CN111435734A

CN111435734A - Porous silicon-carbon composite negative electrode material and preparation method thereof

Info

Publication number: CN111435734A
Application number: CN201911374658.8A
Authority: CN
Inventors: 赵晓锋
Original assignee: Svolt Energy Technology Co Ltd
Current assignee: Svolt Energy Technology Co Ltd
Priority date: 2019-12-27
Filing date: 2019-12-27
Publication date: 2020-07-21

Abstract

The invention provides a porous silicon-carbon composite negative electrode material and a preparation method thereof. The preparation method comprises the following steps: (1) putting yeast into a sucrose solution for fermentation; (2) adding a silane compound and zinc sulfate into the fermented mixed solution to form a precursor solution; (3) carbonizing the precursor solution to obtain a composite material; (4) and (3) carrying out reduction treatment on the composite material to obtain the porous silicon-carbon composite anode material. According to the preparation method provided by the invention, saccharomycetes are used as a biological template agent, the silicon-carbon composite negative electrode material with a unique porous structure can be prepared through fermentation, meanwhile, the silane compound is uniformly doped on the biological template after carbonization, a buffer space is provided for the expansion of the silicon material in the subsequent charging and discharging processes, and hydrophilic groups on the surface of the saccharomycetes have an adsorption effect on the silane compound, so that the carbonized material has better structural stability.

Description

Porous silicon-carbon composite negative electrode material and preparation method thereof

Technical Field

The invention relates to the technical field of lithium ion battery materials, in particular to a porous silicon-carbon composite negative electrode material and a preparation method thereof.

Background

The silicon-carbon cathode material has the advantages of high specific capacity, wide material source and the like, is a preferred material of the cathode material for the lithium ion battery with high specific energy density, but has high expansion rate, conductivity deviation and the like which restrict the wide application. At present, four main methods for reducing the expansion rate of silicon materials are available: firstly, coating a carbon material on the surface of a silicon material to reduce the expansion rate of the composite material; secondly, pores are formed on the surface of the material, so that the expansion of the composite material can be reduced; the third method adopts a template method, coats nano silicon or silicon oxide compounds on the surface of the template, and then removes the template, so that the expansion rate of the composite material can be reduced; and a fourth material with strong conductivity, such as graphene and carbon nanotubes, is coated on the surface of the nano silicon or silicon-oxygen compound, so that the expansion rate of the silicon material can be reduced and the conductivity can be improved.

At present, a silicon-containing compound can be subjected to catalytic hydrolysis in a solution containing an organic template agent under an alkaline condition to prepare porous silica containing the organic template agent, and then the porous silica containing the organic template agent is subjected to suction filtration, washing and carbonization to obtain the silica/carbon composite material. However, the preparation process is complex, the consistency is difficult to control, the cost is high and the environment is not very friendly.

Disclosure of Invention

The present invention has been completed based on the following findings of the inventors:

the inventor finds that the porous silicon-carbon composite negative electrode material can be prepared by adopting a biological template method, and the porous silicon-carbon composite negative electrode material has the advantages of environmental protection, low cost and the like on one hand, and on the other hand, the pores generated by the fermentation of the biological template have proper size and short fermentation time, bioactive macromolecules such as protein, polysaccharide and the like can be generated on the surface of a cell wall under the action of metabolism, and the bioactive macromolecules can provide a plurality of hydrophilic anionic functional groups such as hydroxyl, carboxyl and the like, and the hydrophilic groups can be fully combined with target compounds to improve the structural stability of the material, so that the electrochemical performance of silicon carbon is improved, and the porous silicon-carbon composite negative electrode material also has the advantages of environmental protection, low.

In a first aspect of the invention, a method of making a porous silicon carbon composite anode material is presented.

According to an embodiment of the invention, the method comprises: (1) putting yeast into a sucrose solution for fermentation; (2) adding a silane compound and zinc sulfate into the fermented mixed solution to form a precursor solution; (3) carbonizing the precursor solution to obtain a composite material; (4) and reducing the composite material to obtain the porous silicon-carbon composite anode material.

According to the preparation method provided by the embodiment of the invention, the environment-friendly yeast is used as a biological template, the silicon-carbon composite negative electrode material with a unique porous structure can be prepared through fermentation, meanwhile, the silane compound is uniformly doped on the biological template after carbonization, a buffer space is provided for the expansion of the silicon material in the subsequent charging and discharging processes, and the hydrophilic group on the surface of the yeast has an adsorption effect on the silane compound, so that the carbonized material has better structural stability.

