WO2018032975A1 - 有效缓冲硅体积效应的锂离子电池负极材料的制备方法 - Google Patents

有效缓冲硅体积效应的锂离子电池负极材料的制备方法 Download PDF

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WO2018032975A1
WO2018032975A1 PCT/CN2017/095803 CN2017095803W WO2018032975A1 WO 2018032975 A1 WO2018032975 A1 WO 2018032975A1 CN 2017095803 W CN2017095803 W CN 2017095803W WO 2018032975 A1 WO2018032975 A1 WO 2018032975A1
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silicon
graphene microchip
ion battery
graphene
composite material
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许志
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福建新峰二维材料科技有限公司
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the invention relates to the technical field of a preparation method of a lithium ion battery anode material, in particular to a preparation method of a lithium ion battery anode material which effectively buffers the silicon volume effect.
  • Lithium-ion batteries are ubiquitously used in portable electronics and network storage due to their relatively high discharge voltage, energy density, and good power performance.
  • the electrode material with high theoretical capacity to replace the graphite anode material that has been developed.
  • the silicon-based anode material is the most attractive alternative because it has a very high theoretical capacity of 4200 mAh g-1 (forming a fully lithiated state of Li4.4Si) and a low discharge voltage (the average deintercalation lithium voltage of Si is 0.4V).
  • the cycle life of the electrode is limited due to cracking and pulverization caused by a large volume change (up to 311%) during charge and discharge.
  • Nano silicon-based material preparation techniques for use in the preparation of anode materials for lithium ion batteries have yet to be improved.
  • the present invention provides a method for preparing a lithium ion battery anode material which effectively buffers the silicon volume effect.
  • the technical solution adopted by the present invention is: a method for preparing a negative electrode material for a lithium ion battery that effectively buffers a silicon volume effect, the method comprising the steps of: preparing a modified graphene microchip; and using a graphene microchip Nano-silicon spheres are grown on the surface to obtain graphene microchip-nano-silica composites; a precise thickness of metal oxide layer is deposited on the surface of graphene microchip-nano-silica sphere by atomic layer deposition technique; metal oxide layer is deposited on the surface
  • the graphene microchip-nanosilicon sphere composite material is uniformly dispersed into the electrospinning solution, and is subjected to electrospinning and calcination treatment to obtain a carbon nanofiber composite material; the carbon nanofiber composite material is subjected to acid treatment to completely remove the metal oxide
  • the layer forms a void structure, that is, a void structure is left between the nano-silicon spheres or
  • the method for preparing the modified graphene microchip is to first place the expanded graphite in a container, add 100-1000 ml of an organic solvent, and then oscillate under the condition of an ultrasonic vibration power of 300-1200 W and a temperature of 20-150 ° C.
  • a graphene microchip suspension is obtained; then, it is allowed to stand for 20-300 min, the upper layer suspension is taken, the precipitate is removed, and after filtration, it is dried at 60-80 ° C to obtain a graphene microchip; then the obtained graphene micro Add the tablets to 20-100ml concentrated sulfuric acid, keep the solution temperature below 4 °C, slowly add 0.5-20g potassium permanganate, keep the solution temperature below 10 °C and magnetically stir for 60-120min and during magnetic stirring, Slowly add 150ml of deionized water; stir After the end of the mixing, 1-5 ml of hydrogen peroxide was added, and stirring was continued for 10-30 min; finally, the surface-modified graphene microchip was obtained by filtration and drying.
  • the organic solvent is at least one of NMP, DMF, toluene, chlorobenzene, and trichloroethylene.
  • the nano silicon ball is grown on the surface of the graphene microchip by a chemical vapor deposition (CVD) method; first, the graphene microchip is placed in a reaction chamber, vacuum is applied, and the reaction chamber is heated, when the temperature reaches After the reaction temperature, a carrier gas of 1-500 sccm is introduced to maintain the pressure of the reaction chamber at 0.01 Torr to 10 Torr, and then a reaction gas of 1-500 sccm is introduced into the reaction chamber, and the reaction gas is decomposed at a high temperature to form a nano-silica ball.
