CN112366301B - Silicon/silicon oxide/carbon composite negative electrode material for lithium ion battery and preparation method thereof - Google Patents
Silicon/silicon oxide/carbon composite negative electrode material for lithium ion battery and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a negative electrode material for a lithium ion battery, a preparation method thereof and the battery, and discloses a preparation method of a silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery, a material and the battery x And the amorphous pyrolytic carbon coating layer can well buffer the volume expansion of the nano silicon in the charge-discharge process on the premise of not remarkably reducing the capacity, and the high conductivity and stability of the pyrolytic carbon coating layer are beneficial to enhancing the Si @ SiO x And the stability of an SEI film at the interface of the composite material and an electrolyte solution enables the composite material to have high capacity, excellent rate capability and cycle performance.
Description
Technical Field
The invention relates to a preparation method of a negative electrode material for a lithium ion battery and the battery, in particular to a silicon/silicon oxide/carbon composite negative electrode material, a preparation method thereof and the lithium ion battery adopting the silicon/silicon oxide/carbon composite negative electrode material.
Background
At present, artificial graphite and natural graphite are mainly used as negative active materials of commercial lithium ion batteries, but the theoretical specific capacity of the graphite is only 372mAh/g and is lower, and the energy density of a battery system formed by the graphite and positive materials such as lithium iron phosphate, lithium manganate or nickel cobalt lithium manganate is generally 150 Wh/Kg; meanwhile, the lithium intercalation potential of graphite is close to the lithium deposition potential, and lithium is easily separated to generate lithium dendrite in the process of low-temperature charging or high-rate charging and discharging, so that the safety problem is caused. Therefore, the conventional graphite-based negative electrode material has difficulty in meeting the requirements of multifunctional electronic products on high power and high capacity of the lithium ion battery, and further research and development of a novel lithium ion battery negative electrode material with high energy density, high safety performance and long cycle life is needed.
Silicon as the lithium ion battery cathode material has the outstanding advantages that: the theoretical specific capacity is as high as 4200mAh/g (Li) 4.4 Si) more than 10 times that of commercial graphite; slightly higher potential plateau than graphite (0.4V, Li/Li) + ) The safety is good; the low-temperature performance is excellent; the reserves are abundant.
However, the application of silicon as a negative electrode material of a lithium ion battery has great challenges: 1) during the charging and discharging process, the Li-Si alloying can generate serious volume expansion which can reach more than 300 percent (Li) 4.4 Si) resulting in deactivation of pulverization of silicon particles and poor cycle performance; 2) silicon particles are broken in the charging and discharging process, the active particles and the poor electric contact between the active particles and a current collector form an island effect, and new SE is repeatedly formed on the broken surfaceI film, resulting in irreversible capacity loss and coulombic inefficiency; 3) silicon is a semiconductor and exhibits low electrical conductivity (10) -5 -10 -3 S cm -1 ) And ion diffusion coefficient (10) -14 -10 -13 cm 2 s -1 ) Leading to the reduction of the dynamic performance of lithium ion diffusion; 4) the problems of large specific surface area, low tap density and the like caused by the nano structure effect. The above disadvantages severely restrict the industrial development and application.
In view of the above-mentioned disadvantages of silicon materials, researchers and industries have studied on the aspects of silicon nanostructure design, interface and surface structure design of nano silicon materials, and structural design using graphite as a stable carrier, and the modification methods adopted mainly include nano-modification and composite modification. The nano silicon-based material with special appearance and structure such as silicon nanoparticles, silicon nanowires, silicon nanotubes and silicon-based nano films is prepared, so that the volume change of the cathode active material is more uniform, the cathode material can obtain enough space to relieve the volume change of silicon, but the nano material is easy to agglomerate, a new volume effect can be generated in the circulation process, the problem of the cycling stability of the silicon material cannot be fundamentally solved by single nano treatment, and the nano silicon material with special structure and appearance has high preparation cost and complex process and is not beneficial to industrial popularization; the composite material introduces an active or inactive buffer matrix with good conductivity and small volume effect on the basis of reducing the volume effect of a silicon active phase through nanocrystallization, and improves the cycle stability of the silicon-based negative electrode material by adopting a volume compensation and conductivity increasing mode. The silicon-carbon composite material is a silicon-based material which is most expected to realize large-scale industrialization, but the problems of high cost, complex process, high control difficulty and poor batch stability of the nano silicon powder are urgently needed to be solved. The research aiming at the silicon-based cathode material is mainly divided into a nano silicon cathode material and a nano silicon oxide SiO x Two broad classes of cathode materials. When the lithium ion size of the silicon is less than 150nm, the volume expansion of the silicon is obviously reduced, and the nano silicon negative electrode material has the characteristics of high capacity and high charging and discharging coulombic efficiency, but has poor rate capability and cycle performance; and SiO x Although the capacity and the first coulombic efficiency of the catalyst are lower than those of nano-siliconBut the volume expansion is small, and the cycle performance and rate capability of the material are excellent.
The preparation of Si/SiO by liquid phase solidification-high temperature pyrolysis method x the/C composite material is prepared by mixing nano-silicon, crystalline flake graphite and SiO in carbon source solvent x Si/SiO obtained after dispersion x The composite material of the composite cathode material obtained by the method is easy to agglomerate, and Si and SiO x Are merely mixed together, no chemical bond is formed, and SiO x The carbon layer is mixed with a large amount of Si particles, HF is required for etching, and various factors enable the Si/SiO prepared by the method x The capacity performance, the cycle performance and the rate capability of the/C composite material are poor.
Chinese patent publication No. CN111164803A discloses a composite cathode material comprising a core, a first shell layer and a second shell layer, wherein the core of the cathode material disclosed in the patent is silicon and silicon oxide, the first shell layer is silicate substances and carbon particles, the second shell layer is an externally coated carbon film layer, the first shell layer is prepared by adopting a mechanical mixing and dispersing mode, the sizes of the core, the first shell layer and the second shell layer of the prepared composite cathode material are larger, the size of the core is between 1 and 10 mu m, the size of the first shell layer is between 0.01 and 2 mu m, the thickness of the second shell layer is between 0.01 and 1 mu m, the structural stability of the first shell layer is poor, the preparation method is used for sintering silicon particles, silicon oxide and other materials after physical mixing, the uniformity of components is poor, the complete coating of silicon oxide on silicon particles cannot be realized, and the capacities of active substances of silicon and silicon oxide cannot be effectively exerted, the material also has poor rate capability.
