CN108336346B - Application of germanium-gallium nanowires as electrode material of lithium ion battery - Google Patents

Application of germanium-gallium nanowires as electrode material of lithium ion battery Download PDF

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CN108336346B
CN108336346B CN201810124313.6A CN201810124313A CN108336346B CN 108336346 B CN108336346 B CN 108336346B CN 201810124313 A CN201810124313 A CN 201810124313A CN 108336346 B CN108336346 B CN 108336346B
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gallium
germanium
nanowire
electrolyte
electrode
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CN108336346A (en
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于兆亮
孟祥东
王多
李海波
孙萌
尹默
袁梦
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Jilin Dongchi New Energy Technology Co ltd
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Jilin Normal 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
    • 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
    • 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
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0438—Processes of manufacture in general by electrochemical processing
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    • H01M4/0452—Electrochemical coating; Electrochemical impregnation from solutions
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • 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

Abstract

The invention provides an application of a germanium-gallium nanowire as an electrode material of a lithium ion battery, wherein the germanium-gallium nanowire comprises elemental germanium and elemental gallium in chemical composition, and the atomic ratio of the elemental germanium to the elemental gallium in the germanium-gallium nanowire is (4-9): 1. according to the invention, the germanium-gallium nanowires are used as the electrode material of the lithium ion battery, so that the battery cycle performance and the rate capability of the lithium ion battery can be improved.

Description

Application of germanium-gallium nanowires as electrode material of lithium ion battery
Technical Field
The invention relates to the technical field of electrode materials, in particular to application of germanium-gallium nanowires as an electrode material of a lithium ion battery.
Background
Lithium ion batteries have become the most important energy source in portable devices and industrial energy storage systems due to their advantages of long cycle life, low self-discharge rate, and high operating voltage. However, a low energy density of about 150Wh/kg is a challenge to meet the demands of future mobile devices. Since the graphite anode has a low reversible capacity of 372mAh/g, the development of high capacity lithium alloy anodes using materials such as silicon, germanium, tin and antimony instead of graphite has become a hot spot worldwide. Among them, silicon and germanium are promising materials because their theoretical capacities are up to 4200mAh/g and 1600mAh/g, respectively. However, silicon and germanium have the common disadvantage of large volume expansion (Si: 400% and Ge: 370%) during lithium insertion and extraction, which can lead to pulverization and cracking of the electrode material during cycling, and thus can affect the use effect of the lithium ion battery.
To overcome this difficulty, a great deal of research has been conducted to design materials capable of buffering volume changes, such as nanoparticles, nanowires, nanotubes, and three-dimensional nanostructures. Among all nanomaterials, nanowires not only effectively reduce the volume strain, but also have a higher interfacial area when in contact with an electrolyte and provide an effective channel for electron transport along the length direction. Therefore, germanium nanowires are receiving a great deal of attention. Although the theoretical capacity of germanium is lower than that of silicon, germanium has some promising characteristics, such as high conductivity (10000 times higher than silicon) and excellent lithium ion diffusion coefficient (more than 400 times higher than silicon at room temperature), which makes germanium a promising high-performance lithium ion anode material.
The traditional method of growing germanium nanowires is the gas-liquid-solid (VLS) or solid-liquid (SLS) method. Although both methods are effective for the synthesis of germanium nanowires, they have some inherent disadvantages, such as the requirement for high temperature or low pressure; furthermore, both of these methods typically use refined and expensive toxic semiconductor precursors. The electrochemical liquid-solid (EC LLS) method is a new method for directly electrodepositing germanium nanowires from an aqueous solution, and liquid metal nano liquid drops are used as ultramicroelectrodes and seeds for crystal growth; however, the electrodeposited nanowires obtained by the method have poor electrochemical properties when used as electrode materials.
