A method for preparing a three-dimensional composite silicon-carbon negative electrode material

Abstract

The present invention provides a method for preparing a three-dimensional composite silicon-carbon negative electrode material, comprising the following steps: S1. activating carbon black to obtain porous carbon black; S2. adding 1-10 parts of expanded graphite to 1-300 parts of deionized water, dispersing for 1-5h to obtain a suspension; S3. adding 1-40 parts of porous carbon black to the suspension and dispersing for 0.2-1h to obtain a dispersion, then drying the dispersion to obtain a composite structure carbon; S4. decomposing and depositing a silicon source on the composite structure carbon by CVD to obtain a three-dimensional porous silicon-carbon; S5. mixing the three-dimensional porous silicon-carbon and amorphous carbon, and then carbonizing to obtain a three-dimensional composite silicon-carbon negative electrode material. The preparation method of the three-dimensional composite silicon-carbon negative electrode material of the present invention has a unique three-dimensional structural design, and an ultra-thin nano-silicon layer is deposited inside the porous carbon black and graphene nanosheets, and the volume expansion caused by silicon is alleviated by the porous carbon material space, thereby ensuring the high lithium storage capacity and long cycle stability of the material.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a method for preparing a three-dimensional composite silicon-carbon negative electrode material. Background Art

[0002] With the development of new energy technologies, it has become a consensus to gradually get rid of dependence on fossil energy. The demand for high-energy-density lithium-ion batteries in the field of electric vehicles and various energy storage systems is also increasing. Among the many negative electrode materials, silicon has a theoretical specific capacity ten times that of the current graphite negative electrode and a suitable lithium insertion potential. Therefore, it is regarded as a next-generation lithium-ion battery negative electrode material with great application prospects. However, silicon-based materials are often accompanied by huge volume expansion during the charging and discharging process, which causes the material to break and pulverize, and lose electrical contact with the current collector. At the same time, the SEI film on the surface of the material is constantly broken and regenerated, consuming a large amount of active lithium from the positive electrode, seriously affecting the battery's cycle stability and rate performance.

[0003] The rapid development of mobile electronic devices, electric vehicles and other fields has put forward higher demands on the performance of lithium-ion batteries. The short-term goal of lithium-ion battery development needs to increase the energy density to above 300Wh / kg. It is difficult to make a major breakthrough in the capacity of lithium battery positive electrode materials in the short term, but the capacity of the negative electrode still has huge potential for improvement. Therefore, the development of new high-capacity negative electrode materials is an inevitable choice to further improve the energy density of lithium batteries.

[0004] Silicon has an extremely high theoretical capacity of 4200mAh / g, which is 10 times the capacity of existing commercial graphite negative electrode materials) and a suitable electrochemical lithiation potential, making it the most promising next-generation lithium battery negative electrode material. Electrodes made directly from silicon powder have the problem of poor cycle stability, but studies in recent years have shown that nanosilicon with a particle size of less than 100nm combined with the overall structural design of the electrode and a suitable binder can effectively improve the cycle stability of silicon. Currently, high-capacity lithium battery negative electrodes based on nanosilicon have received great attention from academia and industry.

[0005] Chinese Patent CN 103682287A A lithium ion battery silicon-based composite negative electrode material, preparation method and battery, the method mechanically grinds 5.0-40.0μm silicon particles to obtain 10-500nm nano-silicon, using wet grinding, such as a sand mill; the process cost of preparing nano-silicon is high and the yield is low; and even if ground in an organic solvent, the obtained nano-silicon is easily oxidized; then it is composited with hollow graphite for spray granulation; since hollow graphite is obtained by mechanical processing of natural graphite, artificial graphite, etc., it is difficult to evenly disperse nano-silicon into the gaps of hollow graphite; and if more nano-silicon is doped, the structure of hollow graphite cannot be taken over; nano-silicon agglomerates and is difficult to disperse; in summary, this method is costly and complex; and it is not conducive to industrialization; Chinese Patent CN 106207180A A method for preparing a porous hollow graphite material. The method involves mixing graphite, a strong base, and a carbon source by high-speed stirring, and then requires high-temperature graphitization at 2800-3000 degrees Celsius. The strong base is highly corrosive, and the high-temperature graphitization cycle is long, the cost is high, and the energy consumption is high, making it even less suitable for industrialization.