Chinese patent publication CN105406050A discloses a silicon/silicon oxide/metal/carbon anode material with a core-shell structure. The method is characterized in that a silicon oxide layer is prepared on the surface of silicon particles directly in a physical mixing and dispersing mode, the process is not controllable, but the silicon oxide layer prepared by a physical method has a collapse structure of the silicon oxide layer due to poor stability in a large-charge and discharge process, so that metal nanoparticles are added in the silicon oxide layer to form a nano composite layer. However, the lithium ions are influenced by a certain resistance during the migration and diffusion on the negative electrode material, the rate capability and the cycle performance of the material are influenced, and the capacity of the negative electrode material silicon active substance in the patent cannot be effectively exerted, after the negative electrode material in the patent is prepared into a complete 18650 full cell, the capacity of the cell is only about 1500mAh/g, and the cell is not suitable for large-rate charge and discharge, and because the influencing factors of the 18650 full cell capacity performance and the cycle performance include a positive electrode material, an electrolyte and the like, if the negative electrode material prepared in the patent is simply prepared into a half cell, the cycle performance and the rate performance of the negative electrode material are poorer when the research on the performance of the negative electrode material is carried out.
Based on the problems in the prior art, a new silicon/silicon oxide/carbon composite negative electrode material for lithium ion batteries, a preparation method thereof and a battery are needed to be invented, and the characteristics of high capacity performance of silicon particles and high cycle performance of silicon oxides are further exerted.
Disclosure of Invention
In order to solve the problems of serious agglomeration and SiO existing in the composite cathode material prepared by the prior art in the background technology x The invention provides a silicon/silicon oxide/carbon composite negative electrode material, a preparation method thereof and a battery, aiming at improving the capacity, the cycle performance and the rate performance of a negative electrode material of a lithium ion battery, the invention improves the structural stability and the electrochemical performance of nano silicon by generating a double-shell structure in situ, wherein the inner coating layer of the silicon oxide can effectively inhibit the volume expansion of the nano silicon, and the outer coating layer of amorphous carbon is beneficial to improving the electron transmission of an interface and enhancing the stability of an SEI film of the interface, thereby improving the structural stability and the electrochemical performance of the composite material.
The silicon/silicon oxide/carbon composite cathode material for the lithium ion battery has a core-shell structure, and is a dual-core shell structure.
The core of the core-shell structure is composed of nano silicon particles;
the shell layer has a multilayer structure, and the inner layer is silicon oxide SiO x The buffer layer is 1-50nm thick, and the outer layer is composed of a carbon layer coated outside the silicon oxide layer;
the above-mentionedThe outer coating carbon layer is formed by carbonizing a carbonizable organic substance at the high temperature of 600-1250 ℃, and the nano Si @ SiO x The mass ratio of the core-shell structure material to the carbonizable organic carbon source is 50: 5.0 to 200.0;
the shell is a carbon coating layer coated outside the nano silicon particles and the silicon oxide inner layer thereof, and the mass of the coating layer is 2-200% of the mass of silicon.
The other purpose of the invention is to prepare the silicon/silicon oxide/carbon composite anode material, and the preparation method is realized by the following steps:
preparation of S1 nano-silicon particles: preparing nano silicon powder by one of a solid-phase ball milling method, a liquid-phase ball milling method, a chemical vapor deposition method, a laser sputtering method and a plasma chemical vapor deposition method, wherein the particle size of the prepared silicon powder is 20-300 nm;
in the step, silicon powder particles with different sizes of 20-300 nm, such as 20nm, 50nm, 100nm, 150nm, 200nm, 300nm and the like, can be obtained by a solid phase ball milling method, a liquid phase ball milling method, a chemical vapor deposition method, a laser sputtering method or a plasma chemical vapor deposition method, and the obtained nanoparticles are in a shape of a sphere, a sphere-like shape, a strip shape, a flake shape, a cone shape, a diamond shape or a shape disordered distribution of more than two shapes.
S2 nanometer Si @ SiO x Preparation of core-shell structure material: the prepared nano silicon powder and an oxidant are subjected to in-situ oxidation treatment to prepare Si @ SiO x Core-shell materials, Si @ SiO x SiO of core-shell materials x The thickness of the buffer shell layer is controllable, and is 1-50nm, such as 1nm, 10nm, 20nm, 30nm, 50nm and the like;
in the step, the adopted oxidant is a mixed oxidant consisting of one or more than two of oxygen, potassium permanganate, potassium dichromate, sodium dichromate, nitric acid, potassium chlorate, sodium chlorate, potassium perchlorate, sodium perchlorate, hydrogen peroxide and peroxyacetic acid;
in the step, a layer of SiO is formed on the surface of the nano silicon ions obtained in the step S1 through in-situ oxidation treatment x Lithium storage phase buffer layer and SiO prepared by using method x The coating layer is firmly combined on the surface of the nano silicon particles through chemical bonds, and the volume expansion and contraction of the nano silicon in the charge-discharge process can be well buffered on the premise of not remarkably reducing the capacity. Can well maintain SiO in the process of heavy current charging and discharging x Structural stability of the layer, no structural collapse occurs.
S3 purification treatment: the Si @ SiO prepared in the above way x Acidifying the core-shell structure material by using acid to remove soluble metal ions, and then washing the core-shell structure material by using pure water for at least 3 times for later use;
in the step, the acid used for purification is mixed acid consisting of one or more than two of hydrochloric acid, acetic acid, oxalic acid and phosphoric acid;
the purpose of this step is to remove the SiO x Soluble metal ions incorporated during the layer process to work well on SiO x The surface of the layer is coated with a pyrolytic carbon layer.
S4 mixing and dispersing: the purified Si @ SiO x The mass ratio of the core-shell structure material to the carbonizable organic carbon source is 50: 5.0-200.0 of performing ultrasonic pre-dispersion in a solvent, performing the dispersion process in protective gas with a certain flow velocity, and setting parameters of the rotation speed, frequency, power density and dispersion time of the ultrasonic dispersion to obtain mixed slurry with the solid content of 20-60%;
in the step, the organic carbon source capable of being carbonized is one or more of emulsified asphalt, polyglycol ether, diethyl phthalate, polyethylene glycol, modified alkyd resin, furan resin, phenolic resin, polyvinyl alcohol, methyl cellulose, styrene-butadiene rubber, polymethacrylate, sucrose, glucose, polyvinylpyrrolidone, fatty alcohol-polyoxyethylene ether, alkylphenol ethoxylate, polyoxyethylene alkylamide, fatty acid-polyoxyethylene ester and polyoxyethylene alkylammonium, and the solvent is one or more of deionized water, methanol, ethanol, propanol, isopropanol, acetone, isopropyl ketone, N-hexane, N-methylpyrrolidone, tetrahydrofuran and ethyl acetate;
s5 drying treatment: drying the mixed slurry at 105-300 ℃ by adopting a stirring drying, or fluidized bed drying, or spray drying mode to prepare a precursor;
s6 carbonization: heating the precursor to 350-550 ℃ at a heating rate of 1-10 ℃/min under the protective gas atmosphere, and preserving the heat for 60-180 min to obtain a silicon/silicon oxide/carbon composite anode material precursor;
s7 high-temperature sintering treatment: heating the precursor of the silicon/silicon oxide/carbon composite negative electrode material to the calcining temperature of 600-1250 ℃ at the heating rate of 1-10 ℃/min under the protective gas atmosphere, calcining for 1-10.0 h, and naturally cooling to the room temperature after sintering to obtain the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery;
in the steps S4, S5, S6 and S7, the protective gas is one of nitrogen, helium, neon, argon, krypton or xenon, and the flow rate is 0.2-1.0 m 3 /h。
By utilizing the steps, the core-shell structure silicon/silicon oxide/carbon composite negative electrode material with a stable structure can be obtained.
