CN109817949B

CN109817949B - Silicon or oxide @ titanium dioxide @ carbon core-shell structure composite particle thereof and preparation

Info

Publication number: CN109817949B
Application number: CN201910179288.6A
Authority: CN
Inventors: 肖哲熙; 魏飞; 张晨曦; 于春辉; 林贤清
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2019-03-11
Filing date: 2019-03-11
Publication date: 2021-05-14
Anticipated expiration: 2039-03-11
Also published as: CN109817949A

Abstract

The invention discloses silicon or an oxide @ titanium dioxide @ carbon core-shell structure composite particles thereof, and belongs to the field of lithium ion battery cathode materials. The composite particles are of a compact three-layer structure and comprise a core, a middle layer and an outer layer; wherein the core contains silicon or its oxide, and the intermediate layer contains TiO₂And the outer layer is a carbon-containing C layer. In addition, the invention also provides a preparation method of the composite particle, which comprises a titanium coating step and a carbon coating step; the titanium coating step and the carbon coating step are both completed in a fluidized bed reactor. The core-shell structure composite particles prepared by the method have high specific capacity, and have excellent cycle stability and rate capability.

Description

Silicon or oxide @ titanium dioxide @ carbon core-shell structure composite particle thereof and preparation

Technical Field

The invention relates to the technical field of lithium ion battery cathode materials, in particular to silicon or oxide @ titanium dioxide @ carbon core-shell structure composite particles and a preparation method thereof, and the composite particles can be used for lithium ion battery cathode materials.

Background

Since the advent of lithium ion batteries, lithium ion batteries have been widely used in many fields because of their advantages such as high energy density, high power density, low self-discharge, and high safety. In recent years, the development of high capacity density lithium ion batteries has become an important target in the future. The silicon is taken as the representative of the anode material of the new-generation lithium ion battery, has wide source, low cost, highest theoretical specific capacity (4200mAh/g) and large volume energy density (9786 mAh/cm)³) Etc. and the phase of the silicon compound in the electrochemical reaction for removing lithium is oppositeModerate (0.4V) and is therefore considered to be one of the most promising materials for negative electrodes. However, in practical application, due to the huge volume effect (400%), the silicon-based negative electrode material is susceptible to the adverse effects of electrode pulverization, conductive network destruction, rapid growth of SEI (solid electrolyte interphase) film and the like, so that the capacity is rapidly attenuated. And low conductivity by itself also results in poor rate performance.

Titanium dioxide (TiO)₂) Is a high-melting-point material and has good thermal stability. The self-expansion rate of the material in chemical reaction is low, and the material has excellent electrical property due to high dielectric constant, so that ionic and electronic conduction is facilitated. The composite material is used as a coating layer to be compounded with a silicon-based material, so that the damage of internal volume expansion to the whole structure can be relieved, and the whole electrochemical performance can be improved. Carbon, as an excellent conductor, can significantly improve the overall conductivity of the composite. The existing application reports, for example, Si @ C @ TiO is prepared by taking Si nano particles as cores and performing liquid phase coating by using titanium source and carbon source precursor₂The electrochemical performance of the double-coated composite particles is obviously improved (Song Yan et al, patent publication No. CN 106099062A). However, the existing coating method mainly has the following problems: 1) the coating method mainly focuses on a liquid phase method, a precursor is added to carry out solvothermal or hydrolysis reaction to deposit on the surface of the powder, and then the coating structure is obtained through high-temperature treatment. In the method, a precursor solution and powder are generally physically mixed in advance, but natural density difference exists between various liquid precursors and silicon or oxide powder thereof, so that physical mixing difficulty is easily caused essentially, and coating uniformity is difficult to ensure; 2) the liquid phase system is difficult to be prepared and mass production is difficult; 3) the liquid phase preparation product also needs to be subjected to post-treatment such as centrifugation and suction filtration, and the process is complicated and the efficiency is low.

Aiming at the problems, the invention aims to provide silicon or oxide thereof @ titanium dioxide @ carbon core-shell structure composite particles and a fluidized bed preparation method thereof. The method can solve the problem that the coating uniformity is difficult to ensure by the existing liquid phase method, is more suitable for industrial amplification in production practice, has continuous mass production capacity and high efficiency, and can be used for preparing products with excellent electrochemical performance.

Disclosure of Invention

The embodiment of the invention provides silicon or oxide thereof @ titanium dioxide @ carbon core-shell structure composite particles and a fluidized bed preparation method thereof. The following presents a simplified summary in order to provide a basic understanding of some aspects of the disclosed embodiments. This summary is not an extensive overview and is intended to neither identify key/critical elements nor delineate the scope of such embodiments. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

According to a first aspect of embodiments of the present invention there is provided a silicon or oxide thereof @ titanium dioxide @ carbon core shell structured composite particle;

in some exemplary embodiments, the composite particles are a dense three-layer structure: comprises a core, an intermediate layer and an outer layer; wherein the core contains silicon Si or its oxide SiO_xThe intermediate layer contains titanium dioxide TiO₂And the outer layer is a carbon-containing C layer.

