H-Nb2O5-x negative electrode material prepared at room temperature by lithium reduction method and application thereof

Abstract

The invention provides a brand new method for preparing the H-Nb2O5-x negative electrode material by using a lithium reduction method at room temperature, and the application prospect is wide. The specific operation is as follows: lithium powder and H-Nb2O5-x powder are simply ground at normal temperature, oxygen vacancies are promoted to be generated in the material, and the novel H-Nb2O5-x material is prepared. Compared with a traditional heat treatment method and a preparation method depending on a reducing atmosphere, the lithium reduction method has remarkable advantages. The method is simple in operation process and extremely low in energy consumption, and solves the problems of complex process and high energy consumption of the traditional method. The key step of introducing oxygen vacancies by virtue of a lithium reduction method at room temperature can optimize the electron conduction efficiency among sample particles, so that the reversible capacity, the cycling stability and other electrochemical properties of the material are greatly improved. From the aspect of preparation process, the method is simple and easy to implement, and raw materials are easily available. And when applied to the negative electrode of the lithium ion battery, the composite material shows the characteristics of high specific capacity and ultra-long cycle life, and has great popularization value.

Description

Technical Field

[0001] The present invention belongs to the technical fields of anode materials for lithium-ion batteries and electrochemical devices, and particularly relates to a method for preparing H-Nb 2 O 5-x anode material at room temperature by lithium reduction method and its application. This material is synthesized by lithium reduction method at room temperature and exhibits excellent electrochemical performance when applied as an anode material for lithium-ion batteries. Background Art

[0002] Lithium-ion batteries are widely used in modern life, from smartphones to electric vehicles. Anode materials play a crucial role in lithium-ion batteries and are of great necessity. On the one hand, they participate in the lithium-ion insertion and extraction reactions during battery charging and discharging. Like the "energy storage warehouse" of the battery, they directly affect the energy density of the battery and determine the battery's endurance. On the other hand, stable and reliable anode materials can ensure the battery's cycle life, reduce performance degradation during charging and discharging, and ensure long-term stable power supply for the battery, continuously supplying energy to various electronic devices and new energy transportation vehicles.

[0003] Niobium pentoxide (Nb 2 O 5 ) is a common intercalation-type anode material with high working voltage, structural stability, diffusion efficiency, and low polarization behavior. Therefore, it is often used to develop high-rate and safe lithium-ion batteries. During preparation, due to different heating conditions, Nb 2 O 5 will form various configurations such as TT-Nb 2 O 5 , T-Nb 2 O 5 , etc. Among them, the thermodynamic structure of H-Nb 2 O 5 is the most stable, and that of TT-Nb 2 O 5 is the most unstable. The initial capacity of monoclinic H-Nb 2 O 5 is larger than that of T-Nb 2 O 5 , but its capacity retention and rate performance are much worse. This is because the NbO 2 O 5 / NbO 6 / NbO 7 skeleton of T-Nb 2 O 5 can more efficiently accommodate Li atoms. The rate performance of the other configurations is between the two. Past research has mostly focused on T-Nb 2 O 5 , and improving the electrochemical performance of H-Nb 2 O5 The research focuses on improving electronic conductivity and ion transportability. Common strategies include nanosizing materials or combining them with conductive materials. Micron-sized materials have poor performance, and most researchers tend to nanosize them, which can shorten the solid-phase diffusion path of lithium ions and enhance electrochemical and conductive properties. However, nanomaterials have high synthesis costs and low tap densities, limiting their applications in energy storage platforms. Additionally, due to their high surface reaction activity, side reactions, decomposition, polymerization, etc. are likely to occur. Combining with conductive materials also has drawbacks. The process is complex, increasing manufacturing difficulty and cost, and it will also increase the electrode mass, affecting the battery energy density. In addition, introducing oxygen vacancies into electrode materials also has a certain impact on improving electrochemical performance. It can both open channels to accelerate lithium ion transport and introduce defect energy levels to affect conductivity. However, the heat treatment method and preparation in a reducing atmosphere face many challenges in practical applications. On the one hand, their preparation processes are complex, involving many fine steps and strict conditions; on the other hand, these two methods have high energy consumption, greatly increasing the preparation cost. In view of this, it is urgent to explore and propose a new, efficient and low-consumption oxygen vacancy regulation strategy. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides a method for preparing H-Nb 2 O 5-x negative electrode material by lithium reduction method at room temperature and its application. Oxygen vacancies are introduced into H-Nb 2 O 5 at room temperature by the lithium reduction method to improve its electronic conductivity. The method of this patent has the advantages of simple operation and low energy consumption, which is conducive to the large-scale application of H-Nb 2 O 5-x negative electrode material.

