CN108258228B

CN108258228B - A kind of silicon carbon material with multi-level core-shell structure, preparation method and application

Info

Publication number: CN108258228B
Application number: CN201810086952.8A
Authority: CN
Inventors: 刘贵龙; 刘献明; 赵运霞; 毋乃腾; 刘丰; 刘金强; 袁巍巍; 陈海鹏
Original assignee: Luoyang Normal University
Current assignee: Luoyang Normal University
Priority date: 2018-01-30
Filing date: 2018-01-30
Publication date: 2021-01-22
Anticipated expiration: 2038-01-30
Also published as: CN108258228A

Abstract

A silicon carbon material with a multi-layered core-shell structure and a preparation method and application thereof relate to the technical field of lithium ion battery materials. The silicon carbon material is formed by spaced wrapping of a silicon layer and a carbon layer, wherein the silicon layer is separated from the silicon layer by a carbon layer, and the carbon layer is separated from the carbon layer by a silicon layer; wherein, the silicon carbon material is granular , the particle size is 0.5-10 μm, wherein the radial thickness of the silicon layer is 20-500 nm, and the radial thickness of the carbon layer is 50-1000 nm. The composite material of the present invention has the characteristics of long cycle and high capacity at the same time. The high electrochemical lithium storage capacity and small energy loss of the silicon carbon material make it have broad application prospects.

Description

Silicon-carbon material with multi-layer core-shell structure and preparation method and application thereof

Technical Field

The invention relates to the technical field of lithium ion battery materials, in particular to a silicon-carbon material with a multi-layer core-shell structure and a preparation method and application thereof.

Background

Currently, the lithium ion battery negative electrode material in commercialization is mainly graphite. However, the mass specific energy of the graphite is only 372mAh/g, and the demand of people can not be met. Particularly, energy-saving and new energy automobile industry development planning and action scheme for promoting automobile power battery industry development clearly indicate that the energy density of a single power battery reaches at least over 300Wh/kg in 2020. And batteries using graphite as the negative electrode have difficulty in meeting this requirement.

The silicon is the material with the highest specific energy in all the negative electrode materials discovered nowadays, the mass specific energy can reach 4200mAh/g, and the volume specific energy can reach 9786mAh/cm, which is more than 10 times of that of the graphite-based negative electrode material commercialized at present.

However, since silicon is a semiconductor, its conductivity is poor. The volume expansion of the silicon particles in the lithium intercalation process is up to 300%, on one hand, the stress in the particles can cause the crushing of the particles and the pulverization of the particles; on the other hand, the contact among the material, the conductive agent and the current collector is weakened, so that part of the material falls off from the current collector, and the cycle life of the battery is influenced; in addition, the volume change of silicon in the charging and discharging process causes the SEI film to grow and break continuously, the SEI film becomes thick continuously, and the capacity is attenuated.

Therefore, researchers have made a lot of work to improve the conductivity of silicon materials and reduce the volume change of silicon during the charge and discharge processes to improve the cycle performance of silicon cathodes. Such as: nano-sizing of silicon particles (nanowires, nanotubes, porous silicon, hollow silicon, silicon thin films), composite (amorphous carbon, carbon nanotubes, graphene, titanium dioxide), alloying (FeSi, NiSi), use of novel conductive agents and electrolyte additives (self-healing polymers, conductive polymers), and the like. Among them, the use of silicon in combination with a highly conductive carbon material (e.g., Si/C material) has been the focus of research.

Disclosure of Invention

One of the purposes of the invention is to provide a silicon carbon material with a multilayer core-shell structure; the second purpose of the invention is to provide a preparation method of the silicon carbon material with a multilayer core-shell structure; the invention also aims to provide application of the silicon-carbon material with a multilayer core-shell structure.

The technical scheme adopted by the invention for realizing one of the purposes is as follows:

the silicon-carbon material is formed by alternately wrapping a silicon layer and a carbon layer, wherein the silicon layer is isolated from the silicon layer by the carbon layer, and the carbon layer is isolated from the carbon layer by the silicon layer.

In the invention, the silicon-carbon material is granular, the particle size is 0.5-10 μm, the radial thickness of the silicon layer is 20-500nm, and the radial thickness of the carbon layer is 50-1000 nm.