[0006] Therefore, in order to solve the above problems, it is necessary to prepare nano-silicon at low cost, and a porous carbon material is also needed to be compounded with nano-silicon to solve the long-cycle technical bottleneck of high-capacity silicon-carbon composite materials. Summary of the invention

[0007] The purpose of the present invention is to overcome and supplement the deficiencies in the prior art, and to provide a method for preparing a three-dimensional composite silicon-carbon negative electrode material, wherein porous carbon black is prepared by activating carbon black, and porous carbon black and expanded graphite are ultrasonically dispersed to obtain a composite porous structure material of the two, wherein carbon black provides a porous structure, and silane and / or chlorosilane (such as monochloro, dichloro, trichloro and tetrachlorosilane) are used to prepare nano-silicon at low cost, and an ultra-thin nano-silicon layer is deposited inside porous carbon black and graphene nanosheets, and the volume expansion caused by silicon is alleviated by the carbon material space with large pores and interlayer gaps, thereby ensuring the high lithium storage capacity and long cycle stability of the material. The technical solution adopted by the present invention is:

[0008] A method for preparing a three-dimensional composite silicon-carbon negative electrode material, comprising the following steps:

[0009] S1. activating carbon black to obtain porous carbon black;

[0010] S2. 1-10 parts of expanded graphite are added to 1-300 parts of deionized water and dispersed for 1-5h to obtain a suspension;

[0011] S3. Add 1-40 parts of porous carbon black to the suspension and disperse for 0.2-1h to obtain a dispersion, and then dry the dispersion to obtain a composite structure carbon;

[0012] S4. Decomposing the silicon source by CVD and depositing it on the composite structure carbon to obtain a three-dimensional porous silicon carbon;

[0013] S5. Mix the three-dimensional porous silicon carbon and amorphous carbon, and then carbonize them to obtain a three-dimensional composite silicon-carbon negative electrode material.

[0014] Preferably, in the method for preparing the three-dimensional composite silicon-carbon negative electrode material, the carbon black in step S1 is activated by water vapor or carbon dioxide, the activation temperature is 600-900° C., and the activation time is 1-6 hours.

[0015] Preferably, the method for preparing the three-dimensional composite silicon-carbon negative electrode material, wherein: the carbon black pore size in step S1 is 10-150nm, D50 < 25μm, and the specific surface area is 10-100m 2 / g, porosity is 10-70%.

[0016] Preferably, in the method for preparing the three-dimensional composite silicon-carbon negative electrode material, the expansion ratio of the expanded graphite in step S2 is 30-120 mL / g.

[0017] Preferably, in the method for preparing the three-dimensional composite silicon-carbon negative electrode material, the drying temperature in step S3 is 100-200° C. and the drying time is 0.5-4 h.

[0018] Preferably, in the method for preparing the three-dimensional composite silicon-carbon negative electrode material, the silicon source in step S4 is one or more of silane and chlorosilane.

[0019] Preferably, in the method for preparing the three-dimensional composite silicon-carbon negative electrode material, the chlorosilane is one or more of monochlorosilane, dichlorosilane, trichlorosilane and tetrachlorosilane.

[0020] Preferably, the preparation method of the three-dimensional composite silicon-carbon negative electrode material, wherein: the specific process of step S4 in which the silicon source is decomposed and deposited on the composite structure carbon by CVD is as follows: the composite structure carbon is placed in a rotary furnace, and the silicon source and carrier gas are introduced for deposition, the deposition temperature is controlled to be 400°C-850°C, and the deposition time is 0.1-8h; the carrier gas is nitrogen or argon.

