CN114335540B - Lithium-philic carbon skeleton composite material and preparation method and application thereof - Google Patents
Lithium-philic carbon skeleton composite material and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to a lithium-philic carbon skeleton composite material, which comprises a three-dimensional network structure, wherein the three-dimensional network structure layer contains a lithium-philic material; the lithium-philic material is distributed in the through holes of the three-dimensional network structure; the three-dimensional network structure layer is a carbon skeleton formed by graphitizing fibrous carbon nano materials. The lithium-philic carbon skeleton composite material can reduce nucleation overpotential, optimize lithium deposition sites, attract lithium metal deposition in a three-dimensional structure network, avoid volume expansion of metal lithium and generation of lithium dendrites in a circulation process, isolate contact of electrolyte and lithium metal, reduce occurrence of side reactions, and optimize circulation performance of the material.
Description
Technical Field
The invention relates to the technical field of batteries, in particular to a lithium-philic carbon skeleton composite material and a preparation method and application thereof.
Background
The lithium battery is a novel high-efficiency clean green energy source due to the characteristics of high energy density and long service life. However, lithium metal negative electrodes can exhibit "lithium dendrites" during charging, which can affect the electrical performance of the battery. The prior art shows that the skeleton with a certain mesoporous structure can inhibit the growth of lithium dendrites and the change of volume, and then the lithium metal is loaded through the deposition of the lithium metal and is used for lithium batteries.
However, the poor wettability between the carbon nanotubes and the lithium metal, and the absence of the lithium-philic material supported inside the microsphere, can result in the lithium metal being directly deposited on the surface of the carbon microsphere and between the particles without being attracted to the pores inside the particles. This deposition causes a large volume expansion and lithium dendrite formation, and the direct contact between the lithium metal and the electrolyte causes more side reactions to occur, resulting in consumption of active lithium metal and a large reduction in the cycle life of the final battery.
Generally, lithium metal is deposited on the surface of the particles or between particles. Carbon materials are easy to prepare structures with large specific surface areas and multiple pores, but the carbon materials are generally lithium-phobic and cannot effectively attract lithium metal, and meanwhile, under the condition that the pore structures are few, sufficient space cannot be provided for deposition of the lithium metal.
Disclosure of Invention
The application provides a lithium-philic carbon skeleton composite material aiming at the defects of the prior art, which is a three-dimensional network structure obtained by graphitizing a fibrous carbon nano material, the inside of the composite material contains a lithium-philic material, the nucleation overpotential is reduced, the lithium deposition site is optimized, the lithium metal is attracted to be deposited in the three-dimensional structure network, the volume expansion of the metal lithium and the generation of lithium dendrites in the circulation process are avoided, the contact of electrolyte and the lithium metal is isolated, the occurrence of side reactions is reduced, and the circulation performance of the material is optimized.
According to one aspect of the present application, there is provided a lithium-philic carbon skeleton composite material comprising a three-dimensional network structure containing a lithium-philic material therein; the lithium-philic material is distributed in the through holes of the three-dimensional network structure; the three-dimensional network structure is a carbon skeleton formed by graphitizing fibrous carbon nano materials.
The common pyrolytic carbon porous material has low graphitization degree and unstable structure, and the particles are easy to break when rolling or depositing too much lithium metal, and simultaneously contain closed isolated pores, so that the common pyrolytic carbon porous material cannot provide enough pores for depositing a large amount of lithium metal. And in the carbon skeleton that is woven by the fibrous carbon nanomaterial that draw ratio (fibrous carbon nanomaterial's length and diameter's ratio) is great and is prepared, can carry out certain degree between the carbon nanofiber and slide, not totally fixed, consequently, when because lithium metal deposit or melting get into carbon skeleton, can be because fibrous carbon nanomaterial's slip and the better inflation that holds the volume for holistic structure is more stable, also is safer when follow-up battery is used.
Optionally, the length-to-diameter ratio is in a range of: 5:1 to 200.
Alternatively, the aspect ratio can range from 5:1, 6:1, 7:1, 8:1, 9:1, 10, 1, 20.
The length-diameter ratio is lower than 5:1, and the braided structure cannot be formed, so that the structure is unstable and easy to break; too large an aspect ratio can result in insufficient porosity in the sprayed material.
Optionally, the fibrous carbon nanomaterial is selected from at least one of vapor grown carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube.
Optionally, the fibrous carbon nanomaterial is vapor grown carbon fiber.
