A method for preparing a metal Ge negative electrode with a three-dimensional complex hierarchical structure

Abstract

The application is a preparation method of a metal Ge negative electrode with a three-dimensional complex hierarchical structure. The method comprises the following steps: preparing a zinc germanate nanorod precursor; then dispersing in polydiene dimethyl propyl ammonium chloride solution and poly-p-styrene sulfonic acid sodium solution in sequence to obtain a modified zinc germanate precursor; then adding methanol, dispersing, and then adding zinc nitrate and 2-methyl imidazole in sequence, stirring and reacting for 4-8 hours; after the reaction is completed, centrifuging and washing the product, drying to obtain a solid powder; finally, under the protection of an inert atmosphere, heat treating at a temperature of 800-1000 DEG C for 2-4 hours to obtain a metal Ge negative electrode with a three-dimensional complex hierarchical structure. The application is simpler to operate, can construct a three-dimensional complex hierarchical structure, and overcomes the problems of loose arrangement of low-dimensional metal Ge nanomaterial structure particles and poor structure stability of particles prepared by previous methods.

Description

Technical Field

[0001] This invention belongs to the field of energy storage materials, specifically developing a method for preparing a high-capacity nitrogen-doped carbon-coated metallic Ge anode material with a complex three-dimensional hierarchical structure. The invention utilizes a high-temperature hydrothermal reaction to synthesize zinc germanate nanorods as a precursor, which are then modified and uniformly coated with a carbon precursor (ZIF-8). The precursor is then carbonized at high temperature, and finally, through carbothermal reduction, the zinc germanate nanorods inside the carbon coating are reduced to metallic Ge anode material, simultaneously generating a complex three-dimensional hierarchical structure (i.e., a three-dimensional interconnected hollow network). This material exhibits excellent cycle stability and high reversible specific capacity at low current densities. This novel preparation method for carbon-coated Ge metallic anode material with a three-dimensional interconnected hollow network structure lays the foundation for the application of high-energy-density germanium-based anode materials. Background Technology

[0002] With the rapid development of the new energy electric vehicle industry, the market demand for high-capacity lithium-ion batteries is increasing, while the theoretical capacity of traditional graphite cathodes is only 372 mAh g. -1 This is significantly different from current market demand. Lithium alloy anode materials, especially those containing group IVA elements silicon and germanium, have very high theoretical capacities (silicon is 4200 mAh g). -1 Germanium has a capacity of 1624 mAh g. -1 Therefore, it has been widely studied as a promising candidate for lithium-ion battery anodes. Compared with Si-based materials, metallic Ge exhibits higher Li-to-Li ratios. + The Ge anode exhibits superior diffusion coefficient and higher conductivity (400 times and 104 times that of Si, respectively), resulting in excellent rate capability and cycle stability. However, the Ge anode undergoes significant volume changes during cycling (up to 370% of its original volume upon lithium insertion), leading to rapid capacity degradation and electrode failure.

[0003] To address existing problems with metallic Ge anodes, researchers have proposed various strategies, primarily utilizing template methods to attach germanium oxide, followed by calcination and reduction using an H2 / Ar mixed gas to prepare nanostructured metallic Ge anode materials with unique morphologies, thereby improving their electrochemical performance. For example, reference 10.1016 / j.jechem.2021.12.051 reports a method using PS nanosphere templates to attach germanium oxide, followed by calcination and reduction using an H2 / Ar mixed gas to prepare metallic Ge anode materials with low-dimensional nanosphere morphology. Although this method yields materials with large specific surface area and can shorten Li... +While germanium-based nanostructures offer advantages such as long transmission distance, they require templates, are complex to operate, and can only produce simple low-dimensional nanostructures. These low-dimensional nanostructures are loosely arranged and have poor structural stability, easily leading to capacity decay. Therefore, developing new methods to construct a 3D complex hierarchical structure that retains the advantages of low-dimensional nanostructures while solving problems such as loose particle arrangement and stacking, and providing additional space for volume expansion during alloy anode cycling, is a current challenge for germanium-based nanostructure anode materials. Summary of the Invention