[0021] Preferably, in the method for preparing the three-dimensional composite silicon-carbon negative electrode material, the amorphous carbon in step S5 is one or more of medium-temperature coal tar pitch, high-temperature coal tar pitch, petroleum tar, coal tar, heavy petroleum residue, heavy aromatic hydrocarbons and mesophase tar.

[0022] Preferably, in the method for preparing the three-dimensional composite silicon-carbon negative electrode material, the carbonization temperature of step S5 is 800-950° C. and the carbonization time is 0.5-3 h.

[0023] Advantages of the present invention:

[0024] (1) The preparation method of the three-dimensional composite silicon-carbon negative electrode material of the present invention is that the raw material carbon black of the porous carbon material is widely available and low in cost. The porous carbon black is prepared by physical activation, which is environmentally friendly and pollution-free. The preparation of nano-silicon adopts silane CVD deposition, which has a short process flow, controllable size of nano-silicon, low cost, and easy industrialization.

[0025] (2) The preparation method of the three-dimensional composite silicon-carbon negative electrode material of the present invention is to uniformly deposit a layer of nano-silicon on the surface of the porous carbon black and graphene nanosheet composite material, and then coat a layer of amorphous carbon on the three-dimensional porous silicon-carbon shell, thereby avoiding direct contact between the porous three-dimensional porous silicon-carbon and the electrolyte, reducing the occurrence of its side reactions, and the coated carbon layer improves its conductivity. The structure of this three-dimensional composite silicon-carbon negative electrode material is conducive to improving the rate performance. The porous carbon provides sufficient volume for silicon expansion and allows rapid transmission of lithium ions, and the presence of the coated carbon layer allows for improved formation of the solid / electrolyte interface, thereby improving the structural integrity and conductivity of the material; therefore, the porous carbon composite silicon-carbon negative electrode can maintain excellent cycle stability during cycling, which is extremely important for industrial applications.

[0026] (3) The preparation method of the three-dimensional composite silicon-carbon negative electrode material of the present invention has a unique three-dimensional structural design. By depositing an ultra-thin nano-silicon layer inside the porous carbon black and graphene nanosheets, and using the porous carbon material space to alleviate the volume expansion caused by silicon, the high lithium storage capacity and long cycle stability of the material are ensured.

[0027] (4) The method for preparing the three-dimensional composite silicon-carbon negative electrode material of the present invention has excellent cycle performance and high specific capacity, low industrial cost, and great market competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a process flow chart of the preparation method of the three-dimensional composite silicon-carbon negative electrode material.

[0029] Figure 2 This is a scanning electron microscope image of the three-dimensional composite silicon-carbon negative electrode material of Example 1 of the present invention.

[0030] Figure 3 This is a button battery cycle test curve chart of the three-dimensional composite silicon-carbon negative electrode material of Example 1 of the present invention.

[0031] Figure 4 This is a first cycle curve diagram of a button cell of the three-dimensional composite silicon-carbon negative electrode material of Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with specific drawings and embodiments.

[0033] Example 1

[0034] like Figure 1 As shown, a method for preparing a three-dimensional composite silicon-carbon negative electrode material, wherein: comprising the following steps:

[0035] S1. 10 kg of carbon black was placed in a horizontal activation furnace and activated with water vapor at 600 ° C for 1 h to obtain porous carbon black;

[0036] S2. The 2kg expanded graphite was added to 60kg of deionized water and ultrasonically dispersed in a 1000W industrial ultrasonic disperser for 3h to obtain a suspension;

[0037] S3. 10 kg of porous carbon black was added to the suspension and dispersed for 0.5 h to obtain a dispersion, and then the dispersion was dried in a rotary kiln at 120 ° C for 1 h to obtain a composite structure carbon of porous carbon black and graphene nanosheets;

[0038] S4. In a rotary furnace, silane at 60 L / h and argon at 180 L / h were introduced into the porous carbon composite of the porous carbon black and graphene nanosheets prepared above. The silane deposition temperature was 450 ° C and the deposition time was 2 h, so that a three-dimensional porous silicon carbon composite of nano-silicon deposition was obtained. The particle size of the nano-silicon particles obtained by silane deposition was 90 ± 5 nm, the pore size of the three-dimensional porous silicon carbon was 100 nm, and the specific surface area was 30 m 2 / g; porosity 85%;

[0039] S5. Three-dimensional porous silicon carbon and high-temperature coal tar pitch were added to a VC mixer for uniform mixing and coating, mixed for 30 minutes, and then carbonized at 900°C for 2 hours to obtain a three-dimensional composite silicon-carbon negative electrode material.

