A method for preparing GeO2 micron balls for lithium-ion battery negative electrode

Abstract

The present invention is a method for preparing GeO2 micron balls for lithium ion battery negative electrode. The method comprises the following steps: first, using a vacuum arc melting furnace to melt Al and Ge to form Al (100‑x) Ge x The master alloy ingot is cast and the melt is then sprayed onto a copper wheel to produce a precursor strip. The precursor strip is then ball-milled to produce a precursor powder with a particle size of 2-4 μm. Finally, the precursor powder is immersed in an HCl solution for dealloying for 8-12 hours to obtain GeO2 microspheres. The germanium dioxide anode material prepared by this method is simpler and more environmentally friendly than previous methods and processes. The microspheres are uniform in size and exhibit structural and performance advantages when used as a lithium-ion battery anode material.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery negative electrode materials, in particular to a method for preparing GeO2 micron balls for lithium ion battery negative electrodes. Background Art

[0002] Lithium-ion batteries have high energy density and excellent long cycle life, and are of great significance in energy storage applications such as electric vehicles and portable electronic products. Germanium, as the negative electrode material of lithium-ion batteries, has advantages such as low operating voltage platform, low volume expansion and high diffusion coefficient. The introduction of appropriate proportion of tin can improve the activity of germanium materials and promote the electrochemical reaction rate. Germanium-based negative electrode materials (Ge, GeO, GeO x If the lithium-ion insertion / deinsertion process is reversible, the theoretical capacity of GeO2 can reach up to 2125 mAh / g. Germanium dioxide, as a germanium-based anode material, has attracted widespread attention due to its high theoretical capacity.

[0003] In the prior art, CN115224261A discloses a carbon-coated amorphous micron GeO xA method for preparing a spherical particle composite negative electrode material. The sample is a micron-sized spherical particle. Its preparation process requires sintering in a reducing atmosphere after ball milling, which is highly complex. In addition, when preparing the precursor powder, the suspension needs to be transferred to a high-temperature and high-pressure reactor for reaction for 20 hours. This process requires specialized equipment, which increases equipment costs and prolongs the preparation cycle. 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 quasi-spherical particle. The preparation method utilizes germanium and ammonia water to form a germanium-containing solution, then adds glucose to the mixed solution, and obtains precursor particles after drying. During this process, ammonia water is volatile and toxic, posing a threat to environmental protection and the health of operators. In addition, the precursor particles need to be heat-treated in an H2 / Ar mixed atmosphere at a heat treatment temperature of 650-1000°C. This process has high process complexity and equipment complexity, increased energy loss, and high production costs. CN113087009A discloses a method for preparing mixed-phase germanium dioxide for use as a negative electrode material for lithium-ion batteries. This method involves dropwise adding an HF solution to a uniform mixture of germanium dioxide, ethanol, and water, placing the mixture in a reactor and reacting it for 40 hours. The mixture is then annealed in an argon atmosphere to obtain the mixed-phase germanium dioxide. This process is complex and has a long experimental cycle. In addition, the HF solution is toxic, posing a threat to the health of operators. The paper Electrochimica Acta 2019, 300, 363-372 (DOI: 10.1016 / j.electacta.2019.01.127) discloses a method for achieving stable lithium storage in a nanoporous GeO2 / Cu / Cu2O network. The method obtains Cu-Ge-Al precursor strips by arc melting and melt spinning, and obtains nanoporous network ligaments after dealloying. The composition of this process is relatively complex, and the introduction of copper elements increases the process cost. The resulting ligaments are large in size and low in porosity. There is a serious volume expansion problem during the charge and discharge process. The GeO2 / Cu / Cu2O composite material obtained by this method has a high charge and discharge current of 200mA g -1 After 50 cycles at a current density of 1.5 mAh g -1 , the electrochemical performance needs to be improved. In addition, the paper Chemical Physics Letters 2022, 801, 139747 (DOI: 10.1016 / j.cplett.2022.139747) discloses a method for synthesizing GeO2 / Ge composite materials by magnesium thermal reduction. This synthesis method involves high-temperature heat treatment of magnesium metal, which has certain safety risks. The resulting material is large in size and has uneven particle size. At 200mA g -1 After 40 cycles at a current density of 1.5, the capacity is only 520.2 mAh g -1 , the cycle stability needs to be improved. Summary of the Invention

