Preparation method of hollow germanium nanometer onion for lithium ion battery negative electrode

Abstract

The application is a preparation method of hollow germanium nano-onions for lithium ion battery negative electrode. The method adopts arc melting method to prepare Al (100‑x) Ge x The precursor alloy ingot (wherein x is the atomic percentage of germanium, x=2-5) is obtained, then the precursor strip is obtained by using melt spinning technology, the composition uniformity is increased by using mechanical ball milling to obtain the precursor powder, finally, the aluminum element is filtered out by using dealloying technology, and the germanium negative electrode material with hollow onion structure is obtained. The germanium negative electrode material prepared by the application has smaller size than the previous germanium material, the preparation method and process are simpler and more environmentally friendly, and the hollow germanium nano-onion structure used as the lithium ion battery negative electrode material shows structural and performance advantages.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery negative electrode material, in particular to a preparation method of hollow germanium nano-onion for lithium ion battery negative electrode. BACKGROUND

[0002] Germanium (Ge) is a group IV element, as a negative electrode material of lithium ion battery, has the advantages of high specific capacity, good electrical conductivity and fast lithium ion diffusion rate. Ge has serious volume change during charging and discharging, which causes material pulverization and rapid capacity decay. Preparing Ge into various nanostructures can effectively alleviate the loss of capacity and improve the cycle stability of the battery. In recent years, researchers around the world have carried out extensive research on germanium-based lithium ion battery negative electrode materials and have made certain achievements.

[0003] CN115132989A discloses a preparation method of carbon-coated porous germanium composite material. The sample is a porous germanium / carbon core-shell structure composite material, and the materials do not contact each other and do not form a network structure. The preparation method is to heat the magnesium germanate for 10-25 hours, and then perform carbon coating in an acetylene atmosphere. The process has a long heat treatment time, which increases the preparation period. In addition, the carbon coating is performed in a special gas at 600-750°C, which has high production cost and high process complexity. CN113809314A discloses a preparation method and application of porous silicon-carbon or porous germanium-carbon material. The material is a porous spherical structure, and the spherical particle diameter is large, reaching about 20 pm. The specific surface area is low, which is not conducive to the stable maintenance of the electrochemical performance. In addition, the network structure is not formed. The preparation process obtains micron-sized lithium-zinc-silicon or lithium-zinc-germanium alloy powder through a gas atomization powdering process. The process has high requirements for equipment, and the preparation process needs carbon coating treatment, which increases the equipment cost and process complexity. CN114242960A discloses a hollow spherical particle negative electrode material with an open structure, a preparation method and application thereof. The negative electrode material is composed of a metal oxide and carbon. The method mixes a metal salt solution with urea to configure a precursor solution, and then performs ultrasonic atomization. The precursor solution enters a pyrolysis device through a carrier gas flow to perform pyrolysis. The related process needs professional equipment, which increases the equipment cost and process complexity. In addition, urea has volatility, which has potential threats to the environment and workers' health. Moreover, the preparation method is limited by the product composition of the metal oxide, and cannot prepare metal-state particle materials. CN108281627A discloses a germanium-carbon composite negative electrode material for lithium ion batteries and a preparation method thereof. The germanium-carbon composite negative electrode material is a spherical particle, and the particle diameter is 0.5-10 pm. The particle diameter is large, which will cause obvious particle cracking in the later high-temperature heat treatment and material electrochemical cycling process, thereby affecting the electrochemical performance of the material. In addition, the precursor particles need to be heat treated in a H2 / Ar mixed atmosphere, and the heat treatment temperature is 650-1000°C. The process has high process complexity, high energy consumption and high production cost. The paper Journal of Colloid and Interface Science 2021, 592, 103-115 (DOI: 10.1016 / j.j.2021.02.026) discloses a preparation method of a three-dimensional nano Ge negative electrode with improved cycle stability by embedding Ag nanoparticles. The method obtains a precursor strip through arc melting and melt spinning. The strip is etched in HF solution and HCl solution, respectively, to obtain a germanium-based nano porous ligament network material. The germanium content in the precursor of the material is high, and the porous ligament obtained finally is wide (about 30 nm), and the network size is large. The preparation method needs to be etched in two acidic solutions, one of which is toxic HF solution, which increases the process complexity and threatens the health of the operators. In addition, the method needs to be etched in a mixed solution of HF and HCl, which has high production cost and high process complexity. -1The reversible capacities of the three germanium-based nanoporous materials are 529 mAh g -1 , 953 mAh g -1 , and 204 mAh g -1 , all less than 1000 mAh g -1 , and the electrochemical performance of the obtained materials needs to be improved. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of hollow germanium nano-onions for lithium ion battery negative electrodes in view of the deficiencies in the prior art. (100-x) Ge x The Al (100-x) Ge x intermediate alloy ingot is prepared by vacuum arc melting at 940-950 DEG C, wherein 2≤x≤5, atomic percentage; then the intermediate alloy ingot is remelted at 700-750 DEG C by an induction coil of a vacuum strip caster, and the melt is sprayed onto a copper wheel rotating at 1800-2500 r / min after being kept in a molten state for 3-5 seconds, with a spraying pressure difference of 0.7-1.0 MPa, to obtain a precursor strip with a thickness of 20-30 microns, a width of 2.0-3.0 mm, and a length of 60-90 cm per section.

