CN105576209A - High-capacity silicon-based anode material for lithium ion battery and preparation method thereof, and lithium ion battery - Google Patents

Abstract

The invention discloses a high-capacity lithium-ion battery silicon-based negative electrode material and a preparation method thereof, and a lithium-ion battery. The material includes nano-silicon, graphite, organic pyrolytic carbon and lithium fluoride. The preparation process is to combine nano-silicon, graphite and The pyrolytic carbon organic precursor is mixed, dried and vacuum baked to obtain a composite material precursor, and then the composite material precursor is roasted to obtain a pyrolytic carbon-coated composite material, and then the lithium salt solution and the fluoride solution are used in the composite material. The surface of the material reacts in situ to form a lithium fluoride coating layer, which is a silicon-based negative electrode material for a high-capacity lithium-ion battery. The invention effectively improves the interface characteristics of the material by in-situ generating lithium fluoride on the surface of the silicon-based composite material, and improves the compactness and stability of the solid electrolyte film formed during the first lithium intercalation process of the material, thereby improving the stability of the material. Electrochemical performance, the first charge and discharge efficiency of the battery is above 80%, and the capacity retention rate after 50 charge and discharge cycles is above 85%.

Description

A kind of high-capacity lithium-ion battery silicon-based negative electrode material and preparation method thereof, lithium-ion battery

technical field

The invention relates to the technical field of lithium-ion battery negative electrode materials, in particular to a high-capacity lithium-ion battery silicon-based negative electrode material, a preparation method thereof, and a lithium-ion battery.

Background technique

Lithium-ion secondary batteries have now become the mainstream chemical power source and are widely used in most mobile terminal devices. Compared with nickel-metal hydride, nickel-cadmium and lead-acid batteries, lithium-ion secondary batteries have high operating voltage, high specific energy and Advantages such as long cycle life have been developed rapidly in recent years, and are more and more widely used in mobile devices such as notebook computers, digital cameras, mobile phones, MP3 and MP4. With the development of mobile devices in the direction of miniaturization and multi-function, higher requirements are placed on the energy density and service life of lithium-ion secondary batteries. Also due to the rapid development and wide application of various portable electronic devices and electric vehicles, There is an urgent need for lithium-ion batteries with high energy and long cycle life. At present, the main anode material of commercial lithium-ion batteries is graphite. Due to its low theoretical capacity (372mAh/g) and poor high-rate charge-discharge performance, the further improvement of lithium-ion battery energy is limited.

Since silicon has the highest theoretical specific capacity (4200mAh/g) and low delithiation potential (less than 0.5V), it has become one of the most potential anode materials for lithium-ion batteries to replace graphite in recent years. Li and Si will form Li _x Si (0<x≤4.4) alloy. It is generally believed that at room temperature, the lithium-rich product produced by the alloying of silicon negative electrode and lithium is mainly Li _3.7 Si ₅ phase, with a capacity as high as 3572mAh/g, much larger than The theoretical capacity of graphite, but during the charge and discharge process, silicon will undergo a huge volume change, resulting in material pulverization, peeling, loss of electrical contact, and rapid capacity decay. In the prior art, the cycle stability and initial charge and discharge of silicon-based negative electrodes have been improved to a certain extent by reducing the particle size of silicon materials, making silicon porous materials, reducing the dimensions of silicon materials, and preparing silicon-carbon composite materials. Efficiency, however, most of these improvement measures require high cost, and the corresponding electrolyte needs to be matched to better perform its performance, and the long-term cycle performance of the material is still poor. Therefore, the research and development of a silicon-based anode material with good compatibility with electrolyte, good cycle performance, and relatively low cost is of great significance for improving the performance of lithium-ion batteries.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art, to provide a silicon-based negative electrode material for a lithium ion battery and a preparation method thereof, and a lithium ion battery. Good performance.

In order to solve the problems of the technologies described above, the technical solution proposed by the present invention is:

A high-capacity lithium-ion battery silicon-based negative electrode material, the high-capacity lithium-ion battery silicon-based negative electrode material includes nano-silicon, graphite, organic pyrolytic carbon and lithium fluoride, nano-silicon is attached to the surface of graphite, organic pyrolytic carbon Nano-silicon/graphite is coated, and organic pyrolytic carbon is coated with lithium fluoride. The lithium fluoride is obtained by in-situ generation of lithium salt and fluoride through chemical reaction.

