CN113506871A - Composite negative electrode material for lithium metal battery - Google Patents

Composite negative electrode material for lithium metal battery Download PDF

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CN113506871A
CN113506871A CN202110620655.9A CN202110620655A CN113506871A CN 113506871 A CN113506871 A CN 113506871A CN 202110620655 A CN202110620655 A CN 202110620655A CN 113506871 A CN113506871 A CN 113506871A
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lithium
carbon nitride
negative electrode
buffer layer
porous carbon
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郭强
周旭峰
刘兆平
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Ningbo Institute of Material Technology and Engineering of CAS
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Ningbo Institute of Material Technology and Engineering of CAS
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B21/00—Nitrogen; Compounds thereof
    • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
    • C01B21/0605—Binary compounds of nitrogen with carbon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381—Alkaline or alkaline earth metals elements
    • H01M4/382—Lithium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/04—Particle morphology depicted by an image obtained by TEM, STEM, STM or AFM
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides a composite cathode material for a lithium metal battery, which consists of a cathode material and a buffer layer coated on the surface of the cathode material, wherein the buffer layer is prepared from slurry containing porous carbon nitride microspheres. The invention mainly coats porous carbon nitride microspheres on the surface of a cathode material to form an inorganic buffer layer with multilevel pore channels; the buffer layer can provide a physical space for accommodating and guiding lithium deposition by virtue of stacking macropores; meanwhile, due to the existence of abundant nano-pores, the nano-pores can fully interact with lithium ions, so that a better homogenization effect on the lithium ion flow is realized.

Description

Composite negative electrode material for lithium metal battery
Technical Field
The invention relates to the technical field of lithium metal batteries, in particular to a composite negative electrode material for a lithium metal battery.
Background
With the increasing popularity of portable electronic devices and electric vehicles, the energy density of conventional lithium ion batteries is challenged. Lithium metal due to its low weight density (0.53 g/cm)3) Low redox potential (-3.04V vs standard hydrogen electrode) and high theoretical specific capacity (3860mAh/g), are considered to be the most promising negative electrode materials for high energy density batteries. At the same time, lithium metal negative electrodes are also considered to be key to next generation energy storage systems such as lithium-oxygen or lithium-sulfur batteriesAnd (4) forming a component.
However, the lithium metal secondary battery is seriously hindered in practical use, mainly due to physical/chemical problems of the lithium metal negative electrode during charge and discharge. First, lithium metal deficiency physical regulation: the infinite volume expansion of lithium metal cathodes is a not negligible problem, even worse than graphite and silicon cathodes; meanwhile, the lithium metal negative electrode is easy to deposit in a dendritic form in a completely open space; more importantly, the randomly grown metal lithium increases the porosity of the electrode, increases the contact area between the lithium metal and the electrolyte, and causes the side reaction with the electrolyte to be increased; second, lithium ions lack chemical regulation: the SEI layer is not uniform in chemical composition or has surface defects at the electrode/electrolyte interface, which easily causes a local concentration of lithium ion flux to be too high. Thus, non-uniformity in lithium ion flux tends to lead to lithium dendrite formation. The two problems are mutually influenced, and finally, the lithium metal secondary battery continuously consumes a large amount of electrolyte when in work, so that the coulomb efficiency of the battery is low, the capacity is rapidly reduced, lithium dendrites even pierce through a diaphragm to cause short circuit, and serious safety accidents are caused.
In response to the above problems, researchers have devised different strategies including building artificial protective layers, optimizing electrolytes (e.g., adding functional salts) and current collector modifications to improve lithium metal anodes. Recently, modification of a three-dimensional skeleton buffer layer on a lithium metal negative electrode is considered as an effective method to suppress volume expansion thereof. In addition, due to the non-conductive or weakly conductive nature of the three-dimensional framework, it is easy to avoid the disadvantages of conventional three-dimensional current collector lithium ion tip deposition. Meanwhile, the three-dimensional skeleton with rich polar functional groups is proved to be capable of adjusting lithium ion diffusion in a chemical mode, so that lithium ions are uniformly deposited. In the prior art, nitrogen doping (such as pyridine nitrogen and pyrrole nitrogen) on a carbon material as a typical polar functional group in a three-dimensional framework can strongly interact with lithium ions to enhance the lithium affinity of the carbon material, and the nitrogen doping is proved to be an effective way for relieving the high local concentration of the lithium ions. The high content of nitrogen atoms in the graphitic carbon nitride material (about 57% atomic) proved to have a more significant interaction with lithium ions, which can form lithium-nitrogen transition bonds with lithium ions and strongly promote the kinetics of lithium metal deposition. In addition, ultra-high shear moduli up to 21.6GPa in graphite-type carbon nitride materials may also contribute to the suppression of lithium dendrite growth.