Another object of the present invention is to produce a battery using the silicon/silicon oxide/carbon composite negative electrode material for a lithium ion battery of the present invention.
Compared with the prior art that the composite material obtained by liquid phase solidification is easy to agglomerate, and the surface of the coating layer of the composite material obtained by the method can be doped with a large amount of Si particles to cause serious capacity loss, the invention adopts an oxidant in-situ oxidation method and a high-temperature pyrolysis method, and sequentially grows and coats SiO outside the silicon nano particles in situ from the inside to the outside of the core-shell structure x Layer of Si @ SiO x The pyrolytic carbon layer is coated outside, the problem of agglomeration of the cathode material obtained by the method is solved, Si particles are not doped on the surface of a coating layer of the composite material, and the obtained composite material has the advantages of low capacity loss, high specific capacity and high first coulombic efficiency.
The silicon/silicon oxide/carbon composite negative electrode material prepared by adopting the oxidant in-situ oxidation-high temperature pyrolysis method has the advantages that the sizes of the silicon nanoparticle core and the silicon oxide shell are small, the size of the silicon nanoparticle is less than 300nm, and the size of the silicon oxide shell is less than 50nm, so that the volume of silicon is ensuredThe expansion is obviously reduced, the capacity of active substances is greatly improved, the specific capacity of the obtained cathode material is higher than 2800mAh/g, a silicon oxide layer prepared by in-situ oxidation of an oxide agent is combined with nano silicon particles by chemical bonds, the structure is stable, and the defects that the existing SiO obtained by physical mixing and dispersion is overcome x The coating layer is easy to generate structural collapse under the condition of large-current charge and discharge x The coating layer keeps stable structure in the heavy current charging and discharging process, and well buffers the volume expansion of the nano silicon in the charging and discharging process, so that the Si @ SiO x Simultaneously has high capacity of nano silicon cathode material, higher charging and discharging coulombic efficiency and SiO x The material has the characteristics of excellent cycle performance and rate capability.
The composite cathode material provided by the invention has the high capacity characteristic of the nano-silicon cathode material and the SiO x The material has the characteristics of high cycle performance and excellent rate capability.
In the preparation process of the silicon/silicon oxide/carbon composite anode material, Si @ SiO x After preparation, acid is used for purification, soluble metal ions are blended in silicon oxide in the previous steps for preparing the composite negative electrode material, so that the pyrolytic carbon coating layer can be firmly arranged on SiO x The surface of the layer also avoids the prior art on SiO x The high conductivity and stability of the pyrolytic carbon coating layer in the present invention contribute to the enhancement of Si @ SiO x Stability of an SEI film at an interface with an electrolyte.
After the composite cathode material prepared by the invention is prepared into a button type half cell, after the button type half cell is cycled for 100 weeks at a high rate of 1C, the capacity retention rate is more than 90 percent, after the button type half cell is cycled for 100 weeks at a rate of 0.2C, the capacity retention rate is more than 95 percent, after the button type half cell is cycled for 300 weeks at a rate of 0.2C, the capacity retention rate is more than 85 percent,
the composite material has high capacity, excellent rate performance and cycle performance, and the method for preparing the composite cathode material has the advantages of simple process, environmental friendliness, low production cost and the like, and is suitable for industrial production of the silicon/silicon oxide/carbon composite cathode material for the lithium ion battery and the battery.
Drawings
Fig. 1 is a TEM photograph of the silicon/silicon oxide/carbon composite anode material for a lithium ion battery prepared in example 1, with a scale bar of 100 nm.
Fig. 2 is an HRTEM photograph of the silicon/silicon oxide/carbon composite anode material for the lithium ion battery prepared in example 1, with a scale bar of 5 nm.
Fig. 3 is an X-ray diffraction spectrum of the silicon/silicon oxide/carbon composite anode material for a lithium ion battery prepared in example 1.
Fig. 4 is a charge and discharge curve of a battery made of a silicon/silicon oxide/carbon composite anode material for a lithium ion battery prepared in example 1.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
The silicon/silicon oxide/carbon composite cathode material for the lithium ion battery is of a double-core shell structure. The core of the core-shell structure is composed of nano silicon particles, the size of the nano silicon particles is 20-300 nm, and the nano silicon particles are spherical, quasi-spherical, elongated, flaky, conical or rhombic and the like; the shell layer has a multilayer structure, and the inner layer is silicon oxide SiO x The buffer layer is 1-50nm thick, and the outer layer is composed of a carbon layer coated outside the silicon oxide layer; the outer coating carbon layer is formed by carbonizing a carbonizable organic substance at a high temperature of 600-1250 ℃, and the nano Si @ SiO x The mass ratio of the core-shell structure material to the carbonizable organic carbon source is 50: 5.0-200.0%; the shell is a carbon coating layer coated outside the nano silicon particles and the silicon oxide inner layer thereof, and the mass of the coating layer is 2-200% of the mass of silicon.