[0004] The present invention addresses the shortcomings of current technology by providing a method for preparing GeO2 micron spheres for lithium-ion battery negative electrodes. This method utilizes arc melting to produce a precursor alloy ingot, followed by melt spinning to obtain precursor strips. Mechanical ball milling, alternating forward and reverse rotations, is then introduced to reduce the precursor size to 2-4 μm. Finally, a stirring step is added to the dealloying process to enhance the oxidation reaction of Ge, thereby forming the new dealloyed product, GeO2 micron spheres. The germanium dioxide negative electrode material prepared by this invention is simpler and more environmentally friendly than previous methods and processes for preparing materials. Furthermore, the micron spheres are uniform in size, exhibiting structural and performance advantages for use as a negative electrode material for lithium-ion batteries.

[0005] The technical solution of the present invention is:

[0006] A method for preparing GeO2 micron balls for lithium ion battery negative electrode, the method comprising the following steps:

[0007] The first step is to prepare the precursor strip

[0008] First, Al and Ge ingots are melted into Al at 980-1080℃ in a vacuum arc melting furnace. (100-x) Ge x A master alloy ingot, wherein 1≤x≤3, atomic percent; subsequently, remelting the master alloy ingot at 980-1080° C. through an induction coil of a vacuum strip spinning machine, maintaining the melt in a molten state for 3-5 seconds, and then spraying the melt onto a copper wheel rotating at a speed of 30-40 m / s with a spray pressure difference of 0.8-1.0 MPa to obtain a precursor strip having a thickness of 20-30 μm, a width of 2.0-3.0 mm, and a length of 60-120 cm;

[0009] Wherein, the purity of the Al and Ge ingots is 99.95wt.%, mass percentage;

[0010] Step 2: Prepare precursor powder

[0011] The precursor strips are mechanically ball milled at a speed of 800 to 1000 r / min for 12 to 48 hours, alternating between forward and reverse rotations. The milling direction is reversed every 20 to 40 minutes. The volume ratio of stainless steel grinding balls (2 to 5 mm in diameter) to precursor strips is (4 to 6):1, to obtain a precursor powder with a particle size of 2 to 4 μm.

[0012] Step 3: Preparation of GeO2 micron balls

[0013] The precursor powder obtained in the second step is immersed in an HCl solution for dealloying at 60-80°C for 8-12 hours, and the corrosion process is accompanied by mechanical stirring at a stirring rate of 60-100 rpm. Then, it is washed with anhydrous ethanol 3-5 times and then vacuum dried at 50-70°C for 8-12 hours to obtain GeO2 micron spheres.

[0014] Wherein, 0.1 to 0.5 grams of precursor powder is added to every 60 to 200 ml of HCl solution; the concentration of the HCl solution is 0.5 to 1.5M.

[0015] The spherical GeO2 particles in the obtained material are uniform in size and have a diameter of 1.5 to 2.5 μm.

[0016] The GeO2 micron ball material prepared by the method is used as a negative electrode material for lithium ion batteries.

[0017] The raw materials and equipment used in the above-mentioned method for preparing GeO2 micron balls for lithium-ion battery negative electrode are obtained through well-known routes, and the operating processes used are within the skill of those skilled in the art.

