CN107180951A - A kind of tungstic acid/tungsten dioxide composite for making negative electrode of lithium ion battery and preparation method thereof - Google Patents

Abstract

The invention relates to a tungsten trioxide/tungsten dioxide composite material that can be used as a negative electrode of a lithium-ion battery and a preparation method thereof. Firstly, a citric acid solution and a tungsten source solution are uniformly mixed to obtain a mixed solution A. In the mixed solution A, citric acid and The molar ratio of the tungsten source is (1-4):1; adjust the pH value of the mixed solution A at 1-3, and carry out the homogeneous hydrothermal reaction at 160-200°C; cool to room temperature after the homogeneous hydrothermal reaction, separate The product is washed and dried to obtain a tungsten trioxide/tungsten dioxide composite material that can be used as a negative electrode of a lithium ion battery. In the present invention, tungsten trioxide with higher theoretical capacity but poor cycle performance is combined with tungsten dioxide with lower theoretical capacity, and the metal conductivity of tungsten dioxide is used to solve the problem of large volume of tungsten trioxide in the cycle process. The problem of change; increase the specific capacity, reduce the volume change during the cycle, increase the discharge specific capacity of WO ₃ , and reduce the charge transfer resistance of WO ₃ .

Description

A kind of tungsten trioxide/tungsten dioxide composite material that can be used as negative electrode of lithium ion battery and its preparation method

technical field

The invention belongs to the technical field of composite material preparation, and in particular relates to a tungsten trioxide/tungsten dioxide composite material which can be used as a negative electrode of a lithium ion battery and a preparation method thereof.

Background technique

As an important n-type semiconductor oxide, tungsten trioxide (WO ₃ ) is widely used in chemical sensors, photocatalysis, energy conversion systems and other fields [Jinzhan Su, Liejin Guo, Ningzhong Bao, et al. Nanostructured WO ₃ /BiVO ₄ heterojunction films for efficient photoelectrochemical water splitting [J]. Nano Letters, 2011, 11: 1928-1933.]. Due to its large theoretical capacity (693mAh/g), low cost, and high safety (high melting temperature and mechanical stability), it can be used as an anode material for lithium-ion batteries [Songhun Yoon, Changshin Jo, Soon Young Noh, et al. Development of a high-performance anode for lithium ion batteries using novel ordered mesoporous tungsten oxide materials with high electrical conductivity [J]. Physical Chemistry Chemical Physics, 2011, 13: 11060-11066.]. However, when WO ₃ is used as the negative electrode material, its structure and volume will change greatly during the charging/discharging process, which will destroy the stability of the electrode material, lead to mechanical crushing and the loss of the electronic connection between the active material and the current collector, and eventually The cycle performance of the electrode is reduced[Jiaqin Yang, Lifang Jiao, Qianqian Zhao, et al.Facile preparation and electrochemical properties of hierarchical chrysanthemum-like WO ₃ ·0.33H ₂ O[J].Journal of Materials Chemistry,2012,22:3699- 3701.]. Moreover, due to various factors, the actual capacity is often lower than the theoretical capacity.

Contents of the invention

The purpose of the present invention is to overcome the problems existing in the prior art, to provide a kind of tungsten trioxide/tungsten dioxide composite material which can be used as the negative electrode of lithium ion battery and its preparation method, the specific capacity of the obtained composite material is high, and the cycle performance is better .

In order to achieve the above object, the present invention adopts following technical scheme:

Include the following steps:

(1) Mix the citric acid solution and the tungsten source solution evenly to obtain a mixed solution A, and the molar ratio of the citric acid and the tungsten source in the mixed solution A is (1～4):1;

(2) adjust the pH value of the mixed solution A at 1 to 3 to obtain the mixed solution B;

(3) The mixed solution B is subjected to a homogeneous hydrothermal reaction at 160-200° C.;

(4) After the homogeneous hydrothermal reaction is completed, cool to room temperature, separate the product, wash and dry, and obtain a tungsten trioxide/tungsten dioxide composite material that can be used as a negative electrode of a lithium-ion battery.

