A method for preparing a porous crystalline-amorphous Ge coexisting composite anode material

Abstract

The present invention relates to a method for preparing a porous crystalline-amorphous Ge coexisting composite anode material, and belongs to the technical field of alloyed anode materials for lithium-ion batteries. The present invention uses germanium dioxide as a germanium source, and prepares a reaction product amorphous GeO2 / C by a hydrothermal method. After annealing in an air atmosphere and sintering in a reducing atmosphere, crystalline and amorphous Ge powders are obtained. Then, a porous Ge precursor powder is obtained by high-temperature and high-pressure reaction purification. The porous Ge precursor powder is sintered in a protective atmosphere to obtain a porous crystalline-amorphous Ge coexisting composite anode material. As the anode of a lithium-ion battery, the porous crystalline-amorphous Ge coexisting composite anode material can buffer the volume change during the charge and discharge process, increase the adsorption active sites of lithium ions, reduce the transmission distance of lithium ions, and accelerate the kinetic process of ion diffusion, thereby improving the specific capacity and long-term cycle stability of the lithium-ion battery.

Description

Technical Field

[0001] The invention relates to a preparation method of a porous crystalline-amorphous Ge coexisting composite anode material, belonging to the technical field of alloyed anode materials for lithium ion batteries. Background Art

[0002] Currently, the commercial negative electrode materials for lithium-ion batteries are mainly graphite and lithium titanate. The theoretical capacities of graphite and lithium titanate are 372mAh / g and 175mAh / g, respectively. The energy density and theoretical capacity of graphite and lithium titanate are extremely limited, which results in the battery's cycle capacity being limited and unable to meet the needs of current high-power equipment.

[0003] However, traditional alloy preparation methods require melting copper and gallium separately at high temperatures and then uniformly mixing them together to form the alloy. This method requires high temperatures, complex system equipment, and a cumbersome, time-consuming, and multi-step process. Its high cost and limited usability significantly limit its application. In particular, directly mixing copper powder with liquid metal not only results in poor fusion, but also causes significant oxidation of the liquid metal, significantly affecting alloy formation.

[0004] Anode materials act as Li in lithium-ion batteries + The receiving device is one of the indispensable core components of lithium-ion batteries. The development of high-energy-density and highly stable negative electrode materials and the rational design of the structure can significantly improve the volume energy density and long-cycle cycle stability of the battery during the charge and discharge cycle. With the rapid development of society, the development of new negative electrode materials with high energy density has become one of the key research objects of scientists. The theoretical capacity of the current main commercial negative electrode materials, graphite and lithium titanate, are 372mAh / g and 175mAh / g respectively, and there is almost no room for improvement. Therefore, the development of the next generation of new high-capacity negative electrode materials plays an important role in the rapidly developing society. Summary of the Invention

[0005] In view of the fact that commercial germanium negative electrode materials in the prior art are converted from Li + The huge volume expansion during embedding / de-embedding leads to the problem of rapid capacity decay.

[0006] The present invention uses germanium dioxide as a germanium source and hydrothermally prepares the reaction product, amorphous GeO2 / C. This product is then annealed in air and sintered in a reducing atmosphere to obtain crystalline and amorphous Ge powders. This is then purified under high temperature and high pressure to obtain a porous Ge precursor powder. The porous Ge precursor powder is sintered in a protective atmosphere to obtain a porous crystalline-amorphous Ge coexisting composite anode material. As a lithium-ion battery anode, the porous crystalline-amorphous Ge coexisting composite anode material can buffer volume changes during charge and discharge, increase active sites for lithium ion adsorption, reduce lithium ion transmission distances, and accelerate the kinetics of ion diffusion, thereby improving the specific capacity and long-term cycling stability of lithium-ion batteries.

