CN115986121A - Silicon-based material and preparation method and application thereof - Google Patents
Silicon-based material and preparation method and application thereof Download PDFInfo
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- 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
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Abstract
The invention discloses a silicon-based material and a preparation method and application thereof. The silicon-based material comprises an inner core, a first coating layer and a second coating layer, wherein the inner core comprises silicon-based material particles, and the silicon-based material particles are negatively charged; the first coating layer is formed on at least a portion of a surface of the inner core, the first coating layer comprising a metal-organic framework compound; the second cladding layer is formed on at least a portion of a surface of the first cladding layer, the second cladding layer comprising a carbon material, the second cladding layer being at least partially embedded in the first cladding layer. The silicon-based material disclosed by the invention has lower volume expansion and higher conductivity, so that the specific capacity and the cycle performance of a lithium battery can be improved by taking the silicon-based material as a negative electrode material.
Description
Technical Field
The invention relates to the field of lithium batteries, in particular to a silicon-based material and a preparation method and application thereof.
Background
Since the 90 s of the 20 th century, the battery industry has seen explosive growth. Particularly, lithium ion batteries have the advantages of excellent cycle performance, no memory effect, high operating voltage, environmental friendliness and the like, and therefore, the lithium ion batteries are important in current life, particularly ideal energy sources for electric vehicles and mobile devices.
The negative electrode of the current commercial lithium ion battery is a graphite material, and the theoretical capacity of the graphite is about 372mAh/g; with the progress of technology and the increase of demand, the demand of next generation high specific energy lithium ion battery can not be satisfied. Therefore, there is a strong need for a graphite substitute material in which silicon (theoretical capacity of about 4200 mAh/g) has a high theoretical capacity and suitable Li insertion/extraction + The potential becomes the first choice for the next generation of lithium battery cathodes. However, the rapid decay of capacity due to the large volume expansion effect (about 300%) generated when silicon is alloyed with lithium has been a barrier to commercialization of silicon. Therefore, it has been studied how to suppress the expansion of silicon during charge and discharge.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, the invention aims to provide a silicon-based material, and a preparation method and application thereof. The silicon-based material disclosed by the invention has lower volume expansion and higher conductivity, so that the specific capacity and the cycle performance of a lithium battery can be improved by taking the silicon-based material as a negative electrode material.
In a first aspect of the invention, a silicon-based material is provided. According to an embodiment of the present invention, the silicon-based material includes:
a core comprising silicon-based material particles, the silicon-based material particles being negatively charged;
a first coating layer formed on at least a portion of a surface of the inner core, the first coating layer comprising a metal organic framework compound;
a second cladding layer formed on at least a portion of a surface of the first cladding layer, the second cladding layer comprising a carbon material, the second cladding layer being at least partially embedded in the first cladding layer.
According to the silicon-based material provided by the embodiment of the invention, the inner core comprises silicon-based material particles with electronegativity, and according to the principle of opposite attraction, metal ions in the metal organic framework compound can be actively close to the silicon-based material particles with electronegativity, so that the growth uniformity of the metal organic framework compound can be improved, a first coating layer with the metal organic framework compound uniformly distributed is formed on the surface of the silicon-based material particles, and the three-dimensional network structure provided by the uniformly grown metal organic framework compound can better inhibit the silicon volume expansion, so that the silicon-based material can provide stable high capacity in the battery circulation process. Meanwhile, the second coating layer which is formed on the first coating layer and comprises a carbon material can improve the electrical conductivity of the silicon-based material, and the second coating layer is partially embedded into the pore channels of the metal organic framework compound, namely the second coating layer and the metal organic framework compound of the first coating layer cooperate to inhibit the volume expansion of silicon. Therefore, the silicon-based material disclosed by the invention has lower volume expansion and higher conductivity, so that the specific capacity and the cycle performance of a lithium battery can be improved by taking the silicon-based material as a negative electrode material.
In addition, the silicon-based material according to the above embodiment of the present invention may also have the following additional technical features:
in some embodiments of the invention, the particle size of the core is 20nm to 2000nm, the thickness of the first coating layer is 10nm to 3000nm, and the thickness of the second coating layer is 10nm to 3000nm. Thus, the silicon-based material has lower volume expansion and higher electrical conductivity.
In some embodiments of the invention, the silicon-based material particles have the formula SiO X Wherein X is more than or equal to 0 and less than or equal to 2. In this way,the silicon-based material can be used as a negative electrode material to improve the specific capacity of the lithium battery.
In some embodiments of the invention, the carbon material comprises at least one of graphite, multi-walled carbon nanotubes, single-walled carbon nanotubes, graphene, biomass carbon. Thus, the silicon-based material has lower volume expansion and higher electrical conductivity.