However, in the Current research, the three-dimensional framework has large pores, so that the effective interaction distance between Lithium ions and the nitrogen-containing functional group is difficult to be sufficiently ensured (Stable Lithium ion electrochemical interaction at Ultra-High Current reactions Enabled by 3D PMF/Li Composite Anode). It is well known that the behavior of a lithium ion stream in a three-dimensional framework depends largely on the size of the fluidic channels. In macroscopic fluids, the effect of the electric double layer tends to be neglected due to the large size of the flow channels. However, when the size of the flow channel is further reduced to nanometers, the electric double layer has no comparable advantages in regulating the lithium ion flux. Meanwhile, large pores hardly provide a reasonable space to initiate effective interaction of nitrogen atoms with lithium ions according to the Debye length law. Therefore, in order to be able to ensure effective interaction with lithium ions, the channel distance in the three-dimensional framework buffer layer should be limited at least to the nanometer scale.
At present, a strategy for transferring carbon nitride nanosheets to the surface of Lithium foil through a diaphragm to protect the surface of a Lithium negative electrode (An automatic g-C3N4 Li + -Modulating Layer heated Stable Lithium antibodies) is adopted, and the smooth deposition of Lithium metal is realized by virtue of the affinity of the carbon nitride nanosheets and Lithium ions, and the main defect of the strategy is that effective physical space constraint cannot be provided for the deposition of the Lithium metal. In addition, lithium ions can have steric effects with the two-dimensional nanoplatelets and thus can affect lithium ion diffusion.
There is also a method of preparing a slurry of irregular carbon nitride particles and coating the slurry on the surface of a lithium foil for lithium-negative electrode surface protection (lithium-to-graphite compatibility change of a nitrogen in a graphite carbide cathode lithium plating). The method does not consider that the interaction of lithium ions may not be well achieved due to larger pores between irregular particles, and in addition, the energy density of the lithium metal negative electrode is reduced due to the irregular high-density particles.
Therefore, the effective distance of the interaction force between the nitrogen atoms and the lithium ions is not considered in the above design, that is, only the flow channels provided by the lithium-philic material are small (nanometer scale), and the nitrogen atoms and the lithium ions generate strong interaction force. In addition, most of the existing prepared materials containing nitrogen functional groups have low nitrogen content and are complex to compound with lithium metal.
Disclosure of Invention
The composite negative electrode material can promote lithium ion transmission, homogenize lithium ion flux and realize the dendrite-free deposition of lithium metal.
In view of the above, the present application provides a composite negative electrode material for a lithium metal battery, which is composed of a negative electrode material and a buffer layer coated on a surface of the negative electrode material, wherein the buffer layer is prepared from a slurry including porous carbon nitride microspheres.
Preferably, the preparation method of the porous carbon nitride microsphere specifically comprises the following steps:
mixing melamine and a solvent, and heating to obtain a first solution;
mixing cyanuric acid with a solvent, and heating to obtain a second solution;
mixing and drying the first solution and the second solution to obtain mixed powder;
and calcining the mixed powder in argon and oxygen to obtain the porous carbon nitride microspheres.
Preferably, the solvent in the first solution and the second solution is independently selected from dimethyl sulfoxide, acetonitrile, formaldehyde or methanol.
Preferably, the content of the oxygen in the argon gas and the oxygen gas is 0.1 vol% to 2 vol%.
Preferably, the temperature rise rate of the calcination is 2-5 min-1The temperature is 500-600 ℃, and the time is 3-5 h.
Preferably, the slurry also comprises polyvinylidene fluoride and 1-methyl-2 pyrrolidone.
Preferably, the mass ratio of the porous carbon nitride microspheres to the polyvinylidene fluoride is 1: 1.