The above-mentioned high-capacity lithium-ion battery silicon-based negative electrode material, preferably, the lithium salt is selected from one of lithium chloride, lithium sulfate, lithium nitrate, lithium hydroxide, lithium acetate, and the fluoride is soluble in The compound with water and fluorine as anion is one selected from hydrogen fluoride, sodium fluoride, potassium fluoride, ammonium bifluoride, and ammonium fluoride.

The above-mentioned high-capacity lithium-ion battery silicon-based negative electrode material, preferably, the mass ratio of nano-silicon and graphite is 1:3-20, organic pyrolytic carbon accounts for 5%-20% of the total mass of the silicon-based negative electrode material, fluorine Lithium oxide accounts for 1% to 10% of the total mass of the silicon-based negative electrode material.

The above-mentioned high-capacity lithium-ion battery silicon-based negative electrode material, preferably, the nano-silicon is granular, with a particle size of 5nm to 300nm; the graphite is selected from one or both of artificial graphite and natural graphite, and the Graphite is granular, with a particle size of 0.5 μm to 20 μm.

In the aforementioned high-capacity lithium-ion battery silicon-based negative electrode material, preferably, the organic pyrolytic carbon is obtained by pyrolysis of organic matter under an inert atmosphere, and the organic matter is selected from phenolic resin, citric acid, glucose, sucrose, and chitosan One of sugar, polyvinylidene fluoride, and asphalt.

As a general inventive concept, the present invention also provides a method for preparing the above-mentioned high-capacity lithium-ion battery silicon-based negative electrode material, comprising the following steps:

(1) Add nano-silicon into the solvent for ultrasonic dispersion, then add graphite for mixing and stirring, then add pyrolytic carbon organic precursor and continue mixing and stirring, the obtained mixed solution is evaporated and dried, and then vacuum baked to obtain silicon carbon Precursors of composite materials;

(2) roasting the silicon-carbon composite precursor obtained in step (1) under an inert atmosphere, and then grinding to obtain a nano-silicon/graphite composite coated with organic pyrolytic carbon;

(3) Add the composite material obtained in step (2) into the solvent for stirring and dispersing, then add lithium salt solution and fluoride solution for mixing and stirring, and dry the obtained mixed solution to obtain the high-capacity lithium-ion battery Silicon-based anode materials.

The above-mentioned preparation method, preferably, in the step (1), the mass ratio of nano-silicon and graphite is 1:3～20, and the solvent is deionized water, methanol, ethanol, ethylene glycol, propanol or N-formazol Pyrrolidone, the ultrasonic dispersion time is 10-120 minutes, after adding graphite, mix and stir for 30-120 minutes, the pyrolytic carbon organic precursor is selected from phenolic resin, citric acid, glucose, sucrose, chitosan, polyvinylidene fluoride One of ethylene and pitch, the amount of pyrolytic carbon organic precursor added is calculated according to the carbonization rate of the precursor, combined with the mass fraction (5% to 20%) of organic pyrolytic carbon in the total mass of silicon-based negative electrode materials; adding Continue mixing and stirring for 30-60 minutes after pyrolyzing the carbon organic precursor, the temperature of vacuum baking is 60°C-120°C, and the duration of vacuum baking is 4-20 hours; in the step (2), the inert atmosphere is argon gas, helium or nitrogen, particularly preferably argon, the calcination temperature is 450°C-1000°C, and the calcination time is 3-12 hours.

The above preparation method, preferably, in the step (3), the composite material is added into a solvent for stirring and dispersing for 30 to 60 minutes, the solvent is deionized water; the lithium salt solution is an aqueous solution of lithium salt, and the lithium salt is selected from chlorine Lithium chloride, lithium sulfate, lithium nitrate, lithium hydroxide, lithium acetate, the mass fraction of the lithium salt solution is 1% to 10%, after adding the lithium salt solution, mix and stir for 30 to 60 minutes; the fluoride solution is Aqueous solution of fluoride, fluoride is a compound that is soluble in water and uses fluorine as anion, selected from hydrogen fluoride, sodium fluoride, potassium fluoride, ammonium bifluoride, ammonium fluoride, the mass fraction of the fluoride solution is 1%-10%, after adding the fluoride solution, keep mixing and stirring for 30-60 minutes. The amount of lithium salt solution and fluoride solution added is calculated based on the mass fraction of lithium salt and fluoride solution, combined with the mass fraction (1% to 10%) of lithium fluoride in the total mass of the silicon-based negative electrode material and the corresponding chemical reaction equation. .