Further, the concentration of the citric acid solution in step (1) is 0.5-1 mol/L, and the concentration of the tungsten source solution is 0.5-1 mol/L.

Further, the tungsten source in step (1) is Na ₂ WO ₄ ·2H ₂ O.

Further, in step (1), the mixture is uniformly mixed by stirring at 25-35° C. for 15-35 minutes.

Further, in step (2), a 2-3 mol/L HCl solution is used to adjust the pH value.

Further, in step (3), the mixed solution B is poured into a polytetrafluoroethylene-lined high-pressure hydrothermal reactor with a volume filling ratio of 40% to 60%, and then the polytetrafluoroethylene-lined high-pressure hydrothermal reactor is sealed , put into the homogeneous hydrothermal reaction apparatus for homogeneous hydrothermal reaction.

Further, the time for the homogeneous hydrothermal reaction in step (3) is 20-28 hours.

Further, the drying in step (4) is drying in a vacuum oven at 60-80° C. for 5-10 hours.

A tungsten trioxide/tungsten dioxide composite material that can be used as the negative electrode of lithium-ion batteries prepared by the above-mentioned preparation method, the composite material is monoclinic phase WO ₃ and WO ₂ , at a current density of 100mA/g After 500 cycles, the Coulombic efficiency is 87-95%.

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

In the preparation method of the present invention, the tungsten source is partially reduced through the reduction of citric acid, so that tungsten trioxide with higher theoretical capacity but poor cycle performance is composited with tungsten dioxide with lower theoretical capacity. Oxygen vacancy defects in the lattice and strong metal-metal bonds inside the crystal, therefore, tungsten dioxide (WO ₂ ) has metal conductivity (electronic conductivity is about 3.5×10 ² S/cm), and the use of tungsten dioxide Metal conductivity, as a conductive oxide compounded with WO ₃ , solves the problem of large volume changes of tungsten trioxide during the cycle; the present invention combines tungsten dioxide and tungsten trioxide, which can increase the specific capacity, Reduce the volume change during cycling, increase the discharge specific capacity of WO ₃ , and reduce the charge transfer resistance of WO ₃ .

The invention provides a WO ₃ -WO ₂ composite material that can be used as the negative electrode of lithium ion battery. When used as the negative electrode material of lithium ion battery, it has a higher specific capacity, which can reach 680mAh/g, and a higher coulombic efficiency, 100mA The Coulombic efficiency can reach 95% at a current density of 500 cycles per g.

Description of drawings

Fig. 1 is the XRD spectrum of the WO ₃ -WO ₂ composite material prepared in Example 1 of the present invention.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings.

1) Prepare 0.5-1M C ₆ H ₈ O ₇ ·H ₂ O distilled water solution, 0.5-1M Na ₂ WO ₄ ·2H ₂ O distilled water solution.

2) The above solution is mixed according to the volume ratio of C ₆ H ₈ O ₇ ·H ₂ O:Na ₂ WO ₄ ·2H ₂ O=(1~4):1, and stirred at 25~35°C for 15~35min.

3) Adjust the pH of the above mixed solution to 1-3 with an HCl solution having a concentration of 2-3M.

4) Pour the homogeneously mixed solution into a polytetrafluoroethylene-lined high-pressure hydrothermal reactor, keeping the volume filling ratio at 40% to 60%.

5) Put the sealed reaction kettle into the homogeneous hydrothermal reaction apparatus, set the temperature parameters to 160-200° C., and the reaction time to 20-28 hours.

6) Cool to room temperature after the reaction, centrifuge the final reactant, and wash with deionized water and absolute ethanol three times respectively. The final product is obtained by putting the centrifuged and washed powder into a vacuum oven at 60-80°C for 5-10 hours to dry.

