Method for preparing germanium-carbon nano composite material of lithium ion battery by hydrothermal method

Abstract

The invention belongs to the technical field of lithium ion battery negative electrode materials, and particularly relates to a preparation method for preparing a germanium-carbon nano composite material of a lithium ion battery by a hydrothermal method. The preparation method comprises the following steps: adding germanium dioxide into a sodium hydroxide solution, and violently stirring by using a magnetic stirrer until the germanium dioxide is completely dissolved to obtain a sodium germanate clear solution; dropwise adding concentrated hydrochloric acid into the sodium germanate solution to form a white suspension, and adding a carbon nanotube; putting the mixed solution into a hydrothermal reaction kettle, and carrying out hydrothermal reaction; and repeatedly filtering and washing the material by using absolute ethyl alcohol and ultrapure water, and finally carrying out vacuum drying to obtain the germanium-carbon nano composite material. Germanium dioxide and carbon nanotubes are selected as raw materials, the germanium-carbon composite material with a nano structure is generated through a hydrothermal reaction, no binder or catalyst is used, the preparation process is simple, the cost is low, the obtained material is stable in performance, high in energy density and suitable for long-term storage, and support is provided for commercial application of germanium-based negative electrode materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery materials and relates to a preparation method of a germanium-carbon nanocomposite material for lithium-ion batteries by a hydrothermal method. Background Art

[0002] With the progress of technology and the rapid development of new energy technologies, the requirements for the performance of lithium-ion batteries are also constantly increasing. As an important component of lithium-ion batteries, the performance of the negative electrode material directly affects the energy density, cycle life, and safety of the battery. An ideal lithium-ion battery negative electrode material should have the following characteristics: a higher discharge voltage; a stable crystal structure; a higher reversible capacity; a higher lithium-ion diffusion coefficient; and a high energy density.

[0003] Currently, the commercially available negative electrode material for lithium-ion batteries is mainly graphite. However, the capacity of graphite (the theoretical specific capacity of graphite is 372 mAh·g -1 ) limits the performance of the battery. With the in-depth research, researchers have found that silicon-based negative electrode materials have the advantages of high energy density, rich reserves, low cost, and low de-lithiation potential (generally between 0.3 V and 0.5 V). However, silicon undergoes a huge volume change (the expansion rate exceeds 320%) during charge and discharge, resulting in the rupture of the material structure and the attenuation of battery performance, and it has poor electrical conductivity. Germanium, like carbon and silicon, belongs to Group IV A elements. Compared with other lithium-ion battery negative electrode materials, it has the following advantages: 1) Higher energy density. The theoretical specific capacity of germanium-based negative electrode materials can be as high as 1650 mAh·g -1 , enabling the battery to store more electrical energy under the same volume; 2) Higher electrical conductivity. Germanium has a narrow bandgap width, which is beneficial to more efficient energy transfer and storage in high-power and high-current devices; 3) Faster lithium-ion diffusion rate, which improves the charge and discharge rate and efficiency of the battery; 4) Isotropic lithiation behavior, reducing the structural damage of the negative electrode material during charge and discharge, thereby improving the cycle life and stability of the battery.

[0004] However, metallic germanium as a lithium negative electrode material mainly has the following problems: 1) Under the condition of complete lithiation, the germanium-based material will undergo a huge volume expansion, resulting in the cracking and pulverization of the active material. 2) During the charge and discharge cycle process, the aggregation of active particles increases the resistance of lithium-ion insertion / extraction and generates an additional SEI layer. In recent years, with the continuous development of battery negative electrode material modification technologies, researchers have conducted in-depth research on the modification of germanium-based negative electrode materials through nanometerization and composite technologies. Among them, carbon and germanium composite nanomaterials can effectively alleviate the expansion effect of germanium-based negative electrodes and improve the structural stability and electrochemical performance of germanium-based negative electrode materials, showing broad prospects in the practical application of the new generation of lithium-ion batteries. Summary of the Invention

[0005] The present invention provides a technology for preparing a germanium-carbon nanocomposite anode material for lithium-ion batteries by a hydrothermal method.

