CN114497499B - Multi-stage structure lithium sulfide/carbon composite material and preparation method and application thereof - Google Patents

Multi-stage structure lithium sulfide/carbon composite material and preparation method and application thereof Download PDF

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CN114497499B
CN114497499B CN202210094519.5A CN202210094519A CN114497499B CN 114497499 B CN114497499 B CN 114497499B CN 202210094519 A CN202210094519 A CN 202210094519A CN 114497499 B CN114497499 B CN 114497499B
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lithium sulfide
graphene oxide
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carbon composite
lithium
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CN114497499A (en
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胡康
黄祯
梁士轩
赵高科
刘张波
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China Automotive Innovation Corp
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Abstract

The invention provides a multi-stage structured lithium sulfide/carbon composite material, and a preparation method and application thereof, wherein the preparation method comprises the following steps: mixing a lithium source, a metal salt solution and a graphene oxide solution, drying to obtain a precursor material, carrying out annealing treatment on the precursor material and organic compound powder, and carrying out autocatalysis reaction and thermal reduction reaction under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material. The multi-stage structure lithium sulfide/carbon composite material obtained by the preparation method can stabilize the structure and promote the conductivity through the composite action of lithium sulfide, the reductive graphene oxide and the carbon hybridized nano tube, can effectively relieve the volume change of the lithium sulfide/carbon composite nano material in the charge and discharge process, and has excellent circulation specific capacity and capacity retention rate.

Description

Multi-stage structure lithium sulfide/carbon composite material and preparation method and application thereof
Technical Field
The invention belongs to the technical field of material science, and relates to a multi-stage structure lithium sulfide/carbon composite material, and a preparation method and application thereof.
Background
Lithium sulfur batteries have high theoretical specific energy and abundant raw material resources, and are receiving extensive attention as a new generation of energy equipment with development prospects. The existing lithium sulfur battery anode material can be divided into a carbon/elemental sulfur composite material and a carbon/lithium sulfide composite material, wherein the carbon/elemental sulfur composite material can generate larger volume expansion in the first-round charge and discharge process, the structure of the material is damaged, and the utilization rate of active sulfur is reduced, so that the electrochemical performance of the battery is influenced; the carbon/lithium sulfide composite material has a certain shrinkage of the structure in the first charging process, provides space for lithium intercalation discharge reaction, protects the electrode structure from damage, can also be used for assembling a battery with a non-lithium metal negative electrode material, and effectively avoids potential safety hazards caused by lithium dendrites. Therefore, the carbon/lithium sulfide composite material is widely applied as a positive electrode material of a lithium-sulfur battery.
At present, the carbon/lithium sulfide composite material is mostly prepared by a method of synthesis and then compounding, namely, the carbon material is prepared first, and then lithium sulfide is loaded into the carbon material through various ways, and the synthesis method often causes unsatisfactory dispersion of lithium sulfide active substances in the composite material, thereby affecting the utilization rate of the active substances and finally affecting the electrochemical performance of the lithium-sulfur battery. In addition, the lithium sulfide material is sensitive to moisture, so that the preparation process of the carbon/lithium sulfide composite material is complex and high in price.
CN106784754a discloses a preparation method of a carbon nanotube-lithium sulfide-carbon composite material, which adopts a tetrahydrofuran solution of carbon nanotube/lithium triethylborohydride and an anhydrous toluene solution of sublimed sulfur powder to mix, heat and evaporate to dryness, and then vapor deposition is carried out to obtain the carbon nanotube-lithium sulfide-carbon composite material. The method has complex operation process, is difficult to uniformly compound the carbon material and the lithium sulfide, has very high requirements on production equipment and environment due to the preparation of the lithium sulfide material, and increases the preparation cost of the material intangibly.
CN106229487a discloses a method for preparing a carbon/lithium sulfide composite positive electrode material of a lithium sulfur battery by carbothermic reduction of lithium sulfate, wherein the carbon/lithium sulfide composite material is directly prepared by carbothermic reduction by taking the composite material containing lithium sulfate as a precursor. The method directly uses lithium sulfate and carbon or carbon-containing organic matters to prepare the carbon/lithium sulfide composite material through high-temperature carbothermal reduction. The composite material synthesized by the method has poor shape controllability and unstable material quality, and finally the electrochemical performance of the synthesized composite material can be seriously influenced.
CN105406034a discloses a three-dimensional porous graphene-loaded carbon-coated lithium sulfide positive electrode material, and a preparation method and application thereof, wherein the method comprises the steps of dispersing graphene oxide in water, adding a reducing agent, stirring and dissolving, and then performing hydrothermal reaction for 4-12 h at 120-200 ℃ to obtain a columnar three-dimensional porous graphene solution; adding lithium sulfate and a carbon source into the solution of the columnar three-dimensional porous graphene to form a soaking solution of the columnar three-dimensional porous graphene; freeze-drying the soaking solution to obtain a precursor; calcining the precursor for 2-12 hours at 800-1000 ℃ in a protective atmosphere to obtain the three-dimensional porous graphene-loaded carbon-coated lithium sulfide material. The three-dimensional porous graphene-loaded carbon-coated lithium sulfide material prepared by the method can be directly sliced to prepare a battery anode, and the steps of slurry preparation, coating and drying are omitted.