In some embodiments of the invention, the metal ion in the metal-organic framework compound comprises Cu 2+ 、Zn 2 + 、Co 2+ The organic ligand in the metal-organic framework compound comprises at least one of trimesic acid, terephthalic acid and dimethyl imidazole. Thus, the silicon-based material has a low volume expansion.
In a second aspect of the invention, the invention proposes a method for preparing the above-mentioned silicon-based material. According to an embodiment of the invention, the method comprises: providing silicon-based material particles with electronegativity; (2) Mixing a metal salt, an organic ligand, a solvent with the negatively charged silicon-based material particles to form a first coating layer comprising a metal-organic framework compound on the surface of the silicon-based material particles; (3) Mixing and ball-milling a carbon material with the silicon-based material particles having the first coating layer obtained in step (2) to form a second coating layer comprising the carbon material on the first coating layer, and the second coating layer being at least partially embedded in the first coating layer.
According to the method for preparing the silicon-based material, the silicon-based material particles with electronegativity are mixed with the metal salt, the organic ligand and the solvent, and according to the principle of opposite attraction, metal ions in the metal salt can be actively close to the silicon-based material particles with electronegativity, so that the growth uniformity of the metal-organic framework compound can be improved, a first coating layer with the metal-organic framework compound uniformly distributed is formed on the surfaces of the silicon-based material particles, and the three-dimensional network structure provided by the uniformly grown metal-organic framework compound can better inhibit the volume expansion of silicon, so that the silicon-based material particles can provide stable high capacity in the battery circulation process. Then mixing and ball-milling the carbon material and the silicon-based material particles with the first coating layer, wherein on one hand, a second coating layer comprising the carbon material can be formed on the first coating layer, so that the conductivity of the silicon-based material is improved; on the other hand, partial second coating layer can be embedded into the pore channels of the metal organic framework compound, namely the second coating layer and the metal organic framework compound of the first coating layer cooperatively inhibit the volume expansion of silicon; on the other hand, a second coating layer comprising a carbon material is directly formed in a ball milling mode, so that the convenience of operation is improved, the reaction energy consumption is reduced, the atom utilization rate is improved, and the problems of low atom utilization rate, raw material waste and high energy consumption caused by volatilization of components such as hydrogen and oxygen in the high-temperature carbonization process are solved. Therefore, the method for preparing the silicon-based material can be used for preparing the silicon-based material with lower volume expansion and higher conductivity while reducing reaction energy consumption and raw material waste, so that the specific capacity and the cycle performance of a lithium battery can be improved by taking the silicon-based material as a negative electrode material.
In addition, the method for preparing the above silicon-based material according to the above embodiment of the present invention may further have the following additional technical features:
in some embodiments of the present invention, the negatively charged silicon-based material particles are prepared by the following steps: (1-1) mixing a surfactant, a solvent and silicon-based material particles; (1-2) carrying out solid-liquid separation on the mixed solution obtained in the step (1-1) to obtain silicon-based material particles with electronegativity. Thus, the silicon-based material has a low volume expansion.
In some embodiments of the invention, in step (2), the temperature of the mixing is from 40 ℃ to 60 ℃.
In some embodiments of the present invention, the mass ratio of the negatively charged silicon-based material particles, the metal salt, and the organic ligand is (1-5): (1-50): (1-50). Thus, the silicon-based material has a low volume expansion.
In some embodiments of the present invention, the mass ratio of the silicon-based material particles having the first coating layer to the carbon material is 1: (1-4). Thus, the silicon-based material has lower volume expansion and higher electrical conductivity.
In some embodiments of the invention, the ball milling conditions are: the ball material ratio is (5-10): 1, the rotating speed is 100r/min-500r/min, and the ball milling time is 1h-6h. Thus, the conductivity of the silicon-based material can be improved while reducing the energy consumption.
In a third aspect of the present invention, a negative electrode sheet is provided. According to an embodiment of the invention, the negative electrode plate comprises the silicon-based material or the silicon-based material obtained by the method. Therefore, the electrochemical performance of the negative plate can be improved, and the specific capacity and the cycle performance of the lithium battery are further improved.