In the above preparation method, preferably, in the step (3), the drying is carried out by one of spray drying, washing after suction filtration, vacuum drying or washing after centrifugation, and vacuum drying. The drying method is selected according to different synthetic raw materials. For example, the ammonium acetate obtained by the in-situ reaction of lithium acetate and ammonium fluoride can be decomposed at high temperature, so for this kind of preparation method, spray drying can be used to obtain the final product; for in-situ The reaction produces by-products that are difficult to decompose by heat, which need to be separated and removed by vacuum filtration or centrifugation, and then washed and dried to obtain the final product.

The present invention also provides a high-capacity lithium-ion battery, wherein the negative electrode of the lithium-ion battery is prepared from the above-mentioned high-capacity lithium-ion battery silicon-based negative electrode material, or the silicon-based high-capacity lithium-ion battery prepared by the above-mentioned preparation method The base negative electrode material was prepared.

The present invention prepares nano-silicon/graphite composites by dispersing nano-silicon in the gaps of graphite or attaching them to the surface of graphite, and then performs drying, baking and high-temperature pyrolysis carbonization on the nano-silicon/graphite composites to prepare pyrolysis The carbon-coated nano-silicon/graphite composite material is finally reacted in situ on the surface of the composite material to form a lithium fluoride coating layer to obtain the high-capacity lithium-ion battery silicon-based negative electrode material of the present invention. The preparation method can improve the dispersion of nano-silicon in the silicon-carbon negative electrode material, improve the structural stability of the material in the process of lithium intercalation and deintercalation, and ensure that the material has a high electrical conductivity. The generated lithium fluoride coating layer is effectively wrapped on the surface of the material particles, which can effectively improve the interface characteristics of the material and improve the electrochemical performance of the silicon-carbon negative electrode material.

Compared with the prior art, the present invention has the following advantages:

(1) The present invention disperses nano-silicon among the graphite, which effectively improves the agglomeration effect of nano-silicon, provides space for the volume expansion of nano-silicon during charging and discharging, and avoids performance attenuation caused by nano-silicon cracking.

(2) The present invention uses organic matter pyrolytic carbon to be coated on silicon and graphite particle surface, has improved the electrical conductivity of composite material, also makes nano-silicon and graphite contact more closely simultaneously, reduces the contact resistance between nano-silicon and graphite, has It is beneficial to improve the conductivity of the material.

(3) The present invention generates a lithium fluoride coating layer in situ on the surface of the carbon-coated silicon-based composite material, which can effectively improve the interface characteristics of the material, and make the material form a more stable and dense solid electrolyte membrane during the first lithium intercalation process (SEI film), which reduces the transmission resistance of lithium ions at the interface, greatly improves the cycle performance of the material, and directly adding lithium fluoride to the material will not improve the material surface because it cannot be wrapped on the surface of the material particles. Properties of the formed SEI film.

(4) The lithium fluoride generated in situ on the surface of the carbon-coated silicon-based composite material of the present invention participates in the formation process of the SEI film, and reduces the reduction of the organic solvent in the electrolyte on the surface of the negative electrode material, thereby improving the negative electrode material The first charge and discharge efficiency, and directly adding lithium fluoride to the material will not significantly improve the reduction characteristics of the electrolyte on the surface of the composite material, that is, it will not significantly reduce the reduction of the electrolyte on the surface of the negative electrode material.

(5) The button battery made of the silicon-based negative electrode material of the high-capacity lithium-ion battery of the present invention has a charge-discharge efficiency of more than 80% for the first time, and carries out 50 charge-discharge cycles at a current density of 100mA/g, and its capacity remains The rate is above 85%.

Description of drawings

Fig. 1 is a scanning electron microscope image of a silicon-based negative electrode material for a high-capacity lithium-ion battery obtained in Example 1 of the present invention.

