the total mass of the carbon-silicon composite with customized cavities.

[0056] The hollow carbon-silicon composite according to this embodiment was used as the negative active material to prepare a negative electrode, which was then assembled to obtain a battery. The preparation method and preparation conditions of the negative electrode and the battery were the same as those in Example 1.

[0057] Battery performance test results: At a current density of 0.5C, the coin-type lithium-ion battery has a capacity of 1875mAh / cm 3 It had a specific capacity of 465 cycles and could be stably cycled for 465 cycles.

[0058] Example 3 Preparation of carbon-silicon composites with customized cavities: Silicon particles of 1 to 3 microns, an appropriate concentration of potassium carbonate, reduced graphene oxide, and an aqueous solution of starch were mixed by stirring (mass ratio 1:4:0.2:0.5) to prepare a precursor solution to be spray-dried. The precursor solution had a solute concentration of 0.1 wt%. During spray-drying, the material supply rate was 100 mL / min, the gas inlet temperature was 300°C, the gas outlet temperature was 160°C, and the carrier gas was air. The obtained powder was heat-treated at 475°C for 10 h under an argon gas / hydrogen gas atmosphere to prepare carbon-silicon composite microparticles on whose surface the second phase carbon converted from starch was formed. The fine particles were dispersed in petroleum tar (mass ratio 1:2), stirred in a nitrogen gas / argon gas atmosphere in a reforming mixer for 1 h, and then heated to 250°C, 550°C, and 1400°C in turn in an argon gas / hydrogen gas atmosphere, and kept at each temperature for 2 h, 2 h, and 1 h, respectively, before being cooled to room temperature, washed with deionized water, and dried to obtain a carbon-silicon composite with customized cavities. The particle size of the obtained customized carbon-silicon composite was about 4 μm. The mass content of silicon particles was 50% based on the total mass of the carbon-silicon composite with customized cavities.

[0059] The hollow carbon-silicon composite according to this embodiment was used as the negative active material to prepare a negative electrode, which was then assembled to obtain a battery. The preparation method and preparation conditions of the negative electrode and the battery were the same as those in Example 1.

[0060] Battery performance test results: At a current density of 0.5C, the coin-type lithium-ion battery has a capacity of 1560mAh / cm 3 It had a specific capacity of 1.0 and could be stably cycled for 510 cycles.

[0061] Example 4 Preparation of carbon-silicon composites with customized cavities: Silicon particles of 3 to 5 microns, an aqueous solution of potassium chloride / sodium chloride of appropriate concentration, carbon nanotubes, urea, and protein were mixed by stirring (mass ratio 1:0.1:0.1:0.25:0.3:0.2) to prepare a precursor solution to be spray-dried. The precursor solution had a solute concentration of 35 wt%. During spray-drying, the material supply rate was 10 mL / min, the gas inlet temperature was 275°C, the gas outlet temperature was 140°C, and the carrier gas was air. The obtained powder was heat-treated at 700°C for 1 h under a nitrogen gas atmosphere to prepare carbon-silicon composite microparticles on whose surface the second phase carbon converted from urea and protein was formed. The sealed microparticles were dispersed in coal tar (mass ratio 1:0.65), stirred in an argon gas atmosphere for 12 hours in a modification mixer, and then heated to 250°C, 550°C, and 1050°C in turn in an argon gas atmosphere, and kept at each temperature for 2 hours, 2 hours, and 6 hours, respectively, before being cooled to room temperature, washed with deionized water, and dried to obtain a carbon-silicon composite with customized cavities. The particle size of the obtained customized carbon-silicon composite was about 10 μm. Based on the total mass of the carbon-silicon composite with customized cavities, the mass content of silicon particles was 75%.

[0062] The hollow carbon-silicon composite according to this embodiment was used as the negative active material to prepare a negative electrode, which was then assembled to obtain a battery. The preparation method and preparation conditions of the negative electrode and the battery were the same as those in Example 1.

[0063] Battery performance test results: At a current density of 0.5C, the coin-type lithium-ion battery has a capacity of 1750mAh / cm3 It had a specific capacity of 460 cycles and could be stably cycled for 460 cycles.

