CN114976008A - Low-expansion silicon-carbon negative electrode material for lithium ion battery and preparation method thereof - Google Patents
Low-expansion silicon-carbon negative electrode material for lithium ion battery and preparation method thereof Download PDFInfo
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- HMDDXIMCDZRSNE-UHFFFAOYSA-N [C].[Si] Chemical compound [C].[Si] HMDDXIMCDZRSNE-UHFFFAOYSA-N 0.000 title claims abstract description 65
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 28
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 28
- 239000007773 negative electrode material Substances 0.000 title claims abstract description 28
- 238000002360 preparation method Methods 0.000 title claims abstract description 24
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 53
- 239000000463 material Substances 0.000 claims abstract description 51
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 40
- 239000003575 carbonaceous material Substances 0.000 claims abstract description 32
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 26
- 239000007833 carbon precursor Substances 0.000 claims abstract description 23
- 238000004518 low pressure chemical vapour deposition Methods 0.000 claims abstract description 23
- 229910021389 graphene Inorganic materials 0.000 claims abstract description 22
- 238000000034 method Methods 0.000 claims abstract description 21
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 20
- 238000000151 deposition Methods 0.000 claims abstract description 15
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- 238000006243 chemical reaction Methods 0.000 claims description 13
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- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 6
- 239000010406 cathode material Substances 0.000 claims description 6
- 239000007788 liquid Substances 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 6
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- XDTMQSROBMDMFD-UHFFFAOYSA-N Cyclohexane Chemical compound C1CCCCC1 XDTMQSROBMDMFD-UHFFFAOYSA-N 0.000 claims description 4
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- OBNDGIHQAIXEAO-UHFFFAOYSA-N [O].[Si] Chemical compound [O].[Si] OBNDGIHQAIXEAO-UHFFFAOYSA-N 0.000 claims description 3
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- 239000002243 precursor Substances 0.000 description 3
- 238000005086 pumping Methods 0.000 description 3
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- 229910013716 LiNi Inorganic materials 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 239000006087 Silane Coupling Agent Substances 0.000 description 1
- 239000013543 active substance Substances 0.000 description 1
- 239000010405 anode material Substances 0.000 description 1
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- 229910021383 artificial graphite Inorganic materials 0.000 description 1
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- 239000011239 graphite-silicon composite material Substances 0.000 description 1
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 1
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- 238000005805 hydroxylation reaction Methods 0.000 description 1
- 230000002427 irreversible effect Effects 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- -1 lithium hexafluorophosphate Chemical compound 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
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- 239000011856 silicon-based particle Substances 0.000 description 1
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- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
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- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
- C23C16/26—Deposition of carbon only
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Abstract
A low-expansion silicon-carbon negative electrode material for a lithium ion battery and a preparation method thereof are disclosed, the material is of a core-shell structure and comprises a silica inner core, an intermediate layer coated on the surface of the silica inner core and an outer layer coated on the surface of the intermediate layer, the intermediate layer is a porous carbon material, the outer layer is phosphorus-doped graphene, the porous carbon material is dissolved and dispersed in organic solution of phenolic resin during preparation, the silica material and an oxidant are added, and a silicon-carbon precursor material is obtained through hydrothermal reaction; and depositing the phosphorus-doped graphene outer layer on the silicon-carbon precursor material by an LPCVD (low pressure chemical vapor deposition) method to obtain the low-expansion silicon-carbon negative electrode material for the lithium ion battery. According to the silicon-carbon negative electrode material, the porous carbon material and the amorphous carbon thereof are coated on the inner core silica material, the expansion of silicon in the charging and discharging processes is reduced by utilizing the porous carbon, and the prepared silicon-carbon negative electrode material is high in electronic conductivity, high in carbon deposition density and good in coating uniformity.
Description
Technical Field
The invention belongs to the field of preparation of lithium ion battery materials, and particularly relates to a low-expansion silicon-carbon negative electrode material for a lithium ion battery and a preparation method thereof.
