Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a core-shell type silicon-carbon composite material, which is prepared by doping a silicon-based material into porous hard carbon to improve energy density and restrict expansion, and simultaneously coating a fast ion conductor material on an outer layer, wherein on one hand, the rate of intercalation and deintercalation of lithium ions in a charge-discharge process is improved, and on the other hand, the coating on the outer surface reduces side reaction of the composite material to improve first efficiency.
In order to achieve the technical purpose, the invention adopts the following technical scheme:
The technical purpose of the first aspect of the invention is to provide a core-shell type silicon-carbon composite material, wherein the inner core is a composite material comprising hard carbon, amorphous carbon and silicon-based material components, and the outer shell is a fast ion conductor; the mass percentage of the shell is 1% -10% based on the total weight of the core-shell type silicon-carbon composite material being 100%; based on the total weight of the inner core as 100%, the mass percentage of hard carbon is 50% -90%, the mass percentage of silicon-based material is 5% -40%, and the balance is amorphous carbon; wherein the silicon-based material is a mixture of silicon oxide and silicon powder, and the mass ratio of the silicon oxide to the silicon powder is 1:0.02-0.2, preferably 1:0.05-0.1.
Further, in the core-shell type silicon-carbon composite material, the fast ion conductor is LixNyWz, wherein X is more than or equal to 1.5 and more than or equal to 0.5, Y is more than or equal to3 and more than or equal to 0.5, and N is one of Ni, co, mn, al, cr, fe, mg, V, zn and Cu; w is selected from one of SiO4-、SO42-、MoO42-、PO43-、TiO32- and ZrO43-. Preferably, the fast ion conductor is selected from at least one of LiNiSO4、LiCoMoO4 and liaaltio3.
Further, the particle size ratio of the silicon-based material silicon oxide to silicon powder is 1-5:1, and the particle size of the silicon oxide is 0.5-2 mu m.
Further, in the core-shell type silicon-carbon composite material, the total weight of the core is 100%, wherein the mass percentages of the components are preferably as follows:
50 to 80 percent of hard carbon
10 To 20 percent of silicon-based material
Amorphous carbon 10% -30%
The technical purpose of the second aspect of the invention is to provide a preparation method of the core-shell type silicon-carbon composite material, which comprises the following steps:
Preparing a core: dispersing silicon oxide, silicon powder and a silane coupling agent in an organic solvent, mixing, spray drying, adding the obtained solid material into a starch aqueous solution, mixing, spray drying, and carbonizing in an inert atmosphere to obtain a core;
and (3) coating a shell: and depositing a fast ion conductor on the surface of the inner core by an atomic vapor deposition method to obtain the core-shell type silicon-carbon composite material.
In the preparation method, when preparing the kernel, the raw materials are added according to the following mass ratio: silicon powder: organic solvent: silane coupling agent: starch=50: (1-10): (100-500): (1-10):800-1200.
In the preparation method, the particle size ratio of the silicon oxide to the silicon powder is 1-5:1, and the particle size of the silicon oxide is 0.5-2 mu m.
In the above preparation method, the silane coupling agent is a sulfur-containing silane coupling agent, more specifically, the silane coupling agent is at least one selected from bis (3-propyltriethoxysilane coupling agent) disulfide, bis (3-propyltriethoxysilane coupling agent) tetrasulfide, 3-mercaptopropyl trimethoxysilane, 3-mercaptopropyl triethoxysilane, 3-mercaptopropyl methyldimethoxysilane, 3-mercaptopropyl ethyloxy di (tridecylpenta-diethyl ether) silane, 3-mercaptopropyl ethyloxy di (propylhexa-propyl ether) silane, 3-hexanoylthio-1-propyltriethoxysilane, 3-octanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propylethoxy (2-methyl-1, 3-propanediol subunit) silane.
In the above preparation method, the organic solvent is at least one selected from carbon tetrachloride, N-methylpyrrolidone, xylene and cyclohexane.
In the above preparation method, the starch is at least one selected from potato starch, corn starch, wheat starch and sweet potato starch.
In the preparation method, the carbonization is carried out for 1-6 hours at 800-1200 ℃ under inert atmosphere.