Optionally, the lithium-philic material comprises at least one of gold, silver, zinc, silicon, phosphorus, titanium, and their corresponding oxides or salts.
Optionally, the lithium-philic material comprises gold, a salt comprising an element of gold, silver, a salt comprising an element of silver, zinc, an oxide of zinc, a salt comprising an element of zinc, silicon, an oxide of silicon, phosphorus, tiO 2 And the like.
Optionally, the zinc oxide is ZnO; the oxide of silicon is silicon dioxide; the phosphorus is red phosphorus and/or black phosphorus.
Optionally, the lithium-philic material comprises at least one of gold, silver, zinc, silicon, phosphorus, titanium.
Optionally, the degree of graphitization of the carbon skeleton is 50% to 100%.
When the graphitization degree is not less than 50%, the carbon skeleton has higher stability, better toughness and difficult structure fracture, and can better accommodate the expansion caused by lithium metal deposition.
Optionally, the carbon skeleton has a specific surface area of 1 to 200m 2 /g。
The specific surface area of the material is large, the first coulombic efficiency is low, but the material with the large specific surface area is not easy to grow lithium dendrites. The specific surface area of the material is small, so that the material has higher first effect, and can isolate the electrolyte from permeating into the material to react with lithium metal. Therefore, the specific surface area of the lithium-philic carbon skeleton composite material before coating is large, and after coating, the specific surface area is reduced due to the existence of a compact coating layer.
Optionally, the tap density of the carbon skeleton is 0.2 to 0.8g/cm 3 。
Low tap density (0.2-0.8 g/cm) 3 ) The porosity of the material is higher, and when the porosity of the material is higher, the material is indicated to have more pores, and more pores can accommodate more lithium metal deposition.
Optionally, the three-dimensional network structure layer further comprises a conductive agent.
Optionally, the conductive agent comprises at least one of carbon nanotubes, graphene, carbon black, ketjen black, acetylene black, conductive graphite, metal fibers.
The conductive agent is added, particularly the material with more excellent conductivity is added, and the conductive agent is added to further increase the conductivity and the contact with the lithium-philic material on the basis of the prior art, increase the conductivity in the material and optimize the cycle performance of the material; and the conductive agent can increase the internal surface area of the three-dimensional network structure, thereby providing more space for the deposition of lithium metal and avoiding the nucleation of the lithium metal.
Optionally, the ratio of the conductive agent in the sum of the mass of the carbon skeleton and the mass of the lithium-philic material is A; the value range of A is as follows: 5363 and 0<A is less than or equal to 50 percent.
Optionally, the mass ratio of the carbon skeleton to the lithium-philic material is: 20-90 parts by weight.
Optionally, the lithium-philic carbon skeleton composite further comprises a coating layer.
Optionally, the coating layer encapsulates the three-dimensional network structure.
Optionally, the thickness of the coating layer is 5 to 20nm.
The compact external coating layer can reduce the specific surface area greatly increased by constructing a three-dimensional structure network, isolate the contact of electrolyte and lithium metal, reduce the occurrence of side reactions and optimize the cycle performance of the material. If the coating layer is too thin and is less than 5nm, the coating layer is not compact enough, so that the permeation of electrolyte can not be effectively isolated, and the occurrence of side reactions can be reduced; if the coating layer is too thick and is more than 20nm, the steric hindrance between the lithium-philic substance and the lithium ions is increased, the lithium ion conduction path is increased, the rapid conduction of the lithium ions is isolated, and the electrical property of the material is reduced.
According to another aspect of the present application, there is provided a method of preparing a lithium-philic carbon skeleton composite as described above.
Optionally, the preparation method comprises:
(1) Drying a mixed material containing a carbon skeleton and a lithium-philic material to obtain a carbon microsphere material;
(2) And sintering the carbon microsphere material for the first time to obtain the lithium-philic carbon skeleton composite material.
Alternatively, in step (1), a mixed material containing a carbon skeleton and a lithium-philic material is added to a solvent to form a slurry.
Optionally, the slurry has a solid content of 1% to 20%.
Optionally, the drying is spray drying.
Optionally, in the spray drying, the flow rate is 300-1500 mL/h, the temperature is 120-220 ℃, and the pressure is 0.2-0.4 Mpa.
Optionally, the primary sintering is a staged temperature rise, and is divided into a primary sintering first stage and a primary sintering second stage.