In a fourth aspect of the present invention, a lithium battery is provided. According to an embodiment of the present invention, the lithium battery includes the above negative electrode sheet. The negative plate can form a more stable solid electrolyte interface film (SEI), and reduce the repeated generation of the solid electrolyte interface film to seriously consume the electrolyte, thereby improving the specific capacity and the cycle performance of the lithium battery.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic flow diagram of a method for preparing a silicon-based material according to one embodiment of the present invention;
FIG. 2 is a scanning electron microscope image of the silica nanopowder with the first coating prepared in example 1 of the present invention;
FIG. 3 is a second SEM image of the silica nanopowder with the first coating layer prepared in example 1 of the present invention;
FIG. 4 shows that the concentration of the compound in example 1 of the present invention is 0.5 A.g -1 A current density of (a);
FIG. 5 shows that the concentration of 0.5 A.g in example 2 of the present invention -1 A current density of (a);
FIG. 6 is a graph of rate capability for example 1 of the present invention;
FIG. 7 is a graph of rate capability for example 2 of the present invention;
FIG. 8 shows the results of comparative example 1 of the present invention at 0.5A g -1 A current density of (a);
FIG. 9 shows that the concentration of comparative example 2 of the present invention is 0.5A g -1 A current density of (a);
FIG. 10 is a graph of rate capability of comparative example 1 of the present invention;
FIG. 11 is a graph of rate capability of comparative example 2 of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The technical solution of the present application was completed based on the following findings: in the related technology, nano-silicon is uniformly dispersed into a solution by using a dispersing agent such as Cetyl Trimethyl Ammonium Bromide (CTAB), and then a metal organic framework compound (MOFs) precursor is added to grow on the surface of the nano-silicon; then reducing and carbonizing the porous material by using reducing metal to obtain the N-doped carbon-coated porous material, and specifically comprising the following steps of:
(1) Uniformly mixing nano silicon and CTAB in solvent water to prepare a dispersible solution;
(2) Adding metal salt into the solution obtained in the step (1), adding organic ligands (ethylenediamine tetraacetic acid, lactic acid and the like) for reaction, and centrifuging to obtain the MOFs-coated nano silicon composite material;
(3) And (3) putting the material prepared in the step (2) and reducing metals (Cu, fe and Al) into a tubular furnace filled with argon for full carbonization to obtain nitrogen-doped Si @ MOFs with a buffer structure.
However, this technique has the following disadvantages:
(1) The preparation method comprises the following steps of uniformly dispersing nano-silicon into a solution through a dispersing agent such as CTAB (cetyltrimethyl ammonium bromide), and then adding an MOFs precursor, wherein the MOFs is intended to grow on the surface of the nano-silicon, but the surface of the nano-silicon is not modified in the mode, so that the MOFs can grow unevenly;
(2) The carbonization through a tube furnace filled with argon generally needs to be heated to over 800 ℃, the energy consumption is very high, and the production cost is higher for enterprise production.
(3) In the carbonization process, reducing metal is used, and hydrogen, oxygen and other components in the MOFs are volatilized, so that the atom utilization rate is not high, and raw materials are wasted.
To this end, in a first aspect of the invention, a silicon-based material is proposed. According to an embodiment of the present invention, the silicon-based material includes a core, a first cladding layer, and a second cladding layer.
According to an embodiment of the invention, the core comprises silicon-based material particles, which are negatively charged. The inventor finds that by adopting the silicon-based material particles with electronegativity, metal ions in the metal organic framework compound can be actively close to the silicon-based material particles with electronegativity according to the principle of opposite attraction, so that the growth uniformity of the metal organic framework compound can be improved, a first coating layer with the metal organic framework compound uniformly distributed is formed on the surface of the silicon-based material particles, and the three-dimensional network structure provided by the uniformly grown metal organic framework compound can better inhibit the volume expansion of silicon, so that the silicon can provide stable high capacity in the battery circulation process.
According to an embodiment of the present invention, in order to further reduce the volume expansion of the silicon-based material, the particle size of the core in the present application is 20nm to 2000nm, and may be, for example, 20nm, 50nm, 100nm, 200nm, 500nm, 1000nm, 1500nm, 2000nm, or the like. The inventors found that if the particle size of the core is too large, the structure of the formed first coating layer is unstable, and the first coating layer cannot effectively suppress the volume expansion of silicon during charge and discharge; if the particle size of the core is too small, the cost becomes too high. According to the invention, by controlling the particle size of the core, the cost can be controlled, and the stability of the formed first coating structure can be ensured, so that the volume expansion of silicon can be further inhibited in the charging and discharging processes.
According to an embodiment of the present invention, in order to further reduce the volume expansion of the silicon-based material, the particle size of the silicon-based material particles in the core is 20nm to 1000nm, preferably 20nm to 300nm. The inventors found that if the particle size of the silicon-based material particles is too large, the structure of the formed first coating layer is unstable, and the first coating layer cannot effectively suppress the volume expansion of silicon during charge and discharge; if the particle size of the silicon-based material particles is too small, the cost becomes too high. According to the invention, by controlling the particle size of the silicon-based material particles, the cost can be controlled, and the stability of the formed first coating layer structure can be ensured, so that the volume expansion of silicon can be further inhibited in the charging and discharging processes.
According to an embodiment of the present invention, the silicon-based material particles have the general formula SiO X Wherein X is more than or equal to 0 and less than or equal to 2. Therefore, compared with graphite negative electrode materials, the silicon-based material has higher capacity, so that the capacity of the lithium battery can be improved by taking the silicon-based material as the negative electrode material.
