CN112952059A - Silicon-based negative electrode material and preparation method and application thereof - Google Patents
Silicon-based negative electrode material and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to a silicon-based negative electrode material and a preparation method and application thereof. The preparation method adopts a liquid phase doping method, the organic carbon source and the carbon nano tube are uniformly mixed under the liquid phase condition, the organic carbon source can be pyrolyzed to form the carbon coating layer through one-step carbonization, and the carbon nano tube can be uniformly embedded into the carbon coating layer, so that the prepared silicon-based negative electrode material has excellent conductivity, meets the quality requirement of the lithium ion battery, can be used for preparing the negative electrode plate of the lithium ion battery, simplifies the operation steps, can accurately control the doping amount of the carbon nano tube, and improves the doping stability of the carbon nano tube.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a silicon-based negative electrode material and a preparation method and application thereof.
Background
In recent years, with the increasing demand for portable and high-performance energy storage devices, the energy field, particularly lithium ion batteries and super capacitors, attracts people's extensive attention. The lithium ion battery cathode material widely used in industry is graphite carbon material. The graphite cathode material has excellent conductivity and good chemical stability, is an ideal carbon matrix as an active material of a lithium ion battery, and at present, 90% of the lithium ion battery cathode materials adopt the graphite cathode material. However, graphite cathode materials, although having the advantages of high conductivity and stability, are troublesome in energy density ceilings and have been currently developed to approach its theoretical maximum of 372 mAh/g. Experimental research shows that silicon is the anode material with the largest theoretical capacity at present, and lithium forms Li in silicon4.4When Si is used, the specific capacity is up to 4200mAh/g, which is far higher than the theoretical capacity of graphite, and the Si has the advantages of low lithium intercalation potential and low cost. Therefore, the silicon-based negative electrode material is expected to replace a graphite negative electrode material and becomes a next-generation lithium ion battery negative electrode material.
The research on the silicon-based anode material mainly focuses on the silicon-carbon anode material and the silicon-oxygen anode material, and the electrical conductivity of the silicon-carbon anode material and the silicon-oxygen anode material is poor and far lower than that of the graphite anode material, so that the material capacity and the first efficiency are low. The current research mainly reduces the surface defects of the silicon-based negative electrode material in a carbon coating mode and improves the conductivity of the material. However, the conductivity of the silicon-based negative electrode material is improved only by coating and modifying the surface carbon layer, so that the conductivity of the silicon-based negative electrode material needs to be improved by other approaches. At present, in the pulping process of the silicon-based negative electrode material, a small amount of PVP (polyvinylpyrrolidone) dispersed carbon nanotubes are added in some enterprises to improve the conductivity of the material and improve the capacity exertion of the negative electrode material, but the method does not fundamentally solve the problem of poor conductivity of the silicon-based negative electrode material. Therefore, the prior art discloses a method for coating the carbon nanotubes on the surface of the silicon-based negative electrode material, so as to further improve the conductivity.
CN110828786A discloses a preparation method of a long-circulating silicon oxide/carbon composite negative electrode material, which comprises the steps of doping and crushing SiO powder, coating a layer of pyrolytic carbon on the surface of the doped SiO powder by CLVD (chemical liquid vapor deposition), drying to obtain the pyrolytic carbon-coated doped SiO powder, then generating carbon nanotubes on the outer surface of the pyrolytic carbon in situ by catalytic cracking of a catalyst by CLVD, drying to obtain the doped SiO powder coated by the carbon nanotubes and the pyrolytic carbon in a composite manner, and finally crushing, grading and removing impurities to obtain the long-circulating silicon oxide/carbon composite negative electrode material. The method for in-situ generation of the carbon nano tube comprises the steps of soaking the doped SiO powder coated with the pyrolytic carbon in a liquid carbon source, mixing the doped SiO powder with a catalyst, heating to generate high temperature, boiling the liquid carbon source under the protection of inert gas, and carrying out catalytic cracking on the outer surface of the pyrolytic carbon to generate the carbon nano tube in situ. The method for in-situ generation of carbon nanotubes has the following problems: firstly, the carbon nano tubes are generated in situ on the surface of the pyrolytic carbon layer by adopting a catalytic method, the generated carbon nano tubes only exist on the surface of a material, the quantity of the generated carbon nano tubes is difficult to control, and the combination of the carbon nano tubes on the surface of the pyrolytic carbon is unstable and is easy to peel off in the pulping and material circulation processes; secondly, a catalyst is required to be added to catalyze the production of the carbon nano tube, metal impurities are introduced in the process, the impurities can cause self-discharge of the battery, and the cycle life of the battery is shortened; thirdly, impurities introduced by adding the catalyst need to be removed by acid washing, the process is complex, and the scale-up production is difficult.
