WO2018024184A1 - 锗/石墨烯/二氧化钛纳米纤维复合材料制备方法及电池 - Google Patents

锗/石墨烯/二氧化钛纳米纤维复合材料制备方法及电池 Download PDF

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WO2018024184A1
WO2018024184A1 PCT/CN2017/095366 CN2017095366W WO2018024184A1 WO 2018024184 A1 WO2018024184 A1 WO 2018024184A1 CN 2017095366 W CN2017095366 W CN 2017095366W WO 2018024184 A1 WO2018024184 A1 WO 2018024184A1
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graphene
titanium dioxide
bismuth
preparing
nanofiber composite
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French (fr)
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杨与畅
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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
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • 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
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • 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
    • 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 a lithium ion battery and a sodium ion battery anode material, in particular to a preparation method of a bismuth/graphene/titanium dioxide nanofiber composite material and a metal ion battery.
  • Silicon and germanium have attracted wide attention due to their extremely large theoretical capacity values, and are considered to be the most promising anode materials for the next generation of lithium-ion and sodium-ion batteries.
  • germanium has greater conductivity (more than 100 times that of silicon), and it has a good ion diffusion rate (about 400 times higher than silicon).
  • the object of the present invention is to provide a preparation method and a battery for a bismuth/graphene/titanium dioxide nanofiber composite material, which have high capacity, good cycle stability and good rate performance.
  • the present invention adopts the following technical solutions:
  • a method for preparing a bismuth/graphene/titanium dioxide nanofiber composite comprising the steps of: 1) preparing a bismuth/graphene nanofiber by an electrospinning method; 2) preparing a titanium dioxide by atomic layer deposition on bismuth/graphene 3) Subsequent treatment of the prepared bismuth/graphene/titanium dioxide nanofiber composite.
  • the bismuth/graphene nanofibers are prepared by an electrospinning method, which are specifically as follows: a) preparing an electrospinning solution
  • the graphene and the dispersion solvent are mixed at a mass ratio of 1:200-1:250, and then ultrasonicated for 30-120 minutes to form a uniform graphene dispersion; then the mass ratio of the graphene to 1:25-1 is: 15 ruthenium tetrachloride was added to the ultrasonic mixture of graphene, followed by magnetic stirring at room temperature for 20-90 min; finally, PVP was added at a mass ratio of 1:60 to 1:30 with graphene, and then stirred for 2-8 h. Obtaining an electrospinning solution;
  • the above electrospinning solution is injected into a syringe of a stainless steel nozzle having an inner diameter of 0.3-0.8 mm, and then the nozzle and the receiving device are respectively connected to the two electrodes of the high-voltage power source, and electrospinning is performed to obtain a bismuth/graphene nanofiber composite material.
  • the dispersing solvent in the step a) is at least one of N,N-dimethylamidoamide (DMF), N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), and ethylene glycol.
  • DMF N,N-dimethylamidoamide
  • NMP N-methyl-2-pyrrolidone
  • THF tetrahydrofuran
  • ethylene glycol ethylene glycol
  • the purity of the antimony tetrachloride in the step a) is 99.999%.
  • the high voltage power supply between the two electrodes in the step b) is 10-25 KV.
  • the step 2) preparing titanium dioxide by atomic layer deposition on bismuth/graphene the specific step is: placing the bismuth/graphene nanofiber obtained in step 1) into a reaction chamber, using titanium isopropoxide ( a Ti (OCH (CH 3) 2) and H 2 O as a reaction product, are introduced into the reaction chamber, and H 2 O titanium isopropoxide, titanium isopropoxide, and adjusting the amount of H 2 O such that precise control of titanium dioxide
  • the atomic layer deposition cycle is followed by deposition of a titanium dioxide film at a growth rate of 1 nm per atomic layer deposition cycle at 170 °C - 210 °C.
  • the Ti (OCH(CH 3 ) 2 has a purity of 97%, and the H 2 O is a high pressure liquid phase level H 2 O.
  • the titanium dioxide film deposited in the step 2) has a thickness of 1-20 nm.
  • the specific steps of the step 3) for subsequent treatment of bismuth/graphene/titanium dioxide are as follows:
  • step 2 drying: the bismuth / graphene / titanium dioxide nanofiber composite obtained in step 2) in a vacuum environment oven, drying at a temperature of 40-80 ° C for 20-30h;
  • the invention also discloses a metal ion battery, wherein the anode material of the metal ion battery is the bismuth/graphene/titanium dioxide nanofiber composite material prepared by any of the above.
  • the titanium dioxide film covers the ruthenium/graphene core nanofiber to ensure the structural integrity; the graphene and the titanium dioxide can double protect the ruthenium nanofiber, thereby avoiding the damage caused by the volume expansion during the charging and discharging process. . Therefore, the nanofiber composite prepared by the present invention has excellent electrochemical performance, high capacity, excellent cycle stability, and good rate performance.
  • the first cycle discharge capacity of the lithium ion battery using the anode material reached 1701 mAh/g. After 100 cycles, the capacity remained at 1050 mAh/g, and the first discharge capacity of the sodium ion battery reached 368 mAh/g, after 250 times.
  • the cycle capacity is still maintained at 182mAh/g; the lithium-ion battery and the sodium-ion battery start from the second cycle, and the capacity decay rate per cycle is only 0.13% and 0.04%; the lithium-ion battery and the sodium-ion battery even in the high-current condition Under charge and discharge, the electrode can still maintain a stable cycle and exhibit good rate performance.