Preferably, the concentration of the slurry is 1-15 wt%.
Preferably, the thickness of the buffer layer is 120-250 μm.
Preferably, the negative electrode material is lithium foil or copper foil.
The application provides a composite negative electrode material for a lithium metal battery, which consists of a negative electrode material and a buffer layer coated on the surface of the negative electrode material, wherein the buffer layer is prepared from slurry containing porous carbon nitride microspheres. The composite negative electrode material provided by the application takes the porous carbon nitride microspheres as the buffer layer, and the carbon nitride material has very high nitrogen content (57%) and is suitable for being used as a lithium ion current adjusting material; at the same time, the buffer layer can provide a physical space for effectively accommodating lithium metal deposition; chemically, a large number of nanometer-level pore channels can effectively interact with lithium ions, so that the lithium ion transmission is promoted, the lithium ion flux is uniform, and finally the dendrite-free deposition of lithium metal is realized.
Drawings
FIG. 1 is a schematic flow chart of the present invention for preparing porous carbon nitride;
fig. 2 is SEM and TEM photographs of different anode materials and SEM top and cross-sectional views of different anodes;
FIG. 3 is a BET plot and a pore size distribution plot for BCN, PCNM and SCN particles;
FIG. 4 is a SEM cross-sectional view of different electrodes and a 5mAh cm deposit-2SEM cross-sectional and top views;
FIG. 5 is a graph of coulombic efficiency of different electrodes tested in a lithium-copper half cell;
FIG. 6 is an SEM topography of electrodes coated at different slurry concentrations;
FIG. 7 is a graph of coulombic efficiencies of coated electrodes at different slurry concentrations in a lithium-copper half cell test;
FIG. 8 is a SEM cross-section and surface topography of electrodes obtained for different coating thicknesses;
FIG. 9 is a plot of coulombic efficiency in lithium-copper half cell tests for electrodes obtained at different coating thicknesses;
FIG. 10 is an SEM image of the carbon nitride microspheres obtained under different atmospheres;
fig. 11 is a coulombic efficiency graph of lithium-copper half cell tests for electrode sheets prepared based on carbon nitride microspheres prepared under different atmospheres.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
In the lithium metal secondary battery, the dendritic crystal grows seriously and the volume expansion is prominent under the condition that the lithium metal has no physical restriction; in addition, during the diffusion process of lithium ions, the lithium ions generate the problem of uneven distribution of ion flow on the surface of the lithium foil. The invention mainly coats porous carbon nitride microspheres on the surface of a lithium foil or a copper foil to form an inorganic buffer layer with multilevel pore channels; the buffer layer can provide a physical space for accommodating and guiding lithium deposition by virtue of stacking macropores; meanwhile, due to the existence of abundant nano-pores, the nano-pores can fully interact with lithium ions, so that a better homogenization effect on the lithium ion flow is realized. The embodiment of the invention discloses a composite negative electrode material for a lithium metal battery, which consists of a negative electrode material and a buffer layer coated on the surface of the negative electrode material, wherein the buffer layer is prepared from slurry containing porous carbon nitride microspheres.
In the application, the preparation method of the porous carbon nitride microsphere specifically comprises the following steps:
mixing melamine and a solvent, and heating to obtain a first solution;
mixing cyanuric acid with a solvent, and heating to obtain a second solution;
mixing and drying the first solution and the second solution to obtain mixed powder;
and calcining the mixed powder in argon and oxygen to obtain the porous carbon nitride microspheres.
The molar ratio of the melamine to the cyanuric acid is 1:1, otherwise, the balling/nano of the whole material is weakened, and other irregular carbon nitride impurities are introduced, which is not beneficial to the control of the whole appearance. In the preparation process of the porous carbon nitride microsphere, the solvents in the first solution and the second solution are independently selected from dimethyl sulfoxide, acetonitrile, formaldehyde or methanol.
The calcining atmosphere is performed in argon and oxygen, wherein the content of oxygen is 0.1-2 vol%; introducing trace oxygen, mainly increasing the internal pore structure of the carbon nitride, and simultaneously introducing a small amount of oxygen-containing functional groups; the electrolyte wettability can be further improved, the lithium ion flow can be better homogenized, and the smooth deposition of lithium metal can be facilitated.