None of the above documents effectively solves the problems of unsatisfactory dispersion of lithium sulfide active material in composite materials, and general structural stability of carbon/lithium sulfide composite materials. Therefore, development of a novel carbon/lithium sulfide composite material is urgently needed to further improve the electrochemical performance of the battery.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention aims to provide a multi-stage structure lithium sulfide/carbon composite material, a preparation method and application thereof, and the multi-stage structure lithium sulfide/carbon composite material prepared by the invention has the advantages that the composite effect among the three can stabilize the structure of the material, the conductivity of the material is improved, the layered structure of the reduced graphene oxide and the carbon hybrid nano tube generated in situ have a unique space limiting effect on the lithium sulfide material, and meanwhile, the volume expansion and contraction of the lithium sulfide/carbon composite nano material in the charge and discharge process are relieved, and the cycle specific capacity and the capacity retention rate are excellent.
To achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for preparing a multi-stage structured lithium sulfide/carbon composite material, the method comprising:
mixing a lithium source, a metal salt solution and a graphene oxide solution, drying to obtain a precursor material, carrying out annealing treatment on the precursor material and organic compound powder, and carrying out autocatalysis reaction and thermal reduction reaction under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material.
In the invention, the precursor material comprises a graphene oxide layer, and lithium sources and metal salts which are uniformly dispersed on the two side surfaces of the graphene oxide layer, and the precursor material and the organic compound powder are not mixed in the annealing treatment process, but are respectively placed at the two ends of a porcelain boat to be annealed together. In the annealing process, a lithium source on the surface of the graphene oxide layer reacts under a thermal reduction condition to generate lithium sulfide; the graphene oxide layer generates thermal reduction reaction to generate reduced graphene oxide with better conductivity; in the annealing process, the organic compound powder is subjected to chemical molecular vapor deposition to generate the carbon hybridized nano tube in situ under the self-catalysis of the active metal nano particles. Therefore, thermal reduction reaction and autocatalysis reaction are carried out under the condition of annealing treatment, and the multi-stage structure lithium sulfide/carbon composite material is constructed, wherein the structure is that lithium sulfide particles are dispersed on the two side surfaces of the reducing graphene oxide layer, and simultaneously carbon hybridized nanotubes are grown on the reduction positions on the two side surfaces of the reducing graphene oxide layer.
The multi-stage structure lithium sulfide/carbon composite material obtained by the preparation method provided by the invention has the advantages that the lithium sulfide, the reduced graphene oxide and the carbon hybrid nano tube are simultaneously provided, the composite effect among the three can stabilize the structure of the material, the conductivity of the material is improved, the layered structure of the reduced graphene oxide and the carbon hybrid nano tube generated in situ have a unique space-limited effect on the lithium sulfide material, and meanwhile, the volume expansion and the volume shrinkage of the lithium sulfide/carbon composite nano material in the charge and discharge process are relieved, and the cycle specific capacity and the capacity retention rate are excellent.
As a preferred technical scheme of the invention, the preparation process of the precursor material comprises the following steps:
and after the lithium source is dissolved in the metal salt solution, adding the graphene oxide solution to obtain a mixed solution, separating the mixed solution to obtain a precipitate, and then drying the precipitate to obtain the precursor material.
The lithium source and the metal salt solution in the precursor material can be uniformly dispersed on the surface of the graphene oxide layer, so that the subsequent dispersion of the lithium sulfide active substance in the composite material is ensured to be better. In addition, the concentration of the selected graphene oxide solution is preferably 10mg/mL, and the added volume is 30-100 mL.
As a preferred embodiment of the present invention, the lithium source includes lithium sulfate.
The lithium source in the present invention is preferably lithium sulfate because lithium sulfate is inexpensive and the annealing treatment provided by the present invention can result in the formation of lithium sulfide material. In addition, the addition amount of the lithium source in the present invention is preferably 0.1g.
Preferably, the solute in the metal salt solution comprises Co (NO 3 ) 2 ·6H 2 O、Fe(NO 3 ) 2 ·9H 2 O or Ni (NO) 3 ) 2 ·6H 2 O is more preferably Co (NO 3 ) 2 ·6H 2 O。
Preferably, the concentration of the metal salt solution is 1 to 10wt%, for example, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%, but is not limited to the recited values, and other non-recited values within the range of values are equally applicable; further preferably 4 to 6wt%.
According to the method, a certain mass of metal salt solid is weighed according to the concentration of the metal salt solution, and then the metal salt solid is dissolved in 50mL of deionized water to obtain the metal salt solution.
Preferably, the mass ratio of the lithium source to the graphene oxide in the graphene oxide solution is 1 (3-10), for example, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, but is not limited to the recited values, and other non-recited values in the range of the values are equally applicable; further preferably 1 (3) to (5).
The invention limits that the mass ratio of the lithium source to the graphene oxide in the graphene oxide solution is 1 (3-10), and when the mass ratio is lower than 1:3, the shape controllability of the synthesized lithium sulfide/carbon composite anode material is poor and the material quality is unstable, because the graphene oxide addition amount is less, the lithium sulfate carbothermal reduction reaction and the in-situ self-catalytic reaction of the active metal nano particles are incomplete; when the mass ratio is higher than 1:10, the first-cycle capacity and the cycle capacity of the positive electrode of the lithium-sulfur battery are greatly reduced, because the excessive carbon material reduces the loading amount of the positive electrode active substance lithium sulfide.
As a preferable technical scheme of the invention, the mixed solution is sequentially stirred, ultrasonically dispersed and separated to obtain a precipitate.
Preferably, the stirring speed is 450 to 550rpm/min, for example, 450rpm/min, 470rpm/min, 490rpm/min, 510rpm/min, 530rpm/min or 550rpm/min, but the stirring speed is not limited to the recited values, and other non-recited values within the range of the recited values are equally applicable.
Preferably, the stirring time is 10 to 14 hours, for example, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours or 14 hours, but the stirring time is not limited to the recited values, and other non-recited values within the range are equally applicable.