[0018] The essential features of the present invention are:

[0019] First, in the prior art, the atomic percentage of germanium in the precursor is mostly 10-20%, which is relatively high. (100-x) Ge x (1≤x≤3, atomic percentage) has a low germanium content, and after ball milling, spherical particles of uniform size are formed instead of being connected into a ligament network; secondly, compared with the previous porous structure, the product prepared by the present invention has a micron-spherical structure of uniform size. The micron-spherical structure can effectively promote the penetration of the electrolyte along its radial direction, ensure full contact between the electrolyte and the active material, reduce the lithium ion transmission distance, and accelerate the kinetic process of ion diffusion. In the preparation method, the essential features of the present invention are: first, a ball milling process is introduced during the precursor treatment process, and a forward and reverse alternating method is adopted to increase the uniformity of the precursor composition and reduce the precursor size to 2-4 μm; second, a stirring process is added during the dealloying process to make the oxidation reaction of Ge more complete, thereby forming a new dealloying product, GeO2 micron ball; third, the dealloying reaction process is different from the previous process, and does not involve a carbon layer coating process, and the heat treatment does not need to be carried out under a special atmosphere, which reduces the process complexity, simplifies the process, and saves production costs; fourth, compared with the previous etching solution, the etching solution used in the present invention has a low concentration and does not use toxic reagents, is harmless to the environment, and will not harm human health.

[0020] The beneficial effects of the present invention are:

[0021] The present invention uses Al (100-x) Gex The (1≤x≤3) alloy ingot is melt-spinned and ball-milled, and then dried by corrosion to obtain GeO2 micron spherical particles. This structure is suitable for electron and ion transport and is suitable for use as a negative electrode material for lithium-ion batteries. Specifically,

[0022] (1) The present invention provides a method for preparing GeO2 micron balls for lithium ion battery negative electrode. The obtained micron spherical structure can improve the transmission rate of electrons and lithium ions. The material is at 200mA g -1 After 50 cycles under the same conditions, the reversible capacity still remained at 904.1 mAh g -1 Compared with the GeO2 / Cu / Cu2O composite materials obtained in previous studies Electrochimica Acta 2019,300,363-372 (DOI:10.1016 / j.electacta.2019.01.127) and the GeO2 / Ge composite materials obtained in the paper Chemical Physics Letters 2022,801,139747 (DOI:10.1016 / j.cplett.2022.139747), the reversible capacity is 20.4% and 42.4% higher, respectively, and it has more stable electrochemical properties and is more suitable for use as a negative electrode material for lithium-ion batteries;

[0023] (2) The present invention provides a method for preparing GeO2 micron spheres for lithium ion battery negative electrodes. The micron spheres are uniform in size and have a structure that can buffer the volume change caused by the charge and discharge process, thereby avoiding electrode pulverization, maintaining the integrity of the electrode as a whole, and increasing the active sites of the reaction, thereby improving the specific capacity and cycle stability of the electrode material.

[0024] (3) The present invention provides a method for preparing GeO2 micron spheres for lithium-ion battery negative electrodes. The material is prepared by simple methods such as melt spinning, mechanical ball milling and dealloying. The preparation process does not involve steps such as carbon coating and does not require long-term treatment in a special atmosphere environment. The process is simple, the equipment complexity is reduced, and it is suitable for large-scale production.

[0025] (4) The present invention provides a method for preparing GeO2 micron spheres for lithium ion battery negative electrodes. The raw material composition of the prepared micron spherical GeO2 particles is simple, and the atomic percentage of germanium in the precursor material is low, only 1-3%, which is much lower than the atomic ratio of germanium in the precursor in the prior art (10-20%), and the raw material cost is low;

[0026] (5) The present invention provides a method for preparing GeO2 micron spheres for lithium ion battery negative electrodes. The solution concentration required for material preparation is relatively low, and no toxic reagents are used. There is no significant threat to environmental pollution and operator health. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below with reference to the accompanying drawings and examples.

[0028] Figure 1 This is a scanning electron microscope morphology image of the GeO2 microspheres prepared in Example 1.

[0029] Figure 2 This is the X-ray diffraction pattern of the GeO2 micron spheres prepared in Example 1.