In addition, the preparation method according to the above embodiment of the present invention may further have the following additional technical features:

according to the embodiment of the invention, the fermentation time is 1-12 hours.

According to the embodiment of the invention, the weight ratio of the yeast to the sucrose is (2-6): 1.

According to an embodiment of the present invention, the silane compound includes at least one of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris (β -methoxyethoxy) silane, methacryloxy-functional alkoxysilane, gamma-methacryloxypropyltrimethoxysilane, N- β (aminoethyl) -gamma-aminopropyltrimethoxysilane, gamma-mercaptopropyltriethoxysilane, gamma- (2, 3-glycidoxy) propyltrimethoxysilane, gamma-aminopropyltriethoxysilane, and gamma-aminopropylmethyldiethoxysilane.

According to the embodiment of the invention, the weight ratio of the yeast, the silane compound and the zinc sulfate is (10-30): 50-100): 0.5-2.

According to the embodiment of the invention, the pH value of the precursor solution is adjusted to 8-10.

According to the embodiment of the invention, the carbonization treatment is carried out at 450-550 ℃ for 0.5-1.5 hours.

According to the embodiment of the invention, the reduction treatment is a magnesium thermal reaction at 750-850 ℃ for 1-3 hours, and the weight ratio of the composite material to the magnesium powder is (1-3): 1.

According to the embodiment of the invention, the precursor solution can be pre-reacted for 1-3 hours at 50-150 ℃ before the carbonization treatment.

In a second aspect of the invention, a porous silicon carbon composite anode material is provided.

According to the embodiment of the invention, the porous silicon-carbon composite anode material is obtained by the method.

The porous silicon-carbon composite negative electrode material provided by the embodiment of the invention has a unique porous structure obtained by fermenting with yeast as a biological template, the porous structure is favorable for permeation and diffusion of lithium ions, the migration rate of the lithium ions in the charging and discharging process can be improved, and the silicon-carbon composite negative electrode material is low in preparation cost, stable in structure and excellent in cycle performance. It will be understood by those skilled in the art that the features and advantages described above with respect to the method of preparing the porous silicon carbon composite anode material are still applicable to the porous silicon carbon composite anode material and will not be described herein again.

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 foregoing aspects of the invention are explained in the description of the embodiments with reference to the following drawings, in which:

fig. 1 is a schematic flow chart of a method for preparing a porous silicon-carbon composite anode material according to an embodiment of the invention;

fig. 2 is an electron micrograph of the porous silicon carbon composite anode material according to an embodiment of the present invention.

Detailed Description

The following examples of the present invention are described in detail, and it will be understood by those skilled in the art that the following examples are intended to illustrate the present invention, but should not be construed as limiting the present invention. Unless otherwise indicated, specific techniques or conditions are not explicitly described in the following examples, and those skilled in the art may follow techniques or conditions commonly employed in the art or in accordance with the product specifications.

In one aspect of the invention, a method of making a porous silicon carbon composite anode material is presented. According to an embodiment of the present invention, referring to fig. 1, the preparation method includes:

s100: putting the yeast into a sucrose solution for fermentation.

In some embodiments of the invention, the fermentation time can be 1-12 hours, specifically, for example, 6 hours, and the like, so that the yeast can generate active macromolecules with hydrophilic groups on the cell wall surface through metabolism, in some specific examples, the weight ratio of the yeast to the sucrose can be selected from (2-6): 1, and thus, 10-30 g of the yeast can be added into a sucrose solution with the mass concentration of 500m L of 1% to serve as a fermentation reaction liquid.

S200: and adding a silane compound and zinc sulfate into the fermented mixed solution to form a precursor solution.

In this step, a silane compound and zinc sulfate are added to the mixed solution after fermentation in step S100 to form a precursor solution.

According to an embodiment of the present invention, the silane compound may include at least one of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris (β -methoxyethoxy) silane, methacryloxy-functional alkoxysilane, gamma-methacryloxypropyltrimethoxysilane, N- β (aminoethyl) -gamma-aminopropyltrimethoxysilane, gamma-mercaptopropyltriethoxysilane, gamma- (2, 3-glycidoxy) propyltrimethoxysilane, gamma-aminopropyltriethoxysilane, and gamma-aminopropylmethyldiethoxysilane.