The preparation method of the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery, which is the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery, comprises the following steps:
s1, preparing nano silicon particles: preparing nano silicon ions with the size of 20-300 nm;
s2, nanometer Si @ SiO x Preparation of core-shell structure material:
the prepared nano silicon powder is subjected to in-situ oxidation treatment in an oxidant to prepare Si @ SiO with controllable thickness x Core-shell materials, SiO x The thickness of the shell layer is controllable, and the size of the shell layer can be 1-50 nm;
s3, purification treatment:
the Si @ SiO prepared in the above way x Removing soluble metal ions from the core-shell structure material by acidification treatment, and then washing the core-shell structure material for at least 3 times by pure water for later use;
s4, mixing and dispersing:
the purified Si @ SiO x The mass ratio of the core-shell structure material to the carbonizable organic carbon source is 50: 5.0-200.0, the ultrasonic pre-dispersion is carried out in a solvent, the rotating speed is 150-600 r/min, the frequency is 10-20 kHz, and the power density is 0.25-0.45W/cm 2 After the ultrasonic pre-dispersion time is 30-120 min, obtaining mixed slurry with the solid content of 20-60%;
step S5, drying treatment:
drying the mixed slurry at 105-300 ℃ to prepare a precursor;
s6, carbonizing treatment:
carbonizing the precursor in a protective gas atmosphere to obtain a silicon/silicon oxide/carbon composite anode material precursor;
s7, high-temperature sintering treatment:
sintering the silicon/silicon oxide/carbon composite anode material precursor in a protective gas atmosphere, and naturally cooling to room temperature after sintering to obtain the silicon/silicon oxide/carbon composite anode material for the lithium ion battery;
in some embodiments, the method of preparing the nano silicon powder in step S1 is a solid phase ball milling method, a liquid phase ball milling method, a chemical vapor deposition method, a laser sputtering method, a plasma chemical vapor deposition method, or the like, and the silicon nanoparticles are spherical, or quasi-spherical, or elongated, or thin sheet, or conical, or rhombic, or the like;
in some embodiments, step S2 prepares the nano Si @ SiO x The oxidant used for the inner coating layer of the core-shell structure material is oxygen, potassium permanganate and dichromic acidOne or more mixed oxidants of potassium, sodium dichromate, nitric acid, potassium chlorate, sodium chlorate, potassium perchlorate, sodium perchlorate, hydrogen peroxide, peroxyacetic acid and the like;
in some embodiments, the acid used in step S3 is a mixed acid of one or more of hydrochloric acid, acetic acid, oxalic acid, or phosphoric acid;
in some embodiments, the carbonizable organic carbon source used in step S4 is one or more of emulsified asphalt, polyethylene glycol ether, diethyl phthalate, polyethylene glycol, modified alkyd resin, furan resin, phenolic resin, polyvinyl alcohol, methyl cellulose, styrene butadiene rubber, polymethacrylate, sucrose, glucose, polyvinylpyrrolidone, fatty alcohol polyoxyethylene ether, alkylphenol ethoxylates, polyoxyethylene alkylamides, fatty acid polyoxyethylene esters, and polyoxyethylene alkylammonium; the solvent is more than one of deionized water, methanol, ethanol, propanol, isopropanol, acetone, isopropanol, N-hexane, N-methylpyrrolidone, tetrahydrofuran and ethyl acetate;
in some embodiments, the drying manner adopted in step S5 is one of stirring drying, fluidized bed drying, or spray drying, and the drying temperature is 105-300 ℃;
the atomization rotating speed of spray drying is 8000-20000 r/min;
in some embodiments, the temperature rising rate used in step S6 is 1-10 ℃/min, and the temperature is maintained at 350-550 ℃ for 60-180 min;
in some embodiments, the temperature rising rate used in step S7 is 1-10 ℃/min, and the calcination time at 600-1250 ℃ is 1-10.0 h;
in some embodiments, the protective gas employed in the present invention is nitrogen, helium, neon, argon, krypton, or xenon.
Testing the composite negative electrode material prepared by the method, and determining an XRD (X-ray diffraction) pattern by using an XRD-7000X-ray diffractometer of Shimadzu corporation; observing the morphology and the particle size of the composite material by using a Zeiss Gemini SEM500 field emission scanning electron microscope; observing the thickness of the coating layer by using a FEITalos 200F transmission electron microscope; testing the specific surface area of the composite material by using a JW-DX type specific surface area tester of the Jingwei Gaobao company;
the silicon/silicon oxide/carbon composite negative electrode material prepared by the method is used for electrochemical performance test, and the composite negative electrode materials of examples 1-6 and the silicon-carbon negative electrode material of a comparative example are used as negative electrode active materials for button cell test. Weighing negative active substances including conductive carbon black SP, sodium carboxymethylcellulose CMC and styrene butadiene rubber SBR (85: 8:3: 4) according to a mass ratio, mixing and pulping, coating the mixture with the solid content of 40% on a Cu foil, drying for 12h at 85 ℃, rolling and punching, taking a metal lithium sheet as a counter electrode, and mixing fluoroethylene carbonate FEC: ethylene carbonate EC: ethyl methyl carbonate EMC ═ 1: 2: 7 preparing electrolyte, adopting a polypropylene PP, polyethylene PE and polypropylene PP multilayer composite film (laminated structure) as a diaphragm, and preparing the electrolyte into 2 groups of CR2032 button cells in a German Braun MBRAUN glove box protected by high-purity argon. The method comprises the steps of testing the electrical performance of a button cell by using a CT2001A type cell testing system of blue-electricity electronic products Limited company in Wuhan City, wherein the charging and discharging voltage range is 0.003-2.0V, the first discharging capacity mAh/g of 0.1C and the first efficiency are measured, after 3 weeks of charging and discharging activation of 0.1C are measured, the first group is subjected to 1C charging and discharging cycle testing, the cycle capacity retention rate of 100 weeks is calculated by using the ratio of the 1C discharging capacity of 100 weeks to the 1C discharging capacity of 1 week, the second group is subjected to 0.2C multiplying power charging and discharging cycle, and the cycle capacity retention rates of 100 weeks and 300 weeks are calculated.
Example 1
S1, preparation of nano silicon particles
Adopting a QM-3SP04 planetary ball mill, taking zirconia balls as a ball milling medium, taking micron-sized silicon powder as a raw material, and mixing the raw materials in a ratio of 20: 1, ball milling for 12 hours at the rotating speed of 500r/min to prepare spherical nano silicon powder, wherein the particle size of the silicon powder is 100 nm.
S2, nanometer Si @ SiO x Preparation of core-shell materials
Treating the prepared nano silicon powder for 3 hours at 500 ℃ in an oxygen atmosphere to obtain Si @ SiO with the silicon oxide inner layer thickness of 14nm x A core-shell structured material.
S3, purifying
The Si @ SiO prepared in the above way x The core-shell structure material is acidified by 1mol/L hydrochloric acid for 1h to remove soluble metal ions, and then washed by pure water for 3 times.
S4, mixing and dispersing
The purified Si @ SiO x The mass ratio of the core-shell structure material to the sucrose is 50:50 is subjected to ultrasonic pre-dispersion in water solution, the rotating speed is 300r/min, the frequency is 15kHz, and the power density is 0.35W/cm 2 After the ultrasonic pre-dispersion time is 60min, mixed slurry with the solid content of 45% is obtained;
s5, drying treatment
And stirring and drying the mixed slurry in a beaker at the temperature of 120 ℃ to obtain a precursor.