[0004] This invention addresses the problem of rapid capacity loss and electrode failure caused by volume expansion during cycling of Ge anodes, proposing a method for preparing metallic Ge anodes with a complex three-dimensional hierarchical structure. Unlike previous methods that required templates to determine morphology and then reduction using an H2 / Ar mixed gas, this method uses zinc germanate nanorods as a precursor, employs carbothermal reduction, and utilizes the Kirkendall effect to form a three-dimensional interconnected hollow network, ultimately obtaining a zinc oxide-doped Ge composite material. This invention is simpler to operate and can construct a complex three-dimensional hierarchical structure, overcoming the problems of loose particle arrangement and poor structural stability in low-dimensional metallic Ge nanomaterials prepared by previous methods. Furthermore, the hollow structure provides a buffer space for volume expansion during cycling, which is more conducive to the transport of ions and electrons in the system. The composite material obtained by this invention has a yield of 0.2 A g. -1 The reversible capacity after 350 cycles at a current density reaches 1147 mAh g. -1 .

[0005] The technical solution of this invention is:

[0006] A method for preparing a metallic Ge anode with a three-dimensional complex hierarchical structure, comprising the following steps:

[0007] (1) Add GeO2 and NaOH to deionized water and stir to form solution A; add Zn(CH3COO)2·2H2O to deionized water and stir to form solution B; add solution B dropwise to solution A and stir at room temperature for 5-30 min to obtain white emulsion C; adjust the pH of solution C to 8-10 using NaOH aqueous solution and stir at room temperature for 20-60 min; add the pH-adjusted solution C to a hydrothermal reactor and react at 180-220℃ for 8-16 h; after the reaction is completed, centrifuge, wash with deionized water and dry to obtain zinc germanate nanorod precursor;

[0008] The molar ratio is GeO2:NaOH:Zn(CH3COO)2·2H2O=1:2:2;

[0009] In solution A, add 0.5 mmol GeO2 to every 5–25 mL of deionized water; in solution B, add 1 mmol Zn(CH3COO)2·2H2O to every 5–15 mL of deionized water.

[0010] (2) Disperse the zinc germanate nanorods obtained in the previous step in a polydimethylpropylammonium chloride solution; stir at room temperature for 20-60 min, then centrifuge and wash; then disperse in a solution of dissolved sodium styrene sulfonate, stir at room temperature for 20-60 min, centrifuge and wash to obtain the modified zinc germanate precursor;

[0011] The molar ratio is zinc germanate:PDDA:PSS = 1:0.001~0.01:0.001~0.01;

[0012] The concentrations of the polydimethylammonium chloride solution and the sodium terephthalate sulfonate solution may be the same or different, ranging from 5 to 60 μmol / L; both solutions contain sodium chloride, with a concentration of 2 to 5 μmol / L.

[0013] (3) Carbon precursor (ZIF-8) coating: The modified zinc germanate precursor was transferred to a container, methanol was added, and after dispersion, zinc nitrate and 2-methylimidazole were added in sequence with an interval of 10-20 min. The reaction was stirred for 4-8 h. After the reaction was completed, the product was centrifuged, washed, and dried to obtain a solid powder.

[0014] The molar ratios were: zinc germanate: zinc nitrate = 1:10-30; the molar ratio of zinc nitrate to 2-methylimidazole was 1:10; and 25-100 mL of methanol was added for every 1 mmol of modified zinc germanate precursor.

[0015] The molar amount of the modified zinc silicate precursor is the theoretical value, that is, the molar amount of the unmodified zinc silicate precursor.

[0016] (4) Calcination: The solid powder obtained in the previous step is heat-treated at 800-1000℃ for 2-4 hours under an inert atmosphere to obtain a metal Ge anode with a three-dimensional complex hierarchical structure.

[0017] The inert atmosphere is N2 or Ar.

[0018] The application of the metal Ge anode with a three-dimensional complex hierarchical structure prepared by the method is as an anode material for lithium-ion batteries.