Optionally, the temperature is increased to the temperature of the first stage of the primary sintering or the second stage of the primary sintering at a certain temperature increasing rate.
Optionally, the temperature of the first stage of the primary sintering is 200-400 ℃, and the time is 1-3 h.
Optionally, the rate of heating to the first stage temperature is 4-7 ℃/min.
Optionally, the temperature of the second stage of the primary sintering is 500-900 ℃, and the time is 2-3 h.
Optionally, the rate of heating to the second stage temperature is 1-3 ℃/min.
Optionally, the primary sintering is: sintering conditions are as follows: raising the temperature from room temperature to 300 ℃ at the speed of 5 ℃/min, preserving the heat for 2 hours, raising the temperature to 500-800 ℃ at the speed of 2 ℃/min, and preserving the heat for 2-3 hours.
Optionally, the preparation method further comprises step (3): and coating and sintering the substance subjected to primary sintering for the second time to obtain the lithium-philic carbon skeleton composite material.
Optionally, the secondary sintering is a staged temperature rise, and is divided into a primary sintering first stage and a secondary sintering second stage.
Optionally, the temperature of the first stage of the secondary sintering is 200-400 ℃ and the time is 1-3 h.
Optionally, the temperature of the second stage of the secondary sintering is 500-900 ℃, and the time is 2-3 h.
Optionally, the rate of heating to the first stage temperature of the secondary sintering is 4-7 ℃/min.
Optionally, the rate of heating to the second stage temperature of the secondary sintering is 1-3 ℃/min.
Optionally, the second sintering is: raising the temperature from room temperature to 300 ℃ at the speed of 5 ℃/min, preserving the heat for 2 hours, raising the temperature to 500-900 ℃ at the speed of 2 ℃/min, and preserving the heat for 2-3 hours.
The sintering temperature of the zinc-containing material can not exceed 800 ℃, otherwise zinc can sublimate and escape; the sintering temperature of red phosphorus and black phosphorus is not more than 600 ℃.
Optionally, the coated three-dimensional network has an increase of 10 to 30% relative to the uncoated three-dimensional network.
Optionally, the coated three-dimensional network has an increase of 5 to 20% relative to the uncoated three-dimensional network.
Alternatively, the precursor material may be used to melt lithium prior to coating, after which lithium metal cannot be melted into due to the denser coating layer.
Optionally, in step (3), the coating is in situ coating; the coating time is 12-30 h.
Optionally, the coating material is at least one of polymeric phenolic resin, polydopamine, polypyrrole, tannic acid, polyvinylpyrrolidone and glucose.
Optionally, step (3) comprises: dissolving a coating material in the solution to obtain a solution containing the coating material; and mixing the precursor material with a solution containing a coating material, and coating in situ.
Optionally, step (3) further comprises suction filtration, washing and drying.
Optionally, the drying temperature is 60-100 ℃.
According to yet another aspect of the present application, there is provided a carbon-lithium composite material including a lithium-philic carbon skeleton composite material and lithium metal positioned in a three-dimensional through-hole structure of the lithium-philic carbon skeleton composite material; the lithium-philic carbon skeleton composite material comprises at least one of the lithium-philic carbon skeleton composite materials described in any one of the above.
Alternatively, instead of having isolated pores in the pyrolytic carbon that are not interconnected with other pores, the through-holes are structures in which all the pores inside the lithium-philic carbon skeleton are interconnected.
Optionally, the preparation method of the carbon lithium composite material comprises the following steps: electrochemical recombination and/or melt recombination.
Alternatively, the electrochemical recombination method comprises:
1) Mixing the lithium-philic carbon skeleton composite material with a conductive agent, a binder and water to form slurry;
2) Coating the slurry on a current collector to obtain an electrode plate;
3) And depositing lithium metal on the electrode sheet to obtain the lithium battery cathode.
Alternatively, the electrochemical recombination method comprises: mixing the lithium-philic carbon skeleton composite material, the binder and the conductive agent to prepare slurry, coating the slurry on a current collector, drying to prepare a pole piece, electrifying by taking metal lithium as a counter electrode to deposit lithium metal, and obtaining the carbon-lithium composite material.
Alternatively, the content of lithium metal introduced into the lithium-philic carbon skeleton can be controlled by controlling the current and time.
