CN114447329A - Porous carbon material and preparation method and application thereof - Google Patents
Porous carbon material and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a porous carbon material and a preparation method and application thereof. The porous carbon material comprises secondary particles formed by stacking primary particles, and a first carbon coating layer positioned on the outer layer of the secondary particles; the primary particle includes a three-dimensional carbon framework and a lithium-philic substance. The porous carbon material provided by the invention is applied to a battery, so that metal lithium can be uniformly deposited in the structure, the growth of lithium dendrite is inhibited, the volume expansion is reduced, the specific surface area is reduced, the occurrence of side reaction is reduced, and the first effect and the cycle performance of the battery are further improved.
Description
Technical Field
The invention belongs to the technical field of lithium secondary batteries, and relates to a porous carbon material, and a preparation method and application thereof.
Background
Because of its high theoretical specific capacity and lowest electrochemical potential, lithium metal is recognized as the negative electrode material of the next generation of high energy density battery with the greatest development prospect. However, due to the active chemical property of lithium metal, an unstable Solid Electrolyte Interface (SEI) is formed between the electrode and the electrolyte in the circulation process, and the electrolyte is continuously consumed, so that irreversible deposition of metal lithium is caused, and the stability is affected. Secondly, the generation of lithium dendrites can also puncture the separator causing short circuits inside the battery, creating a serious safety problem, and the formation of dead lithium can lead to low coulombic efficiency. Further, the problem of volume expansion during the cycle also causes damage and breakage of the SEI film, powdering of the material, and the like, which affect the battery life.
The existing lithium metal negative electrode has the problems of extremely large volume expansion, serious lithium dendrite growth and the like, and has great challenges in the aspects of safety, cycling stability and the like.
CN110416522A discloses a lithium-containing composite negative electrode material, which comprises: the three-dimensional framework material comprises a three-dimensional framework material with a core-shell structure and metal lithium compounded in the core shell of the three-dimensional framework material, wherein the three-dimensional framework material takes a carbon-containing cathode material as a core, the surface of the core is covered with a shell layer, the shell layer has a porous carbon structure, and the thickness of the shell layer is larger than the particle size of the core. The lithium-containing composite negative electrode material can realize the storage of double-activity lithium of lithium intercalation/lithium over intercalation and lithium deposition, improve the specific capacity of the negative electrode, enlarge the lithium deposition area to promote the uniform deposition of lithium, reduce the generation of lithium dendrites to improve the safety, and control the volume change of the negative electrode to reduce the polarization of the battery.
CN110197899A discloses a preparation method of lithium foil, which comprises: 1) acidifying carbon nano tubes, 2) preparing a spinning solution, 3) spinning and forming a film, 4) carbonizing, 5) immersing the carbon nano-fiber film serving as a cathode and a lithium metal sheet serving as an anode in an electrolyte for carrying out an electrodeposition reaction to obtain a lithium foil. Compared with the conventional lithium foil, the impedance of the surface SEI film is obviously reduced, and the lithium battery taking the matrix as the negative electrode has high energy density and excellent cycle performance.
According to the method, the carbon conductive network framework is used for adsorbing lithium metal to prepare the lithium-carbon composite negative electrode material, however, the affinity of the carbon material and metal lithium is poor, the lithium metal is deposited on the carbon material to form a large overpotential, and uneven deposition of lithium is easy to occur in the circulation process to induce the generation of lithium dendrites.
Although the generation of lithium dendrites is inhibited to a certain extent by methods such as adding a lithium-philic substance in the prior art, the problems of excessive volume expansion and some side reactions still exist, so how to further solve the problems and better improve the performance of the battery is a technical problem which needs to be solved urgently at present.
Disclosure of Invention
The invention aims to provide a porous carbon material and a preparation method and application thereof. The porous carbon material provided by the invention has a communicated porous structure formed by a large number of communicated pores and a lithium-philic substance inside, and the carbon coating layer is arranged outside, so that metal lithium can be uniformly deposited inside the structure, the growth of lithium dendrites can be inhibited, and the volume expansion and the occurrence of side reactions are reduced. Meanwhile, the existence of the coating layer can also reduce the overlarge specific surface area of the porous carbon material and reduce the contact area of the lithium metal and the electrolyte, so that the first effect and the cycle performance of the battery are further improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a porous carbon material comprising secondary particles formed by stacking primary particles, and a first carbon coating layer on an outer layer of the secondary particles;
the primary particles include a three-dimensional carbon framework formed by connecting carbon material particles and a lithium-philic substance located inside and on the surface of the three-dimensional carbon framework.