Preferably, the time of the ultrasonic dispersion is 20 to 40min, for example, 20min, 22min, 24min, 26min, 28min, 30min, 32min, 34min, 36min, 38min or 40min, but the present invention is not limited to the recited values, and other non-recited values within the range of the values are equally applicable.
The invention adopts the high-power ultrasonic machine basic ultrasonic dispersion.
Preferably, the separation treatment comprises centrifugation.
The rotational speed of the centrifugal separation in the present invention is preferably 8000rpm/min and the time is preferably 5min.
Preferably, the precipitate is pre-treated in liquid nitrogen for 8-12 min before being dried, for example, 8min, 8.5min, 9min, 9.5min, 10min, 10.5min, 11min, 11.5min or 12min, but not limited to the recited values, other non-recited values within the range are equally applicable.
Preferably, the drying time is 10 to 14 hours, for example, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours or 14 hours, but not limited to the recited values, and other non-recited values within the range are equally applicable.
Preferably, the drying comprises vacuum freeze drying.
As a preferable technical scheme of the invention, the precursor material and the organic compound powder are respectively placed at two ends of a porcelain boat, and are annealed after being capped.
The annealing treatment is preferably carried out in a tube furnace.
Preferably, the mass ratio of the organic compound powder to the precursor material is (1-20): 1, for example, 1:1, 2:1, 4:1, 6:1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1 or 20:1, but not limited to the recited values, other non-recited values within the range of values are equally applicable; further preferably (8-12): 1.
The invention limits the mass ratio of the organic compound powder to the precursor material to be (1-20): 1, when the mass ratio is lower than 1:1, active metal nano particles cannot self-catalyze to generate carbon hybrid nano tubes in situ, because a small amount of organic compound powder is completely vaporized at high temperature, and is insufficient for supporting chemical vapor deposition reaction; when the mass is higher than 20:1, the shape controllability of the generated carbon hybridized nano tube is poor, so that the material shows poor electrochemical performance, and the capacity exertion of the lithium sulfide active material is influenced because a large amount of organic compound powder generates the carbon hybridized nano tube with uncontrollable shape in the annealing process.
Preferably, the organic compound powder includes any one of melamine, urea or thiourea, and more preferably melamine.
In a preferred embodiment of the present invention, the annealing treatment is performed at a temperature of 600 to 900 ℃, for example, 600 ℃, 630 ℃, 650 ℃, 680 ℃, 700 ℃, 720 ℃, 750 ℃, 780 ℃, 800 ℃, 830 ℃, 850 ℃, 880 ℃ or 900 ℃, but the annealing treatment is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned value range are equally applicable; further preferably 650 to 750 ℃.
The invention limits the annealing treatment temperature to 600-900 ℃, when the temperature is lower than 600 ℃, the raw material lithium sulfate can not be fully carbothermally reduced to generate lithium sulfide, because the lower temperature does not meet the condition of high-temperature thermal reduction; when the temperature is higher than 900 ℃, in-situ chemical vapor deposition can be caused to generate thicker and shorter carbon hybrid nanorods, because the excessive temperature limits the self-catalytic thermal reduction reaction kinetics of the active metal nanoparticles.
Preferably, the annealing treatment is performed for 0.5 to 2 hours, for example, 0.5 hours, 0.8 hours, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours or 2 hours, but the annealing treatment is not limited to the recited values, and other non-recited values within the range of the recited values are equally applicable; more preferably 0.5 to 1 hour.
The invention limits the annealing treatment time to 0.5-2 h, and when the annealing treatment time is lower than 0.5h, the carbothermic reduction reaction is incomplete, because the shorter annealing time does not meet the condition of high-temperature thermal reduction; when the time is higher than 2 hours, the carbon hybridized nano tube with uncontrollable morphology can be generated in situ, and the carbon hybridized nano tube continuously grows on the surface layer of the reduced graphene oxide in an uncontrollable mode due to the longer annealing time.
Preferably, the heating rate of the annealing treatment is 1 to 20 ℃/min, for example, 1 ℃/min, 2 ℃/min, 4 ℃/min, 6 ℃/min, 8 ℃/min, 10 ℃/min, 12 ℃/min, 14 ℃/min, 16 ℃/min, 18 ℃/min or 20 ℃/min, but the annealing treatment is not limited to the recited values, and other non-recited values within the range of the values are equally applicable; more preferably 5 to 10 ℃/min.
Preferably, the annealing treatment is performed under a protective atmosphere.
As a preferable technical scheme of the invention, the preparation method comprises the following steps:
(1) Dissolving a lithium source in a metal salt solution with the concentration of 1-10wt%, and adding a graphene oxide solution with the concentration of 8-12 mg/mL to obtain a mixed solution, wherein the mass ratio of the lithium source to the graphene oxide in the graphene oxide solution is 1 (3-10);
(2) Stirring the mixed solution obtained in the step (1) for 10-14 h at the rotating speed of 450-550 rpm/min, then performing ultrasonic dispersion for 20-40 min, separating to obtain a precipitate, then placing the precipitate in liquid nitrogen for pretreatment for 8-12 min, and drying for 10-14 h to obtain a precursor material;
(3) And (3) respectively placing the organic compound powder and the precursor material obtained in the step (2) at the two ends of a porcelain boat according to the mass ratio of (1-20): 1, capping, heating to 600-900 ℃ at the heating rate of 1-20 ℃/min under the protective atmosphere, and carrying out annealing treatment for 0.5-2 h, wherein the self-catalytic reaction and the thermal reduction reaction are carried out under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material.
