CN114014319A

CN114014319A - Carbon-coated silicon, preparation method and application thereof, and preparation method of lithium ion battery cathode

Info

Publication number: CN114014319A
Application number: CN202111306027.XA
Authority: CN
Inventors: 郑淞生; 陈思; 郑雷铭; 张叶涵; 王兆林; 李钷
Original assignee: Xiamen University
Current assignee: Xiamen University
Priority date: 2021-11-05
Filing date: 2021-11-05
Publication date: 2022-02-08

Abstract

The invention provides carbon-coated silicon, a preparation method and application thereof, and a preparation method of a lithium ion battery cathode, and belongs to the technical field of electrode materials. According to the invention, metal nano particles are introduced into the carbon-coated silicon carbon layer, so that an electronic channel is provided in the charging and discharging process, the electrochemical performance of the carbon-coated silicon carbon layer is greatly improved, the problem of volume expansion of silicon in the charging and discharging process is effectively solved by using the rigidity of the carbon layer, the conductivity of the carbon layer is greatly improved, and the electrochemical performance of the carbon-coated silicon is improved. The raw materials used by the scheme of the invention have low cost and wide sources; and moreover, the hydrothermal reaction is adopted, the preparation process is simple and convenient, the energy consumption is low, the green and environment-friendly effects are realized, and the industrial production is easy to realize.

Description

Carbon-coated silicon, preparation method and application thereof, and preparation method of lithium ion battery cathode

Technical Field

The invention relates to the technical field of electrode materials, in particular to carbon-coated silicon, a preparation method and application thereof, and a preparation method of a lithium ion battery cathode.

Background

Researches show that when silicon is used as a negative electrode material of a lithium ion battery, the theoretical specific capacity of the silicon is more than ten times that of commercial graphite, and the silicon has a very wide prospect. However, the silicon material has a problem of huge volume expansion during charge and discharge, resulting in extremely poor cycle stability, and thus cannot be directly applied.

The current methods for solving the problem mainly comprise the steps of carrying out nano treatment on silicon particles, preparing the silicon particles into an alloy, constructing silicon with a special structure or preparing a silicon composite material. In a plurality of methods, the problem of volume change of silicon can be greatly relieved by using the silicon-in-carbon, and the electrochemical performance of the material is effectively improved. However, the existing preparation methods mainly include chemical vapor deposition, electrochemical deposition, chemical etching and the like, which not only have high cost, but also have great pollution. Meanwhile, most of carbon layers in the carbon-coated silicon prepared by the methods are amorphous carbon, so that the electrical conductivity is poor, and the electrical performance of the composite material is influenced.

Disclosure of Invention

The invention aims to provide carbon-coated silicon, a preparation method and application thereof, and a preparation method of a lithium ion battery cathode.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of carbon-coated silicon, which comprises the following steps:

mixing a carbon source, a metal source, silicon and water to obtain a reaction solution;

and carrying out hydrothermal reaction and carbonization treatment on the reaction solution in sequence to obtain the silicon-coated carbon.

Preferably, the carbon source comprises one or more of glucose, sucrose, starch, cellulose, cyclodextrin and lignin; the concentration of the carbon source in the reaction solution is 0.1-5 mol/L.

Preferably, the metal source comprises a soluble metal salt comprising a metal acetate salt, a metal nitrate salt or a metal sulfate salt; the metal element in the metal source comprises manganese, copper, nickel, cobalt, iron, palladium, gold or silver.

Preferably, the silicon includes granular silicon, flake silicon, or needle silicon.

Preferably, the mass ratio of the carbon source, the silicon and the metal source is 10 (1-20) to (0.1-5).

Preferably, the temperature of the hydrothermal reaction is 170-300 ℃, and the time of the hydrothermal reaction is 2-24 h.

Preferably, the temperature of the carbonization treatment is 750-1700 ℃, and the heat preservation time is 1-4 h.

The invention provides the carbon-coated silicon prepared by the preparation method in the technical scheme, which comprises silicon particles and a carbon layer coated on the surfaces of the silicon particles, wherein metal nano particles are uniformly dispersed in the carbon layer.