[0005] To achieve the above object, the specific steps of introducing oxygen vacancies into H-Nb 2 O 5 at room temperature by the lithium reduction method are as follows:

[0006] (1) First, commercially available niobium pentoxide powder is placed in a muffle furnace and sintered at 1000 °C for 6 h. After grinding, the powder H-Nb 2 O 5 is obtained;

[0007] (2) Before reduction, a certain amount of the product obtained in step (1) is placed in a vacuum drying oven and dried at 60 °C for 12 hours. After taking it out, it is immediately placed in a glove box filled with Ar gas;

[0008] (3) In the glove box filled with Ar gas, first pour the weighed product in step (2) into a ceramic mortar, and add a certain amount of dimethyl carbonate (DMC). Weigh the content of lithium powder according to 1% of the weighed product in step (2), and add it to the ceramic mortar as well. Then grind it at a speed of 2 seconds / turn for 30 minutes;

[0009] (4) Take out the sample ground in step (3), wash it by suction filtration with absolute ethanol and ultrapure water (1:1), and then place it in a vacuum drying oven. Dry it at 60 °C for 12 hours to obtain the H-Nb 2 O 5-x sample.

[0010] The preparation conditions involved in the present invention are simple and easy for large-scale industrial production. Introducing oxygen vacancies into the material improves the conductivity of the material, thereby showing better electrochemical performance. Description of the Drawings

[0011] Figure 1 is the XRD data graph of H-Nb 2 O 5 and the H-Nb of the present invention 2 O 5-x negative electrode material.

[0012] Figure 2 is the SEM graph of the H-Nb of the present invention 2 O 5-x negative electrode material.

[0013] Figure 3 is the EPR graph of H-Nb 2 O 5 and the H-Nb of the present invention 2 O 5-x negative electrode material.

[0014] Figure 4 is the XPS graph of H-Nb 2 O 5 and the H-Nb of the present invention 2 O 5-x negative electrode material.

[0015] Figure 5 is the cyclic voltammogram of the H-Nb of the present invention 2 O 5-x negative electrode material, the scanning rate is 0.2 mV / s, and the voltage range is 0.01~3V.

[0016] Figure 6 is the cyclic performance graph of the H-Nb of the present invention 2 O 5-x negative electrode material at a magnification of 0.05 A·g -1 times.

[0017] Figure 7 is the rate performance graph of the H-Nb of the present invention 2 O 5-x negative electrode material.

[0018] Figure 8is the H-Nb of the present invention 2 O 5-x The cycling performance graph of the negative electrode material at a current rate of 1 A·g -1 rate. Detailed implementation manners

[0019] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described below in conjunction with the accompanying drawings and specific implementation manners. However, the protection scope of the present invention is not limited to the following embodiments.

[0020] Example 1:

[0021] (1) First, commercially available niobium pentoxide powder is placed in a muffle furnace and sintered at 1000 °C for 6 h. After grinding, the powder H-Nb 2 O 5 is obtained.

[0022] (2) Before reduction, 1 g of the product obtained in step (1) is weighed, placed in a vacuum drying oven and dried at 60 °C for 12 hours. After taking it out, it is immediately placed in a glove box filled with Ar gas;

[0023] (3) In the glove box filled with Ar gas, first pour the weighed product in step (2) into a ceramic mortar, and add a certain amount of dimethyl carbonate (DMC). Weigh the content of lithium powder (10 mg) according to 1% of the weighed product in step (2), and add it to the ceramic mortar as well. Then, grind it at a speed of 2 seconds / rotation for 30 minutes;

[0024] (4) Take out the sample ground in step (3) from the glove box, wash it by suction filtration with absolute ethanol and ultrapure water (1:1), and then place it in a vacuum drying oven and dry it at 60 °C for 12 hours to obtain the H-Nb 2 O 5-x sample.

[0025] Figure 1 It shows that the H-Nb 2 O 5-x negative electrode material is successfully prepared. It can be seen from the spectrum that the phase of the material after lithium powder reduction is the same as that before reduction, and there are no impurity peaks.

[0026] The material H-Nb obtained by the present invention 2 O 5-xWhen used as the anode material of a lithium-ion battery, an electrode is fabricated with the mass ratio of active material:superconductive carbon black:CMC (binder) being 6:3:1. First, carboxymethyl cellulose (CMC) is placed in a 5-ml glass beaker, and an appropriate amount of ultrapure water is added. After magnetic stirring until it becomes clear, the active electrode material and superconductive carbon black are weighed in proportion and then placed in a mortar. After grinding in the mortar for 30 minutes, it is taken out and poured into the glass beaker, stirred for 5 hours, and finally evenly coated on the current collector copper foil. It is then placed in a vacuum drying oven and dried at 60 °C for 12 hours. After taking it out, the electrode sheet is compacted using a tablet press, and then sliced. The diameter of the electrode sheet is 14 mm, and thus the working electrode is obtained. A lithium metal sheet is used as the counter electrode and reference electrode, Celgard 2400 microporous polypropylene is used as the separator, and the electrolyte is an organic solution of LiPF6 (concentration of 1 mol / L) dissolved in ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (volume ratio of 1:1:1). The assembly of the CR2032-type button battery is carried out in a glove box filled with argon, and it is required that the oxygen content and water content in the glove box are both lower than 0.1 ppm. The charge-discharge capacity is calculated based on the mass of the active material.