According to an embodiment of the invention, a first coating layer is formed on at least a portion of the surface of the inner core, the first coating layer comprising a metal organic framework compound. Specifically, as the silicon-based material core with electronegativity is adopted, the first coating layer with uniformly distributed metal framework compounds can be formed on the surface of the silicon-based material core, so that the volume expansion of the silicon-based material is reduced.
According to an embodiment of the present invention, in order to further reduce the volume expansion of the silicon-based material, the thickness of the first cladding layer is 10nm to 3000nm, and may be, for example, 10nm, 100nm, 500nm, 1000nm, 2000nm, 3000nm, or the like. The inventors have found that if the thickness of the first clad layer is too thick, li is not favored during charge and discharge + Insertion/removal of (a); if the thickness of the first cladding layer is too thin, the volume expansion of silicon in the charge and discharge process cannot be effectively inhibited, and the collapse of crystal lattices is further caused. By controlling the thickness of the first coating layer, the invention is not only beneficial to Li in the charge and discharge process + The insertion/extraction of (A) and (B) can also ensure the stability of the silicon-based material, thereby further being beneficial to inhibiting the volume expansion of silicon in the charging and discharging processes.
According to the bookIn an embodiment of the invention, the composition of the metal-organic framework compound in the first coating layer is not particularly limited, and the metal ion in the metal-organic framework compound may include Cu 2+ 、Zn 2+ 、Co 2+ The organic ligand in the metal-organic framework compound may include at least one of trimesic acid, terephthalic acid, and dimethylimidazole. This makes it possible to form a three-dimensional network structure on the surface of the inner core, and thus to suppress the volume expansion of silicon more effectively.
According to an embodiment of the invention, the second cladding layer comprises a carbon material, the second cladding layer being at least partially embedded in the first cladding layer. Specifically, the second coating layer including a carbon material formed on the first coating layer can improve the electrical conductivity of the silicon-based material, and the second coating layer is partially embedded in the pores of the metal-organic framework compound, i.e., the second coating layer and the metal-organic framework compound of the first coating layer cooperate to suppress the volume expansion of silicon.
According to an embodiment of the present invention, in order to further reduce the volume expansion of the silicon-based material, the thickness of the second cladding layer is 10nm to 3000nm, and may be, for example, 10nm, 100nm, 500nm, 1000nm, 2000nm, 3000nm, etc. The inventors found that if the thickness of the second clad layer is too thick, li is not favored + Insertion/removal of (a); if the thickness of the second cladding layer is too thin, the silicon volume expansion cannot be suppressed better. According to the invention, by controlling the thickness of the second coating layer, the conductivity can be enhanced, and the stability of the silicon-based material can be ensured, so that the second coating layer can further inhibit the volume expansion of silicon in the charging and discharging processes.
It should be noted that the composition of the carbon material in the second coating layer is not particularly limited as long as the purpose of providing a certain electrical conductivity to the bulk silicon-based material and inhibiting the volume expansion of silicon together with the first coating layer can be achieved, and the carbon material can be selected by those skilled in the art according to actual needs, and as a preferred scheme, the carbon material may include at least one of graphite, multi-walled carbon nanotube, single-walled carbon nanotube, graphene, and biomass carbon.
Therefore, the silicon-based material disclosed by the invention has lower volume expansion and higher conductivity, so that the specific capacity and the cycle performance of a lithium battery can be improved by taking the silicon-based material as a negative electrode material.
In a second aspect of the invention, the invention provides a method for preparing the above-mentioned silicon-based material. According to an embodiment of the invention, with reference to fig. 1, the method comprises the following steps:
s100: providing negatively charged particles of a silicon-based material
In the step, by providing silicon-based material particles with electronegativity, according to the principle of opposite attraction, in the subsequent mixing process of the silicon-based material particles, metal salt, organic ligand and solvent, metal ions in the metal salt can actively approach the silicon-based material particles with electronegativity, so that the growth uniformity of the metal organic framework compound can be improved, a first coating layer with the metal organic framework compound uniformly distributed is formed on the surfaces of the silicon-based material particles, and the three-dimensional network structure provided by the uniformly grown metal organic framework compound can better inhibit the volume expansion of silicon, so that the silicon-based material particles can provide stable high capacity in the battery circulation process.
According to an embodiment of the present invention, the silicon-based material particles with electronegativity may be prepared by the following steps:
s101: mixing surfactant, solvent and silicon-based material particles
In the step, the surface of the silicon-based material particles is modified by the surfactant, and negatively charged groups dissociated by the surfactant in the solution are attached to the surface of the nanometer silicon, so that the silicon-based material particles can be negatively charged, and the active approach of metal ions in the metal salt is facilitated according to the principle of opposite attraction, so that the growth uniformity of the metal organic framework compound can be improved, a first coating layer with the uniformly distributed metal organic framework compound is formed on the surface of the silicon-based material particles, and the three-dimensional network structure provided by the uniformly grown metal organic framework compound can better inhibit the volume expansion of silicon, so that the silicon-based material particles can provide stable high capacity in the battery circulation process.
