Silicon-carbon electrode material, preparation method and application thereof

Abstract

The application provides a silicon-carbon electrode material and a preparation method and application thereof. The silicon-carbon electrode material comprises porous carbon and silicon-carbon composite nanoparticles distributed in the pore channels of the porous carbon; and a silicon-carbon bond is formed between at least part of silicon atoms and at least part of carbon atoms in the silicon-carbon composite nanoparticles. The silicon-carbon electrode material not only has good electrical conductivity, but also can effectively alleviate the performance attenuation problem caused by the volume expansion of silicon particles, so that the material has good structural stability. When the silicon-carbon electrode material is applied to a secondary battery, the cycle performance of the battery can be improved, and a high-energy-density secondary battery can be prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of secondary batteries, in particular to a silicon-carbon electrode material and a preparation method and application thereof. BACKGROUND

[0002] Silicon has high specific capacity, environmental friendliness, and abundant reserves as a negative electrode material. However, silicon will expand in volume during charging and discharging, leading to material pulverization, SEI film rupture, rapid attenuation of battery specific capacity, shortened cycle life, and the like. In addition, the electrical conductivity of silicon is poor, which cannot meet the demand of large-rate charging and discharging of batteries. The above problems seriously limit the application of silicon-based materials in secondary batteries. Therefore, it is necessary to develop a new type of electrode material to inhibit the volume expansion of silicon and enable the battery to have good cycle performance. SUMMARY

[0003] Therefore, the present application provides a silicon-carbon electrode material, which has good electrical conductivity and good structural stability, can effectively alleviate the performance attenuation problem caused by the volume expansion of silicon particles, and can improve the cycle performance of the battery when applied to a secondary battery, which is conducive to the preparation of a high-energy-density secondary battery.

[0004] The first aspect of the present application provides a silicon-carbon electrode material, which comprises porous carbon and silicon-carbon composite nanoparticles distributed in the pore channels of the porous carbon; and at least part of the silicon atoms and at least part of the carbon atoms in the silicon-carbon composite nanoparticles form silicon-carbon bonds.

[0005] In the silicon-carbon electrode material of the present application, the carbon in the silicon-carbon composite nanoparticles can effectively improve the electrochemical activity of silicon, so that the electrode material has good specific capacity performance. The silicon-carbon bonds formed between the carbon atoms and the silicon atoms can inhibit the expansion effect of silicon. The silicon nanoparticles are distributed between the pore channels of the porous carbon. The pore channel structure of the porous carbon can effectively disperse the silicon nanoparticles, inhibit the agglomeration of the silicon nanoparticles, alleviate the problem of material disintegration caused by the stress concentration of the silicon particle expansion, provide a buffer space for the volume expansion of the silicon particles, reduce the impact of the silicon particle expansion on the overall material, inhibit the pulverization of the material, and improve the cycle performance of the battery.

[0006] Optionally, the silicon-carbon composite nanoparticles comprise silicon particles, carbon, and silicon carbide.

[0007] Optionally, the average particle size of the silicon particles is less than or equal to 4 nm.

[0008] Optionally, the silicon particles comprise amorphous silicon.

[0009] Optionally, the carbon comprises amorphous carbon.

[0010] Optionally, in the silicon-carbon composite nanoparticles, the silicon atoms and the carbon atoms are packed to form a tetrahedral structure.

[0011] Optionally, in the silicon-carbon composite nanoparticles, the mass ratio of the silicon atoms to the carbon atoms is (1.5-4):1.

[0012] Optionally, the porous carbon comprises one or more of artificial graphite, natural graphite, or hard carbon.

[0013] Optionally, the average depth of the pores is 50-150 nm, and the average pore size of the pores is 10-30 nm.

[0014] Optionally, the silicon-carbon electrode material further comprises an amorphous carbon coating layer coated on the surface of the porous carbon and the silicon-carbon composite nanoparticles.

[0015] Optionally, in the silicon-carbon electrode material, the mass percentage of silicon is 20-50%, and the mass percentage of carbon is 50-80%.

[0016] Optionally, the D50 of the silicon-carbon electrode material is 12-18 μm. v 50 is 12-18 μm.

[0017] In a second aspect, the application provides a preparation method of a silicon-carbon electrode material, comprising:

[0018] placing the porous carbon in a heat treatment device, introducing a gaseous silicon source and a gaseous carbon source into the heat treatment device for vapor deposition to obtain a silicon-carbon electrode material; the flow rate ratio of the gaseous silicon source to the gaseous carbon source introduced into the heat treatment device is (0.5-2):1; the temperature of the vapor deposition is 300-630°C.

[0019] Optionally, the gaseous silicon source comprises one or more of SiH4, Si2H6, Si3H8, SiCl4, SiHCl3, Si2Cl6, SiH2Cl2, and SiH3Cl; the gaseous carbon source comprises one or more of C2H2, CH4, C2H6, C2H4, CO, and CO2; the flow rate of the gaseous silicon source and the gaseous carbon source introduced into the heat treatment device is 5-60 sccm, and the aeration time of the mixed gas is 60-480 min.

[0020] Optionally, after the vapor deposition is completed, a precursor is obtained, the precursor is mixed with a solid carbon source, and then sintered at 400-1000°C to obtain the silicon-carbon electrode material; the solid carbon source comprises pitch and a high-molecular organic substance.

[0021] In a third aspect, the application provides a negative electrode sheet, comprising a current collector and a negative material layer arranged on the current collector, wherein the negative material layer comprises the silicon-carbon electrode material according to the first aspect.