[0030] Figure 3 This is a test curve of the cycle performance of GeO2 microspheres prepared in Example 1 and used as negative electrode materials for lithium-ion batteries. DETAILED DESCRIPTION

[0031] Example 1

[0032] The first step is to prepare the precursor strip

[0033] First, Al and Ge ingots are melted into Al at 980℃ in a vacuum arc melting furnace. 99 Ge1 master alloy ingot (atomic percentage); then, the master alloy ingot was remelted at 980°C by the induction coil of a vacuum strip spinning machine. After being held in the molten state for 3 seconds, the melt was sprayed onto a copper wheel rotating at a speed of 35 m / s and a spray pressure difference of 0.9 MPa to obtain a precursor strip with a thickness of 25 μm, a width of 2.5 mm, and a length of 80 cm;

[0034] Wherein, the purity of the Al and Ge ingots is 99.95wt.%, mass percentage;

[0035] Step 2: Prepare precursor powder

[0036] The precursor strips were mechanically ball milled at 1000 rpm for 12 h, alternating between forward and reverse rotations. The milling direction was reversed every 30 minutes. The volume ratio of stainless steel grinding balls (3 mm in diameter) to precursor strips was 5:1, yielding a precursor powder with a particle size of 2 μm.

[0037] The third step is to prepare micron-shaped spherical GeO2 particles

[0038] 0.2 g of the precursor powder prepared in the second step was immersed in 100 ml of 0.8 M HCl solution at 70°C for dealloying for 10 h. The corrosion process was accompanied by mechanical stirring at a stirring rate of 80 rpm. The product was then washed four times with anhydrous ethanol and vacuum dried at 60°C for 10 h to obtain GeO2 micron spheres.

[0039] Figure 1The figure shows the scanning electron microscope morphology of the GeO2 microspheres prepared in Example 1. In the figure, the GeO2 particles are evenly distributed and the particle size is consistent with good consistency. The diameter is 2.0 μm. There is no crack on the surface of the microspheres and the material integrity is good. Figure 2 Shown is the X-ray diffraction pattern of the material, in which an obvious GeO2 diffraction peak can be seen, indicating that the dealloyed product is GeO2.

[0040] The GeO2 micron balls prepared in this embodiment were used as negative electrode materials to assemble a lithium ion battery and perform performance testing, as follows:

[0041] GeO2 microspheres were used as the negative electrode, lithium metal was used as the counter electrode, 1.0 M LiPF6 in ethyl carbonate-diethyl carbonate (volume 1:1) was used as the electrolyte, and Celgard 2400 porous polypropylene was used as the separator. The battery was packaged in an argon-filled glove box (model CR2032). After the packaged battery was left to stand for 6 hours, the performance was tested at 25°C using a battery testing system. Figure 3 The curve of the lithium ion battery cycle performance test of the material prepared in this embodiment is Figure 3 It can be seen that the battery exhibits good reversible capacity and cycle stability. -1 After 50 cycles under the same conditions, the reversible capacity still remained at 904.1 mAh g -1 Compared with the reversible capacity of 715 mAh g of nanoporous GeO2 / Cu / Cu2O composite in previous work (Electrochimica Acta 2019, 300, 363-372. DOI: 10.1016 / j.electacta.2019.01.127), -1 Compared with the previous study, the capacity of this embodiment is increased by 20.4%. In addition, compared with the GeO2 / Ge composite material obtained in Chemical Physics Letters 2022, 801, 139747 (DOI: 10.1016 / j.cplett.2022.139747), the performance of this embodiment is better than that of the GeO2 / Ge composite material obtained in the previous study at 200mA g -1 After 40 cycles, the reversible capacity is 520.2 mAh g -1 In comparison, the capacity is 42.4% higher.

[0042] The above shows that the GeO2 microspheres prepared in this embodiment have better cycle stability as the negative electrode material of lithium-ion batteries than general materials.

[0043] Example 2

[0044] The first step is to prepare the precursor strip

[0045] First, Al and Ge ingots are melted into Al at 1000℃ in a vacuum arc melting furnace. 98 Ge2 master alloy ingot (atomic percentage); then, the master alloy ingot was remelted at 1000°C by the induction coil of a vacuum strip spinning machine. After being held in the molten state for 4 seconds, the melt was sprayed onto a copper wheel rotating at a speed of 40 m / s and a spray pressure difference of 1.0 MPa to obtain a precursor strip with a thickness of 20 μm, a width of 2.0 mm, and a length of 120 cm;

[0046] Wherein, the purity of the Al and Ge ingots is 99.95wt.%, mass percentage;

[0047] Step 2: Prepare precursor powder

[0048] The precursor strips were mechanically ball milled at 900 rpm for 24 h, alternating between forward and reverse rotations. The milling direction was reversed every 20 minutes. The volume ratio of stainless steel grinding balls (2 mm in diameter) to precursor strips was 4:1, yielding a precursor powder with a particle size of 3 μm.