According to a particular embodiment of the invention, the temperature of mixing is between 0 ℃ and 100 ℃. The inventors found that if the mixing temperature is too high, the evaporation rate becomes too high and the coating becomes nonuniform, and if the mixing temperature is too low, the reaction rate becomes too slow. According to the invention, by controlling the temperature conditions, the solvent in the reaction system can be further removed, and silicon-based material particles with electronegativity can be further obtained.
According to the specific embodiment of the invention, the mass ratio of the silicon-based material particles to the surfactant is 100: (1-5). The inventors found that if the ratio of the silicon-based material particles to the surfactant is too high, the electrochemical performance may be degraded by introducing the surfactant during the preparation of the battery, and if the ratio of the silicon-based material particles to the surfactant is too low, the silicon-based material particles may not be completely modified. According to the invention, the proportion of the surfactant to the silicon-based material particles is controlled, so that the modification of the surfaces of the silicon-based material particles can be further facilitated, and the silicon-based material particles with electronegativity can be further obtained.
According to the specific embodiment of the present invention, the composition of the above surfactant is not particularly limited as long as the purpose of negatively charging the silicon-based material particles can be achieved, and the surfactant may be selected by those skilled in the art according to actual needs, and as a preferable embodiment, the surfactant may include at least one of PSS, CTAB and PVA.
According to a specific embodiment of the present invention, the composition of the above solvent is not particularly limited, and may include at least one of water, ethanol, ethylene glycol, and propanol, for example.
S102: solid-liquid separation of the mixed solution obtained in step S101
In the step, liquid is removed through solid-liquid separation, and silicon-based material particles with electronegativity are obtained. The solid-liquid separation method is not particularly limited, and for example, centrifugal separation may be used.
S200: mixing metal salt, organic ligand, solvent and silicon-based material particles with electronegativity
In the step, metal salt, organic ligand and solvent are mixed and stirred with silicon-based material particles with electronegativity, so that a first coating layer comprising a metal organic framework compound can be formed on the surfaces of the silicon-based material particles, metal ions in the metal salt can actively approach the silicon-based material particles with electronegativity, the uniformity of the growth of the metal organic framework compound can be improved, the first coating layer with the metal organic framework compound uniformly distributed is formed on the surfaces of the silicon-based material particles, and a three-dimensional network structure provided by the uniformly grown metal organic framework compound can better inhibit the volume expansion of silicon, so that the silicon-based material particles can provide stable high capacity in the battery circulation process.
According to a particular embodiment of the invention, the temperature of mixing is between 40 ℃ and 60 ℃. The inventors have found that if the mixing temperature is too high, the metal organic framework compound in the first cladding layer cannot be uniformly grown on the silicon-based material particles, and if the mixing temperature is too low, the reaction is too slow, and in the present invention, by controlling the above temperature conditions, it is possible to further contribute to improving the uniformity of the growth of the metal organic framework compound, and further to more effectively suppress the volume expansion of silicon.
According to the specific embodiment of the invention, the mass ratio of the silicon-based material particles with electronegativity, the metal salt and the organic ligand is (1-5): (1-50): (1-50). The inventors have found that if the metal salt and organic ligand are used in too high an amount, the first coating layer formed is too thick to be beneficial to Li during charge and discharge + If the amount of the metal salt and the organic ligand is too low, the first coating layer formed is too thin to effectively suppress the volume expansion of silicon during the charge and discharge processes. The invention can further help to inhibit the volume expansion of silicon by controlling the proportion of the metal salt, the organic ligand and the silicon-based material particles with electronegativity.
According to a specific embodiment of the present invention, the composition of the above solvent is not particularly limited, and may include, for example, at least one of ethanol, ethylene glycol, and propanol.
S300: mixing and ball-milling a carbon material with the silicon-based material particles having the first coating layer obtained in S200
In this step, a second coating layer including a carbon material is formed on the first coating layer by mixing and ball-milling the carbon material with the silicon-based material particles having the first coating layer obtained in S200, and the second coating layer is at least partially embedded in the first coating layer. By mixing and ball-milling the carbon material with the silicon-based material particles having the first coating layer, on the one hand, a second coating layer comprising the carbon material can be formed on the first coating layer, improving the conductivity of the silicon-based material; on the other hand, partial second coating layer can be embedded into the pore channels of the metal organic framework compound, namely the second coating layer and the metal organic framework compound of the first coating layer cooperate to inhibit the volume expansion of silicon; on the other hand, directly form the second cladding layer including the carbon material through the ball-milling mode, both improved the convenience of operation, reduced the reaction energy consumption, improved atom utilization ratio again, and then avoided the problem that hydrogen, oxygen etc. that the high temperature carbonization process brought volatilize and cause the atom utilization ratio not high, raw materials are extravagant and the power consumption is high.