Disclosure of Invention
In view of this, the present invention provides an application of a ge-ga nanowire as an electrode material of a lithium ion battery, so as to improve battery cycle performance and rate capability of the lithium ion battery.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides an application of a germanium-gallium nanowire as an electrode material of a lithium ion battery, wherein the germanium-gallium nanowire comprises elemental germanium and elemental gallium in chemical composition, and the atomic ratio of the elemental germanium to the elemental gallium in the germanium-gallium nanowire is (4-9): 1.
preferably, the diameter of the germanium-gallium nanowire is 50-100 nm, and the length of the germanium-gallium nanowire is 500-1000 nm.
Preferably, the preparation method of the germanium-gallium nanowire comprises the following steps:
in the environment with water oxygen content lower than 2ppm, adding GaCl3、GeCl4Mixing with ionic liquid to obtain electrolyte;
performing constant-voltage electrodeposition on gallium in the electrolyte at 55-65 ℃ and-1.0-1.5V by adopting a three-electrode electrochemical system comprising a working electrode, a counter electrode and a reference electrode, and obtaining gallium deposits on the surface of the working electrode; and continuously performing constant-voltage electrodeposition on germanium at the temperature of 55-65 ℃ and under the pressure of-1.8-2.2V to obtain the germanium-gallium nanowire on the surface of the working electrode.
Preferably, the ionic liquid comprises 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide salt, 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide salt or N-butyl-N-methylpiperidinium bis (trifluoromethylsulfonyl) imide salt.
Preferably, the electrolyte is GaCl3The concentration of (A) is 0.09-0.11 mol/L; GeCl4The concentration of (b) is 0.09-0.11 mol/L.
Preferably, the method for obtaining the deposition voltage required by the constant voltage electrodeposition of gallium and germanium comprises the following steps:
in the environment with water oxygen content lower than 2ppm, adding GaCl3Mixing with ionic liquid to obtain GaCl3An electrolyte; adding GeCl4Mixing with ionic liquid to obtain GeCl4An electrolyte;
the GaCl is applied by a three-electrode electrochemical system comprising a working electrode, a counter electrode and a reference electrode3Electrolyte and GeCl4And respectively scanning cyclic voltammetry curves by the electrolyte, wherein the reduction voltage of gallium in the obtained cyclic voltammetry curves is the voltage when gallium is electrodeposited at constant voltage, and the reduction voltage of germanium in the obtained cyclic voltammetry curves is the voltage when germanium is electrodeposited at constant voltage.
Preferably, the time for constant voltage electrodeposition of the gallium is 30-60 s.
Preferably, the gallium sediments are liquid microspheres, and the particle size of the gallium sediments is 30-60 nm.
Preferably, the time for constant-voltage electrodeposition of the germanium is 150-300 s.
Preferably, the lithium ion battery takes germanium-gallium nanowires as a working electrode, a lithium sheet as a counter electrode, a polyethylene microporous membrane as a diaphragm and 1mol/L LiPF6The mixed solution of ethylene carbonate and ethylene carbonate was dissolved as an electrolyte.
The invention provides an application of a germanium-gallium nanowire as an electrode material of a lithium ion battery, wherein the germanium-gallium nanowire comprises elemental germanium and elemental gallium in chemical composition, and the atomic ratio of the elemental germanium to the elemental gallium in the germanium-gallium nanowire is (4-9): 1. according to the invention, the germanium-gallium nanowires are used as the electrode material of the lithium ion battery, so that the battery cycle performance and the rate capability of the lithium ion battery can be improved. The experimental results in the examples show that the germanium-gallium nanowires are used as working electrodes (cathode materials) and assembled in a CR2025 button battery case to prepare a half battery, under experimental conditions, the first discharge specific capacity and the charge specific capacity of the germanium-gallium nanowires are 1730 mAh/g and 1537mAh/g respectively, and the initial coulombic efficiency is 89%; and starting from the second cycle, the coulomb efficiency can be kept above 95%; the discharge capacity after 50 cycles is 1414mAh/g, and the Ge-Ga nanowire electrode can still maintain the capacity of 1146mAh/g even after 150 cycles. Testing the specific cyclic capacity of the germanium-gallium nanowire electrode half cell under different current densities, wherein the discharge capacities of the germanium-gallium nanowire at 0.16, 0.32, 0.8, 1.6, 3.2, 8 and 16A/g are 1621, 1506, 1409, 1331, 1242, 977 and 687mAh/g respectively; when the current density returns to 0.16A/g, the capacity is restored to 1422mAh/g, and the capacity retention rate reaches 87%.