[0049] The third step is to prepare micron-shaped spherical GeO2 particles

[0050] 0.1 g of the precursor powder prepared in the second step was immersed in 60 ml of 1.5 M HCl solution at 60°C for dealloying for 8 h. The corrosion process was accompanied by mechanical stirring at a stirring rate of 60 rpm. Then, it was washed with anhydrous ethanol 5 times and vacuum dried at 70°C for 8 h to obtain GeO2 micron spheres.

[0051] Among them, the obtained GeO2 particles are evenly distributed, the diameter of the spherical particles is 1.5μm, there is no crack on the surface of the micron spheres, and the material integrity is good.

[0052] Example 3

[0053] The first step is to prepare the precursor strip

[0054] First, Al and Ge ingots are melted into Al at 1080℃ in a vacuum arc melting furnace. 97 Ge3 master alloy ingot (atomic percentage); then, the master alloy ingot was remelted at 1080°C by the induction coil of a vacuum belt spinning machine. After being held in the molten state for 5 seconds, the melt was sprayed onto a copper wheel rotating at a speed of 30 m / s and a spray pressure difference of 0.8 MPa to obtain a precursor strip with a thickness of 30 μm, a width of 3.0 mm, and a length of 60 cm;

[0055] Wherein, the purity of the Al and Ge ingots is 99.95wt.%, mass percentage;

[0056] Step 2: Prepare precursor powder

[0057] The precursor strips were mechanically ball milled at 800 rpm for 48 h, alternating between forward and reverse rotations. The milling direction was reversed every 40 minutes. The volume ratio of stainless steel grinding balls (5 mm in diameter) to precursor strips was 6:1, yielding a precursor powder with a particle size of 4 μm.

[0058] The third step is to prepare micron-shaped spherical GeO2 particles

[0059] 0.5 g of the precursor powder prepared in the second step was immersed in 200 ml of 0.5 M HCl solution at 80°C for dealloying for 12 h. The corrosion process was accompanied by mechanical stirring at a stirring rate of 100 rpm. Then, it was washed three times with anhydrous ethanol and vacuum dried at 50°C for 12 h to obtain GeO2 micron spheres.

[0060] Among them, the obtained GeO2 particles are evenly distributed, the diameter of the spherical particles is 2.5μm, there is no crack on the surface of the micron spheres, and the material integrity is good.

[0061] Comparative Example 1: Selecting Ge 20 Al 80 The precursor was dealloyed under the same conditions as in Example 1. Observation of the sample's surface micromorphology revealed no GeO2 micron-spherical particles, only irregularly shaped bulk Ge particles. Some particles also exhibited surface cracking. The capacity retention of the sample, when used as a negative electrode material for lithium-ion batteries, was less than half that of Example 1.

[0062] Comparative Example 2: The ball mill speed was set to 400 r / min, and other conditions were the same as in Example 1. The surface micromorphology of the sample was observed. No small-sized GeO2 micron balls were obtained, but larger irregular particles were obtained, with a diameter 5 times that of the present invention. The capacity retention rate shown by the particles as the negative electrode material for lithium-ion batteries was less than 2 / 5 of that in Example 1.

[0063] Comparative Example 3: During the dealloying process, the mechanical stirring rate was set to 30 rpm, and other conditions were the same as in Example 1. The sample morphology and composition were detected. It was found that no small-sized GeO2 micron spheres could be obtained, and only larger Ge / GeO2 composite particles were obtained, with a diameter three times that of the present invention. The capacity retention rate exhibited by the composite particles when used as a negative electrode material for lithium-ion batteries was less than 3 / 5 of that in Example 1.