The second technical scheme adopted by the invention for realizing the purpose is as follows:

a preparation method of a silicon carbon material with a multilayer core-shell structure comprises the following steps:

(1) preparing a silicon source and anhydrous alcohol into a solution;

(2) mixing another carbon microsphere with the solution prepared in the step (1), carrying out ultrasonic assistance for a certain time, standing, washing until the filtrate is neutral, and roasting the filtrate in an inert atmosphere;

(3) mixing the roasted substance with magnesium powder, and placing the mixture in a muffle furnace for reaction to obtain a reactant; and soaking the reactant in an acid solution, washing the reactant with deionized water until the filtrate is neutral, and drying to obtain the silicon-carbon material with the multilayer core-shell structure.

In the step (1), one or more of tetraethyl silicate, silicon chloride and organosilane are used as a silicon source, and absolute ethyl alcohol or absolute methyl alcohol is used as a solvent to prepare the silicon source into a solution with the concentration of 0.1-5.0 mol/L.

Wherein, in the step (2), the carbon microsphere: the volume ratio of the solution prepared in the step (1) is 1: (1-10), mixing the two, carrying out ultrasonic assistance for 0.1-3.0h, standing the obtained sample for 2.0-72.0h, washing with deionized water or ethanol, and filtering until the pH value of the filtrate is 7.

Wherein, in the step (2), the filtrate is roasted in an inert atmosphere, the heating rate is 1-10 ℃/min, the roasting temperature is 400-800 ℃, and the roasting time is 1-10 h.

In the step (3), the mass ratio of the roasted sample to the magnesium powder is 1: (0.5-4.0), placing the mixture in a muffle furnace, heating to 600-800 ℃ at the heating rate of 1-5 ℃/min, and reacting for 3-5h to obtain a reactant; soaking the reactant in 0.3-3mol/L hydrochloric acid for 12-48h, filtering and washing the reactant by deionized water until the pH value of the filtrate is 7, and drying the filtrate at the temperature of 40-120 ℃ to obtain the silicon-carbon material with the multilayer core-shell structure.

The carbon microspheres adopted in the step (2) in the invention can be mature products purchased in the market, and can also be brand-new prepared products.

When the carbosphere adopted in the step (2) is a purchased sample, pretreatment is needed before use: putting the carbon microspheres into 9-18mol/L acid, heating and refluxing for 2-24h at 90-100 ℃, filtering and washing with deionized water until the pH value of the filtrate is 7, and drying the filtrate at 40-120 ℃ to obtain the pretreated carbon microspheres.

Or, the carbon microspheres adopted in the step (2) are prepared by the following steps: carrying out hydrothermal treatment on glucose, sucrose or chitosan with the concentration of 0.1-10mol/L at the temperature of 100-200 ℃ for 3-24h, filtering and washing with deionized water until the pH value of the filtrate is 7, and drying the filtrate at the temperature of 40-120 ℃ to obtain the carbon microspheres.

The technical scheme adopted by the invention for realizing the third purpose is as follows:

the invention provides a lithium ion battery using the silicon carbon material with the multilayer core-shell structure as a negative electrode, namely a lithium ion battery, which comprises a negative electrode active substance, wherein the negative electrode active substance is the silicon carbon material with the multilayer core-shell structure.

Has the advantages that:

1. the thinner silicon layer is made of nano silicon, the nano silicon effectively reduces the particle size of the silicon, reduces the transmission path of lithium ions in a silicon phase, reduces the polarization phenomenon of the silicon in the charging and discharging process, and effectively inhibits the expansion and crushing conditions of particles of the silicon in the charging and discharging process.

2. The intermediate carbon layer can effectively construct a buffer skeleton and a conductive network. The carbon layer is in close contact with the silicon layer, so that the conductivity of the silicon can be greatly improved, the polarization phenomenon of the silicon in the charge and discharge process is reduced, and the volume change of the silicon in the charge and discharge process is weakened; the carbon layer is filled in the middle of the silicon layer, so that the volume effect caused by the expansion of the silicon layer can be effectively buffered.

3. The two characteristics can obviously reduce the polarization phenomenon and volume change of silicon in the charging and discharging processes, so that the composite material has the characteristics of high capacity and long cycle. The silicon-carbon material has high electrochemical lithium storage capacity and low energy loss, and has wide application prospect.

Drawings

Fig. 1 is a TEM image of a silicon carbon material with a three-layer core-shell structure in example 1 of the present invention.

Detailed Description

In order to facilitate the understanding of the technical means, the technical features and the objectives achieved by the present invention, the present invention is further described below.