Fig. 2 is the first charging and discharging curve of the button battery made of the silicon-based negative electrode material of the high-capacity lithium-ion battery obtained in Example 1 of the present invention.

Fig. 3 is a charging cycle graph of a button battery made of the silicon-based negative electrode material for a high-capacity lithium-ion battery obtained in Example 1 of the present invention.

4 is a charging cycle graph of a button battery made of the silicon-based negative electrode material for a lithium-ion battery obtained in Comparative Example 1.

detailed description

In order to facilitate the understanding of the present invention, the present invention will be described more fully and in detail below in conjunction with the accompanying drawings and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

Unless otherwise defined, all technical terms used hereinafter have the same meanings as commonly understood by those skilled in the art. The terminology used herein is only for the purpose of describing specific embodiments, and is not intended to limit the protection scope of the present invention.

Example 1

A method for preparing a silicon-based negative electrode material for a high-capacity lithium-ion battery of the present invention, comprising the following steps:

(1) Add 0.5 g of nano-silicon particles with a particle size of 80 nm into 100 ml of absolute ethanol for ultrasonic dispersion for 60 minutes to obtain a nano-silicon dispersion, and add 5 g of artificial silicon particles with a particle size of 0.6 μm to the dispersion under continuous stirring. Graphite was mixed and stirred for 90 minutes, then 6.1 g of citric acid was added to the dispersion and continued to mix and stir for 60 minutes, and the resulting mixed solution was evaporated to dryness in a water bath and vacuum baked at 60°C for 8 hours to obtain a silicon-carbon composite material precursors;

(2) roasting the silicon-carbon composite material precursor obtained in step (1) at 450° C. for 3 hours under argon protection, and then grinding to obtain a pyrolytic carbon-coated nano-silicon/graphite composite material;

(3) Get the composite material that 3g step (2) obtains and join in deionized water and stir and disperse for 60 minutes to obtain a dispersion liquid, then add 40.2g mass fraction in the dispersion liquid and be 1% lithium acetate aqueous solution and carry out mixing and stirring for 45 minutes, Under continuous stirring conditions, slowly add 2.3 g of 10% ammonium fluoride aqueous solution to the dispersion liquid and continue to mix and stir for 30 minutes. The resulting mixed solution can be spray-dried to obtain the high-capacity Silicon-based anode materials for lithium-ion batteries.

The high-capacity lithium-ion battery silicon-based negative electrode material obtained in this embodiment is composed of nano-silicon, artificial graphite, citric acid pyrolytic carbon and lithium fluoride. Figure 1 shows the high-capacity lithium-ion battery silicon-based negative electrode material obtained in this embodiment It can be seen from the scanning electron microscope image that nano-silicon is attached to the surface of artificial graphite, citric acid pyrolytic carbon is coated with nano-silicon/artificial graphite, and lithium fluoride is coated on the surface of citric acid pyrolytic carbon. The mass ratio of nano-silicon to artificial graphite in the silicon-based negative electrode material prepared in this example is 1:10, the mass fraction of pyrolytic carbon in the silicon-based negative electrode material is 10%, and the mass fraction of lithium fluoride is 5%.

The high-capacity lithium-ion battery silicon-based negative electrode material obtained in this embodiment is assembled into a button battery, and the electrochemical performance test is carried out. The first charge and discharge curve, it can be seen from the figure that under the current density of 100mA/g, the first lithium intercalation capacity is 563mAh/g, the first delithiation capacity is 468mAh/g, and the first charge and discharge efficiency is 83.1%; Figure 3 The charge-discharge cycle graph of the button battery made of the silicon-based negative electrode material of the high-capacity lithium-ion battery obtained in Example 1 of the present invention, as can be seen from the figure, under the current density of 100mA/g, the capacity of the cycle is maintained for 50 cycles The rate is 90.2%.