[0007] A method for preparing a porous crystalline-amorphous Ge coexisting composite anode material, the specific steps are as follows:

[0008] (1) Germanium dioxide is ultrasonically dispersed in deionized water to obtain a suspension A, and ammonia water is added dropwise under stirring to completely dissolve the powder in the suspension A into a transparent and clear solution B; the germanium in the solution B exists in the form of NH4H(HGeO3)2;

[0009] (2) at a temperature of 25 to 50° C., the hydroxyethylenediamine solution was added dropwise into deionized water, and lithium difluorooxalatoborate powder was added to obtain solution C, and solution B was slowly added to solution C to obtain a mixed solution D;

[0010] (3) The mixed solution D is placed at a temperature of 160-210° C. for 12-36 hours, cooled to room temperature, and subjected to solid-liquid separation. The solid is washed with deionized water and anhydrous ethanol in sequence, and dried to obtain the reaction product E (amorphous GeO2 / C);

[0011] (4) The reaction product E is placed in an air atmosphere for low-temperature annealing for 3 to 5 hours, cooled naturally to room temperature, and then placed in a reducing gas for reduction sintering. The product is then cooled to room temperature in the furnace to obtain pretreated powder F (amorphous / crystalline Ge).

[0012] (5) Ultrasonic dispersion of the pretreated powder F into the mixed solution to obtain solution G, which was transferred to a high-temperature and high-pressure hydrothermal reactor, reacted at a temperature of 150-200° C. for 10-30 hours, cooled to room temperature, and subjected to solid-liquid separation. The solid was sequentially washed with deionized water and anhydrous ethanol, and dried to obtain a precursor powder (porous Ge); the mixed solution was a mixture of ethylene glycol, deionized water, and hydrofluoric acid;

[0013] (6) The precursor powder is sintered under protective gas and then cooled to room temperature in the furnace to obtain a porous crystalline-amorphous Ge coexisting composite anode material.

[0014] Preferably, the mass concentration of germanium dioxide in the suspension A in step (1) is 5-15%, and the mass concentration of ammonia water is 1-3%.

[0015] Preferably, the mass concentration of the hydroxyethylenediamine solution in solution C in step (2) is 1-10%, and the mass concentration of lithium difluorooxalatoborate is 0.2-2%.

[0016] Preferably, the volume ratio of solution B to solution C in step (2) is 3 to 10:1.

[0017] Preferably, the low-temperature annealing temperature in step (4) is 350-500° C.; the reduction sintering temperature is 500-700° C., and the time is 0.2-3 h.

[0018] Preferably, the reducing gas in step (4) is a hydrogen-argon mixed gas or a hydrogen-nitrogen mixed gas, and the volume content of hydrogen in the reducing gas is 5-15%.

[0019] Preferably, the volume ratio of ethylene glycol to deionized water in the mixed solution of step (5) is 1:1, and the mass concentration of hydrofluoric acid is 0.05-0.2%.

[0020] Preferably, the mass concentration of the pretreated powder F in the solution G in step (5) is 0.5-2.0%.

[0021] Preferably, the protective gas in step (6) is argon or nitrogen, the sintering temperature is 400-700° C., and the sintering time is 1-4 hours.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention uses commercial germanium dioxide as a germanium source, uses ammonia water to adjust the pH value of suspension A to dissolve germanium dioxide, uses hydroxyethylenediamine and lithium difluorooxalatoborate as additives, uses secondary solvent heat to uniformly disperse the germanium source, and grows it into a porous crystalline-amorphous Ge coexisting composite anode material under high temperature and high pressure. The preparation conditions are simple, the process route is simple and has low pollution, the price cost is low and the reproducibility is good, and the performance as a negative electrode of a lithium ion battery is excellent;

[0024] (2) The porous crystalline-amorphous Ge coexisting composite anode material of the present invention has a unique nanopore structure. At the same time, the crystalline and amorphous states coexist. The design of the nanopores can effectively promote the wetting of the electrolyte to the electrode, ensuring sufficient contact between the electrolyte and the active material. At the same time, it can also increase its comparative area, reduce and increase the adsorption active sites of lithium ions, reduce the transmission distance of lithium ions and accelerate the kinetic process of ion diffusion;