[0027] Figure 2 is H-Nb 2 O 5-x SEM image of the anode material. As can be seen from the figure, the particles have an obvious textured surface, and aligned stripes can be clearly observed, with diameters ranging from 0.5 μm to 2 μm.

[0028] Figure 3 is H-Nb 2 O 5 and the H-Nb of the present invention 2 O 5-x EPR image of the anode material. After lithium reduction, the EPR spectrum of the sample H-Nb 2 O 5-x shows a strong signal at g = 2.002, which confirms the existence of oxygen vacancies in the sample H-Nb 2 O 5-x after lithium reduction.

[0029] Figure 4 is H-Nb 2 O 5 and the H-Nb of the present invention 2 O 5-x XPS image of the anode material. The left figure is the spectral diagram of Nb 3d. The two peaks at 207.3 eV and 210 eV of Nb 3d 5 / 2 indicate that Nb in H-Nb2O5 is pentavalent (Nb 3 / 2 ). Due to the introduction of oxygen vacancies, H-Nb 5+ ).2 O 5-x peaks are shifted to lower binding energies, indicating the formation of a lower valence state of Nb (Nb 4+ ); The right figure is the XPS spectrum of O 1s, where the three typical XPS peaks at 530.6, 531.9, and 533.4 eV belong to lattice oxygen, oxygen vacancies, and surface adsorbed oxygen, respectively. It can be seen from the figure that the content of oxygen vacancies in H-Nb 2 O 5-x increases significantly, indicating that active lithium can effectively remove some oxygen elements, thus introducing more oxygen vacancies into the lattice of H-Nb 2 O 5 powder.

[0030] Figure 5 are the CV curves of the H-Nb 2 O 5-x negative electrode material in the first three cycles at a scanning rate of 0.2 mV / s and a voltage range of 0.01 - 3 V. The curves of the three cycles almost overlap, indicating that the electrode material has good cycle reversibility.

[0031] Figure 6 are the cycling performance diagrams of the H-Nb 2 O 5-x negative electrode material at a current density of 0.05 A·g -1 . After 100 cycles, the discharge specific capacity of the material is as high as 530.1 mAh / g, and the capacity retention rate is 99.8%, indicating that the material has good cycle stability.

[0032] Figure 7 are the performance diagrams of the H-Nb 2 O 5-x negative electrode material at different current densities. At current densities of 0.05, 0.2, 0.4, 0.8, 1, 2, and 3 A·g -1 , the discharge specific capacities reach 512.3 mAh / g, 441.3 mAh / g, 387.7 mAh / g, 337.7 mAh / g, 318.0 mAh / g, 269.2 mAh / g, and 241.1 mAh / g, respectively. When the current returns to 0.05 A·g -1 , a high capacity of up to 479.9 mAh / g is obtained for the discharge specific capacity. It can be seen that after cycling at a large current density, when the current is switched back to a small current density state, the rate reversibility of the material is not significantly affected and remains at a good level.

[0033] Figure 8 are the H-Nb 2 O 5-x negative electrode material at 1 A·g -1Long cycle performance graph at high rate. The initial discharge specific capacity is 320.4 mAh / g, the capacity after 500 cycles is 292.9 mAh / g, and the capacity retention rate is 91.4%, indicating that the material has excellent high rate performance and long cycle life.

Claims

1. A H-Nb2O5-x negative electrode material prepared at room temperature by a lithium reduction method, characterized in that: The specific steps are: (1) First, commercial niobium pentoxide powder was placed in a muffle furnace, sintered at 1000°C for 6 h, and then ground to obtain powder H-Nb2O5; (2) Before reduction, a certain amount of the product obtained in step (1) was placed in a vacuum drying oven at 60°C for 12 hours and immediately placed in a glove box filled with Ar gas; (3) In a glove box filled with Ar gas, first pour the product weighed in step (2) into a ceramic mortar, and drop a certain amount of dimethyl carbonate (DMC), weigh the content of lithium powder at a ratio of 1% of the product weighed in step (2), and add it into the ceramic mortar, and then grind at a speed of 2 seconds / turn for 30 minutes; (4) The sample after grinding in step (3) was taken out, filtered and washed with anhydrous ethanol and ultrapure water (1:1), and then placed in a vacuum drying oven and dried at 60°C for 12 hours to obtain H-Nb2O 5-x sample.

2. The H-Nb2O5-x negative electrode material according to claim 1, characterized in that: H-Nb2O prepared by lithium reduction at room temperature 5-x The material is used as negative electrode material for lithium-ion batteries.

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