[0040] Example 2

[0041] like Figure 1 As shown, a method for preparing a three-dimensional composite silicon-carbon negative electrode material, wherein: comprising the following steps:

[0042] S1. 40 kg of carbon black was placed in a horizontal activation furnace and activated with carbon dioxide at 800 ° C for 2 h to prepare porous carbon black;

[0043] S2. 8Kg of expanded graphite 200kg of deionized water, expanded graphite was ultrasonically dispersed in a 1000W industrial ultrasonic disperser for 3h to obtain a suspension;

[0044] S3. 40 kg of porous carbon black was added to the suspension and dispersed for 1 h to obtain a dispersion, and then the dispersion was placed in a rotary kiln and dried at 150 ° C for 1 h to obtain a composite structure carbon of porous carbon black and graphene nanosheets;

[0045] S4. In a rotary furnace, tetrasilane was introduced into the composite structure carbon prepared above at 80 L / h and argon was used as carrier gas at 200 L / h. The silane deposition temperature was 550 ° C and the deposition time was 1.5 h. The nano-silicon particles obtained by silane deposition were 60 ± 5 nm. The pore size of the obtained three-dimensional porous silicon carbon was 110 nm and the specific surface area was 40 m 2 / g, porosity is 90%;

[0046] S5. Add three-dimensional porous silicon carbon and petroleum asphalt into a VC mixer for uniform mixing and coating, mix for 10 minutes, and then carbonize at 800°C for 0.5h to obtain a three-dimensional composite silicon-carbon negative electrode material.

[0047] Example 3

[0048] A method for preparing a three-dimensional composite silicon-carbon negative electrode material, comprising the following steps:

[0049] S1. 10 kg of carbon black was placed in a horizontal activation furnace and activated with water vapor at 700 ° C for 2 h to prepare porous carbon black;

[0050] S2. 2kg of expanded graphite was added to 60kg of deionized water and ultrasonically dispersed in a 1000W industrial ultrasonic disperser for 4h to obtain a suspension;

[0051] S3. 10 kg of porous carbon black was added to the suspension and dispersed for 1 h to obtain a dispersion, and then the dispersion was dried in a rotary kiln at 150 ° C for 1 h to obtain a composite structure carbon of porous carbon black and graphene nanosheets;

[0052] S4. In a rotary furnace, silane was introduced into the composite structure carbon prepared above at 60 L / h and argon was used as carrier gas at 120 L / h. The silane deposition temperature was 700 ° C and the deposition time was 3 h to obtain three-dimensional porous silicon carbon. The nano-silicon particles obtained by silane deposition were 50 ± 5 nm, the pore size of the three-dimensional porous silicon carbon was 100 nm, and the specific surface area was 25 m 2 / g, porosity is 88%;

[0053] S5. Add the three-dimensional porous silicon carbon and the intermediate phase asphalt into the VC mixer and mix them evenly for coating. Mix for 30 minutes and then carbonize at 900°C for 2 hours to obtain the three-dimensional composite silicon-carbon negative electrode material.