[0022] In a fourth aspect, the application provides a secondary battery, comprising the negative electrode sheet according to the third aspect. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A schematic structural diagram of the porous carbon provided in an embodiment of the application;

[0024] Figure 2 An XRD characterization diagram of the silicon-carbon electrode material of Embodiment 1 of the application;

[0025] Figure 3 A comparison diagram of expansion rates of the batteries of various embodiments and comparative examples of the application. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0027] Silicon is considered to be the most potential high-energy-density battery negative electrode material due to its high theoretical specific capacity. However, silicon expands significantly in volume during the process of metal ion deintercalation, and the electrode material is prone to pulverization and peeling, which reduces the cycle performance of the battery. In order to reduce the expansion effect of silicon and improve the structural stability of the electrode material, the application provides a silicon-carbon electrode material, which comprises porous carbon and silicon-carbon composite nanoparticles distributed in the pore channels of the porous carbon. The porous carbon has a pore channel structure, and the silicon-carbon composite nanoparticles are distributed in the pore channels. The porous carbon can provide strong support for the silicon-carbon composite nanoparticles, alleviate the performance degradation caused by the volume expansion of silicon, and the structure can also effectively improve the electrical conductivity of the electrode material and promote the transmission of electrons.

[0028] In some embodiments of the present application, the silicon-carbon composite nanoparticles comprise silicon atoms and silicon atoms bonded to form silicon particles, carbon atoms and carbon atoms bonded to form carbon, and silicon atoms and carbon atoms bonded to form silicon carbide. The carbon in the silicon-carbon composite nanoparticles can improve the electrochemical activity of silicon, enable the capacity of silicon to be fully utilized, and improve the rate performance of the electrode material. In some embodiments, the carbon in the silicon-carbon composite nanoparticles is amorphous carbon. In some embodiments of the present application, the silicon atoms and carbon atoms in the silicon-carbon composite nanoparticles are packed to form a tetrahedral structure, with four carbon atoms around each silicon atom and four silicon atoms around each carbon atom, and the carbon atoms and silicon atoms are distributed at intervals, so that a conductive network is formed inside the silicon-carbon composite nanoparticles, thereby greatly improving the electrical conductivity of the silicon particles. In some embodiments of the present application, the mass ratio of silicon atoms to carbon atoms in the silicon-carbon composite nanoparticles is (1.5-4):1, and the mass ratio of silicon atoms to carbon atoms can be, but is not limited to, 1.5:1, 2:1, 3:1, or 4:1. Controlling the mass ratio of silicon atoms to carbon atoms in the above range can ensure that the silicon-carbon electrode material has both high specific capacity and high rate performance.

[0029] In some embodiments of the present application, the average depth of the porous carbon channels is 50-150 nm, and the average pore size of the channels is 10-30 nm. The depth of the porous carbon channels refers to the length of the porous carbon channels in the direction of extension, and the pore size of the porous carbon channels refers to the diameter of the channels on the outer surface. The average depth of the porous carbon channels can be, but is not limited to, 50 nm, 80 nm, 100 nm, 120 nm, or 150 nm, and the average pore size of the porous carbon channels can be, but is not limited to, 10 nm, 15 nm, 20 nm, or 30 nm. The porous carbon of this structure not only facilitates the dispersion of the silicon-carbon composite nanoparticles, thereby avoiding excessive concentration of stress due to silicon expansion and improving the structural stability of the material, but also facilitates the reduction of the oxidation of the nanosilicon. In some embodiments of the present application, the porous carbon has a hollow structure, and the internal channels have a uniform distribution of columnar structures, i.e., the cross section of the channels is circular. In some embodiments of the present application, the porous carbon comprises one or more of artificial graphite, natural graphite, or hard carbon, and the silicon-carbon composite nanoparticles can interact with the porous carbon through covalent bonds to form a silicon-carbon electrode material with a stable structure.

[0030] In some embodiments of the present application, the average particle size of the silicon particles in the silicon-carbon composite nanoparticles is less than or equal to 4 nm, and in some embodiments, the average particle size of the silicon particles is less than or equal to 4 nm and greater than or equal to 0.5 nm. The average particle size of the silicon particles can be, but is not limited to, 0.5 nm, 1 nm, 2 nm, 3 nm, or 4 nm. Smaller-sized silicon particles not only facilitate the rapid extraction or insertion of lithium ions, thereby improving the rate performance of the material, but also have weak volume expansion and pulverization effects, which are beneficial to improving the structural stability of the electrode material.

[0031] In some embodiments of the present application, the ratio of the total volume of the silicon-carbon composite nanoparticles in the porous carbon pores to the pore volume of the carbon pores is 1:(1.01-1.05), wherein the total volume of the silicon-carbon composite nanoparticles is in units of nm 2 , and the pore volume of the carbon pores is in units of nm 2 . Controlling the ratio of the size of the silicon-carbon composite nanoparticles to the pore volume of the carbon pores is conducive to providing a buffer space for the volume expansion of the silicon particles, reducing the impact of the expansion of the silicon particles on the overall material, inhibiting the pulverization of the material, and ensuring that the overall material has a high capacity.

[0032] In some embodiments of the present application, the silicon-carbon electrode material further comprises a carbon coating layer coated on the surface of the porous carbon and the silicon-carbon composite nanoparticles, and the carbon coating layer comprises one or more of amorphous carbon and graphitized carbon. The carbon coating layer can further improve the structural stability and conductivity of the silicon-carbon electrode material. In some embodiments, the carbon coating layer is an amorphous carbon coating layer, which has good structural stability and rate performance. In some embodiments of the present application, the thickness of the carbon coating layer is 10 nm-200 nm, and the mass percentage of the carbon coating layer in the silicon-carbon electrode material is 5%-10%.

[0033] In some embodiments of the present application, in the silicon-carbon electrode material, the mass percentage of silicon is 20%-50%, and the mass percentage of carbon is 50%-80%. The content of carbon can be measured by a thermogravimetric analyzer, and the content of silicon can be measured by the following method: after the silicon-carbon electrode material is dissolved with hydrofluoric acid, the content of silicon in the electrode material is measured by ICP element analysis. The mass percentage of silicon in the silicon-carbon electrode material can be, but is not limited to, 20%, 30%, 33%, 35%, 37%, 40%, 45%, or 50%. In some embodiments, the mass percentage of amorphous carbon in the silicon-carbon electrode material is 10%-20%. Controlling the content of carbon can ensure that the silicon-carbon electrode material has good ion conductivity, which is conducive to improving the conductivity of the silicon-carbon electrode material to ions, reducing the polarization of the material, promoting the migration of ions, and making the battery have good rate performance. In some embodiments of the present application, the D v 50 of the silicon-carbon electrode material is 12 μm-18 μm, and the D v 50 of the silicon-carbon electrode material can be, but is not limited to, 12 μm, 14 μm, 15 μm, 16 μm, or 18 μm.