In the invention, the multi-stage structure lithium sulfide/carbon composite material is obtained by annealing treatment, and is taken out under protective atmosphere after being cooled to room temperature.
In a second aspect, the present invention provides a multi-stage structured lithium sulfide/carbon composite material, which is prepared by the preparation method described in the first aspect.
As a preferable technical scheme of the invention, the multi-stage structure lithium sulfide/carbon composite material comprises a reducing graphene oxide layer, wherein lithium sulfide particles are dispersed on two side surfaces of the reducing graphene oxide layer, and carbon hybridized nanotubes are grown on two side surfaces of the reducing graphene oxide layer in situ.
In a third aspect, the present invention provides a lithium sulfur battery comprising the multi-stage structured lithium sulfide/carbon composite material of the second aspect.
Compared with the prior art, the invention has the beneficial effects that:
the multi-stage structure lithium sulfide/carbon composite material prepared by the preparation method provided by the invention has the advantages that the lithium sulfide, the reduced graphene oxide and the carbon hybrid nano tube are simultaneously provided, the composite effect among the three can stabilize the structure of the material, the conductivity of the material is improved, the layered structure of the reduced graphene oxide and the carbon hybrid nano tube generated in situ have a unique space-limited effect on the lithium sulfide material, and meanwhile, the volume expansion and the volume shrinkage of the lithium sulfide/carbon composite nano material in the charge and discharge process are relieved, and the cycle specific capacity and the capacity retention rate are excellent.
Drawings
Fig. 1 is a flow chart of the preparation of the multi-stage structured lithium sulfide/carbon composite material provided in examples 1 to 9 of the present invention.
Detailed Description
The technical scheme of the invention is further described by the following specific embodiments. It should be apparent to those skilled in the art that the examples are merely provided to aid in understanding the present invention and should not be construed as limiting the invention in any way.
Example 1
The embodiment provides a preparation method of a multi-stage structure lithium sulfide/carbon composite material, as shown in fig. 1, the preparation method comprises the following steps:
(1) 2.5g of Co (NO 3 ) 2 ·6H 2 O is dissolved in 50mL of deionized water to obtain a cobalt salt solution with the concentration of 5wt%, 0.1g of lithium sulfate is added to dissolve in the cobalt salt solution, and then 50mL of graphene oxide solution with the concentration of 10mg/mL is added to obtain a mixed solution;
(2) Stirring the mixed solution obtained in the step (1) for 12 hours at a rotating speed of 500rpm/min, performing ultrasonic dispersion for 30 minutes, performing centrifugal separation for 5 minutes at a rotating speed of 8000rpm/min to obtain a precipitate, and then placing the precipitate in liquid nitrogen for pretreatment for 10 minutes, and performing vacuum freeze drying for 12 hours to obtain a precursor material;
(3) And (3) respectively placing melamine powder and the precursor material obtained in the step (2) at two ends of a porcelain boat according to the mass ratio of 10:1, capping, heating to 700 ℃ at the heating rate of 5 ℃/min under nitrogen atmosphere, performing annealing treatment for 0.5h, and performing autocatalysis reaction and thermal reduction reaction under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material.
Example 2
The embodiment provides a preparation method of a multi-stage structure lithium sulfide/carbon composite material, as shown in fig. 1, the preparation method comprises the following steps:
(1) 2.5g of Fe (NO) 3 ) 2 ·9H 2 O is dissolved in 50mL of deionized water to obtain an iron salt solution with the concentration of 5wt%, 0.1g of lithium sulfate is added to dissolve in the iron salt solution, and then 50mL of graphene oxide solution with the concentration of 10mg/mL is added to obtain a mixed solution;
(2) Stirring the mixed solution obtained in the step (1) for 12 hours at a rotating speed of 500rpm/min, performing ultrasonic dispersion for 30 minutes, performing centrifugal separation for 5 minutes at a rotating speed of 8000rpm/min to obtain a precipitate, and then placing the precipitate in liquid nitrogen for pretreatment for 10 minutes, and performing vacuum freeze drying for 12 hours to obtain a precursor material;
(3) And (3) respectively placing urea powder and the precursor material obtained in the step (2) at the two ends of a porcelain boat according to the mass ratio of 10:1, capping, heating to 750 ℃ at the heating rate of 5 ℃/min under nitrogen atmosphere, performing annealing treatment for 0.5h, and performing autocatalysis reaction and thermal reduction reaction under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material.
Example 3
The embodiment provides a preparation method of a multi-stage structure lithium sulfide/carbon composite material, as shown in fig. 1, the preparation method comprises the following steps:
(1) 2.5g of Ni (NO 3 ) 2 ·6H 2 O is dissolved in 50mL of deionized water to obtain a nickel salt solution with the concentration of 5wt%, 0.1g of lithium sulfate is added to dissolve in the nickel salt solution, and then 50mL of graphene oxide solution with the concentration of 10mg/mL is added to obtain a mixed solution;
(2) Stirring the mixed solution obtained in the step (1) for 12 hours at a rotating speed of 500rpm/min, performing ultrasonic dispersion for 30 minutes, performing centrifugal separation for 5 minutes at a rotating speed of 8000rpm/min to obtain a precipitate, and then placing the precipitate in liquid nitrogen for pretreatment for 10 minutes, and performing vacuum freeze drying for 12 hours to obtain a precursor material;
(3) And (3) respectively placing melamine powder and the precursor material obtained in the step (2) at the two ends of the ceramic boat according to the mass ratio of 20:1, capping, heating to 800 ℃ at the heating rate of 10 ℃/min under the nitrogen atmosphere, and carrying out annealing treatment for 1h, wherein the self-catalytic reaction and the thermal reduction reaction are carried out under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material.