The silicon or oxide @ titanium dioxide @ carbon core-shell structure composite particle provided by the invention has the following characteristics and technical effects:

the titanium dioxide of the middle layer and the carbon of the outer layer are both formed by powder through a chemical vapor deposition method under the condition of sufficient fluidization, and the formed coating layer is uniform and compact by utilizing the characteristic of high mass and heat transfer rate of the fluidized bed and no reaction dead zone, thereby being beneficial to fully inhibiting the expansion of internal active substances; and secondly, the reaction is carried out at high temperature, the crystallinity of the coating layer is high, the rapid conduction of ion and electron is facilitated, and the reaction performance is further improved.

In the above embodiments, the core may be pure Si and/or SiO_xOr doped with other metal or nonmetal elements such as Si and/or SiO_xIs a mixture of the main body. Approximately, the intermediate layer is titanium oxide, i.e. may be pure TiO₂Or with TiO_xIs a mixture of the main body. The outer layer is a coating layer mainly made of carbon, and can be pure carbon material, such as amorphous carbon, graphene, graphite carbon, etc., or carbon material doped with metal or nonmetal elementsAnd so on.

Preferably, the core is pure Si or SiO_xAnd (3) pulverizing. The pure Si powder has an effect of providing a high capacity, and when the core is the pure Si powder, the composite particle has a high upper limit of the capacity. Pure SiO_xCompared with pure Si powder, the powder has lower expansion rate and better cyclicity, and when the powder is used as a core material, the composite particle has better cyclicity while the capacity is reduced to a certain extent.

Preferably, the intermediate layer is high-purity high-crystallinity TiO₂. Further, the TiO₂The crystallinity of (A) is not less than 80%. Further, the purity thereof is not less than 99%. The titanium dioxide in the middle layer of the composite particle has high crystallinity, and the effects of facilitating ion conduction and improving the ion diffusion performance of the composite are achieved by improving the crystallinity.

Preferably, the outer layer is C with a high degree of graphitization. Further, I of said C_D/I_GNot greater than 1.0. For describing the graphitization degree of the carbon layer, the carbon layer located 1360cm in Raman spectrum is generally adopted^-1D peak intensity of 1580cm^-1D peak to peak intensity ratio (I)_D/I_G). The relative intensity of the D peak is the SP3 vibration of disordered structure carbon, the degree of reaction structure disorder, while the G peak represents the SP2 vibration of a complete graphitized structure, I_D/I_GSmaller means a less defective structure and higher ordered crystallinity. I is_D/I_GNot more than 1.0, the carbon layer has high graphitization degree, corresponding to high conductivity. The outer layer C of the composite particle has high graphitization degree and good conductivity, improves the electron transfer rate and obviously improves the conductivity of the whole composite.

Preferably, the mass fraction of the core is 60-80%, the mass fraction of the middle layer is 1-19%, and the mass fraction of the outer layer is 1-20%, based on 100% of the total weight of the composite particle. The embodiment discloses the optimal proportion of the inner layer and the outer layer in the composite particle, and further optimizes the overall electrochemical performance of the composite particle.

Preferably, the preferred diameter range of the particles of the core is 0.01-10 μm.

Preferably, the thickness of the intermediate layer is 1 to 100 nm.

Preferably, the thickness of the outer layer is 5-100 nm. Further, the thickness of the outer layer is 10-80 nm.

It has been found that the inner core particles should not be too large, and are preferably on the order of nanometers or sub-microns. The large particles easily cause the increase of the whole diffusion distance, the external conduction time and the internal conduction time of the electron ions are prolonged, and the generation efficiency of the electrochemical reaction is influenced. The intermediate layer is used as an ion and electron conduction promoting layer, has a certain buffer volume effect, and can fully play the role of the intermediate layer under the hundred-nanometer level without influencing the whole conduction distance. The outer layer mainly serves to improve the conductivity and prevent the contact between the external electrolyte and the internal components, the carbon layer can improve the electron conduction speed, the carbon layer is too thin to improve the overall conductivity, and the carbon layer with too thick thickness needs to maintain a proper thickness because the crystal lattice stacking effect influences the ion conduction efficiency. The dimensional data of the above examples, set according to the above, further improve the electrochemical performance of the composite particle when the internal structural dimension of the composite particle reaches the above range.

After the composite particles reach the characteristics, the composite particles have excellent electrochemical performances that the specific capacity is not lower than 900mAh/g, and the capacity retention rate is not lower than 88% after the composite particles are cycled for 300 circles under the test condition of constant current charge and discharge of 1A/g.