According to a specific embodiment of the present invention, the mass ratio of the silicon-based material particles having the first coating layer to the carbon material is 1: (1-4). The inventors found that if the amount of the carbon material is too high, the capacity of the material is reduced, and if the amount of the carbon material is too low, the second coating layer cannot be uniformly coated on the surface of the first coating layer. According to the invention, by controlling the proportion of the silicon-based material particles and the carbon material of the first coating layer, on one hand, a second coating layer comprising the carbon material can be formed on the first coating layer, so that the conductivity of the silicon-based material is improved; on the other hand, partial second coating layer can be embedded into the pore channels of the metal organic framework compound, namely the second coating layer and the metal organic framework compound of the first coating layer cooperatively inhibit the volume expansion of silicon; on the other hand, directly form the second cladding layer including the carbon material through the ball-milling mode, both improved the convenience of operation, reduced the reaction energy consumption, improved atom utilization ratio again, and then avoided the problem that hydrogen, oxygen etc. that the high temperature carbonization process brought volatilize and cause the atom utilization ratio not high, raw materials are extravagant and the power consumption is high. The manner of adding the carbon material is not particularly limited, and may be, for example, one-time addition or multiple-time addition.
According to the specific embodiment of the invention, the ball milling conditions are as follows: the ball material ratio is (5-10): 1, the rotating speed is 100r/min-500r/min, and the ball milling time is 1h-6h. The inventors have found that if the ball/material ratio is too high, the yield of the objective product is lowered, and if the ball/material ratio is too low, the polishing is not uniform. If the rotating speed is too high, the energy consumption is too high, and if the rotating speed is too low, the ball milling is not uniform. If the ball milling time is too long, meaningless energy consumption is caused, and if the ball milling time is too short, the ball milling is not uniform. According to the invention, by controlling the ball milling time, the second coating layer comprising the carbon material is favorably formed on the first coating layer, the conductivity of the silicon-based material is improved, and the second coating layer is at least partially embedded into the first coating layer and cooperates with the metal organic framework compound of the first coating layer to inhibit the volume expansion of silicon, the convenience of operation can be improved, the reaction energy consumption is reduced, and the atom utilization rate is improved, so that the problems of low atom utilization rate, raw material waste and high energy consumption caused by volatilization of components such as hydrogen, oxygen and the like in the high-temperature carbonization process are solved.
Therefore, the method for preparing the silicon-based material can be used for preparing the silicon-based material with lower volume expansion and higher conductivity while reducing reaction energy consumption and raw material waste, so that the specific capacity and the cycle performance of a lithium battery can be improved by taking the silicon-based material as a negative electrode material.
It should be noted that the features and advantages described above for the silicon-based material are equally applicable to the method for preparing the silicon-based material and will not be described in detail here.
In a third aspect of the present invention, a negative electrode sheet is provided. According to an embodiment of the invention, the negative electrode plate comprises the silicon-based material or the silicon-based material obtained by the method. In the silicon-based material, the first coating layer has the advantage of stable frame, the silicon-based material can provide high capacity, and the second coating layer provides good conductivity, so that the electrochemical performance of the negative electrode plate can be improved, and the specific capacity and the cycle performance of the lithium battery can be further improved. It should be noted that the features and advantages described above for the silicon-based material and the preparation method thereof are also applicable to the negative electrode plate, and are not described herein again.
In a fourth aspect of the present invention, a lithium battery is provided. According to an embodiment of the present invention, a lithium battery includes the above negative electrode tab. The negative plate can form a more stable solid electrolyte interface film, and reduce the repeated generation of the solid electrolyte interface film to seriously consume the electrolyte, thereby improving the specific capacity and the cycle performance of the lithium battery. The features and advantages described above for the silicon-based material and the method of preparation thereof apply equally to the lithium battery and are not described in further detail here.
The invention will now be described with reference to specific examples, which are intended to be illustrative only and not to be limiting in any way.
Example 1
1. Method for preparing silicon-based materials
(1) Weighing 0.1g of nano silicon powder with the particle size of 20nm-60nm, dissolving the nano silicon powder in 50mL of ethanol solution, adding 0.1mL1vt% PSS solution, mixing at 40 ℃, stirring, and performing centrifugal separation to obtain the electronegative nano silicon powder;
(2) Dissolving 2g of zinc acetate and 2g of dimethyl imidazole in 40ml of ethanol, and adding the electronegative nano silicon powder prepared in the step (1); stirring in water bath at 50 deg.c to evaporate solvent slowly to obtain nanometer silicon powder with the first coating layer;
(3) Weighing 1g of the nano silicon powder with the first coating layer prepared in the step (2), adding 2g of graphite, mixing and ball-milling; the ball-material ratio is 10.