In some embodiments of the present invention, the silane compound may be selected from vinyltriethoxysilane, vinyltrimethoxysilane or γ -methacryloxypropyltrimethoxysilane, and thus, the silane compound selected as a precursor of silicon can make silicon dioxide after carbonization more uniformly doped on the surface of the porous carbon, thereby providing sufficient buffer space for the expansion of the silicon material during charging and discharging, and further making the cycle performance of the carbon-silicon composite material better.

In some embodiments of the invention, the weight ratio of the yeast, the silane compound and the zinc sulfate in the precursor solution may be (10-30): 50-100): 0.5-2, so that the porous structure after carbonization treatment can be more favorable for permeation and diffusion of lithium ions by using the yeast with the above addition amount, thereby making the migration rate of lithium ions in charging and discharging of the carbon-silicon composite material higher.

In some specific examples, after the precursor solution is fully mixed, the pH value of the precursor solution can be adjusted to 8-10, specifically, for example, pH value 9, so that the yeast has high activity under an alkaline condition, and thus, the adsorption capacity between the carbon material and the silane compound can be improved, and further, the structural stability of the carbon-silicon composite material can be improved.

S300: and carbonizing the precursor solution to obtain the composite material.

In this step, the precursor solution prepared in step S200 may be transferred to a tube furnace for carbonization treatment to obtain a composite material. Thus, the yeast in the precursor solution is used as a biological template agent to decompose and synthesize the porous material with developed pore diameter and stable structure, and the silane compound reacts under the action of zinc sulfate to generate silicon dioxide which is uniformly doped in gaps of the porous material.

In some embodiments of the present invention, the carbonization treatment may be performed at 450 to 550 degrees celsius for 0.5 to 1.5 hours, specifically, for example, at 500 degrees celsius for 1 hour, so that the yeast and the silane compound may be sufficiently carbonized into the carbon/silicon dioxide composite anode material.

In some specific examples, the precursor solution may be transferred to a high-pressure reaction kettle in advance before the carbonization treatment at a high temperature, and the pre-reaction is performed at 50-150 ℃ for 1-3 hours, so that the pore size distribution of the porous material after the carbonization treatment is more uniform and the doped silicon material is also more uniformly distributed.

S400: and (3) carrying out reduction treatment on the composite material to obtain the porous silicon-carbon composite anode material.

In this step, the composite material obtained in step S300 may be subjected to a reduction treatment, specifically, for example, a magnesiothermic reduction treatment, to reduce the silica in the carbon/silica composite anode material to silicon monoxide, so as to increase the specific capacity of the porous silicon-carbon composite anode material.

In some embodiments of the invention, the reduction treatment can be a magnesiothermic reaction at 750-850 ℃ for 1-3 hours, and the weight ratio of the composite material to the magnesium powder can be (1-3): 1, so that the silicon dioxide after the carbonization treatment can be fully reduced into silicon monoxide by adopting the above conditions and the added amount of the magnesiothermic reduction reaction, thereby further improving the specific capacity of the prepared porous silicon-carbon composite anode material.

In summary, according to the embodiments of the present invention, the present invention provides a preparation method, in which an environment-friendly yeast is used as a biological template, and a silicon-carbon composite negative electrode material with a unique porous structure is prepared by fermentation, and meanwhile, a silane compound is uniformly doped on the biological template after carbonization, so as to provide a buffer space for expansion of the silicon material in the subsequent charging and discharging processes, and hydrophilic groups on the surface of the yeast have an adsorption effect on the silane compound, so that the carbonized material has a better structural stability.

In another aspect of the invention, the invention provides a porous silicon-carbon composite anode material. According to an embodiment of the present invention, the porous silicon-carbon composite anode material may be obtained by the above-described preparation method.

In summary, according to the embodiments of the present invention, the present invention provides a porous silicon-carbon composite negative electrode material, wherein a unique porous structure obtained by fermenting with yeast as a biological template is provided, the porous structure is favorable for permeation and diffusion of lithium ions, and can improve the migration rate of lithium ions during charging and discharging, and the silicon-carbon composite negative electrode material has low preparation cost, stable structure and excellent cycle performance. It will be understood by those skilled in the art that the features and advantages described above with respect to the method of preparing the porous silicon carbon composite anode material are still applicable to the porous silicon carbon composite anode material and will not be described herein again.