  • the reaction gas, the carrier gas, and the heating device are sequentially turned off to obtain a graphene microchip-nanosilicon ball composite material.
  • nano-silica spheres grown on the surface of the graphene microchip have a size of about 1-100 nm and a reaction temperature of 650 ° C - 1000 ° C.
  • the reaction gas for growing the nano silicon sphere on the surface of the graphene microchip is at least one of silane (SiH 4 ) and dichlorosilane (SiH 2 Cl 2 );
  • the carrier gas is nitrogen (N 2 ), argon At least one of gases (Ar).
  • the metal oxide layer is at least one of nickel oxide, aluminum oxide, tin oxide, titanium oxide, and the like, and the metal oxide layer has a thickness of about 10 to 60 nm.
  • the carbon nanofiber composite material comprises a graphene microchip which is completely covered by the inside, a nano silicon sphere and a graphene microchip-nanosilicon sphere composite material whose edge is not completely coated.
  • the forming a carbon coating layer on the outer surface of the carbon nanofiber composite material is at least one of atomic layer deposition technology (ALD), chemical vapor deposition (CVD), and sugar recombination technology.
  • ALD atomic layer deposition technology
  • CVD chemical vapor deposition
  • sugar recombination technology atomic layer deposition technology
  • an amorphous silicon carbon coating layer is formed on the surface of the carbon nanofiber composite material, and the graphene-nanosilicon sphere composite material with the carbon nanofiber edge not completely coated may be coated to increase the stability of the electrode structure.
  • the present invention has the following advantages over the prior art:
  • the invention provides a negative electrode material for a lithium ion battery as an effective buffering silicon volume effect, and the preparation process is simple.
  • the nano silicon ball is uniform in size and good in dispersion and does not agglomerate.
  • a precise and controllable void structure is formed between the nano silicon ball or the graphene and the carbon nanofiber, which can effectively buffer the volume expansion of the silicon during charging and discharging, and further buffer the silicon by utilizing the high flexibility and high conductivity of the graphene.
  • the volume effect and increase the efficiency of electron and ion transport.
  • the invention further forms a carbon coating layer on the outermost layer to further protect the nano silicon ball, and at the same time can cover the nano silicon ball which cannot be completely covered by the edge of the carbon nanofiber, and ensure that each nano silicon sphere particle is packaged. Cover protection, there is room for free expansion, to ensure the integrity of the electrode structure, increase the stability of the electrode structure.
  • the lithium-ion battery prepared by using the anode material of the invention has the first coulombic efficiency of 84%-90%, and can maintain a specific capacity of 2000 mAh/g after circulating for 1050 cycles at a current density of 700 mA/g, and the average attenuation per cycle.
  • the rate is only about 0.006%, showing excellent long-term cycle stability and rate performance.
  • FIG. 1 is a flow chart of a method for preparing a negative electrode material for a lithium ion battery which effectively buffers a silicon volume effect according to the present invention
  • FIG. 2 is a schematic structural view of a negative electrode material of a lithium ion battery which effectively buffers the volumetric effect of silicon according to the present invention
  • Fig. 3 is a comparison diagram of charge and discharge of an embodiment of the present invention and a comparative example.
  • a method for preparing a negative electrode material for a lithium ion battery that effectively buffers a silicon volume effect comprising the steps of:
  • the structure of an anode material of a lithium ion battery having an effective buffering silicon volume effect prepared by the present invention comprises carbon nanofibers 21, graphene microchips 13 inside and outside the carbon nanofibers, and nano silicon.
  • the anode material can ensure that each nano-silicon sphere particle has a free expansion space during charge and discharge, thereby preparing an ultra-stable lithium ion battery.