[0019] The process includes the following steps: the composite material obtained in (4) is uniformly mixed with conductive carbon and binder at a mass ratio of 8:1:1 and deionized water is added. The mixture is stirred at room temperature for 8 to 24 hours. After stirring, the resulting suspension is uniformly coated on copper foil and vacuum dried at 90 to 120°C for 12 to 24 hours to obtain the negative electrode of the lithium-ion battery. 0.6 to 1.5 mg of composite material is coated on each 12 mm diameter copper foil.

[0020] The lithium-ion battery uses a lithium sheet as the counter electrode; the electrolyte is 1.0 mol / L LiPF6 (the solvent is a mixed solution of dimethyl carbonate (DMC), methyl ethyl carbonate (EMC) and ethylene carbonate (EC) in a volume ratio of 1:1:1); and the separator is a Celgard 2400 membrane.

[0021] The essential features of this invention are:

[0022] In previous papers, traditional preparation methods have yielded Ge-based nanomaterials that generally exhibit low-dimensional nanostructures such as nanoparticles, nanowires, or nanorods. These nanomaterials are prone to capacity decay due to their loose particle arrangement, poor structural stability, and tendency to stack.

[0023] This invention uses one-dimensional zinc germanate nanorods as a precursor. After modification, a carbon precursor is uniformly coated on the outside of the nanorods. During high-temperature carbonization, the zinc germanate nanorods inside the carbon coating are reduced to ZnO-doped metallic Ge anode material using the principle of carbothermal reduction. The inventors discovered that during the reduction of the internal precursor in the carbon coating, the precursors interconnect and form a hollow structure, creating a three-dimensional interconnected hollow network. This nanostructure overcomes the problems of loose and aggregated low-dimensional nanostructures. The internal hollow structure provides a buffer space for volume expansion during alloy anode cycling and also has an ultra-high specific surface area, providing more active sites for electrochemical reactions. Simultaneously, a large amount of zinc oxide produced by precursor decomposition is reduced and emitted from the system, leaving abundant channels in the carbon coating, which is more conducive to the transport of ions and electrons within the system. The remaining zinc oxide is dispersed throughout the system, enhancing its conductivity and further mitigating volume changes during lithiation / delithiation.

[0024] The beneficial effects of this invention are as follows:

[0025] (1) The present invention designs and synthesizes a zinc germanate precursor with uniform nanorod morphology by a simple high-temperature hydrothermal method;

[0026] (2) The carbon precursor is uniformly coated on the surface of the zinc silicate precursor by electrostatic adsorption. The operation process is simple and the experimental conditions are mild.

[0027] (3) Using the principle of carbothermic reduction, the zinc germanate precursor inside is reduced through the carbon coating layer to finally obtain carbon-coated metal Ge composite material.

[0028] (4) By utilizing the zinc volatilization generated from the decomposition of zinc germanate precursor to create pores, a carbon coating layer rich in microporous channels can be obtained, which is more conducive to the transport of ions and electrons in the system.

[0029] (5) During the reduction of zinc germanate precursor to metallic Ge, it can stack and interconnect to form a three-dimensional interconnected hollow network with a stable structure, providing a buffer space for volume expansion during the cycling process; it also has an ultra-high specific surface area, providing more active sites for electrochemical reactions.

[0030] (6) The carbon-coated metal Ge composite material prepared in this experiment was tested at 0.2A g. -1 The reversible specific capacity reaches 1147 mAh g after 350 cycles. -1 .

[0031] (7) This material in 1Ag -1 and 2Ag -1 The reversible specific capacity at the current density reached 752 mAh g. -1 and 631mAh g -1 This provides a theoretical basis for the commercial application of this material in the field of energy storage materials. Attached Figure Description

[0032] Figure 1 This is a SEM image of the zinc germanate precursor (ZGO) in Example 1;

[0033] Figure 2 The X-ray diffraction pattern of the carbon-coated metal Ge composite material (Ge-3D@C-2-800) in Example 1 is shown below.

[0034] Figure 3 The image shows a SEM image of the carbon-coated metal Ge composite material (Ge-3D@C-2-800) in Example 1.

[0035] Figure 4 This is a TEM image of the carbon-coated metal Ge composite material (Ge-3D@C-2-800) in Example 1;

[0036] Figure 5 The graph shows the cycling performance of the carbon-coated metal Ge composite material (Ge-3D@C-2-800) in Example 1.