Background
The silicon-carbon cathode material on the market at present is applied to the lithium ion battery with high specific energy density due to the advantages of high specific energy density, wide material source and the like, but the silicon-carbon cathode material has the problem of large expansion and is easy to cause the deterioration of the cycle performance of the material. The reason for the expansion of the silicon-carbon negative electrode material is that the amorphous carbon does not reserve enough space for the expansion of lithium ions in the charging and discharging process, so that the expansion is large or the mechanical strength of a coating layer is insufficient in the expansion process, so that the structural collapse influences the cycle performance of the silicon-carbon negative electrode material.
In the prior art, expansion is mainly reduced by compounding with graphite, for example, patent (CN 104319367-a) provides a preparation method of a graphite-silicon composite negative electrode material, which mainly comprises the following steps: the method comprises the steps of mixing simple substance silicon particles with graphite, carrying out ball milling to obtain a sample, carrying out hydroxylation treatment on silicon, and treating the product by using a silane coupling agent to obtain the silicon/graphite composite negative electrode material.
Disclosure of Invention
The invention aims to provide a low-expansion silicon-carbon negative electrode material for a lithium ion battery and a preparation method thereof.
The technical scheme adopted by the invention is as follows:
the silicon-carbon negative electrode material is of a core-shell structure and comprises a silica inner core, an intermediate layer and an outer layer, wherein the intermediate layer is coated on the surface of the silica inner core, the outer layer is coated on the surface of the intermediate layer, the intermediate layer is made of a porous carbon material, and the outer layer is phosphorus-doped graphene.
Furthermore, the mass ratio of the middle layer is 5-30 wt%, and the mass ratio of the outer layer is 1-5 wt%.
A preparation method of a low-expansion silicon-carbon negative electrode material for a lithium ion battery comprises the following steps:
(1) dissolving and dispersing a porous carbon material in an organic solution of phenolic resin, adding a silica material for uniform dispersion, adding an oxidant, performing hydrothermal reaction, filtering, and performing vacuum drying to obtain a silicon-carbon precursor material;
(2) and depositing the phosphorus-doped graphene outer layer on the silicon-carbon precursor material by an LPCVD (low pressure chemical vapor deposition) method to obtain the low-expansion silicon-carbon cathode material for the lithium ion battery.
Further, the hydrothermal reaction conditions in the step (1) are as follows: the temperature is 100-200 ℃, the time is 1-6 h, and the pressure is 1-5 Mpa.
Further, the preparation method of the porous carbon material in the step (1) comprises the following steps: adding asphalt and potassium hydroxide into deionized water, uniformly dispersing, performing vacuum drying, performing vacuum filtration, placing a filtered mixture in a tubular furnace, activating for 1-6 h at 150-300 ℃ under the protection of nitrogen, then heating to 600-1000 ℃ for activating for 1-6 h, washing a product to be neutral, filtering and drying to obtain the porous carbon material.
Further, asphalt: potassium hydroxide: the mass ratio of the deionized water is 100: (10-30): (500-1000).
Further, in step (1), porous carbon: phenolic resin: silicon oxygen: mass ratio of oxidant = (5-15); (5-15): 100: (0.5-2).
Further, in the step (1), the mass concentration of the phenolic resin is 1-10 wt%, and the solvent is one or more of ethanol, acetone, ethylene glycol and cyclohexane.
Further, in the step (2), the process of depositing the phosphorus-doped graphene outer layer by using the LPCVD method is as follows: putting a silicon-carbon precursor material into an LPCVD cavity, introducing Ar at a flow rate of 100-300 sccm and introducing a carbon source gas at a flow rate of 100-300 sccm under a pressure of 5-20 Pa in the reaction cavity, heating to 600-1000 ℃, keeping the temperature for 1-6 hours, then introducing a phosphoric acid liquid at a flow rate of 500sccm, and reacting for 0.5-2 hours to carry out gas deposition.
Further, the oxidant is hydrogen peroxide.