The invention provides application of the carbon-coated silicon in the technical scheme in preparation of a lithium ion battery cathode.

The invention provides a preparation method of a lithium ion battery cathode, which comprises the following steps:

mixing carbon-coated silicon, a conductive agent, a binder and water to obtain negative electrode slurry; the carbon-coated silicon is the carbon-coated silicon in the technical scheme;

and coating the negative electrode slurry on a metal foil to obtain the negative electrode of the lithium ion battery.

The invention provides a preparation method of carbon-coated silicon, which comprises the following steps: mixing a carbon source, a metal source, silicon and water to obtain a reaction solution; and carrying out hydrothermal reaction and carbonization treatment on the reaction solution in sequence to obtain the silicon-coated carbon. According to the invention, hydrothermal reaction and carbonization treatment are utilized to prepare the silicon-on-carbon, in the hydrothermal reaction process, a carbon source is subjected to polymerization reaction to generate a polymer layer and successfully wrap the surface of silicon particles, meanwhile, a carbon simple substance containing a small amount of functional groups is formed in the hydrothermal process, and metal ions in a metal source are reduced into metal nano particles and uniformly dispersed in the polymer layer to form spherical particles; the polymer layer wrapped on the surface of the silicon is dehydrogenated and deoxidized through carbonization treatment, so that carbonization is realized to form a carbon layer; meanwhile, the carbon atoms are subjected to catalytic rearrangement by utilizing the catalytic action of the metal nanoparticles, so that the conversion from amorphous carbon to graphite carbon is realized, the graphitization degree of the carbon layer is improved, and the conductivity and the electrical property of the material are further improved. According to the invention, metal nano particles are introduced into the carbon-coated silicon carbon layer, so that an electronic channel is provided in the charge-discharge process, and the electrochemical performance of the carbon-coated silicon carbon layer is greatly improved; and the problem of volume expansion of silicon in the charging and discharging process is effectively solved by using the rigidity of the carbon layer, the conductivity of the carbon layer is greatly improved, and the electrochemical performance of the carbon-coated silicon is improved.

The invention can obtain spherical carbon-coated silicon particles with controllable size and uniform particle size by regulating and controlling the concentration of raw materials, hydrothermal reaction and carbonization condition, temperature and time, realizes controllable thickness of the carbon layer, ensures that the silicon surface has a carbon layer structure with good coating, can effectively solve the problem of volume expansion in the charging and discharging process when silicon is used as an electrode material, and the prepared carbon-coated silicon surface has regular coating of the carbon layer, uniform distribution of metal nano particles, high purity of the metal nano particles, no impurities, and better electrochemical cycle stability, rate capability and better conductivity.

The scheme provided by the invention has the advantages that the used raw materials are low in cost and wide in source; and moreover, the hydrothermal reaction is adopted, the preparation process is simple and convenient, the energy consumption is low, the green and environment-friendly effects are realized, and the industrial production is easy to realize.

Drawings

FIG. 1 is an SEM image (a) and an EDS energy spectrum (b) of silicon-on-carbon prepared in example 1;

fig. 2 is a raman spectrum (a) and an XRD pattern (b) of the silicon-on-carbon prepared in example 1;

FIG. 3 is a C-V diagram of a half cell made of silicon-on-carbon prepared in example 1;

fig. 4 is a graph (a) of the cycling curve and coulombic efficiency for half-cells made from submicron silicon and the silicon-in-carbon of example 1 and a graph (b) of the rate performance for half-cells made from submicron silicon and the silicon-in-carbon of example 1;

fig. 5 is a graph of the ac impedance of half-cells made from submicron silicon and the silicon-in-carbon of example 1.

Detailed Description

In the present invention, the required raw materials are all commercially available products well known to those skilled in the art, unless otherwise specified.

