LU500547B1 - Carbon Nano Composite Material and Application in a Battery Thereof - Google Patents

Abstract

A carbon nano composite material and application in a battery thereof. The preparation method comprises the following steps: carrying out pretreatment on a carbon nano tube, mixing with mixed acid to prepare an acidified carbon nano tube; then prepare SnO2; mix that acidified carbon nanotube with the SnO2, add into deionized water, performing ultrasonic dispersion, heat in a water bath, dropwise adding alkali liquor to make the solution alkaline, filtering and washing the solution to neutrality, sintering at a low temperature and roasting at a high temperature to obtain the carbon nano composite material. When the scanning voltage of the carbon nano composite material prepared by the invention is 0.02-2.5 V, and the current density is 25 mA/g, the initial discharge amount can reach 1,800 mAh/g (much larger than 200 mAh/g of SnO2 and 372 mAh/g of natural graphite); and after 3,000 cycles, the capacity is still about 1,710m Ah/g.

Description

DESCRIPTION Carbon Nano Composite Material and Application in a Battery Thereof

TECHNICAL FIELD The invention relates to the technical field of lithium ion batteries, in particular to a carbon nano composite material and application in batteries thereof.

BACKGROUND The original lithium battery negative electrode material 1s lithium elementary substance, but because dendrites are formed in the charging and discharging process, serious safety problems exist, and the lithium battery negative electrode material cannot be used for practical application. At present, the most common anode materials for lithium ion batteries include carbon materials, tin-based materials and silicon-based materials. The carbon material is currently the most commonly used cathode material and has been used in actual production due to its advantages of stable charge and discharge, low potential of deintercalation lithium (0.2-0.5 V), good cycle stability of the battery, low price, abundant reserves, etc. Carbon materials mainly include graphitized mesophase carbon microspheres, natural graphite and amorphous carbon. As a lithium electrode negative material, mesophase carbon microspheres (MBMC) can realize relatively close stacking and obtain an electrode with higher density because of the spherical micro- morphology, and the spherical surface also overcomes the defect of anisotropy existing in a graphite sheet layer. Therefore, some research and attention have been paid to the preparation, modification and charge-discharge mechanism of mesophase carbon microsphere lithium electrode materials.

When natural graphite is used as the negative electrode material for lithium, the specific capacity can reach the theoretical capacity of 372 mAh/g. However, due to the great influence of the shape, particle size, specific surface area, and crystal defects of graphite on the electrochemical performance of the electrode material, the actual specific capacity may be lower than the theoretical capacity. The graphite anode material reacts with the electrolyte in the first charge-discharge process to form an SEI film, which consumes a part of lithium ions and leads to a lower first coulombic efficiency; In addition, if the formed SEI film is not dense enough, the electrolyte further interacts with the graphite material, easily causing the exfoliation and peeling of the graphite sheet layer and damaging the electrode material.

The structure of the amorphous carbon material consists of graphite microcrystals and amorphous regions. The small molecular escape during heat treatment results in the formation of a large number of nanopores in the amorphous regions, which also makes the charge-discharge capacity of amorphous carbon greater than the theoretical capacity of graphite (372 mAh/g). However, the amorphous carbon anode material has poor lithium electrical stability and low initial charge and discharge efficiency. At the same time, because the theoretical capacity of the carbon cathode material is relatively low, even after modification, it is still difficult to meet the requirements of modern society for high specific capacity and high energy density of lithium ion batteries, which greatly limits its application in the field of high current density.

Although the current commercial anode materials are mainly carbon materials, due to its low theoretical specific capacity, low initial charge and discharge efficiency and organic solvent co-embedding, people began to study high capacity non-carbon anode materials,

such as tin-based materials. At present, the research on tin-based materials mainly focuses on tin-based oxides, tin-based alloys and tin-based composite oxides. The SnO and SnO2 prepared by different preparation methods have different structures, such as crystalline, amorphous, nano-fibrous, and nano-porous, which greatly affect their electrochemical properties (such as specific capacity and cyclicity). Pure tin has a high reactivity for lithium 10ns, but there exists a serious volume expansion during the charge and discharge process, resulting in the decline of 1ts cycle performance.

SUMMARY The invention aims to provide a carbon nano composite material with high specific capacity, high energy density and good cycle stability.