[0005] The technical scheme of the present application is as follows:

[0006] A preparation method of hollow germanium nano-onions for lithium ion battery negative electrodes, comprising the following steps:

[0007] First, a precursor strip is prepared

[0008] First, a vacuum arc melting furnace is used to melt Al Ge

[0009] intermediate alloy ingot from pure Ge and pure Al ingots at 940-950 DEG C, wherein 2≤x≤5, atomic percentage; then the intermediate alloy ingot is remelted at 700-750 DEG C by an induction coil of a vacuum strip caster, and the melt is sprayed onto a copper wheel rotating at 1800-2500 r / min after being kept in a molten state for 3-5 seconds, with a spraying pressure difference of 0.7-1.0 MPa, to obtain a precursor strip with a thickness of 20-30 microns, a width of 2.0-3.0 mm, and a length of 60-90 cm per section.

[0010] The purity of the pure Ge and pure Al is both 99.95%, mass percentage;

[0011] The precursor strip is ball milled at a rotating speed of 600-1000 r / min for 4-8 h by using a mechanical ball milling method, a volume ratio of the milling ball to the precursor strip is (4-5):1, and a precursor powder with a particle size of 1-3 μm is obtained;

[0012] Third step, preparation of hollow germanium nano-onions

[0013] The precursor powder prepared in the second step is immersed in an HCl solution at 45-65 ℃ for 7-12 h to remove alloying, then washed with ultrapure water for 2-4 times, and then vacuum dried at 50-70 ℃ for 7-12 h, so that the hollow germanium nano-onion material is obtained;

[0014] In the formula, 2-3 grams of the precursor powder is added into 300-500 ml of the HCl solution, and the concentration of the HCl solution is 0.5-1.0 M.

[0015] The ultrapure water has a resistivity of 18.2 MΩ·cm.

[0016] The obtained material is a nanoscale aggregate formed by the hollow germanium nano-onions in contact with each other, each nano-onion is an independent structure, but in contact with each other to form a hollow germanium nano-onion porous network, wherein the diameter of the hollow germanium nano-onions is 10-14 nm, the diameter of the internal cavity is 8-12 nm, and the specific surface area is about 250-350 m 2 / g.

[0017] The hollow germanium nano-onion material prepared by the method is used for a lithium ion battery negative electrode material.

[0018] The raw materials and equipment used in the preparation method of the hollow germanium nano-onion for a lithium ion battery negative electrode are obtained through a known way, and the operation process is mastered by a person skilled in the art.