  • the preparation process of the invention is simple, and the nano silicon ball is uniformly distributed on the surface of the graphene microchip by depositing the nano silicon sphere on the surface of the modified graphene microchip, and the dispersibility is good and not agglomerated; and the graphene-nanosilicon sphere composite material is simultaneously used.
  • the surface is deposited with a precisely controllable metal oxide layer, and the metal oxide layer is removed after the carbon nanofiber coating, so that a void structure is formed between the nano silicon sphere and the graphene and the carbon nanofiber, which can effectively buffer the silicon in the surface.
  • the volume expansion during charge and discharge, the high flexibility and high conductivity of graphene can further buffer the volume expansion of silicon and increase the transmission efficiency of electrons and ions; finally, the amorphous carbon coating layer can be formed on the outermost layer.
  • the nano-silicon spheres covered by some carbon nanofiber edges can not be completely covered, and can further buffer the volume expansion of the nano-silicon spheres, ensuring that each nano-silicon sphere particles are coated and protected, and have free expansion space to ensure electrode structure. Integrity.
  • the expanded graphite was placed in a container, 250 ml of NMP was added, stirred uniformly, and then shaken for 10 hours under ultrasonic vibration power of 800 W at a temperature of 75 ° C to obtain a graphene microchip suspension; then allowed to stand for 180 min, and the upper suspension was taken.
  • the obtained graphene microchip is placed in a chemical vapor deposition (CVD) reaction chamber, vacuum is applied, and the reaction chamber is heated.
  • CVD chemical vapor deposition
  • 100 sccm of argon gas is introduced to maintain the pressure of the reaction chamber at 1 Torr.
  • 60sccm of silane (SiH 4 ) is introduced into the reaction chamber, and SiH 4 decomposes at a high temperature to form a nano-silica ball having a size of about 50 nm attached to the surface of the graphene microchip of the substrate material to obtain a graphene microchip- Nano silicon ball composite material;
  • a layer of nickel oxide (NiO) with a thickness of about 24 nm is deposited on the surface of the graphene-nanosilicon composite by atomic layer deposition (ALD); then it is uniformly dispersed into the electrospinning solution and electrospun Silk and calcination treatment method for preparing carbon nanofiber composite material comprising graphene-nanosilicon spheres; then the carbon nanofiber composite material is placed in an acid for acid treatment to remove nickel oxide and remain in the original position of nickel oxide Lower void structure. Finally, an amorphous carbon coating layer is formed on the outermost surface by atomic layer deposition (ALD) to obtain a lithium ion battery anode material.
  • ALD atomic layer deposition
  • the lithium ion battery prepared by the negative electrode material was cycled 1050 times at a current density of 700 mA/g, and still maintained a specific capacity of about 2002 mAh/g, and the first charge and discharge coulombic efficiency reached 86.3%.
  • the expanded graphite was placed in a container, 150 ml of DMF was added, stirred uniformly, and then shaken for 8 hours under the condition of ultrasonic vibration power of 1000 W and temperature of 80 ° C to obtain a graphene microchip suspension; Then, it was allowed to stand for 180 min, the upper layer suspension was taken, the precipitate was removed, and after filtration, it was dried at 70 ° C to obtain a graphene microchip; then the obtained graphene microchip was added to 100 ml of concentrated sulfuric acid to keep the solution temperature below 4 ° C.
  • the obtained graphene microchip is placed in a chemical vapor deposition (CVD) reaction chamber, vacuum is applied, and the reaction chamber is heated.
  • CVD chemical vapor deposition
  • 150 sccm of argon gas is introduced to maintain the pressure of the reaction chamber at 1.3.
  • 80sccm of silane (SiH 4 ) was introduced into the reaction chamber, and SiH 4 was decomposed at a high temperature to form a nano-silica ball having a size of about 50 nm attached to the surface of the graphene microchip of the substrate material to obtain a graphene microchip.