[0064] Comparative Example 4: Unidirectional ball milling was adopted during the ball milling process instead of the forward and reverse alternating form. Other conditions were the same as in Example 1. The sample morphology was detected. It was not possible to obtain GeO2 micron balls with a round shape and uniform size. Instead, GeO2 particles of uneven size were obtained, with a diameter 3 to 5 times that of the present invention. The capacity retention rate exhibited by the negative electrode material for lithium-ion batteries was less than 2 / 5 of that in Example 1.

[0065] In Comparative Example 1, due to the excessively high germanium content in the precursor, the dealloying process could not effectively and efficiently oxidize the product. Consequently, after dealloying, only coarse, irregularly shaped Ge particles were obtained, and cracks occurred on the surface. Compared to Example 1, the electrochemical performance was significantly reduced. In Comparative Example 2, due to the low ball mill speed, the precursor powder composition uniformity was reduced, the size of the formed phase increased, and the material particle size increased, thus affecting the electrochemical performance of the negative electrode material. In Comparative Example 3, due to the low mechanical stirring rate during the dealloying process, the sample corrosion and oxidation kinetics were reduced, the product was not fully oxidized, resulting in increased size, and a portion of Ge residue complicated the product composition. This caused surface cracking during the electrochemical cycle, which was not conducive to maintaining stable electrochemical performance. In Comparative Example 4, due to the use of only a unidirectional ball milling method, the ball milling effect was limited, and the raw materials could not be fully milled from all angles. Only GeO2 particles of uneven size were obtained, which were 3-5 times larger than those obtained using a forward and reverse ball milling method. This caused surface cracking during the electrochemical cycle, which was not conducive to maintaining stable electrochemical performance.

[0066] The above embodiments and comparative examples illustrate a method for preparing GeO2 micron balls for lithium-ion battery negative electrodes. This method is developed by continuously trying arc melting, melt spinning, ball milling and dealloying conditions, strictly controlling each process link, and after repeated practice.

[0067] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing GeO2 micron balls for lithium ion battery negative electrode, The method is characterized in that it comprises the following steps: The first step is to prepare the precursor strip First, Al and Ge ingots are melted into Al at 980-1080℃ in a vacuum arc melting furnace. (100-x) Ge x A master alloy ingot is cast, wherein 1≤x≤3, atomic percentage; subsequently, the master alloy ingot is remelted at 980-1080° C. by an induction coil of a vacuum strip spinning machine, and after being held in a molten state for 3-5 seconds, the melt is sprayed onto a copper wheel rotating at a speed of 30-40 m / s with a spray pressure difference of 0.8-1.0 MPa to obtain a precursor strip; Step 2: Prepare precursor powder The precursor strips are ball-milled at a speed of 800 to 1000 r / min for 12 to 48 hours, with the ball milling being performed alternately in forward and reverse directions, with the ball milling direction being reversed every 20 to 40 minutes. The volume ratio of the stainless steel grinding balls to the precursor strips is (4 to 6):1, to obtain a precursor powder with a particle size of 2 to 4 μm. Step 3: Preparation of GeO2 micron balls The precursor powder obtained in the second step is immersed in an HCl solution for dealloying at 60-80°C for 8-12 hours, and the corrosion process is accompanied by mechanical stirring at a stirring rate of 60-100 rpm. Then, it is washed with anhydrous ethanol 3-5 times and then vacuum dried at 50-70°C for 8-12 hours to obtain GeO2 micron spheres. Wherein, 0.1 to 0.5 grams of precursor powder is added to every 60 to 200 ml of HCl solution; the concentration of the HCl solution is 0.5 to 1.5 M; The purity of the Al and Ge ingots is 99.95wt.%; The thickness of the precursor strip is 20-30 μm, the width is 2.0-3.0 mm, and the length is 60-120 cm; The diameter of the stainless steel grinding balls is 2 to 5 mm; The spherical GeO2 particles in the obtained material are uniform in size and have a diameter of 1.5 to 2.5 μm.

2. The application of the GeO2 micron ball material obtained by the method according to claim 1 is characterized in that it is used as a negative electrode material for lithium ion batteries.

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