CN105552353A - A high-performance lithium-ion battery negative electrode Bi2WO6/C composite material and its preparation method - Google Patents

Abstract

The invention relates to a negative electrode Bi ₂ WO ₆ /C composite material for a high-performance lithium ion battery and a preparation method thereof. In the negative electrode Bi ₂ WO ₆ /C composite material, C is coated on spherical Bi ₂ WO ₆ particles. The preparation method is Bi(NO ₃ ) ₃ ·5H ₂ O as bismuth source,? Na ₂ WO ₄ ·2H ₂ O is the tungsten source, and the two are added to the mixed solution of ethylene glycol and ethanol, and then urea and glucose are added. Finally, the mixed solution was transferred to a hydrothermal reaction tank for reaction, and the product was separated, washed and dried to obtain a Bi ₂ WO ₆ /C composite material. The Bi ₂ WO ₆ /C composite material prepared by the invention has the characteristics of high electrochemical capacity, good cycle stability, excellent rate performance, etc., and has the advantages of simple preparation process, good reproducibility, and easy industrialization.

Description

A high-performance lithium-ion battery negative electrode Bi2WO6/C composite material and its preparation method

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a high-performance lithium ion battery negative electrode Bi ₂ WO ₆ /C composite material and a preparation method thereof.

Background technique

At present, the anode materials used in lithium-ion batteries are generally carbon materials, such as graphite, soft carbon, hard carbon, etc. Although carbon anode materials have some excellent characteristics, they also have obvious disadvantages, such as soft carbon for the first time. High discharge irreversible capacity, no obvious charge and discharge platform; hard carbon has low initial charge and discharge efficiency, no obvious first charge and discharge platform, and large potential hysteresis caused by impurity H. Usually, the theoretical expression of the compound formed by lithium in carbon materials is LiC ₆ , the theoretical specific capacity according to stoichiometry is only 372mAh/g, and its density is relatively small, resulting in a very low volume specific capacity. In addition, when the charging and discharging potential reaches 0V or lower, lithium will be deposited on the graphite electrode to form dendrites, which may pierce the separator and cause a short circuit between the positive and negative electrodes of the battery, thus posing a safety hazard. Therefore, the study of negative electrode materials with high specific capacity and good safety performance is an inevitable trend in the development of lithium-ion battery technology, especially the development of new power lithium-ion batteries. Compared with carbon materials, Bi ₂ WO ₆ has a high specific capacity as an anode material for lithium-ion batteries, which makes it have great development potential as an anode material for a new generation of lithium-ion batteries, but Bi ₂ WO ₆ has poor conductivity, At the same time, during the intercalation/extraction process of lithium ions, Bi ₂ WO ₆ is accompanied by volume expansion/shrinkage, resulting in large volume deformation and easy pulverization of particles, which affects the cycle life.

Contents of the invention

The purpose of the present invention is to solve the above-mentioned technical problems existing in the prior art, and provide a high-performance lithium-ion battery negative electrode Bi ₂ WO ₆ /C composite material and a preparation method thereof.

The purpose of the present invention is to realize through the following technical solutions:

The present invention relates to a lithium ion battery negative electrode Bi ₂ WO ₆ /C composite material, the composite material includes a spherical Bi ₂ WO ₆ and a C coating layer uniformly coated on the outside of the spherical Bi ₂ WO ₆ , the The average particle size of Bi ₂ WO ₆ is 100nm~3000nm, and the C content is 0.5~10%. The smaller the particle size of the Bi ₂ WO ₆ /C composite material, the higher the electrochemical activity, but when it is smaller than 100nm, the material is easy to agglomerate, which affects the electrode coating process of the battery; the larger the particle size of the composite material, the lower the electrochemical activity, so it is not suitable to exceed Large, the particle size should be less than 3000nm. When the C content is less than 0.5%, the electrical conductivity of the Bi ₂ WO ₆ /C composite is poor, and at the same time, the inhibitory effect of C on the volume expansion of Bi ₂ WO ₆ is poor; when the C content is greater than 10%, the Bi ₂ WO ₆ /C The content of Bi ₂ WO ₆ in the composite material decreases, and the specific capacity of the Bi ₂ WO ₆ /C composite material decreases.

