CN110571436A - Preparation method of three-dimensional porous carbon-supported sheet-like molybdenum disulfide current collector for lithium metal anode - Google Patents

Abstract

The invention relates to a preparation method of a three-dimensional porous carbon loaded flaky molybdenum disulfide current collector for a lithium metal cathode, which comprises the following steps: (1) adding a molybdenum source, a sulfur source, a carbon source and a salt template into deionized water for dissolving to prepare a uniform and transparent precursor solution; (2) freeze drying to obtain dry solid powder, and grinding to obtain a mixed powder precursor; (3) is arranged in a hearth of the tubular furnace; heating to 500-750 ℃ in an inert gas atmosphere, preserving heat for a period of time, and then rapidly cooling to obtain a calcined product; (4) carrying out suction filtration, removing NaCl, and drying to obtain the three-dimensional porous carbon loaded flaky molybdenum disulfide material; (5) and preparing the three-dimensional porous carbon loaded flaky molybdenum disulfide composite current collector.

Description

Fabrication of three-dimensional porous carbon-supported sheet-like molybdenum disulfide current collectors for lithium metal anodes backup method

technical field

The invention belongs to the technical field of lithium metal battery electrode materials, and in particular relates to a preparation method of a three-dimensional porous carbon-supported molybdenum disulfide current collector, which can effectively inhibit the generation of lithium dendrites during the deposition and desorption of lithium metal, and prevent the disordered deposition of lithium metal. problems and further production of dead lithium causing battery capacity fading.

Background technique

With the rapid development of electric vehicles, household electronic products and the national grid, people have higher and higher requirements for high-energy-density rechargeable batteries. Traditional lithium-ion batteries cannot be Meet people's energy storage needs. In this context, Li metal has the advantages of the highest theoretical specific capacity (3860mAh g ^-1 ), the lowest electrochemical potential (3.04V vs. standard hydrogen electrode), and the extremely low density (0.53g cm ^-3 ), becoming the The most promising anode materials for next-generation high-energy-density batteries, especially for lithium-sulfur and lithium-oxygen battery systems. However, some problems such as the formation of an unstable solid electrolyte membrane lead to repeated consumption of lithium metal and electrolyte, which reduces the coulombic efficiency and service life of the battery, the uncontrollable growth of lithium dendrites may puncture the battery separator and cause the battery to short circuit, and the huge volume expansion will Destruction of the battery structure, etc. will cause serious safety and recyclability issues, hindering the practical application of lithium metal anodes.

Guiding the ordered deposition of Li metal, suppressing the growth of Li dendrites and volume expansion during Li deposition and desorption can effectively improve the Coulombic efficiency and cycle life of Li metal anodes. In recent years, lithiophilic seeds supported on three-dimensional porous current collectors have been widely used for Li metal anodes. On the one hand, the high specific surface area of the three-dimensional current collector can effectively reduce the local current density of the electrode and make the lithium metal deposition more uniform; on the other hand, the porous structure has enough space to store lithium and inhibit the growth of lithium dendrites. The lithiophilic seeds can guide the uniform deposition of Li metal inside the entire current collector. However, the current research mainly focuses on supporting granular lithiophilic materials or secondary supporting flaky lithiophilic materials, which are not strongly bonded to the matrix. During the deposition and desorption of lithium metal, they may fall off or even agglomerate from the matrix. The uneven distribution of lithium metal will promote the uneven deposition of lithium metal, reducing the coulombic efficiency and service life of the battery.