[0064] Example 5 Preparation of carbon-silicon composites with customized cavities:

[0065] Silicon nanowires with a diameter of about 100 nanometers, aqueous solutions of calcium chloride / sodium carbonate with appropriate concentrations, carbon nanotubes, graphene oxide, ascorbic acid, and citric acid were mixed by stirring (mass ratio 1:4:2:0.5:0.2:0.1:0.2) to prepare a precursor solution to be spray-dried. The precursor solution had a solute concentration of 55 wt%. During spray-drying, the material supply rate was 5 mL / min, the gas inlet temperature was 165°C, the gas outlet temperature was 100°C, and the carrier gas was air. The obtained powder was heat-treated at 650°C for 4 h under an argon gas atmosphere to prepare carbon-silicon composite microparticles sealed in carbon converted from ascorbic acid and citric acid. The sealed fine particles were dispersed in molten coal pitch (mass ratio 1:1), stirred in a nitrogen gas atmosphere for 18 hours in a modifying mixer, and then heated to 250°C, 550°C, and 750°C in a hydrogen gas atmosphere, respectively, and then cooled to room temperature, washed with deionized water, and dried to obtain a carbon-silicon composite with customized cavities. The particle size of the obtained customized carbon-silicon composite was about 7 μm. The mass content of silicon particles was 65% based on the total mass of the carbon-silicon composite with customized cavities.

[0066] The hollow carbon-silicon composite according to this embodiment was used as the negative active material to prepare a negative electrode, which was then assembled to obtain a battery. The preparation method and preparation conditions of the negative electrode and the battery were the same as those in Example 1.

[0067] Battery performance test results: At a current density of 0.5C, the coin-type lithium-ion battery has a capacity of 1680mAh / cm 3 It had a specific capacity of 480 cycles and could be cycled stably.

[0068] Example 6 Preparation of carbon-silicon composites with customized cavities: Silicon nanoparticles of 50 nanometers, an aqueous solution of sodium chloride, carbon nanotubes, and ascorbic acid of appropriate concentration were mixed by stirring (mass ratio 1:2:0.5:0.5) to prepare a precursor solution to be spray-dried. The precursor solution had a solute concentration of 2 wt%. During spray-drying, the material supply rate was 65 mL / min, the gas inlet temperature was 255°C, the gas outlet temperature was 120°C, and the carrier gas was air. The obtained powder was heat-treated at 420°C for 16 h under an argon gas / nitrogen gas atmosphere to prepare carbon-silicon composite microparticles on whose surface the second phase carbon converted from glucose was formed. The sealed microparticles were dispersed in molten petroleum pitch (mass ratio 1:0.15), stirred in a nitrogen gas atmosphere for 3 hours in a modifying mixer, and then heated to 250°C, 550°C, and 1200°C in a hydrogen gas atmosphere, respectively, and then cooled to room temperature, washed with deionized water, and dried to obtain a carbon-silicon composite with customized cavities. The particle size of the obtained customized carbon-silicon composite was about 6 μm. Based on the total mass of the carbon-silicon composite with customized cavities, the mass content of silicon particles was 95%.

[0069] The hollow carbon-silicon composite according to this embodiment was used as the negative active material to prepare a negative electrode, which was then assembled to obtain a battery. The preparation method and preparation conditions of the negative electrode and the battery were the same as those in Example 1.

[0070] Battery performance test results: At a current density of 0.5C, the coin-type lithium-ion battery has a capacity of 2050mAh / cm 3 It had a specific capacity of 1.0 and could be stably cycled for 525 cycles.

[0071] Comparative Example 1 Comparative Example 1 differed from Example 1 in that no pore-forming agent particles were used, and the specific results were as follows.

[0072] Silicon particles of 1 to 3 microns, carbon nanotubes of an appropriate concentration, and an aqueous solution of ascorbic acid were stirred and mixed (mass ratio 1:0.05:0.3) to prepare a precursor solution to be spray-dried. The precursor solution had a solute concentration of 15 wt%. During spray drying, the material supply rate was 10 mL / min, the gas inlet temperature was 220°C, the gas outlet temperature was 110°C, and the carrier gas was air. The obtained powder was heat-treated at 550°C for 2 hours under a nitrogen gas atmosphere to prepare porous carbon-silicon composite microparticles. The porous microparticles were dispersed in molten petroleum pitch (mass ratio 1:0.1), stirred in a nitrogen gas atmosphere for 6 hours in a modifying mixer, and further heated to 250°C, 550°C, and 850°C in sequence under a nitrogen gas atmosphere, and kept at each temperature for 2 hours, then cooled to room temperature, washed with deionized water, dried, and a carbon-silicon composite material with no customized cavities was obtained. The particle size of the obtained non-customized carbon-silicon composite was about 3.5 μm. Based on the total mass of the carbon-silicon composite, the mass content of silicon particles was 92%.