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 shows GaCl on a Cu substrate in example 13Cyclic voltammogram (a) and GeCl of electrolyte4Cyclic voltammogram (b) of the electrolyte;
FIG. 2 is a schematic diagram of the electrodeposition of Ge-Ga nanowires in example 2;
FIG. 3 is a scanning electron image of a gallium deposit after a constant voltage electrodeposition for 60s on a Cu substrate in example 2, at a magnification of 2 ten thousand times;
FIG. 4 is a scanning electron image of Ge-Ga nanowires obtained by performing constant voltage electrodeposition on a Cu substrate for 300s in example 2, with a magnification of 2 ten thousand times;
FIG. 5 is a transmission electron microscope image of a single germanium-gallium nanowire in example 2;
FIG. 6 is a selected area electron diffraction pattern of germanium-gallium nanowires of example 2;
FIG. 7 is the X-ray photoelectron spectroscopy curve of the germanium-gallium nanowire in example 2 after etching without argon ions and 120s etching;
FIG. 8 is an optical photograph of Ge-Ga nanowires on a Cu substrate and an assembled CR2025 half-cell in example 3;
fig. 9 is a graph of cycle stability and coulombic efficiency of the ge-ga nanowire electrode half-cell test in example 3;
FIG. 10 is a cycle chart of the GeGa nanowire electrode half-cell test in example 3 under different current densities;
fig. 11 is a scanning electron microscope image of the ge-ga nanowires of example 3 after 150 cycles of cycling.
Detailed Description
The invention provides an application of a germanium-gallium nanowire as an electrode material of a lithium ion battery, wherein the germanium-gallium nanowire comprises elemental germanium and elemental gallium in chemical composition, and the atomic ratio of the elemental germanium to the elemental gallium in the germanium-gallium nanowire is (4-9): 1. in the invention, the diameter of the germanium-gallium nanowire is preferably 50-100 nm, and the length of the germanium-gallium nanowire is preferably 500-1000 nm.
In the present invention, the method for preparing the germanium-gallium nanowire preferably comprises the following steps:
in the environment with water oxygen content lower than 2ppm, adding GaCl3、GeCl4Mixing with ionic liquid to obtain electrolyte;
performing constant-voltage electrodeposition on gallium in the electrolyte at 55-65 ℃ and-1.0-1.5V by adopting a three-electrode electrochemical system comprising a working electrode, a counter electrode and a reference electrode, and obtaining gallium deposits on the surface of the working electrode; and continuously performing constant-voltage electrodeposition on germanium at the temperature of 55-65 ℃ and under the pressure of-1.8-2.2V to obtain the germanium-gallium nanowire on the surface of the working electrode.
The germanium-gallium nanowires are preferably prepared in an environment with the water oxygen content lower than 2 ppm. The germanium-gallium nanowire is preferably prepared in a glove box; the glove box can control the water oxygen content to be lower than 2 ppm.
The invention preferably uses GaCl in an environment with water oxygen content lower than 2ppm3、GeCl4And mixing with ionic liquid to obtain the electrolyte. In the present invention, GaCl is contained in the electrolyte3The concentration of (b) is preferably 0.09-0.11 mol/L, more preferably 0.1 mol/L; GeCl4The concentration of (b) is 0.09 to 0.11mol/L, more preferably 0.1 mol/L. In the present invention, the GaCl is3The purity of (b) is preferably 99.999%; the GeCl4The purity of (b) is preferably 99.9999%. The invention is directed to said GaCl3And GeCl4The source of (A) is not particularly limited, and commercially available products known to those skilled in the art may be used. In embodiments of the invention, the GaCl3(99.999%) purchased from AlfaAesar; the GeCl4(99.9999%) was purchased from national crystal technologies.