In the invention, a large number of communicated porous structures are arranged in the three-dimensional carbon framework, so that a diffusion channel can be provided for lithium ions and enough active sites can be provided for the deposition of metal lithium; the lithium-philic substance enables the metal lithium to be uniformly and effectively deposited in the particles, so that the generation of lithium dendrite is avoided, and the volume expansion of the pole piece is inhibited; the existence of the first carbon coating layer changes the structure of the material, the larger specific surface area of the three-dimensional main body frame is reduced, the lithium-philic substance is positioned inside the particles, the lithium metal can be better guided to be deposited inside the three-dimensional frame and in the pores, the volume expansion of the pole piece in the circulation process is effectively controlled, the lithium metal is prevented from accumulating on the surface of the material to form lithium dendrites or even dead lithium, meanwhile, the contact between the lithium metal and electrolyte is also reduced, the occurrence of side reaction is effectively controlled, and the circulation performance and the safety performance of the battery are improved.
The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.
Preferably, the porous carbon material further comprises a network pyrolytic carbon.
Preferably, a part of the network pyrolytic carbon is positioned in the three-dimensional carbon framework to connect the three-dimensional carbon framework and the lithium-philic substance, and the other part of the network pyrolytic carbon is positioned on the surface of the primary particle to form a second carbon coating layer to connect the primary particle to form a secondary particle. The introduction of the network pyrolytic carbon is beneficial to stabilizing the structure and increasing the porosity of the material, thereby improving the electrochemical performance of the battery.
Preferably, the thickness of the first carbon coating layer is 100 to 2nm, such as 2nm, 10nm, 30nm, 50nm, 80nm or 100nm, preferably 20 to 40 nm.
Preferably, the raw material of the first carbon coating layer comprises any one or a combination of at least two of polyvinyl alcohol, asphalt, phenolic resin, dopamine, sucrose or glucose.
Preferably, the carbon material particles include any one of activated carbon, expanded graphite, artificial graphite, natural graphite, graphene, carbon nanotubes, hard carbon, or soft carbon, or a combination of at least two thereof.
Soft carbon and hard carbon are well known concepts to those skilled in the art, and in particular, soft carbon refers to carbon having a higher degree of graphitization after the heat treatment temperature reaches the graphitization temperature. Coke, graphitized Mesophase Carbon Microbeads (MCMB), carbon fibers, etc. are commonly used. Hard carbon refers to carbon that is difficult to graphitize, and is a thermal decomposition of a high molecular polymer. For example, a crosslinked resin having a specific structure is thermally decomposed at about 1000 ℃ to obtain hard carbon. Such carbon is difficult to graphitize even at a high temperature of 2500 ℃ or higher, and common hard carbon includes resin carbon, carbon black and the like.
Preferably, the raw material of the lithium-philic substance is a lithium-philic additive.
Preferably, the lithium-philic additive comprises any one of or a sufficient combination of at least two of silver powder, gold powder, aluminum powder, a soluble silver salt, a soluble zinc salt, a soluble titanium salt, zinc oxide, titanium oxide or a silicon material.
The present invention is not limited to specific types of soluble silver salts, soluble zinc salts, and soluble titanium salts, and the soluble silver salts may be, for example, silver nitrate; soluble zinc salts may be, for example, zinc nitrate, zinc acetate; the soluble titanium salt may be, for example, tetrabutyl titanate or lithium titanate.
Preferably, the raw material of the network pyrolytic carbon is an organic binder, and the organic binder comprises any one or a combination of at least two of polyethylene glycol, polyvinylpyrrolidone and sodium carboxymethyl cellulose.
In a second aspect, the present invention provides a method for producing a porous carbon material as described in the first aspect, the method comprising the steps of:
(1) mixing a carbon material, a lithium-philic additive and a solvent to obtain slurry;
(2) spray drying and granulating the slurry obtained in the step (1), and sintering for the first time to obtain a precursor;
(3) and (4) carrying out carbon coating on the precursor, and sintering for the second time to obtain the porous carbon material.
Through spray drying granulation and primary sintering of the slurry, the carbon material forms a sufficient intercommunicated porous structure consisting of intercommunicated pores, so that the lithium-philic substance can be positioned in the pores and further the metallic lithium is guided to deposit in the pores; by carrying out carbon coating on the precursor, the lithium-philic additive can be positioned inside the particles, and can guide the metal lithium to deposit inside the particles, so that the lithium-philic additive is prevented from contacting with the electrolyte, the occurrence of side reactions is reduced, the volume expansion is inhibited, the cycling stability of the battery is improved, meanwhile, the specific surface area of the porous carbon material increased by granulation is effectively controlled, the internal resistance is reduced, and the first effect of the battery is improved.
Preferably, the mixed raw material of step (1) further comprises an organic binder.
In the invention, the organic binder can play a role of a binder in the process of preparing slurry, the carbon material and the lithium-philic additive are tightly combined, and the network pyrolytic carbon can be obtained after sintering, wherein one part of the network pyrolytic carbon is positioned in the three-dimensional carbon frame and connected with the three-dimensional carbon frame and the lithium-philic substance, and the other part of the network pyrolytic carbon is positioned on the surface of primary particles to form a carbon coating layer and connected with the primary particles to form secondary particles.
