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CN111081976B - Silicon-carbon-polymer composite electrode of lithium secondary battery and preparation method thereof - Google Patents

Silicon-carbon-polymer composite electrode of lithium secondary battery and preparation method thereof Download PDF

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CN111081976B
CN111081976B CN201911392122.9A CN201911392122A CN111081976B CN 111081976 B CN111081976 B CN 111081976B CN 201911392122 A CN201911392122 A CN 201911392122A CN 111081976 B CN111081976 B CN 111081976B
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silicon
carbon
pan
composite electrode
polymer composite
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CN111081976A (en
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谭国强
王敬
苏岳锋
陈来
吴锋
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Beijing Institute of Technology BIT
Chongqing Innovation Center of Beijing University of Technology
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Beijing Institute of Technology BIT
Chongqing Innovation Center of Beijing University of Technology
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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Abstract

The invention relates to a silicon-carbon-polymer composite electrode of a lithium secondary battery and a preparation method thereof, belonging to the technical field of negative electrode materials of the lithium secondary battery. The composite electrode is formed by chemically coating nano silicon with cyclized conductive polyacrylonitrile to form a core-shell structure and compounding the core-shell structure with a graphite carbon material. Ball-milling micron silicon and Polyacrylonitrile (PAN) to form a nano composite, adding the obtained composite and graphite into a Dimethylformamide (DMF) solvent of PAN, uniformly stirring, drying, and then placing the mixture in an inert atmosphere for heating treatment to obtain the final composite electrode material. The electrode material has high conductivity and good chemical stability and structural stability. The preparation method is simple, the cost of the raw materials is low, and large-scale production is easy to realize.

