CN109119613B - Method for synthesizing cathode material for lithium-sulfur battery using waste fly ash as raw material - Google Patents

Abstract

The invention relates to a method for synthesizing a positive electrode material for a lithium-sulfur battery using waste fly ash as a raw material, comprising the following steps: (1) pickling the waste fly ash and drying to obtain the fly ash after removing impurities; (2) ) Mixing and grinding the decontaminated fly ash obtained in step (1) with elemental sulfur, then putting it into a closed container for drying and keeping warm, and grinding to obtain a lithium-sulfur battery positive electrode material synthesized by using waste fly ash as a raw material. Compared with the prior art, the raw material of the present invention comes from waste, which greatly reduces the material cost, and the obtained positive electrode material has higher charge-discharge specific capacity and excellent cycle stability. The preparation method is simple, low in cost and excellent in performance, and is suitable for the production of large-scale commercial batteries.

Description

Method for synthesizing cathode material for lithium-sulfur battery using waste fly ash as raw material

technical field

The invention relates to a positive electrode material for a lithium-sulfur battery, in particular to a method for synthesizing a positive electrode material for a lithium-sulfur battery using waste fly ash as a raw material.

Background technique

The energy storage principle of lithium-sulfur batteries is the breaking and regeneration of sulfur-sulfur bonds, and the active material is sulfur. Elemental sulfur mainly exists in the form of S ₈ at room temperature, which is abundant in the earth and has the characteristics of low price and environmental friendliness. The lithium-sulfur battery using sulfur as the positive electrode material has high material theoretical specific capacity and battery theoretical specific energy, reaching 1672mAh·g ^-1 and 2600Wh·kg ^-1 , respectively. It is considered to be one of the lithium secondary battery systems with the most research value and application prospects. Although lithium-sulfur batteries have the advantages of high capacity and high specific energy, they currently have problems such as low utilization of active materials, low cycle life and poor safety, which seriously restrict the development of lithium-sulfur batteries. The main reasons for the above problems are as follows:

1) Elemental sulfur is an electronic and ionic insulator with low conductivity at room temperature. Since there is no ionic sulfur, it is difficult to activate as a positive electrode material, resulting in low rate performance of lithium-sulfur batteries;

2) The high-polymer lithium polysulfide Li ₂ Sn (8> _n >4) produced during the electrode reaction is easily soluble in the electrolyte, forms a concentration difference between the positive and negative electrodes, and migrates under the action of the concentration gradient To the negative electrode, the high polymer lithium polysulfide is reduced to oligomer lithium polysulfide by metal lithium. With the progress of the above reaction, oligomeric lithium polysulfide aggregates in the negative electrode, and finally a concentration difference is formed between the two electrodes, and then migrates to the positive electrode to be oxidized into high-polymerized lithium polysulfide. This phenomenon, known as the shuttle effect, reduces the availability of sulfur active species. At the same time, insoluble Li ₂ S and Li ₂ S ₂ are deposited on the surface of the lithium negative electrode, which further deteriorates the performance of the lithium-sulfur battery, resulting in the low cycle performance of the lithium-sulfur battery;

3) The density of sulfur and the final product Li ₂ S are different. When the sulfur is lithiated, the volume expands by about 79%, which easily leads to the pulverization of Li ₂ S and causes the safety problem of lithium-sulfur batteries.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for synthesizing a positive electrode material for a lithium-sulfur battery using waste fly ash as a raw material in order to overcome the above-mentioned defects in the prior art.

The object of the present invention can be realized through the following technical solutions:

The invention adopts waste fly ash produced in the production process of thermal power plants as raw materials, uses its own unique structure of hollow silica spheres, and loads elemental sulfur into the hollow silica spheres by a melting method to obtain lithium Sulfur battery cathode material.

One of the objectives of the present invention is to provide a positive electrode material for a lithium-sulfur battery, which is prepared by melting and loading elemental sulfur into hollow silica spheres.

The second object of the present invention is to provide a method for synthesizing the above-mentioned lithium-sulfur battery positive electrode material using waste fly ash as a raw material, comprising the following steps:

(1) the waste fly ash is pickled, and the fly ash after the impurity removal is obtained after drying;

(2) the fly ash after removing impurities obtained in step (1) is mixed and ground with elemental sulfur, and then carbon disulfide is added to continue grinding, and then put into a closed container for drying and heat preservation, to obtain a lithium synthesized by using waste fly ash as a raw material Sulfur battery cathode material.