Example 1

1) Prepare 0.5M distilled aqueous solution of C ₆ H ₈ O ₇ ·H ₂ O and 0.5M distilled aqueous solution of Na ₂ WO ₄ ·2H ₂ O.

2) The above solution was mixed according to the volume ratio of C ₆ H ₈ O ₇ ·H ₂ O:Na ₂ WO ₄ ·2H ₂ O=2:1, and stirred at 25° C. for 15 min.

3) Adjust the pH of the above mixed solution to 1 with a 2M HCl solution.

4) Pour the homogeneously mixed solution into a polytetrafluoroethylene-lined high-pressure hydrothermal reactor, keeping the volume filling ratio at 40%.

5) Put the sealed reaction kettle into the homogeneous hydrothermal reactor, set the temperature parameter to 160° C., and the reaction time to 28 hours.

6) Cool to room temperature after the reaction, centrifuge the final reactant, and wash with deionized water and absolute ethanol three times respectively. Put the centrifuged and washed powder in a vacuum oven at 60°C for 10 hours to obtain the final product.

The Coulombic efficiency can reach 95% after 500 cycles at a current density of 100mA/g.

It can be seen from Fig. 1 that the products prepared by the present invention are monoclinic WO ₃ and WO ₂ , and no other impurity peaks appear.

Example 2

1) Prepare 1M C ₆ H ₈ O ₇ ·H ₂ O distilled water solution, 1M Na ₂ WO ₄ ·2H ₂ O distilled water solution.

2) The above solution was mixed according to volume ratio C ₆ H ₈ O ₇ ·H ₂ O:Na ₂ WO ₄ ·2H ₂ O=1:1, and stirred at 35°C for 35 min.

3) Adjust the pH of the above mixed solution to 3 with a 3M HCl solution.

4) Pour the homogeneously mixed solution into a polytetrafluoroethylene-lined high-pressure hydrothermal reactor, keeping the volume filling ratio at 60%.

5) Put the sealed reactor into the homogeneous hydrothermal reactor, set the temperature parameter to 200° C., and the reaction time to 20 h.

6) Cool to room temperature after the reaction, centrifuge the final reactant, and wash with deionized water and absolute ethanol three times respectively. Put the centrifuged and washed powder into a vacuum oven at 80°C for 5 hours to dry to obtain the final product.

The Coulombic efficiency can reach 92% after 500 cycles at a current density of 100mA/g.

Example 3

1) Prepare 0.8M distilled aqueous solution of C ₆ H ₈ O ₇ ·H ₂ O and 0.8M distilled aqueous solution of Na ₂ WO ₄ ·2H ₂ O.

2) The above solution was mixed according to the volume ratio of C ₆ H ₈ O ₇ ·H ₂ O:Na ₂ WO ₄ ·2H ₂ O = 3:1, and stirred at 30° C. for 25 min.

3) Adjust the pH of the above mixed solution to 2 with a 2M HCl solution.

4) Pour the homogeneously mixed solution into a polytetrafluoroethylene-lined high-pressure hydrothermal reactor, keeping the volume filling ratio at 50%.

5) Put the sealed reactor into a homogeneous hydrothermal reactor, set the temperature parameter to 180° C., and the reaction time to 24 hours.

6) Cool to room temperature after the reaction, centrifuge the final reactant, and wash with deionized water and absolute ethanol three times respectively. The final product is obtained by putting the centrifuged and washed powder into a vacuum oven or a freeze drying oven at 70° C. for 8 hours to dry.

The Coulombic efficiency can reach 89% after 500 cycles at a current density of 100mA/g.

Example 4

1) Prepare 0.6M C ₆ H ₈ O ₇ ·H ₂ O distilled water solution, 0.6M Na ₂ WO ₄ ·2H ₂ O distilled water solution.