According to the invention, a carbon source, a metal source, silicon and water are mixed to obtain a reaction solution. In the invention, the carbon source preferably comprises one or more of glucose, sucrose, starch, cellulose, cyclodextrin and lignin; when the carbon source is preferably selected from the above carbon sources, the ratio of different carbon sources is not particularly limited, and any ratio may be used. In the invention, the glucose is preferably one or more of D- (+) -glucose, D- (+) -glucose monohydrate and L- (-) -glucose; when the glucose is a plurality of the glucose, the proportion of different types of glucose is not particularly limited, and the glucose can be prepared in any proportion. In the present invention, the concentration of the carbon source in the reaction solution is preferably 0.1 to 5mol/L, more preferably 0.56 to 4.0mol/L, and still more preferably 1.11 to 3 mol/L.

In the present invention, the metal source preferably comprises a soluble metal salt, preferably comprising an acetic acid-based metal salt, a nitric acid-based metal salt or a sulfuric acid-based metal salt; the metal element in the metal source preferably includes manganese, copper, nickel, cobalt, iron, palladium, gold, or silver.

In the present invention, the silicon preferably includes granular silicon, flaky silicon, or needle-like silicon; the silicon is preferably submicron silicon; the particle size of the submicron silicon is preferably 400-1000 nm, more preferably 400-900 nm, and further preferably 500-800 nm; the sub-micron silicon is preferably derived from photovoltaic industry scrap silicon.

In the invention, the mass ratio of the carbon source, the silicon and the metal source is preferably 10 (1-20): 0.1-5), more preferably 10 (1-15): 0.31-3.5), still more preferably 10 (2-6): 0.5-2, and most preferably 10 (4-5): 1-2.

The mixing process of the carbon source, the silicon, the metal source and the water is not particularly limited, and the materials can be uniformly mixed by adopting the process well known in the field.

After the reaction liquid is obtained, the invention carries out hydrothermal reaction and carbonization treatment on the reaction liquid in sequence to obtain the silicon-coated-carbon. In the invention, the temperature of the hydrothermal reaction is preferably 170-300 ℃, more preferably 190-250 ℃, and further preferably 200-230 ℃, and the time of the hydrothermal reaction is preferably 2-24 h, more preferably 5-12 h, and further preferably 6-8 h. In the invention, the temperature is preferably raised to the temperature of the hydrothermal reaction within 1-6 h from room temperature, and more preferably 2-4 h. In the present invention, the hydrothermal reaction is preferably carried out under stirring, and the stirring rate is not particularly limited in the present invention, and may be carried out by a process well known in the art.

In the hydrothermal reaction process, a carbon source is subjected to polymerization reaction to generate a polymer layer and successfully wraps the surface of the silicon particles, and meanwhile, a carbon simple substance (carbon source hydrothermal product) with reducibility at a high temperature reduces metal ions in a metal source to form metal nanoparticles which are uniformly dispersed in the polymer layer to form spherical particles.

After the hydrothermal reaction is completed, the obtained product system is preferably subjected to post-treatment, the post-treatment mode is preferably solid-liquid separation, the process of the solid-liquid separation is not particularly limited, and the solid-liquid separation can be realized by adopting a process well known in the art.

After the solid-liquid separation is completed, the present invention preferably performs a carbonization treatment on the solid product after the solid-liquid separation. In the invention, the temperature of the carbonization treatment is preferably 750-1700 ℃, more preferably 800-1200 ℃, further preferably 900-1000 ℃, and the heat preservation time is preferably 1-4 h, more preferably 1.5-3 h, further preferably 2-2.5 h; the heating rate for heating to the temperature for the carbonization treatment is preferably 1 to 10 ℃/min, and more preferably 3 to 7 ℃/min. In the present invention, the carbonization treatment is preferably performed under a nitrogen atmosphere.

The polymer layer wrapped on the silicon surface is dehydrogenated and deoxidized through carbonization treatment, so that carbonization is realized, and a carbon layer is formed on the carbon-coated silicon surface; meanwhile, the conversion from amorphous carbon to graphite carbon is realized by utilizing the catalytic action of metal nano particles, so that the graphitization degree of the carbon layer is improved, and the conductivity and the electrical property of the material are improved; and the metal nano particles can provide an electronic channel in the charging and discharging process, so that the electrochemical performance of the carbon-coated silicon is greatly improved.