The invention has the beneficial effects that:
1. according to the invention, the porous carbon material and the amorphous carbon thereof are coated on the inner core silica material, so that on one hand, the expansion of silicon in the charging and discharging process is reduced by using the porous carbon, and meanwhile, the amorphous carbon is filled between the porous carbons, thereby improving the contact between the materials and the electronic conductivity of the material.
2. According to the invention, the phosphorus-doped graphene outer layer is deposited on the outermost layer by an LPCVD method, the characteristics of high carbon deposition density, good coating uniformity and the like are achieved, and the electronic conductivity of the material is further improved by doping phosphorus.
3. According to the invention, the carbon source gas is firstly introduced to deposit graphene on the surface of the silica precursor, the electronic conductivity of the silica precursor of the inner core is improved, the interface impedance of the silica precursor is reduced, then phosphoric acid is introduced to dope the carbon-based materials such as graphene, the specific capacity of the shell is improved by doping phosphorus according to the high specific capacity of phosphorus, and meanwhile, the outermost layer is doped with phosphorus, so that the phosphorus has better compatibility with lithium hexafluorophosphate in the electrolyte, and the storage performance of the material is improved.
Drawings
Fig. 1 is an SEM image of a silicon carbon anode material prepared in example 1.
Detailed Description
The silicon-carbon negative electrode material is of a core-shell structure and comprises a silica inner core, an intermediate layer and an outer layer, wherein the intermediate layer is coated on the surface of the silica inner core, the outer layer is coated on the surface of the intermediate layer, the intermediate layer is made of a porous carbon material, and the outer layer is phosphorus-doped graphene.
Wherein the mass ratio of the middle layer is (5-30) wt%, and the mass ratio of the outer layer is (1-5) wt%.
A preparation method of a low-expansion silicon-carbon negative electrode material for a lithium ion battery comprises the following steps:
(1) dissolving and dispersing a porous carbon material in an organic solution of phenolic resin, adding a silica material for uniform dispersion, adding an oxidant, performing hydrothermal reaction, filtering, and performing vacuum drying to obtain a silicon-carbon precursor material;
(2) and depositing the phosphorus-doped graphene outer layer on the silicon-carbon precursor material by an LPCVD (low pressure chemical vapor deposition) method to obtain the low-expansion silicon-carbon cathode material for the lithium ion battery.
The hydrothermal reaction conditions in the step (1) are as follows: the temperature is 100-200 ℃, the time is 1-6 h, and the pressure is 1-5 Mpa.
The preparation method of the porous carbon material in the step (1) comprises the following steps: adding asphalt and potassium hydroxide into deionized water, uniformly dispersing, performing vacuum drying, performing vacuum filtration, placing a filtered mixture in a tubular furnace, activating for 1-6 h at 150-300 ℃ under the protection of nitrogen, then heating to 600-1000 ℃ for activating for 1-6 h, washing a product to be neutral, filtering and drying to obtain the porous carbon material.
Asphalt: potassium hydroxide: the mass ratio of the deionized water is 100: (10-30): (500-1000).
In step (1), porous carbon: phenolic resin: silicon oxygen: mass ratio of oxidant = (5-15); (5-15): 100: (0.5-2).
In the step (1), the mass concentration of the phenolic resin is (1-10) wt%, and the solvent is one or more of ethanol, acetone, ethylene glycol and cyclohexane.
In the step (2), the process of depositing the phosphorus-doped graphene outer layer by using the LPCVD method comprises the following steps: putting a silicon-carbon precursor material into an LPCVD cavity, introducing Ar at a flow rate of 100-300 sccm and introducing a carbon source gas at a flow rate of 100-300 sccm under a pressure of 5-20 Pa in the reaction cavity, heating to 600-1000 ℃, keeping the temperature for 1-6 hours, then introducing a phosphoric acid liquid at a flow rate of 500sccm, and reacting for 0.5-2 hours to carry out gas deposition.
The oxidant is hydrogen peroxide.