As a preference of the above technical solution, in step (1), the fly ash is pre-treated before pickling, and the pre-treatment methods include grinding, water washing or alcohol washing.

As a preference of the above technical solution, in step (1): the waste fly ash is the waste fly ash after burning coal powder in a thermal power plant.

As a preference of the above technical solution, in step (1): dilute hydrochloric acid or dilute sulfuric acid is used for pickling, and the concentration is 0.01-0.1 mol/L.

As the optimization of the above technical solution, in step (1): the ratio of waste fly ash to acid solution is 1:20-1:200.

As a preference of the above technical solution, the process steps of acid washing in step (1) are: adding an acid solution, stirring or ultrasonicating for 1-24 hours, and washing with deionized water until neutral.

As the optimization of the above technical solution, in step (2): the mass ratio of the fly ash after removing impurities and elemental sulfur is 1:1-1:10, and the grinding time is 1-6h.

As the optimization of the above technical solution, in step (2): the mass ratio of the mixture of fly ash and elemental sulfur to carbon disulfide is 1:5-1:50, and the grinding is continued for 1-5h until the carbon disulfide evaporates completely.

As the optimization of the above technical solution, in step (2): the airtight container is a metal airtight container or a glass airtight container, which can be a clean and impurity-free reaction kettle or a weighing bottle, and the sulfurizing temperature is 150-160 ° C, and the holding time is 150-160 ° C. 0.5-24h.

Mix and grind the prepared positive electrode material with acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1 for 1-5 hours until completely mixed, then add 10-50 mL of N-methylpyrrolidone to obtain a black uniform slurry The material is then coated on aluminum foil, and then dried at 60 °C to obtain the pole pieces of the assembled battery, and finally the lithium-sulfur battery is assembled.

Further, in step (1), the fly ash is pre-treated before pickling, and the pre-treatment methods include grinding, water washing or alcohol washing. Among them, grinding is a simple treatment of the sample particle size of coal ash to prevent excessively large particles or too many agglomerated particles.

Further, in step (1), dilute hydrochloric acid or dilute sulfuric acid is used for pickling, and the concentration is 0.01-1 mol/L. The purpose of pickling is to remove trace metal impurities in the sample.

Further, in step (2): the mass ratio of the fly ash after removing impurities and elemental sulfur is 1:1-1:10, and the grinding time is 1-6h. The ratio of fly ash to elemental sulfur should be within this reasonable range. Too much sulfur will cause a large amount of sulfur on the surface of the sample, which is not conducive to the cycle performance of the battery. Too little sulfur will affect the capacity of the battery to decrease.

Further, the airtight container is a metal airtight container or a glass airtight container, which can be a clean and impurity-free reaction kettle or weighing bottle, the sulfurizing temperature is 150-160°C, and the holding time is 0.5-24h. The sulfurizing temperature is lower than 150℃, elemental sulfur cannot penetrate into the fly ash in a molten state, and the temperature higher than 160℃ will cause the viscosity of sulfur to be too large, which is not conducive to infiltrating into the fly ash.

In the present invention, waste fly ash is used as a raw material, and elemental sulfur is infiltrated into hollow silica balls by a melting method to obtain a positive electrode material for a lithium-sulfur battery. This material can well solve the "shuttle effect" of lithium-sulfur batteries, thereby obtaining lithium-sulfur batteries with high specific capacity and long cycle performance.

In the present invention, the waste fly ash produced by high temperature burning of pulverized coal in the production process of thermal power plants is used as the raw material, and the lithium ion is obtained by infiltrating elemental sulfur into the hollow silica spheres by utilizing the structural characteristics of its own hollow silica spheres. The cathode material of the sulfur battery is simple and effective, and the obtained battery material has excellent energy storage performance. Specifically, the hollow-structured silica can store and solidify sulfur well, and can well protect the polysulfides generated during the charging and discharging process of lithium-sulfur batteries from being lost to the negative electrode. Therefore, the obtained cathode material has excellent energy storage performance (at a charge-discharge current density of 1 C, the specific capacity can still be maintained at 610 mAh·g ^-1 after 600 cycles).

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

1) The hollow structure of the silica sphere cavity provides a good storage space for sulfur, which solves the problem of poor conductivity of elemental sulfur;

2) There are many micropores, mesopores and macropores with a diameter of 1-500 nanometers distributed in the hollow silica spheres. The existence of these pore structures is conducive to the infiltration of elemental sulfur and can prevent polysulfide during the battery charge and discharge process. material shuttle, thereby improving the cycle performance of the battery (at a charge-discharge current density of 1C, after 600 cycles, the specific capacity can still be maintained at 610mAh·g ^-1 );

3) Fly ash is mainly composed of silica, in addition to some carbon components, and the advantage of this silicon-carbon material is that it has a good electron and ion transfer rate, and this advantage can greatly improve the material The reaction kinetics are improved, thereby improving the rate capability of the battery.