Example 4
The embodiment provides a preparation method of a multi-stage structure lithium sulfide/carbon composite material, as shown in fig. 1, the preparation method comprises the following steps:
(1) 5g of Co (NO) 3 ) 2 ·6H 2 O is dissolved in 50mL of deionized water to obtain a cobalt salt solution with the concentration of 10wt%, 0.1g of lithium sulfate is added to dissolve in the cobalt salt solution, and then 100mL of graphene oxide solution with the concentration of 10mg/mL is added to obtain a mixed solution;
(2) Stirring the mixed solution obtained in the step (1) for 12 hours at a rotating speed of 500rpm/min, performing ultrasonic dispersion for 30 minutes, performing centrifugal separation for 5 minutes at a rotating speed of 8000rpm/min to obtain a precipitate, and then placing the precipitate in liquid nitrogen for pretreatment for 10 minutes, and performing vacuum freeze drying for 12 hours to obtain a precursor material;
(3) And (3) respectively placing thiourea powder and the precursor material obtained in the step (2) at two ends of a porcelain boat according to the mass ratio of 10:1, capping, heating to 700 ℃ at the heating rate of 2 ℃/min under nitrogen atmosphere, performing annealing treatment for 2 hours, and performing autocatalysis reaction and thermal reduction reaction under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material.
Example 5
The embodiment provides a preparation method of a multi-stage structure lithium sulfide/carbon composite material, as shown in fig. 1, the preparation method comprises the following steps:
(1) 2.5g of Co (NO 3 ) 2 ·6H 2 O is dissolved in 50mL of deionized water to obtain a cobalt salt solution with the concentration of 5wt%, 0.1g of lithium sulfate is added to dissolve in the cobalt salt solution, and then 50mL of graphene oxide solution with the concentration of 10mg/mL is added to obtain a mixed solution;
(2) Stirring the mixed solution obtained in the step (1) for 12 hours at a rotating speed of 500rpm/min, performing ultrasonic dispersion for 30 minutes, performing centrifugal separation for 5 minutes at a rotating speed of 8000rpm/min to obtain a precipitate, and then placing the precipitate in liquid nitrogen for pretreatment for 10 minutes, and performing vacuum freeze drying for 12 hours to obtain a precursor material;
(3) And (3) respectively placing melamine powder and the precursor material obtained in the step (2) at two ends of a porcelain boat according to the mass ratio of 5:1, capping, heating to 850 ℃ at the heating rate of 20 ℃/min under nitrogen atmosphere, and carrying out annealing treatment for 1h, wherein the self-catalytic reaction and the thermal reduction reaction are carried out under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material.
Example 6
The embodiment provides a preparation method of a multi-stage structure lithium sulfide/carbon composite material, as shown in fig. 1, the preparation method comprises the following steps:
(1) 2.5g of Co (NO 3 ) 2 ·6H 2 O is dissolved in 50mL of deionized water to obtain a cobalt salt solution with the concentration of 5wt%, 0.1g of lithium sulfate is added to dissolve in the cobalt salt solution, and then 100mL of graphene oxide solution with the concentration of 10mg/mL is added to obtain a mixed solution;
(2) Stirring the mixed solution obtained in the step (1) for 12 hours at a rotating speed of 500rpm/min, performing ultrasonic dispersion for 30 minutes, performing centrifugal separation for 5 minutes at a rotating speed of 8000rpm/min to obtain a precipitate, and then placing the precipitate in liquid nitrogen for pretreatment for 10 minutes, and performing vacuum freeze drying for 12 hours to obtain a precursor material;
(3) And (3) respectively placing melamine powder and the precursor material obtained in the step (2) at the two ends of the ceramic boat according to the mass ratio of 20:1, capping, heating to 900 ℃ at the heating rate of 2 ℃/min under the nitrogen atmosphere, and carrying out annealing treatment for 1h, wherein the self-catalytic reaction and the thermal reduction reaction are carried out under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material.
Example 7
The embodiment provides a preparation method of a multi-stage structure lithium sulfide/carbon composite material, as shown in fig. 1, the preparation method comprises the following steps:
(1) 3.2g of Co (NO 3 ) 2 ·6H 2 O is dissolved in 50mL of deionized water to obtain a cobalt salt solution with the concentration of 6wt%, 0.1g of lithium sulfate is added to dissolve in the cobalt salt solution, and then 40mL of graphene oxide solution with the concentration of 10mg/mL is added to obtain a mixed solution;
(2) Stirring the mixed solution obtained in the step (1) for 10 hours at a rotating speed of 550rpm/min, performing ultrasonic dispersion for 20 minutes, performing centrifugal separation for 5 minutes at a rotating speed of 8000rpm/min to obtain a precipitate, and then placing the precipitate in liquid nitrogen for pretreatment for 12 minutes, and performing vacuum freeze drying for 10 hours to obtain a precursor material;
(3) And (3) respectively placing melamine powder and the precursor material obtained in the step (2) at two ends of a porcelain boat according to the mass ratio of 12:1, capping, heating to 650 ℃ at the heating rate of 8 ℃/min under nitrogen atmosphere, performing annealing treatment for 0.5h, and performing autocatalysis reaction and thermal reduction reaction under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material.