In order to achieve the purpose, the invention provides the following scheme: The invention provides a preparation method of a carbon nano composite material, which comprises the following steps: (1) Firstly carry out pretreatment on that carbon nano tubes, wherein the pretreatment process of the carbon nano tubes comprises the following step of: ultrasonically dispersing the carbon nano tubes in a sodium hydroxide solution, soaking and washing, then mixing the carbon nano tubes with concentrated nitric acid and then carrying out reflux under the ultrasonic condition, then mixing the pretreated carbon nano tubes with mixed acid, carrying out reflux treatment, washing and drying to obtain the acidified carbon nano tubes; (2) mixing and dissolving SnCl4:5H20 and polyethylene glycol (PEG) in deionized water, performing ultrasonic dispersion, dropwise adding ammonia water under the stirring condition until the SnCl4-SH2O 1s completely hydrolyzed, and performing suction filtration, washing and sintering to obtain SnO»; And (3) mix that acidified carbon nanotube and the SnO,, add into deionized water, performing ultrasonic dispersion, heat in a water bath, dropwise adding alkali liquor to make the solution alkaline, filtering and washing the solution to neutrality, performing vacuum sintering at 90-110°C for 5-8h, and then roasting at 280-350°C for 2-3 h to obtain the carbon nano composite material.

Further, the carbon nano tubes are multi-walled carbon nano tubes.

As the carbon nano tubes prepared by any method always contain some impurities such as metal catalyst particles, amorphous carbon and nano-carbon particles, which restrict the subsequent application of carbon nano tubes, therefore in the present invention, first, the multi-walled carbon nano tubes are immersed in a sodium hydroxide solution, ultrasonic dispersed, and then mixed with concentrated nitric acid by ultrasonic reflux treatment. On the one hand, the Van der Waals force between the multi-walled carbon nano tubes can be destroyed to avoid their reunion, on the other hand, the catalyst particles and some amorphous carbon impurities can be fully dissolved and the excessive length of carbon nano tubes can be cut off to improve the purity of multi-walled carbon nano tubes, some reactive functional groups, such as carboxyl and hydroxyl groups, can be introduced at the ends or sidewalls of multi-walled carbon nano tubes. The multi- walled carbon nano tubes are almost free of metal catalyst particles and amorphous carbon, and the purity can reach 98-99%. The dispersion and stability in water are improved obviously, which is helpful to the preparation of composite materials.

Further, in that pretreatment process of the carbon nano tube in the step (1), the ultrasonic power is 200-300 W, the frequency 1s 40-50 kHz, the reflux temperature 1s 80-90°C, and the reflux time 1s 8-10 h.

Further, the mixed acid in the step (1) is concentrated sulfuric acid and concentrated nitric acid with the volume ratio of (5-7): 1. Further, after the carbon nanotube pretreated in the step (1) is mixed with the mixed acid, the reflux temperature is 70-80°C, and the reflux time is 3-4 h.

Further, in the step (2), the mass ratio of SnCly5H20 to polyethylene glycol is (2-10): 1. Preferably in a mas ratio of 2, 4, 8 or 10. Further, the molecular weight of PEG 1s 1,000, 2,000 or 4,000. The addition of PEG can promote the crystal development and form a long-range ordered structure, and simultaneously reduce the grain size of SnO,. SnOz prepared by PEG with different molecular weights have different grain morphology and size.

The size of NO» prepared by PEG with molecular weight of 1,000 is within the range of 150-300 nm, and the particle size is relatively low, mainly spherical.

The size of SnOz obtained by PEG with molecular weight of 2,000 is about 100 nm.

The sphericity of SnO, obtained from PEG with molecular weight of 4,000 is similar to that of 2,000, and the size is further reduced to about 75 nm.

When the molecular weight of PEG is too large or too small, it is not conducive to the preparation of subsequent composite materials.

Further, that sinter temperature in the step (2) is 150 to 200°C.

Further, that molar ratio of the acidify carbon nanotube to the SnOz in the step (3) is 1: (1-7). Further, that water bath temperature in step (3) 1s 70-80°C.

The invention also provides a carbon nano composite material prepared by the preparation method.

The invention also provides an application of the carbon nano composite material in a battery, and the carbon nano composite material is used for preparing a lithium ion battery negative electrode material.