Description

Silicon-carbon-polymer composite electrode of lithium secondary battery and preparation method thereof
Technical Field
The invention relates to a silicon-carbon-polymer composite electrode of a lithium secondary battery and a preparation method thereof, belonging to the technical field of negative electrode materials of the lithium secondary battery.
Background
The lithium secondary battery with high energy density is a research hotspot of the next generation lithium battery technology, the traditional lithium ion battery uses graphite as a negative electrode, the theoretical capacity of the traditional lithium ion battery is only 372mAh/g, the dynamic performance of the graphite is poor, a lithium embedding platform of the traditional lithium ion battery is close to metal lithium, the phenomenon of lithium precipitation is easy to occur during rapid charging, and the potential safety hazard of the battery is easy to cause. Therefore, the graphite negative electrode will not satisfy the requirements of the next-generation high energy density lithium secondary battery. The theoretical capacity of the silicon cathode can reach 3572mAh/g and a lithium embedding platform (0.5V vs Li/Li)+) Slightly higher than graphite (0.3V vs Li/Li)+) It is one of the most potential next generation cathode materials. The main challenges of limiting the application of silicon negative electrode materials at present are that the conductivity of silicon is poor, a large amount of conductive networks are required to be added to improve the electronic conductivity of the whole electrode, and in addition, the problems of poor contact between the materials and a current collector, pulverization, inactivation and the like are caused due to huge volume change of an alloy reaction mechanism in the charging and discharging processes, so that the silicon negative electrode often shows rapid capacity attenuation.
At present, mechanically mixed silicon-carbon composite electrode materials and preparation methods thereof are reported, but no composite electrode material with silicon-carbon coated by cyclized conductive polymers and preparation methods thereof are reported.
Disclosure of Invention
In view of the problems of poor conductivity and unstable structure of the silicon-carbon composite electrode in the prior art, which lead to the deterioration of cycle performance, it is an object of the present invention to provide a silicon-carbon-polymer composite electrode for a lithium secondary battery, which has good conductivity and a stable electrode structure, and exhibits high specific capacity, high coulombic efficiency and good retention of battery cycle capacity.
The invention also aims to provide a preparation method of the silicon-carbon-polymer composite electrode of the lithium secondary battery, which is simple and rapid, has rich raw materials, low cost, environmental protection and is easy to realize large-scale production.
The purpose of the invention is realized by the following technical scheme
A silicon-carbon-polymer composite electrode of a lithium secondary battery is formed by coating nano silicon on cyclized PAN through Si-N bonds to form a Si-PAN core-shell structure and compounding the Si-PAN core-shell structure with a carbon material. The PAN is polyacrylonitrile, the Si is micron-sized silicon powder, and the carbon material is one or more of graphite, mesocarbon microbeads (MCMB), needle coke, resin carbon and biomass carbon.
Among them, the average molecular weight of PAN is preferably 150000 g/mol.
Preferably, the silicon has a particle size in the micrometer range.
The mass ratio of PAN to silicon is preferably 0.5:9.5 to 3: 7.
The carbon material is preferably one or more of graphite, MCMB, needle coke, resin carbon and biomass carbon;
the mass ratio of the Si-PAN nano composite material to the carbon material is preferably 0.5: 9.5-9: 1.
The invention relates to a preparation method of a silicon-carbon-polymer composite electrode of a lithium secondary battery, which is a ball milling and heating calcination method and comprises the following steps:
under the protection of inert atmosphere, PAN and silicon are ground and mixed uniformly, and then the mixture is placed in a sealed ball-milling tank for ball milling; wherein the mass ratio of PAN to silicon is 0.5: 9.5-3: 7.
The preferred inert gas is argon with a purity of > 99%.
The preferred PAN to silicon mass ratio is 1: 9.
The preferred ball milling speed is 350 rpm.
Uniformly mixing the Si-PAN nano-composite obtained by ball milling with a carbon material, dispersing the mixture into a DMF (dimethyl formamide) solvent of PAN, uniformly stirring and drying in vacuum, and then placing the mixture into a tubular furnace to be heated and calcined under the protection of inert atmosphere to obtain a final composite electrode material; wherein the mass ratio of the Si-PAN nano composite material to the carbon material is 0.5: 9.5-9: 1; the heating and calcining temperature is 300-900 ℃.
A preferred carbon material is graphite.
The mass ratio of the preferable Si-PAN nano composite material to the mesocarbon microbeads is 1: 9;
the preferred inert gas is argon with a purity of > 99%.
The preferred calcination temperature is 350 ℃.
The invention provides a lithium secondary battery, wherein a cathode used in the battery is a silicon-carbon-polymer composite electrode of the lithium secondary battery.
Advantageous effects
1. The invention provides a silicon-carbon-polymer composite electrode of a lithium secondary battery, which has high conductivity, good electrochemical activity and a stable electrode structure; the composite electrode contains abundant cross-linked pore channel structures and has a buffering effect on the volume expansion of silicon; the composite electrode shows high specific capacity, high coulombic efficiency and good cycling stability;
2. the invention provides a silicon-carbon-polymer composite electrode of a lithium secondary battery, wherein the cyclized PAN in the composite electrode has high conductivity and good flexibility, can be used as a conductive agent and a binder, and improves the cycle life of the battery;
3. the invention provides a silicon-carbon-polymer composite electrode of a lithium secondary battery, wherein the total capacity of an electrode material can be further improved by properly increasing the content of silicon in the composite electrode;
4. the invention provides a preparation method of a silicon-carbon-polymer composite electrode of a lithium secondary battery, wherein a chemical coating layer can be formed on the surface of nano silicon by ball milling, so that the electrochemical activity of the silicon is improved, and the cycling stability of the silicon is improved.
5. The invention provides a preparation method of a silicon-carbon-polymer composite electrode of a lithium secondary battery, which is simple, quick, low in cost, green and environment-friendly and is easy to realize mass production.
Drawings
Fig. 1 is an XRD pattern of a silicon-carbon-polymer composite electrode of a lithium secondary battery prepared in example 2.
Fig. 2 is an SEM image of a silicon-carbon-polymer composite electrode of a lithium secondary battery prepared in example 2.
Fig. 3 is a TEM image of a silicon-carbon-polymer composite electrode of a lithium secondary battery prepared in example 2.
Fig. 4 is a graph showing cycle characteristics of a silicon-carbon-polymer composite electrode for a lithium secondary battery prepared in example 2.
Detailed Description
The present invention will be further illustrated with reference to the following specific examples, but the present invention is not limited to the following examples.
In the following examples 1-10, the test assays used included:
x-ray diffraction (XRD) test: the instrument model is as follows: rigaku Ultima IV, japan;
scanning Electron Microscope (SEM) testing: the instrument model is as follows: SUPRA55, Germany;
projection electron microscope (TEM) testing: the instrument model is as follows: JEOL 3000F
And (3) battery charge and discharge test: the instrument model is as follows: land CT2100A, china.
Example 1
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 2 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 9.2g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.2g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 300 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 567mAh/g, the first coulombic efficiency is 90.6%, the capacity is kept 88.4% after 100 times of circulation, and good circulation stability is shown.
Example 2
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 2 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 6.48g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.2g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 300 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 714mAh/g, the first coulombic efficiency is 90.2%, the capacity is kept at 85.6% after 100 times of circulation, and good circulation stability is shown.
Example 3
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 2 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 4.0g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.2g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 300 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 1064mAh/g, the first coulombic efficiency is 88.2%, the capacity is kept at 82.4% after 100 times of circulation, and the good circulation stability is shown.
Example 4
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 2 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 6.48g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.2g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 400 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 718mAh/g, the first coulombic efficiency is 90.5%, the capacity is kept for 83.6% after 100 times of circulation, and good circulation stability is shown.
Example 5
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 2 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 6.48g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.2g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 500 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 716mAh/g, the first coulombic efficiency is 91.3%, the capacity is maintained at 81.4% after 100 times of circulation, and the good circulation stability is shown.
Example 6
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 2 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 6.48g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.2g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 600 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 720mAh/g, the first coulombic efficiency is 91.5%, the capacity is kept at 80.5% after 100 times of circulation, and the good circulation stability is shown.
Example 7
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 2 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 6.48g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.2g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 700 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 722mAh/g, the first coulombic efficiency is 91.3%, the capacity is kept at 80.3% after 100 times of circulation, and the good circulation stability is shown.
Example 8
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 2 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 6.48g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.2g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 800 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 725mAh/g, the first coulombic efficiency is 91.6%, the capacity is kept at 80.1% after 100 times of circulation, and the good circulation stability is shown.
Example 9
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 2 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 6.48g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.2g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 900 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 723mAh/g, the first coulombic efficiency is 91.3%, the capacity is kept at 79.6% after 100 times of circulation, and good circulation stability is shown.
Example 10
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 4 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 6.48g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.2g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 300 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 708mAh/g, the first coulombic efficiency is 90.5%, the capacity is kept at 86.6% after 100 times of circulation, and good circulation stability is shown.
Example 11
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 6 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 6.48g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.2g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 300 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 706mAh/g, the first coulombic efficiency is 90.7%, the capacity is kept at 86.5% after 100 times of circulation, and good circulation stability is shown.
Example 12
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 8 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 6.48g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.2g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 300 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 705mAh/g, the first coulombic efficiency is 90.2%, the capacity is kept at 86.8% after 100 times of circulation, and good circulation stability is shown.
Example 13
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 2 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 6.48g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.1g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 300 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 703mAh/g, the first coulombic efficiency is 89.6%, the capacity is kept 83.8% after 100 times of circulation, and good circulation stability is shown.
Example 14
Weighing 0.9g of micron silicon and 0.1g of Polyacrylonitrile (PAN), grinding and mixing uniformly, placing in a sealed ball-milling tank under the protection of argon atmosphere, and ball-milling for 2 hours at the rotating speed of 350 r/min to obtain the Si-PAN composite material; weighing 0.8g of Si-PAN composite material and 6.48g of graphite, grinding and uniformly mixing to obtain a mixture 1; weighing 0.3g of polyacrylonitrile to be dissolved in 20mL of a solvent of Dimethylformamide (DMF) to form a transparent mixed solution 2; adding the mixture 1 into the mixed solution 2, uniformly stirring by using a magnetic stirrer, evaporating the solvent to dryness, transferring the solvent to a 60 ℃ oven, and performing vacuum drying for 24 hours to obtain a brown mixture 3; and then placing the mixture 3 in a tube furnace protected by argon atmosphere, sintering for 12h at 300 ℃, cooling to a proper temperature, and grinding to obtain a brown final composite material.
XRD tests show that the silicon-carbon-polymer composite material prepared in example 1 contains characteristic diffraction peaks of silicon, graphite and a small amount of SiC and SiN; the composite material is known to have a rich cross-linked network structure through SEM detection; according to TEM detection, a chemical coating layer is formed on the surface of the nano-particle silicon.
The result of a constant-current charge and discharge test of the battery shows that the first discharge specific capacity of the composite electrode material is 717mAh/g, the first coulombic efficiency is 90.6%, the capacity is kept at 86.8% after 100 times of circulation, and good circulation stability is shown.

