CN113745489A - Low-expansion silicon-carbon composite negative electrode material and preparation method thereof - Google Patents
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Abstract
The invention relates to the technical field of lithium ion battery materials, and provides a low-expansion silicon-carbon composite cathode material which comprises a silicon monoxide material core and a coating layer coated on the surface of the silicon-carbon material core, wherein the coating layer comprises a first coating layer arranged on the surface of the silicon-carbon material core and a second coating layer arranged on the surface of the first coating layer, and the first coating layer is made of materials with electronic conductivity and ionic conductivity; the second coating layer is made of a conductive polymer material with strong flexibility, so that the expansion of the material can be effectively inhibited in the charge and discharge processes of the material, and the structural stability of the material is improved; meanwhile, the first coating layer and the second coating layer are connected through chemical bonds, so that the structural stability of the materials is improved, and the cycle performance is improved.
Description
Technical Field
The invention relates to the technical field of lithium ion battery materials, in particular to a low-expansion silicon-carbon composite negative electrode material and a preparation method thereof.
Background
The silicon carbon material has the advantages of high first-stage energy density, wide material source and the like, and becomes a preferred material of a next-generation high-energy-density lithium ion battery, but the material has poor conductivity and low first-stage efficiency, and the material has large expansion in the charging and discharging processes, so that the cycle performance and the rate performance of the material are poor.
One of the measures for improving the conductivity of the material is to improve the electron-withdrawing capability of the material by doping the surface of the material, for example, doping nitrogen atoms, thereby improving the conductivity of the material and improving the fast-charging performance of the material. Although the conductivity of the material is improved, the expansion of the material is still large, and the cycle performance of the battery and the battery grouping are influenced. The measures for reducing the expansion of the silicon-carbon material are various, such as the nanocrystallization of the material, porous silicon-carbon and the like, but the nanometer silicon-carbon material has strong activity, so that the problems of low initial efficiency, deviation of safety performance, deterioration of later performance of cycle performance, easy water jumping of the battery and the like are caused.
Disclosure of Invention
The invention provides a low-expansion silicon-carbon composite negative electrode material and a preparation method thereof, and solves the problems of poor cycle and rate capability of silicon-carbon materials in the related technology.
The technical scheme of the invention is as follows:
a low-expansion silicon-carbon composite negative electrode material is of a core-shell structure and comprises a core, a first coating layer and a second coating layer from inside to outside in sequence;
wherein the inner core is composed of silicon monoxide, the first coating layer comprises a conductive agent, a solid electrolyte and a silane coupling agent, and the second coating layer is composed of a conductive polymer composite material;
the solid electrolyte is lanthanum lithium zirconate, and the conductive agent is aminated graphene TEPA.
As a further technical scheme, the thickness ratio of the inner core, the first coating layer and the second coating layer is 100 (5-20) to (5-20).
As a further technical scheme, the silane coupling agent comprises one or more of gamma-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, gamma-diethylenetriaminepropylmethyldimethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, N-2-aminoethyl-3-aminopropylmethyldimethoxysilane and gamma-aminopropylmethyldiethoxysilane.
The invention also provides a preparation method of the low-expansion silicon-carbon composite negative electrode material, which comprises the following steps of:
s1, mixing the solid electrolyte, the conductive agent, the silane coupling agent and the organic solvent to obtain a coating solution;
s2, adding silicon monoxide into the coating liquid, and carrying out hydrothermal reaction to prepare a composite material B;
s3, adding a conductive agent B and the composite material B into the polyamic acid solution to prepare spinning solution;
and S4, carrying out electrostatic spinning on the spinning solution, crushing, and heating in an inert atmosphere to obtain the low-expansion silicon-carbon composite negative electrode material.
As a further technical scheme, the organic solvent is one or more of N-methyl pyrrolidone, carbon tetrachloride, butanediol and cyclohexane.
According to a further technical scheme, the mass ratio of the solid electrolyte, the conductive agent, the silane coupling agent, the organic solvent and the silicon monoxide is (1-5): (1-5): (1-5): (100 to 500) and (20 to 50).
As a further technical scheme, in the step S2, the hydrothermal reaction is carried out for 4-6 hours under the conditions that the temperature is 150-160 ℃, the pressure is 2-3 MPa.
As a further technical scheme, the conductive agent B is a single-walled carbon nanotube.
According to a further technical scheme, the mass ratio of the polyamic acid to the conductive agent B to the composite material B is (10-30): (1-5): 100.
as a further technical scheme, the mass concentration of the polyamic acid solution is 0.5-2%.