Due to the existence of sp” hybridized C atom x orbit, the planar carbon atoms on the wall of the carbon nano tube are more active, the dispersibility of the sp? hybridized C atom 7 orbit in an organic solvent and a polymer is simultaneously changed through pretreatment, firstly, the surface of the carbon nano tube is oxidized by some oxidizing substances to generate defects, and then oxygen-containing groups such as a carboxyl group, a hydroxyl group and the like are introduced, the oxygen-containing groups are easier to carry out subsequent reaction, and a target product is finally formed.

Since the smooth surface of tin dioxide can reduce side reactions occurring on the electrode surface during charging, the coulombic efficiency during the first charging is improved.

As an allotrope of graphite, carbon nano tubes also have graphitized structure, but there are still some disadvantages of graphitized carbon materials used to prepare Li- ion batteries, such as easy collapse and excessive swelling.

The inner tube and the tube gap of the carbon nano tube can be used as lithium ion embedding positions, so that the carbon nano tube has more lithium embedding positions than graphite, the conductive property of the carbon nano tube is good, the ion conductivity in the charging and discharging process of the lithium ion battery is facilitated, and the coulombic efficiency is improved; and the multi-wall carbon nano tube has a layered structure similar to graphite, wherein the hollow tube and the space between the tubes are uniform, and the carbon nano tube has a nano size and has better lithium embedding performance. The carbon nano composite material prepared by the invention has a fluffy spherical structure formed by interconnecting the nano sheets, and the fluffy spherical sheet layer structure enables lithium ions to be embedded and separated in all directions of the balls, thereby solving the problems of excessive swelling and collapse of the graphite sheet layer caused by anisotropy of the graphitized carbon material as well as incapability of large current charging and discharging and the like. In addition, the volume expansion of tin can be alleviated by the composite material with the pile-sphere structure, which ensures the sufficient dispersion of tin particles in the composite material and buffer space, so as to maintain the structural stability of the electrode and improve the cycling stability.

The invention disclose that following technical effect: The carbon nano composite material prepared by the invention has a fluffy spherical structure, the size distribution is uniform, the average crystal grain size is 30-40 nm, and the addition of the multi-wall carbon nano tube can limit the growth of the SnO; through the hollow structure of the carbon nano tube to prepare smaller nano particles, and can also improve the dispersibility of the SnO, and the carbon nano tube and avoid agglomeration. When the scanning voltage of the carbon nano composite material prepared by the invention is 0.02-2.5 V, and the current density is 25 mA/g, the initial discharge amount can reach 1,800 mAh/g (much larger than 200 mAh/g of SnO2 and 372 mAh/g of natural graphite); and after 3,000 cycles, the capacity is still about 1,710 mAh/g, and the carbon nano composite material has good cycle stability.

DESCRIPTION OF THE INVENTION Various exemplary embodiments of the present invention are now described in detail, which should not be construed as limiting the invention, but rather as a more detailed description of certain aspects, features, and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

In addition, for numerical ranges in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed.

Each smaller range between any stated value or stated range of intermediate values and any other stated value or intermediate value within the stated range is also included within the present invention.

The upper and lower limits of these smaller ranges may independently be included or excluded from the range.

Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention relates.

While the present invention describes only the preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the practice or testing of the present invention.

All documents mentioned in this specification are incorporated by reference to disclose and describe methods and/or materials related to said documents.

In case of conflict with any incorporated literature, the content of this specification shall prevail.

It will be apparent to those skilled in the art that various modifications and variations can be made to the specific embodiments of the present specification without departing from the scope or spirit of the invention.

Other embodiments will be apparent to those skilled in the art from the description of the invention. The specification and embodiment of that present invention are exemplary only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open ended terms that mean including, but not limited to.

The multi-wall carbon nano tube in the embodiment of the invention is obtained through purchase, the diameter of the carbon nano tube is 8-45 nm, the length is 5-20 um, and the purity 1s about 60%.

In the invention, the concentration of concentrated nitric acid is 68% and the concentration of concentrated sulfuric acid is 70%, which are all mass fractions.