Example 2

A method for preparing a silicon-based negative electrode material for a high-capacity lithium-ion battery of the present invention, comprising the following steps:

(1) Add 0.5 g of nano-silicon particles with a particle size of 8 nm into 200 ml of methanol for ultrasonic dispersion for 120 minutes to obtain a nano-silicon dispersion, and add 2 g of natural graphite with a particle size of 5 μm to the dispersion under continuous stirring. Stir for 120 minutes, then add 3.57g of phenolic resin to the dispersion and continue to mix and stir for 30 minutes. The obtained mixed solution is evaporated to dryness in a water bath and vacuum baked at 120°C for 4 hours to obtain a silicon-carbon composite material precursor;

(2) Calcining the silicon-carbon composite material precursor obtained in step (1) at 750° C. for 6 hours under argon protection, and then grinding to obtain a pyrolytic carbon-coated nano-silicon/graphite composite material;

(3) Get the composite material that 1.5g step (2) obtains and join in deionized water and stir and disperse for 30 minutes to obtain a dispersion liquid, then add 2.7g mass fraction in the dispersion liquid and be 10% lithium chloride aqueous solution and mix and stir for 30 minutes Minutes, under the condition of continuous stirring, slowly add 12.7g of 1% hydrogen fluoride aqueous solution to the dispersion liquid and continue to mix and stir, the stirring time is 60 minutes; the obtained mixed solution is vacuum filtered, and then the obtained The cake was washed and vacuum-dried at 80° C. for 12 hours to obtain the silicon-based negative electrode material for a high-capacity lithium-ion battery of the present invention.

The high-capacity lithium-ion battery silicon-based negative electrode material prepared in this example is composed of nano-silicon, natural graphite, phenolic resin pyrolytic carbon, and lithium fluoride. Nano-silicon is attached to the surface of natural graphite, and phenolic resin pyrolytic carbon is coated with nano Silicon/natural graphite, lithium fluoride coated on the surface of phenolic resin pyrolytic carbon. The mass ratio of nano-silicon to natural graphite in the silicon-based negative electrode material prepared in this embodiment is 1:4, the mass fraction of phenolic resin pyrolytic carbon in the silicon-based negative electrode material is 20%, and the mass fraction of lithium fluoride is 10%. .

The high-capacity lithium-ion battery silicon-based negative electrode material obtained in this example was assembled into a button battery, and the electrochemical performance test was carried out. The results of the charge-discharge cycle test showed that at a current density of 100mA/g, the lithium intercalation capacity for the first time was 665.9 mAh/g, the first delithiation capacity is 576mAh/g, the first charge and discharge efficiency is 81.1%, and the capacity retention rate after 50 cycles is 86.5%.

Example 3

A method for preparing a silicon-based negative electrode material for a high-capacity lithium-ion battery of the present invention, comprising the following steps:

(1) Add 0.5 g of nano-silicon particles with a particle size of 280 nm into 100 ml of N-methylpyrrolidone for ultrasonic dispersion for 40 minutes to obtain a nano-silicon dispersion, and add 10 g of artificial silicon particles with a particle size of 18 μm to the dispersion under continuous stirring. Graphite was mixed and stirred for 30 minutes, then 1.4g of asphalt powder was added to the dispersion and continued to mix and stir for 45 minutes. The resulting mixed solution was evaporated to dryness in a water bath and vacuum baked at 80°C for 12 hours to obtain a silicon-carbon composite material precursor. body;

(2) Calcining the silicon-carbon composite material precursor obtained in step (1) at 950° C. for 12 hours under argon protection, and then grinding to obtain a pyrolytic carbon-coated nano-silicon/graphite composite material;

(3) Get 6.5g of the composite material obtained in step (2) and add it to deionized water and stir and disperse for 45 minutes to obtain a dispersion, then slowly add 2.9g of ammonium bifluoride aqueous solution with a mass fraction of 5% to the dispersion and mix and stir for 60 minutes , under continuous stirring conditions, then add 2.1g of lithium hydroxide aqueous solution with a mass fraction of 5% to the dispersion liquid and continue to mix and stir for 90 minutes; the mixed solution obtained is first subjected to high-speed centrifugation, and then centrifuged to obtain The product was washed and vacuum-dried at 80° C. for 12 hours to obtain the silicon-based negative electrode material for a high-capacity lithium-ion battery of the present invention.