The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The silicon-carbon material is formed by alternately wrapping a silicon layer and a carbon layer, wherein the silicon layer and the carbon layer are wrapped together layer by layer like an onion, the silicon layer is isolated from the silicon layer by the carbon layer, and the carbon layer is isolated from the carbon layer by the silicon layer. Wherein the silicon-carbon material is granular, the granularity of the granules is 0.5-10 mu m, the radial thickness of the silicon layer is 20-500nm, and the radial thickness of the carbon layer is 50-1000 nm.

The thin silicon layer is made of nano silicon, and the nano silicon can effectively inhibit the expansion and crushing of particles of silicon in the charging and discharging processes; the intermediate carbon layer can effectively construct a buffer skeleton and a conductive network, remarkably improve the conductivity of the material, and reduce the polarization phenomenon and volume change of silicon in the charge and discharge processes.

A preparation method of a silicon carbon material with a multilayer core-shell structure mainly comprises the following two steps: preparing or treating carbon microspheres, and preparing the multilayer silicon-carbon material by an impregnation-adsorption method.

The preparation method of the carbon microsphere comprises the following steps: carrying out hydrothermal treatment on glucose, sucrose or chitosan with the concentration of 0.1-10mol/L at the temperature of 100-200 ℃ for 3-24 h. The obtained sample is filtered by deionized water, washed until the pH is =7, and dried at 40-120 ℃ to obtain the carbon microspheres with the size of 0.5-10 mu m.

The used carbon microspheres can also be directly purchased from mature samples and processed before use: placing 0.1-5g of carbon microspheres in sulfuric acid with the concentration of 9-18mol/L, heating and refluxing at 90-100 ℃ for 2-24h, filtering the obtained sample, washing until the pH is =7, and drying at 40-120 ℃ to obtain the treated carbon microspheres.

The process for preparing the multilayer silicon-carbon material by the impregnation-adsorption method comprises the following steps: one or more silicon sources of tetraethyl silicate, silicon chloride and organosilane are prepared into 0.1-5mol/L ethanol/methanol solution. Mixing carbon microspheres: the volume ratio of the silicon solution is 1: (1-10) mixing the two together. And (3) ultrasonic assistance is carried out for 0.1-3.0h, so that a silicon source can enter the carbon spheres, and the obtained sample is kept stand for 2-72h, so that the carbon microspheres are fully infiltrated. Subsequently, washing with deionized water, ethanol or the like, and filtration were performed to pH = 7. The obtained sample is in Ar and N₂Or the calcination is carried out under the inert atmosphere such as He and the like (the heating rate is 1-10 ℃/min, the calcination temperature is 400-800 ℃, and the calcination time is 1-10 h). According to the mass ratio of the roasted sample to the magnesium powder of 1: (0.5-4), and reacting for 3-5h in a muffle furnace at a temperature rise rate of 1-5 ℃/min to 600-800 ℃; and soaking the obtained sample in 0.3-3.0mol/L acid (acid containing hydrogen ions) for 12-48h, filtering, washing to pH =7, and drying at 40-120 ℃ to obtain the silicon-carbon material with the multilayer core-shell structure.

The invention also provides a lithium ion battery using the silicon-carbon material with the multilayer core-shell structure as a negative electrode.

Example 1

(1) preparing a sucrose solution with the molar concentration of 1.5mol/L, placing the obtained solution in a reaction kettle for hydrothermal reaction at 190 ℃ for 5 hours, filtering and washing the obtained reaction product until the pH of the filtrate is =7, and drying the filtrate at 60 ℃ to obtain carbon microspheres with the diameter of 5 mu m;

(2) preparing tetraethyl silicate into 3mol/L ethanol solution; mixing carbon microspheres: the volume ratio of the silicon solution is 1: 1, mixing the two materials together, carrying out ultrasonic assistance for 0.5h to enable a silicon source to enter the carbon spheres, and standing the obtained sample for 24h to fully infiltrate the carbon microspheres; subsequently, the mixture was washed with deionized water, filtered until the filtrate had a pH =7, and the filtrate was calcined under an Ar atmosphere (heating rate 2 ℃/min, calcination temperature 600 ℃, calcination time 3 h). According to the mass ratio of the roasted sample to the magnesium powder of 1: 2, heating to 600 ℃ at a heating rate of 1 ℃/min in a muffle furnace, and reacting for 3 hours; and soaking the obtained sample in 1mol/L HCl for 24h, filtering and washing until the pH of the filtrate is =7, and drying the filtrate at 60 ℃ to obtain the silicon-carbon material with the three-layer core-shell structure.

