CN110875470A - Amorphous germanium-based nanowire-graphene nano composite lithium ion battery cathode material and preparation method thereof - Google Patents

Amorphous germanium-based nanowire-graphene nano composite lithium ion battery cathode material and preparation method thereof Download PDF

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CN110875470A
CN110875470A CN201810998587.8A CN201810998587A CN110875470A CN 110875470 A CN110875470 A CN 110875470A CN 201810998587 A CN201810998587 A CN 201810998587A CN 110875470 A CN110875470 A CN 110875470A
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nanowire
ca5ge2o9
lithium ion
ion battery
carbon black
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CN110875470B (en
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封伟
赵付来
张鑫
王宇
冯奕钰
李瑀
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Tianjin University
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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
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
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    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • 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
    • H01M4/58—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
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • 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
    • 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
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    • 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

Abstract

The invention discloses an amorphous germanium-based nanowire-graphene nano composite lithium ion battery cathode material and a preparation method thereof, and CaGe2Dispersing in deionized water as germanium source, adding organic solvent, reacting under rapid stirring at room temperature, centrifuging, washing the upper layer liquid with methanol and deionized water for three times, and drying to obtain hydrated Ca5Ge2O9Nano wire, annealing to obtain amorphous Ca5Ge2O9The nano wire, the reduced graphene oxide and the conductive carbon black are subjected to ultrasonic suction filtration together, and vacuum drying is carried out to obtain Ca5Ge2O9the/RGO/SP nano composite anode material. The invention has simple synthesis process, and the prepared Ca5Ge2O9a/RGO/SP nanocomposite anode material, wherein Ca5Ge2O9The nanometer wire reduces pulverization in the material circulation process, the addition of RGO with good conductivity and the uniform dispersion of the conductive agent SP, can increase the specific surface area of the material, effectively slow down the volume expansion of the germanium-based material, and simultaneously provides more diffusion channels for lithium ions, thereby enhancing the electronic conductivity of the whole material.

Description

Amorphous germanium-based nanowire-graphene nano composite lithium ion battery cathode material and preparation method thereof
Technical Field
The invention relates to the field of electrochemistry, in particular to an amorphous germanium-based nanowire-graphene nano composite lithium ion battery cathode material and a preparation method thereof.
Background
The lithium ion battery germanium-based negative electrode material has a theoretical capacity as high as 1620mAh/g, which is 4 times that of the traditional graphite negative electrode. And the germanium has higher conductivity, so that the germanium becomes a hotspot for researching high-performance lithium ion batteries. Its lithium ion intercalation/deintercalation mechanism is similar to that of Si, forming Li22Ge5 alloy with lithium. However, the electrode based on pure germanium has large volume change and poor conductivity during charging and discharging, which finally results in serious capacity loss and poor cycle performance. In order to improve the recyclability of germanium-based negative electrode materials, several strategies have been proposed, such as dispersing germanium in an inactive matrix, reducing the particle size (nanocrystallization), and alloying, among others. The problem caused by volume change in the circulation process can be effectively relieved by the nanometer (nano particles, nano wires, nano tubes and nano sheets) of the germanium-based material, so that the performance of the germanium negative electrode material is greatly improved. Another method is to synthesize binary or ternary germanium compounds which can form lithium compounds in situ as buffer matrices during the initial lithium intercalation process. Ternary germanates can reduce germanium content compared to germanium electrode materials, thereby reducing application costs, and these ternary germanates have recently been investigated as negative electrode materials for lithium ion batteries. In particular, ternary germanates based on Ca, Ge, O elements, and metal oxides CaO and Li2O formed in situ after the initial delithiation process, not only serve as buffer matrices to accommodate volume changes of germanium nanoparticles, but also effectively prevent agglomeration of nano-germanium particles formed during the process, and have been the focus of recent research.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides an amorphous germanium-based nanowire-graphene nano composite lithium ion battery cathode material and a preparation method thereof, wherein the amorphous germanium-based nanowire-graphene nano composite lithium ion battery cathode material is composed of a Ca5Ge2O9 nanowire, Reduced Graphene Oxide (RGO) and conductive carbon black (SP). The synthesis process is simple, the Ca5Ge2O9 in the negative electrode material is the nanowire, the pulverization in the material circulation process is reduced, the RGO with good conductivity is added, the conductive agent SP is uniformly dispersed, the specific surface area of the material can be increased, the volume expansion of the germanium-based material is effectively slowed down, more diffusion channels are provided for lithium ions, and the electronic conductivity of the whole material is further enhanced.