Alternatively, the melting compounding method is to heat the lithium-philic carbon skeleton composite material and the metal lithium to a temperature above the melting point of lithium, continuously stir, and melt the liquid metal lithium into the lithium-philic carbon skeleton to obtain the carbon lithium composite material.
Optionally, the mass content of the lithium metal in the carbon-lithium composite material is 1-80%.
Optionally, the lithium metal is present in the carbon-lithium composite material in an amount of 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any of two values by mass.
Because the three-dimensional network structure in the application is obtained by graphitizing the carbon fiber material, and the material does not contain pyrolytic carbon, the carbon nanofiber can slide to a certain extent and is not completely fixed, the expansion of lithium metal can be better accommodated, meanwhile, the porosity of the material is high, the gaps are rich, more lithium metal can be accommodated, and the mass content of the lithium metal in the carbon-lithium composite material can reach 80%.
Meanwhile, the lithium-philic carbon skeleton composite material optimizes lithium metal deposition sites, so that lithium metal is deposited in through holes of particles in the coating layer, and lithium dendrites are not easy to grow to pierce the membrane, short circuit is caused, and safety accidents such as fire explosion and the like are finally caused; and can better accommodate the expansion of lithium metal. Therefore, the safety is good in the circulating process.
According to yet another aspect of the present application, a lithium battery negative electrode is provided.
Optionally, the lithium battery negative electrode includes at least one of the carbon lithium composite materials described in any of the above.
The invention has the following main beneficial effects:
(1) The application provides a lithium-philic carbon skeleton composite material aiming at the defects of the prior art, a three-dimensional network structure obtained by graphitizing a carbon fiber material contains a lithium-philic material inside, and the lithium-philic material can form an alloy with metallic lithium, so that the nucleation overpotential is reduced, the lithium deposition sites are optimized, and lithium metal is attracted to be deposited in the three-dimensional structure network; the three-dimensional network structure has huge internal space, can provide space for the deposition of lithium metal, avoids the volume expansion of metal lithium and the generation of lithium dendrites in the circulation process, and simultaneously can reduce the local current density and alleviate the huge volume change during the circulation process due to the large internal specific surface area and the porous framework. The lithium-philic carbon skeleton composite material can also comprise a coating layer, and the external compact coating layer can reduce the external specific surface area greatly increased by constructing a three-dimensional structure network, isolate the contact between electrolyte and lithium metal, reduce the occurrence of side reactions and optimize the cycle performance of the material.
(2) The lithium-philic carbon skeleton composite material is prepared by methods of spray drying, in-situ coating and the like, and the lithium-philic material and the carbon skeleton are more fully mixed by slurry mixing and spray drying; then sintering is carried out, so that the specific surface area of the carbon skeleton can be increased; the thickness of the coating layer can be controlled by in-situ coating, excessive coating is avoided, secondary sintering is carried out, and the influence of impurities on the material is greatly reduced. Simple process, controllable conditions and easy amplification production of materials.
Drawings
Fig. 1 is a schematic view of a lithium-philic carbon skeleton composite material prepared in example 2 of the present application.
Fig. 2 is a schematic view of a lithium-philic carbon skeleton composite material prepared in example 1 of the present application.
Fig. 3 is a schematic view of a lithium-philic carbon skeleton composite material prepared in example 3 of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The reagents, materials and procedures used herein are those widely used in the corresponding fields and are generally available on the market.
Vapor Grown Carbon Fiber (VGCF)
Example 1
Mixing 125g of VGCF, 125g of ZnO and 2250g of deionized water, stirring and ultrasonically treating until the mixture is uniformly dispersed, transferring the slurry with the total solid content of 10% into a sand mill, and grinding and dispersing the slurry; spray drying at flow rate of 1000mL/h, temperature of 160 deg.C and pressure of 0.4Mpa to obtain the carbon microsphere material.
Sintering the obtained carbon microspheres, wherein the sintering conditions are as follows: heating from room temperature to 300 ℃ at a speed of 5 ℃/min, preserving heat for 2h, heating from 2 ℃/min to 800 ℃, preserving heat for 3h, and finally cooling to room temperature to obtain the precursor material.