  • FIG. 1 is a flow chart of a method for preparing a bismuth/graphene/titanium dioxide nanofiber composite material according to the present invention
  • FIG. 2 is a schematic structural view of a bismuth/graphene/titanium dioxide nanofiber composite material according to the present invention
  • FIG. 3 is a morphological characterization diagram of the bismuth/graphene/titanium dioxide nanofiber composite material of the present invention: wherein a is an SEM image, b is a low magnification TEM image, c is a Ge/G TEM image, and d is an element distribution map. ;
  • FIG 4 of the present invention a germanium / graphene / titania nanostructures FIG fiber composite material characterized by: wherein a is an XRD pattern, b is Ge / G / TiO 2 and the Raman spectra of Ge / G, c is the Ge HRTEM image, d is the corresponding SAED pattern;
  • FIG 5 is a Ge / G / TiO 2, Ge / G, storage characteristics of the lithium ion electrode Ge: wherein A is a cyclic voltammetry Ge / G / TiO 2 in a voltage range 0.01-3V 0.2mV / s scan speed obtained An curve, b is a charge/discharge curve of Ge/G/TiO 2 at 100 mA/g, c is a cycle characteristic of Ge/G/TiO 2 , Ge/G, Ge at a current density of 100 mA/g, d It is the rate performance of Ge/G/TiO 2 , Ge/G, Ge materials at different current densities;
  • Figure 6 shows the sodium ion storage characteristics of Ge/G/TiO 2 , Ge/G, and Ge electrodes: where a is a cycle in which Ge/G/TiO 2 is scanned at a voltage range of 0.01-2.7 V at a scan rate of 0.2 mV/s. Voltammetry curve, b is the charge/discharge curve of Ge/G/TiO 2 at 100 mA/g, c is the cycle characteristic of three materials at a current density of 100 mA/g, and d is Ge/G/TiO 2 , Ge/G And the rate performance of three Ge materials at different current densities;
  • FIG. 7 is a schematic view showing changes in material structure during charging and discharging of bismuth/graphene/titanium dioxide nanofibers prepared by the present invention as a battery anode material;
  • Figure 8 is a schematic diagram showing changes in material structure of a conventional nanofiber during charge and discharge.
  • the ruthenium/graphene/titanium dioxide nanofiber composite prepared by the invention forms a core-shell structure, which is one of the successful protection methods for enhancing battery performance.
  • a suitable electrode protection measure not only improves conductivity, reduces internal resistance, but also significantly increases cycle stability and rate performance, extending the life of rechargeable batteries.
  • graphene As a two-dimensional carbon material, graphene has a wider application due to its outstanding electrical conductivity, excellent mechanical strength and great specific surface area.
  • Graphene in a lithium ion battery or a sodium ion battery can prevent the formation of a solid electrolyte interface between graphite and an electrode.
  • the nanofibers in the process of lithium intercalation/sodium intercalation and delithiation/desodiumation are easily pulverized and cracked due to their large volume expansion, and are peeled off from the surface of the nanofibers, thereby circulating
  • the process causes rapid decay of capacity and is irreversible; in addition, the SEI film will deform or rupture when the crucible expands or contracts, which will form a new SEI film on the new surface, and the gradual accumulation of the SEI film will eventually prevent lithium/sodium ions. Transfer, resulting in low coulombic efficiency.
  • the present invention discloses a method for preparing a bismuth/graphene/titanium dioxide (Ge/G/titanium dioxide) nanofiber composite, the method comprising the following steps:
  • the electrospinning solution is injected into a syringe of a stainless steel nozzle having an inner diameter of about 0.5 mm, and then the nozzle and the receiving device are respectively connected to two electrodes of a 20 kV high-voltage power source, and electrospinning is performed to obtain a bismuth/graphene nanofiber composite material. ;
  • the ruthenium/graphene nanofibers obtained in the step 1) were placed in a reaction chamber with a purity of 97% of titanium isopropoxide (Ti(OCH(CH 3 ) 2 ) and a high pressure liquid phase (HPLC-grade) H. 2 O as a reactant, sequentially introducing titanium isopropoxide and H 2 O, adjusting the amount of both to precisely control an ALD cycle of titanium dioxide, and then at 180 ° C for each ALD cycle is about The growth rate was deposited to obtain a titanium dioxide film having a thickness of about 5 nm.
  • step 2 the bismuth / graphene / titanium dioxide composite obtained in step 2) is placed in a vacuum oven, dried at 60 ° C for 24h;
  • the electrospinning solution is injected into a syringe of a stainless steel nozzle having an inner diameter of about 0.5 mm, and then the nozzle and the receiving device are respectively connected to two electrodes of a 20 kV high-voltage power source, and electrospinning is performed to obtain a bismuth/graphene nanofiber composite material. ;
  • the ruthenium/graphene nanofibers obtained in the step 1) were placed in a reaction chamber with a purity of 97% of titanium isopropoxide (Ti(OCH(CH 3 ) 2 ) and a high pressure liquid phase (HPLC-grade) H. 2 O as a reactant, sequentially introducing titanium isopropoxide and H 2 O, adjusting the amount so that an ALD cycle of titanium dioxide can be precisely controlled, and then about 180 ° C for each ALD cycle is about The growth rate is deposited to obtain a titanium dioxide film having a thickness of about 8 nm.
  • Ti(OCH(CH 3 ) 2 titanium isopropoxide
  • HPLC-grade high pressure liquid phase
  • step 2 the bismuth / graphene / titanium dioxide composite obtained in step 2) was placed in an oven in a vacuum environment, dried at 50 ° C for 28 h;
  • the bismuth/graphene/titanium dioxide (Ge/G/titanium dioxide) nanofiber composite prepared by the present invention comprises a shell 1 and a core 2, and the shell 1 covers the core 2, and the shell 1 is titanium dioxide.
  • the film layer 11, the core 2 is ⁇ 21/graphene 22 nanofibers, and the titanium dioxide film layer is coated with ruthenium/graphene nanofibers to form a titanium dioxide film layer and a graphene double-protected core-shell structure.
  • the thickness of the titanium dioxide thin film layer 11 is 1-20 nm; the nanofibers in the core-shell structure of the present invention comprise graphene, and on the one hand, graphene can accommodate and alleviate enthalpy due to its good bending mechanical properties and stable thermal/chemical properties.
  • the bismuth/graphene/titanium dioxide provided by the present invention is operated, More SEI films are formed on the outer surface of the titanium dioxide film, limiting the number of SEI films and increasing their stability.
  • the ruthenium/graphene (Ge/G) nanofibers were synthesized by the same preparation process but did not cover the titanium dioxide. Specifically, in the same manner as the steps 1) and 3) of the first embodiment, that is, after the step 1), the step 1) is directly performed, and the comparative material 1Ge/G nanofiber composite material is prepared;
  • the ruthenium nanofibers were synthesized by the same preparation process, but no graphene and titanium dioxide were added. Specifically, 2.2 g of DMF (N,N-dimethylamideamide) and 0.214 g of 99.999% pure ruthenium tetrachloride (GeCl 4 ) were mixed and magnetically stirred at room temperature for 30 min; then 0.4 g of polyvinylpyrrolidone was added. (PVP) was added to the above solution, and stirring was continued for 3 hours to obtain an electrospinning solution.