[0019] The substantial features of the present application are:

[0020] Firstly, in the prior art, the atomic percentage of germanium in the precursor is usually 10-30%, which is relatively high, and this is to obtain a continuous porous ligament network structure so as to reduce the interface resistance, but such a high germanium content makes the diameter of the porous ligament relatively large (tens of nanometers), and when the porous ligament is used as a lithium ion battery negative electrode material for long-term charge and discharge cycles, there is a limitation that the active material is coarsened and pulverized, and the electrochemical performance is deteriorated, and the atomic percentage of germanium in the precursor Al (100-x) Ge xThe Ge content in the Ge (2≤x≤5) alloy ingot is less, so that the Ge element concentration is low during the dealloying process, and the network of tough bands cannot be connected, but a special structure of a hollow spherical particle (several nanometers) network is formed, and the cost of raw materials is reduced, and the high electrochemical performance can be maintained when the lithium ion battery negative electrode material is subjected to long-term charge and discharge cycles; secondly, the porous spherical particles or porous tough band network are mostly prepared by the current technology, and the hollow Ge nano-onions prepared by the present application contact each other to form a network, and the structure can accelerate the penetration of the electrolyte and the transmission rate of Li + ; thirdly, the size of the Ge material prepared in the prior art is large, generally 0.5-20 mu m in diameter, and only a few can reach 30 nm, while the diameter of the hollow Ge nano-onions prepared by the present application is only 10-14 nm, which is not easy to crack and powder during the electrochemical cycle process, and the cycle stability of the material can be improved. In the preparation method, the substantial characteristics of the present application are as follows: first, the material particle size is not easy to control in the nanometer level by the chemical synthesis method in the past, and the ball milling process is adopted in the present application to increase the uniformity of the precursor composition, and at the same time, the size of the precursor material is reduced, so that no large size phase in the precursor material is inherited into the product, the size of the dealloying product is only several nanometers, and the hollow onion structure is formed, which brings higher electronic and ionic transmission rate, and sufficient volume buffer space, and improves the electrochemical performance of the negative electrode material; secondly, the carbon layer coating process is not involved in the dealloying reaction process, and the heat treatment does not need to be carried out in a special atmosphere, which reduces the process complexity and saves the production cost; thirdly, compared with the previous work, the present application does not need to dope Ag and other conductive metal elements during the preparation process, which reduces the cost of raw materials; fourthly, compared with the etching liquid in the past, the concentration of the etching liquid used in the present application is low, and no toxic reagent is used, which is harmless to the environment and does not harm human health; fifthly, compared with the previous technology, the process of the present application is simple, and is beneficial to large-scale production.

[0021] The beneficial effects of the present application are as follows:

[0022] The Al (100-x) Ge x (2≤x≤5) alloy ingot is prepared by using the melt spinning and ball milling technology, and the hollow Ge nano-onions network structure is obtained by etching and drying, which is suitable for electronic and ionic transmission and is suitable for being used as a lithium ion battery negative electrode material.

[0023] (1) the preparation method of the hollow Ge nano-onions for the lithium ion battery negative electrode, the hollow Ge nano-onion network structure can improve the electronic and lithium ion transmission rate, and the material can be used as a lithium ion battery negative electrode material. -1After 100 cycles under the above conditions, the reversible capacity remained 1001 mAh g -1 , which is 43% higher than the reversible capacity of 700 mAh g of the sandwich structure Ge / NrGO nanocomposite obtained in the previous study (Crystals 2022, 11, 12 (DOI:10.3390 / cryst11121582)), and is more conducive to the stability of electrochemical performance and is more suitable for use as a negative electrode material for lithium ion batteries. -1

[0024] (2) The preparation method of the hollow germanium nanometer onion for the negative electrode of the lithium ion battery has a small diameter of the hollow nanometer onion, only 10-14 nm, a large specific surface area of 250-350 m 2 / g (about 2-70 m 2 / g of the microporous particles (0.5-20 μm) obtained by the prior art), is conducive to the deintercalation of lithium ions, and provides sufficient volume buffer space for the electrochemical process, which can significantly improve the cycle stability.

[0025] (3) The preparation method of the hollow germanium nanometer onion for the negative electrode of the lithium ion battery uses simple methods such as melt spinning, ball milling and dealloying to synthesize the material, and the preparation process does not involve carbon coating and other processes, and does not need to be treated for a long time in a special atmosphere environment, so the process is simple, the equipment complexity is reduced, and the production is suitable for large-scale production.