S6, carbonizing treatment
And (3) heating the precursor to 400 ℃ at the heating rate of 5 ℃/min under the protection of a nitrogen atmosphere, and preserving the temperature for 120min to obtain the silicon/silicon oxide/carbon composite anode material precursor.
S7, high-temperature sintering treatment
Heating the precursor of the silicon/silicon oxide/carbon composite negative electrode material to the calcining temperature of 700 ℃ at the heating rate of 3 ℃/min in the nitrogen atmosphere, calcining for 8 hours, naturally cooling to the room temperature after sintering to obtain the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery, wherein the size of a nano silicon particle core of the obtained composite negative electrode material is 100nm, and the SiO particle core of the obtained composite negative electrode material is x The size of the shell is 14nm, and the size of the shell is nano Si @ SiO x The mass ratio of the core-shell structure material to the pyrolytic carbon coating layer is 50: 50.
After the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery obtained in the embodiment 1 is sieved by a 250-mesh sieve, structural and morphological characterization and electrochemical performance test are carried out. The 0.1C first discharge capacity of the composite negative electrode material is 2834.3mAh/g, the first efficiency is 80.42%, the cycle capacity retention rate of the first group of batteries 1C in 100 charge-discharge cycles is 90.20%, the capacity retention rate of the second group of batteries 0.2C in 100 charge-discharge cycles is 96.30%, and the capacity retention rate of the second group of batteries 0.2C in 300 charge-discharge cycles is 86.50%, and the test results are summarized in Table 1.
As shown in fig. 3, is the XRD diffraction pattern of the composite material of example 1. By comparison with diffraction peaks of standard PDF cards (PDF #27-1402) of single crystal silicon, strong diffraction peaks observed near 28.4 °, 47.3 ° and 56.1 ° correspond to the (111), (220) and (311) crystal planes of crystalline silicon, respectively. The main components of the composite material can be determined to be Si and amorphous carbon through the analysis of an XRD pattern.
As shown in FIGS. 1 to 2, TEM photographs of the silicon/silicon oxide/carbon composite negative electrode material for lithium ion batteries prepared in example 1 were taken. As can be seen from the photo, the shape of the nano-silicon is spherical, the size of the particle is about 100nm, the particle has a core-shell structure, the core is a nano-silicon particle, the surface of the particle is provided with double coating layers, the inner coating layer is silicon oxide, the thickness is about 14nm, and the outer coating layer is an amorphous carbon coating layer.
Fig. 4 shows the charge/discharge curves of the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery obtained in example 1. The specific capacity of the composite material can be calculated to be 2830mAh/g, and the first efficiency is 80.30%.
Example 2
S1, preparation of nano silicon particles
Adopting a QM-3SP04 planetary ball mill, taking zirconia balls as a ball milling medium, taking micron-sized silicon powder as a raw material, and mixing the materials in a ball material ratio of 20: 1, ball milling for 24 hours at the rotating speed of 300r/min by using a solution of ethanol and water (the volume ratio is 50:50) to prepare slurry of nano silicon powder, wherein the particle size of the silicon is 300 nm.
S2, nanometer Si @ SiO x Preparation of core-shell materials
Treating the prepared nano silicon powder with 0.5mol/L potassium permanganate solution for 0.5h to prepare Si @ SiO with the thickness of 2nm x A core-shell structured material.
S3, purifying
The Si @ SiO prepared in the above way x The core-shell structure material was treated with 2mol/L acetic acid solution to remove soluble metal ions, and then washed with pure water 4 times.
S4, mixing and dispersing
The purified Si @ SiO x The mass ratio of the core-shell structure material to the methyl cellulose is 50: 5.0 ultrasonic predispersion in water at a speed of 150r/min, a frequency of 20kHz and a power density of 0.25W/cm 2 And obtaining mixed slurry with the solid content of 20% after the ultrasonic pre-dispersion time is 30 min.
S5, drying treatment
Drying the mixed slurry at 105 ℃ by adopting a fluidized bed drying mode to prepare a precursor.
S6, carbonizing treatment
Heating the precursor to 350 ℃ at the heating rate of 1 ℃/min in the helium atmosphere, and preserving the temperature for 180min to prepare a silicon/silicon oxide/carbon composite anode material precursor;
s7, high-temperature sintering treatment
Heating the precursor of the silicon/silicon oxide/carbon composite negative electrode material to 600 ℃ at the heating rate of 1 ℃/min in the helium atmosphere, calcining for 10h, naturally cooling to room temperature after sintering to obtain the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery, wherein the size of a nano silicon particle core of the obtained composite negative electrode material is 300nm, and the SiO particle core of the obtained composite negative electrode material is SiO x The size of the shell is 2nm, and the size of the shell is nano Si @ SiO x The mass ratio of the core-shell structure material to the pyrolytic carbon coating layer is 50: 5.
And (3) screening the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery obtained in the example 2 through a 250-mesh sieve, and then carrying out electrochemical performance test. The 0.1C first discharge capacity of the composite negative electrode material is 3250.8mAh/g, the first efficiency is 78.50%, the 1C charge-discharge capacity retention rate in 100 weeks is 88.70%, the 0.2C charge-discharge capacity retention rate in 100 weeks is 95.70%, and the 0.2C charge-discharge capacity retention rate in 300 weeks is 86.10%, and the test results are summarized in Table 1.
Example 3
S1, preparation of nano silicon particles
Adopts chemical vapor deposition method, uses RTL1200 type rotary tube furnace as synthesis equipment, uses SiH 4 Is silicon source, argon gas is protective gas, the pressure of the reaction chamber is 0.2MPa, SiH 4 The flow rate of the reaction is 180ml/min, the reaction temperature is 750 ℃, and spherical nano silicon powder is prepared, and the particle size of the silicon powder is 40 nm;
s2, nanometer Si @ SiO x Preparation of core-shell materials
The prepared nano silicon powder is used with the weight of 0.02mol/LThe potassium chromate solution is treated for 5 hours to obtain Si @ SiO with the thickness of 5nm x A core-shell structured material.
S3, purifying
The Si @ SiO prepared in the above way x The core-shell structure material is stirred and treated with 0.1mol/L oxalic acid for 3h to remove soluble metal ions, and then is washed and treated with pure water for 4 times.
S4, mixing and dispersing
The purified Si @ SiO x The mass ratio of the core-shell structure material to the polyvinyl alcohol is 50:200 is subjected to ultrasonic pre-dispersion in an ethanol water solution (volume ratio of 50:50), the rotating speed is 600r/min, the frequency is 10kHz, and the power density is 0.45W/cm 2 And after the ultrasonic pre-dispersion time is 120min, obtaining mixed slurry with the solid content of 60%.