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

In this example, a porous silicon carbon composite anode material was prepared. The method comprises the following specific steps:

putting 20g of yeast into 500m of L mass percent sucrose solution for fermentation for 6h, adding 80g of vinyltriethoxysilane and 1g of zinc sulfate into the solution, stirring uniformly, adding ammonia water to adjust the pH value to 9, transferring into a high-pressure reaction kettle, reacting at 100 ℃ for 2h, filtering, vacuum drying at 80 ℃ for 48h, transferring into a tube furnace, heating to 500 ℃ under an argon inert atmosphere, carbonizing for 3h to obtain a composite material, weighing 20g of the composite material, carrying out a magnesium thermal reduction reaction on 10g of magnesium powder, heating to 800 ℃ under the argon inert atmosphere, keeping the temperature for 2h, and finally carrying out acid washing and drying by using 0.1 mol/L dilute hydrochloric acid to obtain the porous silicon-carbon composite negative electrode material.

An electron micrograph of the porous silicon carbon composite anode material of this example is shown in fig. 2. As can be seen from FIG. 2, the composite negative electrode material has a granular structure and the particle size is 5-15 μm.

Example 2

In this example, a porous silicon carbon composite anode material was prepared according to substantially the same method and conditions as in example 1. The difference is that in this example, the yeast is added in an amount of 10g, the fermentation time is 1 hour, the silane compound is vinyltrimethoxysilane and the addition amount is 50g, the addition amount of zinc sulfate is 0.5g, the reaction is carried out in a high pressure reactor at 50 ℃ for 1 hour, and the magnesiothermic reduction reaction is carried out at 750 ℃ for 3 hours.

Example 3

In this example, a porous silicon carbon composite anode material was prepared according to substantially the same method and conditions as in example 1. The difference is that in this example, the yeast is added in an amount of 30g, the fermentation time is 12 hours, the silane compound is gamma-methacryloxypropyltrimethoxysilane and the amount is 100g, the zinc sulfate is added in an amount of 2g, the reaction is carried out in a high pressure reactor at 150 ℃ for 1 hour, and the magnesiothermic reduction reaction is carried out at 850 ℃ for 1 hour.

Comparative example 1

In the comparative example, a commercially available silicon oxide composite material with the model number of S500-2A is adopted, and the manufacturer is Shenzhen Beibei New energy materials GmbH.

Example 4

In the embodiment, the porous silicon-carbon composite negative electrode material of the embodiments 1-3 and the silicon oxide composite material of the comparative example 1 are respectively assembled into the button cell, and the specific assembly method comprises the steps of adding a binder, a conductive agent and a solvent into the negative electrode material, stirring and pulping, coating the mixture on a copper foil, drying and rolling to obtain the button cell, wherein the binder is polyvinylidene fluoride (PVDF), the conductive agent is conductive carbon black (SP), the solvent is N-methylpyrrolidone (NMP), and the solute in the electrolyte is lithium hexafluorophosphate (L iPF)₆) The solvent is a mixed solution of Ethylene Carbonate (EC) and diethyl carbonate (DEC), the mixing ratio of the negative electrode materials is SP, PVDF and NMP is 95g, 1g, 4g, 220m L, and L iPF is adopted as the electrolyte₆The volume ratio of the/EC + DEC is 1:1, the metal lithium sheet is used as a counter electrode, the diaphragm is made of a Polyethylene (PE) polypropylene (PP) or polyethylene propylene (PEP) composite film, and the simulated battery is assembled in a hydrogen-filled glove box.

The electrochemical performance test of four button cells was carried out on a Wuhan blue electricity CT2001A type cell tester, with a charge-discharge voltage range of 0.005V to 2.0V and a charge-discharge rate of 0.1C. The electrochemical performance test results are shown in Table 1, wherein the specific surface area test method refers to GB/T-2433sOne 2009.

TABLE 1 button cell Electrical Performance testing of three examples and one comparative example

	Example 1	Example 2	Example 3	Comparative example 1
					First discharge capacity (mAh/g)	925.2	900.4	909.3	570.2
First efficiency (%)	91.9	91.7	90.5	90.7
					Specific surface area (g/m)²)	13.1	11.9	12.4	1.5

As can be seen from table 1, the specific capacity and the first efficiency of the silicon-carbon composite negative electrode materials prepared in examples 1 to 3 are significantly better than those of comparative example 1, because the conductivity and the ion migration rate of the composite material can be improved by doping the silica compound in the biological template method, and simultaneously, the yeast has higher activity under the alkaline condition, the adsorption capacity of the carbon material and the silane compound is improved, so that the structural stability of the material is improved, and the specific surface area of the composite material can also be improved by the holes left after the biological template method is decomposed.