CN111769266A discloses a silicon-based negative electrode material and a lithium ion battery containing the silicon-based negative electrode material, wherein the silicon-based negative electrode material contains a silicon-based material; the surface of the carbon layer contains hydroxyl, and the carbon layer is coated on the surface of the silicon-based material; a polymer layer, wherein the polymer layer comprises polymers and/or polymer monomers which can be bonded with hydroxyl, and the polymer layer coats the surface of the carbon layer; and the carbon nano tube is connected to the surface of the polymer layer through a hydrogen bond and/or a covalent bond. The preparation method of the silicon-based anode material comprises the following steps: s1, coating a carbon layer on the surface of the silicon-based material to obtain a carbon-coated silicon-based material; s2, uniformly dispersing a polymer or a polymer monomer in a nonpolar solvent to obtain a polymer modified solution; s3, uniformly dispersing the carbon-coated silicon-based material in the polymer modification solution, and then filtering, cleaning and drying to obtain a secondary coated silicon-based material; and S4, adding the secondary coated silicon-based material into the carbon nano tube dispersion liquid, uniformly stirring, and then filtering, cleaning and drying to obtain the carbon nano tube. The silicon-based negative electrode material uses a large amount of polymers, the production cost is improved, the preparation method only depends on the reaction of a liquid phase system, the reaction degree cannot be controlled, and the binding force of the generated coating layer is poor.
CN109841823A discloses a negative electrode material, and an electrochemical device and an electronic device using the same, wherein the negative electrode material is a coated negative electrode material, and the negative electrode material is prepared by obtaining silicon compound SiOx particles coated with an oxide MeOy layer by a sintering method, and then uniformly dispersing the silicon compound SiOx particles in a carbon nanotube dispersion liquid for carbonization to form a double-layer coating structure in which an inner oxide MeOy layer is coated with an outer carbon nanotube layer, so as to improve the conductivity of the material. However, this production method has the following problems: firstly, the carbon nano tube is directly wrapped on the surface of the oxide layer and is combined with the negative electrode substrate coated with the oxide by virtue of Van der Waals force, and the carbon nano tube is easy to peel off in the later material mixing pulping and battery circulating processes, so that the conductivity is reduced; secondly, the proportion of the added carbon nano tube is too high, the proportion of the added carbon nano tube is 0.1-10 wt% of the negative electrode material, the carbon nano tube is of a hydrophobic structure, the viscosity of a dispersion system is too high due to excessive addition, the negative electrode base material is agglomerated in the drying process, and the negative electrode material is agglomerated after later carbonization, so that the particle size distribution and the cycle performance of the material are influenced.
In summary, there is a need to develop a silicon-based negative electrode material and a preparation method thereof, which can simplify the preparation method, precisely control the doping amount of the carbon nanotubes, improve the doping stability of the carbon nanotubes, improve the conductivity of the silicon-based negative electrode material, and meet the quality requirements of the lithium ion battery.