Preferably, the mass ratio of the carbon material to the organic binder in the step (1) is 1 (0.01-0.5), such as 1:0.1, 1:0.2, 1:0.3, 1:0.4 or 1:0.5, and preferably 0.1-0.5.
Preferably, the carbon material in step (1) comprises any one of activated carbon, expanded graphite, artificial graphite, natural graphite, graphene, CNT, hard carbon or soft carbon or a combination of at least two of the foregoing.
Preferably, the lithium-philic additive in step (1) comprises any one or a combination of at least two of silver powder, gold powder, aluminum powder, silver nitrate, soluble zinc salt or soluble titanium salt.
Preferably, the organic binder comprises any one of polyethylene glycol, polyvinylpyrrolidone or sodium carboxymethylcellulose or a combination of at least two thereof.
Preferably, the solvent in step (1) comprises any one or a combination of at least two of ethanol, methanol or deionized water.
The mixing method is not limited in the present invention, and the mixing method commonly used in the art is applicable to the present invention, and may be, for example and without limitation, ball milling, sand milling, or high-speed dispersion. Preferably, the solid content of the slurry in the step (1) is 1-20%, such as 1%, 3%, 5%, 7%, 10%, 13%, 16%, 18%, 20%, etc.
Preferably, the air inlet temperature for spray drying granulation in the step (2) is 100 to 250 ℃, for example, 100 ℃, 125 ℃, 150 ℃, 170 ℃, 200 ℃, 225 ℃, 240 ℃ or 250 ℃.
Preferably, the median particle size of the powder obtained by spray drying granulation is 4 to 20 μm, for example 4 μm, 6 μm, 8 μm, 10 μm, 12.5 μm, 16 μm, 18 μm or 20 μm.
Preferably, the temperature of the primary sintering in the step (2) is 600-1000 ℃, such as 600 ℃, 650 ℃, 700 ℃, 725 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, 950 ℃ or 1000 ℃.
Preferably, the time of the primary sintering in the step (2) is 1-5 h, such as 1h, 2h, 2.5h, 3h, 4h or 5 h.
Preferably, the atmosphere of the primary sintering in the step (2) is a protective atmosphere;
preferably, the gas in the protective atmosphere comprises any one of nitrogen, helium, neon, argon, krypton or xenon, or a combination of at least two thereof.
Preferably, the carbon-coating method of step (3) includes a solid phase method or a liquid phase method; when a solid phase method is adopted, the coating material and the porous carbon material are uniformly mixed by grinding; when the liquid phase method is adopted, a solvent is added into the coating material to prepare liquid, then the porous carbon material is added, and stirring is carried out to ensure that the mixture is uniformly mixed.
Preferably, the carbon-coated raw material of step (3) comprises any one or a combination of at least two of polyvinyl alcohol, asphalt, phenolic resin, dopamine, sucrose or glucose.
Preferably, the mass ratio of the carbon-coated raw material in the step (3) to the precursor in the step (2) is (0.1-1): 1.
Preferably, the temperature of the secondary sintering in the step (3) is 600-1000 ℃, such as 600 ℃, 650 ℃, 700 ℃, 725 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, 950 ℃ or 1000 ℃.
Preferably, the time of the secondary sintering in the step (3) is 1-5 h, such as 1h, 2h, 2.5h, 3h, 4h or 5 h.
Preferably, the atmosphere of the secondary sintering in the step (3) is a protective atmosphere.
Preferably, the gas in the protective atmosphere comprises any one of nitrogen, helium, neon, argon, krypton or xenon, or a combination of at least two thereof.
As a preferred embodiment of the present invention, the method for preparing the porous carbon material comprises the steps of:
(1) carrying out ball milling on a carbon material, an organic binder, a lithium-philic additive and a solvent to obtain slurry, wherein the solid content of the slurry is 1-20%;
(2) carrying out spray drying granulation on the slurry obtained in the step (1), wherein the air inlet temperature is 100-250 ℃, and the median particle size of powder obtained by spray drying granulation is 4-20 mu m; sintering the powder obtained by spray drying for 1-5 h at the sintering temperature of 600-1000 ℃ in a protective atmosphere to obtain a precursor;
(3) coating the precursor obtained in the step (2) with carbon by a solid phase method or a liquid phase method, and sintering at the sintering temperature of 600-1000 ℃ for 1-5 h in a protective atmosphere; obtaining the porous carbon material.
In a third aspect, the present invention provides a lithium-containing composite comprising the porous carbon material of the first aspect and lithium metal between the primary particles and inside the first carbon coating layer.
The manner of introducing lithium into the porous carbon material may be a melt compounding method.
The melting compounding method is to heat the porous carbon and the lithium metal to a temperature higher than the melting point of the lithium, and stir to obtain the lithium-containing compound.