Further, the particle size of the core material can be nano-scale or micro-scale. In the prior art, the relative particle size of the micron system is large, and the realization of uniform coating of a multilayer structure is more challenging. While the core of the silicon or its oxide @ titanium oxide @ C core-shell structured composite particles described herein, i.e. containing Si and/or SiO_xWhen the powder is micron-sized powder, the TiO at the middle layer can still be obtained through the high mass and heat transfer efficiency of the fluidized bed when the powder is fully fluidized₂And the outer layer C has a compact and uniform coating effect.

In a second aspect, the invention provides a preparation method for preparing the silicon or the oxide @ titanium dioxide @ C core-shell structure composite particles in the above embodiments.

In some exemplary embodiments, the preparation method is used for preparing the composite particles described in the above embodiments, and the preparation method comprises a titanium coating step and a carbon coating step; the titanium coating step and the carbon coating step are both completed in a fluidized bed reactor.

In the embodiment, the characteristics of efficient heat and mass transfer of the fluidized bed in a fully fluidized state of the powder are utilized, the method is more suitable for industrial amplification in production practice, and the method has continuous mass production capacity and improves efficiency to prepare the high-performance lithium ion battery cathode material. Tests show that the silicon or the oxide thereof @ titanium oxide @ carbon core-shell structure composite particles prepared by the method can realize high-crystallization compact and uniform coating, the conductivity and the ion conductivity of the whole material are obviously improved, the specific capacity is high, the cycling stability is good, and the rate performance is good.

Specifically, the titanium coating step comprises:

mixing Si or SiO_xIntroducing the powder into a fluidized bed reactor, keeping the powder in a fully fluidized state under a first inert atmosphere, and heating the powder to a first reaction temperature; TiCl carried by a first carrier gas₄Introducing steam and water vapor into the fluidized bed respectively for deposition reaction, and stopping introducing TiCl after the first reaction time₄Cooling the steam and the water vapor to room temperature to obtain an intermediate product;

the carbon coating step comprises: heating the intermediate product to a second reaction temperature in a fully fluidized state under a second inert atmosphere; and introducing a carbon source gas carried by a second carrier gas into the fluidized bed for deposition reaction, stopping introducing the carbon source gas after the second reaction time, and cooling to room temperature to obtain a final product, namely the core-shell structure composite particles.

The embodiment provides a specific technical scheme for preparing the composite particles by the fluidized bed, further optimizes the preparation scheme of the composite particles, and further improves a series of electrochemical properties of the composite particles in the embodiment.

The titanium coating step and the carbon coating step are further described below, respectively.

In the titanium coating step:

preferably, the first and second liquid crystal materials are,the first inert atmosphere is argon, and the total space velocity is 200-^-1. Preferably, the total space velocity of the first inert atmosphere is 400h^-1、600h^-1、1000h^-1. The space velocity is too low to ensure that the gas is in a good fluidized state. And the air speed is too high, and the phenomenon of mass entrainment can be caused by exceeding the escape speed of the powder, so that the yield is reduced. Through this embodiment, further promote the electrochemical properties of core-shell structure composite particle.

Preferably, the first reaction temperature is 900-1400 ℃. Preferably, the first reaction temperature is 1000, 1200 and 1400 ℃. Further, in the process of heating the powder to the first reaction temperature under the protection of the first inert atmosphere, the heating rate is 1-25 ℃/min. Preferably, the heating rate is 5, 10, 15 ℃/min. The deposition reaction of titanium dioxide occurs at a temperature of at least 900 ℃ as determined by thermodynamic calculations, with higher temperatures leading to more complete reaction. However, it should be noted that the fluidization process needs to take into consideration the upper temperature resistance limit and the expansion coefficient of the furnace tube material of the whole reactor. The corundum tube has good safety when resisting temperature of about 1400 ℃, the temperature rising speed is not too high, and the corundum tube has great damage to the furnace tube and greatly reduces the service life when exceeding 25 ℃/min. In this embodiment, the first reaction temperature and the temperature rise rate are limited, and the electrochemical performance of the core-shell structure composite particles prepared in the fluidization process is further improved.

Preferably, TiCl₄The volume ratio of the steam to the water vapor is 1: 2-10. Preferably, TiCl₄And water in a volume ratio of 1: 4. 1: 6. 1: 8.

preferably, the first carrier gas is nitrogen, argon or a mixture of the two.

