CN112038635B - Lithium-sulfur battery graphene-loaded cementite particle composite positive electrode material and preparation method thereof - Google Patents
Lithium-sulfur battery graphene-loaded cementite particle composite positive electrode material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a composite cathode material of graphene-like loaded cementite particles for a lithium-sulfur battery and a preparation method thereof, wherein the composite cathode material is prepared from Fe with a graphene-like structure3C/C and elemental sulfur, wherein the elemental sulfur is dispersed in Fe3C/C in the pores; the method comprises the steps of taking hibiscus flower petals as raw materials, carrying out pre-carbonization treatment to obtain biochar with a graphene-like structure, compounding the biochar with potassium ferrate, carrying out heat treatment, wherein the potassium ferrate is used as a pore-forming agent and provides an iron source, and synthesizing Fe with the graphene-like structure in one step3C/C composite material. The invention uses the Fe with a graphene-like structure with high specific surface area and developed pore structure3The C/C is compounded with elemental sulfur, physical adsorption and chemical adsorption are achieved, polysulfide is effectively captured, the shuttle effect in the charging and discharging process is solved, the electrochemical stability of the surface of the electrode is improved, and the electrochemical performance of the electrode material is finally improved.
Description
Technical Field
The invention belongs to the technical field of lithium-sulfur battery positive electrode materials, and relates to Fe with a graphene-like structure3C/C and elemental sulfur are compounded to obtain the lithium-sulfur battery composite positive electrode material and the preparation method thereof.
Background
With the increasing energy crisis and environmental pollution, the development of new renewable energy sources is receiving wide attention. The lithium-sulfur battery has high theoretical specific capacity (1675mAh/g) and theoretical energy density (2600wh/kg), and meanwhile, the positive active substance elemental sulfur has low price, is environment-friendly, rich in storage capacity and easy to mine, so the lithium-sulfur battery is considered to be one of the best choices of the next-generation high-energy-density lithium ion battery, and is expected to become a next-generation energy storage device to be applied.
The commercial application of lithium sulfur batteries is still limited in several respects: on the one hand, the electron conductivity of elemental sulfur itself is too low (5X 10)-30S cm-1At 25 ℃), serious polarization exists, so that the transmission efficiency of electrons on the surface of an active material is low, and the improvement of the battery performance is seriously restricted; on the other hand, the active sulfur can be decomposed to generate polysulfide and other intermediate products which can be dissolved in the electrolyte in the discharging process, so that the more serious shuttle effect is caused to seriously reduce the charging and discharging specific capacity and the coulombic efficiency of the battery; in addition, sulfur will undergo severe volume expansion during charging and discharging. These problems have greatly limited the commercial use of lithium sulfur batteries.
In order to solve the above problems in the lithium-sulfur battery, researchers have proposed that a conductive material (porous carbon, conductive polymer, metal oxide, etc.) is used as a carrier and compounded with elemental sulfur to improve the conductivity. The porous carbon material has good conductivity and a developed pore structure, wherein macropores can provide sites for the attachment of active substances, mesopores can provide channels for the shuttling of ions, and micropores can physically bind polysulfide and are ideal carriers of electrode active substances. A sulfur-carbon composite material in which elemental sulfur is dispersed in a carbon material has been widely used in the research of positive electrode materials for lithium-sulfur batteries. For example, in 2016, Zhang Zhi an et al, disclosed Chinese invention patent "a graphene-like carbon material/sulfur composite positive electrode material for lithium-sulfur batteries and a preparation method and application thereof" (publication No. CN 106058173A). The invention is formed by compounding a three-dimensional porous graphene-like carbon material with a micro-nano structure and elemental sulfur, the three-dimensional porous graphene has the advantages of good conductivity, large specific surface area and the like, and a natural conductive network can be bridged between the three-dimensional porous graphene and the elemental sulfur, so that the composite positive electrode material is beneficial to electronic conduction and lithium ion diffusion, and has positive significance for stabilizing an electrode structure. Although the carbon material not only increases the conductivity of the positive electrode, but also limits the shuttle effect of polysulfide and the volume expansion of sulfur through an internal porous structure, and improves the electrochemical performance of the lithium-sulfur battery to a certain extent, the polysulfide cannot be really firmly bound to the positive electrode only by the physical limiting effect. Eventually, a shuttling effect occurs, causing a capacity fade in the battery cycle.