Example 8
The embodiment provides a preparation method of a multi-stage structure lithium sulfide/carbon composite material, as shown in fig. 1, the preparation method comprises the following steps:
(1) 2g of Co (NO) 3 ) 2 ·6H 2 O is dissolved in 50mL of deionized water to obtain a cobalt salt solution with the concentration of 4wt%, 0.1g of lithium sulfate is added to dissolve in the cobalt salt solution, and then 30mL of graphene oxide solution with the concentration of 10mg/mL is added to obtain a mixed solution;
(2) Stirring the mixed solution obtained in the step (1) for 14 hours at the rotating speed of 450rpm/min, performing ultrasonic dispersion for 40 minutes, performing centrifugal separation for 5 minutes at the rotating speed of 8000rpm/min to obtain a precipitate, and then placing the precipitate in liquid nitrogen for pretreatment for 8 minutes, and performing vacuum freeze drying for 14 hours to obtain a precursor material;
(3) And (3) respectively placing melamine powder and the precursor material obtained in the step (2) at two ends of a porcelain boat according to the mass ratio of 8:1, capping, heating to 600 ℃ at the heating rate of 1 ℃/min under nitrogen atmosphere, performing annealing treatment for 2 hours, and performing autocatalysis reaction and thermal reduction reaction under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material.
Example 9
The embodiment provides a preparation method of a multi-stage structure lithium sulfide/carbon composite material, as shown in fig. 1, the preparation method comprises the following steps:
(1) 0.5g of Co (NO 3 ) 2 ·6H 2 O is dissolved in 50mL of deionized water to obtain a cobalt salt solution with the concentration of 1wt%, 0.1g of lithium sulfate is added to dissolve in the cobalt salt solution, and then 50mL of graphene oxide solution with the concentration of 10mg/mL is added to obtain a mixed solution;
(2) Stirring the mixed solution obtained in the step (1) for 12 hours at a rotating speed of 500rpm/min, performing ultrasonic dispersion for 30 minutes, performing centrifugal separation for 5 minutes at a rotating speed of 8000rpm/min to obtain a precipitate, and then placing the precipitate in liquid nitrogen for pretreatment for 10 minutes, and performing vacuum freeze drying for 12 hours to obtain a precursor material;
(3) And (3) respectively placing melamine powder and the precursor material obtained in the step (2) at two ends of a porcelain boat according to the mass ratio of 1:1, capping, heating to 700 ℃ at the heating rate of 5 ℃/min under nitrogen atmosphere, performing annealing treatment for 0.5h, and performing autocatalysis reaction and thermal reduction reaction under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material.
Example 10
This example differs from example 1 in that 20mL of graphene oxide solution was added in step (1), and the remaining process parameters and operating steps were the same as example 1.
Example 11
This example differs from example 1 in that 120mL of graphene oxide solution was added in step (1), and the remaining process parameters and operating steps were the same as example 1.
Example 12
The difference between this example and example 1 is that the mass ratio of melamine powder in step (3) to the precursor material obtained in step (2) is 0.5:1, and the remaining process parameters and operating steps are the same as in example 1.
Example 13
The difference between this example and example 1 is that the mass ratio of melamine powder in step (3) to the precursor material obtained in step (2) is 22:1, and the remaining process parameters and operating steps are the same as in example 1.
Example 14
This example differs from example 1 in that the annealing temperature in step (3) is 550 ℃, and the remaining process parameters and operating steps are the same as in example 1.
Example 15
This example differs from example 1 in that the annealing temperature in step (3) was 950 ℃, and the remaining process parameters and operating steps were the same as in example 1.
Example 16
The difference between this example and example 1 is that the annealing time in step (3) was 0.3h, and the remaining process parameters and operating steps were the same as in example 1.
Example 17
The difference between this example and example 1 is that the annealing time in step (3) was 2.5h, and the remaining process parameters and operating steps were the same as in example 1.
Comparative example 1
The present comparative example provides a method for preparing a lithium sulfide/carbon composite material, the method comprising:
(1) Dissolving 0.1g of lithium sulfate in 50mL of deionized water, adding 0.15g of porous carbon (C), and uniformly mixing to obtain a mixed solution;
(2) Stirring the mixed solution obtained in the step (1) for 12 hours at a rotating speed of 500rpm/min, performing ultrasonic dispersion for 30 minutes, performing centrifugal separation for 5 minutes at a rotating speed of 8000rpm/min to obtain a precipitate, and then placing the precipitate in liquid nitrogen for pretreatment for 10 minutes, and performing vacuum freeze drying for 12 hours to obtain a precursor material;
(3) And (3) placing the precursor material obtained in the step (3) into a porcelain boat, capping, heating to 700 ℃ at a heating rate of 5 ℃/min under nitrogen atmosphere, and performing annealing treatment for 0.5h to obtain the lithium sulfide/carbon composite material.
Comparative example 2
The present comparative example provides a method for preparing a lithium sulfide/carbon composite material, the method comprising:
(1) Dissolving 0.1g of lithium sulfate in 50mL of deionized water, adding 50mL of graphene oxide solution with the concentration of 10mg/mL, and uniformly mixing to obtain a mixed solution;
(2) Stirring the mixed solution obtained in the step (1) for 12 hours at a rotating speed of 500rpm/min, performing ultrasonic dispersion for 30 minutes, performing centrifugal separation for 5 minutes at a rotating speed of 8000rpm/min to obtain a precipitate, and then placing the precipitate in liquid nitrogen for pretreatment for 10 minutes, and performing vacuum freeze drying for 12 hours to obtain a precursor material;
(3) And (3) placing the precursor material obtained in the step (3) into a porcelain boat, capping, heating to 700 ℃ at a heating rate of 5 ℃/min under nitrogen atmosphere, and performing annealing treatment for 0.5h to obtain the lithium sulfide/carbon composite material.