Claims (7)

1. A silicon ‒ carbon ‒ polymer composite electrode for a lithium secondary battery, which is characterized in that: the composite electrode is composed of silicon, carbon and cyclized conductive Polyacrylonitrile (PAN); the PAN coated on the silicon surface through ball milling forms chemical coating through Si-N chemical bonds, and the cyclized PAN coated on the surface of the silicon-carbon composite material through a solvent has the functions of a conductive agent and a binder;
the preparation method of the silicon ‒ carbon ‒ polymer composite electrode of the lithium secondary battery comprises the following steps:
(1) preparation of nano core-shell structure of Si ‒ PAN
Under the protection of inert atmosphere, uniformly mixing PAN and powdered silicon, placing the mixture into a sealed ball-milling tank according to a certain proportion, and then carrying out ball milling to obtain a Si ‒ PAN nanocomposite material, wherein the nanocomposite material has a nanocrystallized core-shell structure, and a chemical coating layer connected with PAN through Si-N bonds is formed on the surface of silicon;
(2) preparation of composite Si ‒ PAN/C
Uniformly mixing the prepared Si ‒ PAN nano composite material with a carbon material according to a certain proportion, dispersing the mixture into a DMF solvent in which part of PAN is dissolved, uniformly stirring, evaporating the DMF solvent to dryness, drying in vacuum, and then placing the mixture in a tubular furnace to carry out heating treatment under inert atmosphere to obtain the final composite material.
2. The silicon ‒ -carbon ‒ polymer composite electrode of claim 1, wherein: the mass ratio of PAN to silicon in the step (1) is 0.5: 9.5-3: 7.
3. The silicon ‒ -carbon ‒ polymer composite electrode of claim 1, wherein: the rotating speed of the ball milling in the step (1) is 100-500 r/min.
4. The silicon ‒ -carbon ‒ polymer composite electrode of claim 1, wherein: the carbon material in the step (2) is any one or more of graphite, mesocarbon microbeads (MCMB), needle coke, resin carbon and biomass carbon.
5. The silicon ‒ -carbon ‒ polymer composite electrode of claim 1, wherein: the mass ratio of the Si ‒ PAN nano composite material to the carbon material in the step (2) is 0.5: 9.5-9: 1.
6. The silicon ‒ -carbon ‒ polymer composite electrode of claim 1, wherein: the temperature of vacuum drying in the step (2) is 60-80 ℃.
7. The silicon ‒ -carbon ‒ polymer composite electrode of claim 1, wherein: and (3) heating treatment in inert atmosphere in the tube furnace in the step (2) at the temperature of 300-900 ℃.
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