Disclosure of Invention
In order to solve the above problems, an object of the present invention is to provide a lithium-sulfur battery graphene-supported cementite particle composite positive electrode material including Fe having a graphene-like structure with a high specific surface area and a developed pore structure3The C/C is compounded with elemental sulfur, physical adsorption and chemical adsorption are achieved, polysulfide is effectively captured, the shuttle effect in the charging and discharging process is solved, the electrochemical stability of the surface of the electrode is improved, and the electrochemical performance of the electrode material is finally improved.
The invention also aims to provide a preparation method of the graphene-loaded cementite particle composite cathode material for the lithium-sulfur battery, which has the advantages of wide material source, low price and simple and feasible preparation method.
In order to achieve the purpose, the invention adopts the following technical scheme:
a composite positive electrode material of grapheme-loaded cementite particles for lithium-sulfur battery is prepared from Fe with a grapheme-like structure3C/C and elemental sulfur, wherein the elemental sulfur is dispersed in Fe3C/C in the pores.
In the scheme, the Fe of the graphene-like structure3Fe in C/C3The content of C is 10-30 wt%. Fe3The addition of C can effectively improve the conductivity of the electrode material, and Fe3Chemical bond connection is established between C and elemental sulfur, which plays a role in polysulfideThe chemical adsorption effectively inhibits the dissolution of polysulfide, thereby being beneficial to improving the electrochemical performance of the composite material.
In the scheme, the Fe of the graphene-like structure3The total specific surface area of C/C is 1400m2/g～2800m2(ii) in terms of/g. Fe of graphene-like structure3The C/C has higher specific surface area and developed pore structure, can provide effective space for storing elemental sulfur, and limits huge volume change during the conversion between sulfur and polysulfide in the charge-discharge process; meanwhile, the material has a curled carbon layer structure, plays a physical adsorption role on polysulfide and is cooperated with Fe3The chemical adsorption effect of C can more effectively inhibit the dissolution of polysulfide and improve the electrochemical performance of the composite material.
In the scheme, the sulfur content in the composite cathode material is 70-85 wt%.
The invention also provides a preparation method of the graphene-loaded cementite particle composite cathode material for the lithium-sulfur battery, which specifically comprises the following steps:
1) under inert atmosphere, pre-carbonizing by taking hibiscus flower petals as a carbon source to obtain biochar;
2) uniformly dispersing the biochar prepared in the step 1) and potassium ferrate in water, stirring, drying, and calcining in an inert atmosphere to obtain Fe with a graphene-like structure3A C/C composite material;
3) fe prepared in the step 2)3Mixing and grinding the C/C composite material and sublimed sulfur, and preparing Fe with a graphite-like structure by adopting a melting diffusion method under vacuum3C/C @ S composite cathode material.
In the scheme, the hibiscus flower petals in the step 1) are soaked in deionized water for 12-24 hours, ultrasonically cleaned for 1-2 hours, and placed in a vacuum drying oven at 80 ℃ for drying for 12 hours.
In the scheme, the pre-carbonization temperature in the step 1) is 300-450 ℃, the heating rate is 2-10 ℃/min, and the pre-carbonization time is 2-3 h.
In the scheme, the mass ratio of the biochar in the step 2) to the potassium ferrate is 1: 1-1: 3, stirring for 4-8 h, and drying in a forced air drying oven at 80 ℃ for 12 h.
In the scheme, the calcining temperature in the step 2) is 760-800 ℃, the heating rate is 8-15 ℃/min, and the time is 2-3 h; fe3The C/C composite material is washed by water and acid for standby, and the acid washing solution adopts dilute hydrochloric acid or acetic acid.
In the above scheme, the melt diffusion method in step 3) comprises the following specific processes: mixing Fe3C/C and sublimed sulfur are mixed and ground according to the mass ratio of 1: 6-3: 7, then the mixture is placed into a reaction kettle and vacuumized, the reaction kettle is transferred into a muffle furnace, the melting temperature is 150-165 ℃, the temperature rising rate is 2-5 ℃/min, the heat preservation time is 4-12 hours, and the graphite-like structure Fe is obtained3C/C @ S composite cathode material.
The invention has the beneficial effects that:
(1) fe prepared by the invention3The C/C @ S composite positive electrode material has the microscopic morphology of a graphene-like structure, has a high specific surface area and a developed pore structure, is thin in carbon wall and good in conductivity, and simultaneously has a graphene-like curled carbon layer structure to play a physical adsorption role on polysulfide so as to form Fe3The C particles have a chemical adsorption effect on polysulfide, can adsorb polar polysulfide from two aspects of physics and chemical adsorption, effectively inhibit the dissolution of polysulfide, and greatly improve the cycle stability of the lithium-sulfur battery.