[0037] Figure 6 This is a rate performance diagram of the carbon-coated metal Ge composite material (Ge-3D@C-2-800) in Example 1;

[0038] Figure 7 The X-ray diffraction pattern of the carbon-coated metal Ge composite material (Ge-3D@C-2-700) in Example 2 is shown below.

[0039] Figure 8 The X-ray diffraction pattern of the carbon-coated metal Ge composite material (Ge-3D@C-2-900) in Example 3 is shown below.

[0040] Figure 9 The graph shows the cycling performance of the carbon-coated metal Ge composite material (Ge-3D@C-2-900) in Example 3;

[0041] Figure 10 The graph shows the cycling performance of the carbon-coated metal Ge composite material (Ge-3D@C-1-800) in Example 4.

[0042] Figure 11 The graph shows the cycling performance of the carbon-coated metal Ge composite material (Ge-3D@C-3-800) in Example 5. Detailed Implementation

[0043] Example 1

[0044] 1 mmol of GeO2 was dispersed in 10 mL of H2O, and then dissolved in 10 mL of NaOH (0.2 mmol / L) solution to obtain an aqueous solution of Na2GeO3. 2 mmol of Zn(CH3COO)2·2H2O was dissolved in 10 mL of H2O and added dropwise to the prepared Na2GeO3 aqueous solution. The mixture was stirred at room temperature for 15 min. Finally, the pH of the mixture was adjusted to 8 with NaOH (0.5 mmol / L). After stirring for 30 min, the mixture was placed in a reactor and hydrothermally treated at 200 °C for 12 h. After centrifugation and washing, it was dried at 60 °C for 12 h to obtain the precursor zinc germanate nanorods (Zn2GeO4, named ZGO).

[0045] All the product obtained in the previous step was first transferred to an aqueous solution containing sodium chloride and polydiallyldimethylammonium chloride, stirred for 30 min, centrifuged to recover the powder after stirring, and washed with deionized water. The washed product was then directly transferred to an aqueous solution of sodium chloride and sodium poly(p-styrene sulfonate), stirred for 30 min, centrifuged to recover the powder after stirring, and washed with deionized water to obtain the zinc germanate precursor co-modified by polydiallyldimethylammonium chloride and sodium poly(p-styrene sulfonate). The concentrations of polydiallyldimethylammonium chloride and sodium poly(p-styrene sulfonate) were both 10 μmol / L, the concentration of sodium chloride was 2.5 μmol / L, and the solution volume was 400 mL for both solutions.

[0046] The modified zinc germanate precursor obtained above (i.e., theoretically 1 mmol, without considering the loss of germanium and zinc) was transferred to a round-bottom flask, and 75 mL of methanol was added, followed by ultrasonication until uniformly dispersed. Zinc nitrate and 2-methylimidazole (molar ratio 1:10) were added sequentially to the round-bottom flask, and the mixture was stirred for 4 h. After the reaction was complete, the product was collected by centrifugation and dried to obtain a solid powder. The molar ratio of the modified zinc germanate precursor to zinc nitrate in the above reaction was 1:22.

[0047] The obtained solid powder was heat-treated at 800℃ for 2 hours under Ar atmosphere protection at a heating rate of 10℃ / min to obtain carbon-coated metal Ge composite material (Ge-3D@C-2-800).

[0048] The obtained Ge-3D@C-2-800 composite material was uniformly mixed with conductive carbon (Super P) and binder (sodium carboxymethyl cellulose) at a ratio of 8:1:1 (mass ratio) (containing 100 mg of Ge-3D@C-2-800), and 800 μL of deionized water was added. The mixture was stirred at room temperature for 12 h. After stirring, the mixture was uniformly coated onto copper foil and vacuum dried at 100 °C for 12 h. Subsequently, it was cut into 12 mm discs (with an active material Ge-3D@C-2-800 loading of approximately 1 mg) to obtain the negative electrode sheet.