Then, performing in-situ liquid phase coating on the precursor material, dissolving 2.6g of tris (hydroxymethyl aminomethane) in 1000ml of deionized water, then adding 100g of the precursor material into the solution, after uniformly dispersing by magnetic stirring, adding 10g of dopamine hydrochloride into the mixed solution for coating, wherein the coating time is 24h, and the coating amount is 10% (the increment of the coated three-dimensional network structure is 10% relative to the uncoated three-dimensional network structure); finally, carrying out suction filtration, washing and drying (at 80 ℃); sintering the dried material, wherein the sintering conditions are as follows: heating from room temperature to 300 ℃ at a speed of 5 ℃/min, preserving heat for 2 hours, heating from 2 ℃/min to 700 ℃, preserving heat for 3 hours, and finally cooling to room temperature to obtain the lithium-philic carbon skeleton composite material with the coating layer with the thickness of 10 nm.
In the resulting lithium-philic carbon skeleton composite: the specific surface area is 104m 2 (ii)/g; the tap density is 0.4g/cm 3 。
The structure of the obtained lithium-philic carbon skeleton composite material is shown in figure 1, and has a two-layer structure, wherein the coating layer is the outermost side and coats a three-dimensional network structure, and the lithium-philic material is positioned in through holes in the three-dimensional network structure;
example 2
Mixing 125g of VGCF, 125g of ZnO and 2250g of deionized water, stirring and ultrasonically treating until the mixture is uniformly dispersed, transferring the slurry with the total solid content of 10% into a sand mill, and grinding and dispersing the slurry; spray drying at flow rate of 1000mL/h, temperature of 160 deg.C and pressure of 0.4Mpa to obtain the carbon microsphere material.
Sintering the obtained carbon microspheres, wherein the sintering conditions are as follows: heating from room temperature to 300 ℃ at a speed of 5 ℃/min, preserving heat for 2h, heating from 2 ℃/min to 800 ℃, preserving heat for 3h, and finally cooling to room temperature to obtain the lithium-philic carbon skeleton composite material.
In the obtained lithium-philic carbon skeleton composite material, the specific surface area was 167m 2 (ii)/g; the tap density is 0.3g/cm 3 . As shown in fig. 2, the lithium-philic carbon skeleton composite material was obtained without a coating layer and was only a spherical structure containing a lithium-philic material inside.
Example 3
75g of VGCF, 50g of conductive graphene, 100g of nano Ag powder, 25g of ZnO and 2250g of deionized water are mixed, stirred and subjected to ultrasonic treatment until the mixture is uniformly dispersed, and the slurry with the total solid content of 10% is transferred to a sand mill, and the other steps are the same as those in example 1.
The obtained lithium-philic carbon skeleton composite material structure is shown in figure 3 and has a two-layer structure, the coating layer is the outermost side and coats the three-dimensional network structure, the lithium-philic material is positioned in through holes in the three-dimensional network structure, and the conductive agent can increase the inner surface area of the three-dimensional network structure, so that more space is provided for deposition of lithium metal. In the resulting lithium-philic carbon skeleton composite: specific surface area of 52m 2 (ii)/g; the tap density is 0.3g/cm 3 。
Example 4
Mixing 75g of VGCF, 50g of CNTs, 125g of ZnO and 2250g of deionized water, stirring and ultrasonically treating until the mixture is uniformly dispersed, transferring the slurry with the total solid content of 10% into a sand mill, and grinding to break and disperse; spray drying at flow rate of 1000mL/h, temperature of 160 deg.C and pressure of 0.4Mpa to obtain the carbon microsphere material.
Sintering the obtained carbon microspheres, wherein the sintering conditions are as follows: heating from room temperature to 300 ℃ at a speed of 5 ℃/min, preserving heat for 2h, heating from 2 ℃/min to 800 ℃, preserving heat for 3h, and finally cooling to room temperature to obtain the lithium-philic carbon skeleton composite material.
In the obtained lithium-philic carbon skeleton composite material, the specific surface area is 150m 2 (ii)/g; the tap density is 0.3g/cm 3 。
Example 5
Mixing 90g of VGCF, 50g of conductive agent Keqin black, 10g of nano Ag powder and 2350g of deionized water, stirring or ultrasonically treating until the mixture is uniformly dispersed, transferring the slurry with the total solid content of 6% into a sand mill, and grinding to break and disperse; spray drying at flow rate of 1000mL/h, temperature of 160 deg.C and pressure of 0.4Mpa to obtain the carbon microsphere material.
Sintering the obtained carbon microspheres, wherein the sintering conditions are as follows: heating from room temperature to 200 ℃ at the speed of 7 ℃/min, preserving heat for 3h, heating from 3 ℃/min to 900 ℃, preserving heat for 2h, and finally cooling to room temperature to obtain the precursor material.