After the carbonization treatment is completed, the carbonized product is preferably cooled, and the cooling process is not particularly limited in the present invention and may be performed by a process well known in the art.

The invention provides the carbon-coated silicon prepared by the preparation method in the technical scheme, which comprises silicon particles and a carbon layer coated on the surfaces of the silicon particles, wherein metal nano particles are uniformly dispersed in the carbon layer. The carbon-coated silicon is mainly amorphous carbon, and high-degree graphitized carbon exists.

In the invention, the thickness of the carbon-coated silicon carbon layer is preferably 100-600 nm, more preferably 100-300 nm, and further preferably 100-250 nm; the particle size of the carbon-coated silicon is preferably 0.7-2 μm, more preferably 1-1.9 μm, and even more preferably 1-1.7 μm; the particle size of the metal nanoparticles is preferably 15-100 nm, and more preferably 30-80 nm.

The invention provides application of the carbon-coated silicon in the technical scheme in preparation of a lithium ion battery cathode. The method of the present invention is not particularly limited, and the method may be applied according to a method known in the art.

According to the invention, the carbon-coated silicon, the conductive agent, the adhesive and water are mixed to obtain the cathode slurry. In the present invention, the conductive agent is preferably conductive carbon black; the adhesive is preferably sodium alginate; the mass ratio of the carbon-coated silicon to the conductive agent to the adhesive is preferably (6-8) to (1-2), and more preferably 8:1: 1; the invention has no special limit on the using amount of the water, and the viscosity of the cathode slurry can meet the standard of the conventional lithium battery slurry. In the invention, the process of mixing the silicon-on-carbon, the conductive agent, the adhesive and the water is preferably carried out under the condition of stirring, and the stirring time is preferably 6-12 hours, and more preferably 8-10 hours; the stirring rate is not particularly limited in the present invention, and the stirring may be performed at a stirring rate well known in the art. The order of mixing the silicon-on-carbon, the conductive agent, the binder and the water is not particularly limited in the present invention, and the mixing may be performed by a process well known in the art.

After the negative electrode slurry is obtained, the negative electrode slurry is coated on a metal foil to obtain the negative electrode of the lithium ion battery. The metal foil is not particularly limited in the present invention, and a metal foil well known in the art may be used; the coating process is not particularly limited in the present invention, and the coating may be performed by a process well known in the art. In the invention, the thickness of the film layer obtained by coating is preferably 50-300 μm, more preferably 100-250 μm, and further preferably 150-200 μm.

After the coating is finished, the product obtained by coating is preferably subjected to vacuum drying to obtain the lithium ion battery cathode. The temperature of the vacuum drying is preferably 50-110 ℃, and more preferably 80-100 ℃; the vacuum drying time is preferably 6-48 h, more preferably 15-40 h, and further preferably 25-30 h.

The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Silicon: photovoltaic industry waste silicon (particle size 400-1000 nm); carbon source: glucose; metal source: anhydrous copper acetate;

mixing 5g D- (+) -glucose, 3g of photovoltaic industrial waste silicon, 0.5g of anhydrous copper acetate and 50mL of water to obtain a reaction solution, wherein the concentration of the glucose is 0.56mol/L, heating the reaction solution to 190 ℃ within 1h under a stirring condition, preserving heat for 6h to perform hydrothermal reaction, performing solid-liquid separation on the obtained product, heating to 900 ℃ at a heating rate of 10 ℃/min, carbonizing the obtained solid product in a nitrogen atmosphere, preserving heat for 1h, and naturally cooling to obtain silicon-on-carbon (the particle size is 1 mu m, the thickness is 250nm, and the particle size is 30nm when copper nano carbon particles are uniformly dispersed in a carbon layer).