[0006] To achieve the above object, the present invention provides a preparation method for a germanium-carbon nanocomposite material for lithium-ion batteries by a hydrothermal method. The specific preparation steps include: Step 1: Add germanium dioxide to a sodium hydroxide solution and stir vigorously with a magnetic stirrer until the germanium dioxide is completely dissolved to obtain a clear sodium germanate solution. Step 2: Dropwise add 36%-38% concentrated hydrochloric acid into the clear sodium germanate solution, stir vigorously with a magnetic stirrer to form a white suspension, then add carbon nanotubes to the white suspension and continuously stir for 3-5 h to obtain a mixed solution. Step 3: Put the mixed solution into a hydrothermal reaction kettle and carry out a hydrothermal reaction for 5-8 h. Step 4: Repeatedly filter and wash the material prepared in Step 3 with absolute ethanol and ultrapure water, and finally dry it under vacuum to obtain the germanium-carbon nanocomposite material.

[0007] Preferably, in Step 1, the addition amount of germanium dioxide is 0.8 g - 1.2 g; the addition amount of the sodium hydroxide solution is 12 - 18 mL, and the concentration is 1.5 M.

[0008] Preferably, in Step 1, the stirring temperature is set to 20 - 40 °C, and the stirring is carried out at a speed of 500 - 1000 rpm for 0.5 - 1 h.

[0009] Preferably, in Step 2, the dropping speed of the concentrated hydrochloric acid is set to 10 - 20 drops / minute.

[0010] Preferably, in Step 2, the vigorous stirring temperature is set to 20 - 30 °C, and the stirring is carried out at a speed of 500 - 1000 rpm for 15 - 30 min.

[0011] Preferably, the addition amount of the carbon nanotubes is 0.5 g.

[0012] Preferably, in Step 2, the stirring temperature is set to 20 - 30 °C, and the speed is 500 - 800 rpm.

[0013] Preferably, in Step 3, the hydrothermal reaction temperature is 150 °C.

[0014] Preferably, in Step 4, the drying temperature is set to 80 - 100 °C, and the time is 6 - 10 h.

[0015] Compared with the prior art, the beneficial effects of the present invention are: In this invention, germanium dioxide and carbon nanotubes are selected as raw materials. Germanium dioxide reacts with sodium hydroxide and carbon nanotubes in sequence to generate germanic acid that is insoluble in water. Then, germanic acid and carbon nanotubes are reacted in a hydrothermal reactor to produce a germanium-carbon composite material with a nanostructure. During the preparation process of this invention, no binder and catalyst are used. The steps are simple and the cost is low. Moreover, the composite material has stable performance and can be stored in a dry environment for a long time. The prepared lithium-ion battery has a high energy density and good cycle stability, providing strong support for the commercial application of germanium-based anode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the SEM image of the germanium-carbon composite material in Example 1 of this invention; Figure 2 It is the galvanostatic charge-discharge graph of the electrode material prepared in Example 1 of this invention; Figure 3 The long cycle graph of the electrode material prepared in Example 1 of this invention; Figure 4 The rate performance graph of the electrode material prepared in Example 1 of this invention; DETAILED DESCRIPTION OF THE INVENTION

[0017] Next, in combination with the embodiments of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of this invention, rather than all of the embodiments. Based on the embodiments in this invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope protected by this invention.

[0018] The preparation method of the germanium-carbon nanocomposite material for lithium-ion batteries by the hydrothermal method of this invention specifically includes the following preparation steps: Step 1: Add germanium dioxide into a sodium hydroxide solution, and stir vigorously with a magnetic stirrer until the germanium dioxide is completely dissolved to obtain a clear solution of sodium germanate; Step 2: Drop 36%-38% concentrated hydrochloric acid into the clear solution of sodium germanate drop by drop, stir vigorously with a magnetic stirrer to form a white suspension, then add carbon nanotubes into the white suspension, and continuously stir for 3-5 h to obtain a mixed solution; Step 3: Put the mixed solution into a hydrothermal reactor and carry out hydrothermal reaction for 5-8 h; Step 4: Filter and wash the material prepared in Step 3 repeatedly with absolute ethanol and ultrapure water, and finally dry it in vacuum to obtain the germanium-carbon nanocomposite material.