S5, drying treatment
Drying the mixed slurry at 300 deg.C by spray drying at 8000r/min under nitrogen protection with flow rate of 0.2m to obtain precursor 3 /h。
S6, carbonizing treatment
Heating the precursor to 550 ℃ at a heating rate of 10 ℃/min under an argon atmosphere, and preserving the temperature for 60min to obtain a silicon/silicon oxide/carbon composite anode material precursor;
s7, high-temperature sintering treatment
Heating the precursor of the silicon/silicon oxide/carbon composite negative electrode material to the calcination temperature of 1250 ℃ at the heating rate of 10 ℃/min under the argon atmosphere, calcining for 1h, naturally cooling to room temperature after sintering is finished, obtaining the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery, wherein the size of a nano silicon particle core of the obtained composite negative electrode material is 40nm, and the SiO particle core of the obtained composite negative electrode material is SiO x The size of the shell is 5nm, and the size of the shell is nano Si @ SiO x The mass ratio of the core-shell structure material to the pyrolytic carbon coating layer is 50: 200.
And (3) screening the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery obtained in the embodiment 3 through a 250-mesh sieve, and then carrying out electrochemical performance test. The 0.1C first discharge capacity of the composite negative electrode material is 3030.50mAh/g, the first efficiency is 79.80%, the 1C charge-discharge 100-week cycle capacity retention rate is 89.50%, the 0.2C charge-discharge 100-week capacity retention rate is 95.80%, and the 0.2C charge-discharge 300-week capacity retention rate is 86.30%, and the test results are summarized in Table 1.
Example 4
S1, preparation of nano silicon particles
Preparing nanometer silicon powder by laser sputtering method with NPD-4000(A) full-automatic PLD pulsed laser deposition system, laser wavelength of 800nm and power density of 10 5 W/cm 2 Silicon with the purity of 5N is used as a target material, argon is used as protective gas, the vacuum degree is less than 133Pa, the temperature is 800 ℃, the deposition time is 4 hours, and the particle size of the prepared silicon powder is 20 nm.
S2, nanometer Si @ SiO x Preparation of core-shell materials
Treating the prepared nano silicon powder with 0.02mol/L sodium dichromate solution for 8h to obtain Si @ SiO with the thickness of 10nm x A core-shell structured material.
S3, purifying
The Si @ SiO prepared in the above way x The core-shell structure material is acidified by 0.5mol/L phosphoric acid for 2h to remove soluble metal ions, and then washed by pure water for 5 times.
S4, mixing and dispersing
The purified Si @ SiO x The core-shell structure material and the phenolic resin are mixed according to the mass ratio of 50:20 in a mixed solvent of ethanol and acetone (volume ratio of 50:50) at a rotation speed of 300r/min, a frequency of 15kHz and a power density of 0.30W/cm 2 And obtaining mixed slurry with the solid content of 30% after the ultrasonic pre-dispersion time is 60 min.
S5, drying treatment
And drying the mixed slurry at 110 ℃ by adopting a stirring and drying mode to obtain a precursor.
S6, carbonizing treatment
And heating the precursor to 450 ℃ at the heating rate of 3 ℃/min under the argon atmosphere, and preserving the temperature for 90min to obtain the silicon/silicon oxide/carbon composite anode material precursor.
S7, high-temperature sintering treatment
Heating up the precursor of the silicon/silicon oxide/carbon composite anode material at the speed of 3 ℃/min in the argon atmosphereHeating to the calcining temperature of 750 ℃, calcining for 3h, naturally cooling to room temperature after sintering to obtain the silicon/silicon oxide/carbon composite anode material for the lithium ion battery, wherein the size of the nano silicon particle core of the obtained composite anode material is 20nm, and the SiO particle core of the obtained composite anode material is SiO x The size of the shell is 10nm, and the size of the shell is nano Si @ SiO x The mass ratio of the core-shell structure material to the pyrolytic carbon coating layer is 50: 20.
The lithium ion battery obtained in example 4 was subjected to electrochemical performance testing after passing through a 250 mesh sieve using a silicon/silicon oxide/carbon composite negative electrode material. The 0.1C first discharge capacity of the composite negative electrode material is 2790.10mAh/g, the first efficiency is 81.20%, the 1C charge-discharge capacity retention rate in 100 weeks is 91.20%, the 0.2C charge-discharge capacity retention rate in 100 weeks is 96.50%, and the 0.2C charge-discharge capacity retention rate in 300 weeks is 86.70%, and the test results are summarized in Table 1.
Example 5
S1, preparation of nano silicon particles
Adopting a plasma chemical vapor deposition method, taking a German CYRANNUS plasma chemical vapor deposition system as synthesis equipment, the frequency is 2.45GHz, the power is 3kW, and SiH is used 4 Is silicon source, argon gas is protective gas, the pressure of the reaction chamber is 0.15MPa, SiH 4 The flow rate of the reaction is 300ml/min, the reaction temperature is 800 ℃, and the nano silicon powder is prepared, and the particle size of the silicon powder is 50 nm.
S2, nanometer Si @ SiO x Preparation of core-shell materials
Treating the prepared nano silicon powder with 0.05mol/L potassium perchlorate to prepare Si @ SiO with the thickness of 15nm x A core-shell structured material.
S3, purifying
The Si @ SiO prepared above is mixed x The core-shell structure material was acidified with 0.5mol/L hydrochloric acid for 5 hours to remove soluble metal ions, and then washed with pure water 3 times.
S4, mixing and dispersing
The purified Si @ SiO x The core-shell structure material and the styrene butadiene rubber are mixed according to the mass ratio of 50:20 ultrasonic pre-dispersion in water at a rotation speed of 200r/min, a frequency of 15kHz and a power density of 0.30W/cm 2 Ultrasonic pre-dispersion timeAfter 90min, a mixed slurry with a solid content of 50% was obtained.
S5, drying treatment
And drying the mixed slurry at 150 ℃ by adopting a stirring and drying mode to obtain a precursor.
S6, carbonizing treatment
And heating the precursor to 500 ℃ at the heating rate of 5 ℃/min under the nitrogen atmosphere, and preserving the temperature for 90min to obtain the silicon/silicon oxide/carbon composite anode material precursor.