  • DMF N,N-dimethylamideamide
  • EuCl 4 99.999% pure ruthenium tetrachloride
  • PVP polyvinylpyrrolidone
  • the obtained electrospinning solution is injected into a syringe of a stainless steel nozzle having an inner diameter of about 0.5 mm, and then the nozzle and the receiving device are respectively connected to two electrodes of a 20 kV high-voltage power source, and electrospinning is performed to obtain cerium (Ge) nanofibers; Subsequently, the same subsequent treatment as in step 3) of Example 1 was carried out to obtain a comparative material 2Ge nanofiber;
  • the specific procedure of the electrochemical test is as follows: the active material ⁇ /graphene/titanium dioxide nanofiber: acetylene black: carboxymethyl cellulose (CMC) is mixed at a mass ratio of 8:1:1, and then the mixed powder is dissolved in 1.0 g.
  • the active material ⁇ /graphene/titanium dioxide nanofiber acetylene black: carboxymethyl cellulose (CMC) is mixed at a mass ratio of 8:1:1, and then the mixed powder is dissolved in 1.0 g.
  • the average mass of the electrode strip is about 0.8 mg/cm 2 ; lithium metal and sodium metal are used as the counter electrode of the lithium ion battery and the sodium ion battery, respectively; 1 M LiPF 6 ethylene carbonate (EC): diethyl carbonate (DEC) (Volume ratio is 1:1) and 1 M NaClO 4 of ethylene carbonate (EC): dimethyl carbonate (DMC) (volume ratio of 6:4) is an electrolyte of a lithium ion battery and a sodium ion battery, respectively.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • the morphological characterization of the bismuth/graphene/titanium dioxide nanofibers prepared according to the present invention wherein the average diameter of the nanofibers of bismuth/graphene/titanium dioxide is about 10 nm, as shown in FIG. SEM image of magnification, which shows that the surface of the nanofiber is not smooth and contains many nanoparticles; As shown in the middle b diagram, a low-magnification TEM image of bismuth/graphene/titanium dioxide is shown, which shows a complete structure, and it can be observed that the titanium dioxide layer surrounds the periphery of the nanofiber; as shown in c in Fig.
  • FIG. 4 the structural characterization of the bismuth/graphene/titanium dioxide nanofibers prepared according to the present invention is as shown in FIG. 4, which is an XRD pattern of bismuth/graphene/titanium dioxide, which can be seen at 27.28°.
  • the image shows a highly ordered nanocrystal ⁇ with 0.32 nm lattice fringes, equivalent to (111) plane; as shown in the graph of d in Fig. 4, the weak crystals and polycrystalline rings in the selected area electron diffraction (SAED) mode further confirmed the existence of crystal germanium.
  • SAED selected area electron diffraction
  • the electrochemical performance comparison of the ruthenium/graphene/titanium dioxide nanofibers prepared by the present invention and the comparative materials 1Ge/G and the contrast material 2Ge in a lithium ion battery is as shown in a diagram of FIG. It is a cyclic voltammetry curve obtained by ⁇ /graphene/titanium dioxide at a potential range of 00.1-3 V at a scanning speed of 0.2 mV/s.
  • the first cycle is significantly different from the subsequent cycle, especially the discharge process. This difference is caused by the formation of the first cycle of the SEI film.
  • the peak at about 0.12 V is consistent with the reaction of graphene and Li + (C(graphene) + xLi + + xe - ⁇ Li x C).
  • the two peaks at 0.55V and 1.25V are attributed to the alloy conversion process of Li x Ge
  • the cathode curve and the anode curve have good overlap, indicating that they have high reversibility and good overall cycle stability.
  • the charge/discharge cycle curve of ⁇ /graphene/titanium dioxide (Ge/G/titanium dioxide) at a current density of 100 mA/g at a voltage range of 0.01 to 3 V is shown.
  • the first discharge phase coincided with the CV curve at a potential platform of approximately 0.55V.
  • the first coulombic efficiency of a lithium ion battery is about 74%. Due to the formation of the SEI film, it can be explained that the ruthenium/graphene/titanium dioxide electrode loses about 26% of the irreversible capacity during the first discharge. As shown in the graph of c in Fig. 5, it is a cycle characteristic curve of ⁇ /graphene/titanium dioxide, Ge/G, and Ge at a current density of 100 mA/g. For the three, the discharge capacity of the first circle was 1701 mAh/g, 1766 mAh/g, and 1789 mAh/g, respectively.
  • the reversible capacity of Ge drops very quickly, from 1174 mAh/g on the second lap to 495 mAh/g on the 100th lap.
  • the Ge/G electrode exhibited better cycle performance than Ge, and it maintained a specific capacity of 804 mAh/g after 100 cycles.
  • the bismuth/graphene/titanium dioxide composite exhibits the best cycle performance while maintaining a capacity of 1050 mAh/g after 100 cycles. This is sufficient to demonstrate that the graphene and titanium dioxide layers on tantalum and niobium/graphene can increase their cycle characteristics. Its excellent cycle stability was further confirmed at high current densities. As shown in the graph of d in Fig.
  • bismuth/graphene/titanium dioxide has a high specific capacity at current densities of 100, 200, 400, 600, 800, 1000 mA/g, respectively, 1050, 921. , 850, 750, 627, 550 mAh / g.
  • current density returned to 100 mA/g, it still had a reversible capacity of 1000 mAh/g with almost no capacity loss.
  • both Ge or Ge/G have a large capacity loss.
  • the high capacity yield of bismuth/graphene/titanium dioxide is mainly due to its special double-layer protection structure.
  • the electrochemical performance comparison of the ruthenium/graphene/titanium dioxide nanofiber prepared by the present invention and the comparative material 1Ge/G and the contrast material 2Ge in a lithium ion battery is as shown in a diagram of FIG.