Example 2

Silicon: photovoltaic industry waste silicon (particle size 400-1000 nm); carbon source: glucose; metal source: nickel nitrate pentahydrate;

mixing 10g D- (+) -glucose, 5g of photovoltaic industrial waste silicon, 0.3g of nickel nitrate pentahydrate and 50mL of water to obtain a reaction solution, wherein the concentration of the glucose is 1.11mol/L, heating the reaction solution to 250 ℃ within 1h under a stirring condition, preserving heat for 6h to perform hydrothermal reaction, performing solid-liquid separation on the obtained product, heating to 800 ℃ at a heating rate of 10 ℃/min, carbonizing the obtained solid product in a nitrogen atmosphere, preserving heat for 2h, and naturally cooling to obtain silicon-on-carbon (the particle size is 1.7 mu m, the thickness of a carbon layer is 500nm, and nickel nano particles are uniformly dispersed in the carbon layer and have the particle size of 15 nm).

Example 3

Silicon: submicron waste silicon (the particle size is 400-1000 nm); carbon source: starch; metal source: anhydrous cobalt sulfate;

mixing 10g of starch, 5g of submicron waste silicon, 0.5g of anhydrous cobalt sulfate and 50mL of water to obtain a reaction solution, wherein the concentration of the starch in the reaction solution is 0.5mol/L, heating the reaction solution to 200 ℃ within 2h under a stirring condition, keeping the temperature for 12h to perform hydrothermal reaction, performing solid-liquid separation on the obtained product, heating the temperature to 1200 ℃ at a heating rate of 10 ℃/min, carbonizing the obtained solid product in a nitrogen atmosphere, keeping the temperature for 1h, and naturally cooling to obtain silicon-on-carbon (the particle size is 1.9 mu m, the thickness of the carbon layer is 600nm, and the cobalt nanoparticles are uniformly dispersed in the carbon layer and the particle size is 30 nm).

Characterization and testing

1) SEM and EDS tests are carried out on the silicon-on-carbon prepared in example 1, and the results are shown in figure 1, wherein, (a) is an SEM picture, and (b) is an EDS energy spectrum; the carbon-coated silicon pellet prepared in example 1 was subjected to element linear scanning in the diameter direction, and it was found that silicon elements were distributed in the middle of the pellet, and carbon elements were contained in the diameter direction, so that the carbon layer coated silicon and formed spherical particles, and the pellet further contained copper elements.

2) The raman spectrum test and the XRD test were performed on the silicon-on-carbon prepared in example 1, and the test results are shown in fig. 2, where (a) in fig. 2 is a raman spectrum of the silicon-on-carbon, and (b) is an XRD pattern of the silicon-on-carbon, and as can be seen from (a) in fig. 2, the silicon-on-carbon can not only observe distinct elemental metal characteristic peaks (fig. 2(a)) and carbon material characteristic peaks (D peak and G peak), but also achieve a certain degree of graphitization of the carbon layer (ratio of D peak to G peak height). Further, as shown in fig. 2 (b), the peak of silicon and the characteristic peaks of the carbon material and the copper simple substance are contained, and the existence of the copper simple substance and the graphitization to some extent are confirmed.

Test example

Respectively mixing submicron silicon powder (with the particle size of 400-900 nm) and carbon-coated silicon (with the particle size of 500-1000 nm) prepared in example 1 with conductive carbon black and sodium alginate according to the mass ratio of 8:1:1, adding 50mL of water, stirring for 8 hours to obtain mixed slurry, coating the mixed slurry on a metal foil to obtain a coating film with the thickness of 100 micrometers, and performing vacuum drying at 100 ℃ for 6 hours to obtain two lithium ion battery cathodes;

a button-type half cell with the specification of CR 2032 was mounted in a glove box filled with argon (electrolyte: 2.0 wt% of vinylene carbonate was added to a mixed solution of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1: 1; counter electrode: metal lithium plate; separator: Celgard 2500), and allowed to stand for 24 hours to obtain a button-type half cell with the specification of CR 2032.