Preferably, TiCl₄The volume ratio of the first carrier gas to the second carrier gas is 1: 1-10, wherein the volume ratio of the water vapor to the first carrier gas is 1:2 to 20. Preferably, TiCl₄The volume ratio of the first carrier gas to the second carrier gas is 1: 2. 1: 5. 1: 8. preferably, the volume ratio of water vapor to the first carrier gas is 1: 4. 1: 10. 1: 16.

further, the total airspeed of the two paths of gas is 200-1000h^-1. Preferably, the total space velocity of the two paths of gas is 400h^-1、600h^-1、1000h^-1。

In the carbon coating process, the inert gas is introduced at the beginning to play the roles of purging residual air in the tube and providing a fluidizing environment, the inert atmosphere is changed into the reaction atmosphere at the beginning of the reaction, and the total gas velocity of the reaction atmosphere is the same as the gas velocity of the inert atmosphere in order to ensure that the high-temperature reaction is also in normal fluidization. While for TiCl₄The volume ratio with the first carrier gas is defined, mainly by the rate at which the reaction takes place, TiCl being at an elevated temperature₄Too high a concentration can result in too rapid a deposition that is not conducive to adequate deposition throughout the surface. If the concentration is too low, the reaction rate is too slow, so that the reaction time is too long, and the reaction efficiency is affected. The water vapor concentration is defined essentially as described above, depending on TiCl₄The reaction equation with water is adjusted accordingly in stoichiometric ratio. In the equation TiCl₄: the steam is 1:2, but the reaction is a two-way reaction, and increasing the concentration of the reactants is beneficial to increasing the conversion rate. In consideration of cost, the steam content is slightly more than the stoichiometric ratio during feeding, and the overall reaction conversion rate is improved. However, too high a concentration of water vapor can result in slower deposition and affect the efficiency of the reaction. The limitation of this embodiment further improves the electrochemical properties of the core-shell structure composite particles prepared by the fluidization process.

The first reaction time is 10-60 min. Preferably, the first reaction time is 20min, 40min, 60 min.

The first reaction time is primarily related to the amount deposited, i.e., the interlayer cladding thickness. The coating thickness of the intermediate layer needs to be controlled within a certain range, the reaction time is too short, and the coating of the intermediate layer is too thin, so that the promotion effect of the intermediate layer on ionic electrons cannot be fully exerted, and the effect of limiting the internal volume expansion is weakened. The reaction time is too long, the intermediate layer is coated too thick, and the whole diffusion distance is increased, so that the transfer resistance is increased, and the electrochemical reaction is not facilitated. The embodiment further improves the electrochemical performance of the core-shell structure composite particles prepared in the fluidization process.

In the carbon coating step:

preferably, the second inert atmosphere is argon, with a total space velocity of 200 to 1000h^-1. Preferably, the total space velocity of the first inert atmosphere is 400h^-1、600h^-1、1000h^-1. The space velocity is too low to ensure that the gas is in a good fluidized state. And the air speed is too high, and the phenomenon of mass entrainment can be caused by exceeding the escape speed of the powder, so that the yield is reduced. The embodiment further improves the electrochemical performance of the core-shell structure composite particles prepared in the fluidization process.

Preferably, the second reaction temperature is 700-1000 ℃. Preferably, the second reaction temperature is 750, 850 and 950 ℃. Further, in the process of heating the powder to a second reaction temperature under the protection of a second inert atmosphere, the heating rate is 1-25 ℃/min. Preferably, the heating rate is 5, 10, 15 ℃/min. Because of the deposition reaction of carbon of high graphitization degree, the higher the temperature, the higher the crystallinity of the carbon layer, and the better the graphitization degree. However, the higher the temperature is, especially for carbon source gas with high carbon content, the too fast carbon deposition rate is not favorable for uniform deposition, and side reactions such as tar generation at high temperature are obviously aggravated, which easily affects the purity of the final product. The embodiment further improves the electrochemical performance of the core-shell structure composite particles prepared in the fluidization process.

Preferably, the carbon source gas is one or a combination of several of methane, ethane, ethylene, acetylene, propane, propylene, benzene and toluene.

Preferably, the second carrier gas is nitrogen, argon or a mixture of the two.

Preferably, the volume ratio of the carbon source gas to the second carrier gas is 1:1 to 10.

Preferably, the volume ratio of the carbon source gas to the second carrier gas is 1: 3. 1: 6. 1: 9.

preferably, the total space velocity of the mixed gas of the carbon source gas and the second carrier gas is 200-^-1。

Preferably, the total space velocity of the mixed gas of the carbon source gas and the secondary carrier gas is 400h^-1、600h^-1、1000h^-1。

In the above embodiment, while the volume ratio of the carbon source gas to the second carrier gas is defined mainly in terms of the rate at which the reaction occurs, too high a carbon source gas concentration at high temperatures would make the deposition rate too fast for adequate deposition everywhere on the surface. If the concentration is too low, the reaction rate is too slow, so that the reaction time is too long, and the reaction efficiency is affected. The embodiment further improves the electrochemical performance of the core-shell structure composite particles prepared in the fluidization process.

The second reaction time is 10-60 min. Preferably, the second reaction time is 20min, 40min, 60 min.