Therefore, the preparation of three-dimensional porous carbon current collector-supported sheet-like molybdenum disulfide lithiophilic materials with large specific surface area by one-step method can effectively solve this problem. The sheet-like structure is used to increase the contact area between the lithiophilic material and the substrate to improve the binding force, so that the structure of the electrode can be maintained during long cycles. The lithiophilic material promotes the uniform deposition of lithium metal, and the three-dimensional porous current collector provides a large specific surface area to reduce the relative current density and pores to store lithium, and finally obtain a lithium metal battery anode material with excellent electrochemical performance.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a three-dimensional porous carbon-supported molybdenum disulfide current collector that can effectively guide the uniform deposition of lithium metal in the current collector and suppress the generation of lithium dendrites for lithium metal The battery can effectively improve the coulombic efficiency and cycle stability of the battery. The technical solution is as follows:

A method for preparing a three-dimensional porous carbon-supported sheet-like molybdenum disulfide current collector for lithium metal negative electrodes, comprising the following steps:

(1) Mix one or more of sucrose, glucose, citric acid and starch as carbon source, use ammonium molybdate as molybdenum source, use thiourea as sulfur source, use sodium sulfate, sodium chloride, sodium carbonate, One or more of the sodium silicates are mixed as templates, and the molar ratio of molybdenum atoms in the molybdenum source, sulfur atoms in the sulfur source, and carbon atoms in the carbon source is 1: (2～10): (50～ 500), adding molybdenum source, sulfur source, carbon source and salt template into deionized water to dissolve, to prepare a uniform and transparent precursor solution;

(2) freeze-drying the precursor solution prepared in the previous step to obtain a dry solid powder, and grind to obtain a mixed powder precursor;

(3) placing the mixed powder precursor obtained in the previous step in the hearth of the tubular furnace; in an atmosphere of inert gas, the temperature is raised to 500-750°C at a heating rate of 1-10°C, kept for a period of time, and then rapidly cooled for cooling. to obtain a calcined product;

(4) using deionized water to carry out suction filtration of the calcined product obtained in the previous step, removing NaCl, and drying to obtain a three-dimensional porous carbon-supported sheet molybdenum disulfide material;

(5) Mix the three-dimensional porous carbon-supported sheet molybdenum disulfide material prepared in step (4) with polyvinylidene fluoride (PVDF) in a mass ratio of 8:(1-2), and then add an appropriate amount of nitrogen methyl pyrrolidone (NMP) into a slurry, mixed evenly, smeared on the copper foil, and dried to obtain a three-dimensional porous carbon-supported sheet-like molybdenum disulfide composite current collector.

In step (3), the cooling rate is 50-100°C/min on average.

Compared with the prior art, the method of the present invention has the following advantages: (1) The three-dimensional porous carbon-supported sheet-like molybdenum disulfide composite material is prepared by a one-step method, and the contact area between the three-dimensional carbon and the sheet-like molybdenum disulfide is very large , so the combination between the three-dimensional carbon and molybdenum disulfide is very close, so that the position and shape of molybdenum disulfide are not easily changed during the cycling process of lithium metal batteries; (2) molybdenum disulfide can effectively improve the lithophilicity of the three-dimensional carbon matrix. , to promote the uniform deposition of lithium metal inside the entire three-dimensional current collector; (3) the three-dimensional porous structure can accommodate a large amount of lithium metal, which can slow down the volume change of the lithium metal anode during charging and discharging, and obtain a volume-stable lithium metal anode; ( 4) The three-dimensional pore structure increases the specific surface area of the electrode and reduces the effective current density of the electrode, thereby effectively inhibiting the generation of lithium dendrites.

Description of drawings

Fig. 1 is the SEM image of MoS ₂ @3DC powder prepared in Example 1 of the present invention;

2 is a TEM image of MoS ₂ @3DC powder prepared in Example 1 of the present invention;

Fig. 3 is the SEM image after depositing 2.0mAh cm ^-2 and 5.0mAhcm ^-2 lithium metal on the MoS ₂ @3DC current collector prepared in Example 1 of the present invention;

FIG. 4 shows the cyclic Coulomb efficiency of the MoS ₂ @3DC current collector prepared in Example 1 for supporting lithium metal.

What is not described in the present invention applies to the prior art.

Specific examples of the preparation method of the present invention are given below. These examples are only used to illustrate the preparation method of the present invention in detail, and do not limit the protection scope of the claims of the present application.

