Nitrogen-magnesium-coated germanium composite negative electrode material and preparation method and application thereof

Abstract

The invention provides a nitrogen-magnesium coated germanium composite negative electrode material and a preparation method and application thereof.The preparation method comprises the steps that firstly, magnesium germanide powder serves as a precursor to be calcined, a germanium and magnesium nitride composite material is obtained, then argon is closed, secondary nitridation treatment is conducted in the nitrogen atmosphere, an MgGeN2 functional coating is formed on the surface of germanium, finally, magnesium nitride is etched, and the nitrogen-magnesium coated germanium composite negative electrode material is obtained. And washing and drying for multiple times to obtain the nitrogen-magnesium alloy coated germanium composite negative electrode material. The material has a three-dimensional porous structure and can effectively relieve the volume expansion effect of germanium generated in the lithium intercalation / deintercalation process and improve the cycle stability of the electrode material, the functional coating layer of the material forms a Li-Mg alloy and Li3N composite SEI layer after first discharge, and Li3N is an excellent electron / ion conductor, so that the SEI component is optimized, the interface impedance is reduced, and the electrochemical performance of the electrode material is improved. The elastic LiMg alloy is used as a buffer medium, so that interface stripping caused by volume change can be effectively inhibited.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical power sources, and in particular relates to a nitrogen-magnesium-coated germanium composite negative electrode material and a preparation method and application thereof. Background Art

[0002] With the rapid development and application of electric vehicles and portable electronic devices, the demand for high energy density and high power lithium-ion batteries is growing. The theoretical capacity of current commercial graphite anodes is only 372 mAh / g, and its energy density is about 150 kWh / kg, which is difficult to support the dual requirements of energy density and power density for next-generation battery technology. In this context, germanium (Ge) has attracted widespread attention due to its high theoretical specific capacity (1600 mAh / g), its working potential is lower than 0.5V, and its lithium ion diffusion rate and conductivity are 400 times and 10 times higher than those of silicon, respectively. 4 times, making it have the potential for both high energy and high power applications.

[0003] However, the volume expansion of germanium-based materials during the lithium insertion process is as high as 260%, which causes serious structural degradation. Repeated mechanical stress leads to particle crushing and electrode peeling. At the same time, the dynamically changing solid-liquid interface causes the SEI film to continuously reconstruct, resulting in irreversible consumption of active lithium in the battery and rapid capacity decay.

[0004] In the existing modification strategies, although the nano-sizing of germanium-based materials can withstand higher mechanical stress to alleviate the volume expansion effect, the high specific surface area of the nanoparticles can easily cause agglomeration, and the high specific surface area will aggravate the side reactions, thereby reducing the coulombic efficiency of the battery. Therefore, it is necessary to propose a nitrogen-magnesium alloy-coated germanium composite negative electrode material and its preparation method and application. Summary of the Invention

[0005] (1) Technical issues to be solved

[0006] The present invention proposes a nitrogen-magnesium-coated germanium composite negative electrode material and its preparation method and application, in order to solve the technical problems of traditional germanium-based negative electrode materials in lithium-ion batteries, such as poor cycle stability, high interface impedance and unstable SEI layer caused by volume expansion and low conductivity.

[0007] (2) Technical solution

[0008] In order to solve the above technical problems, the present invention proposes a method for preparing a nitrogen-magnesium-coated germanium composite negative electrode material, which comprises the following steps:

[0009] S1 magnesium germanium powder as a precursor, calcined in a mixed gas atmosphere of argon and ammonia to obtain a composite material of germanium and magnesium nitride Mg3N2;

[0010] S2. Turn off the argon gas and perform a secondary nitridation treatment on the composite material in a heated nitrogen atmosphere to form a MgGeN2 functional coating on the germanium surface of the composite material;

[0011] S3. Remove magnesium nitride Mg3N2 from the composite material, wash and dry it, and obtain a nitrogen-magnesium-coated germanium composite negative electrode material.

[0012] Furthermore, in step S1, before calcining in a mixed gas atmosphere of argon and ammonia, the magnesium germanium powder is flattened.

[0013] Furthermore, in step S1, during calcination, the temperature is raised from room temperature to 750°C at a heating rate of 5°C / min and kept at this temperature for 6 hours.

[0014] Furthermore, in step S2, the temperature is raised from 750° C. to 880° C. at a heating rate of 5° C. / min, and a secondary nitriding treatment is performed for 10 to 20 minutes.

[0015] Furthermore, in step S3, 1M HCl is used to etch and remove magnesium nitride Mg3N2 in the composite material.

[0016] Furthermore, in step S3, hydrochloric acid and deionized water are used for multiple washings.

[0017] In addition, the present invention also provides a nitrogen-magnesium-coated germanium composite negative electrode material, which is prepared by the above method.

[0018] Furthermore, the nitrogen-magnesium-coated germanium composite negative electrode material has a three-dimensional porous skeleton structure, and a heterogeneous functional coating is formed in situ on the porous germanium surface.