The reaction time is mainly related to the deposition amount, i.e. to the outer cladding thickness. The thickness of the outer layer coating needs to be controlled within a certain range, and the reaction time also needs to be controlled at a proper reaction. The reaction time is too short, and the intermediate layer is coated too thinly, so that the overall conductivity cannot be effectively improved and the electron transfer efficiency cannot be improved. The reaction time is too long, and the interlayer coating is too thick, because the effect of the lattice stack on the ion conduction is not favorable for the electrochemical reaction. The embodiment further improves the electrochemical performance of the core-shell structure composite particles prepared in the fluidization process.

In summary, in the above embodiments, by utilizing the specific characteristics of efficient heat and mass transfer of the fluidized bed when the powder is in a fully fluidized state, the method is more suitable for industrial scale-up in production practice, and has continuous mass production capability and efficiency improvement, so as to prepare the high-performance lithium ion battery cathode material. Tests show that the prepared silicon or oxide thereof @ titanium oxide @ carbon core-shell structure composite particles can realize high-crystallization compact and uniform coating, the conductivity and the ion conductivity of the whole material are obviously improved, the specific capacity is high, the cycle stability is good, and the rate performance is good.

In conclusion, compared with the similar composite particles prepared by a liquid phase method, the silicon or oxide @ titanium dioxide @ carbon core-shell structure composite particles prepared by the method have the following advantages:

1) the multilayer coating structure is uniform and compact, and the crystallinity is high;

2) easy amplification and easy batch preparation;

3) the product is uniform and stable in quality;

4) the purity is high and no post-treatment is needed;

5) high specific capacity, good cycling stability and excellent rate capability.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.

FIG. 1 is SiO_x@TiO₂The structure schematic diagram of the @ C core-shell structure composite particles;

FIG. 2 is SiO_xSEM images of typical scanning electron microscopy at low and high power of the powder;

FIG. 3 is SiO_x@TiO₂SEM images of the @ C core-shell structure composite particles under low power and high power;

FIG. 4 is SiO_x@TiO₂TEM image of @ C core-shell structure composite particles at low power and high power;

FIG. 5 is SiO_x@TiO₂Raman spectrum of @ C core-shell structure composite particles;

FIG. 6 is SiO_xPowder and SiO_x@TiO₂An XRD (X-ray diffraction) spectrum of the @ C core-shell structure composite particle;

FIG. 7 is SiO_xPowder and intermediate SiO_x@TiO₂And SiO_x@TiO₂N of @ C core-shell structure composite particles₂An adsorption curve;

FIG. 8 is SiO_xPowder and intermediate SiO_x@TiO₂And SiO_x@TiO₂The thermogravimetric curve of the @ C core-shell structure composite particle;

FIG. 9 is SiO_xPowder and SiO_x@TiO₂A comparison graph of electrochemical cycle performance of the @ C core-shell structure composite particles at 300 charge/discharge cycles of 1A/g;

FIG. 10 is SiO_x@TiO₂A rate performance graph of the @ C core-shell structure composite particles.

Detailed Description

The following description and the drawings sufficiently illustrate specific embodiments of the invention to enable those skilled in the art to practice them. The examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others.

The present invention is further illustrated by, but is not limited to, the following examples. FIG. 1 is SiO in an example of the present invention_x@TiO₂The structure of the @ C core-shell structure composite particle is shown schematically.

Example 1

Mixing 100g of SiO_xPlacing the powder in a fluidized bed reactor for 600h^-1Introducing Ar gas at the airspeed of (1) to ensure that the powder is in a fully fluidized state, and then raising the temperature to 1200 ℃ at the temperature rise rate of 15 ℃/min; ar-carried TiCl₄Steam and water vapor with TiCl₄:H₂O is 1: 6 are introduced separately into a fluidized bed for the deposition reaction, wherein TiCl₄:Ar＝1：5,H₂Ar is 1: 10, the total space velocity of the two paths of gas is 600h^-1. Stopping introducing TiCl after 40min₄Steam and water vapor are naturally cooled to room temperature to obtain an intermediate product SiO_x@TiO₂。

The intermediate product SiO_x@TiO₂Placing in a fluidized bed reactor for 600h^-1Introducing Ar gas at the airspeed of (1) to ensure that the powder is in a fully fluidized state, and then raising the temperature to 850 ℃ at the heating rate of 10 ℃/min; c carried by Ar₂H₄Introducing the gas into a fluidized bed for carrying out a deposition reaction, wherein C₂H₄Ar is 1: 6, the total space velocity of the mixed gas is 600h^-1. Stopping introducing C after 40min₂H₄Gas is naturally cooled to room temperature to obtain the final product SiO_x@TiO₂@C。