In the preparation method, the ball milling mode is adopted for twice mixing when preparing the kernel.
In the above preparation method, the atomic vapor deposition method specifically includes: vacuumizing the reaction chamber to 50-100toor, heating to 100-300 ℃, gasifying the fast ion conductor, carrying the fast ion conductor into the reaction chamber by nitrogen at a flow rate of 10-100sccm, adsorbing the fast ion conductor on the surface of the inner core until the air pressure of the reaction chamber reaches 5-20toor, and keeping for 1-120s to realize coating of the fast ion conductor.
The technical purpose of the third aspect of the invention is to provide the application of the core-shell type silicon-carbon composite material as a battery anode material.
The implementation of the embodiment of the invention has the following beneficial effects:
(1) The silicon-carbon composite material has a core-shell structure, the inner core is a composite material of hard carbon and a silicon-based material, the silicon-based material improves specific capacity, and the expansion in the charge and discharge process can be reduced when the silicon-carbon composite material is embedded into the hard carbon; the shell is a fast ion conductor, so that the fast charging performance of the material is improved, the surface of the inner core is coated, the defects of the surface of the inner core are reduced, and the first efficiency of the material is improved. In addition, the silicon-based material silicon oxide and the nano silicon powder are connected through the coupling agent to form a network structure, and the silicon oxide with relatively large particle size is further adopted, so that the agglomeration of the nano silicon can be reduced, the nano silicon powder has the characteristic of high electronic conductivity, and the rate capability in the charge and discharge process is improved.
(2) According to the core-shell type silicon-carbon composite material, starch is adopted as a hard carbon raw material in the preparation process of a core, porous hard carbon is formed after carbonization, and silicon-based materials are doped in pores of the hard carbon in the carbonization process to obtain a composite material core, so that on one hand, the silicon-based materials can improve the specific capacity of the material, and on the other hand, the silicon-based materials are embedded in the carbon-based materials to reduce expansion in the charge and discharge processes; and a silane coupling agent is also added in the preparation process of the inner core to connect carbon with silicon, so that the expansion of the material in the charge and discharge processes is further reduced. The shell deposits the fast ion conductor on the surface of the hard carbon-silicon of the inner core through an atomic vapor deposition method, on one hand, the fast charge performance of the material is improved by virtue of the characteristic of high conductivity in the charge and discharge process of the fast ion conductor, on the other hand, the fast ion conductor is coated on the surface of the inner core through the atomic vapor deposition method, so that the defect of the surface of the inner core is greatly reduced, and the first efficiency of the material is improved.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Core-shell silicon-carbon composites were prepared in examples 1-3:
Example 1
S1, preparing a kernel:
Mixing 50g of silicon oxide, 5g of nano silicon powder and 300g of N-methyl pyrrolidone organic solvent, wherein the average particle size of the silicon oxide is 1000nm, the average particle size of the nano silicon powder is 200nm, adding 5g of bis (3-propyltriethoxysilane coupling agent) disulfide after uniform dispersion, ball milling and spray drying, adding the obtained material into 10000mL of 10wt% potato starch aqueous solution, ball milling and spray drying, and carbonizing at 800 ℃ for 3h under an argon inert atmosphere to obtain the silicon-carbon composite material serving as an inner core.
S2, preparing a shell:
And vacuumizing the reaction chamber to 80toor ℃ by an atomic vapor deposition method, heating to 200 ℃, gasifying LiNiSO4, pulsing into the reaction chamber at a flow rate of 50sccm under the carrying of nitrogen, and adsorbing LiNiSO4 on the surface of the inner core until the air pressure of the reaction chamber reaches 10toor, and maintaining for 60 seconds to obtain the core-shell type silicon-carbon composite material.
Example 2
S1, preparing a kernel:
mixing 50g of silicon oxide, 1g of nano silicon powder and 100g of carbon tetrachloride, wherein the average particle size of the silicon oxide is 500nm, the average particle size of the nano silicon powder is 100nm, adding 1g of bis (3-propyltriethoxysilane coupling agent) tetrasulfide after uniform dispersion, ball milling and spray drying, adding the obtained material into 10000mL of 10wt% corn starch aqueous solution, ball milling and spray drying, and carbonizing at 800 ℃ for 6 hours under an argon inert atmosphere to obtain the silicon-carbon composite material serving as an inner core.