Description of drawings

Fig. 1 is the scanning electron microscope photograph of the hollow silica sphere structure of embodiment 1 fly ash;

Fig. 2 is the transmission electron microscope photograph of the hollow silica sphere structure of embodiment 1 fly ash;

Fig. 3 is the XRD pattern of the hollow silica sphere structure of the fly ash of Example 1;

4 is a graph showing the cycle performance of a lithium-sulfur battery prepared by synthesizing a lithium-sulfur battery cathode material using waste fly ash as a raw material in Example 1. FIG.

Detailed ways

The method obtained in the embodiment of the present invention uses waste fly ash as a raw material, and utilizes the structural characteristics of its own hollow silica spheres to infiltrate elemental sulfur in a molten state to prepare a lithium-sulfur battery as a positive electrode material for a lithium-sulfur battery The electrochemical performance of the test was tested by electrochemical workstation and blue electricity testing system; the electrochemical workstation used was Chenhua electrochemical workstation; the blue electricity testing system was LAND-CT2001. The electrochemical performance was tested by using a 2032 type button battery. The button battery was assembled in a glove box filled with argon gas, and the content of water and oxygen in the glove box were kept below 0.1ppm.

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

Example 1

A method for synthesizing a positive electrode material for a lithium-sulfur battery using waste fly ash as a raw material. Specifically include the following steps:

(1) Collect waste fly ash from a power plant, weigh 1kg, wash it with a large amount of deionized water, and then dry it for use.

(2) The dried product is taken out and ground in a dry environment, pickled, and dried. The grinding time is 30 minutes. The pickling adopts hydrochloric acid with a concentration of 0.2%, and stirs for 12 hours until the metal impurities in the carbon material are removed. Finally, the product was centrifuged and washed to neutrality with deionized water, and then dried at 60°C to obtain hollow silica spheres.

(3) The hollow silica spheres obtained by drying and the elemental sulfur powder are mixed and ground for 1 hour in a mass ratio of 1:3, then 30 mL of carbon disulfide is added, and the grinding is continued until the carbon disulfide is completely evaporated to obtain a uniformly mixed product, and then use Collected in a closed weighing bottle, and finally placed in an oven at 156 °C for 10 h. Finally, a sample of sulfur/hollow silica sphere cathode material was obtained.

(4) After the sample is obtained, it is formulated into a slurry containing a conductive agent, a binder and an organic solvent. The conductive agent is acetylene black, the binder is polyvinylidene fluoride PVDF, and the organic solvent is N-methylpyrrolidone NMP, and then the slurry is coated on the copper foil current collector, and then assembled into a battery in a glove box. Finally, the assembled battery was electrochemically tested in the blue electricity test system and electrochemical workstation, and the samples were subjected to other physical characterizations.

Fig. 1 is a scanning electron microscope photograph of the obtained hollow silica sphere, and the external appearance of the hollow silica sphere material can be clearly seen.

FIG. 2 is a transmission electron microscope photograph of the obtained hollow silica sphere material, and the hollow structure of the hollow silica sphere can be clearly seen.

FIG. 3 is an XRD pattern of the hollow silica spheres, which characterizes the hollow silica spheres as a silicon-carbon material with silica as the main component and carbon as the main component.

Figure 4 is a graph showing the ultra-long cycle performance of the finally obtained sulfur/hollow silica spheres as the cathode material of the lithium-sulfur battery after assembling the lithium-sulfur battery. The data in the figure shows that the battery still maintains 610mAh·g after 600 charge-discharge cycles. ^-1 specific capacity.

Example 2

The method for synthesizing a positive electrode material for a lithium-sulfur battery using waste fly ash as a raw material specifically includes the following steps:

(1) Collect waste fly ash from a power plant, weigh 5kg, wash it with a large amount of deionized water, and then dry it for use.

(2) The dried product is taken out and ground in a dry environment, pickled, and dried. The grinding time is 30 minutes, and the pickling concentration is 0.3% hydrochloric acid, and stirred for 20 hours until the metal impurities in the carbon material are removed. Finally, the product was centrifuged and washed to neutrality with deionized water, and then dried at 60°C to obtain hollow silica spheres.