And (3) electrochemical performance testing:

mixing thickener carboxymethylcellulose sodium (CMC) powder with ultrapure deionized water at a ratio of 1:99 at normal temperature, and stirring at normal temperature for 12h to obtain transparent viscous colloidal solution. According to the active material (silicon or its oxide @ titanium oxide core-shell structure composite particles): conductive agent super P: styrene Butadiene Rubber (SBR) 8: 1: 0.5: 0.5 mass ratio to the transparent viscous colloidal solution. The method specifically comprises the following steps: adding active substances, stirring for 0.5h, adding conductive agent super P, stirring for 1.5h, supplementing the required amount of solvent ultrapure deionized water to make the solid content reach 10 wt.%, stirring for 6h, finally adding binder Styrene Butadiene Rubber (SBR), stirring at low speed for 0.5h to make the solution be in a transparent black state, and obtaining the cathode slurry. According to the conventional production process of the lithium ion button cell, aqueous negative electrode slurry is coated on a current collector by a wet film preparation method, and a negative electrode plate can be obtained by punching a dry film through punching equipment through drying and dehydrating and deoxidizing processes. And assembling the button half cell with a metal lithium sheet, a diaphragm, electrolyte, a positive and negative electrode shell, a spring sheet and a gasket in a glove box, and standing for 12 hours to obtain the lithium ion button half cell with fully soaked interior.

Comparative example 1:

high-purity SiO without coating and roasting treatment_xA lithium-ion button half-cell corresponding to comparative example 1 was prepared according to the electrochemical performance test method described above. Electrochemical performance tests were performed on the lithium ion button half cells prepared in example 1 and comparative example 1, and the comparison results of the charge and discharge cycle performance and the rate performance are shown in fig. 9 and 10.

SiO as shown in FIG. 2_xLow and high SEM of the powder showed that the feedstock had an average particle size of 3 μm and was irregularly shaped. And SiO prepared as shown in FIG. 3_x@TiO₂SEM pictures of the @ C core-shell structure composite particles at low power and high power can show that the particles are well dispersed after high-temperature reaction and are not sintered, agglomerated and the like, and the integral edges and corners of the particles are flat, so that the coating is uniform and complete. FIG. 4 for SiO prepared_x@TiO₂The TEM image of the @ C core-shell structure composite particle under the low power and the high power shows that the particle is well dispersed, the double-layer cladding structure can be clearly seen, and the middle layer is TiO with high crystallinity₂The thickness is about 15nm, the outer layer is a highly graphitized C layer, and the thickness is about 5 nm. FIG. 5 is SiO_x@TiO₂The Raman spectrum of the @ C core-shell structure composite particle can calculate the intensity ratio (I) of the D peak to the G peak_D/I_G) 0.7, shows that the degree of graphitization of the carbon layer is high. At the same time at 210cm^-1、320cm^-1、980cm^-1The more obvious peak is TiO₂Typical Raman shift of TiO was confirmed₂The presence of the phase is also highly crystalline. FIG. 6 is SiO_xPowder and SiO_x@TiO₂The comparison of the XRD pattern of the @ C core-shell structure composite particles can confirm TiO₂And the successful introduction of phase C. FIG. 7 is SiO_xPowder and intermediate SiO_x@TiO₂And SiO_x@TiO₂N of @ C core-shell structure composite particles₂The adsorption curve shows that the surface area is not obviously increased after double-layer coating, and the coating compactness is shown. FIG. 8 is SiO_xPowder and intermediate SiO_x@TiO₂And SiO_x@TiO₂The thermogravimetric curve of the @ C core-shell structure composite particle shows that TiO₂The content of (A) was 4% and the content of C was 11.8%. FIG. 9 is SiO_xPowder and SiO_x@TiO₂The comparison graph of electrochemical cycle performance of the @ C core-shell structure composite particles at 300 charging/discharging cycles of 1A/g shows that the significant capacity attenuation is different from that of raw materials which are not subjected to coating treatment, and the prepared core-shell structure composite particles still keep the cycle capacity of more than 800mAh/g after 300 cycles, and are relatively stable. FIG. 10 is SiO_x@TiO₂The rate performance graph of the @ C core-shell structure composite particle shows that the capacity exceeds 300mAh/g under the heavy current density of 10A/g, and meanwhile, when the current density is recovered to 0.1A/g, the capacity is basically equivalent to the previous level, the attenuation is basically avoided, and the capacity recovery rate is good.

Example 2

Mixing 100g of SiO_xPlacing the powder in a fluidized bed reactor for 200h^-1Introducing Ar gas at the airspeed of (1) to ensure that the powder is in a fully fluidized state, and then raising the temperature to 1000 ℃ at the heating rate of 5 ℃/min; ar-carried TiCl₄Steam and water vapor with TiCl₄:H₂O is 1:2 are introduced separately into a fluidized bed for the deposition reaction, wherein TiCl₄:Ar＝1：1,H₂Ar is 1:2, the total space velocity of the two paths of gas is 200h^-1. Stopping introducing TiCl after 10min₄Steam and water vapor are naturally cooled to room temperature to obtain an intermediate product SiO_x@TiO₂。