Example 5

In this example, the porous silicon-carbon composite negative electrode materials of examples 1 to 3 and the silicon oxide composite material of comparative example 1 were used as negative electrode materials, a nickel-cobalt-manganese ternary material (NCM622) was used as a positive electrode material, and L iPF was used as an electrolyte₆And the/EC + DEC (volume ratio of 1:1, concentration of 1.3 mol/L) and the diaphragm are Celgard 2400 membranes, and the 5Ah soft package battery and the corresponding negative pole piece thereof are prepared.

The liquid absorption and retention capacity, the pole piece resilience, the cycle performance and the pole piece resistivity of the four negative pole pieces are tested, and the test results are respectively shown in tables 2,3 and 4.

TABLE 2 liquid-absorbing and retaining abilities of negative electrode sheets of three examples and one comparative example

As can be seen from table 2, the liquid absorbing and retaining capabilities of the negative electrode materials of examples 1 to 3 are significantly higher than those of comparative example 1, which shows that the negative electrode material of the present invention has higher liquid absorbing and retaining capabilities because the adopted biological template method has a high specific surface area, thereby improving the liquid absorbing and retaining capabilities of the negative electrode sheet.

TABLE 3 rebound and resistivity of the negative pole pieces of three examples and one comparative example

	Rebound Rate (%) of Pole piece	Pole piece resistivity (m omega)
			Example 1	8.8	16.8
Example 2	9.6	17.7
			Example 3	10.1	20.3
Comparative example 1	19.6	192.5

As can be seen from table 3, the rebound rate of the negative electrode plates in examples 1 to 3 is significantly lower than that in comparative example 1, which indicates that the negative electrode plates made of the negative electrode material of the present application have a lower rebound rate, because the silicon dioxide formed by carbonization of the silane compound is uniformly doped between the biological templates and on the surface thereof, so as to provide a buffer space for the expansion of the silicon material during the charging and discharging processes, thereby effectively reducing the expansion probability of lithium ions during the charging and discharging processes. Meanwhile, the negative electrode material in the material pole piece has the advantages that the combination of silica and a carbon material is tight, the electronic conductivity of the pole piece is improved, and the resistivity of the pole piece is reduced.

TABLE 4 negative electrode tab cycling performance of three examples and one comparative example

	Capacity retention (%) after 500 cycles
		Example 1	83.62
Example 2	83.78
		Example 3	83.39
Comparative example 1	72.55

As can be seen from Table 4, the cycle performance of the soft package battery prepared by the negative electrode materials of examples 1-3 is obviously superior to that of comparative example 1, and the reason is that the negative electrode plates of examples 1-3 have a lower expansion rate, so that the expansion is lower in the charging and discharging processes, and the cycle performance of the soft package battery is further improved.

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

1. A method for preparing a porous silicon-carbon composite anode material is characterized by comprising the following steps:

(1) putting yeast into a sucrose solution for fermentation;

(2) adding a silane compound and zinc sulfate into the fermented mixed solution to form a precursor solution;

(3) carbonizing the precursor solution to obtain a composite material;

(4) and reducing the composite material to obtain the porous silicon-carbon composite anode material.

2. The method according to claim 1, wherein the fermentation time is 1 to 12 hours.

3. The method according to claim 1, wherein the weight ratio of the yeast to the sucrose is (2-6): 1.

4. The method of claim 1, wherein the silane compound comprises at least one of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris (β -methoxyethoxy) silane, methacryloxy-functional alkoxysilane, gamma-methacryloxypropyltrimethoxysilane, N- β (aminoethyl) -gamma-aminopropyltrimethoxysilane, gamma-mercaptopropyltriethoxysilane, gamma- (2, 3-glycidoxy) propyltrimethoxysilane, gamma-aminopropyltriethoxysilane, and gamma-aminopropylmethyldiethoxysilane.

5. The method as claimed in claim 1, wherein the weight ratio of the yeast, the silane compound and the zinc sulfate is (10-30): 50-100): 0.5-2.

6. The method according to claim 1, wherein the pH of the precursor solution is adjusted to 8 to 10.

7. The method according to claim 1, wherein the carbonization treatment is carried out at 450 to 550 ℃ for 0.5 to 1.5 hours.

8. The method according to claim 1, wherein the reduction treatment is a magnesium thermal reaction at 750-850 ℃ for 1-3 hours, and the weight ratio of the composite material to the magnesium powder is (1-3): 1.

9. The method according to claim 1, wherein the precursor solution is pre-reacted at 50 to 150 ℃ for 1 to 3 hours before the carbonization treatment.

10. A porous silicon carbon composite anode material, characterized by being obtained by the method of any one of claims 1 to 9.