Then carrying out polypyrrole in-situ liquid phase coating on the precursor material, wherein the coating time is 15h, and the coating amount is 20% (the increment of the coated three-dimensional network structure relative to the uncoated three-dimensional network structure is 20%); finally, carrying out suction filtration, washing and drying (at 80 ℃); sintering the dried material, wherein the sintering conditions are as follows: and heating to 300 ℃ from room temperature at a speed of 6 ℃/min, preserving heat for 3 hours, heating to 900 ℃ at a speed of 3 ℃/min, preserving heat for 2 hours, and finally cooling to room temperature to obtain the lithium-philic carbon skeleton composite material with the coating layer thickness of 18 nm.
In the obtained lithium-philic carbon skeleton composite material: the specific surface area is 75m 2 (iv) g; the tap density is 0.6g/cm 3 。
Example 6
Mixing 400gVGCF,25gCNTs, 25g of red phosphorus and 2050g of deionized water, stirring or ultrasonically treating until the mixture is uniformly dispersed, transferring the slurry with the total solid content of 18% into a sand mill, and grinding the slurry to break and disperse; spray drying at flow rate of 1000mL/h, temperature of 160 deg.C and pressure of 0.4Mpa to obtain the carbon microsphere material.
Sintering the obtained carbon microspheres, wherein the sintering conditions are as follows: heating from room temperature to 400 ℃ at a speed of 4 ℃/min, preserving heat for 1.5h, heating from 1 ℃/min to 500 ℃, preserving heat for 2.5h, and finally cooling to room temperature to obtain the precursor material.
Next, performing tannic acid in-situ liquid phase coating on the precursor material, wherein the coating time is 18h, and the coating amount is 5% (the increment of the coated three-dimensional network structure relative to the uncoated three-dimensional network structure is 5%); finally, carrying out suction filtration, washing and drying (at 80 ℃); sintering the dried material, wherein the sintering conditions are as follows: heating from room temperature to 400 ℃ at a speed of 4 ℃/min, preserving heat for 1.5 hours, heating from 2 ℃/min to 600 ℃, preserving heat for 2.5 hours, and finally cooling to room temperature to obtain the lithium-philic carbon skeleton composite material with a coating layer of 4 nm.
In the obtained lithium-philic carbon skeleton composite material, the specific surface area is 59m 2 (ii)/g; the tap density is 0.7g/cm 3 。
Example 7
Mixing 60g of VGCF, 15g of nano Au powder and 2425g of deionized water, stirring or ultrasonically treating until the mixture is uniformly dispersed, transferring the slurry with the total solid content of 3% into a sand mill, and grinding to break and disperse; spray drying at flow rate of 1000mL/h, temperature of 160 deg.C and pressure of 0.4Mpa to obtain the carbon microsphere material.
Sintering the obtained carbon microspheres, wherein the sintering conditions are as follows: heating from room temperature to 250 ℃ at a speed of 6 ℃/min, preserving heat for 2h, heating to 700 ℃ at a speed of 2.5 ℃/min, preserving heat for 3h, and finally cooling to room temperature to obtain the precursor material.
Carrying out poly-dopamine in-situ liquid phase coating on the precursor material, wherein the coating time is 28h, and the coating amount is 10% (the increment of the coated three-dimensional network structure relative to the uncoated three-dimensional network structure is 10%); finally, carrying out suction filtration, washing and drying (at 80 ℃); sintering the dried material, wherein the sintering conditions are as follows: heating from room temperature to 350 ℃ at a speed of 5 ℃/min, preserving heat for 2.5 hours, heating from 3 ℃/min to 500 ℃, preserving heat for 3 hours, and finally cooling to room temperature to obtain the lithium-philic carbon skeleton composite material with a coating layer position of 5 nm.
In the obtained lithium-philic carbon skeleton composite material, the specific surface area was 76m 2 (ii)/g; the tap density is 0.6g/cm 3 。
Comparative example 1
The same as example 1, except that no lithium-philic material was added, i.e. the composite material was prepared without lithium-philic material, and the other steps were the same as in example.
The composite material obtained in comparative example 1 did not contain a lithium-philic substance and had insufficient internal porosity. The material in the embodiment 1 is a material containing a lithium-philic substance and is in a microspherical shape, the interior of the material is provided with more abundant pores, and meanwhile, the lithium-philic material guides the deposition of metal lithium.