The preparation process of the electrode sheet comprises the following steps of: weighing an active substance (carbon nano composite materials prepared in each embodiment and a comparative embodiment) and a conductive agent (acetylene black) and a binding agent polyvinylidene fluoride (PVDF) according to a mass ratio of 8:1:1, placing the active substance in a small beaker and dropwise adding N-methylpyrrolidone NMP) as a solvent, and stirring into a slurry; placing the slurry on a copper foil, uniformly coating the slurry into sheets by an automatic conformal coating, and uniformly attaching the coating to the surface of the copper foil: placing the prepared electrode material coating in an oven, drying at 80°C for 2 h, transferring into a vacuum drying oven after drying, and performing vacuum drying at 105°C for 12 h, further removing the solvent to completely remove the electrode material coating; The pressed sheets of the dried copper foil are compacted by a counter-roller to increase the tap density of the electrode material, and then a circular electrode sheet with a diameter of 13 mm is punched out by a punching machine, which is taken out and weighed and put into a glove box for later use.

The assembled battery of the invention is a CR2430 type button type experimental battery, the battery is assembled in a glove box filled with Ar atmosphere, and the moisture in the glove box is controlled to be less than 5 ppm in the assembly process. The button-type battery uses a pure metal lithium sheet as a counter electrode and a reference electrode, the diameter of the lithium sheet must be larger than the diameter of the electrode sheet by 13 mm, and the diameter of the lithium sheet adopted by the invention is 15.6 mm; porous polypropylene membrane (Celgard2400) is used as the separator. when it is used, the diameter equal to the inner diameter of CR2430-type positive electrode case, ie, 24mm, is punched by a punching machine. 1 moL of LIPF/EC+DMC+EMC (1:1:1 by volume) is used as the electrolyte.

The assembly steps of the button type lithium ion battery are as follows: the opening face of the positive shell is upward and is arranged on a substrate; The electrode sheet is arranged in that center of the positive plate, an electrolyte is sucked by a rubber-head dropper, the surface of the electrode sheet is wetted, a diaphragm is clamped to cover the electrode sheet, and the electrolyte is sucked again to completely wet the surface of the diaphragm; then that lithium sheet, the gasket and the spring sheet are sequentially clamped and place in the middle position of the electrode shell, and the lithium sheet, the gasket and the spring sheet are strictly aligned, all the steps need to be operated with tweezers and can be fine-tuned; then the negative shell is covered with tweezers and sealed in a sealing pocket, the battery is removed from the glove box, the battery is immediately pressurized and sealed with a hydraulic sealing machine, and the residual electrolyte on the surface of the battery is dried, the electrochemistry test can be carried out after 24 hours.

Embodiment 1 The invention relates to a preparation method of a carbon nano composite material, comprising the following steps: (1) First, pretreatment 1s performed on multi-walled carbon nano tubes: the multi-walled carbon nano tubes are ultrasonically dispersed in sodium hydroxide solution (concentration: 0.50 mg/mL, the same below) for 30 min, immersed for 10 h and then washed, and then mixed with concentrated nitric acid (concentration: 68%) and placed in a single-necked flask under the ultrasonic condition of frequency: 40 kHz and ultrasonic power: 250 W at 85°C for 10 h under reflux.

Then the multi-wall carbon nano tube after pretreatment 1s mixed with mixed acid (concentrated sulfuric acid and concentrated nitric acid which are mixed in a volume ratio of 5: 1), treated for 4h under reflux at 70°C, washed to be neutral by deionized water, and dried for 10 h under 60°C to obtain the acidified carbon nano tube, wherein the purity is 98%; (2) 4.9084g SnClge5SH20 and PEG with the molecular weight of 2,000 are mixed and dissolved in deionized water, the mass ratio of SnClgeSH,0 to PEG is 2: 1, ultrasonic dispersion is carried out, ammonia water is dropwise added under the stirring condition until the SnClyeSH,0 is completely hydrolyzed, and then the SnClsSH>O is obtained through suction filtration, washing and sintering at 150°C; And (3) mix that acidified carbon nanotube and the SnOz in a molar ratio of 1:1, add the mixture into deionized water, carrying out ultrasonic dispersion for 0.5 h under 200 W, heating the mixture in a 70°C water bath, dropwise adding 5 mol/L sodium hydroxide solution to make the solution alkaline, filtering and washing the solution to neutrality,

carrying out vacuum sintering at 90°C for 8 h, and roasting at 280°C for 3 h to obtain the carbon nano composite material.