S2, preparing a shell:
And vacuumizing the reaction chamber to 50toor ℃ by an atomic vapor deposition method, heating to 100 ℃, gasifying LiCoMoO4, carrying nitrogen, pulsing into the reaction chamber at a flow rate of 10sccm, and adsorbing LiCoMoO4 on the surface of the inner core until the air pressure of the reaction chamber reaches 5toor, and keeping for 1s to obtain the core-shell type silicon-carbon composite material.
Example 3
S1, preparing a kernel:
Mixing 50g of silicon oxide, 10g of nano silicon powder and 500g of cyclohexane organic solvent, wherein the average particle size of the silicon oxide is 2000nm, the average particle size of the nano silicon powder is 500nm, adding 10g of 3-mercaptopropyl ethoxy di (tridecyl pentamethylene ether) silane after uniform dispersion, ball milling and spray drying, adding the obtained material into 2000mL of 50wt% wheat starch aqueous solution, ball milling and spray drying, and carbonizing at 800 ℃ for 6 hours under an argon inert atmosphere to obtain the silicon-carbon composite material serving as a core.
S2, preparing a shell:
And vacuumizing the reaction chamber to 100toor ℃ by an atomic vapor deposition method, heating to 300 ℃, gasifying LiAlTiO3, carrying nitrogen, and pulse-entering the reaction chamber at a flow rate of 100sccm, wherein LiAlTiO3 is adsorbed on the surface of the inner core until the air pressure of the reaction chamber reaches 20toor, and maintaining for 120s to obtain the core-shell type silicon-carbon composite material.
Comparative example 1
50G of silicon monoxide is added into 10000mL of 10wt% potato starch aqueous solution, ball milling and spray drying are carried out, and then carbonization is carried out for 3 hours at 800 ℃ under the inert atmosphere of argon, thus obtaining the silicon-carbon composite material.
Comparative example 2
100G of corn starch and 10g of asphalt are uniformly mixed by a ball mill, then the mixture is polymerized for 1h at the temperature of 200 ℃ under the inert atmosphere, then carbonized for 3 h at the temperature of 800 ℃ under the protection of inert gas, and cooled to the room temperature after the completion to obtain the hard carbon composite material.
Comparative example 3
S1, preparing a kernel:
s1 is the same as in example 1.
S2, bonding the shell by a solution method:
Taking 100g of the kernel prepared by S1, adding 5g LiNiSO4 g of asphalt binder and 100mL of butanediol, uniformly mixing and stirring, filtering, transferring into a tube furnace, carbonizing at 800 ℃ for 3h under argon atmosphere, and crushing to obtain the silicon-carbon composite material.
Comparative example 4
The procedure was the same as in example 1 except that 50g of silica was changed to 68.2g of silica (the weight of silicon element added to the system was the same as in example 1), to obtain a core-shell type silicon-carbon composite.
Comparative example 5
The procedure was otherwise identical to example 1 except that no silica was added to obtain a core-shell type silicon-carbon composite.
Comparative example 6
The procedure was as in example 1 except that 50g of silica and 5g of nano-silica powder were replaced with 1g of silica and 50g of nano-silica powder, to obtain a core-shell type silicon-carbon composite.
Performance testing of the materials prepared in the above examples and comparative examples:
(1) SEM test
The core-shell type silicon-carbon composite material prepared in example 1 was subjected to SEM test, and the test results are shown in fig. 1.
As can be seen from FIG. 1, the composite material prepared in example 1 has a granular structure, has a relatively uniform size distribution and has a particle size of 2-10 μm.
(2) Physical and chemical properties and button cell testing
The composite materials prepared in examples 1 to 3 and comparative examples 1 to 6 were subjected to particle size, true density, tap density, specific surface area, ash content and specific capacity tests. The method is tested according to the national standard GBT-24533-2019 lithium ion battery graphite anode material. The test results are shown in Table 1.