  • SiH 4 silane
  • an aluminum oxide layer with a thickness of about 26 nm is deposited on the surface of the graphene-nanosilicon composite by atomic layer deposition (ALD); then it is uniformly dispersed into the electrospinning solution and electrospun and calcined.
  • ALD atomic layer deposition
  • the method of treatment prepares a carbon nanofiber composite comprising graphene-nanosilicon spheres; the carbon nanofiber composite is then placed in an acid for acid treatment to remove the alumina and leave a void structure at the original location of the alumina.
  • an amorphous carbon coating layer is formed on the outermost surface by chemical vapor deposition (CVD) to obtain a lithium ion battery anode material.
  • the lithium ion battery prepared by the negative electrode material was cycled 1050 times at a current density of 700 mA/g, and still maintained a specific capacity of about 1982 mAh/g, and the first charge and discharge coulombic efficiency reached 88.9%.
  • the comparative example is a pure nano-silicon sphere.
  • the negative electrode material circulates at a current density of 700 mA/g, with a very rapid capacity decay from the beginning.

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Abstract

一种有效缓冲硅体积效应的锂离子电池负极材料的制备方法，包括以下步骤：首先制备改性石墨烯微片（S01）；然后在石墨烯微片表面生长纳米硅球，得到石墨烯微片-纳米硅球复合材料（S02）；再通过原子层沉积技术在石墨烯微片-纳米硅球表面沉积金属氧化物层（S03）；再进行静电纺丝及煅烧处理，得到碳纳米纤维复合材料（S04）；再对碳纳米纤维复合材料进行酸处理，去除金属氧化物层形成空隙结构（S05）；最后在碳纳米纤维复合材料外面形成碳包覆层（S06）。该制备方法制备过程简单，材料具有精确可控的空隙结构，有效缓冲硅在充放电过程中的体积膨胀，在最外层形成碳包覆层进一步保护纳米硅球，保证电极结构的完整性，增加电极结构的稳定性。

Description

有效缓冲硅体积效应的锂离子电池负极材料的制备方法 技术领域