[0026] (4) The preparation method of the hollow germanium nanometer onion for the negative electrode of the lithium ion battery has simple raw material composition of the prepared hollow germanium nanometer onion, and the atomic percentage of germanium in the precursor material is only 2-5%, which is much lower than the atomic percentage of germanium in the precursor in the prior art (10-30%), and no other noble metal elements such as Ag are doped in the synthesis process, so the raw material cost is significantly low.

[0027] (5) The preparation method of the hollow germanium nanometer onion for the negative electrode of the lithium ion battery has low solution concentration required for material preparation, and no toxic reagents are used, so there is no potential threat to the environment and the health of workers. BRIEF DESCRIPTION OF DRAWINGS

[0028] The application will be further described below in combination with the drawings and examples.

[0029] Figure 1 The low-magnification transmission electron microscope morphology diagram of the hollow germanium nanometer onion material prepared in Example 1.

[0030] Figure 2 The high-magnification transmission electron microscope morphology diagram of the hollow germanium nanometer onion material prepared in Example 1.

[0031] Figure 3 ​X-ray diffraction pattern of the hollow germanium nano-onion material prepared in Example 1.

[0032] Figure 4 Cycling performance test curve of the lithium ion battery using the hollow germanium nano-onion prepared in Example 1 as negative electrode material. DETAILED DESCRIPTION

[0033] Example 1

[0034] First step, preparation of precursor strip

[0035] First, a vacuum arc melting furnace was used to melt Al 98 and pure Ge (purity 99.95%) ingots into Al Ge2intermediate alloy ingot at 940℃. Subsequently, the intermediate alloy ingot was remelted by the induction coil of a vacuum strip caster at 750℃, and after keeping the melt in a molten state for 3 seconds, the melt was sprayed onto a copper wheel rotating at 2500r / min at a spraying pressure difference of 1.0MPa, to obtain a precursor strip with a thickness of 20μm, a width of 3.0mm, and a length of 60cm per section.

[0036] Second step, preparation of precursor powder

[0037] The precursor strip was ball-milled at a speed of 800r / min for 6h using a mechanical ball-milling method, and the volume ratio of grinding ball (diameter 3mm) to precursor strip was 4:1, to obtain a precursor powder with a particle size of 2μm.

[0038] Third step, preparation of hollow germanium nano-onion

[0039] Two grams of the precursor powder prepared in the second step were de-alloyed in 300ml of 1.0M HCl solution at 65℃ for 7h, then washed twice with ultrapure water, and then vacuum dried at 70℃ for 7h, to obtain a hollow germanium nano-onion material.

[0040] The ultrapure water has a resistivity of 18.2MΩ·cm.

[0041] Figures 1-2 The transmission electron microscope morphology of the hollow germanium nano-onion prepared in Example 1 is shown in the figure, in which the hollow germanium nano-onions are aggregated and in contact with each other to form a hollow germanium nano-onion network. The diameter of the nano-onions is 12nm, the cavity diameter is 10nm, the specific surface area is about 300m 2 / g, the material has good integrity, and the surface is free of cracks. Figure 3 The X-ray diffraction pattern of the material is shown in the figure, in which there are obvious diffraction peaks of germanium in the range of 25-55° diffraction angle, and no other impurity peaks are observed, indicating that the sample only contains germanium phase and does not have oxidation phenomenon.

[0042] The hollow germanium nano-onion negative electrode material prepared in this example was used to assemble lithium ion batteries and perform performance tests. The method is as follows:

[0043] The hollow germanium nano-onion material was used as the negative electrode, lithium metal was used as the counter electrode, 1.0M LiPF6 in ethyl carbonate-diethyl carbonate (volume ratio 1:1) was used as the electrolyte, and porous polypropylene was used as the separator. The battery was packaged in an argon-filled glove box, and the packaged battery (model CR2032) was placed for 6 hours before performance testing at 25°C using a battery testing system. Figure 4 The cycle performance test curve of the lithium ion battery prepared in this example 1 is shown in the figure. The battery showed good reversible capacity and cycle stability. After 100 cycles at 100mA g -1 , the reversible capacity remained at 1001mAh g -1 . Compared with the reversible capacity of 953mAh g -1 of the germanium negative electrode material in the prior work (Journal of Colloid and Interface Science 2021, 592, 103-115 (DOI: 10.1016 / j.j.2021.02.026)), the capacity was increased by 5%, and the material did not contain silver (Ag), saving the cost of raw materials. In addition, the reversible capacity of the sandwich structure Ge / NrGO nanocomposite obtained in this example is 700mAh g -1 , which is 43% higher than that of the prior research (Crystals 2022, 11, 12 (DOI: 10.3390 / cryst11121582)). The above shows that the hollow germanium nano-onion prepared in this example as a lithium ion battery negative electrode material exhibits better cycle stability than the general structure.

[0044] Example 2

[0045] First step, preparation of precursor strip

[0046] First, a vacuum arc melting furnace was used to melt the Ge and Al (99.95%, mass percentage) ingot into an Al 97 Ge3 (atomic percentage) intermediate alloy ingot at 945°C. Subsequently, the intermediate alloy ingot was remelted at 730°C by the induction coil of a vacuum tape casting machine, and after maintaining the molten state for 4 seconds, the melt was sprayed onto a copper wheel rotating at 2300r / min at a pressure difference of 0.8MPa. The precursor strip with a thickness of 25μm, a width of 2.5mm, and a length of 70cm was obtained.

[0047] Second step, preparation of precursor powder

[0048] The precursor strip is ball milled at 1000 r / min for 4 h by a mechanical ball milling method, a volume ratio of the milling ball (3 mm in diameter) to the precursor strip is 5:1, and a particle size of the precursor powder is 1 μm.

[0049] Third step, preparing hollow germanium nano-onions

[0050] The 3 g of the precursor powder prepared in the second step is dealloyed in 400 ml of 0.8 M HCl solution at 55 °C for 12 h, then washed with ultrapure water for 3 times, and then vacuum dried at 60 °C for 8 h, to obtain the hollow germanium nano-onion material.

[0051] The obtained nano-onions have a diameter of 10 nm, a cavity diameter of 8 nm, and a specific surface area of about 350 m 2 / g. The ultrapure water has a resistivity of 18.2 MΩ·cm.

[0052] Example 3

[0053] First step, preparing a precursor strip

[0054] First, a Ge and Al (99.95%, mass percentage) ingot is melted into an Al 95 Ge5 (atomic percentage) intermediate alloy ingot at 950 °C by a vacuum arc melting furnace. Subsequently, the intermediate alloy ingot is remelted at 700 °C by an induction coil of a vacuum strip caster, and the melt is sprayed onto a copper wheel rotating at 1800 r / min after being kept in a molten state for 5 seconds, to obtain a precursor strip with a thickness of 30 μm, a width of 2 mm, and a length of 90 cm.

[0055] Second step, preparing a precursor powder

[0056] The precursor strip is ball milled at 600 r / min for 8 h by a mechanical ball milling method, a volume ratio of the milling ball (3 mm in diameter) to the precursor strip is 4.5:1, and a particle size of the precursor powder is 3 μm.

[0057] Third step, preparing hollow germanium nano-onions

[0058] The 2.5 g of the precursor powder prepared in the second step is dealloyed in 500 ml of 0.5 M HCl solution at 45 °C for 10 h, then washed with ultrapure water for 4 times, and then vacuum dried at 50 °C for 12 h, to obtain the hollow germanium nano-onion material.

[0059] The obtained nano-onions have a diameter of 14 nm, a cavity diameter of 12 nm, and a specific surface area of about 250 m 2 / g. The ultrapure water has a resistivity of 18.2 MΩ·cm.

[0060] Comparative Example 1:

[0061] Al 85 Ge 15 The precursor was subjected to a dealloying process, and other conditions were the same as in Example 1. The surface micro-morphology of the sample was observed, and no hollow germanium nano-onion structure was obtained, only a porous germanium nano-filament network was obtained, and the filament size was large, 5 times the diameter of the present application. When used as a negative electrode material for lithium ion batteries, the capacity retention rate exhibited after 100 cycles at 100 mA g -1 < conditions was less than 3 / 5 of that of Example 1.