[0034] The silicon-carbon electrode material provided by the application has the following advantages: the pore channel structure of the porous carbon can disperse small-size silicon-carbon composite nanoparticles and provide buffer space for the volume change of silicon in the charging and discharging process, thereby improving the structural stability of the material; the carbon atoms in the silicon-carbon composite nanoparticles can effectively improve the electrochemical activity of the electrode material, so that the silicon material has good rate performance and specific capacity performance; and the application of the silicon-carbon electrode material in a secondary battery can improve the rate performance and cycle performance of the secondary battery, which is conducive to the long-term use of the battery.

[0035] The application further provides a preparation method of the silicon-carbon electrode material.

[0036] The porous carbon is placed in a heat treatment device, and a gaseous silicon source and a gaseous carbon source are introduced into the heat treatment device for vapor deposition, so as to obtain the silicon-carbon electrode material.

[0037] Please refer to Figure 1 , Figure 1 The structure of the porous carbon is shown in the structure diagram provided by an embodiment of the application, and the surface of the porous carbon is a porous structure. In some embodiments, the D v 50 is 12 μm to 18 μm, the average depth of the pore channel in the porous carbon is 50 nm to 150 nm, the average pore size of the pore channel is 10 nm to 30 nm, and the porosity of the porous carbon is 5% to 30%. Controlling the size structure of the porous carbon is conducive to the uniform deposition of the silicon-carbon composite nanoparticles in the pore channel of the porous carbon, so as to promote the formation of small-size silicon-carbon composite nanoparticles. In some embodiments of the application, the porous carbon comprises one or more of artificial graphite, natural graphite or hard carbon. In some embodiments of the application, the preparation method of the porous carbon comprises: providing a carbon material, wherein the carbon material comprises one or more of artificial graphite, natural graphite or hard carbon; and placing the carbon material in a heat treatment device, and introducing carbon dioxide into the heat treatment device to etch the carbon material, wherein the etching temperature is 200°C to 800°C, the flow rate of the carbon dioxide gas is 10 sccm to 50 sccm, and the heat treatment device can be a rotary furnace, and the rotation speed of the rotary furnace is 3° / min to 12° / min.

[0038] In the present application, when gaseous silicon source and gaseous carbon source are used for vapor deposition, the gaseous silicon source is cracked to form silicon atoms, and the gaseous carbon source is cracked to form carbon atoms. Since the bond energy of Si-C bond is lower than that of Si-Si bond, the carbon atoms generated by cracking of the gaseous carbon source can form Si-C bonds with the silicon atoms in advance, thereby inhibiting the formation of Si-Si bonds and preventing the growth of silicon after nucleation, so as to form small-sized silicon-carbon composite nanoparticles. In the embodiments of the present application, the flow ratio of the gaseous silicon source to the gaseous carbon source is (0.5-2):1, and the flow ratio of the gaseous silicon source to the gaseous carbon source can be specifically but not limited to 0.5:1, 0.8:1, 1:1, 1.5:1 or 2:1. Controlling the flow ratio of the gaseous silicon source to the gaseous carbon source can ensure the ordered deposition of carbon atoms and silicon atoms to form silicon-carbon composite nanoparticles, thereby promoting the capacity of silicon particles.

[0039] In some embodiments of the present application, the flow rate of the gaseous silicon source is 5-60 sccm, and the flow rate of the gaseous silicon source can be specifically but not limited to 5 sccm, 10 sccm, 20 sccm, 30 sccm, 40 sccm or 60 sccm. In some embodiments of the present application, the flow rate of the gaseous carbon source is 5-60 sccm, and the flow rate of the gaseous carbon source can be specifically but not limited to 5 sccm, 10 sccm, 20 sccm, 30 sccm, 40 sccm or 60 sccm. In some embodiments of the present application, the ventilation time of the mixed gas is 60-480 min. Controlling the flow rate of the gas can promote the uniform deposition of silicon nanoparticles in the pore channels of the porous carbon.

[0040] In the embodiments of the present application, the temperature for vapor deposition is 300-630℃, and the temperature for vapor deposition can be specifically but not limited to 300℃, 400℃, 450℃, 500℃, 600℃ or 630℃. Vapor deposition at this temperature can form amorphous silicon, and carbon atoms can effectively be combined with silicon to form silicon-carbon composite nanoparticles. In some embodiments of the present application, the temperature for vapor deposition is 300-500℃. In view of the fact that the carbon source cracking reaction rate is reduced at low temperature, which affects the utilization rate of the carbon source, a small amount of catalyst is added to the porous carbon, and the catalyst includes copper oxide, nickel oxide or platinum metal catalyst to promote the cracking of the carbon source.

[0041] In some embodiments of the present application, the gaseous silicon source includes one or more of SiH4, Si2H6, Si3H8, SiCl4, SiHCl3, Si2Cl6, SiH2Cl2, and SiH3Cl; and the gaseous carbon source includes one or more of C2H2, CH4, C2H6, C2H4, CO, and CO2. In some embodiments, the gaseous silicon source is SiH4, and the gaseous carbon source is C2H4. When a mixture of SiH4and C2H4is used for vapor deposition, on the one hand, the gas has high cracking efficiency and can be uniformly filled in the pore channels of the porous carbon to form a dense structure material; on the other hand, the hydrogen generated by cracking can be recycled, saving energy.