本发明涉及锂离子电池负极材料的制备方法技术领域，尤其涉及有效缓冲硅体积效应的锂离子电池负极材料的制备方法。
背景技术
锂离子电池(LIBs)由于其相对较高的放电电压、能量密度和很好的功率性能，所以无处不在的应用于便携式电子产品和网络存储。目前更多的研究都在追求高理论容量的电极材料来取代目前已经发展的石墨负极材料。其中，硅基负极材料是最具有吸引力的替代品，因其具有非常高的理论容量4200mAh g-1(形成全锂化状态Li4.4Si)和低放电电压(Si的平均脱嵌锂电压为0.4V)。然而，由于其在充放电过程中的大体积变化(高达311％)所引起的开裂和粉碎，使得电极循环寿命受到限制。
虽然众多的纳米硅基材料包括硅微/纳米管，纳米硅球/碳复合材料，纳米多孔硅和纳米线已被提出是可以提高循环稳定性的硅负极材料，但要使每个硅纳米粒子都有自由膨胀空间的硅基电极制造仍然是一个巨大的挑战。另一个限制硅基电极循环寿命长的关键因素，是不稳定的固体电解质界面(SEI)在电极的表面形成。如果SEI层变形或断裂，在下一个充电过程需要在电极表面形成新的SEI，这将导致电池库仑效率差，同时堆积的固体电解质界面(SEI)也会阻碍锂离子的传输。许多研究都集中在提高电极的稳定性使得锂离子电池在几十甚至到几百次循环仍具有相对高的容量。然而，它仍然是远远无法满足其在实际应用中所需的循环寿命。因此，现 有应用于锂离子电池负极材料的制备方法的纳米硅基材料制备技术还有待改进。
发明内容
针对上述问题，本发明提供了有效缓冲硅体积效应的锂离子电池负极材料的制备方法。
为解决上述技术问题，本发明所采用的技术方案是：有效缓冲硅体积效应的锂离子电池负极材料的制备方法，所述方法包括以下步骤：制备改性石墨烯微片；在石墨烯微片表面生长纳米硅球，得到石墨烯微片-纳米硅球复合材料；通过原子层沉积技术在石墨烯微片-纳米硅球表面沉积精确厚度的金属氧化物层；将表面沉积有金属氧化物层的石墨烯微片-纳米硅球复合材料均匀分散到静电纺丝液中，进行静电纺丝及煅烧处理，得到碳纳米纤维复合材料；对碳纳米纤维复合材料进行酸处理，完全去除金属氧化物层形成空隙结构，即在纳米硅球或石墨烯与碳纳米纤维之间留下空隙结构；在碳纳米纤维复合材料外面形成碳包覆层。
进一步的，所述改性石墨烯微片制备方法为首先将膨胀石墨置于容器中，加入100-1000ml的有机溶剂，然后在超声振荡功率为300-1200W，温度为20-150℃条件下振荡1-24h，得到石墨烯微片悬浮液；接着静置20-300min，取上层悬浮液，去除沉淀物，过滤后在60-80℃下烘干得到石墨烯微片；接着将所得石墨烯微片加入到20-100ml的浓硫酸中，保持溶液温度低于4℃，缓慢添加0.5-20g的高锰酸钾，保持溶液温度低于10℃并磁力搅拌60-120min并在磁力搅拌过程中，缓慢添加150ml的去离子水；搅 拌结束后添加1-5ml的双氧水，再继续搅拌10-30min；最后过滤烘干得到表面改性石墨烯微片。
进一步的，所述有机溶剂为NMP、DMF、甲苯、氯苯、三氯乙烯中的至少一种。
进一步的，所述在石墨烯微片表面生长纳米硅球，是通过化学气相沉积(CVD)方法制备；首先将石墨烯微片放入反应室内，抽真空并对反应腔进行加热，当温度达到反应温度后通入1-500sccm的载气气体，使反应腔室压强保持在0.01Torr-10Torr，然后向反应室通入1-500sccm的反应气体，反应气体在高温下分解反应生成纳米硅球附着在衬底材料石墨烯微片表面，反应结束后，依顺序关闭反应气体、载气气体、及加热装置，得到石墨烯微片-纳米硅球复合材料。
进一步的，所述在石墨烯微片表面生长纳米硅球的尺寸约为1-100nm，反应温度为650℃-1000℃。
进一步的，所述石墨烯微片表面生长纳米硅球的反应气体为硅烷(SiH4)、二氯硅烷(SiH2Cl2)中的至少一种；载气气体为氮气(N2)、氩气(Ar)中的至少一种。