Disclosure of Invention
In view of the problems in the prior art, the invention provides a silicon-based anode material, a preparation method and application thereof. The preparation method adopts a liquid phase doping method, the organic carbon source and the carbon nano tube are uniformly mixed under the liquid phase condition, the organic carbon source can be pyrolyzed to form the carbon coating layer through one-step carbonization, and the carbon nano tube can be uniformly embedded into the carbon coating layer, so that the prepared silicon-based negative electrode material has excellent conductivity, meets the quality requirement of the lithium ion battery, can be used for preparing the negative electrode plate of the lithium ion battery, simplifies the operation steps, can accurately control the doping amount of the carbon nano tube, and improves the doping stability of the carbon nano tube.
In order to achieve the purpose, the invention adopts the following technical scheme:
one objective of the present invention is to provide a silicon-based negative electrode material, which includes a silicon-based negative electrode substrate and a carbon layer, wherein the carbon layer is doped with carbon nanotubes and coated on the surface of the silicon-based negative electrode substrate.
The silicon-based negative electrode material is of a coating structure, so that on one hand, the surface defects of a silicon-based negative electrode substrate are reduced and the first coulombic efficiency is improved through coating of the carbon layer doped with the carbon nano tubes, on the other hand, the conductivity of the silicon-based negative electrode material can be effectively improved through doping the carbon nano tubes in the carbon layer, so that the first coulombic efficiency and the first discharge capacity of the silicon-based negative electrode material are obviously improved, and the cycle performance is also improved.
As a preferred technical solution of the present invention, the silicon-based negative electrode substrate includes any one of or a combination of at least two of silicon monoxide, nano-silicon or silicon carbon, and typical but non-limiting examples of the combination are: a combination of silica and nano-silicon, a combination of nano-silicon and silicon carbon, a combination of silica and silicon carbon, or the like.
Preferably, the carbon layer is an amorphous carbon layer.
Preferably, the carbon nanotubes are single-walled carbon nanotubes and/or multi-walled carbon nanotubes.
The second purpose of the invention is to provide a preparation method of the silicon-based anode material, which comprises the following steps:
(1) weighing an organic carbon source and a carbon nano tube, adding an organic solvent, and uniformly stirring to obtain a dispersion liquid;
(2) and (2) adding a silicon-based negative electrode base material into the dispersion liquid obtained in the step (1), uniformly stirring, and sequentially drying, roasting, cooling and sieving to obtain the silicon-based negative electrode material.
The preparation method of the invention takes the organic carbon source as the coating agent, takes the carbon nano tube as the doping agent, realizes liquid phase doping by uniformly mixing the organic carbon source and the carbon nano tube in the organic solvent, and forms an amorphous carbon coating layer on the surface of the silicon-based cathode substrate after the organic carbon source is decomposed at high temperature through one-step carbonization of high-temperature sintering after drying, and simultaneously uniformly dopes the carbon nano tube in the carbon coating layer, and realizes effective combination between the carbon nano tube and the carbon coating layer, thereby effectively improving the conductivity of the carbon coating layer and the whole silicon-oxygen cathode material system.
In a preferred embodiment of the present invention, the mass ratio of the organic carbon source to the silicon-based negative electrode substrate is (0.5 to 30):100, for example, (0.5: 100), (1: 100), (5: 100), (8: 100), (10: 100), (15: 100), (20: 100), (25: 100) or (30: 100), and preferably, (0.5 to 10):100, but the present invention is not limited to the above-mentioned values, and other values not listed in the above-mentioned value range are also applicable.
Preferably, the mass ratio of the carbon nanotubes to the silicon-based negative electrode substrate is (0.01-0.5):100, for example, 0.01:100, 0.03:100, 0.05:100, 0.07:100, 0.1:100, 0.2:100, 0.4:100, or 0.5:100, and preferably (0.01-0.1):100, but not limited to the enumerated values, and other unrecited values within this range of values are equally applicable.