And (3) characterizing the nano silicon powder with the first coating layer prepared in the step (2) by adopting a scanning electron microscope, and obtaining a scanning electron microscope image as shown in fig. 2-3.
2. Method for preparing negative plate
Weighing the components in a mass ratio of 90:5:5, mixing the silicon-based material, the conductive agent SP and the adhesive PAA with deionized water which is 1.2 times of the weight of the materials, mechanically stirring the mixture on a magnetic stirrer for 12 hours, and slowly and uniformly coating the stirred slurry on a copper foil;
putting the coated copper foil into a vacuum drying oven, drying for 12h at 80 ℃, taking out the copper foil on the next day, and cutting into a 12mm wafer by using a Shenzhenjianke crystal slicer to obtain a negative plate for later use;
3. method for preparing battery
The negative electrode sheet was transferred to a glove box to prepare for assembly of a full cell. The 2032 battery case, the PP diaphragm and the commercialized LB315 electrolyte are used, the prepared negative plate is used as a negative electrode, the lithium plate is used as a counter electrode to assemble a half battery, the assembled battery needs to be kept still for 12 hours, and then an electrochemical test is carried out.
Electrochemical performance test
Different technical tests are carried out by a new Velcro tester: including charge-discharge cycle and rate performance test. The test conditions were: constant temperature and humidity at 25 ℃, and voltage range of 0.01-1.5V;
0.5A. G of example 1 -1 The results of capacity retention after 100 cycles are shown in Table 1 at 0.5 A.g -1 The cycle plot at current density is shown in fig. 2, and the rate performance plot at different current densities is shown in fig. 4.
Example 2
The mass ratio of the silicon-based material particles having the first coating layer to the carbon material in step (3) of the method for producing a silicon-based material in example 2 was 1:1, other steps and conditions were the same as in example 1, and the battery was prepared and tested by the same method as in example 1.
0.5A. G of example 2 -1 The results of capacity retention after 100 cycles are shown in Table 1 at 0.5 A.g -1 The cycle plot at current density is shown in fig. 3, and the rate performance plot at different current densities is shown in fig. 5.
Example 3
The particle size of the nano silicon powder used in the step (1) of the method for preparing the silicon-based material in the embodiment is 1000-2000nm, other steps and conditions are the same as those of the embodiment 1, and a negative pole piece is prepared, and composition and electrochemical performance test of a half cell are carried out through the steps and conditions which are the same as those of the embodiment 1.
The cycle performance and rate performance test results of the battery prepared in the embodiment are similar to those of the battery prepared in the embodiment 1, and the battery has high cycle performance and rate performance.
Example 4
The mass of the silicon-based material particles used in step (1) of the method for preparing a silicon-based material in this example was 0.5g, and other steps and conditions were the same as in example 1, and a negative electrode sheet, a half-cell composition, and an electrochemical performance test were performed by the same steps and conditions as in example 1.
The cycle performance and rate performance test results of the battery prepared in the embodiment are similar to those of the battery prepared in the embodiment 1, and the battery has high cycle performance and rate performance.
Comparative example 1
Using graphite directly as a negative electrode, a negative electrode sheet was prepared, and assembly and electrochemical performance test of a half cell were performed by the same procedure and conditions as in example 1.
0.5A g of comparative example 1 -1 The results of capacity retention after 100 cycles are shown in Table 1 at 0.5 A.g -1 The cycle plot at current density is shown in fig. 6, and the rate performance plot at different current densities is shown in fig. 8.
Comparative example 2
The nano silicon is directly used as a negative electrode, and a negative electrode pole piece is prepared, and assembly and electrochemical performance test of a half cell are carried out by the same steps and conditions as those in the example 1.
0.5A g of comparative example 2 -1 The results of capacity retention after 100 cycles are shown in Table 1 at 0.5 A.g -1 The cycle plot at current density is shown in fig. 7, and the rate performance plot at different current densities is shown in fig. 9.
TABLE 1 at 0.5A g -1 Current density of (2) capacity retention after 100 cycles
| Example numbering | Capacity retention (%) |
| Example 1 | 74.67 |
| Example 2 | 65.35 |
| Comparative example 1 | 77.48 |
| Comparative example 2 | 1.48 |
As can be seen from fig. 2 and 3, the surfaces of the first coating layer metal organic framework compounds coating the silicon powder are in a loose structure, but are connected with each other. When the first coating layer is very uniform after magnification, the MOFs successfully coats nano-silicon therein, so that the volume expansion of silicon in the charging and discharging process can be inhibited to a certain extent.