[0049] In this embodiment, the battery adopts a standard half-cell configuration. The battery casing is a CR2025 stainless steel coin cell, with a lithium electrode as the counter electrode and a Celgard 2400 membrane as the separator. A 1.0 mol / L LiPF6 solution in a mixture of dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), and ethylene carbonate (EC) (1:1:1, volume ratio) is used as the electrolyte. The battery was tested using a LAND CT2001A battery testing system with a voltage range of 0.01–3 V and a test current of 0.2 Ag. -1 .

[0050] Figure 1 This is a SEM image of the zinc germanate precursor (ZGO) in Example 1. ZGO has a nanorod structure with uniform particle dispersion and no particle agglomeration. The length and width of the nanorods are approximately 110 nm and 40 nm, respectively.

[0051] Figure 2 The image shows the X-ray diffraction pattern of Ge-3D@C-2-800, which is composed of metallic Ge.

[0052] Figure 3 This is a SEM image of Ge-3D@C-2-800. The composite material consists of dodecahedral particles with a diameter of approximately 500 nm.

[0053] Figure 4This is a TEM image of Ge-3D@C-2-800. The carbon coating layer exhibits a three-dimensional interconnected hollow network structure.

[0054] Figure 5 The graph shows the cycling performance of Ge-3D@C-2-800. The specific capacity of the composite material during the first cycle is 1500 mAh g, and the specific capacity during the charge cycle is 1039 mAh g. -1 After 350 cycles, the reversible specific capacity reaches 1147 mAh g. -1 The Coulomb efficiency is close to 100%.

[0055] Figure 6 This is a rate performance diagram for Ge-3D@C-2-800. The composite material at 1A g... -1 and 2Ag -1 The reversible specific capacity at the current density reached 752 mAh g. -1 and 631mAh g -1 .

[0056] Example 2

[0057] The steps are the same as in Example 1, except that the pyrolysis temperature of the solid powder under an inert atmosphere is changed to 700℃ for heat treatment, while other conditions remain unchanged, and carbon-coated metal Ge composite material (Ge-3D@C-2-700) is finally obtained. Figure 7 The image shows the X-ray diffraction pattern of Ge-3D@C-2-700, which has the composition ZnO, indicating that the precursor cannot be carbothermally reduced to metallic Ge at 700℃.

[0058] Example 3

[0059] The steps are the same as in Example 1, except that the pyrolysis temperature of the solid powder under an inert atmosphere is changed to 900℃ for heat treatment, while other conditions remain unchanged, and carbon-coated metal Ge composite material (Ge-3D@C-2-900) is finally obtained. Figure 8 The image shows the X-ray diffraction pattern of Ge-3D@C-2-900, which is composed of metallic Ge. Figure 9 The graph shows the cycling performance of Ge-3D@C-2-900. The specific capacities of the composite material during the first cycle are 1427 and 827 mAh g, respectively. -1 The reversible specific capacity after 50 cycles is 719 mAh g. -1 The Coulomb efficiency is close to 100%.

[0060] Example 4

[0061] The steps are the same as in Example 1, except that the molar ratio of the precursor and zinc nitrate is changed to 1:14, and other conditions remain unchanged, and carbon-coated metal Ge composite material (Ge-3D@C-1-800) is finally obtained. Figure 10The graph shows the cycling performance of Ge-3D@C-1-800. The specific capacities for discharge and charge during the first cycle of the composite material are 1527 and 1064 mAh g, respectively. -1 The reversible specific capacity after 350 cycles is 606 mAh g. -1 The Coulomb efficiency is close to 100%.

[0062] Example 5

[0063] The steps are the same as in Example 1, except that the molar ratio of the precursor and zinc nitrate is changed to 1:29, and other conditions remain unchanged, and carbon-coated metal Ge composite material (Ge-3D@C-3-800) is finally obtained. Figure 11 The graph shows the cycling performance of Ge-3D@C-3-800. The specific capacities for discharge and charge during the first cycle of the composite material are 1645 and 1077 mAh g, respectively. -1 The reversible specific capacity after 350 cycles is 869mAh g. -1 The Coulomb efficiency is close to 100%.