[0025] (3) The porous crystalline-amorphous Ge coexisting composite anode material of the present invention can reduce the volume change caused by the charge and discharge process, maintain the integrity of the electrode material structure, increase the active sites for lithium ion reaction, and thus improve the cycle stability and rate performance of the electrode;

[0026] (4) The porous crystalline-amorphous Ge coexisting composite anode material of the present invention retains micron-scale bulk, which can overcome the problem of high surface activity and easy agglomeration of nanoelectrodes. At the same time, the nanopores provide storage sites for lithium ions, providing a basic guarantee for the excellent electrochemical performance of lithium-ion batteries.

[0027] (5) The porous crystalline-amorphous Ge coexisting composite anode material of the present invention has a reversible specific capacity of 1198 mAh / g after 200 charge and discharge cycles at a current density of 200 mA / g, showing excellent specific capacity and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the XRD pattern of the porous crystalline-amorphous Ge coexisting composite anode material of Example 1;

[0029] Figure 2 Transmission electron microscopy, EDS element mapping distribution and selected area electron diffraction (SEAD) spectrum of the porous crystalline-amorphous Ge coexisting composite anode material of Example 1;

[0030] Figure 3 This is the XRD pattern of the porous crystalline-amorphous Ge coexisting composite anode material of Example 2;

[0031] Figure 4 This is a scanning electron microscope spectrum of the porous crystalline-amorphous Ge coexisting composite anode material of Example 2;

[0032] Figure 5 This is a cycle performance diagram of the lithium-ion half-cell of Example 2 after 200 constant current charge and discharge cycles;

[0033] Figure 6 This is the XRD pattern of the porous crystalline-amorphous Ge coexisting composite anode material of Example 3;

[0034] Figure 7 This is a cycle performance diagram of the lithium-ion half-cell of Example 3 after 200 constant current charge and discharge cycles. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0036] Example 1: A method for preparing a porous crystalline-amorphous Ge coexisting composite anode material, the specific steps are as follows:

[0037] (1) 0.5 g of germanium dioxide was ultrasonically dispersed in 100 mL of deionized water to obtain a suspension A. 0.2 mL of 20 wt.% ammonia water was added dropwise under stirring to completely dissolve the powder in the suspension A into a transparent and clear solution B; the germanium in the solution B existed in the form of NH4H(HGeO3)2;

[0038] (2) At 25°C, 1 mL of a 1% hydroxyethylenediamine solution was dropwise added to 50 mL of deionized water, and 0.05 g of lithium difluorooxalatoborate powder was added to obtain solution C. Solution B was slowly added to solution C to obtain a mixed solution D.

[0039] (3) The mixed solution D was placed at a temperature of 160°C for 12 hours, cooled to room temperature, and the solid-liquid separation was carried out. The solid was washed with deionized water and anhydrous ethanol in sequence, and dried to obtain the reaction product E (amorphous GeO2 / C);

[0040] (4) The reaction product E was placed in an air atmosphere and low-temperature annealed at 350°C for 3 h, cooled naturally to room temperature, and then placed in a reducing gas (H2-Ar mixed gas) and reduction-sintered at 500°C for 0.2 h. The product was then cooled to room temperature in the furnace to obtain pretreated powder F (amorphous / crystalline Ge); the volume fraction of H2 in the H2-Ar mixed gas was 5%;

[0041] (5) 0.5 g of pretreated powder F was ultrasonically dispersed into 80 mL of a mixed solution to obtain a solution G, which was transferred to a high-temperature and high-pressure hydrothermal reactor and reacted at a temperature of 150° C. for 10 h. The mixture was cooled to room temperature, and the solid-liquid separation was performed. The solid was washed with deionized water and anhydrous ethanol in sequence, and dried to obtain a precursor powder (porous Ge). The mixed solution was a mixture of ethylene glycol, deionized water, and hydrofluoric acid, the volume ratio of ethylene glycol to deionized water was 1:1, and the mass concentration of hydrofluoric acid in the mixed solution was 0.05%.