Example 2

(1) preparing a glucose solution with the molar concentration of 3mol/L, and placing the obtained solution in a reaction kettle for hydrothermal reaction at 200 ℃ for 24 hours. Filtering and washing the obtained reaction product until the pH of the filtrate is =7, and drying the filtrate at 120 ℃ to obtain carbon microspheres with the diameter of 10 μm;

(2) and tetraethyl silicate was prepared as a 5mol/L methanol solution. Mixing carbon microspheres: the volume ratio of the silicon solution is 1: mixing the two materials together at a ratio of 10, performing ultrasonic assistance for 3h to enable a silicon source to enter the carbon spheres, standing the obtained sample for 72h to fully infiltrate the carbon spheres, washing with deionized water, filtering until the pH of the filtrate is =7, and obtaining a filtrate at N₂Roasting in the atmosphere (the heating rate is 1 ℃/min, the roasting temperature is 800 ℃, and the roasting time is 5 h). According to the mass ratio of the roasted sample to the magnesium powder of 1: 4, heating to 600 ℃ in a muffle furnace at a speed of 2 ℃/min, and reacting for 5 hours; soaking the obtained sample in 3mol/L HCl for 48h, filtering, washing until the pH of the filtrate is =7, and drying the filtrate at 120 ℃ to obtain the five-layer core-shell structureThe silicon carbon material of (1).

Example 3

(1) placing 5g of carbon microspheres in concentrated sulfuric acid with the concentration of 18mol/L by using commercial carbon microspheres of 0.5 mu m as a hard template agent, heating and refluxing for 24h at 100 ℃, filtering and washing an obtained sample until the pH of filtrate is =7, and drying the filtered substance at 120 ℃ to obtain the treated carbon microspheres;

(2) tetraethyl silicate was prepared as a 0.1mol/L methanol solution. Mixing carbon microspheres: the volume ratio of the silicon solution is 1: 5, mixing the two materials together, performing ultrasonic assistance for 3 hours to enable a silicon source to enter the carbon spheres, and standing the obtained sample for 72 hours to fully infiltrate the carbon microspheres; subsequently, the filtrate was washed with deionized water, filtered to pH =7, and the resultant filtrate was calcined under He atmosphere (heating rate 1 ℃/min, calcination temperature 400 ℃, calcination time 1 h). According to the mass ratio of the roasted sample to the magnesium powder of 1: 0.5, heating to 800 ℃ in a muffle furnace at 1 ℃/min, and reacting for 5 hours; and soaking the obtained sample in 0.3mol/L HCl for 48h, filtering and washing until the pH of the filtrate is =7, and drying the filtrate at 40 ℃ to obtain the silicon-carbon material with the two-layer core-shell structure.

Example 4

(1) preparing a sucrose solution with the molar concentration of 10mol/L, placing the obtained solution in a reaction kettle for hydrothermal reaction at 100 ℃ for 3h, filtering and washing the obtained reaction product until the pH of the filtrate is =7, and drying the filtrate at 120 ℃ to obtain carbon microspheres with the diameter of 0.5 mu m;

(2) and preparing tetraethyl silicate into a 3mol/L ethanol solution, mixing carbon microspheres: the volume ratio of the silicon solution is 1: 2, mixing the two materials together, and carrying out ultrasonic assistance for 3 hours to enable a silicon source to enter the carbon spheres, and standing the obtained sample for 72 hours to enable the carbon microspheres to be fully infiltrated. Subsequently, the mixture was washed with deionized water, filtered until the filtrate had a pH =7, and the filtrate was calcined under an Ar atmosphere (heating rate 10 ℃/min, calcination temperature 800 ℃, calcination time 1 h). According to the mass ratio of the roasted sample to the magnesium powder of 1: 2, heating to 600 ℃ in a muffle furnace at a speed of 1 ℃/min, and reacting for 3 hours; and soaking the obtained sample in 1mol/L HCl for 24h, filtering and washing until the pH of the filtrate is =7, and drying the filtrate at 60 ℃ to obtain the silicon-carbon material with the three-layer core-shell structure.

Example 5

The silicon-carbon negative electrode material with the three-layer core-shell structure prepared in example 1 was used as a negative electrode of a lithium ion battery for testing.