[0073] A schematic diagram of the carbon-silicon composite according to this comparative example is shown in FIG. 2. FIG. 2 is a partial enlarged view of the interface configuration of a single particle in a carbon-silicon composite, in which the reference numerals 2 represent the carbon-silicon composite, 20 represent the non-customized pores, 21 represent the silicon particles, and 22 represent the carbon. As can be seen from the drawing, firstly, the porous microparticles are formed under the condition of no pore-forming agent added, and the internal pores are random, which cannot provide the space required for the volume expansion of the silicon particles. Secondly, due to the open pore structure of the porous microparticles, the third phase carbon penetrates from the outside to the inside during the carbon coating process, so that a non-gradient integrated carbon structure is formed inside and outside the particles, and is directly coated on the surface of the silicon particles. This not only prevents and limits the pore space to accommodate the volume expansion of the silicon particles, but also forms an unstable conductive network that is "hard" as a whole, which is prone to cracking and peeling off as the silicon particles expand in volume during the charge and discharge process.

[0074] The carbon-silicon composite material according to this comparative example was used as the negative electrode active material to prepare a negative electrode, which was then assembled to obtain a battery. The preparation method and preparation conditions for the negative electrode and the battery were the same as those in Example 1.

[0075] Battery performance test results: At a current density of 0.5C, the battery has a capacity of 1350mAh / cm 3 However, it could only be cycled 35 times.

[0076] Comparative Example 2 Silicon particles of 1 micron to 3 micron, an aqueous solution of sodium chloride of an appropriate concentration, carbon nanotubes, and ascorbic acid were stirred and mixed (same as in Example 1) to prepare a precursor solution to be spray-dried. The precursor solution had a solute concentration of 15 wt%. During spray-drying, the material supply rate was 20 mL / min, the gas inlet temperature was 220°C, the gas outlet temperature was 110°C, and the carrier gas was air. The obtained powder was heat-treated at 850°C for 2 hours under a nitrogen gas atmosphere to prepare porous carbon-silicon composite microparticles (Figure 7). The microparticles were dispersed in molten petroleum pitch, stirred in a nitrogen gas atmosphere for 6 hours in a modifying mixer, and further heated to 250°C, 550°C, and 850°C in sequence under a nitrogen gas atmosphere, and kept at each temperature for 2 hours, then cooled to room temperature, washed with deionized water, dried, and a carbon-silicon composite material (Figure 8) in which the cavities were not customized was obtained. The particle size of the obtained carbon-silicon composite was about 4 μm. The mass content of silicon particles was 95% based on the total mass of the carbon-silicon composite.

[0077] A schematic diagram of the carbon-silicon composite according to this comparative example is shown in FIG. 2. FIG. 2 is a partial enlarged view of the interface configuration of a single particle in a carbon-silicon composite, in which the reference numerals 2 represent the carbon-silicon composite, 20 represent the non-customized pores, 21 represent the silicon particles, and 22 represent the carbon. As can be seen from the drawing, firstly, the pores inside the microparticles are random, and cannot provide accurate and necessary space for the volume expansion of the silicon particles. The main reason is that the heat treatment temperature during the preparation process exceeds the melting point of the pore-forming agent, so that the pore-forming agent is lost and the customization of the cavity fails. Secondly, due to the loss of the pore-forming agent, an open pore structure is formed in the heat-treated microparticles (as shown in FIG. 7), and the third phase carbon penetrates from the outside to the inside during the coating process, so that a non-gradient integrated carbon structure is formed and directly coated on the surface of the silicon particles. This not only blocks and limits the pore space to accommodate the volume expansion of the silicon particles, but also results in an overall "hard" and unstable conductive network that is prone to cracking and peeling off as the silicon particles expand in volume during the charge and discharge process.

[0078] The carbon-silicon composite material according to this comparative example was used as the negative electrode active material to prepare a negative electrode, which was then assembled to obtain a battery. The preparation method and preparation conditions for the negative electrode and the battery were the same as those in Example 1.

[0079] Battery performance test results: Under a current density of 0.5C, the battery has a capacity of 1430mAh / cm 3 However, it was only able to perform 57 cycles.

[0080] The above examples are merely some embodiments of the present invention, and the description is specific and detailed, but does not limit the scope of the present application. Those skilled in the art may make some modifications or improvements without departing from the spirit of the present application, and these modifications or improvements also belong to the scope of protection of the present invention. Therefore, the scope of protection of the present invention is subject to the contents shown in the claims.