The carbon nano composite material prepared in this embodiment has good sphericity, and the average particle diameter is about 102 nm. when the scanning voltage is 0.02-2.5 V and the current density is 25 mA/g, the initial discharge amount is 1,500 mAh/g, and the capacity is still about 1,300 mAh/g after 3,000 cycles.

Embodiment 2 The invention relates to a preparation method of a carbon nano composite material, comprising the following steps: (1) Firstly carry out pretreatment on that multi-wall carbon nano tubes, namely ultrasonically disperse the multi-wall carbon nano tubes in a sodium hydroxide solution for 30 min, soaking for 10 h and then wash, mix the multi-wall carbon nano tubes with concentrated nitric acid (concentration of 68 percent) and putting the mixture into a single-neck flask, carrying out reflux at 80°C for 9 h under the ultrasonic condition of frequency of 45 kHz and ultrasonic power of 200 W, mixing the multi-wall carbon nano tubes after pretreatment with mixed acid (volume ratio of concentrated sulfuric acid and concentrated nitric acid mixed of 6:1), carrying out reflux treatment at 75°C for 3 h, washing with deionized water to neutrality, and drying at 60°C for 10h to obtain the acidified carbon nano tubes, wherein the purity is 98%.

(2) 4.9084 g SnCly5H20 and PEG with the molecular weight of 2,000 are mixed and dissolved in deionized water, the mass ratio of SnClgeSH,0 to PEG is 2: 1, ultrasonic dispersion is carried out, ammonia water is dropwise added under the stirring condition until the SnCl4+5H2O is completely hydrolyzed, and then the SnClyeSH20 is obtained through suction filtration, washing and sintering at 180°C to obtain SnOz; And (3) mix that acidified carbon nanotube and the SnOz according to the molar ratio of 1:2, adding into deionized water, carrying out ultrasonic dispersion for 0.5 h under 200 W, heating under a 70°C water bath, dropwise adding 5 mol/L sodium hydroxide solution to make the solution alkaline, filtering and washing the solution to neutrality, carrying out vacuum sintering at 100°C for 6 h, and roasting at 300°C for 3 h to obtain the carbon nano composite material.

The carbon nanocomposite prepared in this embodiment has good sphericity, and the average particle size is about 105 nm. When the scanning voltage is 0.02-2.5 V and the current density is 25 mA/g, the initial discharge amount is 1550 mAh/g. After 3,000 cycles, the capacity is still about 1,320 mAh/g.

Embodiment 3 The invention relates to a preparation method of a carbon nano composite material, comprising the following steps: (1) Firstly carry out pretreatment on that multi-wall carbon nano tubes, namely ultrasonically disper the multi-wall carbon nano tubes in a sodium hydroxide solution for min, soaking for 10 h and then washing, mix the multi-wall carbon nano tubes with concentrated nitric acid (concentration of 68 percent) and putting the mixture into a single-neck flask, carrying out reflux at 85°C for 9 h under the ultrasonic condition of frequency of 45 kHz and ultrasonic power of 250 W, then mixing the multi-wall carbon nano tubes after pretreatment with mixed acid (volume ratio of concentrated sulfuric acid and concentrated nitric acid mixed with 6:1), carrying out reflux treatment at 75°C for 4 h, washing with deionized water to neutrality, and drying at 60°C for 8 h to obtain the acidified carbon nano tubes, wherein the purity is 99%. (2) 4.9084 g SnCly5H20 and PEG with the molecular weight of 4,000 are mixed and dissolved in deionized water, the mass ratio of SnCl4+5H20 to PEG 1s 8: 1, ultrasonic dispersion is carried out, ammonia water is dropwise added under the stirring condition until the SnCl4+5H2O is completely hydrolyzed, and then the SnCls5SH>O is obtained through suction filtration, washing and sintering at 160°C to obtain SnO7; And (3) mix that acidified carbon nanotube and the SnOz according to the molar ratio of 1:3, adding into deionized water, carrying out ultrasonic dispersion for 0.5 h under 200 W, heating under a 70°C water bath, dropwise adding 5 mol/L sodium hydroxide solution to make the solution alkaline, filtering and washing the solution to neutrality, carrying out vacuum sintering at 90°C for 8 h, and roasting at 280°C for 3 h to obtain the carbon nano composite material.

The carbon nanocomposite prepared in this embodiment has good sphericity, and the average particle size is about 75 nm.