Example 1
1) Preparation of porous carbon material:
weighing 100g of asphalt and 20g of potassium hydroxide, adding the asphalt and the potassium hydroxide into 800g of deionized water, performing ultrasonic dispersion uniformly, performing vacuum drying at 80 ℃, performing vacuum filtration, placing the filtered mixture in a tubular furnace, activating at 200 ℃ for 3h under the protection of nitrogen, then heating to 800 ℃ for 3h, washing the product to be neutral, and performing filtration and drying to obtain the porous carbon material.
2) Preparing a silicon-carbon precursor material:
weighing 10g of porous carbon, adding the porous carbon into 200ml of 5wt% phenolic resin acetone organic solution, uniformly dispersing, adding 100g of silica material into the solution, uniformly dispersing by ultrasonic, adding 1g of oxidant hydrogen peroxide, transferring the mixture into a high-pressure reaction kettle, performing hydrothermal reaction, controlling the temperature of the hydrothermal reaction at 150 ℃, the time at 3h and the pressure at 3Mpa, and after the reaction is finished, filtering and drying in vacuum to obtain the silicon-carbon precursor material.
3) Phosphorus-doped graphene-coated silicon carbon material:
putting a silicon-carbon precursor material into an LPCVD (low pressure chemical vapor deposition) cavity, pumping the pressure of the reaction cavity to 10 Pa, setting flow meters of Ar and carbon source gases to be 200sccm and 200sccm respectively, opening valves of Ar and a carbon source, heating to 800 ℃, and keeping the temperature for 3 hours; and then opening a phosphoric acid liquid valve, adjusting the flow rate to be 500sccm, volatilizing phosphoric acid by using a low-pressure environment, performing gas deposition for 1h to complete the coating of the phosphorus-doped graphene on the silicon-carbon material, and then cooling to obtain the low-expansion silicon-carbon cathode material.
Example 2
1) Preparation of porous carbon material:
weighing 100g of asphalt and 10g of potassium hydroxide, adding the asphalt and the potassium hydroxide into 500ml of deionized water, performing ultrasonic dispersion uniformly, performing vacuum drying, performing vacuum filtration, placing the filtered mixture in a tubular furnace, activating for 6 hours at 150 ℃ under the protection of nitrogen, then heating to 600 ℃ for activating for 6 hours, washing the product to be neutral, and performing filtration and drying to obtain the porous carbon material.
2) Silicon-carbon precursor material:
weighing 5g of porous carbon, adding the porous carbon into 50ml of 1wt% of phenolic resin glycol organic solution, uniformly dispersing, adding 100g of silica material into the mixture, uniformly dispersing by ultrasonic, adding 0.5g of oxidant hydrogen peroxide, transferring the mixture into a high-pressure reaction kettle, performing hydrothermal reaction, controlling the temperature of the hydrothermal reaction at 100 ℃, the time at 6 hours and the pressure at 1Mpa, and filtering and drying in vacuum after the reaction is finished to obtain the silicon-carbon precursor material.
3) Phosphorus-doped graphene coated silicon carbon material:
putting a silicon-carbon precursor material into an LPCVD (low pressure chemical vapor deposition) cavity, forcibly pumping the pressure of the reaction cavity to 5 Pa, respectively setting the flow meters of Ar and carbon source gases to be 100sccm and 300sccm, opening the valves of Ar and a carbon source, then heating to 600 ℃, and keeping for 6 hours; and then opening a phosphoric acid liquid valve, adjusting the flow rate to be 500sccm, volatilizing phosphoric acid by using a low-pressure environment, performing gas deposition for 0.5h to complete the coating of the phosphorus-doped graphene on the silicon-carbon material, and cooling to obtain the phosphorus-doped graphene-coated silicon-carbon material.
Example 3
1) Preparation of porous carbon material:
weighing 100g of asphalt and 30g of potassium hydroxide, adding the asphalt and the potassium hydroxide into 1000ml of deionized water, performing ultrasonic dispersion uniformly, performing vacuum drying, performing vacuum filtration, placing the filtered mixture in a tube furnace, activating for 1h at 300 ℃ under the protection of nitrogen, then heating to 1000 ℃ for activating for 1h, washing the product to neutrality, filtering and drying to obtain the porous carbon material.