Preferably, the content of the lithium metal is 10% to 70% by mass of the total lithium-containing composite being 100%.
In a fourth aspect, the present invention provides an anode comprising a porous carbon material as described in the first aspect and/or a lithium-containing composite as described in the third aspect.
The preparation method of the negative electrode is not limited, the porous carbon material and the lithium-containing compound can be respectively used as negative electrode active materials to prepare the negative electrode, can be mixed to be used as the negative electrode active materials to prepare the negative electrode, and can be matched with other negative electrode active materials disclosed in the prior art to prepare the negative electrode.
The method for preparing the negative electrode is not limited, and the method can be an electrochemical composite method or a physical bonding method.
Preferably, the electrochemical recombination method comprises: the porous carbon material, the binder and the conductive agent are mixed to prepare slurry, the slurry is coated on a current collector and dried to prepare a porous carbon pole piece, the semi-cell is assembled by taking metal lithium as a counter electrode, and the content of lithium metal introduced into the porous carbon can be regulated and controlled by controlling current and time.
Preferably, the physical attaching method includes: and mixing a porous carbon material, a binder and a conductive agent to prepare slurry, coating the slurry on a current collector, drying to prepare a porous carbon pole piece, then directly attaching the porous carbon pole piece to lithium foils with different thicknesses, and compacting by a roller to obtain the lithium-carbon composite negative electrode.
In a fifth aspect, the present invention also provides a lithium metal battery including the anode of the fourth aspect.
The lithium metal battery refers to: the negative electrode of the battery already contains the metal lithium or the negative electrode contains the metal lithium after being charged, and the lithium ion battery is mainly used for distinguishing the lithium ion battery and can improve the energy density of the battery.
Compared with the prior art, the invention has the following beneficial effects:
(1) the intercommunicated porous structure of the porous carbon material is mainly generated by forming a three-dimensional framework through re-granulation of the carbon material, has high porosity and can provide more active sites for deposition of metal lithium.
(2) The porous carbon material has a special coating layer structure, so that the specific surface area of the porous carbon material increased by granulation is effectively controlled, the internal resistance is reduced, the first effect of the battery is improved, and the first effect after coating is improved by more than 6% compared with that without coating; the coating layer also changes the structure of the material, so that the lithium-philic substance is positioned inside the particles, the lithium metal can be guided to be deposited inside the three-dimensional frame and in the pores, the volume expansion of the pole piece in the circulation process is effectively controlled, the lithium metal is prevented from accumulating on the surface of the material to form lithium dendrites or even dead lithium, meanwhile, the contact between the metal lithium and electrolyte is reduced, the occurrence of side reaction is effectively controlled, the circulation performance, the energy density and the safety performance of the battery are improved, and no matter the surface capacity of the positive pole piece is 4mAh/cm2Or 6mAh/cm2Next, the first coulombic efficiency of the lithium metal battery provided by the invention can be more than 80%, and the cycle retention rate can be 74% or more after 50 weeks of cycle.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The present embodiment provides a porous carbon material including:
secondary particles formed by stacking primary particles, and a first carbon coating layer located on an outer layer of the secondary particles;
the primary particles comprise a three-dimensional carbon frame, nano zinc oxide and network pyrolytic carbon, the three-dimensional carbon frame is formed by connecting activated carbon particles, and the nano zinc oxide is positioned inside and on the surface of the three-dimensional carbon frame; one part of the network pyrolytic carbon is positioned in the three-dimensional carbon frame and connected with the three-dimensional carbon frame and the nano zinc oxide, and the other part of the network pyrolytic carbon is positioned on the surface of the primary particles to form a second carbon coating layer and connected with the primary particles to form secondary particles; wherein the thickness of the first carbon coating layer is 25 nm;
the raw material of the first carbon coating layer is phenolic resin; the raw material of the network-shaped pyrolytic carbon is polyvinylpyrrolidone.
The preparation method of the porous carbon material comprises the following steps:
(1) carrying out ball milling on 7g of activated carbon, 1g of polyvinylpyrrolidone, 2g of nano zinc oxide and deionized water, and uniformly mixing to obtain slurry with the solid content of 20%;
(2) carrying out spray drying granulation on the slurry in the step (1) at a feeding speed of 600ml/h and an air inlet temperature of 140 ℃ to obtain powder with a median particle size of 4 microns, and keeping the powder in a tubular furnace at a calcination temperature of 700 ℃ for 2 hours in a nitrogen atmosphere to obtain a precursor;
(3) and coating the precursor by adopting an in-situ polymerization phenolic resin method, wherein the mass ratio of the phenolic resin to the precursor is 0.5:1, performing suction filtration, and sintering again for 2h at the sintering temperature of 700 ℃ in a nitrogen atmosphere to obtain the porous carbon material.