In the Bi ₂ WO ₆ /C composite material of the present invention, carbon improves the conductivity of Bi ₂ WO ₆ and can buffer the volume expansion of Bi ₂ WO ₆ during charging and discharging of lithium-ion batteries, prolonging its cycle life.

The present invention also relates to a method for preparing a high-performance lithium-ion battery negative electrode Bi ₂ WO ₆ /C composite material, the method comprising the following steps:

S1. Add Bi(NO ₃ ) ₃ .5H ₂ O and Na ₂ WO ₄ .2H ₂ O with a molar ratio of 2:1 to the mixed solution of ethylene glycol and absolute ethanol, wherein Bi(NO ₃ ) ₃ ·The molar ratio of 5H ₂ O and ethylene glycol is 1:100～1:150;

S2. Add urea and glucose to the solution obtained in step S1, wherein the molar ratio of Bi(NO ₃ ) ₃ .5H ₂ O to urea and glucose is 1:(2-5):(2-6);

S3. Under the condition that the reaction temperature is 110-190°C and the reaction time is 3-20 hours, the solution obtained in step S2 is subjected to hydrothermal reaction; the reaction product is separated, washed and dried to obtain the Bi ₂ WO ₆ /C composite material.

Preferably, in step S1, the volume ratio of ethylene glycol and absolute ethanol in the mixed solution of ethylene glycol and absolute ethanol is 1:1˜1:3.

Preferably, in step S3, the hydrothermal reaction is carried out by transferring the solution obtained in step S2 into a hydrothermal reaction kettle and controlling the filling degree to 40-80%.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention prepares the Bi ₂ WO ₆ /C composite material by adopting the improved hydrothermal method, C is evenly coated on the spherical Bi ₂ WO ₆ , carbon improves the conductivity of Bi ₂ WO ₆ , and can buffer Bi ₂ WO at the same time _6. The volume expansion during the working process of the lithium-ion battery improves the stability and cycle life of the electrode.

Compared with the prior art, the present invention has the following beneficial effects:

1) The surface of Bi ₂ WO ₆ is coated with a layer of C, which can effectively improve the conductivity of Bi ₂ WO ₆ and improve its rate performance in lithium-ion batteries. At the same time, the C layer can buffer Bi ₂ WO ₆ during charge and discharge. Volume expansion and contraction, avoiding pulverization of Bi ₂ WO ₆ particles.

2) The Bi ₂ WO ₆ /C of the present invention has excellent high rate performance, cycle stability and lifetime.

3) In the method of the present invention, the raw materials are cheap and easy to obtain, the operation is simple, the repeatability is good, and it is easy for industrialized mass production.

Description of drawings

FIG. 1 is a SEM image of the Bi ₂ WO ₆ /C material prepared according to Example 1.

Fig. 2 is the EDS diagram of the Bi ₂ WO ₆ /C material prepared according to Example 1.

FIG. 3 is a TEM image of the Bi ₂ WO ₆ /C material prepared according to Example 1. FIG.

FIG. 4 is the XRD pattern of the Bi ₂ WO ₆ /C material prepared according to Example 1.

FIG. 5 is a diagram of the rate and cycle performance of the lithium-ion battery assembled with the Bi ₂ WO ₆ /C material prepared in Example 1. FIG.

Fig. 6 is the XRD pattern of the Bi ₂ WO ₆ /C material prepared according to Example 2.

Fig. 7 is a cycle performance graph of a lithium ion battery assembled with Bi ₂ WO ₆ /C materials prepared according to Example 2.

Fig. 8 is the XRD pattern of the Bi ₂ WO ₆ /C material prepared according to Example 3.

Fig. 9 is a cycle performance diagram of a lithium ion battery assembled with Bi ₂ WO ₆ /C materials prepared according to Example 3.

FIG. 10 is an SEM image of the Bi ₂ WO ₆ /C material prepared according to Comparative Example 1.