[0054] Example 4

[0055] S1. 40 kg of carbon black was placed in a horizontal activation furnace and activated with carbon dioxide at 900 ° C for 6 h to prepare porous carbon black;

[0056] S2. 8Kg of expanded graphite was added to 200kg of deionized water and ultrasonically dispersed in a 1000W industrial ultrasonic disperser for 5h to obtain a suspension;

[0057] S3. 40 kg of porous carbon black was added to the suspension and dispersed for 1 h to obtain a dispersion, and then the dispersion was dried in a rotary kiln at 200 ° C for 4 h to obtain a composite structure carbon of porous carbon black and graphene nanosheets;

[0058] S4. In a rotary furnace, tetrasilane at 80 L / h and argon at 240 L / h were introduced into the composite structure carbon prepared above. The silane deposition temperature was 850°C and the deposition time was 6 h to obtain a three-dimensional porous silicon carbon composite of nano-silicon deposition. The nano-silicon particles obtained by silane deposition were 40 ± 5 nm, the pore size of the three-dimensional porous silicon carbon was 120 nm, and the specific surface area was 50 m 2 / g, porosity is 90%;

[0059] S5. Add three-dimensional porous silicon carbon and medium-temperature asphalt into a VC mixer for uniform mixing and coating, mix for 10 minutes, and then carbonize at 900°C for 3 hours to obtain a three-dimensional composite silicon-carbon negative electrode material.

[0060] Comparative Example 1

[0061] A method for preparing a three-dimensional composite silicon-carbon negative electrode material, comprising the following steps:

[0062] S1. 2kg of expanded graphite was first ultrasonically dispersed in a 1000W industrial ultrasonic disperser for 3h to obtain a suspension;

[0063] S2. 10 kg of carbon black was added to the suspension and dispersed for 0.5 h, and then dried in a rotary kiln at 120 ° C for 1 h to obtain a composite structure carbon composed of porous carbon black and graphene nanosheets;

[0064] S3. In a rotary furnace, silane at 60 L / h and argon at 180 L / h were introduced into the composite structure carbon of the porous carbon black and graphene nanosheets prepared above. The silane deposition temperature was 450 ° C and the deposition time was 2 h, so that a three-dimensional porous silicon carbon composite of nano-silicon deposition was obtained. The nano-silicon particles obtained by silane deposition were 90 ± 5 nm, the pore size of the three-dimensional porous silicon carbon was 60 nm, and the specific surface area was 20 m 2 / g, the porosity is 65%, and the three-dimensional porous silicon carbon and high-temperature coal tar are added into a VC mixer for uniform mixing and coating, mixed for 30 minutes, and then carbonized at 900℃ for 2 hours to obtain a three-dimensional composite silicon-carbon negative electrode material.

[0065] Comparative Example 2

[0066] The steps of Comparative Example 2 differ from those of Example 2 in that the carbon black is not activated, nor is the expanded graphite subjected to ultrasonic treatment, but the carbon black is directly compounded with the expanded graphite, and the other steps are the same.

[0067] Embodiment 1-4 Pole piece production and battery assembly,

[0068] 1. Pole sheet preparation: The three-dimensional composite silicon-carbon negative electrode material prepared in Example 1-4, conductive carbon black (SP), and polyacrylic acid (PAA) binder were mixed in a ratio of 70:15:15, placed in a planetary slurry mixer, and deionized water was added to adjust the viscosity; the mixed slurry was poured on a copper foil with a thickness of 9 μm, and the thickness of the scraper on the automatic film applicator was adjusted to make the slurry evenly coated on the copper foil; the coated pole sheet was naturally dried and then transferred to an 80°C blast drying oven for baking; the dried pole sheet was rolled with a roller press to make the active material and the current collector tightly combined, and the rolling thickness of the roller press was controlled to control the surface density of the pole sheet at 1 g / cm 3 Next, the compacted electrode piece is cut into discs using a stamping die with a diameter of 12 or 14 cm, dried, weighed, and a silicon-carbon negative electrode material electrode is obtained.

[0069] 2. Battery assembly: Place the electrode in a glove box under argon atmosphere, use CR2032 battery shell as a mold to make a button battery, add 120 μL of 1 mol / L LiPF6 electrolyte (the solvent is EC:DMC:EMC with a volume ratio of 1:1:1, and contains 10% by mass of the additive FEC) to the silicon-carbon negative electrode material electrode and lithium counter electrode made in the above steps, and place the diaphragm between the silicon-carbon negative electrode material electrode and the counter electrode, and assemble them into a half-cell with a well-sealed composite electrode system in the glove box.