  • a CV curve of a ruthenium/graphene/titanium dioxide electrode in a sodium ion battery no redox peak was observed during the anode and cathode scanning, which proves that the SEI film is formed on the surface of the composite.
  • the graph of b in Fig. 6 it is a charge and discharge graph of bismuth/graphene/titanium dioxide at a current density of 100 mA/g.
  • the bismuth/graphene/titanium dioxide electrode exhibits superior cycle characteristics compared to the fast specific capacity decay of Ge/G and Ge, mainly because of its double layer protection.
  • Protective structure As shown in the graph of d in Fig. 6, the rate performance of the three electrode materials at different current densities is shown.
  • the discharge specific capacity of ruthenium/graphene/titanium dioxide was well maintained at 200, 164, 135, 115, 102, 88 mAh/g at currents of 100, 200, 400, 600, 800, 1000 mA/g. At the same time, returning to 190 mAh/g with a good specific capacity at 100 mA/g is sufficient to demonstrate that the bismuth/graphene/titanium dioxide has excellent rate performance.
  • the method of illustrating the double-layer protection structure can be applied to a sodium ion battery as well.
  • the core-shell structure ⁇ /graphene/titanium dioxide nanofiber composite prepared by the invention can effectively alleviate the volume of ruthenium due to the presence of the outer shell titanium dioxide film layer and graphene during charge and discharge as a battery anode.
  • the pressure brought by the expansion maintains the structural integrity; while the traditional nanofibers cause structural damage during the charging and discharging process due to the large volume expansion of the crucible.
  • the doping of graphene on the crucible of the invention can improve the battery characteristics, and the ultra-thin titanium dioxide thin film layer covering the outer layer of bismuth/graphene can further enhance the cycle stability and rate performance. Further, the bismuth/graphene/titanium dioxide electrode of the lithium ion battery or the sodium ion battery maintained a specific capacity of 1050 and 194 mAh/g after 100 cycles, exhibiting an extremely high and stable specific capacity.
  • ⁇ /graphene/titanium dioxide electrodes can withstand high current densities after charge and discharge processes at different current densities (100, 200, 400, 600, 800, 1000 mAh) /g), it can still recover to 1000 mAh/g for lithium-ion batteries and 194 mAh/g for sodium-ion batteries with almost no capacity loss.
  • the present invention provides bismuth/graphene/titanium dioxide nanofibers with unique dual layer protection structures that extend beyond the manufacture of a wide variety of other functional nanomaterials for energy storage.