FIG. 11 is a cycle performance diagram of a lithium-ion battery assembled with the Bi ₂ WO ₆ /C material prepared in Comparative Example 1. FIG.

FIG. 12 is an SEM image of the Bi ₂ WO ₆ material prepared according to Comparative Example 2.

FIG. 13 is a cycle performance graph of a lithium-ion battery assembled with the Bi ₂ WO ₆ material prepared in Comparative Example 2. FIG.

detailed description

The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings: this embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following the described embodiment.

Example 1

Weigh 4.8507g (0.01mol) Bi(NO ₃ ) ₃ 5H ₂ O, 1.6496g (0.005mol) Na ₂ WO ₄ 2H ₂ O and add them together to a mixed solution of 55.6mL ethylene glycol and 55.6mL absolute ethanol, While ultrasonically dispersing, 1.2012 g (0.02 mol) of urea was added. Weigh 3.6g (0.02ml) of glucose and directly add to the above solution. Finally, the mixed solution was charged into a 100 mL polytetrafluoroethylene-lined hydrothermal reactor with a filling capacity of 60%. The reaction was carried out at 150°C for 15h. Naturally cooled to room temperature, suction filtered, washed, and dried at 50°C for 24 hours to obtain Bi ₂ WO ₆ /C. Its morphology is shown in Figure 1, and the particles are spherical in shape. The X-ray energy spectrum is shown in Figure 2. It can be seen that the material is composed of elements C, Bi, W and O. The image of the high-magnification field emission lens is shown in Figure 3. It can be seen that the surface of Bi ₂ WO ₆ is covered with a C layer. The particles are spherical in shape. Its XRD is shown in Figure 4. Compared with the standard card PDF39-0256, it is found that it is consistent with the standard peak of orthorhombic Bi ₂ WO ₆ . In 0.1-3V, under the condition of charging and discharging at different rates, the relationship between the specific capacity and the cycle of the Bi ₂ WO ₆ /C composite material is shown in Figure 5, which has a good specific capacity.

Example 2

Weigh 7.2765g (0.015mol) Bi(NO ₃ ) ₃ 5H ₂ O, 2.4739g (0.0075mol) Na ₂ WO ₄ 2H ₂ O and add them together into 125mL ethylene glycol and 250mL absolute ethanol mixed solution, ultrasonically disperse While adding 4.5g (0.075mol) urea. Weigh 16.2g (0.09ml) of glucose and directly add to the above solution. Finally, the mixed solution was charged into a 100 mL polytetrafluoroethylene-lined hydrothermal reactor with a filling capacity of 80%. The reaction was carried out at 190°C for 15h. Naturally cooled to room temperature, suction filtered, washed, and dried at 50°C for 24 hours to obtain Bi ₂ WO ₆ /C. Its XRD is shown in Figure 6. Compared with the standard card PDF39-0256, it is found that it is consistent with the standard peak of orthorhombic Bi ₂ WO ₆ . Under the discharge conditions of 0.1-3V, 100mA/g, the relationship between specific capacity and cycle of Bi ₂ WO ₆ /C composite material is shown in Figure 7, which has good electrochemical performance.

Example 3

Weigh 5.8208g (0.012mol) Bi(NO ₃ ) ₃ ·5H ₂ O and 1.9792g (0.006mol) Na ₂ WO ₄ ·2H ₂ O and add them together into a mixed solution of 83.5mL ethylene glycol and 250.5mL absolute ethanol. While ultrasonically dispersing, 2.852 g (0.042 mol) of urea was added. Weigh 8.64g (0.048ml) of glucose and directly add to the above solution. Finally, the mixed solution was charged into a 100 mL polytetrafluoroethylene-lined hydrothermal reactor with a filling capacity of 40%. The reaction was carried out at 110°C for 15h. Naturally cooled to room temperature, suction filtered, washed, and dried at 50°C for 24 hours to obtain Bi ₂ WO ₆ /C. Its XRD is shown in Figure 8. Compared with the standard card PDF39-0256, it is found that it is consistent with the standard peak of orthorhombic Bi ₂ WO ₆ . Under the discharge condition of 0.1-3V, 500mA/g, the relationship between specific capacity and cycle of Bi ₂ WO ₆ /C composite material is shown in Figure 9, which has good electrochemical performance.