When the scanning voltage is 0.02-2.5V and the current density is 25mA/g, the initial discharge capacity is 1800 mAh/g.

After 3000 cycles, the capacity is still about 1710 mAh/g.

Embodiment 4 The invention relates to a preparation method of a carbon nano composite material, comprising the following steps: (1) Perform pretreatment on that multi-wall carbon nano tubes at first, namely ultrasonically disperse the multi-wall carbon nano tubes in a sodium hydroxide solution for 30 min, soaking for 10 h and then washing, mix the multi-wall carbon nano tubes with concentrated nitric acid (concentration of 68 percent) and then putting the mixture into a single-necked flask, performing reflux at 80°C for 8 h under the ultrasonic condition of frequency of 50kHz and ultrasonic power of 300 W, then mixing the multi-wall carbon nano tubes after pretreatment with mixed acid (volume ratio of concentrated sulfuric acid and concentrated nitric acid mixed at 7:1), performing reflux treatment at 70°C for 4 h, washing with deionized water to neutrality, and drying at 60°C for 10h to obtain the acidified carbon nano tubes, wherein the purity is 98%. (2) 4.9084 g SnCly5H20 and PEG with the molecular weight of 1,000 are mixed and dissolved in deionized water, the mass ratio of SnClseSH20 to PEG is 2:1, ultrasonic dispersion is carried out, ammonia water is dropwise added under the stirring condition until the SnClye5H20 is completely hydrolyzed, and then the SnClssSH>0 is obtained through suction filtration, washing and sintering at 200°C; And (3) mix that acidified carbon nanotube and the SnOz in a molar ratio of 1:1, add the mixture into deionized water, carrying out ultrasonic dispersion for 0.5 h under 200 W, heating the mixture in a 70°C water bath, dropwise adding 5 mol/L sodium hydroxide solution to make the solution alkaline, filtering and washing the solution to neutrality, carrying out vacuum sintering at 90°C for 8 h, and roasting at 280°C for 3 h to obtain the carbon nano composite material.

The carbon nano composite material prepared in the embodiment is spherical-like particles, the average particle size is between 150 and 300 nm, and the initial discharge capacity is 1,300 mAh/g when the scanning voltage is 0.02 to 2.5 V and the current density is 25 mA/g.

After 3,000 cycles, the capacity is still about 1,100 mAh/g.

Embodiment 5

The invention relates to a preparation method of a carbon nano composite material, comprising the following steps: (1) Perform pretreatment on that multi-wall carbon nano tubes at first, namely ultrasonically disperse the multi-wall carbon nano tubes in a sodium hydroxide solution for 30 min, soaking for 8 h and then washing, mix the multi-wall carbon nano tubes with concentrated nitric acid (concentration of 68 percent) and putting the mixture into a single-necked flask under the ultrasonic condition of frequency of 45 kHz and ultrasonic power of 250 W at 85°C for 8 h, then mixing the multi-wall carbon nano tubes after pretreatment with mixed acid (volume ratio of concentrated sulfuric acid and concentrated nitric acid mixed at 6:1), carrying out reflux treatment at 80°C for 3 h, washing with deionized water to be neutral, and drying at 60°C for 8h to obtain the acidified carbon nano tubes, wherein the purity is 99%; (2) 4.9084 g SnCly5H20 and PEG with the molecular weight of 4,000 are mixed and dissolved in deionized water, the mass ratio of SnCly5H20 to PEG is 4:1, ultrasonic dispersion is performed, ammonia water is dropwise added under the stirring condition until the SnClye5H20 is completely hydrolyzed, and then the SnClssSH>0 is obtained through suction filtration, washing and sintering at 160°C to obtain the SnO»; And (3) mix that acidified carbon nanotube and the SnOz according to the molar ratio of 1:3, adding into deionized water, carrying out ultrasonic dispersion for 0.5 h under 200 W, heating under a 70°C water bath, dropwise adding 5 mol/L sodium hydroxide solution to make the solution alkaline, filtering and washing the solution to neutrality, carrying out vacuum sintering at 90°C for 8 h, and roasting at 280°C for 3 h to obtain the carbon nano composite material.

The carbon nanocomposite prepared in this embodiment has good sphericity, and the average particle size is about 78 nm.