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Abstract

一种锗/石墨烯/二氧化钛纳米纤维复合材料制备方法及金属离子电池，其中，所述方法包括以下步骤：采用静电纺丝法制备锗/石墨烯纳米纤维；在锗/石墨烯上采用原子层沉积法制备二氧化钛；对制得的锗/石墨烯/二氧化钛纳米纤维复合材料进行后续处理。其中的二氧化钛薄膜覆盖住锗/石墨烯内核纳米纤维，确保了结构的完整性；石墨烯和二氧化钛可以双重保护锗纳米纤维，从而避免锗在充放电过程中因体积膨胀造成损坏。所制备的纳米复合材料具有优异电化学性能、高容量、优异循环稳定性和良好倍率性能。

Description

锗/石墨烯/二氧化钛纳米纤维复合材料制备方法及电池 技术领域
本发明涉及一种锂离子电池、钠离子电池负极材料，尤其涉及锗/石墨烯/二氧化钛纳米纤维复合材料制备方法及金属离子电池。
背景技术
随着不可再生的石化燃料消耗量的增加，全世界面临着严峻的能源挑战。这个问题加速了人们对符合经济效益的储能系统的探索研究。可再充电的锂离子电池和钠离子电池已经被证明是可以用来解决该问题的能源储存装置。然而，对于未来的发展和在电动汽车中的应用，该可充电电池的容量、稳定性和倍率性能仍然需进一步提升。再者，值得一提的是，可以通过寻找合适的电极材料和电极保护方法来进一步提升电池的这些性能。
硅和锗因其极大的理论容量值引起人们的广泛关注，被认为是下一代的锂离子电池和钠离子电池最有希望的负极材料。与硅相比，锗具有更大的导电性(大于硅的100倍)，同时其具有较好的离子扩散率(约比硅高400倍)，锗的这些优势使其在高性能储能装置中具有更大的潜能。然而，其超大的体积膨胀会导致结构退化和不稳定固体电解质界面(SEI)的形成，这将严重限制了其在实际中的应用。迄今为止，为克服这个问题人们已经付出了巨大的努力，如制备各种纳米结构锗(毫微管、多孔结构、薄薄膜等)、锗合金材料、碳或石墨烯包覆锗混合物等。然而，这些方法通常都非常复杂，同时电池循环寿命仍然有待提高。
发明内容
本发明的目的在于提供锗/石墨烯/二氧化钛纳米纤维复合材料制备方法及电池，其具有容量高、循环稳定性好、倍率性能佳。
为实现上述目的，本发明采用以下技术方案：
锗/石墨烯/二氧化钛纳米纤维复合材料制备方法，所述方法包括以下步骤：1)采用静电纺丝法制备锗/石墨烯纳米纤维；2)在锗/石墨烯上采用原子层沉积法制备二氧化钛；3)对制得的锗/石墨烯/二氧化钛纳米纤维复合材料进行后续处理。
优选的，所述步骤1)采用静电纺丝法制备锗/石墨烯纳米纤维，其具体如下：a)制备静电纺丝液
将石墨烯和分散溶剂按质量比为1：200-1：250的进行混合，然后超声处理30-120min，形成均匀石墨烯分散液；然后将和石墨烯的质量比为1：25-1：15的四氯化锗加入超声后的石墨烯混合液，接着在室温下磁力搅拌20-90min；最后加入将和石墨烯质量比为1：60-1：30的PVP，然后搅拌2-8h，得到静电纺丝溶液；
b)静电纺丝
首先将上述静电纺丝液注入内径为0.3-0.8mm的不锈钢喷嘴的注射器中，然后将喷嘴和接收装置分别连接高压电源的两个电极，进行静电纺丝得到锗/石墨烯纳米纤维复合材料。
优选的，所述步骤a)中的分散溶剂为N,N-二甲基酰胺酰胺(DMF)、N-甲基-2-吡咯烷酮(NMP)、四氢呋喃(THF)、乙二醇中的至少一种。
优选的，所述步骤a)中的四氯化锗纯度为99.999％。
优选的，所述步骤b)中两电极之间的高压电源为10-25KV。
优选的，所述步骤2)在锗/石墨烯上采用原子层沉积法制备二氧化钛，具体步骤为：将步骤1)得到的锗/石墨烯纳米纤维放入反应室中，以异丙醇钛(Ti(OCH(CH3)2)和H2O作为反应物，分别往反应室中引入异丙醇钛和H2O， 调整异丙醇钛和H2O的用量使得精确的控制二氧化钛的一个原子层沉积循环，然后在170℃-210℃下以每个原子层沉积循环厚为1nm的生长速率沉积二氧化钛薄膜。
优选的，所述Ti(OCH(CH3)2纯度为97％，所述H2O为高压液相层级的H2O。
优选的，所述步骤2)中沉积的二氧化钛薄膜厚度为1-20nm。
优选的，所述步骤3)对锗/石墨烯/二氧化钛进行后续处理的具体步骤如下：
a)干燥：将步骤2)得到的锗/石墨烯/二氧化钛纳米纤维复合材料在真空环境的烤箱中，以温度为40-80℃进行干燥20-30h；
b)煅烧：将干燥后的锗/石墨烯/二氧化钛复合材料放入空气环境中，在400-600℃温度下锻烧1-5h；
c)退火：接着将锗/石墨烯/二氧化钛复合材料放在H2和Ar体积比为5％：95％的混合气体环境中，在500-800℃下进一步退火1-5h，最终得到锗/石墨烯/二氧化钛纳米纤维复合材料。
本发明还公开了一种金属离子电池，所述金属离子电池的负极材料为上述任一所述制得的锗/石墨烯/二氧化钛纳米纤维复合材料。
本发明采用以上技术方案：二氧化钛薄膜覆盖住锗/石墨烯内核纳米纤维，确保了结构的完整性；石墨烯和二氧化钛可以双重保护锗纳米纤维，从而避免锗在充放电过程中因体积膨胀造成损坏。因此，本发明所制备的纳米纤维复合材料具有优异的电化学性能、高的容量、优异的循环稳定性和良好的倍率性能。采用其作为负极材料的锂离子电池第一次循环放电容量达到1701mAh/g，经过100次循环后，容量仍保持在1050mAh/g，钠离子电池第一次放电容量达到368mAh/g，经过250次循环容量仍保持在182mAh/g；锂离子电池和钠离子电池从第二圈循环开始，其每圈循环的容量衰减率只有0.13％和0.04％；锂离子电池和钠离子电池即使在大电流条件下充放电，电极仍能保持稳定的循环，表现出良好的倍率性能。
附图说明
图1  为本发明所述的锗/石墨烯/二氧化钛纳米纤维复合材料制备方法的流程图；
图2  为本发明所述的锗/石墨烯/二氧化钛纳米纤维复合材料的结构示意图；
图3  为本发明所述的锗/石墨烯/二氧化钛纳米纤维复合材料的形态表征图：其中a为SEM图、b为低倍率TEM图、c为Ge/G的TEM图、d为元素分布图；