It can be seen from fig. 4 and 5 that the batteries prepared in examples 1-2 have higher specific capacity and cycle retention rate. Wherein the battery prepared in example 1 was at 0.5A · g -1 The specific capacity of the second discharge at the current density of the electrode is 1077.2mAh g -1 And the specific capacity after 100 cycles is 804.3mAh g -1 The capacity retention rate is 74.67%; the battery prepared in example 2 was at 0.5A g -1 The specific capacity of the second discharge at the current density is 1149mAh g -1 And the specific capacity after 100 cycles is 750.9mAh g -1 The capacity retention rate was 65.35%. From the aspect of the cycle performance and the specific capacity performance, the capacity performance of the battery prepared in example 1-2 is much higher than that of the battery prepared in comparative example 1, in which graphite is directly used as the negative electrode (as shown in fig. 8, the specific discharge capacity after 100 cycles is 270.76mAh g) -1 ) The cycle performance is better than that of the comparative example 2 which directly uses nano silicon as the negative electrode (as shown in figure 9, 100 times of cycles are not completed).
It can be seen from fig. 6 and 7 that the batteries prepared in examples 1-2 have higher specific capacity and cycle retention rate. It is composed ofIn example 1, the battery was manufactured at 0.1A · g -1 The specific capacity of the second discharge at the current density of (A) is 1134.5mAh g -1 Has undergone 2 A.g -1 High current density cycling and Return 0.1A g -1 The 30 th discharge capacity was 1081.6mAh · g -1 The capacity retention rate is 95.34%; the battery prepared in example 2 was at 0.1A · g -1 The specific capacity of the second discharge at the current density of (A) was 1215.6mAh g -1 Has undergone 2 A.g -1 High current density cycling and Return 0.1A g -1 The 30 th discharge capacity was 1086.5mAh · g -1 The capacity retention rate was 89.38%. The specific capacity of the batteries prepared in the examples 1-2 is higher than that of the battery prepared in the comparative example 1 which directly uses graphite as a negative electrode (as shown in figure 10), and the cycle performance of the battery is better than that of the battery prepared in the comparative example 2 which directly uses nano silicon as the negative electrode (as shown in figure 11). Therefore, the negative electrode material prepared in the embodiment 1-2 can keep good electrochemical performance under high-rate charge and discharge of the battery, and can meet the current requirements of quick charge and quick discharge.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (10)
1. A silicon-based material, comprising:
a core comprising silicon-based material particles, the silicon-based material particles being negatively charged;
a first coating layer formed on at least a portion of a surface of the inner core, the first coating layer comprising a metal organic framework compound;
a second cladding layer formed on at least a portion of a surface of the first cladding layer, the second cladding layer comprising a carbon material, the second cladding layer being at least partially embedded in the first cladding layer.
2. The silicon-based material of claim 1, wherein the core has a particle size of 20nm to 2000nm, the first cladding layer has a thickness of 10nm to 3000nm, and the second cladding layer has a thickness of 10nm to 3000nm.
3. The silicon-based material according to claim 1, wherein the silicon-based material particles have a general formula of SiO X Wherein X is more than or equal to 0 and less than or equal to 2;
optionally, the carbon material comprises at least one of graphite, multi-walled carbon nanotubes, single-walled carbon nanotubes, graphene, biomass char;
optionally, the metal ion in the metal-organic framework compound comprises Cu 2+ 、Zn 2+ 、Co 2+ The organic ligand in the metal-organic framework compound comprises at least one of trimesic acid, terephthalic acid and dimethyl imidazole.
4. A method of making a silicon-based material according to any one of claims 1-3, comprising:
(1) Providing silicon-based material particles with electronegativity;
(2) Mixing a metal salt, an organic ligand, a solvent with the negatively charged silicon-based material particles to form a first coating layer comprising a metal-organic framework compound on the surface of the silicon-based material particles;
(3) Mixing and ball-milling a carbon material with the silicon-based material particles having the first coating layer obtained in step (2) to form a second coating layer comprising the carbon material on the first coating layer, and the second coating layer being at least partially embedded in the first coating layer.
5. The method according to claim 4, wherein said negatively charged particles of a silicon-based material are prepared by the steps of:
(1-1) mixing a surfactant, a solvent and silicon-based material particles;
and (1-2) carrying out solid-liquid separation on the mixed solution obtained in the step (1-1) to obtain silicon-based material particles with electronegativity.
6. The method of claim 4, wherein in step (2), the temperature of the mixing is 40 ℃ to 60 ℃.
7. The method according to claim 4, wherein the mass ratio of the negatively charged silicon-based material particles, the metal salt and the organic ligand is (1-5): (1-50): (1-50).
8. The method according to claim 4, wherein in the step (3), the mass ratio of the silicon-based material particles having the first coating layer to the carbon material is 1: (1-4);
optionally, the ball milling conditions are: the ball material ratio is (5-10): 1, the rotating speed is 100r/min-500r/min, and the ball milling time is 1h-6h.
9. A negative electrode plate comprising the silicon-based material according to any one of claims 1 to 3 or the silicon-based material obtained by the method according to any one of claims 4 to 8.
10. A lithium battery comprising the negative electrode sheet of claim 9.
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