[0042] (6) The precursor powder is placed under protective gas (N2), sintered at 400 ° C for 1 hour, and then cooled to room temperature to obtain a porous crystalline-amorphous Ge coexisting composite anode material;

[0043] The X-ray diffraction (XRD) pattern of the porous crystalline-amorphous Ge coexisting composite anode material of this embodiment is shown in Figure 1 ,Depend on Figure 1 It can be seen that the synthesized Ge sample consists of crystalline and amorphous states;

[0044] The morphology and element mapping distribution of the porous crystalline-amorphous Ge coexisting composite anode material and its crystal / amorphous structure are shown in Figure 2. Figure 2 ,Depend on Figure 2It can be seen from the EDS morphology analysis that Ge element information was detected in the sample, and the selected area electron diffraction SAED showed the characteristics of diffuse amorphous diffraction rings accompanied by crystal diffraction rings, which is consistent with the crystal structure information obtained by XRD.

[0045] Example 2: A method for preparing a porous crystalline-amorphous Ge coexisting composite anode material, the specific steps are as follows:

[0046] (1) 1 g of germanium dioxide was ultrasonically dispersed in 70 mL of deionized water to obtain a suspension A. 0.4 mL of 20 wt.% ammonia water was added dropwise under stirring to completely dissolve the powder in the suspension A into a transparent and clear solution B; the germanium in the solution B existed in the form of NH4H(HGeO3)2;

[0047] (2) At 30°C, 1.5 mL of 5% hydroxyethylenediamine solution was dropwise added to 50 mL of deionized water, and 0.05 g of lithium difluorooxalatoborate powder was added to obtain solution C. Solution B was slowly added to solution C to obtain a mixed solution D.

[0048] (3) The mixed solution D was placed at a temperature of 180°C for 24 hours, cooled to room temperature, and the solid-liquid separation was performed. The solid was washed with deionized water and anhydrous ethanol in sequence, and dried to obtain the reaction product E (amorphous GeO2 / C);

[0049] (4) The reaction product E was placed in an air atmosphere and low-temperature annealed at 400°C for 4 hours, cooled naturally to room temperature, and then placed in a reducing gas (H2-Ar mixed gas) and reduction-sintered at 650°C for 2 hours. The product was then cooled to room temperature in the furnace to obtain pretreated powder F (amorphous / crystalline Ge); the volume fraction of H2 in the H2-Ar mixed gas was 10%;

[0050] (5) 0.7 g of pretreated powder F was ultrasonically dispersed into 100 mL of a mixed solution to obtain a solution G, which was transferred to a high-temperature and high-pressure hydrothermal reactor and reacted at a temperature of 180° C. for 20 h. The mixture was cooled to room temperature, and the solid-liquid separation was performed. The solid was washed with deionized water and anhydrous ethanol in sequence, and dried to obtain a precursor powder (porous Ge). The mixed solution was a mixture of ethylene glycol, deionized water, and hydrofluoric acid, the volume ratio of ethylene glycol to deionized water was 1:1, and the mass concentration of hydrofluoric acid in the mixed solution was 0.1%.

[0051] (6) The precursor powder is placed under protective gas (Ar), sintered at 600 ° C for 3 h, and then cooled to room temperature to obtain a porous crystalline-amorphous Ge coexisting composite anode material;

[0052] The X-ray diffraction (XRD) pattern of the porous crystalline-amorphous Ge coexisting composite anode material of this embodiment is shown in Figure 3 ,Depend on Figure 3 It can be seen that the synthesized Ge sample is composed of both crystalline and amorphous states;

[0053] The scanning electron microscope spectrum of the porous crystalline-amorphous Ge coexisting composite anode material of this embodiment is shown in Figure 4 ,Depend on Figure 4 It can be seen that the synthesized porous crystalline-amorphous Ge has a porous structure with a pore size of about 400nm-1μm;