Experiments of the inventor of the present application show that the addition amount of the carbon nanotubes is not suitable to be too high, because the viscosity of the dispersion liquid is increased after the carbon nanotubes are added, and the dried silicon-based negative electrode material is easy to agglomerate, and can adversely affect the performance of the silicon-based negative electrode material. Moreover, the addition form of the carbon nanotube can be a solid form of a single-walled carbon nanotube and/or a multi-walled carbon nanotube, and can also be a PVP (polyvinylpyrrolidone) dispersion liquid containing the carbon nanotube, and the addition form can be reasonably selected by a person skilled in the art according to the polarity of the actual situation; when a dispersion of PVP (polyvinylpyrrolidone) containing carbon nanotubes is used, the amount of PVP added is effectively removed in the subsequent drying and baking processes, depending on the mass of carbon nanotubes contained in the dispersion.
It is worth to be noted that, because the organic carbon sources are more in variety and the final carbon coating amounts after pyrolysis are different, in order to conveniently characterize the prepared silicon-based negative electrode material, the invention is uniformly characterized by the initial raw material mass ratio, for example, the mass ratio of the organic carbon sources to the silicon-based negative electrode substrate is 5:100, and the mass ratio of the carbon nanotubes to the silicon-based negative electrode substrate is 0.05:100, so that the silicon-based negative electrode material doped with 5% of the carbon nanotubes is prepared.
As a preferred technical scheme of the invention, the organic carbon source in the step (1) comprises any one or a combination of at least two of phenolic resin, glucose, citric acid or asphalt, and typical but non-limiting examples of the combination are as follows: a combination of phenolic resin and glucose, a combination of glucose and citric acid, a combination of citric acid and bitumen or a combination of phenolic resin and bitumen, etc.
Preferably, the organic carbon source of step (1) has a median particle size of 100 μm or less, for example 0.1 μm, 0.5 μm, 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, 30 μm, 50 μm or 70 μm, preferably 0.1 to 10 μm, but is not limited to the recited values, and other values not recited in this range are equally applicable.
In a preferred embodiment of the present invention, the organic solvent in step (1) is an alcohol.
Preferably, the organic solvent of step (1) comprises any one of methanol, ethanol, isopropanol or propanol or a combination of at least two of these, typical but non-limiting examples being: a combination of methanol and ethanol, a combination of ethanol and isopropanol, a combination of isopropanol and propanol or a combination of methanol and propanol, etc., preferably methanol and/or ethanol.
Preferably, the ratio between the volume of the organic solvent and the mass of the organic carbon source in step (1) is (0.5-50) mL:1g, such as 0.5mL:1g, 1mL:1g, 5mL:1g, 10mL:1g, 20mL:1g, 30mL:1g, 40mL:1g, or 50mL:1g, but not limited to the recited values, and other values within this range are equally applicable.
Preferably, the stirring time in step (1) is 1 to 10 hours, such as 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 4 hours, 4.5 hours, 5 hours, 7 hours, 9 hours or 10 hours, etc., preferably 1 to 5 hours, but not limited to the recited values, and other values not recited in the range of values are also applicable.
In a preferred embodiment of the present invention, the silicon-based negative electrode material in step (2) has a median particle diameter of 0.05 to 20 μm, for example, 0.05 μm, 1 μm, 3 μm, 5 μm, 6 μm, 8 μm, 10 μm, 15 μm, or 20 μm, preferably 1 to 8 μm, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.
Preferably, the stirring time in step (2) is 1 to 10 hours, such as 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 4 hours, 4.5 hours, 5 hours, 7 hours, 9 hours or 10 hours, etc., preferably 1 to 5 hours, but not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the drying of step (2) comprises any one of or a combination of at least two of thermal evaporation, rotary evaporation, freeze drying or spray drying, typical but non-limiting examples of which are: a combination of thermal evaporation and rotary evaporation, a combination of rotary evaporation and freeze drying, a combination of freeze drying and spray drying or a combination of thermal evaporation and spray drying, etc., preferably rotary evaporation.
As a preferable technical scheme of the invention, the roasting in the step (2) is carried out in a protective gas atmosphere.
Preferably, the shielding gas comprises any one or a combination of at least two of argon, nitrogen, helium or argon-hydrogen gas mixture, wherein the argon-hydrogen gas mixture belongs to the commercial products commonly used in the field.
Preferably, the temperature for the calcination in step (2) is 600-.