Comparative example 2
The same as example 1, except that VGCF was changed to PVP-pyrolyzed amorphous carbon, that is, the degree of graphitization in the prepared composite material was 0, and the other steps were the same as in example.
The morphology of the composite material prepared by the comparative example is different from that of the lithium-philic carbon skeleton composite material prepared by the example 1, the composite material is not a fibrous carbon skeleton structure, but is a common pyrolytic carbon porous structure, wherein the porous structure contains closed pores, which easily causes the aggregation of lithium metal and the nucleation of lithium metal, and the fibrous carbon skeleton is a through-hole structure, which is convenient for the dispersion of deposited lithium metal and reduces the nucleation phenomenon. A large number of holes in the through hole structure provide space for deposition of lithium metal, and deposition of the lithium metal is facilitated; the closed, isolated pores of pyrolytic carbon are detrimental to the deposition of lithium metal.
Performance testing
1. Electrochemical performance tests are carried out on the lithium-philic carbon framework composite materials prepared in the examples and the comparative examples.
Respectively manufacturing the prepared lithium-philic carbon skeleton composite material into pole pieces, using the pole pieces as working electrodes to assemble a button cell, discharging for 10 hours at a charge cut-off voltage of 0.8V to deposit lithium metal, wherein the surface capacity is 4mAh/cm 2 First coulombic efficiency, 50-cycle retention, and swelling rate were tested. (the same procedure and parameters were used except for the lithium-philic carbon skeleton composite)
Table 1 electrical properties of batteries prepared from the lithium carbon composite materials of examples and comparative examples
As shown in table 1, the expansion ratios of examples 1 to 7 are far smaller than those of comparative example 1 and comparative example 2, which indicates that the three-dimensional network structure obtained by graphitizing the carbon fiber material in the present application has a large internal specific surface area, can provide a space for deposition of lithium metal, and the carbon nanofiber can slide to a certain extent and is not completely fixed, and can better accommodate expansion of lithium metal, so that the overall expansion ratio is reduced; the lithium-philic material is not used in the comparative example 1, so that the lithium metal is not attracted by the lithium-philic material and is deposited in the internal structure of the lithium-philic carbon skeleton when being deposited, but is directly deposited outside the carbon coating layer, so that the great volume expansion is caused, meanwhile, the lithium metal is in direct contact with the electrolyte, and in the circulation process, side reactions are continuously generated, the lithium metal is consumed, so that the very poor circulation performance is caused; comparative example 2 is a network structure of amorphous carbon formed by pyrolysis of carbon, and although a part of lithium metal deposition can be accommodated, there still exists a part of lithium metal deposition on the surface thereof, and since the inner structure thereof is not a through hole, slippage cannot be performed, and thus, volume expansion caused by lithium metal deposition cannot be well alleviated during lithium metal deposition.
TABLE 2 Properties of lithium-philic carbon skeleton composites prepared in examples and comparative examples
As shown in Table 2, examples 1-7 all had higher porosity, much greater than the data associated with comparative example 1 and comparative example 2, especially examples 2 and 4, i.e., no coating present, the porosity was as high as 87%; this indicates that the microsphere structure woven from the fibrous carbon nanomaterial with a relatively large major diameter in the present application is likely to form a high porosity structure. Comparing example 1 with comparative example 1, it can be shown that, in the lithium-philic carbon skeleton material in the present application, the internal structure of the microsphere can be supported due to the existence of the lithium-philic substance, so that the porosity of the material is further improved; the lithium-philic carbon skeleton material has a higher degree of graphitization and thus better stability than comparative example 2. The materials of the examples with and without the coating (examples 2 and 4) have large differences of specific surface areas, which shows the compactness of the coating, isolates the penetration of the electrolyte and prevents the contact between the lithium metal and the electrolyte, and the existence of the coating can form an external compact and internal porous structure and excellently accommodate the expansion caused by the deposition of the lithium metal; finally, a large amount of lithium-philic substances exist, the deposition sites of lithium metal are optimized, the deposition of the lithium metal is guided, and the three substances act together, so that the excellent cycle performance of the material is realized.