(3) Mix and grind the hollow silica spheres obtained by drying and elemental sulfur powder in a mass ratio of 1:6 for 1 hour, then add 1 L of carbon disulfide, and continue grinding until the carbon disulfide evaporates to obtain a uniformly mixed product, and then use Collected in a closed weighing bottle, and finally placed in an oven at 155°C for 20h. Finally, a sample of sulfur/hollow silica sphere cathode material was obtained.

(4) After the sample is obtained, it is formulated into a slurry containing a conductive agent, a binder and an organic solvent. The conductive agent is acetylene black, the binder is polyvinylidene fluoride PVDF, and the organic solvent is N-methylpyrrolidone NMP, and then the slurry is coated on the copper foil current collector, and then assembled into a battery in a glove box. Finally, the assembled battery was electrochemically tested in the blue electricity test system and electrochemical workstation, and the samples were subjected to other physical characterizations.

Example 3

A method for synthesizing a positive electrode material for a lithium-sulfur battery using waste fly ash as a raw material. Specifically include the following steps:

(1) Collect waste fly ash from a power plant, weigh 10kg, wash it with a large amount of deionized water, and then dry it for use.

(2) The dried product is taken out and ground in a dry environment, pickled, and dried. The grinding time is 30 hours, and the acid pickling concentration is 0.4% hydrochloric acid, and stirred for 24 hours until the metal impurities in the carbon material are removed. Finally, the product was centrifuged and washed to neutrality with deionized water, and then dried at 60°C to obtain hollow silica spheres.

(3) Mix and grind the hollow silica spheres obtained by drying and elemental sulfur powder in a mass ratio of 1:4 for 1 hour, then add 2 L of carbon disulfide, and continue grinding until the carbon disulfide evaporates to obtain a uniformly mixed product, and then use Collected in a closed weighing bottle, and finally placed in an oven at 155°C for 20h. Finally, a sample of sulfur/hollow silica sphere cathode material was obtained.

(4) After the sample is obtained, it is formulated into a slurry containing a conductive agent, a binder and an organic solvent. The conductive agent is acetylene black, the binder is polyvinylidene fluoride PVDF, and the organic solvent is N-methylpyrrolidone NMP, and then the slurry is coated on the copper foil current collector, and then assembled into a battery in a glove box. Finally, the assembled battery was electrochemically tested in the blue electricity test system and electrochemical workstation, and the samples were subjected to other physical characterizations.

Example 4

A method for synthesizing a positive electrode material for a lithium-sulfur battery using waste fly ash as a raw material. Specifically include the following steps:

(1) Collect waste fly ash after burning household briquettes, weigh 5kg, wash with a large amount of ethanol, and dry for use.

(2) The dried product is taken out and ground in a dry environment, pickled, and dried. The grinding time is 30 minutes, and the pickling concentration is 0.6 mol/L of hydrochloric acid, and ultrasonicated and stirred for 1 hour until the metal impurities in the carbon material are removed. Finally, the product was centrifuged and washed to neutrality with deionized water, and then dried at 60°C to obtain hollow silica spheres.

(3) Mix and grind the hollow silica spheres obtained by drying and elemental sulfur powder in a mass ratio of 1:1 for 3 hours, then add 1 L of carbon disulfide, and continue to grind until the carbon disulfide evaporates completely to obtain a uniformly mixed product, and then use Collected in a closed weighing bottle, and finally placed in an oven at 150°C for 24h. Finally, a sample of sulfur/hollow silica sphere cathode material was obtained.

(4) After the sample is obtained, it is formulated into a slurry containing a conductive agent, a binder and an organic solvent. The conductive agent is acetylene black, the binder is polyvinylidene fluoride PVDF, and the organic solvent is N-methylpyrrolidone NMP, and then the slurry is coated on the copper foil current collector, and then assembled into a battery in a glove box. Finally, the assembled battery was electrochemically tested in the blue electricity test system and electrochemical workstation, and the samples were subjected to other physical characterizations.

Example 5

A method for synthesizing a positive electrode material for a lithium-sulfur battery using waste fly ash as a raw material. Specifically include the following steps:

(1) Collect the waste fly ash after burning household briquettes, weigh 2kg, wash with a large amount of ethanol, and then dry for use.