[0064] As can be seen from the above examples, the present invention provides a zinc germanate precursor with a uniform nanorod morphology prepared by a high-temperature hydrothermal reaction, and obtains a metallic Ge anode with a three-dimensional interconnected hollow network structure by carbothermic reduction of the internal zinc germanate using a carbon-coated layer. Specifically, by controlling the proportion of the carbon precursor (ZIF-8) and the carbothermic reduction temperature, it can be seen that different carbon coating amounts and reduction temperatures have a certain influence on the molding of the composite material, thereby significantly improving the electrochemical performance of the corresponding composite material.

[0065] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing a metallic Ge anode with a three-dimensional complex hierarchical structure, characterized in that the method includes the following steps: (1) Add GeO2 and NaOH to deionized water and stir to form solution A; add Zn(CH3COO)2·2H2O to deionized water and stir to form solution B; add solution B dropwise to solution A to obtain white emulsion C; adjust the pH of solution C to 8~10 using NaOH aqueous solution and stir at room temperature for 20~60 min; add the pH-adjusted solution C to a hydrothermal reactor and react at 180~220℃ for 8~16 h; after the reaction is completed, centrifuge, wash with deionized water and dry to obtain zinc germanate nanorod precursor; wherein The molar ratio is GeO2:NaOH:Zn(CH3COO)2·2H2O=1:2:2; In solution A, add 0.5 mmol GeO2 to every 5–25 mL of deionized water; in solution B, add 1 mmol Zn(CH3COO)2·2H2O to every 5–15 mL of deionized water. (2) Disperse the zinc germanate nanorods obtained in the previous step in a polydimethylpropylammonium chloride solution; stir at room temperature for 20-60 min, then centrifuge and wash; then disperse in a solution of dissolved sodium styrene sulfonate, stir at room temperature for 20-60 min, centrifuge and wash to obtain the modified zinc germanate precursor; The molar ratio is zinc germanate:PDDA:PSS = 1:0.001~0.01:0.001~0.01; The concentrations of the polydimethylammonium chloride solution and the sodium styrene sulfonate solution may be the same or different, both ranging from 5 to 60 μmol / L; both solutions contain sodium chloride at a concentration of 2 to 5 μmol / L. (3) Carbon precursor ZIF-8 coating: The modified zinc germanate precursor was transferred to a container, methanol was added, and after dispersion, zinc nitrate and 2-methylimidazole were added in sequence with an interval of 10-20 min. The reaction was stirred for 4-8 h. After the reaction was completed, the product was centrifuged, washed, and dried to obtain solid powder. The molar ratios were: zinc germanate: zinc nitrate = 1:10-30; the molar ratio of zinc nitrate to 2-methylimidazole was 1:10; and 25-100 mL of methanol was added for every 1 mmol of modified zinc germanate precursor. (4) Calcination: The solid powder obtained in the previous step is heat-treated at 800~1000℃ for 2~4 h under an inert atmosphere to obtain a metal Ge anode with a three-dimensional complex hierarchical structure.

2. The method for preparing a metallic Ge anode with a three-dimensional complex hierarchical structure as described in claim , characterized in that: The inert atmosphere is N2 or Ar.

3. The application of the metallic Ge anode with a three-dimensional complex hierarchical structure prepared by the method described in claim 1, characterized in that it is used as an anode material for lithium-ion batteries.

4. The application as described in claim 3, characterized in that: Includes the following steps: The composite material obtained in step (4) is uniformly mixed with conductive carbon and binder at a mass ratio of 8:1:1 and deionized water is added. The mixture is stirred at room temperature for 8 to 24 hours. After stirring, the resulting suspension is coated onto copper foil and vacuum dried at 90 to 120°C for 12 to 24 hours to obtain the negative electrode of the lithium-ion battery. 0.6 to 1.5 mg of composite material is coated on each 12 mm diameter copper foil.

5. The application as described in claim 4, characterized in that the lithium-ion battery uses a lithium sheet as the counter electrode; the electrolyte is a 1.0 mol / L LiPF6 solution, and the solvent of the electrolyte is a mixed solution composed of dimethyl carbonate, methyl ethyl carbonate and ethylene carbonate, with a volume ratio of 1:1:1; the separator is a Celgard 2400 membrane.

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