(2) The invention utilizes a one-step method to prepare biochar with a graphene-like structure and doped with cementite nanoparticles, wherein potassium ferrate reacts with water to generate KOH and Fe (OH)3The method has the advantages that KOH serving as a pore-forming agent can generate porous carbon with high porosity, iron sources are provided to generate cementite nanoparticles on the surface of the carbon material in situ, raw materials are selected ingeniously to generate a graphene-like structure, the used raw materials and medicines are low in price, the production cost of the lithium-sulfur battery is greatly reduced, and the industrial production is met.
Drawings
Fig. 1 is a Scanning Electron Microscope (SEM) image of biochar with a graphene-like structure prepared in example 1 of the present invention, and it can be seen that the prepared biochar has a curled graphene-like structure and is uniformly distributed;
FIG. 2 is a Scanning Electron Microscope (SEM) image of a bulk structure of the biochar material prepared in comparative example 2 of the present invention, wherein the bulk biochar is not favorable for lithium ion diffusion because the carbon layer has too large thickness;
FIG. 3 shows Fe with a graphene-like structure prepared in example 1 of the present invention3A Scanning Electron Microscope (SEM) picture of C/C; it can be seen from the figure that Fe is generated in situ on the graphene-like nano sheet3C nano-particles are uniformly distributed, while the surface of the carbon in the figure 1 is relatively smooth, which is in sharp contrast to the morphology after doping, and Fe3C/C well keeps the structure of graphene-like curling;
FIG. 4 shows Fe with a graphene-like structure prepared in example 1 of the present invention3X-ray diffraction (XRD) pattern of C/C composite material, from which Fe is demonstrated3C, successfully doping the biochar;
FIG. 5 shows Fe with a graphene-like structure prepared in example 1 of the present invention3The pore size distribution diagram of the C/C composite material;
FIG. 6 shows Fe with a graphene-like structure prepared in example 1 of the present invention3And a thermogravimetric analysis (TG) diagram of the C/C @ S composite cathode material shows that sulfur is well fused with the composite material.
FIG. 7 shows Fe with a graphene-like structure prepared in example 1 of the present invention3And (3) a cycle performance diagram at 0.5 ℃ after the battery is assembled by the C/C @ S composite positive electrode material.
Detailed description of the preferred embodiments
The invention is further illustrated by the following figures and examples. The following examples are intended to further illustrate the invention, but not to limit it.
Example 1
1) Selecting hibiscus flower petals as a carbon source, soaking in deionized water for 12h, ultrasonically cleaning for 1h, and drying in a vacuum drying oven at 80 ℃ for 12 h; grinding the obtained petals, putting the petals into a tubular furnace filled with inert gas, heating to 400 ℃ at a heating rate of 5 ℃/min, then carrying out carbonization heat preservation for 2 hours at the temperature, naturally cooling the furnace temperature to room temperature to obtain the biochar with a graphene-like structure, and grinding the biochar into powder;
2) according to the mass ratio of 1: 225 respectively weighing the obtained biochar, potassium ferrate and deionized water, uniformly mixing, magnetically stirring for 8 hours, and then placing the mixed solution in a forced air drying oven at 80 ℃ for drying for 12 hours; putting the dried substance into a tubular furnace filled with inert gas, heating the tubular furnace to 800 ℃ at the heating rate of 10 ℃/min, then carrying out carbonization heat preservation for 2 hours at the temperature, cooling the carbonization furnace to room temperature, washing with water, pickling with dilute hydrochloric acid, and drying to obtain the Fe with the graphene-like structure3A C/C composite material;
3) mixing sublimed sulfur with Fe3Mixing and grinding the C/C composite material according to the mass ratio of 6: 1, putting the mixture into a reaction kettle, vacuumizing the reaction kettle, transferring the reaction kettle into a muffle furnace, keeping the temperature for 6 hours at the melting temperature of 155 ℃, the heating rate of 3 ℃/min and the temperature of the muffle furnace to obtain Fe3A C/C @ S composite;
4) mixing the prepared composite material with Super-P and polyvinylidene fluoride (PVDF) according to the mass ratio of 7: 2: 1, preparing slurry by taking N-methylpyrrolidone (NMP) as a solvent, carrying out blade coating on an aluminum foil, putting the coated pole piece into a vacuum drying oven for drying for 12 hours, and punching the pole piece by using a punching machine. Assembling in a glove box filled with argon, taking the cut pole piece as a positive electrode, a lithium piece as a negative electrode, a Celgard2500 polypropylene film as a diaphragm, and 1M LiTFSI/DOL DMC (1:1) + 2% LiNO3And assembling a 2016 type button cell by using the electrolyte. Standing for 12 hours after the button cell is assembled, and carrying out subsequent electrochemical test;
5) the assembled battery was subjected to a cyclic charge and discharge test at a current density of 0.5C, with a charge and discharge interval as a cyclic graph as shown in fig. 7: the first discharge specific capacity is 1099mAh/g, after 200 times of circulation, the discharge specific capacity is 741mAh/g, and the single-turn capacity attenuation rate is 0.017 percent.