2) Silicon-carbon precursor material:
and then dissolving 15g of porous carbon in 150ml of cyclohexane organic solution of 10wt% of phenolic resin, after uniform dispersion, adding 100g of silica material into the solution, performing ultrasonic dispersion, adding 2g of oxidant hydrogen peroxide, transferring the mixture into a high-pressure reaction kettle, performing hydrothermal reaction, controlling the temperature of the hydrothermal reaction at 200 ℃, the time at 1h and the pressure at 5Mpa, and after the reaction is finished, filtering and drying in vacuum to obtain the silicon-carbon precursor material.
3) Phosphorus-doped graphene-coated silicon carbon material:
putting a silicon-carbon precursor material into an LPCVD (low pressure chemical vapor deposition) cavity, forcibly pumping the pressure of the reaction cavity to 20 Pa, respectively setting the flow meters of Ar and carbon source gases to be 300sccm and 100sccm, opening the valves of Ar and a carbon source, then heating to 1000 ℃, and keeping for 1 h; and then opening a phosphoric acid liquid valve, adjusting the flow rate to be 500sccm, volatilizing phosphoric acid by using a low-pressure environment, performing gas deposition for 2 hours to complete the coating of the phosphorus-doped graphene on the silicon-carbon material, and cooling to obtain the phosphorus-doped graphene-coated silicon-carbon material.
Comparative example 1:
the silicon-carbon precursor material is prepared by adopting the steps 1) and 2) in the embodiment 1, then the temperature is raised to 700 ℃ in the argon atmosphere, the heat preservation is carried out for 3h, and the silicon-carbon composite material is obtained by crushing.
Comparative example 2:
the silicon-carbon precursor material prepared in the steps 1) and 2) in the embodiment 1 is adopted, then the silicon-carbon precursor material is placed in an LPCVD cavity, the pressure of the reaction cavity is pumped to 10 Pa, the flow meters of Ar and a carbon source gas are respectively set to be 200sccm and 200sccm, the valves of Ar and a carbon source are opened, then the temperature is raised to 800 ℃, the temperature is kept for 3 hours, and then the temperature is naturally reduced to the room temperature to obtain the silicon-carbon composite material.
Test example 1
The SEM test of the silicon-carbon composite material of example 1 showed that the particle size of the silicon-carbon composite material is 5 to 15 μm, and the embedded nano-scale material particles are present on the surface, as shown in fig. 1.
Test example 2
The physicochemical properties (powder conductivity, tap density, and specific surface area) of the silicon-carbon composites of examples 1 to 3 and the silicon-carbon composites of comparative examples 1 to 2 were measured by the method of the national standard GBT-245332009 graphite-based negative electrode material for lithium ion batteries, and the measurement results are shown in table 1.
TABLE 1 comparison of the physico-chemical properties of the examples and of the comparative examples
As can be seen from Table 1: compared with the comparative example, the powder conductivity of the silicon-carbon composite material is obviously improved because the example material is doped with phosphorus, so that the electronic conductivity of the material is improved, and meanwhile, the density of a coating layer of the material can be higher by the LPCVD technology.
Test example 3
The silicon-carbon composite materials in the embodiments 1-3 and the silicon-carbon composite materials in the comparative examples 1-2 are respectively used as active materials to prepare the pole piece, and the specific preparation method comprises the following steps: adding 9g of active substance, 0.5g of conductive agent SP and 0.5g of binder LA133 into 220mL of deionized water, uniformly stirring to obtain slurry, and coating the slurry on a copper foil current collector to obtain the pole piece.
The pole piece using the silicon-carbon composite material of example 1 as the active material was labeled a, the pole piece using the silicon-carbon composite material of example 2 as the active material was labeled B, the pole piece using the silicon-carbon composite material of example 3 as the active material was labeled C, and the pole pieces using the silicon-carbon composite materials of comparative examples 1 to 2 as the active materials were labeled D and E.