In a further technical scheme, in the step S3, the mass concentration of the spinning solution is 0.5% to 10%.
As a further technical scheme, in the step S4, the heating temperature is 150-250 ℃, and the heating time is 1-6 hours.
The invention has the beneficial effects that:
1. according to the invention, on one hand, the silicon carbon material is coated with a layer of polymer material with good flexibility, so that the initial expansion and the cyclic expansion of the silicon carbon can be restrained in the charging and discharging processes; on the other hand, the polymer material can prevent the silicon carbon material from directly contacting with the electrolyte, reduce the side reaction and improve the cycle and storage performance of the silicon carbon material. According to the invention, the surface of silicon monoxide is coated with the first coating layer of the material with electronic conductivity and ionic conductivity, so that the electronic ionic conductivity of the material is improved; and the second coating layer of the conductive polymer with strong flexibility improves the expansion and finally improves the cycle and rate capability of the silicon-carbon material.
2. The surface of the core silicon monoxide is coated with a first coating layer consisting of a conductive agent, a solid electrolyte and a silane coupling agent, the quick charging performance of the material is improved by utilizing the characteristic of high ionic conductivity of the solid electrolyte, the electronic conductivity of the conductive agent is improved, the electronic conductivity of the conductive agent and the network structure formed by the core silicon monoxide and the shell by the silane coupling agent are improved, the rate and the cycle performance of the material are improved by exerting the synergistic effect of the conductive agent, the solid electrolyte and the silane coupling agent, and the expansion of the material is reduced.
3. The polyamic acid is a high molecular material, has the characteristics of high flexibility, strong binding force and high electronic conductivity, and further reduces the internal resistance of the material and improves the cycle performance of the material. The conductive agent B is a carbon nano tube, on one hand, the conductive agent B is high in conductivity and is of a network structure, the conductive agent B is mixed with polyamic acid to improve the conductivity of the material of the conductive agent B, the polyamic acid and the carbon nano tube are coated on the surface of the composite material B to improve the conductivity of the solid electrolyte material of the composite material B, the ionic conductivity of the solid electrolyte is high, the electronic conductivity is poor, and finally the fibrous structure formed by the polyimide is exerted, so that the fibrous composite material is obtained, the expansion is reduced, and the cycle rate is improved.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Fig. 1 is an SEM image of a silicon carbon composite material prepared in example 1.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any inventive step, are intended to be within the scope of the present invention.
Example 1
S1, mixing 3g of lanthanum lithium zirconate, 3g of aminated graphene TEPA, 3g of gamma-aminopropyltrimethoxysilane and 500g of N-methylpyrrolidone to obtain a coating solution;
s2, adding 20g of silicon monoxide into the coating solution, and carrying out hydrothermal reaction at 150 ℃ and 3MPa for 6h to prepare a composite material B with the surface coated with a solid electrolyte;
s3, mixing 20g of polyamic acid and N-methyl pyrrolidone to prepare a 1% polyamic acid solution, adding 3g of single-walled carbon nanotube and 100g of composite material B, and preparing a spinning solution with the concentration of 6.1 wt%;
s4, spraying the spinning solution on a light plate through electrostatic spinning, then crushing, heating in a nitrogen atmosphere to convert polyamic acid into polyimide, and keeping the heating temperature at 200 ℃ for 3 hours to obtain the silicon-carbon composite material with the polyimide nanofiber membrane as the shell, namely the low-expansion silicon-carbon composite negative electrode material.
Example 2
S1, mixing 1g of lanthanum lithium zirconate, 1g of aminated graphene TEPA, 5g of gamma-aminopropyltriethoxysilane and 100g of carbon tetrachloride to obtain a coating solution;
s2, adding 30g of silicon monoxide into the coating solution, and carrying out hydrothermal reaction at 150 ℃ and 3MPa for 6h to prepare a composite material B with the surface coated with a solid electrolyte;
s3, mixing 10g of polyamic acid and N-methyl pyrrolidone to prepare a 0.5% polyamic acid solution, then adding 5g of single-walled carbon nanotube and 100g of composite material B, and preparing a spinning solution with the concentration of 5.75 wt%;
s4, spraying the spinning solution on a light plate through electrostatic spinning, then crushing, heating in a nitrogen atmosphere to convert polyamic acid into polyimide, and keeping the heating temperature at 150 ℃ for 6 hours to obtain the silicon-carbon composite material with the polyimide nanofiber membrane as the shell, namely the low-expansion silicon-carbon composite negative electrode material.