(2) The dried product is taken out and ground in a dry environment, pickled, and dried. The grinding time is 30 minutes, and the pickling concentration is dilute sulfuric acid with a concentration of 0.7 mol/L, and ultrasonication is performed for 10 hours until the metal impurities in the carbon material are removed. Finally, the product was centrifuged and washed to neutrality with deionized water, and then dried at 60°C to obtain hollow silica spheres.

(3) Mix and grind the hollow silica spheres obtained by drying and elemental sulfur powder in a mass ratio of 1:10 for 6 hours, then add 1 L of carbon disulfide, and continue grinding until the carbon disulfide evaporates completely to obtain a uniformly mixed product, and then use Collected in a closed weighing bottle, and finally placed in an oven at 160°C for 0.5h. Finally, a sample of sulfur/hollow silica sphere cathode material was obtained.

(4) After the sample is obtained, it is formulated into a slurry containing a conductive agent, a binder and an organic solvent. The conductive agent is acetylene black, the binder is polyvinylidene fluoride PVDF, and the organic solvent is N-methylpyrrolidone NMP, and then the slurry is coated on the copper foil current collector, and then assembled into a battery in a glove box. Finally, the assembled battery was electrochemically tested in the blue electricity test system and electrochemical workstation, and the samples were subjected to other physical characterizations.

In the above embodiments, the concentration of hydrochloric acid or sulfuric acid used for pickling can be replaced by 0.01M or 1M.

The foregoing description of the embodiments is provided to facilitate understanding and use of the invention by those of ordinary skill in the art. It will be apparent to those skilled in the art that various modifications to these embodiments can be readily made, and the generic principles described herein can be applied to other embodiments without inventive step. Therefore, the present invention is not limited to the above-mentioned embodiments, and improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should all fall within the protection scope of the present invention.

Claims (9)

1. a method for synthesizing a lithium-sulfur battery positive electrode material with waste fly ash as a raw material, wherein the lithium-sulfur battery positive electrode material is prepared by melting and loading elemental sulfur in a hollow silica sphere; The preparation method includes the following steps: (1) the waste fly ash is pickled, and the fly ash after the impurity removal is obtained after drying; (2) the fly ash after the removal of impurities obtained in step (1) is mixed and ground with elemental sulfur, then carbon disulfide is added, and the grinding is continued until the evaporation is complete, and then put into a closed container for drying and heat preservation, and the waste fly ash is obtained as Lithium-sulfur battery cathode material synthesized from raw materials. 2. the method for synthesizing lithium-sulfur battery positive electrode material with waste fly ash as a raw material according to claim 1, is characterized in that, in step (1), before pickling, fly ash is carried out pretreatment, the mode of pretreatment Including grinding, water washing or alcohol washing. 3. the method for synthesizing lithium-sulfur battery positive electrode material with waste fly ash as raw material according to claim 2, is characterized in that, in step (1): described waste fly ash is discarded after the thermal power plant burns pulverized coal Fly ash, or fly ash left after burning household briquettes or pulverized coal at high temperatures. 4. the method for synthesizing lithium-sulfur battery positive electrode material with waste fly ash as raw material according to claim 1, is characterized in that, in step (1): pickling adopts dilute hydrochloric acid or dilute sulfuric acid, and concentration is 0.01-1mol/ L. 5. the method for synthesizing lithium-sulfur battery positive electrode material with waste fly ash as raw material according to claim 1 or 4, is characterized in that, in step (1): the mass ratio of waste fly ash and acid is 1:20 -1:200. 6. The method for synthesizing a lithium-sulfur battery positive electrode material with waste fly ash as a raw material according to claim 1, wherein the process step of pickling in step (1) is: adding an acid solution, stirring or ultrasonically 1- After 24 h, wash with deionized water until neutral. 7. the method for synthesizing lithium-sulfur battery positive electrode material with waste fly ash as raw material according to claim 1, is characterized in that, in step (2): the mass ratio of fly ash after removing impurity and elemental sulfur is 1 :1-1:10, the grinding time is 1-6h. 8. the method for synthesizing lithium-sulfur battery positive electrode material with waste fly ash as raw material according to claim 1, is characterized in that, in step (2): the mass ratio of the mixture of fly ash and elemental sulfur and carbon disulfide is 1 :5-1:50, continue grinding for 1-5h until the carbon disulfide evaporates completely. 9. The method for synthesizing a lithium-sulfur battery positive electrode material with waste fly ash as a raw material according to claim 1, wherein in step (2): the airtight container is a metal airtight container or a glass airtight container, and drying The temperature is 150-160°C, the holding temperature is 150-160°C, and the holding time is 0.5-24h.

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