Claims

1. a core structure and a coating layer of third phase carbon coating the core structure, the core structure being a structure formed by removing pore-forming agent particles from a first intermediate product particle, the core structure having a custom cavity formed by removing the pore-forming agent particles, the first intermediate product particle being a composite particle including silicon particles, the pore-forming agent particles, first phase carbon, and second phase carbon; The first phase carbon is a carbon nanomaterial having a network structure, the second phase carbon is a carbonaceous material derived from an organic compound; The third phase carbon is a carbonaceous material converted from tar and / or pitch. A carbon-silicon composite having customized cavities, characterized in that

2. The mass content of the silicon particles is 50% to 99%, where the total mass of the hollow customized carbon-silicon composite is 100%. The customized cavity carbon-silicon composite of claim 1.

3. The mass content of the first phase carbon is 0.1% to 49%, the mass content of the second phase carbon is 0.1% to 49%, and the mass content of the third phase carbon is 0.1% to 49%, based on a total mass of the customized hollow carbon-silicon composite being 100%. The customized cavity carbon-silicon composite of claim 2.

4. the silicon particles include one or more of micron-sized silicon particles, nano-sized silicon particles, silicon nanowires, and silicon nanotubes; the carbon nanomaterial comprises one or more of carbon nanotubes, graphene, graphene oxide, reduced graphene oxide, carbon nanofibers, carbon fibers derived from bacterial cellulose, and carbon pilus derived from bacterial cellulose; the organic compound comprises one or more of ascorbic acid, citric acid, glucose, sucrose, fructose, maltose, chitosan, urea, starch and protein; The tar comprises coal tar and / or petroleum tar; The pitch includes coal pitch and / or petroleum pitch. A carbon-silicon composite material with customized cavities according to any one of claims 1 to 3.

5. 1. A method for preparing a carbon-silicon composite with customized cavities, comprising: A step of dispersing silicon particles, first phase carbon which is a carbon nanomaterial having a network structure, pore-forming agent particles which are water-soluble salts, and an organic compound in a solvent to obtain a precursor solution; spray-drying the precursor solution to obtain precursor particles that are mixture particles consisting of the silicon particles, the first phase carbon, the pore-forming agent particles, and the organic compound; subjecting the precursor particles to a first heat treatment in a non-oxidizing atmosphere to convert the organic compounds into carbonaceous materials to form second-phase carbon and obtain first intermediate product particles; coating the first intermediate product particles with molten tar and / or pitch to obtain second intermediate product particles; subjecting the second intermediate product particles to a second heat treatment in a non-oxidizing atmosphere to convert the tar and / or pitch into carbonaceous material and form a coating layer of third phase carbon to obtain third intermediate product particles; removing the pore-forming agent particles from the third intermediate product particles using water to obtain the carbon-silicon composite with customized cavities. A method for preparing a carbon-silicon composite material having customized cavities, comprising:

6. The volume ratio of the silicon particles to the pore-forming particles is 1:0.1-9. A method for preparing the customized cavity carbon-silicon composite material according to claim 5.

7. The spray drying has a material supply rate of 0.5 mL / min to 100 mL / min and a gas inlet temperature of 100° C. to 300° C.; The temperature of the first heat treatment is 300° C. to 700° C. The duration of the first heat treatment is 1 hour to 24 hours; The temperature of the second heat treatment is 600° C. to 1400° C. The second heat treatment time is 1 hour to 24 hours. A method for preparing the customized cavity carbon-silicon composite of claim 5.

8. The non-oxidizing atmosphere includes one or more of a nitrogen gas atmosphere, an argon gas atmosphere, a hydrogen gas atmosphere, and a helium gas atmosphere; The salts include one or more of sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium carbonate, potassium carbonate, and sodium sulfate. A method for preparing the customized cavity carbon-silicon composite material according to claim 5.

9. The solvent comprises water; The mass content of the solvent in the precursor solution is 2% to 99.9%. A method for preparing the customized cavity carbon-silicon composite material according to claim 5.

10. Use of the customized hollow carbon-silicon composite material according to any one of claims 1 to 4 or the customized hollow carbon-silicon composite material prepared by the preparation method according to any one of claims 5 to 9 in a negative electrode active material, a negative electrode, an electrochemical energy storage device or an electrochemical energy storage system.

Images