Comparative example 1

Weigh 4.8507g (0.01mol) Bi(NO ₃ ) ₃ ·5H ₂ O and 1.6496g (0.005mol) Na ₂ WO ₄ ·2H ₂ O and add them together to a mixed solution of 55.6mL ethylene glycol and 55.6mL absolute ethanol. While ultrasonically dispersing, 3.6 g (0.02 ml) of glucose was directly added to the above solution. Finally, the mixed solution was charged into a 100 mL polytetrafluoroethylene-lined hydrothermal reactor with a filling capacity of 60%. The reaction was carried out at 150°C for 15h. Naturally cooled to room temperature, suction filtered, washed, and dried at 50°C for 24 hours to obtain Bi ₂ WO ₆ /C. Its appearance is shown in Figure 10. Under the discharge condition of 0.1-3V, 100mA/g, the relationship between specific capacity and cycle of Bi ₂ WO ₆ /C composite material is shown in Fig. 11 .

Comparative example 2

Weigh 7.2765g (0.015mol) Bi(NO ₃ ) ₃ ·5H ₂ O and 2.4739g (0.0075mol) Na ₂ WO ₄ ·2H ₂ O and add them together into a mixed solution of 125mL ethylene glycol and 250mL absolute ethanol. While ultrasonically dispersing, 4.5 g (0.075 mol) of urea was added. The mixed solution was charged into a 100mL polytetrafluoroethylene-lined hydrothermal reactor with a filling capacity of 80%. The reaction was carried out at 190°C for 15h. Naturally cooled to room temperature, suction filtered, washed, and dried at 50°C for 24 hours to obtain Bi ₂ WO ₆ . Its appearance is shown in Figure 12. Under the discharge condition of 0.1-3V, 100mA/g, the relationship between specific capacity and cycle of Bi ₂ WO ₆ composite material is shown in Fig. 13 .

Claims (4)

1. a lithium ion battery negative Bi ₂wO ₆/ C composite, is characterized in that, described composite material comprises the spherical Bi of class ₂wO ₆and be evenly coated on such spherical Bi ₂wO ₆outside C coating layer, described Bi ₂wO ₆average grain diameter be 100nm ~ 3000nm, C content is 0.5 ~ 10%.

2. a lithium ion battery negative Bi as claimed in claim 1 ₂wO ₆the preparation method of/C composite, is characterized in that, described method comprises the steps:

S1, be the Bi (NO of 2:1 by mol ratio ₃) ₃5H ₂o and Na ₂wO ₄2H ₂o joins in the mixed solution of ethylene glycol and absolute ethyl alcohol, wherein, and Bi (NO ₃) ₃5H ₂the mol ratio of O and ethylene glycol is 1:100 ~ 1:150;

S2, urea and glucose joined in solution that step S1 obtains, wherein, Bi (NO ₃) ₃5H ₂the mol ratio of O and urea, glucose is 1:(2 ~ 5): (2 ~ 6);

S3, be 110 ~ 190 DEG C in reaction temperature, the reaction time is under the condition of 3 ~ 20h, and the solution that step S2 obtains carries out hydro-thermal reaction; Product is carried out separating, washing and drying, obtains described Bi ₂wO ₆/ C composite.

3. lithium ion battery negative Bi as claimed in claim 2 ₂wO ₆the preparation method of/C composite, is characterized in that, in step S1, in described ethylene glycol and absolute ethyl alcohol mixed solution, ethylene glycol and absolute ethyl alcohol volume ratio are 1:1 ~ 1:3.

4. lithium ion battery negative Bi as claimed in claim 2 ₂wO ₆the preparation method of/C composite, is characterized in that, in step S3, described hydro-thermal reaction is that the solution obtained by step S2 is transferred in hydrothermal reaction kettle, and control compactedness 40 ~ 80% is carried out.