图4  为本发明所述的锗/石墨烯/二氧化钛纳米纤维复合材料的结构表征图：其中a为XRD图案、b为Ge/G/TiO2和Ge/G的拉曼光谱、c为Ge的HRTEM图、d为相应的SAED图案；
图5  为Ge/G/TiO2、Ge/G、Ge电极的锂离子存储特性：其中a为Ge/G/TiO2在电压范围0.01-3V以0.2mV/s的扫描速度扫描得到的循环伏安曲线、b为Ge/G/TiO2在100mA/g的充放电曲线图、c为Ge/G/TiO2、Ge/G、Ge三种材料在电流密度100mA/g下的循环特性、d为Ge/G/TiO2、Ge/G、Ge三种材料在不同电流密度下的倍率性能；
图6  为Ge/G/TiO2、Ge/G、Ge电极的钠离子存储特性：其中a为Ge/G/TiO2在电压范围0.01-2.7V以0.2mV/s的扫描速度扫描得到的循环伏安曲线、b为Ge/G/TiO2在100mA/g的充放电曲线图、c为三种材料在电流密度100mA/g下的循环特性、d为Ge/G/TiO2、Ge/G、Ge三种材料在不同电流密度下的倍率性能；
图7  为本发明制备的锗/石墨烯/二氧化钛纳米纤维作为电池负极材料时充放电过程中材料结构变化的示意图；
图8  为传统的纳米纤维在充放电过程中材料结构变化的示意图。
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。
本发明制备的锗/石墨烯/二氧化钛纳米纤维复合材料，形成核壳结构，所述核壳结构是可增强电池性能的成功保护方法之一。通常来讲，一个合适的电极保护措施不仅能提升电导率，降低内电阻，而且能显著增加循环稳定性和倍率性能，延长可充电电池的寿命。石墨烯作为二维碳材料，由于其突出的导电性，卓越的机械强度，极大的比表面积，使其具有更广泛的应用。在锂离子电池或钠离子电池中石墨烯可以防止石墨和电极之间的固体电解质界面的形成。
一般情况下锗纳米纤维在嵌锂/嵌钠和脱锂/脱钠的转变过程中会因其较大的体积膨胀很容易造成电极的粉化和裂化，并从纳米纤维表面剥落，从而在循环过程造成容量的快速衰减且不可逆；再者当锗膨胀或收缩时SEI膜会变形或破裂，这将会在新的表面形成新的SEI膜，SEI膜的逐渐积累将最终阻止锂/钠离子的传输，从而导致低库仑效率。
如图1所示，本发明公开了锗/石墨烯/二氧化钛(Ge/G/二氧化钛)纳米纤维复合材料制备方法，所述方法包括以下步骤：
S101：采用静电纺丝法制备锗/石墨烯纳米纤维；
S102：在锗/石墨烯(Ge/G)上采用原子层沉积法(ALD)制备二氧化钛；
S103：对制得的锗/石墨烯/二氧化钛纳米纤维复合材料进行后续处理。
具体的本发明可以通过以下方法实施：
实施例1:
1)静电纺丝制备锗/石墨烯纳米纤维；
a)制备静电纺丝液
首先将0.01g石墨烯和2.2gDMF(N,N-二甲基酰胺酰胺)进行混合，然后进行超声60min，形成均匀石墨烯分散液；其次将0.214g纯度为99.999％的四氯化锗(GeCl4)加入超声后的石墨烯混合液中，在室温下磁力搅拌30min；最后将0.4g聚乙烯吡咯烷酮(PVP)加入上述溶液，然后持续搅拌3h，得到静电纺丝溶液；
b)静电纺丝
将上述静电纺丝液注入内径约为0.5mm的不锈钢喷嘴的注射器中，然后将喷嘴和接收装置分别连接在20KV高压电源的两个电极上，进行静电纺丝得到锗/石墨烯纳米纤维复合材料；
2)在锗/石墨烯上采用原子层沉积技术制备二氧化钛；
将步骤1)得到的锗/石墨烯纳米纤维放入反应室中，以纯度为97％的异丙醇钛(Ti(OCH(CH3)2)和高压液相层级(HPLC-grade)的H2O作为反应物，顺序引入异丙醇钛和H2O，调整两者用量使得精确的控制二氧化钛的一个ALD循环，然后在180℃下以每个ALD循环厚约为
Figure PCTCN2017095366-appb-000001
的生长速率沉积，得到厚度约为5nm的二氧化钛薄膜。
3)锗/石墨烯/二氧化钛纳米纤维的后续处理；
a)干燥：将步骤2)得到的锗/石墨烯/二氧化钛复合材料放入真空环境的烤箱中，60℃干燥24h；
b)煅烧：将干燥后的锗/石墨烯/二氧化钛复合材料放入空气环境中，在450℃温度下锻烧2h，以去除PVP有机成分；
c)进一步退火：接着将锗/石墨烯/二氧化钛复合材料放入H2：Ar体积比为了5％：95％的混合气体环境中，在600℃下进一步退火3h，将氧化锗还原成锗；最终得到锗/石墨烯/二氧化钛纳米纤维复合材料。
实施例2
1)静电纺丝制备锗/石墨烯纳米纤维；
a)制备静电纺丝液
首先将0.01g石墨烯和2.5gNMP(N-甲基-2-吡咯烷酮)进行混合，然后超声90min，形成均匀石墨烯分散液；其次将0.2g纯度为99.999％的四氯化锗(GeCl4)加入超声后的石墨烯混合液中，接着在室温下磁力搅拌60min；最后将0.5g聚乙烯吡咯烷酮(PVP)加入上述溶液，然后持续搅拌5h，得到静电纺丝溶液。
b)静电纺丝
将上述静电纺丝液注入内径约为0.5mm的不锈钢喷嘴的注射器中，然后将喷嘴和接收装置分别连接有20KV高压电源的两个电极上，进行静电纺丝得到锗/石墨烯纳米纤维复合材料；
2)在锗/石墨烯上采用原子层沉积法(ALD)制备二氧化钛；
将步骤1)得到的锗/石墨烯纳米纤维放入反应室中，以纯度为97％的异丙醇钛(Ti(OCH(CH3)2)和高压液相层级(HPLC-grade)的H2O作为反应物，顺序引入异丙醇钛和H2O，调整用量使得精确的控制二氧化钛的一个ALD循环，然后在180℃下以每个ALD循环厚约为
Figure PCTCN2017095366-appb-000002
的生长速率沉积得到厚度约为8nm的二氧化钛薄膜。
3)锗/石墨烯/二氧化钛纳米纤维的后续处理；
a)干燥：将步骤2)得到的锗/石墨烯/二氧化钛复合材料放入真空环境的烤箱中，50℃干燥28h；
b)煅烧：将干燥后的锗/石墨烯/二氧化钛复合材料放入空气环境中，在480℃温度下锻烧2h，以去除PVP有机成分；
c)进一步退火：接着将锗/石墨烯/二氧化钛复合材料放在体积比为了5％：95％的H2/Ar混合气体环境中，在650℃下进一步退火3h，将氧化锗还原成锗；最终得到锗/石墨烯/二氧化钛纳米纤维复合材料。