Comparative example 1
1) Selecting hibiscus flower petals as a carbon source, soaking in deionized water for 12h, ultrasonically cleaning for 1h, and drying in a vacuum drying oven at 80 ℃ for 12 h; grinding the obtained petals, putting the petals into a tubular furnace filled with inert gas, heating to 400 ℃ at a heating rate of 5 ℃/min, then carrying out carbonization heat preservation for 2 hours at the temperature, naturally cooling the furnace temperature to room temperature to obtain the biochar with a graphene-like structure, and grinding the biochar into powder;
2) respectively weighing the biochar, the potassium hydroxide and the deionized water according to the mass ratio of 1: 3: 25, uniformly mixing, magnetically stirring for 8 hours, and then placing the mixed solution in a forced air drying oven at 80 ℃ for drying for 12 hours; putting the dried substance into a tubular furnace filled with inert gas, heating the tubular furnace to 800 ℃ at the heating rate of 10 ℃/min, then carrying out carbonization heat preservation for 3 hours at the temperature, cooling the carbonization furnace to room temperature, washing with water, pickling with dilute hydrochloric acid, and drying to obtain the carbon material with the graphite-like structure;
3) mixing and grinding sublimed sulfur and the carbon material according to the mass ratio of 6: 1, putting the mixture into a reaction kettle, vacuumizing the reaction kettle, transferring the reaction kettle into a muffle furnace, and keeping the temperature for 6 hours at the melting temperature of 155 ℃, the heating rate of 3 ℃/min to obtain the C @ S composite material;
4) the C @ S composite material is assembled into a battery according to the same process as the embodiment 1, the assembled battery is subjected to a cyclic charge and discharge test at a current density of 0.5C, the discharge specific capacity after stabilization is 695mAh/g, the discharge specific capacity after 200 cycles is 302mAh/g, and the single-turn capacity attenuation rate is 0.28%.
Comparative example 2
1) Selecting rape flower petals as a carbon source, soaking the rape flower petals in deionized water for 24 hours, carrying out ultrasonic cleaning for 2 hours, and drying the cleaned rape flower petals in a vacuum drying oven at 80 ℃ for 12 hours; grinding the obtained rape flower petals, putting the grinded rape flower petals into a tubular furnace filled with inert gas, heating to 450 ℃ at the heating rate of 5 ℃/min, then carrying out carbonization and heat preservation for 2 hours at the temperature, naturally cooling the furnace temperature to room temperature to obtain biochar with a blocky structure, and grinding the biochar into powder;
2) respectively weighing the biochar, the potassium ferrate and the deionized water according to the mass ratio of 1: 2: 25, uniformly mixing, magnetically stirring for 8 hours, and then drying the mixed solution in a forced air drying oven at 80 ℃ for 12 hours; putting the dried substance into a tubular furnace filled with inert gas, heating the tubular furnace to 800 ℃ at the heating rate of 10 ℃/min, then carrying out carbonization heat preservation for 2 hours at the temperature, cooling the carbonization furnace to room temperature, washing with water, washing with dilute hydrochloric acid, and drying to obtain the productBulk structure of Fe3A C/C composite material;
3) mixing and grinding sublimed sulfur and the composite material according to the mass ratio of 6: 1, putting the mixture into a reaction kettle, vacuumizing the reaction kettle, transferring the reaction kettle into a muffle furnace, keeping the temperature for 6 hours at the melting temperature of 155 ℃, the heating rate of 3 ℃/min, and obtaining Fe3A C/C @ S composite;
4) mixing Fe3The C/C @ S composite material is assembled into a battery according to the same process as the embodiment 1, the assembled battery is subjected to a cyclic charge and discharge test at a current density of 0.5C, the discharge specific capacity is 747mAh/g after the battery is stabilized, the discharge specific capacity is 366mAh/g after 200 cycles, and the single-turn capacity attenuation rate is 0.25%.