Example 3
S1, mixing 5g of lanthanum lithium zirconate, 5g of aminated graphene TEPA, 1g of gamma-aminopropyl methyl diethoxy silane and 500g of cyclohexane to obtain a coating solution;
s2, adding 50g of silicon monoxide into the coating solution, and carrying out hydrothermal reaction at 150 ℃ and 3MPa for 6h to prepare a composite material B with the surface coated with a solid electrolyte;
s3, mixing 30g of polyamic acid and N-methyl pyrrolidone to prepare a 2% polyamic acid solution, adding 5g of single-walled carbon nanotube and 100g of composite material B, and preparing a spinning solution with the concentration of 9 wt%;
s4, spraying the spinning solution on a light plate through electrostatic spinning, then crushing, heating in a nitrogen atmosphere to convert polyamic acid into polyimide, and keeping the heating temperature at 250 ℃ for 1 hour to obtain the silicon-carbon composite material with the polyimide nanofiber membrane as the shell, namely the low-expansion silicon-carbon composite negative electrode material.
Example 4
S1, mixing 2g of lanthanum lithium zirconate, 2g of aminated graphene TEPA, 2g of gamma-aminopropyltrimethoxysilane and 300g of butanediol to obtain a coating solution;
s2, adding 35g of silicon monoxide into the coating solution, and carrying out hydrothermal reaction at 150 ℃ and 2MPa for 4h to prepare a composite material B with the surface coated with a solid electrolyte;
s3, mixing 25g of polyamic acid and N-methyl pyrrolidone to prepare 1% polyamic acid solution, adding 1g of single-walled carbon nanotube and 100g of composite material B, and preparing spinning solution with the concentration of 0.5 wt%;
s4, spraying the spinning solution on a light plate through electrostatic spinning, then crushing, heating in a nitrogen atmosphere to convert polyamic acid into polyimide, and keeping the heating temperature at 210 ℃ for 4 hours to obtain the silicon-carbon composite material with the polyimide nanofiber membrane as the shell, namely the low-expansion silicon-carbon composite negative electrode material.
Example 5
S1, mixing 4g of lanthanum lithium zirconate, 3g of aminated graphene TEPA, 4g of gamma-aminopropyltrimethoxysilane and 400g of carbon tetrachloride to obtain a coating solution;
s2, adding 25g of silicon monoxide into the coating solution, and carrying out hydrothermal reaction at 160 ℃ and 2MPa for 5h to prepare a composite material B with the surface coated with a solid electrolyte;
s3, mixing 30g of polyamic acid and N-methyl pyrrolidone to prepare a 2% polyamic acid solution, adding 1g of single-walled carbon nanotube and 100g of composite material B, and preparing a spinning solution with the concentration of 10 wt%;
s4, spraying the spinning solution on a light plate through electrostatic spinning, then crushing, heating in a nitrogen atmosphere to convert polyamic acid into polyimide, and keeping the heating temperature at 220 ℃ for 4 hours to obtain the silicon-carbon composite material with the polyimide nanofiber membrane as the shell, namely the low-expansion silicon-carbon composite negative electrode material.
Comparative example 1
And (3) uniformly mixing 500ml of cyclohexane with 50g of silicon monoxide, then carrying out spray drying, and then carbonizing at 800 ℃ for 6 hours in a nitrogen atmosphere to obtain the silicon-carbon composite material.
Comparative example 2
In comparison with example 1, the amount of lanthanum lithium zirconate was replaced with the same amount of LiTaO3Otherwise, the same as in example 1.
Comparative example 3
The amount of lanthanum lithium zirconate added was 8g as compared with example 1, and the other steps were the same as in example 1.
Comparative example 4
Other steps were the same as in example 1 except that the polyamic acid was replaced with the same amount of polyacrylonitrile and the N-methylpyrrolidone was replaced with the same amount of dimethylsulfoxide as compared with example 1.
Comparative example 5
The amount of polyamic acid added was 40g as compared with example 1, and the other steps were the same as in example 1.
Experimental example 1
SEM tests were performed on the silicon carbon composite of example 1. The test results are shown in fig. 1. As shown in FIG. 1, the silicon-carbon composite material has a particle size of 5 to 15 μm and a fibrous structure on the surface.