In the lithium-philic carbon skeleton material, the excellent carbon fiber three-dimensional skeleton network structure has better conductivity and stability, and provides a space for deposition of lithium metal; the existence of the lithium-philic substance can support more pore structures of the three-dimensional framework material; meanwhile, a larger amount of lithium-philic substances can better guide the deposition of lithium metal; the material with higher porosity has more pore volume, can accommodate more lithium metal for deposition, and has smaller expansion and better cycle performance; without a coating layer, lithium metal is in direct contact with electrolyte, and side reactions are more, so that the first effect and the cycle performance are poor; an excessively thick coating layer impairs the lithium affinity of the lithium-philic substance due to steric hindrance, and even if the internal pores are abundant, no better cycle performance can be achieved.
Finally, it should be noted that: the above-mentioned embodiments are only used for illustrating the technical solution of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (14)
1. A lithium-philic carbon skeleton composite material comprises a three-dimensional network structure and is characterized in that,
the three-dimensional network structure contains a lithium-philic material; the lithium-philic material is distributed in the through holes of the three-dimensional network structure;
the three-dimensional network structure is formed by the length-diameter ratio: 5, 1 to 200, and 1, namely a carbon skeleton formed by graphitizing the fibrous carbon nano material; the graphitization degree of the carbon framework is 50% -100%.
2. The lithium-philic carbon skeleton composite material according to claim 1,
the specific surface area of the carbon skeleton is 1 to 200m 2 /g；
The tap density of the carbon skeleton is 0.2 to 0.8g/cm 3 。
3. The lithiated carbon skeleton composite of claim 1, wherein the three-dimensional network further comprises a conductive agent;
the conductive agent comprises at least one of carbon nano tube, graphene, carbon black, conductive graphite and metal fiber.
4. The lithium-philic carbon skeleton composite material according to claim 1, wherein the mass ratio of the carbon skeleton to the lithium-philic material is: 20 to 90 degrees.
5. The lithiophilic carbon skeleton composite of claim 1, further comprising a coating layer;
the coating layer coats the three-dimensional network structure;
the thickness of the coating layer is 5-20nm.
6. A method of making a lithium-philic carbon matrix composite as in any one of claims 1~5 comprising:
(1) Drying a mixed material containing a carbon skeleton and a lithium-philic material to obtain a carbon microsphere material;
(2) And sintering the carbon microsphere material for one time to obtain the lithium-philic carbon skeleton composite material.
7. The production method according to claim 6, wherein in the step (1), a mixed material containing a carbon skeleton and a lithium-philic material is added to a solvent to form a slurry;
the solid content of the slurry is 1% -20%;
the drying is spray drying.
8. The method according to claim 7, wherein the primary sintering is a stepwise temperature rise, and is divided into a primary sintering first stage and a primary sintering second stage;
the temperature of the first stage of the primary sintering is 200 to 400 ℃, and the time is 1 to 3h;
the rate of raising the temperature to the first stage temperature is 4~7 ℃/min;
the temperature of the second stage of the primary sintering is 500-900 ℃, and the time is 2-3h;
the rate of raising the temperature to the second stage temperature is 1~3 ℃/min.
9. The production method according to claim 6, characterized by further comprising step (3): and coating and sintering the product obtained after the primary sintering for the second time to obtain the lithium-philic carbon skeleton composite material.
10. The method according to claim 9, wherein the secondary sintering is a stepwise temperature rise, and is divided into a primary sintering first stage and a secondary sintering second stage;
the temperature of the first secondary sintering stage is 200 to 400 ℃, and the time is 1 to 3h;
the temperature of the second stage of the secondary sintering is 500-900 ℃, and the time is 2-3h;
the rate of raising the temperature to the first stage temperature is 4~7 ℃/min;
the rate of raising the temperature to the second stage temperature was 1~3 ℃/min.
11. The production method according to claim 9, wherein in the step (3), the coating is in-situ coating; the coating time is 4 to 30h;
the coated substance is at least one of polymeric phenolic resin, polydopamine, polypyrrole, tannic acid, polyvinylpyrrolidone and glucose.
12. A carbon-lithium composite material, comprising a lithium-philic carbon skeleton composite material and lithium metal in a three-dimensional via structure of the lithium-philic carbon skeleton composite material;
the lithium-philic carbon scaffold composite material comprising at least one of the lithium-philic carbon scaffold composite material of any one of claims 1~5.
13. The carbon lithium composite material according to claim 12, wherein the lithium metal is contained in the carbon lithium composite material in an amount of 1 to 80% by mass.
14. A negative electrode for a lithium battery, comprising at least one of the carbon lithium composite materials according to claim 12 or 13.
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