如图2所示，为本发明制备的锗/石墨烯/二氧化钛(Ge/G/二氧化钛)纳米纤维复合材料，其包括外壳1和内核2，外壳1包覆内核2，所述外壳1为二氧化钛薄膜层11，所述内核2为锗21/石墨烯22纳米纤维，所述二氧化钛薄膜层包覆锗/石墨烯纳米纤维形成二氧化钛薄膜层和石墨烯双重保护锗的核壳结构。所述二氧化钛薄膜层11的厚度为1-20nm；本发明的核壳结构中纳米纤维包含石墨烯，一方面，石墨烯由于其良好的弯曲机械性能和稳定的热/化学性能可以容纳和缓解锗碎片在嵌锂/钠过程引起的体积膨胀带来的压力；另一方面，石墨烯作为导电网，锂/钠离子插入时可以提供更多的电子和离子的运输有效通道，从而得到一个高的可逆容量。同时，本发明提供的锗/石墨烯/二氧化钛工作时， 更多的SEI膜在二氧化钛薄膜的外表面形成，限制了SEI膜数量和增加其稳定性。
下面是对本发明制备的纳米纤维复合材料的性能测定：
对比例1
锗/石墨烯(Ge/G)纳米纤维通过一样的制备工艺合成，但没有覆盖二氧化钛。具体同实施例1的步骤1)和3)，即步骤1)后不进行步骤2)而直接进行步骤3)，制备得到对比材料1Ge/G纳米纤维复合材料；
对比例2
锗纳米纤维通过一样的制备工艺合成，但没有添加石墨烯和覆盖二氧化钛。具体为将2.2g DMF(N,N-二甲基酰胺酰胺)和0.214g纯度为99.999％的四氯化锗(GeCl4)进行混合，在室温下磁力搅拌30min；然后将0.4g聚乙烯吡咯烷酮(PVP)加入上述溶液，然后持续搅拌3h，得到静电纺丝溶液。将得到的静电纺丝液注入内径约为0.5mm的不锈钢喷嘴的注射器中，然后将喷嘴和接收装置分别连接在20KV高压电源的两个电极上，进行静电纺丝得到锗(Ge)纳米纤维；接着进行同实施例1步骤3)一样的后续处理，得到对比材料2Ge纳米纤维；
电化学测试具体过程如下：将活性材料锗/石墨烯/二氧化钛纳米纤维：乙炔黑：羧基甲基纤维素(CMC)以质量比为8：1：1进行混合，接着将混合粉末溶于1.0g的去离子水和2.5g乙醇中持续搅拌8h；然后将得到的浆料涂在薄的铜箔上，并在真空烤箱中80℃干燥得到电极条；其中，在扣除铜箔质量的情况下，电极条的平均质量约在0.8mg/cm2；金属锂和金属钠分别作为锂离子电池和钠离子电池的对电极；1M的LiPF6的碳酸乙烯酯(EC):碳酸二乙酯(DEC)(体积比为1：1)和1M的NaClO4的碳酸乙烯酯(EC):碳酸二甲酯(DMC)(体积比为6：4)分别为锂离子电池和钠离子电池的电解液。
如图3所示，为本发明制备的锗/石墨烯/二氧化钛纳米纤维的形态表征图：，其中锗/石墨烯/二氧化钛的纳米纤维的平均直径约为10nm，如图3中a图为放大倍率的SEM图，其显示纳米纤维表面不平滑，包含有许多纳米粒；如图3 中b图所示，显示锗/石墨烯/二氧化钛的低倍率TEM图，其显示出完整的结构，而且可以观察到二氧化钛层围绕着纳米纤维的周围；如图3中c图所示，其显示单一的Ge/G纳米纤维，可看到石墨烯的附着，如图3中d图所示，锗/石墨烯/二氧化钛的元素的均匀分布说明了锗(Ge)，钛(Ti)和氧(O)的分布均匀。
如图4所示，为本发明制备的锗/石墨烯/二氧化钛纳米纤维的结构表征图：如图4中a图所示，为锗/石墨烯/二氧化钛的XRD图案，可看出在27.28°，45.30°，53.68°，66.01°和72.8°的2θ峰分别归因于金刚石立方相锗的(111)，(220)，(311)，(400)和(331)晶格层；如图4中b图所示，拉曼光谱图在约1332.5和1585.8cm-1的两个峰符合于碳的D带和G带；同时，在530cm-1的峰符合二氧化钛的非结晶态，进一步证实石墨烯和二氧化钛的存在；如图4中c图所示，HRTEM用来研究锗/石墨烯/二氧化钛的微观结构，图像显示了一个拥有0.32nm晶格条纹的高度有序的纳米晶体锗，相当于(111)面；如图4中d图所示，在选区电子衍射(SAED)模式下的微弱晶体和多晶环进一步证实了晶体锗的存在。
如图5所示，本发明制备的锗/石墨烯/二氧化钛纳米纤维和对比材料1Ge/G和对比材料2Ge在锂离子电池中应用的电化学性能对比：如图5中的a图所示，为锗/石墨烯/二氧化钛在电位范围为00.1-3V以0.2mV/s的扫描速度下得到的循环伏安曲线。第一圈循环明显不同于后面的循环，特别是放电过程。该不同是由第一圈循环SEI膜的形成引起的。在约0.12V的峰符合于石墨烯和Li+的反应(C(graphene)+xLi++xe-→LixC)。在0.55V和1.25V的两个峰归因于锗到LixGe的合金转化过程
Figure PCTCN2017095366-appb-000003
在之后的循环中，阴极曲线和阳极曲线都有很好的重叠性，说明其具有高的可逆性和良好的整体循环稳定性。如图5中的b图所示，显示了锗/石墨烯/二氧化钛(Ge/G/二氧化钛)在电流密度100mA/g电压范围在0.01-3V下的充/放电循环曲线。第一次放电阶段在约0.55V的电势平台与CV曲线结果相符。锂离子电池的首 次库仑效率约为74％，由于SEI膜的形成，可以说明锗/石墨烯/二氧化钛电极在第一次放电过程中损失了约26％的不可逆容量。如图5中的c图所示，为锗/石墨烯/二氧化钛、Ge/G和Ge三者在电流密度为了100mA/g下的循环特性曲线。三者的，第一圈的放电容量分别为1701mAh/g，1766mAh/g，1789mAh/g。然而，Ge的可逆容量下降非常快，从第2圈的1174mAh/g下降到第100圈的495mAh/g。Ge/G电极同Ge相比，展现出更好的循环性能，其经过100次循环后仍能保持804mAh/g的比容量。当Ge/G用二氧化钛进一步保护，锗/石墨烯/二氧化钛复合材料表现出最好的循环性能在经过100次循环后仍保持1050mAh/g的容量。这足以证明在锗和锗/石墨烯上的石墨烯和二氧化钛层能增加其循环特性。在高电流密度下进一步证实其优异的循环稳定性。如图5中的d图所示，所示，锗/石墨烯/二氧化钛在电流密度分别为100，200，400，600，800，1000mA/g下具有较高的比容量，分别为1050，921，850，750，627，550mAh/g。当电流密度回到100mA/g时，其仍然有1000mAh/g的可逆容量，几乎没有容量损失。然而，当电流密度回到100mA/g时，Ge或Ge/G都有着较大的容量损失。锗/石墨烯/二氧化钛的高容量回报率主要是因为其特殊的双层保护结构。