Preferably, the calcination in step (2) is carried out for a holding time of 1 to 8 hours, for example 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, etc., preferably 2 to 6 hours, but not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the roasting carbonization equipment in the step (2) comprises any one of a tubular carbonization furnace, a box carbonization furnace, a roller kiln, a pushed slab kiln or a chemical vapor deposition furnace or a combination of at least two of the foregoing.
Preferably, the cooling in step (2) is air cooling, i.e. natural cooling to room temperature.
Preferably, the silicon-based negative electrode material of step (2) has a median particle diameter of 1 to 30 μm, for example, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 20 μm, 25 μm or 30 μm, and preferably 3 to 10 μm, but is not limited to the recited values, and other values not recited in this numerical range are also applicable.
As a preferred technical scheme of the invention, the preparation method comprises the following steps:
(1) weighing an organic carbon source and a carbon nano tube, wherein the mass ratio of the organic carbon source to the silicon-based negative electrode substrate is (0.5-30):100, the mass ratio of the carbon nano tube to the silicon-based negative electrode substrate is (0.01-0.5):100, adding an organic solvent, and stirring for 1-10 hours to obtain a dispersion liquid; wherein the organic carbon source comprises any one or the combination of at least two of phenolic resin, glucose, citric acid or asphalt, and the median particle size of the organic carbon source is less than or equal to 100 mu m; the organic solvent comprises any one or the combination of at least two of methanol, ethanol, isopropanol or propanol, and the ratio of the volume of the organic solvent to the mass of the organic carbon source is (0.5-50) mL:1 g;
(2) adding a silicon-based negative electrode base material with the median particle size of 0.05-20 microns into the dispersion liquid obtained in the step (1), stirring for 1-10h, drying by rotary evaporation, heating to 600-1200 ℃ in a protective gas atmosphere, roasting, keeping the temperature for 1-8h, cooling by air cooling, and sieving to obtain the silicon-based negative electrode material with the median particle size of 1-30 microns.
It should be noted that, although the prior art indeed discloses a modification method for carbon coating and in-situ generation of carbon nanotubes for lithium battery negative electrode materials, the modification method is to generate carbon nanotubes in situ by Chemical Liquid Vapor Deposition (CLVD) reaction under the catalytic action of a catalyst, the carbon nanotubes generated in situ are difficult to control, the process route is complicated, the scale-up production is difficult, and the improvement on the electrical conductivity is limited, which is different from the preparation method of the present invention. However, the differences in the technical approaches to solve the problems directly result in the differences in the emphasis points and the attention points during the design of the technical solutions, such as the material selection, the material ratio, and the process parameters, which all have great differences. Therefore, the invention is not comparable to the technical scheme of modifying the silicon-based anode material in the prior art.
The third purpose of the invention is to provide the application of the silicon-based negative electrode material in one purpose, which is used for preparing a negative electrode plate of a lithium ion battery.
Compared with the prior art, the invention at least has the following beneficial effects:
(1) the silicon-based negative electrode material is of a coating structure, so that on one hand, the surface defects of a silicon-based negative electrode substrate are reduced and the first coulombic efficiency is improved by coating the carbon layer doped with the carbon nano tubes, on the other hand, the conductivity of the silicon-based negative electrode material can be effectively improved by doping the carbon nano tubes in the carbon layer, so that the first coulombic efficiency and the first discharge capacity of the silicon-based negative electrode material are obviously improved, the cycle performance is also improved, the quality requirement of a lithium ion battery is met, and the silicon-based negative electrode material can be used for preparing a negative electrode plate of the lithium ion battery;
(2) the preparation method of the invention takes the organic carbon source as the coating agent and the carbon nano tube as the doping agent, realizes liquid phase doping by uniformly mixing the organic carbon source and the carbon nano tube in the organic solvent, and obtains the carbon nano tube doped carbon-coated silicon-based negative electrode material through one-step carbonization of high-temperature sintering after drying.