When the scanning voltage is 0.02-2.5 V and the current density is 25 mA/g, the initial discharge amount is 1,750 mAh/g.

After 3,000 cycles, the capacity is still about 1,610 mAh/g.

Embodiment 6 The invention relates to a preparation method of a carbon nano composite material, comprising the following steps: (1) Firstly carry out pretreatment on that multi-wall carbon nano tubes, namely ultrasonically disperse the multi-wall carbon nano tubes in a sodium hydroxide solution for 30 min, soaking for 10 h and then washing, mix the multi-wall carbon nano tubes with concentrated nitric acid (concentration of 68 percent) and putting the mixture into a single-neck flask, carrying out reflux at 85°C for 9 h under the ultrasonic condition of frequency of 45 kHz and ultrasonic power of 250 W, then mixing the multi-wall carbon nano tubes after pretreatment with mixed acid (volume ratio of concentrated sulfuric acid and concentrated nitric acid mixed with 6:1), carrying out reflux treatment at 75°C for 4 h, washing with deionized water to neutrality, and drying at 60°C for 8h to obtain the acidified carbon nano tubes, wherein the purity is 99%; (2) 4.9084g SnClye5SH20 and PEG with the molecular weight of 4,000 are mixed and dissolved in deionized water, the mass ratio of SnCly-5H20 to PEG is 10:1, ultrasonic dispersion is carried out, ammonia water is dropwise added under the stirring condition until the SnClye5H20 is completely hydrolyzed, and then the SnClssSH>0 is obtained through suction filtration, washing and sintering at 200°C to obtain SnO7;

(3) Mix that acidified carbon nanotube and the SnO» according to the molar ratio of 1:7, adding into deionized wat, carrying out ultrasonic dispersion for 0.5 h under 200 W, heating in a water bath at 80°C, dropwise adding 5 mol/L sodium hydroxide solution to make the solution alkaline, filtering and washing the solution to neutrality, carrying out vacuum sintering at 110°C for 5 h, and roasting at 320°C for 2 h to obtain the carbon nano composite material.

The carbon nano composite material prepared in this embodiment has good sphericity, and the average particle diameter is about 80 nm. when the scanning voltage is 0.02-2.5 V and the current density is 25 mA/g, the initial discharge amount is 1,720 mAh/g, and the capacity is still about 1,580mAh/g after 3000 cycles.

Comparative embodiment 1 The invention relates to a preparation method of a carbon nano composite material, which is the same as that of the embodiment 3, and is different in that the step (1) firstly carries out pretreatment on multi-wall carbon nano tubes: the multi-wall carbon nano tubes are mixed with concentrated nitric acid (concentration of 68 percent) and then put into a single-neck flask, the multi-wall carbon nano tubes are subjected to reflux at 85°C for 9 h under the ultrasonic condition of frequency of 45 kHz and ultrasonic power of 250 W, the multi-wall carbon nano tubes after the pretreatment are mixed with concentrated sulfuric acid, the multi-wall carbon nano tubes are subjected to reflux treatment at 75°C for 4 h, deionized water is washed to be neutral, and dried at 60°C for 8 h, and the acidified carbon nano tubes are obtained with a concentration of 80%. The carbon nanocomposite prepared in this comparative embodiment is spheroidal, with an average particle size of 200-300 nm, an initial discharge capacity of 750 mAh/g at a scanning voltage of 0.02-2.5 V and a current density of 25 mA/g, and a capacity of about 650 mAh/g after 300 cycles.

Comparative embodiment 2 Same as embodiment 3 except that that molecular weight of PEG 1s 6,000.

The carbon nanocomposite prepared in this comparative embodiment had an initial discharge amount of 627 mAh/g at a scan voltage of 0.02-2.5 V and a current density of mA/g, and a capacity of about 423 mAh/g after 200 cycles.