Then, the prepared pole piece is used as a positive pole, and the pole piece, a lithium piece, electrolyte and a diaphragm are assembled into a button cell in a glove box with oxygen and water contents lower than 0.1ppm, wherein the diaphragm is celegard 2400; the electrolyte is LiPF 6 Solution of (2), LiPF 6 Is 1.2mol/L, and the solvent is a mixed solution of Ethylene Carbonate (EC) and diethyl carbonate (DMC) (weight ratio is 1: 1).
Respectively marking the pole pieces A, B, C, D, E corresponding to the button cell as A-1, B-1, C-1 and D-1, E-1, and then testing the performance of the button cell by adopting a blue light tester, wherein the testing conditions are as follows: and (3) carrying out charge and discharge at a multiplying power of 0.1C, wherein the voltage range is 0.05-2V, the cycle is stopped after 3 weeks, and then the full-electricity expansion of the negative pole piece is tested, and the test results are shown in table 2.
TABLE 2 button cell Performance test results
As can be seen from table 2, the silicon-carbon composite material of the present invention has a significantly improved first efficiency compared to the comparative example, and contains phosphorus, which improves the electronic conductivity of the material, reduces the impedance, reduces the irreversible capacity, and improves the first efficiency of the material, and at the same time, the carbon and phosphorus deposited in the shell of the silicon-carbon material in the examples by the PCVD technique have the characteristics of high density, high consistency, and the like, and restrict the expansion of lithium ions during charging and discharging.
Test example 4
The silicon-carbon composite materials of examples 1-3 and comparative examples 1-2 were doped with 90% artificial graphite as a negative electrode material and a positive electrode ternary material (LiNi) 1/3 Co 1/3 Mn 1/3 O 2 ) The electrolyte and the diaphragm are assembled into the 5Ah soft package battery, wherein the diaphragm is celegard 2400, and the electrolyte is LiPF 6 Solution (solvent is mixed solution of EC and DEC with volume ratio of 1:1, LiPF 6 The concentration of the electrolyte is 1.3 mol/L), and the prepared soft package batteries are respectively marked as A-2, B-2, C-2, D-2 and E-2.
The following performance tests were performed on the pouch cells:
(1) dissecting and testing the thickness D1 of the negative pole piece of the soft package batteries A-2-E-2 with constant volume, then circulating each soft package battery for 100 times (1C/1C @25 +/-3 ℃ @ 2.5-4.2V), fully charging the soft package batteries, dissecting and testing the thickness D2 of the negative pole piece after circulation again, and then calculating the expansion rate (the expansion rate is equal to the expansion rate of the negative pole piece after circulation is carried out again
) The test results are shown in table 3.
TABLE 3 negative pole piece expansion ratio test results
As can be seen from table 3, the expansion rate of the negative electrode plate of the soft-package lithium ion battery using the silicon-carbon composite material of the present invention is significantly lower than that of the comparative example, because the material density of the silicon-carbon composite material of the present invention is high and the porous carbon structure thereof reduces the expansion of silicon during the charging and discharging processes.
(2) And (3) carrying out cycle performance test and rate test on the soft package batteries A-2-E-2 under the following test conditions: the charge-discharge voltage range is 2.5-4.2V, the temperature is 25 +/-3.0 ℃, and the charge-discharge multiplying power is 0.5C/1.0C; and (3) rate testing: the material was tested for constant current ratio at 2C and the results are shown in table 4.
Table 4 soft package battery cycle performance test results
As can be seen from table 4, the cycle performance of the soft package lithium ion battery prepared by using the silicon-carbon composite material of the present invention is superior to that of the comparative example at each stage of the cycle, and the reason is that the porous carbon in the silicon-carbon composite material of the present invention reduces the expansion during the charge and discharge processes, improves the structural stability of the material, and improves the cycle performance; meanwhile, the doped phosphorus improves the electronic conductivity of the material and reduces the constant current ratio of the impedance-improving material.