[0042] In some embodiments of the present application, the silicon-carbon electrode material further includes a carbon coating layer coated on the surface of the porous carbon and the silicon-carbon composite nanoparticles. In this case, the porous carbon can be subjected to vapor deposition treatment to obtain a precursor with the silicon-carbon composite nanoparticles distributed in the pore channels of the porous carbon, and then the precursor can be further subjected to carbon coating. In some embodiments, the method for carbon coating includes: uniformly mixing the precursor and a solid carbon source in a stirring tank to obtain a mixture, and then vacuum sintering the mixture at a temperature of 400-1000°C in a vacuum tube furnace for 3-8h to form a carbon coating layer. In this method, the mass ratio of the precursor to the solid carbon source is (9-19):1, the stirring speed is 300-800r / min, and the stirring time is 30-180min. The solid carbon source includes one or more of pitch and high molecular organic matter. The pitch includes one or more of petroleum pitch, coal tar pitch, or natural pitch. The high molecular organic matter includes one or more of alcohol, resin, and sugar. The alcohol includes one or more of polyfurfuryl alcohol or polyvinyl alcohol. The resin includes one or more of epoxy resin, phenolic resin, and melamine resin. The sugar includes one or more of glucose and sucrose.

[0043] In some embodiments, after the carbon coating layer is formed on the surface of the precursor, a second carbon coating layer is further prepared on the surface of the carbon coating layer. The method for preparing the second carbon coating layer includes: placing the precursor with the carbon coating layer in a heat treatment device for vapor phase carbon deposition, and the carbon source for vapor phase carbon deposition includes one or more of methane, ethylene, acetylene, propane, or propylene. The temperature for vapor phase carbon deposition is 300-900°C. In some embodiments, vapor deposition is performed at 300-600°C to form an amorphous carbon coating layer, which has good rate performance.

[0044] In some embodiments of the present application, the method for preparing the silicon-carbon electrode material comprises: placing the porous carbon in a vacuum stainless steel tube furnace, the vacuum stainless steel tube furnace having two air inlets and being capable of simultaneously performing the aeration reaction; introducing the gaseous silicon source and the gaseous carbon source into the tube furnace, the flow rate ratio of the gaseous silicon source to the gaseous carbon source being (0.5-2):1; allowing the gaseous silicon source and the gaseous carbon source to undergo thermal decomposition and co-deposition in the vacuum tube furnace to form silicon-carbon composite nanoparticles, and allowing the silicon-carbon composite nanoparticles to deposit in the pores of the porous carbon to form a silicon-carbon composite material; and placing the silicon-carbon composite material and the solid carbon source in a stirring tank after being uniformly mixed by stirring, and then placing the mixture in the vacuum tube furnace for vacuum sintering to form a carbon coating layer and obtain the silicon-carbon electrode material.

[0045] The method for preparing the silicon-carbon electrode material provided by the present application can obtain an electrode material with a novel structure, and the method is simple in process and conducive to large-scale production.

[0046] The present application also provides a negative electrode sheet, which comprises a current collector and a negative electrode material layer arranged on the current collector, wherein the negative electrode material layer comprises the silicon-carbon electrode material of the present application. In the present application, the negative electrode material layer can be prepared by mixing the silicon-carbon electrode material, a conductive agent, a binder and a solvent to form a negative electrode slurry, and then coating and drying the negative electrode slurry to obtain the negative electrode material layer. When preparing the negative electrode slurry, the binder can be mixed with the solvent, stirred thoroughly, and then the conductive agent can be added, followed by stirring, and then the silicon-carbon electrode material can be added, followed by stirring and sieving to obtain the negative electrode slurry. The conductive agent, the binder and the solvent are conventional choices in the field of batteries. For example, the binder can be selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC) and sodium alginate. The conductive agent can be selected from one or more of carbon nanotubes, carbon black and graphene.

[0047] The present application also provides a secondary battery. In some embodiments of the present application, the secondary battery comprises a positive electrode, a negative electrode, an electrolyte and a separator located between the positive electrode and the negative electrode, wherein the negative electrode comprises the negative electrode sheet provided by the present application. In some embodiments of the present application, the secondary battery comprises a positive electrode, a negative electrode and a solid-state electrolyte or a semi-solid-state electrolyte located between the positive electrode and the negative electrode. In the present application, the secondary battery can be any one of a lithium ion battery, a sodium ion battery, a potassium ion battery, an aluminum ion battery, a zinc ion battery or a magnesium ion battery.

[0048] In the present application, the positive electrode of the secondary battery can be any positive electrode known in the art. In some embodiments, the active material of the positive electrode is a material capable of reversible extraction and intercalation of lithium ions; in some embodiments, the active material of the positive electrode is a material capable of reversible extraction and intercalation of sodium ions; in some embodiments, the active material of the positive electrode is a material capable of reversible extraction and intercalation of potassium ions; in some embodiments, the active material of the positive electrode is a material capable of reversible extraction and intercalation of magnesium ions. In the present application, the separator of the secondary battery can be any separator known to one skilled in the art, for example the separator can be one or more of a polyolefin microporous membrane, polyethylene terephthalate, polyethylene felt, glass fiber felt, or ultra-fine glass fiber paper.

[0049] In the present application, the electrolyte of the secondary battery includes a solution of electrolyte lithium salt in a non-aqueous solvent. In the embodiments of the present application, the electrolyte lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluorosilicate (Li2SiF6), lithium tetraphenylborate (LiB(C6H5)4), lithium chloride (LiCl), lithium bromide (LiBr), lithium chloroaluminate (LiAlCl4), lithium fluorocarbylsulfonate (LiC(SO2CF3)3), LiCH3SO3, LiN(SO2CF3)2, and LiN(SO2C2F5)2. In some embodiments of the present application, the non-aqueous solvent includes one or more of chain acid ester and cyclic acid ester. In some embodiments of the present application, the chain acid ester includes one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), and dipropyl carbonate (DPC). In some embodiments of the present application, the chain acid ester includes chain organic ester containing fluorine, sulfur, or unsaturated bond. In some embodiments of the present application, the cyclic acid ester includes one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), γ-butyrolactone (γ-BL), and sulfolactone. In some embodiments of the present application, the cyclic acid ester includes cyclic organic ester containing fluorine, sulfur, or unsaturated bond. In some embodiments of the present application, the non-aqueous solvent includes one or more of chain ether and cyclic ether solution. In some embodiments of the present application, the cyclic ether includes one or more of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), and 4-methyl-1,3-dioxolane (4-MeDOL). In some embodiments of the present application, the cyclic ether includes cyclic organic ether containing fluorine, sulfur, or unsaturated bond. In some embodiments of the present application, the chain ether includes one or more of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), 1,2-dimethoxypropane (DMP), and diethylene glycol dimethyl ether (DG). In some embodiments of the present application, the chain ether includes chain organic ether containing fluorine, sulfur, or unsaturated bond. In the embodiments of the present application, the concentration of the electrolyte lithium salt in the electrolyte is 0.1 mol / L-15 mol / L. In some embodiments of the present application, the concentration of the electrolyte lithium salt is 1 mol / L-10 mol / L.