The technical purpose of the invention is realized by the following technical scheme.
The amorphous germanium-based nanowire-graphene nano composite lithium ion battery cathode material consists of a Ca5Ge2O9 nanowire, reduced graphene oxide and conductive carbon black, wherein the Ca5Ge2O9 accounts for 50-80% of the total mass of the cathode material, the sum of the reduced graphene oxide and the conductive carbon black accounts for 20-50% of the total mass, and the mass ratio of the reduced graphene oxide to the conductive carbon black is 1: (1-10).
And the Ca5Ge2O9 accounts for 60-70% of the total mass of the negative electrode material, and the sum of the reduced graphene oxide and the conductive carbon black accounts for 30-40% of the total mass.
And the mass ratio of the reduced graphene oxide to the conductive carbon black is 1: (2-7).
Moreover, the Ca5Ge2O9 nanowire is an amorphous Ca5Ge2O9 nanowire obtained by annealing hydrated Ca5Ge2O9 nanowire.
The preparation method of the lithium ion battery negative electrode material comprises the following steps:
step (ii) of1, with CaGe2Dispersing the germanium source in a mixed solvent of water and an organic solvent, reacting at room temperature and normal pressure under the condition of continuous stirring, centrifuging, taking the upper layer liquid, and washing and drying to obtain hydrated Ca5Ge2O9 nanowires;
in step 1, water is deionized water and the organic solvent is acetonitrile, N-Dimethylformamide (DMF) or N, N-dimethylacetamide.
In the step 1, the room temperature is 20-25 ℃, the normal pressure is one atmosphere, the stirring speed is 800-; the reaction time is from 20 to 100 hours, preferably from 30 to 80 hours.
In the step 1, the speed of centrifugal treatment is 3000-.
In step 1, the volume ratio of water to organic solvent is 1: (1-20), preferably 1: (10-20).
In step 1, the molar ratio of CaGe2 to water is 1: (50-1000), preferably 1: (100-800)
Step 2, annealing the hydrated Ca5Ge2O9 nanowire prepared in the step 1 in an inert protective atmosphere to obtain an amorphous Ca5Ge2O9 nanowire;
in step 2, the inert protective atmosphere is nitrogen, helium or argon.
In step 2, the annealing treatment process parameters are as follows: heating to 400 +/-10 ℃ from the room temperature of 20-25 ℃ at the heating rate of 5-10 ℃/min, preserving the temperature for 1-5 hours, and naturally cooling to the room temperature of 20-25 ℃ to obtain the amorphous Ca5Ge2O9 nanowire.
In step 2, the annealing treatment process parameters are as follows: heating to 400 +/-10 ℃ from the room temperature of 20-25 ℃ at the heating rate of 8-10 ℃/min, preserving the heat for 2-4 hours, and naturally cooling to the room temperature of 20-25 ℃ to obtain the amorphous Ca5Ge2O9 nanowire.
And 3, ultrasonically dispersing the amorphous Ca5Ge2O9 nanowire obtained in the step 2, the reduced graphene oxide and the conductive carbon black in isopropanol uniformly, filtering, and then drying in vacuum to obtain the amorphous germanium-based nanowire-graphene nano composite lithium ion battery cathode material (namely the Ca5Ge2O9/RGO/SP nano composite cathode material).
In the step 3, the Ca5Ge2O9 accounts for 50-80% of the total mass of the negative electrode material, the sum of the reduced graphene oxide and the conductive carbon black accounts for 20-50% of the total mass, and the mass ratio of the reduced graphene oxide to the conductive carbon black is 1: (1-10)
In the step 3, the Ca5Ge2O9 accounts for 60-70% of the total mass of the negative electrode material, and the sum of the reduced graphene oxide and the conductive carbon black accounts for 30-40% of the total mass.