[0054] In this embodiment, the porous crystalline-amorphous Ge coexisting composite anode material is used as the negative electrode of the lithium ion half-cell. Ge:acetylene black:PVDF=8:1:1 is mixed and ground, and then evenly coated on copper foil as the battery negative electrode. Metal lithium sheet is used as the reference electrode and counter electrode. The electrolyte is 1 mol / L LiPF6 (EC:DMC:EMC=1:1:1 v / v), and FEC with a volume fraction of 10% is added as a film-forming additive. The cycle performance of the lithium ion half-cell after 200 constant current charge and discharge cycles (current 200 mA / g) is shown in FIG. Figure 5 ,Depend on Figure 5 It can be seen that the lithium-ion half-cell still retains a reversible specific capacity of 1198mAh / g after 200 cycles of charge and discharge, showing excellent cycle stability and surprisingly high specific capacity.

[0055] Example 3: A method for preparing a porous crystalline-amorphous Ge coexisting composite anode material, the specific steps are as follows:

[0056] (1) 1 g of germanium dioxide was ultrasonically dispersed in 50 mL of deionized water to obtain a suspension A. 0.2 mL of 20 wt.% ammonia water was added dropwise under stirring to completely dissolve the powder in the suspension A into a transparent and clear solution B; the germanium in the solution B existed in the form of NH4H(HGeO3)2;

[0057] (2) At a temperature of 50°C, 2 mL of a 10% hydroxyethylenediamine solution was dropwise added to 50 mL of deionized water, and 0.1 g of lithium difluorooxalatoborate powder was added to obtain solution C. Solution B was slowly added to solution C to obtain a mixed solution D.

[0058] (3) The mixed solution D was placed at a temperature of 210°C for 36 hours, cooled to room temperature, and the solid-liquid separation was carried out. The solid was washed with deionized water and anhydrous ethanol in sequence, and dried to obtain the reaction product E (amorphous GeO2 / C);

[0059] (4) The reaction product E was placed in an air atmosphere and low-temperature annealed at 500°C for 5 h, cooled naturally to room temperature, and then placed in a reducing gas (H2-Ar mixed gas) and reduction-sintered at 700°C for 3 h. The product was then cooled to room temperature in the furnace to obtain pretreated powder F (amorphous / crystalline Ge); the volume fraction of H2 in the H2-Ar mixed gas was 15%;

[0060] (5) 0.5 g of pretreated powder F was ultrasonically dispersed into 100 mL of a mixed solution to obtain a solution G, which was transferred to a high-temperature and high-pressure hydrothermal reactor and reacted at a temperature of 200° C. for 30 h. The mixture was cooled to room temperature, and the solid-liquid separation was performed. The solid was washed with deionized water and anhydrous ethanol in sequence, and dried to obtain a precursor powder (porous Ge). The mixed solution was a mixture of ethylene glycol, deionized water, and hydrofluoric acid, the volume ratio of ethylene glycol to deionized water was 1:1, and the mass concentration of hydrofluoric acid in the mixed solution was 0.2%.

[0061] (6) The precursor powder is placed under protective gas (Ar), sintered at 700 ° C for 4 h, and then cooled to room temperature to obtain a porous crystalline-amorphous Ge coexisting composite anode material;

[0062] The X-ray diffraction (XRD) pattern of the porous crystalline-amorphous Ge coexisting composite anode material of this embodiment is shown in Figure 6 ,Depend on Figure 6 It can be seen that the synthesized Ge sample is composed of both crystalline and amorphous states;

[0063] In this embodiment, the porous crystalline-amorphous Ge coexisting composite anode material is used as the negative electrode of the lithium ion half-cell. Ge:acetylene black:PVDF=8:1:1 is mixed and ground, and then evenly coated on copper foil as the battery negative electrode. Metal lithium sheet is used as the reference electrode and counter electrode. The electrolyte is 1 mol / L LiPF6 (EC:DMC:EMC=1:1:1 v / v), and FEC with a volume fraction of 10% is added as a film-forming additive. The cycle performance of the lithium ion half-cell after 200 constant current charge and discharge cycles (current 200 mA / g) is shown in FIG. Figure 7 ,Depend on Figure 7 It can be seen that the lithium-ion half-cell still retains a reversible specific capacity of 1037mAh / g after 200 cycles of charge and discharge, showing excellent cycle stability and surprisingly high specific capacity.