[0050] In the embodiments of the present application, the secondary battery can be prepared by using any one of the stacking process or the winding process.

[0051] The present application also provides an electronic device including the secondary battery provided by the present application, and the secondary battery supplies power to the electronic device.

[0052] The technical solutions of the present application are further described in the following embodiments.

[0053] Embodiment 1

[0054] A preparation method of a silicon-carbon electrode material comprises:

[0055] The graphite is placed in a rotary furnace, and carbon dioxide gas is introduced to etch the graphite to form porous carbon, wherein the rotation speed of the rotary furnace is 6° / min, the temperature is 600℃, the flow rate of the carbon dioxide gas is 15sccm, and the reaction time is 300min.

[0056] 30g of the porous carbon is placed in a vacuum stainless steel tube furnace, the tube furnace is heated to 475℃, and silane and ethylene are introduced into the tube furnace, the flow rate of the silane gas is 10sccm, the flow rate of the ethylene gas is 20sccm, the flow rate ratio of the silane and the ethylene is 0.5:1, the gas flow time is 240min, and a silicon-carbon composite material is obtained; 100g of the silicon-carbon composite material is stirred with 10g of pitch in a stirring tank to obtain a mixture, the stirring speed is 550r / min, and the stirring time is 60min; the mixture is placed in a vacuum tube furnace for vacuum sintering at 600℃ for 6h, and a silicon-carbon electrode material is obtained.

[0057] Preparation of the negative electrode sheet: the silicon-carbon electrode material, sodium carboxymethyl cellulose and acetylene black are mixed in a mass ratio of 8:1:1 to obtain a negative electrode slurry, the negative electrode slurry is coated on a copper foil by using a doctor blade, and after drying, rolling and cutting, a negative electrode sheet is obtained.

[0058] Preparation of the battery: a lithium sheet is used as a counter electrode sheet, a polyethylene / polypropylene (PE / PP) composite separator is used as a separator, and a button cell is made by using a conventional method in the art, and the battery of embodiment 1 is named as S1.

[0059] Embodiment 2

[0060] The same method as in embodiment 1 is used to prepare the porous carbon, 30g of the porous carbon is placed in a vacuum stainless steel tube furnace, the tube furnace is heated to 475℃, and silane and ethylene are introduced into the tube furnace, the flow rate of the silane gas is 20sccm, the flow rate of the ethylene gas is 20sccm, the flow rate ratio of the silane and the ethylene is 1:1, the gas flow time is 120min, and a silicon-carbon composite material is obtained; 100g of the silicon-carbon composite material is stirred with 10g of pitch in a stirring tank to obtain a mixture, the stirring speed is 550r / min, and the stirring time is 60min; the mixture is placed in a vacuum tube furnace for vacuum sintering at 600℃ for 6h, and a silicon-carbon electrode material is obtained.

[0061] The same method as in embodiment 1 is used to prepare the negative electrode sheet and the battery, and the battery of embodiment 2 is named as S2.

[0062] Example 3

[0063] The porous carbon was prepared by the same method as in Example 1, 30 g of the porous carbon was placed in a vacuum stainless steel tube furnace, the tube furnace was heated to 475℃, silane and ethylene were introduced into the tube furnace, the flow rate of the silane gas was 40 sccm, the flow rate of the ethylene gas was 20 sccm, the ratio of the flow rates of the silane and ethylene was 2:1, and the gas flow time was 60 min, to obtain a silicon-carbon composite material; 100 g of the silicon-carbon composite material was mixed with 10 g of pitch in a stirring tank to obtain a mixture, the stirring speed was 550 r / min, and the stirring time was 60 min; the mixture was placed in a vacuum tube furnace for vacuum sintering at 600℃ for 6 h to obtain a silicon-carbon electrode material.

[0064] The negative electrode sheet and the battery were prepared by the same method as in Example 1, and the battery of Example 3 was named S3.

[0065] Example 4

[0066] The silicon-carbon composite material was prepared by the same method as in Example 1; 100 g of the silicon-carbon composite material was mixed with 10 g of pitch in a stirring tank to obtain a mixture, the stirring speed was 550 r / min, and the stirring time was 60 min; the mixture was placed in a vacuum tube furnace for vacuum sintering at 600℃ for 6 h to obtain a silicon-carbon composite material coated with an amorphous carbon layer, and the silicon-carbon composite material coated with the amorphous carbon layer was placed in a vacuum rotary furnace, methane gas was introduced into the vacuum rotary furnace for gas phase coating, the rotation speed of the rotary furnace was 6° / min, the temperature was 800℃, and the flow rate of the methane gas was 20 sccm, to obtain a silicon-carbon electrode material.

[0067] The negative electrode sheet and the battery were prepared by the same method as in Example 1, and the battery of Example 4 was named S4.

[0068] Example 5

[0069] The hard carbon was placed in a rotary furnace, and carbon dioxide gas was introduced to etch the hard carbon to form a porous carbon, wherein the rotation speed of the rotary furnace was 15° / min, the temperature was 900℃, the flow rate of the carbon dioxide gas was 60 sccm, and the reaction time was 300 min.