The silicon-based negative electrode material of the high-capacity lithium-ion battery prepared in this embodiment is composed of nano-silicon, artificial graphite, pitch pyrolytic carbon and lithium fluoride. Nano-silicon is attached to the surface of artificial graphite, and pitch pyrolytic carbon coats nano-silicon/ Artificial graphite, lithium fluoride coated on the surface of pitch pyrolytic carbon. The mass ratio of nano-silicon to artificial graphite in the silicon-based negative electrode material prepared in this example is 1:20, the mass fraction of pitch pyrocarbon in the silicon-based negative electrode material is 5%, and the mass fraction of lithium fluoride is 1%.

The high-capacity lithium-ion battery silicon-based negative electrode material obtained in this example was assembled into a button battery, and the electrochemical performance test was carried out. The results of the charge-discharge cycle test showed that at a current density of 100mA/g, the lithium intercalation capacity for the first time was 473.7 mAh/g, the first delithiation capacity is 415mAh/g, the first charge and discharge efficiency is 87.6%, and the capacity retention rate after 50 cycles is 96.2%.

Comparative example 1

The preparation method of the lithium-ion battery silicon-based negative electrode material of this comparative example comprises the following steps:

(1) Add 0.5 g of nano-silicon particles with a particle size of 80 nm into 100 ml of absolute ethanol for ultrasonic dispersion for 60 minutes to obtain a nano-silicon dispersion, and add 5 g of artificial silicon particles with a particle size of 0.6 μm to the dispersion under continuous stirring. Graphite was mixed and stirred for 90 minutes, then 6.1 g of citric acid was added to the dispersion and continued to mix and stir for 60 minutes, and the resulting mixed solution was evaporated to dryness in a water bath and vacuum baked at 60°C for 8 hours to obtain a silicon-carbon composite material precursors;

(2) roasting the silicon-carbon composite material precursor obtained in step (1) at 450° C. for 3 hours under argon protection, and then grinding to obtain a pyrolytic carbon-coated nano-silicon/graphite composite material;

(3) Get 3g of the composite material obtained in step (2) and add it to deionized water for stirring and dispersing for 60 minutes to obtain a dispersion, then add 0.16g of lithium fluoride to the dispersion and continue mixing and stirring for 30 minutes, and the obtained mixed solution is passed through After spray drying, the silicon-based negative electrode material for the lithium ion battery of this comparative example was obtained.

The high-capacity lithium-ion battery silicon-based negative electrode material prepared in this comparative example is composed of nano-silicon, artificial graphite, citric acid pyrolytic carbon and lithium fluoride. The mass ratio of nano-silicon to artificial graphite is 1:10, and the silicon-based negative electrode material The mass fraction of pyrolytic carbon is 10%, and the mass fraction of lithium fluoride is 5%.

The high-capacity lithium-ion battery silicon-based negative electrode material obtained in this comparative example is assembled into a button cell, and the electrochemical performance test is carried out. Fig. 4 is a charging cycle curve diagram of the lithium-ion battery silicon-based negative electrode material obtained in this comparative example. It can be seen from the figure that at a current density of 100mA/g, the capacity retention rate after 50 cycles is only 59.5%, and the cycle performance is far worse than that of the silicon-based negative electrode material for high-capacity lithium-ion batteries prepared in the present invention.

Claims (10)

1. a high-capacity lithium ion cell silicon based anode material, it is characterized in that, described high-capacity lithium ion cell silicon based anode material comprises nano-silicon, graphite, organic matter pyrolysis carbon and lithium fluoride, nano-silicon is attached to the surface of graphite, organic matter pyrolysis carbon-coated nano silicon/graphite, the coated organic substance RESEARCH OF PYROCARBON of lithium fluoride, described lithium fluoride is that lithium salts and fluoride obtain through chemical reaction in-situ preparation.

2. high-capacity lithium ion cell silicon based anode material as claimed in claim 1, it is characterized in that, described lithium salts is selected from the one in lithium chloride, lithium sulfate, lithium nitrate, lithium hydroxide, lithium acetate, described fluoride is water soluble and take fluorine as the compound of anion, is selected from the one in hydrogen fluoride, sodium fluoride, potassium fluoride, ammonium acid fluoride, ammonium fluoride.

3. high-capacity lithium ion cell silicon based anode material as claimed in claim 1, it is characterized in that, the mass ratio of described nano-silicon and graphite is 1:3 ~ 20, and organic matter pyrolysis carbon accounts for 5% ~ 20% of silicon based anode material gross mass, and lithium fluoride accounts for 1% ~ 10% of silicon based anode material gross mass.