[0019] In addition, the present invention also proposes an application of the nitrogen-magnesium-coated germanium composite negative electrode material, which uses the nitrogen-magnesium-coated germanium composite negative electrode material as a negative electrode material for a lithium-ion battery.

[0020] (3) Beneficial effects

[0021] The present invention provides a nitrogen-magnesium-coated germanium composite anode material, its preparation method, and application. During preparation, magnesium germanium powder is first calcined as a precursor to produce a composite material of germanium and magnesium nitride. The argon gas is then turned off and a secondary nitridation treatment is performed in a nitrogen atmosphere to form a MgGeN2 functional coating on the germanium surface. Finally, the magnesium nitride is etched. After multiple washings and drying, the nitrogen-magnesium alloy-coated germanium composite anode material is obtained. This material exhibits a three-dimensional porous structure that effectively mitigates the volume expansion effect of germanium during lithium extraction and insertion, improving the cycling stability of the electrode material. After the first discharge, the functional coating layer forms a Li-Mg alloy and Li3N composite SEI layer. Because Li3N is an excellent electron / ion conductor, the SEI composition is optimized and the interfacial impedance is reduced. The elastic LiMg alloy acts as a buffer, effectively suppressing interfacial delamination caused by volume changes. The preparation method is simple, efficient, and controllable, with simple subsequent processing and minimal equipment requirements, making it suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 SEM images of the embodiments of the present invention and comparative examples: (a) is the comparative example, (b) is embodiment 1, and (c) is embodiment 2;

[0023] Figure 2 HRTEM images of the embodiments of the present invention and comparative examples: (a) is embodiment 1, (b) is embodiment 2;

[0024] Figure 3 Schematic diagram of the long cycle performance of lithium-ion batteries prepared in Examples of the present invention and Comparative Examples at a current density of 5 A / g;

[0025] Figure 4 Schematic diagram of the coulombic efficiency of lithium-ion batteries prepared in Examples and Comparative Examples of the present invention at a current density of 5 A / g;

[0026] Figure 5 Schematic diagram of the rate performance of lithium-ion batteries prepared in the examples and comparative examples of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below with reference to the accompanying drawings and examples.

[0028] Example 1

[0029] S1. Using magnesium germanium powder as a precursor, 5 g of magnesium germanium powder was evenly spread in a corundum ark. The temperature was raised from room temperature to 750°C at a heating rate of 5°C / min. The calcination was carried out in an Ar / NH3 atmosphere and kept warm for 6 h to obtain a composite material of germanium and magnesium nitride Mg3N2.

[0030] S2. Turn off the argon gas, increase the temperature from 750°C to 880°C in a nitrogen atmosphere at a heating rate of 5°C / min, and perform a secondary nitridation treatment for 10 minutes to form a MgGeN2 functional coating on the germanium surface of the composite material.

[0031] S3. Use 1M HCl to etch away the magnesium nitride Mg3N2 in the composite material, wash it with hydrochloric acid and deionized water several times, and dry it to obtain a nitrogen-magnesium-coated germanium composite negative electrode material.

[0032] The nitrogen-magnesium-coated germanium composite negative electrode material obtained in step S3 was mixed with carboxymethyl cellulose and conductive carbon black in a mass ratio of 7:1:2 in water to form a slurry, coated on copper foil, and vacuum dried for 24 hours to obtain an electrode disc with an area of 1.0 square centimeter, which was used as the electrode negative electrode material of LIBs. Then, a half-cell was assembled in an argon-filled glove box. After standing for 24 hours, the lithium storage performance test was carried out at a constant temperature of 25°C. The cyclic voltammetry curve was recorded in the voltage window of 0.05-2V using an electrochemical workstation, and the electrochemical performance of the above half-cell was recorded using a blue battery test system.

[0033] The SEM image of the prepared nitrogen-magnesium-coated germanium composite negative electrode material is shown in Figure 2. Figure 1 As shown in (b), a continuous porous structure can be observed, which can effectively alleviate the volume expansion caused by lithium extraction / insertion. Figure 2 As shown in (a), the thickness of the nitrogen-magnesium coating layer is 4.1 nm. The coating layer can form a conductive elastic SEI layer during the cycle process, effectively improving the cycle stability and rate performance of the composite material.

[0034] In the lithium storage performance test, the loading amount of the composite material in the single-piece electrode was about 1.0 mg.

[0035] The assembled button cell has an initial discharge capacity of 1556.5 mAh / g at a current density of 5 A / g, an initial coulombic efficiency of 85.9%, and a discharge capacity of 950.1 mAh / g after 150 cycles. The average coulombic efficiency is greater than 99%, indicating that the material has higher cycle stability. Figure 3 and 4 shown.

[0036] Example 2

[0037] The difference from Example 1 is that the secondary nitriding treatment time is 20 minutes.

[0038] like Figure 1 As shown in (c), after 20 minutes of secondary nitriding treatment, the pore structure of the material deteriorates and small particles are formed on the surface. Figure 2As shown in (b), the thickness of the nitrogen-magnesium coating layer is 6.3 nm.