In step 3, the mass ratio of the reduced graphene oxide to the conductive carbon black is 1: (2-7).
In the step 3, the ultrasonic time is 0.5-1h, and vacuum drying is carried out for 12-24h at the temperature of 60-80 ℃ after suction filtration.
In the step 3, when ultrasonic dispersion is carried out, 10-20ml of isopropanol is selected to be used per 100mg of the total mass of the amorphous Ca5Ge2O9 nano wire, the reduced graphene oxide and the conductive carbon black.
Compared with the prior art, the Ca5Ge2O9 nanowire and the Ca5Ge2O9/RGO/SP nanocomposite provided by the invention are simple in preparation process, and the Ca5Ge2O9 nanowire can be obtained by directly dispersing CaGe2 serving as a precursor in deionized water or a mixed solvent and performing rapid stirring reaction at room temperature. Different from the traditional methods of chemical vapor deposition, template method, molecular beam epitaxy, electron beam evaporation and the like, the method has simple process, does not need special equipment for matching and can be prepared in large quantity; the Ca5Ge2O9 nanowire is used as an active material, so that pulverization and volume expansion in the material circulation process are reduced, the graphene has excellent conductivity, and is combined with conductive carbon black SP to fully wrap the Ca5Ge2O9 nanowire to form a three-dimensional conductive network, so that the conductivity of the composite material is greatly improved, and the composite material has excellent rate capability in heavy current discharge; meanwhile, the high specific surface area of the graphene and the conductive carbon black can effectively slow down the volume expansion of the germanium-based material and provide more diffusion channels for lithium ions, and the Ca5Ge2O9/RGO/SP nano composite material has higher structural stability and conductivity and can provide high specific capacity, large multiplying power and long cycle life as a negative electrode material, namely the application of the Ca5Ge2O9/RGO/SP nano composite material in the preparation of the negative electrode material of the lithium ion battery.
Drawings
Fig. 1 is a scanning electron microscope photograph of the annealed and dehydrated Ca5Ge2O9 nanowire obtained in the technical solution of the present invention.
Fig. 2 is an XRD spectrogram before and after annealing of the obtained Ca5Ge2O9 nanowire in the technical solution of the present invention.
Fig. 3 is a transmission electron micrograph of the annealed and dehydrated nanowire Ca5Ge2O9 in the invention.
FIG. 4 is a scanning electron micrograph of Ca5Ge2O9/RGO/SP nanocomposite prepared according to the technical scheme of the invention.
FIG. 5 shows that the battery assembled by the Ca5Ge2O9/RGO/SP nano composite anode material prepared by the invention is 0.1Ag-1A charge-discharge cycle curve at a current density of (a).
FIG. 6 is a graph of the rate charge-discharge cycle of a battery assembled with the Ca5Ge2O9/RGO/SP nanocomposite negative electrode material prepared by the present invention.
Detailed Description
The present invention will be further described with reference to the following embodiments. The following examples of the present invention are given to further illustrate the present invention, but not to limit the scope of the present invention.
Example 1-0.29 g of CaGe2 powder was weighed and dispersed in a mixed solution of 1.4ml deionized water and 28ml DMF and the reaction was stirred at 2000r/min at room temperature for 1 day (24 hours per day). And centrifuging at the rotating speed of 3000r/min, taking the upper layer liquid, carrying out suction filtration, washing with methanol and deionized water for three times respectively, and drying in a vacuum drying oven for 12 hours at the temperature of 80 ℃ to obtain the hydrated Ca5Ge2O9 nanowire. And then heating to 400 ℃ at the speed of 5 ℃/min under the protection of argon in a tube furnace, preserving the heat for 2h, and then naturally cooling to room temperature to obtain the amorphous Ca5Ge2O9 nanowire. The obtained amorphous Ca5Ge2O9 nanowire (56mg), RGO (7mg) and SP (49mg) are weighed and dispersed in 17ml of isopropanol to be subjected to common ultrasonic treatment for 0.5h, then the solution is subjected to suction filtration and vacuum drying at 60 ℃ for 12h, and the Ca5Ge2O9/RGO/SP nanocomposite negative electrode material is obtained.