[0070] The silicon-carbon electrode material, the negative electrode sheet, and the battery were prepared by the same method as in Example 1, and the battery of Example 5 was named S5.

[0071] Example 6

[0072] Example 6

[0073] The negative electrode sheet and the battery were prepared by the same method as in Example 1, and the battery of Example 6 was named S6.

[0074] Example 7

[0075] The porous carbon was prepared by the same method as in Example 1, and 30 g of the porous carbon was placed in a vacuum stainless steel tube furnace, the tube furnace was heated to 475℃, and silane and ethylene were introduced into the tube furnace, the flow rate of the silane gas was 80 sccm, the flow rate of the ethylene gas was 80 sccm, the flow rate ratio of the silane and the ethylene was 1:1, the gas flow time was 60 min, and a silicon-carbon composite material was obtained; 100 g of the silicon-carbon composite material was stirred with 10 g of pitch in a stirring tank to obtain a mixture, the stirring speed was 550 r / min, and the stirring time was 60 min; the mixture was placed in a vacuum tube furnace for vacuum sintering at 600℃ for 6 h, and a silicon-carbon electrode material was obtained.

[0076] The negative electrode sheet and the battery were prepared by the same method as in Example 1, and the battery of Example 7 was named S7.

[0077] Example 8

[0078] The graphite was placed in a rotary furnace, and carbon dioxide gas was introduced to etch the graphite to form a porous carbon, wherein the rotation speed of the rotary furnace was 12° / min, the temperature was 400℃, the flow rate of the carbon dioxide gas was 15 sccm, and the reaction time was 300 min.

[0079] The porous carbon was prepared by the same method as in Example 1, and 30 g of the porous carbon was placed in a vacuum stainless steel tube furnace, the tube furnace was heated to 475℃, and silane and ethylene were introduced into the tube furnace, the flow rate of the silane gas was 10 sccm, the flow rate of the ethylene gas was 20 sccm, the flow rate ratio of the silane and the ethylene was 0.5:1, the gas flow time was 240 min, and a silicon-carbon composite material was obtained; 100 g of the silicon-carbon composite material was stirred with 10 g of pitch in a stirring tank to obtain a mixture, the stirring speed was 550 r / min, and the stirring time was 60 min; the mixture was placed in a vacuum tube furnace for vacuum sintering at 600℃ for 6 h, and a silicon-carbon electrode material was obtained.

[0080] The negative electrode sheet and the battery were prepared by the same method as in Example 1, and the battery of Example 8 was named S8.

[0081] Example 9

[0082] The graphite is placed in a rotary furnace, and carbon dioxide gas is introduced to etch the graphite to form porous carbon, wherein the rotation speed of the rotary furnace is 10° / min, the temperature is 600℃, the flow rate of the carbon dioxide gas is 35sccm, and the reaction time is 300min.

[0083] The 30g of porous carbon is placed in a vacuum stainless steel tube furnace, the tube furnace is heated to 475℃, silane and ethylene are introduced into the tube furnace, the flow rate of the silane gas is 10sccm, the flow rate of the ethylene gas is 20sccm, the flow rate ratio of the silane and the ethylene is 0.5:1, the gas flow time is 240min, and the silicon-carbon composite material is obtained; 100g of the silicon-carbon composite material is stirred with 10g of pitch in a stirring tank to obtain a mixture, the stirring speed is 550r / min, and the stirring time is 60min; the mixture is placed in a vacuum tube furnace for vacuum sintering at 600℃ for 6h, and the silicon-carbon electrode material is obtained.

[0084] The negative electrode sheet and the battery are prepared by the same method as in Example 1, and the battery of Example 9 is named S9.

[0085] Example 10

[0086] The graphite is placed in a rotary furnace, and carbon dioxide gas is introduced to etch the graphite to form porous carbon, wherein the rotation speed of the rotary furnace is 15° / min, the temperature is 600℃, the flow rate of the carbon dioxide gas is 10sccm, and the reaction time is 300min.

[0087] The 30g of porous carbon is placed in a vacuum stainless steel tube furnace, the tube furnace is heated to 475℃, silane and ethylene are introduced into the tube furnace, the flow rate of the silane gas is 10sccm, the flow rate of the ethylene gas is 20sccm, the flow rate ratio of the silane and the ethylene is 0.5:1, the gas flow time is 240min, and the silicon-carbon composite material is obtained; 100g of the silicon-carbon composite material is stirred with 10g of pitch in a stirring tank to obtain a mixture, the stirring speed is 550r / min, and the stirring time is 60min; the mixture is placed in a vacuum tube furnace for vacuum sintering at 600℃ for 6h, and the silicon-carbon electrode material is obtained.

[0088] The negative electrode sheet and the battery are prepared by the same method as in Example 1, and the battery of Example 10 is named S10.

[0089] Comparative Example 1

[0090] Comparative Example 1 is a commercial silicon-carbon product, the structure of which is a granat-like structure. The nano-silicon in the silicon-carbon product is micron-sized silicon particles ground into nano-sized, with an average particle size of 100 nm. The silicon-carbon product is obtained by dispersing the nano-silicon in graphite and amorphous carbon. 100 g of the silicon-carbon composite material is mixed with 10 g of pitch in a stirring tank at a stirring speed of 550 r / min for 60 min. The mixture is placed in a vacuum tube furnace and vacuum sintered at 600 ℃ for 6 h to obtain the silicon-carbon product.

[0091] The same method as in Example 1 is used to prepare the negative electrode sheet and the battery, and the battery of Comparative Example 1 is named D1.

[0092] Comparative Example 2

[0093] The same method as in Example 1 is used to prepare the porous carbon. 30 g of the porous carbon is placed in a vacuum stainless steel tube furnace, and the tube furnace is heated to 475 ℃. Silane and nitrogen are introduced into the tube furnace, with a silane gas flow of 10 sccm and a nitrogen gas flow of 50 sccm, a silane to nitrogen flow ratio of 1:5, and a gas flow time of 240 min, to obtain an uncoated silicon-carbon material. 100 g of the uncoated silicon-carbon material is mixed with 10 g of pitch in a stirring tank at a stirring speed of 550 r / min for 60 min. The mixture is placed in a vacuum tube furnace and vacuum sintered at 600 ℃ for 6 h to obtain a silicon-carbon electrode material.