Experimental example 2
The physical and chemical properties (powder conductivity, tap density) of the silicon-carbon composite materials of the examples and the comparative examples and the silicon-carbon composite material of the comparative example were tested according to the method of the national standard GB/T-2433sa 2009 graphite-type negative electrode material for lithium ion batteries, and the test 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, the graphene is doped in the composite material, the electronic conductivity of the material is improved, and meanwhile, the coupling agent can form the composite material with high density, so that the tap density of the material is improved. In comparative example 1, the tap density and the powder conductivity of the silicon-carbon composite material obtained by the conventional experimental method are far lower than those of the composite material in the embodiment of the invention. The effect of the lanthanum lithium zirconate in the invention cannot be achieved by adopting other solid electrolytes in the comparative example 2, the addition amount of the lanthanum lithium zirconate in the comparative example 3 is higher than that in the example 1, but higher conductivity cannot be brought to the composite material, the conductivity of the composite material cannot be improved by adopting other flexible fiber polymers in the comparative example 4, and the conductivity of the composite material is influenced when the addition amount is larger in the comparative example 5.
Experimental example 3
The silicon-carbon composite material in the embodiment and the silicon-carbon composite material in the comparative example 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, and uniformly stirring to obtain slurry; and coating the slurry on a copper foil current collector to obtain the copper foil current collector.
The pole pieces using the silicon-carbon composite materials of examples 1 to 5 as active materials were respectively labeled as a to E, and the pole pieces using the silicon-carbon composite materials of comparative examples 1 to 6 as active materials were respectively labeled as F to J. And then, the prepared pole piece is used as a positive electrode, and the pole piece, a lithium piece, electrolyte and a diaphragm are assembled into a button cell in a glove box with the oxygen and water contents lower than 0.1 ppm. Wherein the membrane is celegard 2400; the electrolyte is LiPF6Solution of (2), LiPF6Is 1.2mol/L, and the solvent is a mixed solution of Ethylene Carbonate (EC) and diethyl carbonate (DMC) (weight ratio is 1: 1). The button cells are labeled A-1, B-1, C-1, and D-1 … …, respectively. And then testing the performance of the button cell by adopting a blue light tester under the following test conditions: 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 results of performance testing
As can be seen from table 2, the first efficiency of the silicon carbon composite material of the present invention is significantly improved compared to the comparative example, the surface of the silicon carbon composite material is coated with lanthanum lithium zirconate to reduce the irreversible capacity of the silicon carbon composite material and improve the first efficiency of the silicon carbon composite material, and the polymer material in the outer shell of the silicon carbon composite material in the embodiment constrains the expansion of the material during the charging and discharging processes. The first efficiency of the composite material cannot be improved by adopting other solid electrolytes in a synergistic way with other components in the composite material in the comparative example 2, the performance of the silicon-carbon composite material cannot be improved by increasing the content of lanthanum lithium zirconate in the comparative example 3, and although polyacrylonitrile in the comparative example 4 is also a flexible polymer, the inventor researches through experiments, not all flexible fibers can improve the full-charge expansion, and when the addition amount of polyamic acid is large, the improvement on the full-charge expansion cannot be continuously improved, and the irreversible capacity and the first efficiency are influenced.
Experimental example 4
The silicon-carbon composite materials of the examples and the comparative examples were doped with 80% artificial graphite as a negative electrode material and a positive electrode ternary material (LiNi)1/3Co1/3Mn1/3O2) The electrolyte and the diaphragm are assembled into the 5Ah soft package battery. Wherein the diaphragm is celegard 2400, and the electrolyte is LiPF6Solution (solvent is mixed solution of EC and DEC with volume ratio of 1:1, LiPF6The concentration of (1.3 mol/L). The prepared soft package batteries are respectively marked as A-2, B-2, C-2 and D-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 battery A-2-D-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 battery, dissecting again to test the thickness D2 of the negative pole piece after circulation, and then calculating the expansion rate (the expansion rate is equal to the expansion rate of the negative pole piece after circulation)
) 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. The reason is that the silicon-carbon composite material has high density and the expansion rate of the material is reduced by the expansion of polyimide bound silicon-carbon on the outer layer;
(2) and (3) carrying out cycle performance test and rate test on the soft package batteries A-2-D-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 results of the cycle performance test
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, because the outer shell of the silicon-carbon composite material of the present invention has a polymer material for reducing the expansion, and improving the cycle performance; meanwhile, the lanthanum lithium zirconate in the middle layer has the characteristic of high conductivity, and the quick charging performance of the material is improved.