Example 2-0.29 g of CaGe2 powder was weighed and dispersed in a mixed solution of 14ml of deionized water and 140ml of acetonitrile, and the reaction was stirred at 1500r/min at room temperature for 2 days. And centrifuging at the rotating speed of 4000r/min, taking the upper layer liquid, carrying out suction filtration, washing with methanol and deionized water for three times respectively, and drying in a vacuum drying oven for 18h at the temperature of 70 ℃ to obtain the hydrated Ca5Ge2O9 nanowire. And then heating to 400 ℃ at the speed of 8 ℃/min under the protection of argon in a tube furnace, preserving the heat for 3h, and then naturally cooling to room temperature to obtain the amorphous Ca5Ge2O9 nanowire. And (3) weighing the obtained amorphous Ca5Ge2O9 nanowire (65mg), RGO (7mg) and SP (28mg), dispersing in 10ml of isopropanol, carrying out ultrasonic treatment for 0.8h, carrying out suction filtration, and carrying out vacuum drying at 70 ℃ for 18h to obtain the Ca5Ge2O9/RGO/SP nanocomposite negative electrode material.
Example 3-0.29 g of CaGe2 powder was weighed out and dispersed in 28ml of deionized water and the reaction was stirred at 900r/min at room temperature for 4 days. And centrifuging at the rotating speed of 5000r/min, taking the upper layer liquid, carrying out suction filtration, washing with isopropanol and deionized water for three times respectively, and drying in a vacuum drying oven for 24 hours at the temperature of 60 ℃ to obtain the hydrated Ca5Ge2O9 nanowire. And then heating to 400 ℃ at the speed of 10 ℃/min under the protection of argon in a tube furnace, preserving the heat for 4h, and then naturally cooling to room temperature to obtain the amorphous Ca5Ge2O9 nanowire. And (3) weighing the obtained amorphous Ca5Ge2O9 nanowire (80mg), RGO (10mg) and SP (10mg), dispersing in 20ml of isopropanol, performing ultrasonic treatment for 1h, performing suction filtration, and performing vacuum drying at 80 ℃ for 24h to obtain the Ca5Ge2O9/RGO/SP nanocomposite negative electrode material.
And (3) observing the morphology of the product by using a Hitachi S-4800 field emission scanning electron microscope, wherein the annealed product is a nanowire with the diameter of 20-110nm and the length of 1-20um as shown in figure 1. The test is carried out by using a D8Advanced X-ray diffractometer of BRUKER AXS GMBH company, and the result is shown in figure 2, four main peaks of the hydrated Ca5Ge2O9 nanowire completely correspond to the standard card of Ca5Ge2O9nH2O, and after annealing, the crystallization peak disappears, which indicates that the dehydrated product is amorphous Ca5Ge2O9 and is consistent with the report in the literature. The product micro-nano structure and crystallinity are characterized by adopting an jem-2100f field emission transmission electron microscope, as shown in figure 3, the product micro-nano structure and crystallinity are a Ca5Ge2O9 nanowire transmission electron microscope image and a selected diffraction image, and the amorphous property of the Ca5Ge2O9 nanowire is further proved by selecting a diffusion ring of the diffraction image. FIG. 4 is a scanning electron microscope image of Ca5Ge2O9/RGO/SP nanocomposite, and it can be seen that Ca5Ge2O9 nanowires are better wrapped in graphene and conductive carbon black to form a three-dimensional conductive network and an ion transmission channel.