[0094] The same method as in Example 1 is used to prepare the negative electrode sheet and the battery, and the battery of Comparative Example 2 is named D2.

[0095] Comparative Example 3

[0096] Comparative Example 3 is a direct vapor deposition on graphite (without etching the graphite). The same method as in Example 1 is used to prepare the silicon-carbon electrode material, the negative electrode sheet and the battery, and the battery of Comparative Example 3 is named D3.

[0097] Effect Example

[0098] To verify the performance of the silicon-carbon electrode material and the battery prepared in the present application, an effect example is also provided.

[0099] 1) The silicon-carbon electrode materials of the examples and the electrode materials of the comparative examples are characterized by scanning electron microscopy, and the structure parameters of the materials are shown in Table 1.

[0100] Table 1 Structure parameters of the silicon-carbon electrode materials of the examples and the electrode materials of the comparative examples

[0101]

[0102] As can be seen from Table 1, by using the porous carbon with the specific structure and controlling the gas phase deposition conditions, the present application can obtain the silicon nanoparticles with small size, and the silicon nanoparticles are dispersed among the pore channels of the porous carbon, which not only effectively disperses the stress of the silicon particle expansion in the silicon-carbon electrode material, but also effectively alleviates the agglomeration of the small particle silicon, so that the material has good structural stability and electrochemical performance.

[0103] The flow rate of the silicon source in Examples 2 and 3 is larger than that in Example 1, so the particle size of the silicon nanoparticles in the obtained silicon-carbon electrode material is larger. The silicon-carbon electrode material in Example 4 is further coated with carbon by gas phase deposition, and the particle size of the obtained silicon-carbon electrode material is relatively large. In Example 5, the flow rate of the carbon dioxide gas is large when the carbon material is etched, so the pore channel size of the obtained porous carbon is large, and after the gas phase deposition, the size of the obtained silicon nanoparticles is large. The silicon-carbon electrode material in Example 6 does not contain a carbon coating layer, and the particle size of the silicon-carbon electrode material is relatively small. In Example 7, the gas flow rate is large when the silicon-carbon electrode material is prepared, and the nano-silicon particles are easy to agglomerate after the gas cracking, resulting in large size of the nano-silicon particles. In Example 8, the temperature in the tube furnace is low when the carbon material is etched, so the pore channel size of the obtained porous carbon is small, and after the gas phase deposition, the size of the obtained silicon nanoparticles is close to the pore channel size of the porous carbon.

[0104] In Comparative Example 2, the gas phase deposition is carried out by using a mixed system of gaseous silicon source and carrier gas, i.e., the mixed gas does not contain gaseous carbon source, and the particle size of the obtained silicon nanoparticles is large, and the expansion effect of the electrode material is still very significant. In Comparative Example 3, the carbon material is directly deposited with the gas cracking on the surface of the carbon material, resulting in the agglomeration of the nano-silicon, and the expansion effect of the silicon is strong.

[0105] 2) The carbon content in the silicon-carbon electrode materials of the examples and the electrode materials of the comparative examples is characterized by using a thermogravimetric analyzer. After the silicon-carbon electrode material is dissolved with hydrofluoric acid, the silicon content in the electrode material is measured by ICP elemental analysis, and the characterization results are shown in Table 2.

[0106] Table 2 Silicon-carbon content table of the silicon-carbon electrode materials of the examples and the electrode materials of the comparative examples

[0107] Experimental group Silicon content (%) Carbon content (%) Example 1 28 72 Example 2 39 61 Example 3 48 52 Example 4 26 74 Example 5 30 70 Example 6 32 68 Example 7 45 55 Example 8 21 79 Example 9 24 76 Example 10 29 71 Comparative example 1 52 48 Comparative example 2 61 39 Comparative example 3 33 67

[0108] In Table 2, the flow rates of silane and ethylene are different in Example 1, Example 2 and Example 3, and the silicon content in the silicon-carbon electrode material increases with the increase of the silane content. Example 4 is based on Example 1 and further coated with CVD carbon, and the carbon content is about 4%, so the carbon content of Example 4 increases. In Example 5, the etching effect is poor because of the large flow rate of carbon dioxide gas during the etching of the carbon material, but the silicon content and the carbon content are basically not affected. In Example 6, the silicon-carbon material is not coated with carbon, so the carbon content decreases and the silicon content increases accordingly. In Example 7, the flow rates of silane and ethylene increase during the deposition of silicon and carbon, and the porous carbon content is fixed, so the silicon content increases. In Example 8, the average pore size and pore depth of the porous carbon are small, and the silicon deposition process will have a pore blocking phenomenon, and the performance of the silicon deposition is poor, so the silicon content decreases.

[0109] Comparative Example 1 is a commercial silicon-carbon material, and the nanosilicon is compounded with the carbon material by sanding. The content of the nanosilicon can be controlled during the compounding process, and the content of the nanosilicon is 50%. In Comparative Example 2, there is no ethylene gas during the deposition process, so the silicon content is high. In Comparative Example 3, the graphite is not used to create pores compared with Example 1, and the silicon content is less affected.

[0110] 3) The silicon-carbon electrode material of Example 1 is characterized by using an X-ray powder diffractometer. Please refer to Figure 2 , Figure 2 The XRD characterization graph of the silicon-carbon electrode material of Example 1 of the present application is shown in Figure 2 It can be seen that the silicon in the silicon-carbon electrode material is amorphous silicon.

[0111] 4) The batteries of each example and comparative example are tested for electrochemical performance by using a LANHE blue electric battery test system. The test conditions are as follows: the battery is discharged at a current of 0.01C to 0.005V at room temperature, and then charged at a current of 0.1C to 1.5V. This process is recorded as one cycle. The first discharge capacity and the first charge capacity of the battery are recorded, and the first charge capacity corresponds to the first reversible capacity; the first discharge efficiency (%) is calculated as (first charge capacity / first discharge capacity) x 100%. The remaining capacity after 100 cycles refers to the charge capacity of the battery after 100 cycles; the remaining capacity retention rate after 100 cycles is (remaining capacity after 100 cycles / first charge capacity). The battery performance of each example and comparative example is shown in Table 3.