In the present invention, the ionic liquid preferably comprises 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide salt ([ EMIm)]Tf2N), 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide salt ([ BMIm)]Tf2N) or N-butyl-N-methylpiperidine bis (trifluoromethanesulfonyl) imide salt ([ Py)1,4]Tf2N). In the present invention, the ionic liquid is preferably subjected to dehydration treatment in an environment having a water oxygen content of less than 2ppm before use. The present invention is not particularly limited to the dehydration treatment and the equipment used for performing the dehydration treatment, and a technical solution of the dehydration treatment known to those skilled in the art may be used. In the embodiment of the invention, the dehydration treatment is carried out by vacuum distillation on the ionic liquid for 24 hours at 100 ℃ in a glove box filled with protective gas and with the water oxygen content of less than 2 ppm. The source of the ionic liquid in the present invention is not particularly limited, and commercially available products known to those skilled in the art may be used. In an embodiment of the present invention, theIonic liquids were purchased from Io-Li-Tec, germany or from industrial trade, inc. In the invention, the ionic liquid can effectively improve the electrodeposition efficiency, solve the problem of hydrogen embrittlement caused by hydrogen evolution in an aqueous solution, and ensure that the nanowire obtained by deposition is particularly suitable for a lithium ion battery as an electrode material.
The invention is directed to said GaCl3、GeCl4The mixing with the ionic liquid is not particularly limited, and a material mixing method well known to those skilled in the art may be used. In the invention, the mixing is preferably carried out at 20-35 ℃; in the examples of the present invention, the mixing is carried out in particular at room temperature, i.e. without additional heating or cooling. In the invention, the mixing is preferably carried out under a stirring condition, and the stirring rotating speed is preferably 400-600 rpm, more preferably 500 rpm; the stirring time is preferably 10-14 h, and more preferably 12 h. In the examples of the invention, the mixing is carried out in particular in a glove box filled with protective gas and having a water oxygen content of less than 2 ppm.
After the electrolyte is obtained, a three-electrode electrochemical system comprising a working electrode, a counter electrode and a reference electrode is preferably adopted to carry out constant-voltage electrodeposition on gallium in the electrolyte at the temperature of 55-65 ℃ and under the voltage of-1.0-1.5V, and gallium deposits are obtained on the surface of the working electrode; and continuously performing constant-voltage electrodeposition on germanium at the temperature of 55-65 ℃ and under the pressure of-1.8-2.2V, and obtaining germanium-gallium nanowires (Ge-Ga nanowires) on the surface of the working electrode.
The electrolytic cell for holding the electrolyte is not particularly limited in the present invention, and any electrolytic cell known to those skilled in the art may be used, specifically, a polytetrafluoroethylene electrolytic cell. In the embodiment of the invention, in order to apply the prepared germanium-gallium nanowire to a lithium battery for performance test, a polytetrafluoroethylene electrolytic cell is used for limiting the deposition area of the germanium-gallium nanowire to be 1.5cm2。
The working electrode, the counter electrode and the reference electrode in the three-electrode electrochemical system are not particularly limited, and the working electrode, the counter electrode and the reference electrode which are well known by the technical personnel in the field can be adopted; in the embodiment of the invention, a copper substrate is used as a working electrode, a silver wire is used as a reference electrode, and a platinum sheet is used as a counter electrode. In the present invention, the silver wire can provide a sufficiently stable electrode voltage. In the present invention, the copper substrate is preferably washed before use, and the washing preferably includes sequentially performing an acetone wash and an isopropanol wash; the number of washing and the amount of washing agent used in each washing are not particularly limited in the present invention, and washing methods known to those skilled in the art may be used. In the embodiment of the invention, after the copper substrate is washed, the copper substrate needs to be soaked for 1min by using hydrochloric acid with the mass content of 10% to remove the surface oxide.
The electrochemical workstation used in the preparation of the germanium-gallium nanowire is not particularly limited, and an electrochemical workstation which can perform cyclic voltammetry scanning and constant voltage testing and is well known to those skilled in the art, such as 2273 electrochemical workstation or Chenghua electrochemical workstation, can be used. In the embodiment of the invention, the cyclic voltammetry curve scanning and constant voltage testing are carried out by using Power CV and Power CORR software in 2273 electrochemical workstation (princetonoriented Research).