Electrochemical tests were performed on lithium sulfide/carbon composites prepared in examples 1-17 and comparative examples 1-2:
(1) Preparing a positive electrode plate: dispersing lithium sulfide/carbon composite material, conductive carbon black (SP) and polyvinylidene fluoride (PVDF) in N-methyl pyrrolidone (NMP) according to the mass ratio of 8:1:1, uniformly mixing to form slurry, coating the slurry on the surface of an aluminum foil, drying, and stamping to form a positive electrode plate with the diameter of 14 mm.
(2) Assembling a battery: the metal lithium sheet is used as a negative electrode, 1mol/L of lithium bistrifluoromethyl sulfonic acid imide (LiTFSI)/ethylene glycol dimethyl ether (DME) is used as a 1, 3-Dioxolane (DOL), wherein the DOL is 1:1, and the CR2032 button cell is assembled in a glove box filled with argon.
(3) Performance test: charging to 3.6V at a rate of 0.05C, and then discharging to 1.8V; then, charge-discharge and cycle stability tests were performed at a rate of 0.2C (1c=1166ma/g) in a voltage range of 1.7 to 2.8V.
The test results of the electrochemical tests performed on the lithium sulfide/carbon composites prepared in examples 1 to 17 and comparative examples 1 to 2 are shown in table 1.
TABLE 1
From the data of table 1:
(1) The multi-stage structure lithium sulfide/carbon composite materials in examples 1-9 all have excellent circulation specific capacity and capacity retention rate, and the multi-stage structure lithium sulfide/carbon composite material prepared by the preparation method provided by the invention has the advantages that the structure of the material can be stabilized through the composite effect among lithium sulfide, reduced graphene oxide and carbon hybrid nanotubes, the conductivity of the material is improved, and the layered structure of the reduced graphene oxide and the carbon hybrid nanotubes generated in situ have unique space-limiting effect on the lithium sulfide material, and meanwhile, the volume expansion and shrinkage of the lithium sulfide/carbon composite nano material in the charge and discharge process are relieved, so that the multi-stage structure lithium sulfide/carbon composite material has excellent circulation specific capacity and capacity retention rate.
(2) The cycling specific capacity and capacity retention rate of the multi-stage structured lithium sulfide/carbon composite materials in examples 10 and 11 were lower than those in example 1, because the addition amount of the graphene oxide solution in example 10 was too low and that in example 11 was too high. When the addition amount of the graphene oxide is too low, the lithium sulfate carbothermal reduction reaction and the in-situ self-catalytic reaction of the active metal nano particles are incomplete, so that the shape controllability of the synthesized lithium sulfide/carbon composite anode material is poor and the quality of the material is unstable; when the addition amount of the graphene oxide is too high, the excessive carbon material can reduce the load of the positive active substance lithium sulfide, so that the first-circle capacity and the circulating capacity of the positive electrode of the lithium-sulfur battery are greatly reduced.
(3) The cycling specific capacity and capacity retention ratio of the multi-stage structured lithium sulfide/carbon composites of examples 12 and 13 were lower than that of example 1, because the addition amount of the organic compound powder of example 12 was too low, and a small amount of the organic compound powder was completely vaporized at high temperature, which was insufficient to support the chemical vapor deposition reaction, resulting in failure of the active metal nanoparticles to autocatalytically generate carbon hybrid nanotubes in situ; in example 13, the addition amount of the organic compound powder is too high, and a large amount of organic compound powder generates carbon hybridized nanotubes with uncontrollable morphology in the annealing process, so that the capacity exertion of the lithium sulfide active material is affected.
(4) The cycling specific capacity and capacity retention rate of the multi-stage structured lithium sulfide/carbon composite materials in examples 14 and 15 were lower than those in example 1, because the annealing temperature in example 14 was too low to meet the conditions of high-temperature thermal reduction, resulting in failure of complete carbothermal reduction of the raw material lithium sulfate to produce lithium sulfide; the excessive annealing temperature in example 15 limits the kinetics of the autocatalytic thermal reduction reaction of the active metal nanoparticles, resulting in the formation of thicker, shorter carbon hybrid nanorods by in situ chemical vapor deposition.
(5) The cycle specific capacity and capacity retention ratio of the multi-stage structured lithium sulfide/carbon composite materials in examples 16 and 17 were lower than those in example 1, because the annealing time was too short in example 16 to satisfy the conditions of high-temperature thermal reduction, resulting in incomplete carbothermic reaction; in example 17, the annealing time was too long, resulting in uncontrolled continuous growth of carbon hybrid nanotubes on the surface layer of the reduced graphene oxide, resulting in situ formation of carbon hybrid nanotubes with uncontrolled morphology.
(6) The cycling specific capacity and capacity retention rate of the multi-stage structured lithium sulfide/carbon composites of comparative examples 1 and 2 were much lower than those of example 1, since lithium sulfate was added to deionized water in comparative example 1 and porous carbon was used instead of graphene oxide solution, and the addition of organic compound powder was also omitted during annealing; comparative example 2 lithium sulfate was added to deionized water while omitting the organic compound powder during annealing. The composite materials obtained in comparative examples 1 and 2 are not formed into a multi-stage structure lithium sulfide/carbon composite material with lithium sulfide, reduced graphene oxide and carbon hybridized nanotubes, and therefore, the multi-stage structure lithium sulfide/carbon composite material obtained by the preparation method provided by the invention can stabilize the structure of the material through the composite action between the lithium sulfide, the reduced graphene oxide and the carbon hybridized nanotubes, improve the conductivity of the material, effectively relieve the volume expansion and contraction of the lithium sulfide/carbon composite nano material in the charge and discharge process, and has excellent specific circulation capacity and capacity retention rate.