The temperature rise rate of the calcination is 2-5 min-1The temperature is 500-600 ℃, and the time is 3-5 h.
The slurry also comprises polyvinylidene fluoride and 1-methyl-2-pyrrolidone, the mass ratio of the porous carbon nitride microspheres to the polyvinylidene fluoride is 1:1, and if the mass of the porous carbon nitride microspheres is too high, the carbon nitride microspheres have small density and large volume, so that the integral structure is difficult to be bonded and fixed, and the structural toughness is poor; if the mass of the polyvinylidene fluoride is too high, the overall energy density of the negative electrode is influenced, and pores formed by the carbon nitride microspheres are not favorable, so that the pores are buried; therefore, 1:1 is the selection of ensuring that the carbon nitride microspheres can be well adhered and fixed, simultaneously not influencing the rich pores of the carbon nitride microspheres and not influencing the energy density of the battery; the concentration of the slurry is 1-15 wt%.
According to the invention, porous carbon nitride microspheres, polyvinylidene fluoride and 1-methyl-2-pyrrolidone are mixed, stirred to form slurry, the slurry is coated on the surface of a negative electrode material in a thickness of 120-250 microns, and vacuum drying is carried out to obtain the composite lithium metal negative electrode. In the present application, the negative electrode material is selected from a lithium foil or a copper foil.
The invention mainly designs a composite cathode material coated with porous carbon nitride microspheres as a multilevel pore canal buffer layer. The buffer layer adopts a coating process, and the preparation method is simple and convenient; the micron-scale pore canal of the porous carbon nitride microsphere can provide a physical space for accommodating and guiding lithium metal deposition, and prevent the lithium metal deposition from expanding violently; the nanoscale pore channel can effectively interact with lithium ions, so that the lithium ion transmission is promoted, the lithium ion flow is uniform, and finally, the smooth deposition of lithium metal is realized; the porous carbon nitride microspheres have many pores and low density, and cannot influence the energy density of the lithium metal secondary battery; the microspheres have certain physical structure and mechanical strength; the nitrogen content of the microsphere porous carbon nitride material is high, so that more active sites for interacting with lithium ions can be provided.
For further understanding of the present invention, the following examples are given to illustrate the composite anode material provided by the present invention, and the scope of the present invention is not limited by the following examples.
Example 1
1)7.92mmol of melamine dissolved in 40mL of dimethyl sulfoxide (DMSO) (Aladdin, Pur is more than or equal to 99.0%); 7.92mmol of cyanuric acid (Aladdin, Pur is more than or equal to 99.0%) is dissolved in 20mL of DMSO;
2) heating the two solutions to 60 deg.C respectively, stirring and mixing for about 15min, and filtering;
3) washing the filtrate with ethanol and deionized water for several times, and oven drying at 80 deg.C;
4) drying to obtain white powder, and heating at 550 deg.C under argon for 2 min-1Calcining for 4 hours at the heating rate, introducing trace oxygen (0.1-2%) in the calcining process, and finally obtaining yellow porous carbon nitride microsphere powder;
5) mixing the prepared porous carbon nitride microsphere powder and polyvinylidene fluoride (PVDF) in a 1:1 mass ratio in a 1-methyl-2-pyrrolidone (NMP) solvent, and stirring for 10 hours to form stable and uniform slurry with the mass fraction of total materials of 10 wt%;
6) coating the slurry on a lithium foil or a copper foil with a certain thickness by 200 μm;
7) and (3) drying the lithium foil or the copper foil coated with the slurry for 6 hours in vacuum at 80 ℃ to obtain the composite lithium metal negative electrode.
Comparing the composite lithium metal negative electrode prepared in the embodiment with a conventional lithium metal negative electrode material in the prior art, the specific marks are as follows:
SCN: carbon nitride nanosheets; BCN: bulk random carbon nitride; PCNM: porous carbon nitride microspheres; cu: a pure copper foil; cu @ SCN: copper foil coated with SCN; cu @ BCN: copper foil coated with BCN; cu @ PCNM: a copper foil coated with PCNM; PVDF: polyvinylidene fluoride.