The Ca5Ge2O9/RGO/SP nano composite negative electrode material is used as a negative electrode material of a lithium ion battery, and electrochemical performance tests are carried out: 60mg of Ca5Ge2O9/RGO/SP nanocomposite negative electrode material in example 2 and 6.64mg of polyacrylic acid (PAA) were weighed out, mixed and ground uniformly, 500ul of NMP was added as a dispersant, and ground uniformly to obtain a mixed slurry. And then uniformly coating the slurry on a copper foil, and carrying out vacuum drying for 24 hours at the temperature of 60 ℃ to obtain a pole piece for later use. The prepared pole piece is used as a negative electrode, a metal lithium piece is used as a counter electrode, a diaphragm Celgrad3500 (diaphragm type Celgrad3500) and 1mol/L LiPF6/EC-DEC-DMC (volume ratio is 1:1:1) are used as electrolyte (solute is lithium hexafluorophosphate, solvent is a mixed solvent of ethylene carbonate, diethyl carbonate and dimethyl carbonate with the same volume), and the button cell is assembled in a glove box filled with argon. And (5) carrying out constant-current charge and discharge test by adopting a Land battery test system. The voltage range of charge and discharge is 0.01-3V, and the current density is 0.1Ag-1And circulating 100 times, and measuring the charge and discharge performance. And measuring the rate performance of the battery under different charge and discharge rates, wherein the rate is from 0.1Ag-1Gradually increase to 5Ag-1Then gradually decreases to 0.1Ag-1(0.1-0.2-0.5-1-2-5-2-1-0.5-0.2-0.1Ag-1)。
The Ca5Ge2O9/RGO/SP nanocomposite in example 2 was selected as the negative electrode material of lithium ion battery to assemble a battery for testing, as shown in FIG. 5, at 0.1Ag-1Under the current density, the capacity is 806mAhg after the cyclic charge and discharge is carried out for 100 circles-1. FIG. 6 shows the ratio performance of 0.1, 0.2, 0.5, 1, 2, 5Ag-1The down-conversion capacity is 1491, 574, 526, 462, 377, 243mAhg-1And has excellent rate performance. The Ca5Ge2O9/RGO/SP nanocomposites can be prepared with process parameters adjusted as described in the present disclosure, exhibiting essentially the same performance as the examples at 0.1Ag as the negative electrode active material-1Under the current density of (2), the capacity is charged and discharged for 100 circles in a circulating mannerThe amount is 700-900mAhg-1And has excellent rate performance.
The above description of the invention has been made in view of the fact that the preparation of Ca5Ge2O9/RGO/SP nanocomposites with adjustment of the preparation process parameters according to the teachings of the present invention, which have been tested to show substantially consistent performance with the present invention, is exemplary, and it should be noted that any simple modification, amendment or equivalent substitution by a person skilled in the art without expending inventive efforts falls within the scope of the present invention without departing from the core of the present invention.

Claims (10)

1. The amorphous germanium-based nanowire-graphene nano composite lithium ion battery cathode material is characterized by comprising a Ca5Ge2O9 nanowire, reduced graphene oxide and conductive carbon black, wherein the Ca5Ge2O9 accounts for 50-80% of the total mass of the cathode material, the sum of the reduced graphene oxide and the conductive carbon black accounts for 20-50% of the total mass, and the mass ratio of the reduced graphene oxide to the conductive carbon black is 1: (1-10), the Ca5Ge2O9 nanowire is hydrated Ca5Ge2O9 nanowire, and is annealed to obtain an amorphous Ca5Ge2O9 nanowire, and the Ca5Ge2O9 nanowire is wrapped in graphene and conductive carbon black to form a three-dimensional conductive network and an ion transmission channel.
2. The amorphous germanium-based nanowire-graphene nanocomposite lithium ion battery negative electrode material of claim 1, wherein Ca5Ge2O9 accounts for 60-70% of the total mass of the negative electrode material, the sum of the reduced graphene oxide and the conductive carbon black accounts for 30-40% of the total mass, and the mass ratio of the reduced graphene oxide to the conductive carbon black is 1: (2-7).