In the invention, the time for constant voltage electrodeposition of the gallium is preferably 30-60 s. In the invention, the gallium sediment is liquid microspheres, and the particle size of the gallium sediment is preferably 30-60 nm.
In the invention, the time for constant voltage electrodeposition of the germanium is preferably 150-300 s.
In the present invention, the method for obtaining the voltage required for the constant-voltage electrodeposition of gallium and the constant-voltage electrodeposition of germanium preferably comprises the steps of:
in the environment with water oxygen content lower than 2ppm, adding GaCl3Mixing with ionic liquid to obtain GaCl3An electrolyte; adding GeCl4Mixing with ionic liquid to obtain GeCl4An electrolyte;
the GaCl is applied by a three-electrode electrochemical system comprising a working electrode, a counter electrode and a reference electrode3Electrolyte and GeCl4Respectively carrying out cyclic voltammetry curve scanning on the electrolyte to obtain cyclic voltammetry curvesThe reduction voltage of gallium in the ampere curve is the voltage when gallium is electrodeposited at constant voltage, and the reduction voltage of germanium in the cyclic voltammetry curve is the voltage when germanium is electrodeposited at constant voltage.
In the present invention, the GaCl is3The concentration of the electrolyte is preferably 0.09-0.11 mol/L, and more preferably 0.1 mol/L; the GeCl4The concentration of the electrolyte is preferably 0.09-0.11 mol/L, and more preferably 0.1 mol/L. In the present invention, the GaCl is3、GeCl4And the ionic liquid is preferably consistent with the reagent adopted by the technical scheme for preparing the germanium-gallium nanowire.
In the present invention, the GaCl is added3When the cyclic voltammetry curve scanning is carried out on the electrolyte, the scanning range is preferably-2.0-0V; the scanning rate is preferably 50 mV/s; the equilibration time is preferably 15 s.
In the present invention, the GeCl is added4When the cyclic voltammetry curve scanning is carried out on the electrolyte, the scanning range is preferably-2.5-0V; the scanning rate is preferably 50 mV/s; the equilibration time is preferably 15 s.
The three-electrode electrochemical system of the working electrode, the counter electrode and the reference electrode is not particularly limited, and the three-electrode electrochemical system well known by the technicians in the field can be adopted; in the embodiment of the present invention, the three-electrode electrochemical system used for performing the cyclic voltammetry scanning is preferably consistent with the three-electrode electrochemical system used for preparing the ge-ga nanowires according to the above technical scheme of the present application.
After the constant-pressure electrodeposition of germanium is finished, the obtained sample wafer is preferably immersed in isopropanol to be cleaned so as to remove ionic liquid residues, and the germanium-gallium nanowire is obtained. In the present invention, the gallium germanium nanowires need not be separated from the working electrode.
The method starts constant-voltage electrodeposition of Ga at the temperature of 55-65 ℃, and the Ga deposit obtained by deposition is in a liquid state because the melting point of Ga is 29.4 ℃, and is kept in a spherical liquid drop state (namely Ga nanospheres) under the action of surface tension; and then, carrying out constant-voltage electrodeposition on the Ga nanospheres at the temperature of 55-65 ℃. According to the electrodeposition theory, metal ions are preferentially discharged at the positions of the projections of the working electrode. On the substrate on which the Ga nanospheres have been deposited, the Ga nanospheres are raised dots with respect to the working electrode, so that germanium ions preferentially enter into the Ga nanospheres and reach the working electrode through the Ga nanospheres, forming a germanium deposit at the interface of the Ga nanospheres and the working electrode. With the constant-voltage electrodeposition, the germanium sediment is continuously increased, gallium is doped into the germanium sediment in the process, and finally the gallium sediment and the germanium sediment form a nanowire structure to obtain the germanium-gallium nanowire.