Detailed ways

Below first introduce the technical route of the present invention:

_The preparation method of MoS2@3DC composite current collector adopts the following process:

(1) Mix one or more of sucrose, glucose, citric acid and starch as carbon source, use ammonium molybdate as molybdenum source, use thiourea as sulfur source, use sodium sulfate, sodium chloride, sodium carbonate, One or more of the sodium silicates are mixed as templates, and the molar ratio of molybdenum atoms in the molybdenum source, sulfur atoms in the sulfur source, and carbon atoms in the carbon source is 1: (2～10): (50～ 500), adding molybdenum source, sulfur source, carbon source and salt template into deionized water to dissolve, dubbing the solution and stirring for more than 3 hours to obtain a uniform and transparent precursor solution;

(2) The precursor solution prepared in the previous step was placed in a refrigerator at -20°C for more than 48 hours or quickly frozen with liquid nitrogen, and then placed in a vacuum freeze dryer at -50°C and freeze-dried at 20Pa for about 48 hours. The dry solid powder is obtained, and the mixed powder precursor is obtained after grinding;

(3) take about 10g of the powder precursor obtained in the previous step and spread it on a quartz boat, and then place the quartz boat in the furnace chamber of the tubular furnace; use one of N ₂ , He or Ar or a mixed gas as an inert gas source , first pass the inert gas at a flow rate of 500 ccm for 10 to 20 minutes to remove the air, and then use the inert gas as the carrier gas, the flow rate is fixed at 50 ~ 500 ccm, and the temperature is raised to 500 ~ 750 ° C at a heating rate of 1 ~ 10 ° C, and the temperature is kept for 1 ~ 2h, then rapid cooling and cooling (the average cooling rate is 50-100°C/min) to obtain a calcined product;

(4) using deionized water to perform suction filtration on the calcined product obtained in the previous step to remove NaCl, and then drying in a 70°C vacuum drying oven to obtain a three-dimensional porous carbon-supported sheet molybdenum disulfide material;

(5) Mix the three-dimensional porous carbon-supported sheet molybdenum disulfide material prepared in step (4) with polyvinylidene fluoride (PVDF) in a mass ratio of 8:(1-2), and then add an appropriate amount of nitrogen methyl pyrrolidone (NMP) into slurry, stir magnetically for more than 4 hours, spread evenly on the copper foil with a scraper with a thickness of 100-1000 mm, use a heating table to dry at 50 ℃ ~ 80 ℃, and use a cutting machine to cut into discs , a three-dimensional porous carbon-supported sheet-like molybdenum disulfide composite current collector was obtained.

(6) Assembling the three-dimensional porous carbon-supported sheet-like molybdenum disulfide composite current collector prepared in step (5) into a battery, the counter electrode is a lithium sheet, and firstly in the voltage range of 0.01V-3V at 0.05mA cm ^-2 The current density was cycled for 5 times to form a stable SEI film, and then metal lithium was deposited at a current density of 1.0-10.0 mA cm ^-2 for 0.2-10 h, and the battery was disassembled to obtain metal lithium negative electrodes of different capacities.

Example 1

(1) Weigh 0.3532g of ammonium molybdate, 0.3654g of thiourea, 1.4g of citric acid, and 17.55g of sodium chloride, dissolve the mixture in 100ml of deionized water, and magnetically stir for 4h to obtain a homogeneous solution. Pour the evenly mixed liquid into the petri dish, and then place the petri dish in the freezer of the refrigerator at -20°C for 24 hours; put the frozen samples in a freeze-drying machine for freeze-drying, and freeze-drying conditions are: -50°C , 20Pa, lyophilization time 24h. Grind the freeze-dried sample to obtain the precursor composite powder (powder particle size ~ 100 mesh); take 10 g of the ark, put the ark into a tube furnace, pass 500 ccm of argon for 15 minutes to remove the air, and then adjust to 200 ccm , and raised to 750°C at a heating rate of 10°C/min, kept for 2h, and quickly cooled to room temperature after the heat preservation, placed the calcined powder in a 500ml beaker, added 400ml of deionized water, and magnetically stirred for 30min to make the chlorination All sodium was dissolved in water, followed by suction filtration. After repeated three times, the suction-filtered sample was placed in a 70°C vacuum oven to dry for 3 hours to obtain a three-dimensional porous carbon-supported molybdenum disulfide composite material.