The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The low-expansion silicon-carbon composite negative electrode material is characterized in that the composite negative electrode material is of a core-shell structure and comprises a core, a first coating layer and a second coating layer from inside to outside in sequence;
wherein the inner core is composed of silicon monoxide, the first coating layer comprises a conductive agent, a solid electrolyte and a silane coupling agent, and the second coating layer is composed of a conductive polymer composite material;
the solid electrolyte is lanthanum lithium zirconate, and the conductive agent is aminated graphene TEPA.
2. The low-expansion silicon-carbon composite negative electrode material as claimed in claim 1, wherein the thickness ratio of the core, the first coating layer and the second coating layer is 100 (5-20) to (5-20).
3. The low expansion silicon carbon composite anode material according to claim 1, wherein the silane coupling agent comprises one or more of gamma-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, gamma-diethylenetriaminopropylmethyldimethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, N-2-aminoethyl-3-aminopropylmethyldimethoxysilane, gamma-aminopropylmethyldiethoxysilane.
4. The preparation method of the low-expansion silicon-carbon composite negative electrode material is characterized by comprising the following steps of:
s1, mixing the solid electrolyte, the conductive agent, the silane coupling agent and the organic solvent to obtain a coating solution;
s2, adding silicon monoxide into the coating liquid, and carrying out hydrothermal reaction to prepare a composite material B;
s3, adding a conductive agent B and the composite material B into the polyamic acid solution to prepare spinning solution;
and S4, carrying out electrostatic spinning on the spinning solution, crushing, and heating in an inert atmosphere to obtain the low-expansion silicon-carbon composite negative electrode material.
5. The method for preparing the low-expansion silicon-carbon composite anode material as claimed in claim 4, wherein the organic solvent is one or more of N-methyl pyrrolidone, carbon tetrachloride, butanediol and cyclohexane.
6. The preparation method of the low-expansion silicon-carbon composite anode material as claimed in claim 4, wherein the mass ratio of the solid electrolyte to the conductive agent to the silane coupling agent to the organic solvent to the silicon monoxide is (1-5): (1-5): (1-5): (100 to 500) and (20 to 50).
7. The preparation method of the low-expansion silicon-carbon composite anode material as claimed in claim 4, wherein the conductive agent B is a single-walled carbon nanotube.
8. The preparation method of the low-expansion silicon-carbon composite anode material as claimed in claim 4, wherein the mass ratio of the polyamic acid to the conductive agent B to the composite material B is (10-30): (1-5): 100.
9. the method for preparing the low-expansion silicon-carbon composite anode material according to claim 4, wherein the mass concentration of the spinning solution in the step S3 is 0.5-10%.
10. The preparation method of the low-expansion silicon-carbon composite anode material as claimed in claim 4, wherein in the step S4, the heating temperature is 150-250 ℃ and the heating time is 1-6 h.
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Cited By (2)
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| CN114400312A (en) * | 2022-01-24 | 2022-04-26 | 格龙新材料科技(常州)有限公司 | Low-expansion silicon-carbon composite negative electrode material and preparation method thereof |
| CN115020710A (en) * | 2022-07-11 | 2022-09-06 | 陕西君和聚源科技有限公司 | Low-expansion silicon-based composite negative electrode material, preparation method thereof and lithium ion battery |
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| CN104810506A (en) * | 2014-09-15 | 2015-07-29 | 万向A一二三系统有限公司 | High-energy density lithium ion battery |
| CN104916825A (en) * | 2015-06-26 | 2015-09-16 | 田东 | Preparation method of lithium battery high-voltage modified cathode material |
| CN107492645A (en) * | 2017-08-09 | 2017-12-19 | 深圳市金牌新能源科技有限责任公司 | One kind aoxidizes sub- 3 SiC 2/graphite alkene composite and preparation method thereof |
| CN109119617A (en) * | 2018-08-30 | 2019-01-01 | 华为技术有限公司 | A kind of silicon substrate composite negative pole material and preparation method thereof and energy storage device |
| US20210202935A1 (en) * | 2019-12-27 | 2021-07-01 | Industrial Technology Research Institute | Ion-conducting material, core-shell structure containing the same, electrode prepared with the core-shell structure and metal-ion battery employing the electrode |
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| CN114400312A (en) * | 2022-01-24 | 2022-04-26 | 格龙新材料科技(常州)有限公司 | Low-expansion silicon-carbon composite negative electrode material and preparation method thereof |
| CN115020710A (en) * | 2022-07-11 | 2022-09-06 | 陕西君和聚源科技有限公司 | Low-expansion silicon-based composite negative electrode material, preparation method thereof and lithium ion battery |
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