[0070] 3. Battery test: Charge and discharge the assembled battery at a current density of 0.1C in the voltage range of 0.005V-1.5V. Record the charge specific capacity and discharge specific capacity data.

[0071] The battery performance test results of Examples 1-4 and Comparative Examples 1-2 are shown in Table 1

[0072] Table 1 Performance comparison results

[0073]

[0074] As can be seen from Table 1, Examples 1-4 use carbon black that is porous and then composited with graphene nanosheets, followed by silane CVD deposition and amorphous carbon coating. The first efficiency, first charge capacity and cycle retention rate are all higher than those of Comparative Examples 1-2.

[0075] Figure 2 This is a scanning electron microscope image of the three-dimensional composite silicon-carbon negative electrode material of Example 1. Figure 2 It can be clearly seen that the nano-silicon particles are deposited on the surface of the composite material in the voids within the porous composite structure.

[0076] Figure 3This is the charge and discharge cycle curve of the button battery cycle test curve of the three-dimensional composite silicon-carbon negative electrode material of Example 1. It can be seen that the capacity decay is very small after 300 cycles.

[0077] Figure 4 This is the first charge and discharge curve of Example 1, and it can be seen that the first efficiency is high.

[0078] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a three-dimensional composite silicon-carbon negative electrode material, characterized in that: The following steps are involved: S1. Physically activating carbon black to obtain porous carbon black; S2. 1-10 parts of expanded graphite are added to 1-300 parts of deionized water and ultrasonically dispersed in an ultrasonic disperser for 1-5h to obtain a suspension; S3. Add 1-40 parts of porous carbon black to the suspension and disperse for 0.2-1h to obtain a dispersion, and then dry the dispersion to obtain a composite structure carbon; S4. Decomposing the silicon source by CVD and depositing it on the composite structure carbon to obtain a three-dimensional porous silicon carbon; S5. Mixing the three-dimensional porous silicon carbon and the amorphous carbon, and then carbonizing them to obtain a three-dimensional composite silicon-carbon negative electrode material; The amorphous carbon in step S5 is one or more of medium-temperature coal tar, high-temperature coal tar, petroleum tar, coal tar, heavy petroleum residue, heavy aromatic hydrocarbons and mesophase tar; the carbonization temperature is 800-950° C., and the carbonization time is 0.5-3 h; The carbon black in step S1 is activated by water vapor or carbon dioxide at an activation temperature of 600-900°C and an activation time of 1-6h; The carbon black in step S1 has a pore size of 10-150 nm, a D50 of less than 25 μm, and a specific surface area of ​​10-100 m 2 / g, porosity is 10-70%.

2. The method for preparing the three-dimensional composite silicon-carbon negative electrode material according to claim 1, characterized in that: The expansion ratio of the expanded graphite in step S2 is 30-120 mL / g.

3. The method for preparing the three-dimensional composite silicon-carbon negative electrode material according to claim 1, characterized in that: The drying temperature in step S3 is 100-200° C., and the drying time is 0.5-4 h.

4. The method for preparing the three-dimensional composite silicon-carbon negative electrode material according to claim 1, characterized in that: The silicon source in step S4 is one or more of silane and chlorosilane.

5. The method for preparing the three-dimensional composite silicon-carbon negative electrode material according to claim 4, characterized in that: The chlorosilane is one or more of monochlorosilane, dichlorosilane, trichlorosilane and tetrachlorosilane.

6. The method for preparing the three-dimensional composite silicon-carbon negative electrode material according to claim 1, characterized in that: The specific process of step S4 in which the silicon source is decomposed by CVD and deposited on the composite structure carbon is as follows: the composite structure carbon is placed in a rotary furnace, and the silicon source and carrier gas are introduced for deposition, the deposition temperature is controlled to be 400°C-850°C, the deposition time is 0.1-8h, and the carrier gas is nitrogen or argon.

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