Comparative example 3
1) Selecting rape flower petals as a carbon source, soaking the rape flower petals in deionized water for 24 hours, carrying out ultrasonic cleaning for 2 hours, and drying the cleaned rape flower petals in a vacuum drying oven at 80 ℃ for 12 hours; grinding the obtained rape flower petals, putting the grinded rape flower petals into a tubular furnace filled with inert gas, heating to 450 ℃ at the heating rate of 5 ℃/min, then carrying out carbonization and heat preservation for 2 hours at the temperature, naturally cooling the furnace temperature to room temperature to obtain biochar with a blocky structure, and grinding the biochar into powder;
2) respectively weighing the biochar, the potassium hydroxide and the deionized water according to the mass ratio of 1: 3: 25, uniformly mixing, magnetically stirring for 8 hours, and then placing the mixed solution in a forced air drying oven at 80 ℃ for drying for 12 hours; putting the dried substance into a tubular furnace filled with inert gas, heating the tubular furnace to 800 ℃ at the heating rate of 10 ℃/min, then carrying out carbonization heat preservation for 2 hours at the temperature, cooling the carbonization furnace to room temperature, washing with water, pickling with dilute hydrochloric acid, and drying to obtain the porous carbon composite material with the blocky structure;
3) mixing and grinding sublimed sulfur and the composite material according to the mass ratio of 6: 1, putting the mixture into a reaction kettle, vacuumizing the reaction kettle, transferring the reaction kettle into a muffle furnace, and keeping the temperature for 6 hours at the melting temperature of 155 ℃, the heating rate of 3 ℃/min to obtain a C @ S composite material;
4) the C @ S composite material is assembled into a battery according to the same process as the embodiment 1, the assembled battery is subjected to a cyclic charge and discharge test at a current density of 0.5C, the discharge specific capacity after the battery is stabilized is 527mAh/g, the discharge specific capacity after 200 cycles is 138mAh/g, and the single-turn capacity attenuation rate is 0.37%.
Claims (9)
1. A preparation method of a graphene-loaded cementite particle composite positive electrode material for a lithium-sulfur battery is characterized by comprising the following steps of:
1) under inert atmosphere, pre-carbonizing by taking hibiscus flower petals as a carbon source to obtain biochar;
2) uniformly dispersing the biochar prepared in the step 1) and potassium ferrate in water, stirring, drying, and calcining in an inert atmosphere to obtain Fe with a graphene-like structure3A C/C composite material;
3) fe prepared in the step 2)3Mixing and grinding the C/C composite material and sublimed sulfur, and preparing Fe with a graphene-like structure by adopting a melting diffusion method under vacuum3C/C @ S composite positive electrode material;
fe of the graphene-like structure3The C/C @ S composite positive electrode material is prepared from Fe with a graphene-like structure3C/C and elemental sulfur, wherein the elemental sulfur is dispersed in Fe3C/C in the pores.
2. The method of claim 1, wherein: fe of the graphene-like structure3In C/C, Fe3The content of C is 10-30 wt%.
3. The method of claim 1, wherein: fe of the graphene-like structure3The total specific surface area of C/C is 1400m2/g～2800 m2/g。
4. The production method according to any one of claims 1 to 3, characterized in that: the sulfur content of the composite positive electrode material is 70-85 wt%.
5. The method of claim 1, wherein: soaking the hibiscus flower petals obtained in the step 1) in deionized water for 12-24 hours, ultrasonically cleaning for 1-2 hours, and drying in a vacuum drying oven at 80 ℃ for 12 hours.
6. The method of claim 1, wherein: the pre-carbonization temperature in the step 1) is 300-450 ℃, the heating rate is 2-10 ℃/min, and the pre-carbonization time is 2-3 h.
7. The method of claim 1, wherein: and 2) in the step 2), the mass ratio of the biochar to the potassium ferrate is 1: 1-1: 3, the biochar is stirred for 4-8 hours, and the biochar is dried in a forced air drying oven at the temperature of 80 ℃ for 12 hours.
8. The method of claim 1, wherein: step 2), calcining at 760-800 ℃, heating at a rate of 8-15 ℃/min for 2-3 h; fe3The C/C composite material is washed by water and acid for standby, and the acid washing solution adopts dilute hydrochloric acid or acetic acid.
9. The method of claim 1, wherein: the specific process of the melting diffusion method in the step 3) is as follows: mixing Fe3C/C and sublimed sulfur are mixed and ground according to the mass ratio of 1: 6-3: 7, then the mixture is placed into a reaction kettle and vacuumized, the reaction kettle is transferred into a muffle furnace, the melting temperature is 150-165 ℃, the temperature rising rate is 2-5 ℃/min, the heat preservation time is 4-12 hours, and the Fe similar to the graphene structure is obtained3C/C @ S composite cathode material.
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