The embodiment also provides a negative electrode, and the preparation method comprises the following steps: the porous carbon material prepared by the embodiment is used as a negative electrode active substance, the negative electrode active substance, a conductive agent and a binder are dissolved in a solvent to prepare a negative electrode slurry, and the negative electrode slurry is coated on a copper foil and dried to obtain a negative electrode.
Example 2
The present embodiment provides a porous carbon material including:
secondary particles formed by stacking primary particles, and a first carbon coating layer located on an outer layer of the secondary particles;
the primary particles comprise a three-dimensional carbon framework, titanium oxide and network pyrolytic carbon, the three-dimensional carbon framework is formed by connecting expanded graphite particles, and the titanium oxide is positioned inside and on the surface of the three-dimensional carbon framework; one part of the network pyrolytic carbon is positioned in the three-dimensional carbon frame and connected with the three-dimensional carbon frame and the titanium oxide, and the other part of the network pyrolytic carbon is positioned on the surface of the primary particles to form a second carbon coating layer and connected with the primary particles to form secondary particles;
wherein the thickness of the first carbon coating layer is 10 nm;
the raw material of the first carbon coating layer is phenolic resin; the raw material of the network-shaped pyrolytic carbon is polyvinylpyrrolidone.
The preparation method of the porous carbon material comprises the following steps:
(1) carrying out ball milling on 7g of expanded graphite, 3.5g of polyvinylpyrrolidone, 2g of titanium oxide and deionized water, and uniformly mixing to obtain slurry with the solid content of 4%;
(2) carrying out spray drying granulation on the slurry in the step (1) at the feeding speed of 300ml/h and the air inlet temperature of 200 ℃ to obtain powder with the median particle size of 10 microns, and carrying out heat preservation on the powder in a tubular furnace at the calcining temperature of 850 ℃ for 3 hours in a nitrogen atmosphere to obtain a precursor;
(3) and coating the precursor by adopting an in-situ polymerization phenolic resin method, wherein the mass ratio of the phenolic resin to the precursor is 0.2:1, and sintering for 3 hours at the sintering temperature of 850 ℃ in a nitrogen atmosphere to obtain the porous carbon material.
The embodiment also provides a negative electrode, and the preparation method comprises the following steps: the porous carbon material prepared by the embodiment is used as a negative electrode active substance, and the negative electrode active substance, a conductive agent and a binder are dissolved in a solvent to prepare a negative electrode slurry, and the negative electrode slurry is coated on a copper foil and dried to obtain a negative electrode.
Example 3
The present embodiment provides a porous carbon material including:
secondary particles formed by stacking primary particles, and a first carbon coating layer located on an outer layer of the secondary particles;
the primary particles comprise a three-dimensional carbon framework, zinc acetate and network pyrolytic carbon, the three-dimensional carbon framework is formed by connecting expanded graphite particles, and the zinc acetate is positioned inside and on the surface of the three-dimensional carbon framework; one part of the network pyrolytic carbon is positioned in the three-dimensional carbon frame and connected with the three-dimensional carbon frame and the zinc acetate, and the other part of the network pyrolytic carbon is positioned on the surface of the primary particles to form a second carbon coating layer and connected with the primary particles to form secondary particles;
wherein the thickness of the first carbon coating layer is 40 nm;
the raw material of the first carbon coating layer is phenolic resin; the raw material of the network-shaped pyrolytic carbon is polyethylene glycol.
The preparation method of the porous carbon material comprises the following steps:
(1) ball-milling 7g of expanded graphite, 2g of polyethylene glycol, 2g of zinc acetate and ethanol, and uniformly mixing to obtain slurry with the solid content of 15%;
(2) carrying out spray drying granulation on the slurry in the step (1) at a feeding speed of 700ml/h and an air inlet temperature of 200 ℃ to obtain powder with a median particle size of 15 microns, and carrying out heat preservation on the powder in a tubular furnace at a calcination temperature of 1000 ℃ for 1.5 hours under an argon atmosphere to obtain a precursor;
(3) and coating the precursor by adopting an in-situ polymerization phenolic resin method, wherein the mass ratio of the phenolic resin to the precursor is 0.8:1, and sintering for 1.5h at the sintering temperature of 1000 ℃ in an argon atmosphere to obtain the porous carbon material.
The embodiment also provides a negative electrode, and the preparation method comprises the following steps: the porous carbon material prepared by the embodiment is used as a negative electrode active substance, and the negative electrode active substance, a conductive agent and a binder are dissolved in a solvent to prepare a negative electrode slurry, and the negative electrode slurry is coated on a copper foil and dried to obtain a negative electrode.
Example 4
The present embodiment provides a porous carbon material including:
secondary particles formed by stacking primary particles, and a first carbon coating layer located on an outer layer of the secondary particles;
the primary particles comprise a three-dimensional carbon frame and nano zinc oxide, the three-dimensional carbon frame is formed by connecting activated carbon particles, and the nano zinc oxide is positioned inside and on the surface of the three-dimensional carbon frame; wherein the thickness of the first carbon coating layer is 25 nm;
the raw material of the first carbon coating layer is phenolic resin. This example differs from example 1 in that no polyvinylpyrrolidone, i.e. no organic binder, is added in step (1).