4. the high-capacity lithium ion cell silicon based anode material according to any one of claims 1 to 3, is characterized in that, described nano-silicon is graininess, and particle diameter is 5nm ~ 300nm; Described graphite is selected from one in Delanium, native graphite or two kinds, and described graphite is graininess, and particle diameter is 0.5 μm ~ 20 μm.

5. the high-capacity lithium ion cell silicon based anode material according to any one of claims 1 to 3, it is characterized in that, described organic matter pyrolysis carbon is that organic substance obtains through thermal decomposition generation under an inert atmosphere, and described organic substance is selected from the one in phenolic resins, citric acid, glucose, sucrose, shitosan, polyvinylidene fluoride, pitch.

6. a preparation method for the high-capacity lithium ion cell silicon based anode material according to any one of Claims 1 to 5, is characterized in that, comprise the following steps:

(1) nano-silicon is joined in solvent carry out ultrasonic disperse, then add graphite and carry out mix and blend, add RESEARCH OF PYROCARBON organic matter precursor again and continue mix and blend, the mixed solution obtained carries out evaporation drying, then obtains Si-C composite material presoma after carrying out vacuum bakeout;

(2) the Si-C composite material presoma that step (1) obtains is carried out calcination process under an inert atmosphere, then after grinding, obtain the coated nano-silicon/graphite composite material of organic matter pyrolysis carbon;

(3) composite material that step (2) obtains is joined in solvent carry out dispersed with stirring, then add lithium salt solution, fluoride aqueous solution carries out mix and blend, after the mixed solution obtained carries out drying, namely obtain described high-capacity lithium ion cell silicon based anode material.

7. preparation method as claimed in claim 6, it is characterized in that, in described step (1), the mass ratio of nano-silicon and graphite is 1:3 ~ 20, described solvent is deionized water, methyl alcohol, ethanol, ethylene glycol, propyl alcohol or 1-METHYLPYRROLIDONE, the duration of ultrasonic disperse is 10 ~ 120 minutes, the duration carrying out mix and blend after adding graphite is 30 ~ 120 minutes, the duration continuing mix and blend after adding RESEARCH OF PYROCARBON organic matter precursor is 30 ~ 60 minutes, the temperature of vacuum bakeout is 60 DEG C ~ 120 DEG C, and the duration of vacuum bakeout is 4 ~ 20 hours; In described step (2), sintering temperature is 450 DEG C ~ 1000 DEG C, and roasting duration is 3 ~ 12 hours; In described step (3), described solvent is deionized water, it is 30 ~ 60 minutes that the composite material that step (2) obtains joins the duration carrying out dispersed with stirring in solvent, the duration carrying out mix and blend after adding lithium salt solution is 30 ~ 60 minutes, and the duration carrying out mix and blend after adding fluoride aqueous solution is 30 ~ 60 minutes; In described step (3), described drying be adopt spraying dry, wash after suction filtration through vacuumize or centrifugal after any one mode of washing in vacuumize carry out.

8. preparation method as claimed in claim 6, it is characterized in that, in described step (1), described RESEARCH OF PYROCARBON organic matter precursor is the one in phenolic resins, citric acid, glucose, sucrose, shitosan, polyvinylidene fluoride, pitch.

9. preparation method as claimed in claim 6, it is characterized in that, in described step (3), described lithium salts is selected from the one in lithium chloride, lithium sulfate, lithium nitrate, lithium hydroxide, lithium acetate; Described fluoride is water soluble and take fluorine as the compound of anion, is selected from the one in hydrogen fluoride, sodium fluoride, potassium fluoride, ammonium acid fluoride, ammonium fluoride; The mass fraction of described lithium salt solution is 1% ~ 10%, and the mass fraction of described fluoride aqueous solution is 1% ~ 10%.

10. a high-capacity lithium ion cell, it is characterized in that, the negative pole of described lithium ion battery is prepared by the high-capacity lithium ion cell silicon based anode material such as according to any one of Claims 1 to 5, or the high-capacity lithium ion cell silicon based anode material obtained by preparation method according to any one of claim 6 ~ 9 prepares.