[0062] Comparative Example 2:

[0063] The ball mill rotation speed was set to 300 r / min, and other conditions were the same as in Example 1. The surface micro-morphology of the sample was observed, and no hollow germanium nano-onion network was obtained. When used as a negative electrode material for lithium ion batteries, the capacity retention rate exhibited was less than 1 / 2 of that of Example 1.

[0064] Comparative Example 3: The dealloying corrosion concentration was set to 0.2 M, and other conditions were the same as in Example 1. The surface micro-morphology of the sample was observed, and no hollow germanium nano-onion network was obtained, but a microsphere structure with a diameter of 20-40 nm was obtained. When used as a negative electrode material for lithium ion batteries, the capacity retention rate exhibited was less than 3 / 4 of that of Example 1.

[0065] Comparative Example 1 obtained a porous filament network after dealloying due to the high germanium content in the precursor. The filament was relatively thick, and there was no cavity structure. The specific surface area was low, the number of active sites provided was reduced compared to Example 1, the volume expansion buffer area was greatly reduced, the material cracking area was increased, and the electrochemical stability exhibited was greatly reduced. In Comparative Example 2, the rotation speed was low, the uniformity of the precursor powder composition was reduced, the phase size formed was increased, the product size was increased, and the electrochemical performance of the material was affected. In Comparative Example 3, the corrosion liquid concentration was reduced, which reduced the sample corrosion kinetics, the product was not completely corroded, the size was increased, active material cracking and pulverization occurred during the electrochemical process, and the cycle stability was ultimately reduced.

[0066] The above examples and comparative examples illustrate that a preparation method of a hollow germanium nano-onion for a lithium ion battery negative electrode is developed through continuous attempts at arc melting, melt spinning, ball milling, and dealloying conditions, strict control of each process link, and multiple practices.

[0067] The details of the present application are well known.

Claims

1. A method for preparing hollow germanium nanooionp of lithium ion battery anode, The method is characterized in that the method comprises the following steps: The first step is to prepare a precursor strip First, the pure Ge and pure Al ingot are melted into Al (100-x) Ge x The intermediate alloy ingot is remelted by an induction coil of a vacuum spinning machine at 700-750 ℃, and after being kept in a molten state for 3-5 seconds, the melt is sprayed onto a copper wheel rotating at 1800-2500 r / min at a spraying pressure difference of 0.7-1.0 MPa to obtain a precursor strip with a thickness of 20-30 μm and a width of 2.0-3.0 mm. The second step is to prepare a precursor powder The precursor strip is ball milled at a rotating speed of 600-1000 r / min by using a mechanical ball milling method, the ball milling time is 4-8 h, the volume ratio of the milling ball to the precursor strip is (4-5):1, and the precursor powder with a particle size of 1-3 μm is obtained; The third step is to prepare a hollow germanium nano-onion The precursor powder prepared in the second step is immersed in an HCl solution at 45-65 ℃ for 7-12 h to remove the alloy, then washed with ultrapure water for 2-4 times, and then vacuum dried at 50-70 ℃ for 7-12 h, so that the hollow germanium nano-onion material is obtained; 2-3 grams of the precursor powder are added into every 300-500 ml of the HCl solution; The purity of the pure Ge and the pure Al is both 99.95%; In the third step, the concentration of the HCl solution is 0.5-1.0 M; and the resistivity of the ultrapure water is 18.2 MΩ·cm; The obtained material is a nanoscale aggregate formed by hollow germanium nanometer onions contacting each other, each nanometer onion being an independent structure but contacting each other, forming a hollow germanium nanometer onion porous network, wherein the hollow germanium nanometer onion has a diameter of 10-14 nm, the internal cavity has a diameter of 8-12 nm, and the specific surface area is 250-350 m 2 / g.

2. The application of the hollow germanium nano-onion material prepared by the method of claim 1 is used for a lithium ion battery negative electrode material.

Images