进一步的，所述金属氧化物层为氧化镍、氧化铝、氧化锡、氧化钛等中的至少一种，金属氧化物层厚度约为10-60nm。
进一步的，所述碳纳米纤维复合材料包含有内部被其完全包覆的石墨烯微片、纳米硅球和边缘未完全被包覆的石墨烯微片-纳米硅球复合材料。
进一步的，所述在碳纳米纤维复合材料外面形成碳包覆层是通过原子层沉积技术(ALD)、化学气相沉积(CVD)、催糖技术中的至少一种方 式，在碳纳米纤维复合材料表面形成一层非晶硅碳包覆层，可以将碳纳米纤维边缘未完全包覆的石墨烯-纳米硅球复合材料进行包覆，增加电极结构的稳定性。
由上述对本发明结构的描述可知，和现有技术相比，本发明具有如下优点：
1、本发明提供一种作为有效缓冲硅体积效应的锂离子电池负极材料，制备过程简单，通过在改性石墨烯微片表面沉积纳米硅球，使得纳米硅球大小均匀、分散性好不会团聚，同时在纳米硅球或石墨烯与碳纳米纤维之间形成精确可控的空隙结构，能有效缓冲硅在充放电过程中的体积膨胀，利用石墨烯的高柔韧性和高导电性能进一步缓冲硅的体积效应，并增加电子和离子传输效率。
2、本发明在最外层再次形成碳包覆层能进一步保护纳米硅球，同时能包覆部分碳纳米纤维边缘无法完全被包覆的纳米硅球，保证每个纳米硅球粒子都被包覆保护，都有自由膨胀的空间，保证电极结构的完整性，增加电极结构的稳定性。
3、采用本发明负极材料制备的锂离子电池首次库仑效率高达84％-90％，在700mA/g的电流密度下循环1050周期后还能保持2000mAh/g的比容量，平均每个循环的衰减率只有约0.006％，表现出优异的长期循环稳定性能和倍率性能。
附图说明
构成本申请的一部分的附图用来提供对本发明的进一步理解，本发明 的示意性实施例及其说明用于解释本发明，并不构成对本发明的不当限定。在附图中：
图1为本发明有效缓冲硅体积效应的锂离子电池负极材料的制备方法的流程图；
图2为本发明有效缓冲硅体积效应的锂离子电池负极材料的结构示意图；
图3为本发明实施例与对比例的充放电对比图。
具体实施方式
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
如图1所示，有效缓冲硅体积效应的锂离子电池负极材料的制备方法，所述方法包括以下步骤：
S01、制备改性石墨烯微片；
S02、在石墨烯微片表面生长纳米硅球，得到石墨烯微片-纳米硅球复合材料；
S03、通过原子层沉积技术在石墨烯微片-纳米硅球表面沉积精确厚度的金属氧化物层；
S04、将表面沉积有金属氧化物层的石墨烯微片-纳米硅球复合材料均匀分散到静电纺丝液中，进行静电纺丝及煅烧处理，得到碳纳米纤维复合材料；
S05、对碳纳米纤维复合材料进行酸处理，完全去除金属氧化物层形成 空隙结构，即在纳米硅球或石墨烯与碳纳米纤维之间留下空隙结构；
S06、在碳纳米纤维复合材料外面形成碳包覆层。
如图2所示，采用本发明制备的有效缓冲硅体积效应的锂离子电池负极材料的结构，所述负极材料包括碳纳米纤维21、碳纳米纤维内部及边缘的石墨烯微片13、纳米硅球11、空隙结构12、及最外层的碳包覆层22。该负极材料在充放电过程中能保证每个纳米硅球粒子都有自由膨胀空间，从而制备出超稳定的锂离子电池。
本发明制备过程简单，通过在改性石墨烯微片表面沉积纳米硅球，使得纳米硅球均匀的分布在石墨烯微片表面，其分散性好不团聚；同时在石墨烯-纳米硅球复合材料表面沉积精确可控的金属氧化物层，并在碳纳米纤维包覆后去除该层金属氧化物层，使得在纳米硅球和石墨烯与碳纳米纤维之间形成空隙结构，能有效缓冲硅在充放电过程中的体积膨胀，利用石墨烯的高柔韧性和高导电性可以进一步缓冲硅的体积膨胀并增加电子和离子的传输效率；最后在最外层形成非晶碳包覆层，可以包覆部分碳纳米纤维边缘无法完全被包覆的纳米硅球，还能进一步缓冲纳米硅球的体积膨胀，保证每个纳米硅球粒子都被包覆保护，都有自由膨胀的空间，保证电极结构的完整性。