2) The above solution was mixed according to the volume ratio of C ₆ H ₈ O ₇ ·H ₂ O:Na ₂ WO ₄ ·2H ₂ O=4:1, and stirred at 28° C. for 20 min.

3) Adjust the pH of the above mixed solution to 1.5 with a 3M HCl solution.

4) Pour the homogeneously mixed solution into a polytetrafluoroethylene-lined high-pressure hydrothermal reactor, keeping the volume filling ratio at 55%.

5) Put the sealed reactor into the homogeneous hydrothermal reactor, set the temperature parameter to 170°C, and the reaction time to 26h.

6) Cool to room temperature after the reaction, centrifuge the final reactant, and wash with deionized water and absolute ethanol three times respectively. Put the centrifuged and washed powder into a 75°C vacuum oven or a freeze-drying oven to dry for 6 hours to obtain the final product.

The Coulombic efficiency can reach 87% after 500 cycles at a current density of 100mA/g.

Claims (9)

1. a kind of preparation method for the tungstic acid/tungsten dioxide composite for making negative electrode of lithium ion battery, it is characterised in that： Comprise the following steps：

(1) citric acid solution and tungsten source solution are well mixed, obtain citric acid and tungsten source in mixed solution A, mixed solution A Mol ratio is (1~4):1；

(2) pH value of regulation mixed solution A obtains mixed solution B 1~3；

(3) mixed solution B is subjected to homogeneous hydro-thermal reaction at 160~200 DEG C；

(4) homogeneous hydro-thermal reaction is cooled to room temperature after terminating, and isolates product and washs drying, obtains that lithium ion battery can be made bearing The tungstic acid of pole/tungsten dioxide composite.

2. a kind of tungstic acid/tungsten dioxide composite for making negative electrode of lithium ion battery according to claim 1 Preparation method, it is characterised in that：The concentration of citric acid solution is 0.5~1mol/L in step (1), and the concentration of tungsten source solution is 0.5~1mol/L.

3. a kind of tungstic acid/tungsten dioxide composite for making negative electrode of lithium ion battery according to claim 1 Preparation method, it is characterised in that：Tungsten source uses Na in step (1)₂WO₄·2H₂O。

4. a kind of tungstic acid/tungsten dioxide composite for making negative electrode of lithium ion battery according to claim 1 Preparation method, it is characterised in that：It is to be well mixed by stirring 15~35min at 25~35 DEG C in step (1).

5. a kind of tungstic acid/tungsten dioxide composite for making negative electrode of lithium ion battery according to claim 1 Preparation method, it is characterised in that：Using 2~3mol/L HCl solution regulation pH value in step (2).

6. a kind of tungstic acid/tungsten dioxide composite for making negative electrode of lithium ion battery according to claim 1 Preparation method, it is characterised in that：Mixed solution B is poured into polytetrafluoroethyllining lining high-pressure hydrothermal reaction kettle in step (3), volume Then packing ratio seals polytetrafluoroethyllining lining high-pressure hydrothermal reaction kettle 40%~60%, is put into homogeneous hydro-thermal reaction instrument It is middle to carry out homogeneous hydro-thermal reaction.

7. a kind of tungstic acid/tungsten dioxide composite for making negative electrode of lithium ion battery according to claim 1 Preparation method, it is characterised in that：The time of homogeneous hydro-thermal reaction is 20~28h in step (3).

8. a kind of tungstic acid/tungsten dioxide composite for making negative electrode of lithium ion battery according to claim 1 Preparation method, it is characterised in that：Drying in step (4) is to dry 5~10h in 60~80 DEG C of vacuum drying ovens.

9. tungstic acid/titanium dioxide of negative electrode of lithium ion battery can be made made from preparation method described in a kind of utilization claim 1 Composite tungsten material, it is characterised in that：The composite is the WO of monoclinic phase₃And WO₂, circulated under 100mA/g current density 500 times, coulombic efficiency is 87~95%.