The remaining preparation methods and parameters were in accordance with example 1.
Example 5
This example is different from example 1 in that polyvinyl alcohol is coated in step (3), and the remaining preparation method is the same as example 1.
Example 6
The difference between this example and example 1 is that the thickness of the first carbon clad layer in this example is 5nm, and the remaining preparation method and steps are the same as those in example 1.
Example 7
The difference between this example and example 1 is that the thickness of the first carbon clad layer in this example is 70nm, and the remaining preparation method and steps are the same as those in example 1.
Example 8
This example provides a lithium-containing composite including the porous carbon material of example 1 and lithium metal, the content of the lithium metal in the lithium-containing composite being 30 wt%, and a method for preparing the same.
The preparation method of the lithium-containing composite comprises the following steps: the porous carbon material of example 1 and metallic lithium were heated to a temperature higher than the melting point of lithium, and stirred to obtain a lithium-containing composite.
This example also provides a negative electrode prepared in the same manner as in example 1, except that the lithium-containing composite prepared in example 8 was used as a negative electrode active material.
Example 9
This example provides a lithium-containing composite including the porous carbon material of example 1 and lithium metal in an amount of 10 wt% in the lithium-containing composite, and a method for preparing the same.
The preparation method of the lithium-containing composite comprises the following steps: the porous carbon material of example 1 and metallic lithium were heated to a temperature higher than the melting point of lithium, and stirred to obtain a lithium-containing composite.
This example also provides a negative electrode, which was prepared in the same manner as in example 1, except that the lithium-containing composite prepared in example 9 was used as a negative electrode active material.
Example 10
The embodiment provides a negative electrode, the porous carbon material prepared in embodiment 1 is used as a negative electrode active material, the negative electrode active material, a conductive agent and a binder are dissolved in a solvent to prepare a negative electrode slurry, the negative electrode slurry is coated on a copper foil and dried to obtain a porous carbon pole piece, then metal lithium is used as a counter electrode to assemble a half-cell, and the content of lithium metal introduced into the porous carbon is controlled to be 15 wt% by controlling current and time to obtain the lithium-carbon composite negative electrode.
Example 11
The embodiment provides a negative electrode, which is characterized in that the porous carbon material prepared in the embodiment 1 is used as a negative electrode active material, the negative electrode active material, a binder and a conductive agent are mixed to prepare slurry, the slurry is coated on copper foil and dried to prepare a porous carbon pole piece, then the porous carbon pole piece is directly attached to a lithium foil with the thickness of 100 microns, and the lithium-carbon composite negative electrode is obtained by compacting a roller.
Comparative example 1
This comparative example differs from example 1 in that step (3) is not carried out and the remaining preparation process remains the same as in example 1.
Comparative example 2
This comparative example is a commercially available porous carbon with an average particle size of 6 μm and a porosity of 61%.
Comparative example 3
The comparative example is different from example 1 in that the lithium-philic substance nano zinc oxide is not added, and the rest of the preparation method and steps are consistent with example 1.
And (3) performance testing:
(1) the samples obtained in examples 1 to 11 and comparative examples 1 to 3 were tested for porosity and the results are shown in Table 1.
(2) The samples obtained in examples 1-11 and comparative examples 1-3 were tested for pole piece expansion by the following test methods: testing the thickness of the pole piece before assembling the battery, and averaging 5 points; after circulation, the cell was disassembled to clean the pole pieces, 5 points were taken for averaging, and the results are shown in table 1.
(3) Preparation of the cell and testing of first coulombic efficiency and cycle performance
Preparing a battery: dissolving a positive active material NCM811, conductive carbon black and a binder PVDF in a solvent NMP to prepare positive slurry, coating the positive slurry on an aluminum foil, and drying to obtain a positive plate with the surface capacity of 4mAh/cm2、6mAh/cm2。
The negative electrodes prepared by the embodiments and the comparative ratios are adopted, and the positive plate, the diaphragm and the negative plate are overlapped together, the diaphragm is positioned between the positive plate and the negative plate, wound into a battery cell, injected with electrolyte and assembled into the full-cell.
The charging and discharging cutoff voltage is 2.8-4.2V, and the charging and discharging are performed at a constant current of 40mA/g, and the results are shown in tables 2 and 3.