[0039] In the lithium storage performance test, the loading amount of the composite material in the single-piece electrode was about 1.0 mg.

[0040] The assembled button cell has an initial discharge capacity of 1563.2 mAh / g at a current density of 5 A / g, an initial coulombic efficiency of 83.3%, and a discharge capacity of 856.3 mAh / g after 150 cycles. The average coulombic efficiency is greater than 99%, indicating that the material has high cycle stability. Figure 3 and 4 shown.

[0041] Comparative Example

[0042] The difference from Example 1 is that no secondary nitriding treatment is performed.

[0043] The SEM images of the prepared composite materials are shown in Figure 1 As shown in (a), the pore structure of the material that has not undergone secondary nitriding treatment is not obvious and a good porous structure is not formed.

[0044] In the lithium storage performance test, the loading amount of the composite material in the single-piece electrode was approximately 1.0 mg.

[0045] The button cell was assembled. At a current density of 5 A / g, the initial discharge capacity was 1583.5 mAh / g, and the average coulombic efficiency was about 97%. Figure 3 and 4 shown.

[0046] Depend on Figure 5 It can be seen that when the germanium negative electrode materials obtained in Examples 1, 2 and the comparative example are used in LIBs, the rate performance at different current rates is as follows:

[0047] When the current density gradually increases from 0.2 A / g to 0.5, 1.0, 3.0, 5.0, 8.0, 10.0, 12.0, and 15.0 A / g, the discharge specific capacities of Example 1, Example 2, and the comparative example at a current density of 15.0 A / g are 21.9, 118.1, and 308.9 mAh / g, respectively. When the current density is restored to 0.1 A / g, the discharge specific capacities are restored to 1411.6, 1410.2, and 1422.6 mAh / g, respectively. Example 1 exhibits more excellent rate performance.

[0048] The final steady-state discharge specific capacities of the nitrogen-magnesium alloy-coated germanium composite negative electrode materials are 916, 802, 633, 493 and 313 mAh / g, respectively. When the current density returns to 0.1 A / g, its discharge capacity can be restored to 900 mAh / g, indicating that the prepared nitrogen-magnesium alloy-coated germanium composite negative electrode material has good rate performance in a wide current range. The nitrogen-magnesium alloy-coated germanium composite negative electrode material obtained in Example 2 has a reversible specific capacity of 770 mAh / g when the current density is 0.2 A / g.

[0049] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-magnesium-coated germanium composite negative electrode material, characterized in that: The preparation method comprises the following steps: S1 magnesium germanium powder as a precursor, calcined in a mixed gas atmosphere of argon and ammonia to obtain a composite material of germanium and magnesium nitride Mg3N2; S2. Turn off the argon gas and perform a secondary nitridation treatment on the composite material in a heated nitrogen atmosphere to form a MgGeN2 functional coating on the germanium surface of the composite material; S3. Remove magnesium nitride Mg3N2 from the composite material, wash and dry it, and obtain a nitrogen-magnesium-coated germanium composite negative electrode material.

2. The method for preparing the nitrogen-magnesium-coated germanium composite negative electrode material according to claim 1, wherein: In step S1 , magnesium germanium powder is leveled before calcining in a mixed gas atmosphere of argon and ammonia.

3. The method for preparing the nitrogen-magnesium-coated germanium composite negative electrode material according to claim 1, wherein: In step S1, during calcination, the temperature is raised from room temperature to 750°C at a heating rate of 5°C / min and kept at this temperature for 6 hours.

4. The method for preparing the nitrogen-magnesium-coated germanium composite negative electrode material according to claim 1, wherein: In step S2, the temperature is raised from 750°C to 880°C at a heating rate of 5°C / min, and a secondary nitriding treatment is performed for 10 to 20 minutes.

5. The method for preparing the nitrogen-magnesium-coated germanium composite negative electrode material according to claim 1, wherein: In step S3, 1M HCl is used to etch and remove the magnesium nitride Mg3N2 in the composite material.

6. The method for preparing the nitrogen-magnesium-coated germanium composite negative electrode material according to claim 1, wherein: In step S3, washing is performed multiple times using hydrochloric acid and deionized water.

7. A nitrogen-magnesium-coated germanium composite negative electrode material, characterized in that: The nitrogen-magnesium-coated germanium composite negative electrode material is prepared by the method according to any one of claims 1 to 6.

8. The nitrogen-magnesium-coated germanium composite negative electrode material according to claim 7, characterized in that: The nitrogen-magnesium-coated germanium composite negative electrode material has a three-dimensional porous skeleton structure, and a heterogeneous functional coating is formed in situ on the surface of the porous germanium.

9. Use of the nitrogen-magnesium-coated germanium composite negative electrode material according to claim 7 or 8, characterized in that: The nitrogen-magnesium-coated germanium composite negative electrode material is used as the negative electrode material of a lithium-ion battery.

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