The method for applying the germanium-gallium nanowires as the electrode material in the lithium ion battery is not particularly limited, and the method known by the technical personnel in the field can be adopted. In the invention, the lithium ion battery preferably uses germanium-gallium nanowires as a working electrode, a lithium sheet as a counter electrode, a polyethylene microporous membrane as a diaphragm and 1mol/L LiPF6A mixed solution dissolved in ethylene carbonate-ethylene carbonate (EC-DEC) is used as an electrolyte; wherein the volume ratio of EC to DEC in the electrolyte is preferably 1: 1.
the technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
1-Ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide salt ([ EMIm ] m) in a glove box filled with argon and having a water oxygen content of less than 2ppm]Tf2N) vacuum distilling the ionic liquid at 100 deg.C for 24h, and mixing the obtained ionic liquid with GaCl3(99.999%) and GeCl4(99.9999%) and stirred at 500rpm for 12h at room temperature to give 1mol/L GaCl3Electrolyte and 1mol/L GeCl4An electrolyte;
sequentially cleaning a Cu substrate with acetone and isopropanol, soaking in 10% hydrochloric acid for 1min to remove surface oxide, and taking the Cu substrate as a working electrode, a silver wire as a reference electrode and a platinum sheet as a pairElectrodes, using a Teflon cell to limit the deposition area to 1.5cm2GaCl heated to 60 ℃ was separately prepared using 2273 electrochemical workstation (princetonconnected Research)3Electrolyte and GeCl4The electrolyte is scanned by a cyclic voltammetry curve, the reduction voltage of gallium in the obtained cyclic voltammetry curve is the voltage when gallium is electrodeposited at constant voltage, and the reduction voltage of germanium in the obtained cyclic voltammetry curve is the voltage when germanium is electrodeposited at constant voltage; wherein the GaCl is added3When the cyclic voltammetry curve scanning is carried out on the electrolyte, the scanning range is-2.0-0V; the scanning rate is 50 mV/s; the equilibration time was 15 s; adding the GeCl4When the cyclic voltammetry curve scanning is carried out on the electrolyte, the scanning range is-2.5-0V; the scanning rate is 50 mV/s; the equilibration time was 15 s.
FIG. 1 is GaCl3Cyclic voltammogram (a) and GeCl of electrolyte4As for the cyclic voltammogram (b) of the electrolyte, a reduction peak was observed in the negative potential region of FIG. 1(a), and Ga was observed3+Peak of → Ga; in FIG. 1(b), two reduction peaks in the negative potential region are Ge4+→Ge2+With Ge2+Reduction peak of → Ge. According to the figure 1, the invention selects the constant voltage electrodeposition of gallium under the condition of-1.0 to-1.5V and the constant voltage electrodeposition of germanium under the condition of-1.8 to-2.2V.
Example 2
FIG. 2 is a schematic diagram of a process for depositing germanium-gallium nanowires on a Cu substrate, which comprises the following steps:
1-Ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide salt ([ EMIm ] m) in a glove box filled with argon and having a water oxygen content of less than 2ppm]Tf2N) vacuum distilling the ionic liquid at 100 deg.C for 24h, mixing the obtained ionic liquid with GaCl3(99.999%) and GeCl4(99.9999%) and stirred at 500rpm for 12h at room temperature to give GaCl3Concentration and GeCl4Electrolyte with the concentration of 1 mol/L;
sequentially cleaning a Cu substrate with acetone and isopropanol, soaking in 10% hydrochloric acid for 1min to remove surface oxide, taking the Cu substrate as a working electrode, a silver wire as a reference electrode and a platinum sheet as a counter electrode, and limiting deposition by using a polytetrafluoroethylene electrolytic cellThe area is 1.5cm2Adopting 2273 electrochemical workstation (princetonedplied research) to deposit gallium 60s in the electrolyte at the temperature of 60 ℃ and under the voltage of-1.5V for constant voltage electrodeposition, and obtaining gallium deposit on the surface of the working electrode; and continuously performing constant-voltage electrodeposition on the germanium for 300s under the conditions of 60 ℃ and-2.0V to obtain the germanium-gallium nanowire on the surface of the working electrode.