[0064] The above describes the specific embodiments of the present invention in detail, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

Claims

1. A method for preparing a porous crystalline-amorphous Ge coexisting composite anode material, characterized in that: The specific steps are as follows: (1) Germanium dioxide is ultrasonically dispersed in deionized water to obtain suspension A. Ammonia water is added dropwise under stirring to completely dissolve the powder in suspension A into a transparent and clear solution B; (2) At a temperature of 25-50°C, a hydroxyethylenediamine solution is added dropwise into deionized water, and then lithium difluorooxalate borate powder is added to obtain a solution C, and solution B is slowly added to solution C to obtain a mixed solution D; the mass concentration of the hydroxyethylenediamine solution in the solution C is 1-10%, and the mass concentration of lithium difluorooxalate borate is 0.2-2%; the volume ratio of solution B to solution C is 3-10:1; (3) The mixed solution D is placed at a temperature of 160-210°C for 12-36 hours, cooled to room temperature, and the solid-liquid separation is performed. The solid is washed with deionized water and anhydrous ethanol in sequence, and dried to obtain the reaction product E; (4) The reaction product E is placed in an air atmosphere for low-temperature annealing for 3 to 5 hours, cooled naturally to room temperature, and then placed in a reducing gas for reduction sintering, and cooled to room temperature with the furnace to obtain pretreated powder F; the low-temperature annealing temperature is 350 to 500°C; the reduction sintering temperature is 500 to 700°C, and the time is 0.2 to 3 hours; (5) Ultrasonic dispersion of pretreated powder F into a mixed solution to obtain solution G, which is transferred to a high-temperature and high-pressure hydrothermal reactor, reacted at a temperature of 150-200°C for 10-30 hours, cooled to room temperature, and subjected to solid-liquid separation. The solid is sequentially washed with deionized water and anhydrous ethanol, and dried to obtain a precursor powder; the mixed solution is a mixture of ethylene glycol, deionized water, and hydrofluoric acid; (6) The precursor powder is sintered under protective gas and cooled to room temperature in the furnace to obtain a porous crystalline-amorphous Ge coexisting composite anode material.

2. The method for preparing the porous crystalline-amorphous Ge coexisting composite anode material according to claim 1, characterized in that: The mass concentration of germanium dioxide in the suspension A of step (1) is 5-15%, and the mass concentration of ammonia water is 1-3%.

3. The method for preparing the porous crystalline-amorphous Ge coexisting composite anode material according to claim 1, characterized in that: The reducing gas in step (4) is a hydrogen-argon mixed gas or a hydrogen-nitrogen mixed gas, and the volume content of hydrogen in the reducing gas is 5-15%.

4. The method for preparing the porous crystalline-amorphous Ge coexisting composite anode material according to claim 1, characterized in that: The volume ratio of ethylene glycol to deionized water in the mixed solution of step (5) is 1:1, and the mass concentration of hydrofluoric acid is 0.05-0.2%.

5. The method for preparing the porous crystalline-amorphous Ge coexisting composite anode material according to claim 1, characterized in that: The mass concentration of the pretreated powder F in the solution G in step (5) is 0.5-2.0%.

6. The method for preparing the porous crystalline-amorphous Ge coexisting composite anode material according to claim 1, characterized in that: In step (6), the protective gas is argon or nitrogen, the sintering temperature is 400-700°C, and the sintering time is 1-4 hours.

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