[0019] In the said Step 1, the addition amount of germanium dioxide is 0.8 g - 1.2 g; the addition amount of the sodium hydroxide solution is 12 - 18 mL, and the concentration is 1.5 M.

[0020] In step 1, the stirring temperature is set to 20 - 40°C, and stirring is continued for 0.5 - 1 h at a speed of 500 - 1000 rpm.

[0021] In step 2, the dropping rate of concentrated hydrochloric acid is set to 10 - 20 drops per minute.

[0022] In step 2, the vigorous stirring temperature is set to 20 - 30°C, and stirring is continued for 15 - 30 min at a speed of 500 - 1000 rpm.

[0023] The addition amount of carbon nanotubes is 0.5 g.

[0024] In step 2, the stirring temperature is set to 20 - 30°C, and the speed is 500 - 800 rpm.

[0025] In step 3, the hydrothermal reaction temperature is 150°C.

[0026] In step 4, the drying temperature is set to 80 - 100°C, and the time is 6 - 10 h.

[0027] Example 1 A preparation method for preparing a germanium-carbon nanocomposite for a lithium-ion battery by a hydrothermal method. The specific preparation steps include: Step 1: Add 1.2 g of germanium dioxide to 18 mL of a sodium hydroxide solution with a concentration of 1.5 M, and vigorously stir with a magnetic stirrer. The stirring temperature is set to 30°C, and stirring is continued for 1 h at a speed of 800 rpm until the germanium dioxide is completely dissolved to obtain a clear sodium germanate solution. Step 2: Drop 37% concentrated hydrochloric acid into the clear sodium germanate solution at a rate of 15 drops per minute, and vigorously stir with a magnetic stirrer. The stirring temperature is set to 30°C, and stirring is continued for 30 min at a speed of 600 rpm to form a white suspension. Then add 0.5 g of carbon nanotubes to the white suspension, set the temperature to 30°C, the speed to 500 rpm, and continue stirring for 4 h to obtain a mixed solution. Step 3: Put the mixed solution into a hydrothermal reaction kettle for hydrothermal reaction. The temperature of the hydrothermal reaction kettle is 150°C, and the reaction is carried out for 8 h. Step 4: Filter and wash the material prepared in step 3 repeatedly with absolute ethanol and ultrapure water, and finally dry it under vacuum. The drying temperature is set to 100°C, and the time is 10 h to obtain a germanium-carbon nanocomposite.

[0028] Example 2 The difference between this example and Example 1 is: The addition amount of germanium dioxide is 1 g, and the sodium hydroxide is 15 mL, and the other conditions remain unchanged.

[0029] Example 3 The difference between this example and Example 1 lies in that: The addition amount of germanium dioxide is 0.8 g, and that of sodium hydroxide is 12 mL, with other conditions remaining unchanged.

[0030] Comparative Example 1 Step 1: Add 0.4 g of germanium dioxide to ultrapure water, then add 3 mL of 1.5 M sodium hydroxide solution, and stir vigorously with a magnetic stirrer. Set the stirring temperature to 30 °C and stir continuously at a speed of 800 rpm for 1 h until the germanium dioxide is completely dissolved. Step 2: Add 0.5 g of carbon nanotubes to the mixed solution prepared in Step 1, and stir vigorously with a magnetic stirrer. Set the temperature to 30 °C and the speed to 500 rpm, and stir continuously for 4 h. Step 3: Put the mixed solution prepared in Step 2 into a hydrothermal reaction kettle and react at 150 °C for 8 h. Step 4: Filter and wash the material prepared in Step 3 repeatedly with absolute ethanol and ultrapure water, and finally dry it in vacuum. Set the drying temperature to 100 °C and the time to 10 h to obtain the germanium-carbon nanocomposite material.