[0112] Table 3 Battery electrochemical performance of Examples 1-10 and Comparative Examples 1-3

[0113]

[0114] In Table 3, the silicon nanoparticles in the silicon-carbon electrode materials of Example 1 and Example 4 have a small particle size, so the remaining capacity retention rate of the battery is high, the silicon content in the silicon-carbon electrode material of Example 3 is high, so the battery has a high initial reversible capacity, Example 6 is not coated, resulting in poor conductivity of the material and the presence of bare silicon particles on the surface of the silicon-carbon material, the capacity and initial efficiency are relatively low, the capacity retention rate is poor, the silicon-carbon electrode materials of Example 5 and 7 have a large particle size of silicon particles, and the capacity retention rate is poor, and in the silicon-carbon electrode material of Example 8, the silicon particles are not uniformly dispersed in the carbon pore channel during the deposition process, and there are a large number of cavities in the porous carbon, and the capacity retention rate is poor due to the expansion of the silicon material and the interface side reaction.

[0115] 5) The batteries of each example and comparative example were subjected to expansion test, and the test conditions were as follows: Before assembling the button cell, the original thickness of each group of sample electrode was measured with a micrometer. After 50 cycles, the battery was discharged to 0% SOC, disassembled, and the negative electrode was taken out and cleaned with DMC solution. After drying, the thickness was tested, and the expansion rate was calculated. The test results are shown in Table 4.

[0116] Table 4: Battery expansion performance of Examples 1-10 and Comparative Examples 1-3

[0117] Battery number Swelling rate (%) S1 13 S2 16 S3 22 S4 12 S5 31 S6 26 S7 28 S8 20 S9 18 S10 17 D1 46 D2 36 D3 34

[0118] See Figure 3 , Figure 3 The expansion rates of the batteries of each example and comparative example of the present application are compared in the following table 4 and Figure 3 It can be seen that the electrode prepared by using the silicon-carbon electrode material of the present application has better stability, and the expansion rate of the battery is low. For each example, the content of silicon in the silicon-carbon composite nanoparticles prepared in Example 3 is too high, the size of the silicon particles in the silicon-carbon composite nanoparticles is large, and the material has a strong expansion effect; in Example 5, the pore size of the porous carbon in the preparation of the silicon-carbon composite nanoparticles is too large, the size of the silicon particles in the silicon-carbon composite nanoparticles is large, and the material has a strong expansion effect; in Example 7, the gas flow in the preparation of the silicon-carbon composite nanoparticles is too large, the size of the silicon particles is large, and the material has a strong expansion effect.

[0119] It can be seen that the application of the silicon-carbon electrode material of the present application in the battery can effectively improve the cycle performance and rate performance of the battery.

[0120] The above is a preferred embodiment of the present application, but it cannot be construed as limiting the scope of the present application. It should be noted that for ordinary skilled persons in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements are also considered within the scope of protection of the present application.

Claims

1. A silicon-carbon electrode material, characterized in that, The silicon-carbon electrode material comprises porous carbon and silicon-carbon composite nanoparticles distributed in the pores of the porous carbon; at least some silicon atoms and at least some carbon atoms in the silicon-carbon composite nanoparticles form silicon-carbon bonds; in the silicon-carbon electrode material, the mass percentage of silicon is 20%~50%, and the mass percentage of carbon is 50%~80%, and the D of the silicon-carbon electrode material is... v 50 is 12μm~18μm.

2. The silicon-carbon electrode material as described in claim 1, characterized in that, The silicon-carbon composite nanoparticles include silicon particles, carbon, and silicon carbide, wherein the average particle size of the silicon particles is less than or equal to 4 nm.

3. The silicon-carbon electrode material as described in claim 1 or 2, characterized in that, The average depth of the channel is 50nm~150nm; the average pore diameter of the channel is 10nm~30nm.

4. The silicon-carbon electrode material as described in claim 2, characterized in that, The silicon particles include amorphous silicon.

5. The silicon-carbon electrode material according to any one of claims 1-4, characterized in that, The silicon-carbon electrode material also includes a carbon coating layer covering the surface of the porous carbon and the silicon-carbon composite nanoparticles.

6. A method for preparing a silicon-carbon electrode material as described in any one of claims 1-4, characterized in that, include: Porous carbon is placed in a heat treatment device, and a gaseous silicon source and a gaseous carbon source are introduced into the heat treatment device for vapor phase deposition to obtain a silicon-carbon electrode material; the flow rate ratio of the gaseous silicon source and the gaseous carbon source introduced into the heat treatment device is (0.5~2):1; the temperature of the vapor phase deposition is 300℃~630℃.

7. The preparation method according to claim 6, characterized in that, The gaseous silicon source includes one or more of SiH4, Si2H6, Si3H8, SiCl4, SiHCl3, Si2Cl6, SiH2Cl2, and SiH3Cl; the gaseous carbon source includes one or more of C2H2, CH4, C2H6, C2H4, CO, and CO2; the flow rate of the gaseous silicon source and the gaseous carbon source into the heat treatment equipment is 5 sccm to 60 sccm, and the gas flow time of the gaseous silicon source and the gaseous carbon source is 60 min to 480 min.

8. The preparation method according to claim 6 or 7, characterized in that, After the vapor deposition is completed, a precursor is obtained. The precursor is mixed with a solid carbon source and sintered at 400℃-1000℃ to obtain the silicon-carbon electrode material. The solid carbon source includes one or more of pitch and high molecular organic compounds.

9. A negative electrode sheet, comprising a current collector and a negative electrode material layer disposed on the current collector, characterized in that, The negative electrode material layer includes the silicon-carbon electrode material as described in any one of claims 1-5.

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

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