TABLE 1 porosity and Pole piece expansion
| Porosity (%) | Expansion ratio of electrode piece (%) | |
| Example 1 | 75 | 20 |
| Example 2 | 85 | 15 |
| Example 3 | 83 | 14 |
| Example 4 | 73 | 26 |
| Example 5 | 77 | 25 |
| Example 6 | 75 | 30 |
| Example 7 | 75 | 26 |
| Example 8 | 80 | 25 |
| Example 9 | 72 | 26 |
| Example 10 | 76 | 21 |
| Example 11 | 80 | 23 |
| Comparative example 1 | 82 | 40 |
| Comparative example 2 | - | 25 |
| Comparative example 3 | 75 | 35 |
TABLE 2 Positive electrode 4mAh/cm2Performance of area capacity battery
TABLE 3 Positive electrode 6mAh/cm2Performance of area capacity battery
By comprehensively comparing the data results of the examples 1 to 11 with the data results of the comparative examples 1 to 3, the pole piece prepared from the porous carbon material provided by the invention has the advantages of higher porosity, obviously reduced volume expansion rate and more obviously improved electrochemical performance.
As can be seen from the data results of example 1 and example 4, the introduction of the network-like pyrolytic carbon is beneficial to stabilizing the structure and increasing the porosity, and the first coulombic efficiency and the cycle performance of the battery are improved.
From the data results of examples 1 and 6, it is known that when the porous carbon material is coated with carbon, if the thickness is too small, the carbon substrate undergoes volume change during charge and discharge to cause cracking of the carbon layer, and the volume expansion of the electrode sheet cannot be effectively inhibited, so that the expansion rate is large; it also exposes a large amount of metallic lithium to the outside, increasing side reactions. The reason for the slight increase in cycling performance may be that a thinner carbon coating layer is more favorable for intercalation and deintercalation of lithium ions.
From the data results of example 1 and example 7, it is known that when the porous carbon material is carbon-coated, the diffusion resistance of lithium ions increases due to an excessively large thickness of the porous carbon material, and lithium ions cannot rapidly diffuse into the particles during large-current charge and discharge, so that a part of metal lithium is deposited on the surface of the carbon-coated layer.
As is clear from the data results of example 1 and comparative example 1, when the porous carbon material is not coated, metallic lithium is deposited inside the particles, but is in direct contact with the electrolyte, increasing side reactions, and irreversibly consuming active lithium and the electrolyte, which drastically deteriorates the cycle performance of the battery.
As can be seen from the data results of example 1 and comparative example 2, the technical effect that can be achieved by the porous carbon material provided by the present invention cannot be achieved by the commercially available porous carbon material, because the porous carbon material provided by the present invention has an interconnected porous structure inside, and contains a lithium-philic substance capable of providing more active sites for the deposition of metallic lithium and enabling the deposition of metallic lithium inside the structure.
From the data results of example 1 and comparative example 3, it is known that when no lithium-philic substance is added to the porous carbon material, metallic lithium cannot be guided to be uniformly deposited into the particles, lithium dendrites are easily formed on the surface, and the electrolyte is consumed to increase side reactions, so that the first effect is reduced, and the performance of the battery is affected.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.
Claims (10)
1. A porous carbon material, characterized in that the porous carbon material comprises secondary particles formed by stacking primary particles, and a first carbon coating layer located on an outer layer of the secondary particles;
the primary particles include a three-dimensional carbon framework formed by connecting carbon material particles and a lithium-philic substance located inside and on the surface of the three-dimensional carbon framework.
2. The porous carbon material according to claim 1, further comprising a network-like pyrolytic carbon, a part of which is located inside the three-dimensional carbon framework and connects the three-dimensional carbon framework and the lithium-philic substance, and another part of which is located on the surface of the primary particles to form a second carbon coating layer and connects the primary particles to form secondary particles;
preferably, the thickness of the first carbon coating layer in the porous carbon material is 100-2 nm, preferably 20-40 nm;
preferably, the raw material of the first carbon coating layer comprises any one or a combination of at least two of polyvinyl alcohol, asphalt, phenolic resin, dopamine, sucrose or glucose;
preferably, the carbon material particles comprise any one of activated carbon, expanded graphite, artificial graphite, natural graphite, graphene, carbon nanotubes, hard carbon or soft carbon or a combination of at least two of the same;
preferably, the raw material of the lithium-philic substance is a lithium-philic additive;
preferably, the lithium-philic additive comprises any one of silver powder, gold powder, aluminum powder, soluble silver salt, soluble zinc salt, soluble titanium salt, zinc oxide, titanium oxide or silicon material or a combination of at least two of the silver powder, the gold powder, the aluminum powder, the soluble silver salt, the soluble zinc salt, the soluble titanium salt, the zinc oxide, the titanium oxide or the silicon material;
preferably, the raw material of the network pyrolytic carbon is an organic binder;
preferably, the organic binder comprises any one of polyethylene glycol, polyvinylpyrrolidone or sodium carboxymethylcellulose or a combination of at least two thereof.