[0031] The particles of this material are relatively large, the coating is uneven, and the electrochemical capacity can reach 1000 mAh·g -1 However, the attenuation is relatively fast, and it rapidly decays to 300 mAh·g -1 or less after 70 cycles.

[0032] Application Example 1 Preparation of the negative electrode plate: Mix the material, carbon black, and PVDF evenly at a mass ratio of 8:1:1, then coat it on a copper foil (the coating thickness is 200 µm), and cut it into a negative electrode plate after vacuum drying at 50 °C for 12 h.

[0033] Preparation of the lithium-ion battery: Use the above negative electrode plate as the test electrode, metallic lithium as the reference electrode, and a solution containing 1 M LiPF6 / EC:DMC:EMC (V:V:V = 1:1:1) as the electrolyte, and assemble a lithium-ion coin half-cell in a glove box filled with argon.

[0034] Perform 100 charge-discharge cycles for testing. The charge-discharge voltage range is 0.01~2 V, and the current density is 200 mA·g -1 , and the test temperature is room temperature; the specific performance data are shown in Table 1.

[0035] From Figure 1 the SEM image of the material, it can be seen that the germanium-carbon composite material prepared by the present invention has a relatively uniform distribution and shape. Even when magnified to 200KX, the shape and structure of the material can still be clearly seen; from Figure 2From the constant current charge-discharge diagram of the electrode material, it can be seen that for the lithium-ion germanium-carbon composite negative electrode material prepared by the present invention, the specific discharge capacity in the first cycle exceeds 2000 mAh / g, and after 100 charge-discharge cycles, a specific discharge capacity of more than 800 mAh / g is still retained. From Figure 3 From the long cycle diagram of this electrode material, it can be seen that for the lithium-ion germanium-carbon composite negative electrode material prepared by the present invention, the Coulomb efficiency from the 2nd cycle to the 100th cycle is above 95%, proving that this material has good stability as the negative electrode of a lithium-ion battery.

[0036] Application Examples 2 and 3 The germanium-carbon nanocomposite materials in Examples 2 and 3 were made into negative electrode sheets according to the method in Application Example 1 and assembled into lithium-ion button half-cells; the specific performance data are shown in Table 1.

[0037] Application Comparative Example 1 The difference between this application comparative example and Application Example 1 is that: A charge-discharge cycle stability test was carried out. The charge-discharge voltage range was 0.01~2 V, and the current density was 100 mA·g -1 , 200 mA·g -1 , 500 mA·g -1 , 1 A·g -1 , 200 mA·g -1 and 100 mA·g -1 Under these conditions, the cycles were 9, 8, 8, 8, 8, and 8 respectively, and the test temperature was room temperature; the specific performance data are shown in Figure 4 .

[0038] From Figure 4 From the rate performance diagram of the electrode material, it can be seen that for the germanium-carbon nanocomposite negative electrode of the lithium-ion battery prepared by the present invention, at current densities of 100 mA·g -1 , 200 mA·g -1 , 500 mA·g -1 and 1 A·g -1 , the discharge capacities provided were 908 mAh·g -1 , 827 mAh·g -1 , 798 mAh·g -1 and 422 mAh·g -1 respectively. After experiencing different current density changes, for the germanium-carbon nanocomposite negative electrode of the lithium-ion battery prepared by the present invention, at a current density of 100 mA·g -1 , the discharge capacity recovered to 612 mAh·g -1 .

[0039] Application Comparative Example 2 The difference between this application comparative example and Application Example 1 is that: The materials, carbon black and PVDF are mixed evenly at a mass ratio of 8:1:1 and then coated on a copper foil (coating thickness is 150 µm); the specific performance data are shown in Table 1.