具体的本发明可以采用以下实施方式：
实施例1
首先将膨胀石墨置于容器中，加入250ml的NMP，搅拌均匀后在超声振荡功率为800W，温度为75℃条件下振荡10h，得到石墨烯微片悬浮液；接着静置180min，取上层悬浮液，去除沉淀物，过滤后在70℃下烘干得到 石墨烯微片；接着将所得石墨烯微片加入到80ml的浓硫酸中，保持溶液温度低于4℃，缓慢添加1g的高锰酸钾，保持溶液温度低于10℃并磁力搅拌90min，同时在磁力搅拌过程中，缓慢添加150ml的去离子水；搅拌结束后添加3ml的双氧水，再继续搅拌20min；最后过滤烘干得到表面改性石墨烯微片；
接着将得到的石墨烯微片放入化学气相沉积(CVD)反应室内，抽真空并对反应腔室进行加热，当温度达到800℃后通入100sccm的氩气，使反应腔室压强保持在1Torr左右，然后向反应腔室通入60sccm的硅烷(SiH4)，SiH4在高温下分解反应生成大小约为50nm的纳米硅球附着在衬底材料石墨烯微片表面，得到石墨烯微片-纳米硅球复合材料；
然后通过原子层沉积技术(ALD)在石墨烯-纳米硅球复合材料表面沉积一层厚度约为24nm的氧化镍层(NiO)；然后将其均匀分散到静电纺丝液中，并通过静电纺丝及煅烧处理的方法制备包含有石墨烯-纳米硅球的碳纳米纤维复合材料；紧接着将该碳纳米纤维复合材料放入酸中进行酸处理，去除氧化镍并在氧化镍原来的位置留下空隙结构。最后再通过原子层沉积技术(ALD)在最外面再形成一层非晶碳包覆层，得到锂离子电池负极材料。
该负极材料制备的锂离子电池在700mA/g的电流密度下循环1050次，仍保持约2002mAh/g的比容量，首次充放电库仑效率达到86.3％。
实施例2
首先将膨胀石墨置于容器中，加入150ml的DMF，搅拌均匀后在超声振荡功率为1000W，温度为80℃条件下振荡8h，得到石墨烯微片悬浮液； 接着静置180min，取上层悬浮液，去除沉淀物，过滤后在70℃下烘干得到石墨烯微片；接着将所得石墨烯微片加入到100ml的浓硫酸中，保持溶液温度低于4℃，缓慢添加0.5的高锰酸钾，保持溶液温度低于10℃并磁力搅拌120min，同时在磁力搅拌过程中，缓慢添加150ml的去离子水；搅拌结束后添加3ml的双氧水，再继续搅拌30min；最后过滤烘干得到表面改性石墨烯微片；
接着将得到的石墨烯微片放入化学气相沉积(CVD)反应室内，抽真空并对反应腔室进行加热，当温度达到850℃后通入150sccm的氩气，使反应腔室压强保持在1.3Torr左右，然后向反应腔室通入80sccm的硅烷(SiH4)，SiH4在高温下分解反应生成大小约为50nm的纳米硅球附着在衬底材料石墨烯微片表面，得到石墨烯微片-纳米硅球复合材料；
然后通过原子层沉积技术(ALD)在石墨烯-纳米硅球复合材料表面沉积一层厚度约为26nm的氧化铝层；然后将其均匀分散到静电纺丝液中，并通过静电纺丝及煅烧处理的方法制备包含有石墨烯-纳米硅球的碳纳米纤维复合材料；接着将该碳纳米纤维复合材料放入酸中进行酸处理，去除氧化铝并在氧化铝原来的位置留下空隙结构。最后再通过化学气相沉积(CVD)的方法在最外面再形成一层非晶碳包覆层，得到锂离子电池负极材料。
该负极材料制备的锂离子电池在700mA/g的电流密度下循环1050次，仍保持约1982mAh/g的比容量，首次充放电库仑效率达到88.9％。
如图3所示，对比例为纯纳米硅球。该负极材料在700mA/g的电流密度下循环，从一开始就有一个非常快速的容量衰减。
以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在 本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。