S7, high-temperature sintering treatment
Heating the precursor of the silicon/silicon oxide/carbon composite negative electrode material to the calcining temperature of 1000 ℃ at the heating rate of 5 ℃/min under the nitrogen atmosphere, calcining for 3h, naturally cooling to the room temperature after sintering is finished to obtain the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery, wherein the size of a nano silicon particle core of the obtained composite negative electrode material is 50nm, and the SiO particle core of the obtained composite negative electrode material is SiO x The size of the shell is 15nm, and the size of the shell is nano Si @ SiO x The mass ratio of the core-shell structure material to the pyrolytic carbon coating layer is 50: 20.
The lithium ion battery obtained in example 5 was subjected to electrochemical performance testing after passing through a 250 mesh sieve using a silicon/silicon oxide/carbon composite negative electrode material. The 0.1C first discharge capacity of the composite negative electrode material is 2870.90mAh/g, the first efficiency is 80.90%, the cycle capacity retention rate of 1C charge-discharge 100 weeks is 88.60%, the capacity retention rate of 0.2C charge-discharge 100 weeks is 96.02%, and the capacity retention rate of 0.2C charge-discharge 300 weeks is 86.50%, and the test results are summarized in Table 1.
Example 6
S1, preparation of nano silicon particles
Adopting a QM-3SP04 planetary ball mill, taking zirconia balls as a ball milling medium, taking micron-sized silicon powder as a raw material, and mixing the raw materials in a ratio of 20: ball milling is carried out for 24 hours at the rotating speed of 600r/min according to the ball material ratio of 1 to obtain the sphere-like nano silicon powder, and the particle size of the silicon powder is 20 nm.
S2, nanometer Si @ SiO x Preparation of core-shell materials
Treating the prepared nano silicon powder with 3% hydrogen peroxide for 12h to obtain Si @ SiO with the thickness of 50nm x A core-shell structured material.
S3, purifying
The Si @ SiO prepared in the above way x The core-shell structure material is acidified by 0.5mol/L hydrochloric acid for 4h to remove soluble metal ions, and then washed by pure water for 3 times.
S4, mixing and dispersing
The purified Si @ SiO x The mass ratio of the core-shell structure material to the polyvinyl alcohol is 50:50 ultrasonic pre-dispersing in ethanol water solution (volume ratio 1: 1) at 300r/min, 20kHz frequency and 0.25W/cm power density 2 And obtaining mixed slurry with the solid content of 30% after the ultrasonic pre-dispersion time is 120 min.
S5, drying treatment
Drying the mixed slurry at 260 deg.C by spray drying to obtain precursor, wherein the atomization rotation speed is 20000r/min, the flow is 1.0m under nitrogen protection 3 /h。
S6, carbonizing treatment
And heating the precursor to 400 ℃ at the heating rate of 2 ℃/min under the argon atmosphere, and preserving the temperature for 100min to obtain the silicon/silicon oxide/carbon composite anode material precursor.
S7, high-temperature sintering treatment
Heating the precursor of the silicon/silicon oxide/carbon composite negative electrode material to a calcination temperature of 650 ℃ at a heating rate of 2 ℃/min in an argon atmosphere, calcining for 8 hours, naturally cooling to room temperature after sintering to obtain the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery, wherein the size of a nano silicon particle core of the obtained composite negative electrode material is 20nm, and the SiO particle core of the obtained composite negative electrode material is x The size of the shell is 20nm, and the size of the shell is nano Si @ SiO x The mass ratio of the core-shell structure material to the pyrolytic carbon coating layer is 50: 50.
The silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery obtained in example 6 was sieved with a 250 mesh sieve, and then subjected to electrochemical performance test. The 0.1C first discharge capacity of the composite negative electrode material is 2950.60mAh/g, the first efficiency is 80.10%, the 1C charge-discharge capacity retention rate in 100 weeks is 89.90%, the 0.2C charge-discharge capacity retention rate in 100 weeks is 96.80%, and the 0.2C charge-discharge capacity retention rate in 300 weeks is 86.90%, and the test results are summarized in Table 1.
Comparative example 1
A composite silicon negative electrode material is prepared by the following method:
s1, selecting silicon powder with the median particle size of 50-80 nm as nano silicon, placing the nano silicon in a rotary furnace at the rotating speed of 20r/min, introducing mixed gas of argon and oxygen with the volume ratio of 1:0.5 at the gas flow of 0.5L/min, and carrying out heat treatment for 1h at 500 ℃ to obtain primary heat-treated silicon powder;
s2, mixing the primary heat-treated silicon powder, bismuth powder and tin powder according to the mass ratio of 100:5:5, then loading the mixture into a high-energy ball mill, loading zirconium balls with the diameter of 0.5mm, then introducing argon protective gas, and carrying out high-energy ball milling, wherein the rotating speed of the ball mill is 3000r/min, the mass ratio of the grinding balls to the powder is 10:1, and carrying out ball milling for 20 hours to obtain ball-milled mixed powder; then placing the ball-milled mixed powder in a rotary furnace with the rotating speed of 50r/min, introducing argon, and carrying out heat treatment for 2 hours at 800 ℃ to obtain a first precursor;
s3, proportioning the first precursor and asphalt powder with the particle size of 3 mu m according to a mass ratio of 70:30, uniformly mixing, placing in a VC mixer, adjusting the frequency to 50Hz, and mixing for 60min to obtain a second precursor;
and S4, adding the second precursor into a fusion machine, adjusting the rotation speed to 2000rpm, fusing for 5 hours, then placing the second precursor into a high-temperature box-type furnace, introducing nitrogen protective gas, heating to 800 ℃, preserving heat for 3 hours, cooling to room temperature, crushing, screening and demagnetizing to obtain the composite silicon cathode material.
The composite silicon negative electrode material obtained in comparative example 1 had a nano-silicon content of 50 wt%, a nano-composite coating thickness of 20nm, and the nano-composite coating was SiO 1.5 And the nano composite coating is coated with a conductive carbon layer.
And (3) screening the silicon/carbon composite negative electrode material for the lithium ion battery obtained in the comparative example 1 through a 250-mesh sieve, and then carrying out electrochemical performance test. The 0.1C first discharge capacity of the composite negative electrode material is 1683.2mAh/g, the first efficiency is 86.6%, the cycle capacity retention rate after 100 weeks of 1C charge and discharge is 63.8%, the cycle capacity retention rate after 100 weeks of 0.2C charge and discharge is 92.90%, the cycle capacity retention rate after 300 weeks of 0.2C charge and discharge is 73.60%, and the test results of the comparative example are summarized in Table 1.