[0040] Application Comparative Example 3 The difference between this application comparative example and Application Example 1 is that: The materials, carbon black and PVDF are mixed evenly at a mass ratio of 8:1:1 and then coated on a copper foil (coating thickness is 250 µm); the specific performance data are shown in Table 1.

[0041] Application Comparative Example 4 The difference between this application comparative example and Application Example 1 is that: The electrolyte is 1M LiTFSI / DMC:DOL (V:V = 1:1); the specific performance data are shown in Table 1.

[0042] Table 1 Performance data table of lithium-ion coin half-cells It can be seen from the test results in Table 1 that compared with the comparative examples, the germanium-carbon nanocomposite anode of the lithium-ion battery prepared by the present invention has higher capacity and more excellent cycle stability. After 100 charge-discharge cycles, it still has a Coulomb efficiency higher than 95%.

[0043] In summary, the present invention uses a simple and low-cost method to prepare a germanium-carbon nanocomposite anode with high stability. The germanium-carbon nanocomposite anode of the lithium-ion battery of the present invention effectively alleviates the swelling effect of the germanium-based anode material of the lithium-ion battery, and improves the capacity, conductivity and cycle stability of the lithium-ion battery.

[0044] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar methods to replace them, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for preparing a germanium-carbon nanocomposite material for lithium-ion batteries by a hydrothermal method, characterized in that: The specific preparation steps include: Step 1: Add germanium dioxide to sodium hydroxide solution and stir vigorously with a magnetic stirrer until the germanium dioxide is completely dissolved to obtain a clear sodium germanate solution; Step 2: Add 36%-38% concentrated hydrochloric acid dropwise into the sodium germanate clear solution, stir vigorously with a magnetic stirrer to form a white suspension, then add carbon nanotubes into the white suspension, continue stirring for 3-5 hours, and obtain a mixed solution; Step 3: Place the mixed solution into a hydrothermal reactor and perform a hydrothermal reaction for 5-8 hours; Step 4: Repeatedly filter and wash the material prepared in step 3 with anhydrous ethanol and ultrapure water, and finally vacuum dry to obtain a germanium-carbon nanocomposite material.

2. The method for preparing a lithium-ion battery germanium-carbon nanocomposite material by a hydrothermal method according to claim 1, characterized in that: In the step 1, the amount of germanium dioxide added is 0.8g-1.2g; the amount of sodium hydroxide solution added is 12-18mL, and the concentration is 1.5M.

3. The method for preparing a lithium-ion battery germanium-carbon nanocomposite material by a hydrothermal method according to claim 1, characterized in that: In step 1, the stirring temperature is set to 20-40° C., and the stirring is continued at a speed of 500-1000 rpm for 0.5-1 h.

4. The method for preparing a germanium-carbon nanocomposite material for lithium-ion batteries by a hydrothermal method according to claim 1, characterized in that: In step 2, the concentrated hydrochloric acid is dripped drop by drop at a speed of 10-20 drops / minute.

5. The method for preparing a germanium-carbon nanocomposite material for lithium-ion batteries by a hydrothermal method according to claim 1, characterized in that: In step 2, the vigorous stirring temperature is set to 20-30° C., and the stirring is continued at a speed of 500-1000 rpm for 15-30 min.

6. The method for preparing a germanium-carbon nanocomposite material for lithium-ion batteries by a hydrothermal method according to claim 1, characterized in that: The added amount of the carbon nanotubes is 0.5 g.

7. The method for preparing a germanium-carbon nanocomposite material for lithium-ion batteries by a hydrothermal method according to claim 1, characterized in that: In step 2, the stirring temperature is set to 20-30° C. and the stirring speed is set to 500-800 rpm.

8. The method for preparing a lithium-ion battery germanium-carbon nanocomposite material by a hydrothermal method according to claim 1, characterized in that: The hydrothermal reaction temperature in step 3 is 150°C.

9. The method for preparing a lithium-ion battery germanium-carbon nanocomposite material by a hydrothermal method according to claim 1, characterized in that: In step 4, the drying temperature is set to 80-100° C. and the drying time is 6-10 hours.

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