3. A preparation method of an amorphous germanium-based nanowire-graphene nano composite lithium ion battery negative electrode material is characterized by comprising the following steps:
step 1, using CaGe2Dispersing in mixed solvent of water and organic solvent as germanium source, reacting at room temperature and normal pressure under continuous stirring, centrifuging, collecting upper layer liquid, washing, and drying to obtain hydrated Ca5Ge2O9The volume ratio of the nanowire, water and the organic solvent is 1: (1-20), the molar ratio of CaGe2 to water is 1: (50-1000);
step 2, annealing the hydrated Ca5Ge2O9 nanowire prepared in the step 1 in an inert protective atmosphere to obtain an amorphous Ca5Ge2O9 nanowire, wherein the annealing process parameters are as follows: heating to 400 +/-10 ℃ from the room temperature of 20-25 ℃ at the heating rate of 5-10 ℃/min, preserving the heat for 1-5 hours, and naturally cooling to the room temperature of 20-25 ℃ to obtain amorphous Ca5Ge2O9 nanowires;
and 3, ultrasonically dispersing the amorphous Ca5Ge2O9 nanowire, the reduced graphene oxide and the conductive carbon black obtained in the step 2 in isopropanol uniformly, filtering, and then drying in vacuum to obtain the amorphous germanium-based nanowire-graphene nano composite lithium ion battery cathode material, wherein the Ca5Ge2O9 accounts for 50-80% of the total mass of the cathode material, the sum of the reduced graphene oxide and the conductive carbon black accounts for 20-50% of the total mass, and the mass ratio of the reduced graphene oxide to the conductive carbon black is 1: (1-10).
4. The method for preparing the amorphous germanium-based nanowire-graphene nanocomposite lithium ion battery anode material according to claim 3, wherein in the step 1, water is deionized water, and the organic solvent is acetonitrile, N-Dimethylformamide (DMF) or N, N-dimethylacetamide.
5. The method for preparing the amorphous germanium-based nanowire-graphene nanocomposite lithium ion battery anode material according to claim 3, wherein in the step 1, the volume ratio of water to the organic solvent is 1: (10-20), the molar ratio of CaGe2 to water is 1: (100-800).
6. The preparation method of the amorphous germanium-based nanowire-graphene nanocomposite lithium ion battery anode material as claimed in claim 3, wherein in the step 1, the room temperature is 20-25 ℃, the normal pressure is one atmosphere, the stirring speed is 800-2000r/min, preferably 1000-1500 r/min; the reaction time is 20 to 100 hours, preferably 30 to 80 hours; the speed of the centrifugal treatment is 3000-.
7. The preparation method of the amorphous germanium-based nanowire-graphene nanocomposite lithium ion battery anode material according to claim 3, wherein in the step 2, the annealing treatment process parameters are as follows: heating to 400 +/-10 ℃ from the room temperature of 20-25 ℃ at the heating rate of 8-10 ℃/min, preserving the heat for 2-4 hours, and naturally cooling to the room temperature of 20-25 ℃ to obtain amorphous Ca5Ge2O9 nanowires; the inert protective atmosphere is nitrogen, helium or argon.
8. The preparation method of the amorphous germanium-based nanowire-graphene nanocomposite lithium ion battery anode material according to claim 3, wherein in step 3, the Ca5Ge2O9 accounts for 60-70% of the total mass of the anode material, the sum of the reduced graphene oxide and the conductive carbon black accounts for 30-40% of the total mass, and the mass ratio of the reduced graphene oxide to the conductive carbon black is 1: (2-7).
9. The preparation method of the amorphous germanium-based nanowire-graphene nanocomposite lithium ion battery anode material according to claim 3, wherein in the step 3, when ultrasonic dispersion is performed, 10-20ml of isopropanol is used per 100mg of the total mass of the amorphous Ca5Ge2O9 nanowire, the reduced graphene oxide and the conductive carbon black, the ultrasonic time is 0.5-1h, and vacuum drying is performed at 60-80 ℃ for 12-24h after suction filtration.
10. The application of the amorphous germanium-based nanowire-graphene nanocomposite lithium ion battery negative electrode material as claimed in claim 1 or 2 in preparing the lithium ion battery negative electrode material, wherein the content of the amorphous germanium-based nanowire-graphene nanocomposite lithium ion battery negative electrode material is 0.1Ag-1At current density of (2), the capacity is 700-900mAhg after 100 cycles of charge and discharge-1And has excellent rate performance.
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