The gallium deposit obtained in the constant voltage electrodeposition process and the germanium-gallium nanowire finally obtained are characterized, and the results are as follows:
FIG. 3 is a scanning electron image of gallium deposit after constant voltage electrodeposition for 60s on a Cu substrate, with a magnification of 2 ten thousand times; as can be seen from FIG. 3, the gallium deposits are spherical (Ga nanospheres) with particle sizes ranging from 30 to 60 nm.
FIG. 4 is a scanning electron image of the germanium-gallium nanowire after the constant-voltage electrodeposition for 300s on the Cu substrate, with the magnification of 2 ten thousand times; as can be seen from FIG. 4, the finally obtained deposit is nanowires, the diameter of each nanowire is 50-100 nm, and most of the nanowires are in a twisted form and are obviously thinned along the axial direction.
Fig. 5 is a transmission electron microscope image of a single ge-ga nanowire, from which it can be seen that the length of the ge-ga nanowire exceeds 700 nm.
Fig. 6 is an electron diffraction image of a selected region of the ge-ga nanowire, in which there are no diffraction spots of a regular lattice, and the whole shows a polycrystalline diffraction ring, which indicates that the ge-ga nanowire is in a polycrystalline state.
FIG. 7 is a graph of X-ray photoelectron spectroscopy of germanium-gallium nanowires after 120s etching without argon ion etching. When no argon ion etching exists, the original data are subjected to peak separation processing, and the appearance of germanium oxide and gallium oxide can be observed, because the sample is placed into a test instrument to be in inevitable air contact; after 120s of etching, the peak position of the oxide nearly disappears, which shows that the germanium-gallium nanowire is only surface oxidized. And, after 120s of etching, the germanium and gallium contents were 77% and 8.7%, respectively, which resulted in an atomic content ratio of germanium to gallium of about 9: 1. this also indicates that gallium is doped into the interior of the nanowire and not merely present at the surface of the nanowire.
Example 3
The germanium-gallium nanowires are used as working electrodes and assembled in a CR2025 button battery case to prepare a half battery, a lithium sheet is used as a counter electrode, a polyethylene microporous membrane is used as a diaphragm, and 1mol/L LiPF is used6The mixed solution dissolved in ethylene carbonate-ethylene carbonate (EC-DEC) is used as an electrolyte (wherein the volume ratio of EC to DEC is 1: 1), and a new power cell test system (Shenzhen, China) is used for testing the charge and discharge performance of the cell, and the results are as follows:
fig. 8 is an optical photograph of ge-ga nanowires on a Cu substrate and an assembled CR2025 half cell.
FIG. 9 is a graph of cycle stability and coulombic efficiency of germanium-gallium nanowire electrode half-cell test, with a cycle current density of 0.32A/g; as can be seen from fig. 9, the first discharge and charge specific capacities of the Ge — Ga nanowires were 1730 and 1537mAh/g, respectively, and the initial coulombic efficiency was 89%. Compared with the three-dimensional ordered macroporous materials Ge, Ge nanotubes and Ge nanowires prepared by the ionic liquid electrodeposition (the initial coulombic efficiencies are 58%, 77% and 81% respectively) reported previously, the initial coulombic efficiency of the Ge-Ga nanowires is improved; and starting from the second cycle, the coulomb efficiency can be kept above 95%; the discharge capacity after 50 cycles is 1414mAh/g, and the Ge-Ga nanowire electrode can still maintain the capacity of 1146mAh/g even after 150 cycles. The reversible specific capacity of the germanium nanowire after 100 cycles is 1130mAh/g, which is reported in the literature (YUAN et al, ACS Nano,2012,6(11): 9932-.
FIG. 10 is a graph of specific capacity of Ge-Ga nanowire electrode half-cell tests under different current densities; as can be seen from FIG. 10, the test started at 0.16A/g, increased to current densities of 0.32, 0.8, 1.6, 3.2, 8 and 16A/g after 5 cycles, and then returned to 0.16A/g. The discharge capacities of the Ge-Ga nanowires at 0.16, 0.32, 0.8, 1.6, 3.2, 8 and 16A/g are 1621, 1506, 1409, 1331, 1242, 977 and 687mAh/g respectively; when the current density returns to 0.16A/g, the capacity is restored to 1422mAh/g, and the capacity retention rate reaches 87%. The result shows that the Ge-Ga nanowire prepared by ionic liquid electrodeposition can improve the battery cycle performance and rate performance of the pure germanium anode.