According to the silicon carbon material: acetylene black: the mass ratio of the polyvinylidene fluoride is 7: 2: 1, taking N-methyl pyrrolidone as a solvent to prepare negative electrode slurry, uniformly coating the slurry on a copper foil, and drying and slicing to obtain a negative electrode sheet with the diameter of 12 mm.

The lithium sheet is taken as a counter electrode, the battery is assembled in a glove box, an electrical property test is carried out on a Xinwei tester, and the charging and discharging voltage is 0.05-3V; when the current density is 500mA/g, the initial discharge capacity and the charge capacity of the material are 1200mAh/g and 936mAh/g respectively; after 500 cycles, the discharge and charge capacities of the cells were 802mAh/g and 795mAh/g, respectively.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. a silicon-carbon material with a multi-layered core-shell structure, characterized in that: the silicon-carbon material is formed by being separated and wrapped by a silicon layer and a carbon layer, wherein the silicon layer and the silicon layer are separated by a carbon layer, and the carbon layer is separated by a carbon layer. It is separated from the carbon layer by a silicon layer; the silicon carbon material is prepared by the following steps:

(1), take silicon source and anhydrous alcohol to prepare a solution; use tetraethyl silicate as silicon source;

(2), take another carbon microsphere, mix the two together with the volume ratio of the carbon microsphere: the solution prepared in step (1) as 1:(1-10), and ultrasonically assist for 0.1-3.0h, The obtained sample was allowed to stand for 2.0-72.0 h, then washed with deionized water or ethanol, filtered until the pH of the filtrate was 7, and the filtrate was calcined under an inert atmosphere; wherein, the carbon microspheres used were purchased samples, using Before pretreatment: put carbon microspheres in acid with a concentration of 9-18mol/L, heat and reflux at 90-100℃ for 2-24h, filter and wash with deionized water until the pH of the filtrate is 7, at 40 The filtrate was dried at -120°C to obtain pretreated carbon microspheres;

(3) Fully mix the calcined sample and the magnesium powder in a ratio of 1:(0.5-4.0), place it in a muffle furnace, and heat it up to 600-800 at a heating rate of 1-5°C/min ℃ to react for 3-5h to obtain a reactant; soak the reactant with hydrochloric acid with a concentration of 0.3-3mol/L for 12-48h, filter and wash the filtrate with deionized water until the pH of the filtrate is 7, at a temperature of 40-120℃ The filtrate was dried to obtain a silicon carbon material with a multi-layered core-shell structure.

2 . The silicon-carbon material with a multi-layered core-shell structure according to claim 1 , wherein the silicon-carbon material is in granular shape, and the particle size is 0.5-10 μm, wherein the radial thickness of the silicon layer is 2. 3 . 20-500nm, and the radial thickness of the carbon layer is 50-1000nm.

3 . The silicon carbon material having a multi-layered core-shell structure according to claim 1 , wherein in step (1), using absolute ethanol or anhydrous methanol as a solvent, the silicon source is configured to a concentration of 3 . 0.1-5.0mol/L solution.

4 . The silicon carbon material with a multi-layered core-shell structure according to claim 1 , wherein: in step (2), the filtrate is calcined under an inert atmosphere, and the heating rate is 1-10° C./ min, the calcination temperature is 400-800℃, and the calcination time is 1-10h.

5. A silicon-carbon material with a multi-layered core-shell structure, characterized in that: the silicon-carbon material is formed by spaced wrapping of a silicon layer and a carbon layer, wherein the silicon layer and the silicon layer are separated by a carbon layer, and the carbon layer is separated by a carbon layer. It is separated from the carbon layer by a silicon layer; the silicon carbon material is prepared by the following steps:

(2), take another carbon microsphere, mix the two together with the volume ratio of the carbon microsphere: the solution prepared in step (1) as 1:(1-10), and ultrasonically assist for 0.1-3.0h, The obtained sample was allowed to stand for 2.0-72.0h, then washed with deionized water or ethanol, filtered until the pH of the filtrate was 7, and the filtrate was calcined under an inert atmosphere; carbon microspheres were prepared by the following steps: the concentration of 0.1 -10mol/L glucose, sucrose or chitosan is hydrothermally treated at 100-200°C for 3-24h, then filtered and washed with deionized water until the pH of the filtrate is 7, and the filtrate is dried at 40-120°C to obtain carbon Microspheres;

6 . A lithium ion battery, comprising a negative electrode active material, wherein the negative electrode active material is a silicon carbon material having a multi-layered core-shell structure according to any one of claims 1 to 2 .