Drawings
FIG. 1 is a schematic structural diagram of a silicon-based anode material according to the present invention;
fig. 2 is an SEM image of the silicon-based negative electrode material according to example 1 of the present invention;
FIG. 3 is a graph comparing the results of half-cell tests on silicon-based negative electrode materials according to examples 1 and 2 of the present invention and comparative examples 1 and 2;
in the figure: 1-a silicon-based negative electrode substrate; a 2-carbon layer; 3-carbon nanotubes.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
To better illustrate the invention and to facilitate the understanding of the technical solutions thereof, typical but non-limiting examples of the invention are as follows:
as shown in fig. 1, the silicon-based negative electrode material of the present invention includes a silicon-based negative electrode substrate 1 and a carbon layer 2, wherein the carbon layer 2 is doped with carbon nanotubes 3 and coated on the surface of the silicon-based negative electrode substrate 1.
Example 1
The embodiment provides a preparation method of a silicon-based anode material, which comprises the following steps:
(1) weighing 5g of asphalt powder with the median particle size of 5.1 mu m according to the mass ratio of the organic carbon source to the silicon-based negative electrode substrate of 5:100, weighing 0.05g of single-walled carbon nanotube according to the mass ratio of the carbon nanotube to the silicon-based negative electrode substrate of 0.05:100, adding 200mL of ethanol as an organic solvent, and stirring for 3 hours to obtain a dispersion liquid;
(2) adding 100g of silica with the median particle size of 5.1 mu m into the dispersion liquid obtained in the step (1), stirring for 3h, adding into a rotary evaporator, drying at 50 ℃ through rotary evaporation, transferring the dried powder into an alumina crucible, putting the alumina crucible into a tubular carbonization furnace, heating to 950 ℃ in an argon atmosphere, roasting, keeping the temperature for 2h, cooling by air cooling, and sieving by using a 200-mesh sieve to obtain the 5% carbon nanotube doped 5% carbon-coated silicon-based negative electrode material.
Example 2
The embodiment provides a preparation method of a silicon-based anode material, which comprises the following steps:
(1) weighing 10g of phenolic resin with the median particle size of 9.3 mu m according to the mass ratio of the organic carbon source to the silicon-based negative electrode substrate of 10:100, weighing 0.1g of multi-walled carbon nanotube according to the mass ratio of the carbon nanotube to the silicon-based negative electrode substrate of 0.1:100, adding 200mL of ethanol serving as an organic solvent, and stirring for 3 hours to obtain a dispersion liquid;
(2) adding 100g of silica with the median particle size of 5.1 mu m into the dispersion liquid obtained in the step (1), stirring for 3h, adding into a rotary evaporator, drying at 50 ℃ through rotary evaporation, transferring the dried powder into an alumina crucible, putting the alumina crucible into a tubular carbonization furnace, heating to 900 ℃ in argon atmosphere, roasting, keeping the temperature for 2h, cooling by air cooling, and sieving by using a 200-mesh sieve to obtain the 10% carbon nanotube doped 10% carbon-coated silicon-based negative electrode material.
Example 3
This example provides a method for preparing a silicon-based negative electrode material, except that the single-walled carbon nanotube in step (1) is replaced by 0.05g to 0.01g, and the other conditions are exactly the same as those in example 1, so as to obtain a silicon-based negative electrode material with 1%% carbon nanotube doped with 5% carbon coating.
Example 4
This example provides a method for preparing a silicon-based anode material, except that the single-walled carbon nanotube in step (1) is replaced by 0.05g to 0.5g, and the other conditions are exactly the same as those in example 1, so as to obtain a silicon-based anode material with 50%% carbon nanotube doped with 5% carbon.
Example 5
This example provides a method for preparing a silicon-based negative electrode material, except that the single-walled carbon nanotubes in step (1) are replaced by 0.005g from 0.05g, and the other conditions are exactly the same as those in example 1, so as to obtain a silicon-based negative electrode material doped with 0.5%% of carbon nanotubes and coated with 5% of carbon.