3. The method for producing a porous carbon material according to claim 1 or 2, characterized by comprising the steps of:
(1) mixing a carbon material, a lithium-philic additive and a solvent to obtain slurry;
(2) carrying out spray drying granulation on the slurry obtained in the step (1), and sintering for the first time to obtain a precursor;
(3) and carrying out carbon coating on the precursor, and sintering for the second time to obtain the porous carbon material.
4. The method for producing a porous carbon material according to claim 3, wherein the mixed raw material of step (1) further comprises an organic binder;
preferably, the mass ratio of the carbon material to the organic binder is 1 (0.01-0.5), preferably 0.1-0.5;
preferably, the carbon material in step (1) comprises any one of activated carbon, expanded graphite, artificial graphite, natural graphite, graphene, carbon nanotubes, hard carbon or soft carbon or a combination of at least two of the two;
preferably, the lithium-philic additive in step (1) comprises any one or a combination of at least two of silver powder, gold powder, aluminum powder, soluble silver salt, soluble zinc salt, soluble titanium salt, zinc oxide, titanium oxide or silicon material;
preferably, the organic binder comprises any one or a combination of at least two of polyethylene glycol, polyvinylpyrrolidone or sodium carboxymethyl cellulose;
preferably, the solvent in step (1) comprises any one or a combination of at least two of ethanol, methanol or deionized water;
preferably, the solid content of the slurry in the step (1) is 1-20%;
preferably, the air inlet temperature of the spray drying granulation in the step (2) is 100-250 ℃;
preferably, the median particle size of the powder obtained by spray drying granulation is 4-20 μm;
preferably, the temperature of the primary sintering in the step (2) is 600-1000 ℃;
preferably, the time of the primary sintering in the step (2) is 1-5 h;
preferably, the atmosphere of the primary sintering in the step (2) is a protective atmosphere;
preferably, the gas in the protective atmosphere comprises any one of nitrogen, helium, neon, argon, krypton or xenon, or a combination of at least two thereof.
5. The method for producing a porous carbon material according to claim 3 or 4, wherein the method for carbon coating in step (3) comprises a solid phase method or a liquid phase method;
preferably, the carbon-coated raw material in the step (3) comprises any one or a combination of at least two of polyvinyl alcohol, asphalt, phenolic resin, dopamine, sucrose or glucose, without preference;
preferably, the mass ratio of the carbon-coated raw material in the step (3) to the precursor in the step (2) is (0.1-1): 1;
preferably, the temperature of the secondary sintering in the step (3) is 600-1000 ℃;
preferably, the time of the secondary sintering in the step (3) is 1-5 h;
preferably, the atmosphere of the secondary sintering in the step (3) is a protective atmosphere;
preferably, the gas in the protective atmosphere comprises any one of nitrogen, helium, neon, argon, krypton or xenon, or a combination of at least two thereof.
6. The method for producing a porous carbon material according to any one of claims 3 to 5, characterized by comprising the steps of:
(1) carrying out ball milling on a carbon material, an organic binder, a lithium-philic additive and a solvent to obtain slurry, wherein the solid content of the slurry is 1-20%;
(2) carrying out spray drying granulation on the slurry obtained in the step (1), wherein the air inlet temperature is 100-250 ℃, and the median particle size of powder obtained by spray drying granulation is 4-20 mu m; sintering the powder obtained by spray drying for 1-5 hours at the sintering temperature of 600-1000 ℃ in a protective atmosphere to obtain a precursor;
(3) coating the precursor obtained in the step (2) with carbon by a solid phase method or a liquid phase method, and sintering at the sintering temperature of 600-1000 ℃ for 1-5 h in a protective atmosphere; obtaining the porous carbon material.
7. A lithium-containing composite comprising the porous carbon material according to claim 1 or 2 and lithium metal located inside the primary particles and inside the first carbon coating layer.
8. The lithium-containing composite according to claim 7, wherein the content of the lithium metal is 10 to 70% based on 100% by mass of the total lithium-containing composite.
9. An anode comprising the porous carbon material according to claim 1 or 2 and/or the lithium-containing composite according to claim 7 or 8;
preferably, the negative electrode is a lithium-carbon composite negative electrode.
10. A lithium metal battery, characterized in that it comprises the negative electrode of claim 9.
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| CN115838163A (en) * | 2022-07-12 | 2023-03-24 | 宁德时代新能源科技股份有限公司 | Porous carbon material and preparation method thereof, negative electrode plate and lithium ion battery |
| CN117963889A (en) * | 2024-04-01 | 2024-05-03 | 玖贰伍碳源科技（天津）有限公司 | Carbon material, preparation method thereof and sodium ion battery |
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| CN115838163A (en) * | 2022-07-12 | 2023-03-24 | 宁德时代新能源科技股份有限公司 | Porous carbon material and preparation method thereof, negative electrode plate and lithium ion battery |
| CN117963889A (en) * | 2024-04-01 | 2024-05-03 | 玖贰伍碳源科技（天津）有限公司 | Carbon material, preparation method thereof and sodium ion battery |
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