Carbon nitride with the same mass and PVDF with the same mass are prepared into slurry according to the same proportion, and the slurry is coated on a copper foil according to the same thickness of a scraper to form Cu @ BCN, Cu @ PCNM and Cu @ SCN electrodes respectively. SEM images (shown as a-c) and TEM images (shown as d-f) of BCN, PCNM and SCN particles in FIG. 2; SEM top view (as shown in figures g-i) and cross-sectional view (as shown in figures j-l) of BCN, PCNM and SCN particle coated copper foil electrodes. FIG. 3 is a BET plot (outer plot) and a pore size distribution plot (inner plot) of BCN, PCNM and SCN particles; as is obvious from fig. 2, the porous microsphere carbon nitride is formed by self-assembling two-dimensional nano sheets, and has a certain fixed physical space and structural toughness, while the BCN of fig. 2 is in a random particle form, the inside of the BCN is compact, and has no obvious pore structure, the BCN distribution on Cu @ BCN is relatively dispersed, so that the interaction with lithium ions is difficult to be effectively generated, and the SCN has the structural characteristic of a soft 2-dimensional nano sheet and has no more pores; the Cu @ SCN surface also has no obvious physical space structure, so that the physical accommodating space of lithium metal cannot be provided; as can be seen from fig. 3, in addition to the micron-level pores formed by stacking the carbon nitride microspheres, the Cu @ PCNM electrode also has abundant dispersed nanopores on the nanosheets on the microspheres, and the pore size distribution is mainly concentrated at about 60 nm; the electrode material can provide a certain physical space for accommodating the growth of lithium metal, and meanwhile, the abundant nano pores can strengthen the interaction with lithium ion flow and better help the flat deposition of the lithium metal.
SEM cross-sectional view of Cu electrode in FIG. 4 and deposition of 5mAh cm-2SEM cross-section and top-down view (a-c), SEM cross-section of Cu @ SCN electrode and deposition of 5mAh cm-2SEM cross-sectional and top views (d-f), SEM cross-sectional view of Cu @ BCN electrode and deposition of 5mAh cm-2SEM cross-sectional view and top view (g-i), SEM cross-sectional view of Cu @ PCNM electrodeAnd deposit 5mAh cm-2SEM cross-sectional and top views (j-l); from FIG. 4, it can be seen that lithium was deposited at 5mAh cm on pure copper foil, Cu @ SCN and Cu @ BCN-2When the lithium metal is used, obvious dendritic crystals are formed on the surface of the electrode, and more pores are formed in the electrode; and lithium was deposited on Cu @ PCNM at 5mAh cm-2When the lithium metal is used, the surface of the lithium is flat, and the interior of the electrode is relatively dense; the PCNM coating layer can provide a certain physical space to guide the growth of lithium metal, and meanwhile, rich nanopores of the PCNM material can fully homogenize lithium ion flow to promote the flattening deposition of the lithium metal.
FIG. 5 is a plot of coulombic efficiencies for Cu, Cu @ SCN, Cu @ BCN, and Cu @ PCNM tests in a lithium-copper half cell; from the electrochemical data of fig. 5, it can be seen that the Cu @ PCNM electrode exhibits higher coulombic efficiency, longer cycle life in the lithium-copper half cell test; this fully demonstrates that lithium exhibits a dendrite-free lithium deposition morphology on Cu @ PCNM and has a high reversibility.
Example 2
The preparation method is the same as that of example 1, except that: the concentration of the slurry is 5%, a composite electrode is obtained, the performance of the electrode is detected, and the result is specifically as follows:
FIG. 6 is SEM pictures of composite electrodes obtained under different slurry concentration coating, the left picture is the SEM picture of 5% of the composite electrode, and the right picture is the SEM picture of 10% of the composite electrode; FIG. 7 is a plot of coulombic efficiency in lithium-copper half cell tests for electrodes coated at different slurry concentrations (PCNM + PVDF); as shown in fig. 6, the 5% slurry is too diluted, the coated electrode sheet is very uneven, the surface has a dimpled structure, and has a significant copper exposure phenomenon, which is not favorable for the carbon nitride microspheres to protect the copper/lithium foil (fig. 6, left), and the 10% slurry is coated on the surface of the electrode, the surface of the electrode is very uniform and flat (fig. 6, right); it can be seen from figure 7 that the coulombic efficiency of the 10% slurry coated electrode is much better than the 5% slurry coated electrode.