如图6所示，本发明制备的锗/石墨烯/二氧化钛纳米纤维和对比材料1Ge/G和对比材料2Ge在锂离子电池中应用的电化学性能对比：如图6中的a图所示，为锗/石墨烯/二氧化钛电极在钠离子电池中的CV曲线图，在阳极和阴极扫描过程中没有发现氧化还原峰，这就证明了SEI膜是在复合物的表面生成。如图6中的b图所示，是锗/石墨烯/二氧化钛在电流密度100mA/g下的充放电曲线图。在0.4V的位置上有一个较长的放电电压平台，与Ge中Na的嵌入反应相符合。在第5圈和第10圈充放电循环过程的一点点不同说明了钠反应是可逆的。如图6中的c图所示，显示了在电流密度100mA/g,电压范围0.01-2.7V的循环特性。尽管锗/石墨烯/二氧化钛的第一圈库仑效率较低，但其在经过100次循环后仍然有190mAh/g的比容量和高达99％的库仑效率。与Ge/G和Ge的快速比容量衰减相比，锗/石墨烯/二氧化钛电极表现出优越的循环特性，主要是因为其双层保 护结构。如图6中的d图所示，展示3种电极材料在不同电流密度下的倍率性能。锗/石墨烯/二氧化钛的放电比容量在电流100，200，400，600，800，1000mA/g电流下很好的保持在200，164，135，115，102，88mAh/g。同时，回到100mA/g时比容量很好的恢复到190mAh/g,这足以证明了锗/石墨烯/二氧化钛具有很好倍率性能。说明双层保护结构的方法一样可以应用于钠离子电池中。
如图7和图8所示，本发明制备的核壳结构锗/石墨烯/二氧化钛纳米纤维复合材料在作为电池负极在充放电过程中因外壳二氧化钛薄膜层和石墨烯的存在能有效缓解锗体积膨胀带来的压力，保持结构的完整性；而传统的纳米纤维在充放电过程中因锗的大体积膨胀引起结构的破坏。
本发明在锗上掺杂石墨烯可以改善电池特性，同时覆盖在锗/石墨烯外面的超薄二氧化钛薄膜层可以更进一点的增强循环稳定性和倍率性能。再者，锂离子电池或钠离子电池的锗/石墨烯/二氧化钛电极在经过100次循环后分别保持1050和194mAh/g的比容量，展现出极高和稳定的比容量。(比锗或锗/石墨烯高的多)此外，锗/石墨烯/二氧化钛电极也可以承受高电流密度，在不同电流密度下的充放电过程后(100，200，400，600，800，1000mAh/g),其仍然可以恢复到锂离子电池的1000mAh/g和钠离子电池的194mAh/g，几乎没有容量损失。本发明提供锗/石墨烯/二氧化钛纳米纤维其独特的双层保护结构可以延伸出其它应用于储能的各种各样的其它功能纳米材料的制造。
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 (10)

  1. 锗/石墨烯/二氧化钛纳米纤维复合材料制备方法，其特征在于，所述方法包括以下步骤：
    1)采用静电纺丝法制备锗/石墨烯纳米纤维；
    2)在锗/石墨烯纳米纤维上采用原子层沉积法制备二氧化钛；
    3)对制得的锗/石墨烯/二氧化钛纳米纤维复合材料进行后续处理。
  2. 根据权利要求1所述的锗/石墨烯/二氧化钛纳米纤维复合材料的制备方法，其特征在于：所述步骤1)采用静电纺丝法制备锗/石墨烯纳米纤维，其具体如下：
    a)制备静电纺丝液
    将石墨烯和分散溶剂按质量比为1：200-1：250的进行混合，然后超声处理30-120min，形成均匀石墨烯分散液；然后将和石墨烯的质量比为1：25-1：15的四氯化锗加入超声后的石墨烯混合液，接着在室温下磁力搅拌20-90min；最后加入将和石墨烯质量比为1：60-1：30的PVP，然后搅拌2-8h，得到静电纺丝溶液；
    b)静电纺丝
    首先将上述静电纺丝液注入内径为0.3-0.8mm的不锈钢喷嘴的注射器中，然后将喷嘴和接收装置分别连接高压电源的两个电极，进行静电纺丝得到锗/石墨烯纳米纤维复合材料。
  3. 根据权利要求2所述的锗/石墨烯/二氧化钛纳米纤维复合材料的制备方法，其特征在于：所述步骤a)中的分散溶剂为N,N-二甲基酰胺酰胺(DMF)、N-甲基-2-吡咯烷酮(NMP)、四氢呋喃(THF)、乙二醇中的至少一种。
  4. 根据权利要求2所述的锗/石墨烯/二氧化钛纳米纤维复合材料的制备方法，其特征在于：所述步骤a)中的四氯化锗纯度为99.999％。
  5. 根据权利要求2所述的锗/石墨烯/二氧化钛纳米纤维复合材料的制备方法，其特征在于：所述步骤b)中两电极之间的高压电源为10-25KV。
  6. 根据权利要求1所述的锗/石墨烯/二氧化钛纳米纤维复合材料的制备方法，其特征在于：所述步骤2)在锗/石墨烯上采用原子层沉积法制备二氧化钛，具体步骤为：将步骤1)得到的锗/石墨烯纳米纤维放入反应室中，以异丙醇钛(Ti(OCH(CH3)2)和H2O作为反应物，分别往反应室中引入异丙醇钛和H2O，调整异丙醇钛和H2O的用量使得精确的控制二氧化钛的一个原子层沉积循环，然后在170℃-210℃下以每个原子层沉积循环厚为1nm的生长速率沉积二氧化钛薄膜。
  7. 根据权利要求6所述的锗/石墨烯/二氧化钛纳米纤维复合材料的制备方法，其特征在于：所述Ti(OCH(CH3)2纯度为97％，所述H2O为高压液相层级的H2O。
  8. 根据权利要求6所述的锗/石墨烯/二氧化钛纳米纤维复合材料的制备方法，其特征在于：所述步骤2)中沉积的二氧化钛薄膜厚度为1-20nm。
  9. 根据权利要求1所述的锗/石墨烯/二氧化钛纳米纤维复合材料的制备方法，其特征在于：所述步骤3)对锗/石墨烯/二氧化钛进行后续处理的具体步骤如下：
    a)干燥：将步骤2)得到的锗/石墨烯/二氧化钛纳米纤维复合材料在真空环境的烤箱中，以温度为40-80℃进行干燥20-30h；
    b)煅烧：将干燥后的锗/石墨烯/二氧化钛复合材料放入空气环境中，在400-600℃温度下锻烧1-5h；
    c)退火：接着将锗/石墨烯/二氧化钛复合材料放在H2和Ar体积比为5％：95％的混合气体环境中，在500-800℃下进一步退火1-5h，最终得到锗/石墨烯/二氧化钛纳米纤维复合材料。
  10. 一种电池，其特征在于：所述电池的负极材料为权利要求1-9任一所述制得的锗/石墨烯/二氧化钛纳米纤维复合材料。
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