TABLE 1
The composite materials in examples 1-3 and comparative examples 1-6 are used as negative electrode materials of lithium ion batteries to be assembled into button batteries, and the specific preparation method of the negative electrode materials is as follows: adding binder, conductive agent and solvent into the composite material, stirring to slurry, coating on copper foil, oven drying, and rolling. The adhesive is LA132 adhesive, the conductive agent SP, the solvent is secondary distilled water, and the composite material is prepared from the following components: SP: LA132: secondary distilled water = 90g:4g:6g:220mL, preparing a negative electrode plate; a metal lithium sheet is used as a positive electrode; the electrolyte adopts LiPF6/EC+DEC, liPF6 in the electrolyte is electrolyte, the mixture of EC and DEC with the volume ratio of 1:1 is solvent, and the electrolyte concentration is 1.3mol/L; the diaphragm adopts a composite film of polyethylene PE, polypropylene PP or polyethylene propylene PEP. The button cell assembly was performed in an argon filled glove box. Electrochemical performance was performed on a wuhan blue electric CT2001A type battery tester with a charge-discharge voltage ranging from 0.005V to 2.0V and a charge-discharge rate of 0.1C, and the first discharge capacity and first efficiency of the coin cell battery were tested while the rate performance (5C, 0.1C) and cycle performance (0.5C/0.5C, 200 times) were tested. The test results are shown in Table 2.
TABLE 2
As can be seen from table 1 and table 2, the material prepared by the embodiment of the invention has high specific capacity and first efficiency, and is characterized in that the silicon oxide and silicon doped in the material cooperate to improve the specific capacity of the material, meanwhile, the surface of the material is coated with a fast ion conductor, so that the irreversible capacity loss of the material is reduced, the first efficiency and the multiplying power performance of the material are improved, and the atomic vapor deposition method has the characteristic of high coating density, thereby improving the tap density of the material. Compared with the material prepared by the traditional liquid phase cladding method, the material of the embodiment 1 has high density, low electronic impedance, improved activity, specific capacity and first efficiency, and improved rate performance.
(3) Soft package battery test:
The composite materials in examples 1-3 and comparative examples 1-6 were subjected to slurry mixing and coating to prepare a negative electrode sheet, a ternary material (LiNi1/3Co1/3Mn1/3O2) was used as a positive electrode, liPF6 (solvent ec+dec, volume ratio 1:1, electrolyte concentration 1.3 mol/L) was used as an electrolyte, and Celgard2400 membrane was used as a separator to prepare a 1Ah soft-pack battery.
The rate performance of the soft package battery is tested, the charging and discharging voltage ranges from 2.75V to 4.2V, the temperature is 25+/-3.0 ℃, the charging is carried out at 1.0C, 3.0C, 5.0C, 10.0C and 20.C, and the discharging is carried out at 1.0C. The results are shown in Table 3.
TABLE 3 Table 3
As can be seen from table 3, the rate charging performance of the soft pack batteries prepared from the materials of examples 1 to 3 is significantly better than that of comparative examples 1 to 2, i.e., the charging time is shorter, because of the analysis: the migration of lithium ions is needed in the battery charging process, while the surface of the negative electrode material in the embodiment is coated with a fast ion conductor with high lithium ion conductivity, and meanwhile, compared with a solid phase coating method, an atomic vapor deposition method is adopted, and amorphous carbon coated on the surface of a hard carbon material has the characteristics of high density and stable structure, so that the rate capability is improved.
(4) And (3) testing the cycle performance:
The cycle performance test conditions were: the charge and discharge current is 0.5C/1C, the voltage range is 2.5-4.2V, and the cycle times are 1000 times. The test results are shown in Table 4.
TABLE 4 Table 4
It can be seen from Table 4 that the cycle performance of the lithium ion batteries prepared using the composite materials obtained in examples 1 to 3 was significantly better at each stage than that of the comparative example. Experimental results show that the fast ion conductor deposited on the surface of the hard carbon by the atomic vapor deposition method has the characteristics of high density, stable structure and strong ion conductivity, and the expansion of silicon in the process of low-constraint charge and discharge of the hard carbon expansion of the inner core is improved, and the cycle performance is improved.
The foregoing disclosure is illustrative of the present invention and is not to be construed as limiting the scope of the invention, which is defined by the appended claims.