Example 6
This example provides a method for preparing a silicon-based anode material, except that the single-walled carbon nanotube in step (1) is replaced by 0.05g to 0.6g, and the other conditions are exactly the same as those in example 1, so as to obtain a silicon-based anode material doped with 60% carbon nanotube and coated with 5% carbon.
Comparative example 1
The comparative example provides a preparation method of a silicon-based negative electrode material, except that 0.05g of single-walled carbon nanotubes in the step (1) are omitted, and other conditions are completely the same as those in the example 1, so that the silicon-based negative electrode material with 5% carbon coating is prepared.
Comparative example 2
In the comparative example, the silicon-based negative electrode substrate (silicon monoxide) described in example 1 was used as a silicon-based negative electrode material without any treatment.
The silicon-based negative electrode materials in the embodiments and the comparative examples are subjected to characterization of median particle size, specific surface area and powder conductivity, are uniformly mixed with SP, CMC and SBR according to a mass ratio of 90:5:2:3, are subjected to beating, coating and rolling to form a negative electrode piece on a copper mesh, and then a lithium piece is used as a counter electrode to prepare a button cell for charge and discharge tests, wherein the specific test system is as follows: 1500mAh/g specific capacity, 0.1C CC to voltage 0.01V, 0.02C CC to voltage less than or equal to 0.005V, standing for 10min, then discharging to 1.5V at constant current of 0.1C, and circulating for 20 weeks; wherein, the powder conductivity is tested by adopting a four-probe method; the specific test results are shown in table 1.
TABLE 1
From table 1, the following points can be seen:
(1) compared with the comparative examples 1 and 2, the conductivity of the silicon-based negative electrode substrate can be effectively improved through carbon coating, the first discharge capacity and the first discharge capacity are both improved, and the cycle performance is obviously improved; after the carbon nano tubes are further doped in the coated carbon layer, the conductivity of the material is greatly improved compared with a sample coated by pure carbon, the first efficiency and the first discharge capacity are both improved, and the cycle performance of the material is also greatly improved;
(2) compared with the embodiment 1, the embodiment 5 and the embodiment 6, the doping proportion of the carbon nano tube in the carbon coating layer is not too low or too high, the doping proportion is too low, the performance improvement of the material is not particularly obvious, the doping proportion is too high, negative effects are generated, the dried material is agglomerated due to the fact that the carbon nano tube is dispersed in the organic solvent and the viscosity is too high, the particle size of the finally prepared negative electrode material is large, the volume expansion is large in the charging and discharging process, and the cycle performance of the material is influenced;
(3) the preparation method of the invention takes the organic carbon source as the coating agent and the carbon nano tube as the doping agent, realizes liquid phase doping by uniformly mixing the organic carbon source and the carbon nano tube in the organic solvent, and obtains the carbon nano tube doped carbon-coated silicon-based negative electrode material through one-step carbonization of high-temperature sintering after drying.
It is worth to be noted that the raw materials and equipment used in the present invention are all common raw materials and equipment in the field unless otherwise specified; the methods used in the present invention are conventional in the art unless otherwise specified.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, alterations and equivalents of the above embodiments according to the technical spirit of the present invention are still within the protection scope of the technical solution of the present invention.
The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.
It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.
Claims (10)
1. The silicon-based negative electrode material is characterized by comprising a silicon-based negative electrode substrate and a carbon layer, wherein the carbon layer is doped with carbon nanotubes and coated on the surface of the silicon-based negative electrode substrate.
2. The silicon-based anode material as claimed in claim 1, wherein the silicon-based anode substrate comprises any one or a combination of at least two of silicon monoxide, nano-silicon or silicon carbon;
preferably, the carbon layer is an amorphous carbon layer;
preferably, the carbon nanotubes are single-walled carbon nanotubes and/or multi-walled carbon nanotubes.
3. A method for preparing a silicon-based anode material according to claim 1 or 2, wherein the method comprises the following steps:
(1) weighing an organic carbon source and a carbon nano tube, adding an organic solvent, and uniformly stirring to obtain a dispersion liquid;
(2) and (2) adding a silicon-based negative electrode base material into the dispersion liquid obtained in the step (1), uniformly stirring, and sequentially drying, roasting, cooling and sieving to obtain the silicon-based negative electrode material.