1) Electrochemical tests are carried out on the button type half cell with the specification CR 2032, cyclic voltammetry tests are carried out at a test voltage range of 0.01V-3V and a scanning speed of 0.2mV/s, the test results are shown in figure 3, figure 3 is a C-V diagram of the half cell prepared by the carbon-coated silicon of the example 1, as can be seen from figure 3, reduction peaks of the carbon-coated silicon at 1.18V and 0.48V respectively correspond to the formation of SEI films, and peaks at 0.43V and 0.52V correspond to the transfer behaviors of lithium ions.

2) Under the condition that the test voltage range is 0.01-1.2V, the current density of a half-cell prepared from submicron silicon and the carbon-coated silicon prepared in example 1 is 420A-g^-1The constant current charge and discharge cycle test and the constant current charge and discharge test performed under different multiplying power, the test results are shown in fig. 4; in fig. 4, (a) is a cycle curve and a coulombic efficiency graph of the half-cell prepared from the carbon-in-silicon and the submicron silicon of example 1, and as can be seen from (a) in fig. 4, the initial specific discharge capacity of the half-cell prepared from the carbon-in-silicon is 4241.5mAh/g, which is higher than the specific capacity (2757.8mAh/g) of the half-cell prepared from the submicron silicon, the coulombic efficiency after 100 cycles is close to 100%, and the stability of the half-cell prepared from the carbon-in-silicon is far better than that of the half-cell prepared from the submicron silicon; (b) as can be seen from fig. 4 (b), the rate performance of the half-cell prepared from carbon-coated silicon and sub-micron silicon is significantly better than that of sub-micron silicon when charging and discharging at different current densities.

3) Alternating current impedance tests were performed on submicron silicon and the carbon-coated silicon of example 1 at an amplitude of 5mV over a frequency range of 0.01Hz to 100kHz, and the results are shown in fig. 5. as can be seen from fig. 5, the half-cell made of carbon-coated silicon has a smaller impedance radius than the radius of the submicron silicon half-cell, indicating that the carbon-coated silicon of example 1 has better conductivity than the submicron silicon.

The carbon-coated silicon prepared in the embodiments 2 to 3 is subjected to the electrochemical test same as that in the embodiment 1, and the test result is similar to that in the embodiment 1, and the carbon-coated silicon has good electrochemical cycle stability, rate capability and conductivity.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of carbon-coated silicon is characterized by comprising the following steps:

2. The preparation method of claim 1, wherein the carbon source comprises one or more of glucose, sucrose, starch, cellulose, cyclodextrin and lignin; the concentration of the carbon source in the reaction solution is 0.1-5 mol/L.

3. The production method according to claim 1, wherein the metal source comprises a soluble metal salt comprising a metal acetate salt, a metal nitrate salt or a metal sulfate salt; the metal element in the metal source comprises manganese, copper, nickel, cobalt, iron, palladium, gold or silver.

4. The production method according to claim 1, wherein the silicon includes granular silicon, flake silicon, or needle silicon.

5. The method according to any one of claims 1 to 4, wherein the mass ratio of the carbon source, the silicon and the metal source is 10 (1 to 20) to (0.1 to 5).

6. The preparation method according to claim 1, wherein the temperature of the hydrothermal reaction is 170 to 300 ℃ and the time of the hydrothermal reaction is 2 to 24 hours.

7. The preparation method according to claim 1, wherein the carbonization treatment temperature is 750-1700 ℃, and the holding time is 1-4 h.

8. The silicon-on-carbon prepared by the preparation method according to any one of claims 1 to 7, comprising silicon particles and a carbon layer coated on the surfaces of the silicon particles, wherein metal nanoparticles are uniformly dispersed in the carbon layer.

9. Use of the silicon-on-carbon according to claim 8 for the preparation of a negative electrode for a lithium ion battery.

10. A preparation method of a lithium ion battery cathode comprises the following steps:

mixing carbon-coated silicon, a conductive agent, a binder and water to obtain negative electrode slurry; the silicon-on-carbon is the silicon-on-carbon of claim 8;