While the foregoing is directed to embodiments of the present invention, other and further details of the invention may be had by the present invention, it should be understood that the foregoing description is merely illustrative of the present invention and that no limitations are intended to the scope of the invention, except insofar as modifications, equivalents, improvements or modifications are within the spirit and principles of the invention.

Claims (26)

1. A method for preparing a multi-stage structured lithium sulfide/carbon composite material, the method comprising:
mixing a lithium source, a metal salt solution and a graphene oxide solution, wherein the mass ratio of the lithium source to the graphene oxide in the graphene oxide solution is 1 (3-10), drying to obtain a precursor material, respectively placing the precursor material and organic compound powder at two ends of a porcelain boat, capping, and then carrying out annealing treatment, wherein the mass ratio of the organic compound powder to the precursor material is 1-20, and carrying out autocatalysis reaction and thermal reduction reaction under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material;
carbon hybridized nanotubes are grown on the reduction sites on the two side surfaces of the reduced graphene oxide layer in the multi-level structure lithium sulfide/carbon composite material;
the multi-level structure lithium sulfide/carbon composite material is provided with lithium sulfide, reduced graphene oxide and carbon hybridized nano tube;
the solute in the metal salt solution comprises Co (NO 3 ) 2 ·6H 2 O、Fe(NO 3 ) 2 ·9H 2 O or Ni (NO) 3 ) 2 ·6H 2 O is any one of the following;
the organic compound powder comprises any one of melamine, urea or thiourea;
the temperature of the annealing treatment is 600-900 ℃ and the time is 0.5-2 h.
2. The method of claim 1, wherein the precursor material is prepared by a process comprising:
and after the lithium source is dissolved in the metal salt solution, adding the graphene oxide solution to obtain a mixed solution, separating the mixed solution to obtain a precipitate, and then drying the precipitate to obtain the precursor material.
3. The method of claim 1, wherein the lithium source comprises lithium sulfate.
4. The method according to claim 1, wherein the solute in the metal salt solution is Co (NO 3 ) 2 ·6H 2 O。
5. The preparation method according to claim 1, wherein the concentration of the metal salt solution is 1-10wt%.
6. The method according to claim 1, wherein the concentration of the metal salt solution is 4-6wt%.
7. The preparation method of claim 1, wherein the mass ratio of the lithium source to graphene oxide in the graphene oxide solution is 1 (3-5).
8. The preparation method according to claim 2, wherein the mixed solution is subjected to stirring, ultrasonic dispersion and separation in this order to obtain a precipitate.
9. The method according to claim 8, wherein the stirring speed is 450-550 rpm/min.
10. The method according to claim 8, wherein the stirring time is 10 to 14 hours.
11. The method for preparing the ultrasonic dispersion liquid according to claim 8, wherein the ultrasonic dispersion time is 20-40 min.
12. The method of claim 8, wherein the separation process comprises centrifugation.
13. The preparation method of claim 8, wherein the precipitate is placed in liquid nitrogen for pretreatment for 8-12 min before the precipitate is dried.
14. The method according to claim 13, wherein the drying time is 10 to 14 hours.
15. The method of claim 13, wherein the drying comprises vacuum freeze drying.
16. The method according to claim 1, wherein the mass ratio of the organic compound powder to the precursor material is (8-12): 1.
17. The method of claim 1, wherein the organic compound powder is melamine.
18. The method according to claim 1, wherein the annealing treatment is performed at a temperature of 650-750 ℃.
19. The method according to claim 1, wherein the annealing treatment is performed for 0.5 to 1 hour.
20. The preparation method of claim 1, wherein the temperature rise rate of the annealing treatment is 1-20 ℃/min.
21. The preparation method of claim 1, wherein the temperature rise rate of the annealing treatment is 5-10 ℃/min.
22. The method of claim 1, wherein the annealing is performed in a protective atmosphere.
23. The preparation method according to claim 1, characterized in that the preparation method comprises:
(1) Dissolving a lithium source in a metal salt solution with the concentration of 1-10wt%, and adding a graphene oxide solution to obtain a mixed solution, wherein the mass ratio of the lithium source to the graphene oxide in the graphene oxide solution is 1 (3-10);
(2) Stirring the mixed solution obtained in the step (1) at a rotating speed of 450-550 rpm/min for 10-14 h, performing ultrasonic dispersion for 20-40 min, separating to obtain a precipitate, placing the precipitate in liquid nitrogen for pretreatment for 8-12 min, and drying for 10-14 h to obtain a precursor material;
(3) And (3) respectively placing the organic compound powder and the precursor material obtained in the step (2) at the two ends of a porcelain boat according to the mass ratio of (1-20): 1, capping, heating to 600-900 ℃ at the heating rate of 1-20 ℃/min under a protective atmosphere, and carrying out annealing treatment for 0.5-2 h, wherein the self-catalytic reaction and the thermal reduction reaction are carried out under the annealing treatment condition to obtain the multi-stage structure lithium sulfide/carbon composite material.
24. A multi-stage structured lithium sulfide/carbon composite material, characterized in that the multi-stage structured lithium sulfide/carbon composite material is produced by the production method according to any one of claims 1 to 23.
25. The multi-stage structured lithium sulfide/carbon composite material according to claim 24, wherein the multi-stage structured lithium sulfide/carbon composite material comprises a reduced graphene oxide layer, wherein lithium sulfide particles are dispersed on both side surfaces of the reduced graphene oxide layer, and wherein carbon hybrid nanotubes are grown in situ on both side surfaces of the reduced graphene oxide layer.
26. A lithium sulfur battery comprising the multi-stage structured lithium sulfide/carbon composite material of claim 24 or 25.
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