Comparative embodiment 3 The invention relates to a preparation method of a carbon nano composite material, comprising the following steps: (1) Perform pretreatment on that multi-wall carbon nano tubes at first, namely ultrasonically disperse the multi-wall carbon nano tubes in a sodium hydroxide solution for 30 min, soaking for 10 h and then washing, mix the multi-wall carbon nano tubes with concentrated nitric acid (concentration of 68 percent) and then putting the mixture into a single-necked flask, performing reflux at 90°C for 8 h under the ultrasonic condition of frequency of 45 kHz and ultrasonic power of 300 W, then mixing the multi-wall carbon nano tubes after pretreatment with mixed acid (volume ratio of concentrated sulfuric acid and concentrated nitric acid mixed at 6:1), performing reflux treatment at 75°C for 4 h, washing with deionized water to neutrality, and drying at 60°C for 8 h to obtain the acidified carbon nano tubes, wherein the purity is 99%; (2) 4.9084 g SnCly5H20 and PEG with the molecular weight of 4,000 are mixed and dissolved in deionized water, the mass ratio of SnClys5SH,O to PEG is 8:1, ultrasonic dispersion is carried out, ammonia water is dropwise added under the stirring condition until the SnClye5H20 is completely hydrolyzed, and then the SnClssSH>0 is obtained through suction filtration, washing and sintering at 160°C to obtain SnO7; (3) Mix that acidified carbon nanotube and the SnO; according to the molar ratio of 1:3, adding into deionized wat, performing ultrasonic dispersion for 0.5 h under 200 W, heating in a 70°C water bath, dropwise adding 5 mol/L sodium hydroxide solution to make the solution alkaline, filtering and washing the solution to neutrality, and roasting for 11 h under 280°C to obtain the carbon nano composite material.

The carbon nanocomposite prepared in this comparative embodiment had an initial discharge amount of 720 mAh/g at a scan voltage of 0.02-2.5 V and a current density of mA/g, and a capacity of about 410 mAh/g after 100 cycles.

The above-mentioned embodiments are only for describing the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. On the premise of not departing from the design spirit of the present invention, various modifications and improvements made to the technical scheme of the present invention by those of ordinary skill in the art should fall within the protection scope determined by the claims of the present invention.

Claims (10)

CLAIMS:

1. A method for preparing a carbon nano composite material, comprising the steps of: (1) firstly carry out pretreatment on that carbon nano tubes, wherein the pretreatment proces of the carbon nano tubes comprises the following step of: ultrasonically dispersing the carbon nano tubes in a sodium hydroxide solution, soaking and washing, then mixing the carbon nano tubes with concentrated nitric acid and then carrying out reflux under the ultrasonic condition, then mixing the pretreated carbon nano tubes with mixed acid, carrying out reflux treatment, washing and drying to obtain the acidified carbon nano tubes; (2) mixing SnClssSH,O and polyethylene glycol, dissolving in deionized water, performing ultrasonic dispersion, dropwise adding ammonia water under the stirring condition until the SnCly5H:O is completely hydrolyzed, and performing suction filtration, washing and sintering to obtain SnO»; and (3) mix that acidified carbon nanotube and the SnOs, add into deionized water, performing ultrasonic dispersion, heat in a water bath, dropwise adding alkali liquor to make the solution alkaline, filtering and washing the solution to neutrality, performing vacuum sintering at 90-110°C for 5-8 h, and then roasting at 280-350°C for 2-3 h to obtain the carbon nano composite material.

2. The preparation method according to claim 1, wherein in the pretreatment process of the carbon nanotube in step (1), the ultrasonic power is 200-300 W, the frequency is 40- 50 kHz, the reflux temperature is 80-90°C, and the reflux time is 8-10 h.

3. The preparation method according to claim 1, wherein the mixed acid in step (1) 1s concentrated sulfuric acid and concentrated nitric acid in a volume ratio of (5-7): 1.

4. The preparation method according to claim 1, wherein after the carbon nanotube pretreated in step (1) is mixed with the mixed acid, the reflux temperature is 70-80°C and the reflux time is 3-4 h.

5. The preparation method according to claim 1, wherein the mass ratio of SnCl4+5H20 to polyethylene glycol in step (2) 1s (2-10): 1.

6. The preparation method according to claim 1, wherein the sintering temperature in step (2) 1s 150 to 200°C.

7. The preparation method according to claim 1, wherein the molar ratio of the acidified carbon nano tubes to the SnOz in the step (3) 1s 1: (1-7).

8. The preparation method according to claim 1, wherein the water bath temperature in step (3) 1s 70 to 80°C.

9. À carbon nanocomposite prepared by the preparation method according to claim 1.

10. The application of a carbon nanocomposite in a battery according to claim 9, wherein the carbon nanocomposite 1s used to prepare a lithium ion battery cathode material.