Example 3
The preparation method is the same as that of example 1, except that: the thickness of the slurry is 100 μm, a composite electrode is obtained, and the performance of the electrode is detected, and the result is specifically as follows:
as a result, it was found that the electrode sheet obtained with a coating thickness of 100 μm had a non-flat cross-section and surface and had a significant copper-exposure phenomenon (FIG. 8 (a-b)); the cross section and surface of the electrode sheet obtained by coating the sheet with a thickness of 200 μm were very regular and uniform, and no copper exposure occurred (FIG. 8 (c-d)). It can also be seen from fig. 9 that the coulomb efficiency of the electrode sheet with a coating thickness of 200 μm is better than that of the electrode sheet with a coating thickness of 100 μm.
Comparative example 1
The same preparation as in example 1 is carried out, with the only difference that: the calcination was performed under a pure argon atmosphere, and fig. 10 is SEM photographs of the carbon nitride microspheres obtained under different atmospheres, fig. (a) is an SEM photograph of the carbon nitride microspheres obtained under pure argon, and fig. (b) is an SEM photograph of the carbon nitride microspheres obtained in example 1; as can be seen from fig. 10, the nitrided carbon microspheres obtained by calcination in a pure argon atmosphere are denser, have fewer pores, and have an overall structure more biased toward a complete sphere (fig. 10 (a)); after a small amount of oxygen is introduced, the shape of the carbon nitride microspheres becomes more irregular and the pores are obviously improved under the promotion of thermal decomposition of the oxygen (fig. 10 (b)); the porous carbon nitride microspheres are beneficial to the infiltration of the electrolyte in the porous carbon nitride microspheres, and meanwhile, a proper deposition space is provided for lithium metal. FIG. 11 is a coulombic efficiency graph of lithium-copper half cell tests on electrode sheets prepared from carbon nitride microspheres prepared under different atmospheres; it can also be found from fig. 11 that the porous carbon nitride microspheres obtained by lithium metal in an oxygen atmosphere exhibit more stable reversibility.
The above description of the embodiments is only intended to facilitate an understanding of the method of the invention and its core ideas. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. The composite cathode material for the lithium metal battery is composed of a cathode material and a buffer layer coated on the surface of the cathode material, wherein the buffer layer is prepared from slurry containing porous carbon nitride microspheres.
2. The composite anode material of claim 1, wherein the preparation method of the porous carbon nitride microspheres specifically comprises:
mixing melamine and a solvent, and heating to obtain a first solution;
mixing cyanuric acid with a solvent, and heating to obtain a second solution;
mixing and drying the first solution and the second solution to obtain mixed powder;
and calcining the mixed powder in argon and oxygen to obtain the porous carbon nitride microspheres.
3. The composite anode material of claim 2, wherein the solvent in the first solution and the second solution is independently selected from dimethyl sulfoxide, acetonitrile, formaldehyde, or methanol.
4. The composite anode material according to claim 2, wherein the content of the oxygen in the argon gas and the oxygen gas is 0.1 vol% to 2 vol%.
5. The composite anode material of claim 2, wherein the temperature rise rate of the calcination is 2-5 min-1The temperature is 500-600 ℃, and the time is 3-5 h.
6. The composite anode material according to claim 1 or 2, wherein the slurry further comprises polyvinylidene fluoride and 1-methyl-2-pyrrolidone.
7. The composite negative electrode material as claimed in claim 6, wherein the mass ratio of the porous carbon nitride microspheres to the polyvinylidene fluoride is 1: 1.
8. The composite anode material according to claim 1 or 2, wherein the slurry has a concentration of 1 to 15 wt%.
9. The composite anode material of claim 1, wherein the buffer layer has a thickness of 120 to 250 μm.
10. The composite negative electrode material according to any one of claims 1 to 9, wherein the negative electrode material is a lithium foil or a copper foil.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114843486A (en) * 2022-05-27 2022-08-02 江苏理工学院 Lithium ion battery
CN114914446A (en) * 2022-04-26 2022-08-16 中国五洲工程设计集团有限公司 Composite electrode, preparation method of composite electrode and battery

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