(2) Using the obtained powder material, the mass ratio of polyvinylidene fluoride is 8:1, then adding an appropriate amount of NMP, mixing and stirring for 4 hours, and applying a 250mm spatula on the copper foil, and drying at 80 ° C to obtain collector.

( ₃ ) Preparation of Li metal anode using MoS2@3DC. Using the above-prepared current collector as the cathode and lithium metal as the anode, a half-cell was assembled, 2.0 mAh cm ^-2 of metallic lithium was deposited on the MoS ₂ @3DC current collector, and the battery was disassembled to obtain the corresponding lithium metal negative electrode .

(4) Assembly of the lithium metal secondary battery. The lithium metal negative electrode prepared above is assembled with a suitable sulfur positive electrode to form a lithium-sulfur battery or a Li-LMO battery with a suitable LMO (L is lithium, M is a transition metal, and O is oxygen). In this embodiment, a lithium metal half-cell is assembled by using lithium metal as the counter electrode.

(5) Electrochemical test of lithium metal secondary battery. The stable SEI film was first cycled at a current density of 0.05mA cm ^-2 for 5 cycles in the voltage range of 0.01V-3V, and then charged at a capacity of 2.0mAh cm ^-2 at a current density of 1.0mA cm ^-2 . Discharge cycle with a cut-off voltage of 0.5V.

Example 2

Different from Example 1: (1) Weigh 0.3532g of ammonium molybdate, 0.30g of thiourea, 1.4g of citric acid, and 17.55g of sodium chloride, dissolve the mixture in 100ml of deionized water, and magnetically stir for 4h to obtain a uniform solution . Pour the evenly mixed liquid into the petri dish, and then place the petri dish in the freezer of the refrigerator at -20°C for 24 hours; put the frozen samples in a freeze-drying machine for freeze-drying, and freeze-drying conditions are: -50°C , 20Pa, lyophilization time 24h. Grind the freeze-dried sample to obtain the precursor composite powder (powder particle size ~ 100 mesh); take 10 g of the ark, put the ark into a tube furnace, pass 500 ccm of argon for 15 minutes to remove the air, and then adjust to 200 ccm , and raised to 750°C at a heating rate of 10°C/min, kept for 2h, and quickly cooled to room temperature after the heat preservation, placed the calcined powder in a 500ml beaker, added 400ml of deionized water, and magnetically stirred for 30min to make the chlorination All sodium was dissolved in water, followed by suction filtration. After repeated three times, the suction-filtered sample was placed in a 70°C vacuum oven to dry for 3 hours to obtain a three-dimensional porous carbon-supported molybdenum disulfide composite material. The rest are the same as in Embodiment 1, and are not repeated here.

The obtained current collector has a three-dimensional porous structure, but there are many particles on the carbon wall. It is speculated that the molybdenum oxide obtained by the decomposition of ammonium molybdate is not completely left by thiourea vulcanization.

Example 3

Different from Example 1: (1) Weigh 0.3532g of ammonium molybdate, 0.3654g of thiourea, 1g of citric acid, and 17.55g of sodium chloride, dissolve the mixture in 100ml of deionized water, and magnetically stir for 4h to obtain a uniform solution. Pour the evenly mixed liquid into the petri dish, and then place the petri dish in the freezer of the refrigerator at -20°C for 24 hours; put the frozen samples in a freeze-drying machine for freeze-drying, and freeze-drying conditions are: -50°C , 20Pa, lyophilization time 24h. Grind the freeze-dried sample to obtain the precursor composite powder (powder particle size ~ 100 mesh); take 10 g of the ark, put the ark into a tube furnace, pass 500 ccm of argon for 15 minutes to remove the air, and then adjust to 200 ccm , and the temperature was raised to 750°C at a heating rate of 10°C/min, kept for 2 hours, and then quickly cooled to room temperature after the heat preservation. The calcined powder was placed in a 500ml beaker, 400ml of deionized water was added, and magnetic stirring was performed for 30min to make the chlorination All sodium was dissolved in water, followed by suction filtration. After repeated three times, the suction-filtered sample was placed in a 70°C vacuum oven to dry for 3 hours to obtain a three-dimensional porous carbon-supported molybdenum disulfide composite material. The rest are the same as in Embodiment 1, and are not repeated here.