4. The preparation method according to claim 3, wherein the mass ratio of the organic carbon source to the silicon-based anode substrate is (0.5-30):100, preferably (0.5-10): 100;
preferably, the mass ratio of the carbon nanotubes to the silicon-based negative electrode substrate is (0.01-0.5):100, preferably (0.01-0.1): 100.
5. The method according to claim 3 or 4, wherein the organic carbon source of step (1) comprises any one of or a combination of at least two of phenolic resin, glucose, citric acid or pitch;
preferably, the median particle size of the organic carbon source of step (1) is 100 μm or less, preferably 0.1 to 10 μm.
6. The process according to any one of claims 3 to 5, wherein the organic solvent in the step (1) is an alcohol;
preferably, the organic solvent in step (1) comprises any one or a combination of at least two of methanol, ethanol, isopropanol or propanol, preferably methanol and/or ethanol;
preferably, the ratio between the volume of the organic solvent and the mass of the organic carbon source in step (1) is (0.5-50) mL:1 g;
preferably, the stirring time in step (1) is 1 to 10 hours, preferably 1 to 5 hours.
7. The preparation method according to any one of claims 3 to 6, wherein the silicon-based anode material of step (2) has a median particle diameter of 0.05 to 20 μm, preferably 1 to 8 μm;
preferably, the stirring time of the step (2) is 1-10h, preferably 1-5 h;
preferably, the drying in step (2) comprises any one or a combination of at least two of heating evaporation, rotary evaporation, freeze drying or spray drying, preferably rotary evaporation.
8. The production method according to any one of claims 3 to 7, wherein the baking in step (2) is performed in a protective gas atmosphere;
preferably, the shielding gas comprises any one of argon, nitrogen, helium or argon-hydrogen mixed gas or a combination of at least two of the argon, the nitrogen, the helium and the argon-hydrogen mixed gas;
preferably, the roasting temperature in the step (2) is 600-1200 ℃, preferably 800-1000 ℃;
preferably, the roasting in the step (2) has the heat preservation time of 1-8h, preferably 2-6 h;
preferably, the roasting carbonization equipment in the step (2) comprises any one of a tubular carbonization furnace, a box-type carbonization furnace, a roller kiln, a pushed slab kiln or a chemical vapor deposition furnace or a combination of at least two of the foregoing furnaces;
preferably, the cooling in the step (2) is air cooling;
preferably, the silicon-based anode material in the step (2) has a median particle size of 1-30 μm, preferably 3-10 μm.
9. The method according to any one of claims 3 to 8, characterized by comprising the steps of:
(1) weighing an organic carbon source and a carbon nano tube, wherein the mass ratio of the organic carbon source to the silicon-based negative electrode substrate is (0.5-30):100, the mass ratio of the carbon nano tube to the silicon-based negative electrode substrate is (0.01-0.5):100, adding an organic solvent, and stirring for 1-10 hours to obtain a dispersion liquid; wherein the organic carbon source comprises any one or the combination of at least two of phenolic resin, glucose, citric acid or asphalt, and the median particle size of the organic carbon source is less than or equal to 100 mu m; the organic solvent comprises any one or the combination of at least two of methanol, ethanol, isopropanol or propanol, and the ratio of the volume of the organic solvent to the mass of the organic carbon source is (0.5-50) mL:1 g;
(2) adding a silicon-based negative electrode base material with the median particle size of 0.05-20 microns into the dispersion liquid obtained in the step (1), stirring for 1-10h, drying by rotary evaporation, heating to 600-1200 ℃ in a protective gas atmosphere, roasting, keeping the temperature for 1-8h, cooling by air cooling, and sieving to obtain the silicon-based negative electrode material with the median particle size of 1-30 microns.
10. Use of the silicon-based negative electrode material according to claim 1 or 2 for preparing a negative electrode plate of a lithium ion battery.
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