The intermediate product SiO_x@TiO₂Placing in a fluidized bed reactor for 200h^-1Introducing Ar gas at the airspeed of (1) to ensure that the powder is in a fully fluidized state, and then raising the temperature to 700 ℃ at the temperature rise rate of 5 ℃/min; c carried by Ar₃H₆Introducing the gas into a fluidized bed for carrying out a deposition reaction, wherein C₃H₆Ar is 1:1, the total space velocity of the mixed gas is 200h^-1. Stopping introducing C after 10min₃H₆Gas is naturally cooled to room temperature to obtain the final product SiO_x@TiO₂@C。

Example 3

Mixing 100g of SiO_xPlacing the powder in a fluidized bed reactor for 1000h^-1Introducing Ar gas at the airspeed of (1) to ensure that the powder is in a fully fluidized state, and then raising the temperature to 1400 ℃ at the temperature rise rate of 15 ℃/min; ar-carried TiCl₄Steam and water vapor with TiCl₄:H₂O is 1: 10 are introduced separately into a fluidized bed for the deposition reaction, wherein TiCl₄:Ar＝1：10,H₂Ar is 1: 20, the total space velocity of the two paths of gas is 1000h^-1. Stopping introducing TiCl after 60min₄Steam and water vapor are naturally cooled to room temperature to obtain an intermediate product SiO_x@TiO₂。

The intermediate product SiO_x@TiO₂Placing in a fluidized bed reactor for 1000h^-1Introducing Ar gas at the airspeed of (1) to ensure that the powder is in a fully fluidized state, and then raising the temperature to 1000 ℃ at the heating rate of 15 ℃/min; c carried by Ar₂H₂Introducing the gas into a fluidized bed for carrying out a deposition reaction, wherein C₂H₂Ar is 1: 10, the total space velocity of the mixed gas is 1000h^-1. Stopping introducing C after 60min₂H₂Gas is naturally cooled to room temperature to obtain the final product SiO_x@TiO₂@C。

Example 4

Placing 100gSi powder in a fluidized bed reactor for 400h^-1Introducing Ar gas at the airspeed of (1) to ensure that the powder is in a fully fluidized state, and then raising the temperature to 1100 ℃ at the heating rate of 10 ℃/min; ar-carried TiCl₄Steam and water vapor with TiCl₄:H₂O is 1: 4 are introduced separately into the fluidized bed for the deposition reaction, wherein TiCl₄:Ar＝1：2，H₂Ar is 1: 4, the total space velocity of the two paths of gas is 400h^-1. Stopping introducing TiCl after 20min₄Steam and water vapor are naturally cooled to room temperature to obtain an intermediate product SiO_x@TiO₂。

The intermediate product SiO_x@TiO₂Placing in a fluidized bed reactor for 400h^-1Introducing Ar gas at the airspeed of (1) to ensure that the powder is in a fully fluidized state, and then raising the temperature to 800 ℃ at the heating rate of 10 ℃/min; CH carried by Ar₄The gas is introduced into a fluidized bed for the deposition reaction, wherein CH₄Ar is 1: 3, the total space velocity of the mixed gas is 400h^-1. Stopping CH introduction after 20min₄Gas is naturally cooled to room temperature to obtain the final product SiO_x@TiO₂@C。

Example 5

Placing 100gSi powder in a fluidized bed reactor for 800h^-1Introducing Ar gas at the airspeed of (1) to ensure that the powder is in a fully fluidized state, and then raising the temperature to 1300 ℃ at the heating rate of 12 ℃/min; ar-carried TiCl₄Steam and water vapor with TiCl₄:H₂O is 1: 8 are introduced separately into the fluidized bed for the deposition reaction, wherein TiCl₄:Ar＝1：8，H₂Ar is 1: 16, the total space velocity of the two paths of gas is 800h^-1. Stopping introducing TiCl after 50min₄Steam and water vapor are naturally cooled to room temperature to obtain an intermediate product SiO_x@TiO₂。

The intermediate product SiO_x@TiO₂Placing in a fluidized bed reactor for 800h^-1Introducing Ar gas at the airspeed of (1) to ensure that the powder is in a fully fluidized state, and then raising the temperature to 900 ℃ at the heating rate of 8 ℃/min; c carried by Ar₃H₈Introducing the gas into a fluidized bed for carrying out a deposition reaction, wherein C₃H₈Ar is 1:9, the total space velocity of the mixed gas is 800h^-1. Stopping introducing C after 50min₃H₈Gas is naturally cooled to room temperature to obtain the final product SiO_x@TiO₂@C。

The following table shows the results of the electrochemical performance tests of the above examples and comparative examples, which are similar to example 1:

table 1 results of battery testing in various examples

From table 1, it can be seen that the specific capacity of the silicon or its oxide @ titanium oxide @ carbon core-shell structure composite particle prepared by the method is improved, and at the same time, the cycle stability is significantly improved compared with that of a raw material which is not subjected to coating treatment, and the requirements of a next generation of anode material on high specific capacity and high cycle stability are met.