Fig. 11 is a scanning electron microscope image of the Ge-Ga nanowire after 150 cycles of cycling, and it can be seen from the image that the Ge-Ga nanowire still retains its basic shape and is not broken after 150 cycles of charging and discharging, but the diameter of the Ge-Ga nanowire is a little larger, indicating that the Ge-Ga nanowire undergoes volume expansion during the charging and discharging cycles. In addition, the surface of the Ge-Ga nanowire becomes rough and has pores and grooves, and a remarkable texture is formed on the surface of the Ge-Ga nanowire. The porous structure on the germanium gallium Ge-Ga nanowire can provide continuous electric conduction and ion transportation paths, so that the diffusivity of lithium ions is improved, and the stress of volume expansion can be released, so that the structure becomes stable.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (9)

1. The application of the germanium-gallium nanowire as the electrode material of the lithium ion battery is characterized in that the germanium-gallium nanowire comprises elemental germanium and elemental gallium in chemical composition, and the atomic ratio of the elemental germanium to the elemental gallium in the germanium-gallium nanowire is (4-9): 1;
the preparation method of the germanium-gallium nanowire comprises the following steps:
in the environment with water oxygen content lower than 2ppm, adding GaCl3、GeCl4Mixing with ionic liquid to obtain electrolyte;
performing constant-voltage electrodeposition on gallium in the electrolyte at 55-65 ℃ and under the condition of-1.0 to-1.5V by adopting a three-electrode electrochemical system comprising a working electrode, a counter electrode and a reference electrode, and obtaining gallium deposits on the surface of the working electrode; and continuously performing constant-voltage electrodeposition on germanium at the temperature of 55-65 ℃ and under the pressure of-1.8-2.2V, and obtaining the germanium-gallium nanowire on the surface of the working electrode.
2. The use according to claim 1, wherein the germanium-gallium nanowires have a diameter of 50 to 100nm and a length of 500 to 1000 nm.
3. Use according to claim 1, wherein the ionic liquid comprises 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide salt, 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide salt or N-butyl-N-methylpiperidinium bis (trifluoromethylsulfonyl) imide salt.
4. Use according to claim 1, wherein the GaCl in the electrolyte is3The concentration of (A) is 0.09-0.11 mol/L; GeCl4The concentration of (b) is 0.09-0.11 mol/L.
5. The application of claim 1, wherein the method for obtaining the deposition voltage required for constant voltage electrodeposition of gallium and germanium comprises the following steps:
in the environment with water oxygen content lower than 2ppm, adding GaCl3Mixing with ionic liquid to obtain GaCl3An electrolyte; adding GeCl4Mixing with ionic liquid to obtain GeCl4An electrolyte;
the GaCl is applied by a three-electrode electrochemical system comprising a working electrode, a counter electrode and a reference electrode3Electrolyte and GeCl4And respectively scanning cyclic voltammetry curves by the electrolyte, wherein the reduction voltage of gallium in the obtained cyclic voltammetry curves is the voltage when gallium is electrodeposited at constant voltage, and the reduction voltage of germanium in the obtained cyclic voltammetry curves is the voltage when germanium is electrodeposited at constant voltage.
6. The use according to claim 1, wherein the gallium is electrodeposited at constant voltage for a period of 30 to 60 seconds.
7. The use of claim 1, wherein the gallium deposits are liquid microspheres and have a particle size of 30 to 60 nm.
8. The use according to claim 1, wherein the germanium is electrodeposited at constant voltage for a period of 150 to 300 seconds.
9. The application of any one of claims 1 to 8, wherein the lithium ion battery comprises 1mol/L LiPF (lithium ion power factor) and a 1mol/L LiPF (lithium ion power factor) as a working electrode, a lithium sheet as a counter electrode, a polyethylene microporous membrane as a diaphragm6The mixed solution of ethylene carbonate and diethyl carbonate dissolved therein was used as an electrolyte.
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