Claims (9)

  1. 有效缓冲硅体积效应的锂离子电池负极材料的制备方法，其特征在于：所述方法包括以下步骤：
    制备改性石墨烯微片；
    在石墨烯微片表面生长纳米硅球，得到石墨烯微片-纳米硅球复合材料；
    通过原子层沉积技术在石墨烯微片-纳米硅球表面沉积金属氧化物层；
    将表面沉积有金属氧化物层的石墨烯微片-纳米硅球复合材料均匀分散到静电纺丝液中，进行静电纺丝及煅烧处理，得到碳纳米纤维复合材料；
    对碳纳米纤维复合材料进行酸处理，去除金属氧化物层形成空隙结构；
    在碳纳米纤维复合材料外面形成碳包覆层。
  2. 根据权利要求1所述有效缓冲硅体积效应的锂离子电池负极材料的制备方法，其特征在于：所述步骤制备改性石墨烯微片为首先将膨胀石墨置于容器中，加入100-1000ml的有机溶剂，然后在超声振荡功率为300-1200W，温度为20-150℃条件下振荡1-24h，得到石墨烯微片悬浮液；接着静置20-300min，取上层悬浮液，去除沉淀物，过滤后在60-80℃下烘干得到石墨烯微片；接着将所得石墨烯微片加入到20-100ml的浓硫酸中，保持溶液温度低于4℃，缓慢添加0.5-20g的高锰酸钾，保持溶液温度低于10℃并磁力搅拌60-120min并在磁力搅拌过程中，缓慢添加150ml的去离子水；搅拌结束后添加1-5ml的双氧水，再继续搅拌10-30min；最后过滤烘干得到改性石墨烯微片。
  3. 根据权利要求2所述有效缓冲硅体积效应的锂离子电池负极材料的制备方法，其特征在于：所述有机溶剂为NMP、DMF、甲苯、氯苯、三氯乙烯 中的至少一种。
  4. 根据权利要求1所述有效缓冲硅体积效应的锂离子电池负极材料的制备方法，其特征在于：所述在石墨烯微片表面生长纳米硅球，是通过化学气相沉积(CVD)方法制备；首先将石墨烯微片放入反应室内，抽真空并对反应腔进行加热，当温度达到反应温度后通入1-500sccm的载气气体，使反应腔室压强保持在0.01Torr-10Torr，然后向反应室通入1-500sccm的反应气体，反应气体在高温下分解反应生成纳米硅球附着在衬底材料石墨烯微片表面，反应结束后，依顺序关闭反应气体、载气气体、及加热装置，得到石墨烯微片-纳米硅球复合材料。
  5. 根据权利要求4所述有效缓冲硅体积效应的锂离子电池负极材料的制备方法，其特征在于：所述在石墨烯微片表面生长纳米硅球的尺寸约为1-100nm，反应温度为650℃-1000℃。
  6. 根据权利要求4所述有效缓冲硅体积效应的锂离子电池负极材料的制备方法，其特征在于：所述石墨烯微片表面生长纳米硅球的反应气体为硅烷(SiH4)、二氯硅烷(SiH2Cl2)中的至少一种；载气气体为氮气(N2)、氩气(Ar)中的至少一种。
  7. 根据权利要求1所述有效缓冲硅体积效应的锂离子电池负极材料的制备方法，其特征在于：所述金属氧化物层为氧化镍、氧化铝、氧化锡、氧化钛等中的至少一种，金属氧化物层厚度约为10-60nm。
  8. 根据权利要求1所述有效缓冲硅体积效应的锂离子电池负极材料的制备 方法，其特征在于：所述碳纳米纤维复合材料包含有内部被其完全包覆的石墨烯微片、纳米硅球和边缘未完全被包覆的石墨烯微片-纳米硅球复合材料。
  9. 根据权利要求1所述有效缓冲硅体积效应的锂离子电池负极材料的制备方法，其特征在于：所述在碳纳米纤维复合材料外面形成碳包覆层是通过原子层沉积技术(ALD)、化学气相沉积(CVD)、催糖技术中的至少一种方式，在碳纳米纤维复合材料表面形成一层非晶硅碳包覆层。
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