The preparation method is more suitable for industrial amplification by utilizing the specific high-efficiency heat and mass transfer characteristics of the fluidized bed when the powder is in a fully fluidized state, has continuous mass production capacity and improves the efficiency to prepare the high-performance lithium ion battery cathode material. Compared with the similar composite particles prepared by the traditional liquid phase method, the silicon or the oxide @ titanium oxide @ carbon core-shell structure composite particle core prepared by the method has the following advantages:

1) the multilayer coating structure has uniform and compact structure and high crystallinity

The characteristics of high mass and heat transfer efficiency and no dead zone of the fluidized bed reactor when the particles are fully fluidized in the fluidized bed are utilized, and the uniform and compact coating of the multilayer coating structure is realized. Meanwhile, the high-temperature reaction can be carried out in the fluidized bed, and the crystallinity of each layer is fully ensured.

2) Easy to amplify and prepare in batch

The continuous production is realized by utilizing the advantage that the fluidized bed reactor can rapidly feed and discharge materials, the process is easy to enlarge, and the large-scale industrial preparation can be realized.

3) The product has uniform and stable quality

The gas-solid contact of the reaction is sufficient in the full fluidization state, and the consistency of the product is effectively ensured.

4) High purity without post-treatment

High-purity raw materials are adopted, and impurities are not easily introduced in the reaction.

5) High specific capacity, good circulation stability and excellent rate capability

In conclusion, the silicon or the oxide thereof @ titanium oxide @ carbon multilayer core-shell structure composite particle has the characteristics of high uniform and compact crystallinity, good consistency, high specific capacity, good cycling stability and excellent rate performance of each layer of cladding structure, and can be used as a lithium ion battery cathode material, the volume change of internal active substances in the charging and discharging process can be effectively inhibited by the multilayer core-shell structure cladding layer, the transfer efficiency of ionic electrons in electrochemical reaction is improved, and the electrochemical performance is remarkably improved.

It should be understood by those skilled in the art that the above embodiments are only for illustrating the present invention, and not for all the purposes of the present invention, and that the changes and modifications of the above embodiments are within the scope of the present invention as long as they are within the scope of the present invention.

Claims

1. The silicon or oxide @ titanium dioxide @ carbon core-shell structure composite particle is characterized in that the composite particle is a compact three-layer structure and comprises a core, a middle layer and an outer layer; wherein the core contains silicon or its oxide, and the intermediate layer contains titanium dioxide TiO₂The outer layer is a carbon-containing C layer; under the test condition of 1A/g constant-current charge and discharge, the capacity retention rate of the composite particles after 300 cycles is not lower than 88%.

2. The composite particle of claim 1, wherein the core is Si or SiO_xPulverizing; and/or the intermediate layer is TiO₂The crystallinity is not lower than 80%; and/or the outer layer is graphite carbon.

3. The composite particle of claim 2, wherein the core diameter is from 0.01 to 10 μ ι η.

4. The composite particle of claim 2, wherein the intermediate layer has a thickness of 1 to 100 nm.

5. The composite particle of claim 2, wherein the outer layer has a thickness of 1 nm to 100 nm.

6. The composite particle of any one of claims 1-5, wherein the specific capacity of the composite particle is not less than 900 mAh/g.

7. A method for producing a shell-core structured composite particle, characterized by comprising the steps of titanium coating and carbon coating; the titanium coating step and the carbon coating step are both completed in a fluidized bed reactor; the titanium coating step comprises: SiO silicon-containing Si or silicon oxide_xPlacing the powder in the fluidized bed reactor, fluidizing under a first inert atmosphere, and heating to a first reaction temperature; TiCl carried by a first carrier gas₄Introducing steam and vapor into the fluidized bed reactor respectively for deposition reaction, and stopping introducing the TiCl after the first reaction time₄Steam and water vapor are cooled to obtain an intermediate product; the carbon coating step comprises: fluidizing the intermediate product under a second inert atmosphere, and heating to a second reaction temperature; introducing a carbon source gas carried by a second carrier gas into the fluidized bed reactor for deposition reaction, stopping introducing the carbon source gas after the second reaction time, and cooling to obtain the core-shell structure composite particles; in the titanium coating step:

the TiCl₄The volume ratio of the steam to the water vapor is 1: 2-10; the TiCl₄The volume ratio of the steam to the first carrier gas is 1: 1-10, and the volume ratio of the steam to the first carrier gas is 1:2 to 20.

8. The production method according to claim 7, wherein in the carbon coating step:

the volume ratio of the carbon source gas to the second carrier gas is 1: 1-10.

9. The method according to claim 7 or 8,

the first reaction temperature is 900-1400 ℃; and/or the second reaction temperature is 700-1000 ℃.