It should be noted that the above embodiments are only for illustrating the present invention, but the present invention is not limited to the above embodiments, and any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention fall within the protection scope of the present invention.
Claims (10)
1. The low-expansion silicon-carbon negative electrode material for the lithium ion battery is characterized by being of a core-shell structure and comprising a silica inner core, an intermediate layer and an outer layer, wherein the intermediate layer is coated on the surface of the silica inner core, the outer layer is coated on the surface of the intermediate layer, the intermediate layer is made of a porous carbon material, and the outer layer is phosphorus-doped graphene.
2. The low-expansion silicon-carbon negative electrode material for the lithium ion battery as claimed in claim 1, wherein the mass ratio of the intermediate layer is 5-30 wt%, and the mass ratio of the outer layer is 1-5 wt%.
3. A preparation method of a low-expansion silicon-carbon negative electrode material for a lithium ion battery is characterized by comprising the following steps of:
(1) dissolving and dispersing a porous carbon material in an organic solution of phenolic resin, adding a silica material for uniform dispersion, adding an oxidant, performing hydrothermal reaction, filtering, and performing vacuum drying to obtain a silicon-carbon precursor material;
(2) and depositing the phosphorus-doped graphene outer layer on the silicon-carbon precursor material by an LPCVD (low pressure chemical vapor deposition) method to obtain the low-expansion silicon-carbon cathode material for the lithium ion battery.
4. The preparation method of the low-expansion silicon-carbon negative electrode material for the lithium ion battery as claimed in claim 3, wherein the hydrothermal reaction conditions in the step (1) are as follows: the temperature is 100-200 ℃, the time is 1-6 h, and the pressure is 1-5 Mpa.
5. The preparation method of the low-expansion silicon-carbon negative electrode material for the lithium ion battery as claimed in claim 3, wherein the preparation method of the porous carbon material in the step (1) comprises the following steps: adding asphalt and potassium hydroxide into deionized water, uniformly dispersing, performing vacuum drying, performing vacuum filtration, placing a filtered mixture in a tubular furnace, activating for 1-6 h at 150-300 ℃ under the protection of nitrogen, then heating to 600-1000 ℃ for activating for 1-6 h, washing a product to be neutral, filtering and drying to obtain the porous carbon material.
6. The preparation method of the low-expansion silicon-carbon negative electrode material for the lithium ion battery according to claim 5, wherein the asphalt: potassium hydroxide: the mass ratio of the deionized water is 100: (10-30): (500-1000).
7. The method for preparing the low-expansion silicon-carbon negative electrode material for the lithium ion battery according to claim 3, wherein in the step (1), porous carbon: phenolic resin: silicon oxygen: mass ratio of oxidant = (5-15); (5-15): 100: (0.5-2).
8. The preparation method of the low-expansion silicon-carbon negative electrode material for the lithium ion battery as claimed in claim 3, wherein in the step (1), the mass concentration of the phenolic resin is 1-10 wt%, and the solvent is one or more of ethanol, acetone, ethylene glycol and cyclohexane.
9. The preparation method of the low-expansion silicon-carbon negative electrode material for the lithium ion battery as claimed in claim 3, wherein in the step (2), the process of depositing the phosphorus-doped graphene outer layer by using the LPCVD method comprises the following steps: putting a silicon-carbon precursor material into an LPCVD cavity, introducing Ar at a flow rate of 100-300 sccm and introducing a carbon source gas at a flow rate of 100-300 sccm under a pressure of 5-20 Pa in the reaction cavity, heating to 600-1000 ℃, keeping the temperature for 1-6 hours, then introducing a phosphoric acid liquid at a flow rate of 500sccm, and reacting for 0.5-2 hours to carry out gas deposition.
10. The preparation method of the low-expansion silicon-carbon negative electrode material for the lithium ion battery as claimed in claim 3, wherein the oxidant is hydrogen peroxide.
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