According to the silicon/silicon oxide/carbon composite cathode material and the preparation method and the battery thereof, a compact silicon oxide inner buffer layer is formed on the surface of a nano silicon particle and a compact carbon coating layer is formed outside the compact silicon oxide inner buffer layer by constructing the structural design of a core-double shell structure. Li is formed by the silicon oxide inner cladding layer in the first charge-discharge process 2 O and Li 4 SiO 4 The buffer layer can effectively inhibit the volume expansion and contraction of the nano silicon, and the amorphous carbon outer coating layer is beneficial to improving the electron transmission of an interface and enhancing the stability of an SEI film of the interface, so that the structural stability and the electrochemical performance of the composite material are improved by improving the structural stability and the electrochemical performance of the nano silicon.
Compared with the prior art, the method generates the lithium storage active phase SiO on the surface of the nanometer silicon by the double-nucleocapsid structure x And the amorphous pyrolytic carbon coating layer can well buffer the volume expansion of nano silicon in the charge-discharge process on the premise of not remarkably reducing the capacity, and the high conductivity and stability of the pyrolytic carbon coating layer are favorable for enhancing the Si @ SiO x And the stability of an SEI film on an electrolyte interface, so that the composite material has the advantages of high capacity, excellent rate capability and cycle performance, environmental friendliness, low production cost and the like, and is suitable for industrial silicon/silicon oxide/carbon composite cathode materials for lithium ion batteries, preparation methods thereof and batteries.
The preparation method is simple, environment-friendly, easy to control process conditions, low in production cost and easy for industrial production.
Table 1: summary of test results in examples
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and these modifications or substitutions do not depart from the scope of the embodiments of the present invention in nature.
Claims (6)
1. A preparation method of a silicon/silicon oxide/carbon composite negative electrode material for a lithium ion battery is characterized by comprising the following steps:
s1: preparing nano silicon particles with the size of 20 nm-300 nm and the shape of sphere, quasi-sphere, strip, cone or diamond;
s2: preparing a nano silicon/silicon oxide core-shell structure material, namely performing in-situ oxidation treatment on the nano silicon particles prepared in the step S1 by using an oxidant to obtain the silicon/silicon oxide core-shell structure material, wherein the oxidant used in the in-situ oxidation treatment in the step is a mixed oxidant consisting of one or more than two of potassium permanganate, potassium dichromate, sodium dichromate, nitric acid, potassium chlorate, sodium chlorate, potassium perchlorate, sodium perchlorate, hydrogen peroxide and peracetic acid;
s3: a purification step of removing impurities mixed in the step S2, specifically, the silicon/silicon oxide core-shell structure material prepared in the step S2 is acidified by an acid to remove soluble metal ions, and then is washed by pure water for at least 3 times, wherein the acid used in the purification step is a mixed acid composed of one or more of hydrochloric acid, acetic acid, oxalic acid, and phosphoric acid;
s4: mixing and dispersing the carbonizable organic carbon source and the silicon/silicon oxide treated in the step S3;
s5: drying, namely drying the product processed in the step S4;
s6: carbonizing, namely carbonizing the product dried in the step S5 to obtain a silicon/silicon oxide/carbon composite anode material precursor;
s7: sintering at high temperature, namely sintering the silicon/silicon oxide/carbon composite anode material precursor prepared in the step S6, and cooling to obtain the silicon/silicon oxide/carbon composite anode material for the lithium ion battery;
the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery, which is obtained by the preparation method of the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery, has a core-shell structure, wherein the core is formed by nano silicon particles;
the inner layer of the shell layer structure is a silicon oxide buffer layer, and the shell is composed of a pyrolytic carbon layer coated outside the silicon oxide layer;
the thickness of the silicon oxide buffer layer structure coated outside the nano silicon particle core is 1 nm-50 nm, and the mass of the silicon oxide buffer layer is 2% -200% of that of the silicon particle core;
the mass ratio of the nano silicon/silicon oxide core-shell structure material to the pyrolytic carbon coating layer is 50: 5.0 to 200.0.
2. The method for preparing the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery according to claim 1, wherein the method comprises the following steps: the organic carbon source capable of being carbonized adopted in the step S4 is one or a combination of more than two of emulsified asphalt, polyglycol ether, diethyl phthalate, polyethylene glycol, modified alkyd resin, furan resin, phenolic resin, polyvinyl alcohol, methyl cellulose, styrene-butadiene rubber, polymethacrylate, sucrose, glucose, polyvinylpyrrolidone, fatty alcohol-polyoxyethylene ether, alkylphenol ethoxylate, polyoxyethylene alkylamide, fatty acid-polyoxyethylene ester and polyoxyethylene alkylammonium; the solvent is one or more of deionized water, methanol, ethanol, propanol, isopropanol, acetone, isopropanol, N-hexane, N-methylpyrrolidone, tetrahydrofuran and ethyl acetate.
3. The method for preparing the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery according to claim 1, wherein the method comprises the following steps: in the step S4, the mass ratio of the silicon/silicon oxide core-shell structure material purified by the S3 to the carbonizable organic carbon source is 50: 5.0-200.0, and performing ultrasonic pre-dispersion in a solvent, wherein the dispersion process is performed in protective gas, so as to obtain mixed slurry with the solid content of 20-60%.
4. The method for preparing the silicon/silicon oxide/carbon composite negative electrode material for the lithium ion battery according to claim 1, wherein the method comprises the following steps: the steps S4, S5, S6 and S7 are carried out in protective gas, and the protective gas is mixed gas consisting of one or more than two of nitrogen, helium, neon, argon, krypton or xenon.
5. The silicon/silicon oxide/carbon composite negative electrode material for lithium ion batteries, which is obtained by the method for preparing a silicon/silicon oxide/carbon composite negative electrode material for lithium ion batteries according to any one of claims 1 to 4, wherein the structure of the silicon/silicon oxide/carbon composite negative electrode material for lithium ion batteries is a core-shell structure, and the core is composed of nano silicon particles;
the inner layer of the shell layer structure is a silicon oxide buffer layer, and the shell is composed of a pyrolytic carbon layer coated outside the silicon oxide layer;
the thickness of the silicon oxide buffer layer structure coated outside the nano silicon particle core is 1 nm-50 nm, and the mass of the silicon oxide buffer layer is 2% -200% of that of the silicon particle core;
the mass ratio of the nano silicon/silicon oxide core-shell structure material to the pyrolytic carbon coating layer is 50: 5.0 to 200.0;
the size of the core nano silicon particle with the core-shell structure is 20 nm-300 nm, and the shape of the core nano silicon particle is spherical, quasi-spherical, elongated, conical or rhombic.
6. A lithium ion battery, characterized by: the lithium ion battery comprises the silicon/silicon oxide/carbon composite negative electrode material obtained by the preparation method of any one of claims 1 to 4 or the silicon/silicon oxide/carbon composite negative electrode material of claim 5.
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