The obtained current collector has a three-dimensional porous structure and no particulate matter, but the three-dimensional structure is incompletely broken.

Example 4

The difference from Example 1 is: (1) Weigh 1.4 g of citric acid and 17.55 g of sodium chloride, dissolve the mixture in 100 ml of deionized water, and stir magnetically for 4 hours to obtain a uniform solution. Pour the evenly mixed liquid into the petri dish, and then place the petri dish in the freezer of the refrigerator at -20°C for 24 hours; put the frozen samples in a freeze-drying machine for freeze-drying, and freeze-drying conditions are: -50°C , 20Pa, lyophilization time 24h. Grind the freeze-dried sample to obtain the precursor composite powder (powder particle size ~ 100 mesh); take 10 g of the ark, put the ark into a tube furnace, pass 500 ccm of argon for 15 minutes to remove the air, and then adjust to 200 ccm , and raised to 750°C at a heating rate of 10°C/min, kept for 2h, and quickly cooled to room temperature after the heat preservation, placed the calcined powder in a 500ml beaker, added 400ml of deionized water, and magnetically stirred for 30min to make the chlorination All sodium was dissolved in water, followed by suction filtration. After repeated three times, the suction-filtered sample was placed in a 70°C vacuum oven to dry for 3 hours to obtain a three-dimensional porous carbon-supported molybdenum disulfide composite material. The rest are the same as in Embodiment 1, and are not repeated here.

The obtained current collector has a three _- dimensional porous structure, but no MoS2 is present in it according to the XRD test, denoted as 3DC.

Claims (3)

1. a preparation method for a three-dimensional porous carbon-supported sheet molybdenum disulfide current collector for lithium metal negative electrode, comprising the following steps: (1) Mix one or more of sucrose, glucose, citric acid and starch as carbon source, use ammonium molybdate as molybdenum source, use thiourea as sulfur source, use sodium sulfate, sodium chloride, sodium carbonate, One or more of the sodium silicates are mixed as templates, and the molar ratio of molybdenum atoms in the molybdenum source, sulfur atoms in the sulfur source, and carbon atoms in the carbon source is 1: (2～10): (50～ 500), molybdenum source, sulfur source, carbon source and salt template were added into deionized water to dissolve, to prepare a uniform and transparent precursor solution. (2) freeze-drying the precursor solution prepared in the previous step to obtain a dry solid powder, and grind to obtain a mixed powder precursor; (3) placing the mixed powder precursor obtained in the previous step in the hearth of the tubular furnace; in an atmosphere of inert gas, the temperature is raised to 500-750°C at a heating rate of 1-10°C, kept for a period of time, and then rapidly cooled for cooling. to obtain a calcined product; (4) using deionized water to carry out suction filtration of the calcined product obtained in the previous step, removing NaCl, and drying to obtain a three-dimensional porous carbon-supported sheet molybdenum disulfide material; (5) Mix the three-dimensional porous carbon-supported sheet molybdenum disulfide material prepared in step (4) with polyvinylidene fluoride (PVDF) in a mass ratio of 8:(1-2), and then add an appropriate amount of nitrogen methyl pyrrolidone (NMP) into a slurry, mixed evenly, smeared on the copper foil, and dried to obtain a three-dimensional porous carbon-supported sheet-like molybdenum disulfide composite current collector. 2 . The preparation method according to claim 1 , wherein the cooling rate in step (3) is an average of 50-100° C./min. 3 . 3. The three-dimensional porous carbon-supported sheet molybdenum disulfide composite current collector prepared by claim 1 is assembled into a battery, and the counter electrode is a lithium sheet.